Utilizing Copper-Mediated Deprotection of Selenazolidine for Cyclic Peptide Synthesis.

Selenazoliline (Sez) was originally developed as a masked form of selenocysteine (Sec) for the chemical synthesis of challenging proteins. Here, we utilize Sez and our recently reported copper(II)-mediated deprotection for the synthesis of cyclic peptides. This approach allowed one-pot deprotection, cyclization, and deselenization to give several different cyclic peptides in good yields. In Sez-mediated peptide cyclization, the Sec can also be retained, which enhances the oxidative folding of disulfide-rich cyclic proteins such in the case of Kalata S.