Synthesis, crystal structure, insecticidal activities, molecular docking and QSAR studies of some new phospho guanidines and phospho pyrazines as cholinesterase inhibitors

Novel phospho guanidine and phospho pyrazine derivatives were synthesized and characterized by P-31, C-13, (HNMR)-H-1 and IR spectroscopy to obtain novel and human-safe insecticides. Compound 35[(C4H4N2NH)(2)P(O)(C6H6)] was investigated by X-ray crystallography. The inhibitory effects of synthesized compounds were evaluated on human and insect acetylcholinesterase (AChE) using in vitro Ellman method. A few of these compounds, which had low human toxicity, were selected for assessing the killing effects (in vivo) on the elm leaf beetle (X.luteola). The in vitro and in vivo results indicated that compounds bearing both phosphoryl groups and aromatic systems were found to possess a good selectivity for the inhibition of insect AChE over human AChE; up to 550-fold selectivity was achieved for compound 19. Docking studies were performed to explain reasons for the selective behavior of AChE inhibitors. Additionally, the quantitative structure-activity relationship (QSAR) and density functional theory (DFT) results of AChEs demonstrated that the size, shape, dipole moment, and ability to form hydrogen bond played the main role in both models. In addition, the aromatic pi - pi interactions and charge of the amide nitrogen had a major effect on insecticidal activity of the compounds. The present research can be helpful to gain a better understanding of the interactions between the insect AChE and its inhibitors and introduces compounds which are capable of becoming human-safe insecticides.