Synthesis and evaluation of the antiproliferative activity of novel isoindolo[2,1-a]quinoxaline and indolo[1,2-a]quinoxaline derivatives

A novel series of isoindolo[2,1-a]quinoxaline and indolo[1,2-a]quinoxaline derivatives was synthesized and evaluated in vitro against various human cancer cell lines for antiproliferative activity. These new compounds displayed activity against leukemia and breast cancer cell lines in the 3- to 18-µM concentration range.     

Design,synthesis and antimalarial activity of novel bis{N-[(pyrrolo[1,2-a]quinoxalin-4-yl)benzyl]-3-aminopropyl}amine derivatives

Novel series of bis- and tris-pyrrolo[1,2-a]quinoxaline derivatives 1 were synthesized and tested for in vitro activity upon the intraerythrocytic stage of W2 and 3D7 Plasmodium falciparum strains. Biological results showed good antimalarial activity with IC₅₀ in the μM range. In attempting to investigate the large broad-spectrum antiprotozoal activities of these new derivatives, their properties toward Leishmania donovani were also investigated and revealed their selective antiplasmodial profile. In parallel, the in vitro cytotoxicity of these molecules was assessed on the human HepG2 cell line. Structure–activity relationships of these new synthetic compounds are discussed here. The bis-pyrrolo[1,2-a]quinoxalines 1n and 1p were identified as the most potent antimalarial candidates with selectivity index (SI) of 40.6 on W2 strain, and 39.25 on 3D7 strain, respectively. As the telomeres of the parasite could constitute an attractive target, we investigated the possibility of targeting Plasmodium telomeres by stabilizing the Plasmodium telomeric G-quadruplexes through a FRET melting assay by our new compounds.     

Synthesis and antitumor activity of a new class of pyrazolo[4,3-e]pyrrolo[1,2-a][1,4]diazepinone analogs of pyrrolo[1,4]benzodiazepines (PBDs)

A new class of Pyrrolo[1,4]benzodiazepines (PBDs) analogs featuring a pyrazolo[4,3-e]pyrrolo[1,2-a][1,4]diazepinone ring system has been designed and synthesized. In these compounds the A-benzene ring, characteristic of PBDs, has been replaced by a dimethylpyrazole ring, a modification suggested by modelling studies performed on the PBD base structure. Biological evaluation releaved appreciable antitumor activity for compounds 14 and 15 (8.84–22.4 μM) which encourages further investigation of the N⁶ and N⁷ alkyl pyrazole analogs.     

Design and Synthesis of Acyclic Nucleoside Analogs with Chlorinated Imidazo[1,2-a]pyridine Bases

Abstract

A series of acyclic C-nucleoside analogs of 2,6-dichloro- and 2,6,7-trichloroimidazo[1,2-a]pyridine were synthesized and tested for antiviral activity. The appropriate hydroxymethyl-substituted heterocycles were treated successively with thionyl chloride, an appropriate nucleophile, then diisopropylethylamine to obtain the desired acyclic nucleoside analogs. These compounds were evaluated for activity against human cytomegalovirus and herpes simplex virus, type 1. Two of the dichloro analogs, but none of the trichloro analogs demonstrated slight antiviral activity (IC₅₀'s = 20–45 µM) at non-cytotoxic concentrations.     

Synthesis and evaluation of the antiproliferative activity of novel pyrrolo[1,2-a]quinoxaline derivatives,potential inhibitors of Akt kinase. Part II

