Antibacterial spirooxindole alkaloids from Penicillium brefeldianum inhibit dimorphism of pathogenic smut fungi

<jats:p>Three new antibacterial spirooxindole alkaloids, spirobrefeldins A–C (1–3), together with four known analogs, spirotryprostatin M (4), spirotryprostatin G (5), 12β-hydroxyverruculogen TR-2 (6), and 12α-hydroxyverruculogen TR-2 (7), were isolated from terrestrial fungus <jats:italic>Penicillium brefeldianum.</jats:italic> All the new compounds were elucidated extensively by the interpretation of their NMR (1D and 2D) spectra and high-resolution mass data, and their absolute configurations were determined by computational chemistry and CD spectra. The absolute configurations of spiro carbon C-2 in spirotryprostatin G (5) and spirotryprostatin C in literature were reported as <jats:italic>S</jats:italic>, which were revised to <jats:italic>R</jats:italic> based on experimental and calculated CD spectra. All the compounds were evaluated for their antimicrobial activities toward <jats:italic>Pseudomonas aeruginosa</jats:italic> PAO1, <jats:italic>Dickeya zeae</jats:italic> EC1, <jats:italic>Staphylococcus epidermidis</jats:italic>, <jats:italic>Escherichia coli</jats:italic>, and <jats:italic>Sporisorium scitamineum</jats:italic>. Compound 7 displayed moderate inhibitory activity toward dimorphic switch of pathogenic smut fungi <jats:italic>Sporisorium scitamineum</jats:italic> at 25 μM. Compounds 3 and 6 showed weak antibacterial activities against phytopathogenic bacterial <jats:italic>Dickeya zeae</jats:italic> EC1 at 100 μM.</jats:p>