Design and structure-activity relationships of potent and selective inhibitors of blood coagulation factor Xa.

The discovery of a series of non-peptide factor Xa (FXa) inhibitors incorporating 3-(S)-amino-2-pyrrolidinone as a central template is described. After identifying compound 4, improvements in in vitro potency involved modifications of the liphophilic group and optimizing the angle of presentation of the amidine group to the S1 pocket of FXa. These studies ultimately led to compound RPR120844, a potent inhibitor of FXa (K(i) = 7 nM) which shows selectivity for FXa over trypsin, thrombin, and several fibrinolytic serine proteinases. RPR120844 is an effective anticoagulant in both the rat model of FeCl(2)-induced carotid artery thrombosis and the rabbit model of jugular vein thrombus formation.     

Synthesis, characterization, and structure-activity relationships of amidine-substituted (bis)benzylidene-cycloketone olefin isomers as potent and selective factor Xa inhibitors

Factor Xa (FXa) is a trypsin-like serine protease that plays a key role in blood coagulation linking the intrinsic and extrinsic pathways to the final common pathway of the coagulation cascade. During our initial studies, we observed facile photochemical conversion of the known FXa/tPA inhibitor, BABCH ?(E,E)-2, 7-bis(4-amidinobenzylidene)cycloheptan-1-one, 1a, to the corresponding (Z,Z) olefin isomer, 1c (FXa K(i) = 0.66 nM), which was over 25,000 times more potent than the corresponding (E,E) isomer (1a, FXa K(i) = 17 000 nM). In order to determine the scope of this observation, we expanded on our initial investigation through the preparation of the olefin isomers in a homologous series of cycloalkanone rings, 4-substituted cyclohexanone analogues, and modified amidine derivatives. In most cases the order of potency of the olefin isomers was (Z,Z) > (E,Z) > (E,E) with the cycloheptanone analogue (1c) showing the most potent factor Xa inhibitory activity. In addition, we found that selectivity versus thrombin (FIIa) can be dramatically improved by the addition of a carboxylic acid group to the cycloalkanone ring as seen with 8c (FXa K(i) = 6.9 nM, FIIa K(i) > 50,000 nM). Compounds with one or both of the amidine groups substituted with N-alkyl substituents or replaced with amide groups led to a significant loss of activity. In this report we have demonstrated the importance of the two amidine groups, the cycloheptanone ring, and the (Z,Z) olefin configuration for maximum inhibition of FXa within the BABCH template. The results from this study provided the foundation for the discovery of potent, selective, and orally active FXa inhibitors.     

Synthesis and structure-activity relationships of pyrazine-pyridine biheteroaryls as novel, potent, and selective vascular endothelial growth factor receptor-2 inhibitors

There is much evidence that direct inhibition of the kinase activity of vascular endothelial growth factor receptor-2 (VEGFR-2) will result in the reduction of angiogenesis and the suppression of tumor growth. Palladium-catalyzed C-C bond, C-N bond formation reactions were used to assemble various pyrazine-pyridine biheteroaryls as potent VEGFR-2 inhibitors. Among them, 4-{5-[6-(3-chloro-phenylamino)-pyrazin-2-yl]-pyridin-3-ylamino}-butan-1-ol (39) and N-{5-[6-(3-chloro-phenylamino)-pyrazin-2-yl]-pyridin-3-yl}-N',N'-dimethyl-ethane-1,2-diamine (41) exhibited the highest kinase selectivity against fibroblast growth factor receptor kinase, platelet-derived growth factor receptor kinase, and glycogen synthase kinase-3. All of these compounds showed good cellular potency to inhibit VEGF-stimulated proliferation of human umbilical vein endothelial cells (HUVEC) but with modest effects on the unstimulated growth of HUVEC. The low inhibition of these compounds to the growth of tumor cell lines, such as HeLa, HCT-116, and A375 further confirms that these VEGFR-2 inhibitors are not cytotoxic agents. The in vivo antitumor activity of 39 and 41 were demonstrated in the A375 human melanoma xenograft nude mice model. Molecular modeling (QSAR analysis) was conducted in an attempt to rationalize the observed structure-activity relationship.     

