Studies on Keratosulfates

Bovine cornea1 keratosulfate was permethylated in nonaqueous solvent after prior peracetylation.The methyl ethers were isolated after hydrolysis and characterized either as crystalline derivatives or by their physical and chemical properties.The main repeating unit is N-acetyllactosamine polymerized via a 1 + 3 linkage to galactose, as reported previously.About '74% of the N-acetylglucosaminyl groups are sulfated in position 6.However, about 40% of the galactosyl groups are also substituted in position 6, at least in the major portion by sulfate ester groups.This was shown by the isolation and characterization of galactose 6-sulfate from partial acid hydrolysates.In addition, Nacetylglucosamine 6-sulfate and oligosaccharides sulfated to varying degrees were also obtained.The polymer contained about 25% of galactosyl groups in excess of hexosamine.This excess is preferentially hydrolyzed and may indicate branch points.Evidence of N-methylation of glucosamine was obtained.The color reactions and nuclear magnetic resonance spectrum of N-methylglucosamine are compared with those of N-acetylglucosamine.The repeating unit of keratosulfate from bovine cornea was shown by methylation studies (I), to be (1 + 3)-/3+galactopyranosyl-(1 ---) 4)-2-acetamido-2-deoxy-@-n-glucop.yranosyl6sulfate.However, the yields in these experiments were not satisfactory, and the presence of 2,4-di-0-methyl-n-galactose in both methylated native and desulfated polysaccharide indicated either that the products were grossly undermethylated or that position 6 of galactose was blocked.It was therefore thought desirable to reinvestigate the methylation of KS I.1 By carrying out the methylation in organic solvents it was possible to