New bioactive clerodane diterpenoids from the roots of Casearia membranacea.

Bioassay-guided fractionation of the acetone extract of the roots of Casearia membranacea furnished three new clerodane diterpenes, caseamembrins S-U (1-3) and the known caseamembrin Q (4). Their structures were established by extensive spectroscopic analyses, especially 2D-NMR. Compounds 1-4 were tested against human tumor cells, including HeLa (cervical epitheloid carcinoma), DLD-1 (colon carcinoma), Daoy (medulloblastoma), and KB (oral epidermoid carcinoma) cell lines. Caseamembrin T (2) exhibited the most potent activity against Daoy cells (ED(50)=10 ng/ml), superior to that of the standard drug mitomycin.