Chemical Modification of Fucoidan and Their Application

Fucoidan, extracted from brown seaweeds like Saccharina japonica, Sargassum thunbergii, Fucus vesiculosus, Ascopbyllum nodosum, is an acidic sulfated polysaccharide composed primarily of fucose, galactose and sulfate with smaller amounts of mannoses, uronic acid, glucose, rhamnose, arabinose, and xylose. Besides, fucoidans can also be isolated from marine invertebrates, such as sea cucumbers or sea urchins. These fucoidans are simpler than fucoidans found in marine algae. Fucoidans have been reported to possess diverse biological activity of potential medicinal value, such as antioxidant, antiinflammatory, antiallergic, antitumor, antiobesity, anticoagulant, antiviral, anodtihepatopathy, antiuropathy, and antirenalpathy activity (Feldman, S.C., et al., 1999. Antiviral properties of fucoidan fractions from Leathesia difformis. Phytomedicine 6(5) 335–340). The activity of fucoidan depends on several structural parameters, such as type of monosaccharides, the degree and position of sulfation, molecular weight, other substitution groups and position and glycosidic branching. (Huimin, Q., et al., 2005. Antioxidant activity of different molecular weight sulfated polysaccharides from Ulva pertusa Kjellm (Chlorophyta). J. Appl. Phycol. 17(6)527–534; Qi, H., et al., 2006. In vitro antioxidant activity of acetylated and benzoylated derivatives of polysaccharide extracted from Ulva pertusa (Chlorophyta). Bioorg. Med. Chem. Lett. 16(9) 2441–2445). Evidence had proved that chemical modifications of fucoidan provided a possibility to obtain new agents with possible uses in medicine. In this chapter, the different chemical modifications applied on fucoidan will be described emphasizing on the diverse methods to perform each modification, as well as the possible applications of the modified products. Modified fucoidans are those that were not just extracted from their natural sources but got consciously modified by chemical, physical, or enzymatic means afterward. Modification of fucoidan structures may be undertaken to produce “tailored” structures accompanied by specific biological activities, such as anticoagulant or antiviral activities. Thus, chemical (e.g., hydrolysis, oversulfation and desulfation) and enzymatic techniques (e.g., fucoidanases) have been utilized to produce modified fucoidans (Holtkamp, A.D., et al., 2009. Fucoidans and fucoidanases—focus on techniques for molecular structure elucidation and modification of marine polysaccharides. Appl. Microbiol. Biotechnol. 82(1) 1–7).