Synthesis and biological study of 3-(phenylsulfonyl)thieno[2,3-e][1,2,3]triazolo[1,5-a]pyrimidines as potent and selective serotonin 5-HT6 receptor antagonists

A number of 3-(phenylsulfonyl)thieno[2,3-e][1,2,3]triazolo[1,5-a]pyrimidines were prepared and their 5-HT₆ receptor binding affinity and ability to inhibit the functional cellular responses to serotonin were evaluated. 3-[(3-Chlorophenyl)sulfonyl]-N-(tetrahydrofuran-2-ylmethyl)thieno[2,3-e][1,2,3]triazolo[1,5-a]pyrimidin-5-amine 2{5,26} appeared to be the most active in a functional assay (IC₅₀ = 29.0 nM) and 3-(phenylsulfonyl)-N-(2-thienylmethyl) thieno[2,3-e][1,2,3]triazolo[1,5-a]pyrimidin-5-amine 2{1,28} demonstrated the greatest affinity in a 5-HT₆ receptor radioligand binding assay (K_i = 1.7 nM). A screening of 5-HT_2A and 5-HT_2B receptor affinity revealed that 3-(phenylsulfonyl)thieno[2,3-e][1,2,3]triazolo[1,5-a]pyrimidines are highly selective 5-HT₆ receptor ligands.     

Discovery and SAR of a novel series of metabotropic glutamate receptor 5 positive allosteric modulators with high ligand efficiency

We report the optimization of a series of novel metabotropic glutamate receptor 5 (mGlu₅) positive allosteric modulators (PAMs) from a 5,6-bicyclic class of dihydropyrazolo[1,5-a]pyridin-4(5H)-ones containing a phenoxymethyl linker. Studies focused on a survey of non-amide containing hydrogen bond accepting (HBA) pharmacophore replacements. A highly potent and selective PAM, 2-(phenoxymethyl)-6,7-dihydropyrazolo[1,5-a]pyridin-4(5H)-one (11, VU0462054), bearing a simple ketone moiety, was identified (LE = 0.52, LELP = 3.2). In addition, hydroxyl, difluoro, ether, and amino variations were examined. Despite promising lead properties and exploration of alternative core heterocycles, linkers, and ketone replacements, oxidative metabolism and in vivo clearance remained problematic for the series.     

Scaffold-switching: An exploration of 5,6-fused bicyclic heteroaromatics systems to afford antituberculosis activity akin to the imidazo[1,2-a]pyridine-3-carboxylates

A set of 5,6-fused bicyclic heteroaromatic scaffolds were investigated for their in vitro anti-tubercular activity versus replicating and non-replicating strains of Mycobacterium tuberculosis (Mtb) in an attempt to find an alternative scaffold to the imidazo[1,2-a]pyridine and imidazo[1,2-a]pyrimidines that were previously shown to have potent activity against replicating and drug resistant Mtb. The five new bicyclic heteroaromatic scaffolds explored in this study include a 2,6-dimethylimidazo[1,2-b]pyridazine-3-carboxamide (7), a 2,6-dimethyl-1H-indole-3-carboxamide (8), a 6-methyl-1H-indazole-3-carboxamide (9), a 7-methyl-[1,2,4]triazolo[4,3-a]pyridine-3-carboxamide (10), and a 5,7-dimethyl-[1,2,4]triazolo[1,5-a]pyrimidine-2-carboxamide (11). Additionally, imidazo[1,2-a]pyridines isomers (2 and 12) and a homologous imidazo[1,2-a]pyrimidine isomer (6) were prepared and compared. Compounds 2 and 6 were found to be the most potent against H₃₇Rv Mtb (MIC’s of 0.1 μM and 1.3 μM) and were inactive (MIC >128 μM) against Staphylococcus aureus, Escherichia coli and Candida albicans. Against other non-tubercular mycobacteria strains, compounds 2 and 6 had activity against Mycobacterium avium (16 and 122 μM, respectively), Mycobacterium kansasii (4 and 19 μM, respectively), Mycobacterium bovis BCG (1 and 8 μM, respectively) while all the other scaffolds were inactive (>128 μM).     

