Executive Summary : | Both glycoconjugates as well as oligosaccharides are important biomolecules having significant role in several biological processes and that's why, a new strategy for their synthesis is crucial, specifically a protocol for obtaining complex glycans with total stereoselectivity and excellent purity. Among all the reported method, recently emerged organocatalyst effected glycosylation have gained more attention as it follow a more green and mild route to target molecules without requiring the use of harsh reagents or expensive transition metals as catalysts. Many groups performed incredible work in this field such as Schmidt et.al, Toshima et. al, Galan et.al, Jacobsen et.al and many more. However, most of the organocatalysis (such as Bronsted acids, thioureas, and organoboron promoters) reported so far for the synthesis of mainly O-glycosides with limited scopes of glycosyl donors (trichloroacetamidate, glycosyl chloride, phosphate, and glycal). Therefore, the further explorations of organocatalysts are still needed in order to emulate metal or enzyme catalysts. Recently, the bifunctional or trifunctional catalysis concepts involving simultaneous activation of the electrophile as well as the nucleophile to many difficult or unattainable transformations are in progression. Recently, our group too developed the cooperative catalysis involving thiourea and N-benzoylglycine promoted O-glycosides as well as organoboron catalysis promoted C - glycosides The proline-type organocatalysts represent a large class of useful bifunctional catalytic systems, which have facilitated a wide range of asymmetric reactions and so on. In particular, recently we have explored the various L-prolamide derivatives as a catalyst for the synthesis of stereoselective glycosides. In this context, the current proposal aims to explore a new bifunctional organocatalytic glycosylation that can affect the glycosylation efficiently, including examples where not only the stereoselectivity, but also the regioselectivity of the reaction can be controlled by the catalyst and also catalyze a stereoselective glycosylation of various uncommon/rare sugar donors as well as site selective glycosylation. At the outset, we would like to explore various novel bifunctional organocatalysts that are capable to activate wide range of glycosyl donors for the synthesis of not only O-glycoside but also less explored N-, C-and S-glycosides. Benefitting from the mild reaction conditions, various N-phenyl trifluoroacetimidates, benzoxazolyl imidates, benzothiazolyl imidates, thiazolyl imidates, picolinyl, and picolyl donors, opening new avenues for chemoselective, one-pot glycosylation strategies of several bioactive oligosaccharides and highly efficient synthesis of nucleosides drugs capecitabine, galocitabine, and doxifluridine. |