Concise Synthesis of the Two Dissacharide and one Monosaccharide Fragment Required for the Total Synthesis of the Pentasaccharide Produced by Lactobacillus delbrueckii subsp. bulgaricus OLL1073R-1

Roy Chowdhury, Sayani (2017) Concise Synthesis of the Two Dissacharide and one Monosaccharide Fragment Required for the Total Synthesis of the Pentasaccharide Produced by Lactobacillus delbrueckii subsp. bulgaricus OLL1073R-1. Masters thesis, Indian Institute of Science Education and Research Kolkata.

PDF (MS dissertation of Sayani Roy Chowdhury (12MS077)) SAYANI_ROY_CHOWDHURY_THESIS.pdf - Submitted Version Restricted to Repository staff only Download (1MB)

Abstract

Carbohydrates, the most abundant biomolecule on earth, are important for their role in structural architecture of living kingdom and energy storage and transport. However, their implications were not found important till it was established that carbohydrates are important as information carriers too. Carbohydrates play pivotal roles in many cellular functions and disease progression. This makes them important targets for designing novel drugs and therapeutics. In biological system, carbohydrates mostly remain as conjugates with protein (glycoprotein) or lipid (glycolipid) and in most cases the recognition of the conjugates happen through the carbohydrate structure present. Owing to these interesting involvement of carbohydrates, a new area of research named as "glycomics" has started its journey. It was previously known as glycobiology and eventually recognized as one important part in the "mics" family side by genomics and proteomics. With the development in the area, synthetic carbohydrate chemistry has gained its ground to facilitate the biological studies with plethora of pure carbohydrate structures and providing the chemical means to prepare relevant glycosides in quantity. The O-polysaccharide constituents of many pathogenic and non-pathogenic bacterial species 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. Taking advantage of the presence of a variety of sugar residues, these O-antigens are considered to be one of the most diverse classes of molecules present on the bacterial cell wall. They play a key-role as an elicitor of innate immune responses. They also contribute to 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 vaccinetargets. Arguably the oligosaccharide structures can be isolated from nature. However, the isolation process is not a trivial task and often it leads to contaminated samples that are useless for further use. Therefore, synthetic carbohydrate chemistry plays a vital role in this area. One can synthesize the required carbohydrate structure chemically with absolute purity and devoid of batch to batch variation which is important for drug applications. The present thesis describes the chemical synthesis of two disaccharides related to the exopolysaccharide from Lactobacillus delbrueckii subsp. bulgaricus OLL1073R-1 through rational protecting group manipulations and stereoselective glycosylations.

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