A LIPID-COATED LIPASE AS AN ENANTIOSELECTIVE ESTER SYNTHESIS CATALYST IN HOMOGENEOUS ORGANIC-SOLVENTS

A lipid-coated lipase was prepared, in which hydrophilic head groups of lipids interact with the hydrophilic surface of the enzyme and lipophilic alkyl chains extend away from its surface and solubilize the enzyme in hydrophobic organic solvents. Enantioselective esterification of(R)- or (S)-1-phenylethanol with aliphatic acid was studied in the presence of the lipid-coated lipase, solubilized homogeneously in organic solvents, by varying lipase origin, coating lipid molecules, reaction media, and substrate structures. The lipid-coated lipase prepared from the glycolipid (1) and lipase B from Pseudomonas fragi 22-39B showed both a high catalytic activity and enantioselectivity for the esterification of (R)-1-phenylethanol with long-chain aliphatic acid in dry isooctane, relative to other enzyme systems such as poly(ethylene glycol)-grafted lipase, lipase powder directly dispersed in organic solvents, and a water/organic emulsion system. The coating lipids are found to not affect the enzyme reactions and to act simply as lipophilic tails in organic media. The lipid-coated lipase is suitable for studying the reaction mechanism of the enzyme in organic solvents since the reaction is carried out in homogeneous media. It has been found in studying Michaelis-Menten kinetics that the lipid-coated lipase (or native lipase) has two binding sites for long-chain aliphatic acids and for enantiomorphic secondary alcohols having a small methyl and a large phenyl side chain. Aliphatic acid is bound first and then alcohol. The enantioselectivity of the esterification is determined by the nucleophilic attack of the enantiomorphic alcohol, but not in the binding process of the enantiomorphic alcohol.