Part II: piperazinyl-glutamate-pyridines as potent orally bioavailable P2Y12 antagonists for inhibition of platelet aggregation.

Efforts to refine the SAR of the piperazinyl-glutamate-pyridines for more potent analogs with improved pharmacokinetic profiles are described. Exploring substituted piperidines and other ring systems at the 4-pyridyl position led to compounds with improved potency and pharmacokinetic properties over candidate I. In particular, compounds 4t and 5t were discovered with a 10-fold improvement over potency and improved pharmacokinetic profiles in both the rat and dog.

Thienopyrimidine-based P2Y12 platelet aggregation inhibitors.

Herein we describe the design and synthesis of a novel series of potent thienopyrimidine P2Y12 inhibitors and the negative impact protein binding has on the inhibition of platelet aggregation.

Piperazinyl-glutamate-pyrimidines as potent P2Y12 antagonists for inhibition of platelet aggregation.

Piperazinyl-glutamate-pyrimidines were prepared with oxygen, nitrogen, and sulfur substitution at the 4-position of the pyrimidine leading to highly potent P2Y12 antagonists. In particular, 4-substituted piperidine-4-pyrimidines provided compounds with exceptional potency. Pharmacokinetic and physicochemical properties were fine-tuned through modifications at the 4-position of the piperidine ring leading to compounds with good human PRP potency, selectivity, clearance and oral bioavailability.

Piperazinyl-glutamate-pyridines as potent orally bioavailable P2Y12 antagonists for inhibition of platelet aggregation.

Polymer-assisted solution-phase (PASP) parallel library synthesis was used to discover a piperazinyl-glutamate-pyridine as a P2Y(12) antagonist. Exploitation of this lead provided compounds with excellent inhibition of platelet aggregation as measured in a human platelet rich plasma (PRP) assay. Pharmacokinetic and physiochemical properties were optimized leading to compound (4S)-4-[({4-[4-(methoxymethyl)piperidin-1-yl]-6-phenylpyridin-2-yl}carbonyl)amino]-5-oxo-5-{4-[(pentyloxy)carbonyl]piperazin-1-yl}pentanoic acid 22J with good human PRP potency, selectivity, in vivo efficacy and oral bioavailability.

Polymer-assisted solution-phase library synthesis and crystal structure of alpha-ketothiazoles as tissue factor VIIa inhibitors.

A solution-phase synthesis of an alpha-ketothiazole library of the general form D-Phe-L-AA-Arg-alpha-ketothiazole is described. The five-step synthesis is accomplished using a combination of polymeric reagents and polymer-assisted solution-phase purification concepts, including reactant-sequestering resins, reagent-sequestering resins, and tagged reagents. The multistep synthesis affords desired alpha-ketothiazole products in excellent purities and yields. A variety of L-amino acid inputs were used to probe the S2 pocket of tissue Factor VIIa enzyme to influence both potency and selectivity. An X-ray crystal structure of compound 10k bound to the TF/VIIa complex was obtained that explains the observed selectivity. The alpha-ketothiazoles were found to be potent, reversible-covalent inhibitors of tissue Factor VIIa, with some analogues demonstrating selectivity over thrombin.

Design, parallel synthesis, and crystal structures of pyrazinone antithrombotics as selective inhibitors of the tissue factor VIIa complex.

Structure-based drug design (SBDD) and polymer-assisted solution-phase (PASP) library synthesis were used to develop a series of pyrazinone inhibitors of the Tissue Factor/Factor VIIa (TF/VIIa) complex. The crystal structure of a tripeptide-alpha-ketothiazole complexed with TF/VIIa was utilized in a docking experiment to identify the pyrazinone core as a starting scaffold. The pyrazinone core could orient the substituents in the correct spatial arrangement to probe the S1, S2, and S3 pockets of the enzyme. A multistep PASP library synthesis was designed to prepare the substituted pyrazinones varying the P1, P2, and P3 moieties. Hundreds of pyrazinone TF/VIIa inhibitors were prepared and tested in several serine protease enzyme assays involved in the coagulation cascade. The inhibitors exhibited modest activity on TF/VIIa with excellent selectivity over thrombin (IIa) and Factor Xa. The structure-activity relationship of the pyrazinone inhibitors will be discussed and X-ray crystal structures of selected compounds complexed with the TF/VIIa enzyme will be described. This study ultimately led to the synthesis of compound 34, which exhibited 16 nM (IC50) activity on TF/VIIa with >6250 x selectivity vs Factor Xa and thrombin. This potent and highly selective inhibitor of TF/VIIa was chosen for preclinical, intravenous proof-of-concept studies to demonstrate the separation between antithrombotic efficacy and bleeding side effects in a nonhuman primate model of electrolytic-induced arterial thrombosis.

