Synthesis and biological evaluation of novel piperazine derivatives of flavone as potent anti-inflammatory and antimicrobial agent

A series of novel 6-methoxy-2-(piperazin-1-yl)-4H-chromen-4-one and 5,7-dimethoxy-2-(piperazin-1-ylmethyl)-4H-chromen-4-one derivatives of biological interest were prepared and screened for their pro-inflammatory cytokines (TNF-α and IL-6) and antimicrobial activity (antibacterial and antifungal). Among all the compound screened (5a–j and 10k–t), the compounds 5c, 5g, 5h, 10l, 10m, 10n and 10r found to have promising anti-inflammatory activity (up to 65–87% TNF-α and 70–93% IL-6 inhibitory activity) at concentration of 10 μM with reference to standard dexamethasone (71% TNF-a and 84% IL-6 inhibitory activities at 1 μM) while the compounds 5b, 5i, 5j, 10s and 10t found to be potent antimicrobial agent showing even 2 to 2.5-fold more potency than that of standard ciprofloxacin and miconazole at the same MIC value of 10 μg/mL.     

Synthesis and antiprotozoal activity of 2,5-bis[amidinoaryl]thiazoles

Seven novel diamidino 2,5-bis(aryl)thiazoles (5a–g) were synthesized and evaluated against Trypanosoma brucei rhodensiense (T. b. r.) and Plasmodium falciparum (P. f.). The diamidines were obtained directly from the corresponding bis-nitriles (4a–g) by the action of lithium bis(trimethylsilyl)amide. The bis-nitriles 4a–f were synthesized in four steps starting with the Stille coupling of 2-tributyltinthiazole with the appropriate cyanoaryl halide. The bis-nitrile 5g was obtained by the palladium facilitated coupling of the mixed tin-silyl reagent 2-trimethylsilyl-5-trimethyltinthiazole with 2-bromo-5-cyanopyridine. The amidoxime potential prodrugs 6a–e, 6g were obtained by the reaction of hydroxylamine with the bis-nitriles. O-Methylation of the amidoximes gave the corresponding N-methoxyamidines 7a–c, 7e, 7g. The diamidines showed strong DNA binding affinity as reflected by ΔT_m measurements. Four of the diamidines 5a, 5b, 5d and 5e were highly active in vitro against P. f. giving IC₅₀ values between 1.1 and 2.5 nM. The same four diamidines showed IC₅₀ values between 4 and 6 nM against T. b. r. The selectivity indices ranged from 233 to 9175. One diamidine 5a produced one of four cures at an ip dose of 4 × 5 mg/kg in the STIB900 mouse model for acute African trypanosomiasis. The amidoxime and N-methoxyamidine of 5a were the only produgs to provide cures (1/4 cures) in the same mouse model on oral dosage at 4 × 25 mg/kg.     

Design,synthesis and evaluation of novel 7-aminoalkyl-substituted flavonoid derivatives with improved cholinesterase inhibitory activities

A novel series of 7-aminoalkyl-substituted flavonoid derivatives 5a–5r were designed, synthesized and evaluated as potential cholinesterase inhibitors. The results showed that most of the synthesized compounds exhibited potent acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activities at the micromolar range. Compound 2-(naphthalen-1-yl)-7-(8-(pyrrolidin-1-yl)octyloxy)-4H-chromen-4-one (5q) showed the best inhibitory activity (IC₅₀, 0.64 μM for AChE and 0.42 μM for BChE) which were better than our previously reported compounds and the commercially available cholinergic agent Rivastigmine. The results from a Lineweaver–Burk plot indicated a mixed-type inhibition for compound 5q with AChE and BChE. Furthermore, molecular modeling study showed that 5q targeted both the catalytic active site (CAS) and the peripheral anionic site (PAS) of AChE. Besides, these compounds (5a–5r) did not affect PC12 and HepG2 cell viability at the concentration of 10 μM. Consequently, these flavonoid derivatives should be further investigated as multipotent agents for the treatment of Alzheimer’s disease.     

