Transesterification with Candida Cylindracea Lipase in a Biphasic Aqueous-Organic System. Dependence of the Enantiomeric Ratio and the Reaction Rate on the Proportions of Water and Cyclohexane

18 September 1989

A transesterification reaction between 1-phenyl ethyl butyrate and 1-heptanol was carried out with Candida cylindracea lipase. The reaction was studied, with respect to the reaction rate and the enantiomeric ratio at different proportions of water and cyclohexane. A significantly lower reaction rate was observed for incubations with less than 0.5% water compared with those at a higher water content. Transesterification dominated over hydrolysis as the main reaction even at 70% water and a dramatic increase of the enantioselectivity was observed at this high water content. It is proposed that these effects depend on the mechanism of lipase catalysis at the interface of emulsion droplets. This interface binding gives 1-heptanol a positional preference compared with water for nucleophilic attack of the acyl enzyme and may, in addition, induce an optimal conformation for high enantioselectivity of the enzyme.