Tolclofos-methyl (I) [Rizolex, O, phosphorothioate] is an organophosphorus fungicide effective for the control of soil-borne diseases in sugar beet, potato and lettuce caused by Rhizoctonia solani, Corticium rolfsii, Typhula incarnata and Typhula ishikariensis.1) Since the typical use pattern of I is seed treatment or direct soil application, its metabolic pathways in plants after foliar application have not been examined. Studies of the metabolism of organophosphorus pesticides in plants have revealed cleavage of the P-O-aryl linkage and Odealkylation to be among the most predominant metabolic pathways.2) Oxidative desulfuration at the PϭS moiety and oxidation at thioalkyl, alkyl and aryl motifs are known to occur in this class of pesticides and a photo-induced thionothiolo rearrangement has also been detected. However, the polar conjugated metabolites of organophosphorus pesticides and/or their primary metabolites with natural components in plants have not been fully investigated. Although their chemical structures were determined based on those of aglycons released by acid or enzymatic hydrolysis, recent progress in LC-MS and NMR spectroscopies has enabled us to directly obtain structural information. By using these techniques, we have recently identified the cellobiose conjugate of 3-methyl-4-nitrophenol, which was degraded from fenitrothion in tomato.3) This paper deals with the metabolism of I in lettuce following a foliar application. The metabolic pathway was examined by applying extensive spectrometric analyses. MATERIALS AND METHODS ChemicalsNon-radiolabled tolclofos-methyl (I), [2,6- phosphorothioate] (V) were synthesized in our laboratory according to reported methods.4) The glucose conjugate of II [2,6-dichloro-4-methylphenyl b-D-glucopyranoside] (VI) was also synthesized by modifying the procedure reported by Sinnott and Souchard 5) ; 2,3,4,6-tetra-O-acetyl-a-D-glucopyranosyl bromide (Kanto Kagaku, 411 mg) dissolved in 4 ml of acetone was mixed with 5 ml of a 1 M NaOH solution of II (177 mg) and stirred overnight at room temperature. The combined chloroform extracts from the reaction mixture were washed with 1 M NaOH followed by water and then filtered through silicone-treated filter paper with anhydrous MgSO 4 . The crude glucoside obtained by concentration of the filtrate was dissolved in hot ethanol at 60°C and successively purified by re-crystallization at room temperature to yield 2,6-dichloro-4-methylphenyl b-glucopyranoside tetraacetate (33.5 mg). Cleavage of the protective groups was conducted by treating 5 mg of the crude product in 0.5 ml of methanol with 6.5 ml of 28% sodium methoxide at 50°C for 10 min. The reaction mixture was neutralized and then purified by the HPLC method: 0.01% trifluoroacetic acid (Solvent A) and acetoni- Metabolism of Tolclofos-methyl in Lettuce (Lactuca sativa)Keiko ICHISE-SHIBUYA,* Takuo FUJISAWA, Toshiyuki KATAGI and Yoshiyuki TAKIMOTO Environmental Health Science Laboratory, Sumitomo Chemical Co., Ltd., 2-1, Takatsukasa 4-chome, Takarazuka, Hyogo 665-8555...
Phenol and its derivatives are common constituents of numerous natural and synthetic chemicals including pesticides. As a consequence of anthropological activities, a portion of them may reach various water bodies as contaminants which will have a great impact on the aquatic environment including biota. Aquatic plants are known to be one of the major habitants and food for many species and hence the distribution and metabolism of chemicals in aquatic plants is very important in order to understand their effects on the aquatic ecosystem. Duckweed is a representative species of aquatic plant, which is widely distributed in freshwater systems. Although the fate of phenol and its derivatives within duckweed has been extensively investigated, [1][2][3][4][5][6][7] there are few mechanistic studies on the uptake and degradation behavior in relation to their physico-chemical properties. Recently, Tront et al. 8) and Reinhold et al. 9) studied the uptake of various halogenated phenols into Lemna minor and suggested that the extensive metabolic transformation of phenols via phase II reaction has an important role in increasing their uptake by shifting a steady state equilibrium reached between the contaminants in cytosol and medium to a transient state. Tront et al. 8) explained that the fraction in the protonated form of chemicals at a cytosolic pH which was calculated from the corresponding pKa values had a meaningful correlation with the metabolic transformation rate. In their theory, contaminants that were ionized in the cytosol would exhibit limited partitioning into internal membranes, thereby suppressing the substrate accesses to relevant enzymes. On the other hand, Reinhold et al. 9) reported that the chemical status of phenols within the substrate-enzyme complex is very important when evaluating their transformation rates such as deprotonation of the hydroxy group at the reaction site expressed by their pKa values and Hammett's constant (s). However, they could not show any direct evidence of a relationship between the uptake and transformation of chemicals because the latter was not actually measured in their studies.The objective of the present experiment was to examine the uptake and metabolism of phenol and its derivatives by duckweed (Lemna gibba) and to investigate the relationship between the uptake/metabolism behavior of the phenols and various chemical indexes. We also identified some of the phase II metabolites of phenol derivatives produced in duckweed. (Received May 12, 2010; Accepted July 19, 2010) Uptake and transformation of phenol and its five derivatives each labeled with 14 C were examined in duckweed (Lemna gibba). A kinetic analysis on uptake and metabolic transformation was conducted using the assumed compartments. Positive correlation was observed between log P and the logarithm value of relative uptake rate constant with respect to phenol, and an even higher correlation was obtained against the physico-chemical index, EffTox, where the undissociated fraction of phenol was inco...
The metabolic fate of diethofencarb (isopropyl 3,4-diethoxycarbanilate) separately labeled with (14)C at the phenyl ring and 2-position of the isopropyl moiety was studied in grape (Vitis vinifera L.). The acetonitrile solution of (14)C-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 (1)H NMR and atmospheric pressure chemical ionization-liquid chromatography-mass spectrometry together with cochromatographies with synthetic standards.
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