Two novel ent-kauranoid diterpenoids from Isodon japonica Leaves

Two novel ent-kaurane diterpenoids, taihangjaponicain A (1), and taihangjaponicain B (2), and nine known diterpenoids, epinodosin (3), oridonin (4), epinodosinol (5), lasiokaurin (6), 1α-O-β-D-glucopyranosylenmenol (7), lasiodonin (8), rabdosichuanin D (9), shikokianin (10) and rabdoternin A (11) were isolated from I. japonica leaves. The structures of the two new compounds were elucidated using 1-D and 2-D NMR spectroscopy. Compounds 1 and 3-11 were tested against HL-60, HO-8910 and A-549 human tumor cells. Compounds 4, 6 and 10 showed significant cytotoxicity against HL-60 cells with IC 50 values of 4.6, 2.0 and 3.4 μM, respectively, and against A-549 cells with IC 50 values of 17.5,11.4 and 18.8 μM, respectively. Compound 6 exhibited moderate cytotoxicity against HO-8910 cells with an IC 50 value of 17.9 pM.