Synthesis of some novel pyrazolo[3,4-b]pyridine and pyrazolo[3,4-d]pyrimidine derivatives bearing 5,6-diphenyl-1,2,4-triazine moiety as potential antimicrobial agents

The reaction of 5,6-diphenyl-3-hydrazino-1,2,4-triazine (1) with bis(methylthio)methylene]malononitrile (2) afforded 5-amino-1-(5,6-diphenyl-1,2,4-triazin-3-yl)-3-(methylthio)-1H-pyrazole-4-carbonitrile (3). Compound 3 reacted with thiourea to give 3,4-diaminopyrazolo[3,4-d]pyrimidine 5, which was treated with benzoyl chloride to give pyrazolo[5,4,3-kl]pyrimido[4,3-d]pyrimidine 6. Treatment of 3 with acetic anhydride produced 3-methylthio-pyrazolo[3,4-d]pyrimidine derivative 7, which was allowed to react with hydrazine hydrate to give the corresponding hydrazino derivative 8. Heterocyclization of 8 with benzoyl chloride and sodium pyruvate afforded the polyfused heterocycles 9 and 10, respectively. Reaction of 3 with benzoylacetone yielded pyrazolo[3,4-b]pyridine 12, which was allowed to react with malononitrile and acetanilide to get heterocyclic systems 13 and 14, respectively. Interaction of 3 with cyanoacetone gave pyrazolo[3,4-b]pyridine 15, which was refluxed in formic acid to yield pyrazolo[4′,3′:5,6]pyrido[4,3-d]pyrimidine 16. Reaction of 3 with 2 afforded the triazinylpyrazole derivative 17, which was reacted with hydrazine hydrate to give dipyrazolo[1,5-a:3′,4′-d]pyrimidine 19. Furthermore, treatment of the latter compound with methyl anthranilate furnished tetraheterocyclic compound 21. Structures of the products have been determined by elemental analysis and spectral studies. All compounds have been screened for their antibacterial and antifungal activities. Compounds 9, 10, 13, 19 and 21 showed maximum activity comparable to the standard drugs with lower toxicity in the case of 9 and 10.     

Synthesis and preliminary pharmacological evaluation of imidazo[2,1-f]purine-2,4-dione derivatives

A series of N-8-arylpiperazinylpropyl derivatives of 1,3-dimethyl-(1H,8H)-imidazo[2,1-f]purine-2,4-dione (2–10) and amide derivatives of 1,3-dimethyl-6,7-dihydroimidazo[2,1-f]purine-2,4-(1H,3H)-dione-7-carboxylic acid (11–13) were synthesized. Compounds (2–10) evaluated in vitro were potent 5-HT_1A receptor ligands. Preclinical studies indicated that 8-[3-(N4-phenyl)-piperazin-N1-yl-propyl]-1,3-dimethyl-(1H,8H)-imidazo[2,1-f]purine-2,4-dione (2) exerts anxiolytic-like activity in the four-plate test in mice; however its effect was weaker, than that produced by Diazepam. This compound and 8-[3-(N4-2′-metoxyphenyl)-piperazin-N1-yl-propyl]-1,3-dimethyl-(1H,8H)-imidazo[2,1-f]purine-2,4-dione (3) behaved like antidepressants in the forced swimming test in mice; and their activity in that model was comparable with the effect of Imipramine. The obtained results suggested that the long-chain arylpiperazines (LCAPs) linked to tricyclic derivatives of the theophylline remain a worthy of future research for obtaining new derivatives with potential anxiolytic/antidepressant activity.     

Synthesis and in vitro antitumour activity evaluation of 1-aryl-1H,3H-thiazolo[4,3-b]quinazolines

A series of 1H,3H-thiazolo[4,3-b]quinazolines (2a–i) were synthesized and evaluated for their in vitro antitumour activity against ca. 60 human tumour cell lines. They exhibited moderate (2c, 2d, 2f and 2g) to strong (2a, 2b, 2e, 2h and 2i) cell-growth inhibition at a concentration of 10⁻⁴ M, but weak activity at lower concentrations. Only 1-(2,6-dichlorophenyl)-1H,3H-thiazolo[4,3-b]quinazoline (2h) possesses a significant growth inhibitory activity on 22 cell lines at a concentration of 10⁻⁵ M.     

