Analysis of the Core Oligosaccharide ofAeromonas hydrophila(Chemotype III) Lipopolysaccharide Using Fast Atom Bombardment, Electrospray and Low Energy Tandem Mass Spectrometry

Fast-atom bombardment mass spectrometry (FAB-MS) was employed for the structural analysis of the core oligosaccharide ofAeromonas hydrophila(Chemotype III) lipopolysaccharide. Positive ion FAB-MS of the underivatized core oligosaccharide gave the protonated molecular ion, confrrming the correct composition in terms of hexoses, heptoses and Kdo which was present as a bicyclic furanosidic lactone. Negative ion FAB-MS gave the deprotonated molecular ion and fragment ions which were derived from more than two cleavage events with charge retention at the reducing and non-reducing terminals. Positive ion F AB-MS of the permethylated core oligosaccharide afforded fragment ions consistent with the defined sequence and branching patterns of the sugar constituents. The electrospray mass spectrum (ESMS) in the positive ion mode of the underivatized core oligosaccharide afforded the protonated molecular ion in the singly and doubly charged forms. Low energy collision-activated dissociation tandem mass spectrometry (CAD MS/MS) analysis of the protonated molecular ion [M+2H]+2provided additional structural data. ESMS of the permethylated and N-acetylated permethylated core oligosaccharides provided useful structural indices and afforded a characteristic pattern for fragmentions resulting from the opening of the methylated bicyclic Kdo furanosidic 1,7- lactone, which was similar to that obtained in the corresponding FAB-MS.