Dimethoxypyrimidines as novel herbicides. Part 4. Quantitative structure-activity relationships of dimethoxypyrimidinyl(thio)salicylic acids

Abstract

The activity of a number of O-(4,6-dimethoxypyrimidin-2-yl)salicylic acids and their thio analogs inhibiting acetolactate synthase (ALS) preparation was measured. The effects of substituents on the salicylic-benzene ring on the inhibitory activity were analyzed quantitatively with physicochemical substituent parameters. For 6-substituted (thio)salicylic acids, the activity was shown to vary parabolically with the ‘intramolecular’ steric parameter (Es). In addition, the higher steric dimension of substituents in terms of the STERIMOL width or length parameter lowered the activity. The field-inductive electron-withdrawing property of the 6-substituents in terms of the Swain–Lupton–Hansch F was favorable for the activity of salicylic acid series. In 5-substituted salicylic acids, the activity was increased by electron-donating substituents with smaller size. The relationships between ALS inhibitory and herbicidal activities were also analyzed with some weed species. Both pre- and post-emergence activities against barnyard grass, Echinochloa crus-galli, were linearly related to the ALS inhibitory activity after allowing for the hydrophobic factor that may contribute to the transport processes. Those against two broad-leaved weed species, Polygonum convolvulus and Abutilon theophrasti were linearly related to the in-vitro activity with no significant participation of the hydrophobic factor. © 1998 SCI