An Asymmetric Hydrogen Atom Transferase with an Abiological Thiophenol Cofactor

Biocatalytic hydrogen atom transfer (HAT) holds the potential to help address some long-standing challenges in organic synthesis. Although several families of enzymes rely on cysteine to perform HAT, these enzymes are rather impractical for synthetic purposes. To circumvent possible side reactions associated with cysteinyl radicals, we report herein artificial hydrogen atom transferases (AHATases) with an abiological thiophenol cofactor, capitalizing on biotin-streptavidin technology. Chemogenetic optimization afforded an AHATase with good reactivity and high enantioselectivity (er up to 93:7) for the photoinduced radical hydroamination of alkenes. Crystal structures suggest that aromatic-sulfur interactions are key contributing factors to cofactor anchoring and enantioinduction. Mechanistic studies support H atom abstraction and donation processes, both of which are catalyzed by the AHATase. Our work highlights the synthetic potential of thiol-based biocatalytic HAT and expands the repertoire of HAT biocatalysis.