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The work in this paper describes the optimization of the 3-(3-phenyl-3H-imidazo[4,5-b]pyridin-2-yl)pyridin-2-amine chemical series as potent, selective allosteric inhibitors of AKT kinases, leading to the discovery of ARQ 092 (21a). The cocrystal structure of compound 21a bound to full-length AKT1 confirmed the allosteric mode of inhibition of this chemical class and the role of the cyclobutylamine moiety. Compound 21a demonstrated high enzymatic potency against AKT1, AKT2, and AKT3, as well as potent cellular inhibition of AKT activation and the phosphorylation of the downstream target PRAS40. Compound 21a also served as a potent inhibitor of the AKT1-E17K mutant protein and inhibited tumor growth in a human xenograft mouse model of endometrial adenocarcinoma.

A critical unmet clinical need to combat the global tuberculosis epidemic is the development of potent agents capable of reducing the time of multi-drug-resistant (MDR) and extensively-drug-resistant (XDR) tuberculosis therapy. In this paper, we report on the optimization of imidazo[1,2-a]pyridine amide (IPA) lead compound 1, which led to the design and synthesis of Q203 (50). We found that the amide linker with IPA core is very important for activity against Mycobacterium tuberculosis H37Rv. Linearity and lipophilicity of the amine part in the IPA series play a critical role in improving in vitro and in vivo efficacy and pharmacokinetic profile. The optimized IPAs 49 and 50 showed not only excellent oral bioavailability (80.2% and 90.7%, respectively) with high exposure of the area under curve (AUC) but also displayed significant colony-forming unit (CFU) reduction (1.52 and 3.13 log10 reduction at 10 mg/kg dosing level, respectively) in mouse lung.

This paper describes the implementation of a biochemical and biophysical screening strategy to identify and optimize small molecule Akt1 inhibitors that act through a mechanism distinct from that observed for kinase domain ATP-competitive inhibitors. With the aid of an unphosphorylated Akt1 cocrystal structure of 12j solved at 2.25 Å, it was possible to confirm that as a consequence of binding these novel inhibitors, the ATP binding cleft contained a number of hydrophobic residues that occlude ATP binding as expected. These Akt inhibitors potently inhibit intracellular Akt activation and its downstream target (PRAS40) in vitro. In vivo pharmacodynamic and pharmacokinetic studies with two examples, 12e and 12j, showed the series to be similarly effective at inhibiting the activation of Akt and an additional downstream effector (p70S6) following oral dosing in mice.

N-{trans-3-[(5-Cyano-6-methylpyridin-2-yl)oxy]-2,2,4,4-tetramethylcyclobutyl}imidazo[1,2-a]pyrimidine-3-carboxamide (1) was recently identified as a full antagonist of the androgen receptor, demonstrating excellent in vivo tumor growth inhibition in castration-resistant prostate cancer (CRPC). However, the imidazo[1,2-a]pyrimidine moiety is rapidly metabolized by aldehyde oxidase (AO). The present paper describes a number of medicinal chemistry strategies taken to avoid the AO-mediated oxidation of this particular system. Guided by an AO protein structure-based model, our investigation revealed the most probable site of AO oxidation and the observation that altering the heterocycle or blocking the reactive site are two of the more effective strategies for reducing AO metabolism. These strategies may be useful for other drug discovery programs.

In this paper we report the synthesis of three families of new amidine-based aromatic derivatives as potential DNA minor groove binding agents for the treatment of cancer. The preparation of monoguanidine, mono-2-aminoimidazoline, and asymmetric diphenylguanidine/2-aminoimidazoline derivatives (compounds 1a-c to 8a-c) is presented. The affinity of these substrates and of a family of mono- and bis-isoureas (previously prepared in Rozas' laboratory) for DNA was evaluated by means of DNA thermal denaturation measurements. In particular, compounds 2c, 5c, 6c, 7c, and 8c were found to bind strongly both to natural DNA and to adenine-thymine oligonucleotides, showing a preference for the adenine-thymine base pair sequences.

