Access to Molecular Diversity in Glycosaminoglycans: Combinatorial Synthesis of Eight Chondroitin Sulfate Disaccharides

Glycosaminoglycans (GAGs), linear sulfated oligosaccharides, are involved in numerous biological events ranging from tissue structure to protein activity regulation. The combinatorial nature of their oligosaccharidic framework and sulfatation pattern (sulfoforms) prompted us to develop a combinatorial approach toward the synthesis of GAG fragments. Using a liquid-phase split and pool protocol, the eight basic chondroitin sulfate (CS) disaccharides have been prepared from a key CS disaccharide scaffold bearing orthogonal protecting groups. This approach saves 25 steps compared to a multi-parallel synthesis. We chose to prepare restricted libraries, but with a high structural confidence. Each step was followed by HPLC, 1H- and 13C-NMR, and ESI-MS analyses to ascertain the number and structures of the library members. The combinatorial protocol involves sulfatation/group manipulation sequences which rely on the fact that, although previously reported to be labile groups, sulfate esters withstand many classical reactions used in molecular glycochemistry. Thus, we used sulfate groups as efficient hydroxyl protecting groups in a combinatorial glucosyl to glucuronyl oxidation sequence involving a Swern oxidation, followed by direct conversion of the aldehyde to the methyl ester. Split and pool methodology is thus shown to be a powerful tool in gaining access to molecular diversity in GAGs and in the preparation of sulfoforms of a given oligosaccharide.