Quantitative structure-activity relationships for 2-[(phenylmethyl)sulfonyl]pyridine 1-oxide herbicides.

ABSTRACT

Phenyl-substituted analogues of 2-[(phenylmethyl)sulfonyl]pyridine 1-oxide preemergent herbicides were examined in order to determine quantitative relationships between structure and activity against the following three weed species switch grass (Panicum virgatum L.), barnyard grass (Echinochloa crusgalli L. Beauv.), and green foxtail (Setaria viridis L. Beauv.). Analogues were chosen to provide maximum parameter orthogonality. Regression analysis yielded structure-activity relationships wherein the most significant substituent parameters associated with herbicidal activity were found to be the partition coefficient (pi), the molar refractivity (MR), and two indicator variables, Z (denoting the presence of an alpha-methyl group) and H (denoting an ortho substituent capable of hydrogen bonding). For green foxtail, the structure-activity relationship was found to be -log ED50 = 0.43 pi -0.052MR + 0.50H + 0.24Z + 0.61, where ED50 is expressed in moles per acre. The regression equations were found to explain 79-93% of the bioactivity for the three weed species studied. It was further shown that these equations represent the best possible correlations within the limitations of the biological data.