There remains a high unmet medical need for a safe oral therapy for thrombotic disorders. The serine protease factor Xa (fXa), with its central role in the coagulation cascade, is among the more promising targets for anticoagulant therapy and has been the subject of intensive drug discovery efforts. Investigation of a hit from high-throughput screening identified a series of thiophene-substituted anthranilamides as potent nonamidine fXa inhibitors. Lead optimization by incorporation of hydrophilic groups led to the discovery of compounds with picomolar inhibitory potency and micromolar in vitro anticoagulant activity. Based on their high potency, selectivity, oral pharmacokinetics, and efficacy in a rat venous stasis model of thrombosis, compounds ZK 814048 (10b), ZK 810388 (13a), and ZK 813039 (17m) were advanced into development.

A series of thiophene-containing non-amidine factor Xa inhibitors is described. Simple methyl-substituted thiophene analogs were relatively weak inhibitors. However, introduction of hydrophilic substituents at C-4 or C-5 of the thiophene afforded inhibitors with low nanomolar potency. Optimization of the thiophene substituent at C-4 afforded subnanomolar inhibitors with improved in vitro anticoagulant activity. Incorporating basic amine substituents on the thiophene increased hydrophilicity and improved anticoagulant activity. The pharmacokinetic profile of one inhibitor was evaluated in dogs, and the X-ray crystal structure of this compound bound to factor Xa provides insight into the observed SAR for binding to factor Xa.

ZK-807834 (also known as CI-1031) is a small molecule that potently and selectively inhibits Factor Xa. Studies in animals have shown that ZK-807834 attenuates thrombosis and thrombus progression after fibrinolysis and exhibits an increased antithrombotic-to-bleeding risk ratio compared with conventional agents. The present study describes the human in vitro anticoagulant and pharmacodynamic profile ZK-807834. Consistent with its selective inhibition of Factor Xa, ZK-807834 in the range of 0.3-0.5 microM prolonged prothrombin time (PT) and activated partial thromboplastin time (aPPT) twofold without affecting thrombin time (TT). Intersubject variability of in vitro anticoagulant activity was nominal and gender-independent. ZK-807834 inhibited Factor Xa in clot-bound prothrombinase with an average IC50 of 10+/-7 (S.D.) nM. ZK-807834 exhibited no direct effect on ADP- or collagen-induced platelet aggregation. Based on the potency and specificity, ZK-807834 may represent an important advance in the development of selective and safe antithrombotics.