Sialic acids, sources

The methods used for in vivo incorporation of azido-monomers and performing a labeling reaction with live cells are relatively simple. The following protocol is based on the methods of Saxon and Bertozzi (2000), which uses acetylated azidoacetylmannosamine as the azido-monomer source and a biotin-PEG-phosphine compound to biotinylate cell surface glycoproteins at the specific azide-sialic acid incorporation sites (Figure 17.19). 

In about 1936, sialic acid was discovered by Blix, who found it to be a component of submaxillary-gland proteins, and who described many of its properties. However, little notice was taken of this work at the time it was published. In 1941, Klenk, who was working on glycolipids of the brain, described a compound, later shown to be a methyl glycoside of sialic acid, that had been obtained by treatment of a lipid fraction with 5% methanolic hydrogen chloride at 105°. In 1954, Klenk and Faillard reported the first isolation of pure N-acetyl-neuraminic acid from animal sources. 

Example 5 Hayakawa and Noyori group in their studies on new activators for phosphoroamidite coupling reactions have applied the most effective member of the group of acid/azole complexes AT-(phenyl)imidazolium tri-flate (N-PhIMT) in the efficient synthesis of biologically important compounds [20j]. A noteworthy example is synthesis of cytidine-5 -monophos-pho-AT-acetylneuraminic acid. This compound is a source of sialic acid in the sialyltransferase-catalysed biosynthesis of sialyl oligosaccharides [25]. 

The successful application of compound 16 to the synthesis of sialic acid glycosides points to the need for a more direct and efficient route to such systems. Partial synthesis from carbohydrate sources would be a promising alternative to total synthesis. This goal and the goal of extending the scope of the exchange reaction to include secondary sugar alcohol substrates, are now important objectives of our laboratory. 

No. Class Protein Source Mol. wt. Man Gal Fuc G Total neutral sugars GN GalN Total hexo- samine Sialic acid Total sugar residues Refer- ences... 

The use of neuraminidase purified from a number of sources leads to the release from many glycoproteins of the major part of the sialic acid, without any changes in the protein (see Table XII). However,... 

Glycoprotein Mol. Wt. Source of neuraminidase Sialic acid (moles/mole of protein) Total Released Refer- ences... 

Nothing is yet known concerning the formation of lactvl groups found at 0-9 of sialic acids from different sources, reported in Section II. This is also true of the biosynthesis of methyl ether and sulfuric ester groups occurring in some natural sialic ac ids. 

The substrate-specificity studies described in this Subsection show striking similarities between the sialidases from various sources, but also characteristic differences with regard to the N- and O-substitu-tions of Neu, the sialic acid glvcosidic linkages, and the oligosaccharide, glycoprotein, or ganglioside nature of the substrates.55... 

The procedure of isolating the glycosphingolipids is based on their physicochemical properties. The presence of the lipophilic, lipid moiety results in their solubility in such typical solvents for lipids as chloroform-methanol. On the other hand, the presence of the carbohydrate moiety imparts to them hydrophilic properties that increase with increase in the length of the carbohydrate chain and with the presence of such polar monosaccharides as sialic acid. This very property makes it possible to subdivide the glycolipids further, according to their polarity. In principle, the isolation of glycosphingolipids from marine animals does not differ from their isolation from other sources, a procedure comprehensively elucidated in a number of reviews.80 88... 

Sialyltransferases catalyze the transfer of a sialic acid residue from CMP-sialic acid to a galactose, GalNAc, or another sialic acid residue. Sialyltransferases from bacterial and mammalian sources have been extensively studied and used in the enzymatic synthesis of sialosides, sialoglycoconjugates, and enzymatic modiflcation of cell surface. 

Nucleotide sugar donors, such as UDP-GalNAc, UDP-GlcNAc, GDP-fucose, and CMP-sialic acid, serve as substrates for the glycosyltransferases and are the source of the sugars that are added to substrate proteins (Table 1). Nucleotide sugar donors are synthesized in the cytoplasm and imported into the secretory pathway by membrane-resident transporters (1). 

For synthetic purposes, NeuSAc has been isolated from a number of natural sources, including edible bird s nest (2-11% sialic acid by weight) [S-7] and submaxillary gland mucins which contain as much as 1S-2S% sialic acid on a dry weight basis [8, 9]. However the need for a more convenient source of NeuSAc has led to the investigation of both enzymic and chemical methods of preparation. 

Colostrum is a richer source of these sialic acid derivatives than milk, and it was from cow colostrum that JV-acetyl-O-acetylneuraminolactose was isolated in about 0.025% yield however, owing to the extreme lability of the 0-acetyl group, most of the subsequent work has been performed on the A "-acetylneuraminolactose. This compound has been split by influenza virus and Vibrio choleras neuraminidase into lactose and A -acetylneura-... 

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