Acylneuraminic acids

P. Meindl and H. Tuppy, 2-Deoxy-2,3-dehydrosialic acids. II. Competitive inhibition of Vibrio cholerae neuraminidase by 2-deoxy-2,3-dehydro-jV-acylneuraminic acids, Hoppe Seylers Z Physiol. Chem., 350 (1969) 1088-1092. 

Acylneuraminic acids have been found so far only in mammalians and in some bacteria, but never in plants. They are widespread occurrence as components of glycoproteins and glycolipids both in invertebrates and in vertebrates, in cells and in body fluids [4]. 

The widespread occurrence of the sialic acids is related to their great biological importance. A number of vital processes in which the acylneuraminic acids play a decisive part has indeed been found. Some of these have been described below, grouped according to the function (for reviews see Ref [4]) ... 

Negatively charged acylneuraminic acid residues impart a certain strength to cell membranes because of their mutual repulsion, and influence the mutual adhesion of cells in the organ structure. Whereas neuraminic acid allows the aggregation of embryonal muscle cells of the hen, presumably via Ca bridges, it prevents spontaneous clumping of blood platelets, and it so opposes any undesirable formation of blood clots. 

Al-acetylneuraminic acid /V-glycolylneuraminic acid A/-acylneuraminic acid... 

In the methanolysis procedure, as used for the standard quantitative monosaccharide GLC analysis of glycoconjugates [240,241], 1 M methanolic HCl (24 h, 85 C) is applied. However, under these conditions released sialic acids are completely de-Af,0-acylated, which makes this approach unsuitable for the characterization of different types of sialic acid. It is, however, a reliable approach for the determination of the total amount of a mixture of (0-acetylated) A-acylneuraminic acids. When using a milder methanolysis procedure (0.05 M methanolic HCl, 1 h, 80 C) the de-iV-acylation but not the de-O-acylation is strongly reduced [242]. 

Application of the TLC method in a two-dimensional procedure with intermediate ammonia treatment gives information about the type of A-acylneuraminic acid of the constituting A,0-acylneuraminic acids. In this way a differentiation is possible for example between co-migrating Neu9Ac5Gc and Neu5,7Ac2 [6]. In principle, de-O-acetylations can also be carried out by sialate 0-acetylesterases [266]. 

In the following the principles of the El MS identification procedure will be explained. Typical derivatives are trimethylsilylated methyl ester or pertrimethylsilylated derivatives of AfG-acylneuraminic acids or of A -acyl-O-alkylneuraminic acids, acetylated 7 f-acyl-... 

Fig. 6. Survey of the selected fragment ions A-H worked out for the following derivatives trimethylsilylated methyl ester or pertrimethylsilylated derivatives of /V,0-acylneuraminic acids or of A/-acyl-0-alkylneuraminic acids, and trimethylsilylated/methylated /V,/V-acyl,methyl-neuraminic acid methyl ester methyl glycosides [ 15].

In additional studies, the suitability of chemical ionization (Cl) for the GLC-MS analysis of pertrimethylsilylated IV,0-acylneuraminic acids has been investigated. Isobu-... 

Nevertheless, chemical characterization of the first gangliosides isolated by these methods led to the identification of their constituent parts. Thus, on hydrolysis, sphingosine, fatty acids, N-acylneuraminic acid, and sugars were obtained. 

In gangliosides, the N-acylneuraminic acids are in a-D anomeric (69) conjugation with hexopyranosides, as already mentioned, and are split off enzymically with neuraminidase.198... 

Synthetic alkyl and aralkyl glycosides of N-acylneuraminic acid, obtained by the method of Koenigs and Knorr,191 are split with neuraminidase, like the natural glycosides of N-acylneuraminic acid. In contrast, the /3-D anomers (70), obtained from N-acylneuraminic acid and the appropriate alcohol in the presence of hydrogen ion, are resistant to neuraminidase.191,199 200... 

Some types of virus can attach cells with the aid of cell membrane bound acylneuraminic acids. Red blood cells are agglutinated by myxovirus, which include a number of types that are pathogenic for animals or for man, e.g. 

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