Oligo- and Polysaccharide Synthesis

Oligo- and Polysaccharide Synthesis with Sucrose Analogues... 

For the synthesis of highly defined polysaccharides, glucosylsaccharides are the only option available. Specialized oligo- and polysaccharides for food and medical applications can be synthesized, and also hybrid structures with non-natural macromolecules or surfaces. 

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. 

Over 70 pyruvated saccharide structures from natural sources are known today, but only a few representative examples are summarized here. The choice has been determined by the synthesis of pyruvated saccharides as discussed in the Sections below. Reference [2] gives a more concise overview of the great structural diversity found among naturally occurring pyruvated oligo- and polysaccharides. 

The selective preparation of 1,2-czs-linkages in the D-manno and L-rhamno series is still one of the major challenges in oligosaccharide synthesis. Several new and promising approaches deal with this problem [59]. Since a number of pyru-vated oligo- and polysaccharides also contain o-mannosyl and j -L-rhamnosyl residues (Table 1), eCBcient strategies for their preparation are also needed here. 

Unlike the synthesis of protein or nucleic acid, the assembly of oligo- and polysaccharides is susceptible only to a very limited range of inhibitors, especially where they are used on intact cells. This is partly a reflection of the high specificity of the enzymes involved in glycosyl transfers, but, nevertheless, some inhibitors have proved very useful and promise well for the future. 

It is clear, then, that perhaps no other group of compounds is as well suited to enzyme-based synthesis as is the carbohydrates. During the past several years, we have developed a range of enzyme-based syntheses for mono-, oligo-, and polysaccharides. This paper reviews some of our efforts on the use of aldolases and transketolase for monosaccharide synthesis, as well as the use of Leloir and non-Leloir pathway enzymes for glycosidic bond formation. 

Synthesis of Oligo- and Polysaccharides Using Glycosyl-transferases... 

All these oligo- and polysaccharides in nature are synthesized in vivo) via sucrose. Technical synthesis (in vitro) found industrial practices mainly for oligofructose, Neo-amylose and dextran following the reaction pathways as outlined in Figure 9.3.7. 

In general, it is possible to obtain higher degrees of polymerization by ring-opening polymerization than with polycondensation. Two types are used in oligo and polysaccharide syntheses orthoester synthesis and cationic anhydrosugar polymerization. 

The purpose of this chapter is to deal exclusively with the use of furan conqtounds and the exploitation of specific features related to furan chemistry with the aim of synthesizing polymeric materials. Imphcit in this treatment is the fact that vegetable renewable resources, in the form of mono, oligo and polysaccharides, are excellent sources of two first generation furans which, in turn, represent sources of a variety of monomers and other derivatives relevant to polymer synthesis. Although this topic has been reviewed on previous occasions [4], important advances have enriched it in recent years. An attempt will therefore be made to provide here a balanced treatment covering both the most salient achievements reported in the past several decades and novel promising contributions and perspectives. 

The activated sugar can take part in various metabolic reactions. Of particular importance is the transfer of the sugar moiety to the OH-group of another molecule, e.g. in the synthesis of oligo-and polysaccharides (see Carbohydrate metabolism). 

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