Synthesis and SAR of benzamidine factor Xa inhibitors containing a vicinally-substituted heterocyclic core.

The selective inhibition of coagulation factor Xa has emerged as an attractive strategy for the discovery of novel antithrombotic agents. Here we describe highly potent benzamidine factor Xa inhibitors based on a vicinally-substituted heterocyclic core.

Discovery of 1-[3-(aminomethyl)phenyl]-N-3-fluoro-2'-(methylsulfonyl)-[1,1'-biphenyl]-4-yl]-3-(trifluoromethyl)-1H-pyrazole-5-carboxamide (DPC423), a highly potent, selective, and orally bioavailable inhibitor of blood coagulation factor Xa.

Factor Xa (fXa) plays a critical role in the coagulation cascade, serving as the point of convergence of the intrinsic and extrinsic pathways. Together with nonenzymatic cofactor Va and Ca2+ on the phospholipid surface of platelets or endothelial cells, factor Xa forms the prothrombinase complex, which is responsible for the proteolysis of prothrombin to catalytically active thrombin. Thrombin, in turn, catalyzes the cleavage of fibrinogen to fibrin, thus initiating a process that ultimately leads to clot formation. Recently, we reported on a series of isoxazoline and isoxazole monobasic noncovalent inhibitors of factor Xa which show good potency in animal models of thrombosis. In this paper, we wish to report on the optimization of the heterocyclic core, which ultimately led to the discovery of a novel pyrazole SN429 (2b; fXa K(i) = 13 pM). We also report on our efforts to improve the oral bioavailability and pharmacokinetic profile of this series while maintaining subnanomolar potency and in vitro selectivity. This was achieved by replacing the highly basic benzamidine P1 with a less basic benzylamine moiety. Further optimization of the pyrazole core substitution and the biphenyl P4 culminated in the discovery of DPC423 (17h), a highly potent, selective, and orally active factor Xa inhibitor which was chosen for clinical development.

Synthesis and activity studies of conformationally restricted alpha-ketoamide factor Xa inhibitors.

Conformationally restricted borolysine compounds containing a 2-(2-cyanophenylthio) benzoyl in the P3 position unexpectedly led to enhanced factor Xa inhibition. In an effort to improve both the potency and selectivity of this series by extending into the S' domain, we have replaced the boronic acid with alpha-ketoamides, utilizing a novel process that was developed in our labs.

Preparation of pyrrolidine and isoxazolidine benzamidines as potent inhibitors of coagulation factor Xa.

The serine protease factor Xa is a critical enzyme in the blood coagulation cascade. Recently, the inhibition of factor Xa has begun to emerge as an attractive strategy for the discovery of novel antithrombotic agents. Here we describe pyrrolidine and isoxazolidine benzamidines as novel and potent inhibitors of factor Xa.

Preparation of meta-amidino-N,N-disubstituted anilines as potent inhibitors of coagulation factor Xa.

The serine protease factor Xa is a critical enzyme in the blood coagulation cascade. Recently, the inhibition of factor Xa has begun to emerge as an attractive strategy for the discovery of novel antithrombotic agents. Here we describe a series of meta-amidino-N,N-disubstituted anilines as structurally simple and very potent inhibitors of factor Xa.

Rational design of boropeptide thrombin inhibitors: beta, beta-dialkyl-phenethylglycine P2 analogs of DuP 714 with greater selectivity over complement factor I and an improved safety profile.

The potent boropeptide thrombin inhibitor DuP 714 caused side effects in laboratory animals that appear to be related to its ability to inhibit complement factor I, thereby activating the complement cascade. Using X-ray crystal structure information, we have designed compounds that have greater selectivity for thrombin over factor I and that have reduced tendency to produce these side effects.

Biochemical and crystallographic characterization of homologous non-peptidic thrombin inhibitors having alternate binding modes.

The X-ray crystallographic structure of [N-(3-phenylpropionyl)-N-(phenethyl)]-Gly-boroLys-OH (HPBK, Ki = 0. 42 nM, crystallographic R factor to 1.8 A resolution, 19.6%) complexed with human alpha-thrombin shows that the boron adopts a tetrahedral geometry and is covalently bonded to the active serine, Ser195. The HPBK phenethyl aromatic ring forms an edge-to-face interaction with the indole side chain of Trp215. Four HPBK analogs containing either electron-withdrawing or electron-donating substitutents at the 3' position of the phenethyl ring were synthesized in an attempt to modulate ligand affinity by inductive stabilization of the edge-to-face interaction. Refined crystallographic structures of the trifluoromethyl (Ki = 0.37 nM, crystallographic R factor to 2.0 A resolution = 18.7%), fluoro (Ki = 0.60; R factor to 2.3 A resolution = 18.4%), methoxy (Ki = 0.91 nM, R factor to 2.2 A resolution = 19.8%) and methyl (Ki = 0.20 nM, R factor to 2.5 A resolution = 16.9%) HPBK analogs complexed with thrombin revealed two binding modes for the closely related compounds. A less than 1.5-fold variation in affinity was observed for analogs (trifluoromethyl-HPBK and fluoro-HPBK) binding with the edge-to-face interaction. The slight inductive modulation is consistent with the overall weak nature of the edge-to-face interaction. Owing to an unexpected rotation of the phenethyl aromatic ring, the 3' substituent of two analogs, methoxy-HPBK and methyl-HPBK, made direct contact with the Trp215 indole side chain. Increased affinity of the 3' methyl analog is attributed to favorable interactions between the methyl group and the Trp215 indole ring. Differences in inhibitor, thrombin and solvent structure are discussed in detail. These results demonstrate the subtle interplay of weak forces that determine the equilibrium binding orientation of inhibitor, solvent and protein.