The introduction of a second heteroatom into the furanose ring would result in several new classes of nucleoside analogs. The presence of multihetero atoms in the five-membered ring is desired to retain the required conformation for the recognition between the nucleoside and the target enzyme (reverse transcriptase). 2a,3c Indeed, the use of oxygen or sulfur atoms has produced several diheteroatom-substituted analogs 2 (2a, X = O; 2b, X = S), and some of the ...
