Five novel highly oxygenated diterpenes of Orthosiphon stamineus from myanmar

Five novel highly oxygenated diterpenes, orthosiphols K (1), L (2), M (3), and N (4) and norstaminone A (5), were isolated from the aerial part of Ort hosiphon stamineus, together with three known diterpenes, orthosiphols A (6 ) and B (7) and neoorthosiphol A (8). Orthosiphol L (2) is an isopimarane-t ype diterpene with a hydroxyl group at C-12, which supports the biogenesis of staminane-type diterpenes, i.e., migration of a vinylic group from C-13 of isopimarane to C-12. Norstaminone A (5) has a staminane carbon framework and supports the biosynthetic pathway from staminols to norstaminols via s taminolactones. All the isolated compounds showed mild to weak antiprolifer ative activities toward highly liver metastatic colon 26-L5 carcinoma and h uman HT-1080 fibrosarcoma cell lines.