Chemical synthesis of mouse pro-opiomelanocortin(1-74) by azido-protected glycopeptide ligation via the thioester method.

The thioester method is a peptide condensation reaction, which requires the protection of Lys side chains for chemoselective ligation. We recently found that the azido group could be used as an amino protecting group in the peptide condensation by the thioester method. In this study, we synthesized the glycosylated mouse pro-opiomelanocortin (1-74) by the thioester method. The N-terminal peptide thioester segment, whose Lys side chain was protected by an azido group, was prepared using a 9-fluorenylmethoxycarbonyl (Fmoc) strategy and an N-alkylcysteine (NAC)-assisted thioesterification reaction. The C-terminal azido-glycopeptide segment carrying N- and O-linked glycans was also prepared by the Fmoc chemistry and condensed with the N-terminal segment by the silver ion-free thioester method. These results showed that our azido-based strategy was fully compatible with the NAC-assisted method and glycoprotein synthesis.