Studies related to carba-pyranoses: a radical decarboxylation approach to monocarba-disaccharides

Abstract

(1→1), (1→3) and (1→4) acetal-linked monocarba-disaccharides have been synthesised from a series of glucosylated γ- and δ-lactonic acids prepared from common intermediate 2, obtained from the Diels–Alder reaction of maleic anhydride and (E)-1-(2′,3′,4′,6′-tetra-O-acetyl-β-D-glucopyranosyloxy)-3-(trimethylsiloxy)buta-1,3-diene 1. Thiohydroxamic ester 14, prepared from γ-lactonic acid 9, gave, upon treatment with tert-butyl thiol and light, the lactone 15. Subsequent lithium aluminium hydride reduction and acetylation gave the (1→3) acetal-linked monocarbadisaccharides 1,6-di-O-acetyl-3-O-(2′,3′,4′,6′-tetra-O-acetyl-β-D-glucopyranosyl)-2,4-dideoxy-5a-carba-β-L-threo-hexopyranose 16. In a similar manner, protected monocarba-disaccharides 13, 19, 30, and 35 possessing L-ido, L-xylo, D-arabino and L-ido configurations of the carba-pyranose ring have been prepared.

Treatment of thiohydroxamic esters 14 and 17 with either tert-butyl thiol or trityl thiol, dimethyl sulfide, oxygen and light gave alcohols 20 and 22. Subsequent lithium aluminium hydride reduction and acetylation gave the monocarbadisaccharides 1,4,6-tri-O-acetyl-3-O-[2′,3′,4′,6′-tetra-O-acetyl-β-D-glucopyranosyl]-2-deoxy-5a-carba-β-L-arabino-hexopyranose 21 and 1,2,4,6-tetra-O-acetyl-3-O-(2′,3′,4′,6′-tetra-O-acetyl-β-D-glucopyranosyl)-5a-carba-β-L-glucopyranose 23 respectively.