Isomerization and Peroxidizing Phytotoxicity of Thiadiazolidine Herbicides

Y ukiharu Sato, Toshinobu Hoshi, Tetsuji Iida, Chifuyu Ogino, B eate Nicolaus*, Ko W akabayashi, and P eter Böger* Graduate School of Agriculture, Tamagawa University, Machida-shi, Tokyo 194, Japan * Lehrstuhl für Physiologie und Biochemie der Pflanzen, Universität Konstanz, D-78434 Konstanz, Bundesrepublik Deutschland Z. Naturforsch. 49c, 49-56 (1994); received November 12,1993 Proherbicide, Isomerization, Triazolidinonethiones, Thiadiazolidinones, Echinochloa Certain 5-(arylimino)-3,4-tetramethylene-l,3,4-thiadiazolidin-2-ones (thiadiazolidines) are peroxidizing bleaching herbicides which interrupt chlorophyll biosynthesis, inhibit the activity of protoporphyrinogen oxidase, lead to accumulation of protoporphyrin IX, and induce ethane formation in the light. The same effects are caused by their isomers, the 4-aryl-l,2-tetramethylene-l,2,4-triazolidin-3-one-5-thiones (triazolidines). Couples of thia­ diazolidines and corresponding triazolidine isomers were synthesized. Thiadiazolidines with a 4-bromophenylimino, 4-chlorophenylimino, 4-chloro-2-methylphenylimino, 4-chloro2-fluorophenylimino, 4-chloro-2-fluoro-5-propargyloxyphenylimino and 4-chloro-2-fluoro5-isopropoxyphenylimino moiety were converted to the corresponding triazolidines both with Echinochloa seedlings or a spinach homogenate present, depending on the 5-arylimino moiety. The 5-[4-(chlorobenzyloxy)phenylimino]-3,4-tetramethylene-l,3,4-thiadiazolidin-2one analogue did not convert to the corresponding triazolidine under both conditions. Thiadiazolidines as well as triazolidines having a 4-chloro-2-fluoro-5-methoxycarbonylmethylthiophenyl moiety were converted to an unidentified compound whose structure is assumed to be 4-(4-chloro-2-fluoro-5-carboxymethylthiophenyl)-l,2-tetramethylene-l,2,4triazolidin-3-one-5-thione. Apparently, the general conversion mechanism is caused by enzymatic hydrolysis of thiadiazolidines to an unstable intermediate which rapidly and spon­ taneously changes to the corresponding triazolidine isomer.