Abietane Diterpenoids from Clerodendrum bungei

Five new naturally occurring abietane diterpenoids (1-5) along with three known diterpenoids (6-8) were isolated from an acetone-soluble extract of the roots of Clerodendrum bungei. The structures of the new compounds were elucidated on the basis of spectroscopic analysis and chemical methods. In addition, all compounds were evaluated for cytotoxic activity against the cultured B16 (murine melanoma), HGC-27 (human gastric), and HEK-293 (human epithelial kidney) cell lines. Uncinatone (7) exhibited moderate cytotoxicity, inhibited cell proliferation, and induced cell-cycle G(2)/M phase arrest.