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

Flavonoid-Quinoxaline Hybrid Compounds as Cathepsin Inhibitors Against Fascioliasis

Fasciola hepatica is a parasitic trematode that infects livestock animals and humans, causing significant health and economic burdens worldwide. The extensive use of anthelmintic drugs has led to the emergence of resistant parasite strains, posing a threat to treatment success. The complex life cycle of the liver fluke, coupled with limited funding and research interest, have hindered progress in drug discovery. Our group has been working in drug development against this parasite using cathepsin proteases as molecular targets, finding promising compound candidates with in vitro and in vivo efficacy. Here, we evaluated hybrid molecules that combine two chemotypes, chalcones and quinoxaline 1,4-di- N-oxides, previously found to inhibit F. hepatica cathepsin Ls and tested their in vitro activity with the isolated targets and the parasites in culture. These molecules proved to be good cathepsin inhibitors and to kill the juvenile parasites at micromolar concentrations. Also, we performed molecular docking studies to analyze the compounds-cathepsins interface, finding that the best inhibitors interact at the active site cleft and contact the catalytic dyad and residues belonging to the substrate binding pockets. We conclude that the hybrid compounds constitute promising scaffolds for the further development of new fasciolicidal compounds.

Expanding the chemical space of ester of quinoxaline-7-carboxylate 1,4-di-N-oxide derivatives as potential antitubercular agents

Tuberculosis is a worldwide health problem that warrants attention given that the current treatment options require a long-term chemotherapeutic period and have reported the development of Mycobacterium tuberculosis (M. tuberculosis) multidrug resistant strains. In this study, n-butyl and isobutyl quinoxaline-7-carboxylate 1,4-di-N-oxide were evaluated against replicating and non-replicating H37Rv M. tuberculosis strains. The results showed that seventeen of the twenty-eight derivatives have minimum inhibitory concentration (MIC) values lower than isoniazid (2.92 μM). The most active antimycobacterial agents were T-148, T-149, T-163, and T-164, which have the lowest MIC values (0.53, 0.57, 0.53, and 0.55 μM respectively). These results confirm the potential of quinoxaline-1,4-di-N-oxide against M. tuberculosis to develop and obtain new and more safety antituberculosis drugs.

In silico virtual screening for the identification of novel inhibitors against dihydrodipicolinate reductase (DapB) of Mycobacterium tuberculosis, a key enzyme of diaminopimelate pathway

IMPORTANCE

Non-compliance to lengthy antituberculosis (TB) treatment regimen, associated side effects, and emergence of drug-resistant strains of Mycobacterium tuberculosis (M. tb) emphasize the need to develop more effective anti-TB drugs. Here, we have evaluated the role of M. tb dihydrodipicolinate reductase (DapB), a component of the diaminopimelate pathway, which is involved in the biosynthesis of both lysine and mycobacterial cell wall. We showed that DapB is essential for the in vitro as well as intracellular growth of M. tb. We further utilized M. tb DapB, as a target for identification of inhibitors by employing in silico virtual screening, and conducted various in vitro screening assays to identify inhibitors with potential to inhibit DapB activity and in vitro and intracellular growth of M. tb with no significant cytotoxicity against various mammalian cell lines. Altogether, M. tb DapB serves as an important drug target and a hit molecule, namely, 4-(3-Phenylazoquinoxalin-2-yl) butanoic acid methyl ester has been identified as an antimycobacterial molecule in our study.

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.

Novel Benzylamine Derivatives: Synthesis, Anti-Mycobacterium Tuberculosis Evaluation and Predicted ADMET Properties

Background:

Tuberculosis (TB), a disease caused by the bacillus bacteria Mycobacterium tuberculosis is one of the major contributors of ill health in the world. TB is ranked in the top 10 causes of death globally and it is the leading killer associated with a single infectious agent. According to the World Health Organization (WHO), global number of deaths associated with TB have been slowly declining with 1.3 million in reported 2016 and 2017, and 1.2 million reported in 2018 and 2019.

