Synthesis of Chondroitin Sulfate Oligosaccharides Using N-(Tetrachlorophthaloyl)- and N-(Trifluoroacetyl)galactosamine Building Blocks

Abstract

We have explored synthetic routes for the preparation of chondroitin sulfate (CS) oligosaccharides based on the use of N-tetrachlorophthaloyl- (N-TCP) and N-trifluoroacetyl-substituted (N-TFA) galactosamine building blocks. Using N-TCP units, we carried out the total synthesis of two CS disaccharides, demonstrating the compatibility of TCP protection with the final deprotection/sulfation steps. However, an attempted 2 + 2 coupling of N-TCP-containing disaccharides for the synthesis of CS tetrasaccharides failed. In contrast, a synthetic route using N-TFA galactosamine units efficiently led to biologically relevant CS-like oligosaccharides. The N-TFA groups could easily be removed at the end of the synthesis, and microwave irradiation greatly facilitated the sulfation reactions. The utility of this approach is illustrated with the total synthesis of two CS-like tetrasaccharides with different sulfate distribution patterns. Finally, we used a fluorescence polarization assay to estimate the relative abilities of the synthesized compounds to inhibit the interaction between FGF-2 and heparin.