The Grignard condensation of the protected adenosine derivative (I) with trimethylsilylethynyl magnesium bromide (II) in THF gives the diastereomeric mixture (III), which is separated by column chromatography. The desired isomer (IV) is treated with ammonia in methanol to yield the isopropylidene derivative of the target compound (V), which is finally deprotected with 90% aqueous TFA.

The reaction of the protected carbohydrate (I) with trimethylsilylacetylene (II) gives adduct (III) with no stereoselectivity at the reaction point. The oxidation of the OH group of (III) with DMP gives the corresponding oxo compound (IV), which is stereoselectively reduced with N-Selectride to yield the (R)-diastereomer (V) in a 33:1 ratio. The desilylation of (V) with TBAF in THF affords the free compound (VI), which is benzoylated with Bz2O, TEA and DMAP in acetonitrile to provide the tribenzoate (VII). The reaction of (VII) with Ac2O, H2SO4 and AcOH gives the 1-acetoxy compound (VIII), which is condensed with N6-benzoyladenine (IX) by means of Tms-OTf and TEA in acetonitrile, yielding the adenosine derivative (X). Finally, this compound is debenzoylated with ammonia in methanol.