Chemical–Genetic Profiling of Imidazo[1,2-a]pyridines and -Pyrimidines Reveals Target Pathways Conserved between Yeast and Human Cells

Small molecules have been shown to be potent and selective probes to understand cell physiology. Here, we show that imidazo[1,2-a]pyridines and imidazo[1,2-a]pyrimidines compose a class of compounds that target essential, conserved cellular processes. Using validated chemogenomic assays in Saccharomyces cerevisiae, we discovered that two closely related compounds, an imidazo[1,2-a]pyridine and -pyrimidine that differ by a single atom, have distinctly different mechanisms of action in vivo. 2-phenyl-3-nitroso-imidazo[1,2-a]pyridine was toxic to yeast strains with defects in electron transport and mitochondrial functions and caused mitochondrial fragmentation, suggesting that compound 13 acts by disrupting mitochondria. By contrast, 2-phenyl-3-nitroso-imidazo[1,2-a]pyrimidine acted as a DNA poison, causing damage to the nuclear DNA and inducing mutagenesis. We compared compound 15 to known chemotherapeutics and found resistance required intact DNA repair pathways. Thus, subtle changes in the structure of imidazo-pyridines and -pyrimidines dramatically alter both the intracellular targeting of these compounds and their effects in vivo. Of particular interest, these different modes of action were evident in experiments on human cells, suggesting that chemical–genetic profiles obtained in yeast are recapitulated in cultured cells, indicating that our observations in yeast can: (1) be leveraged to determine mechanism of action in mammalian cells and (2) suggest novel structure–activity relationships.     

Spiro(imidazo[1,2-a]pyrano[2,3-c]pyridine-9-indenes) as inhibitors of gastric acid secretion

Asymmetric and symmetric spiro(imidazo[1,2-a]pyrano[2,3-c]pyridine-9-indenes) were prepared using a synthetic approach that comprised a cross-metathesis reaction and an acid-catalyzed cycloisomerisation as key steps. The target compounds constitute potent inhibitors of the gastric proton pump enzyme with inhibitory activity comparable to potassium-competitive acid blockers (P-CABs) belonging to the known 9-aryl-7H-8,9-dihydropyrano[2,3-c]imidazo[1,2-a]pyridine series. Spiro(imidazo[1,2-a]pyrano[2,3-c]pyridine-9,2′-indenes) represent the first example for P-CABs, in which the distance between the heterocyclic scaffold and the aryl residue has been modified, and are promising candidates for further development as anti-ulcer drugs.     

Synthesis and SAR study of new phenylimidazole-pyrazolo[1,5-c]quinazolines as potent phosphodiesterase 10A inhibitors

A series of phenylimidazole-pyrazolo[1,5-c]quinazolines 1a-q was designed, synthesized and characterised as a novel class of potent phophodiesterase 10A (PDE10A) inhibitors. In this series, 2,9-dimethyl-5-(2-(1-methyl-4-phenyl-1H-imidazol-2-yl)ethyl)pyrazolo[1,5-c]quinazoline (1q) showed the highest affinity for PDE10A enzyme (IC₅₀ = 16 nM).     

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).     

Design and synthesis of 2,6-disubstituted-8-amino imidazo[1,2a]pyridines,a promising privileged structure

Imidazo[1,2a]pyridines have gained much interest in the field of medicinal chemistry research. In the aim of accessing new privileged structure, we decided to design and synthesize 8-aminated-imidazo[1,2a]pyridines substituted on positions 2 and 6. This scaffold, rarely found in the literature, was obtained via palladium-catalyzed coupling reactions (Suzuki reaction or N-hydroxysuccinimidyl activated ester method) and tested on adenosine receptor A_2A. We demonstrated how incorporation of an exocyclic amine enhanced affinity towards this receptor while maintaining low cytotoxicity.     

2-Phenylimidazo[1,2-b]pyridazine derivatives highly active against Haemonchus contortus

A series of 2-phenylimidazo[1,2-b]pyridazine derivatives were synthesized and evaluated for their in vitro anthelmintic activity against Haemonchus contortus. The most active compounds had in vitro LD₉₉ values of 30 nM, which is comparable to that of the benchmark commercial nematocide, Ivermectin.     