Synthesis of novel bioactive derivatives of 3-(4-chlorophenyl)-2-hydrazino-5,6,7,8-tetrahydrobenzo(b)thieno[2,3-d]pyrimidine-4(3H)-ones

A series of triazolo[4,3-a]tetrahydrobenzo(b)thieno[3,2-e]pyrimidine-5(4H)-ones (12a–n) were synthesized and evaluated for CNS depressant, skeletal muscle relaxant and anticonvulsant activities by photoactometer, Rotarod and pentylenetetrazole induced the convulsions method respectively in Swiss albino mice. Diazepam was used as standard drug. The five derivatives 12b, 12c, 12d, 12i and 12m showed the CNS depressant and skeletal muscle relaxant activities comparable to those of diazepam at a dose of 5 mg/kg. These derivatives also exhibited good activity when tested for anticonvulsant activity in mice at different dose levels. The ED₅₀ values for these derivatives are in the range of 4.40–9.33 mg/kg.     

Synthesis and anticonvulsant activity of some new thiazolo[3,2-a][1,3]diazepine, benzo[d]thiazolo[5,2-a][12,6]diazepine and benzo[d]oxazolo[5,2-a][12,6]diazepine analogues

A new series of 6,7-dihydro-thiazolo[3,2-a][1,3]diazepines (9–12), benzo[d]thiazolo[5,2-a][12,6]diazepines (19–21) and benzo[d]oxazolo[5,2-a][12,6]diazepine (24) analogues were synthesized and evaluated for their anticonvulsant activity. Compounds (E)-2-bromo-6,7-dihydro-thiazolo[3,2-a][1,3]diazepine-8(5H)-thione (12), 3-chloro-benzo[d]thiazolo[5,2-a][12,6]diazepin-10-one (20), and 4-chloro-benzo[d]oxazolo[5,2-a][12,6] diazepin-10-one (24) showed 100% protection against PTZ- and bicuculline-induced seizures; 70%, 33%, 70% protection against MES-induced tonic extension; and 70%, 66%, 100% protection against picrotoxin-induced convulsions, respectively. Compounds 12, 20, and 24 proved to act as GABA_A receptor agonists, with ED₅₀ values of 252, 380, 251 mg/kg; TD₅₀ values of 398, 417, 355 mg/kg; PI values of 1.58, 1.09, 1.41; LD₅₀ values of 380, 617, 537 mg/kg and TI values of 1.51, 1.62, 2.14, respectively.     

Synthesis and inhibition study of monoamine oxidase, indoleamine 2,3-dioxygenase and tryptophan 2,3-dioxygenase by 3,8-substituted 5H-indeno[1,2-c]pyridazin-5-one derivatives

Previous studies on 5H-indeno[1,2-c]pyridazin-5-one derivatives as inhibitors of MAO-B revealed that it was possible to increase the MAO-B inhibitory potency of 5H-indeno[1,2-c]pyridazin-5-ones by substituting the central heterocycle in the 3-position or C-8 with lipophilic groups which occupy the substrate cavity or the entrance of the binding site, respectively. Here, four new 5H-indeno[1,2-c]pyridazin-5-one derivatives containing lipophilic groups at both positions were synthesized and their inhibitory potency against human monoamine oxidase A and B were evaluated. Selectivity of these compounds against IDO and TDO, two enzymes sharing substrate similarity with MAO and involved in the serotonergic and kynurenine pathways was also studied. All compounds showed higher activity and selectivity against MAO-B, the most effective one being 3-methyl-8-meta-chlorobenzyloxy-5H-indeno[1,2-c]pyridazin-5-one (9a) which was shown to be a competitive inhibitor with a K_i value of 0.11 μM. Replacing the methyl group in the 3-position with a meta–CF₃–phenyl group (7a, 7b and 7c) abolished the inhibitory potency against MAO-B. Indeed, the substitution of the 5H-indeno[1,2-c]pyridazin-5-one core in the 3-position dramatically influences the MAO-inhibiting properties of these compounds. Molecular docking studies of 9a within MAO-B suggest that the 5H-indeno[1,2-c]pyridazin-5-one scaffold is well stabilized into the substrate cavity with the meta-chlorobenzyloxy side chain extending towards a rather hydrophobic pocket at the entrance cavity.     

Synthesis of 4H-chromene, coumarin, 12H-chromeno[2,3-d]pyrimidine derivatives and some of their antimicrobial and cytotoxicity activities

Condensation of 3-N,N-diethylaminophenol (1) with α-cyanocinnamonitriles (2a-c) and ethyl α-cyanocinnamates (2d-f) provided compounds 3a-f and 4a-c. 12H-Chromeno[2,3-d]pyrimidine derivatives 6, 11-13 and 16 were obtained by treatment of 4H-chromene compounds (3) with different electrophiles followed by nucleophilic reagents. Structures of these compounds were established on the basis of IR, UV, ¹H NMR, ¹³C NMR and MS data. Some of the new compounds were evaluated for antimicrobial and cytotoxicity activities.     

