Structure-activity-relationship of inhibitors of photosynthetic electron flow. Herbicidal N-alkylated-ureas and ringclosed N-acylamides as inhibitors of photosystem II.

The inhibitory action of some herbicides on photosynthetic electron flow at photosystem II in isolated chloroplasts was investigated. Emphasis in the study is on compounds, whose chemical structure seemed to be in disaccordance with the basic structural element, proposed to be required for a photosystem II inhibitor. The effective inhibition of photosynthetic oxygen evolution by N-alkylated urea-, pyrrolidoneand by substituted pyridazine-derivatives without a free NH-group is reported. A revised basic chemical structural element responsible for inhibition is deduced in order to include lactames (ringclosed N-acylamides) with and without hetero atoms. From this new groups of potential inhibitors, like triazolone-, thiadiazoloneand oxadiazolone-derivatives may be conceived.