Chemoenzymatic preparation of (S)-p-nitrostyrene oxide from p-nitrophenacyl bromide by recombinant Escherichia coli cells expressing a novel halohydrin dehalogenase

• A novel halohydrin dehalogenase SyHhdh was functionally expressed in E. coli.
• re-SyHhdh exhibited high activity towards rac-BNPE at 100% conversion.
• re-SyHhdh prefers (R)-pNSO in the nitrite-mediated ring opening of rac-pNSO.
• A chemoenzymatic route producing (S)-pNSO (99% ee) from pNPB was first constructed.

A codon-optimized gene Syhhdh encoding a novel halohydrin dehalogenase (SyHhdh) was synthesized and expressed in Escherichia coli. Optimal pH and temperature of recombinant SyHhdh for the dehalogenation ring-closure and asymmetric ring-opening reactions were 9.0 and 45 °C, and 6.5 and 35 °C, respectively. It displayed low enantioselectivity for the dehalogenation of racemic 2-bromo-1-(4-nitrophenyl)ethanol (rac-BNPE), giving rac-BNPE in 100% conversion and racemic p-nitrostyrene oxide (rac-pNSO) in 91.1% yield, while high enantioselectivity for the nitrite-mediated ring opening of rac-pNSO. (S)-pNSO with a 99% ee and a 23.8% yield was obtained from p-nitrophenacyl bromide by a chemoenzymatic route via one-step chemical synthesis and two-step biocatalysis using whole cells of E. coli/Syhhdh.

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