Subject thiophosphates

Thiophosphates (Table 13-7) were subjected to hydrolysis with both add and alkaline phosphatases. Most authors claimed that these compounds are substrates for alkaline phosphatases, but the reaction rate is much lower than with the corresponding phosphates1128, 126L Neumann11291, however, reported that these same S-substituted analogs are resistant to alkaline phosphatases but hydrolyzed by add phosphatases. 

The biocatalytic oxidation of racemic 0,5-dimethyl O-p-nitrophenyl phosphor-odithioate (5// )-288 catalyzed by chloroperoxidase from Caldariomyces fumago led to the formation of the corresponding (—)-(5)-thiophosphate 289 and unoxidized substrate (+)-(/ )-288. The thionoester (5// )-288 was subjected to oxidation with hydrogen peroxide in the presence of chloroperoxidase (CPO) in a mixture of citrate buffer, pH 5, and ethanol. Both compounds were prepared with 99.6% and 97% ee, respectively. The thicmation of the ( )-(5)-phosphate 289 with Lawesson s reagent gave (—)-(5)-phosphorodithioate 288 with full stereospecificity, while the oxidation of unreacted substrate (+)-(/ )-288 with iodoxybenzene resulted in the formation of (-i-)-(/ )-289 with 94.9% ee (Scheme 95) [192]. 

Many of these are phosphate or thiophosphate esters. Some organophosphorus insecticides and other pesticide products are almost immediately toxic to humans, while others appear to be nontoxic, at least in the short and medium term. Specialised references need to be consulted. Best known of the extremely toxic varieties are Parathion and tetraethylpyrophosphate (TEPP), both of which can be rapidly fatal by inhalation, ingestion or skin absorption. Potential long-term hazards from residual traces of relatively non-toxic pesticides (or their breakdown products) are currently the subject of much investigation and concern. 

DFP is a phosphoric triester consequently, it is not subjected to bioactivation through desulfuration, as in the case of thiophosphates such as chlorpyrifos, mala-thion, and other OP compoimds used as insecticides. DFP can be enzymatically hydrolyzed by the enzymes called phosphotriesterases or phosphoric triester hydrolases according to the nomenclature of the International Union of Biochemistry and Molecular Biology (Table 57.3). The hydrolysis of DFP releases the fluoride ion and the acidic moiety of DFP, the DIP. This hydrolysis must be considered a detoxication reaction (Sogorb and Vilanova, 2010). 

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