Convenient Preparation, Thermal Properties and X-ray Structure Determination of 2,3-Dihydro-5,6,7,8-tetranitro-1,4-benzodioxine (TNBD): A Promising High-Energy-Density Material.

2,3-dihydro-5,6,7,8-tetranitro-1,4-benzodioxine (TNBD), molecular formula = CHNO, is a completely nitrated aromatic ring 1,4-benzodioxane derivative. The convenient method of TNBD synthesis was developed (yield = 81%). The detailed structure of this compound was investigated by X-ray crystallography.

An Efficient Synthesis and Preliminary Investigation of Novel 1,3-Dihydro--benzimidazol-2-one Nitro and Nitramino Derivatives.

The preparation and properties of a series of novel 1,3-dihydro--benzimidazol-2-one nitro and nitramino derivatives are described. A detailed crystal structure of one of the obtained compounds, 4,5,6-trinitro-1,3-dihydro--benzimidazol-2-one (TriNBO), was characterized using low temperature single crystal X-ray diffraction, namely an orthorhombic yellow prism, space group 'P 2 21 21', experimental crystal density 1.767 g/cm (at 173 K).

Investigation of oxygen influence to the optical properties of tirapazamine.

New data on 3-amino-1,2,4-benzotriazine 1,4-dioxide (tirapazamine) fluorescence has been obtained using the Perkin-Elmer Lambda 950 UV-Vis-NIR spectrophotometer experimental technique in combination with the extensive DFT-theory approach. Based on the results obtained, we revealed that the optical properties of the molecule under study remain significantly unchanged when the number of oxygen substitutions decreases from 2 to 0. Here we also present the results of the study of the influence of acetonitrile and ethyl acetate on the fluorescence of tirapazamine with the different number of oxygen atoms.

Benzimidazole Derivatives as Energetic Materials: A Theoretical Study.

The explosive properties and stability of benzimidazole compounds are studied to determine the influence of substituents and their position. The results obtained reveal the conjugation of substituents as one of the crucial factors for the thermal stability of these compounds. We also found that two -CH substituents increase the thermal stability of the parent compound, while nitro groups decrease it.

Aerobic Cytotoxicity of Aromatic Oxides: The Role of NAD(P)H:Quinone Oxidoreductase (NQO1).

Derivatives of tirapazamine and other heteroaromatic oxides (ArN→O) exhibit tumoricidal, antibacterial, and antiprotozoal activities, which are typically attributed to bioreductive activation and free radical generation. In this work, we aimed to clarify the role of NAD(P)H:quinone oxidoreductase (NQO1) in ArN→O aerobic cytotoxicity. We synthesized 9 representatives of ArN→O with uncharacterized redox properties and examined their single-electron reduction by rat NADPH:cytochrome P-450 reductase (P-450R) and ferredoxin:NADP oxidoreductase (FNR), and by rat NQO1.

Reactions of Ferredoxin:NADP Oxidoreductase with Redox Cycling Xenobiotics: A Mechanistic Study.

Ferredoxin:NADP oxidoreductase from (FNR) catalyzes the NADPH-dependent reduction of ferredoxin (Fd), which provides redox equivalents for the biosynthesis of isoprenoids and fatty acids in the apicoplast. Like other flavin-dependent electrontransferases, FNR is a potential source of free radicals of quinones and other redox cycling compounds. We report here a kinetic study of the reduction of quinones, nitroaromatic compounds and aromatic oxides by FNR We show that all these groups of compounds are reduced in a single-electron pathway, their reactivity increasing with the increase in their single-electron reduction midpoint potential ().

Antiplasmodial Activity of Nitroaromatic Compounds: Correlation with Their Reduction Potential and Inhibitory Action on Glutathione Reductase.

With the aim to clarify the mechanism(s) of action of nitroaromatic compounds against the malaria parasite , we examined the single-electron reduction by ferredoxin:NADP oxidoreductase (FNR) of a series of nitrofurans and nitrobenzenes ( = 23), and their ability to inhibit glutathione reductase (GR). The reactivity of nitroaromatics in FNR-catalyzed reactions increased with their single-electron reduction midpoint potential (). Nitroaromatic compounds acted as non- or uncompetitive inhibitors towards GR with respect to NADPH and glutathione substrates.

