Cytotoxic <i>ent</i> -abietane diterpenoids from the leaves of <i>Croton crassifolius</i>

Two new <i>ent</i>-abietane diterpenoids, 2<i>β</i>,15-dihydroxy-<i>ent</i>-abieta-7,13-dien-3-one (<b>1</b>) and 6<i>β</i>,13<i>α</i>-dihydroxy-<i>ent</i>-abieta-8(14)-en-3-one (<b>2</b>), together a known <i>ent</i>-abietane diterpenoid 3<i>α</i>,7<i>β</i>-dihydroxy-<i>ent</i>-abieta-8,11,13-triene (<b>3</b>), were isolated from the 80% acetone extract of the leaves of <i>Croton crassifolius</i>. The structures of the new compounds were elucidated by spectral methods such as 1D and 2D (¹H-¹H COSY, HMQC, and HMBC) NMR spectroscopy, as well as high resolution mass spectrometry. The isolated compounds were tested <i>in vitro</i> for cytotoxic activity against five urologic carcinoma cell lines. Consequently, compound <b>3</b> exhibited some cytotoxicities against all the tested tumor cell lines with IC₅₀ value less than 20.0 μM.