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A series of sulfonamide-derived quinoxaline 1,4-dioxides were synthesized and evaluated as inhibitors of carbonic anhydrases (CA) with antiproliferative potency. Overall, the synthesized compounds demonstrated good inhibitory activity against four CA isoforms. Compound 7g exhibited favorable potency in inhibiting a CA IX isozyme with a K i value of 42.2 nM compared to the reference AAZ ( K i = 25.7 nM). Nevertheless, most of the synthesized compounds have their highest activity against CA I and CA II isoforms over CA IX and CA XII. A molecular modeling study was used for an estimation of the binding mode of the selected ligand 7g in the active site of CA IX. The most active compounds (7b, 7f, 7h, and 18) exhibited significant antiproliferative activity against MCF-7, Capan-1, DND-41, HL60, and Z138 cell lines, with IC 50 values in low micromolar concentrations. Moreover, derivatives 7a, 7e, and 8g showed similar hypoxic cytotoxic activity and selectivity compared to tirapazamine (TPZ) against adenocarcinoma cells MCF-7. The structure-activity relationships analysis revealed that the presence of a halogen atom or a sulfonamide group as substituents in the phenyl ring of quinoxaline-2-carbonitrile 1,4-dioxides was favorable for overall cytotoxicity against most of the tested cancer cell lines. Additionally, the presence of a carbonitrile fragment in position 2 of the heterocycle also had a positive effect on the antitumor properties of such derivatives against the majority of cell lines. The most potent derivative, 3-trifluoromethylquinoxaline 1,4-dioxide 7h, demonstrated higher or close antiproliferative activity compared to the reference agents, such as doxorubicin, and etoposide, with an IC 50 range of 1.3-2.1 μM. Analysis of the obtained results revealed important patterns in the structure-activity relationship. Moreover, these findings highlight the potential of selected lead sulfonamides on the quinoxaline 1,4-dioxide scaffold for further in-depth evaluation and development of chemotherapeutic agents targeting carbonic anhydrases., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The World Health Organization (WHO) reports that tuberculosis (TB) is one of the top 10 leading causes of global mortality. The increasing incidence of multidrug-resistant TB highlights the urgent need for an intensified quest to discover innovative anti-TB medications In this study, we investigated four new derivatives from the quinoxaline-2-carboxylic acid 1,4-dioxide class. New 3-methylquinoxaline 1,4-dioxides with a variation in substituents at positions 2 and 6(7) were synthesized via nucleophilic aromatic substitution with amines and assessed against a Mycobacteria spp. Compound 4 showed high antimycobacterial activity (1.25 μg/mL against M. tuberculosis ) and low toxicity in vivo in mice. Selection and whole-genomic sequencing of spontaneous drug-resistant M. smegmatis mutants revealed a high number of single-nucleotide polymorphisms, confirming the predicted mode of action of the quinoxaline-2-carboxylic acid 1,4-dioxide 4 as a DNA-damaging agent. Subsequent reverse genetics methods confirmed that mutations in the genes MSMEG_4646, MSMEG_5122, and MSMEG_1380 mediate resistance to these compounds. Overall, the derivatives of quinoxaline-2-carboxylic acid 1,4-dioxide present a promising scaffold for the development of innovative antimycobacterial drugs.

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.

In this study, the in vitro antimicrobial, antiparasitic, antiproliferative and cytotoxic activities of essential oil from Baccharis parvidentata Malag. (EO-Bp) and Lippia origanoides Kunth (EO-Lo) were explored. The relevant effects were observed against the parasitic protozoans Plasmodium falciparum, Trypanosoma cruzi, Trypanosoma brucei and Leishmania amazonensis (ranging 0.6 to 39.7 µg/mL) and malignant MCF-7, MCF-7/HT, 22Rv1, and A431 cell lines (ranging 6.1 to 31.5 µg/mL). In parallel, EO-Bp showed better selective indexes in comparison with EO-Lo against peritoneal macrophages from BALB/c mice and MRC-5 cell line. In conclusion, EO-Lo is known to show a wide range of health benefits that could be added as another potential use of this oil with the current study. In the case of EO-Bp, the wide spectrum of its activities against protozoal parasites and malignant cells, as well as its selectivity in comparison with non-malignant cells, could suggest an interesting candidate for further tests as a new therapeutic alternative.

