Structural features of a polysaccharide from Astragalus membranaceus (Fisch.) Bge. var. mongholicus (Bge.) Hsiao

A polysaccharide Astragalus polysaccharide (APS) was obtained from the boiling water extract of Astragalus membranaceus (Fisch.) Bge. var. mongholicus (Bge.) Hsiao. The results of gas chromatography (GC) indicated that APS consisted of l-rhamnose (l-Rha), d-xylose (d-Xyl), d-glucose (d-Glc), and d-galactose (d-Gal) in the molar ratio of 1:4:5:1.5. Its molecular weight was determined to be 3.01 × 10(5) by high-performance gel filtration chromatography. The results of (1)H NMR and (13)C NMR spectral analysis indicated that APS had a linear backbone mainly consisting of 1,3-linked β-d-Gal residues with insertion of β-Glc, 1,6-linked α-Gal, 1,5-linked β-Xyl, 1,4-linked β-Gal, β-d-Gal, 1,2-linked α-Rha, 1,2,4-linked α-Rha residues. HSQC spectrum indicated that C-2 and C-6 may link with H.