20(S)-Ginsenoside-Rf2, a novel triterpenoid saponin from stems and leaves of Panax ginseng Studies on the Minor Saponins from Leaves of Panax ginseng C.A.Meyer Chemical constituents in acid hydrolysates of total saponins from stems and leaves of Panax ginseng A new triterpene natural product from stems and leaves of Panax ginseng