Screening and reaction engineering for the bioreduction of ethyl benzoylacetate and its analogues

Microbial reduction of benzoylacetates is already an established part of the synthetic toolbox to obtain chiral ethyl 3-hydroxy-3-phenylpropionate although bioreduction yields are low to moderate. A 30% increase in the enantioselectivity to 99% ee and a significant improvement in the yields to around 85% were achieved by combining simple screening procedures and a reaction engineering strategy. Three experimental parameters were selected for investigation: the influences of glucose, enzymatic inhibitor and biocatalyst immobilization. The screened yeasts Pichia kluyveri, Pichia stipitis and Candida utilis were found to give better yields and eeʹs for ethyl benzoylacetate 1a, p-nitrobenzoylacetate 1b and p-methoxybenzoylacetate 1c, respectively, with addition of glucose, α-chloroacetophenone as inhibitor and immobilization of the yeasts in alginate beads. Our results demonstrate that the optimized process can be implemented on a preparative scale without any loss in yield and ee.