Reducing metabolites, reactions with

The role of N-sulfonyloxy arylamines as ultimate carcinogens appears to be limited. For N-hydroxy-2-naphthylamine, conversion by rat hepatic sulfotransferase to a N-sulfonyloxy metabolite results primarily in decomposition to 2-amino-l-naphthol and 1-sulfonyloxy-2-naphthylamine which are also major urinary metabolites and reaction with added nucleophiles is very low, which suggests an overall detoxification process (9,17). However, for 4-aminoazobenzene and N-hydroxy-AAF, which are potent hepatocarcinogens in the newborn mouse, evidence has been presented that strongly implicates their N-sulfonyloxy arylamine esters as ultimate hepatocarcinogens in this species (10,104). This includes the inhibition of arylamine-DNA adduct formation and tumorigenesis by the sulfotransferase inhibitor pentachlorophenol, the reduced tumor incidence in brachymorphic mice that are deficient in PAPS biosynthesis (10,115), and the relatively low O-acetyltransferase activity of mouse liver for N-hydroxy-4-aminoazobenzene and N-OH-AF (7,114,115). 

When the resulting mixture of benzoylformic acid and (i )-mandelic acid was treated with a cell free extract of Streptomyces faecalis IFO 12964 in the presence of NADH,the keto acid can be effectively reduced to (i )-mandelic acid (Fig. 1). Fortunately the presence of A. bronchisepticus and its metabolite had no influence on the reduction of the keto acid. The regeneration of NADH was nicely achieved by coupling the reaction with reduction by formic acid with the aid of formate dehydrogenase. As a whole, the total conversion of racemic mandelic acid to the i -enantiomer proceeded with very high chemical and optical yields. The method is very simple and can be performed in a one-pot procedure [6]. 

Precursors. Precursors for this reaction are compounds exhibiting keto-enol tau-tomerism. These compounds are usually secondary metabolites derived from the glycolysis cycle of yeast metabolism during fermentation. Pyruvic acid is one of the main precursor compounds involved in this type of reaction. During yeast fermentation it is decarboxylated to acetaldehyde and then reduced to ethanol. Acetone, ace-toin (3-hydroxybutan-2-one), oxalacetic acid, acetoacetic acid and diacetyl, among others, are also secondary metabolites likely to participate in this kind of condensation reaction with anthocyanins. 

For. some nitro xenobiotics. biorcduction appears to be a minor metabolic pathway in vivo, because of competing oxidative and conjugative reactions. Under artificial anaerobic in viux) incubation conditions, however, these same nitro xenobiotics are enzymatically reduced rapidly. For example, most of the urinary metabolites of metronidazole found in humans are either oxidation or conjugation products. Reduced metabolites of metronidazole have not been detected. " When incubated anaerobically with guinea pig liver preparations, however, metronidazole undergoes considerable nitro reduction. ""... 

Aminobiphenyl is one of a number of chemicals that cause methemoglobinemia, or conversion of hemoglobin to methemoglobin, which reduces the ability of the blood to carry oxygen to tissues. In addition, the active metabolite (see above) is believed to produce cancer through its reaction with cellular DNA. In animal studies, the observed incidence of 4-aminobiphenyl adducts with bladder epithelium DNA correlated well with the observed bladder tumor incidence. 

Human biomonitoring involves the measurement of a parent chemical and/or metabolites or a product of its reaction with cellular components (e.g. protein adduct, nucleic acid adduct) in selected tissues, body fluids such as blood, iffilk, urine or sweat, or expired breath of an exposed individual. Most lAs for pesticides are sensitive enough for biomonitoring. Many analytes could be determined without any sample preparation other than dilution with water or buffer. In some cases the sample was Altered. Slightly reduced sensitivity or higher blank values due to matrix effects were sometimes found when... 

Fermenting must is a reducing medium, so no oxidation can occm, but reactions with yeast metabolites may give the color an orange tinge. Direct A+ T reactions also produce colorless compounds that react when the wine is... 

Camphor, a bicyclic monoterpene, is extracted from the woods of Cinnamomum camphora, a tree located in Southeast Asia and North America. Furthermore, it is also one of the major constituents of the essential oil of common sage (Salvia officinalis). Solid camphor forms white, fatty crystals with intensive camphoraceous odor and is used commercially as a moth repellent and preservative in pharmaceuticals and cosmetics (Wichtel, 2002). In dogs, rabbits, and rats, camphor is extensively metabolized whereas the major hydroxylation products of d- and L-camphor were 5-endo-md 5-ex -hydroxycamphor. A small amount was also identified as 3-e do-hydroxycamphor (Figure 8.2). Both 3- and 5-bornane groups can be further reduced to 2,5-bornanedione. Minor biotransformation steps also involve the reduction of camphor to borneol and isoborneol. Interestingly, all hydroxy-lated camphor metabolites are further conjugated in a Phase II reaction with glucuronic acid... 

Figure 1 Flavonoids and their in vivo metabolite forms may act by direct reaction with oxidizing species in the body, thereby reducing the accumulation of end products of oxidative damage in the cell, or by modulation of intracellular signaling events.

Step in their determination consists of borohydride reduction, by which the corticosteroids and their metabolites are converted to their dihydroxy derivatives. At the same time, the 17-oxo steroids present are reduced to secondary alcohols which are not affected by bismuthate or periodate (see below) and do not give the Zimmermann reaction. The next step consists of bismuthate or periodate oxidation, by which the dihydroxy derivatives are converted to 17-oxosteroids. These are then estimated by their reaction with m-dinitrobenzene in alcoholic alkali to give a purple compound (the Zimmermann reaction). 

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