1,2,3-Thiadiazolyl-Pheny 1-Ureas, New Inhibitors of Photosynthetic and Respiratory Energy Conservation

Substituted 1,2,3-thiadiazolyl-phenyl-ureas were found to be inhibitors of energy conservation in respiration and photosynthesis. The most effective dichlorophenylderivative uncouples ATP formation in isolated chloroplasts or mitochondria, at a concentration of about 2 and 9 /uu respec­ tively. At a certain concentration range the compounds also appear to be energy transfer inhibitors, similar to the well known inhibition by carbodiimides. The significance of the chemical relation of carbodiimides to ureas in the mode of action on energy transfer is discussed. The thiadiazolylphenyl-ureas are inhibitors of electron flow only at relatively high concentrations, pointing out that sterig hindrance by two large aromatic rings at both nitrogens of the urea moiety abolishes the highly effective inhibition of photosynthetic electron flow by substituted urea derivatives, like DCMU.