Ronald Eby

The use of 1-O-tosyl-d-glucopyranose derivatives in α-d-glucoside synthesis

Abstract 1-O-Tosyl- d -glucopyranose derivatives having a nonparticipating benzyl group at O-2 have been shown to react rapidly in various solvents with low concentrations of alcohols, either methanol or methyl 2,3,4-tri-O-benzyl-α- d -glucopyranoside. The stereospecificity of the glucoside-forming reaction could be varied from 80% of β to 100% of α anomer by changing the solvent or modifying the substituents on the 1-O-tosyl- d -glucopyranose derivative. 2,3,4-Tri-O-benzyl-6-O-(N-phenylcarbamoyl)-1-O-tosyl-α- d -glucopyranose in diethyl ether gave a high yield of α- d -glucoside. Kinetic measurements of reaction with various alcohols (methanol, 2-propanol, and cyclohexanol) show a high rate even at low concentrations of alcohol, and give some insight into the reaction mechanism. The high rate and stereoselectivity of their reaction suggest that the 1-O-tosyl- d -glucopyranose derivatives may be used as reagents for oligosaccharide synthesis.

Synthesis and conformational studies of 2-β-chloro, 2-α-fluoro, and 2-β-fluoro derivatives of 2-deoxy-N-acetyl-neuraminic acid

Abstract 5-Acetamido-4,7,8,9-tetra- O -acetyl-2,3,5-trideoxy-2-fluoro- d - glycero -α- and -β- d - galacto -2-nonulosonic acid methyl esters and the β-chloro analog were synthesized from N -acetylneuraminic acid. Their 1 H- and 13 C-n.m.r. spectra were completely assigned by using single-frequency decoupling, off-resonance decoupling, and spin-simulation programs. Bond angles estimated from the 1 H coupling-constants indicate that all of the compounds adopt the 2 C 5 ( l ) conformation with minor conformational differences in the C 3 side chain. 5-Acetamido-2,3,5-tri-deoxy-2-fluoro- d - glycero -α- and -β- d - galacto -2-nonulosonic acid and their methyl esters were also prepared.

The use of 1-O-sulfonyl-d-mannopyranose derivatives in β-d-mannopyranoside synthesis

Abstract Several 1- O -sulfonyl derivatives of d -mannopyranose having a nonparticipating benzyl ether group at C-2 and ester functions at C-6 and C-4 were synthesized from the corresponding d -mannopyranosyl chloride derivatives with silver sulfonates in acetonitrile. The reaction of 1- O -sulfonyl- d -mannopyranose compounds with methanol in various solvents at room temperature gave high yields of glycosides with low degrees of stercoselectivity. On the other hand, 1- O -suffonyl- d -mannopyranose derivatives having an acyl participating-group at O-2 and benzyl ethers at C-3, C-4, and C-6 gave high yields and high stereoselectivity of α- d -mannopyranosides with primary and secondary alcohols in several solvents. Model studies were carried out to determine the best combination of 2- O -acyl group, solvent, time, temperature, and 1- O -sufonyl group to give high yields with high stereoselectivity. The method has been used to prepare in good yields more complex glycosides, including perbenzylated methy 2- O -(α- d -mannopyranosyl)-α- d -mannopyranoside.

The use of positively charged leaving-groups in the synthesis of α-D-linked glucosides. Synthesis of methyl 2,3,4-tri-O-benzyl-6-O-(2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl)-α-D-glucopyranoside

Abstract Quaternary ammonium and triphenylphosphonium salts of 2,3,4-tri- O -benzyl-6- O -( N -phenylcarbamoyl)- D -glucopyranosyl bromide were readily prepared by reaction with tertiary amines and triphenylphosphine under anhydrous conditions. Methanolysis of these salts was studied to determine the conditions of solvent and temperature that would produce the highest yields of α- D -glucosides. The quaternary ammonium salts gave the highest yields with solvents of low dielectric constant and room temperature. The phosphonium salts gave moderate yields with diethyl ether at 50°. The synthesis of methyl 2,3,4-tri- O -benzyl-6- O -(2,3,4,6-tetra- O -benzyl-α- D -glucopyranosyl)-α- D -glucopyranoside by treatment of the quaternary ammonium salt of 2,3,4,6-tetra- O -benzyl-α- D -glucopyranosyl bromide with methyl 2,3,4-tri- O -benzyl-α- D -glucopyranoside was studied as a model for the synthesis of oligosaccharides. The anomeric composition of the disaccharide product could be easily determined from the optical rotation since the specific rotations of both the final product and of the gentiobioside analog are known. Under the best conditions, the yield of disaccharide was low (50%) and the reactions were not completely stereoselective.

