Nine-carbon sugars

V-Acetylneuraminic acid is a common group in glycoproteins, and it contains both the amide and carboxyl chromophores. As shown in formula 11, this nine-carbon sugar derivative has an equatorial amido group on C-5 and both a hydroxyl group and a carboxyl group on the anomeric carbon atom. 

The most representative example of this family is iV-acetylneuraminic acid (Neu5Ac 1 Scheme 2), a nine-carbon sugar, ubiquitous in the animal kingdom and especially... 

Anion of N-Acetylneuraminic acid (NeuAc), one of the Sialic acids (Sia), nine carbon sugars found in many glycoproteins. 

Sialic acid is the general name of a mily of nine-carbon sugars, which are N- and 0-acyl derivatives of neuraminic add, 5-amino-3,5-dideoxy-D-gi ero-D-ga/ac/o-2-nonulopyranosic add such as 5-N-acetylneuraminic acid (NeuSAc, 1) which is the most natural occurring sialic add [1]. 

MOE was pioneered with the sialic acid biosynthetic pathway [15], which has proved to be especially amenable at accommodating the flux of nonnatural metabolic intermediates. This path converts (V-acetyl-D-mannosamine (ManNAc) into the nine-carbon sugar sialic acid through condensation with phospho-enolpyruvate and then installs the cytidine monophosophate (CMP)-derivatized form of this sugar onto the termini of newly synthesized glycans by the action of one of 20 sialyltransferases (see refs. 16 to 18 for more information on sialic acid metabolism). Almost two decades of experiments have established... 

In the antibiotic substance, this nine-carbon sugar derivative is attached glycosidically to the C-7 hydroxyl group of 3-[4-hydroxy-3-(3-methyl-2-butenyl)benzamido3-4,7-dihydroxy-8-methylcoumarin (56). 

Figure 17.2 The three basic forms of sialic acids, and the natural sialic acid diversity of sialoconjugates [4, 12]. The standard nine-carbon sugar backbone common to...

Sialic acids are acidic nine-carbon sugars that meet all the above discussed aspects and are special because the addition of sialic acid to glycoconjugates occurs exclusively at the non-reducing end. Because of this outstanding position, sialoglycoconjugates form the communication front of animal cells. Mandal and colleagues review this richness of the sialome with a focus on the O-acetylation of sialic acids. O-Acetylation represents a developmentally regulated modification and a marker of some cancer cells such as lymphoblasts in acute lymphoblastic leukemia. 

A-acetyl-mannosamine is an important precursor for the biosynthesis of the nine carbon sugar acid, iV-acetyl-D-neuraminic acid (see section 10.5 and Fig. 10.8A) that is frequently found as a monosaccharide in glycoproteins and glyco-lipids (see Chapter 9). 

Biosynthesis of Eight- and Nine-Carbon Sugars N-Acetyl-D-Neuraminic Acid, N-Acetyl-o-Muramic Acid, and 2-Keto-3-Deoxy-D-Mannooctulosonic Acid (KDO)... 

A -acetyl-D-neuraminic acid is biosynthesized from A -acetyl-D-mannosamine and phosphoenol pyruvate, catalyzed by N-acetyl-D-neuraminic acid synthase. The first step involves the addition of an electron pair from the double bond of the phosphoenol pyruvate to the aldehyde group to give an aldol-type condensation (see Fig. 10.8A). The product is the nine-carbon sugar acid, A -acetyl-D-neuraminic acid [23]. In some instances the enzyme requires A-acetyl-D-mannosamine-6-phosphate as the substrate and forms A-acetyl-D-neuraminic acid-9-phosphate. Various hydroxyl groups on C-4, -7, -8, and -9 can be acetylated by specific acetyl transferases using acetyl CoAas the donor. KDO (2-keto-3-deoxy-D-mannooctulosonic acid) is biosynthesized by a very similar condensation between D-arabinose-5-phosphate and pyruvic acid, catalyzed by KDO synthase (see Fig. 10.8B) [24]. 

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