Enzymic asymmetric hydrolysis of d , l ‐ p ‐hydroxyphenylglycine methyl ester in aqueous ionic liquid co‐solvent mixtures

An aqueous solution of ionic liquid BMIM·BF 4 (1‐butyl‐3‐methylimidazolium tetrafluoroborate) was used as the reaction medium for the asymmetric hydrolysis of d , l ‐ p ‐hydroxyphenylglycine methyl ester to enantiopure l ‐HPG ( l ‐ p ‐hydroxyphenylglycine) for the first time. Papain was screened out from five proteases and two lipases tested because of its high activity and enantioselectivity for this reaction. A comparative study demonstrated that papain is more active, enantioselective and stable in the sodium phosphate buffer solution of BMIM·BF 4 than in aqueous buffer and in the buffer solutions of several typical organic solvents examined. l ‐HPG with an e.e. (enantiomeric excess) of 95.6% and the yield of 47.4% (on a mole basis) could be obtained when the reaction was performed in a buffer solution of 12.5% (v/v) BMIM·BF 4 (pH 7.0). The aqueous ionic liquid co‐solvent increased papain's half‐life by 3.1‐, 3.8‐, 4.7‐ and 16.3‐fold when compared with aqueous buffer, aqueous propan‐2‐ol, aqueous acetonitrile and aqueous 1,4‐dioxan co‐solvent respectively at 40 °C. When hydrolysis was conducted under reduced pressure, the yield, the e.e. of the l ‐HPG and the e.e. of remaining d ‐hydroxyphenylglycine methyl ester achieved were as high as 49.8, 98.1 and >99.0% respectively.