Non-Natural Sialoconjugates

Owing to their prominent role in receptor interactions, the preparation of sialic acids and structural modifications is thus of great interest for pharmaceutical 

C-C bond formation renders the addition essentially irreversible. Our first preparative screening efforts have shown that the enzyme exhibits a broad substrate tolerance, particularly by accepting variously C5-modified NeuSAc derivatives as substrates with complete stereocontrol [20, 21]. Thus, the enzyme seems to be practically equivalent to the commercial aldolase, except that reactions attain complete conversion without a need to drive an equilibrium by a large excess of substrate, which strongly simplifies product isolation. 

Several CMP conjugates made available by this procedure could be transferred effectively to N-acetyl-lactosamine as an acceptor by using the a-2,6-sialyltrans-ferase from rat liver (Fig. 2.2.5.4). In this manner, several trisaccharides 74-77 could be generated carrying natural as well as non-natural sialic acids in good yields [47], limited so far only by the high cost of the commercial glycosyltransferase. 

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