Positive-ion fragmentation in matrix-assisted laser desorption/ionization tandem time of flight mass spectrometry of synthetic analogs of the O-specific polysaccharide of Vibrio cholerae O:1.

Saccharides (mono- to hexamers) that mimic the terminal epitopes of O-antigens of Vibrio cholerae O:1, serotypes Ogawa and Inaba have been studied by matrix-assisted laser desorption/ionization tandem time-of-flight (MALDI ToF/ToF) mass spectrometry (MS). Cationized adducts are the characteristic ions formed through the capture of sodium or potassium cations under MALDI MS conditions. Three characteristic pathways dominate in the fragmentation of model substances under MALDI ToF/ToF collision-induced dissociation MS/MS conditions of measurement. The first is the elimination which shortens the length of the oligosaccharide. In this way, conversion of the Ogawa to Inaba fragments takes place under the conditions of measurement. In the second, the conjugated transfer of electrons in the upstream unit of oligosaccharides takes place. The third route brings about the elimination of one alpha-hydroxy-gamma-butyrolactone molecule from the 4-(3-deoxy-L-glycero-tetronamido) group. The MALDI ToF/ToF MS/MS provided sufficient information about molecular mass, the number of saccharide residues, the structure of saccharides, the C(4)- amide of 3-deoxy-L-glycero-tetronic acid (DGT) of the compounds investigated, and allows to distinguish between Ogawa and Inaba serotypes.