Synthesis and herbicidal activity of sulfonanilides having a pyrimidinyl-containing group at the 2'-position

Abstract

The total acreage of rice in Japan in 2009 was 1.62 million ha and most of the paddy fields are mechanically transplanted, using young seedlings grown in nursery boxes.1) It is also noteworthy that most Japanese rice farmers apply so-called one-shot herbicides, which are now essential tools for weed control in paddy fields.2) This has been made possible by the wide variety of one-shot herbicides now available on the Japanese market. While sulfonylurea (SU) herbicides are most commonly used as the active principles in the formulation of one-shot herbicides, because SU herbicides control a wide range of paddy weeds including annual broadleaves and perennial Cyperaceae and about 90% of one-shot herbicides contain 3 to 4 active ingredients. 2)We have so far developed and commercialized our original pyrimidinyl carboxy (PC) herbicides, viz. bispyribac-sodium, pyrithiobac-sodium and pyriminobac-methyl.3-5) These herbicides exhibit their activities by specifically and strongly inhibiting ALS enzyme of plants, which is involved in the biosynthesis of branched-chain amino acids in plants, such as valine, leucine and isoleucine. 6) Because mammals lack ALS enzyme, these herbicides are inherently safe for mammals and, coupled with high activity with low use rates, these PC herbicides are extensively used worldwide as environmentally friendly herbicides.In the course of our researches on PC herbicides, we confirmed that in order for a compound to exhibit high ALS inhibitory activity and high herbicidal activity, the hydrophobic group, pyrimidine ring and acidic group need be placed in a suitable spatial position linked by a suitable spacer group via a suitable linkage group. 7) Based on the findings, we have conducted extensive studies to place various hydrophobic groups and acidic groups in an appropriate position on the pyrimidine ring.PC herbicides have a carboxyl group, but due to their relatively high water solubility as a result of their acidity, PC herSynthesis and herbicidal activity of sulfonanilides having a pyrimidinyl-containing group at the 2-position A novel series of sulfonanilides having a pyrimidinyl-containing group at the 2Ј-position was prepared and their herbicidal activities against paddy weeds and selectivity against rice plants were assessed. The structure-activity relationships were probed by substitution of the sulfonyl group, bridge and benzene ring. Among the sulfonamides, difluoromethyl compound showed comparatively high activity and a broad spectrum to control weeds, including Echinochloa oryzicola. The most preferable substitution position on the benzene ring was in the 6-position and the lower alkyl group showed high herbicidal activity and a broad weed control spectrum, and among the compounds tested, the methoxymethyl group was the best. In respect of the bridge moiety, the hydroxyl group was the best. Among the compounds examined, 2Ј-[(4,6-dimethoxypyrimidin-2-yl)(hydroxy)methyl]-1,1-difluoro-6Ј-(methoxymethyl)methanesulfonanilide, applied at rates between 4 to 16 g a.i./ha, showed excelle...

Properties of controlled-release formulation of pyrimisulfan as a one-shot herbicide in a paddy field

“…e mode of action of pyrimisulfan is presumed to be as ALS-inhibiting. 9,14) SU herbicides, which are ALS inhibitors and have already been used in paddy elds, are not su ciently e ective against Echinochloa spp. and SU-resistant weeds.…”

“…1, Table 1). Pyrimisulfan is e ective against a wide range of weeds, including grass weeds, 8,9) and has high selectivity between weeds and transplanted rice. To develop a one-shot herbicide containing only pyrimisulfan as an active ingredient, a controlled-release formulation of pyrimisulfan, optimized for paddy eld conditions, has been developed.…”

Latest generation of halogen‐containing pesticides

“…The sulfonanilide pyrimisulfan (Fig. ), contains a difluoro‐methylsulfonyl group, has broad spectrum, pre‐emergence herbicidal activity against the grass Exserohilum orzicola , sedge, and broadleaf weeds, with selectivity on transplanted and water‐seeded rice.…”

Current status of chirality in agrochemicals

“…Racemic pyrimisulfan (Fig. S5) has broad spectrum and pre‐emergence herbicidal activity against grass, sedge and broadleaf weeds, with selectivity on transplanted and water‐seeded rice, including late watergrass ( Exserohilum orzicola ) . The chirality hydroxyl‐substituted centre combines the aryl with the pyrimidyl moieties.…”