The Metabolic Behavior of the Insecticidal Phosphorus Ester GS-130051

The metabolic fate of 14C-labe1ed GS-13005 ( S - ((2- methoxy-5-oxo-Δ2-1,3,4-thiadiazolin-4-yl) methyl) O,O -dimethyl phosphorodithioate), the active ingredient of the insecticide Supracide® was followed in plants, soil, and animals. A rapid degradation of this insecticide in all investigated was observed. In addition to the hydrolysis of the ester bond, the heterocyclic moiety of GS-13005 was cleaved, and the fragments originating were oxidized to CO2 which represented the main metabolite. The pattern of metabolites in bean and alfalfa plants consisted of almost exclusively polar substances, approximately ⅓ of which liberated GS-12956 (2-methoxy-Δ2-1,3,4-thiadiazolin-5-one) after hydrolysis. Only trace amounts of the corresponding P-O derivative, GS-13007 ( O -[(2-methoxy-5-oxo-Δ2-1,3,4-thiadiazolin-4-yl)-methyl] O,O -dimethyl phosphorothioate, and of G5-12956 were detected. The pronounced degradation of GS-13005 in 2 types of soil was suppressed after steam sterilization emphasizing the role of the soil microorganisms. Locusts metabolized the thiadiazole ring of GS-13005 resulting in the liberation of 14CO2 and an increasing amount of water-soluble metabolites. Urine and expired air were the main routes for the excretion of metabolites of GS-13005 orally applied to rats. ro accumulation of GS-13005 or its metabolites was observed in any organ of the rat after feeding the insecticide for 10 days. In addition to 14CO2, the sulfoxide derivative, GS-28370 (2-methoxy-4-methylsulfinylmcthylorganisms Δ2-1,3,4-thiadiazolin-5-one), and the sulfone derivative, GS-28369 (2-methoxy-4-methylsulfonylmethyl-Δ2-1,3,4-thiadiazolin-5-one), were determined as the main metabolites of the urine. These metabolites are not cholinesterase esterase inhibitors and have acute toxicities in the range of only 1/15-1/50 of the parent insecticide. The metabolic fate of these metabolites and of GS-12956 was followed to determine the sequence of the metabolic reactions taking place in the course of the degradation of GS-13005 in the rat. The mechanism of the degradation of GS-13005 in the rat was investigated in vitro systems demonstrating methionine as the methyl donor for the synthesis of the main metabolites. Absence of GS-13005 and its oxidation product, GS-13007, in the milk of a goat was demonstrated. Only 0.6% of the dose orally applied was found in the form of polar metabolites.