Cytotoxic steroidal saponins from Panicum turgidum Forssk

Three new bidesmosidic cholestane-type steroidal glycosides, 16-o-beta-D-glucopyranosyl-cholest-5-en-3 beta,16 beta-dio1-22-one-3-o-alpha-L-rhamnopyranosyl-(1 -> 2)-o-[beta-D-glucopyranosyl(1 -> 4)]-o-beta-D-glucopyranoside (1), 16-o-beta-D-glucopyranosylcholest-5-en-3 beta,16 beta-diol-22-one-3-o-alpha-L-rhamnopyranosyl-(1 -> 2)-o-beta-D-glucopyranoside (2), and 16-o-beta-D-glucopyranosylcholestan-3 beta,16 beta-dio1-6,22-dione-3-o-alpha-L-rhainnopyranosyl-(1 -> 2)-o-beta-D-glucopyranosid 3) were isolated from a methanolic extract of Panicum turgidum. In addition four known compounds, pennogenin 3 beta-o-alpha-L-rhamnopyranosyl-(1 -> 2)-O-[alpha-L-rhamnopyranosyl-(1 -> 4)-o-alpha-L-rhamrtopyranosyl-(1 -> 4)]-o-beta-D-glucopyranoside (4), yamogeriin 3 beta-o-alpha-L-rhamnopyranosyl-(1 -> 2)-o-[alpha-L-rhamiiopyranosyl-(1 -> 4)]-o-beta-D-glucopyranoside (5), yamogenin 3 beta-O-alpha-L-rhamnopyranosyl-(1 -> 2)-O-[alpha-L-rhamnopyranosyl-(1 -> 4)-o-alpha-L-rhamnopyranosyl-(1 -> 4)]-o-beta-D-glucopyranoside (6), and pennogenin 3 beta-o-alpha-L-rhamnopyranosyl-(1 -> 2)-o-[alpha-L-rharrmopyranosyl-(1 -> 4)]-o-beta-D-glucopyranoside (7) were also isolated and characterized. Their structures were established using extensive spectroscopic methods including 1D and 2D NMR and HRESIMS. The isolated compounds were screened for cytotoxicity towards a panel of mammalian cell lines and 4-7 were found to be cytotoxic.