Glycosylation reactions enzymatic approach

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. 

The anticoagulant fondaparinux, a synthetic analogue of the terminal fragment of heparin, is synthesized using multiple protection/deprotection steps that result in a route of up to 50 steps. There is, as yet, no enzymatic system that approaches the capability to make such a molecule." As this modified pentasaccharide is a natural product, it should, in theory, be accessible through a series of biotransformations, but we currently lack the biocatalytic tools to achieve more than a few steps and would stiU need to use some protection steps to avoid multiple products. Enzymatic synthesis in vivo depends largely on the levels and selectivities of glycosylating enzymes to achieve multistep reactions, a situation that has been mimicked in vitro for simpler systems." ... 

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