title: Negative ion CID fragmentation of O-linked oligosaccharide aldoses--charge induced and charge remote fragmentation.
abstract: Collision induced dissociation (CID) fragmentation was compared between reducing and reduced sulfated, sialylated, and neutral O-linked oligosaccharides. It was found that fragmentation of the [M - H](-) ions of aldoses with acidic residues gave unique Z-fragmentation of the reducing end GalNAc containing the acidic C-6 branch, where the entire C-3 branch was lost. This fragmentation pathway, which is not seen in the alditols, showed that the process involved charge remote fragmentation catalyzed by a reducing end acidic anomeric proton. With structures containing sialic acid on both the C-3 and C-6 branch, the [M - H](-) ions were dominated by the loss of sialic acid. This fragmentation pathway was also pronounced in the [M - 2H](2-) ions revealing both the C-6 Z-fragment plus its complementary C-3 C-fragment in addition to glycosidic and cross ring fragmentation. This generation of the Z/C-fragment pairs from GalNAc showed that the charges were not participating in their generation. Fragmentation of neutral aldoses showed pronounced Z-fragmentation believed to be generated by proton migration from the C-6 branch to the negatively charged GalNAc residue followed by charge remote fragmentation similar to the acidic oligosaccharides. In addition, A-type fragments generated by charge induced fragmentation of neutral oligosaccharides were observed when the charge migrated from C-1 of the GalNAc to the GlcNAc residue followed by rearrangement to accommodate the (0,2)A-fragmentation. LC-MS also showed that O-linked aldoses existed as interchangeable α/β pyranose anomers, in addition to a third isomer (25% of the total free aldose) believed to be the furanose form.
authors.affiliation: School of Chemistry, National University of Ireland, Galway, Ireland.
authors.forename: Roisin A
authors.initials: RA
authors.lastname: Doohan
authors.forename: Catherine A
authors.initials: CA
authors.lastname: Hayes
authors.forename: Brendan
authors.initials: B
authors.lastname: Harhen
authors.forename: Niclas Göran
authors.initials: NG
authors.lastname: Karlsson
mesh_terms: D000116:Acetylgalactosamine / Q000737:chemistry; D002853:Chromatography, Liquid; D054794:Glycomics; D006108:Graphite / Q000737:chemistry; D007477:Ions / Q000737:chemistry; D019158:N-Acetylneuraminic Acid / Q000737:chemistry; D009844:Oligosaccharides / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D013402:Sugar Alcohols / Q000737:chemistry; D013431:Sulfates / Q000737:chemistry
chemical_list: D007477:Ions; D009844:Oligosaccharides; D013402:Sugar Alcohols; D013431:Sulfates; D006108:Graphite; D019158:N-Acetylneuraminic Acid; D000116:Acetylgalactosamine