CAL-B-Catalyzed deacylation of benzylic acetates: Effect of amines addition. Comparison of several approaches.

Herein, we report an efficient enantioselective cleavage of the acyl-moity of some secondary benzylic acetate derivatives catalyzed by lipase B from Candida antarctica (CAL-B) in the presence of triethylamine, as additive, in non aqueous media. The influence of the hydrophobicity of two solvent, the basicity of three amines and the amount of CAL-B were studied in the presence/absence of molecular sieves 4Å. The best results in term of selectivity are achieved using the triethylamine as basic additive and in that case, the reactivity is only best at low conversion. To establish the effect of the parallel and/or competitive hydrolysis and its impact on the reactivity and selectivity of the enzymatic resolution, the kinetic profiles of three CAL-B-deacylation approaches of phenylethylacetate have been compared, using different nucleophiles in competition with the internal water mediated by: Na2 CO3 , EtOH and by using the Et3 N as additive. Furthermore, a comparison between these deacylations with the acylation of 1-phenylethanol with isopropenylacetate, has been made. The appropriate modulation of some crucial parameters allows an optimal conversion and a high selectivity depending on the acetate structure and the introduced base. In the majority of cases, the (R)-alcohols are obtained with ee>99% and selectivities E>200 under mild conditions.