Cytotoxic Clerodane Diterpenes from Casearia rupestris

Four new clerodane diterpenes, casearupestrins A-D (1-4), were isolated from the leaves of Casearia rupestris. Compounds 1 and 4 were acetylated to yield 2,7-di-O-acetylcasearupestrin A (5) and 2,6-di-O-acetylcasearupestrin D (6), All compounds were evaluated for cytotoxicity against a small panel of human cancer cell lines. Caseartipestrin A (1) exhibited the most potent activity against MDA/MB-435 (human Melanoma) and SF-295 (human glioblastoma) cells, superior to that of the standard drug:doxorubicin.