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At least 163 records · Page 9Linked to original sources
PubMed2006

Chemoselective hydrogenation of nitro compounds with supported gold catalysts.

The selective reduction of a nitro group when other reducible functions are present is a difficult process that often requires stoichiometric amounts of reducing agents or, if H2 is used, the addition of soluble metals. Gold nanoparticles supported on TiO2 or Fe2O3 catalyzed the chemoselective hydrogenation of functionalized nitroarenes with H2 under mild reaction conditions that avoided the accumulation of hydroxylamines and their potential exothermic decomposition. These chemoselective hydrogenation gold catalysts also provide a previously unknown route for the synthesis of the industrially relevant cyclohexanone oxime from 1-nitro-1-cyclohexene.

Journal Article↗
PubMed1991

Solubilization of guanylyl cyclase from bovine rod outer segments and effects of lowering Ca2+ and nitro compounds.

Guanylyl cyclase from bovine rod outer segments was solubilized using Triton X-100 and a high concentration of KCl, and its regulation was studied. The efficiency of solubilization was about 50-90% of total activity. When the Ca2+ content was lowered (less than 80 nM), guanylyl cyclase was activated about 2-fold. In the presence of higher concentrations of Ca2+ (greater than 140 nM), the activity was decreased. The regulation by Ca2+ was also demonstrated with solubilized preparations. In the presence of 186 nM Ca2+ which inhibited guanylyl cyclase, La3+ activated the enzyme about 2-fold, suggesting that the Ca2(+)-binding protein similar to other Ca2(+)-binding proteins associates with guanylyl cyclase regulation. Sodium nitroprusside and nitric oxide which are activators of soluble guanylyl cyclase in other tissues also activated the retinal guanylyl cyclase. Maximum activation by sodium nitroprusside was 20-fold using Mg2+ as a cofactor. Activation by nitric oxide and related compounds suggests that retinal guanylyl cyclase contains a heme prosthetic group that may participate in a novel regulatory mechanism for this enzyme.

Animals↗
PubMedDate not supplied

[EPR study of the mechanism of photooxidation of chlorophyll a by nitro compounds].

An ESR signal with g-value of 2,0026 and peak-to-peak with 8,5 Oe was observed in ethanole solutions of chlorophill a and nitroderivatives of naphtalene under red light illumination. The ESR signal consisted of chlorophyll cation radical resonance, superimposed on an nitronaphtalene anion radical. Less than the ratio greater than between the quantities of these radicals and the character of decay kinetics are influenced by the medium acidity. An analysis of kinetic curves is performed, and the effect of the medium acidity on the mechanism of one-electron transfer reaction between chlorophyll and nitronaphtalene molecules is explained.

Chlorophyll↗
PubMedDate not supplied

[Characteristics of nitroreduction as the key stage in the microbial destruction of aromatic nitro compounds].

The reduction of nitrogroups of 2,4,6-trinitrotoluene (TNT) and other nitroaromatic compounds under the influence of Pseudomonas denitrificans and Escherichia coli enzymes was investigated. Quantitative measurements of the immediate stable products of TNT reduction showed that its reducing attack increased with bacterial age. However, preferential reduction of the nitrogroup in position 2 was typical of bacterial cells of any age, being maintained at pH 5.5 to 7.8. The bacterial reduction in vitro was NAD(P)H- (or NAD(P)H-generating systems) dependent. The nitroreduction was stimulated by only FAD and Mn2+ and Mg2+ out of flavins and metal ions tested. The lack of substrate specificity in the nitroreductases under study is indicated by the reducing capacity (in descending order) of nitroderivatives of benzene, toluene, benzoate, and phenol.

Escherichia coli↗
PubMed1987

[Calcium-blocking effect of nitro compounds in human platelets: correlation with changes in the cyclic guanosine monophosphate level].

The effects of nitrates on Ca2+ increase and cyclic nucleotide content in human platelets were studied. Nitroglycerin, isosorbide dinitrate and sodium nitroprusside were found to inhibit the intracellular Ca2+ increase induced by the platelet activating factor, ADP and a stable thromboxane A2 analog--U46619. The inhibiting effect of sodium nitroprusside manifested itself at lower concentrations than those of nitroglycerin and isosorbide dinitrate. Nitroglycerin suppressed the Mn2+ entry into the cells and caused a 2-fold increase of the cGMP content which correlates with the calcium blocking activity. Methylene blue, a guanylate cyclase and glutathione reductase inhibitor, decreased the calcium blocking effect of nitroglycerin and its influence on the cyclic nucleotide content but failed to suppress the inhibitory effect of sodium nitroprusside. The data obtained suggest that the effects of nitrates on platelets are mediated by their influence on guanylate cyclase which leads to a cyclic nucleotide content increase and to a calcium blocking effect.

Blood Platelets↗
PubMed1980

Participation of cytochrome P-450 in the reduction of nitro compounds by rat liver microsomes.

