Identification and structural analysis of synthetic oligosaccharides of Shigella sonnei using MALDI-TOF MS

MALDI-TOF mass spectroscopy was used for the molecular weight determination of protected synthetic oligosaccharides related to a cell surface bacterial polysaccharide. By-products containing chlorinated protecting groups caused isotopic patterns characteristic of the natural isotopic distribution of chlorine, were identified on the basis of isotopic distribution. 2,4,6-Trihydroxyacetophenone (THAP) as a matrix was better than 2,5-dihydroxybenzoic acid (DHB) for compounds containing chlorine, since monoisotopic resolution and no fragmentation were observed. In the post source decay (PSD) mode the identification of the oligosaccharide sequence through cleavage of the interglycosidic linkages was also possible, thus providing a sensitive and accurate tool for the structural verification of synthetic oligosaccharide intermediates.