Efficient Reduction of Ethyl 2‐Oxo‐4‐phenylbutyrate at 620 g⋅L−1 by a Bacterial Reductase with Broad Substrate Spectrum

A β‐ketoacyl‐ACP reductase (FabG) gene from Bacillus sp. ECU0013 was heterologously overexpressed in Escherichia coli and the encoded protein was purified to homogeneity. The recombinant reductase could reduce a broad spectrum of prochiral ketones including aromatic ketones and keto esters and showed the highest activity in the asymmetric reduction of ethyl 2‐oxo‐4‐phenylbutyrate (OPBE). Using E. coli cells coexpressing both FabG and glucose dehydrogenase (GDH) genes, as much as 620 g⋅L⁻¹ of OPBE was almost stoichiometrically converted to ethyl (S)‐2‐hydroxy‐4‐phenylbutyrate [(S)‐HPBE] with excellent (>99%) enantiomeric excess. More importantly, the process could be performed smoothly without external addition of an expensive cofactor as usually done and could be scaled up very easily. All these positive features demonstrate the applicability of this reductase for the large‐scale production of optically active α‐hydroxy acids/esters.