Chiral recognition of alcohol enantiomers in acyl transfer reactions catalysed by Candida antarctica lipase B

A description of the substrate-enzyme interactions involved in the discrimination of sec-alcohol enantiomers in acyl transfer reactions catalysed by the highly enantioselective Candida antarctica lipase B is presented. Experimentally found activities and enantioselectivities from kinetic resolutions of a series of secondary alcohol substrates were used together with molecular modelling for the elucidation of the stereoselective substrate-enzyme interactions. Matching experimental and calculated results allowed conclusions regarding the orientation of the tetrahedral intermediates in the active site. The finding, valid for substrates of a specific activity above 1 mu mol min(-1) mg(-1) protein, describes the origin of enantioselectivity as a combination of a binding site of limited size, the "stereospecificity pocket", and principally different productive orientations of the two enantiomers.