4-Cyano-2-oxo-1,2,4-oxadiazolo[2,3-a]quinoxaline 5-N-oxides. New synthetic method and reaction with alcohols. Potential cytotoxic activity

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.

An appraisal on synthetic and pharmaceutical perspectives of quinoxaline 1,4-di-N-oxide scaffold

Quinoxaline 1,4-di-N-oxides (QdNOs) exhibit multifaceted biological properties, wherein antimicrobial, anticancer, antitrypanosomal, and anti-inflammatory properties are included. Because of their various activities in clinical practice and research, they have a wide spectrum of uses and possibilities. QdNOs have received a significant amount of attention, and research into their medicinal chemistry is still a part of experimental investigation and analytical studies. In this review, QdNOs are classified depending on their actions, which include antibacterial and anti-mycobacterial, anticancer or antitumor, antimalarial, antifungal, and other activities. In a conclusion, it's important to base the development of novel synthetic techniques and the design of new QdNO derivatives on the most up-to-date knowledge gleaned from recent research. With the summarised structure-activity relationship of fascinating QdNOs, this review aims to provide insights into the developments in the chemistry and biological activity of QdNO derivatives.

New hits as phase II enzymes inducers from a focused library with heteroatom-heteroatom and Michael-acceptor motives

The increased activity of phase-II-detoxification enzymes, such as quinone reductase (QR) and glutation S-transferase (GST), correlates with protection against chemically induced carcinogenesis. Herein we studied 11 different chemotypes, pyrazole, 1,2,4-oxadiazole, 1,2,5-oxadiazole, 1,2,3-thiadiazole, 1,2,4-thiazole, 1,3,4-oxathiazole, thienyl hydrazone, α,β-unsaturated-oxime, α,β-unsaturated-N-oxide, coumarin and α,β-unsaturated-carbonyl, as phase-II enzymes inducers in order to identify new pharmacophores with chemopreventive activity. Fifty-four compounds were analyzed on wild-type mouse-hepatoma Hepa-1c1c7 and on the aryl-hydrocarbon-nuclear-translocator (Arnt)-defective mutant BpRc1 cells. New monofunctional inducers of QR and GST were identified, the 1,2,5-oxadiazol-2-oxide (3), the 1,2,4-triazine-4-oxides (23) and (32) and the tetrahydropyrimidinones (28) and (49). It was confirmed that Nrf2 nuclear translocation is the operative molecular mechanism that allows compound (3) to exert protective effects via expression of downstream phase-II enzymes.

Cancer chemoprevention is the prevention, delay or reversal of the carcinogenesis by administration of drugs. A group of chemopreventative agents includes quinone reductase and glutation S-transferase. Herein we have studied 11 chemotypes, trying to identify new pharmacophores for chemopreventives. We found new inducers of quinone reductase and glutation S-transferase, with excellent in vitro chemopreventive indexes, the 1,2,5-oxadiazol-2-oxide (3), the 1,2,4-triazine-4-oxides (23) and (32) and the tetrahydropyrimidinones (28) and (49), confirming that Nrf2 nuclear translocation is the operative molecular mechanism that allows compound (3) to exert protection. We have therefore highlighted good candidates for further in vivo studies of cancer chemopreventive activity.

New quinoxaline 1,4-di-N-oxides. Part 1: Hypoxia-selective cytotoxins and anticancer agents derived from quinoxaline 1,4-di-N-oxides

Hypoxic cells which are common feature of solid tumors are resistant to both anticancer drugs and radiation therapy. Thus, the identification of drugs with the selective toxicity toward hypoxic cells is an important target in anticancer chemotherapy. Tirapazamine has been shown to be an efficient and selective cytotoxin after bioreductive activation in hypoxic cells which is thought to be due to the presence of the 1,4-di-N-oxide. A new series of quinoxaline 1,4-di-N-oxides and fused quinoxaline di-N-oxides were synthesized and evaluated for hypoxic-cytotoxic activity on EAC cell line. Compound 10a was the most potent cytotoxin IC(50) 0.9 microg/mL, potency 75 microg/mL, and was approximately 15 times more selective cytotoxin (HCR>111) than 3-aminoquinoxaline-2-carbonitrile which has been used as a standard (HCR>7.5). Compounds 4 and 3a,b were more selective than the standard. In addition, antitumor activity against Hepg2 (liver) and U251 (brain) human cell lines was evaluated, compounds 9c and 8a were the most active against Hepg2 with IC(50) values 1.9 and 2.9 microg/mL, respectively, however, all the tested compounds were nontoxic against U251 cell line.

Synthesis and anticancer activity evaluation of new 2-alkylcarbonyl and 2-benzoyl-3-trifluoromethyl-quinoxaline 1,4-di-N-oxide derivatives

As a continuation of our research in quinoxaline 1,4-di-N-oxide and with the aim of obtaining new anticancer agents, which can improve the current chemotherapeutic treatments, new series of 2-alkylcarbonyl and 2-benzoyl-3-trifluoromethylquinoxaline 1,4-di-N-oxide derivatives have been synthesized and evaluated for in vitro antitumor activity against a 3-cell line panel, consisting of MCF7 (breast), NCI-H460 (lung), and SF-268 (CNS). These active compounds were then evaluated in the full panel of 60 human tumor cell lines derived from nine cancer cell types. The results have shown that, in general, anticancer activity depends on the substituents in the carbonyl group, improving in the order: ethyl<isopropyl<tert-butyl<phenyl-ones. Among these, the compounds 4c, 6e, their difluorinated analogs (4g and 6g), and 5c were the most active, with mean GI(50) values of 1.02, 0.42, 0.52, 0.15, and 0.49microM, respectively. All of them were also found to inhibit the growth of the all of the Leukemia cell lines studied (with 75% of the GI(50) values less than 0.15microM) and therefore, were selected for further evaluation for the in vivo hollow fiber assays.

Evidence for an aryl migration during the electron impact induced fragmentation of substituted aryloxymethylquinoxalines

The electron impact (EI) mass spectra of 34 differently substituted 2-phenoxymethyl-, 2-naphthyloxymethyl-, 2-pyridinyloxymethyl- and 2-chinolinyloxymethylquinoxalines were recorded. The fragmentation patterns were examined by metastable ion analysis and exact mass measurements, employing finally also selective deuterium labelling. The inclusion of the substituted aryl ring moiety appears to be important for the fragmentation of the aryloxymethylquinoxalines. A molecular ion rearrangement is proposed for the observed loss of OH* and CHO* radicals. The influence of the different substituents on the aryl ring moiety on the rearrangement in the gas phase and on the resulting fragmentation was investigated.

Synthesis and biological evaluation of 1,2,5-oxadiazole N-oxide derivatives as potential hypoxic cytotoxins and DNA-binders

Several new 1,2,5-oxadiazole N-oxide derivatives were synthesized to be tested both as potential selective hypoxic cell cytotoxins and as DNA-binding agents. The compounds prepared included bis(1,2,5-oxadiazole N-oxide) derivatives and oxadiazole rings linked to naphthyl residues. The compounds were tested for their cytotoxicity in oxia and hypoxia and they proved to be non-selective and less active than the parent compounds 3-formyl-4-phenyl-1,2,5-oxadiazole N2-oxide (3) and 3-chloromethyl-4-phenyl-1,2,5-oxadiazole N2-oxide (4). The DNA-affinity assays showed that the compounds tested have poor affinity for this biomolecule.