A New Approach to the Characterization of Sulfated and Sialyl Lewis-Type Glycosphingolipids Using Positive-Ion FABMS, ESIMS, and CID-MS/MS

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Positive-ion fast atom bombardment (FAB) and electrospray ionization (ESI) mass spectrometry have been used in the structural characterization of sulfated and sialyl Lewis (Le)-type glycosphingolipids. Both FAB and ESI collision-induced dissociation tandem mass spectrometry (CID-MS/MS) of acidic glycosphingolipids allowed identification of the sulfated and sialyl sugars, and provided information on the sugar chain sequences. The positive-ion tandem FABMS of sulfated Le-type glycosphingolipids gave the daughter ions produced by the elimination of (fucose-H₂O) unit from the fragment ions containing the non-reducing end. On the other hand, the CID-MS/MS of sialyl analogs showed the characteristic ions derived from the loss of (N-acetylneuraminic acid-H₂O) unit, in addition to the elimination of (fucose-H₂O) unit. The ESI CID-MS/MS of multiple-charged ions provided even more detailed structural information, and some of the daughter ions useful for structural studies appeared in the higher mass region than the precursor owing to a lower charge-state. These methodologies can be applied to the structural analyses of glycoconjugates with much larger molecular masses and higher polarity, such as the poly-sulfated and sialyl analogs.