Kinetics of Flavoenzyme-Catalyzed Reduction of Tirapazamine Derivatives: Implications for Their Prooxidant Cytotoxicity.

Derivatives of tirapazamine and other heteroaromatic oxides (ArN→O) exhibit promising antibacterial, antiprotozoal, and tumoricidal activities. Their action is typically attributed to bioreductive activation and free radical generation. In this work, we aimed to clarify the mechanism(s) of aerobic mammalian cell cytotoxicity of ArN→O performing the parallel studies of their reactions with NADPH:cytochrome P-450 reductase (P-450R), adrenodoxin reductase/adrenodoxin (ADR/ADX), and NAD(P)H:quinone oxidoreductase (NQO1); we found that in P-450R and ADR/ADX-catalyzed single-electron reduction, the reactivity of ArN→O ( = 9) increased with their single-electron reduction midpoint potential (), and correlated with the reactivity of quinones.

Mechanism of Two-/Four-Electron Reduction of Nitroaromatics by Oxygen-Insensitive Nitroreductases: The Role of a Non-Enzymatic Reduction Step.

Oxygen-insensitive NAD(P)H:nitroreductases (NR) reduce nitroaromatics (Ar-NO₂) into hydroxylamines (Ar-NHOH) through nitroso (Ar-NO) intermediates. Ar-NO may be reduced both enzymatically and directly by reduced nicotinamide adenine dinucleotide or its phosphate NAD(P)H, however, it is unclear which process is predominant in catalysis of NRs. We found that NR-A (NfsA) oxidizes 2 mol of NADPH per mol of 2,4,6-trinitrotoluene (TNT) and 4 mol of NADPH per mol of tetryl.

Modeling and investigation of new explosive materials based on N-(3,5-dimethyl-2,4,6-trinitrophenyl)-1H-1,2,4-triazol-3-amine.

This study presents an investigation of the effects of adding extra nitro group substituents to N-(3,5-dimethyl-2,4,6-trinitrophenyl)-1H-1,2,4-triazol-3-amine (HEM-II) on its thermal and chemical stability as well as its explosive performance. An analysis of the thermal stabilities of HEM-II and HEM-II-based molecules based on an investigation of the binding energy per atom for each molecule was performed. The values of the gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) as well as those of the chemical hardness and softness for HEM-II and the HEM-II-based molecules were studied to determine the chemical stabilities of these molecules.

Flavoenzyme-mediated reduction reactions and antitumor activity of nitrogen-containing tetracyclic ortho-quinone compounds and their nitrated derivatives.

Nitrogen-based tetracyclic ortho-quinones (naphtho[1'2':4.5]imidazo[1,2-a]pyridine-5,6-diones, NPDOs) and their nitro-substituted derivatives (nitro-(P)NPDOs) were obtained by condensation of substituted 2,3-dichloro-1,4-naphthoquinones with 2-amino-pyridine and -pyrimidine and nitration at an elevated temperature. The structural features of the compounds as well as their global and regional electrophilic potency were characterized by means of DFT computation.

Aziridinyl-substituted benzo-1,4-quinones: A preliminary investigation on the theoretical and experimental studies of their structure and spectroscopic properties.

The detailed structure, chemical and spectroscopic properties of the derivatives of the selected 2,5-bis(1-aziridinyl)-benzo-1,4-quinone conformers were studied by applying quantum chemical and experimental methods. The relationship between the structure and chemical activity of the selected 3 bifunctional bioreductive quinonic anticancer agents - aziridinyl benzoquinones (AzBQ compounds) was obtained. The results obtained showed that the position of aziridine rings influenced by the chemical activity of the investigated compound were more significant than the substitutions of the benzene ring of the AzBQ compounds.

