Structural features of pectic polysaccharide from Angelica sinensis (Oliv.) Diels

The structure of the pectic polysaccharide (ASP3) isolated from roots of Angelica sinensis (Oliv.) Diels was investigated using partial acid hydrolysis, enzymic digestion combined with methylation analysis, and further supported by 1H and 13C NMR spectroscopy techniques. The results indicated that ASP3 contained a backbone of linear homogalacturonan fragments as “smooth regions” and rhamnogalacturonan fragments as “hairy regions” with repeating unit of [→ 4)-α-d-GalpA-(1 → 2)-α-l-Rhap-(1 →]. A total of 58.8% rhamnopyranose residues in the backbone were substituted at O-4 position by the side chains. The side chains contained mainly β-1,6- and β-1,4-galactopyranan bearing 3,6- and 4,6-substituted β-d-galactopyranose residues as branched points and short α-1,5-arabinofuranan possessing 3,5-substituted α-l-arabinofuranose residues as branching points. In addition, β-1,6-galactopyranan side chains were highly branched with α-1,5-arabinofuranan carrying 3-O-substituents (1,3,6-Gal) and terminated by the α-arabinofuranose residues which form arabinogalactan.