In this paper, we report the synthesis of three new 2-aminoimidazoline (compounds 4b, 5b, and 6b) and three new guanidine derivatives (compounds 7b, 8b, and 9b) as potential alpha(2)-adrenoceptor antagonists for the treatment of depression. Their pharmacological profile was evaluated in vitro in human brain tissue and compared to the potential antidepressant 1 and the agonists 2 and 3. All new substrates were evaluated by in vitro functional [(35)S]GTPgammaS binding assays in human prefrontal cortex to determine their agonistic or antagonistic activity. Compound 8b was found to be an antagonist in vitro and was subjected to in vivo microdialysis experiments in rats. Moreover, a new synthesis of the precursor amines for compounds 4b-9b is presented.

This paper reports the synthesis of a new series of 3-(5-imidazo[2,1-b]thiazolylmethylene)-2-indolinones which were tested as potential antitumor agents at the National Cancer Institute. Two derivatives are now under review by BEC (Biological Evaluation Committee of NCI). To investigate the mechanism of action, the effect on cell cycle progression was studied by monitoring them in colon adenocarcinoma HT-29: both were able to block HT-29 in mitosis. 3-[(2,6-Dimethylimidazo[2,1-b]thiazol-5-yl)methylene]-5-chloro-2-indolinone was the most active compound.

1-[(Aryl)(4-aryl-1H-pyrrol-3-yl)methyl]-1H-imidazoles were recently reported by our group as potent anti-Candida agents belonging to the antifungal azole class. In the present paper the synthesis, anti-Candida activities, and QSAR studies on a novel series of N-substituted 1-[(aryl)(4-aryl-1H-pyrrol-3-yl)methyl]-1H-imidazole derivatives are reported. The newly synthesized azoles were tested against 12 strains of Candida albicans together with bifonazole, miconazole, itraconazole, fluconazole, and compounds 1a, 1b, 3a, 3b, and 3c used as reference drugs. In general, tested derivatives showed good antifungal activities, and the most potent compound was 1d (MIC(90) = 0.032 microg/mL), which was from 4- to 250-fold more potent than reference drugs. Catalyst software was applied to develop a quantitative pharmacophore model to be used for the rational design of new antifungal azoles. Some key interactions, as well as excluded volumes, further to the coordination bond of azole antifungals with the demethylase enzyme, are highlighted.

Compounds presenting an additional fused ring on the xanthine nucleus have been reported to exhibit antagonistic activity with various levels of affinity and selectivity toward the four adenosine receptors subtypes A(1), A(2A), A(2B), and A(3). This paper reports synthesis and biological evaluation of new 1-benzyl-3-propyl-1H,6H-pyrrolo[2,1-f]purine-2,4-diones and 1-benzyl-3-propyl-1H,8H-imidazo[2,1-f]purine-2,4-diones, among which we identified potent and selective A(3) adenosine receptors antagonists. In particular, 1-benzyl-7-methyl-3-propyl-1H,8H-imidazo[2,1-f]purine-2,4-dione (11e) shows a K(i) (hA(3)) value from binding assay of 0.8 nM.

This paper reports synthesis and antitumor activity of new guanylhydrazones from imidazo[2,1-b]thiazoles and from the new heterocyclic system thiazolo[2',3':2,3]imidazo[4,5-c]quinoline. The compounds were tested as potential antitumor agents at the National Cancer Institute. The effect of the guanylhydrazone of 2-chloro-6-(2,5-dimethoxy-4-nitrophenyl)imidazo[2,1-b]thiazole-5-carbaldehyde (41) was investigated, and it was found to be an inhibitor of Complex III of the mitochondrial respiratory chain and is able to induce apoptosis in the cell lines HT29 and HL60.

Antagonizing the robust stimulation of food intake by neuropeptide Y represents a new potential therapeutic approach for the treatment of obesity. Earlier pharmacological studies have pointed to the Y1 and Y5 receptors as the most likely mediators of the NPY orexigenic response. In this paper, we describe a new series of small molecule Y5 antagonists derived from a 2,4-diaryl-1H-imidazole lead. The main objectives of our structural optimization efforts were to produce novel and potent Y5 antagonists with an improved oral pharmacokinetic profile and less affinity for the hERG potassium channel compared to the lead 2,4-diarylimidazole structures. These goals were accomplished by replacement of the 2-aryl ring with a cyclohexyl ring and subsequent elaboration of the 4-position of the cyclohexyl ring with a variety of hydrophilic functionalities. The resulting compound, N-(2-hydroxy-tert-butyl)(4-[4-[3-(trifluoromethyl)phenyl]imidazol-2-yl]cyclohexyl)carboxamide (20), displayed good potency at the Y5 receptor (K(i) = 3 nM), while interactions at the hERG channel were essentially eliminated (6% inhibition at a concentration of 3 microM). Importantly, the pharmacokinetic properties of 20 (F = 36%) represented a marked improvement over that of the initial 2,4-diarylimidazole structures.

