Trichloromethyl metabolites

The simple herbacic acid (938) was isolated from Dysidea herbacea from the Great Barrier Reef, and may be a precursor to more complex trichloromethyl metabolites (990). Another collection of Dysidea sp. from Australia s Great Barrier Reef yielded five new metabolites (939-943) for which the absolute stereochemistry was determined by correlation with (-)-(.S )-4,4,4-trich loro-3-methyl butanoic acid (991). Dysidea herbacea from the Great Barrier Reef contains (-)-neodyside-nin (944), which is an isomer of the well-known and often isolated dysidenin. 

The degradation of tetrachloromethane by a strain of Pseudomonas sp. presents a number of exceptional features. Although was a major product from the metabolism of CCI4, a substantial part of the label was retained in nonvolatile water-soluble residues (Lewis and Crawford 1995). The nature of these was revealed by the isolation of adducts with cysteine and A,A -dimethylethylenediamine, when the intermediates that are formally equivalent to COClj and CSClj were trapped—presumably formed by reaction of the substrate with water and a thiol, respectively. Further examination of this strain classified as Pseudomonas stutzeri strain KC has illuminated novel details of the mechanism. The metabolite pyridine-2,6-dithiocarboxylic acid (Lee et al. 1999) plays a key role in the degradation. Its copper complex produces trichloromethyl and thiyl radicals, and thence the formation of CO2, CS2, and COS (Figure 7.64) (Lewis et al. 2001). 

Methods for Determining Biomarkers of Exposure and Effect. Covalent adducts between reactive carbon tetrachloride metabolites (e.g., the trichloromethyl radical) and cellular proteins, lipids and nucleic acids are known to occur, but at present these can only be measured using radiolabeled carbon tetrachloride. Development of immunological or other methods to detect such adducts in humans exposed to carbon tetrachloride could be of value in estimating past exposures to carbon tetrachloride. 

The cytochrome P-450 destroyed may be a specific isoenzyme, as is the case with carbon tetrachloride and allylisopropylacetamide (Table 5.28). Indeed, with carbon tetrachloride the isoenzyme destroyed is the one, which is responsible for the metabolic activation (CYP1A2). With allylisopropylacetamide, it is the phenobarbital-inducible form of the enzyme, which is preferentially destroyed as can be seen from Table 5.25. It seems that it is the heme moiety, which is destroyed by the formation of covalent adducts between the reactive metabolite, such as the trichloromethyl radical formed from carbon tetrachloride (see chap. 7), and the porphyrin ring. 

Metabolites of carbon tetrachloride may also give a positive result with tiiis test, but carbon tetrachloride is only partially metabolised to trichloromethyl compounds and the test may fail to detect this agent. If carbon tetrachloride poisoning is suspected, evidence of hepato-toxicity should be sought by carrying out appropriate serum-enzyme assays. 

Carbon tetrachloride is metabolized by cytochrome P-450 to the reactive metabolites trichloromethyl free radical and trichloromethylperoxy free radical. The trichloromethyl free radical may bind directly to cellular macromolecules such as lipids and proteins, and also to DNA, disrupting cell processes and breaking down membranes. The free radical can take part in anaerobic reactions, subsequently forming such toxic compounds as chloroform, hexachloroethane, and carbon monoxide. Aerobic biotransformation of the... 

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