[C:1]([C:5]1[C:12]2[S:11][C:10]([NH2:13])=[N:9][C:8]=2[NH:7][N:6]=1)([CH3:4])([CH3:3])[CH3:2].N1C=CC=CC=1.[O:20]1[CH:24]=[CH:23][CH:22]=[C:21]1[C:25](Cl)=[O:26].C(O)C(N)(CO)CO>CN(C1C=CN=CC=1)C.C1COCC1>[C:1]([C:5]1[C:12]2[S:11][C:10]([NH:13][C:25]([C:21]3[O:20][CH:24]=[CH:23][CH:22]=3)=[O:26])=[N:9][C:8]=2[NH:7][N:6]=1)([CH3:4])([CH3:2])[CH3:3]
To a stirring solution of 3-tert-Butyl-1H-pyrazolo[3,4-d]thiazol-5-ylamine (30 mg, 0.153 mmol) and pyridine (74 μL, 0.92 mmol), or alternatively PS-DMAP (Argonaut resin, 6 equiv.), in THF (0.75 mL) was added furan-2-carbonyl chloride (75 μL, 0.76 mmol). The reaction mixture was stirred at 70° C. for 23 h, then cooled to room temperature and treated with THF (1 mL) and PS-trisamine (Argonaut resin, 20 equiv.) for 2 h. The resin was filtered, washed with DMF and the solvent was evaporated. The residue was treated with MeOH (1 mL) and a 4N aqueous solution of NaOH (0.25 mL) and the solution was stirred at room temperature for 2 h. The reaction mixture was neutralized to pH 7 with a 1N aqueous solution of HCl and extracted with ethyl acetate (3×). Purification on silica gel with 0-10% MeOH in CH2Cl2 as eluent provided 36 mg (82%) of furan-2-carboxylic acid (3-tert-butyl-1H-pyrazolo[3,4-d]thiazol-5-yl)-amide as an off-white solid. 1H-NMR (d6-DMSO) δ: 12.8 (broad s, 1H, NH), 12.7 (broad s, 1H, NH), 8.03 (d, 1H), 7.69 (broad s, 1H), 6.74 (dd, 1H), 1.36 (s, 9H); HPLC/MS m/z: 291 [MH]+.
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