Attenuation of protein kinases by selective inhibitors is an extremely active field of activity in anticancer drug development. Therefore, Akt, a serine/threonine protein kinase, also known as protein kinase B (PKB), represents an attractive potential target for therapeutic intervention. Recent efforts in the development and biological evaluation of small molecule inhibitors of Akt have led to the identification of novel inhibitors with various heterocycle scaffolds. Based on previous results obtained on the antiproliferative activities of new pyrrolo[1,2-a]quinoxalines, a novel series was designed and synthesized from various substituted phenyl-1H-pyrrole-2-carboxylic acid alkyl esters via a multistep heterocyclization process. These new compounds were tested for their in vitro ability to inhibit the proliferation of the human leukemic cell lines K562, U937, and HL60, and the breast cancer cell line MCF7. The first biological evaluation of our new substituted pyrrolo[1,2-a]quinoxalines showed antiproliferative activity against the tested cell lines. From a general SAR point of view, these preliminary biological results highlight the importance of substitution at the C-4 position of the pyrroloquinoxaline scaffold by a benzylpiperidinyl fluorobenzimidazole group, and also the need for a functionalization on the pyrrole ring.     

Synthesis of new 4-[2-(alkylamino)ethylthio]pyrrolo[1,2-a]quinoxaline and 5-[2-(alkylamino)ethylthio]pyrrolo[1,2-a]thieno[3,2-e]pyrazine derivatives,as potential bacterial multidrug resistance pump inhibitors

The synthesis of new 4-[2-(alkylamino)ethylthio]pyrrolo[1,2-a]quinoxaline derivatives 1a-l is described in five or six steps starting from various substituted nitroanilines 2a-e. The bioisostere 5-[2-(alkylamino)ethylthio]pyrrolo[1,2-a]thieno[3,2-e]pyrazine 1m was also prepared. The new derivatives were evaluated as efflux pump inhibitors (EPIs) in a model targeting the NorA system of Staphylococcus aureus. The antibiotic susceptibility of two strains overproducing NorA, SA-1199B and SA-1, was determined alone and in combination with the neo-synthesised compounds by the agar diffusion method and MIC determination, in comparison with reserpine and omeprazole taken as reference EPIs. A preliminary structure-activity relationship study firstly allowed to clarify the influence of the substituents at positions 7 and/or 8 of the pyrrolo[1,2-a]quinoxaline nucleus. Methoxy substituted compounds, 1b and 1g, were more potent EPIs than the unsubstituted compounds (1a and 1f), followed by chlorinated derivatives (1c-d and 1h). Moreover, the replacement of the N,N-diethylamino group (compounds 1a-e) by a bioisostere such as pyrrolidine (compounds 1f-h) enhanced the EPI activity, in contrast with the replacement by a piperidine moiety (compounds 1i-k). Finally, the pyrrolo[1,2-a]thieno[3,2-e]pyrazine compound 1m exhibited a higher EPI activity than its pyrrolo[1,2-a]quinoxaline analogue 1a, opening the way to further pharmacomodulation.     

Synthesis and antifungal activity of imidazo[1,2-b]pyridazine derivatives against phytopathogenic fungi

A series of 3,6-disubstituted imidazo[1,2-b]pyridazine derivatives have been synthesized and characterized with spectroscopic analyses. The antifungal activities of these compounds against nine phytopathogenic fungi were evaluated by the mycelium growth rate method. The in vitro antifungal bioassays indicated that most of compounds displayed excellent and broad-spectrum antifungal activities. Especially, compounds 4a, 4c, 4d, 4l and 4r exhibited 1.9–25.5 fold more potent than the commercially available fungicide hymexazol against Corn Curvalaria Leaf Spot (CL), Alternaria alternate (AA), Pyricularia oryzae (PO) and Alternaria brassicae (AB) strains. Structure-activity relationship analysis showed that the enhanced antifungal activity is significantly affected by the substituents on the benzene ring and pyridazine ring.     

Targeting the human parasite Leishmania donovani: Discovery of a new promising anti-infectious pharmacophore in 3-nitroimidazo[1,2-a]pyridine series

We report herein the discovery of antileishmanial molecules based on the imidazo[1,2-a]pyridine ring. In vitro screenings of imidazopyridines belonging to our chemical library, toward the promastigotes stage of Leishmania donovani, J774A.1 murine and HepG2 human cells, permitted to identify three selective hit-compounds (12, 20 and 28). New derivatives were then synthesized to allow structure–activity and –toxicity relationships analyses, enabling to characterize a lead-compound (44) displaying both a high potency (IC₅₀ = 1.8 μM) and a good selectivity index, in comparison with three antileishmanial reference drug-compounds (amphotericin B, miltefosine and pentamidine). Moreover, lead-compound 44 also exhibits good in vitro activity against the intracellular amastigote stage of L. donovani. Thus, the 6-halo-3-nitro-2-(phenylsulfonylmethyl)imidazo[1,2-a]pyridine scaffold appears as a new promising selective antileishmanial pharmacophore, especially when substituted at position 8 by a bromine atom.     

