Potent and selective TF/FVIIa inhibitors containing a neutral P1 ligand

Design, synthesis and biological evaluation of novel FXIa inhibitors with 2-phenyl-1H-imidazole-5-carboxamide moiety as P1 fragment

Factor XIa, as a blood coagulation enzyme, amplifies the generation of the last enzyme thrombin in the blood coagulation cascade. It was proved that direct inhibition of factor XIa could reduce pathologic thrombus formation without an enhanced risk of bleeding. WSJ-557, a nonpurine imidazole-based xanthine oxidase inhibitor in our previous reports, could delay blood coagulation during its animal experiments, which prompted us to investigate its action mechanism. Subsequently, during the exploration of the action mechanism, it was found that WSJ-557 exhibited weak in vitro factor XIa binding affinity. Under the guide of molecular modeling, we adopted molecular hybridization strategy to develop novel factor XIa inhibitors with WSJ-557 as an initial compound. This led to the identification of the most potent compound 44g with a Ki value of 0.009 μM, which was close to that of BMS-724296 (Ki = 0.0015 μM). Additionally, serine protease selectivity study indicated that compound 44g display a desired selectivity, more 400-fold than those of thrombin, factor VIIa and factor Xa in coagulation cascade. Moreover, enzyme kinetics studies suggested that the representative compound 44g acted as a competitive-type inhibitor for FXIa, and molecular modeling revealed that it could tightly bind to the S1, S1' and S2' pockets of factor XIa. Furthermore, in vivo efficacy in the rabbit arteriovenous shunt model suggested that compound 44g demonstrated dose-dependent antithrombotic efficacy. Therefore, these results supported that compound 44g could be a potential and efficacious agent for the treatment of thrombotic diseases.

Beyond Basicity: Discovery of Nonbasic DENV-2 Protease Inhibitors with Potent Activity in Cell Culture

The viral serine protease NS2B-NS3 is one of the promising targets for drug discovery against dengue virus and other flaviviruses. The molecular recognition preferences of the protease favor basic, positively charged moieties as substrates and inhibitors, which leads to pharmacokinetic liabilities and off-target interactions with host proteases such as thrombin. We here present the results of efforts that were aimed specifically at the discovery and development of noncharged, small-molecular inhibitors of the flaviviral proteases. A key factor in the discovery of these compounds was a cellular reporter gene assay for the dengue protease, the DENV2proHeLa system. Extensive structure-activity relationship explorations resulted in novel benzamide derivatives with submicromolar activities in viral replication assays (EC₅₀ 0.24 μM), selectivity against off-target proteases, and negligible cytotoxicity. This structural class has increased drug-likeness compared to most of the previously published active-site-directed flaviviral protease inhibitors and includes promising candidates for further preclinical development.

Discovery of Phenylglycine Lactams as Potent Neutral Factor VIIa Inhibitors

Inhibitors of Factor VIIa (FVIIa), a serine protease in the clotting cascade, have shown strong antithrombotic efficacy in preclinical thrombosis models with minimal bleeding liabilities. Discovery of potent, orally active FVIIa inhibitors has been largely unsuccessful because known chemotypes have required a highly basic group in the S1 binding pocket for high affinity. A recently reported fragment screening effort resulted in the discovery of a neutral heterocycle, 7-chloro-3,4-dihydroisoquinolin-1(2H)-one, that binds in the S1 pocket of FVIIa and can be incorporated into a phenylglycine FVIIa inhibitor. Optimization of this P1 binding group led to the first series of neutral, permeable FVIIa inhibitors with low nanomolar potency.

Structure-Based Design of Macrocyclic Coagulation Factor VIIa Inhibitors

On the basis of a crystal structure of a phenylpyrrolidine lead and subsequent molecular modeling results, we designed and synthesized a novel series of macrocyclic FVIIa inhibitors. The optimal 16-membered macrocycle was 60-fold more potent than an acyclic analog. Further potency optimization by incorporation of P1' alkyl sulfone and P2 methyl groups provided a macrocycle with TF/FVIIa Ki = 1.6 nM, excellent selectivity against a panel of seven serine proteases, and FVII-deficient prothrombin time EC2x = 1.2 μM. Discovery of this potent, selective macrocyclic scaffold opens new possibilities for the development of orally bioavailable FVIIa inhibitors.

Discovery methodology for the development of direct factor VIIa inhibitors

INTRODUCTION

Heparin and warfarin have historically been the only antithrombotics available. Recently, however, newer anticoagulants have been developed. Factor VIIa (fVIIa) inhibitors represent one of the new and potentially exciting classes of anticoagulants currently under development. Indeed, several methodologies have been used to develop fVIIa inhibitors.

AREAS COVERED

The authors highlight some of the methologies applied for the discovery of fVIIa inhibitors including phage display, isolation of endogenous peptides from hematophagous animals and the use of the 1,5-benzothiazepine molecular scaffolds and screens of large chemical libraries previously used to identify other serine protease inhibitors. Although these screens were intended to identify thrombin and factor Xa inhibitors, the compounds often had concomitant fVIIa activity. The authors also discuss the utilization of medical chemistry techniques for the discovery of these compounds.

EXPERT OPINION

FVIIa inhibitors represent a viable option for the development of new anticoagulants. There are theoretical advantages that fVIIa inhibitors may possess over existing anticoagulants and highly specific inhibitors that possess oral bioavailability and low bleeding risk may succeed.

Tissue factor-fVIIa inhibition: update on an unfinished quest for a novel oral antithrombotic

The tissue factor-coagulation factor VIIa complex (TF-fVIIa) is a well-validated biological target and has been the focus of extensive research directed toward the discovery of novel oral antithrombotics. This review briefly summarizes the key antithrombotic target validation data and provides an update on recent advances in small molecule TF-fVIIa inhibitors.

Design, synthesis, and biological evaluation of pyrazinones containing novel P1 needles as inhibitors of TF/VIIa

Herein is described the design, synthesis, and enzymatic activity of a series of substituted pyrazinones as inhibitors of the TF/VIIa complex. These inhibitors were designed to explore replacement and variation of the P1 amidine described previously [J. Med. Chem.2003, 46, 4050]. The P1 needle replacements were selected based upon their reduced basicity compared to the parent phenyl amidine (pKa approximately 12). A contributing factor towards the oral bioavailability of a compound is the ionization state of the compound in the intestinal tract. The desired outcome of the study was to identify an orally bioavailable TF-VIIa inhibitor.

Inhibitors of Factor VIIa/tissue factor

The formation of the proteolytic complex composed of the serine protease Factor VIIa and the cell-associated glycoprotein tissue factor (FVIIa/TF) initiates a cascade of amplified zymogen activation reactions leading to thrombus formation. The critical role of the coagulation cascade in pathological thrombosis has been the basis for significant efforts to design selective inhibitors of the protease components as new anticoagulant alternatives for the treatment of thrombotic diseases. However, for the new generation of anticoagulant drugs in development that primarily target protease complexes distal from FVIIa/TF, the differential between efficacy and safety as defined by bleeding is unresolved. Targeting the FVIIa/TF complex has several theoretical advantages that exploit the amplified nature of the coagulation cascade. However, progress on the development of clinical-stage FVIIa/TF-based anticoagulants has not been as successful to date. This review summarizes recent efforts in the discovery of synthetic inhibitors of FVIIa/TF.