A Biocatalytic Platform for Synthesis of Chiral α-Trifluoromethylated Organoborons

There are few biocatalytic transformations that produce fluorine-containing molecules prevalent in modern pharmaceuticals. To expand the scope of biocatalysis for organofluorine synthesis, we have developed an enzymatic platform for highly enantioselective carbene BH bond insertion to yield versatile alpha-trifluoromethylated (alpha-CF3) organoborons, an important class of organofluorine molecules that contain stereogenic centers bearing both CF3 and boron groups. In contrast to current carbene transferase enzymes that use a limited set of simple diazo compounds as carbene precursors, this system based on Rhodothermus marinus cytochrome c (Rma cyt c) can accept a broad range of trifluorodiazo alkanes and deliver versatile chiral alpha-CF3 organoborons with total turnovers up to 2870 and enantiomeric ratios up to 98.5:1.5. Computational modeling reveals that this broad diazo scope is enabled by an active-site environment that directs the alkyl substituent on the heme CF3-carbene intermediate toward the solvent-exposed face, thereby allowing the protein to accommodate diazo compounds with diverse structural features.