Sialic acid N-acetylneuraminic

Gangliosides branched oligosaccharide chains terminating in the 9-carbon sugar, sialic acid (N-acetylneuraminic acid, NANA)... 

Synthetic studies for sialic acid and its modifications have extensively used the catabolic enzyme N-acetylneuraminic acid aldolase (NeuA E.C. 4.1.3.3), which catalyzes the reversible addition of pyruvate (70) to N-acetyl-D-mannosamine (ManNAc, 11) to form the parent sialic acid N-acetylneuraminic acid (NeuSNAc, 12 Scheme 2.2.5.23) [1, 2, 45]. In contrast, the N-acetylneuraminic acid synthase (NeuS E.C. 4.1.3.19) has practically been ignored, although it holds considerable synthetic potential in that the enzyme utilizes phosphoenolpyruvate (PEP, 71) as a preformed enol nucleophile from which release of inorganic phosphate during... 

In the late 1970s and early 1980s—the time when P. falciparum could be cultured continuously in the laboratory—there was mounting evidence that the receptor for P. falciparum differed from that of P. vivax and P. knozvlesi. Several laboratories reported that a receptor for P. falciparum merozoites was sialic acid (N-acetylneuraminic acid) since human erythrocytes treated with neuraminidase or trypsin resisted invasion by P. falciparum merozoites and this was unlike the situation with P. vivax and P. knozvlesi where stripping by chymotrypsin but not trypsin blocked invasion. Further, Tn erythrocytes, which lack a glycosyltransfer-ase that results in cells deficient in sialic acid, were also refractory to invasion, as were En (a-) cells and when and S-s-U (-) cells, which were... 

Recently, other aldolases have been used, such as sialic acid (N-acetylneuraminic add) aldolase, which catalyses the condensation between pyruvate as the nucleophile and the open-chain form of N-acetylmanno-samine (7) as the electrophilic component of the reaction (Scheme 5.9). In... 

A similar approach has been used to prepare oligosaccharides that contain sialic acid (N-acetylneuraminic acid) (8). We saw earlier that sialic acid itself can be prepared using an aldolase reaction, and this forms the starting point for another cascade of enzyme-catalysed reactions. In this instance, sialic acid is firstly activated as its cytidine monophosphate (CMP) derivative via coupling with cytidine triphosphate (CTP) in the... 

Sialic acid (N-acetylneuraminic acid) has been reported to be present in the ovomucoid and ovomucin fractions of egg-white [112, 169, 311, 458] however, sialic acid does not appear to have a major role in the maintenance of the physical structure of egg-white [169]. 

N-Acetylneuraminic acid N-Acetylneuraminic acid (NANA) is a member of the family of sialic acids, each of which is acylated at a different site. These compounds are usually found as terminal carbohydrate residues of oligosaccharide side chains of glycoproteins, glycolipids, or, less frequently, of glycosaminoglycans. The]... 

The doubly labelled sialic acids N-acetyl-[2-i4C,9-3H]neuraminic acid (NOhle and Schauer 1981) and N-glycolyl-[2-i4C,9-3H]neuraminic acid (NOhle et al. 1982) were prepared from sodium[2-i4C]pyruvate and either N-acetyl-[6-3H]mannosamine or N-glycolyl-[6- H]mannosamine, with the aid of the N-acetylneuraminate lyase from Clostridium perfringens. The metabolic fate of these compounds was studied after oral and intravenous application to mice and rats. 

Jacques, L. W., Riesco, B. F., and Weltner, W., 1980, NMR spectroscopy and calcium binding of sialic acids N-glycolylneuraminic acid and periodate-oxidized N-acetylneuraminic acid, Car-bohydr. Res. 83 21-32. 

Neuraminic acid itself has not been isolated due to its intrinsic instability. The naturally occurring A -acylated forms (i.e., sialic acids) are stabilized through conversion of the amino group to amide. The most common of the sialic acids, AT-acetylneuraminic acid (NANA), has the systematic name 5-acetamido-3,5-dideoxy-D-g/yc ro-D-ga/acro-nonulo-sonic acid when named as an open-chain compound. N-Glycolylneura-... 

DeWitt, C. W., and Rowe, J. A., 1961, Sialic acids (N,7-diacetylneuraminic acid and N-acetylneuraminic acid) in Escherichia coli. I. Isolation and identification, J. Bacteriol. 82 838. 

N-Acetylneuraminic acid aldolase (or sialic acid aldolase, NeuA EC 4.1.3.3) catalyzes the reversible addition of pyruvate (2) to N-acetyl-D-mannosamine (ManNAc (1)) in the degradation of the parent sialic acid (3) (Figure 10.4). The NeuA lyases found in both bacteria and animals are type I enzymes that form a Schiff base/enamine intermediate with pyruvate and promote a si-face attack to the aldehyde carbonyl group with formation of a (4S) configured stereocenter. The enzyme is commercially available and it has a broad pH optimum around 7.5 and useful stability in solution at ambient temperature [36]. 

IonPac KC-811 column separated the labile compounds N-acetylneuraminic acid and N-glycolylneuraminic acid released by mild acid hydrolysis of bovine vitronectin.245 Sialic acid is extremely labile to conditions of handling and must be released by mild acid hydrolysis.246 Derivatization with phe-nylisothiocyanate and separation by reversed phase chromatography was found useful in analysis of hexosamines from gastric mucosa.247 A review on separation of sugars and other carbohydrates which covers many important aspects is available.248... 

C H19N09-2H20 5-Acetamido-3,5-dideoxy-D-gh/eero-/ -D-galacto-nonulopyran-osonic acid, dihydrate (N-acetylneuraminic acid, dihydrate) (sialic acid, dihydrate) SIALAC 31 350... 

The neuraminic acids (also called sialic acids), which occur in the terminal positions of carbohydrate moieties of many glycoproteins and ganglio-sides, must be hydrolyzed under very mild conditions. For example, hydrolysis with 0.01 M hydrochloric acid for 30 min at 100° causes 20% decomposition of N-acetylneuraminic acid. Sialic acids are more tolerant to methanolysis they may also be removed enzymically. 

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]. 

N-acetylneuraminic acid (sialic acid, 5), is a characteristic component of glycoproteins. Other acidic monosaccharides such as D-glu-curonic add, D-galacturonic add, and liduronic add, are typical constituents of the glycosa-minoglycans found in connective tissue. 

N-Acetvlneuraminic Acid Aldolase. A new procedure has also been developed for the synthesis of 9-0-acetyl-N-acetylneuraminic acid using the aldolase catalyzed reaction methodology. This compound is an unusual sialic acid found in a number of tumor cells and influenza virus C glycoproteins (4 ). The aldol acceptor, 6-0-acetyl-D-mannosamine was prepared in 70% isolated yield from isopropenyl acetate and N-acetyl-D-mannosamine catalyzed by protease N from Bacillus subtilis (from Amano). The 6-0-acetyl hexose was previously prepared by a complicated chemical procedure (42.) The target molecule was obtained in 90% yield via the condensation of the 6-0-acetyl sugar and pyruvate catalyzed by NANA aldolase (Figure 6). With similar procedures applied to KDO, 2-deoxy-NANA and 2-deoxy-2-fluoro-NANA were prepared from NANA. 

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