Synthesis of Two Disaccharide Fragments of the Tetrasaccharide Repeating Unit from the O-polysaccharide of Escherichia coli O77

Swaminathan, Mithun (2017) Synthesis of Two Disaccharide Fragments of the Tetrasaccharide Repeating Unit from the O-polysaccharide of Escherichia coli O77. Masters thesis, Indian Institute of Science Education and Research Kolkata.

PDF (MS dissertation of Mithun Swaminathan (11MS041)) Mithun_Thesis.pdf - Submitted Version Restricted to Repository staff only Download (1MB)

Abstract

Carbohydrates, the most abundant biomolecule on the earth, are responsible for many biological processes that are the key for life. They are the molecules responsible for building structures of the living bodies and storage and transport of energy. In addition, carbohydrates are involved in various other biological processes. Bacterial O-antigens are important for their interactions with the host cells that regulates the infection. The carbohydrate-protein or carbohydrate-carbohydrate interactions involved in the process of bacterial adhesion to the host cells may be intervened by the application of glycoconjugates bearing same oligosaccharide chains. Arguably, the oligosaccharide structures may be isolated from natural sources. However, isolation and purification of specific oligosaccharide structures from heterogeneous mixtures is not a trivial task. Therefore, chemical synthesis of these structures become inevitable. Using the techniques of organic synthesis, the complex oligosaccharides may be prepared with extreme precision. The bacterial O-polysaccharides are important for the adhesion of the pathogens. These class of molecules play diverse roles in determining and regulating the biology of the organisms. The bacterial O-antigens, constituents of the lipopolysaccharides of the bacterial cell wall consist of many repeats of the oligosaccharide units. The presence of various sugar units make these O-antigens to be one of the most diverse classes of molecules present on the bacterial cell wall. The O-antigens play critical role in the innate immune responses and the pathogenicity by virtue of their protecting ability of the infecting bacteria by killing serum complement and phagocytosis. Due to this antigenic character of bacterial O-antigens, they are widely studied as potential vaccine-targets. The present thesis describes the synthesis of two disaccharide fragments of the tetrasaccharide repeating unit from the O-polysaccharide of Escherichia coli O77 through rational protecting group manipulations and stereoselective glycosylations.

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