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In Fortführung der bisher in dieser Forschungsgruppe durchgeführten Studien mit (2,4,6-Trimethoxyphenyl)silanen wurden im Rahmen der vorliegenden Arbeit weitere Untersuchungen zu den Schutzgruppen-Eigenschaften der Si-(2,4,6-Trimethoxyphenyl)-Gruppe angestellt und anschließend die hierbei gewonnenen Erkenntnisse verwendet, um Sila-Analoga bereits bekannter biologisch aktiver Verbindungen über neue Synthesewege mit (2,4,6-Trimethoxyphenyl)silanen darzustellen. Des Weiteren wurden im Rahmen der Untersuchungen zur C/Si-Bioisosterie die pharmakologischen Eigenschaften dieser bereits auf anderem Weg synthetisierten Wirkstoffe in Kooperation mit anderen Forschungsgruppen vervollständigt. Darüber hinaus wurden auch die Arbeiten zum Thema „(2,4,6-Trimethoxyphenyl)silane als Silylierungsreagenzien für O-Nucleophile“ weitergeführt.
Die Synthese der (2-Aminoethyl)cycloalkylphenylsilanole Sb (Sila-Trihexyphenidyl), 6b (SilaCycrimin), 7 b (Sila-Procyclidin) und Sb wird beschrieben. Sb- Sb wurden - ausgehend von Cl\(_2\)(C\(_6\)H\(_5\))SiCH = CH\(_2\) (9) - durch eine fünfstufige Reaktionsfolge mit einer Gesamtausbeute von 32- 40% erhalten. Am isolierten Ileum des Meerschweinchens wurden die C/Si-Paare Sa, b- 8a, b vergleichend auf ihre antimuskarinische Aktivität geprüft. Die durch die Sila-Substilution von Sa-8a erreichte Zunahme der Affinität zum Muskarinrezeptor ist deutlich weniger ausgeprägt als bei den strukturverwandten C/Si-Paaren I a, b- 4a, b.
(Acetoxymethyl)methylphenylgerman: Synthese, thermisches Verhalten und olfaktorische Eigenschaften
(1991)
No abstract available.
No abstract available.
(I\(_2\)GaS-i-C\(_3\)H\(_7\))\(_2\), das erste butterfly-Molekül mit vierfach koordiniertem Gallium
(1985)
No abstract available
Die erstmalige Synthese der (Thioacetoxy-S-methyl)diorganylsilane (CH\(_3\))\(_2\)Si(H)CH\(_2\)SC(O)CH\(_3\) (9) und (C\(_6\)H\(_5\))\(_2\)Si(H)CH\(_2\)SC(O)CH\(_3\) (10) und der (Mercaptomethyl) diorganylsilane (CH\(_3\))\(_2\)Si(H)CH\(_2\)SH (11) und (C\(_6\)H\(_5\))\(_2\)Si(H)CH\(_2\)SH (12) wird beschrieben. Während sich die Silane 9 und 10 leicht handhaben lassen, neigen die strukturanalogen (Hydroxymethyl)diorganylsilane (CH\(_3\))\(_2\)Si(H)CH\(_2\)OH (1) und (C\(_6\)H\(_5\))\(_2\)Si(H)CH\(_2\)OH (2) zu einer basenkatalysierten Zersetzung (Bildung oligomerer (polymerer) Alkoxysilane und Wasserstoff). Im Gegensatz zu den thermisch labilen (Acetoxymethyl)diorganylsilanen (CH\(_3\))\(_2\)Si(H)CH\(_2\)OC(O)CH\(_3\) (3) und (C\(_6\)H\(_5\))\(_2\)Si(H)CH\(_2\)OC(O)CH\(_3\) (4) (--+ Umlagerung zu den entsprechenden Acetoxy(methyl) diorganylsilanen (CH\(_3\)) \(_3\)SiOC(O)CH\(_3\) (5) und CH\(_3\)(C\(_6\)H\(_5\))\(_2\)SiOC(O)CH\(_3\) {6)) sind die Thio-Analoga 9 und 10 thermisch stabil (I-molare Lösungen in C\(_6\)D\(_6\), 30 h bei 180 o C).
The isolation and structure elucidation of rac-dioncophyllacine A from the leaves of Triphyophyllun peltatum, is described. Unlike all other naphthylisoquinoline alkaloids, this fully dehydrogenated representative has an additional methoxy group at C-4, the position of which is deduced from NOE results. Dioncophyllacine A has a 7,1' site of the biaryl axis, as in dioncophylline A. Its constitution is confirmed by an X-ray structure analysis, which shows that the crystalline form of this new alkaloid is racemic.
Reaktionen von 1,3-Butadien und einigen seiner Methylderivate mit 1a und 1- Methyl-1,2-cyclohexadien 1b sowie den Übergang der [2 + 2]-Cycloaddukte 2 und 3 in das bisher unbekannte 1,2,3,5,8,8a-HexahydronaphthaJin 4a und einige seiner Methylderivate
No abstract available
In the molecular structure of the title compound, C34H58B2N2, each B atom of the diborane(4) is connected to one dimethylamino group and one Tip ligand (Tip = 2,4,6-triisopropylphenyl). These findings indicate that the increased steric demand of the Tip groups exerts influence solely on the B—B separation but not on the overall geometry of the title compound.
No abstract available
No abstract available
In food and pharmaceutical analysis, the classical indices peroxide value (PV), acid value (AV) and p-anisidine value (ANV) still play an important role as quality and authenticity control parameters of fats and oils. These indices are sum parameters for certain deterioration products (PV for hydroperoxides, AV for free fatty acids, ANV for aldehydes) and are obtained using volumetric or UV/VIS spectroscopic analytical approaches. 1H NMR spectroscopy provides a fast and simple alternative to these classical approaches. In the present work, novel 1H NMR methods to determine hydroperoxides, free fatty acids and aldehydes in fats and oils were developed.
Hydroperoxides:
The influence of solvent, water, free fatty acids and sample weight on the hydroperoxide group proton (OOH) signal was investigated. On the basis of the obtained results, the sample preparation procedure of the new 1H NMR method was established. A rough assignment of the hydroperoxide group signals in edible fats and oils to methyl oleate, methyl linoleate and methyl linolenate was conducted. Furthermore, to gain information on how many different hydroperoxide species originate from trioleate autoxidation, a kinetic study on trioleate monohydroperoxides was performed. The evaluation of the data strongly indicates that all of the conceivable 18 trioleate monohydroperoxides were formed during trioleate autoxidation. The analytical performance of the NMR method was compared to that of the classical PV approach by means of the so-called “relative sensitivity” according to Mandel. It was shown that both methods exhibit a similar analytical performance. A total of 444 edible oil samples were analysed using both methods. For some oil varieties considerable discrepancies were found between the results. In the case of black seed oil and olive oil two substances were identified that influence the classical PV determination and thus cause positive (black seed oil) and negative (olive oil) deviations from the theoretical PV expected from the NMR values.
Free fatty acids:
In order to find the optimal solvent mixture to measure the carboxyl group protons (COOH) of free fatty acids in fats and oils, the effect of solvent on the COOH signal was investigated for different mixtures of CDCl3 and DMSO-d6. The comparison of the NMR method with the classical AV method by means of the relative sensitivity revealed that both methods exhibit a similar analytical performance. 420 edible oil samples were analysed by both approaches. Except for pumpkin seed oil, where slight deviations were observed, there was a good compliance between the results obtained from the two methods. Furthermore, the applicability of the 1H NMR assay to further lipids with relevance in pharmacy was tested. For hard fat, castor oil, waxes and oleyl oleate modifications of the original sample preparation procedure of the NMR method were necessary to achieve comparable results for both methods.
Aldehydes:
The new 1H NMR method enables the determination of the molar amounts of n-alkanals, (E)-2-alkenals and (E,E)-2,4-alkadienals. It was illustrated that the ANV can be modelled as a linear combination of the NMR integrals of these aldehyde species. A functional relationship was derived on the basis In conclusion, the new 1H NMR methods provide an excellent alternative to of calibration experiments. The suitability of the model was shown by comparing the NMR-determined ANVs with the measured classical ANVs of 79 commercially available edible oils of different oil types.
In conclusion, the new 1H NMR methods provide an excellent alternative to the determination of the classical indices PV, AV and ANV. They have several advantages over the classical methods including the consumption of small solvent amounts, the ability to automatize measurement and to acquire several different parameters out of the same NMR spectrum. Especially concerning their selectivity, the 1H NMR methods are highly superior to the classical methods.
The He (I) photoelectron spectra of 2-bicyclo[2.1.l]hexene (1), 2,3-bis(methylene)bicyclo[2.1.l]hexane (3), and 3,4-bis(methylene)tricyclo[3.l.O.0\(^{2.6}\)]hexane (4) have been investigated. The assignment given is based on a ZDO model and semiempirical calculations. Tagether with the PE data of benzvalene (2), the reported data allow a comparison between 1-2 and 3-4. This yields a measure of the interactions between 8 cyclobutane or 8 bicyclobutane moiety and a double bond system within a ZDO model. The resonance integral found in the case of 1 and 3 amounts to -1.9 eV, that for 2 and 4, to -2.3 eV. The investigations furthermore reveal that the electronic factors which contribute to the higher reactivity of the bicyclobutane compounds amount to 5 kcal/mol.
Phenyl(tricyclo[4.1.0.0\^(^{2,7}\)] hept-4-en-3-yl)sulfone 8 has been prepared in two steps from 4,S-dlbromohomobenzvalene (6) and deprotonated to give the title compound 9. The carbon-13 NMR spectrum of 9 reveals a considerable interaction between the allyl anion moiety and the bicyclobutane system.
In der vorliegenden Arbeit werden Studien zur selektiven bakteriellen Hydroxylierung von Fettsäuren vorgestellt. Unter Verwendung von Linolsäure als Substrat wurden aus Bodenproben verschiedene Mikroorganismen isoliert, die polare Metabolite bildeten. Die phänotypische und genotypische Charakterisierung eines Stammes führte zu dessen Identifizierung als Stenotrophomonas maltophilia. Die Strukturaufklärung der drei Hauptreaktionsprodukte erfolgte mittels Hochleistungsflüssigchromatographie-Massenspektrometrie (HPLC-MS), Gaschromatographie-Massenspektrometrie (GC-MS) sowie ein- und zweidimensionalen NMR-Experimenten (1H-NMR, 13C-NMR, 13C-DEPT, H/H-COSY, HMQC, HMBC). Linolsäure wurde von Stenotrophomonas maltophilia zu 3-Hydroxy-Z6-dodecensäure, 3-Hydroxy-Z5,Z8-tetradecadiensäure und 3-Hydroxy-Z7,Z10-hexadecadiensäure umgesetzt. In einem anschließenden Substratscreening wurden 32 Verbindungen als Edukte für die Biotransformation eingesetzt und so die strukturellen Voraussetzungen ermittelt, die für eine effiziente Umsetzung von Fettsäuren durch Stenotrophomonas maltophilia notwendig sind. Zum Einsatz kamen Substrate mit unterschiedlicher Anzahl an C-Atomen sowie mit Variationen bezüglich Anzahl, Position und Konformation von Doppelbindungen. Weiterhin wurden Substanzen verwendet, die bereits funktionelle Gruppen im Molekül aufwiesen (z. B. Ricinolsäure). Die Bestimmung der Enantiomerenverteilung der bakteriell gebildeten 3-Hydroxysäuren mittels multidimensionaler Gaschromatographie (MDGC) ergab einen deutlichen Enantiomerenüberschuss (ee 84 – 98 Prozent). Die Aufklärung der Absolutkonfiguration erfolgte über die Synthese von Dodecan-1,3-diolen und deren anschließende Analytik mittels MDGC. Zusätzlich wurde die Konfiguration mit Hilfe der CD Exciton Chirality-Methode bestimmt. Weiterhin wurde untersucht, ob die bakteriell gebildeten 3-Hydroxysäuren als Substrate oder Inhibitoren des Enzyms Lipoxygenase L-1 aus Sojabohnen fungieren. Die im Rahmen dieser Arbeit durchgeführten Studien zur Darstellung von optisch aktiven 3-Hydroxysäuren belegen das Potential des Bodenbakteriums Stenotrophomonas maltophilia, exogen zugeführte Fettsäuren im Rahmen der b-Oxidation zu kettenverkürzten, an Position 3 hydroxylierten Metaboliten abzubauen. Dabei liegen jedoch deutliche Abweichungen zur b-Oxidation in anderen Organismen vor, die auf Unterschieden in der Enzymausstattung bzw. deren Aktivität beruhen. Durch die gewonnenen Erkenntnisse zum b-Oxidationsmechanismus in Stenotrophomonas maltophilia kann diese Aktivität durch geeignete Substratauswahl gezielt zur Synthese von optisch aktiven 3-Hydroxysäuren eingesetzt werden, deren chemische Synthese gegenüber dieser Biotransformation deutlich schwieriger zu realisieren ist. Für solche Verbindungen besteht in der organischen Synthese von Naturstoffen wie Pheromonen, Vitaminen und Antibiotika Bedarf.
Aufbauend auf einen Datensatz von etwa 70 antimalaria-aktiven Verbindungen wurde mit Hilfe des CoMSIA-Verfahrens ein QSAR(Qantitative Structure Activity Relationship)-Modell erstellt, das in der Lage ist antiplasmodiale Aktivitäten von Verbindungen aus der Substanzklasse der Naphthylisochinolin-Alkaloide vorherzusagen. Da die behandelten Strukturen ein sehr kompliziertes konformatives Verhalten aufweisen, mussten für ein möglichst flexibles Alignment (unter Verwendung von FLEXS und GASP) eigene Abläufe entwickelt werden, die schließlich weitestgehend automatisiert werden konnten. Das erstellte Modell erlaubte es darüber hinaus, die für die Aktivität verantwortlichen strukturellen Merkmale zu identifizieren und so entscheidende Anregungen zur Vereinfachung des relativ komplizierten Grundgerüsts zu geben. Die Vorschläge wurden zu einem großen Teil bereits synthetisch verwirklicht, wobei die anschließend experimentell gefundenen Aktivitäten die vorher berechneten sehr gut bestätigten. Die neu entwickelten Substanzen befinden sich derzeit im Patentprüfungsverfahren.
4-Bromoctavalen und zwei (Brommethylen)homobenzvalene anstelle eines erwarteten Bromoctabisvalens
(1988)
No abstract available.
