Neuraminic acid preparation

However, two recent papers suggest that DMF is also a good solvent for this type of condensation under appropriate activation conditions of the donor. A simple and efficient method for the preparation of thioglycosides of N-acetyl-neuraminic acid has been developed [30]. This procedure involves the selective in situ S-deacetylation and activation of the 2-S-acetyl NeuSAc (24a) and the displacement of primary bromide of methyl glycosides (28a, 28b). The desired a(2->6) thioglycosides (29a,29b) were obtained in 75 and 82% yield. Condensation of the sodium salt (24b), freshly derived from (24 a) by selective S-deacetylation with sodium methoxide [16], with (28c) in DMF at 45 °C also gave the expected compound (29c) in 76% yield (Scheme 8) [31]. 

The sialic acid aldolase-catalyzed condensation of D-mannose 8 and pyruvate led, in an excellent yield, to the synthesis of KDN 9 [33], a natural deaminated neuraminic acid first isolated from rainbow trout eggs [34] and then discovered in other species. The discovery that sialic acid aldolase accepts as substrates D-mannose substituted on the 2-position, even by bulky substituents such as phenyl, azido, or bromine, opened the route to novel unnatural sialic acid derivatives [35-39]. Pentoses also are substrates. N-Substituted neuraminic acids could be prepared either directly from the corresponding Af-substituted mannosamine, such as N-thioacyl derivatives [40], or after reduction and acylation of 5-azido-KDN [41]. Recently, AT-carbobenzyloxy-D-mannosamine was converted, in a good yield, into the N-carbobenzyloxy-neurarninic acid, further used as a precursor of a derivative of castanospermine [42]. 

M.-J. Kim, W. J. Hennen, H. M. Sweers, and C.-H. Wong, Enzymes in carbohydrate synthesis 79-Acetylneuraminic acid aldolase catalyzed reactions and preparation of 7V-aceiyl-2-deoxy-D-neuraminic acid derivatives, J. Am. Chem. Soc. 770 6481 (1988). 

H. S. Conradt, A. Biinsch, and R. Brossmer, Preparation of 9-fluoro-9-deoxy-Ai-[2-14C]acetyl-neuraminic acid, FEES Lett. 770 295 (1984). 

Precoated silica gel plates (silica gel 60) were purchased from Scientific Products. Bio-Sil A (200 - 400 Mesh) was obtained from Bio-Rad Laboratories. Fatty acid methyl esters, sphingosine and dihydrosphingosine were products of Supelco, Inc. as were 10% DEGS-PS, 3% SP-2340 and 3% OV-17 (all on Supelcoport support). N-acetyl and N-glycolyl neuraminic acid, DEAE-Sephadex A50 and neuraminidase type IX were obtained from Sigma Company. Ganglio-side standards from human brain and neutral glycosphingolipid standards from bovine erythrocytes were prepared in this laboratory. 

The 1,3 dipole diazomethane is a mild reagent to furnish methyl esters (see Chapter 13), but it has some disadvantages, too it is volatile, toxic and furthermore explosive. For this reason it has to be prepared by reaction of KOH with 7V-methyl-7V-nitroso-/ ara-toluenesulfon-amide (carcinogenic ) or in situ.11 Another simple method to protect the COOH functionality of the neuraminic acid is the esterification with methanol as solvent and reactand under H+ catalysis e. g. ion exchanger. 

The use of chiral 1-oxa-l,3-butadienes for the stereoselective preparation of carbohydrates has also been investigated by Schmidt et al. [479]. The elegant syntheses of N-acetyl-/J-D-neuraminic acid derivatives are an impressive result of these studies [480]. 

Usually, immunoglobulins are N-glycosylated at the Fc part in some cases, terminal neuraminic acid may be missing. This leads to slightly different isoelectric points of the various members in the family called isoforms. Therefore, an IgG preparation which exhibits a single band in sodium dodecyl sulfate (SDS) electrophoresis exhibits a characteristic band pattern in isoelectric focusing (Fig. 4). 

A preparation of colominic acid [poly-(V-acetylneuraminic acid)] prepared from a culture filtrate of a certain strain of Escherichia coli could be fractionated by ion-exchange chromatography into several fractions containing ultraviolet-absorbing material. One fraction contained uridine pjTophosphate linked to a neuraminic peptide. It is suggested that the... 

Free neuraminic acid, having a free 2-keto group and an amino group on C-5, has the same tendency toward formation of a nitrogen-containing, 5-membered ring. N-(Benzyloxycarbonyl)neuraminic acid (108a) is prepared by the condensation of 2-[(benzyloxycarbonyl)-... 

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