Cucurbitacins: differential cytotoxicity, dereplication and first isolation from Gonystylus keithii.

A characteristic pattern of differential cytotoxicity of extracts of Iberis amara seeds, predominantly toward renal tumor, brain tumor, and melanoma cell lines in the NCI human disease-oriented tumor screening panel, was traced to cucurbitacins E [1] and I [2]. This same differential cytotoxicity profile was detected in extracts of Begonia plebeja and Gonystylus keithii. Computer-assisted recognition of these profiles was followed by a rapid chemical fractionation, thus permitting the efficient dereplication of those extracts containing cucurbitacins B [3] and D [4], respectively. This is the first report of cucurbitacins from the genus Gonystylus.