Herbicides compounds

One example of a naturally occurring diazirine, duazomycin A (137 Scheme 11.20), has been reported, isolated in 1985 from a Streptomyces species during a screen for herbicidal compounds [196], It was fotind to inhibit de novo starch synthesis and it was suggested that this is due to direct inhibition of protein synthesis. Duazomycin A is structurally related to 6-diazo-5-oxo-L-norleucine (138), also reported as a natural product from Streptomyces [197], which acts as a glutamine antagonist and inhibits purine biosynthesis [198],... 

Wellborn, T.L., Jr. Toxicity of nine therapeutic and herbicidal compounds to striped bass. Prog. Fish Cult, 31 27-32, 1969. 

The natural herbicidal compounds permitted in organic agriculture are not very active, so they must be applied in relatively large quantities. Ironically, this may lead to undesirable environmental effects. 

The identification of the metabolites of drugs in humans and animal species forms the basis of a separate chapter in this volume. However, some studies have been carried out on metabolism of model herbicide compounds in plants and these are reviewed briefly here. 

Takahashi, M., Kawamura, S., Miyakado, M., Sanemitsu, Y., Tanaka, S. (1993) Uptake and translocation of bleaching herbicidal compounds in radish seedlings. Pestic. Sci. 39, 159-177. 

Herbicides are chemicals used to destroy unwanted plants (terrestrial or aquatic) called weeds. Herbicides fall into two broad categories inorganic (e.g., copper sulfate, sodium chlorate, and sodium arsenite) and organic (e.g., chlorophenoxy compounds, dinitrophenols, bipyridyl compounds, carbamates, and amide herbicides). Historically, inorganic compounds were the first available and the first used. There has been over a long period a continuous effort to develop herbicide compounds that are more selective—that affect weeds, as opposed to desirable plants. 

The future of herbicides remains promising. New and better compounds with greater safety to crops, to man, and the environment will become available. If the increased food needs of the world are met, they will be met and man s labor burden eased, in part, by the use of suitable herbicidal compounds. 

An Example Synthesis of a Primary Amide/Ester Library as a Source of Herbicidal Compounds... 

Compounds 144 containing a 2,3-epoxy and 2,3-epithiocyclohexyl substituents were synthesized and claimed as herbicidal compounds <1992US5169426, 1985EP0172502>. Although they potentially possess multiple stereoisomers, which presumably display different potency, the stereochemical details were not provided. 

The EPA has set a maximum contaminant level for simazine at 4 parts per billion (ppb), because it is believed that exposure to this level of herbicidal compound has not induced health problems. 

The thermospray LC/MS with selected ion monitoring is applicable to multiresidue sulfonylurea herbicides. This method offers simultaneous extraction and analysis of three herbicide compounds in a fast and efficient way, in addition to good recovery. 

The herbicide compounds 2,4-D and 2,4,5-T, found to be 280 and 610 ppm in the feedstock, respectively, were also destroyed during the process to levels less than detectable, which were 0.01 ppm. 2,4,5/2,4,6-trichlorophenol and 2,4-dichlorophenol, found at 55 ppm and 10 ppm in the feedstock, were destroyed to levels less than detectable, which were 1 ppm. Chlorinated organic pesticides and PCBs were not detected in the feedstock hence, destruction could not be evaluated. Earlier AER tests conducted by Huber on the destruction of PCBs and carbon tetrachloride in soil for Toxic Substance Control Act (TOSCA) and Resource Conservation and Recovery Act (RCRA) permits have shown the process to be highly effective. 

Potassium cyanate (KOCN) is a herbicidal compound for the selective control of broad-leaved weeds in monocotyledonous crops, such as onion (Hedlin, 1948). It is readily soluble in water (65 g/100 ml at 10°C). Its usual rate of application is 6-14 kg/ha in the form of a 1-3% aqueous solution. Potassium cyanate is rapidly degraded in the soil. Its acute oral u>,o for rats is 850 mg/kg. 

In the subsequent years intensive research work was carried out for the further development of the herbicidal compounds of this group by various substitutions of the phenyl group. This work continues today. A few new derivatives with higher selectivity and safer application than earlier compounds have been developed. On the basis of the patent literature, the introduction of further new compounds is to be expected. It is noteworthy that mainly European firms have excelled in the further development of this type. 

The cause in some of the cases is of a physical character. Herbicidal compounds poorly soluble in water are located in the upper layer of the soil, and are thus absorbed by the shallow-rooted weeds, which are killed while they do not reach the roots of the deep-rooted crop plants, which can grow unhindered. Translocation proceeding at different rates in tolerant and sensitive plants and the detoxication of the translocating herbicide through deposition in parts of the plant, such as the cell... 

Research on symmetrical triazine derivatives and the screening of these as herbicide compounds began in Bern in 1952 in the research laboratories of the Swiss company Geigy. This was the work that led to the development of one of the most important groups of herbicides known today, the triazine herbicides. 

Chlorsulfuron is the active ingredient in Du Pont Glean Weed Killer. A very important feature of this new selective herbicide compound is its very high herbicidal activity at very low application rates. The compound controls most broad-leaved weeds in small grains at 10-40 g/ha. It is nonvolatile and is active due to uptake through both foliage and root system. 

Brief mention will be made here of the use of fluorinated 1,2,4-triazolones as agrochemical agents. Novel 4-difluoromethyl-l-aryl-l,2,4-tiiazolm-5-ones function as important herbicidal compounds for broad-spectrum weed control for use on such crops as corn, soybean, and wheat. The mode of action has been identified as inhibition of protoporphyrinogen oxidase. Two examples are sulfentrazone 151 and carfentrazone-ethyl 152. A more detailed and comprehensive discussion of agrochemical applications of fluorinated heterocyclic compounds can be found in another chapter of this book. 

These mutants demonstrate that glutamine synthetase is a potential target for herbicidal compounds and they indicate that photosynthetic tissue is most vulnerable for herbicidal damage caused by GS inhibitors. 

QSAR models describing phytotoxicity (Table 5.12) are limited to a few chemical classes, mostly those with relatively well-understood modes of action such as herbicidal compounds. 

Safener Increases tolerance of crops to the toxic effects of herbicidal compounds... 

Cutler, H. G., Herbicidal compounds from higher plants, in Phytochemical Resources for medicine and agriculture (H. G. Nigg and D. S. Seigler, eds.), 205-226, Plenum Press, New York, 1992. 

Cutler, H. G., Herbicidal compounds from higher plants, in Phyto-... 

Herbicidal compounds have been prepared with aryl ring systems, such as those shown in Figure 10. The substituent effects on the herbicidal activity for derivatives of the other ring systems is similar to their effect in the phenyl series. Thiophene has the advantage of short soil residual activity (See Brown and Kearney, this volume). 

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