Solvent-Dependent Chemoselectivity Switch to Arg-Lys Imidazole Cross-Links.

Herein, we report a trifluoroethanol-mediated, chemoselective method for the formation of Arg-Lys imidazole cross-links with methylglyoxal and its application in the selective macrocyclization of peptides between Lys and Arg and the late-stage diversification of Lys-containing peptides with guanidine. Our findings highlight the critical role of solvent choice in controlling chemoselectivity, providing valuable insights into solvent-dependent peptide modification.