[SH:1][C:2]1[NH:3][C:4](=[O:12])[C:5]2[CH:10]=[N:9][N:8]([CH3:11])[C:6]=2[N:7]=1.C(=O)([O-])[O-].[K+].[K+].Br[CH:20]([CH2:26]Br)[C:21]([O:23][CH2:24][CH3:25])=[O:22]>CN(C)C=O>[CH2:24]([O:23][C:21]([CH:20]1[S:1][C:2]2=[N:7][C:6]3[N:8]([CH3:11])[N:9]=[CH:10][C:5]=3[C:4](=[O:12])[N:3]2[CH2:26]1)=[O:22])[CH3:25]In 150 ml of dimethylformamide was dissolved 8.42 g (46.2 mmol) of 4,5-dihydro-6-mercapto-1-methylpyrazolo[3,4-d]pyrimidin-4(1H)-one [Helv. Chim. Acta, 42, 349 (1959)], and 12.8 g (92.4 mmol) of potassium carbonate and 18.0 ml (69.3 mmol) of ethyl 2,3-dibromopropionate were added to the solution, followed by stirring at 80° C. for 6 hours. After evaporation of the solvent, the residue was subjected to partition between chloroform and water, and the chloroform layer was concentrated to dryness under reduced pressure. The residue was subjected to silica gel column chromatography and eluted with chloroform to give 3.16 g (24%) of Compound 42. The compound was recrystallized from ethanol for purification.
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