1-(2-Naphthyl)-1H-pyrazole-5-carboxylamides as potent factor Xa inhibitors. Part 2: A survey of P4 motifs

A variety of P4 motifs have been examined to increase the binding affinity and in vitro anticoagulant potency of our biphenyl 1-(2-naphthyl)-1H-pyrazole-5-carboxylamide-based fXa inhibitors. Highly potent 2-naphthyl-P1 fXa inhibitors (K(i)< or =2 nM) with improved in vitro anticoagulant activity (2xTG< or =1 microM) and respectable pharmacokinetic properties have been discovered.     

Selective and dual action orally active inhibitors of thrombin and factor Xa

The synthetic entry to new classes of dual fXa/thrombin and selective thrombin inhibitors with significant oral bioavailability is described. This was achieved through minor modifications to the sulfonamide group in our potent and selective fXa inhibitor (E)-2-(5-chlorothien-2-yl)-N-{(3S)-1-[(1S)-1-methyl-2-(morpholin-4-yl)-2-oxoethyl]-2-oxopyrrolidin-3-yl}ethenesulfonamide and these observed activity changes have been rationalised using structural studies.     

Anthranilamide inhibitors of factor Xa

SAR about the B-ring of a series of N(2)-aroyl anthranilamide factor Xa (fXa) inhibitors is described. B-ring o-aminoalkylether and B-ring p-amine probes of the S1' and S4 sites, respectively, afforded picomolar fXa inhibitors that performed well in in vitro anticoagulation assays.     

Discovery of N-[(1R,2S,5S)-2-{[(5-chloroindol-2-yl)carbonyl]amino}-5-(dimethylcarbamoyl)cyclohexyl]-5-methyl-4,5,6,7-tetrahydrothiazolo[5,4-c]pyridine-2-carboxamide hydrochloride: A novel,potent and orally active direct inhibitor of factor Xa

In the early 1990’s, we reported on the low-molecular selective fXa inhibitor DX-9065a having two amidino groups. However, it had poor oral bioavailability due to its strong basic amidino groups. To obtain fXa inhibitors with improved oral bioavailability, we investigated various non-amidino fXa inhibitors and finally discovered cis-1,2-diaminocyclohexane derivative 4c to have potent fXa inhibition, promising anticoagulant activity, and good oral bioavailability, compared with amidino compound DX-9065a. In addition, we will discuss the influence of the third substituent on the cyclohexane ring on anti-fXa activity, anticoagulant activity, PK profile, and lipophilicity.     

Halothiophene benzimidazoles as P1 surrogates of inhibitors of blood coagulation factor Xa

Neutral weak halothiophene benzimidazole inhibitors of the serine protease factor Xa were identified via screening of a compound library. The X-ray crystal structure of representative 3a bound to human fXa confirmed the S1 binding mode. Starting from 3a a series of halothiophene benzimidazoles was synthesized and investigated for their factor Xa inhibitory activity. This led to potent and selective achiral inhibitors against fXa such as compounds 9k and 9w.     

Nonbenzamidine isoxazoline derivatives as factor Xa inhibitors

Factor Xa (fXa) is an important serine protease in the blood coagulation cascade. Inhibition of fXa has emerged as an attractive target for potential therapeutic applications in the treatments of both arterial and venous thrombosis. Herein, we describe a series of non-benzamidine isoxazoline derivatives as fXa inhibitors. The chloroaniline group was found to be the most potent benzamidine mimic in this series. Chloroaniline 1 (ST368) has a K(i) value of 1.5 nM against fXa and is highly selective for fXa relative to thrombin and trypsin.     

Cycloalkanediamine derivatives as novel blood coagulation factor Xa inhibitors

This paper describes the synthesis of orally available potent fXa inhibitors 2 and 3 by modification of the piperazine part of lead compound 1. Carbonyl derivative 3 showed potent fXa activity but not sulfonyl derivative 2. Among the compounds synthesized, cyclohexane derivatives 3g and 3h and cycloheptane derivative 3j had potent anticoagulant activity as well as anti-fXa activity. Synthetic study of the optical isomers of 3g demonstrated that (-)-3g had more potent activity.     

Nonbenzamidine tetrazole derivatives as factor Xa inhibitors

Factor Xa (fXa) is an important serine protease that holds the central position linking the intrinsic and extrinsic activation mechanisms in the blood coagulation cascade. Therefore, inhibition of fXa has potential therapeutic applications in the treatments of both arterial and venous thrombosis. Herein we describe a series of tetrazole fXa inhibitors containing benzamidine mimics as the P(1) substrate, of which the aminobenzisoxazole moiety was found to be the most potent benzamidine mimic. SR374 (12) inhibits fXa with a K(i) value of 0.35 nM and is very selective for fXa over thrombin and trypsin.     

Structure-activity relationship and pharmacokinetic profile of 5-ketopyrazole factor Xa inhibitors

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.     

Structure- and property-based design of factor Xa inhibitors: pyrrolidin-2-ones with acyclic alanyl amides as P4 motifs

Structure-based drug design was exploited in the synthesis of 3-(6-chloronaphth-2-ylsulfonyl)aminopyrrolidin-2-one-based factor Xa (fXa) inhibitors, incorporating an alanylamide P4 group with acyclic tertiary amide termini. Optimized hydrophobic contacts of one amide substituent in P4 were complemented by hydrophobicity-modulating features in the second, producing potent fXa inhibitors including examples with excellent anticoagulant properties.     

