Protoporphyrinogen-IX oxidase inhibitors: Bioactivation of thiadiazolidines

Masaki Hiraki, Shinpei Ohki, Yukiharu Sato, Istvan Jablonkai, Peter Böger, Ko Wakabayashi

Research output: Contribution to journalArticle

16 Citations (Scopus)


The bioactivation of thiadiazolidine-type peroxidizing compounds was examined with thiosemicarbazides as model intermediates. Peroxidizing activities of three sets of thiadiazolidines (5-arylimino-3,4-tetramethyl-ene-1,3,4-thiadiazolidines), thiosemicarbazides (4-aryl-1-ethylthiocarbonyl-1,2-tetramethylenethiosemicarbazides), and triazolidines (4-aryl-1,2-tetramethylene-1,2,4-triazolidines) were assayed for protoporphyrinogen-IX oxidase (Protox) inhibition with Protox isolated from corn etioplasts and for phytotoxic parameters of growth, chlorophyll content, and ethane evolution obtained with Scenedesmus acutus cells. Protox inhibitory activity of thiosemicarbazides was intermediate between that of thiadiazolidines and triazolidines. Phytotoxic parameters of thiosemicarbazides obtained from S. acutus cells were quite identical to those of triazolidines, although phytotoxic parameters of thiadiazolidines exhibited a slightly different pattern. Phytotoxic activities of 5-(4-bromophenyl)-3,4-tetramethylene-1,3,4-thiadiazolidin-2-one (thiadiazolidine 1) and 5-(4-chloro-2-fluoro-5-propargyloxyphenyl)-3,4-tetramethylene-1,3,4- thiadiazolidin-2-one (thiadiazolidine 4) were similar to those of the corresponding triazolidines, but phytotoxicities exhibited by 5-(4-(4-chlorobenzyloxy)phenyl)-3,4-tetramethylene-1,3,4- thiadiazolidin-2-one (thiadiazolidine 7) were 10 times less active with S. acutus than those of the corresponding triazolidine. Three thiosemicarbazides exhibited rapid conversion into triazolidines both in buffer at pH 7 (ca. 25-50%, 5 min incubation) and in Scenedesmus cultures (ca. 75%, 5 h incubation). Thiadiazolidines 1 and 4 were converted into corresponding triazolidines (ca. 70%) in S. acutus but were converted in buffer only in the presence of glutathione S-transferase plus ethylmercaptan, although thiadiazolidine 7 was not converted in the Scnedesmus culture. Apparently, the conversion step from thiadiazolidine to the thiosemicarbazide intermediate is enzymatic and the thiosemicarbazide intermediate to triazolidine is a spontaneous, nonenzymatic step.

Original languageEnglish
Pages (from-to)159-167
Number of pages9
JournalPesticide Biochemistry and Physiology
Issue number3
Publication statusPublished - Jan 1 2001


  • Bioactivation
  • Glutathione S-transferase
  • SH compounds
  • Thiadiazolidines
  • Thiol intermediate
  • Thiosemicarbazides
  • Triazolidines

ASJC Scopus subject areas

  • Agronomy and Crop Science
  • Health, Toxicology and Mutagenesis

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