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

Abstract The roots of the medicinal ornamental plant Clerodendrum trichotomum yielded a series of rearranged abietane diterpenoids, including three 17(15 → 16)- abeo -abietane ( 1 – 3 ) and three 17(15 → 16),18(4 → 3)- diabeo -abietane ( 4 – 6 ) derivatives. Their structures were elucidated by means of spectroscopic methods. The absolute configuration of (10 R ,16 R )-12,16-epoxy-11,14,17-trihydroxy-6-methoxy-17(15 → 16)- abieta -5,8,11,13-tetraene-7-one ( 1 ) was deduced by a combination of single crystal X-ray diffraction analysis and the observed Cotton effects in its circular dichroism (CD) spectrum. All isolates were tested for their cytotoxicities against five human cancer cell lines (BGC-823, Huh-7, KB, KE-97, and Jurkat). Among them, compounds 4 , 6 , 9 , 10 , 12 , and 14 , each possessing a common 17(15 → 16),18(4 → 3)- diabeo -abietane framework, were found to have remarkable cytotoxic effects with IC 50 values ranging from 0.83 to 50.99 μM.