One-Step Microbial Conversion of a Racemic Mixture of Pantoyl Lactone to Optically Active d -(—)-Pantoyl Lactone

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Abstract
Washed cells of Rhodococcus erythropolis IFO 12540 were found to convert only the l-(+)-isomer of pantoyl lactone to the d-(—)-isomer in a racemic mixture of pantoyl lactone. Under suitable reaction conditions, the amount of d-(—)-pantoyl lactone synthesized was 18.2 mg/ml (94.4% enantiomer excess; molar yield, 90.5%). This conversion was suggested to proceed through the following successive reactions: first, the enzymatic oxidation of l-(+)-pantoyl lactone to ketopantoyl lactone; second, the rapid and spontaneous hydrolysis of the ketopantoyl lactone to ketopantoic acid; and then, the enzymatic reduction of the ketopantoic acid to d-(—)-pantoic acid. After the reaction d-(—)-pantoic acid could be lactonized by means of acid treatment. During the conversion, the d-(—)-isomer, which was initially present in the reaction mixture, did not undergo any modification.