Objective:

The synthesis, characterisation, biological evaluations, and the prediction of ADMET properties of the novel benzylamine derivatives.

Methods:

Commercially available reagents and solvents were purchased from Sigma Aldrich and Merck (South Africa). All chemicals were used as received, unless otherwise stated. The synthesised crude compounds were purified by flash silica gel column chromatography (5 – 30% ethyl acetate in hexane). The successful formation and purity of the synthesised compounds was confirmed by NMR, HRMS and melting point.

Results:

The respective organic compounds were synthesised by treating 3-ethoxysalcyladehyde, 5-bromo-3-ethoxysalcyladehyde, 5-chloro-3-ethoxysalcyladehyde with various aromatic amines and the products were obtained in good to excellent yields. The 1H and 13C NMR spectra of all the products showed the appearance of the methylene signals ranging from 3.88 – 4.68 ppm and 42.25 – 52.57 ppm respectively. Additionally, most compounds showed anti-Mycobacterium tuberculosis activity that ranged between 20 and 28 µM.

Conclusion:

A total of 36 compounds were synthesised and successfully biologically evaluated against Mycobacterium tuberculosis (Mtb) H37RV strain. All compounds showed activity against Mtb at concentrations of > 20 µM < 28 µM with the exception of compound one that was active against Mtb at higher concentration (MIC90 > 125 µM).

Synthesis and Characterization of Novel 2-Acyl-3-trifluoromethylquinoxaline 1,4-Dioxides as Potential Antimicrobial Agents

The emergence of drug resistance in pathogens leads to a loss of effectiveness of antimicrobials and complicates the treatment of bacterial infections. Quinoxaline 1,4-dioxides represent a prospective scaffold for search of new compounds with improved chemotherapeutic characteristics. Novel 2-acyl-3-trifluoromethylquinoxaline 1,4-dioxides with alteration of substituents at position 2 and 6 were synthesized via nucleophilic substitution with piperazine moiety and evaluated against a broad panel of bacteria and fungi by measuring their minimal inhibitory concentrations. Their mode of action was assessed by whole-genomic sequencing of spontaneous drug-resistant Mycobacterium smegmatis mutants, followed by comparative genomic analysis, and on an original pDualrep2 system. Most of the 2-acyl-3-trifluoromethylquinoxaline 1,4-dioxides showed high antibacterial properties against Gram-positive strains, including mycobacteria, and the introduction of a halogen atom in the position 6 of the quinoxaline ring further increased their activity, with 13c being the most active compound. The mode of action studies confirmed the DNA-damaging nature of the obtained quinoxaline 1,4-dioxides, while drug-resistance may be provided by mutations in redox homeostasis genes, encoding enzymes potentially involved in the activation of the compounds. This study extends views about the antimicrobial and antifungal activities of the quinoxaline 1,4-dioxides and can potentially lead to the discovery of new antibacterial drugs.

Targeting Non-Replicating Mycobacterium tuberculosis and Latent Infection: Alternatives and Perspectives (Mini-Review)

Latent tuberculosis infection (LTBI) represents a major challenge to curing TB disease. Current guidelines for LTBI management include only three older drugs and their combinations-isoniazid and rifamycins (rifampicin and rifapentine). These available control strategies have little impact on latent TB elimination, and new specific therapeutics are urgently needed. In the present mini-review, we highlight some of the alternatives that may potentially be included in LTBI treatment recommendations and a list of early-stage prospective small molecules that act on drug targets specific for Mycobacterium tuberculosis latency.

Quinoxaline Moiety: A Potential Scaffold against Mycobacterium tuberculosis

Background. The past decades have seen numerous efforts to develop new antitubercular agents. Currently, the available regimens are lengthy, only partially effective, and associated with high rates of adverse events. The challenge is therefore to develop new agents with faster and more efficient action. The versatile quinoxaline ring possesses a broad spectrum of pharmacological activities, ensuring considerable attention to it in the field of medicinal chemistry. Objectives. In continuation of our program on the pharmacological activity of quinoxaline derivatives, this review focuses on potential antimycobacterial activity of recent quinoxaline derivatives and discusses their structure-activity relationship for designing new analogs with improved activity. Methods. The review compiles recent studies published between January 2011 and April 2021. Results. The final total of 23 studies were examined. Conclusions. Data from studies of quinoxaline and quinoxaline 1,4-di-N-oxide derivatives highlight that specific derivatives show encouraging perspectives in the treatment of Mycobacterium tuberculosis and the recent growing interest for these scaffolds. These interesting results warrant further investigation, which may allow identification of novel antitubercular candidates based on this scaffold.

