Application and Structural Analysis of Triazole-Bridged Disulfide Mimetics in Cyclic Peptides.

Ruthenium-catalysed azide-alkyne cycloaddition (RuAAC) is an emerging tool for organic and medicinal chemistry that provides access to 1,5-disubstituted 1,2,3-triazole motifs for applications in peptide engineering. Despite its growing popularity, investigation of this motif as a disulfide mimetic in backbone cyclic peptides has been limited, and structural consequences remain to be studied. Here, we establish synthetic strategies to install various triazole linkages in cyclic peptides using backbone cyclisation and RuAAC cross-linking reactions. These linkages were evaluated in four serine protease inhibitors based on the sunflower trypsin inhibitor-1 framework. NMR and X-ray crystallography revealed exceptional consensus of bridging distance and backbone conformations (RMSD <0.5 A) of the triazole linkages when compared to the parent disulfide molecules. The triazole-bridged peptides displayed superior half-lives in liver S9 stability assays compared to disulfide-bridged peptides. This work establishes a strong foundation for the application of 1,5-disubstituted 1,2,3-triazoles as disulfide mimetics.