Effect on herbicidal activity

As a starting point for structural optimization of the second lead, we divided the core structure into three subsections, the phenyl (X), the imino group (Y), and the thiazoline nucleus (R and R ) (Figure 5 ). First, we synthesized the 2-(N-ethoxycarbonylimino)-l,3-thiazolines that possessed a variety of substituents at each position of the phenyl ring to examine the effect on herbicidal activity. Preemergence activities are summarized in Figure 6. Substitution on the phenyl moiety was preferred in the meta position and we observed a progressive... 

According to the study on acylphosphonates by Baillie et al., substituent R in monosodium acylphosphonates 1 (Scheme 2.3) greatly affected both enzyme inhibitory activity andherbicide activity of compounds. Therefore, and R in structure lo were firstly modified to examine their effect on herbicidal activity. Me, Et or n-Pr as R and R was introduced into the structure lo to form IB (Scheme 2.3). In the IB series, where Me as R" was kept, further optimization was focused on the modification of R and Yj,. 

It was also very interesting to examine the effect on herbicidal activity by the introduction of pyridyl group as into the structure IC to form a new series of IJ. 

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

Examination of the relevant theory indicates that the adjuvant effect of surface-active agents on herbicide action is maximized when the quantity FI = yL cos 0, or the film pressure at the liquid/solid interface, has a maximum value. Measurement of surface tension of 1.0% aqueous solutions and of contact angle on a number of substrates (Teflon, paraffin) and plant-leaf surfaces (soybean, com) as a function of hydrophile-lipophile balance show at least one maximum, and these values are in good agreement with earlier experimental data on herbicidal activity. 

It thus appears that the adjuvant effect of surface-active agents on herbicidal activity can be explained in terms of the surface-chemical interactions between the droplet of herbicide solution and the plant-leaf surface. Although, as we have seen, capillary penetration is one aspect of... 

Information to date suggests that surfactants do not have a direct effect on herbicide translocation [28] though the addition of adjuvants will increase the uptake, and hence the percentage translocation of applied herbicide. However, in cases where the uptake of the active and adjuvant is so rapid or so large, localised tissue death can occur (contact... 

Greenhouse evaluation in a random herbicide screen showed that 3-chloro-4-methyl-6-[m-(trifluoro-methyl)phenyl)pyridazine was sufficiently active to serve as a lead for a synthesis project. Related 3-chloropyridazines were prepared by a sequence based on the addition of acyl anion equivalents of substituted benzaldehydes to the appropriately substituted acrylate esters. Using 3-chloro-pyridazines as key intermediates, a variety of other 3-substituted-pyridazines were prepared. The effect of altering substitution at each position of the pyridazine and phenyl rings on herbicidal activity was examined. 

At a concentration of 10 pM these herbicides have no effect on ACC activity in vitro. 

Site-directed mutagenesis was used to make additional amino acid substitutions at these sites in yeast ALS. At some of the sites, e.g. alall7, prol92, or trp586, nearly any substitution for the wild type amino acid that was tested resulted in a herbicide-resistant enzyme (Table I). Each of the mutant enzymes was characterized by enzyme assays to compare its activity, and its sensitivity to the sulfonylurea herbicide chlorimuron ethyl, to the wild type enzyme. These analyses have indicated that some of the mutations have little adverse effect on the activity of the enzyme, while decreasing sensitivity to the herbicide from three to greater than one thousandfold. The characteristics of these mutant enzymes were further evaluated in vivo in order to investigate the utility of particular herbicide/mutant enzyme combinations (Falco et al., manuscript in preparation). 

George et al. (19S4) studied the effect of the alcohol component (R) of N-phenylcarbamic acid esters on herbicidal activity. 

Table 2.5.6 Effect of substituent(s) Y on the benzene ring of 6-phenoxypyrimidinylsalicylic acids on herbicidal activity and rice phytotoxicity at post-emergence application. ...

Table 3.3 Effects of uracil N-substituents on herbicidal activity of analogs of compound 34.

Table II shows the positional effect of the dimethylaminocarbonyl substituent on herbicidal activity. It is apparent that only the compound substituted at the 3-position showed high herbicidal activity.

Table IV Effects of Second Substituent on Herbicidal Activity ...

Lee and Tadros [24-27] carried out some fundamental studies on a model EC of xylene containing a nonionic and a cationic surfactant. The objective was to study the effect of stability of the resulting emulsion on herbicidal activity of a model compound, namely 2,4-dichlorophenoxyacetic add ester. The nonionic surfactant used was Synperonic NPE 1800 (supplied by ICI), ethoxylated-propoxylated nonyl-phenol (14.1). The cationic surfactant was Ethoduomeen T20 (ET 20) (Supplied by Armour Hess) (14.2). 

There seems to be little more evidence in the literature to allow a more coherent discussion of the effects of surfactants on herbicide activity and explanation of their intrinsic phytotoxicity. It may be that with such a diversity of plant structures the task of rationalizing the activity of surfactants (with the complex pattern of wetting effects, evaporation retardation, solubilization, particle size alteration of precipitated active ingredient, membrane permeability effects and intrinsic biological effects on enzyme systems) will be more daunting than with the relatively simple problem that must be faced with surfactant effects on the human organism. It is likely, however, that study of surfactant effects on plant cells will give useful information to help in the elimination of effects on mammalian cells. 

In order to examine the effect of size of R R and R" on herbicidal activity. Me, Et and Pr as R and R, H as R were introduced into stmcture lo to design a series of 1-(substituted phenoxyacetoxy)aIkylphosphonates IB. 

The IC50 values of some IB and lA against cucumber (Cucumis sativa) were tested to compare the effect of R R, and R" on herbicidal activity. The results are listed in Table 2.18. 

The IC50 values of some IC-IF against cucumber Cucumis sativa) were measured in order to further confirm the effect of substituent on herbicidal activity (Tables 2.29, 2.30 and 2.31). 

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