Galactomannan from Cassiaabsus seed. I. Nature of sugars present, methylation, and periodate oxidation studies

Abstract

A galactomannan composed of D-galactose (1 mole) and D-mannose (3 moles) was isolated from the seed of Cassiaabsus. Methylation and hydrolysis of the galactomannan produced 2,3,4,6-tetra-O-methyl-D-galactose (2 moles), 2,3,6-tri-O-methyl-D-mannose (4.2 moles), 2,3-di-O-methyl-D-mannose (1 mole), and 4,6-di-O-methyl-D-mannose (1 mole). Periodate consumption was 1.09 moles for each hexose unit with concomitant liberation of 0.26 mole of formic acid. The periodate oxidized and the reduced galactomannan afforded, on hydrolysis, glycerol (1.94 moles), erythritol (5 moles), and D-mannose (1.08 moles).On the basis of the above findings, a structure for the galactomannan can be proposed in which mannose units form the main chain and the galactose units are present as branches, the former being attached mostly through 1 → 4 (ca. 85%) and the rest which is nearly half the branch points through 1 → 3 or 1 → 2, and branches of single galactose units are attached through 1 → 6 (ca. 50%) and the rest through 1 → 2 or 1 → 3.