Cytotoxic ent-kaurane diterpenoids from Isodon racemosa (Hemsl) Hara

A new ent-kaurane diterpenoid racemosin A (1) and three known compounds, leukamenin E (2), glaucocalyxin A (3) and wangzaozin A (4), have been isolated from the leaves of Isocion racemosa (Hemsl) Hara. The new diterpenoidis identified as 14β-hydroxy-3β, 7α-acetoxy-ent-kaur-16-en-15-one on the basis of spectral data, especially by 2D NMR techniques. Compounds 1-4 show significant cytotoxic activity against Bel-7402 and HO-8910 cells in the range of 1.51-2.57 and 3.33-4.02 μg/mL, respectively. This may be due to the presence of conjugated exo-methylene systen in an ent-kaurane skeleton.