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.

The new ent-kaurane diterpenoid weisiensin C (1) (1α,7α,14β ,18,20-pentahydroxy-ent-kaur-16- en-15-one), together with four known ent-kaurene diterpenoids, glaucocalyxin A (2), kamebanin (3), macrocalyxin D (4), and excisanin K (5), was isolated from the leaves of Isodon weisiensis C.Y. Wu. The structure of the new constituent (1) was elucidated by spectroscopic methods and confirmed by single-crystal X-ray diffraction.

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A new ent-kaurane diterpenoid, weisiensin B (1), was isolated from the leaves of Isodon weisiensis C. Y. Wu, along with four known ones, kamebanin (2), kamebacetal A (3), macrocalyxin D (4) and excisanin D (5). Their structures were determined by spectroscopic means. Compound 1-4 showed significant cytotoxic activity against Bel-7402 and HO-8910 cells.

Three new cytotoxic ent-kaurane diterpenoids, (1 alpha,7 alpha,14 beta)-1,7,14-trihydroxy-ent-kaur-16-en-15,18-dione (1), (1 alpha,7 alpha,140 beta)-1,7,14,18,20-pentahydroxy-ent-kaur-16-en-15-one (2), and (3 beta,7 alpha,14 beta)-3,7,14-tris(acetyloxy)ent-kaur-16-en-15-one (3), were isolated from Isodon weisiensis C. Y. Wu. Their structures were elucidated by spectroscopic methods, including 2D-NMR techniques, and the crystal structure of 1 was determined by single-crystal X-ray-diffraction analysis. The chosen crystal of 1 was orthorhombic, space group P2(1)2(1)2(1), and there were two molecules with little difference in bond length and bond angle in the least-asymmetry unit. Compounds 1-3 showed significant cytotoxic activities against human-cancer cell lines Bel-7402 and HO-8910.

A new ent-kaurane diterpenoid, excisoidesin (1), was isolated from the acetone extract of the leaves of Isodon excisoides (Sun ex C. H. Hu) C. Y. Wu et H. W. Li, along with kamebacetal B (2), glaucocalyxin A (3), leukamenin E (4), kamebanin (5) and wangzaozin A (6). The structure of the new compound was determined as 7α,14β,18-trihydroxy- ent-kaur-16-en-3,15-dione by spectroscopic methods. Compound 1–6 showed significant cytotoxic activity against human tumor Bel-7402 cells.