Novel pyrazole integrated 1,3,4-oxadiazoles: Synthesis,characterization and antimicrobial evaluation

A novel series of 2-(5-methyl-1,3-diphenyl-1H-pyrazol-4-yl)-5-phenyl-1,3,4-oxadiazoles 7(a–m) were synthesized either by cyclization of N′-benzoyl-5-methyl-1,3-diphenyl-1H-pyrazole-4-carbohydrazide 4a using POCl₃ at 120 °C or by oxidative cyclization of hydrazones derived from various arylaldehyde and (E)-N′-benzylidene-5-methyl-1,3-diphenyl-1H-pyrazole-4-carbohydrazide 5(a–d) using chloramine-T as oxidant. Newly synthesized compounds were characterized by analytical and spectral (IR, ¹H NMR, ¹³C NMR and LC–MS) methods. The synthesized compounds were evaluated for their antimicrobial activity and were compared with standard drugs. The compounds demonstrated potent to weak antimicrobial activity. Among the synthesized compounds, compound 7m emerged as an effective antimicrobial agent, while compounds 7d, 7f, 7i and 7l showed good to moderate activity. The minimum inhibitory concentration of the compounds was in the range of 20–50 μg mL⁻¹ against bacteria and 25–55 μg mL⁻¹ against fungi. The title compounds represent a novel class of potent antimicrobial agents.     

Green synthesis,inhibition studies of yeast α-glucosidase and molecular docking of pyrazolylpyridazine amines

An efficient and environmentally benign simple fusion reaction of 3-chloro-6-(3,5-dimethyl-1H-pyrazol-1-yl)pyridazine (1a) or 3-chloro-6-(3,5-dimethyl-4-nitro-1H-pyrazol-1-yl)pyridazine (2a) with different aliphatic/aromatic amines have produced a series of novel pyrazolylpyridazine amines (4a–4c & 5a–5m). All compounds exhibited moderate in vitro yeast α-glucosidase inhibition except m-chloro derivative 5g, which was found potent inhibitor of this enzyme with IC₅₀ value of 19.27 ± 0.005 µM. The molecular docking further helped in understanding the structure activity relationship of these compounds including 5g.     

Benzyl 1,2,3,5,11,11a-hexahydro-3,3-dimethyl-1-oxo-6H-imidazo[3′,4′:1,2]pyridin[3,4-b]indole-2-substituted acetates: One-pot-preparation,anti-tumor activity,docking toward DNA and 3D QSAR analysis

To discover the anti-tumoral indoles a series of benzyl 1,2,3,5,11,11a-hexahydro-3,3-dimethyl-1-oxo-6H-imidazo[3′,4′:1,2]pyridin[3,4-b]indole-2-substituted acetates (2a–n) are prepared via one-pot-preparation. The IC₅₀ values of 2a–n in vitro against human lung carcinoma, prostate cancer, nasopharyngeal carcinoma, vincristine-resistant KB subline and human breast carcinoma cells range from 40 nM to 60 μM. On Sarcoma 180 (S180) tumor-bearing mouse model four of them (2e,g,h,i) significantly inhibited the tumor growth. At the dose of 0.1 mg/kg the efficacy of the most potent 2h was equal to that of 1.0 mg/kg of doxorubicin. In contrast to doxorubicin, at 1.0 mg/kg of dose 2e,g,h,i did not induce the treated S180 mice to have organ atrophy and body emaciation. The healthy mice receiving 10, 100 and 500 mg/kg of 2e,g,h,i gave no any neurotoxic response. Even up to the dose of 500 mg/kg the healthy mice occurred no death. The interaction of 2a–n with DNA was confirmed by the fluorescence quenching experiments and automated flexible ligand docking. By 3D QSAR analysis the IC₅₀ values of 2a–n against prostate cancer cells were correlated with the structures and conformations of their side chains. To increase the data related to their physical-chemical properties the experimental Log P values were also provided.     

