Structural elucidation of the polysaccharide from Sterculia apetala gum by a combination of chemical methods and NMR spectroscopy

The polysaccharide, isolated from Sterculia apetala, contains galactose, arabinose, xylose and uronic acids. These acid sugars are represented by Galacturonic acid, glucuronic acid and its 4-O-methyl derivative. Application of 1D- and 2D NMR spectroscopy to degraded products, obtained by acid hydrolysis and Smith-degradation processes, and to one oligosaccharide, led to confirm some structural features. Backbone of the structure is a galacturo-rhamnan. These residues are 4-O-linked. The branches are constituted of galactose, arabinose, xylose, rhamnose, β-d-glucuronic acid and its 4-O-methyl derivative. There were observed interesting homonuclear (proton–proton) and heteronuclear (proton–carbon) chemical shift correlations.