Synthesis and biological activity of pyrazolo[3,4-d]thiazolo[3,2-a]pyrimidin-4-one derivatives: in silico approach

Xanthine oxidase (XO) is responsible for the pathological condition called gout. Inhibition of XO activity by various pyrazolo[3,4-d]thiazolo[3,2-a]pyrimidine-4-one derivatives was assessed and compared with the standard inhibitor allopurinol. Out of 10 synthesized compounds, two compounds, viz. 3-amino-6-(2-hydroxyphenyl)-1H-pyrazolo[3,4-d]thiazolo[3,2-a]pyrimidin-4-one (3b) and 3-amino-6-(4-chloro-2-hydroxy-5-methylphenyl)-1H-pyrazolo[3,4-d]thiazolo[3,2-a]pyrimidin-4-one (3g) were found to have promising XO inhibitory activity of the same order as allopurinol. Both compounds and allopurinol inhibited competitively with comparable Ki (3b: 3.56?µg, 3g: 2.337?µg, allopurinol: 1.816?µg) and IC₅₀ (3b: 4.228?µg, 3g: 3.1?µg, allopurinol: 2.9?µg) values. The enzyme–ligand interaction was studied by molecular docking using Autodock in BioMed Cache V. 6.1 software. The results revealed a significant dock score for 3b (?84.976?kcal/mol) and 3g (?90.921?kcal/mol) compared with allopurinol (?55.01?kcal/mol). The physiochemical properties and toxicity of the compounds were determined in silico using online computational tools. Overall, in vitro and in silico study revealed 3-amino-6-(4-chloro-2-hydroxy-5-methylphenyl)-1H-pyrazolo[3,4-d]thiazolo[3,2–a]pyrimidin-4-one (3g) as a potential lead compound for the design and development of XO inhibitors.     

Synthesis of New Bis(pyrazolo[1,5-a]pyrimidines) Linked to Different Spacers as Potential MurB Inhibitors

An efficient protocol was adopted to efficiently prepare three new series of bis(pyrazolo[1,5-a]pyrimidines) linked to different spacers. The new bis(pyrazolo[1,5-a]pyrimidines) were prepared in 80–90 % yields by reacting the respective bis(enaminones) and 4-(4-substituted benzyl)-1H-pyrazole-3,5-diamines in pyridine at reflux temperature for 5–7 h. The new products showed a wide spectrum of antibacterial activity against six different bacterial strains. In general, propane- and butane-linked bis(pyrazolo[1,5-a]pyrimidines), which are attached to 3-(4-methyl- or 4-methoxybenzyl) units, had the best antibacterial activity with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values up to 2.5 and 5.1 μM, respectively. Additionally, the previous products demonstrated promising MurB inhibitory activity with IC₅₀ values up to 7.2 μM.     

Synthesis and antiproliferative evaluation of 6-arylindeno[1,2-c]quinoline derivatives

