Enzym‐katalysierte Reaktionen, 7. Enantioselektive Veresterung racemischer Cyanhydrine und enantioselektive Hydrolyse oder Umesterung racemischer Cyanhydrinester mittels Lipasen

Enzyme‐Catalyzed Reactions, 71). – Enantioselective Esterification of Racemic Cyanohydrins and Enantioselective Hydrolysis or Transesterification of Cyanohydrin Esters by Lipases Pure cyanohydrin enantiomers (S)‐1/(R)‐1 and their O‐acyl derivatives (R)‐3/(S)‐3 are obtained from three different lipasecatalyzed reactions: i) enantioselective hydrolysis of aliphatic and aromatic racemic cyanohydrin esters 3, ii) enantioselective acylation of racemic cyanohydrins 1, iii) enantioselective transesterification of 3 with primary alcohols. Both the cyanohydrin esters and the free cyanohydrins (which are prone to racemization) are isolated as enantiomers with high optical purity on a preparative scale. Hydrolysis of the racemic butyrates 3b, e with Candida cylindracea lipase and pseudomonas sp. lipase, respectively, for example, affords the free (S)‐cyanohydrins (S)‐2‐hydroxypentanenitril [(S)‐1a] and (S)‐mandelonitrile [(S)‐1b)] in high yield with 97 and 96% ee, respectively. (S)‐1a is obtained with the same optical purity by candida sp. lipase‐catalyzed transesterification of 3b with 1‐octanol.