Synthesis of Linker-Armed Oligosaccharides Related to Bacterial O-Antigens

Das, Subrata (2026) Synthesis of Linker-Armed Oligosaccharides Related to Bacterial O-Antigens. PhD thesis, Indian Institute of Sciences Education and Research Kolkata.

Text (PhD thesis of Subrata Das (21RS081)) 21RS081.pdf - Submitted Version Restricted to Repository staff only Download (29MB)

Abstract

Unicellular bacteria are continuously intriguing us with newer complex oligosaccharides that are posing challenges for the synthetic carbohydrate chemists for their chemical synthesis. The potential of O-antigen repeating units towards the development of synthetic/semi-synthetic vaccines continues to attract synthetic chemists to formulate accurate and scalable synthetic protocols to get these complex oligosaccharides in the purest possible form. The thesis demonstrates the total synthesis of oligosaccharides from bacterial origin through rational protecting group manipulation and stereoselective glycosylation’s. The conjugation ready oligosaccharides are perfect for further conjugation and possible vaccine designing. Chapter 1 is divided in two sections. The section 1A gives the brief history of the genesis and development of carbohydrate chemistry and the section 1B describes the classification and biological implications of carbohydrates. Chapter 2 reviews the recent advances on the synthesis of amino sugars and 1,2-cis glycosylation’s with mannose and rhamnose. For the amino sugars, different amine protecting groups and novel glycosylation’s strategies are discussed. Recent developments for the synthesis of the 1,2-cis linked mannosides and rhamnosides are also discussed as it is important for the current work. Chapter 3 describes the chemical synthesis of 6-deoxy-D-talose containing a tetra saccharide repeating unit of the O-specific polysaccharide from Enterobacter cloacae G3422 in the form of its 2-aminoethyl glycoside. This amino linker could be used to attach the oligosaccharide repeating unit to carrier protein for glycoconjugate vaccine designing. Chapter 4 deals with total synthesis of linker-armed tetra saccharide repeating unit of the O-polysaccharide from E. Coli O50. Hydrogen-bond-mediated-aglycon delivery (HAD) method is used for the synthesis of the 1,2-cis rhamnoside linkage. Chapter 5 illustrates the total synthesis β-L-rhamnose, rare α-D-QuiNAc and α-D-FucNAc containing Penta saccharide related to the O-antigen from Aromonous hydrophila pt679 in the form of its 2-aminoethyl glycoside. The consecutive 1,2-cis linkages in the repeating unit have been a challenge. Use the hydrogen bond mediated aglycon delivery (HAD) method has been for formation of 1,2-cis rhamnosidic linkage.

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