Some structural features of the mucilage from the bark of Ulmus fulva (slippery elm mucilage)

Slippery elm mucilage contains residues of l-rhamnose, d-galactose, 3-O-methyl-d-galactose, and d-galacturonic acid. The methylated polysaccharide yields 3-O- and 4-O-methyl-l-rhamnose, 2,3,4,6-tetra- and 2,3,6-tri-O-methyl-d-galactose, and 2,3,4-tri- and 2,3-di-O-methyl-d-galacturonic acid, in addition to trace amounts of 2,3,4-tri and 3,4-di-O-methyl-l-rhamnose and 2,4,6-tri-O-methyl-d-galactose. Borohydride reduction of the periodate-oxidised polysaccharide yields a polyalcohol, which, on partial hydrolysis with acid, affords O-(3-O-methyl-d-galactopyranosyl)-(1 → 4)-O-(3-O-methyl-d-galactopyranosyl)-(1 → 4)-O-(3-O-methyl-d-galactopyranosyl)-(1 → 4)-l-rhamnose. Mild, acid hydrolysis yields a Smith-degraded polysaccharide. Methylation analyses are reported for the polyalcohol and for the Smith-degraded polysaccharide. It is concluded that the polysaccharide contains chains of 3-O-methyl-d-galactose residues attached to the C-4 positions of certain l-rhamnose residues, and that 3-O-methyl-d-galactose residues occur in some cases as non-reducing end-groups. d-Galactose is attached as single residues or as 4-O-substituted residues to the C-3 positions of some l-rhamnose residues. This evidence indicates that the polysaccharide is more highly branched than was at one time supposed.