Identification and characterization of a cytotoxic polysaccharide from the flower of Abelmoschus manihot

A low molecular weight polysaccharide was identified from the flower of Abelmoschus manihot (Linn.) Medicus, a popular herbal medicine also known as Flos A. manihot. The polysaccharide, AMPS-a, was obtained from the ethanol-extracted debris of Flos A. manihot by successive purification through DEAE-cellulose-52 and Sephadex G-100 column. AMPS-a has an estimated molecular weight of 8.8×10(3)Da and is mainly composed of β-d-glucose, α-d-mannose, α-d-galactose and α-l-fucose at a molar ratio of 1.00:0.91:2.14:1.09. The preliminary structural features were studied by hydrolysis-methylation analysis, GC-MS, FT-IR and (1)H and (13)C NMR spectroscopy. AMPS-a contains a backbone composed of repeating units of →6)α-d-Galp-(1→6)α-d-Manp-(1→6)α-d-Galp-(1→ with β-d-Glcp (1→3)α-Fucp-(1→ branching at O-3 of mannose. AMPS-a exhibited potent inhibitory effects on the proliferation of hepatic (SMMC-7721, HepG2) and gastric (MGC-803, MKN-45) cancer cells in vitro, and the sugar branches were indispensible for the cytotoxicity. Our work contributes to the first report of a novel cytotoxic polysaccharide from Flos A. manihot that may provide a potential source of anti-tumor agent.