Plant gums of the genus Khaya. Part IV. Major component of Khaya ivorensis gum

Abstract

Fractionation of deacetylated Khaya ivorensis gum affords a major polysaccharide component in essentially homogeneous form. Partial acid hydrolysis of this gives a degraded galacturonan and the following oligosaccharides, 2-O-(α-D-galactopyranosyluronic acid)-L-rhamnose (I), 4-O-(4-O-methylglucopyranosyluronic acid)galactose (II), 4-O-(galactopyranosyluronic acid)galacturonic acid (III), and O-(galactopyranosyluronic acid)-(1 → 2)-O-rhamnopyranosyl-(1 → 4)-O-(galactopyranosyluronic acid)-(1 → 2)-rhamnose (IV). Hydrolysis of the methylated polysaccharide after reduction with lithium aluminium hydride indicates the presence therein of residues of 2,3,4-tri- and 3,4-di-O-methyl-D-glucuronic acid, 2,3-di-O-methyl-D-galacturonic acid, 2,3,5-tri-O-methyl-L-arabinose, 3,4-di- and 3-mono-O-methyl-L-rhamnose, L-rhamnose, and 2,3,4,6-tetra-, 2,3,4- and 2,3,6-tri-, and 2,4-di-O-methyl-D-galactose. The results show that this polysaccharide contains a lower proportion of hexuronic acid residues than the major polysaccharide components of other Khaya gums but is of the same general structural type.