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Introduction: Factor XIa (FXIa) is a novel target for safer antithrombotic therapy. BMS-962212 is a potent (Ki = 0.7nM), selective, reversible, active-site inhibitor of human FXIa designed for parenteral use. BMS-962212 has been studied in rabbits, but not in higher preclinical species. Hypothesis: Blockade of FXIa provides robust antithrombotic activity with minimal impact on hemostasis. Methods: Arterial thrombosis was produced in the carotid artery by electrical stimulation in anesthetized monkeys. Hemostasis was assessed using a provoked kidney bleeding time (KBT) model. In vivo thrombosis, KBT as well as ex vivo clotting times were monitored in the same animal. BMS-962212 (0.5+1.4 and 2+5.6 (mg/kg+mg/kg/h)) (n=6 per group) or vehicle (n=6) were administered intravenously as a bolus dose plus infusion from 30 min prior to initiation of thrombosis until the end of the experiment. Thrombus weight, KBT and clotting times were determined. Clotting times, including activated partial thromboplastin time (aPTT) and prothrombin time (PT), were measured. Results: BMS-962212 at 0.5+1.4 and 2+5.6 mg/kg+mg/kg/h reduced thrombus weight by 35±9* and 74±5%*, respectively (*P<0.05, vs. vehicle), and did not increase KBT when compared to vehicle (99±12 and 143±18 sec vs. 124±12 sec in vehicle). BMS-962212 increased ex vivo aPTT by 2.4±0.1-fold* and 2.9±0.1-fold* (*P<0.05, vs. 1.1±0.1 in vehicle) without changing PT (1.01±0.01-fold). In companion monkey studies, the standard of care antiplatelet agent clopidogrel at a clinically-equivalent dose (0.3 mg/kg/day given orally for 3 days) reduced thrombus weight by 49±6%, but increased KBT by 7.4±0.4-fold (756±44 sec vs. 103±5 sec in vehicle, n=6/group). Conclusions: BMS-962212 produces significant antithrombotic activity with minimal impact on hemostasis as compared to clopidogrel in monkeys. These results support that FXIa inhibition is a potentially safer drug target to prevent arterial thrombosis. [ABSTRACT FROM AUTHOR]

This manuscript describes the discovery of a series of macrocyclic inhibitors of FXIa with oral bioavailability. Assisted by structure based drug design and ligand bound X-ray crystal structures, the group linking the P1 moiety to the macrocyclic core was modified with the goal of reducing H-bond donors to improve pharmacokinetic performance versus 9. This effort resulted in the discovery of several cyclic P1 linkers, exemplified by 10, that are constrained mimics of the bioactive conformation displayed by the acrylamide linker of 9. These cyclic P1 linkers demonstrated enhanced bioavailability and improved potency., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Pyridine-based Factor XIa (FXIa) inhibitor (S)-2 was optimized by modifying the P2 prime, P1, and scaffold regions. This work resulted in the discovery of the methyl N-phenyl carbamate P2 prime group which maintained FXIa activity, reduced the number of H-bond donors, and improved the physicochemical properties compared to the amino indazole P2 prime moiety. Compound (S)-17 was identified as a potent and selective FXIa inhibitor that was orally bioavailable. Replacement of the basic cyclohexyl methyl amine P1 in (S)-17 with the neutral p-chlorophenyltetrazole P1 resulted in the discovery of (S)-24 which showed a significant improvement in oral bioavailability compared to the previously reported imidazole (S)-23. Additional improvements in FXIa binding affinity, while maintaining oral bioavailability, was achieved by replacing the pyridine scaffold with either a regioisomeric pyridine or pyrimidine ring system., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The synthesis, structural activity relationships (SAR), and selectivity profile of a potent series of phenylalanine diamide FXIa inhibitors will be discussed. Exploration of P1 prime and P2 prime groups led to the discovery of compounds with high FXIa affinity, good potency in our clotting assay (aPPT), and high selectivity against a panel of relevant serine proteases as exemplified by compound 21. Compound 21 demonstrated good in vivo efficacy (EC50=2.8μM) in the rabbit electrically induced carotid arterial thrombosis model (ECAT)., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Compound 2 was previously identified as a potent inhibitor of factor XIa lacking oral bioavailability. A structure-based approach was used to design analogs of 2 with novel P1 moieties with good selectivity profiles and oral bioavailability. Further optimization of the P1 group led to the identification of a 4-chlorophenyltetrazole P1 analog, which when combined with further modifications to the linker and P2' group provided compound 32 with FXIa Ki=6.7 nM and modest oral exposure in dogs., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

