Efficient Stereoselective Synthesis of Ethyl (R)-2-Hydroxy-4-Phenylbutyrate by a Bacterial Reductase Coupled with Cofactor Regeneration

(R)-2-Hydroxy-4-phenylbutyrate is an important chiral intermediate in the synthesis of ACE inhibitors. Asymmetric reduction of OPBE to (R)-HPBE using recombinant strain could provide high enantioselectivity. However, cofactor regeneration is a critical issue in the application of recombinant strain. In our study, a carbonyl reductase gene (iolS) and a glucose dehydrogenase gene (gdh) from Bacillus subtilis were cloned, and three coexpression strategies were attempted for the coexpression vector construction. Recombinant E. coli strain containing polycistronic plasmid pET-G-T7-I showed excellent carbonyl reductase activity, and the specific activity of both IolS and GDH in crude cell extract reached 1.5 U/mg. In the asymmetric reducing of OPBE to (R)-HPBE by recombinant E. coli cells in aqueous system, the yield and optical purity of (R)-HPBE reached 100% and 99.5% enantiomeric excess (ee) at 10 g/L of OPBE. In water/octanol biphasic system, higher product titer could be achieved with 99.5% ee. This study provides a practical approach for further the asymmetric synthesis of (R)-HPBE and other chiral alcohol enantiomers.