page_title: Glycopeptide
section_title: Native chemical ligation
hierarchical_section_title: Glycopeptide / Glycopeptide synthesis / Native chemical ligation
caption_attribution_description: English: GlcNAc_Beta_Asn
context_page_description: Glycopeptides are peptides that contain carbohydrate moieties covalently attached to the side chains of the amino acid residues that constitute the peptide.
  Over the past few decades it has been recognised that glycans on cell surface and those bound to proteins play a critical role in biology. For example, these constructs have been shown to play important roles in fertilization, the immune system, brain development, the endocrine system, and inflammation.
  The synthesis of glycopeptides provides biological probes for researchers to elucidate glycan function in nature and products that have useful therapeutic and biotechnological applications.
context_section_description: Native chemical ligation (NCL) is a convergent synthetic strategy based on the linear coupling of glycopeptide fragments. This technique makes use of the chemoselective reaction between a N-terminal cysteine residue on one peptide fragment with a thio-ester on the C-terminus of the other peptide fragment as illustrated below.
  Unlike standard SPPS (which is limited to 50 amino acid residue) NCL allows the construction of large glycopeptides. However the strategy is limited by the fact that it requires a cysteine residue at N-terminus, an amino acid residue that is rare in nature. However this problem has partly been address by the selective desulfurization of the cysteine residue to an alanine.
caption: Scheme 3 Mechanism of native chemical ligation