ESI-MS Differential Fragmentation of Positional Isomers of Sulfated Oligosaccharides Derived from Carrageenans and Agarans

We have prepared a number of isomeric red seaweed galactan-derivative sulfated oligosaccharides to determine whether there were diagnostic differences among the isomeric mass spectra obtained using ESI CID MS/MS (triple quadrupole instrument). Fragmentation of the single or multicharged molecular ions from di-, tetra-, and hexasaccharides indicated that the relative positioning of the sulfate groups and type of monosaccharide unit affect the rate of cleavage of the glycosidic bonds. We also performed a comparative [M-Na](-) fragmentation study of positional isomers of sulfated disaccharides that present all four monosulfation possibilities on the galactopyranosidic ring. In this case, negative-ion ESI CID MS/MS approach gave diagnostic product ions from cross-ring cleavages along with the same main B, ion (from sulfated Galp), at m/z 241, for all isomers. The isomeric disaccharides were also submitted to increased spray energy conditions inducing in-source fragmentation; preformed B-1 ions were then fragmented to give similar product ions as those found in [M-Na](-) analysis. Evaluation of the relative abundances mainly for cross-ring fragment ions at m/z 138, 139, 151, 153 allowed clear distinction among the members of the disaccharide series. The different ratios for m/z 151/153 ions were consistent with the predominance of m/z 153 being related to the cases when the bond involved in the cleavage process links a sulfated carbon. A quadrupole ion trap instrument (MS analysis) was also utilized to compare the results obtained with the triple quadrupole instrument. (J Am Soc Mass Spectrom 2010, 21, 1404-1416) (C) 2010 American Society for Mass Spectrometry