Sarin hydrolysis pathway

FIGURE 19.2 Hydrolysis pathway of sarin (GB), soman (GD), and cyclosarin (GIO hydrolysis pathway of nerve agents proceeds through the alkyl methylphosphonic acids, isopropyl methylphosphonic acid (IMPA), pinacolyl methylphosphonic acid (PMPA), and cyclohexyl methylphosphonic acid (CMPA) to methylphos-ponic acid (MPA). Analysis of the alkyl methylphosphonic acids allows identification of the parent agent, while assay of MPA is nonspecific. 

Metal ion catalysis of salicyl phosphate hydrolysis is much more complicated than that of Sarin, since the former substrate can combine with metal ions to give stable complexes, and some of the complexes formed do not constitute pathways for the reaction. In addition the substrate undergoes intramolecular acid-base-catalyzed hydrolysis which is dependent on pH because of its conversion to a succession of ionic species having different reaction rates. Therefore a careful and detailed equilibrium study of proton and metal ion interactions of salicyl phosphate would be required before any mechanistic considerations of the kinetic behavior in the absence and presence of metal ions can be undertaken. 

VX appears to follow a similar pathway, the major metabolite being ethyl MPA (EMPA). An additional metabolite, derived from the diisopropy-laminoethyl substituent, was identified in human plasma following an assassination with VX (45). The sulfide (17), derived from enzymatic S-methylation of the hydrolysis product HSCH2CH2N(i-Pr)2, was identified in human serum by GC/MS after simple extraction. Experiments in rats confirmed the rapid metabolic formation of (17) from HSCH2CH2N(i-Pr)2 (46). Identification of this metabolite distinguishes VX from the O-ethyl analogue of sarin. 

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