The diverse array of chemical functionality displayed by the 20 canonical amino acids presents both challenges and opportunities for the site-selective modification of peptides and proteins. An extensive range of reactions have been reported to modify the majority of the proteinogenic residues, providing tools to enable the study and manipulation of biological systems, and the preparation of therapeutic/diagnostic agents.¹ To be effective, bioconjugation techniques must be rapid, high-yielding under mild conditions, and chemoselective. Owing to the superior nucleophilicity of the thiol group of cysteine, Cys, and its relatively low abundance across eukaryotic proteomes, circa 2%, many reported techniques target this residue to selectively install groups of interest.

Site-selective installation of Nε-modified sidechains (Lys PTMs) via visible-light-mediated desulfurative C-C bond formation.²

To further contribute to this synthetic tool kit, we are exploring the site-selective modification of peptides and proteins via interception of free-radical-mediated desulfurization. By exploiting the homolytic lability of the C-S bond of Cys, we have developed a visible-light-mediated desulfurative C(sp³)–C(sp³) bond forming reaction that enables the site-selective installation of N^ε-modified sidechains into peptides and proteins of interest, see figure.² Rapid, operationally simple, and tolerant to ambient atmosphere, we demonstrate the installation of a range of lysine, Lys, post-translational modifications, PTMs, and PTM mimics³ into model peptides and proteins.

Furthermore, by utilizing persistent radical traps, we have developed a broadly applicable bioconjugation technique to install groups of interest via formation of an amino-oxy linkage.⁴ The reaction is rapid, high yielding and chemoselective; the resulting bioconjugate is stable at varying pH and high temperature, and selectively cleavable under mildly acidic conditions with the addition of a low oxidation state transition metal. This method translates well onto larger and more complex peptides and proteins carrying a wealth of chemical diversity.

References

1. Omar Boutureira and Gonçalo J. L. Bernardes. Advances in Chemical Protein Modification. Chem. Rev. 2015, 115, 2174-2195

2. Rhys C. Griffiths, Frances R. Smith, Jed E. Long, Daniel Scott, Huw E. L. Williams, Neil J. Oldham, Robert Layfield, Nicholas J. Mitchell. Site-Selective Installation of N^ε-Modified Sidechains into Peptide and Protein Scaffolds via Visible-Light-Mediated Desulfurative C–C Bond Formation. Angew. Chem. Int. Ed. 2022, 61, e202110223

3. Rhys C. Griffiths, Frances R. Smith, Diyuan Li, Jasmine Wyatt, David M. Rogers, Jed E. Long, Lola M. L. Cusin, Patrick J. Tighe, Robert Layfield, Jonathan D. Hirst, Manuel M. Müller, Nicholas J. Mitchell. Cysteine-Selective Modification of Peptides and Proteins via Desulfurative C−C Bond Formation. Chem. Eur. J. 2023, DOI: 10.1002/chem.202202503

4. Rhys C. Griffiths, Frances R. Smith, Jed E. Long, Huw E. L. Williams, Robert Layfield, Nicholas J. Mitchell. Site-Selective Modification of Peptides and Proteins via Interception of Free-Radical-Mediated Dechalcogenation. Angew. Chem. Int. Ed. 2020, 59, 23659-23667