Highly diastereoselective acylation of l-menthol by a lipase from Stenotrophomonas maltophilia CGMCC 4254

Abstract

l-menthol, one of the world’s largest flavor components, is widely utilized in food and cosmetics industries. Disappointingly, menthol which was synthesized by thymol hydrogenation route consisted of diastereomeric menthol mixture, containing several isomers leading to undesirable taste. Therefore, there is a need for efficient and economical way of preparing optically pure l-menthol from diastereomeric mixture. In our work, Stenotrophomonas maltophilia CGMCC 4254 lipase (SML) was chosen as a potential biocatalyst for diastereoselective acylation of l-menthol. Subsequently, different reaction factors were investigated, such as organic solvent, acyl donors, temperature, menthol concentration and molar ratio of donor to l-menthol. SML-catalyzed l-menthol acetylation reaction at 641mM concentration and 35°C resulted in 95.1% conversion (24h) and 93.4% diastereomeric excess (d.e.p), which were much better than commercially available lipases tested. Finally, the acetylation reaction was scaled up to 0.9L, resulting in an average l-menthyl acetate volumetric productivity 1.33g/L/h with 93.4% d.e.p and 95.1% conversion. Therefore, SML is a potentially promising biocatalyst for preparation of optically pure l-menthol from diastereomeric mixture in an industrial scale.