8- Nitro-4- -xanthines

Spin trapping has been widely used for superoxide detection in various in vitro systems [16] this method was applied for the study of microsomal reduction of nitro compounds [17], microsomal lipid peroxidation [18], xanthine-xanthine oxidase system [19], etc. As DMPO-OOH adduct quickly decomposes yielding DMPO-OH, the latter is frequently used for the measurement of superoxide formation. (Discrimination between spin trapping of superoxide and hydroxyl radicals by DMPO can be performed by the application of hydroxyl radical scavengers, see below.) For example, Mansbach et al. [20] showed that the incubation of cultured enterocytes with menadione or nitrazepam in the presence of DMPO resulted in the formation of DMPO OH signal, which supposedly originated from the reduction of DMPO OOH adduct by glutathione peroxidase. 

The SOD activity measurements using the xanthine-xanthine oxidase nitro blue tetrazolium (NBT) method [45] indicated that a concentration of 0.75 xM of [Mn(OBz)(H-3,5-/-Pr2pz)(L 1)] 1 and 0.8 iM of the related [Mn(OBz)(Ll)] 2 complex exert the same SOD activity as one unit of native SOD. The high SOD activity of the tris(pyrazolyl)borate complexes was attributed to their structural similarities to the MnSOD active site [45],... 

K.K. Colvert, P.P. Fu, Xanthine oxidase-catalyzed DNA binding of dihydrodiol derivatives of nitro-polycyclic aromatic hydrocarbons. Biochem. Bioph. Res. Co. 141, 245-250 (1986)... 

The substrate half-reactions are displayed in Tables I and II. In each case, a two-electron process seems to be involved. Only in nitro-genase are greater numbers of electrons transferred, and the discussion earlier in this paper summarizes the evidence that these processes occur in two-electron steps. The two-electron reaction of the molybdenum site never appears to be simply an electron transfer reaction. In the case of nitrogenase, each substrate takes up an equal (or greater) number of protons to form the product. In the other molybdenum enzymes, proton transfer and addition or removal of H20 are also required. In each case, however, there is at least one proton transferred in the same direction as the pair of electrons. These data, taken in conjunction with the EPR evidence for proton transfer from the substrate to the active site in xanthine oxidase, suggest that the molybdenum site in all the enzymes... 

Electron-releasing groups are required in the purine ring system before nitration can occur. In this way 8-nitro-caffeine (149), -theophylline (150), and -theobromine (151) have been prepared by nitration of the appropriate purine with nitric acid, neat or in acetic acid (71HC(24-2)i, p. 402). Similarly, 9-methylxanthine, but not xanthine, undergoes nitration to 9-methyl-8-nitroxanthine (60JA3773). 

Recently, xanthine and its A-methyl derivatives were nitrated to the corresponding 8-nitro derivatives under different reaction conditions. ... 

In order to achieve nitration of the more sensitive jV-substituted xanthine derivatives, nitronium tetrafluoroborate is applied in various solvents at elevated temperatures e.g. nitration of 3-benzyl-7-methylxanthine to give the 8-nitro product 3 (R = H R = Bn R = Me). ... 

One may mention the relative lack of information on the possible toxicity mechanisms of other groups of explosives. The administration of hexahydro-l,3,5-trinitro-l,3,5-triazine (RDX 30-300 mg kg-1 daily for 13 weeks) to rats caused hypotriglycidire-mia, convulsions, and death [4], In contrast, pentaerythritol tetranitrate (PETN 0.5%-1.0% in standard diet for 13 weeks) was nontoxic to rats [80], RDX was much less cytotoxic to V79 and TK-6 mammalian cell cultures than TNT [9], There also are very few data on their reactions with mammalian enzymes. Rabbit liver cytochrome P-450 2B4 (EC 1.14.14.1) converted RDX into 4-nitro-2,4-diazabutanal, two nitrite ions, ammonium, and formaldehyde, consuming one equivalent NADPH [81]. However, it is unclear whether this slow reaction (kcat < 0.01 s-1) may contribute to the toxicity of RDX. Xanthine oxidase transformed octohydro-l,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) at a lower rate, 10.5 nmol h 1 mg 1 protein under anaerobic conditions, into nitrite, formaldehyde, nitrous oxide, formic acid, and ammonium [82], Our preliminary observations show that RDX was much less reactive substrate for P-450R and E. cloacae NR than NTO or ANTA [53], Thus, the mechanisms underlying toxicity of RDX remain undisclosed. 

Tatsumi K, Inoue A, and Yoshimura H, Mode of reactions between xanthine oxidase and aromatic nitro compounds, J. Pharmacobiodyn., 4, 101, 1981. 

Formation of the third oxazole ring can also be realized by a reaction of epichlorohydrin with 8-nitro- or 8-(methanesulfonyl)-4-(2-hydroxypropyl)-xanthine derivatives (75JPR745). 

We report here on the mechanism of DNA strand breakage and poly(ADP-ribosyl)ation by AO in comparison to the methylating agent N-methyl-N -nitro-N-nitrosoguanidine (MNNG) in promotable JB6 clone 41 cells. We also summarize first results on the identity of the nuclear proteins which serve as poly(ADP-ribose) acceptors in response to AO. We chose xanthine/xanthine oxidase (X/XO) as a source of extracellular AO because it produces a mixture of superoxide and H2O2 which resembles the oxidants released by macrophages and mouse epidermal cells JB6 because promotable (clone 41) and non-promotable (clone 30) variants are available (9). 

Superoxide radicals are produced by a xanthine-xanthine oxidase system. Xanthine is able to generate 02 and H2O2 by using xanthine oxidase as a substrate. The superoxide radicals are able to reduce the yellow colored nitro triazolium blue (NTE) to the blue formazan, which is used for monitoring the reaction. The superoxide anions are measured spectrophotometricaUy. This test method was developed to explore the reaction between antioxidants and 02. So the inhibition of the superoxide reductase is a mark for the ability of antioxidative activity. 

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