A series of novel 1,3-benzodioxole-pyrimidine
derivatives were
designed and synthesized. The in vitro bioassay indicated
that compounds 4e, 4g, 4n, 5c, and 5e displayed excellent fungicidal activities
against test fungal strains. Especially, in the in vitro experiments, 5c exhibited a broad spectrum of fungicidal
activity against Botrytis cinerea, Rhizoctonia solani, Fusarium oxysporum, Alternaria solani, and Gibberella zeae with EC50 values of 0.44,
6.96, 6.99, 0.07, and 0.57 mg/L, respectively, which were significantly
more potent than those of positive control boscalid (EC50: 5.02, >50, >50, 0.16, and 1.28 mg/L). In vivo testing
on tomato fruits and leaves showed that 5c displayed
considerable protective and curative efficacy against A. solani. Scanning electron microscopy analysis
indicated that 5c possessed a strong ability to destroy
the surface morphology of mycelia and seriously interfere with the
growth of the fungal pathogen. In the in vitro enzyme
inhibition assay, 5c exhibited pronounced succinate dehydrogenase
(SDH) inhibitory activity with an IC50 value of 3.41 μM,
equivalent to that of boscalid (IC50: 3.40 μM). In
addition, fluorescence quenching experiment further confirmed the
strong interaction of 5c with SDH. Through chiral resolution, 5c was separated into two enantiomers. Among them, (S)-5c exhibited stronger fungicidal activity
(EC50: 0.06 mg/L) and SDH inhibitory (2.92 μM) activity
than the R-enantiomer (EC50: 0.17 mg/L
and SDH IC50: 3.68 μM), which was in accordance with
the molecular docking study (CDOCKER Interaction Energy for (R)-5c and (S)-5c: −28.23 and −29.98 kcal/mol, respectively). These
results presented a promising lead for the discovery of novel SDHIs
as antifungal pesticides.