Laser desorption ionization Fourier transform ion cyclotron resonance (L.D.I.-F.T.-I.C.R.) mass spectrometric studies of some underivatized bacterial oligosaccharides

This thesis describes the novel application of laser desorption ionization Fourier transform ion cyclotron resonance (l.d.i.-F.t.-i.c.r.) mass spectrometry for determining the sequence of underivatized oligosaccharides. As a starting point, four model oligosaccharides obtained from bacteriophage degradation of the corresponding bacterial capsular polysaccharides were analyzed. The experiments progressed from a linear pentasaccharide (Klebsiella K44), to a linear pentasaccharide containing an acid-labile pyruvic acid (Klebsiella K3), to a linear tetrasaccharide containing an acetamido hexose and an acid-labile neuraminic acid (E. coli K9), and finally to a "3+1" branched tetrasaccharide containing an lactic acid ether and a base-labile O-acetate (Klebsiella 22). The glycosidic bond and significant ring cleavage fragmentations observed in the mass spectra could be used for the sequencing of all three linear oligosaccharides. Furthermore, these unusual ring-cleaved fragments also provided some tentative indication on the positions of linkage on several monosaccharide residues. The fragments derived from these model oligosaccharides were used to propose a logical interpretation of the l.d.i.-F.t.-i.c.r. mass spectra of commercially available polysaccharide reported by others. Polysaccharides that have similar primary and tertiary structures gave similar mass spectra. This may be rationalized by the fact that fragmentation occurred at the sample layer or the selvedge. Consequently, the mass spectra reflected the primary and tertiary structures of the polysaccharides in the solid state. Finally, this l.d.i.-F.t.-i.c.r. technique was employed to sequence an unknown oligosaccharide obtained by anhydrous hydrogen fluoride degradation of the bacterial capsular polysaccharide. It was concluded that the unknown sample is composed of two tetrasaccharides with the same carbohydrate components, but with one structure substituted with serine and the other with threonine. Furthermore, indirect evidence suggests that the amino acids are linked to the carboxylic acid group of the hexuronic acid. However, two possible structures could be proposed for these oligosaccharides. The experimental results showed that l.d.i.-F.t.-i.c.r. mass spectrometry is well suited for the analysis of underivatized oligosaccharides, where the abundant ring fragments observed, can be used for a tentative indication of positions of linkage information. Furthermore, the high resolution data can be used to confirm the presence of unusual sugars and substituents.Science, Faculty ofChemistry, Department ofGraduat