Studies on artificial oligosaccharide-protein antigens: induction of precipitating antibodies to defined epitopes on natural and synthetic dextrans and mannans

Seventeen di- and trisaccharides, composed of alpha-1-6-, alpha-1-2-, alpha-1-3- and alpha-1-4-linked glucosyl and alpha-1-6- and alpha-1-2-linked mannosyl residues, were synthesized. The oligosaccharides (OS) were transformed into the corresponding 2-(4-aminophenyl) ethyl alpha-D-glucosides or mannosides, which were either diazotized or converted into isothiocyanato derivatives and then coupled to BSA, edestin or hemocyanin to give artificial antigens. In this way immunogenic analogues of branched natural and linear synthetic dextrans, linear synthetic mannans and glucomannans were obtained. Upon immunization of rabbits with these conjugates, antibodies to the OS moieties carrying alpha-1-6, alpha-1-2 and alpha-1-3 glucosyl and alpha-1-6 mannosyl residues were elicited. These antibodies cross-reacted with and precipitated natural or synthetic polymers carrying the corresponding epitope pattern. The minimal size of an immunogenic OS residue required for cross-reactivity with the corresponding polymer was found to be either two or between one and two monosaccharide units. To obtain maximum and reliable elicitation of anti-OS antibodies of IgG isotype the use for coupling of an OS density corresponding to 10-25 moles of OS/mole of BSA is recommended. Other strongly immunogenic carriers may be used. In the case of homopolymers, each OS residue should have a length of at least six-eight sugar units.

The synthesis of trisaccharide antigenic determinants for the branch points in natural dextrans and their protein conjugates

Abstract Three O -allyl-di- O -benzyl-6- O -( N -phenylcarbamoyl)-1- O -tosyl- d -glucopyranose derivatives were coupled with 2-[4-( p -toluenesulfonamido)phenyl]ethanol to give the corresponding α- d -glucopyranosides. Decarbanilation and deallylation gave the corresponding 2,3-, 2,4-, and 3,4-di- O -benzyl-α- d -glucopyranosides. Reaction of the diols with two equivalents of 2,3,4-tri- O -benzyl-6- O -( N -phenylcarbamoyl)-1- O -tosyl- d -glucopyranose gave the branched trisacchalides having an α- d -glucopyranosyl group at O-6 and one at either O-2, O-3, or O-4. The oligosaccharides were deblocked with sodium in liquid ammonia to give the 2-(4-aminophenyl)ethyl α- d -glucoside, which were converted into the isothiocyanate derivatives with thiophosgene. The functionalized oligosaccharides were coupled to bovine serum albumin to give protein conjugates.

The synthesis of α- and β-(1 → 2)- and -(1 → 3)-linked glucopyranose disaccharides and their protein conjugates

Abstract 2,3,4-Tri- O -benzyl-6- O -( N -phenylcarbamoyl)-1- O -tosyl- d -glucopyranose and 3,4,6-tri- O -benzyl-2- O - p -nitrobenzoyl-1- O -tosyl- d -glucopyranose were allowed to react with partially blocked 2-[4-( p -toluenesulfonamido)phenyl]ethyl α- and β- d -glucopyranosides. Disaccharides having the structure α- d -Glc p -(1 → 2)-α- d -Glc p , α- d -Glc p -(1 → 3)-α- d -Glc p , β- d -Glc p -(1 → 2)-β- d -Glc p , and β- d -Glc p -(1 → 3)-α- d -Glc p were synthesized. The oligosaccharides were debenzylated with sodium in liquid ammonia to give disaccharides having a free primary aromatic amino group, which were converted into isothiocyanate derivatives and then coupled to various proteins to give the corresponding conjugates.

Chemical synthesis of a (1→2)-d-glucopyranan

Abstract 1,2-Anhydro-3,4,6-tri- O -benzyl-α- d -glucopyranose was polymerized with a number of Lewis acids. Phosphorus pentafluoride at −60° caused polymerization to a product rich in β linkages. Other Lewis acids at higher temperatures gave perbenzylated polysaccharides of lower molecular weight with less stereoselectivity. Debenzylation of the most-regular derivative gave a polysaccharide whose specific rotation was +14.7° and whose 13 C-n.m.r. spectrum had six absorptions corresponding to those of natural (1→2)-β- d -glucopyranans and additional minor peaks presumably due to some α-anomeric configurations. It was estimated to have ∼90% of β linkages.

Conformational analysis of 1,2-anhydro-3,4,6-tri-O-benzyl-α-d-glucopyranose and -β-d-mannopyranose

Abstract The 1 H- and 13 C-n.m.r. spectra of 1,2-anhydro-3,4,6-tri- O -benzyl-α- d -glucopyranose and -β- d -mannopyranose were completely assigned by using single-frequency decoupling, off-resonance decoupling, and a spin-simulation program. The conformations of the two anhydro sugars were determined from their proton coupling-constants. The gluco isomer was found to be 4 H 5 (half-chair). The conformation of the manno derivative was found to be predominantly 4 H 5 , with some ring flattening.

The synthesis of α-isomalto-oligosaccharide derivatives and their protein conjugates

Abstract 2-[4-( p -Toluenesulfonamido)phenyl]ethyl 2,3,4-tri- O -benzyl-α- D -glucopyranoside was condensed with 2,3,4-tri- O -benzyl-6- O -( N -phenylcarbamoyl)-1- O -tosyl- D -glucopyranose to give 2-[4-( p -toluenesulfonamido)phenyl]ethyl 2,3,4,2′,3′,4′-hexa- O -benzyl-6′- O -( N -phenylcarbamoyl)α-isomaltoside. The disaccharide was decarbanilated in ethanol with sodium ethoxide. The sequence of coupling with the 1- O -tosyl-glucose derivative followed by decarbanilation was repeated to form the tri- and tetra-saccharide derivatives. The di-, tri-, and tetra-oligo-saccharides, were deblocked with sodium in liquid ammonia to give the 2-(4-aminophenyl)ethyl α-isomalto-oligosaccharides, which were diazotized with sodium nitrite in acid, and then coupled to bovine serum albumin and edestin to give the protein conjugates.