Emerging antifungal azoles and effects on Magnaporthe grisea

Derivatives of pyrazolo[1,5-a][1, 3, 5]triazine-2,4-dione,pyrazolo[1,5-c][1, 3, 5]thiadiazine-2-one, pyrazolo[3,4-d][1, 3]thiazine-4-one, and pyrazolo[3,4-d][1, 3]thiazine-4-thione were screened for antifungal activity against the causal agent of rice blast disease, Magnaporthe grisea. The compounds were tested at doses ranging from 10 to 200 μg ml⁻¹, using the commercial fungicide tricyclazole as reference compound. All triazine derivatives inhibited the growth and pigmentation of the mycelia less effectively than tricyclazole. The thiadiazine derivatives proved to be more effective than their triazine counterparts, but only 4-(butylimino)-7-methylpyrazolo[1,5-c][1,3,5]thiadiazine-2-one (2h) and 4-(cyclohexylimino)-7-methylpyrazolo[1,5-c][1,3,5]thiadiazine-2-one (2j) were more effective than tricyclazole. Pyrazolo[3,4-d][1,3]thiazine-4-one derivatives were active only at the highest doses, whereas members of the pyrazolo[3,4-d][1,3]thiazine-4-thione series inhibited fungal growth at the lowest concentrations used, at which tricyclazole had no effect. A dose-dependent mechanism might be responsible for this effect, with lipophilicity as the governing factor. Within a given set, the presence of a cyclohexyl or an n-butyl group generally increased antifungal activity, with respect to both growth inhibition and cell de-pigmentation of the mycelium, suggesting that a higher lipophilicity might improve transport inside the cells. SEM and TEM of M. grisea hyphae showed that treatment with the most active substance (2h) caused significant ultrastructural effects, particularly on the endomembrane system, suggesting a mechanism of action similar to that of most azole fungicides. Dissimilarities were also observed, with no alterations of the cell wall evident. In conclusion, several compounds showed greater inhibition than tricyclazole, and therefore provide useful new chemistry for control of M. grisea infections.     

Design and synthesis of novel 2-methyl-4,5-substitutedbenzo[f]-3,3a,4,5-tetrahydro-pyrazolo[1,5-d][1,4]oxazepin-8(7H)-one derivatives as telomerase inhibitors

Eight novel 4,5-tetrahydropyrazolo[1,5-d][1,4]oxazepine derivatives have been synthesized and purified to be screened for anticancer activity. By a modified TRAP assay, some titled compounds were tested against telomerase, and compound 4a showed the most potent inhibitory activity with IC₅₀ value at 0.78 ± 0.22 μM. Western blot assays showed that compounds 4a and 4b could inhibit expression of Cyclin D1, TERT, phospho-AKT and PI3K/AKT pathway.     

A hit to lead discovery of novel N-methylated imidazolo-, pyrrolo-, and pyrazolo-pyrimidines as potent and selective mTOR inhibitors

A series of N-7-methyl-imidazolopyrimidine inhibitors of the mTOR kinase have been designed and prepared, based on the hypothesis that the N-7-methyl substituent on imidazolopyrimidine would impart selectivity for mTOR over the related PI3Kα and δ kinases. The corresponding N-Me substituted pyrrolo[3,2-d]pyrimidines and pyrazolo[4,3-d]pyrimidines also show potent mTOR inhibition with selectivity toward both PI3α and δ kinases. The most potent compound synthesized is pyrazolo[4,3-d]pyrimidine 21c. Compound 21c shows a K_i of 2 nM against mTOR inhibition, remarkable selectivity (>2900×) over PI3 kinases, and excellent potency in cell-based assays.     

