[2-anilino-1,3,4-thiadiazoles, inhibitors of oxidative and photosynthetic phosphorylation (author's transl)].

2-anilino-1,3,4-thiadiazoles carrying various substituents in the 5-position as well as in the benzene-ring were synthesized. The compounds were tested with rat-liver-mitochondria and with spinach-chloroplasts and revelaed to be potent uncouplers of both, oxidative and photosynthetic phosphorylation, with pI50-values rangeing from 6.79 to 4.05. At higher concentrations all compounds are inhibitors of the Hill-reaction. In mitochondria a fair correlation exists between pKa of the acidic NH-group and the uncoupling activity; a maximum is obtained around pKa equals 6.8, whereas in chloroplasts activity is shifted to more acid pKa-values. The compounds meet the requirements for uncouplers according to the chemi-osmotic theory, being lipophilic weak acids. N-methylation causes total loss of activity in mitochondrial oxidative phosphorylation. The ingibitory action on photosynthetic electron transport is located within photosystem II. This latter activity is almost independent of substituent effects in contrast to uncoupling of either respiratory- or photo-phosphorylation.