Naotaka Yamaoka

Proton magnetic resonance spectra of D-gluco-oligosaccharides and D-glucans

Abstract The p.m.r. spectra of some D -gluco-oligosaccharides and D -glucans in deuterium oxide were studied with respect to the anomeric proton. In (1→2)-linked glucobioses, the effect of change in configuration of the hydroxyl group at C-1 on the chemical shifts of the glycosidic proton is noted. Equilibrium mixtures of (1→2)-linked glucobioses contained more α-anomer than did the other examples, despite the cis configuration of substituents at C-1 and C-2. Some D -glucans were investigated with regard to the degree of branching, although solubility was a limitation.

13 C nuclear magnetic resonance spectra of glucobioses, glucotrioses, and glucans

Natural-abundance carbon-13 n.m.r. spectra of all the glucobioses and of four selected glucotrioses in aqueous solution have been measured and are discussed. Peak assignments were made on the basis of comparison with the spectra of methyl glucopyranosides, four mono-O-methylglucoses and five methyl glucobiosides. Carbon-13 n.m.r. spectroscopy proved to be a useful tool for stereochemical characterisation of these oligosaccharides. In addition, carbon-13 n.m.r. spectra of the β-limit dextrins from glycogen and amylopectin have been measured and the differences between them are discussed.

Steric and electrostatic effects on the elimination of 2- and 3-sulphonyloxy-groups from methyl 4,6-O–benzylidenehexopyranosides

The elimination of 2- and 3-sulphonyloxy-groups from methyl 4,6-O–benzylidenehexopyranosides by the Tipson–Cohen reaction (sodium iodide–zinc in NN-dimethylformamide) has bsen studied. The β-glucoside 2,3-disulphonate (3) or (4) is rapidly changed into the 2,3-unsaturated sugar (8) in high yield, whereas the yield of 2-enoside (7) from the α-anomer (1) is only 55%. The α-mannoside sugar disulphonate (6) was converted into the unsaturated sugar (8) in 66% yield, whereas the β-isomer gave the enoside (7) in low yield. The differences in reactivity are discussed in the light of steric and electrostatic effects.

Synthesis of a (2,3-dideoxyglyc-2-enopyranosyl)thymine and a (2,3-dideoxyglycopyranosyl)thymine via a 2,2′-anhydro-nucleoside

2,2′-Anhydro-1-(4,6-O-benzylidene-3-O-methylsulphonyl-β-D-mannopyranosyl)thymine (5), prepared quantitatively from the 2′,3′-bismethanesulphonate (3), was converted into the corresponding unsaturated nucleoside (8) in 56% yield by the action of sodium iodide in boiling NN-dimethylformamide. Debenzylidenation of (8) with acid gave a free unsaturated nucleoside (12) in 91% yield. Reduction of (12) over palladium–carbon gave the (2,3-dideoxyhexopyranosyl)thymine (14). A mechanism for the formation of unsaturated nucleoside is described.

New synthetic route to 2′,3′-unsaturated pyranosyl thymine from the corresponding O2,2′-cyclonucleoside

Treatment of the O2,2′-cyclonucleoside (3) with NaI–Zn gives the corresponding 2′,3′-unsaturated nucleoside (4) in fair yield.