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 [-> 4GlcA beta 1,2Man alpha 1 ->], 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. (C) 2012 Elsevier Ltd. All rights reserved.