2-Deoxy- 3-KDO

Several enzymatic procedures have been developed for the synthesis of carbohydrates from acyclic precursors. Aldolases appear to be useful catalysts for the construction of sugars through asymmeteric C-C bond formation. 2-deoxy-KDO, 2-deoxy-2-fluoro-KDO, 9-0-acetyl sialic acid and several unusual sugars were prepared by a combined chemical and enzymatic approach. Alcohol dehydrogenases and lipases have been used in the preparation of chiral furans, hydroxyaldehydes, and glycerol acetonide which are useful as building blocks in carbohydrate synthesis. 

Figure 5. Chemical conversion of KDO to 2-deoxy- -KDO and 2-deoxy-2-fluoro-KDO...

Methanolysis of 199, followed by oxidative degradation of the furan ring proceeded smoothly, providing KDO derivative 66. Transformation of 199 into 2-deoxy-KDO required the hydrogenation in the first step leading after several transformation to the methyl ester of the resulted acid. 

This ketene dithioacetal protocol was employed to deliver all the isomeric 3-deoxy-heptulosonic and heptulosaric acids, as well as their 2-deoxy counterparts [130]. Further, by this route the synthesis of KDO and 2-deoxy-KDO was accomplished [133]. This methodology was also utilized for direct construction of naturally occurring KDO disaccharides [134]. 

Different concept of 2-deoxy-KDO synthesis was presented by Craig [151]. The synthetic route started from epoxide 281 and 3,3-dimethoxy-l-(phenylsulfonyl)-propane which were transformed, after several manipulation, to bicyclic alcohol 284 (Scheme 60). 

An interesting new route to 2-deoxy-Kdo is illustrated in Scheme 6. Although not relevant to the overall synthesis, it is noteworthy that the epiixm shown was produced highly stereoselectively in the initial addition of ethyl diazoacetate. The final intramolecular insertion reaction was also... 

Molecular orbital calculations have been carried out on 2-fluoro- and 2-chloro-tetrahydropyrans as models for examining the anomeric effect in gtycosyl halides. The calculated population of the axial conformer decreased as the solvent polarity increased, which indicated a consequent decrease in the anomeric effect.The synthesis of a series of 2-(perfluoroall yl) ethyl glycosides is mentioned in Chapter 3, and some 3 -fluorinated ribonucleosides are covered in Chapter 20. The syntheses of 2-fluoro-L-daunosaniine and 2-fluoro-D-ristosamine are discussed in Chapter 9, while 2 -fluorocarminontydn is described in Chapter 19, and some fluorinated 2-deoxy KDO analogues are covered in Chapter 16. 

The 5-0-a-L-rhamnopyranosyl derivative of KDO and KDO 7-(2-aminoethylphosphate) have both been isolated from the inner core region of the lipopolysaccharide (LPS) of E.coli K12. The syntheses of KDO-7-phosphate and 7-(2-acetamidoethyl phosphate) have been carried out by phosphorylation of an appropriately-protected derivative. It has been shown that in solution KDO 8-phosphate exists as a mixture of a-pyranose (66%), P-pyranose (3%), a-furanose (19%) and P-furanose (12%) forms. By use of the two isomeric 2-deoxy analogues of KDO 8-phosphate it was shown that KDO 8-phosphate phosphatase is speciflc for the a-pyranose form of the substrate, so that a mutarotation must be involved before the next stage in the formation of LPS, since CMP-KDO synthetase is specific for the P-pyranose form of KDO. 0 Other references to 2-deoxy-KDO and 2-deoxy-NeuNAc can be found in Section 1 of this Chapter. 

Starting from L-arabinose is noted in Chapter 24. A synthesis of the enzyme inhibitor 2-deoxy- -KDO is referred to in Chapter 16. 

The phosphonate analogue of cytldine 5 -monophospho-3-deoxy-D-manno-oct-2-ulosonic acid has been synthesized as illustrated in Scheme 14, and "azacyclic-2-deoxy-KDO" was produced from KDO as shown in... 

The biosynthesis of Kdo and neuraminic acid is known to involve enol-pyruvate phosphate and D-arabinose or 2-acetamido-2-deoxy-D-mannose, respectively. Nothing is known about the biosynthesis of all the other glycu-losonic acids. One interesting problem is, for example, whether the two 5,7-diamino-3,5,7,9-tetradeoxynonulosonic acids are synthesized analogously to neuraminic acid, from a three- and a six-carbon fragment, by modification of neuraminic acid on the sugar nucleotide level, or by a third, less obvious route. 

