Generation of Radical Anions of Nifurtimox and Related Nitrofuran Compounds By Ascorbate

Nifurtimox analogues bearing triazol-4-yl, benzimidazol-1-yl, triazin-4-yl or related groups as counterpart of the (5-nitro-2-furfurylidene) amino group were reduced to their nitro anion radicals by ascorbate in anaerobic solutions at high pH. The ESR spectra of the radical anions showed hyperfine spin couplings restricted to the nitrofuran moiety. With these compounds, the spin density at the nitro group was greater than with nifurtimox, nitrofurazone and nitrofurantoin. At neutral pH, solutions containing ascorbate and nitrofuran derivatives consumed oxygen, the compounds bearing unsaturated nitrogen heterocycles being the most effective. Superoxide dismutase and catalase decreased the rate of oxygen consumption, thus demonstrating the production of superoxide and hydrogen peroxide, respectively. NMR spectra of the triazol-4-yl and triazin-4-yl nitrofuran derivatives showed a deshielding effect for the azomethine proton, which was undetectable with nifurtimox and nitrofurazone.     

Nitro and amino substitution within the A-ring of 5H-8,9-dimethoxy-5-(2-N,N-dimethylaminoethyl)dibenzo[c,h][1,6]naphthyridin-6-ones: influence on topoisomerase I-targeting activity and cytotoxicity

Recently, 5H-8,9-dimethoxy-5-(2-N,N-dimethylaminoethyl)-2,3-methylenedioxydibenzo[c,h][1,6]naphthyridin-6-one, 1, was identified as a TOP1-targeting agent with pronounced antitumor activity. In the present study, the effect on activity of substituting a single nitro or amino group in the A-ring in lieu of the methylenedioxy moiety of 1 was evaluated. The presence of either a nitro or amino substituent at the 4-position had a pronounced adverse affect on both TOP1-targeting activity and cytotoxicity. To a lesser extent, derivatives with a nitro or amino substituent at the 1-position were also less active than 1. Replacement of the methylenedioxy moiety of 1 with either a nitro or amino substituent at either the 2- and 3-position did result in analogues with potent TOP1-targeting activity and cytotoxicity.     

Nitrofuran inhibition of microsomal lipid peroxidation

Two nitrofuran compounds, nifurtimox and nitrofurantoin, inhibited in a concentration-dependent manner the NADPH-, iron-induced lipid peroxidation in rat liver microsomes, as shown by the decreased rate of MDA accumulation. Other nitro compounds (benznidazole and chloramphenicol) were relatively inactive. Nifurtimox inhibition affected polyenoic fatty acids and cytochrome P-450 degradation that follows lipid peroxidation. The ascorbate- or tert-butyl hydroperoxide-dependent lipid peroxidations were much less inhibited than the NADPH-dependent one. Nifurtimox and nitrofurantoin, but not benznidazole and chloramphenicol, strongly stimulated the microsomal NADPH-oxidase activity, thus supporting electron diversion, as the main cause of the inhibition of peroxidation initiation.     

Structure-activity relationships of nitro and methyl-nitro derivatives of indoline, indole, indazole and benzimidazole in Salmonella typhimurium

The mutagenic activities of eleven nitro derivatives and eleven N-methyl-nitro derivatives of indoline, indole, indazole and benzimidazole were investigated in Salmonella TA98 and TA100. The presence of a nitro group at C4 or C7 resulted in only weakly or nonmutagenic compounds, while a nitro group at C2, C5 or C6 usually resulted in measurable mutagenic activity in the non-N-methylated compounds. Methylation of a ring nitrogen usually reduced the mutagenic activity of these nitroheterocyclics except 2-nitro-benzimidazole, which resulted in a better than 300-fold increase in mutagenic activity. A proposed mechanism for the increased mutagenic activity obtained by methylation of imidazole nitrogens may provide insights into the reasons for the potent mutagenicities observed for several similarly methylated cooked-food mutagens.     

Reduction of nifurtimox and nitrofurantoin to free radical metabolites by rat liver mitochondria. Evidence of an outer membrane-located nitroreductase

Nifurtimox and nitrofurantoin are reduced by intact rat liver mitochondria to nitro anion radicals whose autoxidation generates superoxide anion as detected by direct electron spin resonance spectroscopy and by spin-trapping experiments, respectively. Although nitroreduction occurred in the presence of respiratory substrates such as beta-hydroxybutyrate, malate-glutamate, succinate, or endogenous substrates, nitro anion radical formation activity was much greater on addition of exogenous reduced pyridine nucleotides. NAD(P)H generated from endogenous mitochondrial NAD(P)+ by intramitochondrial reactions could not be used for the NAD(P)H nitroreductase reactions unless the mitochondria were solubilized by detergent. In addition, NAD(P)H nitroreductase activity was detected in the crude mitochondrial outer membrane fraction, with a higher activity than in mitoplasts and intact mitochondria. These results provide direct evidence of a nitrofuran reductase activity associated with the mitochondrial outer membrane that is far more important than that of respiratory chain enzymes.     

