Herbicides sulfonylurea type

The last ten years have seen important developments in this respect in the three most important families of pesticides fungicides of the triazole group applied at about 100 g/ha, insecticides of the synthetic pyrethroid type at 20 g/ha and herbicides of the sulfonylurea type at 30 and even as little as 5 g/ha exert an effect which could be achieved with the pesticides of 15-20 years earlier only at rates of a few kilograms per hectare. These modern highly efficient preparations form only a small part of the selection of pesticides available today, but a rapid increase in their share of the total is to be expected as a result of purposeful research work. Another approach toward diminishing environmental contamination by chemicals is the development of new active substances which are less volatile, are degraded more rapidly or are more readily adsorbed by soil particles. 

Herbicides are used widely throughout the world to control weeds and exist in a wide variety of different types. Examples of classes of herbicide include the triazine, sulfonylurea, phenoxy, and quaternary ammonium herbicides. 

Although the ALS inhibitor herbicides have been used for approximately 20 years, the number of resistant weed biotypes for this group now exceeds those for all other types of herbicides. Singh and Shaner (1995) and Boutsalis (2001) reported that a total of five chemical families or herbicide classes are commercially marketed as inhibitors of ALS, and that these herbicides comprise more than 50 active ingredients for selective use in many different crops. They include sulfonylureas, imidazolinones, triazolopyrimidines, sulfonylamino-carbonyl-triazolinones, and pyrimidinyl (thio)benzoates. 

In Australia, two types of sulfonylurea resistance have been reported (Bumet et al, 1994). Rigid ryegrass exhibited cross-resistance to certain sulfonylurea and imidazolinone herbicides following selection for resistance to other... 

Scheme 4.45 Different types of fluorine-containing herbicide. From top to bottom carotenoid biosynthesis inhibitors, aryloxyphenoxypropionates, pyridyloxyacetic acids, sulfonylureas, trifluoromethane sulfonanilides, benzylamine derivatives [3 — 14].

Figure 4. Field tests of transformed tobacco. Wild type tobacco (WT) and tobacco transformed with the HRA gene (SUR) were sprayed at 4X the typical field application rate with a commercial sulfonylurea herbicide preparation.

Acetolactate synthase (ALS) is the target enzyme for three unrelated classes of herbicides, the sulfonylureas, the imidazolinones, and the triazolopyrimidines. We have cloned the genes which specify acetolactate synthase from a variety of wild type plants, as well as from plants which are resistant to these herbicides. The molecular basis of herbicide resistance in these plants has been deduced by comparing the nucleotide sequences of the cloned sensitive and resistant ALS genes. By further comparing these sequences to ALS sequences obtained from herbicide-resistant yeast mutants, two patterns have become clear. First, the ALS sequences that can be mutated to cause resistance are in domains that are conserved between plants, yeast and bacteria. Second, identical molecular substitutions in ALS can confer herbicide resistance in both yeast and plants. 

Genomic DNA libraries were prepared from two herbicide-resistant lines of tobacco, the C3 and Hra lines, and probed with the cloned tobacco ALS gene. The C3 line is 100-fold more resistant to the sulfonylurea herbicide chlorsulfuron than is wild type... 

Site-directed mutagenesis was used to make additional amino acid substitutions at these sites in yeast ALS. At some of the sites, e.g. alall7, prol92, or trp586, nearly any substitution for the wild type amino acid that was tested resulted in a herbicide-resistant enzyme (Table I). Each of the mutant enzymes was characterized by enzyme assays to compare its activity, and its sensitivity to the sulfonylurea herbicide chlorimuron ethyl, to the wild type enzyme. These analyses have indicated that some of the mutations have little adverse effect on the activity of the enzyme, while decreasing sensitivity to the herbicide from three to greater than one thousandfold. The characteristics of these mutant enzymes were further evaluated in vivo in order to investigate the utility of particular herbicide/mutant enzyme combinations (Falco et al., manuscript in preparation). 