In this paper we show that 4-aryl-CH2-imidazole-substituted benzopyran compounds with 3S,4R-stereochemistry are cardioprotective by inhibiting the F1F0 mitochondrial ATP hydrolase. Compounds (e.g., 13) with 3R,4S-stereochemistry act as mitochondrial KATP openers. This resulted from an inversion of stereochemistry for the F1F0 mitochondrial ATP hydrolase vs mitochondrial KATP. Structure-activity relationships for the inhibition of mitochondrial ATP hydrolase are also delineated. It is not clear how 13 (3R,4S) can selectively inhibit the hydrolytic activity of the F1F0 mitochondrial enzyme without interfering with the synthase activity.

As a part of a program aimed at discovering compounds endowed with alpha(1)-adrenoceptor (AR) blocking properties, in this paper we describe the synthesis and biological characterization of the compounds designed to fully match a three-dimensional pharmacophore model for alpha(1)-AR antagonists previously developed by our research group. Accordingly, the structure of trazodone (1), identified during a database search performed by using the model as a 3D query, was chosen as the starting point for this study and modified following suggestions derived from a literature survey. In particular, the triazolopyridine moiety of trazodone was replaced with different heteroaromatic rings (such as imidazole, benzimidazole, and indole), and a pyridazin-3(2H)-one moiety was inserted into the scaffold of the new compounds to increase the overall length of the molecules and to allow for a complete fit into all the pharmacophore features. Our aim was also to study the influence of the position of both the chloro and the methoxy groups on the piperazine phenyl ring, as well as the effect of the lengthening or shortening of the polymethylene spacer linking the phenylpiperazine moiety to the terminal heterocyclic portion. Compounds obtained by such structural optimization share a 6-(imidazol-1-yl)-, 6-(benzimidazol-1-yl)-, or 6-(indol-1-yl)pyridazin-3(2H)-one as a common structural feature that represents an element of novelty in the SAR of arylpiperazine compounds acting toward alpha(1)-AR. Biological evaluation by radioligand receptor binding assays toward alpha(1)-AR, alpha(2)-AR, and 5-HT(1A) serotoninergic receptors indicated compounds characterized by very good alpha(1)-AR affinity and selectivity. Very interestingly, chemical features (such as the o-methoxyphenylpiperazinyl moiety and an alkyl spacer of three or four methylene units) that generally do not allow for 5-HT(1A)/alpha(1) selectivity led to compounds 2c and 6c with a 5-HT(1A)/alpha(1) ratio of 286 and 281, respectively. Finally, compounds with the best alpha(1)-AR affinity profile (2c, 5f, and 6c) were demonstrated to be alpha(1)-AR antagonists.

Nitrobenzyl quaternary salts of nitrogen mustards have been previously reported as hypoxia-selective cytotoxins. In this paper we describe the synthesis and evaluation of a series of heterocyclic analogues, including pyrrole, imidazole, thiophene, and pyrazole examples, chosen to cover a range of one-electron reduction potentials (from -277 to -511 mV) and substitution patterns. All quaternary salt compounds were less toxic in vitro than mechlorethamine, and all were more toxic under hypoxic than aerobic conditions, although the differentials were highly variable within the series. The most promising analogue, imidazole 2, demonstrated DNA cross-linking selectively in hypoxic RIF-1 cells, and was active in vivo in combination with radiation or cisplatin. However, 2 also produced unpredictable toxicity in vivo, suggestive of nonspecific nitrogen mustard release, and this has restricted further development of these compounds as hypoxia-selective cytotoxins.

