Phosphonate (III) was prepared by the Michaelis-Arbuzov reaction by heating a mixture of 2-chloroethyl chloromethyl ether (I) and tris(2,2,2-trifluoroethyl)phosphite (II) at 160 C. The chloroethoxy derivative (III) was then converted to the corresponding iodide (IV) by treatment with NaI under Finkelstein reaction conditions. Alkylation of 2-amino-6-chloropurine (V) with iodide (IV) in the presence of DBU furnished the phosphonyl purine (VI). The 6-chloro group of (VI) was finally displaced with p-methoxythiophenol (VII) in hot DMF, yielding the target thioether.