Deracemization of a-Hydroxy Nitriles

In order to clarify the proposed mechanism, the reduction of ethyl 3-oxo-3-phenyl propionate was carried out, resulting in the exclusive formation of the (S)-enantiomer confirming the presence of (S)-specific reductase. When the pure (S)-enantiomer was used as the substrate for deracemization, the product recovered retained the configuration as well as the optical purity without any loss, clearly supporting the presence of an (S)-specific reductase, which does not oxidize the (S)-hydroxy ester to the corresponding keto ester. 

The generality of the reaction was established by using different substituents in the standard substrate ethyl 3-hydroxy 3-phenyl propionate. The presence of electron donating and electron withdrawing groups in the para position does not affect the deracemization reaction, while substitution in the ortho position hinders the same. On a preparative scale, up to 500 mg of racemic substrate incubated with the cells were deracemized with isolated yields close to 80%. 

Cyanohydrins are versatile and important building blocks in organic synthesis [20]. Consequently, their enantioselective synthesis has attracted considerable attention 

A similar reaction procedure has also been successfidly apphed to the deracemization of cyanohydrines containing heterocyclic structures [25]. 

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R = Ar, naphtyl, furyl, cyclohexyl Scheme 13.8 Deracemization of a-hydroxy nitriles. 

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