New quinoxaline 1,4-di-N-oxides for treatment of tuberculosis

Quinoxaline 1,4-Dioxides: Advances in Chemistry and Chemotherapeutic Drug Development

N-Oxides of heterocyclic compounds are the focus of medical chemistry due to their diverse biological properties. The high reactivity and tendency to undergo various rearrangements have piqued the interest of synthetic chemists in heterocycles with N-oxide fragments. Quinoxaline 1,4-dioxides are an example of an important class of heterocyclic N-oxides, whose wide range of biological activity determines the prospects of their practical use in the development of drugs of various pharmaceutical groups. Derivatives from this series have found application in the clinic as antibacterial drugs and are used in agriculture. Quinoxaline 1,4-dioxides present a promising class for the development of new drugs targeting bacterial infections, oncological diseases, malaria, trypanosomiasis, leishmaniasis, and amoebiasis. The review considers the most important methods for the synthesis and key directions in the chemical modification of quinoxaline 1,4-dioxide derivatives, analyzes their biological properties, and evaluates the prospects for the practical application of the most interesting compounds.

Recent advances in the transition-metal-free synthesis of quinoxalines

Quinoxalines, also known as benzo[a]pyrazines, constitute an important class of nitrogen-containing heterocyclic compounds as a result of their widespread prevalence in natural products, biologically active synthetic drug candidates, and optoelectronic materials. Owing to their importance and chemists' ever-increasing imagination of new transformations of these products, tremendous efforts have been dedicated to finding more efficient approaches toward the synthesis of quinoxaline rings. The last decades have witnessed a marvellous outburst in modifying organic synthetic methods to create them sustainable for the betterment of our environment. The exploitation of transition-metal-free catalysis in organic synthesis leads to a new frontier to access biologically active heterocycles and provides an alternative method from the perspective of green and sustainable chemistry. Despite notable developments achieved in transition-metal catalyzed synthesis, the high cost involved in the preparation of the catalyst, toxicity, and difficulty in removing it from the final products constitute disadvantageous effects on the atom economy and eco-friendly nature of the transformation. In this review article, we have summarized the recent progress achieved in the synthesis of quinoxalines under transition-metal-free conditions and cover the reports from 2015 to date. This aspect is presented alongside the mechanistic rationalization and limitations of the reaction methodologies. The scopes of future developments are also highlighted.

In vitro antimicrobial activities of animal-used quinoxaline 1,4-di-N-oxides against mycobacteria, mycoplasma and fungi

Background

The quinoxaline 1,4-di-N-oxides (QdNOs) were known as potent antibacterial agents. For the purpose of evaluating the bioactivity of existing animal-used QdNOs drugs against representative pathogenic microorganism, the representative drugs of quinoxalines including cyadox, mequindox, quinocetone and their metabolites were submitted to the in vitro evaluation for antituberculosis, antimycoplasma, antifungal and antiviral activities.

Results

In antituberculosis assays, the prototype compounds were active (MIC = 4 ~ 8 μg/mL) against Mycobacterium tuberculosis H37Rv and M. bovis. Combined antimicrobial susceptibility test indicated that cyadox, mequindox and quinocetone combined with rifampicin had additive effect against M. tuberculosis complex with Fractional Inhibitory Concentration Index (FIC) of 0.75. Results of antifungal assays showed that quinocetone was active against Microsporum canis with MIC of 8 μg/mL. Antimycoplasma screening showed a generally good activity of quinocetone against Mycoplasma gallisepticum and Mycoplasma hyopneumoniae, with MIC between 8 and 16 μg/mL. As shown from the combined antimicrobial susceptibility test, cyadox, mequindox and quinocetone combined with tetracycline had additive effect against Mycoplasma gallisepticum with FIC of 0.75. These compounds were also submitted to antiviral assay against infectious bursal disease virus, porcine reproductive and respiratory syndrome virus, porcine parvovirus and classical swine fever virus. The results obtained showed that these QdNOs and their metabolites have no inhibitory activity against these viruses in vitro.

Conclusions

QdNOs exhibit antimicrobial activities against mycobacteria, mycoplasma and fungi. This study gives new insight in further application of QdNOs and offers a way to promote the healthcare of animal husbandry.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-016-0812-7) contains supplementary material, which is available to authorized users.