Synthesis and anti-tumor activity of novel ethyl 3-aryl-4-oxo-3,3a,4,6-tetrahydro-1H-furo[3,4-c]pyran-3a-carboxylates

A series of ethyl 3-aryl-4-oxo-3,3a,4,6-tetrahydro-1H-furo[3,4-c]pyran-3a-carboxylates were prepared through the metal-catalyzed domino reaction of alkylidene malonates and 1,4-butynediol under a one-pot reaction condition at room temperature. Their in vitro anti-proliferative activities were subsequently evaluated in A549, QGY and HeLa cells. The majority of the compounds showed potent anti-tumor activity against HeLa cells. In particular, compound 3l was the most potent compound with IC₅₀ value of 5.4 μM. For the first time, the X-ray structure of the anti-tumor ethyl 3-aryl-4-oxo-3,3a,4,6-tetrahydro-1H-furo[3,4-c]pyran-3a-carboxylates is determined.     

Bactericidal Activity of an Imidazo[1, 2-a]pyridine Using a Mouse M. tuberculosis Infection Model

Tuberculosis remains a global threat due in part to the long treatment regimen and the increased prevalence of drug resistant M. tuberculosis strains. Therefore, new drug regimens are urgently required to combat this deadly disease. We previously synthesized and evaluated a series of new anti-tuberculosis compounds which belong to the family of imidazo[1,2-a]pyridines. This family of compounds showed low nM MIC (minimal inhibitory concentration) values against M. tuberculosis in vitro. In this study, a derivative of imidazo[1,2-a]pyridines, (N-(4-(4-chlorophenoxy)benzyl)-2,7-dimethylimidazo[1,2-a]pyridine-3-carboxamide) (ND-09759), was selected as a promising lead compound to determine its protective efficacy using a mouse infection model. Pharmacokinetic analysis of ND-09759 determined that at a dosage of 30 mg/kg mouse body weight (PO) gave a maximum serum drug concentration (C_max) of 2.9 µg/ml and a half-life of 20.1 h. M. tuberculosis burden in the lungs and spleens was significantly decreased in mice treated once daily 6 days per week for 4-weeks with ND-09759 compared to untreated mice and this antibiotic activity was equivalent to isoniazid (INH) and rifampicin (RMP), two first-line anti-TB drugs. We observed slightly higher efficacy when using a combination of ND-09759 with either INH or RMP. Finally, the histopathological analysis revealed that infected mice treated with ND-09759 had significantly reduced inflammation relative to untreated mice. In conclusion, our findings indicate ND-09759 might be a potent candidate for the treatment of active TB in combination with current standard anti-TB drugs.     

Synthesis and antitubercular evaluation of amidoalkyl dibenzofuranols and 1H-benzo[2,3]benzofuro[4,5-e][1,3]oxazin-3(2H)-ones

A new class of amidoalkyl dibenzofuranols and 1H-benzo[2,3]benzofuro[4,5-e][1,3]oxazin-3(2H)-ones was synthesized in very good yields through polyphosphoric acid supported on silica (PPA-SiO₂) catalyzed one-pot three component condensation of 2-dibenzofuranol; aromatic aldehydes and acetamide or benzamide or urea under solvent free conditions. At 125 °C the reaction led to the formation of amidoalkyl dibenzofuranols 5a-k where as at 160 °C cyclization take place to give oxazin-3(2H)-one analogues 6a-e. Screening all the 16 compounds for in vitro antimycobacterial activity against Mycobacterium tuberculosis H37Rv (MTB) resulted 1-((4-chlorophenyl)(2-hydroxydibenzo[b,d]furanyl)methyl)urea 5h; 1-((4-bromophenyl)(2-hydroxydibenzo[b,d]furanyl)methyl)urea 5i; 1-phenyl-1H-benzo[2,3]benzo furo[4,5-e][1,3]oxazin-3(2H)-one 6a (MIC 3.13 μg/mL) and 1-(4-chlorophenyl)-1H-benzo[2,3]benzofuro[4,5-e][1,3]oxazin-3(2H)-one 6b; 1-(4-bromophenyl)-1H-benzo[2,3]benzofuro [4,5-e][1,3]oxazin-3(2H)-one 6c (MIC 1.56 μg/mL) as most active antitubercular agents.     

