Resolution of racemic carboxylic acids via the lipase-catalyzed irreversible transesterification of vinyl esters.

The lipase-catalyzed irreversible transesterification procedure using vinyl esters was applied to the resolution of racemic 2-phenoxypropanoic acids. Aspergillus niger lipase showed high enantioselectivities and reasonable reaction rates. The enantioselectivity was found to be affected profoundly by several variables, e.g., the alcohol as nucleophile, the organic solvent used, and the reaction temperature. A gram-scale resolution of (RS)-2-phenoxypropanoic acid was achieved after optimization of the reaction conditions. Then this irreversible transesterification procedure was applied to the resolution of some related 2-substituted carboxylic acids. Thus, racemic 2-methoxy-2-phenylacetic acid was resolved via the A. niger lipase-catalyzed transesterification of the corresponding vinyl ester. 2-Phenylpropanoic acid and 2-phenylbutanoic acid were resolved using Pseudomonas sp. lipase. A gram-scale resolution of 2-phenylbutanoic acid was achieved by this procedure coupled with the porcine liver esterase-catalyzed hydrolysis of the resulting methyl ester.