摘要:

AbstractHerbicides inhibiting branched‐chain amino acid biosynthesis represent a signal advance in crop protection chemistry, with implications for both practical weed control and basic agricultural science. In practical terms, at least 20 different active ingredients are currently marketed or are in development, and more may be expected. They offer selectivity in virtually every major crop, unprecedented low use rates, and inherently selective toxicity to plants. In scientific terms, the research behind these compounds shows modern agricultural chemistry at its best. Synthesis has been integrated with other disciplines to understand and rapidly optimize properties. In the process, basic knowledge has been gained in chemistry, biochemistry, and strategies for finding new agrochemicals.This issue provides the first unified, interdisciplinary overview of the three major classes of inhibitors–sulfonylureas, imidazolinones, and triazolopyrimidines. The following introductory note explores some implications of this resea

ISSN:0031-613X    

DOI:10.1002/ps.2780290302

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe discovery of the sulfonylurea class of herbicides is one of the most dramatic breakthroughs in herbicide research in several decades. Sulfonylureas possess unprecedented levels of herbicidal activity–as low as 1 g ha−1–very low mammalian toxicity, and very desirable environmental properties. This review will discuss the structure‐activity relationships of sulfonylureas, their physical and chemical properties, and their methods of sy

ISSN:0031-613X    

DOI:10.1002/ps.2780290303

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe sulfonylurea herbicides are characterized by broad‐spectrum weed control at very low use rates (c. 2–75 g ha−1), good crop selectivity, and very low acute and chronic animal toxicity. This class of herbicides acts through inhibition of acetolactate synthase (EC 4.1.3.18; also known as acetohydroxyacid synthase), thereby blocking the biosynthesis of the branched‐chain amino acids valine, leucine and isoleucine. This inhibition leads to the rapid cessation of plant cell division and growth. Crop‐selective sulfonylurea herbicides have been commercialized for use in wheat, barley, rice, corn, soybeans and oilseed rape, with additional crop‐selective compounds in cotton, potatoes, and sugarbeet having been noted. Crop selectivity results from rapid metabolic inactivation of the herbicide in the tolerant crop. Under growth‐room conditions, metabolic half‐lives in tolerant crop plants range from 1–5 h, while sensitive plant species metabolize these herbicides much more slowly, with half‐lives>20 h. Pathways by which sulfonylurea herbicides are inactivated among these plants include aryl and aliphatic hydroxylation followed by glucose conjugation, sulfonylurea bridge hydrolysis and sulfonamide bond cleavage, oxidative O‐demethylation and direct conjugation with (homo)glutathione. Sulfonylurea herbicides degrade in soil through a combination of bridge hydrolysis and microbial degradation. Hydrolysis is significantly faster under acidic (pH 5) than alkaline (pH 8) conditions, allowing the use of soil pH as a predictor of soil residual activity. Chemical and microbial processes combine to give typical field dissipation half‐lives of 1–6 weeks, depending on the soil type, location and compound. Very short residual sulfonylurea herbicides with enhanced susceptibility to hydrolysis (DPX‐L5300) and microbial degradation (thifensulfuron

ISSN:0031-613X    

DOI:10.1002/ps.2780290304

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractSeveral new structurally diverse classes of herbicide, including the sulfonylurea herbicides, act by inhibiting acetolactate synthase, the first common enzyme of branched‐chain amino acid biosynthesis. The interaction of acetolactate synthase isozyme II (ALSII) from Salmonella typhimurium with sulfometuron methyl (SM), a sulfonylurea herbicide, has been used as a paradigm in elucidating the mode of action of these herbicides at the molecular level. A number of different studies have collectively suggested that SM binds to ALSII near thiamine pyrophosphate and flavin adenine dinucleotide (FAD), with its binding site overlapping the second pyruvate (or ketobutyrate) substrate site. Most of SM, however, must be accommodated on ALSII at a site that is not equivalent to substrate or co‐factor binding sites. The identity of this herbicide‐specific site has recently been suggested by the discovery that poxB, the gene for pyruvate oxidase, shares substantial sequence homology with ilvB, ilvG and ilvI, the genes for the large subunits of ALSI, ALSII, and ALSIII, respectively. Unlike ALSII, pyruvate oxidase uses its FAD for normal redox chemistry, and binds one additional co‐factor in vivo, ubiquinone‐40. The latter co‐factor binds to pyruvate oxidase in a spatially and kinetically equivalent way to SM with ALSII, suggesting that the herbicide binding site of ALSII has a common evolutionary heritage with the ubiquinone site of pyruv

