Structure-activity relationships of acetolactate synthase inhibition amongnew benzenesulfonylureas in rice (Oryza sativa) and barnyardgrass (Echinochloa crus-galli var. oryzicola)

Structure-activity relationships of 15 new benzenesulfonylurea derivatives were investigated using acetolactate synthase (ALS) assays in vitro and in vivo in rice (Oryza sativa) and barnyardgrass (Echinochloa crus-galli var. oryzicola). In vitro ALS activities of both rice and barnyardgrass were sig nificantly inhibited by the compounds with smaller numbers of carbon atoms and alpha -fluorine substituents in the R radical of the new benzenesulfony lurea structure. Among the stereoisomers, erythro forms showed 10 times hig her ALS inhibition than three forms. However, the in vitro ALS assay did no t clearly account for the selectivity of the compounds tested in rice and b arnyardgrass. The selectivity could, however, be explained by the results o f the in vitro ALS assay using an inhibitor of ketol-acid reductoisomerase, 1,1-cyclopropanedicarboxylic acid. Among the analogues tested, the compoun d K-8 was the most potent ALS inhibitor in vitro, and it has a good selecti vity in in vivo ALS assays in rice and barnyardgrass. These results should lead to an assay model for structure-activity relationships for the synthes is and development of new ALS-inhibiting herbicides. (C) 2000 Academic Pres s.