This paper describes the synthesis of a series of azo compounds able to deliver 5-aminosalicylic acid (5-ASA) and a potent platelet activating factor (PAF) antagonist in a colon-specific manner for the purpose of treating ulcerative colitis. We found it possible to add an amino group on the aromatic moiety of our reported 1-[(1-acyl-4-piperidyl)methyl]-1H-2-methylimidazo[4,5-c]pyridine derivatives or on British Biotech compounds BB-882 and BB-823 maintaining a high level of activity as PAF antagonist. A selected compound UR-12715 (49c) showed an IC(50) of 8 nM in the in vitro PAF-induced aggregation assay, and an ID(50) of 29 microg/kg in the in vivo PAF-induced hypotension test in normotensive rats. Through attachment of 49c to the 5-ASA via azo functionality we obtained UR-12746 (70). Pharmacokinetics experiments with [14C]-70 allow us to reach the following conclusions, critical in the design of these new prodrugs of 5-ASA. Neither the whole molecule 70 nor the carrier 49c were absorbed after oral administration of [14C]-70 in rat as was demonstrated by the absence of plasma levels of radioactivity and the high recovery of it in feces. Effective cleavage of azo bond (84%) by microflora in the colon is achieved. These facts ensure high topical concentrations of 5-ASA and 49c in the colon. Additionally, 70 exhibited a potent anticolitic effect in the trinitrobenzenesulfonic acid-induced colitis model in the rat. This profile suggests that UR-12746 (70) provides an attractive new approach to the treatment of ulcerative colitis.

A series of heteroaryl modified 1,2-diarylimidazoles has been synthesized and found to be potent and highly selective (1000-9000-fold) inhibitors of the human COX-2. 3-Pyridyl derived COX-2 selective inhibitor (25) exhibited excellent activity in acute (carrageenan induced paw edema, ED(50) = 5.4 mg/kg) and chronic (adjuvant induced arthritis, ED(50) = 0.25 mg/kg) models of inflammation. The relatively long half-life of 25 in rat and dog prompted investigation of the pyridyl and other heteroaromatic systems containing potential metabolic functionalities. A number of substituted pyridyl and thiazole containing compounds (e.g., 44, 46, 54, 76, and 78) demonstrated excellent oral activity in every efficacy model evaluated. Several orally active diarylimidazoles exhibited desirable pharmacokinetics profiles and showed no GI toxicity in the rat up to 100 mg/kg in both acute and chronic models. The paper describes facile and practical syntheses of the targeted diarylimidazoles. The structure-activity relationships and antiinflammatory properties of a series of diarylimidazoles are discussed.

The discovery of 8-(5,8-dichloro-1,2,3,4-tetrahydro-naphthalen-2-yl)-1-phenyl-1,3,8-triazaspiro[4.5]decan-4-one, 1a, as a high-affinity ligand for the human ORL1 (orphanin FQ/nociceptin) receptor led to the synthesis of a series of optimized ligands. These compounds exhibit high affinity for the human ORL1 receptor, exhibit moderate to good selectivity versus opioid receptors, and behave as full agonists in biochemical assays. In this paper we present the synthesis, structure-activity relationship (SAR), and biochemical characterization of substituted 1-phenyl-1,3,8-triazaspiro[4.5]decan-4-ones culminating in the discovery of 8-(5-methyl-1,2,3,4-tetrahydro-naphthalen-1-yl)-1-phenyl-1,3,8-triazaspiro[4.5]decan-4-one, 1p, and 8-acenaphten-1-yl-1-phenyl-1,3,8-triazaspiro[4.5]decan-4-one 1q, two high-affinity, potent ORL1 receptor agonists with good to moderate selectivity versus the other opioid receptors.

Phosphodiesterase type 5 (PDE5) inhibitors with improved PDE isozyme selectivity relative to sildenafil may result in agents for the treatment of male erectile dysfunction (MED) with a lower incidence of PDE-associated adverse effects. This paper describes the discovery of 14, a PDE5 inhibitor with improved potency and selectivity in vitro compared to sildenafil. This compound shows activity in a functional assay of erectile function comparable to that of sildenafil.

Series of 1,2-diarylimidazoles has been synthesized and found to contain highly potent and selective inhibitors of the human COX-2 enzyme. The paper describes a short synthesis of the target 1,2-diarylimidazoles starting with aryl nitriles. Different portions of the diarylimidazole (I) were modified to establish SAR. Systematic variations of the substituents in the aryl ring B have yielded very potent (IC50 = 10-100 nm) and selective (1000-12500) inhibitors of the COX-2 enzyme. The study on the influence of substituents in the imidazole ring established that a CF3 group at position 4 gives the optimum oral activity. A number of the diarylimidazoles showed excellent inhibition in the adjuvant induced arthritis model (e.g., ED50 = 0.02 mpk for 22 and 34). The diarylimidazoles are also potent inhibitors of carrageenan-induced edema (ED50 = 9-30 mpk) and hyperalgesia (ED50 = 11-40 mpk). Several orally active diarylimidazoles show no GI toxicity in the rat and mouse up to 200 mpk.