Administration of a small molecule tissue factor/factor VIIa inhibitor in a non-human primate thrombosis model of venous thrombosis: effects on thrombus formation and bleeding time.

INTRODUCTION: Pharmacological treatment of deep vein thrombosis (DVT) in the future may target inhibitors of specific procoagulant proteins. This study used a non-human primate model to test the effect of PHA-798, a specific inhibitor of the tissue factor/Factor VIIa complex (TF/VIIa), on venous thrombus formation. MATERIALS AND METHODS: PHA inhibits the TF/VIIa complex with an IC(50) of 13.5 nM (K(i) 9 nM) and is more than 2000-fold selective for the TF/VIIa complex with respect to IC(50)s for factor Xa and thrombin. In the model, a thrombogenic surface was introduced into the vena cava of a primate, and the amount of thrombus accumulated after 30 min was determined. RESULTS: PHA-798 reduced thrombus formation on the thrombogenic surface in a dose-dependent manner (56+/-1.9% and 85+/-0.3% inhibition with 100 and 200 microg/kg/min PHA-798, respectively) indicating that the model is sensitive to TF/VIIa inhibition. Treatment with 1 mg/kg intravenous (IV) acetyl salicylic acid (ASA) resulted in only a slight (4-12%), non-significant inhibition of thrombus formation. However, the combination of 100 microg/kg/min PHA-798 and 1 mg/kg ASA resulted in an 89% inhibition of thrombus formation. Additionally, while ASA alone increased bleeding time (BT) from 3.3 min at baseline to 4.6 min following treatment, addition of PHA-798 (100 microg/kg/min) to ASA did not significantly increase the BT further (4.7 min). CONCLUSIONS: The results of this study indicate that inhibition of TF/VIIa may be safe and effective for the prevention of the proprogation of venous thrombosis and that the combination of ASA and PHA may provide increased efficacy with little change in safety.

Piperazinyl glutamate pyridines as potent orally bioavailable P2Y12 antagonists for inhibition of platelet aggregation.

Polymer-assisted solution-phase (PASP) parallel library synthesis was used to discover a piperazinyl glutamate pyridine as a P2Y(12) antagonist. Exploitation of this lead provided compounds with excellent inhibition of platelet aggregation as measured in a human platelet rich plasma (PRP) assay. Pharmacokinetic and physiochemical properties were optimized through modifications at the 4-position of the pyridine ring and the terminal nitrogen of the piperazine ring, leading to compound (4S)-4-[({4-[4-(methoxymethyl)piperidin-1-yl]-6-phenylpyridin-2-yl}carbonyl)amino]-5-oxo-5-{4-[(pentyloxy)carbonyl]piperazin-1-yl}pentanoic acid 47s with good human PRP potency, selectivity, in vivo efficacy, and oral bioavailability. Compound 47s was selected for further preclinical evaluations.

Pharmacological intervention at disparate sites in the coagulation cascade: comparison of anti-thrombotic efficacy vs bleeding propensity in a rat model of acute arterial thrombosis.

The Tissue Factor/Factor VIIa (TF/FVIIa) complex is an attractive target for pharmacological interruption of thrombin generation and hence blood coagulation, as this complex is the initiation point of the extrinsic pathway of coagulation. TF is a cell membrane-associated protein that interacts with soluble FVIIa to activate factors IX and X resulting in a cascade of events that leads to thrombin generation and eventual fibrin deposition. The goal of this non-randomized study was to evaluate XK1, a specific protein inhibitor of TF/FVIIa, and compare antithrombotic efficacy and bleeding propensity to a previously described Factor Xa (FXa) inhibitor (SC-83157/SN429) and a direct-acting thrombin inhibitor (SC-79407/L-374087) in an acute rat model of arterial thrombosis. All saline-treated animals experienced occlusion of the carotid artery due to acute thrombus formation within 20 minutes. Rats treated with XK1 exhibited a dose-dependent inhibition of thrombus formation with full antithrombotic efficacy and no change in bleeding time or total blood loss at a dose of 4.5 mg/kg, i.v. administered over a 60 minute period. FXa inhibition with SC-83157 resulted in complete inhibition of thrombus formation at a dose of 1.2 mg/kg, i.v.; however, this effect was associated with substantial blood loss. Thrombin inhibition with SC-79407 also afforded complete protection from thrombus formation and occlusion at a dose of 2.58 mg/kg, i.v., and like SC-83157, was associated with substantial blood loss. These data imply that TF/FVIIa inhibition confers protection from acute thrombosis without concomitant changes in bleeding, indicating that this target (TF/FVIIa) may provide improved separation of efficacy vs. bleeding side-effects than interruption of coagulation by directly inhibiting either FXa or thrombin.

