Late-stage generation of ¹⁴C/³H-radiolabeled lysine residues via hydroformylation of peptides.

Peptides constitute a well-established and rapidly expanding field in the contemporary pharmaceutical drug landscape. Studies with C- or H-radiolabeled analogs are the gold standard for drug development, yet access to C-peptides is costly and limited to derivatization of the native structure with tags or lengthy multi-step syntheses. In this work, we report a platform that installs C- or H-radiolabeled lysine residues directly on solid-supported peptides. The workflow constitutes a mild, peptide-compatible hydroformylation process of allylglycine residues to generate labeled allysine, followed by reductive amination that furnishes radiolabeled lysine residues directly upon cleavage from the solid support. The hydroformylation setup can be tuned for flexible isotope introduction by using CO from solid precursors and H from standard tritium manifolds. We show that the optimized workflow tolerates diverse sequences and enables functionalization of peptides as complex as semaglutide analogs.