A novel halogen bond and a better-known hydrogen bond cooperation of neonicotinoid and insect nicotinic acetylcholine receptor recognition

Neonicotinoid insecticides target the insect nicotinic acetylcholine receptor (nAChR) and are highly effective against the piercing-sucking pests. To explore the molecular interaction mechanism between the neonicotinoids and the insect nAChR, some key neonicotinoid compounds were docked into Aplysia californica acetylcholine binding protein (Ac-AChBP), which serves as a suitable structural surrogate of the insect nAChR. The binding mode study showed that the hydrogen bond force between the electronegative pharmacophore of the neonicotinoids and Cys190NH of the target binding pocket is crucial to the high efficiency of the neonicotinoids. Increasing the coplanarity between the guanidine or amidine and the electronegative pharmacophore of the neonicotinoids could increase the Π-Π stacking effect with Tyr188 of the Ac-AChBP and thus enhance the insecticidal potency. The introduction of an azide group to the chloropyridine ring of the neonicotinoids would reduce its binding ability due to the disappearance of a novel halogen bonding interaction. A series of novel neonicotinoid molecules were designed based on the halogen bonding interaction and two compounds with 6-bromopyridine-3-yl and 6-(trifluoromethyl)-3-pyridinyl were found to be with potential insecticidal activities.