Araucaria bidwilli GUM

Abstract

The polysaccharide exudate from the gymnosperm, Araucaria bidwilli, contains residues of d-galactose, l-arabinose, l-rhamnose, and d-glucuronic acid (in part as the 4-methyl ether). Graded hydrolysis affords 6- O-(β- d-glucopyranosyluronic acid)- d-galactose and 6- O-(4- O-methyl-β- d-glucopyranosyluronic acid)- d-galactose. The methylated polysaccharide contains residues of 2,3,4,6-tetra-, 2,3,4- and 2,4,6-tri-, and 2,4-di- O-methylgalactose,2,3,4-, and 2,3,5-tri-, and 2,5-di- O-methylarabinose, 2,3,4-tri- O-methylrhamnose, and 2,3,4-tri- O-methylglucuronic acid. Successive degradations by periodate oxidation, borohydride reduction, and mild acid hydrolysis, furnish arabinogalactan A and galactan B in which I→3 linkages predominate. It is concluded that the polysaccharide possesses a highly branched structure with a main chain of I→3-linked d-galactopyranose residues to which are attached side-chains carrying more d-galactopyranose residues in I→6 linkages and terminated by d-glucuronic acid, d-galactopyranose, l-arabinofuranose, l-arabinopyranose, and l-rhamnopyranose residues.