17-Norpimaranes and (9βH)-17-Norpimaranes from the Tuber of Icacina trichantha.

Seven new 17-norpimarane and (9βH)-17-norpimarane diterpenoids, icacinlactones A-G (1-7), were isolated from the tuber of Icacina trichantha. The structures were elucidated by spectroscopic and HRMS techniques, and the absolute configuration of 2 was determined by means of X-ray crystallographic analysis. Compounds 1-7, as well as four known related structures, were evaluated for cytotoxic activity against MDA-MB-435 (human melanoma cancer), MDA-MB-231 (human breast cancer), and OVCAR3 (human ovarian cancer) cell lines. Several of these natural products displayed significant cytotoxic activity, with humirianthenolide C being the most active.