Neuraminic acid, amino sugar derivatives

C-6,209,214 anhydro sugars,branched monosaccharides, fluori-nated amino sugars,difluorinated monosaccharides, and fluorinated monosaccharide phosphates,and phosphonates have been described. Further progress has been achieved in the synthesis and n.m.r.-spectral analysis of fluorinated avermectin Bu, tylono-lide, and neuraminic acid derivatives. " ... 

Natural sialic acids (Schauer 1982 1991) are derivatives of 5-amino-3,5-dideoxy- D-glycero-D-galacto-nonu osonic acid 12.1. This awkward name has been replaced by neuraminic acid . The most common derivative is N-acetyl-neuraminic acid 12.2 whose configuration is easy to memorize because, in the Fischer representation, 12.3, it is presented as an aldolic condensation product of N-acetylmannosamine (2-acetamido-2-deoxy-D-mannose) and pyruvic acid. When the expression sialic acid is used without any other precision, it is in reference to derivative 12.2. It exists in the free state or glycosidated in the d-conformation, which allows an equatorial disposition of the three-carbon side chain. Structure 12.2 represents the stable /3-anomer of the free sugar with an axial anomeric hydroxyl group and all-equatorial non-anomeric substituents. An X-ray spectrum of this crystallized /3- anomer confirms this conformation and reveals, moreover, that the side chain has the zig-zag conformation with two... 

Sialic acid is the general name of a family of nine-carbon sugars, which are N- and O-acyl derivatives of neuraminic acid, 5-amino-3,5-dideoxy-D-glycero-D-galacto-2-nomlopyranosic acid such as 5-N-acetylneuraminic acid (NeuSAc, 1) which is the most natural occurring sialic acid [1]. 

Neuraminic acid is more complex. It is a nine-carbon amino sugar formed by the condensation of mannosamine 6-phosphate and phosphoenolpyruvate (PEP). It is the parent substance of the sialic acids which are acyl derivatives of neuraminic acid, e.g. N-acetylneuraminic acid. Sialic acids are found as constituents of glycoproteins and glycolipids and are believed to have an important bearing on the formation of the acquired integuments of the teeth (Chapter 34). 

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