(9βH)-Pimaranes and Derivatives from the Tuber of Icacina trichantha

New 17-nor-pimaranes (1, 2), (9βH)-pimaranes (3, 4), and 17-nor-(9βH)-pimarane (5) were isolated from the tuber of Icacina trichantha. The structures were elucidated based on spectroscopic and HRMS data. The absolute configurations of 3 and 5 were determined by single-crystal X-ray diffraction. Compound 5 possesses a unique 19,20 - lactone moiety. Compound 3 showed cytotoxicity against MDA-MB-435 (human melanoma cancer) cells with an IC50 value of 7.04 ΜM. A plausible biogenetic pathway for compounds 1-5 is proposed.