Alsinol, an arylamino alcohol derivative active against Plasmodium, Babesia, Trypanosoma, and Leishmania: past and new outcomes

Malaria, babesiosis, trypanosomosis, and leishmaniasis are some of the most life-threatening parasites, but the range of drugs to treat them is limited. An effective, safe, and low-cost drug with a large activity spectrum is urgently needed. For this purpose, an aryl amino alcohol derivative called Alsinol was resynthesized, screened in silico, and tested against Plasmodium, Babesia, Trypanosoma, and Leishmania. In silico Alsinol follows the Lipinski and Ghose rules. In vitro it had schizontocidal activity against Plasmodium falciparum and was able to inhibit gametocytogenesis; it was particularly active against late gametocytes. In malaria-infected mice, it showed a dose-dependent activity similar to chloroquine. It demonstrated a similar level of activity to reference compounds against Babesia divergens, and against promastigotes, and amastigotes stages of Leishmania in vitro. It inhibited the in vitro growth of two African animal strains of Trypanosoma but was ineffective in vivo in our experimental conditions. It showed moderate toxicity in J774A1 and Vero cell models. The study demonstrated that Alsinol has a large spectrum of activity and is potentially affordable to produce. Nevertheless, challenges remain in the process of scaling up synthesis, creating a suitable clinical formulation, and determining the safety margin in preclinical models.

Primaquine-quinoxaline 1,4-di-N-oxide hybrids with action on the exo-erythrocytic forms of Plasmodium induce their effect by the production of reactive oxygen species

Background

The challenge in anti-malarial chemotherapy is based on the emergence of resistance to drugs and the search for medicines against all stages of the life cycle of Plasmodium spp. as a therapeutic target. Nowadays, many molecules with anti-malarial activity are reported. However, few studies about the cellular and molecular mechanisms to understand their mode of action have been explored. Recently, new primaquine-based hybrids as new molecules with potential multi-acting anti-malarial activity were reported and two hybrids of primaquine linked to quinoxaline 1,4-di-N-oxide (PQ–QdNO) were identified as the most active against erythrocytic, exoerythrocytic and sporogonic stages.

Methods

To further understand the anti-malarial mode of action (MA) of these hybrids, hepg2-CD81 were infected with Plasmodium yoelii 17XNL and treated with PQ–QdNO hybrids during 48 h. After were evaluated the production of ROS, the mitochondrial depolarization, the total glutathione content, the DNA damage and proteins related to oxidative stress and death cell.

Results

In a preliminary analysis as tissue schizonticidals, these hybrids showed a mode of action dependent on peroxides production, but independent of the activation of transcription factor p53, mitochondrial depolarization and arrest cell cycle.

Conclusions

Primaquine–quinoxaline 1,4-di-N-oxide hybrids exert their antiplasmodial activity in the exoerythrocytic phase by generating high levels of oxidative stress which promotes the increase of total glutathione levels, through oxidation stress sensor protein DJ-1. In addition, the role of HIF1a in the mode of action of quinoxaline 1,4-di-N-oxide is independent of biological activity.

Novel antimalarial chloroquine- and primaquine-quinoxaline 1,4-di-N-oxide hybrids: Design, synthesis, Plasmodium life cycle stage profile, and preliminary toxicity studies

Emergence of drug resistance and targeting all stages of the parasite life cycle are currently the major challenges in antimalarial chemotherapy. Molecular hybridization combining two scaffolds in a single molecule is an innovative strategy for achieving these goals. In this work, a series of novel quinoxaline 1,4-di-N-oxide hybrids containing either chloroquine or primaquine pharmacophores was designed, synthesized and tested against both chloroquine sensitive and multidrug resistant strains of Plasmodium falciparum. Only chloroquine-based compounds exhibited potent blood stage activity with compounds 4b and 4e being the most active and selective hybrids at this parasite stage. Based on their intraerythrocytic activity and selectivity or their chemical nature, seven hybrids were then evaluated against the liver stage of Plasmodium yoelii, Plasmodium berghei and Plasmodium falciparum infections. Compound 4b was the only chloroquine-quinoxaline 1,4-di-N-oxide hybrid with a moderate liver activity, whereas compound 6a and 6b were identified as the most active primaquine-based hybrids against exoerythrocytic stages, displaying enhanced liver activity against P. yoelii and P. berghei, respectively, and better SI values than primaquine. Although both primaquine-quinoxaline 1,4-di-N-oxide hybrids slightly reduced the infection of mosquitoes, they inhibited sporogony of P. berghei and compound 6a showed 92% blocking of transmission. In vivo liver efficacy assays revealed that compound 6a showed causal prophylactic activity affording parasitaemia reduction of up to 95% on day 4. Absence of genotoxicity and in vivo acute toxicity were also determined. These results suggest the approach of primaquine-quinoxaline 1,4-di-N-oxide hybrids as new potential dual-acting antimalarials for further investigation.

