Chiral synthons via chloroperoxidase catalysis

Recent experiments from several laboratories have shown that chloroperoxidase is able to catalyze a broad spectrum of stereoselective hydroxylation, sulfoxidation and epoxidation reactions. Our laboratory has investigated the substrate specificity of chloroperoxidase for chiral epoxidation of mono- and disubstituted alkenes. Chloroperoxidase is able to efficiently utilize alkenes having chain lengths of nine or fewer carbon atoms except for monosubstituted olefins which often function as reversible suicide inhibitors of the enzyme. Excellent substrates are created by cis-I-methyl and 2-methyl substitutions on the olefinic double bond. Kinetic, enantioselectivity and epoxide yield data have been obtained on a series of brominated and unbrominated methallyl alkenes and substituted styrenes. The results indicate that methallyl alkenes and styrenes can function as good substrates. K-m values for the methallyl substrates are in the millimolar range and the V-max's reach turnovers of 200 per min. Hammett plot data are consistent with the formation of a radical as opposed to a carbocation intermediate in the rate determining step in the epoxidation of substituted styrenes. Many of the epoxide products derived from chloroperoxidase catalysis can serve as chiral synthons for drug and natural product synthesis. (C) 1998 Elsevier Science B.V. All rights reserved.