Oligosaccharide synthesis enzymatic reactions

This report surveys new routes for the synthesis of oligosaccharides, with emphasis on enzymatic reactions, since they offer unique properties, proceeding highly regio-and stereo-selectively in water solution, and generally afford high yields. Summarized... 

Oligosaccharide syntheses employing enzymatic reactions would in principle greatly benefit from being performed on a polymer support since the support might effectively facilitate isolation of the final product. Presumably, a water-soluble polymeric support will be preferable to any insoluble support since reaction rates could otherwise become too slow. Glycosidases as synthetic enzymes would be the best candidates to study this type of the enzymic approach to oligosaccharide synthesis. 

On the other hand, the enzymatic synthesis of glycoconjugates and oligosaccharides leads to high product yields in a short time by stereo- and regioselective one-step reactions. All enzymatic reactions are easy to scale up and are carried out in aqueous media under mild conditions. A whole set of enzymes is now available to build up OAT bonds in monosaccharides, COP bonds in activated monosaccharides e.g. phosphorylated sugars or nucleotide sugars, and C-O-C bonds in di- and oligosaccharides (Fig. 1). However, all these enzymatic reactions are limited by the substrate spectrum of the individual enzyme. 

Schroder S, Schmidt U, Thiem J, Kowalczyk J, Kunz M, Vogel M. Synthesis of oligosaccharides as potential novel food 32. components and upscaled enzymatic reaction employing the P-galactosidase from bovine testes. Tetrahedron 2004 60 2601-... 

According to the Warwick Biotransformation Club Database in 1987/88 [60], approximately 65% of all applications reported fell into the classes of esterolytic reactions (ester hydrolysis, synthesis or transesterification) (40%) and dehydrogenase reactions (25%). Next in importance were oxygenase-mediated reactions, peptide and oligosaccharide synthesis, which together comprise 24% of the total. Reports of enzymatic procedures for carbon-carbon bond formation were very few in number (2%). All other reaction types comprised less than 10% of the total. 

In conclusion, compared with solution-phase synthesis, solid-phase enzymatic synthesis, generally, needs higher concentrations of enzyme, longer reaction times, and a large excess of donors. Although there is still room for improvement in terms of yields and scale-up of syntheses, in solid-phase synthesis purification procedures are straightforward so it is expected that this approach will open the route to automated oligosaccharide synthesis in the near future. 

The first surface-initiated enzymatic polymerization reported was the synthesis of amylose brushes on planar and spherical surfaces [145]. For this, silica or silicone surfaces were modified with self-assembled monolayers of (3 amino-propyl)trimethoxysilane or chlorodimethylsilane, respectively. To these functionalities, oligosaccharides were added via (a) reductive amidation of the oligosaccharides to surface-bound amines, (b) conversion of the oiigosaccharide to the according aldonic acid lactone and reaction with surface bound amines, and (c) incorporation... 

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