Design,synthesis, assessment,and molecular docking of novel pyrrolopyrimidine (7-deazapurine) derivatives as non-nucleoside hepatitis C virus NS5B polymerase inhibitors

Hepatitis C virus (HCV) infection is highly persistent and presents an unmet medical need requiring more effective treatment options. This has spurred intensive efforts to discover novel anti-HCV agents. The RNA-dependent RNA polymerase (RdRp), NS5B of HCV, constitutes a selective target for drug discovery due to its absence in human cells; also, it is the centerpiece for viral replication. Here, we synthesized novel pyrrole, pyrrolo[2,3-d]pyrimidine and pyrrolo[3,2-e][1,2,4]triazolo[4,3-c]pyrimidine derivatives. The non-toxic doses of these compounds on Huh 7.5 cell line were determined and their antiviral activity against HCVcc genotype 4a was examined. Compounds 7j, 7f, 5c, 12i and 12f showed significant anti HCV activity. The percent of reduction for the non-toxic doses of 7j, 7f, 5c, 12i and 12f were 90%, 76.7 ± 5.8%, 73.3 ± 5.8%, 70% and 63.3 ± 5.8%, respectively. The activity of these compounds was interpreted by molecular docking against HCV NS5B polymerase enzyme.     

Synthesis,molecular modeling and SAR study of novel pyrazolo[5,1-f][1,6]naphthyridines as CB2 receptor antagonists/inverse agonists

Pyrazolo[5,1-f][1,6]naphthyridine-carboxamide derivatives were synthesized and evaluated for the affinity at CB₁ and CB₂ receptors. Based on the AgOTf and proline-cocatalyzed multicomponent methodology, the ethyl 5-(p-tolyl)pyrazolo[5,1-f][1,6]naphthyridine-2-carboxylate (12) and ethyl 5-(2,4-dichlorophenyl)pyrazolo[5,1-f][1,6]naphthyridine-2-carboxylate (13) intermediates were synthesized from the appropriate o-alkynylaldehydes, p-toluenesulfonyl hydrazide and ethyl pyruvate. Most of the novel compounds feature a p-tolyl (8a–i) or a 2,4-dichlorophenyl (8j) motif at the C₅-position of the tricyclic pyrazolo[5,1-f][1,6]naphthyridine scaffold. Structural variation on the carboxamide moiety at the C₂-position includes basic monocyclic, terpenoid and adamantine-based amines. Among these derivatives, compound 8h (N-adamant-1-yl-5-(p-tolyl)pyrazolo[5,1-f][1,6]naphthyridine-2-carboxamide) exhibited the highest CB₂ receptor affinity (K_i = 33 nM) and a high degree of selectivity (K_iCB₁/K_iCB₂ = 173:1), whereas a similar trend in the near nM range was seen for the bornyl analogue (compound 8f, K_i = 53 nM) and the myrtanyl derivative 8j (K_i = 67 nM). Effects of 8h, 8f and 8j on forskolin-stimulated cAMP levels were determined, showing antagonist/inverse agonist properties for such compounds. Docking studies conducted for these derivatives and the reference antagonist/inverse agonist compound 4 (SR144528) disclosed the specific pattern of interactions probably related to the pyrazolo[5,1-f][1,6]naphthyridine scaffold as CB₂ inverse agonists.     

Synthesis,anticancer activity and mitochondrial mediated apoptosis inducing ability of 2,5-diaryloxadiazole–pyrrolobenzodiazepine conjugates

A series of 2,5-diaryloxadiazole linked pyrrolo[2,1-c][1,4]benzodiazepine conjugates have been prepared and evaluated for their anticancer activity. These conjugates have shown promising activity with GI₅₀ values ranging from <0.1 to 0.29 μΜ. It is observed that some of these conjugates particularly 4a, 4d, 4i and 4l exhibit significant anticancer activity. Some detailed biological assays relating to the cell cycle aspects associated to Bax and caspases have been examined with a view to understand the mechanism of action of these conjugates.     

1,5-Benzodiazepine inhibitors of HCV NS5B polymerase

Optimization through parallel synthesis of a novel series of hepatitis C virus (HCV) NS5B polymerase inhibitors led to the identification of (R)-11-(4-benzyloxy-2-fluorophenyl)-6-hydroxy-3,3-dimethyl-10-(6-methylpyridine-2-carbonyl)-2,3,4,5,10,11-hexahydro-dibenzo[b,e][1,4]diazepin-1-one 11zc and (R)-11-(4-benzyloxy-2-fluorophenyl)-6-hydroxy-3,3-dimethyl-10-(2,5-dimethyloxazol-4-carbonyl)-2,3,4,5,10,11-hexahydro-dibenzo[b,e][1,4]diazepin-1-one 11zk as potent (replicon EC₅₀ = 400 nM and 270 nM, respectively) and selective (CC₅₀ > 20 μM) inhibitors of HCV replication. These data warrant further lead-optimization efforts.     