A number of 6-arylindeno[1,2-c]quinoline derivatives were synthesized and evaluated for their antiproliferative activities against the growth of five cancer cell lines including human hepatocelluar carcinoma (Hep G2, Hep 3B and Hep2.2.1), non-small cell lung cancer (A549 and H1299), and normal diploid embryonic lung cell line (MRC-5). The preliminary results indicated that 9-(3-(dimethylamino)propoxy)-6-(4-(3-(dimethylamino)propoxy)phenyl)-2-fluoro-11H-indeno[1,2-c]quinolin-11-one (14c) was the most potent with GI₅₀ values of 0.61, 0.67, 0.59, and 0.72 μM against the growth of Hep G2, Hep 3B, Hep 2.2.1, and H1299 cells, respectively. Results have also shown that 2,9-bis(3-(dimethylamino)propoxy)-6-(4-(3-(dimethylamino)propoxy)phenyl)-11H-indeno[1,2-c]quinolin-11-one (17), which exhibited GI₅₀ of 0.60 and 0.68 μM against the growth of Hep G2 and A549, respectively, was more active than the positive topotecan and irinotecan. Compound 17 was less toxic than topotecan against the growth of normal cell (MRC-5) and therefore, was selected for further evaluation. Results indicated that compound 17 induce cell cycle arrest in G2/M phase, DNA fragmentation, and disrupt the microtubule network in A549 cells. The apoptotic induction may through the cleavage of PARP.     

Synthesis, X-ray crystal structure and optical properties of novel 2-aryl-3-ethoxycarbonyl-4-phenylpyrido[1,2-a]benzimidazoles

A series of novel 2‐aryl‐3‐ethoxycarbonyl‐4‐phenylpyrido[1,2‐a]benzimidazole derivatives were synthesized by the tandem reaction of 2‐benzoyl benzimidazole and (Z)‐ethyl 4‐bromo‐3‐arylbut‐2‐enoate in the presence of potassium carbonate. The compounds were characterized using IR, ¹H‐NMR, ¹³C‐NMR, HRMS and the structure of 6f was further determined by X‐ray crystallography. Both absorption and fluorescence spectra characteristics of the compounds were investigated in acetonitrile and dichloromethane. The results showed that the absorption maxima of the compounds varied from 220 to 284 nm, depending on the structure of 2‐aryl group. The fluorescence results revealed that these compounds exhibited blue‐green fluorescence (463–475 nm) in dilute solutions and showed acceptable fluorescence quantum yields (Ф_PL = 0.13–0.73) in dichloromethane. Copyright © 2011 John Wiley & Sons, Ltd.     

Furo[3′,2′:3,4]naphtho[1,2-d]imidazole derivatives as potential inhibitors of inflammatory factors in sepsis

Synthesis and anti-inflammatory effects of certain furo[3′,2′:3,4]naphtho[1,2-d]imidazole derivatives 12–18 were studied. These compounds were synthesized from naphtho[1,2-b]furan-4,5-dione (10) which in turn was prepared from the known 2-hydoxy-1,4-naphthoquinone (7) in a one pot reaction. Furo[3′,2′:3,4]naphtho[1,2-d]imidazole (12) was inactive (IC₅₀ value of >30 μM) while its 5-phenyl derivative 13, with an IC₅₀ value of 16.3 and 11.4 μM against lysozyme and β-glucuronidase release, respectively, was comparable to the positive trifluoperazine. The same potency was observed for 5-furan derivative 16 with an IC₅₀ value of 19.5 and 11.3 μM against lysozyme and β-glucuronidase release, respectively. An electron-withdrawing NO₂ substituted on 5-phenyl or 5-furanyl group led to the devoid of activity as in the cases of 14 and 17. Among them, compound 15 exhibited significant inhibitory effects, with an IC₅₀ value of 7.4 and 5.0 μM against lysozyme and β-glucuronidase release, respectively.For the LPS-induced NO production, the phenyl derivatives 12–15 were inactive while the nitrofuran counterparts 17 and 18 suppress LPS-induced NO production significantly, with an IC₅₀ value of 1.5 and 1.3 μM, respectively, which are more active than that of the positive 1400 W. Compounds 16–18 were capable of inhibiting LPS-induced iNOS protein expression at a dose-dependent manner in which compound 18, with an IC₅₀ of 0.52 μM in the inhibition of iNOS expression, is approximately fivefold more potent than that of the positive 1400 W. In the CLP rat animal model, compound 18 was found to be more active than the positive hydrocortisone in the inhibition of the iNOS mRNA expression in rat lung tissue. The sepsis-induced PGE2 production in rat serum decreased 150% by the pretreatment of 18 in a dose of 10 mg/kg.     

