Large-scale separation of silybin diastereoisomers using lipases

The flavonolignan silybin (1), isolated from the seeds of milk thistle (Silybum marianum), occurs in nature as an equimolar mixture of two diastereoisomers, silybin A and silybin B, that exhibit different biological activities. The preparative production of optically pure silybin A and B in a diastereoisomeric purity greater than 95% was accomplished using immobilized Candida antarctica lipase B (Novozym 435) in a combination of two reactions: regioselective acetylation of a natural silybin mixture (1) and subsequent stereoselective alcoholysis of the resulting 23-O-acetylsilybin (2). Several grams of the optically pure substances can be produced within one week using this new, robust and scalable process, which is selective, mild and high-yielding.