Sulfonylurea selectivity

M. Rodriguez and D.B. Orescan, Confirmation and quantitation of selected sulfonylurea, imida-zolinone, and sulfonamide herbicides in surface water using electrospray LC/MS, Anal. Chem., 70, 2710-2717 (1998). 

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. 

Differential herbicide sensitivity at the site of action is a second possible selectivity mechanism, with good precedence in the aryloxyphenoxy and cyclo-hexanedione grass herbicides (2Q, 51). However, several studies now clearly indicate that the inherent sulfonylurea crop selectivities listed in Table 1 are not based on differential sensitivity at the site of action. ALS preparations isolated fix>m crops and weeds are equally sensitive to several selective sulfonylurea herbicides (28.32.33). Although data have not appeared for all of the compounds shown in Table 1, we conclude that differential active site sensitivity is not a general sulfonylurea selectivity mechanism. The clear exceptions to this generalization are the cases of genetically-altered plants (crops and we s) which have acquired through mutation or deliberate transformation a resistant form of the ALS enzyme (see below). 

Table IV. Ionization and Hydrolysis of Selected Sulfonylurea 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. 

A single multiresidue method was developed to determine 109 priority compoimds listed in the 76/464/EEC Coimcil Directive on Pollution of the EU [49]. For trapping analytes, automated off-line SPE with a polymeric sorbent "Oasis" 60 mg cartridge, was optimized. A multianalyte method for the confirmation and quantitation of 16 selected sulfonylurea, imidazolinone, and sulfonamide herbicides in surface water has been proposed [50]. This method is based on analyte extraction with a polymeric material (RP-102) and extract cleanup with a strong anion exchanger (SAX) cartridge stacked on... 

Relative potency alone does not determine dmg selection because maximal effectiveness is similar for all agents. A single daily dose of any sulfonylurea, except tolbutamide, is sometimes adequate to control blood glucose in NIDDM patients. 

A triple-quadrupole mass spectrometer with an electrospray interface is recommended for achieving the best sensitivity and selectivity in the quantitative determination of sulfonylurea herbicides. Ion trap mass spectrometers may also be used, but reduced sensitivity may be observed, in addition to more severe matrix suppression due to the increased need for sample concentration or to the space charge effect. Also, we have observed that two parent to daughter transitions cannot be obtained for some of the sulfonylurea compounds when ion traps are used in the MS/MS mode. Most electrospray LC/MS and LC/MS/MS analyses of sulfonylureas have been done in the positive ion mode with acidic HPLC mobile phases. The formation of (M - - H)+ ions in solution and in the gas phase under these conditions is favorable, and fragmentation or formation of undesirable adducts can easily be minimized. Owing to the acid-base nature of these molecules, negative ionization can also be used, with the formation of (M - H) ions at mobile phase pH values of approximately 5-7, but the sensitivity is often reduced as compared with the positive ion mode. 

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. 

Sulfonylurea . Sulfonylurea herbicides are a relatively new class of herbicides generally used for selective pre- and post-emergence control of broad leaved weeds in croplands. Sulfomcturon—methyl is used for broad-spec (ruin selective or nonsclcciive weed control in noncroplands. 

In a retrospective case-control study, a primary diagnosis of hypoglycemia was identified in 413 patients registered as diabetic in 1993 (164). Five controls of the same age and sex, without hypoglycemia, were selected for each case from the same cohort. The relative risks of hypoglycemia with ACE inhibitors, beta-blockers, calcium antagonists, and salicylates were determined. There was an association between enalapril and sulfonylureas. However, other ACE inhibitors could not be identified as a risk factor. There was no interaction with beta-blockers, calcium channel blockers, or salicylates. 

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. 

Brown, H.M. (1990). Mode of action, crop selectivity and soil relations of the sulfonylurea herbicides. Pesticide Sci., 29 263-281. Brown, H.M., F.T. Lichtner, J.M. Hutchison, and J.A. Saladine (1995). The impact of sulfonylurea herbicides in cereal crops. Brighton Crop Prot. Conf.-Weeds,3 1143-1152. 

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