合成路线1

Finally this compound can be deprotected by conventional methods: (a) The acylation of 1,2-O-isopropylidene-alpha-D-xylofuranose (I) with benzoyl chloride and pyridine gives the 5-O-benzoyl derivative (II), which is acylated again with Ac2O in pyridine to yield the 3-O-acetyl-5-O-benzoyl derivative (III). The reaction of (III) with Ac2O in acetic acid affords the triacetyl derivative (IV) which is condensed with fully silylated thymine (V) by means of SnCl4 in acetone to provide the corresponding adduct (VI). The selective hydrolysis of the acetate groups of (VI) with sulfuric acid in hot acetonitrile gives 1-(5-O-benzoyl-beta-D-xylofuranosyl)thymine (VII), which is treated with MsCl and pyridine to yield the dimesylate (VIII). The reaction of (VIII) with NaI in refluxing dimethoxyethane affords, after column chromatography, 5'-O-benzoyl-3'-deoxy-2',3'-dideoxythymidine (IX), which is finally deprotected with NaOMe in methanol. (b) The reaction of the 5-O-benzoyl derivative (II) with MsCl and pyridine gives the mesylate (X), which is acylated with Ac2O in HOAc to yield 1,2-di-O-acetyl-5-O-benzoyl-3-O-(methylsulfonyl)-alpha-D-xylofuranose (XI). The condensation of (XI) with the fully silylated thymine (V) by means of SnCl4 in acetone affords the expected adduct (XII), which is treated with H2SO4 in hot MeCN to provide 1-(5'-O-benzoyl-3'-O-(methylsulfonyl)-beta-D-xylofuranosyl)thymine (XIII). Finally this compound is treated with MsCl and pyridine to yield the dimesylate (VIII), already reported. (c) The 1-(5-O-benzoyl-beta-D-xylofuranosyl)thymine (VII) can also be treated with TsCl and pyridine to give the ditosylate (XIV), which is then treated with NaI in refluxing dimethoxyethane to yield 5'-O-benzoyl-3'-deoxy-2',3'-dideoxythymidine (IX), already reported.