Abstract: The primary structure of polysaccharides from leaves of Gynura davaricata (L.) DC (GDPs) was characterized by gas chromatography, periodate oxidation reaction, Smith reaction, partially acid hydrolysis and 13C-NMR. Congo red test and X-ray diffraction were applied to explore their advanced structures. The inhibitory activity against α-glucosidase of GDPs was also investigated. GC analysis revealed that GDPs-1 was composed of D-Fru, L-Rha, L-Ara, D-Xyl, D-Man, D-Glu and D-Gal with a molar ratio of 0.2:0.4:1:1:1:2:7 and GDPs-2 of L-Ara, D-Man, D-Glu and D-Gal with a molar ratio of 0.4:2:2:0.1. Periodate oxidation reaction, Smith reaction, partially acid hydrolysis and 13C-NMR suggested that GDPs-1 had a backbone of α-(1→2)-linked galactose residues with branches composed of α-(1→3)-linked-Xyl, α-(1→2)-linked-Glu, α-(1→3)-linked- Man and Me-α-Araf, while GDPs-2 had a backbone of α-(1→3)-linked mannose residues with branches composed of α-(1→2)- linked-Glu and α-(1→6)-Glu. The results of Congo red test and X-ray diffraction showed that there was a stable triple spiral structure in GDPs-2 and both polysaccharides had poor molecular regularity. The polysaccharides showed extremely low inhibitory activities against α-glucosidase, which suggest that it is not relevant to the mechanism of glucose modulation.

Key words: Gynura davaricata (L.)DC, polysaccharide, structure characterization, inhibitory activity on α-glucosidase