Enantioselective cascade biocatalysis for deracemization of 2-hydroxy acids using a three-enzyme system

BACKGROUND Enantiopure 2-hydroxy acids are key intermediates for the synthesis of pharmaceuticals and fine chemicals. We present an enantioselective cascade biocatalysis using recombinant microbial cells for deracemization of racemic 2-hydroxy acids that allows for efficient production of enantiopure 2-hydroxy acids. RESULTS The method was realized by a single recombinant Escherichia coli strain coexpressing three enzymes: (S)-2-hydroxy acid dehydrogenase, (R)-2-keto acid reductase and glucose dehydrogenase. One enantiomer [(S)-2-hydroxy acid] is firstly oxidized to the keto acid with (S)-2-hydroxy acid dehydrogenase, while the other enantiomer [(R)-2-hydroxy acid] remains unchanged. Then, the keto acid obtained reduced to the opposite enantiomer with (R)-2-keto acid reductase plus cofactor regeneration enzyme glucose dehydrogenase subsequently. The recombinant E. coli strain coexpressing the three enzymes was proven to be a promising biocatalyst for the cascade bioconversion of a structurally diverse range of racemic 2-hydroxy acids, giving the corresponding (R)-2-hydroxy acids in up to 98.5 % conversion and >99 % enantiomeric excess. CONCLUSIONS In summary, a cascade biocatalysis was successfully developed to prepare valuable (R)-2-hydroxy acids with an efficient three-enzyme system. The developed elegant cascade biocatalysis possesses high atom efficiency and represents a promising strategy for production of highly valued (R)-2-hydroxy acids.