[Cl:1][C:2]1[N:10]=[C:9]2[C:5]([NH:6][CH:7]=[N:8]2)=[C:4]([NH:11][C:12]2[CH:17]=[CH:16][C:15]([N+:18]([O-:20])=[O:19])=[CH:14][CH:13]=2)[N:3]=1.C(=O)([O-])[O-].[Cs+].[Cs+].[CH:27](I)([CH3:29])[CH3:28].O1CCOCC1>C(OCC)(=O)C.CN(C=O)C.O>[Cl:1][C:2]1[N:10]=[C:9]2[C:5]([N:6]=[CH:7][N:8]2[CH:27]([CH3:29])[CH3:28])=[C:4]([NH:11][C:12]2[CH:13]=[CH:14][C:15]([N+:18]([O-:20])=[O:19])=[CH:16][CH:17]=2)[N:3]=1
A mixture comprising 0.87 g (3 mmol) of 2-chloro-6-(4-nitro-phenyl-amino)-purine, 0.15 g (4.5 mmol) of caesium carbonate and 1.8 ml (18 mmol) of isopropyl iodide is stirred in 22 ml of a mixture comprising dioxane:water:DMF in a ratio of 2:1:4 at 100° C. for 48 h. Thereafter, the reaction mixture is diluted with ethyl acetate and the organic phase is washed with water and dried over sodium sulfate. After removal of the solvent, the residue is chromatographed over silica gel (mobile phase: CH2Cl2:methanol=9:1). The crystalline precipitate obtained on concentration is filtered off and dried. 2-Chloro-9-isopropyl-6-(4-nitro-phenyl-amino)-9H-purine is obtained; m.p.>260° C.; FAB-MS: (M+H)+=333; Rf=0.8 (CH2Cl2:methanol=9:1).
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