Hans Hultberg

A novel, reductive ring-opening of carbohydrate benzylidene acetals☆

Abstract Further examples are given of a facile, highly regioselective, reductive opening of benzylidene acetals of hexopyranosides using sodium cyanoborohydride-hydrogen chloride. For 4,6-benzylidene acetals, the benzyl group in the product is at O-6 and HO-4 is free. For dioxolane benzylidene acetals, the direction of reductive opening of the five-membered ring depends on the stereochemistry at the asymmetric, benzylidene acetal carbon.

Reductive Ring Openings of Carbohydrate Benzylidene Acetals Using Borane-Trimethylamine and Aluminium Chloride. Regioselectivity and Solvent Dependance

Regioselective reductive ring openings of 4, 6-O-benzylidene acetals of hexopyranosides are described using borane trimethylamine-aluminium chloride. Using toluene as solvent, 4-O-benzyl ethers with the 6-OH free are obtained. Using tetrahydrofuran as solvent. 6-O-benzyl ethers with the 4-OH free are obtained.

Characterization of the extended carbohydrate binding site of concanavalin A: Specificity for interaction with the nonreducing termini of α-(1→2)-linked disaccharides

Abstract p -Nitrophenyl 2- O -α- d -galactopyranosyl-α- d -mannopyranoside and p -nitrophenyl 2- O -α- d -glucopyranosyl-α- d -mannopyranoside were synthesized and the interactions of these disaccharides with concanavalin A (con A) were characterized. The kinetics of binding of the galactopyranosyl-containing disaccharide to con A were found to be similar to those observed with monosaccharides in that monophasic time dependencies for binding were observed. The glucopyranosyl-containing disaccharide, however, exhibited biphasic time dependencies which were similar to those previously observed for the binding of p -nitrophenyl 2- O -α- d -mannopyranosyl-α- d -mannopyranoside to con A. These results support a model wherein the α-(1→2)-linked disaccharides which exhibit biphasic binding kinetics must be able to bind to con A in two different and mutually exclusive orientations. The ability to bind to con A in two orientations is shared by α-(1→2)-linked disaccharides in which both glycosyl residues can interact separately with the primary glycosyl binding site of con A. According to the model, the initial fast phase of the biphasic reaction reflects binding of the ligand in two orientations so that two complexes are formed in amounts determined by the relative values of the rate constants for formation of each complex. The subsequent slow phase is proposed to reflect a slow equilibration of the less stable complex to the thermodynamically more stable one. In the more stable complex, the glycosyl residue at the reducing end of the disaccharide occupies the primary glycosyl binding site. The added stability of this complex is attributed to extended interactions between con A and groups on the second glycosyl residue. An axial orientation of OH-2 of the second glycopyranosyl residue appears to be the most important determinant for the extended interaction.

Synthesis of two 3-O-(3,6-dideoxy-α-d-xylo-hexopyranosyl)-α-d-mannopyranosides suitable for covalent attachment to a protein carrier

Abstract 3- O -(3,6-Dideoxy-α- d - xylo -hexopyranosyl)-α- d -mannopyranosides of 8-methoxycarbonyloctan-1-ol and of p -trifluoroacetamidophenol were synthesised by the reaction of 2,4-di- O -benzyl-3,6-dideoxy-α- d - xylo -hexopyranosyl bromide with suitably protected mannosides, using halide-assisted glycosylation, and then deprotecting the products of glycosylation.

A regioselective reductive ring opening of 4,6-O-prop-2-enylidene acetals of hexopyranosides

The 4,6-O-prop-2-enylidene acetals (1)–(3) on reductive cleavage with sodium cyanoborohydride–hydrogen chloride in tetrahydrofuran yield the 6-O-prop-2-enyl ethers (4), (6), and (7) in good yield. The reduction is thus compatible with the presence of glycosidic bonds, benzyl, benzoyl, and acetamido-groups and gives ready access to protected hexopyranosides with free 4-hydroxy-group.