Fondaparinux:一个新的选择性Ⅹa因子抑制剂

fondaparinux是一个化学合成的全新戊聚糖化合物 ,能够有效地预防大型的下肢骨科手术后常见的静脉血栓栓塞。本文就其药效学、药动学、临床应用及其现状等作一综述。     

Approaches to selective peptidic inhibitors of factor Xa

Inhibitors of procoagulant enzymes, such as factor Xa (fXa) and thrombin, are important for treating thrombosis. Thrombin has complex pro- and anti-coagulant roles and thus fXa is thought to represent an ideal target. Discrete kcat and Km values for cleavage of a library of fluorescence-quenched substrates by fXa were determined. The results highlighted the low selectivity of fXa at its prime sites, and its poor efficiency compared with thrombin, creating a challenge for the design of fXa-specific peptidic inhibitors. We hypothesized that Km rather than kcat/Km values may be better indicators of inhibitor potential for a peptidic sequence, leading us to design peptide sequences for both fXa and thrombin in three forms: fluorescence-quenched substrates, standard alpha-peptides and peptides containing a beta-homoarginine at the cleavage site. Kinetic and competitive inhibition assays with both fXa and thrombin showed the fluorescence-quenched substrates to be the best inhibitors, while the inhibitory effect of the beta-homoarginine peptides varied for the two proteases. Importantly, fXa was inhibited to a much greater extent by the beta-peptides than the corresponding alpha-peptides, resulting in an increased selectivity for fXa inhibition over thrombin for those peptides containing a beta-amino acid at the cleavage site.     

Synthesis and structure-activity relationships of (aryloxy)quinazoline ureas as novel, potent, and selective vascular endothelial growth factor receptor-2 inhibitors

In our continuing search for medicinal agents to treat proliferative diseases, quinazoline derivatives were synthesized and evaluated pharmacologically as epithelial growth factor receptor and vascular endothelial growth factor receptor 2 (VEGFR-2) tyrosine kinase inhibitors. A quantitative structure-activity relationship analysis was conducted to rationalize the structure-activity relationship and to predict how similar the inhibitor-binding profiles of two protein kinases are likely to be on the basis of the docking of lead coumpounds into the ATP-binding site. This model was used to direct the synthesis of new compounds. A series of N-(aromatic)-N'-{4-[(6,7-dimethoxyquinazolin-4-yl)oxy]phenyl}urea were identified as potent and selective inhibitors of the tyrosine kinase activity of VEGFR-2 (fetal liver kinase 1, kinase insert domain-containing receptor). An efficient route was developed that enabled the synthesis of a wide variety of analogues with substitution on several positions of the template. Substitution of diarylurea, competitive with ATP, afforded several analogues with low nanomolar inhibition of enzymatic activity of VEGFR-2. In this paper, we describe the synthesis, structure-activity relationships, and pharmacological characterization of the series.     

Synthesis and structure-activity relationships of a series of novel benzopyran-containing platelet activating factor antagonists.

A class of N-substituted tetrahydrobenzopyrano[3,4-c]pyridines, I, have been identified as antagonists of platelet activating factor (PAF). The structural features essential for PAF binding were determined by systematic modification of three sites in the molecule. While O-alkyl analogues had little effect on binding potency, N-alkyl analogues exhibited a wide range of activity. Structural changes in the core ring system generally resulted in a loss of binding activity. Optimization of the N- and O-substituents resulted in the analogues 25-27 which exhibited Ki values ranging between 131 and 167 nM in a [3H]PAF binding assay. Compound 23 was also active in a model of PAF-induced shock in the mouse following intravenous administration.     

