Electrophilic Products Research Articles

Diazabicycloalkanes with nitrogen atoms in nodal positions. 13. Reactions of benzo[b]-1,4-diazabicyclo[2.2.2]octene with electrophiles

The reactions of electrophiles with benzo[b]-1,4-diazabicyclo[2.2.2]octene have been examined. Electrophilic substitution is found to take place in the aromatic ring under severe conditions, in the case of halogenation giving high yields. The structures of the electrophilic substitution products indicate that the heteroatoms have a m-directing influence.

Quantitative methodology for corticosteroids based on chemical oxidation to electrophilic products for electron capture-negative chemical lonization using capillary gas chromatography-mass spectrometry: I. Assessment of feasibility in the analysis of horse urine for dexamethasone

Sensitive and specific methodology based on capillary column gas chromatography-electron capture-negative chemical ionization-mass spectrometry has been developed for the quantitative analysis of corticosteroids from biological fluids. The feasibility of this method is demonstrated in the quantitative analysis of dexamethasone in horse urine following administration of the drug. A structurally similar compound, 6α-methylprednisolone, is added to the urine as an internal standard. The free dexamethasone and the internal standard are extracted and oxidized to high-electron-affinity 1,4-androstadiene-3,11,17-trione structural analogs and then analyzed by capillary column gas chromatography-electron capture-negative chemical ionization-mass spectrometry.

Evidence for a one-electron mechanism of 2-aminofluorene oxidation by prostaglandin H synthase and horseradish peroxidase.

Previous studies have shown that the primary arylamine carcinogen 2-aminofluorene (2-AF) is oxidized by the prostaglandin H synthase peroxidase to mutagenic and electrophilic products capable of covalent binding to macromolecules. The present study was designed to identify the potential reactive intermediate(s) responsible for binding, and to characterize further the metabolic intermediates in 2-AF peroxidation. Both prostaglandin H synthase and horseradish peroxidase, with H2O2, oxidize 2-AF to azofluorene, 2-aminodifluorenylamine (2-ADFA), 2-nitrofluorene, polymeric and nonorganic-extractable material. Both enzymes show greater activity at pH 5.0 than at pH 7.0. In the presence of either 2-t-butyl-4-methoxyphenol or 2,6-dimethylphenol, arylamine/phenol adducts were formed in high yield, with the nitrogen of either 2-AF or 2-ADFA coupled to the para position of the phenol (loss of -OCH3 with 2-t-butyl-4-methoxyphenol). These structures were confirmed by mass spectrometry and NMR spectroscopy. Acid hydrolysis of N-hydroxy-2-AF to yield the nitrenium ion, in the presence of a phenol, also results in adduct formation, but only at times greater than 2 h and in very limited yield. The peroxidase-catalyzed adduct formation, however is rapid (less than 2 min) and extensive. These and other data support a one-electron pathway for 2-AF peroxidation, with a free radical or a free radical-derived product responsible for binding to protein and DNA. An N-hydroxy intermediate may therefore not be obligatory in the enzymatic activation of 2-AF to a mutagenic product.

Reactive Metabolites From the Bioactivation of Toxic Methylfurans

An important mechanism of toxicity of furans involves the cytochrome P-450 monooxygenase-catalyzed bioactivation of the compound in situ directly within the target tissues to highly reactive electrophilic products. The unsaturated aldehydes acetylacrolein and methylbutenedial have been identified as the principal reactive intermediates of 2- and 3-methylfuran, respectively, that are produced and bound covalently to tissue macromolecules in hepatic and pulmonary microsomal systems in vitro.

Chemically induced nephrotoxicity: role of metabolic activation.

Renal xenobiotic metabolism can result in production of electrophiles or free radicals that may covalently bind macromolecules or initiate lipid peroxidation. The mechanisms of renal xenobiotic metabolism may vary in different anatomical regions. Kidney cortex contains a cytochrome P-450 system while medulla contains a prostaglandin endoperoxidase. Recently cysteine conjugated-lyase has been implicated in production of reactive intermediates. Metabolic activation may be amplified by accumulation of xenobiotics within renal cells due to tubular concentrating and/or secretory mechanisms. Additionally, renal xenobiotic detoxicification can occur by conjugation with glucuronide, sulfate or glutathione.

Metabolic Basis for the Pulmonary Clara Cell as a Target for Pulmonary Carcinogenesis

The furan compound, 4-ipomeanol, is activated in lung tissue by cytochrome P-450 dependent oxidation to a highly reactive, electrophilic product that binds covalently to tissue macromolecules. Although the reactive metabolite(s) of 4-ipomeanol have not yet been definitively identified, recent studies with 3-methylfuran have indicated that a highly reactive, unsaturated dialdehyde is formed from microsomal oxidation and ring-opening of the furan nucleus. Metabolic experiments with 4-ipomeanol in intact lungs, lung slices, lung cells, lung microsomes and purified lung cytochromes P-450, supported the conclusion that the Clara cell is an important locus of cytochrome P-450 monooxygenase activity in lung. In vivo, 4-ipomeanol was bound covalently and caused necrosis preferentially in the pulmonary Clara cells of laboratory animals. Similarly, N-nitrosamines require metabolic activation mediated by the cytochrome P-450 monooxygenase system in the host organism. A number of nitrosamines which are lung carcinogens in rats and hamsters have been shown to bind preferentially to bronchial and bronchiolar Clara cells in these species. Early pathological changes occurred specifically in Clara cells and lung tumors that developed under continuous nitrosamine treatment originated from such altered Clara cells. The well-differentiated counterparts of these tumors clearly retained their ability to bind the nitrosamine that had induced their formation. Thus, the studies on these two different classes of compounds together supported the view that metabolism may be a factor critical to the progenitor role of the Clara cell in chemically-induced bronchogenic lung cancer.

Irreversible inactivation of the flavoenzyme alcohol oxidase with acetylenic alcohols

Summary Alcohol oxidase is irreversibly inactivated by the acetylenic substrates propargyl alcohol and 1,4-butynediol. In both cases, inactivation results from affinity labeling of amino acid residues in the active site of the enzyme by propynal and 4-hydroxy-2-butynal, the electrophilic products of the oxidation of these alcohols. The inactivation by 4-hydroxy-2-butynal occurs with the aldehyde bound in the active site of the enzyme in the orientation which is opposite to that in which it had been produced. Alcohol oxidase is inactivated by acetylenic substrates in a fundamentally different manner than are the formally similar flavin-dependent α-hydroxy acid oxidases.

Inactivation of alcohol dehydrogenase by 3-butyn-1-ol

Horse liver and yeast alcohol dehydrogenases are rapidly inactivated during their catalysis of the oxidation of 3-butyn-1-ol. In the case of the horse liver enzyme, the inactivation is secondary to covalent modification of the apoenzyme by an electrophilic product that accumulates in the reaction solution and that can also react with water, glutathione, and other enzymes. The modified protein exhibits enhanced ultraviolet absorbance, which is not bleached upon dialysis of the denatured enzyme at pH 7.4 for 24 h. The inactivation by 3-butyn-1-ol is more rapid than that which is afforded by the related alcohols 2-propyn-1-ol and 2-propen-1-ol under identical conditions and no inactivation is seen upon incubation with 3-hydroxypropanoic nitrile plus nicotinamide-adenine dinucleotide.