Analysis of structural heterogeneity of fucoidan from Hizikia fusiforme by ES-CID-MS/MS

A fucoidan from the brown alga Hizikia fusiforme was extracted with hot water and fractionated by anion-exchange chromatography. The main fraction YF5 was depolymerized by partial acid hydrolysis and further purified by gel filtration chromatograph. The sequences of oligosaccharides generated were then determined by ES-CID-MS/MS, which gave directly information on the structural heterogeneity of fucoidan from H. fusiforme. It was shown that YF5 had a backbone of a repeating disaccharide unit of [→4GlcAβ1,2Manα1→], in good agreement with previous report by NMR and methylation analysis. In the product-ion spectra, the unique (0.2)A type fragmentation was important to establish the presence of a 2-linked Man in the backbone structure. In addition, abundant novel heterogeneous branched structural fragments were also detected and characterized: Fuc1,3Fuc, Fuc1,3Gal, Fuc1,4GlcA, Gal1,4Gal, Gal1,4GlcA and GlcA1,4GlcA. The sulfation mainly occurred at C2 or C4 of the fucose residue and C2, C4 or C6 of the galactose residue.