Isolation, Structural Elucidation, and Cytotoxicity of Three New ent-Kaurane Diterpenoids from Isodon japonica var. glaucocalyx

Abstract

Three new ent-kaurane diterpenoids, glaucocalyxin H (1), glaucocalyxin I (2), and glaucocalyxin J (3), together with four known diterpenoids (4-7), were isolated from the leaves of Isodon japonica Hara var. glaucocalyx. Their structures were elucidated by spectroscopic analysis, and the structures of compounds 2 and 3 were further confirmed by X-ray crystallographic analysis. Compounds 1, 4, and 5 were evaluated for their cytotoxicity in vitro against CE-1, U87, A-549, MCF-7, Hela, K-562, and HepG-2 human tumor cell lines. Compound 1 showed potent inhibitory activities against six tumor cell lines with IC₅₀ values ranging from 1.86–10.95 µM, and compounds 4 and 5 exhibited significant selective cytotoxicity on seven tumor cell lines.

Key words

Labiatae - Isodon japonica Hara var. glaucocalyx - ent-kaurane diterpenoid - cytotoxicity

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