Soil metabolism of flupyrsulfuron in winter wheat crops

Abstract

The sulfonylurea herbicide flupyrsulfuron was applied post‐emergence in March at the rate of 10 g a.i. ha−1 on winter wheat crops. In the 0–8 cm surface soil layer of the crops grown on sandy loam and loam soils, the flupyrsulfuron half‐life was 64 and 40 days respectively. Flupyrsulfuron and its metabolites were not detected during both crops or 1 month after crop harvest in the 8–15 and 15–20 cm soil layers. Soil degradation of flupyrsulfuron successively generated the cyclization products 1‐(4,6‐dimethoxypyrimidine‐2‐yl)‐2,4‐diketo‐7‐trifluoromethyl‐1,2,3,4‐tetrahydropyrido[2,3‐d]pyrimidine 2 and N‐(4,6‐dimethoxypyrimidine‐2‐yl)‐N‐(3‐methoxycarbonyl‐6‐trifluoromethylpyridine‐2‐yl)‐amine 3, which were the main metabolites of flupyrsulfuron in soil. Hydrolysis of 3 successively generated N‐(4,6‐dimethoxypyrimidine‐2‐yl)‐N‐(3‐car‐ boxylic acid‐6‐trifluoromethylpyridine‐2‐yl)‐amine 4 and N‐(4‐methoxy‐6‐hydroxypyrimidine‐2‐yl)‐N‐(3‐carboxylic acid‐6‐trifluoromethylpyridine‐2‐yl)‐amine 5. Low and temporary concentrations of 2‐sulfonamido‐3‐carbomethoxy‐6‐trifluoromethyl‐pyridine 6 and 2‐amino‐4,6‐dimethoxypyrimidine 7 were observed. Bioassays with sugarbeet as test plants indicated that 2, 3, 4, 5, 6 and 7 had herbicide activities corresponding to 100%, 80%, 75%, 75%, 75% and 15% of that of flupyrsulfuron respectively. The metabolites thus extended the herbicidal protection given by flupyrsulfuron and explain the high herbicidal protection given by the low dose of flupyrsulfuron applied. One month after the harvest of the winter wheat, no more significant residue of flupyrsulfuron or of its metabolites was detected in soil.

The cyclization transformation of the sulfonylurea herbicide flupyrsulfuron in the soil of winter wheat crops

“…When flupyrsulfuron was applied post‐emergence in March at the rate of 10 g ha −1 on winter wheat crops, we observed that its degradation in soil generated, successively, the pyrido[2,3‐ d ]pyrimidine cyclization product 1‐(4,6‐dimethoxypyrimidin‐2‐yl)‐7‐trifluoromethyl‐1,2,3,4‐tetrahydropyrido[2,3‐ d ]pyrimidine‐2,4‐dione ( 2) and the condensation product methyl 2‐(4,6‐dimethoxypyrimidin‐2‐ylamino)‐6‐trifluoromethylnicotinamide ( 3 ) corresponding to the elimination of the sulfonylurea bridge of flupyrsulfuron (Fig 1). 2, 3 The compounds 2 and 3 were the main metabolites of flupyrsulfuron in soil. The maximum concentration of the pyrido[2,3‐ d ]pyrimidine 2 in soil occurred 1.5 months after the application of flupyrsulfuron, and thereafter decreased; the maximum concentration of the 3 occurred 2.5 months after the treatment.…”

“…Bioassays with sugar beet as test plant indicated that the pyrido[2,3‐ d ]pyrimidine metabolite 2 has a herbicidal activity equivalent to that of flupyrsulfuron 3. Product 3 also has herbicidal activity, but somewhat lower than that of flupyrsulfuron and compound 2 .…”

“…Alternatively, it has been postulated that the rearrangement of the sulfonylurea bridge could, after the elimination of SO 2 , generate the carbamoyl derivative 9 which would then cyclize into the pyrido[2,3‐ d ]pyrimidine 2b which has the dimethoxypyrimidine substituent at position 1(Fig 3). 2, 4 The isomer 2b has been postulated to be formed in soil and in water but, to our knowledge, no experimental evidence has been published on this 2–4. In fact, none of the IR, MS, 1 H or 13 C NMR spectra of compound 2 generated from flupyrsulfuron in a sterile water buffer at pH 9 or in soil provided evidence whether 2 was the isomer 2a or 2b 3.…”

“…2, 4 The isomer 2b has been postulated to be formed in soil and in water but, to our knowledge, no experimental evidence has been published on this 2–4. In fact, none of the IR, MS, 1 H or 13 C NMR spectra of compound 2 generated from flupyrsulfuron in a sterile water buffer at pH 9 or in soil provided evidence whether 2 was the isomer 2a or 2b 3. Moreover, there is no mechanistic consideration from organic chemistry (the Smiles rearrangement, for instance) which could ascertain the formation of one isomer and not the other.…”

Evaluation of Synthesis of Methyl 3-Chloro-5-(4,6-dimethoxypyrimidin- 2-ylcarbamoylsulfamoyl)-1-methylpyrazole-4-carboxylate Using Green Metrics

“…For example, chlorsulfuron has been used in wheat and barley, but could stay vigorous in the soil for more than a few years and harm legumes and oilseeds [9]. Flupyrsulfuron methyl-sodium which was reported as a new 5-substituted sulfonylurea herbicide used to control grasses and broadleaf weeds in cereals [10] it has less than one month residual life [11]. Since then, several other 5-substituted sulfonylureas which show similar characteristics have been reported [12][13][14].…”