Design and synthesis of novel quinoxaline derivatives as potential candidates for treatment of multidrug-resistant and latent tuberculosis

Twenty-four quinoxaline derivatives were evaluated for their antimycobacterial activity using BacTiter-Glo microbial cell viability assay. Five compounds showed MIC values <3.1 μM and IC50 values<1.5 μM in primary screening and therefore, they were moved on for further evaluation. Compounds 21 and 18 stand out, showing MIC values of 1.6 μM and IC50 values of 0.5 and 1.0 μM, respectively. Both compounds were the most potent against three evaluated drug-resistant strains. Moreover, they exhibited intracellular activity in infected macrophages, considering log-reduction and cellular viability. In addition, compounds 16 and 21 were potent against non-replicating Mycobacterium tuberculosis and compound 21 was bactericidal. Therefore, quinoxaline derivatives could be considered for making further advances in the future development of antimycobacterial agents.

Quinoxaline 1,4-di-N-Oxides: Biological Activities and Mechanisms of Actions

Quinoxaline 1,4-di-N-oxides (QdNOs) have manifold biological properties, including antimicrobial, antitumoral, antitrypanosomal and antiinflammatory/antioxidant activities. These diverse activities endow them broad applications and prospects in human and veterinary medicines. As QdNOs arouse widespread interest, the evaluation of their medicinal chemistry is still in progress. In the meantime, adverse effects have been reported in some of the QdNO derivatives. For example, genotoxicity and bacterial resistance have been found in QdNO antibacterial growth promoters, conferring urgent need for discovery of new QdNO drugs. However, the modes of actions of QdNOs are not fully understood, hindering the development and innovation of these promising compounds. Here, QdNOs are categorized based on the activities and usages, among which the antimicrobial activities are consist of antibacterial, antimycobacterial and anticandida activities, and the antiprotozoal activities include antitrypanosomal, antimalarial, antitrichomonas, and antiamoebic activities. The structure-activity relationship and the mode of actions of each type of activity of QdNOs are summarized, and the toxicity and the underlying mechanisms are also discussed, providing insight for the future research and development of these fascinating compounds.

Design and synthesis of novel quinoxaline derivatives as potential candidates for treatment of multidrug-resistant and latent tuberculosis

Twenty-four quinoxaline derivatives were evaluated for their antimycobacterial activity using BacTiter-Glo microbial cell viability assay. Five compounds showed MIC values <3.1 μM and IC50 values<1.5 μM in primary screening and therefore, they were moved on for further evaluation. Compounds 21 and 18 stand out, showing MIC values of 1.6 μM and IC50 values of 0.5 and 1.0 μM, respectively. Both compounds were the most potent against three evaluated drug-resistant strains. Moreover, they exhibited intracellular activity in infected macrophages, considering log-reduction and cellular viability. In addition, compounds 16 and 21 were potent against non-replicating Mycobacterium tuberculosis and compound 21 was bactericidal. Therefore, quinoxaline derivatives could be considered for making further advances in the future development of antimycobacterial agents.

E-2-[3-(3,4-dichlorophenyl)-1-oxo-2-propenyl]-3-methylquinoxaline-1,4-dioxide: a lead antitubercular agent which alters mitochondrial respiration in rat liver

A series of 2-(3-aryl-1-oxo-2-propenyl)-3-methylquinoxaline-1,4-dioxides 1a-l and 2-acetyl-3-methylquinoxaline-1,4-dioxide 2 were evaluated against Mycobacterium tuberculosis H(37)Rv. With the exception of the 4-nitro analog 1k, significant antitubercular potencies were observed in series 1 and 2 which have IC(50) values in the range of 1-23 microM. Negative correlations were noted between the IC(50) values of 1a-j, l towards M. tuberculosis and both the sigma and pi constants of the substituents in the benzylidene aryl ring. In particular, 1h emerged as a lead compound having IC(50) and IC(90) figures of 1.03 microM and 1.53 microM, respectively. This molecule affected respiration in rat liver mitochondria which is likely one way that 1h and the bioactive analogs exert their antitubercular properties. The quinoxaline 2, which lacks an alpha,beta-unsaturated group, has no effect on mitochondrial respiration using concentrations which inhibit the growth of M. tuberculosis.

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.

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.

Unexpected reduction of ethyl 3-phenylquinoxaline-2- carboxylate 1,4-di-N-oxide derivatives by amines

The unexpected tendency of amines and functionalized hydrazines to reduce ethyl 3-phenylquinoxaline-2-carboxylate 1,4-di-N-oxide (1) to afford a quinoxaline 1c and mono-oxide quinoxalines 1a and 1b is described. The experimental conditions were standardized to the use of two equivalents of amine in ethanol under reflux for two hours, with the aim of studying the distinct reductive profiles of the amines and the chemoselectivity of the process. With the exception of hydrazine hydrate, which reduced compound 1 to a 3-phenyl-2-quinoxalinecarbohydrazide derivative, the amines only acted as reducing agents.