Synthesis, characterization and antibacterial activity of 2-[1-(5-chloro-2-methoxy-phenyl)-5-methyl-1H-pyrazol-4-yl]-5-(substituted-phenyl)-[1,3,4]oxadiazoles

In the present investigation a series of novel 2-[1-(5-chloro-2-methoxy-phenyl)-5-methyl-1H-pyrazol-4-yl]-5-(substituted-phenyl)-[1,3,4]oxadiazoles (4a–j) were synthesized by cyclization of substituted-benzoic acid N′-[1-(5-chloro-2-methoxy-phenyl)-5-methyl-1H-pyrazole-4-carbonyl]-hydrazide by using phosphorousoxychloride at 120 °C. The chemical structure of the newly synthesized compounds was characterized by analytical and spectral (IR, ¹H NMR, ¹³C NMR and LC–MS) methods. The title compounds were screened for qualitative (zone of inhibition) and quantitative antibacterial activity (MIC) by agar cup plate and microtitration methods, respectively. Among the synthesized compounds in this series compound 2-[1-(5-chloro-2-methoxyphenyl)-5-methyl-1H-pyrazol-4-yl]-5-(4-fluorophenyl)-1,3,4-oxadiazole (4b) was found to exhibit significant antibacterial activity with MICs of 22.4, 29.8, 29.6 and 30.0 μg/mL against Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae, respectively. The other compounds exhibited moderate activity when compared to standard substance Ampicillin.     

Novel 4-aryl-pyrido[1,2-c]pyrimidines with dual SSRI and 5-HT1A activity: Part 2

Derivatives of 4-aryl-5,6,7,8-tetrahydro-pyrido[1,2-c]pyrimidine were synthesized. These compounds contain the 3-(4-piperidyl)-1H-indole residue or its 5-methoxy or 2-methyl derivative. In vitro binding tests were performed to determine the affinity of the compounds for the 5-HT_1A receptor and serotonin transporter (SERT) proteins in the rat brain cortex. In vivo studies, particularly the inducible hypothermia test and forced swimming test, were conducted to determine agonistic/antagonistic activity with pre- and postsynaptic 5-HT_1A receptors. Molecular modeling techniques were used to determine the binding modes of the selected compounds at the 5-HT_1A receptor and SERT. The SAR analysis showed that the presence of the 3-(4-piperidyl)-1H-indole group or its 5-methoxy derivative, as well as a para substitution with –OCH₃ or –F in the aryl ring of 4-aryl-5,6,7,8-tetrahydro-pyrido[1,2-c]pyrimidine, results in an increased affinity for both the 5-HT_1A receptors and SERT. In contrast, the presence of the 2-methyl-3-(4-piperidyl)-1H-indole group resulted in a considerable decrease in binding affinity.     

Single step synthesis of new fused pyrimidine derivatives and their evaluation as potent Aurora-A kinase inhibitors

A simple, facile, efficient and one pot three-component procedure for the synthesis of pyrazolo[1,5-a]pyrimidines, triazolo[1,5-a]pyrimidines and pyrimido[1,2-a]benzimidazoles ring systems incorporating phenylsulfonyl moiety was developed via the reaction of 1-aryl-2-(phenylsulfonyl)ethanone derivatives 1a-d with the appropriate heterocyclic amine and triethyl orthoformate and evaluated as Aurora-A kinase inhibitors. The cytotoxic activity of the newly synthesized compounds against HST116 colon tumor cell line was investigated. 2,7-Diphenyl-6-(phenylsulfonyl)pyrazolo[1,5-a]pyrimidine (4b) and its p-methoxy analogue 4c were found to be equipotent to Doxorubicin as a reference drug. Molecular modeling study was carried out in order to rationalize the in vitro anti-tumor results.     

Synthesis and anticonvulsant activity of 7-phenyl-6,7-dihydro-[1,2,4]triazolo[1,5-a]pyrimidin-5(4H)-ones and their derivatives

Herein, we described the syntheses and anticonvulsant activities of 7-(substituted-phenyl)-6,7-dihydro-[1,2,4]triazolo[1,5-a]pyrimidin-5(4H)-ones (1a-1o) and their derivatives. Most of the synthesized compounds exhibited potent anticonvulsant activities in the maximal electroshock test (MES). The most promising compound 1i showed significant anticonvulsant activity in MES test with ED₅₀ value of 19.7 mg/kg. It displayed a wide margin of safety with protective index much higher than the standard drugs. In addition, the potence of compound 1i against seizures induced by Pentylenetetrazole, Isoniazid, Thiosemicarbazide, 3-Mercaptopropionic acid, and Bicuculline in the chemical-induced seizure tests suggested that compound 1i displayed broad spectrum activity in several models, and it is likely to have several mechanisms of action including inhibiting voltage-gated ion channels and modulating GABAergic activity.     