Discovery of novel nitrogenous heterocyclic-containing quinoxaline-1,4-di-N-oxides as potent activator of autophagy in M.tb-infected macrophages

As a continuation of our research on antimycobacterial agents, a series of novel quinoxaline-1,4-di-N-oxides (QdNOs) containing various nitrogenous heterocyclic moieties at the R₆ position were designed and synthesized. Antimycobacterial activities, as well as the cytotoxic effects, of the compounds were assayed. Four compounds (6b, 6f, 6n, and 6o), characterized by 2-carboxylate ethyl or benzyl ester, 6-imidazolyl or 1,2,4-triazolyl, and a 7-fluorine group, exhibited the most potent antimycobacterial activity against M.tb strain H37Rv (MIC ≤ 0.25 μg/mL) with low toxicity in VERO cells (SI = 169.3-412.1). Compound 6o also exhibited excellent antimycobacterial activity in an M.tb-infected macrophage model and was selected for further exploration of the mode of antimycobacterial action of QdNOs. The results showed that compound 6o was capable of disrupting membrane integrity and disturbing energy homeostasis in M.tb. Furthermore, compound 6o noticeably increased cellular ROS levels and, subsequently, induced autophagy in M.tb-infected macrophages, possibly indicating the pathways of QdNOs-mediated inhibition of intracellular M.tb replication. The in vivo pharmacokinetic (PK) profiles indicated that compounds 6o was acceptably safe and possesses favorable PK properties. Altogether, these findings suggest that compound 6o is a promising antimycobacterial candidate for further research.

Synthesis of novel quinoxaline-alkynyl derivatives and their anti-Mycobacterium tuberculosis activity

The study report on the synthesis of a series of novel quinoxaline-alkynyl derivatives that were evaluated for their activity against Mycobacterium tuberculosis (Mtb) H₃₇R_V strain. A total of 19 compounds bearing an alcohol, aldehyde, mesylate and ester groups on the alkynly group, and also containing a chloro and nitro groups at the 6-position, were prepared. Seven compounds (3c, 4a-b, 5a, 5c, 6c and 6i), were found to have MIC₉₀ < 10 µM, while five compounds (3b, 6a, 6b, 6d and 6h) had MIC₉₀ in the range 10-20 µM. Compounds bearing a nitro substituent in the 6-position were generally more active and demonstrated a better safety profile, when compared to the unsubstituted and 6-chloro derivatives. Of the seven most active compounds, four contained nitro group at the 6-position.

Quinoxaline 1,4-di-N-Oxide Derivatives: Are They Unselective or Selective Inhibitors?

BACKGROUND

For decades, the quinoxaline 1,4-di-N-oxide ring has been considered a privileged structure to develop new antibacterial, antitumoural, and antiprotozoal agents, among others, however its mechanism of action is not clear.

OBJECTIVE

The main aim of this mini-review was to analyze the mechanism of action of quinoxaline 1,4-di-N-oxide derivatives reported as antibacterial, antitumoural and antiprotozoal agents.

RESULTS

Initially, the mechanism of action of quinoxaline 1,4-di-N-oxide derivatives against bacteria, tumoural cell lines, and parasites has been described as nonspecific, but recently, the results against different organisms have shown that these compounds have an inhibitory action on specific targets such as trypanothione reductase, triosephosphate isomerase, and other essential enzymes.

CONCLUSION

In summary, quinoxaline 1,4-di-N-oxide is a scaffold to develop new anti-Mycobacterium tuberculosis, antitumoural and antiprotozoal agents, however, understanding the mechanism of action of quinoxaline 1,4-di-N-oxide derivatives in each microorganism could contribute to the development of new, and more potent selective drugs.

