In this work, we report the discovery of a small phenyl molecule with four isosteric thiolate-reactive groups of sequentially-varied reactivity, and how this molecule was exploited in combination with cysteine/penicillamine thiolates of different nucleophilic reactivity for precisely-regulated and one-pot locking (PROP-Locking) of linear peptides into multicyclic topologies. The PROP-Locking relies on multistep and sequential thiolate/fluorine nucleophilic substitutions, which is not only rapid but highly specific, thus enabling rapid locking of peptides with high amino acid diversities without protecting groups. Several tricyclic peptide templates and bioactive peptides were designed and synthesized via the PROP-Locking strategy. We believe that tricyclic peptides precisely locked through stable thioether bonds should be promising structurally-constrained scaffolds for developing potential therapeutics and target ligands.
