Biological
control of plant pathogens is considered as one of the
green and effective technologies using beneficial microorganisms or
microbial secondary metabolites against plant diseases, and so microbial
natural products have played important roles in the research and development
of new and green agrochemicals. To explore the potential applications
for natural γ-lactam alkaloids and their derivatives, 26 γ-lactams
that have flexible substituent patterns were synthesized and characterized,
and their in vitro antifungal activities against
eight kinds of plant pathogens belonging to oomycetes, basidiomycetes,
and deuteromycetes were fully evaluated. In addition, the high potential
compounds were further tested using an in vivo assay
against Phytophthora blight of pepper to verify a
practical application for controlling oomycete diseases. The potential
modes of action for compound D1 against Phytophthora capsici were also investigated using
microscopic technology (optical microscopy, scanning electron microscopy,
and transmission electron microscopy) and label-free quantitative
proteomics analysis. The results demonstrated that compound D1 may be a potential novel fungicidal agent against oomycete
diseases (EC50 = 4.9748 μg·mL–1 for P. capsici and EC50 = 5.1602 μg·mL–1 for Pythium aphanidermatum) that can act on steroid biosynthesis,
which can provide a certain theoretical basis for the development
of natural lactam derivatives as potential antifungal agents.
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