Redox inhibitors

MK-886 (170), which is highly selective for inhibition of 5-LO products by virtue of its interaction with FLAP, was shown not to affect production of IL-1, implying that such effects seen with redox inhibitors such as (31), (39) and (66) are probably due to mechanisms other than 5-LO inhibition... 

Boswellinic acids Leukotrienes appear to play a special role as inflammation mediators in the pathogenesis of PBC they also correlate closely with the increase in cholestasis-indicating enzymes. Boswellinic acids are selective non-redox inhibitors of 5-lipoxygen-ase and therefore inhibit leukotriene biosynthesis. So far, they have not been used in PBC treatment. Based on existing pharmacological data, their application should now be considered. 

Boswellinic acids are seen as selective non-redox inhibitors of leu-kotriene biosynthesis. Leukotrienes are mediators of inflammation. Boswellic adds proved to be antiphlogistic, hepatoprotective and immunosuppressive in their impact (H.P.T. Ammon et at, 1991). Although there has been no therapeutic application in hepatology up to now, it is likely that future discussion will focus on this pharmacologically interesting group of substances, (s. pp 652, 659)... 

The methoxytetrahydropyran moiety has been exploited by other groups. Merck Frosst identified a class of lignans derived from a natural product, Justicidin E, as moderately potent redox inhibitors of 5-LO (163). Abbott also described compounds in this arena (164). These compounds were very weak inhibitors of 5-LO in broken cell preparations, as was ZD2138, although many compounds with potent whole blood activity were obtained. These data imply a different mode of action for this series than direct 5-LO inhibition and are inconsistent with a substrate inhibitor. 

Justicidin E from Justicia procumbens is a potent non-redox inhibitor of 5-LOX activity that inhibits the biosynthesis of LTB4 by human leukocytes with an IC50 = 70 nM [291], Of the different semisynthetic principles, only the 5-phenylpyridyl derivative was more potent (about three times more) than justicidin E as a LOX inhibitor. 

Safayhi, H., Thomas, M., Jaochin, S., et al., Boswellic acids novel specific non redox inhibitors of 5-lipoxygenase, J. Pharmacol. Exp. Ther. (1992)261(3), 1143-1146. 

Isothermal polymerizations are carried out in thin films so that heat removal is efficient. In a typical isothermal polymerization, aqueous acrylamide is sparged with nitrogen for 1 h at 25°C and EDTA (C2QH2 N20g) is then added to complex the copper inhibitor. Polymerization can then be initiated as above with the ammonium persulfate—sodium bisulfite redox couple. The batch temperature is allowed to rise slowly to 40°C and is then cooled to maintain the temperature at 40°C. The polymerization is complete after several hours, at which time additional sodium bisulfite is added to reduce residual acrylamide. 

Electron Transport Between Photosystem I and Photosystem II Inhibitors. The interaction between PSI and PSII reaction centers (Fig. 1) depends on the thermodynamically favored transfer of electrons from low redox potential carriers to carriers of higher redox potential. This process serves to communicate reducing equivalents between the two photosystem complexes. Photosynthetic and respiratory membranes of both eukaryotes and prokaryotes contain stmctures that serve to oxidize low potential quinols while reducing high potential metaHoproteins (40). In plant thylakoid membranes, this complex is usually referred to as the cytochrome b /f complex, or plastoquinolplastocyanin oxidoreductase, which oxidizes plastoquinol reduced in PSII and reduces plastocyanin oxidized in PSI (25,41). Some diphenyl ethers, eg, 2,4-dinitrophenyl 2 -iodo-3 -methyl-4 -nitro-6 -isopropylphenyl ether [69311-70-2] (DNP-INT), and the quinone analogues,... 

Another method for producing petoxycatboxyhc acids is by autoxidation of aldehydes (168). The reaction is a free-radical chain process, initiated by organic peroxides, uv irradiation, o2one, and various metal salts. It is terrninated by free-radical inhibitors (181,183). In certain cases, the petoxycatboxyhc acid forms an adduct with the aldehyde from which the petoxycatboxyhc acid can be hberated by heating or by acid hydrolysis. If the petoxycatboxyhc acid remains in contact with excess aldehyde, a redox disproportionation reaction occurs that forms a catboxyhc acid ... 

Environment Increase redox potential of solution Addition of anodic inhibitors Passivation of stainless steel by additions of O2, HNO3 or other oxidising species to a reducing acid Additions of chromates, nitrates, benzoates, etc. to neutral solutions in contact with Fe inhibitive primers for metals, e.g. red lead, zinc chromate, zinc phosphate... 

The absolute rate constants for attack of carbon-centered radicals on p-benzoquinone (38) and other quinones have been determined to be in the range I0M08 M 1 s 1.1 -04 This rate shows a strong dependence on the electrophilicity of the attacking radical and there is some correlation between the efficiency of various quinones as inhibitors of polymerization and the redox potential of the quinone. The complexity of the mechanism means that the stoichiometry of inhibition by these compounds is often not straightforward. Measurements of moles of inhibitor consumed for each chain terminated for common inhibitors of this class give values in the range 0.05-2.0.176... 

Without the addition of corrosion inhibitors, acid cleaning or pickling processes to remove oxides and scales would result in severe corrosion of exposed metal surfaces. Acid corrosion is an electrochemical or redox process, and raising cleaning temperatures or acid strength (lowering the pH) increases the hydrogen ion concentration and consequently the rate of corrosion. 

Fig. 14. Plot of the g values g,g ) and of the average g value g vs rhombicity (UJ of (a) wild type (open symbol) and variant forms (closed symbols) of the Rieske protein in yeast bci complex where the residues Ser 183 and Tyr 185 forming hydrogen bonds into the cluster have been replaced by site-directed mutagenesis [Denke et al. (35) Merbitz-Zahradnik, T. Link, T. A., manuscript in preparation] and of (b) the Rieske cluster in membranes of Rhodobacter capsulatus in different redox states of the quinone pool and with inhibitors added [data from Ding et al. (79)]. The solid lines represent linear fits to the data points the dashed lines reproduce the fits to the g values of all Rieske and Rieske-type proteins shown in Fig. 13.

Fig. 15. EPR spectra of the Rieske cluster in membranes of Paracoccus denitrificans in different redox states of the quinone pool and with inhibitors added. Q x, ascorbate reduced Qred) reduced with trimethylhydroquinone dissolved in dimethyl sulfoxide +EtOH, reduced with trimethylhydroquinone dissolved in 90% ethanol +Myxo, ascorbate reduced with myxothiazol added + Stigma, ascorbate reduced with stigmatellin added. Only the gy and signals are shown. The dotted line has been drawn at...

Hard, S. and Kanner, J. (1989). Haemoglobin and myoglobin as inhibitors of hydroxyl radical generation in a model system of iron redox cycle. Free Rad. Res. Commun, 6, 1-10. 

The equilibrium constant K for (por)Fe(OH2) (por)Fe, which determines the molar fraction of the 5-coordinate redox-active Fe catalyst. This constant was estimated from analysis of the catalytic turnover frequencies in the presence of varying concentrations of an inhibitor, CN, which competes with both O2 and H2O for the 5-coordinate Fe porphyrin. 

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