Condensation between aminomalononitrile (I) and benzyl isocyanate (II) produces imidazole (III). This is then cyclized with benzoyl isothiocyanate (IV) in the presence of NaOH to furnish the mercaptopurine derivative (V). Finally, alkylation of thiol (V) with 2-bromoethanol (VI) gives rise to the target hydroxyethyl sulfide.