TY  - JOUR
A1  - Huang, Guozheng
A1  - Schramm, Simon
A1  - Heilmann, Jörg
A1  - Biedermann, David
A1  - Kren, Vladimír
A1  - Decker, Michael
T1  - Unconventional application of the Mitsunobu reaction: Selective flavonolignan dehydration yielding hydnocarpins
JF  - Beilstein Journal of Organic Chemistry
N2  - Various Mitsunobu conditions were investigated for a series of flavonolignans (silybin A, silybin B, isosilybin A, and silychristin A) to achieve either selective esterification in position C-23 or dehydration in a one-pot reaction yielding the biologically important enantiomers of hydnocarpin D, hydnocarpin and isohydnocarpin, respectively. This represents the only one-pot semi-synthetic method to access these flavonolignans in high yields.
KW  - Mitsunobu
KW  - dehydration
KW  - flavonoid
KW  - hydnocarpin
KW  - silybin
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-160986
VL  - 12
ER  - 
TY  - JOUR
A1  - Sawatzky, Edgar
A1  - Drakopoulos, Antonios
A1  - Rölz, Martin
A1  - Sotriffer, Christoph
A1  - Engels, Bernd
A1  - Decker, Michael
T1  - Experimental and theoretical investigations into the stability of cyclic aminals
JF  - Beilstein Journal of Organic Chemistry
N2  - Background: Cyclic aminals are core features of natural products, drug molecules and important synthetic intermediates. Despite their relevance, systematic investigations into their stability towards hydrolysis depending on the pH value are lacking.

Results: A set of cyclic aminals was synthesized and their stability quantified by kinetic measurements. Steric and electronic effects were investigated by choosing appropriate groups. Both molecular mechanics (MM) and density functional theory (DFT) based studies were applied to support and explain the results obtained. Rapid decomposition is observed in acidic aqueous media for all cyclic aminals which occurs as a reversible reaction. Electronic effects do not seem relevant with regard to stability, but the magnitude of the conformational energy of the ring system and pK a values of the N-3 nitrogen atom.

Conclusion: Cyclic aminals are stable compounds when not exposed to acidic media and their stability is mainly dependent on the conformational energy of the ring system. Therefore, for the preparation and work-up of these valuable synthetic intermediates and natural products, appropriate conditions have to be chosen and for application as drug molecules their sensitivity towards hydrolysis has to be taken into account.
KW  - quantum mechanics
KW  - hydrolysis
KW  - kinetics
KW  - molecular mechanics
KW  - natural products
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-160976
VL  - 12
ER  -