Phomanolides C-F from a Phoma sp.: Meroterpenoids Generated via Hetero-Diels-Alder Reactions.

Phomanolides C-F (1-4), four new meroterpenoids, were isolated from a Phoma sp., together with the known phomanolides A (5) and B (6); their structures were elucidated primarily by NMR experiments. The absolute configurations of 1-3 were assigned by electronic circular dichroism calculations, and that of 4 was established by X-ray diffraction analysis using Cu Kα radiation. Compounds 1-3 incorporate an unprecedented trioxa[4.4.3]propellane subunit in their skeletons. Compounds 2 and 4 were weakly cytotoxic.