From heparin to EP217609: the long way to a new pentasaccharide-based neutralisable anticoagulant with an unprecedented pharmacological profile.

The elucidation of the structure of the antithrombin binding sequence in heparin has given a large impulse to the rational design of heparin related drugs. De novo chemical synthesis of the corresponding pentasaccharide as well as simplified analogues has provided very specific, antithrombin-mediated inhibitors of factor Xa with various pharmacokinetic profiles. Fondaparinux and idraparinux are examples of such compounds that have found clinical application as antithrombotics. Because of the very specific binding to antithrombin the pharmacokinetics of pentasaccharides can be predicted and transferred to other molecules covalently bound to them. The new chemical entities thus obtained display a wide array of antithrombotic activities, giving improved heparin molecules as well as new anticoagulants, devoid of the undesired side effects of heparin and with unprecedented pharmacological profiles. In this context, a direct thrombin inhibitor was covalently coupled to a pentasaccharide by an inert spacer. This compound, EP42675 exerts antithrombin mediated anti-factor Xa activity together with direct thrombin inhibiting capacity. It displays favourable pharmacokinetics as imposed by the pentasaccharide. EP42675 was further modified by the introduction of a biotin moiety in its structure. The new entity obtained, EP217609 exerts the same pharmacological profile as EP42675 and it can be instantaneously neutralised by injection of avidin. Due to this unprecedented mechanism of anticoagulant activity and its ability to be neutralised, EP217609 deserves to be investigated in clinical settings where direct thrombin inhibition is required.