Enzymatic kinetic resolution of primary alcohols by direct esterification in solvent-free system

Abstract

Direct enzymatic esterification catalyzed by immobilized Candida antarctica lipase B (CALB) and Rhizomucor miehei lipase (RML) was evaluated for kinetic resolution of some primary alcohols with a chiral center at the next carbon atom: 2-methoxy-2-phenylethanol ( 1), 2-phenyl-1-propanol ( 2) and 1-phenyl-1,2-ethanediol ( 3). The reactions were performed in solvent-free system with removal of water at low pressure. CALB was superior to RML in both reaction rates and enantioselectivity. The influence of acid species on enantioselectivity of CALB was studied on esterification of 1. In a series of free fatty acids, the highest enantioselectivity value was obtained for decanoic acid. Among other acid species investigated, 4-oxopentanoic acid gave the best results. The position of the double bond in pentenoic acid affected the reaction rate and enantioselectivity. Enantioselectivity of CALB increased significantly with reducing the reaction temperature. Direct esterification for kinetic resolution of 2 and 3 was also investigated. RML has a stricter substrate selectivity towards both: the acid and alcohol. Lowering the reaction temperature had no effect on enantioselectivity.