Keto-fluorothiopyranosyl nucleosides: a convenient synthesis of 2- and 4-keto-3-fluoro-5-thioxylopyranosyl thymine analogs

The synthesis of a new series of 2′- and 4′-keto-3′-fluoro-5-thioxylopyranonucleosides of thymine, 9 and 15, is reported. The target compounds were prepared via two flexible synthetic routes, by the sequence of suitable protection and deprotection reactions, while in both routes, the key precursor is the newly synthesized 1,2-O-isopropylidene analog of 5-thioxylopyranose 3.