The structure of Acacia campylacantha gum

Abstract

Acacia campylacantha trees exude a polysaccharide containing d-galactose (54%), l-arabinose (29%), l-rhamnose (8%), d-glucuronic acid (7%), and 4- O-methyl- d-glucuronic acid (2%). Linkage analysis gives 3- O-α- d-galactopyranosyl- l-arabinose, 3- O-β- l-arabinopyranosyl- l-arabinose, 3- O-β- l-arabinofuranosyl- l-arabinose, 3- O-β- d-galactopyranosyl- d-galactose, and 6- O-β- d-galactopyranosyl- d-galactose. The O-methyl derivative of the gum was examined, after methanolysis, by g.l.c.; 2,3,4-tri- O-methyl- l-rhamnose, 2,3,5- and 2,3,4-tri-, and 2,5-di- O-methyl- l-arabinose, 2,3,4,6-tetra-, 2,4,6- and 2,3,4-tri-, and 2,4-di- O-methyl- d-galactose, and 2,3,4-tri- and 2,3-di- O-methyl- d-glucuronic acid were detected. Degraded-gum A, obtained after controlled, acid hydrolysis, was examined by linkage and methylation analysis, and was subjected to a Smith-degradation. The whole gum was subjected to five successive Smith-degradations; the polysaccharides obtained after each degradation were examined by methylation and linkage analysis. The structural evidence suggests that A. campylacantha gum is based on a branched galactan core, to which are attached uronic acid, rhamnose, and unusually short chains containing not more than three arabinose residues. Acacia campylacantha gum is broadly similar in structure to the gums from A. senegal and A. laeta, although differences in fine structure can be distinguished.