Ent-Pimaranes isolated from Flickingeria fimbriata and their activities

Two new and six known ent-pimaranes were isolated from Flickingeria fimbriata. One of them possesses a rare carbon skeleton. It is the first time such a compound with this specific carbon skeleton has been isolated from a natural source. The structure and absolute configuration were determined by NMR, MS, and X-ray diffraction analysis. The biosynthetic pathway of the rare skeleton was proposed and suggested a new pathway for these norent-pimarane analogues. All isolated compounds were screened for inhibitory activity against acetylcholinesterase (AChE). The compound 4 exhibits potent inhibitory effect on AChE with the 50% inhibitory concentration (IC50) being 5.8 mu M, which is close to that of the positive control (Huperzine A). This is the first report about inhibitory activity on AChE of ent-pimaranes.