Structure-activity relationship of new antimalarial 1-aryl-3-susbtituted propanol derivatives: Synthesis, preliminary toxicity profiling, parasite life cycle stage studies, target exploration, and targeted delivery

Design, synthesis, structure-activity relationship, cytotoxicity studies, in silico drug-likeness, genotoxicity screening, and in vivo studies of new 1-aryl-3-substituted propanol derivatives led to the identification of nine compounds with promising in vitro (55, 56, 61, 64, 66, and 70-73) and in vivo (66 and 72) antimalarial profiles against Plasmodium falciparum and Plasmodium berghei. Compounds 55, 56, 61, 64, 66 and 70-73 exhibited potent antiplasmodial activity against chloroquine-resistant strain FCR-3 (IC₅₀s < 0.28 μM), and compounds 55, 56, 64, 70, 71, and 72 showed potent biological activity in chloroquine-sensitive and multidrug-resistant strains (IC₅₀s < 0.7 μM for 3D7, D6, FCR-3 and C235). All of these compounds share appropriate drug-likeness profiles and adequate selectivity indexes (77 < SI < 184) as well as lack genotoxicity. In vivo efficacy tests in a mouse model showed compounds 66 and 72 to be promising candidates as they exhibited significant parasitemia reductions of 96.4% and 80.4%, respectively. Additional studies such as liver stage and sporogony inhibition, target exploration of heat shock protein 90 of P. falciparum, targeted delivery by immunoliposomes, and enantiomer characterization were performed and strongly reinforce the hypothesis of 1-aryl-3-substituted propanol derivatives as promising antimalarial compounds.

ImmunoPEGliposomes for the targeted delivery of novel lipophilic drugs to red blood cells in a falciparum malaria murine model

Most drugs currently entering the clinical pipeline for severe malaria therapeutics are of lipophilic nature, with a relatively poor solubility in plasma and large biodistribution volumes. Low amounts of these compounds do consequently accumulate in circulating Plasmodium-infected red blood cells, exhibiting limited antiparasitic activity. These drawbacks can in principle be satisfactorily dealt with by stably encapsulating drugs in targeted nanocarriers. Here this approach has been adapted for its use in immunocompetent mice infected by the Plasmodium yoelii 17XL lethal strain, selected as a model for human blood infections by Plasmodium falciparum. Using immunoliposomes targeted against a surface protein characteristic of the murine erythroid lineage, the protocol has been applied to two novel antimalarial lipophilic drug candidates, an aminoquinoline and an aminoalcohol. Large encapsulation yields of >90% were obtained using a citrate-buffered pH gradient method and the resulting immunoliposomes reached in vivo erythrocyte targeting and retention efficacies of >80%. In P. yoelii-infected mice, the immunoliposomized aminoquinoline succeeded in decreasing blood parasitemia from severe to uncomplicated malaria parasite densities (i.e. from ≥25% to ca. 5%), whereas the same amount of drug encapsulated in non-targeted liposomes had no significant effect on parasite growth. Pharmacokinetic analysis indicated that this good performance was obtained with a rapid clearance of immunoliposomes from the circulation (blood half-life of ca. 2 h), suggesting a potential for improvement of the proposed model.

New hydrazine and hydrazide quinoxaline 1,4-di-N-oxide derivatives: In silico ADMET, antiplasmodial and antileishmanial activity

We report the design (in silico ADMET criteria), synthesis, cytotoxicity studies (HepG-2 cells), and biological evaluation of 15 hydrazine/hydrazide quinoxaline 1,4-di-N-oxide derivatives against the 3D7 chloroquine sensitive strain and FCR-3 multidrug resistant strain of Plasmodium falciparum and Leishmania infantum (axenic amastigotes). Fourteen of derivatives are novel quinoxaline 1,4-di-N-oxide derivatives. Compounds 18 (3D7 IC₅₀=1.40μM, FCR-3 IC₅₀=2.56μM) and 19 (3D7 IC₅₀=0.24μM, FCR-3 IC₅₀=2.8μM) were identified as the most active against P. falciparum, and they were the least cytotoxic (CC₅₀-values>241μM) and most selective (SI>86). None of the compounds tested against L. infantum were considered to be active. Additionally, the functional role of the hydrazine and hydrazide structures were studied in the quinoxaline 1,4-di-N-oxide system.

