Mesquite gum. I. The 4-O-methylglucuronogalactan core

Abstract

A re-examination of mesquite gum has shown that partial hydrolysis of the gum furnishes a mixture of acidic oligosaccharides including 6-O-(4-O-methyl-β-D-glucopyranosyluronic acid)-D-galactose (1), 4-O-(4-O-methyl-α-D-glucopyranosyluronic acid)-D-galactose (2), 6-O-(β-D-glucopyranosyluronic acid)-D-galactose (3), O-(4-O-ethyl-β-D-glucopyranosyluronic acid)-(1→6)-O-β-D-galactopyranosyl-(1→6)-D-galactose (4), and O-(4-O-methyl-α-D-glucopyranosyluronic acid)-(1→4)-O-β-D-galactopyranosyl-(1→3)-D-galactose (5). A series of degradations of the gum affords successively, arabinose-free degraded gum A, carboxy-reduced degraded gum A, and degraded gums B and C. Degraded gum C contains a high proportion of 1→3′ linked β-D-galactopyranose residues. The structure of the 4-O-methylglucuronogalactan core of the gum is re-assessed in the light of these and other results.