IN-VITRO METABOLISM OF THIAZOPYR PLANT METABOLITES BY RAT-LIVER ENZYMES

Thiazopyr [methyl 2-(difluoromethyl)-5-(4,5-dihydro-2-thiazolyl)-4-(2-methylpropyl)-6-(trifluoromethyl)-3-pyridinecarboxylate] is an experimental herbicide being developed for weed control in cotton, citrus, and other crops. The in vitro metabolic fate of key thiazopyr crop metabolites in animals was investigated using rat liver homogenates. The thiazopyr crop metabolites studied were sulfoxide ester, sulfone ester, nitrile ester, amide acid, and sulfonic diacid. Our results showed that the ester crop metabolites were extensively metabolized by rat liver homogenates to products previously observed during in vivo rat metabolism studies. Metabolites were identified using several techniques including high-performance liquid chromatography coelution with standards, direct identification by mass spectrometry and comparison with standards, and derivatization followed by mass spectrometry. In contrast, the acidic crop metabolites (amide acid and sulfonic diacid) were not metabolized, likely due to their water solubility and high polarity. Our study showed that these crop metabolites, if absorbed by rats, are further transformed to polar products that are likely to be eliminated rapidly from the body. (C) 1995 Academic Press, Inc.