Kinetic Resolution of 2-Methylbutyric Acid and Its Ester by Esterification and Hydrolysis with Lipases

The resolution of 2-methylbutyric acid, one of the typical flavor compounds, is difficult by the enzymatic kinetic method because the steric differences between the methyl and ethyl groups attached to its chiral carbon atom are too small to allow efficient stereochemical recognition by enzyme. The capacity of some commercial lipases and a lipase from Rhizopus chinensis (RCL) to catalyze enantioselective esterification and enantioselective hydrolysis of 2-methylbutyric acid and its ester in different systems was investigated. The results showed that, RCL not only had a certain esterification enantioselectivity in non-aqueous media but also had higher hydrolysis enantioselectivity in aqueous phase. The ee value of 92.4% of (R)-ethyl 2-methylbutyrate was obtained after 10 h hydrolysis reaction. Furthermore, the influence of temperature on the esterification and hydrolysis resolution catalyzed by RCL was investigated. A higher enantioselectivity was obtained at 4 degree C, and the ee value of (R)-ethyl 2-methylbu