Bioactivities of synthetic salicylate‐substituted carboxyl (E)‐β‐Farnesene derivatives as ecofriendly agrochemicals and their binding mechanism with potential targets in aphid olfactory system

BACKGROUND:The aphid alarm pheromone,(E)-β-farnesene (EβF), is a natural product secreted from the aphid cornicle as a signal to warn companions of danger. Odorant binding proteins (OBPs) are the vitaltargetsin insect signal transduction pathways. To improve bioactivity of EβFasmore economic and stable aphid control agents, EβF derivatives containing an active substructure,salicylic acid moiety,were designed, synthesized, and evaluated for theirbioactivitiesina structure-function study underlaboratory conditions. RESULTS:EβFderivatives, (E)-3,7-dimethylocta-2,6-dien-1-yl-2-hydroxy-3-methylbenzoateand(E)-3,7-dimethylocta-2,6-dien-1-yl-2-hydroxy-3-methoxybenzoateshowed outstanding aphid-repellent activity at a dose of 5 µgagainst Acyrthosiphon pisum(repellency proportions of 67.3% and 71.2%, respectively) and Myzus persicae(repellency proportionsof 80.0% and 74.4%, respectively)in laboratory. EβF and most of its derivatives bound strongly to ApisOBP9with a higheraffinity than thoseof the reported potential targetsAphisOBP3 and ApisOBP7. The binding affinitiesto these three ApisOBPswere generally consistentwith the in vivoaphid-repellent activity. A molecular docking study suggested that the hydrophobic effectwas crucial fortheinteractions between the derivatives and the OBPs.
CONCLUSION: New EβFderivatives containing salicylic acid moietyand their repellent activity, binding mechanism with three potential OBPs are presented. A new OBP, ApisOBP9, was characterizedas a potentialEβF and EβF derivativesbinding proteinfor the first time. The hydrophobic nature of these analogues is responsible for their activity. Two analogues 3band 3ewith outstanding aphid-repellent activity could be newleadsfor aphid control agents.