To discover novel fungicidal agrochemicals for treating wheat scab, 39 novel camphor sulfonohydrazide/sulfonamide derivatives 4a−4t and 6a−6s were designed and synthesized. In the in vitro antifungal/antioomycete assay, compounds 4g, 4n, and 4o displayed significant inhibitory activities against Fusarium graminearum, Botryosphaeria dothidea, and Phytophthora capsici. Among them, 4n exhibited the best antifungal activity against F. graminearum with an EC 50 value of 0.41 mg/L, which was at the same level as that of pydiflumetofen. The in vivo experiment revealed that 4n presented excellent protective and curative efficacy toward F. graminearum. In the antifungal mechanism study, 4n could increase the cell membrane permeability and reduce the exopolysaccharide and ergosterol content of F. graminearum. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses revealed that 4n could significantly damage the surface morphology and the cell ultrastructure of mycelia to interfere with the growth of F. graminearum. Furthermore, 4n exhibited potent succinate dehydrogenase (SDH) inhibitory activity in vitro with an IC 50 value of 3.94 μM, which was equipotent to pydiflumetofen (IC 50 = 4.07 μM). The molecular dynamics simulation and docking study suggested that compound 4n could well occupy the active site and form strong interactions with the key residues of SDH. The above-mentioned results demonstrated that the title camphor sulfonohydrazide/sulfonamide derivatives could be promising lead compounds for further succinate dehydrogenase inhibitor (SDHI) fungicide development.

BACKGROUND To explore further potential natural product‐based antifungal agents, a series of novel nopol‐based carboxamide and hydrazide derivatives containing a natural pinene structure were designed, synthesized, and evaluated for their inhibitory activities against seven phytopathogenic fungi and oomycetes. RESULTS The bioassay results indicated that some compounds exhibited good inhibitory activities against Gibberella zeae, Sclerotinia sclerotiorum, and Phytophthora capsici. Among them, compound 3h displayed excellent in vitro activities against G. zeae, with EC50 values of 1.09 mg L−1, which was comparable with the commercial fungicides bixafen and carbendazim (median effective concentration [EC50] = 1.21 and 0.89 mg L−1, respectively). Notably, in vivo bioassay results suggested that compound 3h also showed prominent protective and curative effects (95.6% and 94.2%) at 200 mg L−1 against G. zeae. The scanning electron microscopy study indicated that compound 3h could destroy the morphological integrity of G. zeae hyphae. The in vitro enzyme inhibitory bioassay revealed that compound 3h exhibited potent inhibitory activity against laccase with median inhibitory concentration (IC50) values of 4.93 μm, superior to positive control cysteine (IC50 = 35.50 μm), and its binding modes with laccase were elucidated by molecular docking study. In addition, the fluorescent imaging of the dansylamide‐labeled derivatives 8 on wheat leaf epidermal cells and the hyphae of G. zeae revealed that this class of hydrazide derivatives could readily permeate into wheat leaves and reached the laccase target in fungal cells. CONCLUSION Some nopol‐based hydrazide derivatives exhibited excellent anti‐G. zeae activity and laccase inhibitory activity, which merits further development as a new fungicide candidate for controlling Fusarium head blight. © 2023 Society of Chemical Industry.

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Twelve novel camphor sulfonamide derivatives 2a -2l were synthesized and characterized by 1 H-NMR, 13 C-NMR and HRMS spectra. The anti-fungal/oomycete activity bioassay showed that some of the title compounds displayed moderate to good anti-fungal/oomycete activities against B. dothidea and P. capsici. Compound 2d exhibited the best in vitro antifungal activity toward B. dothidea. The in vivo experiment revealed that compound 2d possessed considerable anti-B. dothidea effect at 200 mg/L. Mechanism study showed that compound 2d could increase the cell membrane permeability. In addition, the in vitro enzyme inhibition assay and molecular docking results indicated that compound 2d could be a potential SDH inhibitor.

To discover novel laccase inhibitors as potential fungicides, twenty-six novel L-menthol hydrazide derivatives were designed and synthesized. In the in vitro antifungal assay, most of the target compounds displayed pronounced antifungal activity against Sclerotinia sclerotiorum, Fusarium graminearum, and Botryosphaeria dothidea. Especially, the EC 50 of compounds 3 b and 3 q against B. dothidea was 0.465 and 0.622 mg/L, which was close to the positive compound fluxapyroxad (EC 50 = 0.322 mg/L). Scanning electron microscopy (SEM) analysis showed that compound 3 b could significantly damage the mycelial morphology of B. dothidea. In vivo antifungal experiments on apple fruits showed that 3 b exhibited excellent protective and curative effects. Furthermore, in the in vitro laccase inhibition assay, 3 b showed outstanding inhibitory activity with the IC 50 value of 2.08 μM, which is much stronger than positive control cysteine and PMDD-5Y. These results indicated that this class of L-menthol derivatives could be promising leads for the discovery of laccase-targeting fungicides.