Biocatalytic Generation of Trifluoromethyl Radicals by Nonheme Iron Enzymes for Enantioselective Alkene Difunctionalization
James G. Zhang, Anthony J. Huls, Philip M. Palacios, Yisong Guo, Xiongyi Huang
Abstract
The trifluoromethyl (−CF 3 ) group represents a highly prevalent functionality in pharmaceuticals. Over the past few decades, significant advances have been made in the development of synthetic methods for trifluoromethylation. In contrast, there are currently no metalloenzymes known to catalyze the formation of C(sp 3 )–CF 3 bonds. In this work, we demonstrate that a nonheme iron enzyme, hydroxymandelate synthase from Amycolatopsis orientalis ( Ao HMS), is capable of generating CF 3 radicals from hypervalent iodine(III) reagents and directing them for enantioselective alkene trifluoromethyl azidation. A high-throughput screening (HTS) platform based on Staudinger ligation was established, enabling the rapid evaluation of Ao HMS variants for this abiological transformation. The final optimized variant accepts a range of alkene substrates, producing the trifluoromethyl azidation products in up to 73% yield and 96:4 enantiomeric ratio (e.r.). The biocatalytic platform can be further extended to alkene pentafluoroethyl azidation and diazidation by altering the iodine(III) reagent. In addition, anion competition experiments provide insights into the radical rebound process for this abiological transformation. This study not only expands the catalytic repertoire of metalloenzymes for radical transformations but also creates a new enzymatic space for organofluorine synthesis.