Asymmetric Synthesis of Novel Thioiso Dideoxynucleosides with Exocyclic Methylene as Potential Antiviral Agents

Abstract

Novel thioiso pyrimidine and purine nucleosides substituted with exocyclic methylene have been synthesized, starting from D-xylose. The glycosyl donor 14 was synthesized from D-xylose, using cyclization of dimesylate 10 with sodium sulfide as a key step. Cyclization proceeded in pure SN2 reaction without going through SN1 reaction in the presence of an allylic functional group at low reaction temperature (0 °C) in polar solvent (DMF), affording compound 12 as a major product. At higher temperatures, S N2′ product 11 was almost exclusively obtained as a major product. On the other hand, glycosylation of 14 with 6-chloropurine under Mitsunobu conditions afforded the desired SN2 product 26, while palladium-catalyzed glycosylation resulted in the sole formation of S N2′ product 34.