To a stirred solution of 3-(3,5-dimethoxyphenyl)-1,4-dimethyl-1H-pyrazolo[3,4-b]pyridin-6(7H)-one (1.0 g, 3.34 mmol) in DMF (5 ml) were added DIPEA (1.17 ml, 6.68 mmol) and ethyl 2-bromoacetate (0.56 ml, 5.01 mmol). After stirring at 90° C. for 1 h the mixture was cooled to rt, water was added and extracted three times with CH2Cl2. The organic phases were dried over Na2SO4, filtered and concentrated under reduced pressure. The resulting crude product was purified by column chromatography (eluent 50% hexane in EtOAc) to yield 910 mg (71%) of the title compound. [1H-NMR (DMSO-d6, 600 MHz): δ 6.71 (d, 2H), 6.61 (s, 1H), 6.57 (br s, 1H), 4.98 (s, 2H), 4.18 (q, 2H), 3.91 (s, 3H), 3.78 (s, 6H), 2.37 (s, 3H), 1.21 (t, 3H); UPLC-MS RtJ=1.21 min; [M+H]+=386.1]