Discovery of pyrrolo[1,2-b]pyridazine-3-carboxamides as Janus kinase (JAK) inhibitors

A new class of Janus kinase (JAK) inhibitors was discovered using a rationally designed pyrrolo[1,2-b]pyridazine-3-carboxamide scaffold. Preliminary studies identified (R)-(2,2-dimethylcyclopentyl)amine as a preferred C4 substituent on the pyrrolopyridazine core (3b). Incorporation of amino group to 3-position of the cyclopentane ring resulted in a series of JAK3 inhibitors (4g–4j) that potently inhibited IFNγ production in an IL2-induced whole blood assay and displayed high functional selectivity for JAK3–JAK1 pathway relative to JAK2. Further modifications led to the discovery of an orally bioavailable (2-fluoro-2-methylcyclopentyl)amino analogue 5g which is a nanomolar inhibitor of both JAK3 and TYK2, functionally selective for the JAK3–JAK1 pathway versus JAK2, and active in a human whole blood assay.     

Antibacterial activity of 3-methylbenzo[d]thiazol-methylquinolinium derivatives and study of their action mechanism

The increasing incidence of multidrug resistant bacterial infection renders an urgent need for the development of new antibiotics. To develop small molecules disturbing FtsZ activity has been recognized as promising approach to search for antibacterial of high potency systematically. Herein, a series of novel quinolinium derivatives were synthesized and their antibacterial activities were investigated. The compounds show strong antibacterial activities against different bacteria strains including MRSA, VRE and NDM-1 Escherichia coli. Among these derivatives, a compound bearing a 4-fluorophenyl group (A2) exhibited a superior antibacterial activity and its MICs to the drug-resistant strains are found lower than those of methicillin and vancomycin. The biological results suggest that these quinolinium derivatives can disrupt the GTPase activity and dynamic assembly of FtsZ, and thus inhibit bacterial cell division and then cause bacterial cell death. These compounds deserve further evaluation for the development of new antibacterial agents targeting FtsZ.     

3-[2-Amino-2-imidazolin-4-yl] alanine, 2-[2-amino-2-imidazolin-4-yl] acetic acid, 2-aminoimidazole and other guanidine derivatives in the tephrosieae

The distribution of enduracididine, 2-[2-amino-2-imidazolin-4-yl] acetic acid, 2-aminoimidazole, canavanine, homoarginine, γ-hydroxyhomoarginine and other unidentified guanidino compounds in seeds of spp. of the Tephrosieae is described. Within Lonchocarpus enduracididine and 2-[2-amino-2-imidazolin-4-yl] acetic acid were found only in American spp. and canavanine only in African spp.     

Preclinical in vitro screening of newly synthesised amidino substituted benzimidazoles and benzothiazoles

Newly synthesised benzimidazole/benzotiazole derivatives bearing amidino, namely 3,4,5,6-tetrahydropyrimidin-1-ium chloride, substituents have been evaluated for their potential antitumor activity in vitro. Compounds and standard drugs (doxorubicin, staurosporine and vandetanib) were tested on three human lung cancer cell lines A549, HCC827 and NCI-H358. We tested compounds in MTS citotoxicity assay and in BrdU proliferative assay performed on 2 D and 3 D assay format. Because benzmidazole scaffold is similar to natural purines, we tested the most active compounds for ability to induce cell apoptosis of A549 by binding to DNA in comparison with doxorubicin and saturosporine. Additionally, the ADME properties of the most active benzothiazole/benzimidazole and non-active compounds were determined to see if the different ADME properties are the cause of different activity in 2 D and 3 D assays, as well as to see if the tested active compounds have drug like properties and potency for further profilation. ADME characterisation included solubility, lipophilicity, permeability, metabolic stability and binding to plasma proteins. In general, the benzothiazole derivatives were more active in comparison to their benzimidazole analogues. The exception was 2-phenyl substituted benzimidazole 6a being active with very pronounced activity especially towards HCC827 cells. All active compounds have similar mode of action on A549 cell line as standard compound doxorubicin, which binds to nucleic acids with the DNA double helix. Tested active benzothiazole compounds were characterised by moderate to good solubility, good metabolic stability, low permeability and high binding to plasma proteins. One tested active benzimidazole derivative showed ADME properties, but lower lipophilicity resulted in low PPB and higher metabolic instability. In addition, no significant difference was observed in ADME profile between active and non-active compounds.     

