Icacinlactone H and Icacintrichantholide from the Tuber of Icacina trichantha

The 17-norpimarane diterpene is a small group of natural products. A new member, icacinlactone H (1), and a new rearranged 17-norpimarane with an unprecedented carbon skeleton, icacintrichantholide (2), were isolated from Icacina trichantha. Their structures including the absolute configuration were elucidated by spectroscopic analysis, single-crystal X-ray diffraction, and electronic circular dichroism analysis. A plausible biogenetic pathway for 1 and 2 is proposed. Both 1 and 2 showed no significant activity against herpes simplex viruses HSV-1 and HSV-2 as well as the Epstein–Barr virus at 50 μM.