Sulfated alpha-L-fucans from brown algae (also known as
fucoidan) have complex and heterogeneous structures but recent studies revealed the occurrence of ordered repeat units in the
sulfated fucans from several species. Even in these cases, the presence of highly branched portions and the complex distributions of
sulfate and acetyl groups highlight the heterogeneity of algal fucans. Another source of sulfated alpha-L-fucans (and their parental compounds sulfated alpha-L-
galactans and
fucosylated chondroitin sulfate) is marine invertebrates. The invertebrate
polysaccharides have simple, ordered structures, which differ in the specific patterns of sulfation and/or position of the glycosidic linkages within their repeating units. The algal and invertebrate
sulfated fucans have potent
anticoagulant activity, mediated by
antithrombin and/or
heparin cofactor II. As most of the studies were carried out with algal fucans it was not easy to trace a structure versus activity relationship. This aspect was clarified as studies were extended to invertebrate
polysaccharides. These definitively established that regular, linear sulfated alpha-L-fucans and sulfated alpha-L-
galactans express
anticoagulant activity, which is not simply a function of charge density, but depends critically on the pattern of sulfation and
monosaccharide composition. Sulfated alpha-L-fucans and
fucosylated chondroitin sulfate also express antithrombotic activity when tested on in vivo models of venous and arterial
thrombosis in experimental animals. These
polysaccharides constitute potential therapeutic compounds as alternative to
heparin and may help to design structure-based drugs with specific activity on each type of
thrombosis episode and few side effects. They can also serve as research
reagents to investigate and distinguish among a variety of interrelated events, such as coagulation,
bleeding,
thrombosis and platelet aggregation.