A Biocatalyst for the Preparation of ( R ) and ( S )‐2‐Hydroxycarboxylic Acids

“Biocatalytic enantiomer resolution of 2‐hydroxycarboxylic acids”, rac ‐1 , has been achieved with the (nonisolated) 2‐oxoacid reductase from Proteus vulgaris . This enzyme is usually employed to reduce 2‐oxomonocarboxylic acids to ( R )‐2‐hydroxycarboxylic acids (> 99% ee) with methyl‐ or benzylviologen as electron mediator. The use of carbamoylmethylviologen has allowed, for the first time, the reverse reaction to be carried out. Only the ( R ) enantiomer of rac ‐ 1 undergoes dehydrogenation; the ( S )‐2‐hydroxycarboxylic acid remains unchanged. The mediator can be regenerated.