Exploring the scope of new arylamino alcohol derivatives: Synthesis, antimalarial evaluation, toxicological studies, and target exploration

Synthesis of new 1-aryl-3-substituted propanol derivatives followed by structure-activity relationship, in silico drug-likeness, cytotoxicity, genotoxicity, in silico metabolism, in silico pharmacophore modeling, and in vivo studies led to the identification of compounds 22 and 23 with significant in vitro antiplasmodial activity against drug sensitive (D6 IC₅₀ ≤ 0.19 μM) and multidrug resistant (FCR-3 IC₅₀ ≤ 0.40 μM and C235 IC₅₀ ≤ 0.28 μM) strains of Plasmodium falciparum. Adequate selectivity index and absence of genotoxicity was also observed. Notably, compound 22 displays excellent parasitemia reduction (98 ± 1%), and complete cure with all treated mice surviving through the entire period with no signs of toxicity. One important factor is the agreement between in vitro potency and in vivo studies. Target exploration was performed; this chemotype series exhibits an alternative antimalarial mechanism.

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New aryl-substituted propanol derivatives (APD) show promising antimalarial activity.

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γ-amino alcohol moiety is significant antimalarial chemotype.

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Compound 22 displays excellent in vivo parasitemia reduction (98%) and complete cure.

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APD are active against drug sensitive and multidrug resistant strains.

Synthesis, biological evaluation and structure-activity relationships of new quinoxaline derivatives as anti-Plasmodium falciparum agents

We report the synthesis and antimalarial activities of eighteen quinoxaline and quinoxaline 1,4-di-N-oxide derivatives, eight of which are completely novel. Compounds 1a and 2a were the most active against Plasmodium falciparum strains. Structure-activity relationships demonstrated the importance of an enone moiety linked to the quinoxaline ring.

Novel quinoxaline 1,4-di-N-oxide derivatives as new potential antichagasic agents

As a continuation of our research and with the aim of obtaining new agents against Chagas disease, an extremely neglected disease which threatens 100 million people, eighteen new quinoxaline 1,4-di-N-oxide derivatives have been synthesized following the Beirut reaction. The synthesis of the new derivatives was optimized through the use of a new and more efficient microwave-assisted organic synthetic method. The new derivatives showed excellent in vitro biological activity against Trypanosoma cruzi. Compound 17, which was substituted with fluoro groups at the 6- and 7-positions of the quinoxaline ring, was the most active and selective in the cytotoxicity assay. The electrochemical study showed that the most active compounds, which were substituted by electron-withdrawing groups, possessed a greater ease of reduction of the N-oxide groups.

The in vivo antimalarial activity of methylene blue combined with pyrimethamine, chloroquine and quinine

The effectiveness of methylene blue (MB) combined with pyrimethamine (PYR), chloroquine (CQ) or quinine (Q) was examined in a classical four-day suppressive test against a causative agent of rodent malaria, Plasmodium berghei. A marked potentiation was observed when MB was administered at a non-curative dose of 15 mg/kg/day in combination with PYR (0.19 mg/kg/day) or Q (25 mg/kg/day). No synergy was found between MB (15 mg/Kg) and CQ (0.75 mg/Kg). Our results suggest that the combination of MB with PYR or Q may improve the efficacy of these currently used antimalarial drugs.

New amide derivatives of quinoxaline 1,4-di-N-oxide with leishmanicidal and antiplasmodial activities

Malaria and leishmaniasis are two of the World's most important tropical parasitic diseases. Continuing with our efforts to identify new compounds active against malaria and leishmaniasis, twelve new 1,4-di-N-oxide quinoxaline derivatives were synthesized and evaluated for their in vitro antimalarial and antileishmanial activity against Plasmodium falciparum FCR-3 strain, Leishmania infantum and Leishmania amazonensis. Their toxicity against VERO cells (normal monkey kidney cells) was also assessed. The results obtained indicate that a cyclopentyl derivative had the best antiplasmodial activity (2.9 µM), while a cyclohexyl derivative (2.5 µM) showed the best activity against L. amazonensis, and a 3-chloropropyl derivative (0.7 µM) showed the best results against L. infantum. All these compounds also have a Cl substituent in the R⁷ position.

Novel sulfonylurea derivatives as H3 receptor antagonists. Preliminary SAR studies

The combination of antagonism at histamine H(3) receptor and the stimulation of insulin secretion have been proposed as an approach to new dual therapeutic agents for the treatment of type 2 diabetes mellitus associated with obesity. We have designed and synthesized a new series of non-imidazole derivatives, based on a basic amine ring connected through an alkyl spacer of variable length to a phenoxysulfonylurea moiety. These compounds were initially evaluated for histamine H(3) receptor binding affinities, suggesting that a propoxy chain linker between the amine and the core ring could be essential for optimal binding affinity. Compound 56, 1-(naphthalen-1-yl)-3-[(p-(3-pyrrolidin-1-ylpropoxy)benzene)]sulfonylurea exhibited the best H(3) antagonism affinity. However, since all these derivatives failed to block K(ATP) channels, the link of these two related moieties should not be considered a good pharmacophore for obtaining new dual H(3) antagonists with insulinotropic activity, suggesting the necessity to propose a new chemical hybrid prototype.

