Bipoladien A, a Sesterterpenoid Containing an Undescribed 5/8/5/7 Carbon Skeleton from Bipolaris maydis

Bipoladiens A–E (1–5), five
new ophiobolin-derived
sesterterpenoids, and a known compound 6 (bipolaricin
R) were isolated from the cultures of the phytopathogenic fungus Bipolaris maydis. Their structures and absolute configurations
were elucidated based on comprehensive spectroscopic analyses, HRESIMS,
electronic circular dichroism (ECD) calculations, and single-crystal
X-ray diffraction analyses. Notably, compound 1 has an
undescribed tetracyclic 5/8/5/7 fused carbon skeleton, and compound 2 possesses a rare multicyclic caged ring system. The biosynthetic
pathway of 1 was proposed starting from 6 via a series of oxidation and cyclization reactions. Compound 6 showed excellent antiproliferation and apoptosis induction
effects against A549 cell line. Additionally, compounds 5 and 6 exhibited noticeable antimicrobial ability against Bacillus cereus, Staphylococcus aureus, and Staphylococcus epidermidis. These
findings not only developed the chemical and bioactivities diversities
of ophiobolin-sesterterpenoid but also provided an idea to boost the
application of natural products in the control of food pathogens.