In an effort to identify a potential back-up to apixaban (Eliquis®), we explored a series of diversified P4 moieties. Several analogs with substituted gem-dimethyl moieties replacing the terminal lactam of apixaban were identified which demonstrated potent FXa binding affinity (FXa Ki), good human plasma anticoagulant activity (PT EC2x), cell permeability, and oral bioavailability., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

We have discovered that phenyltriazolinone is a novel and potent P1 moiety for coagulation factor Xa. X-ray structures of the inhibitors with a phenyltriazolinone in the P1 position revealed that the side chain of Asp189 has reoriented resulting in a novel S1 binding pocket which is larger in size to accommodate the phenyltriazolinone P1 substrate., (Copyright 2010 Elsevier Ltd. All rights reserved.)

Introduction of the phenyl piperidinone and phenyl pyridinone P4 moieties in the anthranilamide scaffold led to potent, selective, and orally bioavailable inhibitors of factor Xa. Anthranilamide 28 displayed comparable efficacy to apixaban in the rabbit arteriovenous-shunt (AV) thrombosis model.

Efforts to further optimize the clinical candidate razaxaban have led to a new series of pyrazole-based factor Xa (fXa) inhibitors. Designed to prevent the potential formation of primary aniline metabolites in vivo, the nitrogen of the carboxamido linker between the pyrazole and proximal phenyl moiety of the razaxaban scaffold was replaced with a methylene group. The resulting ketones demonstrated excellent potency and selectivity for fXa but initially had poor oral bioavailability. Optimization by conversion from a P1 aminobenzisoxazole to a P1 p-methoxyphenyl residue, replacing the 3-trifluoromethylpyrazole with a 3-amidopyrazole, and employing a pyridone P4 group provided a fXa inhibitor with a potency and pharmacokinetic profile equivalent to that of razaxaban and improved selectivity over thrombin.

The synthesis, SAR, pharmacokinetic profile, and modeling studies of both monocyclic and fused pyrazoles containing substituted N-arylpiperidinyl P4 moieties that are potent and selective factor Xa inhibitors will be discussed. Fused pyrazole analog 16a, with a 2'-methylsulfonylphenyl piperidine P4 group, was shown to be the best compound in this series (FXa Ki = 0.35 nM) based on potency, selectivity, and pharmacokinetic profile.

The bicyclic dihydropyrazolopyridinone scaffold allowed for incorporation of multiple P1 moieties with subnanomolar binding affinities for blood coagulation factor Xa. The compound 3-[6-(2'-dimethylaminomethyl-biphenyl-4-yl)-7-oxo-3-trifluoro-methyl-4,5,6,7-tetrahydro-pyrazolo[3,4-c]pyridine-l-yl]-benzamide 6d shows good fXa potency, selectivity, in vivo efficacy and oral bioavailability. Compound 6d was selected for further pre-clinical evaluations.

