Adenine (I) was oxidized with hydrogen peroxide in aqueous acetic acid to give adenine 1-N-oxide (II). Diazotization of (II) with sodium nitrite and acetic acid, followed by hydrolysis of the diazonium salt provided hypoxanthine 1-N-oxide (III). 2,6-Dichloropurine (IV) was then obtained by treatment of (III) with phosphoryl chloride in the presence of triethylamine. Displacement of the 6-chlorine atom of (IV) by benzylamine (V) in boiling n-butanol yielded 6-benzylamino-2-chloropurine (VI), which was subsequently alkylated at the 9-N with isopropyl iodide and NaH to give (VII). Finally, the remaining 2-chloro atom of (VII) was displaced by thiomorpholine (VIII) to furnish the title compound.