Die humane afrikanische Trypanosomiasis (Schlafkrankheit, HAT) wird durch die Parasiten Trypanosoma brucei rhodesiense und Trypanosoma brucei gambiense ausgelöst und führt unbehandelt zum Tod. Wegen begrenzter Therapiemöglichkeiten sowie vernachlässigter Kontrollprogramme ist HAT eine gegenwärtige Bedrohung, was die Suche nach neuen Wirkstoffen notwendig macht. Ausgangspunkt für die Leitstrukturfindung war das 7-Amino-4-chinolon-3-carboxamid IV mit einem IC50-Wert (T. b. brucei) von 1.2 µM. Die 4-Chinolon-3-carboxamid-Grundstrukturen wurden unter Verwendung der Gould-Jacobs- (1-Alkyl-Derivate) bzw. der Grohe-Heitzer-Synthese (1-Aryl-Derivate) aufgebaut und anhand strukturierter Variation der Substituenten in Pos. 1, 3 und 7 die für die antitrypanosomale Wirksamkeit essenziellen Strukturelemente identifiziert: Pos.1: Die Alkylkettenverlängerung von Ethyl zu n-Butyl bewirkte eine stetige Aktivitätssteigerung, welche auch einem Aryl-Rest in dieser Position überlegen war. Pos.3: Benzylamide mit HBD-Funktionen führten zur Aktivitätsabnahme, während HBA-Funktionen und unsubstituierte Reste zur Steigerung der Wirksamkeit, teilweise in den nanomolaren Konzentrationsbereich, beitrugen. Pos.7: Neben cyclischen sek. Aminen wurden auch aliphatische prim. Amine via konventioneller oder Mikrowellen-unterstützter SNAr eingeführt. Dabei zeigten sich die sek. Amine mit einer antitrypanosomalen Aktivität im teilweise submikromolaren Bereich den acyclischen Aminen deutlich überlegen. Vor allem der Morpholin-Rest bewirkte eine sprunghafte Wirksamkeitsverbesserung. Durch Kombination der Einzelresultate konnte schließlich die den Lipinski’s „Rule of 5“ entsprechende Leitstruktur 33 mit vielversprechender antitrypanosomaler Wirksamkeit (IC50 (T. b. brucei) = 47 nM, IC50 (T. b. rhodesiense) = 9 nM) und geringer Zytotoxizität erhalten werden (SI = 19000). Erste Untersuchungen zur Identifikation des Targets der 4-Chinolon-3-carboxamide ergaben folgende Erkenntnisse: Fluoreszenzmikroskopieuntersuchungen zeigten eine deutliche Veränderung der Morphologie des Mitochondriums bei behandelten BSF-T. b. brucei-Zellen. Anhand einer Zellzyklus-Analyse wurde die Beeinträchtigung der Segregation des Kinetoplasten beobachtet, was zu einem Segregationsdefekt führte. Die Topoisomerase (TbTopoIImt) wurde durch ein „Knockdown“-Experiment als Haupt-Target ausgeschlossen. Trotz der bemerkenswerten biologischen Aktivität war eine In-vivo-Untersuchung der Leitstruktur wegen zu geringer Wasserlöslichkeit nicht möglich, welche auf eine hochgeordnete Schichtgitterstruktur zurückzuführen war. Da die Löslichkeit im Wesentlichen eine Funktion der Lipophilie und der intermolekularen Wechselwirkungen ist, wurden zur Verbesserung der Wasserlöslichkeit pharmazeutisch-technische Methoden angewandt sowie chemische Strukturmodifikationen vorgenommen: Es wurde eine Lipid-basierte, selbstemulgierende Formulierung entwickelt. Durch Ausbildung stabiler Emulsionen war 33 bis zu einer Konzentration von 10 mg/ml im Wässrigen löslich und somit für die In-vivo-Untersuchung zugänglich. Nach 4-tägiger peroraler Behandlung von NMRI-Mäusen mit einer wässrigen 1:1-Verdünnung der Formulierung konnte keine In-vivo-Aktivität festgestellt werden. Die Sprühtrocknung von 33 resultierte in amorpher Modifikation, welche in Gegenwart von PVP bzw. Eudragit®L100 stabilisiert wurde. Beide Partikel ermöglichten die Übersättigung von 33 im Wässrigen, was im Fall der Eudragit®L100-Partikel zu 200-facher Löslichkeitssteigerung gegenüber der kristallinen Wirkstoffmodifikation führte und somit die In-vivo-Untersuchung ermöglichte. Zusammen mit ersten Metabolismus-Untersuchungen von 33, welche die Berechnung einer Abbau-Kinetik bzw. Clearance ermöglichte, konnte mittels der Software Simcyp® ein Plasmakonzentrationsprofil der Verbindung 33 (Eudragit®L100-Partikel) erstellt werden. Basierend auf diesem Studiendesign wurde die In-vivo-Untersuchung von 33 an mit T. b. rhodesiense infizierten Mäusen durchgeführt und zeigte nach 8-tägiger Behandlung einen deutlichen Rückgang der Parasitämie. Im Fokus der chemischen Strukturmodifikation stand das Einführen polarer und ionisierbarer Strukturelemente, um 4-Chinolon-3-carboxamid-Derivate mit erhöhter Hydrophilie (logP 1 - 3) bzw. Salz- und Co-Kristall-Strukturen zu erhalten. Sämtliche Strukturvariationen trugen zur Verbesserung der Wasserlöslichkeit und der „drug-like“ Eigenschaften im Vergleich zu Verbindung 33 bei, waren allerdings von Aktivitätsverlusten gegenüber T. b. brucei begleitet. Anhand der „ligand efficiency“- und „lipophilic ligand efficiency“-Analyse wurden schließlich die vielversprechendsten Derivate (94 und 96) für die weitere Untersuchung ausgewählt. Mit IC50 (T. b. rhodesiense)-Werten von 4 nM (94) und 33 nM (96) und geringer Zytotoxizität wurden Selektivitätsindizes bis zu 25000 gefunden, welche jene von 33 übertrafen. Aufgrund einer Löslichkeit im millimolaren Bereich, einer moderaten Membranpermeabilität und einer Plasmastabilität von > 2 h können die Verbindungen 94 und 96 somit als erste Wirkstoffkandidaten angesehen werden. Die vollständige physiko-chemische Charakterisierung wurde mittels eines Sirius-T3-Titrationssystems durchgeführt. Unter Verwendung dieser Parameter wurden für die Derivate 94 und 96 je zwei Plasmakonzentrationsprofile mit der Software Simcyp® simuliert. Basierend auf diesem Studiendesign wurde jeweils die hohe Dosis beider Derivate im Mausmodel (T. b. rhodesiense) untersucht. Während nach 5-tägiger Behandlung mit 94 und 96 bei sämtlichen Tiere keine Parasiten mehr nachweisbar waren, wurde ein leichter Rückfall in beiden Versuchsgruppen an Tag 8 beobachtet. Gegenwärtig wird die Behandlung mit beiden Derivaten fortgesetzt.
Im Mittelpunkt dieser Arbeit stand die Substanzgruppe der 4-Chinolone, die zum einen über ein intrinsisches antiparasitäres Potenzial gegen Erreger wie Plasmodien, Trypanosomen oder Mykobakterien verfügt und zum anderen über gezielte Substitution auch die Möglichkeit zu strukturellen Modifikationen bietet. Vorrangiges Ziel dieser Arbeit war der Aufbau einer strukturell möglichst diversen Substanzbibliothek und deren sukzessive Testung innerhalb des SFB630. Auf diese Weise sollten neue antiparasitäre Leitstrukturen als Ausgangspunkt für weitere strukturelle Optimierungen erhalten werden. Der Chinolon-Grundkörper sollte hierzu gemäß Gould-Jacobs-Reaktion aufgebaut werden. Zur Synthese diverser Amid-Derivate wurden verschiedene Synthese-strategien verfolgt. Alternativ wurden, ebenfalls über eine nukleophile Substitution (Piperidin-Derivat), in 7-Position modifizierte Verbindungen generiert, die unter Verwendung des Kupplungs-reagenzes PyBOB (Benzotriazol-1-yloxytri-pyrrolidinophosphonium Hexafluorphosphat) in die entsprechenden 1-Alkyl-1,4-dihydro-7-piperidinyl-4-oxo-chinolin-3-carboxamide transformiert wurden. Die in dieser Arbeit generierte Substanzbibliothek wurde anschließend innerhalb des SFB630 getestet. Hierbei zeigte sich, dass die Amidierung der 3-Carbonsäurefunktion eine Steigerung der antimikrobiellen Wirkung gegen Trypanosoma brucei mit sich brachte. Es kristallisierten sich aktive Verbindungen heraus, die erstmals eine Aktivität derartiger Derivate gegen Trypanosomen belegen und so zukünftig als Leitstrukturen für weitere strukturelle Modifizierungen herangezogen werden können. Mit dem in dieser Arbeit angewandten Random-Chemistry-Verfahren sollte in die Suche nach neuen Leitstrukturen gezielt das Zufallsprinzip integriert werden bzw. es sollten neue aktive Verbindungen generiert werden, die über die klassischen kombinatorischen Syntheseschemata bzw. die gängigen Reaktionsmechanismen nur schwer zugänglich sind. Eine Reihe von Fluorchinolon-Derivaten wurden in verschiedenen Lösungsmitteln, meist DMSO mit Zusätzen von Methanol oder Chloroform, gelöst bzw. suspendiert und anschließend einer ionisierenden γ-Strahlung von 500 kGy ausgesetzt. Die Testung mittels HPLC / FCPC generierter Fraktionen ergab zum Teil höhere antitrypanosomale Aktivitäten als die der korrespondie¬renden Ausgangsverbindungen. Eine Aktivität gegen Makrophagen konnte nicht festgestellt werden. Darüber hinaus wurde im Rahmen dieser Arbeit in Kooperation mit Prof. Schneider-Schaulies an der Identifizierung viraler Fusionsinhibitoren ausgewählter Paramyxoviren (Masern-Virus, Nipah-Virus) gearbeitet. Aus einer Ähnlichkeitssuche, basierend auf dem literaturbekannten Masern-Fusionsinhibitor 2-(4-Chlorphenyl)-N-(2-hydroxy-4-nitrophenyl)acetamid (AM-2), konnte die Struktur eines Chinolinamides identifiziert werden, woraufhin die generierte Substanzbibliothek auf antiviral-aktive Verbindungen gescreent werden sollte. Die Kristallstruktur des Nipah-Virus-Fusionsproteins wurde im Jahre 2006 aufgeklärt. Mit diesen Informationen konnte mittels Molecular-Modelling eine Bindetasche innerhalb der HR1-Domäne des F-Proteins identifiziert werden, mit der die erzielten inhibitorischen Aktivitäten gut in Einklang gebracht werden konnten. Diese Bindetasche befindet sich in einem Bereich weitreichender Umstrukturierungsvorgängen: Durch die Einlagerung des Liganden 7-(4-Carbamoyl-piperidin-1-yl)-N-(2,4-dichlorbenzyl)-1-cyclopropyl-6-fluor-4-oxo-1,4-dihydro-chinolin-3-carboxamid, in diese hydrophobe Tasche werden Wechselwirkungen mit den korrespondierenden Aminosäuren in der HR2-Domäne und so auch dessen Anlagerung unterbunden. In 1 μmolarer Konzentration konnte die Fusionsaktivität um 42% reduziert werden, die verwendeten Referenzsubstanz (OX-1) erzielte in selbiger Konzentration keine Wirkung.
Die vorliegende Arbeit beschäftigte sich mit der Entwicklung und Synthese von Inhibitoren der Deoxyhypusin-Hydroxylase (DOHH), die einen wichtigen Schritt in der Aktivierung des eukaryotischen Translationsinitiations-Faktors-5A (eIF-5A) katalysiert. Die Hemmung dieses Metalloenzyms durch kleine Moleküle, die mit dem katalytischen Eisenatom im aktiven Zentrum der DOHH einen Chelatkomplex bilden, hat einen antiproliferativen Effekt auf parasitäre Erreger, wie Plasmodien, Trypanosomen und Leishmanien zur Folge. Ausgehend von den antiplasmodial wirksamen Eisenkomplexbildnern und Pyridon-Derivaten Ciclopirox und Mimosin wurden besser wirksame 2,6-Diaryl-4-oxopiperidincarbonsäuremono- und -diester-Derivate abgeleitet, deren 4-Piperidon-Grundgerüst als Leitstruktur für die Entwicklung von antiplasmodialen und antitrypanosomalen Wirkstoffen fungierte. Entsprechend dieser Leitstrukturen gelang im Zuge dieser Arbeit durch verschiedene Modifikationen der Doppel-Mannich-Reaktion die Erstellung einer weitreichenden Bibliothek 52 strukturell diverser 4-Hydroxytetrahydropyridin-3,5-dicarbonsäurediester 1 – 6, darunter auch erstmals Derivate mit t-Butyl-esterfunktionen und 4-Hydroxytetrahydropyridin-3-carbonsäuremonoester 7 – 8. Dabei konnten vor allem Derivate mit der gewünschten nitroaromatischen Substitution in den Positionen 2 und 6 synthetisiert werden. Darüber hinaus wurden vielfältige Strukturabwandlungen dieser Substanzen in Form von verschiedenen 4-Piperidonderivaten ohne Esterfunktionen, deren Oximen sowie von 4-Hydroxychinoloncarbonsäureestern syn-thetisiert. Die hergestellten Derivate wurden In-vitro-Testungen an Plasmodium falciparum, Trypanosoma brucei brucei und Leishmania major unterzogen. Zusätzlich wurde die Zytotoxizität an der Makrophagen-Zelllinie J774.1 ermittelt.
Das exo/endo--lsomerenverhältnis Ja: Jb bei der bekannten [2 + 2]-Cycloaddition von Styrol an 1,2-Cyclohexadien (2) wurde als tempcraturabhingiaaefunden. Der Einsatz von (Z)-Dcutcriostyrollicfene den Beweis der Zweistufiakeit dieser Reaktion, und das Diradikal 4 wird als wahrscheinlichste Zwischenstufe anaesehen. Erhitzen von Jb auf 140-170°C führte zur Binstellung des thermodynamischen Gleichgewichts mit Ja (Ja:3b = 93:7), wobei wieder das Diradikal4 als Zwischenstufe fungieren dürfte. Mit Hilfe kinetischer Messungen ermittelte man die Aktivierungsparameter für das System Ja~ 3b. - Aus 2 und den Abfangreagenzien p-Methoxystyrol, 1,1-Diphenylethylen sowie 1-Phenylpropen gingen mit bescheidenen Ausbeuten die Titelverbindungen 6a, b, 7 bzw. 8 hervor. Analoa zu 2 wurde sein l-Methylderivat 13 aus 6,6-Dibrom-1-methylbicyclo[3.1.0]hexan (9) durch Methyllithium freigesetzt. In Gegenwart von Styrol entstand neben den Abfanaprodukten 14a, b auch das Dimere 12 von lJ. - Die 1H-NMR-Spektren der Titelverbindungen belegen eine starre Halbsesselkonformation des Cyclohexentcils mit äquatorial anellienem Cyclobutanring.
7-Azatetracyclo[4.1.0.0<sup>2,4</sup>.0<sup>3,5</sup>]heptan - ein neues Valenzisomeres des Azepins
(1979)
No abstract available
7-Thiatetracyclo[4.1.0.0\(^{2,4}\).0\(^{3,5}\)]heptan (Benzvalensulfid) - Synthese und Reaktionen
(1982)
No abstract available
Das Sila-Dimetacrin (3a), ein Sila-Analogon des Psychopharmakons Dimetacrin (2), und sein N,N-Diethylderivat 3 b sowie sein 3-Chlorderivat 3 c wurden, von den o-Halogenanilinen 4 a- c ausgehend, über die teilweise unbekannten Stufen 5 a- c bis 10a- d synthetisiert, in ihren Eigenschaften beschrieben und in ihrer Struktur über Elementaranalysen, \(^1\)H-NMR- und Massenspektren sichergestellt. Die Synthese des Zwischenproduktes Bis(2-bromphenyl)amin (9a) konnte optimiert werden.
No abstract available
In der vorliegenden Arbeit wird über die Synthese, Struktur und katalytische Aktivität von borverbrückten Gruppe 4 Metallocenophanen berichtet, die als Katalysatoren in der Ziegler-Natta-artigen Olefinpolymerisation eingesetzt werden können. Neben den bereits bekannten [1]Borametallocenophanen wurden weitere Komplexe mit unterschiedlichen Substituenten, als auch die bislang unbekannten [2]Borametallocenophane synthetisiert und charakterisiert. Vergleichende Polymerisationsstudien einer Reihe von unterschiedlich substituierten [n]Borametallocenophanen (n = 1,2) wurden unter definierten Standardbedingungen durchgeführt, um einen möglichen Einfluss der am Boratom gebundenen Substituenten zu beobachten. Weitergehende Untersuchungen bezogen sich auf den Einfluss dieser Substituenten auf sterische und elektronische Einflüsse, die mit den Polymerisationsergebnissen korreliert wurden. Hierbei wurden die sterischen Einflüsse der verschiedenen Substituenten anhand der Kristallstrukturen festgemacht; elektronische Einflüsse sollten anhand von CO Schwingungen, die mittels Infrarotspektroskopie beobachtet werden können, von korrespondierenden Carbonylkomplexen und alternativ mittels 91Zr-NMR Spektroskopie untersucht werden.