ISSN:0031-613X    

DOI:10.1002/ps.2780290305

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe imidazolinone herbicides were prepared from reaction of an α‐ methylvaline fragment with an o‐dicarboxylic acid. Early syntheses were completed through an imide amide intermediate, such asIorXV, followed by further cyclization to 2,5‐dionesIIIorXXI. Reaction of these diones with nucleophiles led to imidazolinonesIVandV. The significant and interesting activity of these compounds led to new and versatile methods of synthesis, including resolution of the α‐methylvaline fragments, development of a metallation‐carboxylation route, a one‐step picoline to imidazolinone route, and several pyridine and fused‐ring pyr

ISSN:0031-613X    

DOI:10.1002/ps.2780290306

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe structure of the imidazolinone herbicides consists of three distinct moieties: the imidazolinone ring, the carboxylic acid and the backbone. The effect of changes in each of these on herbicidal activity, crop selectivity and AHAS enzyme inhibition has been studied. Though both whole‐plant and enzyme activity were drastically affected by changes in the carboxylic acid or imidazolinone ring portions of the molecule, a variety of backbones and of substituents on the backbones afforded good activity. Methyl‐isopropyl was found to be the best combination of substituents on the imidazolinone ring. While pyridine backbones generally gave the most active herbicides, benzene backbones led to the strongest enzyme inhibition. A QSAR study in the pyridine series generated two equations which proved useful for guiding the analog program toward the synthesis of potent heteropyridyl compounds. Selectivity in wheat is dependent upon differences in the rate of metabolism of key groups. Rapid metabolism of either the imidazolinone ring or backbone alkyl groups occurs rapidly in soybeans compared with susceptible we

ISSN:0031-613X    

DOI:10.1002/ps.2780290307

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractImidazolinone herbicides inhibit the first enzyme of branched‐chain amino acid biosynthesis, acetohydroxyacid synthase. The inhibition of the enzymein vitroby these herbicides increases with incubation time, but is not irreversible, as deduced by reaction progress curves. In contrast to this result is the apparent irreversible inhibition of the enzyme by these imidazolinones that occurs when the herbicide is applied to intact corn plants. Plants treated with imidazolinone herbicide and then extracted showed dramatically reduced enzyme activity. This effect on extractable enzyme level occurred with several different imidazolinone herbicides in either foliar or soil application. The decrease in extractable enzyme activity could be observed within four hours after treatment. Herbicides other than imidazolinones did not reduce the extractable enzyme level. These findings suggest that the enzyme‐ imidazolinone interactionin vivomay be different from the interaction observed in vi

ISSN:0031-613X    

DOI:10.1002/ps.2780290308

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractTwo new structural classes of herbicide have been discovered which are based on the 1,2,4‐triazolo[1,5‐a]pyrimidine ring system. These compounds are related to the known herbicidal sulfonylureas and imidazolinones and other studies have shown that they have a similar mode of action, involving the inhibition of branched‐chain amino acid biosynthesis, the site of action being the enzyme acetolactate synthase. The design, synthesis and structure‐ activity relationships of these new classes of compounds are de

ISSN:0031-613X    

DOI:10.1002/ps.2780290309

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe substituted 1,2,4‐triazolo[1,5‐a]pyrimidines are a new class of highly active herbicides. Protection of Arabidopsis thaliana seedlings from triazolopyrimidine‐induced injury by the branched‐chain amino acids was observed. Acetolactate synthase (EC 4.1.3.18) was isolated and found to be quite sensitive to inhibition. I50values for inhibition of the enzyme from a number of plant sources show little variation and no correlation to whole‐plant response, suggesting uptake, translocation and metabolism play key roles in modulating herbicidal activity. Further studies indicate that these chemicals are slow, tight‐binding inhibitors that are readily dissociated by gel filtration. Some correlations between in‐vitro activity and in‐vivo activity were observed for ortho‐substituted analogs on selected

ISSN:0031-613X    

DOI:10.1002/ps.2780290310

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractIn order to identify the factors providing the triazolopyrimidines with a wide range of selectivity amongst agriculturally important plant species, studies were made on the uptake and metabolism of a representative compound, N‐(2,6‐dichlorophenyl)‐5,7‐dimethyl‐1,2,4‐triazolo[1,5‐a]pyrimidine‐ 2‐sulfonamide. This compound is much more phytotoxic to dicots than to monocots. Experiments showed that variations in leaf morphologies and geometries relative to spray applications resulted in different herbicide dosages applied to plant species used in selectivity evaluations. However, this parameter did not have a statistically significant correlation to herbicide selectivity measurements. Characterization of the metabolic pathways showed that the major herbicide metabolites involved methyl hydroxylation or hydroxylation of the aniline ring followed by glucose conjugation. Since these metabolites were not exclusive to either monocots or dicots, herbicide selectivity does not appear dependent on the pathway of metabolism. Studies on the kinetics of metabolism suggest instead that metabolic rate was important. Monocots metabolized the herbicide rapidly and generally were tolerant while the opposite w

ISSN:0031-613X    

DOI:10.1002/ps.2780290311

出版商:John Wiley&Sons, Ltd    

年代:1990

数据来源: WILEY