Structural analysis of permethylated oligosaccharides by electrospray tandem mass spectrometry

Electrospray tandem mass spectrometry used in conjunction with reversed-phase liquid chromatography was applied to characterize permethylated oligosaccharides. N-Acetylhexosamine-containing carbohydrates yielded under these conditions promoted molecular ions which underwent extensive fragmentation, even under low-energy collision-induced dissociation. MS/MS spectra of [M + H]+ ions are characterized by simple fragmentation patterns which result from cleavage of the glycosidic bonds and thus allow a straightforward interpretation. A systematic study of various oligosaccharides showed that information on sugar sequence and branching could be obtained. The nature of the substituent linked in position 3 of HexNAc-containing fragments could easily be assigned as the result of a specific secondary fragmentation process. The nature of some internal fragments was established on the basis of MS/MS spectra of derivatives 18O-labeled at the reducing end. Furthermore, MS/MS experiments carried out on fragment ions were proven to be useful for the structural characterization of oligosaccharide subunits. Thus, this approach constitutes a powerful tool for the structural assignment of moieties derived from larger glycans.