A Modular PMDA Linker Enables Lysine-Selective Cyclization of Unprotected Peptides and Automated Macrocycle Assembly

-amines, tolerating all other nucleophilic side chains, including cysteine, across a broad range of peptide sequences and linker spacings. The resulting macrocycles support stepwise bicyclization and modular postcyclization conjugation with nucleic acids, small-molecule drugs, and affinity tags. Application to antimicrobial peptides demonstrates enhanced conformational constraint and markedly improved proteolytic stability. Importantly, the chemistry is intrinsically compatible with solid-phase peptide synthesis and fully integrated, end-to-end automated workflows without hardware modification. This PMDA-mediated stapling strategy establishes a versatile, automation-ready linker platform for rapid assembly and functional diversification of macrocyclic peptides.