C‐14 oxygenated quassinoids with control effect against larvae of Diaphorina citri Kuwayama from fruits of Picrasma quassioides

Diaphorina citri is one of the most severe pests affecting citrus production worldwide. Our previous research identified a series of quassinoids that exhibit insecticidal activity against D. citri adults. However, the larvae of D. citri also pose a significant threat to the citrus industry. In an effort to discover novel larvicidal lead compounds, a systematic phytochemical study on the relatively understudied fruits of Picrasma quassioides was conducted, and the insecticidal mechanism was also explored preliminarily. Ten new (1-10) and 15 known quassinoids (11-25) were isolated from P. quassioides fruits. All these new compounds possess a hydroxyl group at C-14 except for compound 5, which is a rare example of quassinoid with a double bond located at C-14 and C-15. In terms of biological actions, compounds 2, 3, 5, 7, 10-16 and 18-23 had potent insecticidal activity. Preliminary structure and activity relationship (SAR) studies have shown that the insecticidal activity of quassinoids is closely related to the types of substituents at positions C-12, C-14 and C-16. Real-time quantitative polymerase chain reaction analysis demonstrated that compounds 7, 11 and 12 disturbed the expression of cytochrome P450, carboxylate esterase and glutathione S-transferase genes. Quassinoids isolated from fruits of P. quassioides demonstrate significant efficacy in managing the larvae of D. citri. These active compounds may serve as crucial lead structures for the development of highly effective plant-derived insecticides and control citrus Huanglongbing which mainly transmitted by D. citri.