In the second approach, herbicide-resistance mutations in the Arabidopsis ALS gene were studied in E. coli. To do this, wild type and mutant Arabidopsis genes were functionally expressed in E. coli, such that the plant genes complemented a branched chain amino acid auxotrophy in the bacteria (Smith et al. 1989, PNAS in press). ALS enzyme assays on extracts prepared from E. coli expressing the mutant Arabidopsis gene indicated that the mutant enzyme is resistant to sulfonylurea herbicides but is sensitive to the imidazolinone herbicide imazaquin. This selective... 

ESI, triazines) [537]. Recoveries observed were > 80% except for carbendazim, bu-tocarboxim, aldicarb and molinate, all better than 67% [500]. An aoTOF-MS interfaced by ESI was used to screen and identify unknown compounds and pesticides in water samples by MS and MS/MS. Structures for compounds observed besides pesticides were proposed [538]. Traces of the phenylurea pesticides Hnuron and monolinuron in water were determined quantitatively. Calibration graphs obtained after Supelclean ENVI-18 SEE were Hnear with detection limits < 25 pg [511]. Large numbers of phenylurea herbicide analyses led to the elaboration of on-line preconcentration techniques coupled to ESI-LC-MS. The procedure was demonstrated and validated with several pesticides using 10 ml of sample, resulting in detection Hmits of about 10 ng [539]. ESI-LC-MS and MS/MS were applied to quantify and to confirm 16 different herbicides of sulfonylurea [527] type in surface water samples. Surface water samples were extracted by SPE (Spe-ed RP-102). As confirmation criteria RT, molecular ion and two fragment ions besides ion abundance ratios were defined. Quantitation at 0.1 and 1.0 ppb level was demonstrated [540]. 

Pyrimidinylsalicylates is the class of ALS-inhibiting herbicides disclosed in the late 1990s by Kumiai Chemical Industry and Ihara Chemical Industry. Their biological activities are as potent as those of the sulfonylureas (SUs). Further research led to the pyrimidinylglycolates, which are experimental herbicides. Since both types have the carboxyl moiety in their chemical structure, they are called pyrimidinylcarboxylates (PCs) or pyrimidinyl carboxy (PC) herbicides. 

Numerous substituted p pmidine and tiiazine amines have found utility as precursors to highly active and crop selective sulfonylurea herbicides. In the process of optimizing herbicidal efficacy and crop safety within this class, a variety of structurally diverse heterocyclic amines have been synthesized and evaluated. This paper reviews the methods of preparation that have been developed for some of the different structural types used as intermediates to active sulfonylurea herbicides. These methods include cyclizations, rearrangements, and side-chain metalations that have led to furo[2,3-d]pyriiindines, pyrazinones, and selectively functionalized pyrimitoes, triazines, triazoles, and pyridines. 

All four herbicides belong to completely different chemical classes sethoxydim is a cyclohexanone, fluazif op-butyl a phenoxyphenoxy-type con und, imazaquin an imidazolinone, and chlorimuron-ett l a sulfonylurea. The mode of action of fluazifop-butyl and imazaquin is inhibition of acetyl-CoA carboxylase (ACC) (, 7 ) Obviously, this is reflected by the similarity of the response patterns. The way it corresponds is not a direct one we can say nothing ed>out fatty acid biosynthesis inhibition by looking at the response pattern. What we see is the influence on other meted>olites, which are in most cases only indirectly connected with fatty acid biosynthesis. But the patterns are strikingly similar. 

Three distinct classes of herbicidally active chemicals inhibit ALS sulfonylureas, imidazolinones, and triazolopyrimidine sulfonamides. " Recently, a fourth type, pyrimidinyl oxobenzoic acids, has been patented. ... 

ALS shows a high degree of primary sequence homology with pyruvate carboxylase and pyruvate oxidase the ubiquinone cofactors of pyruvate oxidase inhibit ALS, and it has been proposed that the ubiquinone-binding site of the ancestral enzyme also is the site of both SMM and imidazolinone binding. Recent evidence suggests, however, that these two types of herbicide interact differently with ALS (a) imidazolinones cause a rapid decrease in the levels of extractable ALS activity in maize, whereas SMM does not and can protect the ALS activity from this in vivo effect of imidazolinones and (b) not all imidazolinone-tolerant cell lines are insensitive to sulfonylureas. Sulfonylureas and imidazolinones do not, however, show synergistic inhibition of maize ALS in vitro. ... 

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