Side chain-to-side chain cyclization by click reaction.

Cu(I)-catalyzed azide-alkyne 1,3-dipolar Huisgen's cycloaddition (CuAAC) is a click reaction that has drawn a lot of attention, in general, and in the field of peptide and protein sciences, in particular. Among several reported applications, the preparation of novel heterodetic cyclopeptides by an intramolecular side chain-to-side chain CuAAC, forming a 1,4-disubstituted[1,2,3]triazolyl-containing bridge, is of great interest. Herein, we provide a detailed protocol for the syntheses of model heterodetic cyclopeptides as a prototypical intramolecular CuAAC, using as a model a sequence derived from parathyroid hormone-related protein.