Stereoretentive Post-Translational Protein Editing

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Chemical post-translational methods now allow convergent side-chain editing of proteins as a form of direct chemical mutagenesis without needing to resort to genetic intervention. Current approaches that allow the creation of constitutionally native side-chains via C–C formation using off-protein carbon-centred C• radicals added to unnatural amino acid radical acceptor SOMOphile ‘tags’ such as dehydroalanine are benign and wide-ranging. However, they also typically create epimeric mixtures of D-/L-residues. Here we describe a light-mediated desulfurative method that, through the creation and reaction of stereoretained on-protein L-alanyl C β • radicals, allows C β –H γ , C β –O γ , C β –Se γ , C β –B γ and C β –C γ bond formation to flexibly generate site-selectively edited proteins with full retention of native stereochemistry under mild conditions from a natural amino acid. This methodology shows great potential to explore protein side-chain diversity and construct useful bioconjugates.