PREPARATION OF ALPHA-LINKED 6-DEOXY-D-ALTRO-HEPTOPYRANOSIDIC RESIDUES

alpha-linked D-altropyranosidic derivatives were obtained by configura tional change at C-3 of alpha-D-mannopyranosides as the key step in pr eparation of allyl and methyl alpha-D-glycopyranosides of 6-deoxy-D-al tro-heptose. The manno-altro conversion was effected by sequential rea ctions of Swern oxidation and stereoselective borohydride reduction. A llyl lidene-2-O-p-methoxybenzyl-alpha-D-mannopyranoside was transforme d to the corresponding altropyranoside via 3-oxo-arabino-hexopyranosid e. Allyl 3,4-O-isopropylidene-alpha-D-altro-heptopyranoside has been p repared as a glycosyl acceptor to be coupled with beta-D-GlcpNAc-(1--> 3)-alpha-D-Galp glycosyl donor for the synthesis of an O-antigen repea ting unit of Campylobacter jejuni serotypes 0:23 and 0:36. Stereoselec tive borohydride reduction also succeeded in yielding methyl tri-O-ben zyl-6-deoxy-alpha-D-altro-heptopyranoside from the corresponding 3-oxo -alpha-D-arabino-heptopyranoside. C-6 Homologation was achieved by seq uential reactions of cyanide displacement of 6-sulphonates, reduction of the resulting heptopyranosidurononitrile with diisobutylaluminum hy dride, hydrolysis of the imine, and further reduction with sodium boro hydride.