We present herein an in‐depth study of complexes in which a molecule containing a boron‐boron triple bond is bound to tellurate cations. The analysis allows the description of these salts as true π complexes between the B−B triple bond and the tellurium center. These complexes thus extend the well‐known Dewar‐Chatt‐Duncanson model of bonding to compounds made up solely of p block elements. Structural, spectroscopic and computational evidence is offered to argue that a set of recently reported heterocycles consisting of phenyltellurium cations complexed to diborynes bear all the hallmarks of \(\pi\)‐complexes in the \(\pi\)‐complex/metallacycle continuum envisioned by Joseph Chatt. Described as such, these compounds are unique in representing the extreme of a metal‐free continuum with conventional unsaturated three‐membered rings (cyclopropenes, azirenes, borirenes) occupying the opposite end.
No abstract available
No abstract available
A cyclic (alkyl)(amino)carbene (CAAC) has been shown to react with a covalent azide similar to the Staudinger reaction. The reaction of \(^{Me}\)CAAC with trimethylsilyl azide afforded the N‐silylated 2‐iminopyrrolidine (\(^{Me}\)CAAC=NSiMe\(_{3}\)), which was fully characterized. This compound undergoes hydrolysis to afford the 2‐iminopyrrolidine and trimethylsiloxane which co‐crystallize as a hydrogen‐bonded adduct. The N‐silylated 2‐iminopyrrolidine was used to transfer the novel pyrrolidine‐2‐iminato ligand onto both main‐group and transition‐metal centers. The reaction of the tetrabromodiborane bis(dimethyl sulfide) adduct with two equivalents of \(^{Me}\)CAAC=NSiMe\(_{3}\) afforded the disubstituted diborane. The reaction of \(^{Me}\)CAAC=NSiMe\(_{3}\) with TiCl\(_{4}\) and CpTiCl\(_{3}\) afforded \(^{Me}\)CAAC=NTiCl\(_{3}\) and \(^{Me}\)CAAC=NTiCl\(_{2}\)Cp, respectively.
A comparative ab initio study of the Si\(_2\)C\(_4\), Si\(_3\)C\(_3\), Si\(_4\)C\(_2\) clusters
(1994)
Various structural possibilities for the Si\(_2\)C\(_4\) and Si\(_4\)C\(_2\) clusters are investigated by employing a basis set of triple-zeta plus polarization quality; electron correlation is generally accounted for by second-order M0ller-Plesset and, in certain instances, by higher-order perturbation (CASPT2) approaches. The building-up principle recently suggested from an analysis of Si\(_3\)C\(_3\) clusters is found to be fully operative for Si\(_2\)C\(_4\) and Si\(_4\)C\(_2\) clusters. A comparison of the structure and stability of various geometrical arrangements in the series C\(_6\) , Si\(_2\)C\(_4\) , Si\(_3\)C\(_3\) , Si\(_4\)C\(_2\), and Si\(_6\) shows that linear and planar structures become rapidly less stable if carbons are replaced by silicons and that the three-dimensional bipyramidal forms become less favorable as soon as silicons are exchanged by carbons in the parent Si\(_6\) structure. The effects can be rationalized in qualitative terms based on differences in silicon and carbon bonding.
The implantation of any foreign material into the body automatically starts an immune reaction that serves as the first, mandatory step to regenerate tissue. The course of this initial immune reaction decides on the fate of the implant: either the biomaterial will be integrated into the host tissue to subsequently fulfill its intended function (e.g., tissue regeneration), or it will be repelled by fibrous encapsulation that determines the implant failure. Especially neutrophils and macrophages play major roles during this inflammatory response and hence mainly decide on the biomaterial's fate. For clinically relevant tissue engineering approaches, biomaterials may be designed in shape and morphology as well as in their surface functionality to improve the healing outcome, but also to trigger stem cell responses during the subsequent tissue regeneration phase.
The main focus of this thesis was to unravel the influence of scaffold characteristics, including scaffold morphology and surface functionality, on primary human innate immune cells (neutrophils and macrophages) and human mesenchymal stromal cells (hMSCs) to assess their in vitro immune response and tissue regeneration capacity, respectively. The fiber-based constructs were produced either via melt electrowriting (MEW), when the precise control over scaffold morphology was required, or via solution electrospinning (ES), when the scaffold design could be neglected. All the fiber-based scaffolds used throughout this thesis were composed of the polymer poly(ε caprolactone) (PCL).
A novel strategy to model and alleviate the first direct cell contact of the immune system with a peptide-bioactived fibrous material was presented in chapter 3 by treating the material with human neutrophil elastase (HNE) to imitate the neutrophil attack. The main focus of this study was put on the effect of HNE towards an RGDS-based peptide that was immobilized on the surface of a fibrous material to improve subsequent L929 cell adhesion. The elastase efficiently degraded the peptide-functionality, as evidenced by a decreased L929 cell adhesion, since the peptide integrated a specific HNE-cleavage site (AAPV-motif). A sacrificial hydrogel coating based on primary oxidized hyaluronic acid (proxHA), which dissolved within a few days after the neutrophil attack, provided an optimal protection of the peptide-bioactivated fibrous mesh, i.e, the hydrogel alleviated the neutrophil attack and largely ensured the biomaterial's integrity. Thus, according to these results, a means to protect the biomaterial is required to overcome the neutrophil attack.
Chapter 4 was based on the advancement of melt electrowriting (MEW) to improve the printing resolution of MEW scaffolds in terms of minimal inter-fiber distances and a concomitant high stacking precision. Initially, to gain a better MEW understanding, the influence of several parameters, including spinneret diameter, applied pressure, and collector velocity on mechanical properties, crystallinity, fiber diameter and fiber surface morphology was analyzed. Afterward, innovative MEW designs (e.g., box-, triangle-, round , and wall-shaped scaffolds) have been established by pushing the printing parameters to their physical limits. Further, the inter-fiber distance within a standardized box-structured scaffold was successfully reduced to 40 µm, while simultaneously a high stacking precision was maintained. In collaboration with a co-worker of my department (Tina Tylek, who performed all cell-based experiments in this study), these novel MEW scaffolds have been proven to facilitate human monocyte-derived macrophage polarization towards the regenerative M2 type in an elongation-driven manner with a more pronounced effect with decreasing pore sizes.
Finally, a pro-adipogenic platform for hMSCs was developed in chapter 5 using MEW scaffolds with immobilized, complex ECM proteins (e.g., human decellularized adipose tissue (DAT), laminin (LN), and fibronectin (FN)) to test for the adipogenic differentiation potential in vitro. Within this thesis, a special short-term adipogenic induction regime enabled to more thoroughly assess the intrinsic pro-adipogenic capacity of the composite biomaterials and prevented any possible masking by the commonly used long-term application of adipogenic differentiation reagents. The scaffolds with incorporated DAT consistently showed the highest adipogenic outcome and hence provided an adipo-inductive microenvironment for hMSCs, which holds great promise for applications in soft tissue regeneration.
Future studies should combine all three addressed projects in a more in vivo-related manner, comprising a co-cultivation setup of neutrophils, macrophages, and MSCs. The MEW-scaffold, particularly due to its ability to combine surface functionality and adjustable morphology, has been proven to be a successful approach for wound healing and paves the way for subsequent tissue regeneration.
This PhD thesis introduced several concepts for the construction of new supramolecular assem-blies in polar solvents. Although the building blocks differ in their binding mode and association strength they follow the same principle: one main driving force for the self-assembly in polar solutions in combination with one texturing force. The main self-assembly process is based on the mutual interaction of hydrogen-bond enforced ion pairs which deliver the association energy needed for stable, supramolecular structures even in polar solvents. The texturing force itself is represented by the linkers between the zwitterionic building blocks or parts of them. The different length and functionalization of the linkers have a tremendous influence on the mode of self-assembly leading to cyclic dimers, vesicles, layers or solid spheres. Hence, this principle is suitable for the construction of programmable monomers. Since the derivatisation of the main binding motive is rather simple it offers a great number of new and undoubtedly fascinating structures with potential applications in material and biomimetic science.
The hyperfine structures of the isoelectronic molecules CCO. CNN, and NCN in their triplet ground states (X\(^3 \sum ^-\)) are investigated by means of ab initio methods. The infrared frequencies and geometries are detennined and compared with experiment. Configuration selected multireference configuration interaction calculations in combination with perturbation theory to correct the wave function (MRD-CI/B\(_K\)) employing extended atomic orbital (AO) basis sets yielded very accurate hyperfine properties. The theoretical values for CCO are in excellent agreement with the experimental values determined by Smith and Weltner [J. Chem. Phys. 62,4592 (1975)]. For CNN, the first assignment of Smith and Weltner for the two nitrogen atoms has to be changed. A qualitative discussion of the electronic structure discloses no simple relation between the structure of the singly occupied orbitals and the measured hyperfine coupling constants. Vibrational effects were found to be of little importance.
Staphylococcus epidermidis, the common inhabitant of human skin and mucosal surfaces has emerged as an important pathogen in patients carrying surgical implants and medical devices. Entering the body via surgical sites and colonizing the medical devices through formation of multi-layered biofilms leads to refractory and persistent device-related infections (DRIs). Staphylococci organized in biofilms are more tolerant to antibiotics and immune responses, and thus are difficult-to-treat. The consequent morbidity and mortality, and economic losses in health care systems has strongly necessitated the need for development of new anti-bacterial and anti-biofilm-based therapeutics. In this study, we describe the biological activity of a marine sponge-derived Streptomyces sp. SBT348 extract in restraining staphylococcal growth and biofilm formation on polystyrene, glass, medically relevant titan metal, and silicone surfaces. A bioassay-guided fractionation was performed to isolate the active compound (SKC3) from the crude SBT348 extract. Our results demonstrated that SKC3 effectively inhibits the growth (MIC: 31.25 \(\mu\)g/ml) and biofilm formation (sub-MIC range: 1.95-<31.25 \(\mu\)g/ml) of S. epidermidis RP62A in vitro. Chemical characterization of SKC3 by heat and enzyme treatments, and mass spectrometry (HRMS) revealed its heat-stable and non-proteinaceous nature, and high molecular weight (1258.3 Da). Cytotoxicity profiling of SKC3 in vitro on mouse fibroblast (NIH/3T3) and macrophage (J774.1) cell lines, and in vivo on the greater wax moth larvae Galleria mellonella revealed its non-toxic nature at the effective dose. Transcriptome analysis of SKC3 treated S. epidermidis RP62A has further unmasked its negative effect on central metabolism such as carbon flux as well as, amino acid, lipid, and energy metabolism. Taken together, these findings suggest a potential of SKC3 as a putative drug to prevent staphylococcal DRIs.
Xiphophorus meyeri n. sp. is described as an endemic to Muzquiz, Coahuila, Mexico. It appears to be the northernmost species of the genus. The new species is related to X. couchianus and X. gordoni, but differs morphologically from those by dorsal fin ray number, by the expression of some gonopodial features and most markedly by the appearance of macromelanophores or tr-melanophores.
Priority tasks of the present thesis were to generate various enantiopure C-3-substituted pyroglutamates as well as C-3-substituted glutamates, and furthermore to ameliorate the serious drawback of the bad atom-economy in the reaction sequence of previously published silylether-mediated procedures. To meet these requirements, the ortho ester functionality (OBO ester) developed by Corey was introduced. According to the plan of synthesis, the starting material, non-racemic (S)-pyroglutamic acid, was converted to the corresponding oxetane ester via a DCC-mediated esterification. The latter was N-protected to provide N-acceptor substituted pyroglutamic acid oxetane esters (Acceptor=Boc,Cbz,CO2Me). After rearrangement with boron trifluoride, the ortho ester derivatives (Acceptor=Cbz,CO2Me) were at hand and exclusively the N-Cbz derivative was converted to the corresponding alpha,beta-unsaturated lactam via a syn-elimination reaction. The formation of the C-3-substituted ortho ester compounds (R=methyl,ethyl,butyl,allyl,phenyl,4-chlorophenyl,biphenyl,naphthyl) was performed via a copper-mediated conjugate addition to the alpha,beta-enone system of the N-Cbz-alpha,beta-unsaturated lactam. The OBO functionality hence was envisaged to support perfect trans selectivity in this cuprate addition to the Michael system of the N-Cbz-alpha,beta-unsaturated lactam. Spectroscopic NMR-data, on the basis of 1H-, 13C- and DEPT spectra, proved the assumption that the C-3-substituted ortho ester derivatives exclusively are trans-configurated, i.e. the alkyl derivatives (R=methyl,ethyl,butyl,allyl) are (2S,3S)-configurated and the aryl derivatives (R=phenyl,4-chlorophenyl,biphenyl,naphthyl) are (2S,3R)-configurated). The C-3-substituted ortho ester derivatives were completely deprotected to yield the C-3-substituted pyroglutamates (R=ethyl,phenyl,4-chlorophenyl,naphthyl). Finally, ring opening reaction via route A-2 lead to the desired enantiopure C-3-substituted glutamates. Alternatively, latter preferably were reacted via route A-1 to yield the C-3-substituted glutamates (R=methyl,ethyl,butyl,phenyl,4-chlorophenyl,naphthyl). Their (2S,3R)-configuration (R=aryl) and (2S,3S)-configuration (R=alky), respectively, unambiguously was proved on the basis of available spectroscopic NMR-data. To ensure this assumption, diastereomeric (2S,3R)-3-methyl glutamic acid (i.e. cis-configurated) examplarily was synthesized via route A-3 and spectroscopic NMR-data was compared to that of (2S,3S)-3-methyl glutamic acid (i.e. trans-configurated). Conclusively, there can be recorded the fact that the serious drawback of the bad atom-economy in the reaction sequence previously used can be circumvented by the introduction of the OBO functionality, so the concept of an improved atom-economy is achieved. Additionally, in comparison to the silyl-ether-mediated synthesis, the OBO functionality provided crystalline ortho ester derivatives, which facilitated their purification as well as characterization.
This work deals with the sintering of multi-material composites. It aims at the establishment of an alternative to the existing complex models for sintering. The development of the associated experimental procedure is also included in this work. The developed material model must be able to predict (i) the sintering kinetics and (ii) the viscous moduli of a material. An experimental approach with free sintering and hot-forging measurements is favoured in this work. The prediction of the sintering kinetics is addressed with the construction of a map of sintering kinetics data: the Master Sintering Diagram (MSD). The MSD is based on a generalized equation for solid-state diffusion, thus is suitable for any thermal activated diffusion. The MSD allows the prediction of sintering kinetics for a large range of temperatures and external loads. A novel approach to the determination of the viscous moduli is developed in this work: the cyclic unloading method. It is a hot-forging measurement (sintering under uniaxial compression) where the applied load is released for short periods. The measurements are carried out with continuous heating, so that the viscous moduli are determined over large ranges of temperatures and densities. The advantage of this method is the measurement of the viscous moduli in anisotropic microstructures. The material model is validated in two steps. Firstly, the predictions of sintering kinetics with the MSD are compared with experimental results: changes of thermal profile and changes of load are predicted with a maximum deviation of 10%. Secondly, the experimentally determined viscous moduli are used for the prediction of a bi-layer curvature using models for warpage from literature. The prediction is qualitatively good for a maximum deviation of 27%. The study of a sintering glass-ceramic tape on a rigid substrate is presented. It shows that this co-sintering problem can be qualitatively investigated with requirement of the material model. The formation of anisotropy intrinsic to the hot-forging experiments is also reported in this work. It appears to be a important point to address in the future for a better understanding of the cosintering.
