Selectivity imidazolinones

Sample preparation consists of homogenization, extraction, and cleanup steps. In the case of multiresidue pesticide analysis, different approaches can have substantially different sample preparation procedures but may employ the same determinative steps. For example, in the case of soil analysis, the imidazolinone herbicides require extraction of the soil in 0.5 M NaQH solution, whereas for the sulfonylurea herbicides, 0.5M NaOH solution would completely decompose the compounds. However, these two classes of compounds have the same determinative procedure. Some detection methods may permit fewer sample preparation steps, but in some cases the quality of the results or ruggedness of the method suffers when short cuts are attempted. For example, when MS is used, one pitfall is that one may automatically assume that all matrix effects are eliminated because of the specificity and selectivity of MS. 

The 1,3-dipolar cycloaddition of imidazolinone 123 with ethyl m-4,4,4-trifluorocrotonate 124 provided, after 36 h at reflux, the regio- and stereoisomer 125 (90%), accompanied with traces of three other unidentified cycloadducts (10%) <2001JFC275>. Compound 125 was isolated in 70% yield (Scheme 15). The structures of the final product were elucidated by nuclear Overhauser effect (NOE) experiments. This high selectivity is the result of a preferred ///////-orientation of both ester and CF3 groups in the transition state and of an impeded ////////-approach of the CFj-substituted terminus of the alkene to the sterically hindered ct-site of 123. 

The development of herbicide-resistant weeds has also been an influence on the selection of herbicides used on field corn or soybean. Weed resistance now affects nearly every decision a farmer makes about herbicide selection either a farmer is trying to control resistant weeds or is selecting herbicides that may reduce the possibility of weed populations becoming resistant. The adoption of the imidazolinone- and sulfonylurea-tolerant com hybrids mentioned above was in part a response to the presence of atrazine-tolerant pigweeds or kochia in many fields. However, a recent decrease in die use of imidazolinone and sulfonylurea herbicides can also be attributed to the development of populations of weeds that have become resistant to these 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... 

Baumgartner, J.R., K. Al-Khatib, and R.S. Currie (1999). Cross-reference of imazethapyr-resistant common sunflower (Helianthus annuus) to selected imidazolinone, sulfonylurea, and triazolopyrimidine herbicides. Weed Technol. 13 489 -93. 

Acetolactate synthase (ALS, EC 4.1.3.18) is the first common enzyme in the biosynthetic route to the branched chain amino acids, valine, leucine and isoleucine. It is the primary target site of action for at least three structurally distinct classes of herbicides, the imidazolinones (IM), sulfonylureas (SU), and triazolopyrimidines (TP) (Figure 1). SU and IM were discovered in greenhouse screening programs whereas TP was subsequently targeted as a herbicide. Numerous substitution patterns can be incorporated into the basic structure of all three classes of herbicides to provide crop selectivity as well as broad spectrum weed control. This is amply demonstrated in the seven products based on SU and four based on IM already in the market. A number of others are in various stages of development. The rapid success of ALS inhibitors as herbicidal products has attracted a world-wide research commitment. Not since the photosystem II... 

The use of dual-SPE approaches has also been described, e.g., extraction of A-methylcarbamates insecticides and their metabolites from urine by means of GCB and further clean-up using NHj-modified silica [18], or the use of RP-102 extraction cartridges with further clean-up of extracts on a strong anion-exchange column in the determination of selected sulfonylurea and imidazolinone herbicides [51]. 

SIM with three compound specific ions can be applied, as for instance demonstrated by Wang and Budde [101] for sixteen carbamate, urea and thioiuea pesticides and herbicides, by Rodriguez and Orescan [51] for selected sulfonylurea, imidazolinone, and sulfonamide herbicides, and by Yu et al. [17] for 52 carbamates, thiocaibamates, and phenylureas. In the latter case, computer-controlled optimization of the MS measurement conditions is performed. The most prominent ion, either a protonated or an ammoniated molecule, is used for quantitation. The dwell time for each ion in SIM was 0.02 s with an inter-charmel delay of 0.02 s, i.e., 2 s are needed for each data point in the chromatogram. Detection limits ranged from 0.09 to 19 pg/1 with 50-pl injections. 

M. Rodriguez, D.B. Orescan, Confirmation and quantitation of selected sulfonylurea, imidazolinone, and sulfonamide herbicides in surface water using LC-ESI-MS, Anal. Chem., 70 (1998) 2710. 

