Syntheses of 2-acetamido-2-deoxy-4-O-βD-galacto-pyranosyl-D-mannose and -D-glucose and of 2-acetamido-2-deoxy-4-O-βD-mannopyranosyl-D-mannose and -D-glucose

Preparative production and separation of 2-acetamido-2-deoxymannopyranoside-containing saccharides using borate-saturated polyolic exclusion gels

A new separation method based on the combination of exclusion and ion exchange chromatography in borate buffer was developed. It allows semi-preparatory and preparatory separation of isobaric N-acylhexosamines (C-2 epimers) and corresponding methyl glycosides (anomers and tautomers). Three types of polyolic gels were tested for these separations. Ion-exchange HPLC was used as a rapid and reliable method for the quantification of the respective analytes. NMR studies of the interactions of N-acetylhexosamines with borate confirmed the importance of a proper stereochemical arrangement of acetamido sugars for their interactions with borate anions.

High affinity binding of the Entamoeba histolytica lectin to polyvalent N-acetylgalactosaminides

Entamoeba histolytica trophozoites initiate pathogenic colonization by adherence to host glycoconjugates via an amebic surface lectin which binds to galactose (Gal) and N-acetylgalactosamine (GalNAc) residues. Monovalent and multivalent carbohydrate ligands were screened for inhibition of E. histolytica lectin-mediated human red cell hemagglutination, revealing that: (i) the synthetic multivalent neoglycoprotein GalNAc39BSA (having an average of 39 GalNAc residues linked to bovine serum albumin) was 140,000-fold more potent an inhibitor than monovalent GalNAc and 500,000-fold more potent than monovalent Gal; and (ii) small synthetic multivalent ligands which bind with high affinity to the mammalian hepatic Gal/GalNAc lectin do not bind with high affinity to the E. histolytica lectin. Radioligand binding studies revealed saturable binding of 125I-GalNAc39BSA to E. histolytica membranes (KD = 10 +/- 3 nM, Bmax = 0.9 +/- 0.08 pmol/mg membrane protein). Maximal binding required the presence of calcium chloride (300 microM) or sodium chloride (50 mM), and had a broad pH maximum (pH 6-9). GalNAc39BSA was 200,000-fold more potent than monovalent GalNAc in blocking radio-ligand binding. Among synthetic saccharide-derivatized linear polymers, the GalNAc beta and GalNAc alpha 3Gal beta derivatives were the most potent, with GalNAc alpha and GalNAc alpha 3(Fuc alpha 2)Gal beta derivatives much weaker. The data support a model in which a unique pattern of spaced multiple GalNAc residues are the highest affinity targets for the E. histolytica lectin.

Separation of sugars by ion-exclusion chromatography on a cation-exchange resin

A method for the separation of N-acetylmannosamine and N-acetylglucosamine is described, which consists of chromatography of the two sugars on a column (30 x 1 cm) of the cation-exchange resin, Dowex 50W-X2, in borate buffer at pH 7.8. N-Acetylmannosamine is eluted near the void volume, while N-acetylglucosamine emerges in a more retarded position. It is postulated that the separation occurs as a result of the combined effects of ion exclusion and gel permeation. Thus, in borate solution, N-acetylmannosamine presumably exists largely as a negatively charged complex and is therefore excluded from the sulfonated polystyrene matrix, while N-acetylglucosamine occurs mainly as the free sugar in the equilibrium mixture and, being a neutral compound, has free access to the porous resin. The proposed mechanism for the separation was supported by the finding that glucose and glucose 6-phosphate could also be separated on a column of the same resin, with water as the eluent.

Binding characteristics of N-acetylglucosamine-specific lectin of the isolated chicken hepatocytes: similarities to mammalian hepatic galactose/N-acetylgalactosamine-specific lectin

Binding characteristics of N-acetylglucosamine- (GlcNAc) specific lectin on the chicken hepatocyte surface were probed by an inhibition assay using various sugars and glycosides as inhibitors. Results indicated that the binding area of the lectin is small, interacting only with GlcNAc residues whose 3- and 4-OH's are open. The combining site is probably of trough-type, since substitution with as large a group as monosaccharide is permitted on the C-6 side of GlcNAc, and on the C-1 side, the aglycon of GlcNAc can be very large (e.g., a glycoprotein). These binding characteristics are shared with the homologous mammalian lectin specific for galactose/N-acetylgalactosamine, suggesting that tertiary structure of the combining area of these two lectins is similar. This is understandable, since there is approximately 40% amino acid sequence identity in the carbohydrate recognition domain of these two lectins [Drickamer, K., Mannon, J. F., Binns, G., & Leung, J. O. (1984) J. Biol. Chem. 259, 770-778]. A series of glycosides, each containing two GlcNAc residues separated by different distances (from 0.8 to 4.7 nm), were synthesized. Inhibition assay with these and other cluster glycosides indicated that clustering of two or more GlcNAc residues increased the affinity toward the chicken lectin tremendously. Among the ligands containing two GlcNAc residues, the structure which allows a maximal inter-GlcNAc distance of 3.3 nm had the strongest affinity, its affinity increase over GlcNAc (monosaccharide) amounting to 100-fold. Longer distances slightly diminished the affinity, while shortening the distance caused substantial decrease in the affinity.(ABSTRACT TRUNCATED AT 250 WORDS)

High-performance anion-exchange chromatography of oligosaccharides using pellicular resins and pulsed amperometric detection