Post-transcriptional RNA modification methods are in high demand for site-specific RNA labelling and analysis of RNA functions. In vitro-selected ribozymes are attractive tools for RNA research and have the potential to overcome some of the limitations of chemoenzymatic approaches with repurposed methyltransferases. Here we report an alkyltransferase ribozyme that uses a synthetic, stabilized S-adenosylmethionine (SAM) analogue and catalyses the transfer of a propargyl group to a specific adenosine in the target RNA. Almost quantitative conversion was achieved within 1 h under a wide range of reaction conditions in vitro, including physiological magnesium ion concentrations. A genetically encoded version of the SAM analogue-utilizing ribozyme (SAMURI) was expressed in HEK293T cells, and intracellular propargylation of the target adenosine was confirmed by specific fluorescent labelling. SAMURI is a general tool for the site-specific installation of the smallest tag for azide-alkyne click chemistry, which can be further functionalized with fluorophores, affinity tags or other functional probes.
Product identification tags are of great importance in a globalized world with increasingly complex trading routes and networks. Beyond currently used coding strategies, such as QR codes, higher data density, flexible application as well as miniaturization and readout indication are longed for in the next generation of security tags. In this work, micron‐sized supraparticles (SPs) with encoded information (ID) are produced that not only exhibit multiple initially covert identification levels but are also irreversibly marked as “read” upon readout. To achieve this, lanthanide doped CaF\(_{2}\) nanoparticles are assembled in various quantity‐weighted ratios via spray‐drying in presence of a broad‐spectrum stealth fluorophore (StFl), yielding covert spectrally encoded ID‐SPs. Using these as pigments, QR codes, initially dominated by the green fluorescence of the StFl, could be generated. Upon thermal energy input, these particle‐based tags irreversibly switch to an activated state revealing not only multiple luminescent colors but also spectral IDs. This strategy provides the next generation of material‐based security tags with a high data density and security level that switch information upon readout and can be, therefore, used as seal of quality.
Here, a postpolymerization modification method for an α-terminal functionalized poly-(N-methyl-glycine), also known as polysarcosine, is introduced. 4-(Methylthio)phenyl piperidine-4-carboxylate as an initiator for the ring-opening polymerization of N-methyl-glycine-N-carboxyanhydride followed by oxidation of the thioester group to yield an α-terminal reactive 4-(methylsulfonyl)phenyl piperidine-4-carboxylate polymer is utilized. This represents an activated carboxylic acid terminus, allowing straightforward modification with nucleophiles under mild reaction conditions and provides the possibility to introduce a wide variety of nucleophiles as exemplified using small molecules, fluorescent dyes, and model proteins. The new initiator yielded polymers with well-defined molar mass, low dispersity, and high end-group fidelity, as observed by gel permeation chromatography, nuclear magnetic resonance spectroscopy, and matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy. The introduced method can be of great interest for bioconjugation, but requires optimization, especially for protein conjugation.
Vibronically averaged values for K =0 and K = 1 bending levels in the energy range between 0 and 25 000 cm\(^{-1}\) are computed for the \(^{14}\)N, H, and D atoms in NH\(_2\), NHD, and ND\(_2\) The pure ab initio electronic potentials, as well as those derived by fitting of experimentally observed band positions are employed. Effects of vibronic coupling and local perturbations of close-lying levels belanging to different electronic states are discussed.
Potential energy and spectroscopic constants for the X\(^2 \sum^+ _\mu\) ground state of a;, were calculated by configuration-interaction (Cl) methods, using large basis sets with polarization and diffuse functions. From these CI wavefunctions, the isotropic (a\(_{iso}\)) and dipolar (A\(_{dip}\)) components of the hyperfine coupling constant were obtained. The effects of various s, p basis sets, polarization and diffuse functions, as well as the influence of reference configurations and configuration selection thresholds were investigated. The best values obtained are 35·31 G for a\(_{iso}\) and 29·440 for A\(_{dip}\)• tobe compared with experimental values of 37 ± 1 G and 32 ± 1 G, respectively. It is shown that the contributions to a1so of the K and L shells are opposite in sign, differing by about 4 G. Upon vibrational averaging, both a\(_{iso}\) and A\(_{dip}\) move towards smaller values as v increases. An adiabatic electron affinity of 2·46eV was obtained for CL\(_2\) , and a vertical electron detachment energy of 3·71 eV for Cl;.
Various structural possibilities for Si\(_3\)C\(_3\) clusters are investigated by ab initio calculations employing basis sets of double- and triple-zeta quality augmented by d polarization functions. Correlation effects are included by a second-order Moeller Piesset perturbation treatment. For the two lowest-lying structures higher-order correlation corrections and multi-reference effects are also included. Bonding features are investigated by two different types of population analyses to obtain insight into the nature of chemical bonding. A total of 17 stationary points were investigated, 14 of which correspond to local minima and three being transition states. The energetically lowest-lying structures are: A "pyramidlike" structure with various multicenter bonds, followed by a es symmetric isomer closely related to the ground state Si6 structure. Planar structures, favoured in small carbon clusters, lie higher in energy and are transition states. The lowest-lying triplet system is found to be the linear nonsymmetric Si - C-C-C-Si -Si structure, which is calculated to lie about 38 kcalfmole above the singlet ground state. A building-up principle based on bonding criteria is suggested for the occurence of the various structural possibilities.
Results ofan ab initio study ofthe hyperfine structure of the X\(^2\)A', A\(^2\) A" ( 1\(^2 \Pi\)) system ofthe formyl radical are presented. Special attention is paid to the analysis of the interplay between the vibronic and magnetic hyperfine etfects. The results of computations are in very good agreement with the available experimental findings. The values for the hyperfine coupling constants in lower bending Ievels of both electronic species are predicted.
The hyperfine coupling constants (isotropic hfcc and four Cartesian components of the ani~ tropic tensor) are calculated for all three atoms of C\(_2\)H in its three lowest-lying electronic states at various molecu)ar geometries by means of the ab initio configuration interaction ( MRO.CI) method. The off-diagonal electronic matrix elements involving the two species ofthe A' symmetry are also computed. A diabatic transforrnation is perforrned Jeading to simple geometrical depen· dences of the hyperline coupling constants.
The vibronically averaged values for tbe hyperfine coupling constants in the X\(^2 \sum\)-A\(^2 \Pi\) system of the ethynyl radical are computed by means of tbe ab initio metbod calculations. The results point at tbe importance of taking into account the coupling of a1l tbree electronic states in question ( I\(^2\)A', 2\(^2\)A', and 1\(^2\)A") for a reliable explanation of the available experimental findings. The mean values of the hfcc's for K = 0 and 1 levels in \(^{13}\)C\(_2\)H and \(^{13}\)C\(_2\)D in the energy range up to 6000 cm\(^{-1}\) are predicted.
The energy difference between the three lowest-lying isomers of C\(_6\) the linear \(^3 \sum ^-\) state and the two ring forms,the benzene structure (\(^1\)A\(_{18}\)) possessing D\(_{6h}\) symmetry and a distorted cyclic form ( \(^1\)A'\(_1\), D\(_{3h}\) symmetry) have been calculated using various ab initio methods. Variational methods such as multireference configuration interaction (MR-CI) and complete active space second order perturbatiOn treatment (CASPT2) have been applied, as weil as perturbational treatments and coupled cluster calculations (CCD). The correlation of all valence shell electrons is found to be important for a balanced description of the isomers of C\(_6\) . Methods which do not account for higher-order effects appropriately proved to be unsuitable for calculating the energy difference correctly. The results from multireference configuration interaction methods show that the isomers are close in energy with the cyclic forms somewhat lower than the linear form. The ring form possessing D\(_{3h}\) symmetry (\(^1\)A'\(_1\)} is found tobe the lowest-lying structure.
The present work consists of two parts. The first one deals with theoretical questions and tests the performance of orbitals obtained from a self-interaction free KS method, the LHFapproach, in multireference ab initio methods. The purpose of this part is to enable a more efficient computation of excitation energies, which is important for the spectroscopic characterization of many organic and bioorganic molecules. The second part focuses on bioorganic questions and studies the base pairing properties of the purine base xanthine in order to explain, e.g., the unusually high stability of selfpairing xanthine alanyl-PNA double strands and the mutagenicity of xanthine formed in DNA. Part1: In contrast to HF- and standard DFT-methods, the LHF-approach leads to a fully bound virtual orbital spectrum, because Coulomb self interactions are exactly canceled in the LHFansatz. Furthermore, the energies of the occupied orbitals are not upshifted, like it is the case for standard DFT-methods, so that Koopmans' theorem remains valid. In line with this, also the occupied LHF-orbitals are somewhat more compact than standard DFT-orbitals. The present work shows that both properties are of great benefit for MR methods. The virtual LHF-orbitals are well optimized and allow an efficient description of excited states and static correlation in both MRCI- and MRPT2-approaches. Furthermore, the higher compactness of the occupied LHF- compared to standard DFT-orbitals leads to a better description of the center ion of Rydberg states. However, for each of the two advantages mentioned at least one example molecule has been found, for which LHF-orbitals actually perform worse than HF-and/or standard DFT-orbitals. This shows, that even though LHF virtual orbitals allow an excellent MRCI- and MRPT2-description for the electronically excited states of a large number of molecules, this cannot be generalized and their performance needs to be tested for each individual case. In the second part of the present work, the base pairing properties of xanthine and xanthine derivatives were studied. The purpose of this part was to find an explanation for the unexpectedly high stability of the xanthine alanyl PNA double strand. Furthermore, it was analyzed, why xanthine, that is formed from guanine in DNA under chemical stress, is able to form mismatched base pairs with the pyrimidine base thymine. Stability of xanthine alanyl PNA: In the first step, the regioisomer present in the considered alanyl PNA was identified to be the N7-regioisomer of xanthine by a theoretical analysis of the 13C-NMR spectrum. To analyze the stability of the xanthine self-pairing, a simplified model was set up, in which the stability of the PNA double strand was explained solely by the energy contributions from H-bonding and base stacking. For that purpose, the dimerization and stacking energies for the xanthine-xanthine, guaninecytosine, adenine-thymine and xanthine-2,6-diaminopurine base pairs were computed using DFT and MP2 methods. Solvent effects were taken into account by the conductor like screening model. The influence of the peptide backbone on the stacking geometry was considered by force field optimizations. While the individual contributions from hydrogen bonding and stacking do not correlate with the melting temperature Tm, the sum of both correlates linearly with Tm. This correlation is somewhat surprising, because this means that the effects of the entropy and the molecular water environment either cancel or are similar for all systems compared. In this model, the stability of the xanthine selfpairing mainly stems from an enlarged stacking interaction, while the H-bonds give only minor contributions to the stability of the xanthine selfpaired double strand of alanyl-PNA. Base pairing properties of N9-Xanthine: The computation of the base pairing properties of N9-xanthine revealed a strong variation in the individual H-bond strengths for the selfpairing of xanthine, that range from -4 to -11 kcal/mol in the gas phase and -2.5 to -5 kcal/mol in polar solvent. By comparison with model systems it was shown that the strong variance of the H-bond strength is mainly due to attractive or repulsive secondary electrostatic interactions. For the homodimer of hypoxanthine it was shown that the increase of aromaticity in the pyrimidine ring upon dimer formation leads to a strengthening of the hydrogen bonds. Mutagenicity of hypoxanthine and xanthine: Several neutral and anionic Watson-Crick base pairs of xanthine were computed with MP2- and DFT-methods in order to explain the mutagenicity of hypoxanthine and xanthine. Also basepairs involving tautomeric forms of xanthine and hypoxanthine were considered. To evaluate the dimerization energies found, the dimers were classified into pairings that have the exact geometry of the canonical base pairs and those that realize a distorted Watson-Crick pairing mode. The computations show that a stable pairing which realizes the exact geometry of a canonical Watson Crick base pairing is only possible for the pairing of xanthine to cytosine, however, the base pairs are only weakly bound. The dimerization energies of both the neutral and the anionic pairing is around 0 kcal/mol, so that the xanthine-cytosine base pairs are incorporated into DNA solely because the base pairs fulfill the geometric demands of DNA polymerase, but it does not profit from any additional stabilization due to hydrogen bonding. The bonding that in the Watson-Crick pairing mode xanthine has almost no affinity to cytosine is in correspondence with the experimental result that the cytosine-xanthine base pair is incorporated into DNA at a much lower rate than the cytosine-guanine base pair, which has a very strong hydrogen bonding. While the affinity of xanthine to cytosine is very low, the computations predict that xanthine is able to form a stable Watson-Crick pairing with thymine. However, the pairing has a somewhat distorted Watson-Crick geometry, so that its high stability is outbalanced by the worsened fit to the binding pocket of DNA-polymerase. As a consequence, the xanthinethymine pairing is incorporated into DNA not at a faster, but only at a rate comparable to that of the xanthine-cytosine pairing.
Thermoresponsive polymers are frequently involved in the development of materials for various applications. Here, polymers containing poly(2- benzhydryl-2-oxazine) (pBhOzi) repeating units are described for the first time. The homopolymer pBhOzi and an ABA type amphiphile comprising two flanking hydrophilic A blocks of poly(2-methyl-2-oxazoline) (pMeOx) and the hydrophobic aromatic pBhOzi central B block (pMeOx-b-pBhOzi-b-pMeOx) are synthesized and the latter is shown to exhibit inverse thermogelling properties at concentrations of 20 wt.% in water. This behavior stands in contrast to a homologue ABA amphiphile consisting of a central poly(2-benzhydryl-2-oxazoline) block (pMeOx-b-pBhOx-b-pMeOx). No inverse thermogelling is observed with this polymer even at 25 wt.%. For 25 wt.% pMeOx-b-pBhOzi-b-pMeOx, a surprisingly high storage modulus of ≈22 kPa and high values for the yield and flow points of 480 Pa and 1.3 kPa are obtained. Exceeding the yield point, pronounced shear thinning is observed. Interestingly, only little difference between self-assemblies of pMeOx-b-pBhOzi-b-pMeOx and pMeOx-b-pBhOx-b-pMeOx is observed by dynamic light scattering while transmission electron microscopy images suggest that the micelles of pMeOx-b-pBhOzi-b-pMeOx interact through their hydrophilic coronas, which is probably decisive for the gel formation. Overall, this study introduces new building blocks for poly(2-oxazoline) and poly(2-oxazine)-based self-assemblies, but additional studies will be needed to unravel the exact mechanism.
Quantum chemical calculations of circular dichroism (CD) spectra in combination with experimental CD studies are one of the most efficient analytical tools for the elucidation of the three-dimensional structure of a chiral molecule. In the present work 18 chiral compounds of most different molecular structures and origins were investigated using various theoretical methods (the semiempirical CIS methods, the time-dependent DFT and DFT/MRCI approaches). The advantages and limitations of the applied methods were discussed in the context of the studied compounds. Furthermore, the last part of this work deals with the CD investigations of a chiral compound in the crystalline state. A well-known natural product with a specific conformation/CD spectrum behavior was used as a model compound to examine a novel solid-state CD method and to investigate the possibility of its improvement to provide a higher reliability for the assignment of the absolute configuration.
Sekundäre Pflanzenstoffe sind aufgrund ihrer großen Strukturvielfalt sowohl als Leit- und Wirkstoffe für die Pharma- und Pflanzenschutzforschung in den Industrieländern als auch zur unmittelbaren medizinischen Grundversorgung der Entwicklungsländer von herausragender Bedeutung für den Menschen. Eine Klasse pharmakologisch, biogenetisch und chemotaxonomisch interessanter Sekundärmetabolite sind die Naphthylisochinolin-Alkaloide, die ausschließlich in den eng verwandten tropischen Pflanzenfamilien Ancistrocladaceae und Dioncophyllaceae vorkommen. Der Untersuchung der Biosynthese dieser acetogeninen Metabolite (z.B. Dioncophyllin A), einschließlich einiger Vorstufenderivate (z.B. Plumbagin, Droseron und Isoshinanolon), durch die konsequente Etablierung von in-vitro-Systemen sowie der Biologie ihrer pflanzlichen Produzenten am Naturstandort und in Kultur, wurde das Hauptaugenmerk in dieser Arbeit gewidmet. Außerdem wurden die biologischen Aktivitäten der Substanzen getestet. Daneben wurde die Strategie der stabilisotopenmarkierten Vorstufenverfütterung exemplarisch auf eine Art aus den nahe verwandten Nepenthaceen ausgeweitet, indem der natürliche Aufnahmemechanismus der carnivoren Pflanze ausgenutzt wurde. Anhand von Verfütterungsexperimenten mit ebenfalls neu etablierten Zellkulturen konnte außerdem die Struktur eines neuartigen Pyridon-Alkaloids (Antidesmon) aus Antidesma membranaceum, das ursprünglich als Isochinolin beschrieben worden war, revidiert werden und dessen ungewöhnliche Biosynthese aus Acetat und Glycin aufgeklärt werden.
