SuFEx-Enabled Acyl Fluoride Chemistry for High-Concentration Minimal-Oligomerization Peptide Macrocyclization.

Head-to-tail macrocyclization is a cornerstone transformation in cyclic peptide synthesis, yet its practical implementation remains constrained by extensive oligomerization under concentrated conditions. Here we report a SuFEx-enabled acyl fluoride activation strategy that intrinsically biases peptide macrocyclization toward intramolecular amide bond formation, enabling highly selective head-to-tail cyclization at concentrations up to 100 mM. In contrast to conventional uronium- and phosphonium-based coupling reagents, which generate complex oligomeric mixtures under identical conditions, the SuFEx-derived acyl fluoride pathway consistently affords cyclic monomers with minimal dimerization across diverse peptide sequences. Density functional theory calculations reveal that acyl fluoride activation reshapes the macrocyclization energy landscape by favoring irreversible ring closure while disfavoring oligomer growth, providing a mechanistic basis for the observed chemoselectivity. The method exhibits broad substrate scope, tolerating variations in ring size, sequence composition, and functionalized residues, and is readily translated to solid-phase and automated synthesis platforms. These results establish SuFEx-enabled acyl fluoride activation as a fundamentally distinct and practically robust solution to peptide macrocyclization under high-concentration conditions.