Sialylation in oligosaccharide synthesis

Construction of the equatorial a-sialyl linkage still poses a challenge in oligosaccharide synthesis [51-53]. One way to enhance the a-selectivity in the sialylation is... 

An associated enzyme, al-3-fucosyltransferase, has also been used in syntheses to provide the Lewis x and sialyl Lewis x structural motifs [65]. Increasing availability of fucosyltransferases via cloning techniques are expected to have a strong influence on oligosaccharide synthesis in the near future. 

Based on die highly developed art of oligosaccharide synthesis, orgamc-chemical, enzyme-catalyzed, and combined organic-enzyme-catalyzed syntheses of the Sialyl-Lewis structure and related oligosaccharides have been devised. Selected examples of these syntheses are discussed in Section IV, some of them including recently developed procedures of glycoside formation. 

The synthetic utilities of sialyltransferases as alternative methods to sialylate oligosaccharide and glycoconjugates have been further explored by Halcomb who described the synthesis of a novel anomeric sulfur analogue of CMP-sialic acid (103). The key step in the synthesis of this novel CMP-sialic acid was a tetrazole-promoted coupling of a cytidine-5 -phosphoramidite with a glycosyl thiol of a protected sialic acid. The rate of solvolysis of (103) in aqueous buffer was reported to be 50-fold slower than that of CMP-sialic acid. Thioester (103) was a substrate for the transferase with a three-fold higher than the of the... 

Sialidases are another class of enzymes that have been used in the synthesis of sialylated oligosaccharides. In addition to hydrolysis activity, sialidases are capable... 

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