Non-reducing terminal linkage position determination in intact and permethylated synthetic oligosaccharides having a penultimate amino sugar: fast atom bombardment ionization, collisional-induced dissociation and tandem mass spectrometry.

Certain linkage positions in oligosaccharides can be discerned by collision-activated dissociation mass spectrometry, rationalized by molecular modelling. Previous work on synthetic oligosaccharides has suggested that daughter ion patterns can distinguish among intact compounds which terminate in alpha-L-fucose and have a penultimate amino sugar. The current study indicates that these observations can be extended to oligosaccharides terminating in beta-D-galactose. In addition, we have observed that protonated, ammoniated and lithiated molecular ions all produce linkage-specific daughter ion spectra in these two sets of oligosaccharides. Sodiated molecular ions could be fragmented usefully under high collision energy offset conditions; potassiated ions were stable and not dissociable under conditions available in a triple-quadrupole instrument. We also show linkage discernment among the permethylated set of these six synthetic oligosaccharides. Methylated derivatives of this set of compounds give more useful product ions, including a 3-linkage specific ion. A novel relationship was noted by a plot of collision energy against (daughter ion/parent ion) ratio, which gave a unique slope for each of the non-reducing terminal linkage positions 3, 4 and 6 in the set of six compounds. The slope of this plot is related to the ability of each linkage position in the oligosaccharide to absorb collisional energy. Rotational freedom of the individual glycosidic linkage is hypothesized to play a role in this phenomenon.