Efficient production of ethyl (R)-2-hydroxy-4-phenylbutyrate using a cost-effective reductase expressed in Pichia pastoris

Abstract Recombinant strains of Pichia pastoris expressing carbonyl reductase Cg KR2 from Candida glabrata were constructed for stereoselective reduction of ethyl-2-oxo-4-phenylbutyrate (OPBE) to ethyl ( R )-2-hydroxy-4-phenylbutyrate [( R )-HPBE], an important building block for synthesis of angiotensin-converting enzyme (ACE) inhibitors. An intracellular expression level of 6.67 g L −1 and a secretion expression level of 3.0 g L −1 were obtained, respectively, by high cell density fermentation. By using whole cells of KM71/ Cg KR2 in aqueous system, the Cg KR2-mediated bioreduction was performed, achieving a complete conversion of 1.0 M OPBE at 0.5 L scale, with a final yield of 77.9% and an enantiomeric excess ( ee ) of 97.3%. The secreted enzyme Cg KR2 appeared to be a better catalyst with respect to the perfect ee of the product ( R )-HPBE (>99%) when comparing with the recombinant cells of KM71/ Cg KR2. The cost of the resultant ( R )-HPBE was reduced by 1/4 using the secreted Cg KR2.