Synthesis of substituted diphenyl sulfones and their structure–activity relationship with the antagonism of 5-НТ6 receptors

Substituted diphenyl sulfones (10a–n) were synthesised, and the structures were confirmed by NMR, LC–MS and X-ray crystallography. Their antagonistic activities towards 5-HT₆ receptor were assessed in a cell-based functional assay. Diphenyl sulfone 10a, in spite of being the smallest and simplest known sulfonyl-containing 5-HT₆R antagonist, showed a strong potency (K_i = 1.6 μM). Its derivative with a methylamine substituent, 10g (N-methyl-2-(phenylsulfonyl)aniline), was ～66-times as active as diphenyl sulfone (K_i = 24.3 nM). Addition of a piperazinyl moiety in the para-position relative to the sulfonyl group in compound 10m (N-methyl-2-(phenylsulfonyl)-5-piperazin-1-ylaniline) led to a further 150-fold increase in potency (K_i = 0.16 nM) to block the serotonin-induced response of HEK-293 cells that were stably transfected with the human recombinant 5-HT₆ receptor.     

Chemotherapy of leishmaniasis. Part XI: Synthesis and bioevaluation of novel isoxazole containing heteroretinoid and its amide derivatives

Novel isoxazole containing heteroretinoid (4) and its amide derivatives (5a–j) have been synthesized and evaluated for their in vivo antileishmanial activity against Leishmania donovani in hamsters. Compounds 3, 5a, 5d, 5k and 5l inhibited 70–76% parasite growth at 50 mg kg^?1 × 5 days. The present study has helped us in identifying a new lead that could be exploited as a potential antileishmanial agent.     

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.     

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.     

Synthesis,antimycobacterial activity and docking study of 2-aroyl-[1]benzopyrano[4,3-c]pyrazol-4(1H)-one derivatives and related hydrazide-hydrazones

A new convenient method for preparation of 2-aroyl-[1]benzopyrano[4,3-c]pyrazol-4(1H)-one derivatives 5b–g and coumarin containing hydrazide-hydrazone analogues 4a–e was presented. The antimycobacterial activity against reference strain Mycobacterium tuberculosis H37Rv and cytotoxicity against the human embryonic kidney cell line HEK-293 were tested in vitro. All compounds demonstrated significant minimum inhibitory concentrations (MIC) ranging 0.28–1.69 μM, which were comparable to those of isoniazid. The cytotoxicity (IC₅₀ > 200 µM) to the “normal cell” model HEK-293T exhibited by 2-aroyl-[1]benzopyrano[4,3-c]pyrazol-4(1H)-one derivatives 5b–e, was noticeably milder compared to that of their hydrazone analogues 4a–e (IC₅₀ 33–403 µM). Molecular docking studies on compounds 4a–e and 5b–g were also carried out to investigate their binding to the 2-trans-enoyl-ACP reductase (InhA) enzyme involved in M. tuberculosis cell wall biogenesis. The binding model suggested one or more hydrogen bonding and/or arene-H or arene-arene interactions between hydrazones or pyrazole-fused coumarin derivatives and InhA enzyme for all synthesized compounds.     

Schiff’s base derivatives bearing nitroimidazole moiety: New class of antibacterial,anticancer agents and potential EGFR tyrosine kinase inhibitors

New Schiff’s base derivatives 5a–5h have been synthesized by reaction between 1-(4-bromophenyl)-2-(2-methyl-5-nitro-1H-imidazol-1-yl)ethanone 3 and various benzohydrazide 4a–4h in presence of nickel (II) nitrate as a catalyst in ethanol at room temperature in good yield (54–88%). All compounds were tested for antibacterial as well as anticancer and inhibition of EGFR. Of the compounds studied, compounds 5d, 5f and 5g in the case of antiproliferation and inhibition of EGFR as well as compounds 5b, 5c, 5e and 5h in the case of antibacterial activity were found to be most effective compounds in the series. Compound 5f shows effective inhibition (IC₅₀ = 0.21 ± 0.02 μM) by binding in to the active pocket of EGFR receptor with minimum binding energy (ΔG_b = ?49.4869 kcal/mol).     