Rational design,synthesis, and structure-activity relationships of novel factor Xa inhibitors: (2-substituted-4-amidinophenyl)pyruvic and -propionic acids

An inhibitor of factor Xa (fXa), the m-substituted benzamidine AXC1578 (1a), was structurally modified with the aim of increasing its potency. In particular, pyruvic acid and propionic acid substituents were incorporated into the P1 benzamidine moiety to introduce a favorable interaction with the oxy-anion hole in the catalytic triad region of fXa. This strategy was based on computational docking studies using the extracted active site of fXa. The validity of the computational model was supported by the acquisition of X-ray crystal structures of the 1a-trypsin and 3b-trypsin complexes (the homology around the active sites of fXa and trypsin is high). The above modifications significantly increased the inhibitory activity toward fXa, whereas the high selectivity for fXa versus thrombin was maintained or enhanced. Compounds 3b, 3c, 3e, and 4b are considered to be potential lead compounds for the development of orally active anticoagulant drugs because they demonstrated potent activity when administered orally to cynomolgus monkeys.     

7-fluoroindazoles as potent and selective inhibitors of factor Xa

We have developed a novel series of potent and selective factor Xa inhibitors that employ a key 7-fluoroindazolyl moiety. The 7-fluoro group on the indazole scaffold replaces the carbonyl group of an amide that is found in previously reported factor Xa inhibitors. The structure of a factor Xa cocrystal containing 7-fluoroindazole 51a showed the 7-fluoro atom hydrogen-bonding with the N-H of Gly216 (2.9 A) in the peptide backbone. Thus, the 7-fluoroindazolyl moiety not only occupied the same space as the carbonyl group of an amide found in prior factor Xa inhibitors but also maintained a hydrogen bond interaction with the protein's beta-sheet domain. The structure-activity relationship for this series was consistent with this finding, as the factor Xa inhibitory potencies were about 60-fold greater (DeltaDelta G approximately 2.4 kcal/mol) for the 7-fluoroindazoles 25a and 25c versus the corresponding indazoles 25b and 25d. Highly convergent synthesis of these factor Xa inhibitors is also described.     

Discovery and structure-activity relationships of novel piperidine inhibitors of farnesyltransferase

A novel piperidine series of farnesyltransferase (FTase) inhibitors is described. Systematic medicinal chemistry studies starting with the lead compound, discovered from a 5-nitropiperidin-2-one combinatorial library, resulted in a potent series of novel FTase inhibitors. We found that all of four substituents of the piperidine core played an important role for FTase inhibition. A 10-fold increase in potency was observed by changing the piperidine-2-one core to the corresponding piperidine core. This class of compounds was found to inhibit farnesyltransferase in a Ras competitive manner. Optical resolution of several potent inhibitors revealed that the (+)-enantiomers showed potent farnesyltransferase inhibition. (+)-8 inhibited FTase with an IC(50) of 1.9 nM.     

Synthesis and structure-activity relationships of novel arylfluoroquinolone antibacterial agents

A series of novel arylfluoroquinolones has been prepared. These derivatives are characterized by having a fluorine atom at the 6-position, substituted amino groups at the 7-position, and substituted phenyl groups at the 1-position. Structure-activity relationship (SAR) studies indicate that the in vitro antibacterial potency is greatest when the 1-substituent is either p-fluorophenyl or p-hydroxyphenyl and the 7-substituent is either 1-piperazinyl, 4-methyl-1-piperazinyl, or 3-amino-1-pyrrolidinyl. The electronic and spatial properties of the 1-substituent, as well as the steric bulk, play important roles in the antimicrobial potency in this class of antibacterials. As a result of this study, compounds 45 and 41 were found to possess excellent in vitro potency and in vivo efficacy.     

Synthesis and structure-activity relationship for a novel class of potent and selective carbamate-based inhibitors of hormone selective lipase with acute in vivo antilipolytic effects

Hormone-sensitive lipase (HSL) is an intracellular enzyme that has a central role in the regulation of fatty acid metabolism. The enzyme, therefore, is a potentially interesting pharmacological target for the treatment of insulin resistance and dyslipidemic disorders. Based on a high throughput screening, a carbamate based HSL inhibitor was identified and optimized into the selective HSL inhibitors 4-hydroxymethyl-piperidine-1-carboxylic acid 4-(5-trifluoromethylpyridin-2-yloxy)-phenyl ester (13f) and 4-hydroxy-piperidine-1-carboxylic acid 4-(5-trifluoromethylpyridin-2-yloxy)-phenyl ester (13g), with IC50 values of 110 and 500 nM, respectively. Both inhibitors were active in acute antilipolytic experiments in vivo and none of the inhibitors inhibited the cytochrome P450 (CYP) isoforms 2D6, 3A4, and 1A2.     

