To the solution of 3-(8,9-diphenyl-9H-purin-6-ylamino)propanal obtained in step 2 (0.73 g, 2.13 mmol) and 1-(2,3-dichlorophenyl)piperazine hydrochloride (0.6 g, 2.13 mmol) in 1.2-dichloroethane was added Na(OAc)3BH (0.72 g, 3.40 mmol) and acetic acid (0.24 mL, 4.25 mmol) at room temperature and stirred for 18 hours at 45° C. The resulting reaction mixture was concentrated under reduced pressure. The residue was diluted with CH2Cl2, and washed with water. The organic layer thus separated was dried over anhydrous MgSO4, filtered, and concentrated in vacuo. The crude product thus obtained was purified by preparative HPLC (purification system, Gilson) to provide the title compound (460 mg) as a white solid.
