Daniel Charon

Synthesis and acidic degradation of 3-deoxy-ketoaldonic acids

The syntheses of 3-deoxy-D-threo-2-hexulosonic acid and 3-deoxy-D-arabino-2-heptulosonic acids are described. Upon treatment with acid. 6-, 7-, and 8-carbon 3-deoxy-ketoaldonic acids first yield enolic 1,4-lactones, which are further transformed into 5-(hydroxyalkyl)-2-furoic acids.

Pyranoside derivatives of 3-deoxyald-2-ulosonic acids

At pH 11.5 in 0.2M-sodium tetraborate solution and in the presence of Ni2+, 2-O-benzyl-D-arabinose reacts with oxaloacetic acid to give a 50–60% yield of 5-O-benzyl-3-deoxyoct-2-ulosonic acids (mixed D-gluco- and D-manno-isomers). The methyl esters of these were separated and the α-methyl glycoside of the D-manno-isomer was prepared. The conformation of the compounds was established by n.m.r. spectroscopy at 250 MHz. It was observed that esterification of the carboxy-group greatly increases the stability of the glycosidic bond of 3deoxy-D-manno-octulosonic acid while the benzyl substituent in position 5 exerts only a weak stabilising effect. 2-O-Benzyl-D-glyceraldehyde, when treated with oxaloacetic acid in the presence of Ni2+ at pH 7 in the absence of borate, yields 5-O-benzyl-3-deoxyhex-2-ulosonic acids, the predominant D-erythro-isomer being isolated as its methyl ester.

Furanose derivatives of 3-deoxy-D-manno-oct-2-ulosonic acid

Acylation of methyl 3-deoxy-D-manno-oct-2-ulosonate leads essentially to furanose derivatives, whereas acetylation of the free acid or of its ammonium salt gives pyranose derivatives. Upon treatment with HBr in acetic acid, the pentabenzoate of methyl 3-deoxy-D-manno-oct-2-ulofuranosonate yielded a crystalline 2-bromo-derivative which, when treated with MeOH–Ag2CO3 was transformed into a single methyl furanoside of undetermined anomeric configuration. Reaction of methyl 3-deoxy-D-manno-oct-2-ulosonate with MeOH in the presence of an acidic catalyst gives a mixture of pyranoside(s) and furanosides separable by g.l.c.; they can be identifed by the characteristic fragments at m/e 217 for the furanosides and m/e 158 for the pyranoside(s).

[6] Estimation of 3-deoxy-2-ketoaldonic acids

Publisher Summary This chapter describes the estimation of 3-deoxy-2-ketoaldonic acids. In estimation with thiobarbituric acid, treatment of 3-deoxy-2-ketoaldonic acids with periodate yields 2,4-dioxobutyrate, which condenses with 2-thiobarbituric acid to give a red dye having an absorption maximum at 549 nm. Only free— that is, unsubstituted, 3-deoxy-2-ketoaldonic acids can be estimated reliably with periodate/thiobarbiturate. Indeed, to obtain quantitative results, one molar equivalent of 2,4-dioxobutyrate “ β -formyl pyruvate” must be released during the oxidation reaction, and this reaction must take place at a rate considerably greater than the destruction of the dioxobutyrate itself by periodate. In the case of phosphorylated aldulosonic acids with 5–8 carbon atoms dephosphorylation is carried out with acid phosphatase prior to the periodate cleavage; the incubation with the enzyme is carried out in a volume of 0.1–0.3 ml, which is then diluted to the appropriate volume with the cold NaIO 4 /H 2 SO 4 solution. In the case of 5-0-substituted 3-deoxy-2-ketooctonic acids, the molar absorption coefficient was found to be about 13,000 for both compounds, and it is probable that this value will be valid for all 5-0-substituted 3-deoxyoctulosonates. The molar absorption coefficient in the conditions of the cold acid method has not been determined. In estimation with diphenylamine, 3-Deoxy-D-manno - octulosonic acid is heated with diphenylamine in acid solution; a condensation product of unknown composition is formed whose absorption is used for the estimation of the aldulosonate. The method can be applied successfully for the accurate estimation of 5- 0 -glycosylated 3-deoxyoctulosonic acids, and very probably, to that of free and 0-substituted 3-deoxy-2-ketoaldonic acids in general, provided that the 0-substituent is acid labile.

Phosphorylated sugars. Part XX. Synthesis of 3-deoxy-D-manno-octulosonic acid 8-(dihydrogen phosphate)

The title compound was obtained by base-catalysed condensation of 2-O-benzly-D-arabinose 5-phosphate with oxalacetate, followed by hydrogenolytic removal of the benzyl group. It was separated from the simultaneously formed D-gluco-isomer by ion-exchange chromatography.

Chemistry of bacterial endotoxins. Part 1. Block synthesis of 6-O-{4-O-ammonio(hydrogen)phosphono-2-deoxy-2-[(3R)-3-hydroxy-tetradecanamido]-β-D-glucopyranosyl}-2-deoxy-2-[(3R)-3-hydroxy-tetradecanamido]-D-glucose

The synthesis of the disaccharide present in the hydrophobia region of many endotoxins, a 2-amino-2-deoxy-β-D-glucopyranosyl-(1 → 6)-2-amino-2-deoxy-D-glucose in which the amino groups are acylated by (3R)-3-hydroxytetradecanoic acid residues and the 4″-hydroxy group is esterified by phosphate, is described. Two synthons carrying the specific substituents were prepared and condensed; stepwise removal of the protecting groups from the disaccharide thus formed afforded the title compound.

