Simplifusidic acids A–K (1–11), 11 new fusidane-type nortriterpenoids,
were isolated from the
marine-derived fungus Simplicillium sp. SCSIO 41513.
Compound 1 possessed an unprecedented fusidane triterpene
skeleton with a 6/6/7/5/5 polycyclic system. Their structures were
elucidated by spectroscopic methods, and their absolute configurations
were further determined by quantum chemical calculations of ECD spectra,
comparison of experimental ECD spectra, and single-crystal X-ray diffraction
analysis. Compound 9 showed strong antibacterial activity
toward Staphylococcus aureus with an MIC value of
0.078 μg/mL. Their structure–bioactivity relationship
was also discussed.