title: Sugar-assisted glycopeptide ligation with complex oligosaccharides: scope and limitations.
abstract: We have previously shown sugar-assisted ligation (SAL) to be a useful method for the convergent construction of glycopeptides. However to date SAL has only been carried out on systems where the thiol auxiliary is attached to a monosaccharide. For SAL to be truly applicable to the construction of fully elaborated glycopeptides and glycoproteins, it must be possible to carry out the reaction when the thiol auxiliary is attached to more elaborate sugars, as these are frequently what are observed in nature. Here we examine the effects of glycosylation at C-3, C-4, and C-6 of the C-2 auxiliary-containing glycan. Model glycopeptides where synthesized chemoenzymatically and reacted with peptide thioesters used in our previous work. These studies reveal that SAL is sensitive to extended glycosylation on the auxiliary-containing sugar. While it is possible to carry out SAL with extended glycosylation at C-4 and C-6, the presence of glycosylation at C-3 prevents the ligation from occurring. Additionally, with glycosylation at C-4 the ligation efficiency is affected by the identity of the N-terminal AA, while the nature of the C-terminal residue of the peptide thioester does not appear to affect ligation efficiency. These studies provide useful guidelines in deciding when it is appropriate to use SAL in the synthesis of complex glycopeptides and glycoproteins and how to choose ligation junctions for optimal yield.
authors.affiliation: Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA.
authors.forename: Clay S
authors.initials: CS
authors.lastname: Bennett
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Dean
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Payne
authors.forename: Simon
authors.initials: S
authors.lastname: Ficht
authors.forename: Ashraf
authors.initials: A
authors.lastname: Brik
authors.forename: Chi-Huey
authors.initials: CH
authors.lastname: Wong
mesh_terms: D000116:Acetylgalactosamine / Q000737:chemistry; D000117:Acetylglucosamine / Q000737:chemistry; D000596:Amino Acids / Q000138:chemical synthesis / Q000737:chemistry; D006020:Glycopeptides / Q000138:chemical synthesis*; D006031:Glycosylation; D016695:Glycosyltransferases / Q000737:chemistry; D009844:Oligosaccharides / Q000737:chemistry*; D011134:Polysaccharides / Q000737:chemistry; D013438:Sulfhydryl Compounds / Q000737:chemistry
chemical_list: D000596:Amino Acids; D006020:Glycopeptides; D009844:Oligosaccharides; D011134:Polysaccharides; D013438:Sulfhydryl Compounds; D016695:Glycosyltransferases; D000116:Acetylgalactosamine; D000117:Acetylglucosamine