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.

To establish a new approach for the synthesis of quinoxaline 1,4-dioxides as hypoxia-selective cytotoxic agents, an original multi-step preparation of derivatives possessing the diamine moiety at position 7 was evaluated. Herein, we present the synthesis of a series of novel 7-amino-6-halogeno-3-phenylquinoxaline-2-carbonitrile 1,4-dioxides 13a-h, 14a,b,g based on the regioselective Beirut reaction. Comparison of antitumor properties of derivatives possessing the diamine moiety at position 7 with structurally close congeners possessing the corresponding amino groups at position 6 revealed key differences in the cytotoxicity profiles and HIF-1α inhibition. All the synthesized 7-amino-6-halogeno derivatives 13a-h, 14a,b,g demonstrated significant cytotoxic activities against breast cancer cell lines (MCF7, MDA-MB-231) in normoxia and hypoxia with IC50 values ranging from 0.1 to 7.6 μM. Most of these novel derivatives can circumvent the multidrug resistance of tumor cells caused by P-glycoprotein over expression. The lead compounds 13a, 14a and 14b can suppress the expression of HIF-1α at low micromolar concentrations and induce apoptosis in breast cancer MCF7 cells. In addition, compound 14b effectively inhibits BCL2 and ERα expression in MCF7 cells. The current research opens a new direction for targeting hypoxia and drug resistance of cancer cells., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

In this article, we describe the synthesis of 3-phenylquinoxaline-2-carbonitrile 1,4-dioxides bearing cyclic diamine residues at positions 6 or 7; the synthesis is based on the nucleophilic substitution of halogens. All synthesized 6(7)-aminoquinoxaline-2-carbonitrile 1,4-dioxides 3-6 demonstrated higher cytotoxicity and hypoxia selectivity compared to the reference agent tirapazamine against breast adenocarcinoma cell lines (MCF7, MDA-MB-231). The structure and position of the diamine residue considerably affects the antiproliferative properties of the quinoxaline-2-carbonitrile 1,4-dioxides. The introduction of a halogen atom at position 7 in the quinoxaline ring of 4a considerably increases the cytotoxicity of compounds 5a and 6a under both normoxic and hypoxic conditions. However, the most hypoxia-selective derivatives were non-halogenated 7-aminosubstituted 3-phenylquinoxaline-2-carbonitrile 1,4-dioxides 3a-j. Of the 32 novel synthesized derivatives, approximately 20 of the 6(7)-amino-3-phenylquinoxaline-2-carbonitrile 1,4-dioxides demonstrated high antiproliferative potency against wild type leukemia cells K562 and drug-resistant subline K562/4 with the expression of p-glycoprotein (p-gp) compared to the reference agent doxorubicin, which exhibited one order of magnitude lower activity towards K562/4 cells than towards K562 cells. Lead compounds 5a and 3f inhibited HIF-1α expression and activity and induced apoptosis in hypoxic tumor cells, which was confirmed by poly(ADP-ribose)polymerase (PARP) cleavage. Moreover, 5a and 3f showed strong antiestrogenic potencies in MCF7 breast cancer cells. Thus, the described series of quinoxaline 1,4-dioxides has high anticancer potential and good aqueous solubility. Therefore, these compounds are promising for further drug development of hypoxia-targeted anticancer agents., (Copyright © 2020 Elsevier Inc. All rights reserved.)

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., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)

A series of 3-aryl/hetarylquinoxaline-2-carbonitrile-1,4-dioxides was synthesized and evaluated against breast cancer cell lines in normoxia and hypoxia. Selected compounds in this series demonstrated better cytotoxicity and comparable hypoxia selectivity than tirapazamine. In contrast to Dox, quinoxaline-1,4-dioxides showed potent cytotoxicity against different MDR cells. Compound 2g inhibits of cancer cell growth through p53-independent mechanisms. Our results showed that compound 2g sensitized MCF-7 cells to metformin in hypoxia. Treatment with 2g results in the increase of ROS accumulation in cancer cells. Compound 2g can be considered as the lead compound for further anticancer drug design, evaluation, and development of new potent antitumor agents.