Decarboxylative alkylation for site-selective bioconjugation of native proteins via oxidation potentials


The advent of antibody–drug conjugates as pharmaceuticals has fuelled a need for reliable methods of site-selective protein modification that furnish homogeneous adducts. Although bioorthogonal methods that use engineered amino acids often provide an elegant solution to the question of selective functionalization, achieving homogeneity using native amino acids remains a challenge. Here, we explore visible-light-mediated single-electron transfer as a mechanism towards enabling site- and chemoselective bioconjugation. Specifically, we demonstrate the use of photoredox catalysis as a platform to selectivity wherein the discrepancy in oxidation potentials between internal versus C-terminal carboxylates can be exploited towards obtaining C-terminal functionalization exclusively. This oxidation potential-gated technology is amenable to endogenous peptides and has been successfully demonstrated on the protein insulin. As a fundamentally new approach to bioconjugation this methodology provides a blueprint toward the development of photoredox catalysis as a generic platform to target other redox-active side chains for native conjugation.

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Figure 1: Photoredox-catalysed decarboxylative functionalization as a novel electron transfer mechanism towards site- and chemoselective bioconjugation.
Figure 2: Proposed mechanism for the C-terminal-selective photoredox decarboxylative conjugate addition.
Figure 3: Scope of the photoredox decarboxylative conjugate addition applied to endogenous peptides.
Figure 4: Photoredox-mediated decarboxylative functionalization of human insulin.


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The authors acknowledge financial support provided by the NIHGMS (R01 01GM093213-04) and gifts from Merck and BMS. D.K.K. acknowledges the Deutsche Forschungsgemeinschaft (DFG) for a postdoctoral fellowship (KO 4867/2-1). The authors thank T. Muir, Z. Brown, R. Thompson and members of the Muir Laboratory for their advice and analytical support. The authors also thank I. Pelczer and K. Conover for assistance with NMR spectroscopy.

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S.B., C.L. and D.K.K. performed and analysed the experiments. S.B., C.L., D.K.K. and D.W.C.M. designed the experiments and prepared this manuscript. J.X.Q., Y.Z., M.A.P. and W.R.E. provided discussions. J.X.Q. assisted with peptide synthesis.

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Correspondence to David W. C. MacMillan.

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Bloom, S., Liu, C., Kölmel, D. et al. Decarboxylative alkylation for site-selective bioconjugation of native proteins via oxidation potentials. Nature Chem 10, 205–211 (2018).

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