Amino- and urea-substituted thiazoles inhibit photosynthetic electron transfer

Amino- and urea-substituted thiazoles exhibited in vivo herbicidal activity on duckweed (Lemna paucicostata Hegelm. strain 6746) cultures and appeared to act via inhibition of photosynthetic electron transport system. A small number of the thiazole derivatives tested were active but only at relative ly high concentrations. The most active structures were the amino-substitut ed thiazoles with isopropyl and n-butyl side chains and the urea-substitute d thiazole with p-chlorophenyl side chain. Decreasing the length of the sid e chain had a negative effect on the PSII inhibitory activity. The urea-sub stituted series was as a group less active than the amino series, and the f ree acid series had no biological activity. The most active compounds compe ted for the same binding site as atrazine on PSII. Computer modeling highli ghted the structural similarities between some of the thiazoles and the com mercial herbicides diuron and atrazine.