3-Trifluoromethylquinoxaline N,N'-dioxides as anti-trypanosomatid agents. Identification of optimal anti-T. cruzi agents and mechanism of action studies

For a fourth approach of quinoxaline N,N'-dioxides as anti-trypanosomatid agents against T. cruzi and Leishmania, we found extremely active derivatives. The present study allows us to state the correct requirements for obtaining optimal in vitro anti-T. cruzi activity. Derivatives possessing electron-withdrawing substituents in the 2-, 3-, 6-, and 7-positions were the most active compounds. With regard to these features and taking into account their mammal cytotoxicity, some trifluoromethylquinoxaline N,N'-dioxides have been proposed as candidates for further clinical studies. Consequently, mutagenicity and in vivo analyses were performed with the most promising derivatives. In addition, with regard to the mechanism of action studies, it was demonstrated that mitochondrial dehydrogenases are involved in the anti-T. cruzi activity of the most active derivatives.

Quinoxaline 1,4-di-N-oxide and the potential for treating tuberculosis

New drugs active against drug-resistant tuberculosis are urgently needed to extend the range of TB treatment options to cover drug resistant infections. Quinoxaline derivatives show very interesting biological properties (antibacterial, antiviral, anticancer, antifungal, antihelmintic, insecticidal) and evaluation of their medicinal chemistry is still in progress. In this review we report the properties and the recent developments of quinoxaline 1,4-di-N-oxide derivatives as potential anti-tuberculosis agents. Specific agents are reviewed that have excellent antitubercular drug properties, are active on drug resistant strains and non-replicating mycobacteria. The properties of select analogs that have in vivo activity in the low dose aerosol infection model in mice will be reviewed.

Aryl piperazine and pyrrolidine as antimalarial agents. Synthesis and investigation of structure-activity relationships

Piperazine and pyrrolidine derivatives were synthesised and evaluated for their capacity to inhibit the growth of Plasmodium falciparum chloroquine-resistant (FCR-3) strain in culture. The combined presence of a hydroxyl group, a propane chain and a fluor were shown to be crucial for the antiplasmodial activity. Five compounds of the aryl-alcohol series inhibited 50% of parasite growth at doses ≤10 μM. The most active compound 1-(4-fluoronaphthyl)-3-[4-(4-nitro-2-trifluoromethylphenyl)piperazin-1-yl] propan-1-ol was almost 20-40 times more active on P. falciparum (IC(50): 0.5 μM) than on tumorogenic and non-tumorogenic cells. In vivo it has a very weak effect; inhibiting 35% of parasite growth only, at 10 mg/kg/day against Plasmodium berghei infected mice without any impact on survival time. In silico molecular docking study and molecular electrostatic potential calculation revealed that this compound bound to the active site of Plasmodium plasmepsin II enzyme.

Synthesis and biological evaluation of new quinoxaline derivatives as antioxidant and anti-inflammatory agents

We report the synthesis, anti-inflammatory, and antioxidant activities of novel quinoxaline and quinoxaline 1,4-di-N-oxide derivatives. Microwave-assisted methods have been used to optimize reaction times and to improve yields. The tested compounds presented important scavenging activities and promising in vitro inhibition of soybean lipoxygenase (LOX). Two of the best LOX inhibitors (compounds 7b and 8f) were evaluated as in vivo anti-inflammatory agents using the carrageenin-induced edema model. One of them (compound 7b) showed important in vivo anti-inflammatory effect (41%) similar to that of indomethacin (47%) used as the reference drug.

Trypanocidal properties, structure-activity relationship and computational studies of quinoxaline 1,4-di-N-oxide derivatives

Pyrazole and propenone quinoxaline derivatives were tested against intracellular forms of Leishmania peruviana and Trypanosoma cruzi. Both series were tested for toxicity against proliferative and non-proliferative cells. The pyrazole quinoxaline series was quite inactive against T. cruzi; however, the compound 2,6-dimethyl-3-f-quinoxaline 1,4-dioxide was found to inhibit 50% of Leishmania growth at 8.9 μM, with no impact against proliferative kidney cells and with low toxicity against THP-1 cells and murine macrophages. The compounds belonging to the propenone quinoxaline series were moderately active against T. cruzi. Among these compounds, two were particularly interesting, (2E)-1-(7-fluoro-3-methyl-quinoxalin-2-yl)-3-(3,4,5-trimethoxy-phenyl)-propenone and (2E)-3-(3,4,5-trimethoxy-phenyl)-1-(3,6,7-trimethyl-quinoxalin-2-yl)-propenone. The former possessed selective activity against proliferative cells (cancer and parasites) and was inactive against murine peritoneal macrophages; the latter was active against Leishmania and inactive against the other tested cells. Furthermore, insilico studies showed that both series respected Lipinski's rules and that they confirmed a linear correlation between trypanocidal activities and LogP. Docking studies revealed that compounds of the second series could interact with the poly (ADP-ribose) polymerase protein of Trypanosoma cruzi.

