Stereoselective Glycosidations and Application to the Mycobacterial Arabinogalactan by Gold(III) Catalysis

Abstract

Glycoconjugates are important for variety of intracellular and extracellular biological events. Synthesis of glycoconjugates is still a formidable task in spite of various developments over the last one century. Activation of propargyl glycosides with catalytic amount of gold(III) salts has emerged as a new, efficient and powerful alternative and it has been widely used to synthesize wide spectrum of glycosides. In addition, stereoselective glycosidation is more challenging and locking of C1, C2 positions as orthoesters is one of the best options. Propargyl 1,2-orthoesters are investigated for the synthesis of glycomonomers such as glyco- acrylates, acrylamides, 1,6-anhydro sugars and aminooxyglycosides. These methodologies have been gauged with a diverse panel of substrates and found the products of the glycosidation are pure enough to undergo polymerizations easily. Salient features of these methods are: (i) catalytic, (ii) easy purification, and (iii) high yielding. In yet another effort, propargyl 1,2-orthoesters are exploited for the stereoselective synthesis of 1,2- trans furanosides under gold catalysis repertoire. Resulting 1,2-trans furanosides were shown to undergo epimerisation at C -2 position by oxido-reduction to afford 1,2- cis glycosides in a bio-inspired manner. Identified protocols were effectively utilized for the synthesis of pentadodecafuranosyl arabinogalactan of Mycobacterium tuberculosis cell wall. Details of the research work carried out over the last five years will be presented in the thesis.