SYNTHESIS AND TOXICOLOGICAL STUDIES ON DISTYRYL-SUBSTITUTED HETEROCYCLIC INSECTICIDES

The toxicity of four pyridine-containing neonicotinoid analogues as potential insecticides against cowpea aphid, Aphis craccivora Koch, has been evaluated. The four pyridine compounds are 2-((2-oxopropyl)thio)-4,6-distyrylnicotinonitrile ( 2 ), 2-acetyl-3-amino-4,6-distyrylthieno[2,3- b ]pyridine ( 3 ), ethyl 2-((3-cyano-4,6-distyrylpyridin-2-yl)thio)acetate ( 4 ), and ethyl 3-amino-4,6-distyrylthieno[2,3- b ]pyridine-2-carboxylate ( 5 ). By screening the insecticidal activity for compounds ( 2-5 ) against the cowpea aphid nymphs after 24 h of treatment, the LC 50 values were 0.133, 0.687, 0.171, and 0.771 ppm, respectively, and after 48 h of treatment, the LC 50 values were 0.016, 0.111, 0.029, and 0.058 ppm, respectively. Also, by screening the insecticidal activity for compounds ( 2-5 ) against the cowpea aphid adults after 24 h of treatment, the LC 50 values were 1.655, 5.611, 0.421, and 7.957 ppm, respectively, and after 48 h of treatment, the LC 50 values were 0.116, 0.431, 0.062, and 0.539 ppm, respectively. These results proved that the presence of different functional groups in the structure of the aforementioned compounds furnished a range of biological activities as promising insecticides. The insecticidal activity results against cowpea aphid for these compounds showed a good biological activity using acetamiprid insecticide as a reference.