Synthesis and biological evaluation of new quinoxaline derivatives as antioxidant and anti-inflammatory agents

We report the synthesis, anti-inflammatory, and antioxidant activities of novel quinoxaline and quinoxaline 1,4-di-N-oxide derivatives. Microwave-assisted methods have been used to optimize reaction times and to improve yields. The tested compounds presented important scavenging activities and promising in vitro inhibition of soybean lipoxygenase (LOX). Two of the best LOX inhibitors (compounds 7b and 8f) were evaluated as in vivo anti-inflammatory agents using the carrageenin-induced edema model. One of them (compound 7b) showed important in vivo anti-inflammatory effect (41%) similar to that of indomethacin (47%) used as the reference drug.

Synthesis and antimycobacterial activity of new quinoxaline-2-carboxamide 1,4-di-N-oxide derivatives

As a continuation of our research and with the aim of obtaining new anti-tuberculosis agents which can improve the current chemotherapeutic anti-tuberculosis treatments, forty-three new quinoxaline-2-carboxamide 1,4-di-N-oxide derivatives were synthesized and evaluated for in vitro anti-tuberculosis activity against Mycobacterium tuberculosis strain H(37)Rv. Active compounds were also screened to assess toxicity to a VERO cell line. Results indicate that compounds with a methyl moiety substituted in position 3 and unsubstituted benzyl substituted on the carboxamide group provide an efficient approach for further development of anti-tuberculosis agents.

New 3-methylquinoxaline-2-carboxamide 1,4-di-N-oxide derivatives as anti-Mycobacterium tuberculosis agents

Mycobacterium tuberculosis (M.Tb) is a bacillus capable of causing a chronic and fatal condition in humans known as tuberculosis (TB). It is estimated that there are 8 million new cases of TB per year and 3.1 million infected people die annually. Thirty-six new amide quinoxaline 1,4-di-N-oxide derivatives have been synthesized and evaluated as potential anti-tubercular agents, obtaining biological values similar to the reference compound, Rifampin (RIF).

New 1-aryl-3-substituted propanol derivatives as antimalarial agents

This paper describes the synthesis and in vitro antimalarial activity against a P. falciparum 3D7 strain of some new 1-aryl-3-substituted propanol derivatives. Twelve of the tested compounds showed an IC₅₀ lower than 1 µM. These compounds were also tested for cytotoxicity in murine J774 macrophages. The most active compounds were evaluated for in vivo activity against P. berghei in a 4-day suppressive test. Compound 12 inhibited more than 50% of parasite growth at a dose of 50 mg/kg/day. In addition, an FBIT test was performed to measure the ability to inhibit ferriprotoporphyrin biocrystallization. This data indicates that 1-aryl-3-substituted propanol derivatives hold promise as a new therapeutic option for the treatment of malaria.

A narrow and highly significant linkage signal for severe bipolar disorder in the chromosome 5q33 region in Latin American pedigrees

We previously reported linkage of bipolar disorder to 5q33-q34 in families from two closely related population isolates, the Central Valley of Costa Rica (CVCR) and Antioquia, Colombia (CO). Here we present follow up results from fine-scale mapping in large CVCR and CO families segregating severe bipolar disorder, BP-I, and in 343 population trios/duos from CVCR and CO. Employing densely spaced SNPs to fine map the prior linkage peak region increases linkage evidence and clarifies the position of the putative BP-I locus. We performed two-point linkage analysis with 1134 SNPs in an approximately 9 Mb region between markers D5S410 and D5S422. Combining pedigrees from CVCR and CO yields a LOD score of 4.9 at SNP rs10035961. Two other SNPs (rs7721142 and rs1422795) within the same 94 kb region also displayed LOD scores greater than 4. This linkage peak coincides with our prior microsatellite results and suggests a narrowed BP-I susceptibility regions in these families. To investigate if the locus implicated in the familial form of BP-I also contributes to disease risk in the population, we followed up the family results with association analysis in duo and trio samples, obtaining signals within 2 Mb of the peak linkage signal in the pedigrees; rs12523547 and rs267015 (P = 0.00004 and 0.00016, respectively) in the CO sample and rs244960 in the CVCR sample and the combined sample, with P = 0.00032 and 0.00016, respectively. It remains unclear whether these association results reflect the same locus contributing to BP susceptibility within the extended pedigrees.

