Aryloxyphenoxypropionates

Cummins I, Edwards R (2004) Purification and cloning of an esterase from the weed black-grass (Alopecurus myosuroides), which bioactivates aryloxyphenoxypropionate herbicides. Plant J 39 894-904... 

Graphitized carbon black (GCB) materials are frequently used for off-line SPE as well. GCB behaves as a nonspecific sorbent, but because positively-charged adsorption sites are present, it also acts as an anion exchanger, which is useful for the enrichment of acidic compounds [75]. Examples involve the enrichment of chlorinated phenoxy acids [42], aryloxyphenoxypropionic herbicides [45], sulfonylurea herbicides [50], and imidazolinone herbicides [65]. 

A. Lagana, G. Fago A. Marino, M. Mosso, Soil column extraction followed by LC ESI-MS for the efficient determination of aryloxyphenoxypropionic herbicides in soil samples atng/g levels. Anal. Chim. Acta, 375 (1998) 107. 

Aryloxyphenoxypropionates have selective activity against different grass species [5]. This class of substance inhibits fatty acid biosynthesis. The first example of this type of compound was Didofop-methyl, which is structurally derived... 

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].

It appears that resistance to the aryloxyphenoxypropionate herbicides, the cyclohexanedione herbicides and to the sulfonylurea herbicides is unlikely to be due to reductions in the sensitivity or increases in the amounts of their respective target enzymes (Figures 2 3). Studies have not yet been performed to examine if die resistance to the dinitroaniline herbicide trifluralin is associated with any change at the tubulin polymerization site. 

Any major differences in the sensitivity of the enzymic target sites of the aryloxyphenoxypropionate, cyclohexanedione or sulfonylurea herbicides. 

In eukaryotes and prokaryotes, ACCase is a key enzyme in fatty acid biosynthesis [1]. The reaction product, malonyl-CoA, is both an intermediate in the de novo synthesis of primary fatty acids and also a substrate in the formation of long-chain fatty acids and flavonoids in plants [2, 3]. Aryloxyphenoxypropionates (APPs) and cyclohexandiones (CHDs) are two chemical classes of molecules that selectively inhibit homomeric, chloroplastic ACCase from grasses [4, 5], which makes them post emergent herbicides used worldwide to control grassy weeds. 

Soil column extraction (SCE) SCE consists on a specific solvent percolation to a column packed with the sampled material (soil, sediment) containing herbicides. About 100mmoll potassium phosphate buffer adjusted to pH 8 at ambient temperature readily extracts imidazolinones, diphenyl ethers, sulfonyl ureas, aryloxyphenoxypropionic acids, and triazolopyrimidines from soil samples. The same SCE procedure was applied to 0.2-0.4% carbon-containing sediments for isolation of sulfonamides and triazines with recoveries ranging from 63% to 99%. Further cleanup (e.g., on Carbograph cartridges) or concentration (SPME) may sometimes be necessary. 

Imidazolinones, diphenyl ethers, sulfonylureas, aryloxyphenoxypropionic acids, triazolopyrimidines, sulfonanilides LC/MS/MS TISP ( + ) (MRM) ngmr level Environmental water... 

Six aryloxyphenoxypropionic acids (clodlnafop, fluazifop, haloxyfop, diclofop-methyl, fenoxaprop, quizalofop) were extracted from drinking water and spring water and separated on a C g column (A = 240nm) with a complex 25-min 42/58 -> 12/88 water (0.1% TFA)/(70/30/0.025 methanol/acetonitrile/TFA)... 

Alban, C., Baldet, P. and Douce, R. (1994) Localization and characterization of two structurally different forms of acetyl-CoA carboxylase in young pea leaves, of which one is sensitive to aryloxyphenoxypropionate herbicides, Biochem. J. 300, 557-565. 

LaganA, A., Fago, G., and Marino, A., Determination of aryloxyphenoxypropionic acid herbicides in water using different solid-phase extraction procedures and liquid chromatography-diode array detection, /. Chromatogr. A, 796, 309,1998. 

GSTs in plants were first studied because of their ability to detoxify herbicides (30, 16). GST-based metabolism imparts herbicide tolerance in several plant species especially to the sulfonylureas, aryloxyphenoxypropionates, triazinone sulfoxides, and thiocarbamates herbicide families that are susceptible to GSH conjugation (16,31-35). There is a positive correlation of both GSH levels and the activity of specific GST enzymes wifti the rate of herbicide conjugation and detoxification (36-39). 