Synthesis and evaluation of 8-amino-[1,2,4]triazolo[4,3-a]pyridin-3(2H)-one derivatives as glycogen synthase kinase-3 (GSK-3) inhibitors

New potent glycogen synthase kinase-3 (GSK-3) inhibitors, 8-amino-[1,2,4]triazolo[4,3-a]pyridin-3(2H)-one derivatives, were designed by modeling, synthesized and evaluated in vitro. Compound 17c showed good potency in enzyme and cell-based assays (IC₅₀ = 111 nM, EC₅₀ = 1.78 μM). Moreover, it has demonstrated desirable water solubility, PK profile, and moderate brain penetration.     

Synthesis and in vitro evaluation of [18F]BMS-754807: A potential PET ligand for IGF-1R

Radiosynthesis and in vitro evaluation of [¹⁸F](S)-1-(4-((5-cyclopropyl-1H-pyrazol-3-yl)amino)pyrrolo[2,1-f][1,2,4]triazin-2-yl)-N-(6-fluoropyridin-3-yl)-2-methylpyrrolidine-2-carboxamide ([¹⁸F]BMS-754807 or [¹⁸F]1) a specific IGF-1R inhibitor was performed. [¹⁸F]1 demonstrated specific binding in vitro to human cancer tissues. Synthesis of reference standard 1 and corresponding bromo derivative (1a), the precursor for radiolabeling were achieved from 2,4-dichloropyrrolo[2,1-f][1,2,4]triazine (4) in three steps with 50% overall yield. The radioproduct was obtained in 8% yield by reacting 1a with [¹⁸F]TBAF in DMSO at 170 °C at high radiochemical purity and specific activity (1–2 Ci/μmol, N = 10). The proof of concept of IGF-IR imaging with [¹⁸F]1 was demonstrated by in vitro autoradiography studies using pathologically identified surgically removed grade IV glioblastoma, breast cancer and pancreatic tumor tissues. These studies indicate that [¹⁸F]1 can be a potential PET tracer for monitoring IGF-1R.     

Synthesis and biological activity of 5-styryl and 5-phenethyl-substituted 2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indoles

Syntheses, biological evaluation, and structure–activity relationships for a series of novel 5-styryl and 5-phenethyl analogs of dimebolin are disclosed. The novel derivatives and dimebolin share a broad spectrum of activities against therapeutically relevant targets. Among all synthesized derivatives, 2,8-dimethyl-5-[(Z)-2-phenylvinyl]-2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole and its 5-phenethyl analog are the most potent blockers of 5-HT₇, 5-HT₆, 5-HT_2C, Adrenergic α₂ and H₁ receptors. The general affinity rank order towards the studied receptors was Z-3(2) > 4(2) ? 4(3) ? dimebolin, all of them having highest affinities to 5-HT₇ receptors.     

Synthesis and anticancer activity of novel 4-morpholino-7,8-dihydro-5H-thiopyrano[4,3-d]pyrimidine derivatives bearing chromone moiety

Herein, we designed and synthesized of a novel series of 7,8-dihydro-5H-thiopyrano[4,3-d]pyrimidine derivatives bearing chromone moiety (10a–j, 13a–j). All the compounds were evaluated for the IC₅₀ values against five cancer cell lines (A549, PC-3, MCF-7, Hela and HepG2). Seven of the target compounds exhibited moderate to excellent cytotoxicity. For these compounds, we tested their inhibitory activities against mTOR kinase, and four of them were tested their inhibitory activities against PI3Kα kinase in further. The results indicated that the optimized compound 10j showed excellent inhibitory activity and cytotoxicity against mTOR kinase, PI3Kα kinase and five cancer cell lines with IC₅₀ values of 1.1 μM, 0.92 μM and 8.77–14.3 μM. Structure–activity relationships (SARs) and docking studies indicated that the thiopyrano[4,3-d]pyrimidine scaffolds exerted little effect on antitumor activities of target compounds. Substitutions of chromone moiety at C-6 position with carboxyl were benefit to the antitumor activities.     

