Here, we present a novel approach for the chemical synthesis of chondroitin and dermatan sulfate oligosaccharides. A key point of this strategy is the preparation and use of an N-trifluoroacetyl galactosamine building block containing a 4,6-O-di-tert-butylsilylene group. Glycosylation reactions proceeded in good yields (74-91%) with our protecting group distribution. Using this approach, we have synthesized, for the first time, a chondroitin/dermatan sulfate-like tetrasaccharide that contains both types of uronic acids, D-glucuronic and L-iduronic acid. Moreover, we have employed a fluorescence polarization competition assay to evaluate the interactions between the synthesized oligosaccharides and FGF-2 (basic fibroblast growth factor). Our results show that this method, using standard instrumentation and minimal sample consumption, is a powerful tool for the rapid analysis of the glycosaminoglycan affinity for proteins in solution.

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Based on the structure of the regular heparin, we have prepared a smart library of heparin-like trisaccharides by incorporating some sulfate groups in the sequence α-D-GlcNS- (1-4)-α-L-Ido2S-(1-4)-α-D-GlcN. According to the 3D structure of heparin, which features one helix turn every four residues, this fragment corresponds to the minimum binding motif. We have performed a complete NMR study and found that the trisaccharides have a similar 3D structure to regular heparin itself, but their spectral properties are such that allow to extract very detailed information about distances and coupling constants as they are isotropic molecules. The characteristic conformational equilibrium of the central iduronate ring has been analyzed combining NMR and molecular dynamics and the populations of the conformers of the central iduronate ring have been calculated. We have found that in those compounds lacking the sulfate group at position 6 of the reducing end glucosamine, the population of (2)S(0) of the central iduronate residue is sensitive to the temperature decreasing to 19% at 278 K. On the contrary, the trisaccharides with 6-O-sulfate in the reducing end glucosamine keep the level of population constant with temperature circa 40% of (2)S(0) similar to that observed at room temperature. Another structural feature that has been revealed through this analysis is the larger flexibility of the L-IdoAS- D-GlcN glycosidic linkage, compared with the D-GlcNS-L-IdoA. We propose that this is the point where the heparin chain is bended to form structures far from the regular helix known as kink that have been proposed to play an important role in the specificity of the heparin-protein interaction.