Novel bifunctional alkylating agents, 5,10-dihydropyrrolo[1,2-b]isoquinoline derivatives, synthesis and biological activity

A series of linear pyrrolo[1,2-b]isoquinoline derivatives was synthesized for antitumor evaluation. The preliminary antitumor studies reveal that both bis(hydroxymethyl) and their bis(alkylcarbamate) derivatives show significant antitumor activity in inhibiting various human tumor cell growth in vitro. 1,2-Bis(hydroxymethyl)-3-methyl-5,10-dihydropyrrolo[1,2-b]isoquinoline (20a) was selected for antitumor studies in animal models. The results show that this agent can induce complete tumor remission or significant suppression in nude mice bearing human breast (MX-1) xenograft and ovarian (SK-OV-3) xenografts, respectively. Alkaline agarose gel shifting assay showed that 20a is able to cross-link with DNA. Studies on the cell cycle inhibition revealed that this agent induces cell arrest at G2/M phase. The results warrant further antitumor investigation against other human tumor growth in animal models.     

Design and synthesis of spirotryprostatin-inspired diketopiperazine systems from prolyl spirooxoindolethiazolidine derivatives

Based on the spirotryprostatin-A structure, we designed, synthesized, and evaluated different series of compounds belonging to the diketopiperazine structural class as potential cell cycle modulators and cytotoxic agents. Starting from the spirooxoindolthiazolidine scaffold, amide coupling with Pro derivatives and intramolecular cyclization reactions are suitable synthetic methods to generate chemically diverse diketopiperazine system, such as hexahydropyrrolo[1,2-a][1,3]thiazolo[3,2-d]pyrazine-5,10-dione (structure I), hexahydropyrrolo[1,2-a] [1,3]thiazolo[3,4-d]pyrazine-5,10-dione (structure II) and spiroindol-2-one[3,3′]hexahydro-5,10H-pyrrolo[1,2-a][1,3]thiazolo[3,4-d]pyrazine-5,10-dione (structure III). Some of these compounds, especially those who belong to the series I and II, showed interesting cytotoxic activity.     

Platinum(II) diphosphine complexes as catalysts for the Baeyer-Villiger oxidation of ketones: Is it possible to increase the concentration of the active species?

The synthesis and characterization of new bis-aquo platinum(II) complexes of the type [Pt(H₂O)(P-P)][OTf]₂ (OTf = triflate anion), in which the diphosphine P-P is a series of 1,n-bis-diphenyphosphinoalkanes (1a-d, with n = 1-4), 1,2-bis-(di-n-fluorophenylphosphino)ethanes (2a-c, with n = 2, 4-5) and 1,2-bis-dialkylphosphinoethanes (3a-e), where the alkyl substituents at phosphorus have been systematically changed (dmpe) (3a), (depe) (3b), (dippe) (3c), (dcype) (3d) are reported. These complexes were used as catalysts in the Baeyer-Villiger oxidation of 2-methylcyclohexanone, 2-methylcyclopentanone and cyclobutanone with 35% hydrogen peroxide as an environmentally friendly oxidant. The reactions were performed at 25 °C in a chlorinated solvent/H₂O two-phase system. All the investigated catalysts performed better than the corresponding dimeric complexes of general formula [Pt(μ-OH)(P-P)]₂[BF₄]₂ as a consequence of the positive effect imparted by the triflate counter-anion on catalysts speciation.     

New imidazo[1,2-a]pyridines carrying active pharmacophores: Synthesis and anticonvulsant studies

Five new series of imidazo[1,2-a]pyridines carrying biologically active pyrazoline (4a–e), cyanopyridone (5a, b), cyanopyridine (6a–f), 2-aminopyrimidine (7a–f) and pyrimidine-2-thione (8a–d) systems were designed and synthesized as prominent anticonvulsant agents. The target compounds were screened for their in vivo anticonvulsant activity following maximal electroshock (MES) and subcutaneous pentylene tetrazole (scPTZ) methods at a small test dose of 10 mg/kg. Further, Rotarod toxicity method was used to study the toxicity profile of selected compounds. Compounds 4b, 5a, 5b, 6a, 7e and 8d possessing 4-fluorophenyl substituent at 2nd position of imidazo[1,2-a]pyridine ring displayed potent anticonvulsant activity without displaying any toxicity. Enhanced activity profile was observed for new compounds in PTZ method over MES method.     

