Excisanin H, a Novel Cytotoxic 14,20-Epoxy-<i>ent</i>-Kaurene Diterpenoid, and Three New <i>e</i><i>nt</i>-Kaurene Diterpenoids from <i>Rabdosia</i> <i>e</i><i>xcisa</i>
A novel 14,20-epoxy-ent-kaurene diterpenoid, excisanin H (1), and three new ent-kaurenediterpenoids, 2-4, were isolated from aerial parts of Rabdosia excisa along with eight known ent-kaurenediterpenoids, 5-12. The structural elucidations were made using spectral (HREIMS, IR, (1)H, (13)C, and 2D NMR) methods. The absolute configuration of 1 was determined by demonstrating that oxidation of kamebakaurin