Anticoagulant sulfated polysaccharides: Part I. Synthesis and structure–activity relationships of new pullulan sulfates

In order to develop new anticoagulants as potential heparin alternatives, two pullulans with different molecular weight (MW) were used as starting polymers for the partial synthesis of a structurally new class of sulfated polysaccharides. Sulfation of these linear α-1,4-/1,6-glucans was carried out by a method with a SO3–pyridine complex in DMF, which had been optimized for the modification of β-1,3-glucans. Modifications of this methods resulted in pullulan sulfates with degrees of sulfation (DS) ranging from 0.17 to 1.99 and MW between 15 and 250 kDa. More than 50% of the sulfate groups were bound to the secondary C atoms in positions 2, 3 and 4 of the glucose monomers. The anticoagulant activity of the obtained pullulan sulfates was determined in the coagulation assays prothrombin time (PT), activated partial thromboplastin time (APTT), Heptest® and thrombin time (TT). They represent potent anticoagulants reaching the efficacy of heparin. Their activity not only improves with increasing DS and MW, but also with increasing part of sulfate groups in positions 2, 3 and 4. In addition, their action profile changes in dependence on their individual structure as reflected by the ratio of the TT- to the APTT-activity. The pullulan sulfates specifically interfere with different stages of the coagulation cascade, and these interactions have different requirements on the chemical structure.