Effective biosynthesis of ethyl (R)-4-chloro-3-hydroxybutanoate by supplementation of l-glutamine, d-xylose and β-cyclodextrin in n-butyl acetate–water media

To avoid adding NAD + and effectively transform ethyl 4-chloro-3-oxobutanoate, the mixture of l -glutamine (200   mM) and d -xylose (250   mM) was added into in n -butyl acetate–water (10:90, v/v) biphasic system instead of NAD + for increasing the biocatalytic efficiency. To further improve the synthesis of optically pure ethyl ( R )-4-chloro-3-hydroxybutanoate (>99% ee ), β-cyclodextrin was also added into this reaction media, and ethyl ( R )-4-chloro-3-hydroxybutanoate (>99% ee ) could be effectively synthesized from 800   mM ethyl 4-chloro-3-oxobutanoate in the yield of 100% by whole-cells of recombinant E. coli CCZU-A13. Finally, the possible mechanism for improving the reductase activity by supplementation of l -glutamine, d -xylose and β-CD was proposed. In conclusion, this strategy has high potential for the effective biosynthesis of ethyl ( R )-4-chloro-3-hydroxybutanoate (>99% ee ).