Discovery of novel D/L-camphor derivatives containing oxime ester as fungicide candidates: Antifungal activity, structure-activity relationship and preliminary mechanistic study

To develop new environmentally friendly fungicides, we designed and synthesized a novel series of D/L-configured camphor oxime ester derivatives based on the natural product camphor as a lead compound. We investigated the in vitro antifungal activity of these compounds against six common plant pathogenic fungi. Among them, compounds B1-6, B1-17 and B2-6 displayed great in vitro activity against Rhizoctonia solani with EC₅₀ values of 7.28, 4.64, and 7.62 μg/mL. The HOMO and LUMO calculations indicated that strong electron-withdrawing halogen elements exhibit better activity compared to electron-donating alkyl groups. Preliminary mechanistic studies, using SEM and TEM, indicated that compound B1-17 induced disordered entanglement of hyphae, shrinkage of hyphal surfaces, and vacuole swelling and rupture, which disrupted normal hyphal growth. Additionally, compound B1-17 induced the production and accumulation of ROS, disrupted MMP, and effectively inhibited the germination and formation of sclerotia in Rhizoctonia solani. These compounds hold potential as new antifungal agents for further research.