Tandem mass spectrometry of fucoidan-derived fragments, labeled with heavy-oxygen.

A procedure for the partial depolymerization of sulfated fucans and selective labeling with 18O was developed. A tandem electrospray ionization mass spectrometry (ESI MS/MS) was applied for the direct analysis of mixtures of structurally-different oligosaccharides, derived from the fucoidans of known structure. The presence of label allowed unambiguous distinguishing between the fragment ions of 0,2X0-type at m/z 287 and 2,4A-type at m/z 285, since 18O at the reducing end gave +2 mass shifting. Thus, ESI MS/MS was able to detect (1,2)-type of linkage in disaccharides from the fucoidan of brown alga S. cichorioides for the first time. It was also discovered that 2,4A-type fragments in 4-linked disaccharides that were incorrectly assigned to 0,2X-type previously, suggested, probably, substitution at C-4 in mono- and disaccharide fragments, derived from the fucoidan of the brown alga F. evanescens.