Research paperHighly efficient bioreduction of 2-hydroxyacetophenone to (S)- and (R)-1-phenyl-1,2-ethanediol by two substrate tolerance carbonyl reductases with cofactor regeneration

- Two stereocomplementary NADH-dependent carbonyl reductases were discovered for the first time for highly stereoselective bioreduction of 2-HAP to enantiopure PED.
- Strong substrate tolerance of the two enzymes was demonstrated.
- Effective cofactor regeneration system was constructed by glucose dehydrogenase, complete conversions were achieved.
- Biotransformation of 2-HAP (at 54 g/L scale) to enantiopure PED with recombinant E. coli whole cells was achieved without external addition of an expensive cofactor.

Optically pure 1-phenyl-1,2-ethanediol is a very important chiral building block and intermediate in fine chemical and pharmaceutical industries. Reduction of 2-hydroxyacetophenone provides a straightforward approach to access these important compounds. In this study, two enantiocomplementary carbonyl reductases, BDHA (2,3-butanediol dehydrogenase from Bacillus subtilis) and GoSCR (polyol dehydrogenase from Gluconobacter oxydans) were discovered for the first time to convert 2-hydroxyacetophenone (2-HAP) to (R)-1-phenyl-1,2-ethanediol ((R)-PED) and (S)-1-phenyl-1,2-ethanediol ((S)-PED) with excellent stereochemical selectivity, respectively. The two enzymes were purified and characterized. In vitro bioreduction of 2-HAP catalyzed by BDHA and GoSCR coupled with glucose dehydrogenase (GDH) from Bacillus subtilis for cofactor regeneration were demonstrated, affording both (R)-PED and (S)-PED in >99% ee and 99% conversion. Recombinant Escherichia coli whole cells co-expressing both GDH and BDHA or GoSCR genes were used to asymmetric reduction of 2-HAP to (R)-PED or (S)-PED. Under the optimized conditions, the bioreduction of 400 mM (54 g/L) substrate was proceeded smoothly without the external addition of cofactor, and the product (R)-PED and (S)-PED were obtained with 99% yield, >99% ee and 18.0 g/L/h volumetric productivity. These results offer a practical biocatalytic method for the preparation of both (R)-PED and (S)-PED with high volumetric productivity.