The condensation of 2,6-dichloropurine (I) with 4-methoxybenzylamine (II) in butanol at 120 C gives 2-chloro-6-(4-methoxybenzylamino)purine (II), which is treated with isopropyl iodide (IV) and NaH in DMF yielding 2-chloro-9-isopropyl-6-(4-methoxybenzylamino)purine (V). Finally, this compound is condensed with diethanolamine (VI) in DMSO at 160 C.