Highly efficient synthesis of sialylglycopeptides overcoming unexpected aspartimide formation during activation of Fmoc-Asn(undecadisialyloligosaccharide)-OH

Aspartimide formation between amide nitrogen at the reducing end and α-carboxyl acid of oligosaccharyl Fmoc-asparagine was found to occur during activation of α-carboxyl acid and this side reaction resulted in low coupling yields of oligosaccharyl Fmoc-sparagine with peptide-resin.