Trichotomone, a new cytotoxic dimeric abietane-derived diterpene from Clerodendrum trichotomum

A novel dimeric diterpene (named trichotomone, 1) was isolated from the roots of the medicinal ornamental plant Clerodendrum trichotomum. Compound 1 is a rare phenolic ketal of a regular abietane derivative cyrtophyllone B and a rearranged abietane derivative containing a 17(15→16),18(4→3)-diabeo-abietane framework related to uncinatone. The structure was elucidated by extensive spectroscopic methods. The absolute configuration was defined by comparison of experimental and calculated electronic circular dichroism (ECD) spectra. Trichotomone (1) exhibited in vitro cytotoxicities against several human cancer cell lines (A549, Jurkat, BGC-823 and 293T WT) with IC50 values ranged from 7.51 to 19.38 μM.