Files
Abstract
Group A Streptococcus (GAS) is a leading cause of many deadliest diseases in humans, which lead to millions of deaths every year. GAS is the sole species of Lancefield group A and all GAS serotypes express the Lancefield group A carbohydrate (GAC), which is comprised of a polyrhamnose backbone with an immunodominant N-acetylglucosamine (GlcNAc) side chain. The hurdle towards a carbohydrate-based vaccine includes the potential of the GAC GlcNAc side chain to provoke cross-reactive antibodies that are relevant to the immunopathogenesis of rheumatic fever. Researchers have reported that antibodies to GAC lacking the GlcNAc side chain and containing only the polyrhamnose promoted opsonophagocytic killing of multiple GAS serotypes and protected against systemic GAS challenge after passive immunization. Several synthetic challenges associated with these oligosaccharide antigens, including sensitivity and reactivity of the substrate, etc. need to be addressed. Besides, lack of structure-activity relationships for the cross-reactive antibody makes it challenging to understand the pathogenesis of the GAS autoimmunity at a molecular level. Moreover, it greatly complicates the design and the development of safe and effective GAS vaccine candidates.In this dissertation, we have described a synthetic methodology that can rapidly provide a library of well-defined GAC oligosaccharides with different GlcNAc side chain variations and chain lengths. It is based on the use of a key disaccharide to modularly assemble GAC oligosaccharides with different chain variations and lengths. We have discovered two new chemical reactions, i.e., PMB migration and the 4+4 in situ bond cleavage polymerization. Having conducted comprehensive studies, we proposed effective mechanisms for the discovered reactions as we successfully synthesized biologically important GAC oligosaccharide antigens. Besides, we have collaborated with biologists at Utrecht University to conduct comprehensive biological investigations of the GAC library and the glycoconjugate vaccine candidate. Different types of GAS antibodies were investigated by the GAC-microarray. The binding study showed that each antibody recognized multiple compounds and exhibited distinct structurebinding relationships. The GAC-microarray data made it possible to investigate and validate the influences of different lengths and side-chain variations on the structurebinding relationships with type-specific antibodies. The array data supports a notion that the side-chain variation and length can have significant influences on the structurebinding relationships and provide valuable insights to the cross-reactivity associated with the autoimmunity of the GAS infections.