Differentiation of the fucoidan bulding blocks sulfated l-fucose isomers by electrospray ionization mass spectrometry, hyphenated capillary electrophoresis and theoretical molecular calculations

α-l-Fucose, the monosaccharide component of fucoidan, is found in the polysaccharide mainly as its sulfated form where sulfate groups are in position 2 and/or 4 and/or 3. The correlation between biological activities and structure of fucoidan requires the determination of the sulfation pattern of the fucose residues. Therefore, it is of importance to discriminate between the isobaric sulfated fucose isomers. For this purpose, the three isomers 2-O-, 3-O-, and 4-O-sulfated fucose have been analyzed using electrospray ion trap mass spectrometry and capillary electrophoresis. The results reported herein show that it is possible to differentiate between these three positional isomers of sulfated fucose based on their fragmentation pattern upon MS/MS experiments. 3-O-Sulfated fucose was characterized by the loss of the hydrogenosulfate anion HSO4- as the main fragmentation product, while the two other isomers 2-O-, and 4-O-sulfated fucose exhibited cross-ring fragmentation yielding to distinctive 0,2X and 0,2A daughter ion, respectively. A computational study of the conformation of the sulfated fucose isomers was carried out providing an understanding of the fragmentation pattern with respect to the position of the sulfate group.