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

• CgKR2 was successfully expressed in Pichia pastoris with high level.
• Up to 1 M OPBE was converted to (R)-HPBE using CgKR2 as catalyst.
• Secreted CgKR2 showed to be a better catalyst.
• CgKR2 is cost-effective.

Recombinant strains of Pichia pastoris expressing carbonyl reductase CgKR2 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/CgKR2 in aqueous system, the CgKR2-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 CgKR2 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/CgKR2. The cost of the resultant (R)-HPBE was reduced by 1/4 using the secreted CgKR2.