Chemical Synthesis of Biologically Active Oligosaccharides Isolated from Bacterial Strain and Medicinal Plant

Bera, Madhumita (2023) Chemical Synthesis of Biologically Active Oligosaccharides Isolated from Bacterial Strain and Medicinal Plant. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Madhumita Bera (17RS070)) 17RS070.pdf - Submitted Version Restricted to Repository staff only Download (13MB)

Abstract

Carbohydrates which are compose of carbon, hydrogen, and oxygen, are the most important natural bio-polymers performing various biological function like energy storage, structural motifs, energy transport, and most importantly as information carriers. They are responsible for the structural architecture in plant. In recent decades carbohydrate-based drugs and vaccine draw a lot of attention in the field of research. The cell surfaces of the bacterial pathogens are covered by oligo- and polysaccharides that take part in cell adhesion and organism invasion. This sugar-directed cell adhesion causes diseases in our body. So, protein bound glycan can be attractive targets for vaccine design. The present thesis explains the importance of chemical synthesis of the oligosaccharides. Although oligosaccharides can be isolated from the natural sources. However, isolation of oligosaccharides from nature in high purity and quantity is a cumbersome and expensive task. Therefore, chemical synthesis of those biologically active bacterial and plant oligosaccharide is really important for vaccine development purpose. Chapter 1 illustrates initial introduction carbohydrates through their structural identification, classifications, importance in various biological processes and their use in modern day therapeutics. Chapter 2 reviews nicely explained the literature reports on various rare sugar and their structure, source. This chapter also highlights details explanation of chemical and enzymatic synthesis of rare sugar and health benefits of this rare sugar. We also review some total synthesis of biologically active bacterial oligosaccharide containing rare sugar in recent year’s publication. Chapter 3 illustrates the synthetic strategy developed for the chemical synthesis of the pentasaccharide repeating unit of the O-antigen from Escherichia albertii O2. Chapter 4 demonstrates the chemical synthesis of the Tetrasaccharide Repeating Unit of the O-antigen from Pseudomonas putida BIM B-1100 having Rare D-Fucp2NAc and DQuip3NAc. This chapter deals with the new synthetic path for the synthesis of rare DFucp2NAc and D-Quip3NAc. This chapter also shows the path for synthesis of rare sugar moiety 3-acetamido-3,6-dideoxy-D-glucose (D-Quip3NAc) and 2-acetamido-2-deoxy-Dfucose (D-Fucp2NAc). A radical mediated 6-deoxygenation with subsequent protecting group manipulation strategy is used for the preparation of the rare D-FucpNAc and D-Quip3NAc derivatives from suitable d-glucosamine derivatives. In both the case 2-aminoethyl glycoside of the target Pentasaccharide and tetrasaccharide will leave the scope for further conjugation with suitable aglycon without hampering the stereochemistry of the reducing end sugar. Chapter 5 deals with the chemical synthesis of the apiose containing pentasaccharide Isolated from Medicinal Plant Aster tataricus L. f. Allyl linker was conjugated at the reducing end of oligosaccharide which can be deprotected selectively without hampering other linkage and the resultant hemiacetal may be converted to the corresponding trichloroacetimidate derivative for further conjugation.

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