R-(−)-mandelic acid production from racemic mandelic acids by Pseudomonas polycolor with asymmetric degrading activity

Abstract

The microbial asymmetric degradation of S-(+)-mandelic acid was investigated in order to develop a practical process for R-(−)-mandelic acid production from racemic mandelic acids. Among the 790 culture strains tested, microorganisms belonging to the Brevibacterium, Pseudomonas, Rhodococcus, Rhodotorula, Rhodosporidium, Sporobolomyces and Gibberella genera exhibited high S-(+)-mandelic acid degrading activity. Pseudomonas polycolor IFO 3918 was determined to be the best strain and used as a biocatalyst for eliminating the S-(+)-isomer. The maximum rate of S-(+)-isomer degradation was obtained at 30°C and pH 7.0. Under these optimal conditions, the S-(+)-isomer in a racemic mandelic acid 45 g/ l mixture was completely degraded within 24 h, with 20 g of R-(−)-mandelic acid per liter remaining in the reaction mixture. Crystalline R-(−)-mandelic acid with a chemical purity greater than 99% and optical purity of 99.9% enantiomeric excess was obtained at a yield of 35% by acidification of the reaction mixture, extraction with ethyl acetate and subsequent concentration.