Metabolism of fungicide diethofencarb in grape (Vitis vinifera L.):: Definitive identification of thiolactic acid conjugated metabolites

The metabolic fate of diethofencarb (isopropyl 3,4-diethoxycarbanilate) separately labeled with C-14 at the phenyl ring and 2-position of the isopropyl moiety was studied in grape (Vitis vinifera L.). The acetonitrile solution of C-14-diethofencarb at a rate of 500 g a.i. ha(-1) was once applied topically to fruits or leaves at the maturity stage of fruits (PHI 35 days), and the plants were grown in the greenhouse until harvest. In the grape plants, diethofencarb was scarcely translocated to the untreated portion and was degraded more in the fruit as compared to the leaf. For the fruit, diethofencarb primary underwent O-deethylation at the 4-position of the phenyl ring to form the phenolic derivative, isopropyl 3-ethoxy-4-hydroxycarbanilate (0.9% of the total radioactive residue, TRR). This metabolite was successively transformed via conjugation with glucose at the phenolic hydroxy group (8.1-18.1% TRR) or with thiolactic acid at the 5-position of the phenyl ring (1.5-1.7% TRR). The thiolactic acid conjugate was further metabolized mainly to two different types of glucose conjugates at the 4-position of the phenyl ring (8.7-13.5% TRR) and the hydroxy group in the thiolactic acid moiety (6.4-7.3% TRR), as evidenced by H-1 NMR and atmospheric pressure chemical ionization-liquid chromatography-mass spectrometry together with cochromatographies with synthetic standards.