Design and Synthesis of Novel Insecticides Based on the Serotonergic Ligand 1-[(4-Aminophenyl)ethyl]-4-[3-(trifluoromethyl)phenyl]piperazine (PAPP)

1-[(4-Aminophenyl)ethyl]-4-[3-(trifluoromethyl)phenyl]piperazine (PAPP) is a 5-HT1A agonist and was reported to display high affinity for serotonin (5-HT) receptor from the parasitic nematode Haemonchus contortus. The present investigation explored the possibility of using PAPP as a lead compound of new insecticides with novel mode of action. On the basis of the PAPP scaffold, a series of 1-arylmethyl-4-[(trifluoromethyl)pyridin-2-yl]piperazine derivatives were designed, synthesized, and evaluated for biological activities against the armyworm Pseudaletia separata (Walker). Bioassays showed that most of the target compounds displayed certain growth-inhibiting activities or larvicidal activities against armyworm. The quantitative structure-activity relationship (QSAR) for growth-inhibiting activities was also analyzed and established.