2-Octulosonic acid lipopolysaccharides

Some examples of transformations involving carbonyl ylides are listed in Table 4.20. Entry 1 illustrates the conversion of P-acyloxy-a-diazoesters into a-acyloxyacrylates by ring fission of a cyclic carbonyl ylide [978]. This reaction has been used for the synthesis of the natural aldonic acid KDO (3-deoxy-Z)-manno-2-octulosonic acid), which is an essential component of the cell wall lipopolysaccharide of gram-negative bacteria (Figure 4.15). 

The occurrence of 3-deoxy-D-manno-octulosonic acid in lipopoly-saccharides has prompted its synthesis,537 together with the D-gal-octo158 and the D-gluco analogs.157 Although gas-liquid chromatography was successfully used to analyze the products of these syntheses, it has been reported that methanolysis of a bacterial endotoxin lipopolysaccharide failed to yield 3-deoxy-D-manno-octulosonic acid, presumably because of the lability of the latter to acid.381 However, Kasai and Nowotny have reported four peaks for the O-trimethylsilyl derivatives of 3-deoxy-D-manno-octulosonic acid obtained by methanolysis of the glycolipid from a Salmonella minnesota mutant.538 Reduced 3-deoxy-D-manno-octulosonic acid and its methyl ester have also been analyzed successfully as their acetates.339,539... 

The polysaccharide component of a lipopolysaccharide can be separated from the lipid component by selective hydrolysis of the glyco-sidic linkages of the 3-deoxy-D-manno-octulosonic acid residues connecting these two components. The conditions for the hydrolysis are mild, namely, 0.1 M acetic acid for 1.5 h at 100° (Ref. 18). Similar conditions, namely, M formic acid for 1 h at 100° or 0.05 M hydrogen chloride in methanol for 1 h at 85°, were used to split off the sialic acid residues from gangliosides.19,20... 

FIGURE 7-32 Bacterial lipopolysaccharides. (a) Schematic diagram of the lipopolysaccharide of the outer membrane of Salmonella ty-phimurium. Kdo is 3-deoxy-o-manno-octulosonic acid, previously called ketodeoxyoctonic acid Hep is L-glycero-D-mannoheptose AbeOAc is abequose (a 3,6-dideoxyhexose) acetylated on one of its hydroxyls. There are six fatty acids in the lipid A portion of the molecule. Different bacterial species have subtly different lipopolysaccharide structures, but they have in common a lipid region (lipid A), a core oligosaccharide, and an "O-specific" chain, which is the prin-... 

The six-carbon chain of ManNAc 6-P can be extended by three carbon atoms using an aldol-type condensation with a three-carbon fragment from PEP (Eq. 20-7, step c) to give N-acetylneuraminic acid (sialic acid).48 Tire nine-carbon chain of this molecule can cyclize to form a pair of anomers with 6-membered rings as shown in Eq. 20-7. In a similar manner, arabi-nose 5-P is converted to the 8-carbon 3-deoxy-D-manno-octulosonic acid (KDO) (Fig. 4-15), a component of the lipopolysaccharide of gram-negative bacteria (Fig. 8-30), and D-Erythrose 4-P is converted to 3-deoxy-D-arafrmo-heptulosonate 7-P, the first metabolite in the shikimate pathway of aromatic synthesis (Fig. 25-1).48a The arabinose-P used for KDO synthesis is formed by isomerization of D-ribulose 5-P from the pentose phosphate pathway, and erythrose 4-P arises from the same pathway. 

Two of the most frequent monosaccharide components of bacterial polymers belonging to this group have been the subjects of articles in this Series. They are 3-deoxy-D-manno-2-octulosonic acid,247 a normal constituent of the core region of bacterial lipopolysaccharides that is also present in some other polymers, and N-acetylneuraminic acid,248 found in several capsular polysaccharides. Enolpyruvate phosphate serves as the precursor of the C-l-C-3 fragment of the monosaccharides, with D-arabinose 5-phosphate or 2-acetamido-2-deoxy-D-mannose 6-phosphate being an acceptor for transfer of the three-carbon unit. Characteristic, activated forms of these monosaccharides are the CMP derivatives. 

