Structure of the polysaccharide from tamarind kernel

Abstract

Tamarind-kernel powder, on fractionation, afforded a homogeneous polysaccharide composed of D-glucose, D-xylose, D-galactose, and L-arabinose in the molar ratios of 8:4:2:1. Whereas acetolysis of the polysaccharide afforded 4- O-β- D-glucopyranosyl- D-glucose (cellobiose) and 2- O-β- D-galactopyranosyl- D-xylopyranose, hydrolysis with an enzyme preparation, “Hemicellulase”, produced 4- O-β- D-galactopyranosyl- D-glucose (lactose) and 6- O-α- D-xylopyranosyl- D-glucopyranose. Methylation of the polysaccharide, followed by hydrolysis, yielded the following methylated sugars: 2,3,5-tri- O-methyl- L-arabinose (1 mole); 2,3,4-tri- O-methyl- D-xylose (3 moles); 2,3,4,6-tetra- O-methyl- D-galactose(2 moles); 3,4-di- O-methyl- D-xylopyranose (1 mole); 2,3,6-tri- O-methyl- D-glucopyranose (2 moles); and 2,3-di- O-methyl- D-glucopyranose (6 moles). On oxidation of the polysaccharide with sodium metaperiodate, 1.35 moles of oxidant were consumed and 0.34 mole of formic acid was liberated. On reduction with sodium borohydride, followed by acid hydrolysis, the oxopolysaccharide gave erythritol, glycerol, and glyceraldehyde in molar ratios of 8:2.5:1. Partial hydrolysis of the polysaccharide with acid produced a degraded polymer composed of glucose and a small proportion of xylose. The degraded polymer on methylation and hydrolysis afforded 2,3,4,6-tetra- O-methyl- D-glucose; 2,3,4-tri- O-methyl- D-xylose; 2,3,6-tri- O-methyl- D-glucose; and 2,3-di- O-methyl- D-glucose. On the basis of the above results, a structure for the polysaccharide of tamarind kernel is proposed.