Isolation of 2-amino-2-deoxy-d-galactoside disaccharide from chondroitin sulfate C

Purified chondroitin sulfate prepared from shark cartilage (chondroitin sulfate C) was desulfated and esterified with methanolic HCl. Chondroitin methyl ester (II) was reduced with NaBH₄ to give carboxyl-reduced chondroitin (III), which was submitted to hydrazinolysis to remove the acetyl group of the 2-acetamido-2-deoxy-d-galactopyranose moiety. The N-deacetylated carboxyl-reduced chondroitin (IV) was dyrolyzed with HCl and the hydrolyzate was passed down a Dowex-50 (H⁺) column. A disaccharide (V) and 2-amino-2-deoxy-d-galactopyranose adsorbed on the column were eluted with dilute HCl. Both the substances were N-acetylated and separated effectively by means of a cellulose powder column (Solvent B), and a novel disaccharide, ${}_4\text{-O-(β-2-}\text{acetamido-2-deoxy}\text{-}\text{d}\text{-}\text{galactopyranosyl}\text{)-}\text{d}\text{-}\text{glucopyranose}$ (VII), was isolated. The reducing end of the isolated disaccharide was reduced with NaBH₄ to give ${}_4\text{-O-(β-2-}\text{acetamido-2-deoxy}\text{-}\text{d}\text{-}\text{galactopyranosyl}\text{)-}\text{d}\text{-}\text{glucitol}$ (VIII). Acid hydrolysis of this substance gave d-glucitol (IX) and 2-amino-2-deoxy-d-galactopyranose (X), which were characterized by infrared spectra and by paper chromatography. The structures of these substances (VII, VIII) were confirmed by means of periodate oxidation.