Structural analyses of xyloglucan heptasaccharide by the post-source decay fragment method using matrix-assisted...

In the post-source decay (PSD) fragment spectrum of a reduced xyloglucan heptasaccharide (XXXGol) from tamarind seeds, eleven sodium-adduct fragment ions and a precursor ion [M + Na]+ were clearly observed by using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). Each fragment ion interval corresponded to the absence of unhydroxylose, unhydroglucose, and glucitol residues, indicating that PSD fragmentation cleavage in the sugar compound occurred only at glycosidic linkages close to the oxygen atom of saccharide ring members, and not in inner sugar ring bonds. The PSD fragment ions were classified into two series, one involving the reducing end and the other involving the non-reducing end. Structural information from both the reducing and non-reducing ends could therefore be simultaneously obtained from the measurement of the positive ion mode. Almost all the fragment ions from species larger than trisaccharide residues could be detected in this PSD fragment experiment. Such fragmentation information will enable the structural determination of xyloglucan oligosaccharides.