Activating Organic Phosphorescence via Heavy Metal–π Interaction Induced Intersystem Crossing
(2022)
Heavy‐atom‐containing clusters, nanocrystals, and other semiconductors can sensitize the triplet states of their surface‐bonded chromophores, but the energy loss, such as nonradiative deactivation, often prevents the synergistic light emission in their solid‐state coassemblies. Cocrystallization allows new combinations of molecules with complementary properties for achieving functionalities not available in single components. Here, the cocrystal formation that employs platinum(II) acetylacetonate (Pt(acac)\(_{2}\)) as a triplet sensitizer and electron‐deficient 1,4,5,8‐naphthalene diimides (NDIs) as organic phosphors is reported. The hybrid cocrystals exhibit room‐temperature phosphorescence confined in the low‐lying, long‐lived triplet state of NDIs with photoluminescence (PL) quantum yield (Φ\(_{PL}\)) exceeding 25% and a phosphorescence lifetime (τ\(_{Ph}\)) of 156 µs. This remarkable PL property benefits from the noncovalent electronic and spin–orbital coupling between the constituents.
Activation of Ge−H and Sn−H Bonds with N‐Heterocyclic Carbenes and a Cyclic (Alkyl)(amino)carbene
(2023)
A study of the reactivity of several N‐heterocyclic carbenes (NHCs) and the cyclic (alkyl)(amino)carbene 1‐(2,6‐di‐iso‐propylphenyl)‐3,3,5,5‐tetramethyl‐pyrrolidin‐2‐ylidene (cAAC\(^{Me}\)) with the group 14 hydrides GeH2Mes2 and SnH2Me2 (Me=CH\(_{3}\), Mes=1,3,5‐(CH\(_{3}\))\(_{3}\)C\(_{6}\)H\(_{2}\)) is presented. The reaction of GeH\(_{2}\)Mes\(_{2}\) with cAAC\(^{Me}\) led to the insertion of cAAC\(^{Me}\) into one Ge−H bond to give cAAC\(^{Me}\)H−GeHMes\(_{2}\) (1). If 1,3,4,5‐tetramethyl‐imidazolin‐2‐ylidene (Me\(_{2}\)Im\(^{Me}\)) was used as the carbene, NHC‐mediated dehydrogenative coupling occurred, which led to the NHC‐stabilized germylene Me\(_{2}\)Im\(^{Me}\)⋅GeMes\(_{2}\) (2). The reaction of SnH\(_{2}\)Me\(_{2}\) with cAAC\(^{Me}\) also afforded the insertion product cAAC\(^{Me}\)H−SnHMe\(_{2}\) (3), and reaction of two equivalents Me\(_{2}\)Im\(^{Me}\) with SnH\(_{2}\)Me\(_{2}\) gave the NHC‐stabilized stannylene Me\(_{2}\)Im\(^{Me}\)⋅SnMe\(_{2}\) (4). If the sterically more demanding NHCs Me\(_{2}\)Im\(^{Me}\), 1,3‐di‐isopropyl‐4,5‐dimethyl‐imidazolin‐2‐ylidene (iPr\(_{2}\)Im\(^{Me}\)) and 1,3‐bis‐(2,6‐di‐isopropylphenyl)‐imidazolin‐2‐ylidene (Dipp\(_{2}\)Im) were employed, selective formation of cyclic oligomers (SnMe\(_{2}\))\(_{n}\) (5; n=5–8) in high yield was observed. These cyclic oligomers were also obtained from the controlled decomposition of cAAC\(^{Me}\)H−SnHMe\(_{2}\) (3).
Insulin-like growth factor-I (IGF-I) is a 70-amino acid polypeptide with a molecular weight of approximately 7.6 kDa acting as an anabolic effector. It is essential for tissue growth and remodeling. Clinically, it is used for the treatment of growth disorders and has been proposed for various other applications including musculoskeletal diseases. Unlike insulin, IGF-I is complexed to at least six high-affinity binding proteins (IGFBPs) exerting homeostatic effects by modulating IGF-I availability to its receptor (IGF-IR) on most cells in the body as well as changing the distribution of the growth factor within the organism.1-3 Short half-lived IGF-I have been the driving forces for the design of localized IGF-I depot systems or protein modification with enhanced pharmacokinetic properties. In this thesis, we endeavor to present a versatile biologic into which galenical properties were engineered through chemical synthesis, e.g., by site-specific coupling of biomaterials or complex composites to IGF-I. For that, we redesigned the therapeutic via genetic codon expansion resulting in an alkyne introduced IGF-I, thereby becoming a substrate for biorthogonal click chemistries yielding a site-specific decoration.
In this approach, an orthogonal pyrrolysine tRNA synthetase (PylRS)/tRNAPyl CUA pair was employed to direct the co-translational incorporation of an unnatural amino acid—¬propargyl-L-lysine (plk)—bearing a clickable alkyne functional handle into IGF-I in response to the amber stop codon (UAG) introduced into the defined position in the gene of interest. We summarized the systematic optimization of upstream and downstream process alike with the ultimate goal to increase the yield of plk modified IGF-I therapeutic, from the construction of gene fusions resulting in (i) Trx-plk-IGF-I fusion variants, (ii) naturally occurring pro-IGF-I protein (IGF-I + Ea peptide) (plk-IGF-I Ea), over the subsequent bacterial cultivation and protein extraction to the final chromatographic purification. The opportunities and hurdles of all of the above strategies were discussed. Evidence was provided that the wild-type IGF-I yields were pure by exploiting the advantages of the pHisTrx expression vector system in concert with a thrombin enzyme with its highly specific proteolytic digestion site and multiple-chromatography steps. The alkyne functionality was successfully introduced into IGF-I by amber codon suppression. The proper folding of plk-IGF-I Ea was assessed by WST-1 proliferation assay and the detection of phosphorylated AKT in MG-63 cell lysate. The purity of plk-IGF-I Ea was monitored with RP-HPLC and SDS-PAGE analysis. This work also showed site-specific coupling an alkyne in plk-IGF-I Ea by copper (I)-catalyzed azide-alkyne cycloaddition (CuAAC) with potent activities in vitro. The site-specific immobilization of plk-IGF-I Ea to the model carrier (i.e., agarose beads) resulted in enhanced cell proliferation and adhesion surrounding the IGF-I-presenting particles. Cell proliferation and differentiation were enhanced in the accessibility of IGF-I decorated beads, reflecting the multivalence on cellular performance.
Next, we aimed at effectively showing the disease environment by co-delivery of fibroblast growth factor 2 (FGF2) and IGF-I, deploying localized matrix metalloproteinases (MMPs) upregulation as a surrogate marker driving the response of the drug delivery system. For this purpose, we genetically engineered FGF2 variant containing an (S)-2-amino-6-(((2-azidoethoxy)carbonyl)amino)hexanoic acid incorporated at its N-terminus, followed by an MMPs-cleavable linker (PCL) and FGF2 sequence, thereby allowing site-directed, specific decoration of the resultant azide-PCL-FGF2 with the previously mentioned plk-IGF-I Ea to generate defined protein-protein conjugates with a PCL in between. The click reaction between plk-IGF-I Ea and azide-PCL-FGF2 was systematically optimized to increase the yield of IGF-FGF conjugates, including reaction temperature, incubation duration, the addition of anionic detergent, and different ratios of the participating biopharmaceutics. The challenge here was that CuAAC reaction components or conditions might oxidize free cysteines of azide-PCL-FGF2 and future work needs to present the extent of activity retention after conjugation. Furthermore, our study provides potential options for dual-labeling of IGF-I either by the introduction of unnatural amino acids within two distinct positions of the protein of interest for parallel “double-click” labeling of the resultant plk-IGF-I Ea-plk or by using a combination of enzymatic-catalyzed and CuAAC bioorthogonal coupling strategies for sequentially dual-labeling of plk-IGF-I Ea.
In conclusion, genetic code expansion in combination with click-chemistry provides the fundament for novel IGF-I analogs allowing unprecedented site specificity for decoration. Considerable progress towards IGF-I based therapies with enhanced pharmacological properties was made by demonstrating the feasibility of the expression of plk incorporated IGF-I using E. coli and retained activity of unconjugated and conjugated IGF-I variant. Dual-labeling of IGF-I provides further insights into the functional requirements of IGF-I. Still, further investigation warrants to develop precise IGF-I therapy through unmatched temporal and spatial regulation of the pleiotropic IGF-I.
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Die ersten Beispiele für Lewis-Basen-Addukte des Stammboraphosphaketens H\(_{2}\)B-PCO und ihre cyclischen Dimere wurden hergestellt. Eines dieser Addukte zeigt unter milden Bedingungen eine Decarbonylierung und anschließende Insertion des Phosphinidens in die B-C-Bindung eines Borols, was in der Bildung sehr seltener Beispiele für 1,2-Phosphaborinine, B,P-Isostere von Benzol, resultiert. Die starken Donoreigenschaften dieser 1,2-Phosphaborinine wurden durch die Synthese ihrer π-Komplexe mit Metallen der Gruppe 6 bestätigt.
Adenosine receptor ligands: coumarin−chalcone hybrids as modulating agents on the activity of hARs
(2020)
Adenosine receptors (ARs) play an important role in neurological and psychiatric disorders such as Alzheimer's disease, Parkinson's disease, epilepsy and schizophrenia. The different subtypes of ARs and the knowledge on their densities and status are important for understanding the mechanisms underlying the pathogenesis of diseases and for developing new therapeutics. Looking for new scaffolds for selective AR ligands, coumarin–chalcone hybrids were synthesized (compounds 1–8) and screened in radioligand binding (hA\(_1\), hA\(_{2A}\) and hA\(_3\)) and adenylyl cyclase (hA\(_{2B}\)) assays in order to evaluate their affinity for the four human AR subtypes (hARs). Coumarin–chalcone hybrid has been established as a new scaffold suitable for the development of potent and selective ligands for hA\(_1\) or hA\(_3\) subtypes. In general, hydroxy-substituted hybrids showed some affinity for the hA\(_1\), while the methoxy counterparts were selective for the hA\(_3\). The most potent hA\(_1\) ligand was compound 7 (K\(_i\) = 17.7 µM), whereas compound 4 was the most potent ligand for hA\(_3\) (K\(_i\) = 2.49 µM). In addition, docking studies with hA\(_1\) and hA\(_3\) homology models were established to analyze the structure–function relationships. Results showed that the different residues located on the protein binding pocket could play an important role in ligand selectivity.
Adipose tissue defects and related pathologies still represent major challenges in reconstructive surgery. Based on to the paradigm ‘replace with alike’, adipose tissue is considered the ideal substitute material for damaged soft tissue [1-3]. Yet the transfer of autologous fat, particularly larger volumes, is confined by deficient and unpredictable long term results, as well as considerable operative morbidity at the donor and recipient site [4-6], calling for innovative treatment options to improve patient care.
With the aim to achieve complete regeneration of soft tissue defects, adipose tissue engineering holds great promise to provide functional, biologically active adipose tissue equivalents. Here, especially long-term maintenance of volume and shape, as well as sufficient vascularization of engineered adipose tissue represent critical and unresolved challenges [7-9]. For adipose tissue engineering approaches to be successful, it is thus essential to generate constructs that retain their initial volume in vivo, as well as to ensure their rapid vascularization to support cell survival and differentiation for full tissue regeneration [9,10]. Therefore, it was the ultimate goal of this thesis to develop volume-stable 3D adipose tissue constructs and to identify applicable strategies for sufficient vascularization of engineered constructs. The feasibility of the investigated approaches was verified by translation from in vitro to in vivo as a critical step for the advancement of potential regenerative therapies.
For the development of volume-stable constructs, the combination of two biomaterials with complementary properties was successfully implemented. In contrast to previous approaches in the field using mainly non-degradable solid structures for mechanical protection of developing adipose tissue [11-13], the combination of a cell-instructive hydrogel component with a biodegradable porous support structure of adequate texture was shown advantageous for the generation of volume-stable adipose tissue. Specifically, stable fibrin hydrogels previously developed in our group [14] served as cell carrier and supported the adipogenic development of adipose-derived stem cells (ASCs) as reflected by lipid accumulation and leptin secretion. Stable fibrin gels were thereby shown to be equally supportive of adipogenesis compared to commercial TissuCol hydrogels in vitro. Using ASCs as a safe source of autologous cells [15,16] added substantial practicability to the approach. To enhance the mechanical strength of the engineered constructs, porous biodegradable poly(ε caprolactone)-based polyurethane (PU) scaffolds were introduced as support structures and shown to exhibit adequately sized pores to host adipocytes as well as interconnectivity to allow coherent tissue formation and vascularization. Low wettability and impaired cell attachment indicated that PU scaffolds alone were insufficient in retaining cells within the pores, yet cytocompatibility and differentiation of ASCs were adequately demonstrated, rendering the PU scaffolds suitable as support structures for the generation of stable fibrin/PU composite constructs (Chapter 3).
Volume-stable adipose tissue constructs were generated by seeding the pre-established stable fibrin/PU composites with ASCs. Investigation of size and weight in vitro revealed that composite constructs featured enhanced stability relative to stable fibrin gels alone. Comparing stable fibrin gels and TissuCol as hydrogel components, it was found that TissuCol gels were less resilient to degradation and contraction. Composite constructs were fully characterized, showing good cell viability of ASCs and strong adipogenic development as indicated by functional analysis via histological Oil Red O staining of lipid vacuoles, qRT-PCR analysis of prominent adipogenic markers (PPARγ, C/EBPα, GLUT4, aP2) and quantification of leptin secretion. In a pilot study in vivo, investigating the suitability of the constructs for transplantation, stable fibrin/PU composites provided with a vascular pedicle gave rise to areas of well-vascularized adipose tissue, contrasted by insufficient capillary formation and adipogenesis in constructs implanted without pedicle. The biomaterial combination of stable fibrin gels and porous biodegradable PU scaffolds was thereby shown highly suitable for the generation of volume-stable adipose tissue constructs in vivo, and in addition, the effectiveness of immediate vascularization upon implantation to support adipose tissue formation was demonstrated (Chapter 4).
Further pursuing the objective to investigate adequate vascularization strategies for engineered adipose tissue, hypoxic preconditioning was conducted as a possible approach for in vitro prevascularization. In 2D culture experiments, analysis on the cellular level illustrated that the adipogenic potential of ASCs was reduced under hypoxic conditions when applied in the differentiation phase, irrespective of the oxygen tension encountered by the cells during expansion. Hypoxic treatment of ASCs in 3D constructs prepared from stable fibrin gels similarly resulted in reduced adipogenesis, whereas endothelial CD31 expression as well as enhanced leptin and vascular endothelial growth factor (VEGF) secretion indicated that hypoxic treatment indeed resulted in a pro-angiogenic response of ASCs. Especially the observed profound regulation of leptin production by hypoxia and the dual role of leptin as adipokine and angiogenic modulator were considered an interesting connection advocating further study. Having confirmed the hypothesis that hypoxia may generate a pro-angiogenic milieu inside ASC-seeded constructs, faster vessel ingrowth and improved vascularization as well as an enhanced tolerance of hypoxia-treated ASCs towards ischemic conditions upon implanatation may be expected, but remain to be verified in rodent models in vivo (Chapter 5).
