Herbicide structure-activity relationships

Estimation of Phvtotoxicity. Several investigators have used cell cultures to study herbicide phytotoxicity (3. 5. 18-20). Callus and cell suspensions have potential in the estimation of phytotoxicity, especially in detecting the inherent phytotoxicity of a molecule that fails to penetrate into or translocate in a whole plant. Alteration of the molecule to enhance penetrability may provide a usable herbicide. Structure activity relationships have also been examined to determine the comparative potency of different plant growth regulators in cell cultures in comparison to whole plants (21). 

It was not until 1962 that the first quantitative structure-activity relationship was published by Corwin Hansch and co-workers [13], relating to the herbicidal activity of a series of phenoxyacetic acids ... 

The discovery, mode of action, and empirical structure-activity relationships of these new herbicides will be reviewed. 

Lee DL, Knudsen CG, Michaely WJ, Chin H-L, Nguyen NH, Carter CG, CromartieTH, Lake BH, Shribbs JM, Fraser T, The structure-activity relationships of the triketone class of HPPD herbicides, Pestic Sci 54 377—384, 1998. 

The herbicidal activity of the bipyridyliums depends on their redox properties. Their abilities as one-electron acceptors of the right redox potential (-350 mV for diquat and -450 mV for paraquat) allow them to siphon electrons out of the photosynthetic electron-transport system, competing with the natural acceptors. The radical anion produced is then reoxidized by oxygen, generating the real toxicant, hydrogen peroxide, which damages plant cells. Structure-activity relationships in this series have been reviewed (60MI10701). 

Braumann, T., Weber, G., Grimme, H. (1983) Quantitative structure-activity relationship for herbicides. Reversed-phase liquid chromatographic retention parameter log kw versus liquid-liquid partition coefficient as a model of the hydrophobicity of phenylureas s-tria/ines and phenoxycarbonic acid derivatives. J. Chromatogr. 261, 329-343. 

Mitsutake, K.-I., Iwasmura, H., Shimizu, R., Fujita, T. (1986) Quantitative structure-activity relationships of photosystem II inhibitors in chloroplasts and its link to herbicidal action. J. Agric. Food Chem. 34, 725-732. 

Where other books on this subject highlight the fuzzier aspects, this one covers the hard science. It explores the latest developments in the field, discusses structure-activity relationships and SAR studies, and provides a foundation for the development of new natural herbicides. Designed as a practical, bench-friendly book, AUelopatlty Chemistry and Mode of Action of Allelochemicals is a convenient, easy-to-use resource that puts the latest information within easy reach. 

Structure-activity relationships between several nonionic surfactants and three water-soluble herbicides have been studied (58). In general it has been shown that the herbicide, the surfactant concentration, the hydrophilic constitution (ethylene oxide content), and the hydrophobic portion of the molecule all markedly influence toxicity. 

Studies on structure-activity relationships between herbicides and homologous series of surfactants indicate that definite relationships exist between the herbicide and surfactant structure for maximum herbicide penetration. The length of the molecular chains (either hydrophilic or lipophilic) of a surfactant molecule appears to have considerable influence on herbicide penetration, and the surfactant concentration also influences this process markedly. 

The well-known herbicide spike is prepared in high yield by heating in toluene a mixture of pivalic acid, JV-methylthiosemicarbazide, sulfuric acid and polyphosphoric acid to give (228 R = H), which on further treatment with methyl isocyanate yields (228 R = CONHMe) (81USP4283543). Other patented processes are known (76GEP2541115). Details on the structure-activity relationship of compounds in this class are available (70MI42700). A thiadiazole-containing insecticide is methidathion (229). 

Recent general spectral studies of such nitriles include the vibration spectra of 2-pyrazinecarbonitrile and a (> 99%)15N-isotopic version 1172 the mass spectra of 2,3-pyrazinedicarbonitrile, its 5,6-diphenyl derivative, and 2,3,5,6-pyrazinetetracarboni-trile for comparison with those of analogous heterocyclic nitriles 1406 and the 15C NMR spectra of 2-pyrazinecarbonitrile and the like for correlation with their reactivities toward acetone enolate anions.251 The structure-activity relationship of pyrazinecarbonitriles as herbicides has been reported.1048... 

