Structural studies of the pectic polysaccharide from Siberian fir (Abies sibirica Ledeb.)

The pectic polysaccharide named abienan AS-A was isolated from the wood greenery of Abies sibirica using dilute hydrochloric acid (pH 4.0) at 70 °C. The structure of abienan AS-A was elucidated using sugar composition analysis, ion-exchange chromatography and partial acid hydrolysis followed by NMR spectroscopy. The linear region of abienan AS-A was shown to contain linear 1,4-α-d-galactopyranosyluronan partially substituted with methyl esters or 3-O-acetyl groups and rhamnogalacturonan blocks consisting of 1,4-α-d-galacturonan partially substituted with methyl ester groups and connected by 2-O-substituted α-rhamnopyranose residues. The branched region of abienan AS-A was found to be made of RG-I. The side chains of RG-I were shown to contain 1,4-β-galactan and branched arabinan. Some 4-O-substituted β-galactopyranose residues were shown to be attached to the 4-position of the 2-O-substituted α-rhamnopyranose residues of the RG-I backbone. The arabinan groups were made up of a 1,5-linked α-l-arabinofuranan backbone that was 3-O-, 2-O-, and 2,3-di-O-substituted with the terminal and 1,3-linked α-l-arabinofuranose residues.