Heterocyclic-2-carboxylic acid (3-cyano-1,4-di-N-oxidequinoxalin-2-yl)amide derivatives as hits for the development of neglected disease drugs

Neglected diseases represent a major health problem. It is estimated that one third of the world population is infected with tuberculosis (TB). Besides TB, Chagas disease, affects approximately 20 million people. Quinoxalines display great activities against TB and Chagas. Forty new quinoxaline 1,4-di-N-oxide derivatives have been prepared and tested against M. tuberculosis and T. cruzi. Carboxylic acid quinoxaline 1,4-di-N-oxides (CAQDOs) 5 and 17 showed MIC values on the same order as the reference antituberculosis drug, rifampicin. Meanwhile, CAQDOs 12 and 22 presented IC(50) values in the same order as the anti-chagasic drug, nifurtimox.

Anti-leishmanial and structure-activity relationship of ring substituted 3-phenyl-1-(1,4-di-N-oxide quinoxalin-2-yl)-2-propen-1-one derivatives

A series of ring substituted 3-phenyl-1-(1,4-di-N-oxide quinoxalin-2-yl)-2-propen-1-one derivatives were synthesized and tested for in vitro leishmanicidal activity against amastigotes of Leishmania amazonensis in axenical cultures and murine infected macrophages. Structure-activity relationships demonstrated the importance of a radical methoxy at position R3', R4' and R5'. (2E)-3-(3,4,5-trimethoxy-phenyl)-1-(3,6,7-trimethyl-1,4-dioxy-quinoxalin-2-yl)-propenone was the most active. Cytotoxicity on macrophages revealed that this product was almost six times more active than toxic.

New amide derivatives as melanin-concentrating hormone receptor 1 antagonists for the treatment of obesity

Melanin-concentrating hormone (MCH) is a recently discovered central nervous system (CNS) target for treating obesity. Two novel series of amide derivatives were synthesized and evaluated biologically as MCH-R1 (melanin-concentrating hormone receptor 1) antagonists. The results showed that diphenyl substituents on the amide lead to better activity than biphenyl substituents.

Selective activity against Mycobacteriumtuberculosis of new quinoxaline 1,4-di-N-oxides

New series of 3-phenylquinoxaline 1,4-di-N-oxide with selective activity against Mycobacterium tuberculosis have been prepared and evaluated. Thirty-four of the seventy tested compounds showed an MIC value less than 0.2 microg/mL, a value on the order of the MIC of rifampicin. Furthermore, 45% of the evaluated derivatives showed a good in vitro activity/toxicity ratio. The most active and selective compounds carry a fluorine atom in the quinoxaline 7-position or in the phenyl substituent para-position. In conclusion, the potency, low cytotoxicity and selectivity of these compounds make them valid lead compounds for synthesizing new analogues, particularly compound 7-methyl-3-(4'-fluoro)phenylquinoxaline-2-carbonitrile 1,4-di-N-oxide (MIC <0.2 microg/mL and SI > 500).

Efficacy of quinoxaline-2-carboxylate 1,4-di-N-oxide derivatives in experimental tuberculosis

This study extends earlier reports regarding the in vitro efficacies of the 1,4-di-N-oxide quinoxaline derivatives against Mycobacterium tuberculosis and has led to the discovery of a derivative with in vivo efficacy in the mouse model of tuberculosis. Quinoxaline-2-carboxylate 1,4-di-N-oxide derivatives were tested in vitro against a broad panel of single-drug-resistant M. tuberculosis strains. The susceptibilities of these strains to some compounds were comparable to those of strain H(37)Rv, as indicated by the ratios of MICs for resistant and nonresistant strains, supporting the premise that 1,4-di-N-oxide quinoxaline derivatives have a novel mode of action unrelated to those of the currently used antitubercular drugs. Specific derivatives were further evaluated in a series of in vivo assays, including evaluations of the maximum tolerated doses, the levels of oral bioavailability, and the efficacies in a low-dose aerosol model of tuberculosis in mice. One compound, ethyl 7-chloro-3-methylquinoxaline-2-carboxylate 1,4-dioxide, was found to be (i) active in reducing CFU counts in both the lungs and spleens of infected mice following oral administration, (ii) active against PA-824-resistant Mycobacterium bovis, indicating that the pathway of bioreduction/activation is different from that of PA-824 (a bioreduced nitroimidazole that is in clinical trials), and (iii) very active against nonreplicating bacteria adapted to low-oxygen conditions. These data indicate that 1,4-di-N-oxide quinoxalines hold promise for the treatment of tuberculosis.

In vitro and in vivo antimycobacterial activities of ketone and amide derivatives of quinoxaline 1,4-di-N-oxide

OBJECTIVES

To evaluate a novel series of quinoxaline 1,4-di-N-oxides for in vitro activity against Mycobacterium tuberculosis and for efficacy in a mouse model of tuberculosis (TB).

