Chemo-enzymatic D-enantiomerization of DL-lactate

We investigated the total conversion of racemic lactate, L-lactate, and pyr uvate into D-lactate, which is very useful as a starting material for the s ynthesis of chiral compounds and much more valuable than the L-enantiomer b y means of coupling of L-specific oxidation of the racemate with L-lactate oxidase and non-enantiospecific reduction of pyruvate to DL-lactate with so dium borohydride. In this one-pot system, L-lactate was enantiospecifically oxidized to an achiral product, pyruvate, which was chemically reduced to DL-lactate leading to a turnover. Consequently, either DL-lactate, L-lactat e, or pyruvate was fully converted to the D-enantiomer. We optimized the re action conditions: DL-lactate was converted to D-lactate in 99% of the theo retical yield and with more than 99% enantiomeric excess. DL-alpha -Hydroxy butyrate and alpha -ketobutyrate were converted also to D-alpha -hydroxybut yrate in the same way, though slowly. (C) 2001 John Wiley & Sons, Inc.