Synthesis and in vitro anti-hepatitis B virus activity of 6H-[1]benzothiopyrano[4,3-b]quinolin-9-ols

A series of novel 6H-[1]benzothiopyrano[4,3-b]quinoline derivatives were prepared and evaluated for their anti-hepatitis B virus (HBV) activity and cytotoxicity in human hepatoblastoma-derived liver Hep-G2 cells. Compounds 10g, 10h, 10j, 10l and 10o were found to be potent anti-HBV compounds with IC₅₀ values less than 50 μM. The most promising compound was 10l, with an IC₅₀ value of 14.7 μM and a SI value of 12.4. This is the first report of the anti-HBV effects of 6H-[1]benzothiopyrano[4,3-b] quinolin-9-ols.     

8-Substituted 1,3-dimethyltetrahydropyrazino[2,1-f]purinediones: Water-soluble adenosine receptor antagonists and monoamine oxidase B inhibitors

Multitarget approaches, i.e., addressing two or more targets simultaneously with a therapeutic agent, are hypothesized to offer additive therapeutic benefit for the treatment of neurodegenerative diseases. Validated targets for the treatment of Parkinson’s disease are, among others, the A_2A adenosine receptor (AR) and the enzyme monoamine oxidase B (MAO-B). Additional blockade of brain A₁ ARs may also be beneficial. We recently described 8-benzyl-substituted tetrahydropyrazino[2,1-f]purinediones as a new lead structure for the development of such multi-target drugs. We have now designed a new series of tetrahydropyrazino[2,1-f]purinediones to extensively explore their structure–activity-relationships. Several compounds blocked human and rat A₁ and A_2AARs at similar concentrations representing dual A₁/A_2A antagonists with high selectivity versus the other AR subtypes. Among the best dual A₁/A_2AAR antagonists were 8-(3-(4-chlorophenyl)propyl)-1,3-dimethyl-6,7,8,9-tetrahydropyrazino[2,1-f]purine-2,4(1H,3H)-dione (41, K_i human A₁: 65.5 nM, A_2A: 230 nM; K_i rat A₁: 352 nM, A_2A: 316 nM) and 1,3-dimethyl-8-((2-(thiophen-2-yl)thiazol-4-yl)methyl)-6,7,8,9-tetrahydropyrazino[2,1-f]purine-2,4(1H,3H)-dione (57, K_i human A₁: 642 nM, A_2A: 203 nM; K_i rat A₁: 166 nM, A_2A: 121 nM). Compound 57 was found to be well water-soluble (0.7 mg/mL) at a physiological pH value of 7.4. One of the new compounds showed triple-target inhibition: (R)-1,3-dimethyl-8-(2,1,3,4-tetrahydronaphthalen-1-yl)-6,7,8,9-tetrahydropyrazino[2,1-f]purine-2,4(1H,3H)-dione (49) was about equipotent at A₁ and A_2AARs and at MAO-B (K_i human A₁: 393 nM, human A_2A: 595 nM, IC₅₀ human MAO-B: 210 nM) thus allowing future in vivo explorations of the intended multi-target approach.     

Synthesis,anti-thymidine phosphorylase activity and molecular docking of 5-thioxo-[1,2,4]triazolo[1,5-a][1,3,5]triazin-7-ones

In our lead finding program, a series of 5-thioxo-[1,2,4]triazolo[1,5-a][1,3,5]triazin-7-ones and their 5-thio-alkyl derivatives were designed and synthesized which contained different substituents at ortho-position of 2-phenyl ring attached to the fused ring structure. The preliminary pharmacological evaluation demonstrated that the synthesized compounds exhibited a varying degree of inhibitory activity towards thymidine phosphorylase (TP), comparable to reference compound, 7-Deazaxanthine (7-DX, 2) (IC₅₀ value = 42.63 μM). The study also inferred that the ortho-substituted group at the phenyl ring and 5-thio-alkyl moiety imparted steric hindrance effects in the binding site of the enzyme, leading to a reduced inhibitory response. In addition, compound 3a was identified as a mixed-type inhibitor of TP. Moreover, computational docking study was performed to illustrate the important structural information on the plausible ligand-enzyme binding interactions.     