The results in Table XII show that Hansch correlations carried out on pooled herbicidal data gathered in the presence and absence of Tween 80 for a given classification of TFMS compounds acting on a particular weed type produce significantly poorer ultimate structure—activity relationships than those which are obtained if the activity data gathered in the presence and absence of surfactant are fitted separately. For both... 

Molecules of similar biochemical activity often show common 3D shape features. Consequently, the characterization of the shapes of formal molecular bodies and the recognition, description, and, ultimately, the numerical evaluation of similarity among molecules are of major importance in modern pharmaceutical research, as well as in pesticide and herbicide chemistry. The analysis of molecular shape is an important component of research aimed at the elucidation of drug-receptor interactions and in studies of quantitative structure-activity relationships in contemporary drug design. 

Miyashita, Y, Ohsako, H., Takayama, C. and Sasaki, S. (1992). Multivariate Structure-Activity Relationships Analysis of Fungicidal and Herbicidal Thiocarbamates Using Partial Least Squares Method. Quant.Struct.-Act.Relat, 11,17-22. 

The first chapter in the herbicide section is devoted to synthetic efforts related to the herbicide Command, currently being developed by FMC Corporation. Here we see detailed the various synthetic and structure-activity relationships of this important group of compounds. These compounds exert their phytotoxic effect by their bleaching action on a wide variety of economic weeds. An important observation was that soybeans were not affected at normal use rates. These compounds act upon the carotene and chlorophyll biosynthesis of the plant. Here are a group of synthetic pathways that are peculiar to plants and a few microorganisms and are susceptible to chemical attack. 

The workers at American Cyanamid present some of the synthetic and biological characteristics of the sulfur analogs of their imidazoline family of herbicides. This is an example of replacing the carbonyl of the imidazoli-none with an isosteric moiety. This is an interesting account of the synthesis and structure-activity relationships in a very active series of herbicides. 

Several 2-aryl- and 2-phenylmethyl-3,5-isoxazolidine-dlones were synthesized and found to be bleaching herbicides with good tolerance by soybeans. The most active member, 2-(2-chlorophenyl)methyl-4,4-dimethyl-3,5-isoxazolidinedione, failed to perform in the field due to its instability in soil. To improve the chemical stability by molecular modifications, a series of 3-isoxazolidinones were prepared and found to be highly active bleaching herbicides with excellent soybean tolerance. Synthesis and structure-activity relationships are discussed. One of the most active compounds,... 

In an effort to find new agricultural herbicides a new class of broad spectrum soybean herbicides, the 3-isoxazolidinones, was discovered. The discovery, synthesis, and structure - activity relationships of this new class of herbicides and the related compounds will be discussed. 

Structure-activity Relationships. It has been found that the position of substitution on the phenyl ring is critical for herbicidal activity. For example, a series of chloro-substituted benzyl-3-isoxazolidinones shown in Table VIII demonstrates activity ranging from inactive to very active. It is clear from this table that the ortho-substituent is necessary for activity. In addition to the ortho-position, the second substituent must be at the C4 or C5 position to be active. 

Herbicidal Activity. The subject furanones are primarily active as preemergence and preplant incorporated (PRE/PPI) materials and are moderately active when applied postemergence. The structure-activity relationships discussed below pertain to the preemergence activity. 

A novel series of chiral grass herbicides based on the benzyloxy substituted tetrahydrofuran ring system has been prepared. These compounds are readily accessible synthetically from diacetone-D-glucose which serves as a chiral template possessing the appropriate stereochemistry for elaboration to the active herbicides. The degree of herbicidal activity is related to the molecular shape of these compounds and especially to the orientation of the substituents around the tetrahydrofuran ring. The chemistry and empirical structure-activity relationships of these compounds will be discussed. 

In view of the structural novelty of this series of chiral herbicides, it was imperative to determine to what extent herbicidal activity is specifically linked to its molecular structure, and to define its structure-activity relationship requirements as a preliminary step toward designing even more potent representatives for this new series of herbicides. The... 

In our attempts to optimize the herbicidal activity of this novel series of chiral compounds, a systematic study of the structure-activity relationships was undertaken. Practically all parts of the basic tetrahydrofuran ring were subjected to structural variations. The key structural modifications around the tetrahydrofuran ring can be classified as follows ... 

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