Attempts to further optimize the pyrazole factor Xa inhibitors centered on masking the aryl aniline P4 moiety. Scaffold optimization resulted in the identification of a novel bicyclic pyrazolo-pyridinone scaffold which retained fXa potency. The novel bicyclic scaffold preserved all binding interactions observed with the monocyclic counterpart and importantly the carboxamido moiety was integrated within the scaffold making it less susceptible to hydrolysis. These efforts led to the identification of 1-[3-aminobenzisoxazol-5'-yl]-3-trifluoromethyl-6-[2'-(3-(R)-hydroxy-N-pyrrolidinyl)methyl-[1,1']-biphen-4-yl]-1,4,5,6-tetrahydropyrazolo-[3,4-c]-pyridin-7-one 6f (BMS-740808), a highly potent (fXa Ki=30 pM) with a rapid onset of inhibition (2.7x10(7) M-1 s-1) in vitro, selective (>1000-fold over other proteases), efficacious in the AVShunt thrombosis model, and orally bioavailable inhibitor of blood coagulation factor Xa.

Modification of a series of pyrazole factor Xa inhibitors to incorporate an aminobenzisoxazole as the P(1) ligand resulted in compounds with improved selectivity for factor Xa relative to trypsin and plasma kallikrein. Further optimization of the P(4) moiety led to compounds with enhanced permeability and reduced protein binding. The SAR and pharmacokinetic profile of this series of compounds is described herein. These efforts culminated in 1-(3'-aminobenzisoxazol-5'-yl)-3-trifluoromethyl-N-[2-fluoro-4-[(2'-dimethylaminomethyl)imidazol-1-yl]phenyl]-1H-pyrazole-5-carboxyamide (11d), a potent, selective, and orally bioavailable inhibitor of factor Xa. On the basis of its excellent in vitro potency and selectivity profile, high free fraction in human plasma, good oral bioavailability, and in vivo efficacy in antithrombotic models, the HCl salt of this compound was selected for clinical development as razaxaban (DPC 906, BMS-561389).

The in vitro and in vivo disposition of DPC 423 was investigated in mice, rats, dogs and humans and the metabolites characterized by LC/MS, LC/NMR and high field-NMR. The rodents produced several metabolites that included an aldehyde (M1), a carboxylic acid (M2), a benzyl alcohol (M3), glutamate conjugates (M4 and M5), an acyl glucuronide (M6) and its isomers; a carbamyl glucuronide (M7); a phenol (M8) and its glucuronide conjugate (M9), two glutathione adducts (M10 and M11), a sulfamate conjugate (M12), isomers of an oxime metabolite (M13), and an amide (M14). Humans and dogs produced less complex metabolite profiles than rats. While unchanged DPC 423 was the major component in plasma and urine samples, differences in the metabolic disposition of this compound among species were noted. M1 is believed to be rapidly oxidized to the carboxylic acid (M2), which forms the potentially reactive acyl glucuronide (M6). The formation of novel glutamate conjugates (M4 and M5) and their role in depleting endogenous glutathione have been described previously. The carbamyl glucuronide M7, found as the major metabolite in rats and in other species, was considered nonreactive and was easily hydrolyzed to the parent compound in the presence of beta-glucuronidase. The identification of GSH adducts M10 and M11 led us to postulate the existence of at least two reactive intermediates responsible for their formation, an epoxide and possibly a nitrile oxide, respectively. Although the formation of GSH adducts such as M10 from epoxides has been described before, there are no reports to date describing the existence of a GSH adduct (M11) of an oxime. The formation of a sulfamate conjugate (M12) formed by direct coupling of sulfate to the nitrogen of benzylamine is described. A mechanism is proposed for the formation of the oxime (M13) that involves sequential oxidation of the benzylamine to the corresponding hydroxylamine and nitroso intermediate. The rearrangement of the nitroso intermediate is believed to produce the oxime (M13). In vitro studies suggested that both the oxime (M13) and the aldehyde (M1) were precursors to the carboxylic acid (M2). This is the first demonstration of carboxylic acid formation via an oxime intermediate produced from an amine. The stability of DPC423 in plasma obtained from several species was studied. Significant species differences in the plasma stability of DPC 423 were observed. The formation of the aldehyde metabolite (M1) was found to be catalyzed by a semicarbazide-sensitive monoamine oxidase (SSAO) found in plasma of rabbits, dogs, and rhesus monkeys. Rat, chimpanzee, and human plasma did not form M1.