Paraoxon parathion conversion

A typical example is the conversion of Parathion to its oxygen analog (i. e., Paraoxon) in soil and microbial cultures Fig. 11). 

El-Refai, A. and Hopkins, T.E. Parathion absorption, translocation, and conversion to paraoxon in bean plants, /. Agric. Food Chem., 14(6) 588-592, 1966. 

Spencer, W.F., Adams, J.D., Shoup, T.D., and Spear, R.C. Conversion of parathion to paraoxon on soil dusts and clay minerals as affected by ozone and UV light, J. Agric. Food Chem., 28(2) 366-371, 1980. 

Smolen JM, Stone AT (1998) Organophosphorous ester hydrolysis catalyzed by dissolved metals and metal containing surfaces. In PM Huang et al. (eds) Soil chemistry and ecosystem health. Soil Sci Soc Am Spec Publ 52 Madison, Wisconsin, pp 157-171 Spencer WF, Shoup TD, Spear RC (1980) Conversion of parathion to paraoxon on soil dusts and clay-minerals as affected by ozone and UV-Ught. J Agric Food Chem 28 366-371 Stevenson FJ (1982) Humus chemistry. Wiley, New York Stevenson FJ (1986) Cycles of soil. Wiley Interscience, New York... 

Methyl parathion itself is not a strong cholinesterase inhibitor, but one of its metabolites, methyl paraoxon, is an active inhibitor. Methyl paraoxon inactivates cholinesterase by phosphorylation of the active site of the enzyme to form the dimethylphosphoryl enzyme. Over the following 24-48 hours there is a process, called aging, of conversion to the monomethylphosphoryl enzyme. ... 

Desulfuration is the term given to removal of sulfur from a molecule. One of the most common desulfuration reactions occurs with sulfur bonded to phosphorus. A common desulfuration reaction is the enzyme-mediated conversion of parathion to paraoxon (see discussion of organophosphate insecticides in Section 18.7) ... 

In the body, parathion is converted to paraoxon (structure in Figure 18.8), which is a potent inhibitor of acetylcholinesterase. Because this conversion is required for parathion to have a toxic effect, symptoms develop several hours after exposure, whereas the toxic effects of TEPP or... 

A specific example of this type of reaction is the conversion of parathion to paraoxon, mentioned... 

Parathion gave a field half-life of 5 minutes for conversion to paraoxon (Table IV). The reaction was considerably slower when the experiment was repeated after sunset. Laboratory experiments gave a half-life of 23 min when irradiation was carried out with ozone present, and was only slightly slower without ozone. Without light very little or no reaction occurred. 

Figure 9. Conversion of parathion to paraoxon by heat and enzymatic action...

Figure 9.17. Organophosphate inhibitors of acetylcholinesterase. a The catalytic mechanism, shown here for diiso-propylfluorophosphate(DFP).b Stmcturesof soman and tabun. Like DFP, these were developed during world war II as nerve gases , c Stractures of the insecticides parathion and malathion, and of paraoxon, which is the achve metabolite of parathion. (Malathion likewise requires conversion to malaoxon.) The arrow above the malathione stmcture indicates the esterase cleavage sites in its leaving group esterase cleavage occurs in human plasma and renders the molecule non-toxic.

The phosphorothioates and phosphorodithioates, shown in Table 1 of Chapter 2, were developed when the nerve agents were found to be too toxic and volatile for use in agriculture. These OP insecticides contain a P-S-alkyl and/ or a P=S group in their structure. The best known member of this class is parathion, the most widely used insecticide at one time and responsible for more cases of accidental poisoning and death than any other OP compound. The activation and conversion of this weak AChEI (parathion) to the more active and potent form (paraoxon) was demonstrated to lake place in the liver (Diggle and Gage, 1951 Gage, 1953). 

The versatility of the P450 oxygenases is summarized in Figure 9.3. Epoxides can be introduced into aromatic rings or across double bonds. The former reaction leads to a hydroxy or dihydodiol. It is most unlikely to observe aldrin in environmental samples since it is rapidly converted to dieldrin, a common environmental contaminant that is very stable. Aliphatic chains can be hydroxylated and ethers, thioethers, and substituted amines dealkylated. The conversion of parathion to the more reactive paraoxon is a factor in the mechanism of toxic action, as well as its environmental stability (see Hydrolysis, Chapter 8). The situation can be complicated by the fact that a substrate can often undergo more than one reaction. 

Conversion to a phosphoryl derivative is necessary for insecticidal action, that is, in order that phosphorylating action can ensue and the compound becomes active. In the case of parathion, this may happen by thiono-thiolo isomerisation (12.99), or by in vivo oxidation with suitable enzymes to paraoxon (12.96c). Highly purified parathion, mp = 6°C, has a relatively low toxicity. The toxic technical-grade material is an impure dark brown liquid which has a garlic-like odour. Parathion and paraoxon are both decomposed by alkali. 

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