Bicyclic nucleosides related to pyrimidine nucleosides. Part III. 3-(β-D-ribofuranosyl)isoguanine

Abstract

Ring closure of 4,5,6-triaminopyrimidin-2-one with thiourea was followed by conversion into 8-iodoisoguanine. Condensation of 8-iodoisoguanine with 2,3,5-tri-O-benzoyl-D-ribofuranosyl bromide afforded a good yield of 8-iodo-3-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)isoguanine. The isomeric and anomeric structure of this nucleoside was established by successful conversion into 3-(β-D-ribofuranosyl)xanthine. Debenzoylation of 8-iodo-3-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)isoguanine followed by dehalogenation of the unprotected nucleoside furnished the bicyclic cytidine nucleoside analogue 3-(β-D-ribofuranosyl)isoguanine.