Syntheses of methyl glycosides of 6-deoxyheptoses

Methyl α-D-glycopyranosides of 6-deoxy-D-altro-heptose, 6-deoxy-D-manno-heptose, and 6-deoxy-D-talo-heptose have been prepared. Displacements of methyl 2,3,4-tri-O-benzylhexopyranoside 6-trifluoromethanesulfonates with potassium cyanide, followed by reduction of the resulting heptopyranosidurononitriles with diisobutylaluminum hydride, hydrolysis of the imine, further reduction with sodium borohydride, and catalytic O-debenzylation, give the corresponding methyl 6-deoxyheptopyranosides. Configurational change at C-4 of methyl 6-deoxy-7-O-tert-butyldiphenylsilyl-α-D-manno-heptopyranoside to give the talo isomer was effected by oxidation followed by stereoselective reduction. 1H nuclear magnetic resonance data of the glycosides, and gas chromatography of acetylated glycosides of (R)- and (S)-2-butanol serve to establish ring and enantiomeric configurations of the parent sugars when these are encountered as constituents of lipopolysaccharides or extracellular carbohydrate polymers, as in Campylobacter species.