Evaluation of the phytotoxic and antifungal activity of C(17) ‐sesquiterpenoids as potential biopesticides

BACKGROUND: Natural products are a promising source for the development of new pesticides with alternative mechanisms of action. In this study, we evaluated the phytotoxic and antifungal activity of a novel family of natural C(17)‐sesquiterpenoids and performed a study of the effect caused by the elimination of the α‐methylene‐γ‐butyrolactone system and its importance to their biological activity. RESULTS: Many tested compounds exhibited a strong phytotoxic activity. Lappalone and pertyolide B were the most potent molecules from the tested group. Lappalone displayed a strong inhibition profile against selected weed species, reaching a half‐maximal inhibitory concentration (IC(50)) value of 5.0 μm against Echinochloa crus‐galli L. shoot and 5.7 μm against the germination rate of Amaranthus viridis L., as well as a good stimulation of the germination of Phelipanche ramosa L. Pertyolide B demonstrated excellent inhibition against Amaranthus viridis L. (IC(50): 56.7, 70.3 and 24.0 μm against the root and shoot growth, and germination rate, respectively) and Allium cepa L. (representative of the Liliaceae family, with IC(50) values of 25.3 and 64.4 μm against root and shoot growth). Regarding the antifungal activity, pertyolide B presented significant activity against Colletotrichum fragareae and Fusarium oxysporum with a minimum inhibitory concentration of 6.6 μg μL(−1). CONCLUSION: The bioassays revealed that frequently the presence of the α‐methylene‐γ‐butyrolactone system is not essential for the bioactivities of sesquiterpene lactones, and suggest that C(17)‐sesquiterpenoids may function through a different mechanism of action not related to the widely assumed Michael addition. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.