Enantioselective acylation of alpha-aminonitriles catalysed by Candida antarctica lipase. An unexpected turnover-related racemisation

Candida antarctica lipase B (Novozyme 435) catalysed the enantioselective a cylation of 2-amino-2-phenylacetonitrile 1 with ethyl phenylacetate affordi ng a near enantiopure product in 47% yield. Acylation of 1 and 2-amino-4-ph enylbutyronitrile with ethyl acetate yielded an unexpected partially racemi sed final product. The racemisation was shown to be turnover related and is ascribed to the increased acidity of the alpha -proton in the formation of the tetrahedral intermediate in the active site of the enzyme. (C) 2001 El sevier Science Ltd. All rights reserved.