Kinetic resolution of (R,S)-ethyl 2-hydroxyl-4-phenylbutyrate via lipase-catalyzed hydrolysis and transesterification in isooctane

In the enantioselective hydrolysis of (R,S)-ethyl 2-hydroxy-4-phenylbutyrate ((R,S)-EHPB) in isooctane or in a biphasic solution, Lipase PS having an enantiomeric ratio (i.e. the E value) of 22 for the (S)-enantiomer was screened as the best lipase to produce the remaining (R)-ethyl 2-hydroxy-4-phenylbutyrate ((R)-EHPB). When (R)-2-hydroxy-4-phenylbutanoic acid ((R)-HPBA) was the desired product, one might employ Novozym 435, possessing (R)-stereoselectivity with E=22, as the biocatalyst. The results of using Lipase PS in the enantioselective transesterification of (R,S)-EHPB in isooctane indicated that addition of more vinyl acetate (VA) could suppress the hydrolysis side-reaction, leading to an apparent E value >100. The result of E>100 was also found when initial VA concentration was fixed at 80 mM and (R,S)-EHPB concentrations increased from 5.4 to 190 mM. Vinyl laurate was further selected as the best acyl donor after comparing the enzyme performances among all vinyl esters employed and considering the easiness of product separation in the down-stream process.