Enantioselective Biohalogenation of Spiro-Epoxyoxindoles Enabled by Engineered Halohydrin Dehalogenases

We herein describe a biocatalytic halogenation approach that harnesses the reverse dehalogenation reaction of halohydrin dehalogenases. Through the integration of enzyme screening and structure-guided protein engineering, a double mutant of HheC (T134S/W139M) was created for the enantioselective halogenation of spiro-epoxyoxindoles, delivering chiral β-haloalcohols in high yields (up to 50%) and optical purity (up to 98% ee). Meanwhile, a nonenantioselective double mutant of HheG (I104F/N196G) was identified for the efficient halogenation of racemic or enantiopure spiro-epoxyoxindoles, affording the corresponding β-haloalcohols in up to 98% yield. The biohalogenation systems were performed using copper halides as the halogenating reagent under whole-cell catalysis and exhibit satisfactory substrate generality. When cell-free extract was used as the biocatalyst, several other halide salts were also proved effective for the biohalogenation reaction. Remarkably, seawater served as a natural halogenating agent, enabling gram-scale synthesis of chiral β-haloalcohols. Representative downstream transformations of chiral β-haloalcohols further showcased the synthetic utility of the enantioselective biohalogenation platform. Together, these findings not only expand the catalytic repertoire of halohydrin dehalogenases but also provide a viable biohalogenation strategy for the synthesis of chiral β-haloalcohols from readily available epoxides.