Influence of stereoisomeric glucose, galactose and mannose residues on fragmentation at their glycosidic linkages in post-source decay fragment analyses for oligosaccharides using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

The isomeric sugar branched beta-cyclodextrin (CD) derivatives (Glc-beta CD, Gal-beta CD, and Man-beta CD) were analyzed by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. In the MALDI post-source decay (PSD) fragmentation of Glc-beta CD, Gal-beta CD and Man-beta CD, the fragment ions of [M-Glc]+, [M-Gal]+ and [M-Man]+ were produced by the one-site cleavage of the alpha 1-6 glycosidic linkage at the branch (Y-type fragmentation). The abundances of [M-Gal]+ ions were much higher than that of [M-Man]+. These results indicated that Glc-beta CD and Gal-beta CD were distinguishable from Man-beta CD and that Y-type fragmentations of the branched glycosidic linkage at the glycosyl donors of alpha-D-Glc and alpha-D-Gal were more predominant than that at the glycosyl donor of alpha-D-Man by MALDI-PSD fragment analysis. It was concluded that the abundances of PSD fragment ions depended on the stereochemistry of the glycosyl donors in the cleavage of the glycosidic linkage of the oligosaccharides in MALDI-TOF mass spectra.