The products after glycosylation modification of polypeptides are called glycopeptides, which can be used as model tools to play an important role in the scientific study of the structure and function of glycoproteins. Therefore, the synthesis of glycopeptides is particularly important.

At present, the connecting bonds between oligosaccharides and polypeptide chains mainly include C-, N-, O-, S-glycosidic bonds, of which N-, O-glycosidic bonds are the most commonly used. The chemical instability of glycosidic bonds greatly increases the complexity of peptide synthesis. Glycosidic bonds are usually hydrolyzed under acidic conditions, and for all glycosylserine and threonine derivatives there is a possibility of elimination even under very weak basic conditions.

N-linked glycosylation can introduce -glycosamine, protect asparagine through amide and carboxyl group binding, this method does not require special protection of sugars or peptides, and can be linked to asparagine residues in the polypeptide chain by glycosaminoglycans group to obtain an N-linked glycopeptide. In the synthesis of linked glycopeptides, the hydroxyl groups of serine and threonine act as acceptors of glycosyl groups, which require protection of the sugar and peptide.

The selective removal of the protecting groups of glycosylamino acids or glycopeptides is still a long-standing unsolved problem, although this problem has been proposed as early as the late 1970s, without breaking the glycosidic bond. Under these conditions, the z group of glycosylamino acid derivatives cannot be removed with HBr/AcOH. Although removal of the Boc residue is achievable under certain conditions, the deprotection reaction under acidic conditions in glycopeptide synthesis still needs to be carefully weighed. As mentioned, base-sensitive glycosylserine or threonine derivatives (elimination reactions) further limit the scope of reactions for deprotection. Therefore, protecting groups can only be removed under mild or neutral reaction conditions

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