Having previously been utilized for bone and cartilage engineering [17-19], as well as for revascularization and wound healing applications [20-22], stromal-vascular fraction (SVF) cells were investigated as a novel cell source for adipose tissue engineering. Providing cells with adipogenic differentiation as well as vascularization potential, the SVF was applied with the specific aim to promote adipogenesis and vascularization in engineered constructs in vivo. With only basic in vitro investigations by Lin et al. addressing the SVF for adipose repair to date [23], the present work thoroughly investigated SVF cells for adipose tissue construct generation in vitro, and in particular, pioneered the application of these cells for adipose tissue engineering in vivo.
Initial in vitro experiments compared SVF- and ASC-seeded stable fibrin constructs in different medium compositions employing preadipocyte (PGM-2) and endothelial cell culture medium (EGM-2). It was found that a 1:1 mixture of PGM-2 and EGM-2, as previously established for co-culture models of adipogenesis [24], efficiently maintained cells with adipogenic and endothelial potential in SVF-seeded constructs in short and long-term culture setups. Observations on the cellular level were supported by analysis of mRNA expression of characteristic adipogenic and endothelial markers. In preparation of the evaluation of SVF-seeded constructs under in vivo conditions, a whole mount staining (WMS) method, facilitating the 3D visualization of adipocytes and blood vessels, was successfully established and optimized using native adipose tissue as template (Chapter 6).
In a subcutaneous nude mouse model, SVF cells were, for the first time in vivo, elucidated for their potential to support the functional assembly of vascularized adipose tissue. Investigating the effect of adipogenic precultivation of SVF-seeded stable fibrin constructs in vitro prior to implantation on the in vivo outcome, hormonal induction was shown beneficial in terms of adipocyte development, whereas a strong vascularization potential was observed when no adipogenic inducers were added. Via histological analysis, it was proven that the developed structures were of human origin and derived from the implanted cells. Applying SVF cells without precultivation in vitro but comparing two different fibrin carriers, namely stable fibrin and TissuCol gels, revealed that TissuCol profoundly supported adipose formation by SVF cells in vivo. This was contrasted by only minor SVF cell development and a strong reduction of cell numbers in stable fibrin gels implanted without precultivation. Histomorphometric analysis of adipocytes and capillary structures was conducted to verify the qualitative results, concluding that particularly SVF cells in TissuCol were highly suited for adipose regeneration in vivo. Employing the established WMS technique, the close interaction of mature adipocytes and blood vessels in TissuCol constructs was impressively shown and via species-specific human vimentin staining, the expected strong involvement of implanted SVF cells in the formation of coherent adipose tissue was confirmed (Chapter 7).
With the development of biodegradable volume-stable adipose tissue constructs, the application of ASCs and SVF cells as two promising cell sources for functional adipose regeneration, as well as the thorough evaluation of strategies for construct vascularization in vitro and in vivo, this thesis provides valuable solutions to current challenges in adipose tissue engineering. The presented findings further open up new perspectives for innovative treatments to cure soft tissue defects and serve as a basis for directed approaches towards the generation of clinically applicable soft tissue substitutes.
Micron‐sized supraparticles, consisting of a plurality of discrete nano‐ and microscale functional units, are assembled and fused by means of a droplet extrusion process. By combining nano magnetite, activated carbon, and conductive carbon with a polymeric binder matrix, particles are obtained which unite good magnetic properties, electrical conductivity, and adsorber activity through the high accessible surface area of the incorporated activated carbon of about 570 m\(^{2}\) g\(^{-1}\), thereby enabling a new approach toward sustainable water treatment processes. Due to the interplay of the components, it is possible to adsorb target substances, dissolved in the water which is demonstrated by the adsorption of the model dye methylene blue. A very fast adsorption kinetic and an adsorption capacity of about 400 mg g\(^{-1}\) is determined. By using the developed composite particles, it is also possible to electrochemically alter substances flowing through a magnetically‐stabilized fluidized‐bed reactor by electrochemically charging/discharging, significantly supported by the magnetic field enabling alternatingly optimum mobility/adsorption phases with contact/charging intervals. The electrochemical conversion can be increased up to 151% depending on the applied flow‐rate and electrical voltage. By applying an external magnetic field, a further increase of electrochemical conversion of up to 70% can be observed.
In an attempt to assess the structural requirements of hexahydro-sila-difenidol for potency and selectivity, a series of analogues modified in the amino group and the phenyl ring were investigated for their affinity to muscarinic M1- (rabbit vas deferens), Mr (guinea-pig atria) and Mr (guinea-pig ileum) receptors. All compounds were competitive antagonists in the three tissues. Their affinities to the three muscarinic receptor subtypes differed by more than two orders of magnitude and the observed receptor selectivities were not associated with high affinity. The pyrrolidino and hexamethyleneimino analogues, compounds substituted in the phenylring with a methoxy group or a chlorine atom as weil as p-fluoro-hexahydro-difenidol displayed the same affinity profile as the parent compound, hexahydro-sila-difenidol: M1 = M3 > M2 • A different selectivity patternwas observed for p-fluoro-hexahydro-sila-difenidol: M3 > M1 > M2 • This compound exhibited its highest affinity for M3-receptors in guinea-pig ileum (pA 2 = 7.84), intermediate affinity for M1-receptors in rabbit vas deferens (pA 2 = 6.68) and lowest affinity for the Mrreceptors in guinea-pig atria (pA 2 = 6.01). This receptor selectivity profile of p-fluoro-hexahydro-sila-difenidol was confirmed in ganglia (M1), atria (M2 ) and ileum (M 3 ) of the rat. Furthermore, dose ratios obtained with either pirenzepine (Mt) or hexahydrosila- difenidol (M2 and M3) and the p-fluoro analogue used in combination suggested that the antagonism was additive, implying mutual competition with a single population of muscarinic receptor subtypes. These results indicate that p-fluoro-hexahydro-sila-difenidol represents a valuable tool for characterization of muscarinic receptor subtypes.
No abstract available
In order to develop all-fish expression vectors for microinjection into fertilized fish eggs, we have prepared the following cunstructs: rainbow trout metallothionein a/b and the gilthead seabream growth hormone cDNA (ptMTa-gbsGHcDNA, ptMTb-gsbGHcDNA), carp ß-actin gilthead seabream GH cDNA (pcAßgsbGHcDNA). The inducible metallothionein promoters a and b were cloned from rainbow trout, and the constitutive promoter ß-actin was isolated from carp. The metallothionein promoters were cloned by using the PCR technique. The tMTa contains 430 bp, while the tMTb contains 260 bp (Hong et al. 1992). These two promoters were introduced to pGEM-3Z containing the GH cDNA of Sparus aurata to form ptMTa-gsbGH and ptMTb-gsbGH, respectively. The carp cytoplasmic ß-actin gene was chosen as a source for isolating strong constitutive regulatory sequences. One of these regulatory sequences in pUC118 was Iigated to GH cDNA of S. aurata to form the pcAß-gsbGHcDNA. Expression of the constructs containing the metallothionein promoters was tested in fish cell culture and was found tobe induced effectively by zinc. The ptMTa gsb-GH cDNA construct was microinjected into fertilized carp eggs, and integration in the genome of carp was detected in the DNA isolated from fins at the age of two months.
No abstract available
In LAS-Glaskeramiken, die besondere Verbreitung bei Anwendungen als Kochfläche, Brandschutzglas und Bauteil für präzise Optik gefunden haben, werden vorrangig die Keimbildner TiO2 und ZrO2 eingesetzt. Transparente Glaskeramiken weisen jedoch eine mehr oder weniger starke Gelbfärbung auf, die vorrangig aus dem Einsatz von TiO2 zusammen mit unvermeidbaren Fe2O3-Verunreinigungen resultiert. Die Minimierung dieser Gelbfärbung gewinnt zunehmend an Bedeutung. Ziel der vorliegenden Arbeit ist die Prüfung, inwiefern die Verringerung der Eigenfarbe einer transparenten LAS-Glaskeramik durch Ersatz des färbenden Keimbildners TiO2 durch einen weniger färbenden Keimbildner möglich ist, ohne dass das gute Keimbildungsvermögen beeinträchtigt wird. Verschiedene alternative Keimbildner zu TiO2 wurden stets in Kombination mit ZrO2 hinsichtlich Keimbildungsvermögen und Färbung/Transmission untersucht sowie andere Kerneigenschaften im Vergleich zu der Standardkeimbildnerkombination TiO2/ZrO2 diskutiert. Signifikante Vorteile bzgl. Eigenfarbe und Transmission gegenüber dem TiO2/ZrO2-gekeimten Referenzmaterial konnten nur bei der Keimbildnerkombination SnO2/ZrO2 gefunden werden. Die Transmission ist mit 89% statt 87% beim Referenzmaterial höher, die Eigenfarbe ist mit dem Farbort a*/b* = -0,1/+2,3 deutlich näher am Unbuntpunkt als die Referenz a*/b* = -0,6/+5,1, der Yellowness Index reduziert sich von 9,5 auf 4,6.
Amber Light Control of Peptide Secondary Structure by a Perfluoroaromatic Azobenzene Photoswitch
(2023)
The incorporation of photoswitches into the molecular structure of peptides and proteins enables their dynamic photocontrol in complex biological systems. Here, a perfluorinated azobenzene derivative triggered by amber light was site‐specifically conjugated to cysteines in a helical peptide by perfluoroarylation chemistry. In response to the photoisomerization (trans→cis) of the conjugated azobenzene with amber light, the secondary structure of the peptide was modulated from a disorganized into an amphiphilic helical structure.
Die muscarinischen Rezeptoren sind ein wichtiger Bestandteil des parasympathischen Nervensystems. Sie gehören zur großen Gruppe der G-Protein-gekoppelten Rezeptoren, die nach ihrer Verwandtschaft in drei große Klassen eingeteilt werden können. Die muscarinischen Rezeptoren gehören zur Klasse A, den rhodopsinähnlichen Rezeptoren. Durch die im Jahr 2000 vorgenommene Aufklärung der hochauflösenden Röntgenkristallstruktur des Rinderrhodpsins und die hohe Aminosäuresequenzähnlichkeit der G-Protein-gekoppelten Rezeptoren hat man eine sehr gute Modellvorstellung über den Aufbau der G-Protein-gekoppelten Rezeptoren. Die Rezeptoren bestehen aus sieben transmembranalen Helices, die von drei intrazellulären und drei extrazellulären Loops stabilisiert werden. Bis heute konnten fünf Rezeptorsubtypen gentechnisch klassifiziert werden, die sich durch ihre Gewebeverteilung und Funktion unterscheiden. Allen Subtypen ist eine hohe Sequenzhomologie im Bereich der orthosteren Bindungsstelle gemeinsam, so dass die Entwicklung von subtyp-spezifischen orthosteren Liganden sehr schwierig ist. Außer der orthosteren Bindungsstelle konnte noch eine weitere Bindungsstelle am muscarinischen Rezeptor identifiziert werden. Diese befindet sich weiter außerhalb im Rezeptor in einem Bereich, der über die fünf Rezeptorsubtypen nicht sehr stark konserviert ist, so dass die Entwicklung von subtyp-spezifischen Liganden möglich ist. An dieser zweiten Bindungsstelle binden allostere Modulatoren. Hierbei handelt es sich um Substanzen, die ohne den orthosteren Liganden keinen Effekt am Rezeptor auslösen, dafür aber die Gleichgewichtsbindung des orthosteren Liganden beeinflussen können. Der Einfluss auf die Gleichgewichtsbindung geschieht wechselseitig und kann positiv, neutral oder negativ kooperativ sein. Zusätzlich üben allostere Modulatoren einen Effekt auf die Dissoziation des orthosteren Liganden aus. Die meisten bisher gefunden allosteren Modulatoren erniedrigen die Dissoziationsgeschwindikeit des orthosteren Liganden vom Rezeptor. Die Summe dieser Eigenschaften machen die allosteren Modulatoren sehr interessant für die Arzneimitteltherapie. Das Ziel dieser Arbeit war die Synthese strukturell neuer allosterer Modulatoren des muscarinischen Rezeptors unter Anwendung des postulierten Pharmakophormodells. Als Ausgangspunkt sollten geländerhelicale Moleküle dienen, die strukturell abgewandelt dieses Pharmakophormodell sehr gut erfüllen. Die geländerhelicalen Moleküle ähneln in ihrem dreidimensionalen Aufbau dem Geländer einer Wendeltreppe. Sie sind durch die Brücken zwischen den aromatischen Bereichen sehr rigide Moleküle, so dass es nur wenige genau definierte Konformationen gibt. Grundsätzlich können drei Atropisomere unterschieden werden, wobei zwei zueinander enantiomer sind. Geplant war die Synthese eine Reihe von tertiären Aminen oder quartären Ammoniumsalzen. Die Synthese der Ausgangsverbindung konnte nach der Vorschrift von Kiupel erfolgen, war aber nur mit geringer Ausbeute möglich. Deshalb wurde dieser Syntheseweg nicht weiterverfolgt. Als Alternative bot sich an, auf die Brücken zwischen den aromatischen Ringen zu verzichten. Die so entstandenen Verbindungen sind weniger rigide und können sich deshalb gegebenenfalls besser an den Rezeptor anpassen. Grundsätzlich können je nach Substitutionsmuster zwei Synthesewege verfolgt werden. Beide Varianten erfüllen das postulierte Pharmakophormodell. Der Aufbau des Grundgerüstes erfolgt mittels einer nickelkatalysierten Grignard-Kupplung. Danach erfolgen eine Wohl-Ziegler-Seitenkettenbromierung und eine Verlängerung der Seitenkette im Sinne einer Alkylierung mittels Malonsäurediethylester und einer Hilfsbase. Anschließend erfolgen die Decarboxylierung und die Umsetzung zum Amid, das zum Amin reduziert werden kann. Betrachtet man die Lage der Pharmakophorelemente so variiert der Abstand der positiv geladenen Stickstoffe je nach Konformation zwischen 5 Å und 15 Å, so dass ein weiter Bereich abgedeckt werden kann. Der Abstand der aromatischen Bereiche bleibt relativ stabil. Die pharmakologische Testung der Verbindungen auf ihre allostere Potenz und Affinität zum muscarinischen Rezeptor erfolgte in der Arbeitsgruppe von Prof. Mohr in Bonn. Hierzu werden Membranhomogenate vom Herzventrikelgewebe des Hausschweines verwendet. Diese enthalten mit großer Prävalenz muscarinische M2-Rezeptoren. Es wurden Gleichgewichtsbindungs- und Dissoziationsexperimente durchgeführt. Bis jetzt sind noch nicht alle Verbindungen getestet worden. Die bisher getesteten Verbindungen weisen alle eine Affinität zum mit [3H]-N-Methylscopolamin besetzten muscarinischen M2-Rezeptor im mikro-molaren Bereich auf. Sie liegen damit im oberen Bereich der bisher synthetisierten allosteren Modulatoren. Das postulierte Pharmakophormodell konnte also mit Hilfe der synthetisierten Substanzen bestätigt werden.
To understand basic principles about the interaction of electromagnetic radiation with matter is often a challenge in chemical education due to the difficult theoretical background of this topic. The present contribution therefore offers an experimental based introduction into the basic principles of UV/Vis spectroscopy following a three-step strategy. The starting point is to construct a simple self-built spectrometer working within the visible range of light. Learners can explore the most important components of such a device and understand their functions without previous knowledge. In a second step, emission spectra of different common light sources are investigated and compared. Finally, spectroscopic experiments are suggested for chemical education such as the qualitative detection of cations and the quantitative analysis of the dye carmine in food. This context-based introduction links chemical applications with the everyday life. It can be presumed that this way, learners are provided an easier access to radiation-matter interaction.