The synthesis and herbicidal activities of various imidazolinthiones, in particular the thiono isosteres of imazapyr, imazethapyr and imazamethabenz are discussed. In the synthesis area it is shown that the imidazolinthione ring functions as an ortho-directing group in aromatic lithiations. In the biological activity area it is shown that replacement of the imidazolinone carbonyl with a thio-carbonyl results in changes in weed toxicity and crop selectivity. 

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... 

This paper follows the evolution of the imidazolinone-resistant hybrid corn project at American Cyanamid. The initial considerations that provided the rationale for the project are discussed. The selection, regeneration, and characterization of the herbicide-resistant plants is described. Finally, options for commercializing the herbicide-hybrid package are discussed. 

The procedure by which imidazolinone-resistant corn was selected has been described previously, and will be reviewed only briefly here (7). The program was directed by Dr. Paul Anderson of Molecular Genetics Incorporated (MGI), under a contract with American Cyanamid. Scientists at MGI were among the first to regenerate corn routinely from tissue culture. 

The project to develop corn hybrids resistant to imidazolinone herbicides has been very successful. Corn with excellent resistance characteristics was selected, and semidominant resistance alleles are being introduced into proprietary inbred lines of Pioneer Hi-Bred International, Inc. Commercial corn hybrids resistant to imidazolinone herbicides will be the first major biotechnology product in cereals to enter the marketplace. 

Imidazolinone herbicides (especially imazethapyr) have been extracted from soils. Water alone gave low recoveries from soils and among the extractants tested. The mixture water/triethylamine (TEA) gave excellent extractability, even though matrix materials (mainly humic acids) were also extracted. However, to achieve good extraction along with high selectivity, the use of ammonium acetate buffer (pH 10) was recommended. 

Swanson, E.B., M.J. HergeseU, M. Arnaldo, D.W. Sipell, and R.S.C. Wong. 1989. Microspore mutagenesis and selection—canola plants with Held tolerance to the imidazolinones. Theoretical and Applied Genomics 78, 525-530. 

The imidazolinone herbicides (Table 2.3.1) are a family of six compounds that were discovered and developed by American Cyanamid Corporation. Readers may obtain comprehensive and detailed information in The Imidazolinone Herbicides [1], a book authored by the researchers who discovered and developed the herbicides. The herbicides as a class are broad spectrum and are active both pre-and postemergence. Imidazolinones are absorbed and moved through both xylem and phloem, eventually accumulating in the meristematic tissue. Activity is characterized by rapid cessation of growth followed by plant death days or weeks after treatment. Selectivity is based most often on metabolic inactivation except for selection-developed target site based resistance. 

These imidazolinone tolerance traits in different crops were developed by various methods. These methods included tissue culture selection (maize), pollen mutagenesis (maize), microspore selection (canola), seed mutagenesis (wheat and rice) and incorporation of resistance trait from a weedy relative (sunflower). Details of these methods have been previously reviewed [31, 32]. In all of these cases, the basis of tolerance is due to the presence of an altered form of AHAS that is resistant to inhibition by imidazolinones. The resistant enzyme is produced due to a single base pair change in the gene encoding the large subunit... 

Shaner, D. L., Bascomb, N. F., Smith, W. Imidazolinone-resistant crops Selection, characterization, and management. In Herbicide Resistant Crops, Duke, S. O. (Ed), Lewis Publishers, Boca Raton, FL, 1996. 

This section includes data for herbicide resistant crops generated by both selection and biotechnology processes. The first commercially available herbicide resistant crop in the United States was imidazolinone resistant corn introduced in 1992. This was followed by glyphosate resistant soybean and canola in 1996. 

Imidazolinones (e.g., imazethapyr and imazapyr), like sulfonylureas, inhibit ALS. CF com, commercialized in 1992, was developed by mutagenesis and selection of an imidazolinone insensitive ALS allele. Since its introduction in 1992, CF com has been used in approximately 4 to 7% of the total corn acres (Fig. 6.1.4). 

The static headspace injector has been selected and flic method developed for water soluble products using water as dissolution medium or using N,N-dimethylformamide for water-insoluble products. IfN,N dimethylacetamide and/or N,N-dimethylformamide are suspected in the drug under investigation 1,3-dimethyl 2-imidazolinone (DMI) is used as dissolving medium. 

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