Specimens of fucoidan extracted from Fucus evanescens were purified from protein and polyphenols, deacetylated and depolymerized by fucoidanase for evaluation of their biological activity. Deacetylation did not modify the capacity of fucoidan to inhibit thrombin and factor Xa, while purification from protein and polyphenols reduced this capacity. Depolymerization of fucoidan increased its capacity to inhibit thrombin mainly through heparin cofactor II. All the studied specimens formed complexes with protamine sulfate.

Fucoidans isolated from Fucus evanescens and Laminaria cichorioides kelp can inhibit thrombin and factor Xa of the blood coagulation system. In rats, intravenous injection of fucoidans dose-dependently increased anticoagulant activity of the plasma. Fucoidans can form complexes with protamine sulfate. The observed quantitative differences in the action of fucoidans can result from different sulfation degree and the presence of various types of glycoside bonds in polysaccharide molecules.

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Original synthetic peptide derivatives exhibit anticoagulant activity in vitro and in vivo. They delayed fibrin clot formation from human blood plasma in tests for the intrinsic coagulation pathway (activated partial thromboplastin time) and final stage of plasma coagulation (thrombin time) and inhibited amidolytic activity of thrombin. We determined the minimum effective dose of the most active compound providing a 2-fold lengthening of blood clotting time (activated partial thromboplastin time test and thrombin time test), which persisted for 2-3 h.