Lipase-catalyzed enantioselective transesterification toward esters of 2-bromo -tolylacetic acids

Abstract

Lipases from Candida antarctica, Pseudomonas cepacia and Rhizomucor miehei were tested in the resolution of seven racemic substrates belonging to the ( RS)-2-bromo tolyl acetate ester category, but differing either in the position of the methyl substituent on the acyl part of the aromatic ring, or in the structure of the alkyl group. Lipase-catalyzed kinetic resolution via transesterification reaction between the ester and octanol in octane revealed that, of the three enzymes tested, P. cepacia lipase is the most efficient for resolution of the various racemates, with R-enantiopreference. In addition, the position of the methyl substituent was found to play a key role in governing the enantioselectivity of the reaction. Using P. cepacia lipase and 2-bromo- m/ p-tolyl- or 2-bromophenylacetic acid esters E-values of >50 were measured, whereas with the ortho derivatives, E-values dramatically decreased to <6.