Design, Synthesis, and Antifungal Activity Evaluation of Novel Hydrazide-Containing L-Perillaldehyde Derivatives as Potential Fungicides

In this study, 36 novel hydrazide-containing L-perillaldehyde derivatives were designed, synthesized, and evaluated for their antifungal activity. In the in vitro antifungal assays, most of the target compounds exhibited remarkable antifungal activity. Notably, compound C4 displayed exceptional antifungal activities against Rhizoctonia solani (EC₅₀ = 0.260 μg/mL), Fusarium graminearum (EC₅₀ = 0.480 μg/mL), Sclerotinia sclerotiorum (EC₅₀ = 0.240 μg/mL), and Valsa mali (EC₅₀ = 0.512 μg/mL), outperforming carbendazim, which showed EC₅₀ values of 0.651, 0.804, 0.520, and 0.898 μg/mL, respectively. Meanwhile, in vivo assays against R. solani and S. sclerotiorum revealed compound C4's potential as a novel agricultural antifungal agent. In the investigation of the antifungal mechanism, scanning electron microscopy and transmission electron microscopy observations revealed that compound C4 induced significant morphological alterations in R. solani mycelia, including mitochondrial swelling and rupture, thereby inhibiting mycelial growth. Determination of cellular content leakage and propidium iodide (PI) staining experiments indicated that compound C4 compromised the integrity of the R. solani cell membrane, leading to cytoplasmic efflux and, subsequently, inhibiting normal mycelial development. The detection of reactive oxygen species indicated that the antifungal activity of compound C4 may stem from inducing accumulation of reactive oxygen species within cells. The mitochondrial membrane potential detection demonstrated that compound C4 could decrease the mitochondrial membrane potential, thereby damaging mitochondria. Furthermore, compound C4 (IC₅₀ = 14.5 μg/mL) exhibited potent succinate dehydrogenase (SDH) inhibitory activity comparable to that of boscalid (IC₅₀ = 12.6 μg/mL). Molecular dynamics simulations confirmed that compound C4 could establish strong interactions with key residues of SDH. These results offer significant insights and guidance for the development of novel antifungal agents.