Most protein-encoding genes in Eukaryotes are separated into alternating coding and non-coding sequences (exons and introns). Following the transcription of the DNA into pre-messenger RNA (pre-mRNA) in the nucleus, a macromolecular complex termed spliceosome removes the introns and joins the exons to generate mature mRNA that is exported to the cytoplasm. There, it can be interpreted by ribosomes to generate proteins. The spliceosome consists of five small nuclear ribonucleic acids (snRNAs) and more than 150 proteins. Integral components of this complex are RNA-protein particles (RNPs) composed of one or two snRNAs, seven common (Sm) and a various number of snRNP-specific proteins. The Sm proteins form a ring-structure around a conserved site of the snRNA called Sm site. In vitro, Sm proteins (B/B', D1, D2, D3, E, F, G) and snRNA readily assemble to form snRNPs. In the context of the cell, however, two macromolecular trans-acting factors, the PRMT5 (protein arginine methyltransferases type 5) and the SMN (survival motor neuron) complex, are needed to enable this process. Initially, the Sm proteins in the form of heterooligomers D1/D2, D3/B and F/E/G are sequestered by the type II methyltransferase PRMT5. pICln, a component of the PRMT5 complex, readily interacts with Sm proteins to form two distinct complexes. Whereas the first one comprises pICln and D3/B the second one forms a ring consisting of pICln, D1/D2 and F/E/G (6S). It has been found that pICln prevents the premature interaction of snRNAs with the Sm proteins in these complexes and thus functions as an assembly chaperone imposing a kinetic trap upon the further assembly of snRNPs. PRMT5 catalyzes the symmetrical dimethylation of arginine residues in B/B', D1 and D3 increasing their affinity towards the SMN complex. Finally, the SMN complex interacts with the pICln-Sm protein complexes, expels pICln and mediates snRNP assembly in an ATP-dependent reaction. So far, only little is known about the action of PRMT5 in the early phase of snRNP assembly and especially how the 6S complex is formed. Studies of this have so far been hampered by the unavailability of soluble and biologically active PRMT5 enzyme. The composition of the SMN complex and possible functions of individual subunits have been elucidated or hypothesized in recent years. Still, the exact mechanism of the entire machinery forming snRNPs is poorly understood. In vivo, reduced production of functional SMN protein results in the neurodegenerative disease spinal muscular atrophy (SMA). How specific SMN mutations that have been found in SMA patients cause the disease remains elusive, yet, are likely to interfere with either SMN complex stability or snRNP assembly. The aim of this work was to establish an in vitro system to recapitulate the cytoplasmic assembly of snRNPs. This was enabled by the recombinant production of all PRMT5 and SMN complex components as well as Sm proteins in a combination of bacterial and insect cell expression systems. Co-expression of human PRMT5 and its direct interaction partner WD45 (WD-repeat domain 45) in Sf21 (Spodoptera frugiperda 21) insect cells resulted for the first time in soluble and biologically active enzyme. Recombinant PRMT5/WD45 formed complexes with Sm protein heterooligomers as well as pICln-Sm protein complexes but not with F/E/G alone. Also, the enzyme exhibited a type II methyltransferase activity catalyzing the mono- (MMA) and symmetrical dimethylation (sDMA) of Sm proteins B, D1 and D3. Two experimental setups were devised to quantitatively analyze the overall methylation of substrates as well as to identify the type and relative abundance of specific methylation types. Methylation of Sm proteins followed Michaelis-Menten kinetics. Complex reconstitutions and competition of the methylation reaction indicate that 6S is formed in a step-wise manner on the PRMT5 complex. The analysis of the methylation type could be applied to deduce a model of sequential MMA and sDMA formation. It was found that large Sm protein substrate concentrations favored monomethylation. Following a distributive mechanism this leads to the conclusion that PRMT5 most likely confers partial methylation of several different substrate proteins instead of processing a single substrate iteratively until it is completely dimethylated. Finally, the human SMN complex was reconstituted from recombinant sources and was shown to be active in snRNP formation. The introduction of a modified SMN protein carrying a mutation (E134K) present in spinal muscular atrophy (SMA) proved that mutated complexes can be generated in vitro and that these might be applied to elucidate the molecular etiology of this devastating disease.
Additive manufacturing or 3D printing as an umbrella term for various materials processing methods has distinct advantages over many other processing methods, including the ability to generate highly complex shapes and designs. However, the performance of any produced part not only depends on the material used and its shape, but is also critically dependent on its surface properties. Important features, such as wetting or fouling, critically depend mainly on the immediate surface energy. To gain control over the surface chemistry post-processing modifications are generally necessary, since it′s not a feature of additive manufacturing. Here, we report on the use of initiator and catalyst-free photografting and photopolymerization for the hydrophilic modification of microfiber scaffolds obtained from hydrophobic medical-grade poly(ε-caprolactone) via melt-electrowriting. Contact angle measurements and Raman spectroscopy confirms the formation of a more hydrophilic coating of poly(2-hydroxyethyl methacrylate). Apart from surface modification, we also observe bulk polymerization, which is expected for this method, and currently limits the controllability of this procedure.
Using a new divergent approach, conjugated triarylborane dendrimers were synthesized up to the 2nd generation. The synthetic strategy consists of three steps: 1) functionalization, via iridium catalyzed C−H borylation; 2) activation, via fluorination of the generated boronate ester with K[HF\(_{2}\)] or [N(nBu\(_{4}\))][HF\(_{2}\)]; and 3) expansion, via reaction of the trifluoroborate salts with aryl Grignard reagents. The concept was also shown to be viable for a convergent approach. All but one of the conjugated borane dendrimers exhibit multiple, distinct and reversible reduction potentials, making them potentially interesting materials for applications in molecular accumulators. Based on their photophysical properties, the 1st generation dendrimers exhibit good conjugation over the whole system. However, the conjugation does not increase further upon expansion to the 2nd generation, but the molar extinction coefficients increase linearly with the number of triarylborane subunits, suggesting a potential application as photonic antennas.
Dipole moments and various spectroscopic constants of some low-lying electronic states of the CaF molecule have been calculated using the multireference single· and double-excitation configuration-interaction (MRD-CI) method. The electronic structure of the highly ionic molecule in various excited states can be explained in tenns of different polarisations of the mainly Cacentered valence electron in the field of the F\(^-\) anion. Plots of natural orbitals occupied by the valence electron in the different states give a qualitative picture of the charge distribution and provide a visualisation of the different polarisations of the valence electron in the various states. Comparisons with the electrostatic polarisation model ofTörring, Ernstand Kändler (TEK model) are made. The unknown A' \(^2 \Delta\) state is predicted to lie about 21200 cm\(^{-1}\) above the ground state.
Melanotic melanoma (MM) of Xiphophorus (Teleostei: Poeciliidae) was studied by conventional preparations and freeze-etch preparations for electron microscopy. MM of Xiphophorus exhibits tightly packed pigment cells with prominent dendritic processes and interdigitations of their plasma membranes. The most impressive feature of MM cells is the occurrence of Iarge lobulated nuclei with numerous nuclear pores and some nuclear pockets. Abundant spheroidal or ellipsoidal melanosomes (diameter 200-650 nm) and vesicular structures are distributed throughout the cellular dendrites, whereas the perinucJear cytoplasm is free of melanosomes.
A further characteristic feature of melanoma cells in fish is the occurrence of melanosome complexes (i.e., "compound melanosomes"). These melanosome complexes consist of a few to numerous melanosomes, which are enveloped by a separate rnembrane. Pinocytotic vesicles couJd be demonstrated with distinct differences in frequency and distribution patterns, indicating differences in the metabolic activities of the cells in the same melanoma. Intercellular junctions are lacking in the MM cells.
The conventional TEM technique showed clear advantages in the demonstration of intemal architecture of organelles, whereas FE bad considerable potential in respect to the visualization of membrane surface specializations.
Analyse der chemischen Reaktionen ungesättigter Verbindungen mit FEL- und Synchrotronstrahlung
(2013)
Brilliante Strahlungsquellen werden heute vielfach in der Forschung eingesetzt um Kristallstrukturen, Oberflächeneigenschaften oder Reaktionen zu untersuchen. Als Strahlungsquellen werden dafür bevorzugt Freie Elektronenlaser (FEL) oder Synchrotrons eingesetzt, da sie über weite Bereiche durchstimmbar sind und einen hohen Photonenfluss bereitstellen. Im Rahmen der vorliegenden Dissertation werden beide Lichtquellen verwendet um einerseits Isomere von Kohlenwasserstoffradikalen zu identifizieren und andererseits das Verhalten von Borylen und ungesättigten Verbindungen bei Photoionisation zu dokumentieren. Als erstes Experiment am FEL wurde ein IR-Spektrum von gasförmigen Allylradikalen aufgenommen. Das Allyl war ein Testlauf, da es als Kohlenwasserstoffradikal mit einer kleinen Dipolmomentänderung ein gutes Beispiel für ähnliche Verbindungen ist. Trotz der kleinen Änderung des Dipolmoments und der geringen Teilchendichte der Radikale in der Gasphase konnte ein gutes IR-Spektrum mit der IR-UV-Doppelresonanzmethode aufgenommen werden und die beobachteten Banden mit der Literatur zugeordnet werden. Das 3-Trifluoromethyl-3-Phenyl-carben (TFPC) wurde pyrolytisch aus 3-Trifluoromethyl-3-Phenyl-diazirin erzeugt. Dabei kam es beim Großteil der Carbene zu einer Umlagerung zu Trifluorstyrol. Neben dem Hauptprodukt Trifluorstyrol wurde das Triplett TFPC als Nebenprodukt identifiziert. Zusätzlich wurden die Isomerisierungsbarrieren für den Triplett- und Singulett-Übergangszustand berechnet. Die Radikale 1-Phenylpropargyl und 3-Phenylpropargyl sind anhand ihrer IR-Spektren unterscheidbar und lagern sich nicht ineinander oder in Indenyl um. Ausgehend von beiden Radikalen bilden sich die identischen Dimerisierungsprodukte im Massenkanal m/z = 230 (p-Terphenyl) und 228 (1-Phenylethinylnaphthalin (1PEN)). Außergewöhnlich war die Exklusivität dieser Produkte. Somit müssen deren Reaktionsmechanismen kinetisch viel schneller sein. Die Massen m/z = 230 und 228 waren bereits aus einer massenspektrometrischen Studie ausgehend von Benzol und Ethin bekannt, in der ihre Struktur jedoch nicht geklärt wurde. Somit müssen die gefundenen Dimerisierungsprodukte p-Terphenyl und 1PEN wichtige Intermediate bei der Entstehung von polyzyklischen aromatischen Kohlenwasserstoffen (PAK) und Ruß sein. Von gasförmigen NTCDA wurde mittels der TPEPICO-Methode am Synchrotron Schwellenphotoelektronenspektren aufgenommen. Dabei konnte die adiabatische Ionisierungsenergie (IE(ad)) zu 9.66 eV bestimmt werden. Weiterhin wurden noch fünf angeregte Zustände beobachtet, die mittels quantenmechanischer Berechnungen zugeordnet wurden. Es wurde die Photoionisation des Cycloheptatrienradikals (Tropyl) untersucht. Dabei wurde die erste Bande bei 6.23 eV der IE(ad) zugeordnet. Mit einer Franck-Condon Simulation wurden die beiden Schwingungsprogressionen einer CC-Streckschwingung (ν16+) und einer Kombination aus einer Ringatmung (ν2+) und ν16+ zugeordnet. Der erste Triplett- und Singulettzustand des angeregten Tropylkations konnte in Übereinstimmung mit der Literatur zugeordnet werden. Eine Schulter bei 9.85 eV und die intensivste Bande bei 11.6 eV konnten nicht eindeutig interpretiert werden. Neben dem Tropyl erscheint bei etwa 10.55 eV sein dissoziatives Zersetzungsprodukt, das Cyclopentadienylkation. Die IE(ad) des Borylenkomplex [(CO)5CrBN(SiMe3)2] wurde zu 7.1 eV bestimmt. Mit steigender Photonenenergie wurden alle CO-Liganden sequenziell abgespalten, während der Borligand auch bei 15 eV noch nicht dissoziierte. Von den fünf abgespaltenen CO-Liganden konnte die Auftrittsenergie bei 0 K unter Berücksichtigung der kinetischen Verschiebung gefittet werden. Durch einen einfachen thermodynamischen Zyklus wurden aus den Auftrittsenergien der Kationen die Bindungsenergien berechnet. Dabei zeigte sich, dass die zweite Bindungsenergie im Kation erheblich stärker ist als die erste. Dies deutet einen starken trans-Effekt des Borliganden an. In der Dissertation wurden die adiabatische Ionisierungsenergie der Moleküle sowie die Auftrittsenergien der Fragmente und die Bindungsenergien bestimmt. Zudem konnten Isomere anhand ihrer IR-Spektren unterschieden und ihre Dimerisierungsprodukte identifiziert werden. Damit wurden mit p-Terphenyl und 1PEN zwei weitere bedeutende Intermediate im Bildungsmechanismus von Ruß strukturell aufgeklärt. Die Beteiligung dieser Dimerisierungsprodukte am Bildungsmechanismus der PAK initiiert zukünftige Fragen. Was geschieht z.B. mit p-Terphenyl und 1PEN nach ihrer Bildung? Reagieren sie chemisch zu größeren Molekülen oder setzt bei ihnen bereits die Akkumulation zu Partikeln ein? Zusätzlich ist die Frage, ob Phenylpropargyl aus der Reaktion von Phenyl- und Propargylradikalen entsteht noch offen. Die erzielten Resultate haben einen wichtigen Schritt im Bildungsmechanismus der PAK identifiziert und damit die Grundlage für zukünftige Experimente gelegt.
