Functionalized Pyridines: Design, Synthesis, and Insecticidal Activity as Neonicotinoid Analogues Against Aphis fabae

ABSTRACT Neonicotinoid analogues can be synthesized through the reaction of cyanoguanidine with pyridine or pyrimidine derivatives in the presence of a catalytic amount of piperidine and methanol as the solvent. The resulting compounds exhibit characteristic features of neonicotinoids, with all chemical analogues containing the aminocyano (NHCN) moiety in their structures. Spectral and elemental analyses were used to confirm the chemical structures of the new compounds. All synthesized neonicotinoid analogues were tested in toxicity experiments to evaluate their toxicological efficacy against nymphs and adults of the black bean aphid ( Aphis fabae ) under laboratory conditions. The results revealed that compound 2 exhibited the highest toxicological activity, with LC 50 values of 0.14 ppm for nymphs and 2.57 ppm for adults. The other synthesized compounds demonstrated moderate to high levels of toxicological efficacy. The LD 50 value was used to determine the susceptibility level of the target insect population. Among different tested target compounds, compound 2 was the most toxic with the lowest LD 50 0.068 mg.kg −1 to mustard aphid.