Potential anti-TB investigational compounds and drugs with repurposing potential in TB therapy: a conspectus

The latest WHO report estimates about 1.6 million global deaths annually from TB, which is further exacerbated by drug-resistant (DR) TB and comorbidities with diabetes and HIV. Exiguous dosing, incomplete treatment course, and the ability of the tuberculosis bacilli to tolerate and survive current first-line and second-line anti-TB drugs, in either their latent state or active state, has resulted in an increased prevalence of multidrug-resistant (MDR), extensively drug-resistant (XDR), and totally drug-resistant TB (TDR-TB). Although a better understanding of the TB microanatomy, genome, transcriptome, proteome, and metabolome, has resulted in the discovery of a few novel promising anti-TB drug targets and diagnostic biomarkers of late, no new anti-TB drug candidates have been approved for routine therapy in over 50 years, with only bedaquiline, delamanid, and pretomanid recently receiving tentative regulatory approval. Considering this, alternative approaches for identifying possible new anti-TB drug candidates, for effectively eradicating both replicating and non-replicating Mycobacterium tuberculosis, are still urgently required. Subsequently, several antibiotic and non-antibiotic drugs with known treatment indications (TB targeted and non-TB targeted) are now being repurposed and/or derivatized as novel antibiotics for possible use in TB therapy. Insights gathered here reveal that more studies focused on drug-drug interactions between licensed and potential lead anti-TB drug candidates need to be prioritized. This write-up encapsulates the most recent findings regarding investigational compounds with promising anti-TB potential and drugs with repurposing potential in TB therapy.

Oxidative Stress Modulation and Radiosensitizing Effect of Quinoxaline-1,4-Dioxides Derivatives

Background:

Quinoxaline-1,4-dioxide (QNX) derivatives are synthetic heterocyclic compounds with multiple biological and pharmacological effects.

Objective:

In this study, we investigated the oxidative status of quinoxaline-1,4-dioxides derivatives in modulating melanoma and glioma cell lines, based on previous results from the research group and their capability to promote cell damage by the production of Reactive Oxygen Species (ROS).

Methods:

Using in vitro cell cultures, the influence of 2-amino-3-cyanoquinoxaline-1,4-dioxide (2A3CQNX), 3- methyl-2-quinoxalinecarboxamide-1,4-dioxide (3M2QNXC) and 2-hydroxyphenazine-1,4-dioxide (2HF) was evaluated in metabolic activity, catalase activity, glutathione and 3-nitrotyrosine (3-NT) quantitation by HPLC in malignant melanocytes (B16-F10, MeWo) and brain tumor cells (GL-261 and BC3H1) submitted to radiotherapy treatments (total dose of 6 Gy).

Results:

2HF increased the levels of 3-NT in non-irradiated MeWo and glioma cell lines and decreased cell viability in these cell lines with and without irradiation.

Conclusions:

Quinoxaline-1,4-dioxides derivatives modulate the oxidative status in malignant melanocytes and brain tumor cell lines and exhibited a potential radiosensitizer in vitro action on the tested radioresistant cell lines.

Revision of the Regioselectivity of the Beirut Reaction of Monosubstituted Benzofuroxans with Benzoylacetonitrile. 6-Substituted quinoxaline-2-carbonitrile 1,4- dioxides: Structural Characterization and Estimation of Anticancer Activity and Hypoxia Selectivity

BACKGROUND

Quinoxaline 1,4-dioxides have a broad range of biological activity that causes a growing interest in their derivatives for drug discovery. Recent studies demonstrated that quinoxaline 1,4- dioxides have a promising anticancer activity and good hypoxia-selectivity.

OBJECTIVE

The preparation, isolation, structure characterization, and screening for anticancer activity of the first representatives of 6-substituted quinoxaline-2-carbonitrile 1,4-dioxides have been described.

