CHIRAL INVERSION OF 2-PHENYLPROPIONIC ACID BY CORDYCEPS MILITARIS

Fifty-nine microbial cultures were screened for their ability to carry out the chiral inversion of (R,S) and (R)-2-phenylpropionic acid unde r both growing and non-growing conditions, While a number of these mic ro-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 occurri ng, The rare of inversion was faster for C, militaris is but in both c ases 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 accou nt fur the equilibrium enantiomeric ratios (S:R) of 90:10 and 70:30 fo r C. militaris and V. lecanii, respectively, Optimization studies reve aled 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 p roduction of pure enantiomers from racemic mixtures and, in addition, provide an in vitro model system for the study of a unique and interes ting biotransformation.