Inhibition of monoamine oxidase A (MAO A) is believed to cause antidepressant and possibly antianxiety effects. The previous paper had developed structure-activity relationships (SAR) for in vitro MAO A inhibition by tricyclic N-arylamides. It is shown in this paper that the same in vitro SAR can be carried over to tricyclics whose potentially toxic amide function is replaced by an appropriately substituted imidazoline, a 1,2,4- or 1,3,4-oxadiazole, or an alkylated tetrazole moiety. Dialysis of the inhibitor from the enzyme was used as a measure of reversibility which correlates with a low ability to cause a blood pressure rise with ingested tyramine ("cheese effect").

The second in this series of papers concerns our further investigations into the search for a potent bioavailable acyl-CoA:cholesterol O-acyltransferase (ACAT) inhibitor suitable for the treatment of atherosclerosis. The design, synthesis, and structure-activity relationship for a series of ACAT inhibitors based on the 2-(1,3-dioxan-2-yl)-4,5-diphenyl-1H-imidazole pharmacophore are described. Compounds such as 13a bearing simple alkyl or hydroxymethyl substituents at the 5-position of the 1,3-dioxane ring are potent bioavailable inhibitors of the rat hepatic microsomal enzyme in vitro (IC50 < 100 nM) but are only weak inhibitors of the human hepatic enzyme. We have found however that 1,3-dioxanes substituted at the 5-cis position with pyrazolylalkyl or aminoalkyl groups are potent inhibitors in vitro of human macrophage ACAT, the potency depending on the nature of the terminal heterocycle and the length of the alkyl chain. An ex vivo bioassay herein demonstrates that potent inhibitors such as 13t (IC50 = 10 nM) which contain lipophilic terminal heterocycles do not appear to be systematically available. Less potent but more water soluble compounds such as 13h (IC50 = 60 nM) and 13n (IC50 = 70 nM) are absorbed following oral dosing and achieve plasma levels significantly in excess of their IC50 for ACAT inhibition. These compounds are therefore possible candidates for further investigation as oral antiatherosclerotic agents.

Following the discovery of moderately potent antagonist activity platelet-activating factor (PAF) in 2-methyl-1-phenylimidazo[4,5-c]pyridine (2) (IC50 = 840 nM), 19 derivatives (3-21) were prepared which incorporated various lipophilic groups attached to the phenyl 4-position. Structure-activity relationships were evaluated where PAF antagonist activity was measured in vitro by determining the concentration of compound (IC50) required to inhibit the PAF-induced aggregation of rabbit washed platelets and in vivo by determining the oral dose (ED50) which protected mice from a lethal injection of PAF. [1,5]Benzodiazepines, e.g., 14 (2,3-dihydro-1-methyl-4-[4-(2-methylimidazo[4,5-c] pyrid-1-yl)phenyl]-1H-[1,5]benzodiazepin-2-one) (IC50 = 4.9 nM, Ed50 = 0.03 mg/kg po), were found to possess equivalent or superior potency to the 1,4-dihydropyridine PAF antagonist UK-74,505 (1,4-(2-chlorophenyl)-1,4-dihydro-3-(ethoxycarbonyl)-6-methyl-2- [4-(2-methylimidazo[4,5-c]pyrid-1-yl)phenyl]-5-[N-(2-pyridyl) carbamoyl]pyridine) in vitro and in vivo. Furthermore, a potent benzazepine, 21 (7,8-dichloro-1-methyl-4-[4-(methylimidazo[4,5-c]pyrid-1-yl) phenyl]-2,3,4,5-tetrahydro-1H-1-benzazepin-2-one) (IC50 = 0.5 nM, ED50 = 0.03 mg/kg po), was discovered. These investigations prompted the synthesis and evaluation of additional diazepine derivatives, which are described in the following paper. The relationship between the key PAF antagonist pharmacophores of 2-methyl-1-phenylimidazo[4,5-c]pyridine, a triazolothienodiazepine (WEB2170), and a pyrrolothiazolidine (RP-52,770) is discussed.

