Structure-herbicidal activity

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 ... 

Trigard 75 WP is a new insecticide with a unique mode of action and a unique triazine structure. It is a solid formulated as a wettable powder and is packaged in water-soluble bags. The active ingredient in Trigard has the common name cyromazine. Cyromazine is a triazine, but, unlike the well-known triazine herbicides, this compound has insecticidal properties and no herbicidal activity. Cyromazine has low mammalian toxicity and low vapor pressure. It is hydrophilic, so dermal penetration is expected to be... 

Table I shows the herbicidal activity of a number of structures already discussed. These are greenhouse data and, although not obtained in a side-by-side test, they do give some indication of their relative activity. The term "control rate" as used in Tables I-III is defined as the amount of chemical required to produce a 91-100% reduction of growth of the weed when compared to the control plant.

None of these had pronounced herbicidal activity but rather PGR activity. Compound % for example, has been shown to be an auxin transport inhibitor, a property probably shared by the other members of this class also. A structure activity analysis for this group of compounds has been reported by Katekar ( ) ... 

Based on these and other compounds prepared in this series, several conclusions on the effect of structure on herbicidal activity can be drawn ... 

Matsuzawa M, Graziano MJ, Casida JE, Endothal and cantharidin analogues Relation of structure to herbicidal activity and mammalian tawsity, J Agric Food Chem 35 823-829, 1987. 

Chloroacetamide derivatives such as N,N-diallyl (5) and N-alkoxymethyl-N-2,6-diethylphenyl (<5) analogs are widely used as upland field herbicides. By modification of chloroacetamide structure, Fujinami et al. found that the N-chloroacetyl-N-phenylglycine esters (7) show varying degrees of inhibitory activity, in particular, against shoot growth of annual grasses 17). They developed Eq. 15 and 16 for the herbicidal activities of various esters where the aromatic substituents are fixed... 

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). 

So we were induced to try this approach, too, and we started synthesis work in the field of s-triazines. The result of our primary working hypothesis was disappointing derivatives bearing anilino radicals showed no herbicidal effects. Surprisingly, however, the herbicidal activity reappeared in the structure 2-chloro-4,6-bis-diethylamino-s-triazine, compound G-25804 shown previously. The awareness that we were confronted with a completely new herbicidal matrix with apparently superior usefulness led us to intensive work around the s-triazine ring system. 

But let us return to the problem of selecting, out of the myriads of possible 2,4,6-s-triazine derivates, those which have herbicidal activity and from these, those which would be useful under practical conditions. Starting from the structure of G-25804 we initiated variation along four main lines in order to explore the consequences with regard to the biological characteristics. 

New. v-triazines were developed at a very rapid pace in the project. Therefore, by 1956 there were many compounds in various stages of development. New information on triazine derivatives and herbicidal activity was released to the public at the British Weed Control Conference (Gysin and Kniisli 1956). Table 2.1 (Gunther and Gunther 1970) provides the internal codes and common names, chemical structure and properties of some of these compounds. 

As shown by the structures in Figure 15.9, a bipyridilium compound contains two pyridine rings per molecule. The two important pesticidal compounds of this type are the herbicides diquat and paraquat other members of this class of herbicides include chlormequat, morfamquat, and difenzoquat. Applied directly to plant tissue, these compounds rapidly destroy plant cells and give the plant a frostbitten appearance. However, they bind tenaciously to soil, especially the clay mineral fraction, which results in rapid loss of herbicidal activity so that sprayed fields can be planted within a day or two of herbicide application. 

Despite the chemical diversity of the several hundred structures representing herbicidal activity, most reactions of herbicides fall within only a limited number of mechanistic types oxidation, reduction, nucleophilic displacements (such as hydrolysis), eliminations, and additions. "Herbicides", after all, are more-or-less ordinary chemicals, and their principal transformations in the environment are fundamentally no different from those in laboratory glassware. Figure 2 illustrates three typical examples which have received their share of classical laboratory study—the alkaline hydrolysis of a carboxylic ester (in this case, an ester of 2,4-dichlorophenoxyacetic acid, IX), the cycloaddition of an alcohol to an olefin (as in the acetylene, VI), and the 3-elimination of a dithiocarbamate which provides the usual synthetic route to an isothiocyanate (conversion of an N.N-dimethylcarbamic acid salt, XI, to methyl isothiocyanate). Allow the starting materials herbicidal action (which they have), give them names such as "2,4-D ester" or "pronamide" or "Vapam", and let soil form the walls of an outdoor reaction kettle the reactions and products remain the same. 

Generic structures (41) and (42) are examples of thiadiazoles with herbicidal activity (75USP3874873, 79GEP2728523). 

An interesting sidelight of the organic structural classification study was that herbicidal activity could also be predicted 6). The nitrodiphenylethers could be divided into compounds which were strong herbicides and those compounds which showed little or no herbicidal activity. Both Faradaic and capacitive responses could be used to separate these classes for over half the experimental conditions examined. As was found in the classification of structure, capacitive factorial features performed somewhat better than Faradaic factorial features. It also appeared that classifications of herbicidal activity using Faradaic factorial features could be improved considerably by working at high pH and without surfactant present. The information content of Faradaic or capacitive variable effects data could be improved by variations in % ethanol. 

Aryloxyphenoxypropanoates and cyclohexanediones are two classes of herbicides that control many monocotyledoneous species. Although these herbicides are structurally very different (Fig. 1), there has been some conjecture that they have a similar mode of action because of their similarity in selectivity and symptomology. This paper describes the experiments that led to the discovery that aryloxyphenoxypropanoate and cyclohexanedione herbicides inhibit acetyl coenzyme A carboxylase (acetyl-coenzyme A bicarbonate ligase [ATP], EC 6.4.1.2) activity in susceptible species (1). In addition, evidence is presented indicating that the inhibition of acetyl coenzyme A carboxylase (ACCase) is well correlated to observed herbicidal activity. Similar, independent findings have recently been reported by two other research groups (2.3). 

---