Determination of 6,4′-bis-(2-imidazolinylhydrazone)-2-phenylimidazo[1,2-a]pyridine in plasma and whole blood by high-performance liquid chromatography

A selective and sensitive HPLC assay for the quantitative determination of a new antifilarial drug, 6,4′-bis-(2-imidazolinylhydrazone)-2-phenylimidazo[1,2-a]pyridine (CDR 101) is described. After extraction from plasma and blood, CDR 101 was analysed using a C₁₈ Nucleosil ODS column (250×4.6 mm, 5 μm particle size) and mobile phase of acetonitrile-0.05 M ammonium acetate adjusted to pH 3.0, with UV detection at 318 nm. The mean recoveries of CDR 101 in plasma and blood over a concentration range of 25–500 ng/ml were 95.5±2.01% and 83.3±1.87%, respectively. The within-day and day-to-day coefficient of variations for plasma were 3.23-6.21% and 2.59-9.90%, respectively, those for blood were 2.59-5.92% and 2.89-6.82%, respectively. The minimum detectable concentration for CDR 101 was 1 ng/ml in plasma and 2.5 ng/ml in whole blood. This method was found to be suitable for clinical pharmacokinetic studies.     

Four metal-organic networks based on benzene-1,4-dioxyacetic acid and dipyrido[3,2-a:2′,3′-c]phenazine ligand

Four structurally diverse complexes, [Cd(dppz)(bdoa)]_n (1), [Zn(dppz)(bdoa)(H₂O)]_n (2), [Fe(dppz)₂(bdoa)]_n·2nH₂O (3), and [Co₂(dppz)₂(bdoa)₂(H₂O)]_n·3nH₂O (4), where H₂bdoa = benzene-1,4-dioxyacetic acid and dppz = dipyrido[3,2-a:2′,3′-c]phenazine, have been hydrothermally synthesized. Compounds 1-4 feature chain structures. There exist π-π interactions in the structures of 1, 2 and 4. Two neighboring chains of 1 are linked through the π-π interactions into a double chain supramolecular structure. The chains of 2 and 4 are further extended by the π-π interactions to form 3D and 2D supramolecular structures, respectively. The structural differences among such complexes show that the transition metals have important influences on their structures. The photoluminescent property of complex 2 and the magnetic property of complex 4 have also been investigated.     

Synthesis and in vitro antimicrobial activity of novel N-(6-chlorobenzo[d]thiazol-2-yl) hydrazine carboxamide derivatives of benzothiazole class

In this study, a series of novel 1,2,4-triazolo-[3,4-b]-1,3,4-thiadiazole (6a–g) and 1,3,4-oxadiazole (7a–g, 8) were synthesized from N-(6-chlorobenzo[d]thiazol-2-yl) hydrazine carboxamide derivatives of benzothiazole class. Antimicrobial properties of the title compound derivatives were investigated against one Gram (+) bacteria (Staphylococcus aureus), three Gram (?) bacteria (Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae) and five fungi (Candida albicans, Aspergillus niger, Aspergillus flavus, Monascus purpureus and Penicillium citrinum) using serial plate dilution method. The investigation of antibacterial and antifungal screening data revealed that all the tested compounds showed moderate to good inhibition at 12.5–100?µg/mL in DMSO. It has been observed that triazolo-thiadiazole derivatives are found to be more active than 1,3,4-oxadiazole derivatives against all pathogenic bacterial and fungal strains.