The best characterized extraneous site ir bitors are the many chemical classes of herbicidal inhibitors of acetolactate synthase. These have been extensively reviewed elsewhere (i, 8,9,52,56,81,92). Extraneous site inhibitors are also exemplified by four classes of grass selective herbicides the aryloxyphenoxypropionic acids represented by diclofop, the cyclohexanediones typified by clethc m (for a recent review see (57)), the triazinediones (82) and the perhydroindolizinediones (83) (Figure 7). The following discussion is limited to the first two classes. Both classes of herbicides are potent, reversible inhibitors of acetyl-CoA carboxylase (ACC) from susceptible plants, the putative rate limiting enzyme in lipid biosynthesis. With wheat... 

The next enzyme in the fatty acid biosynthesis pathway is the acetyl-CoA carboxylase. The acetyl-CoA carboxylase from grasses (Poaceae) can specifically be blocked by herbicides (see Fig. 3) of the cyclohexane-1,3-dione (sethoxydim, cycloxydim, clethodim) and aryloxyphenoxypropionic acid-type (diclofop, fenoxaprop, haloxyfop, fluazifop) which was shown by us only recently (Focke and Lichtenthaler 1987, Kobek et al. 1988). 

Fig. 3 Chemical structure of cyclohexane-1,3-diones (left side) and aryloxyphenoxypropionic acid-type herbicides (right side).

The cyclohexane-1,3-dione and aryloxyphenoxypropionic acid-type herbicides are used as selective grass herbicides in several economical important crop cultures. They are known to block de novo fatty acid synthesis in the chloroplasts of sensitive grasses (Poaceae). These herbicides have been suggested to be inhibitors of an enzyme of the fatty acid synthetase complex, because they block the incorporation of labelled malonic acid into the fatty acid fraction. The aim of this work was to identify the single target enzyme of this herbicides. 

FIuazifop (2-[4-(5-trifluoromethyl-2-pyr1dyloxy)phenoxy]propionate) is a grass-specific herbicide. It is an aryloxyphenoxypropionate compound and these herbicides have been shown to kill sensitive species by causing necrosis of meristematic tissues. A number of studies on the mode of action of the aryloxyphenoxypropionates have only been able to demonstrate an inhibition of lipid metabolism. No detectable effects on CO2 fixation or carbohydrate, amino acid or nucleic acid metabolism have been shown ( Walker 1988a,). Cyclohexanedione herbicides, such as sethoxydim,... 

Burton JD, Gronwald JW, Somers DA, Connelly JA, Gengenbach BG, Wyse DL. Inhibition of plant acetyl-coenzyme A carboxylase by the herbicides Sethoxydim and Haloxyfop. Biochem Biophys Res Comm 1987 148 1039-1044. Parker WB, Marshall LC, Burton JD et al. Dominant mutations causing alterations in acetyl-coenzyme A carboxylase confer tolerance to cyclohexanedione and aryloxyphenoxypropionate herbicides in maize. Proc Natl Acad Sci USA 1990 87 7175-7179. 

The aryloxyphenoxypropionates and cylcohexanediones are two important classes of grass-selective herbicides which have been developed... 

Figure 3.8. Structures of some aryloxyphenoxypropionates and cyclohexanediones that have been shown to inhibit acetyl-CoA carboxylase in sensitive species.

Early work on aryloxyphenoxypropionates failed to show any metabolic effects except those on acyl lipid synthesis. The general inhibition of labeling of all acyl lipid classes but not that of sterols or terpenoids led to the idea that de novo fatty acid synthesis was being reduced. In fact, there is little effect on fatty acid elongation (e.g.. Table 3.13). Of the two enzyme systems involved in de novo synthesis, it has now been established that the aryloxyphenoxypropionates and cyclohexanediones only affect acetyl-CoA carboxylase. Moreover, this carboxylase from dicotyledons (resistant) appears to be different from that in monocotyledons (sensitive) because the selectivity of herbicides (including stereospecificity) is retained during in vitro measurements (Table 3.14). 

Comparisons of relative activities of aryloxyphenoxypropionates on acetyl-CoA carboxylase measured in vitro with results from whole-plant... 

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