LC–MS/MS-Guided Molecular Networking for Targeted Discovery of Undescribed and Bioactive Ophiobolins from Bipolaris eleusines

An
integrated purification procedure through the LC–MS/MS-based
molecular networking strategy combined with bioactive evaluation was
first ushered for discovering bioactive ophiobolins from Bipolaris eleusines. Ophiobolins were mainly dispersed
in five clusters, which were classified based on different ring systems
and functional groups. Nine undescribed ophiobolins (1–6 and 9–11)
and an undescribed natural product (8) along with two
known analogs (7 and 12) were isolated in
target. The undescribed structures were characterized by HR-ESI-MS,
NMR spectra, and X-ray diffraction experiments. Compounds 3–12 exhibited strong phytotoxic effects on green
foxtails by producing visible lesions, and compounds 1–10 and 12 displayed different levels
of cytotoxic activities against cancer cell lines B16, Hep G2, and
MCF-7, from which the possible structure–activity relationships
were then suggested. The results have supported that bioactivity-guided
molecular networking is an efficient strategy to expedite the discovery
of undescribed bioactive natural products.