Enzyme-catalysed reactions between some 2-substituted 5-nitrofuran derivatives and glutathione

1. A glutathione transferase present in rat and human liver supernatant catalyses the reaction of some 2-substituted 5-nitrofuran derivatives with GSH, with formation of a conjugate and release of the nitro group as inorganic nitrite. Some of the substrates undergo the same reaction at a slower rate in the absence of enzyme. Nitrofuran derivatives commonly used as drugs, and five other drugs containing nitro groups, did not react. 2. Substrate activity in the nitrofuran derivatives showed an approximate correlation with the lability of the nitro group to alkali. 3. Optimum pH values ranging from 6.6 to 9.0 were found for the enzymic reaction with various derivatives, the values being influenced by alkali-lability and pK values of the compounds. 4. Tenfold purification of rat liver glutathione S-aryl-transferase resulted in an equal purification of the activities that catalyse the reaction of two of the nitrofuran derivatives with GSH.     

5-Nitrofuranes and 5-nitrothiophenes with anti-Trypanosoma cruzi activity and ability to accumulate squalene

Chagas disease represents a serious public health problem in South America. The first line of treatment is Nifurtimox and Benznidazole which generate toxic effects in treated patients. We have recently shown that a number of 5-nitrofuranes possess activity against Trypanosoma cruzi through oxidative stress and inhibition of parasite ergosterol biosynthesis, specifically at the level of squalene epoxidase. Here, we identify new 5-nitrofuranes and the thia-analogues with excellent effects on the viability of T. cruzi and adequate parasite/mammal selectivity indexes. Analysis of the free sterols from parasite incubated, during 120 h, with the compounds showed that some of them accumulated squalene suggesting the squalene epoxidase activity inhibition of the parasite. Nifurtimox was able to accumulate squalene only at lower incubation times. Due to this fact some derivatives were also tested as antifungal agents. Quantitative structure–activity relationship studies were also performed showing relevant features for further new derivatives design. Taken together, the results obtained in the present work point to a more general effect of 5-nitrofuranes and 5-nitrothiophenes in trypanosomatids, opening potential therapeutic possibilities of them for these infectious diseases.     

Mutagenic activities of selected nitrofluoranthene derivatives in Salmonella typhimurium strains TA98, TA98NR and TA98/1,8-DNP6

The mutagenic activities of novel nitrofluoranthene derivatives in Salmonella strains TA98, TA98NR and TA98/1,8-DNP6 (with and without S9 addition) are given. These derivatives were produced from the reactions of fluoranthene (FL) and its directly mutagenic 2- and 3-nitro derivatives with covalent dinitrogen pentoxide (N2O5) in CCl4 solution at ambient temperature. The influence of the addition of a nitro group on the observed activity of the resulting di- and tri-nitrofluoranthenes is discussed.     

Synthesis and structure–activity relationships of sinenxan A derivatives as multidrug resistance reversal agents

Two types of sinenxan A derivatives with different side chains at C-5 were synthesized and evaluated for their in vitro multidrug resistant reversal activities. Several derivatives exhibited better activities than the positive control verapamil. The structure–activity relationships of these derivatives suggested that a carbonyl group at C-13 and the length of side chain at C-5 are important for the activity.     

Biological evaluation of some quinoline derivatives with different functional groups as anticancer agents

Due to a great deal of biological activities, quinoline derivatives have drawn attention for synthesis and biological activities in the search for new anticancer drug development. In this work, a variety of substituted (phenyl, nitro, cyano, N‐oxide, and methoxy) quinoline derivatives ( 3 ‐ 13 ) were tested in vitro for their biological activity against cancer cell lines, including rat glioblastoma (C6), human cervical cancer cells (HeLa), and human adenocarcinoma (HT29). 6‐Bromo‐5‐nitroquinoline ( 4 ), and 6,8‐diphenylquinoline (compound 13 ) showed the greatest antiproliferative activity as compared with the reference drug, 5‐fluorouracil (5‐FU), while the other compounds showed low antiproliferative activity. 6‐Bromo‐5‐nitroquinoline ( 4 ) possesses lower cytotoxic activity than 5‐FU in HT29 cell line. Due to its the apoptotic activity 6‐Bromo‐5‐nitroquinoline ( 4 ) has the potential to cause cancer cell death.     