Design, synthesis and antimycobacterial evaluation of novel 3-substituted-N-aryl-6,7-dimethoxy-3a,4-dihydro-3H-indeno[1,2-c]pyrazole-2-carboxamide analogues

In the present investigation, a series of 3-substituted-N-aryl-6,7-dimethoxy-3a,4-dihydro-3H-indeno[1,2-c]pyrazole-2-carboxamide analogues were synthesized and were evaluated for antitubercular activity by two fold serial dilution technique. All the newly synthesized compounds showed moderate to high inhibitory activities against Mycobacterium tuberculosis H₃₇Rv and INH resistant M. tuberculosis. The compound N,3-bis(4-fluorophenyl)-6,7-dimethoxy-3a,4-dihydro-3H-indeno[1,2-c]pyrazole-2-carboxamide (4c) was found to be the most promising compound active against M. tuberculosis H₃₇Rv and isoniazid resistant M. tuberculosis with minimum inhibitory concentration 0.78 μM.     

Discovery of imidazo[1,2-a]pyrazine-based Aurora kinase inhibitors

The synthesis and structure–activity relationships (SAR) of novel, potent imidazo[1,2-a]pyrazine-based Aurora kinase inhibitors are described. The X-ray crystal structure of imidazo[1,2-a]pyrazine Aurora inhibitor 1j is disclosed. Compound 10i was identified as lead compound with a promising overall profile.     

Design,synthesis, and evaluation of novel VEGFR2 kinase inhibitors: Discovery of [1,2,4]triazolo[1,5-a]pyridine derivatives with slow dissociation kinetics

For the purpose of discovering novel type-II inhibitors of vascular endothelial growth factor receptor 2 (VEGFR2) kinase, we designed and synthesized 5,6-fused heterocyclic compounds bearing a anilide group. A co-crystal structure analysis of imidazo[1,2-b]pyridazine derivative 2 with VEGFR2 revealed that the N1-nitrogen of imidazo[1,2-b]pyridazine core interacts with the backbone NH group of Cys919. To retain this essential interaction, we designed a series of imidazo[1,2-a]pyridine, [1,2,4]triazolo[1,5-a]pyridine, thiazolo[5,4-b]pyridine, and 1,3-benzothiazole derivatives maintaining a ring nitrogen as hydrogen bond acceptor (HBA) at the corresponding position. All compounds thus designed displayed strong inhibitory activity against VEGFR2 kinase, and the [1,2,4]triazolo[1,5-a]pyridine 13d displayed favorable physicochemical properties. Furthermore, 13d inhibited VEGFR2 kinase with slow dissociation kinetics and also inhibited platelet-derived growth factor receptor (PDGFR) kinases. Oral administration of 13d showed potent anti-tumor efficacy in DU145 and A549 xenograft models in nude mice.     

Synthesis,anticancer assessment on human breast,liver and colon carcinoma cell lines and molecular modeling study using novel pyrazolo[4,3-c]pyridine derivatives

The key intermediate 3-aminopyrazolo[4,3-c]pyridine-4,6-dione (2) is considered as a precursor for some novel pyrazolo[4,3-c]pyridines 4a-c, arylhydrazopyrazolo[4,3-c]pyridines 8a-e, pyrazolo[4,5,1-ij][1,6]naphthyridines 11a-e and pyrido[4′,3′:3,4]pyrazolo[1,5-a]-pyrimidines 15a-d through Knovenegal condensation, coupling reaction and Michael addition. Some of the newly synthesized pyrazolo[4,3-c]pyridine derivatives were investigated for anticancer activity. The results of the cytotoxic activity revealed that compound 6b was the most active compound against the breast and liver carcinoma cell lines which gives IC₅₀ values of 1.937 and 3.695 µg/mL, respectively compared to reference drug (doxorubicin) with IC₅₀ values of 2.527 and 4.749 µg/ml, respectively. Moreover, compound 6c was potent compound against the colon carcinoma cell line which gives the value of IC₅₀ = 2.914 µg/ml compared to doxorubicin with IC₅₀ value of 3.641 µg/ml. Some selected of the novel synthesized compounds were docked inside the active site of ERK2 enzyme and were found display a suitable binding with the active site amino acids according to their bond lengths, angles and conformational energy.