Chitin biosynthesis inhibition and fungicidal effect of thiosemicarbazones of 2-formyl- and 2-acetylpyridine, their hydrogenated derivatives and copper complexes thereof

Several thiosemicarbazones of 2‐formyl‐ and 2‐acetylpyridine dialkylated on N4 and non‐alkylated on N2 were found to be broad‐spectrum protectant fungicides with activity particularly against oomycetes. The effect of some of the compounds on chitin biosynthesis was studied, but the low inhibitory activity observed combined with the fungicidal activity spectrum—particularly the high activity against oomycetes—excludes this as their main mode of action. Attempts at enhancing the systemic properties of the compounds by chemical modifications failed.