METHODS

Ketone and amide derivatives of quinoxaline 1,4-di-N-oxide were evaluated in in vitro and in vivo tests including: (i) activity against M. tuberculosis resistant to currently used antitubercular drugs including multidrug-resistant strains (MDR-TB resistant to isoniazid and rifampicin); (ii) activity against non-replicating persistent (NRP) bacteria; (iii) MBC; (iv) maximum tolerated dose, oral bioavailability and in vivo efficacy in mice; and (v) potential for cross-resistance with another bioreduced drug, PA-824.

RESULTS

Ten compounds were tested on single drug-resistant M. tuberculosis. In general, all compounds were active with ratios of MICs against resistant and non-resistant strains of <or=4.00. One compound, 5, was orally active in a murine model of TB, bactericidal, active against NRP bacteria and active on MDR-TB and poly drug-resistant clinical isolates (resistant to 3-5 antitubercular drugs).

CONCLUSIONS

Quinoxaline 1,4-di-N-oxides represent a new class of orally active antitubercular drugs. They are likely bioreduced to an active metabolite, but the pathway of bacterial activation was different from PA-824, a bioreducible nitroimidazole in clinical trials. Compound 5 was bactericidal and active on NRP organisms indicating that activation occurred in both growing and non-replicating bacteria leading to cell death. The presence of NRP bacteria is believed to be a major factor responsible for the prolonged nature of antitubercular therapy. If the bactericidal activity and activity on non-replicating bacteria in vitro translate to in vivo conditions, quinoxaline 1,4-di-N-oxides may offer a path to shortened therapy.

Synthesis and structure-activity relationship of 3-phenylquinoxaline 1,4-di-N-oxide derivatives as antimalarial agents

As a continuation of our research and with the aim of obtaining new antimalarial agents, new series of 3-phenylquinoxaline 1,4-di-N-oxide derivatives have been synthesized following the classical Beirut reaction. Antiplasmodial activity was evaluated in vitro against Plasmodium falciparum by the incorporation of [3H]-hypoxanthine. Cytotoxicity was tested in KB cells by AlamarBlue assay. Twenty-one of the 60 compounds that were assayed against 3D7 (CQ-sensitive) showed enough activity to be also evaluated against K1 (CQ-resistant) strain. Ten of them were shown to be more active than chloroquine in the resistant strain. The most interesting compounds are 7-(methyl or methoxy)-3-(4'-fluoro or chloro)phenylquinoxaline-2-carbonitrile 1,4-di-N-oxides because of their low IC50 and their high SI shown for the K1 strain, making them valid new leads.

Substitutions of fluorine atoms and phenoxy groups in the synthesis of quinoxaline 1,4-di-N-oxide derivatives

The unexpected substitution of fluorine atoms and phenoxy groups attached to quinoxaline or benzofuroxan rings is described. The synthesis of 2-benzyl- and 2-phenoxy-3-methylquinoxaline 1,4-di-N-oxide derivatives was based on the classical Beirut reaction. The tendency of fluorine atoms linked to quinoxaline or benzofuroxan rings to be replaced by a methoxy group when dissolved in an ammonia saturated solution of methanol was clearly demonstrated. In addition, 2-phenoxyquinoxaline 1,4-di-N-oxide derivatives became 2-aminoquinoxaline 1,4-di-N-oxide derivatives in the presence of gaseous ammonia.

Synthesis and antiplasmodial activity of 3-furyl and 3-thienylquinoxaline-2-carbonitrile 1,4-di-N-oxide derivatives

The aim of this study was to identify new compounds active against Plasmodium falciparum based on our previous research carried out on 3-phenyl-quinoxaline-2-carbonitrile 1,4-di-N-oxide derivatives. Twelve compounds were synthesized and evaluated for antimalarial activity. Eight of them showed an IC(50) less than 1 microM against the 3D7 strain. Derivative 1 demonstrated high potency (IC(50)= 0.63 microM) and good selectivity (SI=10.35), thereby becoming a new lead-compound.

Antiplasmodial structure–activity relationship of 3-trifluoromethyl-2-arylcarbonylquinoxaline 1,4-di-N-oxide derivatives

Derivatives of 3-trifluoromethyl-2-arylcarbonylquinoxaline 1,4-di-N-oxide (4b-g, 5b-g, 6a-g) were synthesized and evaluated for their capacity to inhibit the growth of chloroquine-resistant Plasmodium falciparum FCB1 strain in culture. Compound 7-chloro-2-(2-furylcarbonyl)-3-trifluoromethyl-1,4-quinoxaline di-N-oxide (5g) was the most active being almost 5 times more active than chloroquine. It was also 50 times more active against P. falciparum than toxic toward MCF7 cells. Structural characteristics for a quinoxaline to be active were defined: bioisosteric modification of phenyl group by 2-thienyl or 2-furyl subunits, R2 position must be free or occupied by a methyl group and R1 position must be free or occupied by Cl, CH3, OCH3 or CF3.