Identification of Novel Chemical Scaffolds Inhibiting Trypanothione Synthetase from Pathogenic Trypanosomatids.

Background: The search for novel chemical entities targeting essential and parasite-specific pathways is considered a priority for neglected diseases such as trypanosomiasis and leishmaniasis. The thiol-dependent redox metabolism of trypanosomatids relies on bis-glutathionylspermidine [trypanothione, T(SH)2], a low molecular mass cosubstrate absent in the host. In pathogenic trypanosomatids, a single enzyme, trypanothione synthetase (TryS), catalyzes trypanothione biosynthesis, which is indispensable for parasite survival.

Naphtho[1',2':4,5]imidazo[1,2-a]pyridine-5,6-diones: Synthesis, enzymatic reduction and cytotoxic activity.

Naphtho[1',2':4,5]imidazo[1,2-a]pyridine-5,6-diones (NPDOs), a new type of N-heterocycle-fused o-quinones, have been synthesized. They have been found to be efficient electron-accepting substrates of NADPH-dependent single-electron-transferring P-450R and two-electron transferring NQO1, generating reactive oxygen species (ROS) with a concomitant decrease in NADPH, which is consistent with redox-cycling. The reactivity of NPDOs toward P-450R (in terms of kcat/Km) varied in the range of 10(6)-10(7)M(-1)s(-1), while their reduction by NQO1 proceeded much faster, approaching the diffusion control limit (kcat/Km∼10(8)-10(9)M(-1)s(-1)).

Study of Bioreductive Anticancer Agent RH-1-Induced Signals Leading the Wild-Type p53-Bearing Lung Cancer A549 Cells to Apoptosis.

Unlabelled: Aziridinylquinone RH-1 (2,5-diaziridinyl-3-hydroxymethyl-6-methyl-cyclohexa-2,5-diene-1,4-dione) is a potential anticancer agent. RH-1 action is associated with

Nad(p)h: quinone oxidoreductase (NQO1) which reduces this diaziridinylbenzoquinone into DNA-alkylating hydroquinone and is overexpressed in many tumors. Another suggested mechanism of RH-1 toxicity is the formation of reactive oxygen species (ROS) arising from its redox cycling.

Quantitative proteomic analysis of anticancer drug RH1 resistance in liver carcinoma.

Unlabelled: Acquired resistance of tumor cells to the therapeutic treatment is a major challenge in virtually any chemotherapy. A novel anticancer agent 2,5-diaziridinyl-3-(hydroxymethyl)-6-methyl-1,4-benzoquinone (RH1) is designed to be activated by

Nad(p)h: quinone oxidoreductase, an enzyme expressed at high levels in many types of tumors. Here we investigated the potential mechanisms of acquired RH1 drug resistance in cancer cells by applying high-throughput differential quantitative proteomic analysis of the newly established RH1-resistant hepatoma cell lines.

The study of NADPH-dependent flavoenzyme-catalyzed reduction of benzo[1,2-c]1,2,5-oxadiazole N-oxides (benzofuroxans).

Unlabelled: The enzymatic reactivity of a series of benzo[1,2-c]1,2,5-oxadiazole N-oxides (benzofuroxans; BFXs) towards mammalian single-electron transferring NADPH:cytochrome P-450 reductase (P-450R) and two-electron (hydride) transferring

Nad(p)h: quinone oxidoreductase (NQO1) was examined in this work. Since the =N+ (→O)O- moiety of furoxan fragments of BFXs bears some similarity to the aromatic nitro-group, the reactivity of BFXs was compared to that of nitro-aromatic compounds (NACs) whose reduction mechanisms by these and other related flavoenzymes have been extensively investigated. The reduction of BFXs by both P-450R and NQO1 was accompanied by O2 uptake, which was much lower than the NADPH oxidation rate; except for annelated BFXs, whose reduction was followed by the production of peroxide.

Redox properties and prooxidant cytotoxicity of a neuroleptic agent 6,7-dinitrodihydroquinoxaline-2,3-dione (DNQX).

