Structural identification of methyl protodioscin metabolites in rats' urine and their antiproliferative activities against human tumor cell lines

Methyl protodioscin (MPD), a furostanol saponin, is a preclinical drug shown potent antiproliferative activities against most cell lines from leukemia and solid tumors. The metabolites of MPD in rats' urine after single oral doses of 80 mg/kg were investigated in this research. Ten metabolites were isolated and purified by liquid-liquid extraction, open-column chromatography, medium-pressure liquid chromatography, and preparative high-performance liquid chromatography. The structural identification of the metabolites was carried out by high resolution mass spectra, NMR spectroscopic methods including H-1 NMR, C-13 NMR and 2D NMR, as well as chemical ways. The 10 metabolites were elucidated to be dioscin (M-1), pregna-5,16-dien-3 beta-ol-20-one-O-alpha-L-rhamnopyranosyl-(1 -> 2)-[alpha-L-rhamnopyranosyl-(1-4)]-beta-D-glucopyranoside (M-2), diosgenin (M-3), protobioside (M-4), methyl protobioside (M-5), 26-O-beta-D-glucopyrannosyl(25R)-furan-5-ene-3 beta, 22 alpha, 26-trihydroxy-3-O-alpha-L-rhamnopyranosyl-(1 -> 4)-beta-D-glucopyranoside(M-6), 26-O-beta-D-glucopyranosyl(25R)-furan-5-ene-3 beta, 26-dihydroxy-22-methoxy-3-O-alpha-L-rhamnopyranosyl-(1 -> 4)-beta-D-glucopyraooside (M-7), prosapogenin A of dioscin (M-8), prosapogenin B of dioscin (M-9), and diosgenin-3-O-beta-D-glucopyranoside (M-10), respectively. M-1 was the main urinary metabolite of MPD in rats. Some metabolites showed potent antiproliferative activities against HepG2, NCI-H460, MCF-7 and HeLa cell lines in vitro. (c) 2006 Elsevier Inc. All rights reserved.