Structure of a Water-Soluble Polysaccharide from the Seeds of Cassia angustifolia

Abstract

A water-soluble galactomannan consisting of D-galactose and D-mannose in the molar ratio 3:2 has been isolated from the seeds of Cassia angustifolia. Hydrolytic fission of the methylated polysaccharide resulted in three methylated sugars: (a) 2, 3-di-O-methyl-D-mannose, (b) 2, 3, 4-tri-O-methyl-D-galactose, and (c) 2, 3, 4, 6-tetra-O-methyl-D-galactose in the molar ratio 2:1:2. Partial acid hydrolysis of the polysaceharide afforded five oligosaccharides: (a) epimelibiose, (b) galactobiosylmannose, (c) mannobiose, (d) mannotriose, and (e) galactobiose. Periodate oxidation of the polysaceharide indicated 59.7% end group while methylation gave 60%. Sodium borohydride reduction of the periodate oxidised polysaceharide and subsequent hydrolysis revealed the presence of (1→4) and (1→6)-glycosidic bonds. Thus, the main chain of the galactomannan was found to consist of (1→4)-linked mannoypyranosyl units having β-glycosidic bonds while (1→6)-linked α-glycosidically bonded galactopyranosyl units form the branching points.