Synthesis and structure-activity relationship of 3-phenylquinoxaline 1,4-di-N-oxide derivatives as antimalarial agents

As a continuation of our research and with the aim of obtaining new antimalarial agents, new series of 3-phenylquinoxaline 1,4-di-N-oxide derivatives have been synthesized following the classical Beirut reaction. Antiplasmodial activity was evaluated in vitro against Plasmodium falciparum by the incorporation of [3H]-hypoxanthine. Cytotoxicity was tested in KB cells by AlamarBlue assay. Twenty-one of the 60 compounds that were assayed against 3D7 (CQ-sensitive) showed enough activity to be also evaluated against K1 (CQ-resistant) strain. Ten of them were shown to be more active than chloroquine in the resistant strain. The most interesting compounds are 7-(methyl or methoxy)-3-(4'-fluoro or chloro)phenylquinoxaline-2-carbonitrile 1,4-di-N-oxides because of their low IC50 and their high SI shown for the K1 strain, making them valid new leads.

Synthesis and biological evaluation of new 2-arylcarbonyl-3-trifluoromethylquinoxaline 1,4-di-N-oxide derivatives and their reduced analogues

As a continuation of our research in the quinoxaline 1,4-di-N-oxide new series of 2-arylcarbonyl-3-trifluoromethylquinoxaline, 1,4-di-N-oxide derivatives have been synthesized and evaluated in a full panel of 60 human tumor cell lines. Selective reductions were carried out on two compounds which allowed us to determine the compound structures by comparison of the 1H NMR spectra. In general, all the di-N-oxidized compounds showed good cytotoxic parameters. The best activity was observed in derivatives with electron-withdrawing groups in position 6 or 7 on the quinoxaline ring and in the unsubstituted analogues, whereas loss of one or two oxygens reduced the cytotoxicity. The best five compounds were selected for evaluation for the in vivo hollow fiber assays. In vitro studies reveal that compound 5h efficiently generates reactive oxygen species via redox cycling in the presence of the NADPH/cytochrome P450 enzyme system, providing a plausible molecular mechanism for the observed aerobic cytotoxicity of these quinoxaline N-oxides.

Novel series of substituted biphenylmethyl urea derivatives as MCH-R1 antagonists for the treatment of obesity

We have designed and synthesized two novel series of MCH-R1 antagonists based on a substituted biphenylmethyl urea core. SAR was explored, suggesting that optimal binding with the receptor was achieved when the biphenylmethyl group and the linker were substituted on the same nitrogen of the urea moiety. Compound 1-(3'-cyano-4-biphenylmethyl)-3-(2-hydroxy-1,1-dimethylethyl)-1-{2-[1-(4-methylbenzyl)-4-piperidinyl]ethyl}urea 2t showed the best antagonist binding activity to the MCH-R1 with a 43 nM K(i).

Synthesis and antimalarial activity of new 3-arylquinoxaline-2-carbonitrile derivatives

New series of 3-arylquinoxaline-carbonitrile derivatives have been synthesized from various 5-substituted or 5,6-disubstituted benzofuroxanes and tested for their in vitro and in vivo activity against the erythrocytic development of Plasmodium falciparum strain with different chloroquine-resistance status. Quinoxaline 1,4-dioxide derivatives showed superior antimalarial activity in respect to reduced quinoxaline analogues. The best activity was observed with nonsubstituted quinoxaline 1,4-dioxides in positions 6 and 7 of the aromatic ring and with a hydrogen or chloro substituent in para position of the phenyl group.

Synthesis of new quinoxaline-2-carboxylate 1,4-dioxide derivatives as anti-Mycobacterium tuberculosis agents

Twenty-nine new 6(7)-substituted quinoxaline-2-carboxylate 1,4-dioxide derivatives were synthesized and evaluated for in vitro antituberculosis activity. In general, the in vitro activity is significantly affected by substituents on the quinoxaline nucleus. It has been observed that the presence of a chloro, methyl, or methoxy group in position 7 of the benzene moiety reduces the MIC and IC(50) values. However, antituberculosis activity principally depends on the substituents in the carboxylate group, improving in the following order: benzyl > ethyl > 2-methoxyethyl > allyl > tert-butyl. Fourteen compounds have been selected for macrophage assay, and the results show that ethyl and benzyl 3-methylquinoxaline-2-carboxylate 1,4-dioxide derivatives with the chlorine group in position 7 of the benzene moiety (compounds 10 and 26) and the unsubstituted derivatives (compounds 11 and 27) have good antitubercular activity, including activity in macrophages. In addition, compounds 7 and 28 (the only ones tested up to now) are active against drug-resistant strains of M. tuberculosis H(37)Rv. In conclusion, the potency, selectivity, and low cytotoxicity of these compounds make them valid leads for synthesizing new compounds that possess better activity.