UPLC-Q-TOF-MS/MS analysis of ophiobolins sesterterpenoids and bioactive analogs from Bipolaris eleusines

In order to elucidate the mass fragmentation patterns and unveil more undescribed ophiobolin analogs, the mass fragmentation patterns of ophiobolins were analyzed based on UPLC-Q-TOF-MS/MS experiments. Different kinds of rearrangements (including McLafferty rearrangement) were the main cleavage patterns. Twenty-six (9-31) analogs were then tentatively characterized based on their mass analysis, and three undescribed ophiobolins (6-8) and a known analogue (5) were isolated in target. Compound 5 possesses a rare polycyclic carbon skeleton only recently reported, and compound 6 contains an undescribed lactone ring system fused with A/B ring at C-3/C-21, whereas compounds 7 and 8 have a peroxyl group in the side chain, which is the first reported in all ophiobolins. Compounds 5 and 7 displayed significant cytotoxicity against MCF-7 cancer cells.