Monomeric and dimeric ent-kauranoid-type diterpenoids from rabdosia japonica and their cytotoxicity and anti-HBV activities.

Two new ent-kauranoid-type diterpenoids (1 and 2) and one new rare dimer of ent-kauranoids (3) with a cyclobutane ring by a [2+2] cycloaddition, together with nine known diterpenoids (4-12) were obtained from the aerial parts of Rabdosia japonica. Their chemical structures were established by 1D and 2D NMR techniques and mass spectrometry and by comparison with spectroscopic data reported. All ent-kauranoids were test for their cytotoxic effects against A549, HCT116, CCRF-CEM and HL-60 tumor cell lines. Compounds 1, 2, 4, 5, 7, 10 and 12 showed potent and selective cytotoxicity. In addition, some selected ent-kauranoids were test for their anti-HBV activities, and the results showed compound 8 had inhibitory effect on HBsAg with a 59% inhibition ratio at the concentration of 20μg/mL.