Structure-Herbicidal Activity Relationships

Structure-herbicidal activity relationships of IG, IH, and U can be summarized as follows Similarly to the SAR analyses for lA-IF, herbicidal activity was highly dependent upon the structure and position of substituents Y in the phenoxyacetyl substructure and R. ... 

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. 

Endothall is a structural analogue of cantharidin (Fig. 20). Its mode of action is apparently inhibition of protein phosphatase(s). A struc-ture/activity relationship study demonstrated that the presence of the oxygen bridge and the location of the two carboxylic groups play important roles in the activity of the molecules. The unusual 7-oxabicyclo[2.2.1]heptane ring of endothal is similar to that of cinmethylin, another natural product-like herbicide for which the mode of action has also eluded scientists for many years. 

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... 

Besides providing mathematical relationships correlating structural changes to herbicidal activity variations among TFMS series members, Hansch analyses brought to light other facts which undoubtedly would have been overlooked had the TFMS herbicides not been examined by the Hansch method. In particular, the stepwise regression procedure demonstrated that ... 

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