Native chemical ligation strategy for the synthesis of glycopeptide 1. Reagents and conditions: (a) 1. 6 M Gn•HCl, 100 mM NaH2PO4, 50 mM TCEP, pH 7.5, 67%; 2. piperidine, DMSO, 61%; 3. 0.2M MeONH2, 60%; (b) 6 M Gn•HCl, 100 mM NaH2PO4, 50 mM TCEP, pH 7.5, 23%; (c) 6 M Gn•HCl, 100 mM NaH2PO4, 50 mM TCEP, 200 mM MPAA, pH 7.8, 40%; (d) TCEP, VA-044, tBuSH.