Ophiobolins P-T, five new cytotoxic and antibacterial sesterterpenes from the endolichenic fungus Ulocladium sp.
Five ophiobolane sesterterpenes, ophiobolins P-T, and three known compounds, 6-epi-21,21-O-dihydroophiobolin G, 6-epi-ophiobolin G and 6-epi-ophiobolin K, were isolated from the acetone extract of the endolichenic fungus Ulocladium sp. by using OSMAC method. Their structures were elucidated on the basis of spectroscopic analysis. The absolute configuration of the 18,19-diol moieties in ophiobolin Q was assigned using the Frelek's method. The cytotoxic effects on KB and HepG2 cell lines, antibacterial activity against Bacillus subtilis, methicillin-resistant Staphylococcus aureus, and Bacille Calmette-Guerin were evaluated for all isolated compounds. Ophiobolin T and 6-epi-ophiobolin G exhibited the most potent cytotoxic activity against HepG2 with IC₅₀ of 0.24 and 0.37 μM, respectively. In antibacterial assay, ophiobolins P and T showed moderate antibacterial activity against B. subtilis and meticillin-resistant S. aureus. Ophiobolin T also displayed moderate antibacterial activity against the Bacille Calmette-Guerin strain.