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. © 2014 Novotná et al; licensee Beilstein-Institut.
Novotná, M., Gažák, R., Biedermann, D., Di Meo, F., Marhol, P., Kuzma, M., … Křen, V. (2014). Cis-trans isomerization of silybins A and B. Beilstein Journal of Organic Chemistry, 10, 1047–1063. https://doi.org/10.3762/bjoc.10.105