Increased enantioselectivity of lipase in the transesterification of dl-(±)-3-phenyllactic acid in ionic liquids

Abstract

Three lipases from different sources (Pseudomonas aeruginosa MTCC 5113 (PAL), porcine pancreatic (PPL) and Candida rugosa (CRL)) were screened for the transesterification of dl-3-phenyllactic acid (dl-3-PLA) in three different ionic liquids (1-butyl-3-methyl imidazolium tetrafluoroborate ([BMIM][BF4]), 1-butyl-3-methyl imidazolium hexafluorophosphate ([BMIM][PF6]) and 1-ethyl-3-methyl imidazolium tetrafluoroborate ([EMIM][BF4])) in combination with different organic solvents (e.g. hexane, cyclohexane, isooctane, toluene, vinyl acetate and dichloromethane). CRL efficiently catalyzed the esterification of dl-3-PLA to l-O-acetyl-3-PLA using vinyl acetate as acyl donor, showing excellent enantioselectivity (E~100) and conversion in all three ionic liquids. PPL exhibited enantioselectivity only in the presence of [BMIM][BF4] and was not able to catalyze dl-3-PLA esterification in the other two ionic liquids. PAL did not show any reactivity with dl-3-PLA in any of the ionic liquids. Various parameters such as solvent and ionic liquid concentration, reaction time, substrate and enzyme concentration on the activity and enantioselectivity of CRL were studied.