Triazinone herbicides

Engelhard G, W Ziegler, PR Wallnofer, HJ Jarcszyk, L Oehhnann (1982) Degradation of the triazinone herbicide metamitron by Arthrobacter sp. DSM 20389. J Agric Food Chem 30 278-282. 

Fedtke, C. (1983). Leaf peroxisomes deaminate as-triazinone herbicides Method of detoxification by tolerant plants. Naturwissenschaften, 70 199-200. 

Fedtke, C. (1986a). Selective metabolism of triazinone herbicides. Pest. Sci., 17 65-66. 

Several processes may play a role in the environmental dissipation of -triazine herbicides. Dissipation processes can include microbial or chemical degradation in soil metabolism or conjugation in plants photodegradation in air, water, and on soil and plant surfaces and volatilization and transport mechanisms. This chapter will address photolytic degradation and abiotic hydrolysis of the currently used triazine herbicides, the triazinone herbicides (metribuzin and metamitron), and the triazinedione herbicide hexazinone. 

It is not enough for a multiple parameter equation just to work and to give an improved correlation as Higuchi and Davis have emphasized recently (64). The correlation must have a physicochemical significance. Recently, Equation 31 has been presented by Biichel and his co-workers for the inhibition of the Hill reaction with 1,2,4-triazinone herbicides (65). 

Triazinone herbicide Metribuzin and its major conversion products, deaminometribuzin, diketometribuzin,... 

Metribuzin is a member of the substituted as-triazinone group of herbicides. Activity is due to interference with photosystem II electron transport in plant chloroplasts (Dodge, 1983). The metabolism of metribuzin in plants has been the subject of many short-term and long-term studies dating back to the early 1970s. 

Weed resistance to the triazine herbicides was first identified in the late 1960s, with a biotype of common groundsel that was resistant to simazine (Ryan, 1970). Since then, resistance to triazine herbicides has been reported in many weed species (Holt and LeBaron, 1990 LeBaron and McFarland, 1990 Gronwald, 1994). Most cases of triazine resistance have been reported in the US, Canada, and Europe, where triazine herbicides have been used extensively in corn monocultures (LeBaron and McFarland, 1990 Stephenson et al., 1990 LeBaron, 1991). Most of the. v-triazinc-resistant weed species have been selected against atrazine and usually show a high level of cross-resistance to other. v-triazine herbicides. In most cases, these weeds also show a low level of resistance to as-triazinones (e.g., metribuzin). Triazine-resistant weeds are often less vigorous than nonresistant weeds, which facilitates their management. 

Target site cross-resistance, in which a change at the site of action of one herbicide also confers resistance to herbicides from a different class (e.g., selection by triazine-resistant D1 protein that is also less sensitive to triazinones). 

Carfentrazone is an aryl triazinone broadleaf herbicide used at a low rate of 0.1kg a.i./ha/season as a directed postemergence application. Sugarcane is subject to injury, which may limit product use. 

Sulfentrazone is an aryl triazinone broadleaf and sedge herbicide that can be applied preemergence, and/or post-directed up to layby. The maximum total annual rate cannot exceed 0.42kg a.i./ha. 

Herbicides that seem to have a single site of action on the photochemical pathway, which is associated closely with photosystem 11 are the chlorinated pheny 1 ureas, Ws-carbamates such as phenmedipham, chlorinated s-triazines, substituted uracils, pyridazinones, diphenylethers, 1,2,4-triazinones, azido-s-triazines, cyclopropane-carboxamides, p-alkylanilides, p-alkyl-thioanilides, aminotriazinones, and urea-carbamates (2). 

These esters can be used as fragrances with harmonious fruit odor or as intermediates for the syntheses of herbicides (e.g. triazinones) and of L-amino acids. Also in this reaction, the weakly acidic boron pentasil zeolite and even better the Cs-doped boron pentasil zeolite are the most favored catalysts and are superior to other heterogeneous catalyst systems (Fig. 15.2). 

A new synthesis of 2-aryl-1,2,4-triazin-3-ones and 2-aryl-l,2,4-triazepin-3-ones from convenient starting materials has been demonstrated. Of these compounds, the triazin-3-ones were found to have herbicidal properties and with appropriate aromatic substituents, weed control can be obtained at low application rates. However, the weed control/crop tolerance ratio may limit the commercial application of the more active triazinones. 

In the research laboratories of the Bayer AG the attention of Westphal and his coworkers was turned to this new group of compounds. Owing to their similarity to nucleic acids a series of 1,2,4-triazinone compounds were synthesised and tested for biological activity. This led to the recognition of the herbicidal activity of the group (Westphal et al.. 1966). 

Herbicides containing the asymmetric 1,2,4-triazinone ring were developed in the research laboratories of the Bayer AG (Schmidt et al., 1975a Schmidt et al., 1975b). 

