Light-driven post-translational installation of reactive protein side chains

Abstract

Post-translational modifications (PTMs) greatly expand the structures and functions of proteins in nature 1,2 . Although synthetic protein functionalization strategies allow mimicry of PTMs 3,4 , as well as formation of unnatural protein variants with diverse potential functions, including drug carrying 5 , tracking, imaging 6 and partner crosslinking 7 , the range of functional groups that can be introduced remains limited. Here we describe the visible-light-driven installation of side chains at dehydroalanine residues in proteins through the formation of carbon radicals that allow C-C bond formation in water. Control of the reaction redox allows site-selective modification with good conversion efficiencies and reduced protein damage. In situ generation of boronic acid catechol ester derivatives generates RH2C • radicals that form the native (β-CH2-γ-CH2) linkage of natural residues and PTMs, whereas in situ potentiation of pyridylsulfonyl derivatives by Fe(II) generates RF2C • radicals that form equivalent β-CH2-γ-CF2 linkages bearing difluoromethylene labels. These reactions are chemically tolerant and incorporate a wide range of functionalities (more than 50 unique residues/side chains) into diverse protein scaffolds and sites. Initiation can be applied chemoselectively in the presence of sensitive groups in the radical precursors, enabling installation of previously incompatible side chains. The resulting protein function and reactivity are used to install radical precursors for homolytic on-protein radical

Late-stage difluoromethylation: concepts, developments and perspective

“…88 In 2020, Davis and Gouverneur reported for the first time a protocol enabling precise incorporation of a CF 2 H group on a protein (Scheme 30F). 134 2-PySO 2 CF 2 H was employed to release a CF 2 H radical capable of reacting at the terminal carbon of a SOMOphilic dehydroalanine (Dha) residue. The reaction is performed at ambient and biocompatible conditions, allowing for the preparation of hydrodifluoromethylated proteins in high yields (up to quantitative) and short reaction times.…”

“…Seminal work in this direction has recently been reported by Davis, Gouverneur and co-workers, who developed site-selective photocatalytic hydrodifluoromethylation and difluoromethylation of dehydroalanine and tryptophan residues in proteins, respectively. 99,134…”

Photocatalysis in Chemical Biology: Extending the Scope of Optochemical Control and Towards New Frontiers in Semisynthetic Bioconjugates and Biocatalysis

“…The CÀ C bond forming reaction are initiated by photocatalyzed radical formation, a reaction manifold that is compatible with the aqueous environment required for proteins and thereby underpins its tremendous utility. [67] Additionally, organoborates have also been used to functionalize complex antibiotic peptides (thiostrepton and nisin) at Dha and dehydrobutyrine (Dhb) residues. [68] A highly watersoluble analog of [Ir(dF(CF 3 )ppy) 2 (dtbbpy)]PF 6 with quaternary ammonium in lieu of the t Bu groups allowed peptide and protein modification with low reagent and catalyst loading in physiologically relevant conditions.…”

Dehydroamino acid chemical biology: an example of functional group interconversion on proteins

“…Another recent study reported the photochemical generation of carbon radicals using visible light that subsequently reacted with Dha residues selectively. 48 The technique demonstrated broad applicability, with the synthesis of over 50 novel side chains bearing a variety of different functionalities on diverse protein scaffolds.…”