Abstract
Previous phytochemical studies of the bulbs of Ornithogalum saundersiae, an ornamental perennial plant native to South Africa, resulted in the isolation of 29 new cholestane glycosides, some of which were structurally unique and showed potent cytotoxic activity against cultured tumor cell lines. Therefore, we aimed to perform further phytochemical examinations of methanolic extracts obtained from Ornithogalum saundersiae bulbs, isolating 12 new cholestane rhamnosides (1–12) and seven known compounds (13–19). The structures of the new compounds (1–12) were identified via NMR-based structural characterization methods, and through a sequence of chemical transformations followed by spectroscopic and chromatographic analysis. The cytotoxic activity of the isolated compounds (1–19) and the derivatives (1a and 6a) against HL-60 human promyelocytic leukemia cells and A549 human lung adenocarcinoma cells was evaluated. Compounds 10–12, 16, and 17 showed cytotoxicity against both HL-60 and A549 cells. Compound 11 showed potent cytotoxicity with an IC50 value of 0.16 µM against HL-60 cells and induced apoptotic cell death via a mitochondrion-independent pathway.
Highlights
IntroductionOrnithogalum saundersiae (Baker), of the Asparagaceae (formerly Liliaceae) family, is an ornamental perennial plant native to South Africa
Ornithogalum saundersiae (Baker), of the Asparagaceae family, is an ornamental perennial plant native to South Africa
Fresh bulbs obtained from O. saundersiae were extracted with hot MeOH
Summary
Ornithogalum saundersiae (Baker), of the Asparagaceae (formerly Liliaceae) family, is an ornamental perennial plant native to South Africa. Our systematic phytochemical examinations of a methanolic extract of Ornithogalum saundersiae bulbs resulted in the isolation of 29 new cholestane glycosides including 16,23-epoxy-5β-cholestane glycoside [1], 22-homo-23-norcholestane glycosides [2,3,4,5,6], and polyoxycholestane glycosides [7,8,9,10,11,12]. Especially those with an aromatic acyl group, showed potent cytotoxic activity against cultured tumor cell lines, including HL-60 human promyelocytic leukemia cells. We first isolated 3β,16β,17α-trihydroxycholest-5-en-22-one 16-O-(2-O-4-methoxybenzoyl-β-Dxylopyranosyl)-(1→3)-(2-O-acetyl-α-L-arabinopyranoside), an acylated cholestenol glycoside commonly called OSW-1, from O. saundersiae bulbs in 1992 [9]. The cytotoxic activity of OSW-1 against tumor cells was approximately 10–100 times more potent than that of clinically used anticancer agents, with low toxicity against healthy cells [10]. The structural diversity and potent cytotoxic activity of the cholestane glycosides obtained from O. saundersiae bulbs prompted us to carry out a further
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