Quantitative structure‐activity relationships of light‐dependent herbicidal 4‐pyridone‐3‐carboxanilides III. 3‐D (comparative molecular field) analysis including light‐dependent diphenyl ether herbicides

Abstract

Using a set of representative members selected from 4‐pyridone‐3‐carboxanilides and ortho‐chlorinated diphenyl ethers exhibiting light‐dependent herbicidal activity, we examined the three‐dimensional structure‐activity relationships quantitatively. The most stable conformation of each compound, regarded as the ‘active conformation’, was determined by either semi‐empirical or ab initio molecular orbital calculations. With a hypothesis defining a common substructural skeleton between the two different compound series. each molecule was superimposed. We first analysed the structure‐activity relationship using an index for the substructure shape similarity according to the superimposed conformations. After finding the relevance of the hypothesis, we examined the three‐dimensional structure‐activity relationship using the comparative molecular field analysis procedure. The results suggested that the two different series of compounds have a common region of the receptor site. The variations in the light‐dependent herbicidal potency were governed by hydrophobicty and three‐dimensional steric and electronic field parameters of molecules participating in the transport process and the interaction with the receptor site. The result was consistent with that derived from our previous quantitative analysis with the use of free‐energy‐related substituent parameters and the traditional regression procedure for a large number of pyridone‐carboxanilides.

Quantitative Structure-Activity Relationships of Herbicidal <i>N</i>-Alkyl-<i>N</i>-(4-substituted benzyl)-4-chloro-2-pentenamides against <i>Echinochloa oryzicola</i>

“…the Amide Nitrogen Atom For compounds (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19) in Table 1 where the X substituent is fixed as 4-Cl, the activity varied considerably with variations in the structure of the R substituent. The activity was highest when R is n-Pr (in 3), i-Bu (in 6), and c-Pent (in 10), but very low when R is lengthy in such substituents as n-Oct (in 13) and multiply branched in such substituents as t-Bu (in 18) and t-Pent (in 19).…”