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partment, the pharmacokineticprofile of these agents would also feature a low volume ofdistributionand low systemicclearance.Based on several years of study and development, wehave identified the potent, highly selective and direct FXainhibitor, apixaban. Letrozole Apixaban isone of the most promising particular, single-target oralanticoagulants in late clinical development. In clinical trials,apixaban has been shown to provide predictable andconsistent anticoagulation, accompanied by promisingefficacy and safety profiles within the prevention and treatmentof various thromboembolic illnesses. The pharmacologicaland clinical profiles of apixaban suggest that ithas the possible to address several of the limitations ofwarfarin therapy, at present the standard of care in chronicoral anticoagulation.
Letrozole In this overview, we summarize thechemistry and pre-clinical profile of apixaban.ChemistryApixaban can be a small-molecule, selective FXa inhibitor. It ischemically described as 1--7-oxo-6--4,5,6,7-tetrahydro-1H-pyrazolopyridine-3-carboxamide. The molecular formulafor apixaban is C25H25N5O4, which corresponds to amolecular weight of 459.5.Discovery of apixabanIn the early 1990s, DuPont scientists invested a greatamount of effort within the development of inhibitors of glycoproteinIIb/IIIa. These efforts resulted in numerous compoundsthat were advanced to clinical trials as potentialanti-platelet agents. By the mid-1990s, scientists at DuPonthad recognized similarities in between the platelet glycoproteinGPIIb/IIIa peptide sequence Arg-Gly-Aspandthe prothrombin substrate FXa sequence, Glu-Gly-Arg.
Consequently, a high-throughput mapk inhibitor lead evaluationprogram was initiated to screen the IIb/IIIa library for FXainhibitory activity. This effort resulted within the identificationof a small number of isoxazoline derivatives including 1. Employing molecular modelingand structure-based design, an optimization strategyresulted within the identification of a benzamidine containingFXa inhibitor 2with enhanced potencyand potent antithrombotic activity in anexperimental model of thrombosis. Aside from thekey amidine P1 and also the enzyme Asp189 interaction, thebiarylsulfonamide P4 moiety was designed to neatly stackin the S4 hydrophobic box of FXa, which contains theresidues Tyr99, Phe174 and Trp215, with the terminalO-phenylsulfonamide ring producing an edge-to-face interactionwith Trp215.
Subsequent re-optimizations led tovicinally substituted isoxazole analogs including compound3, which retained anti-FXa potencyand a pyrazole analog 4, which demonstrated13 pM binding affinity against FXa and good antithromboticactivity inside a rabbit model of thrombosis. Thediscovery of SN429 was tremendously important NSCLC in that mapk inhibitor itset the stage for an optimization technique that led to thediscovery of numerous important compounds, including 5, a phase I clinical candidate having a long terminalhalf-life of around 30 h in humans, and 6, a compound that was advanced to aphase II proof-of-principle clinical trial. In reality, razaxabanwas the very first small molecule FXa inhibitor to provideclinical validation of the effectiveness of FXa inhibitionstrategies.Development of razaxaban was rapidly followed by theidentification of a novel bicyclic tetrahydropyrazolo-pyridinoneanalog 7.
The evolution of the bicyclic pyrazole template allowed forthe incorporation of a diverse set of P1 groups, the mostimportant of which was the p-methoxyphenyl analog 8. Compound 8 retained Letrozole potent FXaaffinity and good anticoagulant activity in vitro, was efficaciousin in vivo rabbit antithrombotic models andshowed high oral bioavailability in dogs. A significantbreakthrough was subsequently achieved, by way of the incorporationof a pendent P4 lactam group plus a carboxamidopyrazole moiety, that led towards the discovery of 9, a highly potent andselective FXa inhibitor with good efficacy in various animalmodels of thrombosis. Importantly, compound 9 alsoshowed a superb pharmacokinetic profile in dogs, withlow clearance, low volume of distribution and high oralbioavailability.
The superior pre-clinical profile demonstratedby mapk inhibitor 9 enabled its fast progression into clinicaldevelopment as apixaban. Figure 2 illustrates theX-ray structure of apixaban bound to FXa and shows thep-methoxyphenyl P1 deeply inserted into the S1 pocket,with the aryllactam P4 moiety neatly stacked in thehydrophobic S4 pocket.In vitro pharmacologyPotency, selectivity and kinetic mode of inhibitionApixaban can be a highly potent, reversible, active-site inhibitorof human FXa, having a Ki of 0.08 nM at 25*C and 0.25 nMat 37*C within the FXa tripeptide substrateassay. Analysis ofenzyme kinetics shows that apixaban acts as a competitiveinhibitor of FXa versus the synthetic tripeptide substrate,indicating that it binds within the active website. Apixaban producesa fast onset of inhibition below various conditionswith association rate constant of 20of 1.3 nM. Insummary, apixaban is capable of inhibiting the activity offree FXa, thrombus-associated FXa and FXa within theprothrombinase complex. Apixaban