High-performance liquid chromatography using pellicular quaternary amine-bonded resins was used to separate a variety of neutral, sialylated, and phosphorylated oligosaccharides. At pH 4.6, sialylated compounds were separated according to number of negative charges, sialic acid linkage [alpha(2,3) compared to alpha(2,6)], and position of sialic acid linkage along a linear saccharide chain. At pH 13, the neutral sugar portion of the sialylated chain had a significant effect on the separation, due to oxyanion formation. Specifically, sialylated tetrasaccharides containing the Gal beta(1,3)GlcNAc sequence were retained much more than their Gal beta(1,4)GlcNAc- or Gal-beta(1,4)GalNAc-sialylated counterparts. Linear phosphorylated oligosaccharides could be completely separated according to number of charges and net carbohydrate content. Partial separation of linear-chain positional isomers, differing in either location of Man-6-PO4 in the chain or linkage position of Man or Man-6-PO4, was accomplished. Branched-chain phosphorylated compounds could be completely separated according to which antennae contained the Man-6-PO4. The electrochemical current generated by oxidation of sialylated, phosphorylated, and neutral oligosaccharides was compared to that of a glucose. The relative molar response factors for neutral, sialylated, and phosphorylated oligosaccharides ranged from 0.2 to 3.2. Neutral oligosaccharides gave the following molar responses for each group of structurally related compounds: (1) mono- and disaccharide, 1-1.3; (2) linear tri- and tetrasaccharides, 1.5-2.0; and (3) branched pentasaccharide-nonasaccharides, 2.4-3.1. Response factors for the sialyated compounds were not as consistent and were affected by linkage position of sialic acid. For oligosaccharides of the same size, increasing phosphorylation resulted in a twofold decrease in response factor for each added phosphate group. Therefore, conversion of sialylated and phosphorylated oligosaccharides to their neutral counterparts, using alkaline phosphatase or neuraminidase, respectively, was required for quantitative analysis of oligosaccharide mixtures using electrochemical response. Using this approach, complete separation of the parent neutral structures was obtained, the relative proportions of the neutral species were quantified, and the amount of sialic acid released was easily determined in a neuraminidase digest.

Synthesis of glycolipids

The chemical syntheses of naturally occurring glycolipids derived from sphingosine bases and glycerol derivatives, and the syntheses of polyisoprenoid lipid intermediates and other miscellaneous glycolipids recorded up to the end of 1977 are reviewed.

The synthesis of 2-acetamido-2-deoxy-4-O-beta-D-mannopyranosyl-D-glucose

Condensation of 4,6-di-O-acetyl-2,3-O-carbonyl-alpha-D-mannopyranosyl bromide with 2-amino-2-N,3-O-carbonyl-5.6-O-isopropylidene-D-glucose diethyl acetal gave, unexpectedly, 2-amino-2-N,3-O-carbonyl-2-deoxy-4-O-(4,6-di-O-acetyl-2,3-O-carbonyl-alpha-D-mannopyranosyl)-5,6-O-isopropylidene-D-glucose diethyl acetal, futher transformed, by de-esterification followed by acetylation, into the previously known 2-amino-2-N,3-O-carbonyl-2-deoxy-5,6-O-isopropylidene-4-O-alpha-D-mannopyranosyl-D-glucose diethyl acetal and its tetra-O-acetyl derivative. Benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-beta-D-glucopyranoside was condensed with 2-O-acetyl-3,4,6-tri-O-benzyl-beta-D-glucopyranosyl bromide to give benzyl 2-acetamido-4-O-(2-O-acetyl-3,4,6-tri-O-benzyl-beta-D-glucopyranosyl)-3,6-di-O-benzyl-2-deoxy-beta-D-glucopyranoside. Removal of the 2-O-acetyl group, followed by oxidation with acetic anhydridedimethyl sulfoxide, gave a beta-D-arabino-hexosid-2-ulose (25). After reduction with sodium borohydride, removal of the benzyl groups gave crystalline 2-acetamido-2-deoxy-4-O-beta-D-mannopyranosyl-D-glucose (27). The anomeric configuration of the glycosidic linkage was ascertained by comparison with the alpha-D-linked disaccharide.

Synthesis of 2-acetamido-2-deoxy-3-O-beta-D-mannopyranosyl-D-glucose

Condensation of 4,6-di-O-acetyl-2,3-O-carbonyl-alpha-D-mannopyranosyl bromide with benzyl 2-acetamido-4,6-O-benzylidene-2-deoxy-alpha-D-glucopyranoside (2) gave an alpha-D-linked disaccharide, further transformed by removal of the carbonyl and benzylidene groups and acetylation into the previously reported benzyl 2-acetamido-4,6-O-benzylidene groups and acetylation into the previously reported benzyl 2-acetamido-4,6-O-benzylidene-2-deoxy-3-O-(2,3,4,6-tetra-O-acetyl-alpha-D-mannopyranosyl)-alpha-D-glucopyranoside. Condensation of 3,4,6-tri-O-benzyl-1,2,-O-(l-ethoxyethylidene)-alpha-D-glucopyranose or 2-O-acetyl-3,4,6-tri-O-benzyl-alpha-D-glucopyranosyl bromide with 2 gave benzyl 2-acetamido-3-O-(2 O-acetyl-3,4,6-tri-O-benzyl-beta-D-glucopyranosyl)-4,6-O-benzylidene-2-deoxy-alpha-D-glucopyranoside. Removal of the acetyl group at O-2, followed by oxidation with acetic anhydride-dimethyl sulfoxide, gave the beta-D-arabino-hexosid-2-ulose 14. Reduction with sodium borohydride, and removal of the protective groups, gave 2-acetamido-2-deoxy-3-O-beta-D-mannopyranosyl-D-glucose, which was characterized as the heptaacetate. The anomeric configuration of the glycosidic linkage was ascertained by comparison with the alpha-D-linked analog.