The stereochemical dependence of unimolecular dissociation of monosaccharide-glycolaldehyde anions in the gas phase: a basis for assignment of the stereochemistry and anomeric configuration of monosaccharides in oligosaccharides by mass spectrometry via a key discriminatory product ion of disaccharide fragmentation, m/z 221.
Mass spectrometry of hexose-containing disaccharides often yields product ions of m/z 221 in the negative ion mode. Using a Paul trap, isolation and collision-induced dissociation of the m/z 221 anions yielded mass spectra that easily differentiated their stereochemistry and anomeric configuration, for all 16 stereochemical variants. The ions were shown to be glycopyranosyl-glycolaldehydes through chemical synthesis of their standards. The stereochemistry dramatically affected fragmentation which was dependent on four relative stereochemical arrangements: (1) the relationship between the hydroxyl group at position 2 and the anomeric configuration, (2) a cis relationship of the anomeric position and positions 2 and 3 (1,2,3-cis), (3) a 1,2 trans-2,3 cis relationship, and (4) the relationship between the hydroxyl group at position 4 and the anomeric configuration. After labeling the reducing carbonyl oxygen of a series of disaccharides with 18O to mass-discriminate between their monosaccharide components, it was demonstrated that m/z 221 anions are comprised of an intact nonreducing sugar glycosidically linked to a 2-carbon aglycon derived from the reducing sugar, irrespective of the linkage position between monosaccharides. This enabled the location of the intact sugar to be assigned to the nonreducing side of a glycosidic linkage. Detailed studies of experimental factors necessary for reproducibility demonstrated that the unique mass spectrum for each m/z 221 anion could be obtained from month-to-month through the use of an internal energy-input calibrant ion that ensured reproducible energy deposition into the ions. The counterparts to these ions for the 2-acetamido-2-deoxyhexoses were m/z 262 anions, and the anomeric configuration and stereochemistry of these anions could also be reproducibly discriminated for N-acetylglucosamine and N-acetylgalactosamine. The fragmentation patterns of m/z 221 anions provide a firm reproducible basis for assignment of sugar stereochemistries in the gas phase.
Fang
Tammy T
TT
Department of Cellular and Developmental Biology, University of Colorado at Denver and Health Sciences Center, Aurora, Colorado 80045, USA.
Bendiak
Brad
B
D000079:Acetaldehyde / Q000031:analogs & derivatives* / Q000737:chemistry; D000081:Acetamides / Q000737:chemistry; D000838:Anions / Q000737:chemistry; D004187:Disaccharides / Q000737:chemistry*; D005740:Gases / Q000737:chemistry*; D005998:Glycine / Q000737:chemistry; D006031:Glycosylation; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D015394:Molecular Structure; D009005:Monosaccharides / Q000737:chemistry*; D009844:Oligosaccharides / Q000737:chemistry*; D010084:Oxidation-Reduction; D015203:Reproducibility of Results; D012996:Solutions; D013237:Stereoisomerism
D000081:Acetamides; D000838:Anions; D004187:Disaccharides; D005740:Gases; D009005:Monosaccharides; D009844:Oligosaccharides; D012996:Solutions; C030686:acetamide; D000079:Acetaldehyde; D005998:Glycine; C010972:glycolaldehyde