Structural features of an arabinogalactan gum exudates from Spondias dulsis (Anacardiaceae)

The tree Spondias dulcis, located in Venezuela, exudes a light-brown gum. The polysaccharide, isolated from the original gum, contains galactose, arabinose, mannose, rhamnose, glucuronic acid, and its 4- O-methyl derivative. Application of chemical methods, in combination with 1D and 2D NMR spectroscopy afforded interesting structural features of the gum polysaccharide. The unequivocal presence of rhamnose in the polymer structure was confirmed by chemical and spectral data [ 1H (1.03 ppm); 13C (16.92 ppm)]. Also confirmed was the existence of 3- O- and 6- O-substitutes galactose residues by the spectral data correlations observed in Heteronuclear Multiple Quantum Coherence (HMQC) and Heteronuclear Multiple Bond Correlation (HMBC). Also observed were unequivocal resonances for β- d-glucuronic acid and its 4- O-methyl derivative, and the presence of 3- O-α- l-arabinofuranose and 3- O-β- l-arabinopyranose residues. Chemical and 1-D and 2-D NMR spectral data give a possible model for the backbone of the polysaccharide from Spondias dulcis gum.