Synthesis and biological activity of novel N-cycloalkyl-(cycloalkylaryl)-2-[(3-R-2-oxo-2H-[1,2,4]triazino[2,3-c]quinazoline-6-yl)thio]acetamides

In this paper the novel N-cycloalkyl-(cycloalkylaryl)-2-[(3-R-2-oxo-2H-[1,2,4]triazino[2,3-c]quinazoline-6-yl)thio]acetamides synthesis by aminolysis of activated by thionyl chloride or carbonyldiimidazole [(3-R-2-oxo-2H-[1,2,4]triazino[2,3-c]quinazolin-6-yl)-thio]acetic acids and alkylation of the 3-R-6-thio-6,7-dihydro-2H-[1,2,4]triazino[2,3-c]quinazoline-2-ones potassium salts with N-cycloalkyl-(cycloalkylaryl)-2-chloroacetamides are proposed. The structures of compounds are determined by ¹H, ¹³C NMR, LC-MS and EI-MS analysis. The in vitro anticancer, antibacterial activity and Photobacterium leiognathi Sh1 bioluminescence inhibition of synthesized compounds were revealed. SAR results were discussed. Compound 4.10 was found to be the most anticancer active one, selectively influenced on the non-small cell lung and CNS cancer cell lines, especially on the HOP-92 (log GI₅₀ = −6.01) and U251 (log GI₅₀ = −6.00).     

Synthesis and evaluation of A-seco type triterpenoids for anti-HIV-1protease activity

2,3-Seco-dioic acids derived from four different triterpene skeletons were prepared and evaluated for their anti-HIV-1 protease activity. Two A-seco derivatives showed potent inhibitory activity against HIV-1 protease (3c and 3e, IC₅₀ 5.7 and 3.9 μM, respectively), while four other derivatives showed moderate to weak inhibition (3a, 3b, 3d and 3f, IC₅₀ 15.7–88.1 μM). The combination of a 2,3-seco-2,3-dioic acid functional group in ring A and a free acid group at C-28 or C-30 significantly enhanced HIV-1 protease inhibitory activity (3a, 3c–3e, IC₅₀ 3.9–17.6 μM). On the other hand, all A-seco derivatives were found to be very weak inhibitors of HCV, renin and trypsin proteases (IC₅₀ > 80 μM). These findings indicate that A-seco triterpenes with a carboxyl group at C-28 or C-30 are novel and highly selective HIV-1 protease inhibitors.     

Synthesis and antitumor activity of new sulfonamide derivatives of thiadiazolo[3,2-a]pyrimidines

New series of sulfonamide derivatives of [1,3,4]thiadiazolo[3,2-a]pyrimidine were synthesized and investigated as antitumor agents. Some of the newly prepared compounds were tested for their in vitro and in vivo antitumor activities. Preliminary biological studies revealed that compounds 4c, 4f, and 4j exhibited the highest affinity to DNA, while compounds 4h,i, 6a-c, 8 and 12-14 exhibited moderate activity. Also, compounds 4j, 4f and 4c showed the highest percentage increase in lifespan of mice inoculated with Ehrlich ascites cells over 5-flurouracil (positive control). The detailed synthesis, spectroscopic and biological data are reported.     

Derivatives of pyrrolo[3,4-d]pyridazinone, a new class of analgesic agents

A series of N2-{2-[4-aryl(benzyl)-1-piperazinyl(piperidinyl)]ethyl}pyrrolo[3,4-d]pyridazinones 4 and related derivatives 5 were synthesized as potential analgesic agents. The structures of the new compounds were elucidated by micro, spectral and X-ray analysis. Analgesic activity of the compounds was investigated in the phenylbenzoquinone induced ‘writhing’ and ‘hot plate’ test in mice and at radioligand binding assay. At ‘writhing’ test all compounds, without exception, were more active than acetylsalicylic acid (ASA) with ED₅₀ values ranging from 0.04 to 11 mg/kg (i.p.) (ED₅₀ for ASA - 39.15 mg/kg). Analgesic effect at the ‘hot plate’ test was observed for three compounds 4c,e,f at the dose 3-5 times higher then that of morphine (ED₅₀-3.39 mg/kg). At radioligand binding assay of 4c,e,f only compound 4f exhibited affinity for the μ-opioid receptors similar to that of Tramadol. The acute toxicity of the pyrrolopyridazinones 4, 5 were also studied and non toxic effect was observed at the 2000 mg/kg (5a 1420 mg/kg) i.p. dose level. On the basis of the available pharmacological data S-A relationship is discussed. The preferred conformational characteristic of 4, taken 4c as an example, was also described.     