Observation of displacement effects resulting from O-substitution, and use of standards, led to the assignment of the chemical structure of the polysaccharide of Neisseria meningitidis serogroup 29e, which consists of 2-acetamido-2-deoxy-D-galactosyl and partly acetylated 3-deoxy-D-manno-octulosylonic acid (KDO) residues.166 The 13C-n.m.r. spectrum of the O-deacetylated polymer (see Fig. 36,B) contained 15 signals out of the possible 16 expected from an alternating structure. Comparison of these resonances with those of the anomers of 2-aceta-... 

KDO appears to be unique to Gram-negative bacteria. In the LPS that have been studied, KDO residues are situated at the reducing ends of the polysaccharide domains, linking them, by ketosidic bonds, to the fatty-acid-substituted 2-amino-2-deoxy-D-glucosyl disaccharides referred to as lipid A. Fig. 2 is a block diagram indicating the location of KDO in the LPS from Salmonella. 

Following the synthesis by Comforth and his associates18 of NeuAc from oxalacetate and 2-acetamido-2-deoxy-D-mannose, Ghalambor and Heath29,31 prepared KDO (isolated as the crystalline methyl 2,4,5,7,8-penta-0-acetyl-3-deoxy-D-manno-2-octulopyranosonate, 70) from D-arabinose and oxalacetate by an analogous reaction (see Scheme 20). 

Heath and Ghalamboi29 31 had obtained a 2-deoxyheptose of unknown configuration by degradation with ceric sulfate of 15 (see Scheme 8), the product obtained upon reduction of KDO with sodium borohydride. Perry and Adams94 had shown this 2-deoxyheptose to be identical with 2-deoxy-D-manno-heptose (62 see Scheme 18), synthesized by Perry.91... 

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. 

Anomeric triphenylphosphonium salts have been used as well as phenylsul-fides,but in the latter case extra stabilization is necessary (see below). Anomeric nitrosugars, which have been extensively studied in C-glycosylation reactions by Vasella, will be covered in Sect. 2.2.1 and ester enolates derived from 3-deoxy-2-ketoulosonic acids (sialic acid and KDO derivatives), which bear a structural similarity to 2-deoxy pyranosides, will be covered in Sect. 4.4. Deprotonation of anomeric phenylsulfones has been discussed in Sect. 2.1.1 and additional transformations on closely related compounds are presented in Scheme 14 [20]. Alkylation of phenylsulfone 54 with epoxide 55 provides adduct 56 which eliminates benzenesulfinic acid at room temperature to give the C(l)-alkylated glycal 57 a similar elimination is also observed with adducts derived from... 

Synthesis and Use of 3-Deoxy-D -manno-2-octulosonate (KDO) in Escherichia coli... 

The requirement of the remaining enzymes, KD0-8-phosphate synthase, KD0-8-phosphate phosphatase and CMP-KDO synthetase, for their natural substrates, D-arabinose-5-phosphate + PEP, KD0-8-phosphate and KDO + CTP, respectively, was specific and the inhibition studies with substrate analogues were disappointing. Of the compounds tested as potential substrates of KD0-8-phosphate synthase, only the isosteric phosphonate analogue (Compound 11, Table III) of D-arabinose-5-phosphate was an alternate substrate (see Ref. 28). There were a number of weak competitive inhibitors of the synthase reaction (Compounds 2, 5, 6, 7, 15,and 19,Table III) the best inhibitor of the synthase reaction was 2-deoxy-2-fluoro-D-arabinonate-5-phosphate (compound 14, Table III). 

Isshiki, Y., Zahringer, U., Kawahara, K. Structure of the core oligosaccharide with a characteristic D-glycero-a-D-talo-oct-2-ulosonate-(2- -4)-3-deoxy-D-manno-oct-2-ulosonate [a-Ko-(2- -4)-Kdo] disaccharide in the lipopolysaccharide of Burkholderia cepacia. Carbohydr Res 338 (2003) 2659-2666. 

Vinogradov, E., Korenevsky, A., Beveridge, T.J. The structure of the rough-type lipooligosaccharide from Shewanella oneidensis MR-1, containing 8-amino-8-deoxy-Kdo and an open-chain form of 2-acetamido-2-deoxy-D-galactose. Carbohydr Res 338 (2003) 1991-1997. 

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