Structural Optimization of Aphid Repellents Based on the Low-Energy Conformation of (E)-β-Farnesene

Aphids cause significant agricultural damage, prompting the search for eco-friendly control methods. Although pheromones offer a natural alternative to synthetic insecticides, the low stability of aphid alarm pheromones limits their use. To develop more stable repellents, we computed the low-energy conformations of (E)-β-farnesene (EBF), revealing five conformations with a conserved spatial region, and used these insights to modify the para-pheromone IV-30. Molecular superimposition confirmed that IV-30 mimics EBF’s conformations. A series of analogues were synthesized, and experiments showed that an ester group on the six-membered ring’s left side is crucial for repellent activity, while electron-rich groups on the right side enhance it. Notably, compound V-9 demonstrated repellent efficacy comparable to EBF, deepening the understanding of structure–activity relationships and supporting the development of novel aphid repellents for integrated pest management.