Remarkable enhancement in the DNA-binding ability of C2-fluoro substituted pyrrolo[2,1-c][1,4]benzodiazepines and their anticancer potential

C2-Fluoro substituted DC-81, and its dimers that comprise of two C2-fluoro substituted DC-81 subunits tethered to their C8-position through simple alkane spacers as well as piperazine moiety side-armed with symmetrical alkyloxy spacers have been designed and synthesized. These fluoro substituted pyrrolo[2,1-c][1,4]benzodiazepines have shown remarkable DNA-binding ability and most of them possess promising anticancer activity, having GI₅₀ values in micromolar to nanomolar concentration range. DNA thermal denaturation studies show that some of these compounds (14a–c and 15) increase the ΔT_m values in the range of 28.9–38 °C, and this is further confirmed by the restriction endonuclease studies. This study illustrates the importance of introducing fluoro substitution at the C2-position apart from the incorporation of a piperazine ring in between the alkyloxy linker for enhancement of the DNA-binding ability in comparison to DSB-120 and SJG-136 (ΔT_m = 10.2 and 25.7 °C). Moreover, the variations in the DNA-binding ability with respect to fluoro substitution in this class of dimers has been investigated by molecular modeling studies. Some representative C2-fluoro substituted dimers (8a and 14a) have also exhibited significant anticancer activity in the 60 cancer cell line assay of the National Cancer Institute (NCI).     

Synthesis,pharmacological studies and molecular modeling of some tetracyclic 1,3-diazepinium chlorides

Seven new 1,3-diazepinium chlorides exhibiting some structural similarities to the 1,4-benzodiazepines were synthesized. In a Hippocratic screen using mice, three of these salts, 3-methoxy-6-oxo-7,13-dihydro-6H-benzofuro[2,3-e]pyrido[1,2-a][1,3]diazepin-12-ium chloride (8a), 3-methoxy-9-methyl-6-oxo-7,13-dihydro-6H-benzofuro[2,3-e]pyrido[1,2-a][1,3]diazepin-12-ium chloride (8c) and 3-methoxy-11-methyl-6-oxo-7,13-dihydro-6H-benzofuro[2,3-e]pyrido[1,2-a][1,3]diazepin-12-ium chloride (8e) were examined for their effect on the central nervous system, and their activities compared to that of diazepam. On their own, salts 8a, 8c and 8e solicited no sedative effects on the behaviour of the animals. However, they elicited significant effects in combination with diazepam on diazepam-induced activities such as decreased motor activity, ataxia and loss of righting reflex. Compounds 8a and 8c were fitted into the pharmacophore/receptor model developed by Cook et al. with interaction at the L₁, H₁ and A₂ sites indicating that they are potential inverse agonists of the Bz receptor. The compounds displayed some affinity for the α1 isoform of the GABA_A/BzR (L_Di interaction) but are non-selective for α5 (no L₂ interaction). Results of binding affinity studies showed that compound 8a is mildly selective for the α1 receptor although not very potent (K_i = 746.5 nM). The significant potentiation of diazepam-induced ataxia and decreased motor activity by compounds 8a and 8c in the Hippocratic screen may be associated with α1 selectivity.     

1,4-Dihydropyrazolo[4,3-d]imidazole phenyl derivatives: A novel type II Raf kinase inhibitors

The synthesis of a novel series of 1,4-dihydropyrazolo[4,3-d]imidazole phenyl derivatives 1a–b, 2a–v and their antiproliferative activities against A375P and WM3629 human melanoma cell line were described. Most compounds showed competitive antiproliferative activities to sorafenib, the reference standard. Among them, pyrazoloimidazole phenyl urea compounds 2a, 2d, 2g, 2i, 2t exhibited potent activities on WM3629 cell lines (IC₅₀ = 0.56–0.86 μM). Especially, 2t was found to be a potent and selective C-Raf inhibitor, showing a possibility as melanoma therapeutics.