An improved procedure for the analysis of linkage positions in 2-acetamido-2-deoxy-D-glucopyranosyl residues by the reductive-cleavage method

Authentic standards for the reductive-cleavage method. The positional isomers of partially methylated and acetylated or benzoylated methyl 2-(acetylmethylamino)-2-deoxy-beta-D-glucopyranoside

Described herein is the synthesis of eight positional isomers of methylated and acetylated or benzoylated methyl 2-(acetylmethylamino)-2-deoxy-beta-D-glucopyranoside. The compounds were generated simultaneously from methyl 2-(acetylmethylamino)-2-deoxy-beta-D-glucopyranoside by sequential partial methylation and benzoylation and isolated in pure form by high-performance liquid chromatography (HPLC). The desired acetates were obtained by debenzoylation and acetylation of the pure isomers. Reported herein are the 1H NMR spectra of the benzoates and the electron-ionization mass spectra of the acetates and the tri-O-methyl derivative. Also reported for the acetates and the tri-O-methyl derivative are their linear temperature-programmed gas-liquid chromatography (GLC) retention indices on three different capillary columns.

Isolation and characterization of the cell-surface polysaccharides of Porphyromonas gingivalis ATCC 53978

The cell-surface carbohydrates of Porphyromonas gingivalis strain ATCC 53978 were isolated and partially characterized. Three separate polysaccharides were found to be present: an extracellular polysaccharide, capsular polysaccharide and lipopolysaccharide. The capsular polysaccharide, which had peculiar, gel-like viscoelastic properties, was found to be comprised of mannuronic acid, glucuronic acid, galacturonic acid, galactose, and 2-acetamido-2-deoxy-D-glucose in relative molar ratios of 0.6:0.9:0.5:0.5:1.0, respectively. The extracellular polysaccharide was found to contain mannose, rhamnose, glucose, galactose, and 2-acetamido-2-deoxy-D-glucose in relative molar ratios of 13.5:1.4:1.0:2.0:1.0, respectively. The lipopolysaccharide was found to contain an O-antigen with a regular tetrasaccharide repeat unit comprised of 4-linked alpha-L-rhamnopyranosyl, 6-linked alpha-D-glucopyranosyl, 3-linked alpha-D-galactopyranosyl, and 4-linked 2-acetamido-2-deoxy-beta-D-glucopyranosyl residues in equimolar proportions.

Mechanism of anomerization of cyclohexyl 2-deoxy-3,4,6-tri-O-methyl-2-(N-methylacetamido)-alpha- and beta-D-hexopyranosides under reductive-cleavage conditions

The fully methylated cyclohexyl glycosides of 2-acetamido-2-deoxy-alpha- and beta-D-hexopyranoses having the gluco, manno, and galacto configurations were each subjected to reductive-cleavage conditions using one of three promoters, namely trimethylsilyl trifluoromethanesulfonate, a mixture of trimethylsilyl methanesulfonate and boron trifluoride etherate, or boron trifluoride etherate alone. As expected, the fully methylated 1,2-trans-linked acetamido sugar derivatives were rapidly converted to their respective oxazolinium ions with all three promoters. Surprisingly, however, the fully methylated 1,2-cis-linked acetamido sugar derivatives were also converted to their respective oxazolinium ions, albeit at a much slower rate. In the latter case, evidence was obtained for anomerization to the 1,2-trans-linked isomers under reductive-cleavage conditions. Since the anomerization was relatively slow at room temperature in dichloromethane, a modified procedure was developed in which the reaction was carried out at 70 degrees C in 1,2-dichloroethane. Using the modified procedure, all 1,2-cis- and 1,2-trans-linked acetamido sugar derivatives were rapidly converted into their respective oxazolinium ions and subsequent quenching of the reactions with anhydrous methanol gave the respective 1,2-trans-linked methyl glycoside derivatives in quantitative yield. The modified procedure is recommended for the total reductive cleavage of polysaccharides comprised of acetamido sugar residues.

Reductive cleavage of glycosides with borane complexes in the presence of boron trifluoride etherate

Mixtures consisting of five equivalents each of borane.methyl sulfide and boron trifluoride etherate per equivalent of acetal or five equivalents of various amine-borane complexes and 10 equivalents of boron trifluoride etherate readily accomplished reductive cleavage of the glycosidic linkages of several per-O-methylated monosaccharides and polysaccharides. In all cases, the expected products were obtained in the expected molar proportions and no artifactual products were observed. Reductive-cleavage analysis using these reagents is particularly convenient because the reagents themselves are easy to handle and because subsequent acetylation of the products is accomplished in situ.

Analysis by the reductive-cleavage method of a polysaccharide containing 2-acetamido-2,6-dideoxy-D- and -L-galactopyranosyl residues

Modifications of the reductive-cleavage method for the analysis of 2-acetamido sugars were tested using a polysaccharide containing alpha-linked 2-acetamido-2,6-dideoxy-L-galactopyranosyl (Fuc pNAc) residues, beta-linked D-Fuc pNAc residues and 2-linked D-glucopyranosyl residues. Reductive cleavage of the fully methylated O-antigenic polysaccharide of Pseudomonas aeruginosa ATCC 33358 in the presence of triethylsilane and trimethylsilyl trifluoromethanesulfonate, followed by quenching with methanol and subsequent acetylation, unexpectedly resulted in nearly complete cleavage of all glycosidic linkages to yield 2-O-acetyl-1,5-anhydro-3,4,6-tri-O-methyl-D-glucitol (1a) and methyl 3-O-acetyl-2,6-dideoxy-4-O-methyl-2-(N-methylacetamido)-beta-D- and -L- galactopyranosides (3a and 4a) as the major products. When the reductive-cleavage reaction was quenched with (S)-2-butanol, the major FucNAc derivatives were the diastereomeric (S)-2-butyl glycosides 15a and 17a, confirming the presence of enantiomeric FucNAc residues in the repeating unit of the polysaccharide. However, compounds 15a and 17a were not detected in equimolar proportions, presumably as a consequence of diastereoselectivity in the reaction of the chiral alcohol with the respective intermediate oxazolinium ions. Reductive cleavage of the fully methylated polysaccharide in the presence of a mixture of trimethylsilyl methanesulfonate and boron trifluoride etherate, followed by quenching with methanol, resulted in incomplete cleavage, giving rise to three disaccharide derivatives whose sequences overlap that of the trisaccharide repeating unit in the polysaccharide. The lack of selectivity for cleavage at beta-D-FucNAc residues suggests that the alpha-L-FucNAc residues underwent anomerization prior to transglycosidation.