CHIRAL INVERSION OF 2-PHENYLPROPIONIC ACID BY CORDYCEPS MILITARIS

摘要

Fifty-nine microbial cultures were screened for their ability to carry out the chiral inversion of (R,S) and (R)-2-phenylpropionic acid under both growing and non-growing conditions, While a number of these micro-organisms metabolized, the substrate, only Verticillium lecanii IMI 68689 and Cordyceps militaris CBS 128.25 were able to invert the (R)-enantiomer to its (S)-antipode with no other biotransformation occurring, The rare of inversion was faster for C, militaris is but in both cases the reaction was independent of growth and reached an equilibrium after 5 d incubation, Evidence suggests that the (R) to (S) inversion is inhibited in the presence of excess (S)-enantiomer which may account fur the equilibrium enantiomeric ratios (S:R) of 90:10 and 70:30 for C. militaris and V. lecanii, respectively, Optimization studies revealed that the fastest rates of reaction for C. militaris were found at lon er substrate concentrations (100 mu g ml(-1)) whilst the greatest yield of (S)-2-PPA was obtained at 250 mu g ml(-1). Optimum inversion was found to occur using Sorensen's phosphate buffer at pH 5.5. These results may have implications for the use of micro-organisms in the production of pure enantiomers from racemic mixtures and, in addition, provide an in vitro model system for the study of a unique and interesting biotransformation.