ent-Kaurane- and ent-pimarane-type diterpenoids from Siegesbeckia pubescens and their cytotoxicity in Caki cells.

ent-Kaurane- and ent-pimarane-type diterpenoids were isolated from the methanol extract of Siegesbeckia pubescens by column chromatography. Their structures were elucidated as ent-16α H,17-hydroxy-kau­ran-19-oic acid (1), ent-4,17-dihydroxy-16α -methyl-kau­ran-19-oic acid (2), ent-16β ,17-dihydroxy-kauran-19-oic acid (3), kirenol (4) and ent-16β ,17,18-trihydroxy-kauran­19-oic acid (5) by spectral analysis. The cytotoxicity of these compounds in Caki cells was assayed by a cell counting kit. Only one group treated with kirenol (4), an entpimarane-type diterpenoid, showed the inhibition of the cell growth in Caki cells.