Synthesis and biological investigation of new equatorial (β) stereoisomers of 3-aminotropane arylamides with atypical antipsychotic profile

A series of novel 3β-aminotropane derivatives containing a 2-naphthalene or a 2-quinoline moiety was synthesised and evaluated for their affinity for 5-HT_1A, 5-HT_2A and D₂ receptors. Their affinity for the receptors was in the nanomolar to micromolar range. p-Substitution (6c, 6f, 6i, 6l, 6o), as well as substitution with chlorine atoms (6g, 6h, 6i), led to a significant increase in binding affinity for D₂ receptors with compounds 6f (K_i = 0.6 nM), 6c and 6i (K_i = 0.4 nM), having the highest binding affinities. m-Substituted derivatives were the most promising ligands in terms of 5-HT_2A receptor binding affinity whereas 2-quinoline derivatives (10a, 10b) displayed the highest affinity for 5-HT_1AR and were the most selective ligands with K_i = 62.7 nM and K_i = 30.5 nM, respectively. Finally, the selected ligands 6b, 6d, 6e, 6g, 6h, 6k, 6n and 6o, with triple binding activity for the D₂, 5-HT_1A and 5-HT_2A receptors, were subjected to in vivo tests, such as those for induced hypothermia, climbing behaviour and the head twitch response, in order to determine their pharmacological profile. The tested ligands presented neither agonist nor antagonist properties for the 5-HT_1A receptors in the induced hypothermia and lower lip retraction (LLR) tests. All tested compounds displayed antagonistic activity against 5-HT_2A, with 6n and 6o being the most active. Four (6b, 6k, 6n and 6o) out of eight tested compounds could be classified as D₂ antagonists. Additionally, evaluation of metabolic stability was performed for selected ligands, and introduction of halogen atoms into the benzene ring of 6h, 6k, 6n and 6o improved their metabolic stability. The project resulted in the selection of the lead compounds 6n and 6o, which had antipsychotic profiles, combining dopamine D₂-receptor and 5-HT_2A antagonism and metabolic stability.     

Synthesis and evaluation of new N6-substituted adenosine-5′-N-methylcarboxamides as A3 adenosine receptor agonists

A number of N⁶-substituted adenosine-5′-N-methylcarboxamides were synthesised and their pharmacology, in terms of their receptor affinity, selectivity and cardioprotective effects, were explored. The first series of compounds, 4a–4f and 5a–5f, showed modest receptor affinity for the A₃AR with K_i values in the low to mid μM range. However, the incorporation of a 4-(2-aminoethyl)-2,6-di-tert-butylphenol group in the N⁶-position (in compounds 4g and 5g) significantly improved the affinity with K_i values of 30 and 9 nM, respectively. Improvements in affinity, as well as selectivity were seen when a functionalised linker was introduced. The N⁶-phenyl series, compounds 7a–7d, demonstrated low to mid nanomolar receptor affinities (K_i = 2.3–45.0 nM), with 7b displaying 109-fold selectivity for the A₃AR (vs A₁). The N⁶-benzyl series 9a–9c also proved to be potent and selective A₃AR agonists and the longer chain length linker 13 was tolerated at the A₃AR without abrogation of affinity or selectivity. Cardioprotection was demonstrated by a simulated ischaemia cell culture assay, whereby 7b, 7c, 9a, 9b and 9c all showed cardioprotective effects at 100 nM comparable or better than the benchmark A₃AR agonist IB-MECA, but which were indistinguishable by statistical analysis. For example, compound 9c reduced cell death by 68.0 ± 3.6%.     