CoMFA-SIMCA model for antichagasic nitrofurazone derivatives

The physico-chemical properties of some 5-nitro-2-furaldehyde semicarbazones (nitrofurazones) and thiophene analogues were compared with their in vitro and in vivo trypanocidal activity against Trypanosoma cruzi (Tulahuen strain). 3D-QSAR models were obtained by applying the SIMCA methodology to the electrostatic and steric fields (CoMFA fields) of the molecules. Nitrofurazones bearing N4 substituents. which cover a range of 14-17 A from the nitro group with a thickness of about 6 A when considering the extended conformer. produced complete survival in infected mice. The in vitro model allows larger N4 substituents than the SURVival model, but they must not bear positive centres in the region 15-16 A from the nitro group. Moreover, the in vitro model is in agreement with the active site of trypanothione reductase (TR). Both models can be of use in the design of novel drugs bearing an amide-like group at a distance of 7-9 A from an easily reducible group.     

Quinoxaline N,N'-dioxide derivatives and related compounds as growth inhibitors of Trypanosoma cruzi. Structure-activity relationships

Quinoxaline derivatives presented good inhibitor activity of growth of Trypanosoma cruzi in in vitro assays. The 50% inhibitory doses were of the same order of that of Nifurtimox. Derivative 13, a quinoxaline N,N'-dioxide derivative, and the reduced derivatives 19 and 20 were the most cytotoxic compounds against the protozoan. Structural requirements for optimal activity were studied by computational methods. From statistical analysis we could establish a multiple correlation between activity and lipophilic properties and LUMO energy.     

Generation of nitro radical anions of some 5-nitrofurans, 2- and 5-nitroimidazoles by norepinephrine, dopamine, and serotonin. A possible mechanism for neurotoxicity caused by nitroheterocyclic drugs

Catecholamine neurotransmitters such as norepinephrine, dopamine, and related catecholamine derivatives reduce nitroheterocyclic drugs such as nitrofurantoin, nifurtimox, nifuroxime, nitrofurazone, misonidazole, and metronidazole in slightly alkaline solutions. Drugs which contain 5-nitrofurans are reduced at lower pH than drugs which contain 2- and 5-nitroimidazoles. 5-Nitroimidazole derivatives such as metronidazole and ronidazole are known to be more difficult to reduce than 2-nitroimidazole derivatives, due to their lower redox potential. Catecholamines, when reducing nitro drugs, undergo concomitant oxidation to form semiquinone radicals. Both semiquinone radicals and nitro anion radicals formed in a reaction of nitro drug and catecholamine derivative were detected by electron spin resonance spectroscopy. Oxygen consumption studies in solutions containing nitro drug and catecholamine derivative showed that nitro anion radicals formed under aerobic conditions reduce oxygen to form the superoxide radical and hydrogen peroxide. Quinones formed in the reaction of catecholamine and nitro drug were detected by optical spectroscopy. Biosynthetic precursors and some metabolic products of catecholamines were also used in these studies, and they all exhibited reactions similar to catecholamines. Bovine chromaffin granules which synthesize and store catecholamines produced the nitrofurantoin anion radical when intact granules were treated with nitrofurantoin. These radicals formed inside the granules were observed by ESR spectroscopy. The formation of nitrofurantoin radical, semiquinone radicals of catecholamines, and oxygen-derived radicals by chromaffin granules is proposed to cause damage to adrenal medulla, and this process may lead to neurotoxicity.     

Antileishmanial activity screening of 5-nitro-2-heterocyclic benzylidene hydrazides

A series of 53 nitro derivatives rationally designed were obtained by parallel synthesis and screened against Leishmania donovani. Six compounds exhibited IC(50) values lower than standard drugs. Brief SAR analysis revealed that substitution is important to the activity. Nitrothiophene analogues were more potent than the nitrofuran ones. This was attributed to the ability of sulfur atoms in accommodating electrons from nitro group, which facilitate its reduction and therefore the formation of free radicals lethal to parasites.     

The reductive metabolism of nifurtimox and benznidazole in Crithidia fasciculata is similar to that in Trypanosoma cruzi

1. Addition of nifurtimox or benznidazole to the NADH-containing mitochondrial fraction of Crithidia fasciculata led to the appearance of the characteristic ESR spectra corresponding to their nitro anion radicals, suggesting that the nitro anion radical is a necessary intermediate in the reduction of both nitro compounds. 2. Nifurtimox anion radical generation by the mitochondrial fraction was insensitive to rotenone and antimycin A but was enhanced by KCN. 3. The nifurtimox anion radical reacted with oxygen under aerobic conditions leading to an increase in the cyanide-insensitive respiration of the intact cells and in the rate of O2- and H2O2 production by the C. fasciculata mitochondrial fraction. 4. In contrast, generation of O2- and H2O2 was not stimulated with pharmacological concentrations of benznidazole. Furthermore, benznidazole inhibited the cyanide-insensitive respiration of the intact cells.     

