Improved biosynthesis of ethyl (S)-4-chloro-3-hydroxybutanoate by adding l-glutamine plus glycine instead of NAD+ in β-cyclodextrin–water system

To reduce dependence on the expensive cofactor and effectively biotransform ethyl 4-chloro-3-oxobutanoate, l -glutamine and glycine were found to enhance the content of intracellular NADH and the reductase activity. Adding the mixture of 200   mM of l -glutamine and 500   mM of glycine to the reaction media, a 1.67-fold of reductase activity was increased over the control without the addition of the two compounds. Moreover, β-cyclodextrin (0.4   mol β-cyclodextrin/mol ethyl 4-chloro-3-oxobutanoate) was also added into this reaction media, and the biocatalytic activity of the whole-cell biocatalyst of Escherichia coli CCZU-K14 was increased by 1.34-fold than that without β-cyclodextrin. In this β-cyclodextrin–water media containing l -glutamine (200   mM) plus glycine (500   mM), ethyl ( S )-4-chloro-3-hydroxybutanoate (>99% ee ) could be obtained from 3000   mM ethyl 4-chloro-3-oxobutanoate in the yield of 98.0% after 8   h. All the positive features demonstrate the potential applicability of the bioprocess for the large-scale production of ethyl ( S )-4-chloro-3-hydroxybutanoate.