Neuraminic acid glycosides, synthesis

Attempts to use appropriate glycal derivatives with carbomethoxy or acetoxymethyl groups at C-1 and the fi-iodosuccinimide procedure for the synthesis of neuraminic acid glycosides and disaccharides were successful only when simple alcohols were used (Chapter 3). 

Vasella has applied the concept of anomeric anion stabilization by a nitro group to the /3-D-JV-acetyl-D-glucosamine derivative 177, available in four steps from N-acetyl-n-glucosamine [52] (Scheme 39). Reaction of the tetraethylammonium nitronate derived from 177 with aldehyde 178 provides anti-179 which then undergoes stereoselectively reduction (see Sect. 2.2.1) to provide -C-glycoside 180, intermediate in a synthesis of N-acetyl-neuraminic acid. 

J. O. Nagy and M. D. Bednarski, The chemical-enzymatic synthesis of a carbon glycoside of W-acetyl neuraminic acid, Tetrahedron Lett. 32 3953 (1991). 

The synthesis of a 4-methylumbelliferyl glycoside of A-acetyl-a-D-neuraminic acid has been reported for use as a substrate for the fluorometric detection and estimation of a-neuraminidase. ... 

Details of methods which should be suitable for the large scale synthesis of a- and p-sialoglycosides are given in Scheme 8. The corresponding glycoside bromide was used in a simple procedure for the synthesis of the methyl and benzyl glycosides of iV-acetyl-neuraminic acid and its 4-epimer. ... 

Some photoreactive CMP-neuraminic acids 32 have been prepared as substrates for a-(2- 6)-sialyltransferases, and synthesis of some thio-umbelliferyl glycosides of ulosonic acids is mentioned in Chapter 3. The ethyl thioglycoside 33 was prepared in 47% overall yield from neuraminic acid and used as a glycosyl... 

A-Acetylneuraminic acid contains no C-3 substituent but carries a carboxy group at position 2. Both factors complicate the stereoselective and efficient formation of the desired a-2,3-sialoside in example 2 [31], A neighboring group at C-3, required for stereoselective synthesis, can be introduced temporarily (SPh, SePh) and removed after completion of the sialylation [32]. This strategy, however, requires additional steps and results in reduced overall yield. Recently, thioalkyl/aryl sialosides and 5-sialosyl xanthates have been used to achieve regio- and stereoselective formation of a-glycosides of iV-acetyl neuraminic acid derivatives (Scheme 6) [33-35]. 

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