Rearranged abietane diterpenoids from the roots of Clerodendrum trichotomum and their cytotoxicities against human tumor cells

►Rearranged abietane diterpenoids were isolated from Clerodendrum trichotomum. ► The absolute configuration of compound 1 was ascertained. ► Compound 6 possessed a rare 3,4-epoxy moiety in its structure. ► Some isolates exhibited remarkable cytotoxic effects against human cancer cells.