Undobolins A–L, Ophiobolin-Type Sesterterpenoids from Aspergillus undulatus

Twelve previously undescribed ophiobolin-type sesterterpenoids, undobolins A–L (1–12), were isolated from Aspergillus undulatus, and their structures were elucidated by spectroscopic analysis, ECD calculations, and single-crystal X-ray diffraction experiments. Compound 1 was the second example of 20-nor-ophiobolin reported, while compounds 2–6 were notable for oxygenation of C-2, and compound 6 showed significant inhibitory activity against ConA-induced T lymphocyte proliferation with an IC50 value of 2.3 μM, which suggests a promising new direction in the quest for immunosuppressive agents.