Arginine-Selective Bioconjugation of Peptide and Proteins

Selective chemical modification of native proteins provides a powerful approach to introduce new functionality and interrogate protein function. While established bioconjugation methods predominantly target cysteine and lysine, expanding the chemical toolbox to other amino acids remains an important challenge in chemical biology. Arginine represents an attractive yet underexplored target because of its prevalence at functional protein interfaces and its distinctive guanidinium functionality. However, its high basicity and low nucleophilicity make selective covalent modification challenging. Here, we report an arginine-selective bioconjugation strategy based on a Biginelli–Atwal-type reaction using β-ketoamide-derived electrophiles. The reaction converts peptide-bound arginine into a stable dihydropyrimidine scaffold and exhibits high chemoselectivity in unprotected peptides containing other reactive residues. Importantly, this chemistry translates from peptides to intact proteins, demonstrating its potential for selective protein modification. Incorporation of a terminal alkyne provides a modular handle for downstream click chemistry and functionalization. In summary, this approach expands the bioconjugation toolbox to an underexplored amino acid and provides a framework for developing arginine-targeted covalent inhibitors against proteins containing functionally important or ligandable arginine residues.