INHIBITION OF PHOTOSYSTEM-II ELECTRON-TRANSPORT AND STRUCTURE-ACTIVITY-RELATIONSHIPS AMONG HERBICIDALLY ACTIVE 3-BUTENANILIDES

A new class of herbicidal 3-butenanilides, which displays a range of phytotoxicity in greenhouse tests, has symptomology indicative of photosystem II electron transport inhibition. Several of the more active molecules caused increased florescence in Brassica kaber and Glycine max leaf discs in a manner similar to that of atrazine. The lead compound, LY221204 (trans-4-chloro-N-(4-chlorophenyl)-2,2-dimethyl-3-butenamide), inhibited electron transport in isolated spinach thylakoids, presenting an IC50 similar to that of atrazine. Binding inhibition experiments showed that LY221204 was an effective inhibitor of [14C]atrazine binding to spinach thylakoids. Scatchard analysis of the [14C]atrazine binding inhibition of LY221204 has shown it to be a competitive inhibitor. A quantitative structure-activity relationship (QSAR) analysis of the [14C]atrazine binding inhibition of LY221204 and related analogs suggests that a significant amount of the binding can be explained by STERIMOL B1 and L parameters (minimum width and overall length), as well as Swain and Lupton's resonance constant R. The potential for further enhancement of activity is discussed. © 1992.