Synthesis of new 3-(2-mercapto-4-oxo-4H-quinazolin-3-yl)-benzenesulfonamides with strong inhibition properties against the tumor associated carbonic anhydrases IX and XII

We report a series of novel metanilamide-based derivatives 3a–q bearing the 2-mercapto-4-oxo-4H-quinazolin-3-yl moiety as tail. All compounds were synthesized by means of straightforward condensation procedures and were investigated in vitro for their inhibition potency against the human (h) carbonic anhydrase (CA; EC 4.2.1.1.1) isoforms I, II, IX and XII. Among all compounds tested the 6-iodo 3g and the 7-fluoro 3i derivatives were the most potent inhibitors against the tumor associated CA IX and XII isoform (K_Is 1.5 and 2.7 nM respectively for the hCA IX and K_Is 0.57 and 1.9 nM respectively for the hCA XII).The kinetic data reported here strongly support compounds of this type for their future development as radiotracers in tumor pathologies which are strictly dependent on the enzymatic activity of the hCA IX and XII isoforms.     

Design and synthesis of thiourea derivatives with sulfur-containing heterocyclic scaffolds as potential tyrosinase inhibitors

Tyrosinase is a key enzyme during the production of melanins in plants and animals. A class of novel N-aryl-N′-substituted phenylthiourea derivatives (3a–i, 6a–k) were designed, synthesized and their inhibitory effects on the diphenolase activity of mushroom tyrosinase were evaluated. The results showed some 4,5,6,7-tetrahydro-2-[[(phenylamino)thioxomethyl]amino]-benzo[b]thiophene-3-carboxylic acid derivatives (3a–i) exhibited moderate inhibitory potency on diphenolase activity of tyrosinase. When the scaffold of 4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxylic acid was replaced with 2-(1,3,4-thiadiazol-2-yl)thio acetic acid, the inhibitory activity of compounds (6a–k) against tyrosinase was improved obviously; especially, the inhibitory activity of compound 6h (IC₅₀ = 6.13 μM) is significantly higher than kojic acid (IC₅₀ = 33.3 μM). Moreover, the analysis on inhibition mechanism revealed that compound 6h might plays the role as a noncompetitive inhibitor.     

Derivatives of schisandrin with increased inhibitory potential on prostaglandin E2 and leukotriene B4 formation in vitro

Four derivatives of schisandrin, a major dibenzo[a,c]cyclooctadiene lignan of Schisandra chinensis (Turcz.) Baillon were synthesized and structurally characterized by means of NMR and mass spectroscopy. Furthermore, axial chirality of the biphenyl system was determined by comparison of calculated with measured circular dichroism (CD) spectra. Three of the obtained derivatives showed a ring contraction during chemical modification. While the original lignans were inactive on the performed bioassays, the compounds which showed the cycloheptadiene skeleton revealed remarkable activities. For the inhibition of LTB₄ production the IC₅₀ values of aR-6,7-dihydro-6-(1′-hydroxyethyl)-3,9-dimethoxy-6-methyl-5H-dibenzo[a,c]cycloheptene-1,2,10,11-tetraol (6) and aR-6-(1′-iodoethyl)-1,2,3,9,10,11-hexamethoxy-6-methyl-5H-dibenzo[a,c]cycloheptene (8) were 4.2 ± 0.3 μM and 4.5 ± 0.2 μM, respectively. aR-6,7-Dihydro-6-(1′-hydroxyethyl)-6-methyl-5H-dibenzo[a,c]cycloheptene-1,2,3,9,10,11-hexaol (5) revealed dual inhibition on COX-2 (IC₅₀ 32.1 ± 2.5 μM) and on LTB₄ production (37.3 ± 5.5% inhibition at 50 μM).     