Determination of the anomeric configuration in glycosides of 3-deoxy-2-aldulosonic acids by circular dichroism and X-ray crystallography

Methyl (methyl 3-deoxy-D-arabino-2-heptulopyranosid)onate was obtained by acid-catalysed esterification and glycosidation of the free 2-aldulosonic acid. The molecular geometry of the glycosidic ester was determined by X-ray crystallography, and indicated both that the molecule was the α-anomer and that the ring oxygen and the carboxy-group were very nearly coplanar. The c.d. spectrum showed a negative n →π* transition band centred at 224 nm. The c.d. spectra of a number of methyl glycopyranosides derived from 6-, 7-, and 8-carbon 3-deoxy-2-aldulosonic acids demonstrated that all the compounds believed to be α-glycosides had negative maxima, and all those believed to be β-glycosides had positive maxima around 220 nm independent of their 2C5 or 5C2 conformation. The only known furanoside, believed to be a β-anomer, also had a positive maximum. The chirality of the anomeric carbon atom of this class of compound can thus be conveniently established by determining the sign of the Cotton effect at 220 nm.

[20] 3-deoxy-2-ketoaldonic acids

Publisher Summary This chapter describes 3-deoxy-2-ketoaldonic acids. The α -hydroxy group of a 3-deoxyaldonic acid is selectively oxidized by chlorate in the presence of vanadium oxide and phosphoric acid, and the keto acid is isolated by chromatography on cellulose powder. Methyl 3-deoxyheptonate is prepared from commercial 2- deoxy -D-arabino- hexose (2- deoxyglucose). But, the melting point of the crystalline material varies from one preparation to another owing to the presence of varying amounts of epimers (D-gluco and D-manno-) in the sample. The ratio of the epimers does not affect the yield or the quality of the final product. Galactometasaccharinic acid lactone is a mixture of 3-deoxy D-xylo- and D-lyxo-hexonic acid lactones. For the preparation of ammonium 3-deoxy D -threo- hex-2-ulosonate, this lactone (3.2 g) is first hydrolyzed with sodium hydroxide and then treated with sodium chlorate (740 mg), vanadium oxide (120 mg), and phosphoric acid (0.1 ml) as described for the 7-carbon homolog. Detection of 3-deoxyaldulosonic acids on chromatograms and detection of polyhydroxy compounds on paper chromatograms are also discussed.

Chemistry of bacterial endotoxins. Part 6. Synthesis of allyl 5-O-(α-D-mannopyranosyl)-(3-deoxy-α-D-manno-oct-2-ulopyranosid) onic acid and of allyl 5-O-(α-D-mannopyranosyl)-(3-deoxy-α-D-manno-oct-2-ulopyranosid)onic acid 4-phosphate and their copolymers with acrylamide

A mixture of methyl (allyl-7,8-O-cyclohexylidene-3-deoxy-α-, and -β-D-manno-oct-2-ulopyranosid)onates (3 : 1) was prepared from methyl 2,4,5,7,8-penta-O-acetyl-3-deoxy-α-D-manno-oct-2-ulopyranosonate in 3 steps and the anomers were separated by chromatography. Sequential treatment of the α-glycoside with dibutyltin oxide and tert-butyldimethylsilyl chloride gave the corresponding 4-O-tert-butyldimethylsilyl 1,5-lactone. Transformation of the lactone with MeONa to the corresponding ester, was accompanied by partial migration of the silyl group and yielded a 2:1 mixture of the 4-O-, and 5-O-tert-butyldimethylsilyl derivatives which were separated by chromatography. Condensation of the former with 2,3,4,6-tetra-O-benzoyl-α-D-mannopyranosyl bromide in 1,2-dichloroethane in the presence of N,N,N′,N′-tetramethylurea and under silver trifluoromethanesulphonate catalysis afforded a 71% yield of the protected α-linked disaccharide. The silyl group was removed selectively with tetrabutylammonium fluoride, whereafter deprotection by conventional methods produced the unprotected title disaccharide. The alcohol obtained after the removal of the silyl group was treated with bis(trichloroethyl) phosphorochloridate to afford the corresponding phosphotriester which, after deprotection, gave the phosphorylated title disaccharide. Both were copolymerized with acrylamide. 1H NMR revealed that the phosphorylated disaccharide formed a complex with Ca2+ involving Man 4-O, 6-O, and oxygen atoms of the phosphate group.

Chemistry of bacterial endotoxins. Part 4. Synthesis of anomeric 2-deoxy-2[(3R)-3-hydroxytetradecanamido]-D-glucopyranosyl phosphate and pyrophosphate derivatives related to ‘Lipid A’

Syntheses of both anomers of 2-deoxy-2-[(3R)-3-hydroxytetradecanamido]-D-glucopyranosyl phosphate and of 2-amino-2-deoxy-D-glucopyranosyl 2-aminoethyl phosphate are reported, as well as those of two pyrophosphate derivatives of glucosamine, namely 2-deoxy-2-[(3R)-3-hydroxytetradecanamido]-α-D-glucopyranosyl pyrophosphate and P1-(2-aminoethyl)P2-{2-deoxy-2-[(3R)-3-hydroxytetradecanamido]-α-D-glucopyranosyl}pyrophosphate, structures that have been identified as being present in the hydrophobic region (Lipid A) of endotoxins.