Oligosaccharide structures, synthesis

The synthesis of libraries of structurally defined compounds can potentially be achieved either by split-mix synthesis or by parallel synthesis of individual compounds. The synthesis requires a reliable methodology of oligosaccharide synthesis, where stereochemistry and regioselectivity have to be achieved unlike other library approaches. Development of synthetic methodologies that can provide access to any oligosaccharide structure is underway. 

N. K. Kochetkov, in L. Anderson and F. M. Unger (Eds.), Synthesis of O-antigenic polysaccharides. Pathways for the polymerization of oligosaccharide repeating units, Bacterial Lipopolysaccharides Structure, Synthesis and Biological Activities, ACS Symp. Ser., Vol. 231, Amer. Chem. Soc., New York, 1983, pp. 65-81. 

S. Oscarson, U. Tedebark, and D. Turek, Synthesis of colitose-containing oligosaccharide structures found in polysaccharides from Vibrio cholerae 0139 synonym Bengal using thioglycoside donors, Carbohydr. Res., 299 (1997) 159-164. 

Chemoenzymatic techniques provide relatively fast routes to complex oligosaccharide structures. Nevertheless, they always combine biochemical and synthetic elements and therefore require the cooperation of both fields. To date, few glycosyltransferases have been cloned, expressed, and produced in quantities sufficient for preparative enzymatic syntheses. Given the advantages of enzymatic synthesis of oligosaccharides over traditional schemes, research into overexpression of glycosyltransferases will continue to flourish and will offer the benefit of preparative enzymology techniques for carbohydrate chemists in the future. 

Through the development of effective methods for the stereoselective synthesis of L-glycero-D-manno-heptopyxanose, the synthesis of oligosaccharide structures, including this residue, became possible. Several good methods appeared at about the same time. 

As a conclusion, the internal aglycon delivery approach works well in furano-sidic systems and provides a convenient stereospecific route to )3-fructofurano-sidic disaccharides. The scope and limitations of this method will be further evaluated in the synthesis of larger oligosaccharides structures containing -fructofuranosyl residues. 

Paulsen, H, Wilkens, R, Brockhausen, I, Building units of oligosaccharides. CIV. Synthesis of branched tetrasaccharide and pentasaccharide structures of A-glycoproteins methylated at 4 -OH of the branching unit, Liebigs Ann. Chem., 1303-1313, 1992. 

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