Herbicidal, Insecticidal and Structure-Activity Relationship Studies on Pyranopyrazole and Oxinobispyrazole Derivatives

Nine pyranopyrazole and oxinobispyrazole derivatives were synthesized and their structures were confirmed by spectral analysis. The inhibitory effects of prepared compounds were evaluated on germination and seedling growth of Lolium temulentum. In addition, the insecticidal activity of synthesized compounds was tested against the fourth instar larvae of Culex pipiens. The structureactivity relationships of compounds were disclosed. The results of herbicidal activity assay revealed that the prepared compounds caused significant reduction of L. temulentum seed germination. Compounds 4 and 7 showed the highest seed germination reduction at the tested concentrations (0.5, 1 and 5 mM) with complete inhibition (100%) of seed germination at 5 mM. In contrary, compounds 2 and 9 showed the weakest reduction of germination. The tested compounds also exhibited strong root growth inhibition with compound 7 being the most potent one and compound 1 being the less potent one. Similarly the tested compounds revealed pronounced inhibition of shoot growth of L. temulentum. Compounds 4 and 7 caused the highest shoot growth reduction at the tested concentrations. The inhibition of root growth by all compounds was greater than that of shoot growth. When tested for their insecticidal activity against the fourth instar larvae of C. pipiens, the tested compounds showed variable toxicity. However, compounds 4, 7 and 8 were the most potent toxicants toward the larvae, while compound 2 showed the lowest activity among the tested compounds. The results revealed that compounds bearing cyanide (CN) group at the position C-5 such as 4, 7 and 8 were the most active compounds against the tested weed and insect. Inaddition, the presence of phenyl moiety at N-1 significantly increased the herbicidal and insecticidal activity of compounds such as 7 and 8 compared with other compounds. Therefore, pyranopyrazole derivatives with these substitutions may be suitable for developing new pesticides.