1. The subcellular distribution of nitrobenzene reduction activity in rat liver cells indicated the existence of two different enzyme systems, one localized in microsomes and the other localized in cytosol. The activity in the cytosol was mainly attributable to xanthine oxidase, judging from its substrate specificity and the inhibition by allopurinol. 2. The participation of the microsomal electron transport system in nitrobenzene reduction was examined by using antibodies against four components of the system, NADPH-cytochrome c reductase (fpT), NADH-cytochrome b5 reductase (fpD), cytochrome b5, and cytochrome P-450. Both NADH- and NADPH-dependent nitrobenzene reduction activities were strongly inhibited by anti-fpT IG and also by anti-P450 IG, but not inhibited by anti-fpD IG or anti-b5 IG. The reduction of nitrosobenzene and phenylhydroxylamine, which are supposed to be the intermediates of nitrobenzene reduction, was also examined, and it was found that NADH- and NADPH-dependent reduction of both compounds were strongly inhibited by anti-fpT IG and anti-P450 IG, but not by anti-fpD IG or anti-b5 IG. 3. Reconstruction experiments using purified NADPH-cytochrome P-450 reductase and cytochrome P-450 were also carried out and it was confirmed that the reduction of nitrobenzene, nitrosobenzene, and phenylhydroxylamine to aniline could be effected by these two components. 4. Nitrobenzene reduction by microsomes exhibited a short initial time lag and was activated by the addition of purified NADPH-cytochrome c reductase, whereas nitrosobenzene and phenylhydroxylamine reductions did not show any initial time lag and were not activated by the reductase. These observations suggest that the reduction of nitrobenzene to an intermediate, possibly nitrosobenzene or phenylhydroxylamine, limits the rate of aniline formation, and such an initial step of nitrobenzene reduction can be catalyzed by NADPH-cytochrome c reductase alone. Cytochrome P-450 is essential at least in the final step of nitrobenzene reduction to aniline. This conclusion was further confirmed by determination of these intermediates in nitrobenzene reduction.

Animals↗
PubMed1984

Not all aromatic nitro compounds form free radicals.

One-electron reduction of the aromatic nitro-containing drug, clonazepam, by rat hepatic microsomes was found to produce a nitro anion radical which was observable by electron paramagnetic resonance (EPR) spectrometry under anaerobic conditions. It was determined that NADPH-cytochrome P-450 reductase may be the enzyme responsible for this reduction and that this free radical reacts rapidly with oxygen to produce superoxide. The vasodilator nifedipine, another aromatic nitro-containing drug, was found not to be reduced by rat hepatic microsomes to a free radical nor to stimulate superoxide production. Based on a series of experiments, we propose that the inability of nifedipine to be bioreduced to its nitro anion free radical is the result of geometric restrictions which prevent the transfer of an electron from cytochrome P-450 reductase to nifedipine.

Animals↗
PubMed1985

Mechanism of toxicity of nitro compounds used in the chemotherapy of trichomoniasis.

The mechanism of the trichomonicidal activity of metronidazole and other 5-nitroimidazoles appears to depend on the ferredoxin-mediated reduction of their nitro group, with generation of a reactive metabolite or metabolites which interact with DNA leading to a subsequent inhibition of nucleic acid and protein synthesis. Redox cycling of these compounds under aerobic conditions appears to be a detoxification reaction by inhibiting net reduction of the drugs, thereby inhibiting their uptake. On the other hand, redox cycling of nitrofurans or other compounds with more positive reduction potential results in formation of high steady-state concentrations of oxygen-derived metabolites that might be of toxicological significance. It seems likely that reduced metabolites of nitroimidazoles (perhaps through covalent binding to tissue macromolecules and/or thiols depletion) are also involved in the nitroimidazoles' toxic effects to animal tissues and in their mutagenic and carcinogenic action.

Animals↗
PubMed1991

Evaluation of secondary nitroalkanes, their nitronates, primary nitroalkanes, nitrocarbinols, and other aliphatic nitro compounds in the Ames Salmonella assay.

The secondary nitroalkanes 2-nitropropane, 2-nitrobutane, 3-nitropentane and nitrocyclopentane, as well as their anionic forms (nitronates); the primary nitroalkanes 1-nitropropane, 1-nitrobutane, and 1-nitropentane and their respective nitronates; the nitrocarbinols 2-nitro-1-propanol, 2-nitro-1-butanol, 3-nitro-2-butanol, and 3-nitro-2-pentanol and their respective nitronates; 2-methyl-2-nitropropane, and 2-nitroso-2-nitropropane were tested in the Ames Salmonella assay using strains TA98, TA100 and TA102. Nitronates of the secondary nitroalkanes 2-nitropropane, 2-nitrobutane, 3-nitropentane, and nitrocyclopentane were significantly mutagenic in Salmonella strains TA100 and TA102 at 10-80 mumoles/plate, but the parent compounds were mutagenic at only a single dose level or were not mutagenic at all in the same dose range. The primary nitroalkanes and the nitrocarbinols were not mutagenic, or only marginally so, at the concentrations tested. The nitronates of the primary nitroalkanes and the nitrocarbinols reprotonated too rapidly under the conditions of the assay for adequate evaluation of mutagenicity. 2-Methyl-2-nitropropane was not mutagenic in strains TA100 and TA102; 2-nitroso-2-nitropropane was also not mutagenic in strains TA100 and TA102, but induced an equivocal mutagenic response in TA98. The positive Salmonella mutation data for the nitronates of the secondary nitroalkanes studied correlate very well with the very slow rate of reprotonation of secondary nitroalkane nitronates at pH 7.7 (Conaway et al. (1991) Cancer Res., 51, 3143), and provide further evidence that nitronates of secondary nitroalkanes, rather than the neutral parent forms with which they may be in equilibrium, are the more proximate mutagenic species.

Carcinogenicity Tests↗
PubMed1986

The reduction of aromatic nitro compounds with Zn/Cu. A new synthesis of N-acetoxy-N-acetyl-arylamines.

A new and simple synthesis is described for N-acetoxy-N-acetyl-derivatives of trans-4-aminostilbene, 2-aminofluorene and 2-aminophenanthrene using a Zn/Cu-couple for the reduction of the nitro-aromatics. This method produces good yields and should also be applicable for other N-aryl-compounds. It can also be used for the reduction of nitro-aromatics to the respective arylamines and arylamides.

Copper↗