Sargassum Fucose Glycan Structure Of The Sulfate

Fucoidan, a mixture of sulfated fucose-containing polysacchrides, have unique molecular structure and many biological activities. Now the structure-activity relationship of fucoidan is widely studied. Fucoidan were extracted from brown seaweed Sargassum fusiforme, and the alga was cultured in the coast of Dongtou of ZheJiang province. Fucoidan was separated by anion-exchange chromatography on Q-Sepharose FF into three fractions (F-l, F-2 and F-3). The second fraction which named as F-2 was more homogeneous and abounded in both fucose residues and sulfated esters. We chose F-2 for the further structural studies to the analysis of their chemical compositions and average molecular weight. Analysis methods of HPSEC, GC, TLC, IR, acid hydrolysis, methylation reaction (GC-MS) and NMR were used to elucidate its structure.The average molecular weight of F-2 was estimated at 160,000, based on HPSEC. The IR spectrum displayed that disulfated fucose existed in F-2. F-2 and its desulfated derivative F-2d were subjected to methylation analysis by GC-MS. It showed that a (1 - 3)-linkage was major linkage pattern in fucose residues and (1-6)-linkage was major linkage pattern in galactose residues. Sulfate groups were substituted mainly at C-4 positions and C-2 of fucose residues, some of fucose residues were disulfated at C-2,4 positions.After hydrolyzation with TFA of F-2 and ultrafiltration (MWCO 5000), the mixture was applied to Bio-gel P4 column, three hydrolytic products were obtained (F-2-a, F-2-b and F-2-c). By comparing their chemical compositions and average molecular weight with F-2, we deduce that main chains of F-2 composed of fucose, galactose, mannose and glucose, and a considerable amount of galactofucan side chains (F-2-c) with about 6-8 sugar units. Sulfation occurs on both main and side chains.The NMR analysis of oligosaccharide F-2-c was consistent with the methylation analysis, including the mainly linkage pattern and substituted positions. We found F-2-c mainly formed by (l-3)-linked a-fucose residues (sulfated at C-4 or C-2,4 positions), and also found some fucose residues with configuration, but (1 -3)-linkage was major linkage pattern of p-galactose residues in the side chains of F-2.