Synthesis of the library of heparan sulfate hexasaccharide mimetics

Project summary: Heparan sulfate (HS) play roles in many important biological events, including cancer metastasis, anti- coagulation, and Alzheimer’s disease development. HS structures in nature are heterogeneous with a wide range sulfation patterns and backbone structures. The interactions of HS with their biological partners are known to be significantly impacted by the fine structures of HS. Thus, for a thorough understanding of the structure-activity relationships of HS, it is critical that large libraries of HS structures are available. However, synthesis of HS oligosaccharide libraries remains a tremendous challenge due to the complexity of HS structures. To overcome this bottleneck, through an innovative industry/academia collaboration, Glycan Therapeutics will develop a HS like hexasaccharide library with diverse and well-defined molecular structures. The novel hexasaccharide mimetics will be designed through head-to-tail linkage of HS disaccharides, thus greatly simplifying the overall synthetic process enabling the preparation of a large number of compounds for library synthesis. In aim 1, solution phase based methodologies will be developed to synthesize HS like hexasaccharides mimicking native HS. Robust linker chemistry will be designed to link the disaccharide modules in a head-to-tail fashion. In aim 2, methods will be developed for expedient synthesis of the key disaccharide building blocks. To cover the diverse HS sequences bearing 2-O, 6-O and N-sulfation encountered in nature, 16 disaccharides are needed. Rather than starting from the corresponding monosaccharides de novo, a new divergent synthetic strategy will be developed where the 16 disaccharides will be derived from two key advanced disaccharide building blocks. This process reduces the total number of synthetic steps needed to produce the building blocks by ~50%. In aim 3, automation chemistry will be developed to enable machine aided synthesis of the HS like hexasaccharide mimetic library. The structure of each compound (>98% purity) will be confirmed by 1D/2D NMR and high-resolution mass spectrometry. All mimetics will be functionalized with a linker at the reducing end to enable facile bioconjugation and microarray production. In Phase I studies, two key strategically protected advanced disaccharide intermediates (500 mg each), and 6 new hexasaccharide mimetics (2 mg each) will be produced. In addition, automated method will be developed to synthesize two hexasaccharide like compounds (2 mg each). In Phase II, the synthesis will be scaled up to produce a library of 300 HS like hexasaccharides (2 mg each). The extensive HS hexasaccharide mimetics that will be assembled from this project will be the largest and the most comprehensive HS mimic library available. The commercial availability of these products would greatly accelerate research on the understanding of the fascinating biological functions of HS, as well as the development of novel HS-based therapeutics.