In previous papers, we have described the discovery of a new series of compounds, 4,5,6,7-tetrahydro-5-methylimidazo[4,5,1-jk][1,4]benzodiazepin-2(1 H)- ones, TlBO (1 and 1a), with potent anti-HIV-1 activity and the synthesis of analogues to better define the structure-activity relationships (SAR) in terms of changes in substituents at the N-6 position and variations of the five-membered urea ring as well as the seven-membered diazepine ring. This paper describes the synthesis of TlBO analogues with various substitutents on the aromatic ring and their SAR in terms of anti-HIV-1 properties. Substituents on the 8-position furnished the most rewarding results and gave a large improvement in potency versus the parent compound. These included halogen, thiomethyl, and methyl. Analogues like 8-cyano, -methoxy, and -acetylene were equipotent, while 8-amino, -acetylamino, -dimethylamino, and -nitro were inactive (Table 1). Substituents at the 9-position tended to have little effect on activity, and 10-substituents decreased activity. The 8-chloro compound 6a with IC50 = 0.0043 microM is currently under clinical development.

Antifolate inhibitors of thymidylate synthase (TS) have primarily been based on the structure of folic acid. This paper describes the identification and development of novel 6,7-imidazotetrahydroquinoline TS inhibitors by iterative ligand design, synthesis, and crystallographic analysis of protein-inhibitor complexes. Beginning with a high-resolution crystal structure of E. coli TS (TS, EC 2.1.1.45), an imidazotetrahydroquinoline inhibitor was designed de novo to occupy the folate binding pocket. Structural modifications of the initial compound 1h (Ki approximately 5 microM human/E. coli TS) were then made on the basis of feedback from additional cocrystal structures and activity data. An amino group in the 2-position of the imidazole was found to increase the potency of the series by 1-2 orders of magnitude. Other substitutions on the imidazole ring (1-CH3, 2-CH3, 2-NHCH3, 2-SCH3) generally led to weaker inhibition. Additional improvements in activity were obtained by modification of the substituents on the tetrahydroquinoline nitrogen, bringing the Ki of three of the compounds below 15 nM against the human TS enzyme. The compounds were tested for cytotoxicity and were shown to inhibit the growth of three tumor cell lines in vitro.

In the first paper of this series a new structure with anti-HIV-1 activity was disclosed and analogues were synthesized to explore the structure-activity relationship of changes in the substituent (R) attached at the N-6 position of 9. This study describes the syntheses and anti-HIV-1 testing of analogues with variations of the five-membered urea ring of the 4,5,6,7-tetrahydro-5-methylimidazo[4,5,1-jk] [1,4]benzodiazepin-2(1H)-one (TIBO) structures. Although many different rings were synthesized to replace the cyclic urea of TIBO, most were found to be inactive in inhibiting the replication of the HIV-1 virus in MT-4 cells. The exceptions were replacement of the urea oxygen with sulfur or selenium to give the corresponding thio- or selenoureas. These were found to be more active than the oxygen counterparts. A small series of analogues was synthesized and tested which allowed direct comparison of urea and thiourea derivatives. Without exception, the latter were always more active than the former. The most active compound of this series (8d) was found to inhibit the HIV-1 virus with an IC50 of 0.012 microM which is comparable to that of AZT.

A new class of potent antihypertensives has been discovered that exert their effect through blockade of the angiotensin II (AII) receptor. Most AII antagonists reported so far are peptide mimics of the endogenous vasoconstrictor octapeptide angiotensin II. The compounds of this paper are nonpeptides and therefore constitute a new class of potent AII receptor antagonists. Based on the overlap of a conformation of AII with literature lead 3, a hypothesis was developed suggesting the need for an additional acidic functionality to increase the lead's potency. The substitution of an additional carboxylic acid resulted in a 10-fold increase in binding affinity observed for diacid 4. The binding affinities for subsequent compounds were eventually increased 1000-fold over that of the literature leads through a systematic SAR study. Thus the AII receptor binding affinity [IC50 (microM)] of 15 microM for literature lead 1, for example, was increased to 0.018 and 0.012 microM for compounds 33 and 53. A structure-affinity relationship has been found requiring the presence of four key elements for good activity: (1) an additional phenyl ring at the N-benzyl para position of the benzylimidazole nucleus, (2) an acidic functionality at the ortho position of the terminal aromatic ring, (3) a lipophilic side chain at the imidazole 2-position of three to five carbon atoms in length, and (4) a group at the imidazole 5-position capable of hydrogen bonding. The synthesis as well as the pharmacological activity of the compounds in this new series of AII receptor antagonists are presented.

