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Abstract

A multistep synthesis of a monoraethylated beta linked disaccharide of biological significance, 6-O-(4-O-methyl-0-D-glucopyranosyl)-D-galactose is described for the first time. A key intermediate in this synthesis was 4-0-methyl-D-glucose, which was obtained by a synthetic route involving open chain carbohydrate derivatives, and by isolation from mesquite gum, a polysaccharide that contains ^-O-methyl-D-glucose as the uronic acid. Condensation of the derived 2,3,6-tri-0-acetyl-4-0-methyl-CL-D-glucopyranosyl bromide with 1,2»3»^-di-O-isopropylidene-a-D-galactopyranose and subsequent removal of the blocking groups afforded 6-O-(4-O-methyl-0-D-glucopyranosyl)-D-galactose in 55% yield. The synthesis of alpha linked glucosides using 0-D-gluco-pyranosyl bromides having a non-participating benzyl group at C-2 has been investigated. Two of these bromides were used in glycoside forming reactions, 2-0-benzyl-3,4,6-tri-0-p_-nitrobenzoyl-P-D-gluco-pyranosyl bromide, and 2,3-di-0-benzyl-^,6-di-0-p_-nitrobenzoyl-p-D-glucopyranosyl bromide. The preparation of a glucosyl bromide having a non-participating 2,3-carbonate function was attempted, but was unsuccessful. Isomaltose and 6-0-a-D-glucopyranosyl-D-galactose were prepared using the 2,3-dibenzyl compound. Isomaltose, 6-0-a-D-glucopyranosyl-D-mannose and 4-0-cu D-glucopyranosyl-L-rhamnose were synthesized using the 2-benzyl compound. The latter disaccharide represents the first a-linked glucoside containing L-rhamnose to be synthesized. The synthesis of several methylated sugars useful for the analysis of polysaccharide structures is described. 73-O-Methyl-D-galactose was prepared in a multistep synthesis involving l,2i 5,6-di-O-isopropylidene-a-D-galactofuranose. Finally, a new synthesis of 3»^»6-tri-O-methyl-D-glucose, D-galactose and D-mannose is described.