Structure of sialic acid

Mass spectrometry has been used successfully to establish the structure of sialic acids, and the type of their bonds in the oligosaccharide chain. For this purpose, the fragmentation of various derivatives containing both the cyclic and the acyclic forms of sialic acid has been comprehensively studied. The methyl esters of sialic acid methyl ketosides, obtained as a... 

Tuppy H, Gottschalk A (1972) The structure of sialic acids and their quantitation. 

Our inhibition data, also taking into consideration the previous results [27a], show that the modifications on the structure of sialic acid increase the binding with HA, but not in an enough significant amount to use these type of analogues as anti-influenza drugs. 

Sialosides have a distinct mechanism of hydrolysis for its unusual sugar structure of sialic acid. For example, the large 8-dideuterium and small primary kinetic isotope effects observed at the anomeric carhon and the large secondary kinetic isotope effect observed at the carboxylate carbon in the acid-catalyzed solvolysis of CMP-Af-acetyl neuraminate 24 support an oxocarbenium ion-like transition state 25 having the 5S conformation without nucleophilic participation of carboxylate and with the carboxylate anion in a looser environment than in the ground state [15] (O Fig. 3). Such a zwitterion structure is consistent with the results from calculations using the COSMO-AMI method for aqueous solutions [16]. 

Truncated structures of sialic acids show the moieties required for binding to various sialic acid-specific lectins. LFA is Limaxfiavus agglutinin [231] and WGA is wheat germ agglutinin [5]. The binding importance of sialic acid C-4 and C-7 hydroxyls for MAG has not yet been determined. R indicates that LFA tolerates a variety of equatorial bulky substituents on the C-5 W-acyl group of sialic acids... 

In order to obtain information about the structure of sialic acids, HPLC is a very usefiil... 

Fig.(4). Structure of sialic acid binding site on the HA1 subunit (reproduced from Nature with the permission of McMillan Publishers).

W. D. Gathmann and D. Aminoff, Periodate oxidation studies in the elucidation of the structures of sialic acid containing oligosaccharides, Biochem. Biophys. Res. Comm., 100 (1981) 1453-1458. 

Figure 5.23 Structures of sialic acid (top), zanamivir (left) and oseltamivir.

These are glycosphingolipids which contain a ceramide linked to a glucosylgalactosylsialic add (jS-D-iV-acetylneuraminic acid)moiety. Other monosaccharide and sialic acid residues may also be present. The structure of sialic acid is ... 

Fig. 9. Membrane lipids. Structure of sialic acids. The hydroxyl groups marked with an arrow are involved in glycosidic linkages in ganglioside oligosaccharides, either SA(a2 -t 3)Gly or SA(a2 - 8)SA, where SA > sialic acid and Gly = a monosaccharide residue.

Fig. 1 Structures of sialic acid and sialoglycans described in this chapter. R, CH3CO-, NeuSAc ...

These methods have their value in the relative ease of use and adaptation to large sample numbers. However, although tentative assignment of N- and 0-acyl substitutions can be made, the unequivocal determination of the structure of sialic acids must be made with mass spectrometry and n.m.r. spectroscopy as described in chapters F and G. 

Tuppy, H., and Gottschalk, A., 1972, The structure of sialic acids and their quantitation, in Glycoproteins. Their Composition, Structure and Function (A. Gottschalk, ed.), 2nd ed., pp. 403-449, Elsevier Publishing Co., Amsterdam. 

Comb and Roseman (1958c, 1960) found the same enzyme using Clostridium perfringens cell-free medium and further identified the acylhexosamine product as N-acetyl-D-mannosamine. This elegant piece of work showed for the first time the presence of this aminosugar in nature and also led to a revision of the structure of sialic acid, as shown in Figure 5. 

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