摘要:
                                Oxidation of 2',3'-di-O-acetyl-5'-S-(4-methoxyphenyl)-5'-thiouridine (2a) with 3-chloroperoxybenzoic acid (MCPBA) gave the diastereomeric sulfoxides 4a.  Treatment of 2a with xenon difluoride or 4a with (diethylamino)sulfur trifluoride/antimony(III) chloride gave efficient conversions to the 2',3'-di-O-acetyl-5'-fluoro-5'-S-(4-methoxyphenyl)-5'-thiouridine diastereomers 6a.  The stereochemistry and conformation of 6a(5'R) were established by X-ray crystallography.  The alpha-fluoro thioethers were oxidized to their sulfoxide and sulfone derivatives with MCPBA, deprotected, and characterized.