- Cis-trans isomerization of silybins A and B
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Methods were developed and optimized for the preparation of the 2,3-cis- and the 10,11-cis-isomers of silybin by the Lewis acid catalyzed (BF 3-OEt2) isomerization of silybins A (1a) and B (1b) (trans-isomers). The absolute configuration of all optically pure compounds was determined by using NMR and comparing their electronic circular dichroism data with model compounds of known absolute configurations. Mechanisms for cis - trans-isomerization of silybin are proposed and supported by quantum mechanical calculations.
- Novotna, Michaela,Gazak, Radek,Biedermann, David,Di Meo, Florent,Marhol, Petr,Kuzma, Marek,Bednarova, Lucie,Fuksova, Katerina,Trouillas, Patrick,Kren, Vladimir
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- Enzymatic kinetic resolution of silybin diastereoisomers
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In nature, the flavonolignan silybin (1) occurs as a mixture of two diastereomers, silybin A and silybin B, which in a number of biological assays exhibit different activities. A library of hydrolases (lipases, esterases, and proteases) was tested for separating the silybin A and B diastereomers by selective transesterification or by stereoselective alcoholysis of 23-O-acetylsilybin (2). Novozym 435 proved to be the most suitable enzyme for the preparative production of both optically pure silybins A and B by enzymatic discrimination. Gram amounts of the optically pure substances can be produced within one week, and the new method is robust and readily scalable to tens of grams.
- Monti, Daniela,Gazak, Radek,Marhol, Petr,Biedermann, David,Purchartova, Katerina,Fedrigo, Mirko,Riva, Sergio,Kren, Vladimir
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experimental part
p. 613 - 619
(2010/07/13)
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