Synthesis of 5-deazaflavin derivatives and their activation of p53 in cells

A family of 5-deazaflavin derivatives has been synthesised using a two-step convergent strategy. The biological activity of these compounds was evaluated in cells, by assessing their ability to stabilize and activate p53. These compounds may act as low molecular weight inhibitors of the E3 activity of HMD2 in tumours that retain wild-type p53. Importantly, we have demonstrated that the nitro group present in all three of the original lead compounds [1-3 (HL198C-E)] is not essential for observation of this biological activity.     

Mutagenicity of nitro derivatives induced by exposure of aromatic compounds to nitrogen dioxide

Mutagenic nitro derivatives were readily induced when 6 kinds of chemicals were exposed to 10 ppm of nitrogen dioxide (NO2). Single nitro derivatives were formed from pyrene, phenanthrene, fluorene or chrysene. Carbazole and fluoranthene each produced 2 derivatives substituted with nitro groups at different positions. The formation of nitro derivatives was enhanced by exposure of pyrene to NO2 containing nitric acid (HNO3, less than 100-fold enhancement) or sulphur dioxide (SO2, less than 15-fold enhancement). After 24 h of exposure the yields of the nitro derivative were 0.02% with 1 ppm of NO2 in air and 2.85% with NO2 (1 ppm) containing traces of HNO3. The nitro derivatives from all but phenanthrene and carbazole were chemically identified by means of gas chromatography (GC) and mass spectrometry (MS), and the mutagenicity of the 4 kinds of authentic nitro derivatives was tested by using Salmonella strains TA98 and TA1538 with or without the S9 fraction from rat liver treated with Aroclor 1254. The nitro derivative induced from pyrene was determined to be 1-nitropyrene; that of chrysene was 6-nitrochrysene; that of fluorene was 2-nitrofluorene; and those of fluoranthene were 3-nitrofluoranthene, and 8-nitrofluoranthene. Tested with strain TA98 in the absence of the S9 fraction, the first 4 of these derivatives yielded, respectively, 3050, 269, 433 and 13 400 revertants per nmole. Thus, each nitro derivative formed was potentially a direct-acting frameshift-type mutagen. Each compound exposed to NO2 showed a decreased mutagenic activity when tested in the presence of S9 mix. A possible explanation comes from experiments in which 1-nitropyrene was incubated with the S9 mix at 37 degree C for 10 min, and 1-aminopyrene was formed. The mutagenic activity of 1-aminopyrene was appreciable, but only about one-tenth of that of 1-nitropyrene in the Ames test.     

Synthesis and antimicrobial activity of novel 2-thiazolylimino-5-arylidene-4-thiazolidinones

New 2-thiazolylimino-5-arylidene-4-thiazolidinones (compounds 4a-j), unsubstituted or carrying hydroxy, methoxy, nitro and chloro groups on the benzene ring, were synthesized and assayed in vitro for their antimicrobial activity against Gram positive and Gram negative bacteria, yeasts and mould. The compounds were very potent towards all tested Gram positive microorganisms (MIC ranging from 0.03 to 6 microg/mL in most of the cases) and Gram negative Haemophilus influenzae (MIC 0.15-1.5 microg/mL), whereas no effectiveness was exhibited against Gram negative Escherichia coli and fungi up to the concentration of 100 microg/mL. The 5-arylidene derivatives showed an antibacterial efficacy considerably greater than that of the parent 2-(thiazol-2-ylimino)thiazolidin-4-one 3, suggesting that the substituted and unsubstituted 5-arylidene moiety plays an important role in enhancing the antimicrobial properties of this class of compounds. The remarkable inhibition of the growth of penicillin-resistant staphylococci makes these substances promising agents also for the treatment of infections caused by microorganisms resistant to currently available drugs.     

Heterocyclic benzazole derivatives with antimycobacterial in vitro activity

The series of 2-benzylsulfanyl derivatives of benzoxazole and benzothiazole were synthesized, evaluated for their in vitro antimycobacterial activity against Mycobacterium tuberculosis and non-tuberculous mycobacteria, and the activity expressed as the minimum inhibitory concentration (MIC) in micromol/L. The substances bearing two nitro groups (4e, 4f, 5e, 5f) or a thioamide group (4i, 4j, 5i, 5j) exhibited appreciable activity particularly against non-tuberculous strains. The most active compounds were subjected to the toxicity assay and were evaluated as moderately cytotoxic.