Structural determination and chemical modifications of the polysaccharide from seeds of Prosopis chilensis Mol. (Stuntz)

Abstract

The polysaccharide extracted from Prosopis chilensis seeds in acidic medium showed by total hydrolysis and gas-liquid chromatography analysis of the alditol acetates to be composed of galactose and mannose in the molar ratio 1.0:1.9. Studies by methylation and H-1 and C-13 NMR spectroscopy indicated that the polysaccharide was a galactomannan with a chain of D-mannopyranosyl residues linked beta 1 -> 4 which carried alternatively a-D-galactopyranosyl residues at position O-6 of D-mannose units. The chemical modification of the galactomannan by reaction with sodium chloroacetate afforded in 95.3% yield, a derivative which gave a very viscous solution with water. By titration it was determined a carboxymethylation degree of 0.42 indicating that 64% of the alcoholic groups were etherified. Reaction of the galactomannan with TEMPO-NaCl-NaOBr system gave a water soluble polysaccharide. The DEPT 135 degrees NMR spectrum indicated that the primary alcoholic groups of galactopyranosyl and unbranched mannopyranosyl residues were fully oxidised.