Process for obtaining chondroitin sulphated at the 4- or 6- positions of N-acetyl-galactosamine residues

Disclosed is a process for the prodn. of chondroitin sulfate, wherein N-​acetylgalactosamine residues sulfated at the 4-​or 6-​positions are present on the same polysaccharide chain. The process comprises steps of: (1) forming the resp. 4,​6-​benzylidene deriv. of N-​acetylgalactosamine of chondroitin in acid form, (2) acylating the OH groups on 2 and 3 position of gluconic acid residue, (3) oxidatively opening the benzylidene cycle, (4) sulfating the 4 and 6 OH groups of galactosamine residue, (5) removing the benzyl protective groups and the acetyl protective groups on 2 and 3 OH groups of gluconic acid residue and (6) purifying the 4,​6-​sulfated chondroitin.