The 3-deoxy-D-ma/ino-2-octulosonic acid 8-phosphate synthase (KDO synthase or KdoS EC 4.1.2.16) is an enzyme involved in the biosynthesis of the eight-carbon sugar KDO [63], a constituent of the capsular polysaccharides (K-antigens) and outer membrane lipopolysaccharides (LPS, endotoxin) of Gram-negative bacteria [156], as well as of the cell wall of algae and a variety of plants [157], In vivo, the enzyme catalyzes the irreversible addition of 26 to D-arabinose 5-phosphate (Ara5P, 32) to form KDO 8-phosphate 33 [158]. The... 

Brozek, K.A., Hosaka, K., Robertson, A.D., Raetz, C.R.H. Biosynthesis of lipopolysaccharide in Escherichia coli cytoplasmic enzymes that attach 3-deoxy-D-manno-octulosonic acid to lipid A. J Biol Chem 264 (1989) 6956-6966. 

Kanipes, M.I., Lin, S., Cotter, R.J., Raetz, C.R. Ca2+-induced phosphoethanolamine transfer to the outer 3-deoxy-D-manno-octulosonic acid moiety of Escherichia coli lipopolysaccharide. A novel membrane enzyme dependent upon phosphatidylethanolamine. J Biol Chem 276 (2001) 1156-1163. 

The key component of the cell wall lipopolysaccharide of Gram-negative bacteria, KDO (3-deoxy-D-manno-2-octulosonic acid), was synthesized by S.D. Burke and co-workers. One of the key transformations in the synthetic sequence was a doubie SAD of a 6-vinyldihydropyran-2-carboxylate template. This 1,4-diene was cleanly converted to a mixture of two C7 epimeric tetraols in a 20 1 ratio. The endocyclic olefin had an intrinsic preference for dihydroxyiation from the 3-face and not from the desired a-face. This stereofacial bias was impossible to override with any ligand normally used in the SAD, so later in the synthesis these two stereocenters had to be inverted in order to give the required stereochemistry at C4 and C5. 

ABSTRACT This article describes recent developments in the chemistry of an important family of complex monosaccharides which have diverse structures and participate in a wide range of biological processes. For example 3-deoxy-D-/n nno-2-octulosonic acid (KDO) is a key component of the lipopolysaccharides (LPS) of Grammnegative bacteria, 3-deoxy-D-araftmo-2-heptulosonic acid (DAH) is a key intermediate in the biosynthesis of aromatic amino acids in bacteria and plants. A number of their syntheses that were achieved by homologation reactions of the natural carbohydrate units using enzymatic or chemical methods, as well as by total synthetic approaches are here included. Special emphasis is placed on new methodologies and their correlation with the biosynthetic pathway of the corresponding ulosonic acids. 

Figure 2.9 Generalized structures of lipopolysaccharide and lipid A. Abbreviations Abe, abequose Man, Mannose Rha, rhamnose Gal, galactose Glc, glucose Hep, heptose KDO, 3-deoxy-D-manno-octulosonic acid 0, phosphate EtN, ethanolamine M, myristate Mo, y3-hydroxymyristate. Reproduced with permission from Harwood and Russell (1984).

Gram-negative bacteria contain lipopolysac-charide in the outer membrane of their cell envelope. The lipopolysaccharide is a complex polymer with four parts. On the outside is a polysaccharide of very variable structure which is then attached to a core polysaccharide which itself is divided into an outer core and a backbone. The outer cores are variable in composition but the link which connects the backbone to lipid A is usually composed of 3-deoxy-D-manno-octulosonic acid (KDO). The presence of KDO (Fig 3.3) is often used as a marker for lipopolysaccharide or outer membrane. 

The proportions of D-glucose, D-galactose, and D-mannose in the lipopolysaccharides of five colonial types of Neisseria gonorrhoeae vary from strain to strain. The virulent types 1 and 2 generally contain a higher proportion of hexose and higher ratios of o-mannose or D-galactose to 3-deoxy-D-manno-2-octulosonic acid than the avirulent types 3, 4, and 5. 

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