In order to characterize the possible mechanism(s) of cytotoxicity of a neuroleptic agent 6,7-dinitrodihydroquinoxaline-2,3-dione (DNQX) we examined the redox properties of DNQX, and its mononitro- (NQX) and denitro- (QX) derivatives. The irreversible electrochemical reduction of the nitro groups of DNQX was characterized by the reduction peak potentials (Ep,7) of -0.43 V and -0.

Single-electron reduction of quinone and nitroaromatic xenobiotics by recombinant rat neuronal nitric oxide synthase.

We examined the kinetics of single-electron reduction of a large number of structurally diverse quinones and nitroaromatic compounds, including a number of antitumour and antiparasitic drugs, and nitroaromatic explosives by recombinant rat neuronal nitric oxide synthase (nNOS, EC 1.14.13.

Quinone- and nitroreductase reactions of Thermotoga maritima peroxiredoxin-nitroreductase hybrid enzyme.

Thermotoga maritima peroxiredoxin-nitroreductase hybrid enzyme (Prx-NR) consists of a FMN-containing nitroreductase (NR) domain fused to a peroxiredoxin (Prx) domain. These domains seem to function independently as no electron transfer occurs between them. The reduction of quinones and nitroaromatics by NR proceeded in a two-electron manner, and follows a 'ping-pong' scheme with sometimes pronounced inhibition by quinone substrate.

Redox reactions of the FAD-containing apoptosis-inducing factor (AIF) with quinoidal xenobiotics: a mechanistic study.

Mitochondrial apoptosis-inducing factor (AIF) is a FAD-containing protein that under certain conditions translocates to the nucleus and causes a programmed cell death, apoptosis. The apoptogenic action of AIF is redox controlled as the NADH-reduced AIF dimer has lower affinity for DNA than the oxidized monomer. To gain further insights into the mechanism of AIF, we investigated its interaction with a series of quinone oxidants, including a number of anticancer quinones.

Antiplasmodial activity of quinones: roles of aziridinyl substituents and the inhibition of Plasmodium falciparum glutathione reductase.

Although quinones have been the subject of great interest as possible antimalarial agents, the mechanism of their antimalarial activity is poorly understood. Flavoenzyme electrontransferase-catalyzed redox cycling of quinones, and their inhibition of the antioxidant flavoenzyme glutathione reductase (GR, EC 1.8.

Reduction of aliphatic nitroesters and N-nitramines by Enterobacter cloacae PB2 pentaerythritol tetranitrate reductase: quantitative structure-activity relationships.

Enterobacter cloacae PB2 NADPH:pentaerythritol tetranitrate reductase (PETNR) performs the biodegradation of explosive organic nitrate esters via their reductive denitration. In order to understand the enzyme substrate specificity, we have examined the reactions of PETNR with organic nitrates (n = 15) and their nitrogen analogues, N-nitramines (n = 4). The reactions of these compounds with PETNR were accompanied by the release of 1-2 mol of nitrite per mole of compound, but were not accompanied by their redox cycling and superoxide formation.

Enzymatic redox properties of novel nitrotriazole explosives implications for their toxicity.

The toxicity of conventional nitroaromatic explosives like 2,4,6-trinitrotoluene (TNT) is caused by their enzymatic free radical formation with the subsequent oxidative stress, the formation of alkylating nitroso and/or hydroxylamino metabolites, and oxyhemoglobin oxidation into methemoglobin. In order to get an insight into the mechanisms of toxicity of the novel explosives NTO (5-nitro-1,2,4-triazol-3-one) and ANTA (5-nitro-1,2,4-triazol-3-amine), we examined their reactions with the single-electron transferring flavoenzymes NADPH: cytochrome P-450 reductase and ferredoxin:NADP+ reductase, two-electron transferring flavoenzymes mammalian NAD(P)H:quinone oxidoreductase (DT-diaphorase), and Enterobacter cloacae NAD(P)H:nitroreductase, and their reactions with oxyhemoglobin. The reactivity of NTO and ANTA in the above reactions was markedly lower than that of TNT.