Heterocycle derivatives that inhibit Factor Xa

Discovery and characterization of a potent and selective non-amidine inhibitor of human factor Xa

Benzothiophene-anthranilamide 1 (3-chloro-N-[2-[[(4-fluorophenyl)amino]carbonyl]-4-methylphenyl]benzo[b]thiophene-2-carboxamide) was discovered by high throughput screening to be a highly potent and selective non-amidine inhibitor of human factor Xa with a K(i) of 15+/-4nM. Compound 1 is a selective inhibitor of human factor Xa as suggested by the K(i)((app)) determined for nine other human serine proteases and bovine trypsin. The activity of reconstituted human prothrombinase complex was inhibited by compound 1 when assayed in physiological concentrations of the substrate prothrombin. However, 27-fold higher inhibitor concentrations were needed to achieve the same level of inhibition than were required for the inhibition of free factor Xa, due in part to non-specific binding of the inhibitor to phospholipid under the assay conditions. Failure to demonstrate enzymatic cleavage of compound 1 suggests that compound 1 is solely an inhibitor rather than a substrate for factor Xa. The inhibition of factor Xa by compound 1 was reversible upon dilution of the enzyme/inhibitor mixture. Analyses of the inhibition mechanism with Dixon, Cornish-Bowden, and Lineweaver-Burk plots showed that compound 1 is a linear mixed-type inhibitor with 5-fold higher affinity for free factor Xa than the factor Xa/substrate complex. The linear mixed-type inhibition suggests that compound 1 binds to the active site region of factor Xa, but its binding cannot be fully displaced by the substrate S2222 (1:1 mixture of N-benzoyl-Ile-Glu-Gly-Arg-p-nitroanilide and N-benzoyl-Ile-Glu(gamma-OMe)-Gly-Arg-p-nitroanilide hydrochloride). Thus, the inhibition mechanism for compound 1 is novel compared to most serine protease inhibitors including amidine-containing factor Xa inhibitors, which rely on binding to the S1 pocket of the enzyme active site. Compound 1 represents an attractive, novel structural template for further development of efficacious, safe, and potentially orally active human factor Xa inhibitors.

Small, noncovalent serine protease inhibitors

Thrombin and factor Xa (fXa) are the only serine proteases for which small, potent, selective, noncovalent inhibitors have been developed, which are ultimately intended as drug development candidates (in this case as anticoagulants). Noncovalent inhibitors may be more selective and chemically and metabolically less reactive than covalent inhibitors. In addition, noncovalent inhibitors are more likely to have fast-binding kinetics which is particularly important in the development of thrombin inhibitors. TAME derived noncovalent thrombin inhibitors argatroban, napsagatran, and UK 156,406 have entered clinical trials as anticoagulants, the latter as an orally active agent. Serine trap deletion from substrate-like peptides led to the development of inogatran and melagatran, both of which have entered clinical trials as intravenous agents. The use of 3-aminopyridinone and pyrazinone acetamide peptidomimetic templates has resulted in the development of L-375,378 which has been chosen for clinical development as an orally active anticoagulant. Recently, compounds which do not have the conventional hydrogen bonding capabilities of peptides have begun to appear in the thrombin literature. Publications on noncovalent fXa inhibitors cover this type of peptidomimetic almost exclusively.