Hydroxy Acids by Stereoinversion

The method is similar to the deracemization of a-amino acids (see Section 

1) with a combination of amino acid oxidase and amino transferase or amino acid dehydrogenase. Although the co-factor regeneration is considered a solved problem, the application of the method to obtaining a-hydroxy acids of wide structural variety and of both configurations is also in this case dependent on enzyme availabihty [13], 

Alternatively, a one-pot, single-step deracemization of sec-alcohols has been achieved by employing two different microorganisms in a single reaction vessel. However, the number of examples of this type is limited and the oxidation and reduction steps are usually performed sequentially in a one-pot, two-step procedure. For instance, racemic mandeUc acid was deracemized in the presence of whole cells of Pseudomonas polycdor and Micrococcus freudenreichii [14]. Separate experiments showed that P. polycolor was responsible for the oxidation, while M. freudenreichii was needed for reduction of the corresponding a-keto acid. After 24h, (R)-mandelic acid 4 was isolated in a 60% yield and 99% e.e. [14], 

The two-enzyme system was also used to convert L-lactate into D-lactate with a yield better than 97%. L-Lactate is oxidized by L-lactate dehydrogenase to give pymvate. The keto acid is reduced in an electrochemical system at the cathode to racemic lactate and NADH is oxidized to NAD at the anode. The continuous 

System A oxidative enzyme L-lactate dehydrogenase reducing system electrochemical reduction 

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