Pharmacological interruption of acute thrombus formation with minimal hemorrhagic complications by a small molecule tissue factor/factor VIIa inhibitor: comparison to factor Xa and thrombin inhibition in a nonhuman primate thrombosis model.

This study was designed to evaluate the antithrombotic efficacy and bleeding propensity of a selective, small-molecule inhibitor of tissue factor/factor VIIa (TF/VIIa) in comparison to small-molecule, selective inhibitors of factor Xa and thrombin in a nonhuman primate model of thrombosis. Acute, spontaneous thrombus formation was induced by electrolytic injury to the intimal surface of a femoral blood vessel, which results in thrombus propagation at the injured site. The TF/FVIIa inhibitor 3-amino-5-[1-[2-([4-[amino(imino)methyl]benzyl]amino)-2-oxoethyl]-3-chloro-5-(isopropylamino)-6-oxo-1,6-dihydropyrazin-2-yl]benzoic acid dihydrochloride (PHA-927F) was fully effective in prevention of thrombosis-induced vessel occlusion at a dose of 400 microg/kg/min, i.v., in the arterial vasculature (femoral artery). Neither the effective dose nor multiples up to 4.4-fold the effective arterial plasma concentration elicited any significant effect on bleeding time or blood loss from either the bleeding time site or the surgical (femoral isolation) site. Small-molecule inhibitors of factor Xa or thrombin were effective arterial antithrombotic agents; however, in contrast to the TF/FVIIa inhibitor, they both elicited substantial increases in bleeding propensity at the effective dose and at multiples of the effective plasma concentration. These data indicate that TF/VIIa inhibition effectively prevented arterial thrombosis with less impact on bleeding parameters than equivalent doses of factor Xa and thrombin inhibitors.

Polymer-assisted solution-phase (PASP) parallel synthesis of an alpha-ketothiazole library as tissue factor VIIa inhibitors.

A solution-phase synthesis of an alpha-ketothiazole library of the general form D-Phe-L-AA-L-Arg-alpha-ketothiazole is described. The five-step synthesis is accomplished using a combination of polymeric reagents and polymer-assisted solution-phase purification protocols, including reactant-sequestering resins, reagent-sequestering resins, and tagged reagents. The multi-step synthesis affords the desired alpha-ketothiazole products in excellent purities and yields. A variety of L-amino acid inputs were used to probe the S2 pocket of the tissue factor (TF) VIIa enzyme to influence both potency and selectivity. An X-ray crystal structure of compound 10e bound to the TF/VIIa complex was obtained that explains the observed selectivity. The alpha-ketothiazoles were found to be potent, reversible-covalent inhibitors of tissue factor VIIa, with some analogues demonstrating selectivity versus thrombin.

Structure-based drug design of pyrazinone antithrombotics as selective inhibitors of the tissue factor VIIa complex.

Structure-based drug design coupled with polymer-assisted solution-phase library synthesis was utilized to develop a series of pyrazinone inhibitors of the tissue factor/Factor VIIa complex. The crystal structure of a tri-peptide ketothiazole complexed with TF/VIIa was utilized in a docking experiment that identified a benzyl-substituted pyrazinone as a P(2) surrogate for the tri-peptide. A 5-step PASP library synthesis of these aryl-substituted pyrazinones was developed. The sequence allows for attachment of a variety of P(1) and P(3) moieties, which led to synthesis pyrazinone 23. Compound 23 exhibited 16 nM IC(50) against TF/VIIa with >6250x selectivity versus Factor Xa and thrombin. This potent and highly selective inhibitor of TF/VIIa was chosen for pre-clinical intravenous proof-of-concept studies to demonstrate the separation between antithrombotic efficacy and bleeding side effects in a primate model of thrombosis.