ENANTIOSELECTIVITY OF LIPASE-CATALYZED HYDROLYSIS OF SOME 2-CHLOROETHYL 2-ARYLPROPANOATES STUDIED BY CHIRAL REVERSED-PHASE LIQUID-CHROMATOGRAPHY

A technique based exclusively on chiral reversed-phase liquid chromatography has been shown to greatly facilitate studies of enantioselectivity in lipase-catalyzed hydrolysis of chiral organic esters. Only two sets of experimental data are needed to ca cu ate the enantioselectivity (E) of a kinetically controlled enantiomer-differentiating reaction of this kind, viz. the enantiomeric excess of the product (ee(p)) or substrate (ee(s)), and the degree of substrate conversion (c). The product enantiomers are well separated on a BSA-based column, giving ee(p) directly. In addition, separation of the (unresolved) ester substrate from the enantiomeric products gives c by integration. Via an optimization of the mobile phase used in the chiral chromatographic system, both these parameters can often be determined in a single run. Highly precise and detailed kinetic studies of the enzymatic reaction can thus be performed. In this way, E-values have been determined for a series of 2-chloroethyl 2-arylpropanoates hydrolyzed in the presence of a Candida cylindracea lipase at pH 6.0 and 7.1. Effects on the E-values from a partial purification and further processing of the lipase have also been studied.