The shape of the active site of the receptor for sweet molecules was previously defined on the basis of a combination of both rigid (saccharins) and flexible (aspartame) molds. In this paper, the sweetness receptor is refined with use of the shapes of 3-anilino-2-styryl-3H-naphtho[1,2-d]imidazolesulfonate (sweet) and of 3-anilino-2-phenyl-3H-naphtho[1,2-d]imidazolesulfonate (tasteless), two large and almost completely rigid tastants. The minimum-energy conformations of the flexible portions of these tastants have been determined by using a detailed conformational analysis based on ab initio calculations. The refined receptor site is still consistent with all previously examined sweet molecules. In order to unequivocally assign the prochiral beta-CH2 protons of the Phe moiety of aspartame, (2S,3S)-[2H]-alpha-L-Asp-L-PheOMe was synthesized and examined by 500-MHz 1H NMR spectroscopy. The results indicate that the minimum-energy conformation for aspartame in water, DMSO-d6, and CDCl3 (as a crown ether complex) is different from that originally proposed (FIIDII instead of FIDII, according to a notation referred to the side chains). Although this conformation is not directly consistent with the shape of the sweet receptor, the interconversion of FIIDII to FIDII was found to require only 1 kcal/mol. Furthermore, a 120-ps molecular dynamics simulation in vacuo confirms the high flexibility of aspartame and the accessibility of the FIDII conformer whose topology is fully consistent with our model.

The structure-activity relationships of a series of 4,5-dihydro-6-[4-(1H-imidazol-1-yl)phenyl]-3(2H)-pyridazinones and related compounds were investigated for the in vivo inhibition of different forms of cyclic nucleotide phosphodiesterase (PDE) isolated from guinea pig ventricular muscle. With few exceptions, these 4,5-dihydropyridazinones were potent inhibitors of cardiac type III phosphodiesterase, which is a low Km, cyclic AMP specific form of the enzyme. The inhibitory effects on cardiac type I and type II phosphodiesterase, both of which hydrolyze cyclic AMP as well as cyclic GMP, were minimal. The most selective PDE III inhibitor was CI-930 (10), the 5-methyl analogue of imazodan (CI-914, 1), with an IC50 of 0.6 microM. The most potent inhibitor of PDE III was the 4,5,6,7-tetrahydrobenzimidazole analogue of 10 (31), with an IC50 of 0.15 microM. This paper describes the structural features that impart both selectivity for inhibiting type III phosphodiesterase and potency of inhibition. In addition, correlations between in vitro PDE inhibitory potency, in vivo positive inotropic potency, and physicochemical properties are discussed.

Impromidine (1) is a potent and selective histamine H2 receptor agonist and its structure comprises a strongly basic guanidine group containing two different imidazole-containing side chains. In this paper we report the synthesis of analogues in which both of the side chains and the guanidine group are modified and tested as agonists or antagonists at histamine H2 receptors on guinea pig atrium. A protonated amidine group linked by a chain of three carbon atoms to a tautomeric imidazole ring appears to be an essential feature for agonist activity and it is suggested that the second imidazole-containing side chain in impromidine mainly contributes toward affinity for histamine H2 receptors.

N-{trans-3-[(5-Cyano-6-methylpyridin-2-yl)oxy]-2,2,4,4-tetramethylcyclobutyl}imidazo[1,2-a]pyrimidine-3-carboxamide (1) was recently identified as a full antagonist of the androgen receptor, demonstrating excellent in vivo tumor growth inhibition in castration-resistant prostate cancer (CRPC). However, the imidazo[1,2-a]pyrimidine moiety is rapidly metabolized by aldehyde oxidase (AO). The present paper describes a number of medicinal chemistry strategies taken to avoid the AO-mediated oxidation of this particular system. Guided by an AO protein structure-based model, our investigation revealed the most probable site of AO oxidation and the observation that altering the heterocycle or blocking the reactive site are two of the more effective strategies for reducing AO metabolism. These strategies may be useful for other drug discovery programs. [ABSTRACT FROM AUTHOR]