By analogy with the rearrangement of styrene oxide compounds, more complicated substances, e. g. phenylpyruvic acid methyl ester derivatives, can be synthesized from readily available glycidic acid esters, as shown in Figure 3. These esters can be used as intermediates for herbicides (e. g. the triazinones) and for the synthesis of L-amino acids. 

As already stressed, the mutation Set264 Gly is one which has been observed in nature. It is found by now in all countries and in a variety of weeds which are rendered resistant t ainst triazines and triazinones (see Table 1). It should be noted, that atrazine-resistant rape with a modified Dl protein (Ser264 Gly) is used as a crop in Canada. Resistance against ureas is comparably small and against phenolic herbicides like i-dinoseb, ioxynil and DNOC negative cross resistance is observed. 

Changes in binding affinities for herbicides in the Leu275 Phe mutant are marginal. It should only be stressed that triazinones are rendered resistant in this mutant and supersensitivity is observed against the phenolic herbicide ioxynil. 

A large number of commercial herbicides such as arylureas, triazines, triazinones and phenolic compounds act as competitors to plastoquinones (Fig. 1). They occupy the Qp-binding site of the D1 protein, thereby displacing from its binding niche and prevent the oxidation of reduced Q/v. The displacement of electron mediator Qp from the D1 protein leads to interruption of the electron flow and, consequently, results in plant s death. 

Due to their difference in chemistry, all PSII-inhibiting herbicides demonstrate different binding properties. For example, urea/triazine type inhibitors were proposed to be oriented towards Set 264, triazinones towards Ala 251 and phenolic herbicides were oriented towards His 215 (Table 1). ... 

Approximately half of all commercial herbicides act by inhibiting photosynthesis by interacting with specific sites along the photosynthetic electron transport chain. A number of diverse chemicals including the ureas, amides, triazines, triazinones, uracils, pyridazinones, quinazolines, thiadiazoles, and certain phenols are thought to act specifically at a common inhibitory site at the reducing side of photosystem II (PS II) (U ). 

Mild trypsin treatment has been shown also to alter the affinity for a number of other chemical families of PS II directed herbicides in a manner similar to that of the -triazines. Trypsin-mediated decreases in inhibitory activity are found for uracil (19), urea, pyridazinone ( 9, 28) and triazinone (28) herbicides. In contrast, phenol-type"Terbicides increase in inhibitory activity following brief trypsin treatment (j, 28), although the trend was reversed over longer treatment perio 3 . 

The first are the electron-transport inhibitors such as ureas, symmetric triazines, triazinones, and certain phenylpyridazinones also included are phenol compounds, bentazon or some diphenylethers (for chemical names of herbicides or formulas see legend of Figure 2). All have been shown to affect the B/plasto-... 

Two families of inhibitors interfere with the plastoquinone or herbicide binding site on the D-1 polypeptide, i.e. on one of the reaction center subunits of PS II. The phenol and urea/triazinone family of PS II inhibitors are different in their functional inhibitory pattern (reviewed in [1]), although they both bind to the D-1 polypeptide and displace each other from the binding site (1). Both QSAR studies (2) and - more refined - quantum mechanical calculations... 

Many herbicides, lilce ureas and triazines of the serine family share a common substructure a sp carbon attached to a nitrogen with a free electron pair and a positive n-charge (2,18,28). Their QSARs show usually a dependence on electronic and lipophilicity parameters. Individual compounds, chemically different, displace each other from the membrane (14.29). This family looses inhibitory potency in tris-treated cbloroplast membranes (7,18). Cross resistance studies of chloroplasts in triazine/triazinone or DCHU tolerant plants and algae have indicated subfamilies (reviewed in 13,18). None of these mutants are tolerant to phenol-type inhibitors. 

Electrochemical reduction of 4-amino-3-methyl-6-phenyl-l,2,4-triazin-5(4//)-one, known as the herbicide metami-tron, in acidic media has been studied <1998JEC177>. The first step has been shown to be reduction of the 1,6-azomethine bond by means of transfer of two electrons to the protonated form of 1,2,4-triazinone, while the second step is reduction of the 2,3-azomethine bond. The 1,6-double bond is reduced at potentials approximately 0.5 V more positive than that of the 2,3-azomethine bond <1998JEC177>. It is interesting to note that in the chemical reaction of the same triazin-5(4//)-one with sodium borohydride the 2,3-G=N bond is reduced first <1996JHC2063>. 

With the goal of a com herbicide, research efforts continued in the field of triazinones, and N-alkyl derivatives, and various sulfur [62], oxygen [62], nitrogen [62-65] and carbon substituents [66] were filed for patent. In 1981 a compound with the internal code number BAY KRA 4145 was synthesized and taken into development after intensive field tests [67] (Scheme 10.3). 

The binding affinities for several triazine herbicides and one triazinone were determined for WT and T1... 

Triazines, amides, phenylureas, triazoles, triazinones, benzimidazoles, phenoxyalkanoic herbicides LC/MS and LC/MS/MS ESI (-) for acidic compounds APCI ( + ) 20-100 pgmr 2-6pgmr Environmental water... 

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). 

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