Benzimidazole-based fXa inhibitors with improved thrombin and trypsin selectivity

Optimization of the benzimidazole-based fXa inhibitors for selectivity versus thrombin and trypsin was achieved by substitution on the benzimidazole ring and replacement of the naphthylamidine group. Substitution of a nitro group at the 4-position on the benzimidazole improves both potency against fXa and selectivity versus thrombin. Alternatively, replacement of the naphthylamidine with either a biphenylamidine or propenylbenzamidine not only improves fXa potency and selectivity versus thrombin, but selectivity versus trypsin as well.     

Design and synthesis of orally active pyrrolidin-2-one-based factor Xa inhibitors

A series of novel, non-basic 3-(6-chloronaphth-2-ylsulfonyl)aminopyrrolidin-2-one-based factor Xa (fXa) inhibitors, incorporating an alanylamide P4 group, was designed and synthesised. Within this series, the N-2-(morpholin-4-yl)-2-oxoethyl derivative 24 was shown to be a potent, selective fXa inhibitor with good anticoagulant activity. Moreover, 24 possessed highly encouraging rat and dog pharmacokinetic profiles with excellent oral bioavailabilities in both species.     

Generation of potent coagulation protease inhibitors utilizing zinc-mediated chelation

Inhibition of coagulation proteases such as thrombin, fXa, and fVIIa has been a focus of ongoing research to produce safe and effective antithrombotic agents. Herein, we describe a unique zinc-mediated chelation strategy to streamline the discovery of potent inhibitors of fIIa, fXa, and fVIIa. SAR studies that led to the development of selective inhibitors of fXa will also be detailed.     

Prodrug-based design, synthesis, and biological evaluation of N-benzenesulfonylpiperidine derivatives as novel, orally active factor Xa inhibitors

We describe here our investigation of a new series of orally active fXa inhibitors based on a prodrug strategy. Solid-phase parallel synthesis identified a unique series of fXa inhibitors with a substituted benzenesulfonyl group as a novel S4 binding element. This series resulted in compound 39, which exhibited potent inhibitory activity against fXa (IC50 = 13 nM) and excellent selectivity over thrombin (>7000-fold). The masking of its highly hydrophilic groups led to the creation of related prodrug 28, which demonstrated an anticoagulant effect after oral dosing.     

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 (BMS-740808) a highly potent, selective, efficacious, and orally bioavailable inhibitor of blood coagulation factor Xa

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.     

Amido-(propyl and allyl)-hydroxybenzamidines: development of achiral inhibitors of factor Xa

The design, synthesis and SAR of amido-(propyl and allyl)-hydroxybenzamidine coagulation factor Xa inhibitors is described. These achiral inhibitors are selective for fXa vis a vis structurally related serine proteases and are readily prepared in 6-7 linear steps. The most potent member 9j (fXa Ki = 0.75 nM) is selective (>1000-fold) and an effective anticoagulant in mammalian plasma.     

Design and synthesis of aminophenol-based factor Xa inhibitors

A novel potent and selective aminophenol scaffold for fXa inhibitors was developed from a previously reported benzimidazole-based naphthylamidine template. The aminophenol template is more synthetically accessible than the benzimidazole template, which simplified the introduction of carboxylic acid groups. Substitution of a propenyl-para-hydroxy-benzamidine group on the aminophenol template produced selective, sub-nanomolar fXa inhibitors. The potency of the inhibitors is partially explained with the aid of a trypsin complex crystal structure.     

Design, synthesis and biological activity of amidinobicyclic compounds (derivatives of DX-9065a) as factor Xa inhibitors: SAR study of S1 and aryl binding sites

Since factor Xa (fXa) plays a pivotal role in the blood coagulation cascade, inhibition of fXa is thought to be an effective treatment for a variety of thrombotic events. (2S)-2-[4-[[(3S)-1-Acetimidoyl-3-pyrrolidinyl]oxy]phenyl]-3-(7-amidino-2-naphthyl)propanoic acid hydrochloride pentahydrate (DX-9065a) was previously found in our laboratory as a novel orally active factor Xa inhibitor. DX-9065a exhibits a strong inhibitory activity toward fXa by occupying the substrate recognition (called S1) sites and aryl binding sites of fXa. Herein we describe conversions of the amidinonaphthalene and the acetimidoylpyrrolidine moieties of DX-9065a. Some compounds showed remarkably increased in vitro anti-factor Xa and PRCT activities compared with those of DX-9065a. The most promising compound 38 showed four times the prolongation of APTT against DX-9065a after oral administration to rats.     

Solid-phase optimisation of achiral amidinobenzyl indoles as potent and selective factor Xa inhibitors

Starting from the achiral and potent factor Xa inhibitor 1, a new and flexible solid-phase optimisation strategy is described to reduce its cationic character. By replacing one positively charged side chain by a lipophilic substituent, a novel series of highly potent and selective achiral factor Xa inhibitors was discovered. The identified lipophilic replacements in the S4 pocket might be valuable for other approaches towards fXa inhibitors.     

Design, synthesis, and biological activity of non-basic compounds as factor Xa inhibitors: SAR study of S1 and aryl binding sites

Compound 7 was identified as the active metabolite of 6 by HPLC and mass spectral analysis. Modification of lead compound 7 by transformation of its N-oxide 6-6 biaryl ring system and fused aromatics produced a series of non-basic fXa inhibitors with excellent potency in anti-fXa and anticoagulant assays. The optimized compounds 73b and 75b showed sub to one digit micromolar anticoagulant activity (PTCT2). Particularly, anti-fXa activity was detected in plasma of rats orally administered with 1mg/kg of compound 75b.