Cysteine‐Selective Modification of Peptides and Proteins via Desulfurative C−C Bond Formation

Abstract

The site-selective modification of peptides and proteins facilitates the preparation of targeted therapeutic agents and tools to interrogate biochemical pathways. Among the numerous bioconjugation techniques developed to install groups of interest, those that generate C(sp 3 )À C(sp 3 ) bonds are significantly underrepresented despite affording proteolytically stable, biogenic linkages. Herein, a visiblelight-mediated reaction is described that enables the site-selective modification of peptides and proteins via desulfurative C(sp 3 )À C(sp 3 ) bond formation. The reaction is rapid and high yielding in peptide systems, with comparable translation to proteins. Using this chemistry, a range of moieties is installed into model systems and an effective PTM-mimic is successfully integrated into a recombinantly expressed histone.

Kinetic Resolution of Epimeric Proteins enables Stereoselective Chemical Mutagenesis

“…A chemical challenge, especially in the context of PTM research, is the requirement for precise, minimally perturbing linkages between the protein and new functional groups. Creative solutions for this problem are Cys alkylation, frequently used to install methyllysine analogs, 39 and recent desulfurative [40][41][42][43] strategies to incorporate useful functional groups such as spin labels, PTMs, and their analogues.…”

Recent progress in photoinduced direct desulfurization of thiols

“…In 2022 and 2023, the photoinduced one-step cleavage of C sp 3 –SH of peptide or proteins and the subsequent addition to CC bonds (200 equiv.) were achieved by Mitchell et al 30 with the use of TCEP (5–10 equiv.) catalyzed by Ir[dF(CF 3 )ppy] 2 (dtbpy)PF 6 (5 mol%) in 34%–81% yields in aqueous buffer solution.…”

Peptide macrocyclisation via intramolecular interception of visible-light-mediated desulfurisation

“…59 In previous work, we demonstrated desulfurisation using an iridium( iii ) photocatalyst (PC) and employed alkenes to intercept the alanyl radical species, enabling installation of Lys sidechains carrying natural modifications as well as effective mimics of this modified sidechain. 54,55 This reaction is initiated via excitation of the Ir( iii ) PC by a photon of visible light. The activated catalyst is then reduced by the thiol group producing a thiol radical cation which forms a thiyl radical on deprotonation.…”

“…We recently reported a novel strategy for the site-selective modification of peptides and proteins via visible-light-mediated desulfurative C(sp 3 )–C(sp 3 ) bond formation. 54,55 Desulfurisation of Cys (and alternative non-proteinogenic thiol-containing amino acids 56–58 ) can be applied post-peptide ligation as an elegant method to access a broad range of ligation junctions and facilitate chemical protein synthesis. 56,59–67 A widely used free-radical-mediated Cys desulfurative protocol, 59 developed by Danishefsky and co-workers, proceeds via a thiophosphoranyl radical species generated using a radical initiator (VA-044) to form a thiyl radical from the thiol sidechain of Cys in the presence of the water-soluble phosphine, tris(2-carboxyethyl)phosphine hydrochloride (TCEP).…”