Engineering non-haem iron enzymes for enantioselective C(sp3)-F bond formation via radical fluorine transfer.

In recent years there has been a surge in the development of methods for the synthesis of organofluorine compounds. However, enzymatic methods for C-F bond formation have been limited to nucleophilic fluoride substitution. Here, we report the incorporation of iron-catalysed radical fluorine transfer, a reaction mechanism that is not used in naturally occurring enzymes, into enzymatic catalysis for the development of biocatalytic enantioselective C( )-F bond formation. Using this strategy, we repurposed ()-2-hydroxypropylphosphonate epoxidase from (HppE) to catalyse an -fluoroamide directed C( )-H fluorination. Directed evolution has enabled HppE to be optimized, forming diverse chiral benzylic fluoride products with turnover numbers of up to 180 and with excellent enantiocontrol (up to 94% e.e.). Mechanistic investigations showed that the N-F bond activation is the rate-determining step, and the strong preference for fluorination in the presence of excess NaN can be attributed to the spatial proximity of the carbon-centered radical to the iron-bound fluoride.