New Strategies for the Synthesis of Bio-medically Relevant Oligosaccharides: Recent Updates on 1,2-cis-O-Glycosylation and α-O-Sialylation

The last decade has been characterized by an extraordinary development of glycochemistry. Availability of synthetic glycoconjugates is, therefore, becoming more and more crucial to disclose the structural and functional aspects of glycoconjugates naturally present in cells and living organisms. Modern carbohydrate chemistry is engaged in the challenging task of providing more efficient methods to deliver pure well-defined oligosaccharides for bio-medical research. The main challenge of carbohydrate synthesis is represented by the stereocontrol of glycosylation that limits application of many procedures for the fast assembly of oligosaccharides. In the last ten years new glycosyl donors enabling the installation of 1,2-O-glycosyl and α-O-sialyl linkages are deeply impacting the production of bio-medically relevant oligosaccharides. Albeit noexpeditious general strategy offering easy and reliable access to all full range of oligosaccharides of interest is to date available, recent achievements render closer the routinely application of automated solid supported synthesis for a variety of glycans. Furthermore, improved methods for the stereocontrol of 1,2-cis-O-glycosylation and α-Osialylation in combination with modern strategies for oligosaccharide assembly are offering fast access to a number of complex carbohydrate structures. Keywords: Carbohydrates, glycochemistry, glycoconjugates, 1, 2-cis-O-glycosylation, oligosaccharides, α-O-sialylation.