Four highly oxygenated isopimarane-type diterpenes of Orthosiphon stamineus

Four highly oxygenated isopimarane-type diterpenes, named orthosiphols O, P and Q and nororthosiphonolide A, have been isolated from the aerial parts of Orthosiphon stamineus from Myanmar, together with three known diterpenes, orthosiphols D and E and orthosiphonone A. Their structures were determined on the basis of extensive spectral analysis. All the isolated compounds displayed mild antiproliferative activities against highly liver metastatic colon 26-L5 carcinoma and human HT-1080 fibrosarcoma cell lines.