Biarylmethoxy isonipecotanilides as potent and selective inhibitors of blood coagulation factor Xa

New chloro-substituted biarylmethoxyphenyl piperidine-4-carboxamides were synthesized and assayed in vitro as inhibitors of the blood coagulation enzymes factor Xa (fXa) and thrombin. An investigation of effects of the amidine and isopropyl groups attached at the piperidine nitrogen and 5-(halogenoaryl)isoxazol-3-yl groups as biaryl substituents led us to identify new compounds which proved to be selective fXa inhibitors, with inhibition constants in the low nanomolar range. The most potent compound 21e, that incorporates 2-Cl-thiophen-5-yl group as the P1 motif and 1-isopropylpiperidine P4 group, inhibited fXa with K_i value of 0.3 nM and very high selectivity over thrombin and some other tested serine proteases, achieving moderate levels of anticoagulant activity in the low micromolar range, as assessed by the prothrombin time clotting assay (PT₂ = 3.30 μM). Based on reliable docking simulations, molecular modeling provided a rationale for interpreting structure–activity relationships. The predicted binding modes highlighted the structural requirements for addressing the subsites S1 and S4 of the fXa enzyme.     

Synthesis and structure-activity relationship for a novel class of potent and selective carbamoyl-triazole based inhibitors of hormone sensitive lipase

The central role of the intracellular enzyme hormone-sensitive lipase (HSL) in regulating fatty acid metabolism makes it an interesting pharmacological target for the treatment of insulin resistant and dyslipidemic disorders where a decrease in delivery of fatty acids to the circulation is desirable, e.g., in individuals with type 2 diabetes, metabolic syndrome, or impaired glucose tolerance. On the basis of a lead structure from high throughput screening, we have identified a very potent type of carbamoyl-triazole inhibitors of HSL. As part of the lead optimization program, four new classes of carbamoyl-triazoles were synthesized and tested with respect to potency, efficacy and selectivity. Methyl-phenyl-carbamoyl-triazoles were identified as potent and efficacious HSL inhibitors. These compounds do not inhibit other hydrolases such as hepatic lipase, lipoprotein lipase, pancreatic lipase, and butyrylcholine esterase. However, the inhibitors 4b and 4g with IC(50) values for HSL of 0.17 and 0.25 microM, respectively, were the only inhibitors selective against acetylcholine esterase. A reversible pseudosubstrate inhibition mechanism is proposed for this class of inhibitors.     

Novel selective PDE4 inhibitors. 2. Synthesis and structure-activity relationships of 4-aryl-substituted cis-tetra- and cis-hexahydrophthalazinones

A series of 4-aryl-substituted cis-4a,5,8,8a-tetra- and cis-4a,5,6,7,8,8a-hexahydro-2H-phthalazin-1-ones with high inhibitory activity toward cAMP-specific phosphodiesterase (PDE4) was synthesized. To study structure-activity relationships various substituents were introduced to the 2-, 3-, and 4-positions of the 4-phenyl ring. Substitution at the 4-position of the phenyl ring was restricted to a methoxy group, probably due to unfavorable steric interactions of larger groups with the binding site. The introduction of many alkoxy substituents including distinct ring systems and functional groups was allowed to the 3-position. It was found that in general the cis-4a,5,8,8a-tetrahydro-2H-phthalazin-1-ones are more potent than their hexahydrophthalic counterparts, the best activity residing in (4-imidazol-1-yl-phenoxy)butoxy analogue 16o (pIC(50) = 9.7).     

