Studies on uronic acid materials. Part XVII. Some structural features of Acacia senegal gum (gum arabic)

Abstract

Acacia Senegal gum is subjected to seven successive Smith degradations. The O-methyl derivatives of each of the polysaccharides obtained from the first five degradations are analysed, after methanolysis, by gas-liquid partition chromatography. After the fifth degradation, the O-methyl sugars characterised from the methylated polysaccharide are 2,3,4,6-tetra-, 2,4,6- and 2,3,4-tri-, and 2,6- and 2,4-di-O-methyl-D-galactose; partial acid hydrolysis of this galactan affords 6-O-β-D-galactopyranosyl-D-galactose, 3-O-β-D- galactopyranosyl-D-galactose, and the β1,3-linked galactotriose. The same sample of A. senegal gum is degraded by autohydrolysis: the methylated autohydrolysed gum contains 2,3,4,6-tetra-, 2,4,6- and 2,3,4-tri-, and 2,4-di-O-methyl-D-galactose, 2,3,4-tri-O-methyl-D-glucuronic acid, and trace amounts of 2,3,5-tri-O-methyl-L-arabinose. As a result of these investigations, modifications to the accepted structural features of the gum are proposed.