Patrick Y.S. Lam

Apixaban, an oral, direct and highly selective factor Xa inhibitor: in vitro, antithrombotic and antihemostatic studies

Summary.u2002 Background:u2002Apixaban is an oral, direct and highly selective factor Xa (FXa) inhibitor in late‐stage clinical development for the prevention and treatment of thromboembolic diseases. Objective:u2002We evaluated the in vitro properties of apixaban and its in vivo activities in rabbit models of thrombosis and hemostasis. Methods:u2002Studies were conducted in arteriovenous‐shunt thrombosis (AVST), venous thrombosis (VT), electrically mediated carotid arterial thrombosis (ECAT) and cuticle bleeding time (BT) models. Results:u2002In vitro, apixaban is potent and selective, with a Ki of 0.08u2003nm for human FXa. It exhibited species difference in FXa inhibition [FXa Ki (nm): 0.16, rabbit; 1.3, rat; 1.7, dog] and anticoagulation [EC2× (μm, concentration required to double the prothrombin time): 3.6, human; 2.3, rabbit; 7.9, rat; 6.7, dog]. Apixaban at 10u2003μm did not alter human and rabbit platelet aggregation to ADP, γ‐thrombin, and collagen. In vivo, the values for antithrombotic ED50 (dose that reduced thrombus weight or increased blood flow by 50% of the control) in AVST, VT and ECAT and the values for BT ED3× (dose that increased BT by 3‐fold) were 0.27u2003±u20030.03, 0.11u2003±u20030.03, 0.07u2003±u20030.02 and >u20033u2003mgu2003kg−1u2003h−1 i.v. for apixaban, 0.05u2003±u20030.01, 0.05u2003±u20030.01, 0.27u2003±u20030.08 and >u20033u2003mgu2003kg−1u2003h−1 i.v. for the indirect FXa inhibitor fondaparinux, and 0.53u2003±u20030.04, 0.27u2003±u20030.01, 0.08u2003±u20030.01 and 0.70u2003±u20030.07u2003mgu2003kg−1u2003day−1 p.o. for the oral anticoagulant warfarin, respectively. Conclusions:u2002In summary, apixaban was effective in the prevention of experimental thrombosis at doses that preserve hemostasis in rabbits.

Copper-promoted/catalyzed CN and CO bond cross-coupling with vinylboronic acid and its utilities

Abstract The mildest method of N-vinylation has been discovered. The synthetic utilities of the N- and O-vinylated products include protecting group, cyclopropanation and Grubbs’ ring closure metathesis reactions.

Copper promoted CN and CO bond cross-coupling with phenyl and pyridylboronates

Abstract Acyclic and cyclic esters, as well as anhydride (boroxine) of phenylboronic acids are efficient phenylating agents in copper promoted Cue5f8N and Cue5f8O bond cross-coupling reactions. The first successful Cue5f8N cross-coupling of a heterocyclic boronate with heteroarenes, such as indazole, has been demonstrated.

N-arylation of α-aminoesters with p-tolylboronic acid promoted by copper(II) acetate

Copper-promoted N-arylation of α-amino esters with p-tolylboronic acid at room temperature was accomplished with little or no racemization.

Copper-promoted CN bond cross-coupling with phenylstannane

Abstract Copper-promoted Cue5f8N bond cross-coupling of NH-containing substrates with phenylstannane at room temperature was accomplished with the addition of TBAF.

Preclinical pharmacokinetics and pharmacodynamics of apixaban, a potent and selective factor Xa inhibitor.

Apixaban is a potent, highly selective, reversible, oral, direct factor Xa (fXa) inhibitor in development for thrombosis prevention and treatment. The preclinical pharmacokinetic (PK) attributes of apixaban feature small volume of distribution (Vd), low systemic clearance (CL), and good oral bioavailability. Apixaban is well absorbed in rat, dog, and chimpanzee, with absolute oral bioavailability of approximately 50% or greater. The steady-state Vd of apixaban is approximately 0.5, 0.2, and 0.17xa0l/kg in rats, dogs, and chimpanzees, while CL is approximately 0.9, 0.04, and 0.018xa0l/h/kg, respectively. In vitro metabolic clearance of apixaban is also low. Renal clearance comprises approximately 10–30% of systemic clearance in rat, dog, and chimpanzee. Anti-fXa activity, prothrombin time (PT), and HEPTEST® clotting time (HCT) prolongation correlated well with plasma apixaban concentration in rat, dog and chimpanzee. There was no lag time between apixaban plasma concentration and the pharmacodynamic (PD) markers, suggesting a rapid onset of action of apixaban. The PK/PD analyses were performed using an inhibitory Emax model for anti-fXa assay and a linear model for PT and HCT assays. The IC50 values for anti-fXa activity were 0.73xa0±xa00.03 and 1.5xa0±xa00.15xa0μM for rat and dog, respectively. The apparent Ki values for PT were approximately 1.7, 6.6, and 4.8xa0μM for rat, dog and chimpanzee, respectively. The apparent Ki for HCT was approximately 1.3xa0μM for dog. Apixaban exhibits desirable PK and PD properties for clinical development with good oral bioavailability, small Vd, low CL, and direct, predictable, concentration-dependent PD responses.

