Ent-Abietanoids Isolated from Isodon serra.

Four new ent -abietane diterpenoids, along with four known ones were isolated from the aerial parts of Isodon serra , a traditional Chinese folk medicine. The new diterpenoids were named as serrin K ( 1 ), xerophilusin XVII ( 2 ), and enanderianins Q and R ( 3 and 4 ), while the known ones were identified as rubescansin J ( 5 ), (3α,14β)-3,18-[(1-methylethane-1,1-diyl)dioxy]- ent -abieta-7,15(17)-diene-14,16-diol ( 6 ), xerophilusin XIV ( 7 ), and enanderianin P ( 8 ), respectively. Their structures were elucidated by extensive spectroscopic analysis and comparison with the literature. Compound 1 showed remarkable inhibitory activity towards NO production in LPS-stimulated RAW264.7 cells (IC50 = 1.8 μM) and weak cytotoxicity towards five human tumor cell lines (HL-60, SMMC-7721, A-549, MCF-7, SW480).