Glycosyl transferases glycoside synthesis

Biosynthesis synthesis As a consequence of the structural diversity of the O. (linkage sites, branching sites, a-/5 coupling of the glycoside units) zip processes like those for protein biosynthesis are not possible for O. In general, the formation of a saccharide bond requires a specific enzyme, a glycosyl transferase. For synthesis, see Lit. ... 

Recent developments in the enzymatic synthesis of carbohydrates can be classified into four approaches 1) asymmetric C-C bond formation catalyzed by aldolases (1-10 2) enzymatic synthesis of carbohydrate synthons (loll) 3) asymmetric glycosidic formation catalyzed by glycosidases (12.-17) and glycosyl transferases (18-23.) and 4) regioselective transformations of sugars and derivatives (24-25). These enzymatic transformations are stereoselective and carried out under mild conditions with minimum protection of functional groups. They hold promise in preparative carbohydrate synthesis. In connection with this book, we focus on the first two approaches. 

Scheme 4.22 Glycosyl transferases in stereoselective glycosidic bond synthesis.

Crout DHE, Vic G. Glycosidases and glycosyl transferases in glycoside and ohgosaccharide synthesis. Curr. Opinion. In Chem. Biol. 1998 2 98-111. 

Fig. 15.9 Synthesis of mutan from sucrose by S. mutans. (a) Reaction of sucrose with glycosyl transferase (see text), (b) Fates of the products, (i) The sucrose is hydrolyzed at its glycoside bond (red O atom also shown in c-i). The glucose moiety b-i is briefly enzyme bound as indicated in [c(ii)] and polymerized to mutan by the enzyme interacting at the Cl and C3 positions. The fructose is transferred intracellularly and metabolized to lactose which is secreted. The fructose metabolism provides energy, (c) Glucosyl transferase mode of action (see text)...

Enzymatic approaches to glycoside synthesis may circumvent these problems. Enzymes (i.e. nucleoside glycosyl transferases) are stereospecific and regioselective catalyzing glycosyl transfer reaction under mild conditions. Extensive protection-deprotection schemes are unnecessary and the control of anomeric configuration is managed. 

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