MATERIALS AND METHODS

A series of 7- and 6-halogeno-3-phenylquinoxaline-2-carbonitrile 1,4-dioxides was synthesized by the Beirut reaction. The cytotoxicity was assessed by MTT test (72 h incubation) in normoxia (21% O2) and hypoxia (1% O2) conditions.

RESULTS

We found that during the Beirut reaction between a benzofuroxan bearing an electron withdrawing group and benzoylacetonitrile in the presence of triethylamine, in addition to well-known 7-substituted quinoxaline-2-carbonitrile 1,4-dioxides 7-11a, the 6-isomers 7-11b are formed. Moreover, the yield of the 6- isomers increased with the increase in the electron-withdrawing character of the substituent. For benzofuroxans with CO2Me and CF3 groups, 6-substituted quinoxaline-2-carbonitrile 1,4-dioxides 10-11b were the major products. Despite similarities in physicochemical and spectroscopic properties, the obtained isomers exhibit considerable differences in their anticancer activity and hypoxia selectivity.

CONCLUSION

Substituents and their electronic effects play a key role in the formation of 7- and 6-substituted quinoxaline-2-carbonitrile 1,4-dioxides in the Beirut reaction and in the cytotoxicity properties of the obtained isomers.

Quinoxaline-1,4-dioxide derivatives inhibitory action in melanoma and brain tumor cells

Aim: Quinoxaline-1,4-dioxide derivatives are synthetic heterocyclic compounds with multiple biological and pharmacological effects. In this study, we investigated the bioactivity of five quinoxaline-1,4-di-N-oxides derivatives in different animal cell lines. Materials & methods: Using in vitro cell cultures, we evaluated the influence of quinoxaline-1,4-dioxide, 2-methylquinoxaline-1,4-dioxide, 2-amino-3-cyanoquinoxaline-1,4-dioxide, 3-methyl-2-quinoxalinecarboxamide-1,4-dioxide and 2-hydroxyphenazine-N,N-dioxide (2HF) in the viability, migration and proliferation of nonmalignant (3T3-L1 and human dermal microvascular endothelial cell) and malignant (B16-F10, MeWo, GL-261 and BC3H1) cell lines. Results: The viability IC₅₀ concentrations for each quinoxaline-1,4-di-N-oxide derivative were calculated, and a concomitant reduction of migration and proliferation was observed mainly in malignant cell lines. Conclusion: 2HF exhibited potent anti-viability, anti-migration and anti-proliferative actions selectively in tumor cells, nevertheless more studies are required to further investigate 2HF promising biologic effects.

Enzyme-Activated Generation of Reactive Oxygen Species from Heterocyclic N-Oxides under Aerobic and Anaerobic Conditions and Its Relevance to Hypoxia-Selective Prodrugs

Enzymatic one-electron reduction of heterocyclic N-oxides can lead to the intracellular generation of reactive oxygen species via several different chemical pathways. These reactions may be relevant to hypoxia-selective anticancer drugs, antimicrobial agents, and unwanted toxicity of heterocylic nitrogen compounds.

Potassium Iodide-Promoted One-Pot Synthesis of Fluoroalkylated Quinoxalines via a Tandem Michael Addition/Azidation/Cycloamination Approach

Fluoroalkylated quinoxlines with various groups were efficiently synthesized via a one-pot tandem Michael addition/azidation/cycloamination process. Under the mild and metal-free conditions, a bis-imine intermediate (4a) was detected and isolated for the first time. KI played a crucial role in this reaction. The mechanism was described.

Quinoxaline: An insight into the recent pharmacological advances

Quinoxaline, a fused heterocycle of benzene and pyrazine rings has gained considerable attention in the field of contemporary medicinal chemistry. The moiety is of substantial importance because of its wide array of pharmacological activities viz. anti-cancer, antimalarial, anti-inflammatory, antimicrobial, anti-HIV etc. Diversely substituted quinoxalines are important therapeutic agents in the pharmaceutical industry. This review focusses on the quinoxaline derivatives developed during the last decennial period and their biomedical applications. A compilation of patents on quinoxaline is also included herein.