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.

Razaxaban, a direct factor Xa inhibitor, in combination with aspirin and/or clopidogrel improves low-dose antithrombotic activity without enhancing bleeding liability in rabbits

Coactivation of platelets and the blood coagulation cascade contributes to the pathophysiology of arterial thrombosis. Combination therapy with antiplatelet and anticoagulant drugs may be needed for maximizing the prevention and treatment of arterial thrombosis. Few studies have thoroughly investigated the combined antithrombotic and bleeding effects of these antithrombotic agents. We, therefore, evaluated the antithrombotic and bleeding profiles of dual and triple therapy with razaxaban, a direct factor Xa inhibitor, plus aspirin and/or clopidogrel in rabbit models of electrolytic injury-induced carotid artery thrombosis and cuticle bleeding time, respectively. Compounds were infused either IV or into the portal vein from 1xa0h before arterial injury or cuticle transection to the end of experiment. Carotid blood flow was used as a marker of antithrombotic effect. We first evaluated the antithrombotic potency of razaxaban, and examined its ex vivo effects on coagulation parameters to confirm its selectivity. Antithrombotic ED50 of razaxaban averaged 0.22xa0±xa00.05xa0mg/kg/h (nxa0=xa06). Razaxaban at 3xa0mg/kg/h IV produced full antithrombotic efficacy, increased significantly ex vivo activated partial thromboplastin time and prothrombin time by 2.2xa0±xa00.1- and 2.3xa0±xa00.1-fold, respectively, and inhibited ex vivo factor Xa activity significantly by 91xa0±xa05% (nxa0=xa06, Pxa0<xa00.05) without affecting ex vivo thrombin activity. Razaxaban at concentrations up to 10xa0μM did not alter in vitro platelet aggregation responses to ADP, γ-thrombin or collagen. To identify additive or synergistic antithrombotic effects of the various combination therapies, we purposefully used marginally effective doses of razaxaban at 0.1xa0mg/kg/h, aspirin at 0.3xa0mg/kg/h and clopidogrel at 1xa0mg/kg/h. Dual combination of threshold doses of razaxaban and aspirin or clopidogrel produced an enhanced antithrombotic effect without further increases in bleeding time. When compared with dual therapy with aspirin and clopidogrel (38xa0±xa05% increase in blood flow), addition of razaxaban increased blood flow to 75xa0±xa05% without additional bleeding time effects (nxa0=xa06/group, Pxa0<xa00.05). In summary, razaxaban was an effective antithrombotic agent in a rabbit model of arterial thrombosis. Low-dose razaxaban was useful in combination with sub-optimal doses of aspirin and/or clopidogrel for the prevention of occlusive arterial thrombosis without excessive bleeding.

Achieving structural diversity using the perpendicular conformation of alpha-substituted phenylcyclopropanes to mimic the bioactive conformation of ortho-substituted biphenyl P4 moieties: Discovery of novel, highly potent inhibitors of Factor Xa

Ortho-substituted biphenyl moieties are widely used in drug design. We herein report a successful use of the perpendicular conformation of the alpha-substituted phenylcyclopropyl groups to mimic the aplanar, biologically active conformation of the ortho-substituted biphenyl moieties to achieve structural diversity. This is exemplified by the design and synthesis of a series of highly potent pyrazole bicyclic-based Factor Xa (FXa) inhibitors bearing alpha-substituted phenylcyclopropyl P4 moieties. The designed perpendicular conformation was confirmed by the X-ray structure of FXa-bound compound 2r. The potential structural basis for the high FXa potency in the phenylcyclopropyl P4 analogs and their improved FXa inhibitory activities compared with the biphenyl P4 counterparts are discussed.

Transformation of anionically activated trifluoromethyl groups to heterocycles under mild aqueous conditions.

The (hetero)aromatic trifluoromethyl group is present in many biologically active molecules and is generally considered to be chemically stable. In this paper, a convenient one-step synthesis of C-C linked aryl-heterocycles or heteroaryl-heterocycles in good to excellent yields via the reaction of anionically activated trifluoromethyl groups with amino nucleophiles containing a second NH, OH, or SH nucleophile in 1 N sodium hydroxide is reported. The method has high functional group tolerability and is potentially useful in parallel synthesis.