Synthesis, biological evaluation, and structure-activity relationships of a novel class of apurinic/apyrimidinic endonuclease 1 inhibitors

APE1 is an essential protein that operates in the base excision repair (BER) pathway and is responsible for ≥95% of the total apurinic/apyrimidinic (AP) endonuclease activity in human cells. BER is a major pathway that copes with DNA damage induced by several anticancer agents, including ionizing radiation and temozolomide. Overexpression of APE1 and enhanced AP endonuclease activity have been linked to increased resistance of tumor cells to treatment with monofunctional alkylators, implicating inhibition of APE1 as a valid strategy for cancer therapy. We report herein the results of a focused medicinal chemistry effort around a novel APE1 inhibitor, N-(3-(benzo[d]thiazol-2-yl)-6-isopropyl-4,5,6,7-tetrahydrothieno[2,3-c]pyridin-2-yl)acetamide (3). Compound 3 and related analogues exhibit single-digit micromolar activity against the purified APE1 enzyme and comparable activity in HeLa whole cell extract assays and potentiate the cytotoxicity of the alkylating agents methylmethane sulfonate and temozolomide. Moreover, this class of compounds possesses a generally favorable in vitro ADME profile, along with good exposure levels in plasma and brain following intraperitoneal dosing (30 mg/kg body weight) in mice.     

Synthesis and structure-activity relationships of novel arylpiperazines as potent and selective agonists of the melanocortin subtype-4 receptor

The melanocortin receptors have been implicated as potential targets for a number of important therapeutic indications, including inflammation, sexual dysfunction, and obesity. We identified compound 1, an arylpiperazine attached to the dipeptide H-d-Tic-d-p-Cl-Phe-OH, as a novel melanocortin subtype-4 receptor (MC4R) agonist through iterative directed screening of nonpeptidyl G-protein-coupled receptor biased libraries. Structure-activity relationship (SAR) studies demonstrated that substitutions at the ortho position of the aryl ring improved binding and functional potency. For example, the o-isopropyl-substituted compound 29 (K(i) = 720 nM) possessed 9-fold better binding affinity compared to the unsubstituted aryl ring (K(i) = 6600 nM). Sulfonamide 39 (K(i) = 220 nM) fills this space with a polar substituent, resulting in a further 2-fold improvement in binding affinity. The most potent compounds such as the diethylamine 44 (K(i) = 60 nM) contain a basic group at this position. Basic heterocycles such as the imidazole 50 (K(i) = 110 nM) were similarly effective. We also demonstrated good oral bioavailability for sulfonamide 39.     

Discovery and structure-activity relationships of piperidinone- and piperidine-constrained phenethylamines as novel, potent, and selective dipeptidyl peptidase IV inhibitors

Dipeptidyl peptidase IV (DPP4) inhibitors are emerging as a new class of therapeutic agents for the treatment of type 2 diabetes. They exert their beneficial effects by increasing the levels of active glucagon-like peptide-1 and glucose-dependent insulinotropic peptide, which are two important incretins for glucose homeostasis. Starting from a high-throughput screening hit, we were able to identify a series of piperidinone- and piperidine-constrained phenethylamines as novel DPP4 inhibitors. Optimized compounds are potent, selective, and have good pharmacokinetic profiles.     

Synthesis and structure-activity relationships of truncated bisubstrate inhibitors of aminoglycoside 6'-N-acetyltransferases

Truncated aminoglycoside-coenzyme A bisubstrate analogues were efficiently prepared using a convergent approach where the amine and the thiol are coupled in one pot with the addition of a linker, without the need for protecting groups. These derivatives were tested for their effect on the activity of the resistance-causing enzyme aminoglycoside 6'-N-acetyltransferase Ii, and key structure-activity relationships are reported. Moreover, one of the inhibitors is able to block aminoglycoside resistance in cells expressing this enzyme.     

Quantitative structure-activity relationships of renin inhibitors

A review is presented on quantitative structure-activity relationships (QSARs) of renin inhibitors which have potential as antihypertensive and cardiovascular agents. They inhibit the renin, an enzyme that is involved in the rate-limiting first step of the renin angiotensin system (RAS). Most of the renin inhibitors are peptidomimetics but recently some nonpeptidomimetic renin inhibitors with low molecular weight have also been developed. In both types of renin inhibitors, the QSARs have exhibited that their inhibition activity would largely depend upon the molecular weight of the compounds, van der waals radius related parameters of the substituents, and the localized electronic effects, particularly of the side chain of the residues substituted in the peptides.