Biocatalytic anti-Prelog stereoselective reduction of ethyl acetoacetate catalyzed by whole cells of Acetobacter sp. CCTCC M209061.

The biocatalytic anti-Prelog stereoselective reduction of ethyl acetoacetate (EAA) to ethyl (R)-3-hydroxybutyrate {(R)-EHB} was successfully conducted in the aqueous system using immobilized Acetobacter sp. CCTCC M209061 cells. Among various microorganisms tested, Acetobacter sp. CCTCC M209061 gave the best performance and showed great potential for the bioreduction of EAA to (R)-EHB. Acetobacter sp. CCTCC M209061 cells were immobilized on calcium alginate and then coated with chitosan, and the immobilized cells clearly surpassed the free cells in terms of better thermal stability, storability and recyclability. The optimal co-substrate for the reaction was found to be glucose. The optimal substrate concentration, buffer pH, glucose concentration, reaction temperature, biocatalyst concentration and shaking speed were 35.0 mmol/L, 5.5, 80.0 mmol/L, 35 °C, 0.45 g/mL and 200 rpm, respectively. Under the optimized conditions, the initial reaction rate, the yield and the enantiomeric excess (e.e.) of the product were 1.28 μmol/min, 82.6% and above 99.0%, respectively, which were much higher than those reported previously. The efficient whole-cell biocatalytic process was feasible on a 500-mL preparative scale, and the immobilized cells showed excellent operational stability and could be re-used for at least 10 batches. Additionally, the product e.e. constantly remained above 99.0% regardless of re-use cycles of the biocatalyst.