The cyclization of 5,6-diamino-1-propylpyrimidine-2,4(1H,3H)-dione (I) with 4-bromobenzoic acid (II) by means of EDC and HOBT in DMF gives 8-(4-bromophenyl)-3-propylxanthine (III), which is treated with P2S5 in refluxing pyridine to yield the 6-thioxanthine (IV). The reaction of (IV) with Me-I and NaOH in ethanol affords the methylsulfanylpurin-2-one (V), which is treated with ethanolamine (VI) in DMSO at 150 C to provide the 2-hydroxyethylamino derivative (VII). Finally, this compound is cyclized by means of SOCl2 in refluxing chloroform to provide the target imidazopurine.