Studies related to carba-pyranoses: a strategy for the synthesis of β-1,3-glycosidically linked aminomonocarba-disaccharides

Abstract

The reaction of (E)-1-(2′,3′,4′,6′-tetra-O-acetyl-β-D-glucopyranosyloxy)-3-(trimethylsiloxy)buta-1,3-diene 1 and maleic anhydride gives cycloadduct 10 and ketone 12. Reduction of ketone 13, formed by acidic hydrolysis of silyl enol ether 10, with sodium cyanoborohydride in acetic acid gives an 83 ∶ 17 mixture of the γ- and δ-lactone 14 and 15. γ-Lactone 14 is transformed into the aminomonocarba-disaccharide, 4-acetamido-2,4-dideoxy-3-O-(β-D-glucopyranosyl)-5a-carba-β-L-lyxo-hexopyranose 7, using a five-step procedure involving the Curtius rearrangement of acyl azide 16. A similar sequence using γ-lactone 21, prepared from ketone 12, gives the protected aminomonocarba-disaccharide, 4-acetamido-1,6-di-O-acetyl-2,4-dideoxy-3-O-(2′,3′,4′,6′-tetra-O-acetyl-β-D-glucopyranosyl)-5a-carba-β-D-lyxo-hexopyranose 8.

Reaction of cycloadduct 10 with dimethyldioxirane gives acyloin 26. Acetylation under acidic conditions followed by reduction with sodium cyanoborohydride in acetic acid gives a 75 ∶ 25 mixture of the γ- and δ-lactone 28 and 29. Using a sequence similar to that employed for the preparation of compounds 7 and 8, γ-lactone 28 is converted into the fully substituted aminomonocarba-disaccharide, 4-acetamido-1,2,6-tri-O-acetyl-4-deoxy-3-O-(2′,3′,4′,6′-tetra-O-acetyl-β-D-glucopyranosyl)-5a-carba-β-L-galactopyranose 9.