[C:1]1([C:29]2[CH:34]=[CH:33][CH:32]=[CH:31][CH:30]=2)[CH:6]=[CH:5][C:4]([CH2:7][N:8]2[CH:16]=[C:15]3[C:10]([N:11](CC4C=CC(OC)=CC=4)[C:12](=[O:19])[N:13]([CH3:18])[C:14]3=[O:17])=[N:9]2)=[CH:3][CH:2]=1.C(O)(C(F)(F)F)=O.FC(F)(F)S(O)(=O)=O>C(Cl)Cl>[C:1]1([C:29]2[CH:34]=[CH:33][CH:32]=[CH:31][CH:30]=2)[CH:2]=[CH:3][C:4]([CH2:7][N:8]2[CH:16]=[C:15]3[C:10]([NH:11][C:12](=[O:19])[N:13]([CH3:18])[C:14]3=[O:17])=[N:9]2)=[CH:5][CH:6]=1To a solution of 2-(biphenyl-4-ylmethyl)-7-(4-methoxybenzyl)-5-methyl-2H-pyrazolo[3,4-d]pyrimidine-4,6(5H,7H)-dione in CH2Cl2 (90 mL) is added TFA (10 mL) slowly at room temperature, followed by adding trifluoromethanesulfonic acid (4 mL) dropwise. After the reaction mixture is stirred at r.t. for 3 hours, solvent is removed under reduced pressure, and the obtained residue is basified by adding cold pre-diluted ammonium hydroxide (NH3 content, 7%) at 0° C. The mixture is extracted with ethyl acetate four times. The combined organic phase is washed with brine, dried over anhydrous Na2SO4, and then filtered. The filtrate is evaporated to dryness to give crude product in almost quantitative yield. MS (ESI) m/z 333.1 [M+H]+.
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