Optically Active Cyanohydrins and Enzyme Catalysis

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Abstract
The possibilities for the preparation of optically active aliphatic and /wra-substituted aromatic cyanohydrins (X-C6H4-CH(OH)CN) by lipase catalysis in organic solvents has been studied. Pseudomonas cepacia lipase catalyzed deacylation and acylation result in acylated aromatic (R)-and (S)-cyanohydrins, respectively, with high optical purity (mostly e.e. > 95%). A convenient access to increase the chemical yield of acylated (S)-cyanohydrins is to combine the base-catalyzed in situ racemization of the less reactive (R)-counterpart with a kinetic resolution. The nature of the para-substituent has not an effect on the enantioselectivity of lipase PS catalysis. In the Candida cylindracea lipase catalyzed deacylation, the optical purity of the less reactive (S)-enantiomer is high (e.e. > 95%) in the case of the aromatic compounds with electron-donating substituents X. PPL catalysis can be used to acylate aliphatic cyanohydrins, but it is not possible to use the in situ racemization of the less reactive (R)-cyanohydrin owing to the enantiomeric stability of most aliphatic compounds studied.