Cytotoxicity-guided fractionation of the dichloromethane-methanol extract of the roots of Casearia arborea yielded five novel clerodane diterpenes, casearborins A-E (1-5), as well as cucurbitacin B. The presence of cucurbitacins glycosides was also detected. The absolute configuration of casearborin E was determined by X-ray crystallography.
Laboratory of Drug Discovery Research & Development, Developmental Therapeutics Program, Division of Cancer Treatment & Diagnosis, National Cancer Institute-FCRDC, Bldg. 1052, Rm. 121, Frederick, Maryland 21702-1201, USA.