Structural elucidation of fucoidans from Sargassum pallidum

The brown alga Sargassum pallidum has been used as a traditional Chinese medicine to treat a variety of diseases. Fucoidan is an important bioactive component in S. pallidum; however, its chemical structure has not been thoroughly investigated. In the present study, two fucoidan fractions (SPF-1 and SPF-2) from S. pallidum were obtained by extraction with hot-water, ethanol precipitation, anion-exchange, and size-exclusion chromatography. The structural characterizations of SPF-1 and SPF-2 were investigated using the high-performance gel permeation chromatography (HPGPC) and gas chromatography (GC), followed by periodate oxidation, Smith degradation, and methylation analysis. The results revealed the monosaccharide composition of SPF-1 and SPF-2 to be fucose, mannose, and galactose with small amounts of glucose, xylose, and rhamnose. The molecular weight of SPF-1 and SPF-2 was estimated to be 61.5 kDa and 167.6 kDa, respectively. The backbone of SPF-1 was mainly constituted by (1→3) linked Fuc, (1→3) linked Man, and (1→3,4) linked Man whereas the branches were composed of (1→3) linked Fuc. SPF-2 was a branched polysaccharide with a backbone consisted of (1→3) linked Fuc, (1→3) linked Gal, and (1→3,4) linked Gal and branches composed of (1→3) linked Fuc or Gal. In vitro bioassay revealed that SPF-2 showed higher cytotoxic activity than SPF-1 against P388 and A549 cells. These results provided an insight into the utilization and development of seaweed resources.