Synthesis, antifungal activity, and molecular simulation study of nootkatone-based thiazole-hydrazone compounds as novel succinate dehydrogenase inhibitor.

Background: Plant diseases cause huge losses in agriculture worldwide every year, but the prolonged use of current commercial fungicides has led to the development of resistance in plant pathogenic fungi. Therefore, there is an urgent need to develop new, efficient, and green fungicides.

Results: Twenty-three nootkatone-based thiazole-hydrazone compounds were designed, synthesized, and characterized by Fourier-transform infrared (FTIR), proton (H) nuclear magnetic resonance (NMR), carbon-13 (C) NMR, and high-resolution mass spectrometry (HRMS). The antifungal activities results showed that all the target compounds displayed certain antifungal activity against eight tested fungi. Among them, target compounds 3a (88.7%), 3b (92.5%), 3d (88.7%), 3f (84.9%), 3j (88.7%), and 3l (92.5%) were comparable or superior to the positive control boscalid (88.7%) in their inhibitory activities against Physalospora piricola. Meanwhile, target compound 3l had half maximal effective concentration (EC) values of 18.0172, 18.8236, 16.5914, 18.5044, and 16.5660 μg/mL against Fusarium oxysporum f. sp. cucumerinum, Alternaria solani, Gibberella zeae, Bipolaris maydis, and Colleterichum orbicalare, respectively, exhibiting outstanding and broad-spectrum fungicidal activity. Moreover, a three-dimensional quantitative structure-activity relationship (3D-QSAR) study was carried out to investigate the relationship between the molecular structures of target compounds 3a-3w and their antifungal activity. Furthermore, the target compound 3l [half maximal inhibitory concentration (IC) = 4.936 μmol/L] showed significantly better inhibitory activity against succinate dehydrogenase (SDH) than boscalid (IC = 6.631 μmol/L). The possible binding mode between target compound 3l and homology-modeling built SDH, was also explored by molecular docking.

Conclusion: Target compound 3l deserved further study as the promising candidate for the development of novel SDH inhibitor. © 2025 Society of Chemical Industry.