RESUMO
Chondroitin sulfates A, B, and C produce well-resolved 13C-n.m.r. spectra which allow for a more complete characterization than that available from their p.m.r. spectra. The 13C data fully support earlier evidence as to the main structural features of these glycosaminoglycans, but they also show that many chondroitin preparations are substantially heterogeneous in composition. Thus, spectra of chondroitin A and C have the appearance of composites representative of both types of polymer: specimens of A may contain 25% of the C-type of structural sequence, and C,30% of the A-type of sequence; 10-20% of unidentified constituents, including a residue bearing a 6-sulfate group, are present in the specimens of chondroitin B. Chemical-shift and 1JC-H values found for the L-iduronic acid residues of chondroitin B, as well as the effect of gadolinium nitrate on the relaxation properties of its 13C nuclei, indicate that this moiety possesses the alpha configuration and favors the 1C4(L) conformation. Corresponding data for the acetamidodeoxy-D-galactose and D-glucuronic acid residues of the chondroitins are consistent with the beta-anomeric configuration and 4C1(D) conformation in all instances.