Structural diversity, oligosaccharides

Among structurally diverse glycoprotein oligosaccharides, those containing repeating N-acetyl-lactosamine structures attract much attention in connection with various biological events, most notably as onco-differentiation markers. 

A key related property of carbohydrates in their role as mediators of cellular interactions is the tremendous structural diversity possible within this class of molecules. Carbohydrates are built from monosaccharides, small molecules that typically contain from three to nine carbon atoms and vary in size and in the stereochemical configuration at one or more carbon centers. These monosaccharides may be linked together to form a large variety of oligosaccharide structures. The unraveling of these oligosaccharide structures, the discovery of their placement at specific sites within proteins, and the determination of their function are tremendous challenges in the field of proteomics. 

Sect. 2 below summarizes some of the important structures containing pyruvic acid acetals. The structural diversity, methods for structure elucidation, biosynthesis and biological function of these oligo- and polysaccharides will be briefly discussed. Sect. 3 gives an overview of the synthetic methods for the stereoselective preparation of pyruvated building blocks for oligosaccharide synthesis. Here, special attention is paid to pyruvated glycosyl donors, and their application to the synthesis of selected structures is presented in Sect. 4. 

The structural complexity of oligosaccharides goes far beyond that of proteins and nucleotides [1-4], Because with nucleotides or amino acids only hnear chains with just one linkage type are formed, a tetramer of nucleotides or amino acids with four different monomeric subunits can have only 24 different stractures, while in excess of 10,000 different stractures are possible for a tetrasaccharide. The various stereochemical centres, the anomeric centre, the multiple linkage types, and the ability to form branched stractures all contribute to this structural diversity. 

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