Novel reversed cyclonucleoside analogues with a d-ribofuranose glycone

Two novel ribofuranose cyclonucleoside analogues have been synthesised by a route using 5-azido-5-deoxy-1,2-O-isopropylidene-α-d-ribofuranose as the starting material. This derivative was converted into two azole-reversed nucleosides, which were cyclised regiospecifically and stereospecifically by formation of a pentofuranosylamine. An alternative route, starting from a methyl β-d-ribofuranoside, was much less efficient, reflecting the need for the correct anomeric configuration in the cyclisation step.