Design,synthesis, and X-ray structural studies of BACE-1 inhibitors containing substituted 2-oxopiperazines as P1′-P2′ ligands

We report the design and synthesis of a series of BACE1 inhibitors incorporating mono- and bicyclic 6-substituted 2-oxopiperazines as novel P1′ and P2′ ligands and isophthalamide derivative as P2-P3 ligands. Among mono-substituted 2-oxopiperazines, inhibitor 5a with N-benzyl-2-oxopiperazine and isophthalamide showed potent BACE1 inhibitory activity (K_i = 2 nM). Inhibitor 5g, with N-benzyl-2-oxopiperazine and substituted indole-derived P2-ligand showed a reduction in potency. The X-ray crystal structure of 5g-bound BACE1 was determined and used to design a set of disubstituted 2-oxopiperazines and bicyclic derivatives that were subsequently investigated. Inhibitor 6j with an oxazolidinone derivative showed a BACE1 inhibitory activity of 23 nM and cellular EC₅₀ of 80 nM.     

Synthesis,pharmacological screening and in silico studies of new class of Diclofenac analogues as a promising anti-inflammatory agents

A novel series of 5-[2-(2,6-dichlorophenylamino)benzyl]-3-(substituted)-1,3,4-oxadiazol-2(3H)-thione (4a–k) derivatives have been synthesized by the Mannich reaction of 5-[2-(2,6-dichlorophenylamino)benzyl]-1,3,4-oxadiazol-2(3H)-thione (3) with an appropriately substituted primary/secondary amines, in the presence of formaldehyde and absolute ethanol. Structures of these novel compounds were characterized on the basis of physicochemical, spectral and elemental analysis. The title compounds (4a–k) were screened for in vivo acute anti-inflammatory and analgesic activities at a dose of 10 mg/kg b.w. Compound 4k exhibited the most promising and significant anti-inflammatory profile while compounds 4a, 4d, 4e, 4i, and 4j showed moderate to good inhibitory activity at 2nd and 4th h, respectively. These compounds were also found to have considerable analgesic activity (acetic acid induced writhing model) and antipyretic activity (yeast induced pyrexia model). In addition, the tested compounds were also found to possess less degree of ulcerogenic potential as compared to the standard NSAIDs. Compounds that displayed promising anti-inflammatory profile were further evaluated for their inhibitory activity against cyclooxygenase enzyme (COX-1/COX-2), by colorimetric COX (ovine) inhibitor screening assay method. The results revealed that the compounds 4a, 4e, 4g and 4k exhibited effective inhibition against COX-2. In an attempt to understand the ligand–protein interactions in terms of the binding affinity, docking studies were performed using Molegro Virtual Docker (MVD-2013, 6.0) for those compounds, which showed good anti-inflammatory activity. It was observed that the binding affinities calculated were in agreement with the IC₅₀ values.     

Synthesis and evaluation of N-((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)nicotinamides as potential anticancer agents that inhibit tubulin polymerization

A series of N-((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)nicotinamides (4) was synthesized and tested for their anticancer activity against a panel of 60 human cancer cell lines. Some of the representative compounds such as 4a, 4b, 4f, 4g, 4i and 4t were selected for the five dose study and amongst them 4g and 4i displayed significant anticancer activity with GI₅₀ values ranging from 0.25 to 8.34 and 1.42 to 5.86 μM, respectively. Cell cycle analysis revealed that these compounds induced cell cycle arrest at G2/M phase in MCF-7 cells. The most active compound in this series 4g also inhibited tubulin polymerization with IC₅₀ value 1.93 μM superior to that of E7010. Moreover, assay to investigate the effect on caspase-9, Hoechst staining and DNA fragmentation analysis suggested that these compounds induced cell death by apoptosis. Docking experiments showed that they interact and bind efficiently with tubulin protein. Overall, the results demonstrate that N-((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)nicotinamide scaffold possess anticancer property by inhibiting the tubulin polymerization.