Synthesis of biologically important carbohydrates and glycoconjugates by solution phase and polymer supported approaches
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Carbohydrates and glycoconjugates play essential roles in cell-cell communication, immune response, cancer metastasis, protein folding, embryogenesis, neural and tissue development, and many other biological processes. In nature, many of these carbohydrates are found in low concentrations and in microheterogeneous forms. To study their biological functions in detail, procurement of sufficient amount of glycoconjugates is necessary, requiring the development of efficient synthetic methodology. A novel methodology has been developed for the synthesis of oligosaccharides using high molecular weight branched polymers as supports in combination with membrane nanofiltration for product purification. In this method, four and eight arm polyethylene glycol ethers of molecular weight 10,000 and 40,000 Da respectively, have been used as supports. Highmolecular weight polymer-bound intermediates have been purified using Biomax disc membrane with 5,000 Da molecular-weight cut-off. A tetrasaccharide and antigen Lewisx have been synthesized using this new methodology (Figure 1). Recently, a new class of glycoprotein has been identified, known as proteophosphoglycans, which contain oligosaccharides linked to serine or threonine via phosphodiesters. These proteophosphoglycans are found in Leishmania major, Leishmania mexicana, and Leishmania donovani. They play a significant role in the infection process of leishmaniasis. A novel methodology has been developed for the synthesis of fragments of these proteophosphoglycans. Using this new methodology, proteophosphoglycans of Leishmania major ppg1, ppg2, fppg and Leishmania mexicana ppg1, ppg2, fppg have been synthesized (Figure 2). These compounds will be useful for detailed understanding of the biological functions of proteophosphoglycans. A new methodology for glycosylation using base catalyzed anionic conjugate addition has been developed. A disaccharide has been synthesized using this methodology. This methodology can be explored for the synthesis of various O- and C-glycosides.