Synthesis and in vitro leishmanicidal activity of 2-(1-methyl-5-nitro-1H-imidazol-2-yl)-5-substituted-1,3,4-thiadiazole derivatives

A series of 2-(1-methyl-5-nitroimidazol-2-yl)-5-(1-piperazinyl, 1-piperidinyl and 1-morpholinyl)-1,3,4–thiadiazoles (3a–g) were synthesized and evaluated for in vitro leishmanicidal activity against Leishmania major promastigotes. The leishmanicidal data revealed that compounds 3a–g had strong and much better leishmanicidal activity than the reference drug pentostam. Compound 3c (piperazine analog) was the most active compound (IC₅₀ = 0.19 μM).     

Design and synthesis of 2-phenylimidazo[1,2-a]pyridines as a novel class of melatonin receptor ligands

A novel class of imidazo[1,2-a]pyridines as melatonin receptor ligands is designed and synthesized. The affinities of 3-(6-methoxy-2-phenylimidazo[1,2-a]pyridine-3-yl)-N-methyl-propionamide 8, N-[2-(6-methoxy-2-phenylimidazo[1,2-a]pyridine-3-yl)-ethyl]-acetamide 13 and N-(1-hydroxy-3-(5-methoxy-2-phenyl-1H-indol-3-yl)propan-2-yl)acetamide 18 are evaluated for binding on melatonin receptors. Compound 8 present good selectivity for MT₂ over MT₁ (MT₁/MT₂ = 19) and compound 13 have good affinities for both MT₁ (Ki :28 nM) and MT₂ (Ki : 8 nM).     

5H-[1,2,4]Oxadiazolo[5,4-d][1,5]benzothiazepines as anticonvulsant agents in DBA/2 mice

A series of 3a,4-dihydro-5H-[1,2,4]oxadiazolo[5,4-d][1,5]benzothiazepines have been synthesized by 1,3-dipolar cycloaddition reaction of benzonitriloxide to the CN double bond of 1,5-benzothiazepine derivatives, and the stereochemical features of compounds obtained have been determined by NMR spectroscopy. The results of evaluation of their activity in preventing seizures induced by audiogenic stimulation in DBA/2 mice are also reported and discussed. The 5-(4-bromophenyl)-1,3-diphenyl derivative 3b, the most active compound of the series, is over 20 times more active than the parent benzothiazepine 1b and shows an activity comparable to clobazam and better than desmethylclobazam.     

Synthesis, photochemical E (trans) → Z (cis) isomerization and antimicrobial activity of 2-chloro-5-methylpyridine-3-olefin derivatives

2-Chloro-5-methylpyridine-3-olefin derivatives (3a-e) have been synthesized from 2-chloro-5-methylnicotinaldehyde (1) and studied their photochemical E (trans) → Z (cis) isomerization upon direct irradiation and triplet sensitized excitation for the first time. The triplet sensitized excitations of the compounds yielded high Z (4a–e) isomer composition, whereas the direct excitation results in less Z (4a–e) isomer composition, indicating triplet pathway is very efficient in converting the E (trans) → Z (cis) isomer. Thus synthesized E (3a–c and 3e) and generated Z (4a–c and 4e) isomers were tested for antimicrobial activity. Antifungal activity of these pyridine derivatives are closely comparable to the standard used.     

Design, synthesis and antimycobacterial activity of some novel imidazo[1,2-c]pyrimidines

Tuberculosis, due to its relentless nature, is now a major public health threat. The concomitant resurgence of TB with the MDR- or XDR-TB and HIV/AIDS pandemic has exposed the frailties of the current drug armatorium. Based on isosteric replacement and good 3D structural similarity between PA-824, a novel antimycobacterial agent undergoing clinical trials, and imidazo[1,2-c]pyrimidines, we have designed novel imidazo[1,2-c]pyrimidines. The designed molecules were synthesized by nucleophilic displacement of chloro group of various substituted 4-chloropyrimidines by ethanolamine followed by cyclisation of these 4-(2-hydroxyethyl)aminopyrimidines to imidazo[1,2-c]pyrimidines in good yield. All the compounds were screened for their antimycobacterial activity on Mycobacterium tuberculosis H37Rv strain by 1% proportion method. Some of the synthesized compounds exhibited potent antimycobacterial activity with MIC values in the range of 2–20 μg/mL.