Influence of sulfate and carboxylate groups on the conformation of chondroitin sulfate related disaccharides.

1H NMR and 13C NMR spectral parameters of eight sulfated uronic acid containing disaccharides 1-8 were used to determine the conformational preferences that depend on the pattern of sulfation. Three sulfated derivatives of benzyl beta-D-Gal-(1-->4)-beta-D-GlcA (1), its 6'-sulfate 2, 4'-sulfate 3, and 4',6'-disulfate 4 were used as models for the beta-(1-->4) glycosidic linkage of chondroitin sulfates and three sulfated derivatives of benzyl beta-D-GlcA-(1-->3)-beta-D-Gal (5), its 6-sulfate 6, 4-sulfate 7, and 4,6-disulfate 8 were used as models for the beta-(1-->3) glycosidic linkage of chondroitin sulfates. To determine the dependence of conformational preferences on the charged groups, the sulfated disaccharides 2, 3, and 4 were compared to their unsulfated parent compound 1, and 6, 7, and 8 were compared to their parent compound 5. The 3JH-5,H-6 coupling constants were determined by high-order analysis of the spin systems, and from these the preferred populations of the hydroxymethyl groups were calculated. Selective 1D NOEs and ROEs were measured from H-1' across the glycosidic linkage to obtain the average distance of the protons adjacent to the glycosidic linkage. Derivatives of beta-D-Gal-(1-->4)-beta-D-GlcA carrying a sulfate group in the 6'-position (2) and in the 4'- and 6'-position (4) show a slight repulsive effect between the 6'-sulfate groups and the carboxylate group as expressed in small changes of the preferred populations of the glycosidic linkage and the sulfonyloxymethyl group. The 4-sulfate groups in 3 and 4 do not show a significant influence on the glycosidic linkage. However, the two sulfate groups in 4 exhibit a repulsive effect leading to a very high population of the gt conformation of the sulfonyloxymethyl group. In contrast hereto, the sulfate group at C-4 of beta-D-GlcA-(1-->3)-beta-D-Gal disaccharides 7 and 8 and the carboxylate group exert an attractive interaction that leads to a change of the conformation of the glycosidic linkage in 7 and 8 by about 30 degrees. The 6-sulfate groups of the disaccharides 6 and 8 show a slight repulsive interaction with the carboxylate and/or 4-sulfate group. Changes in 13C NMR chemical shifts support the interpretation obtained from the NOE and ROE analysis.(ABSTRACT TRUNCATED AT 400 WORDS)