Die Initiation der DNA-Replikation ist in Eukaryonten ein hochkonservierter Prozess. Zuerst bindet der „origin recognition complex“ (ORC) an Replikationsstartpunkte chromosomaler DNA und stellt das Startsignal für die Assemblierung des präreplikativen Komplexes (pre-RC) dar. Anschließend assoziieren die Initiationsfaktoren CDC6 und CDT1 mit dem ORC. Durch die Rekrutierung des MCM-Komplexes wird der pre-RC schließlich vervollständigt. Die Aktivität der CDC7/DBF4-Kinase und die Anlagerung von CDC45 lizensiert den Origin für die DNA-Replikation. Ein Ziel dieser Arbeit war, den vollständigen murinen ORC rekombinant darzustellen. Um den gesamten Komplex durch Copräzipitation zu isolieren, wurden ORC1, 3, 4, 5 und 6 als Wildtyp-Proteine und ORC2 mit einer N-terminalen Poly-His-Domäne mit Hilfe von Baculoviren koexprimiert. Nach der Aufreinigung konnten, mit Ausnahme von ORC3, alle ORC-Untereinheiten in den Elutionsfraktionen immundetektiert werden. Eine Gelfiltration der Fraktionen ließ auf die Isolierung eines 450 kD großen Komplexes schließen, der mindestens fünf der sechs ORC-Untereinheiten enthielt. Dies zeigt, dass der murine ORC als Holokomplex rekombinant isoliert werden kann. In einem weiteren Teil dieser Arbeit sollte die Rolle des MCM-Komplexes bei der Termination der DNA-Replikation am 3'-Ende muriner rDNA-Transkriptionseinheiten untersucht werden. Durch polare Replikationsgabelbarrieren im 3'-Bereich der ribosomalen Gene wird über die Kontrahelikaseaktivität von TTF-I die Bewegungsrichtung der Replikation auf die Richtung der Transkription limitiert. In dieser Arbeit sollte festgestellt werden, ob dies auch bei der murinen MCM4/6/7-Helikase der Fall ist. Um MCM4/6/7-Hexamere zu isolieren, wurden die Untereinheiten MCM4 und 7 in Wildtyp-Form und MCM6 mit einem N-terminal fusionierten HA-Tag mittels Baculoviren koexprimiert. Zur Durchführung der Kontrahelikasestudien musste die Helikaseaktivität der isolierten Komplexe ermittelt werden. Bereits mit kurzen partiell doppelsträngigen M13-Substraten (17 nt) zeigte sich eine geringere Entwindungsfähigkeit als in der Literatur beschrieben. Bei weiteren Helikasestudien wurden DNA-Substrate (30 nt) mit einem 5'-Überhang sowie SSB bzw. RPA eingesetzt. Zwar konnte so eine Steigerung der Helikaseaktivität von MCM4/6/7 verzeichnet werden, jedoch fand diese nicht in ausreichendem Maße statt. Zudem war das entwundene Oligonukleotid einem Abbau unterworfen, dessen Ursache nicht aufgeklärt werden konnte. Aufgrund der zu geringen Helikaseaktivität im Hinblick auf die TTF-I-Kontrahelikasestudien wurden diese Arbeiten eingestellt. Ein weiterer Aspekt dieser Arbeit war der Transport von MCM-Proteinen in den Zellkern. Der MCM-Komplex ist in fast allen Organismen konstitutiv im Zellkern lokalisiert. Die Überexpression einzelner exogener MCM-Proteine zeigte allerdings, dass nur MCM2 und 3 mit Hilfe ihrer ihrer NLS-Motive in den Kern transportiert werden, während dies bei MCM4 bis 7 nicht erfolgt. Two-Hybrid-Studien unserer Arbeitsgruppe ließen auf paarweise Wechselwirkungen der MCM4 bis 7-Untereinheiten mit MCM2 bzw. MCM3 schließen. Deshalb wurden EGFP-MCM-Proteine zusammen mit Wildtyp-MCM-Proteinen in Mauszellen koexprimiert. Dabei zeigte sich, dass MCM2 die Proteine MCM4, 6 und 7 in den Kern transportiert, während MCM3 nur MCM5 in den Zellkern einschleust. Weitere Interaktionen zwischen MCM6 und 4 sowie zwischen MCM6 und 7 konnten bei MCM4/6/7-Aufreinigungen beobachtet werden. Zuletzt wurde noch die Lokalisation von CDT1 in der OBR-Region des murinen rDNA-Cistrons untersucht. Bislang wurde nur in S. cerevisiae eine sequenzspezifische ORC-Bindung an ACS-Bereiche identifiziert. In unserer Arbeitsgruppe konnte im murinen rDNA-Cluster stromaufwärts des Transkriptionsstartpunktes ein Origin charakterisiert und die Bindungstelle verschiedener Initiatorproteine um die Position -2500 eingegrenzt werden. Die Assoziation von CDT1 mit derselben Region würde die Assemblierung eines pre-RC in dem untersuchten Bereich zusätzlich bestätigen. Zur Umsetzung von ChIP-Studien wurden CDT1-Antikörper hergestellt. Um die Assemblierung von CDT1 mit dem Origin in Abhängigkeit des Zellzyklus zu untersuchen, wurden FM3A-Mauszellen in früher G1-, später G1-, G1/S-, S- und in der G2/M-Phase arretiert. Die Auswertung der ChIP-Analysen, die den zu analysierenden Bereich von -2837 bis -1820 umspannten, zeigte, dass CDT1 ausschließlich während der G1-Phase mit dem Chromatin assoziiert ist. Dies ist konsistent mit der Aktivität von CDT1 während des Zellzyklus in Säugern. Der höchste Anteil an DNA-gebundenem CDT1 konnte in dem Bereich -2519 bis -2152 festgestellt werden. Eine Sequenzanalyse des OBR der murinen rDNA lieferte keine Homologie zu anderen bekannten Origins. Jedoch wurden diverse DNA-Strukturelemente, wie z.B. HSS, DUEs oder CpG-Inseln, sowie verschiedene Protein-Bindungsstellen gefunden, die potentiellen Einfluss auf die Festlegung des murinen OBR haben könnten.
Ziel dieser Arbeit war es, unbekannte (Minor)-Komponenten aus Apfelsaft zu identifizieren und deren Beitrag zur chemopräventiven Wirkung des Saftes zu bestimmen. Deren Motivation war begründet, dass bisher identifizierte niedermolekulare phenolische Verbindungen als Mischung nicht das gleiche chemopräventive Potential wie ein polyphenolangereicherter Apfelsaftextrakt aufgewiesen hatten. Zunächst wurden sieben Apfelsäfte verschiedener Erntejahre sowie 14 polyphenolangereicherte Saftextrakte auf ihre stoffliche Zusammensetzung hin untersucht. Dabei zeigte sich, dass die Polyphenolzusammensetzung der Apfelsäfte und -extrakte sowohl zwischen verschiedenen Produktionsjahren als auch abhängig von der verwendeten Produktionstechnologie stark variierte. Insbesondere der durch enzymatische Tresterverflüssigung erhaltene Saftextrakt (AE03B) wies eine deutliche Anreicherung an Quercetin- und Phloretinglycosiden sowie eine Abreicherung an phenolischen Säuren auf. Die Klärung von trüben Säften hatte keinen signifikanten Einfluss auf die Verteilung niedermolekularer Flavonoide. Tendenziell waren die Extrakte der trüben Säfte leicht an Phloretinglycosiden abgereichert. Im Gegensatz dazu wurde eine leichte Anreicherung der phenolischen Säuren in den untersuchten klaren Säften im Vergleich zu den trüben festgestellt. Der Gehalt hochmolekularer Procyanidine variierte in den untersuchten Säften und Saftextrakten produktions- und sortenbedingt ebenfalls stark. An klaren und trüben Säften einer Charge wurde eine signifikante Abnahme sowohl des Gehaltes als auch des mittleren Polymerisationsgrades durch den Klärungsprozess nachgewiesen. Ferner zeigten Reinfruchtsäfte aus Mostapfelsorten höhere Gehalte und mittlere Polymerisationsgrade als verschnittene Apfelsäfte mit einem Anteil an Tafeläpfeln. Als nicht phenolische Bestandteile wurden in den Säften und Saftextrakten (R)-Oktan-1,3-diol, (R)-5-(Z)-Okten-1,3-diol, 3-Hydroxy-2-pyron und 3-Hydroxy-beta-damascon detektiert. Zwei ausgewählte Saftextrakte aus den Jahren 2004 und 2006 wurden unter Zuhilfenahme unterschiedlicher präparativer Trennmethoden fraktioniert. Im Verlauf der Auftrennung wurden durch präparative Isolierung Quercetin, Qercetin-3-O-glucosid, Quercetin-3-O-galactosid, 3-Hydroxyphloretin-2’-glucosid, 3-Hydroxyphloretin-2’-xyloglucosid, Phloretin-2’-xyloglucosid und Phloretin-2’,4’-diglucosid erhalten. Die erhaltenen Subfraktionen und Reinstoffe wurden in vitro auf ihre Hemmwirkung der Proteintyrosinkinase (PTK) des epidermalen Wachstumsfaktor-Rezeptor (EGFR) untersucht. Darüber hinaus wurden die antioxidativen (DPPH, ORAC, X/XO), die antiinflammatorischen und antihormonellen (COX-1, CYP19) Eigenschaften sowie die Fähigkeit zur Modulation des Fremdstoffmetabolismus (CYP1A, QR) überprüft. Die Procyanidine des Apfels erwiesen sich in Abhängigkeit ihres Polymerisationsgrades als starke Inhibitoren der PTK des EGFR. So zeigten ausschließlich hochpolymere Procyanidine enthaltende Fraktionen (NP.4 und NP.5) eine deutlich stärkere Hemmung als Fraktionen, die nur aus niedermolekularen phenolischen Verbindungen zusammengesetzt waren. Auf die Enzyme Cytochrom P450 1A und Aromatase (CYP19) hatten die Procyanidine ebenfalls einen entscheidenden Einfluss. Die antioxidativen Eigenschaften der Apfelsaftextrakte waren sowohl vom Gehalt polymerer Procyanidine als auch von dem niedermolekularer Polyphenole abhängig. Die für die Apfelsaftextrakte nachgewiesenen Radikalfängereigenschaften und die Hemmung der Superoxidanionbildung wurden für beide Gruppen ebenfalls bestätigt. Dahingegen wurden Peroxylradikale im ORAC-Test fast ausschließlich von niedermolekularen Verbindungen abgefangen. Die 3-Hydroxyphloretin(glycoside) zeigten, mit Ausnahme des Xyloglucosids, am EGFR eine stärkere inhibitorische Wirkung als die entsprechenden Phloretin(glycoside). Die Untersuchung der Enzyme des Fremdstoffmetabolismus zeigte ein uneinheitliches Bild. So war Phloretin ein effektiverer Hemmstoff der CYP1A im Vergleich zum 3-Hydroxyphloretin. Bei den Glycosiden zeigten 3-Hydroxyphloretin-2’-glucosid die etwas bessere Wirkung. Ähnlich verhielt es sich bei der antioxidativen Kapazität. Die 3-Hydroxyphloretin(glycoside) wiesen im DPPH und X/XO-Assay eine größere Aktivität auf. Hydroxylperoxidradikale wurden nur durch das dihydroxylierte freie Aglykon besser abfangen. Weiterhin wurde mit 3-Hydroxy-beta-damascon erstmals ein hochpotenter Induktor der Chinonreduktase in Apfelsaft identifiziert. Die in dieser Arbeit erlangten Erkenntnisse hinsichtlich der neu identifizierten bioaktiven Inhalsstoffe leisten einen Beitrag zum besseren Verständnis der potentiell chemopräventiven Wirkungen von (trüben) Apfelsäften. Ferner ist die Quantifizierung dieser Substanzen in technologisch unterschiedlich behandelten Säften für weiterführende Studien von Relevanz.
Melanoma formation in Xiphophorus hybrids is mediated by a growth factor receptor tyrosine kinase oncogene encoded by the Tu locus. In the wild-type parental fish no tumors occur due to the activity of a locus that regulates the activity of the melanoma oncogene. Molecu/ar identification of this regulatory locus (R) requires a precise physical map of the chromosomal region. Therefore we studied esterase isozymes in Xiphophorus, two of which have been previously reported to be linked to locus R. We confinn that ES 1 is a distant marker for R ( approx. 30cM), and contrary to earlier studies, we show that this isozyme is present in all species of the genus and at similar activity Ievels in all organs tested. ES4, which has also been reported to be linked to R, was found to be a misclassification of liver ES1. In an attempt to identify markersthat bridge the large distance between ESl and R, we have generated DNA probes which are highly polymorphic. They will be useful in finding Iandmarks on a physical map of the R-containing chromosomal region.
Analysis of Drug Impurities by Means of Chromatographic Methods: Targeted and Untargeted Approaches
(2022)
The presented works aimed on the analysis of new impurities in APIs and medicinal products. Different subtypes of LC were coupled to suitable detection methods, i.e. UV and various MS techniques, depending on the chemical natures of the analytes and the analytical task.
Unexpected impurities in medicinal products and APIs caused several scandals in the past, concomitant with fatalities or severe side effects in human and veterinary patients. The detection of nitrosamines in sartans led to the discovery of nitrosamines in various other drugs, of which the antibiotic rifampicin was analyzed in this work. An examination of the synthesis of rifampicin revealed a high potential for the formation of 4-methyl-1-nitrosopiperazine (MeNP). An LC-MS/HRMS method suitable for the quantification of MeNP was applied in the analysis of drugs collected from Brazil, Comoros, India, Nepal, and Tanzania, where a single dose of rifampicin is used in the post-exposure prophylaxis of leprosy. All batches were contaminated with MeNP, ranging from 0.7-5.1 ppm. However, application of rifampicin containing up to 5 ppm MeNP was recommended by the regulatory authorities for the post-exposure prophylaxis of leprosy.
In the 1990s the aminoglycoside antibiotic gentamicin attracted attention after causing fatalities in the USA, but the causative agent was never identified unequivocally. The related substance sisomicin was recognized as a lead impurity by the Holzgrabe lab at the University of Würzburg: sisomicin was accompanied by a variety of other impurities and batches containing sisomicin had caused the fatalities. In 2016, anaphylactic reactions were reported after application of gentamicin. A contamination of the medicinal products with histamine, an impurity of the raw material fish peptone used upon the production, could be identified as the cause of the adverse effects. Batches of gentamicin sulfate, which had been stored at the University of Würzburg since the earlier investigations, were analyzed regarding their contamination with histamine to determine whether the biogenic amine was responsible for the 1990s fatalities as well. Furthermore, a correlation with the lead impurity sisomicin was checked. Histamine could be detected in all analyzed batches, but at a lower level than in the batches responsible for the anaphylactic reactions. Moreover, there is no correlation of histamine with the lead impurity sisomicin. Hence, the causative agent for the 1990s fatalities was not histamine and remains unknown.
Another source of impurities is the reaction of APIs with excipients, e.g. the esterification of naproxen with PEG 600 in soft gel capsules. The influence of the formulation’s composition on this reaction was investigated by means of LC-UV. Therefore, the impurity naproxen-PEG-ester (NPEG) was synthesized and used for the development of a method suitable for the analysis of soft gel capsule formulations. Different formulations were stressed for 7 d at 60 °C and the relative amount of NPEG was determined. The formation of NPEG was influenced by the concentrations of water and lactic acid, the pH, and the drug load of the formulation, which can easily be explained by the chemistry behind esterification reactions.
Keeping in mind the huge variety of sources of impurities, it might be impossible to predict all potential impurities of a drug substance/product. Targeted and untargeted approaches were combined in the impurity profiling of bisoprolol fumarate. Eight versions of an LC-HRMS method were developed to enable the detection of a maximum number of impurities: an acidic and a basic buffered LC was coupled to MS detection applying ESI and APCI, both in positive in negative mode. MS and MS/MS data were acquired simultaneously by information dependent acquisition. In the targeted approach, potential impurities were derived from a reaction matrix based on the synthesis route of the API, while the untargeted part was based on general unknown comparative screening to identify additional signals. 18 and 17 impurities were detected in the targeted and the untargeted approach, respectively. The molecular formulae were assessed based on the exact mass and the isotope pattern. Theoretical fragment spectra generated by in silico fragmentation were matched with experimental data to estimate the plausibility of proposed/elucidated structures. Moreover, the detected impurities were quantified with respect to an internal standard.
Estrogens, namely 17β-estradiol (E2) and estrone (E1) are considered to play an important role in the initiation and promotion of breast cancer (summarized in Raftogianis et al., 2000), a malignancy responsible for around 500,000 deaths per year (summarized in Ghislain et al., 2016). Two major mechanisms have been postulated to explain the carcinogenic effects of estrogens: (1) the estrogen receptor-mediated stimulation of breast cell proliferation with a concomitant enhanced rate of mutations and (2) the metabolism of hydroxylated estrogens to quinone derivatives which can react with the DNA (Russo and Russo, 2006, summarized in Yager and Davidson, 2006). Nevertheless, as a detoxifying mechanism, E1, E2, and their hydroxylated and methoxylated metabolites are reversibly conjugated into sulfates and glucuronides devoid of biological activity (summarized in Guillemette et al., 2004). Yet, despite the key detoxifying function of these conjugates, the study of their circulating levels face some significant problems: (1) analysis by techniques such as radioimmunoassay lack specificity and accuracy and requires enzymatic/chemical hydrolysis before analysis, being unable to differentiate between sulfates and glucuronides (summarized in Stanczyk et al., 2007, summarized in Wang et al., 2016), (2) very little knowledge in healthy women, which has been identified as a barrier to advance in breast cancer research (summarized in Liu, 2000), and (3) far fewer studies in pre- than in postmenopausal women (summarized in Samavat and Kurzer, 2015). Therefore, to get more insights into the research of breast cancer etiology and prevention, the analysis of circulating levels of estrogens (including metabolites and conjugates) in women without breast cancer through reliable analytical techniques, is required.