Abstract
Heparan sulfate (HS) is a member of the glycosaminoglycan (GAG) family and plays significant roles in a diverse set of biological processes, including viral infection, blood coagulation, inflammatory response, cell adhesion, cell growth regulation, and tumor metastasis. HS are consisting of linear polyanionic polysaccharides characterized by a repeating disaccharide unit of D-glucosamine (GlcN) attached to uronic acid [either L-iduronic (IdoA) or D-glucuronic acid (GlcA)]. However, unraveling the HS code has been extremely challenging due to the enormous structural variations. Chemical synthesis is considered as one of the most practical way to obtain the pure and structurally verified oligosaccharides at a considerable scale. To understand HS interaction with protein in detail, we investigated the possibility of assembling a library of HS oligosaccharides Here we employed a divergent strategy to afford a HS repeating disaccharide unit of all 48 theoretical possibilities from just two orthogonally protected disaccharide (GlcN-GlcA/IdoA) precursors. This dissertation describes the detail synthetic steps to achieve 12 disaccharides. With the full disaccharide library in hand, affinity screening with fibroblast growth factor-1 (FGF-1) revealed that four of the synthetic sugars bind to FGF-1. The molecular details of the interaction were further clarified through X-ray analysis of the sugar–protein co-crystals. After successfully studying the disaccharide library, we choose the hexasaccharide library as our next target. A major challenge in HS oligosaccharide synthesis is stereoselective α 1,4-cis-glycosydic linkage between glucosamine and the uronic acid. Therefore, we choose a new glucosamine building block carrying the orthogonal and stero-directing protecting groups for the formation of cis-1,4-linked product. On the other hand, in order to achieve the rapid construction of the hexasaccharide library, we developed a new one-pot glycosylation strategy. In addition, from just two orthogonally protected disaccharides all of the required thioglycoside disaccharide modules for library preparation could be generated in a divergent manner, which greatly simplified the building block preparation. This allowed rapid assembly of HS hexasaccharides with systematically varied and precisely controlled backbone structures in a combinatorial fashion. This dissertation summerizes the detail synthetic steps to achieve 4 hexasaccharides.