A facile synthesis of 5-thio-l-fucose and 5-thio-d-arabinose from d-arabinose

5-Thio-l-fucopyranose tetraacetate was synthesized in 11 steps from 5-O-trityl-d-arabino-furanose or d-arabinose diethyl dithioacetal by one-carbon elongation at C-5. Highly diastereo-selective addition of MeLi in ether to a 1,2-O-isopropylidene-β-d-arabino-pentodialdo-1,4-furanose derivative was achieved to give the corresponding 6-deoxy-β-d-altrofuranose isomer in good yield. A sulfur atom was introduced at C-5 of 6-deoxy-d-altrofuranose derivatives via substitution of a 5-tosylate with KSAc in HMPA with inversion of configuration, giving 5-thio-l-fucopyranose. A 3-O-substituted-l-fucose derivative was also prepared from 6-deoxy-β-d-altrofuranose derivatives. 5-Thio-d-arabinopyranose tetraacetate, the 5-demethyl analog of 5-thio-l-fucose, was also synthesized from 5-O-trityl-d-arabinofuranose in 5 steps. 5-Thio-d-arabinose showed weak inhibitory activity against α-l-fucosidase from bovine kidney (Ki = 0.77 mM).