A mixture of tert-butyl {(3S)-1-[5-[(tert-butoxycarbonyl)amino]-1-(4-methoxybenzyl)-1H-pyrazolo[3,4-b]pyridin-4-yl]piperidin-3-yl}carbamate (0.50 g, 0.90 mmol) and HCl in dioxane (4.0 M; 10 mL, 40 mmol) was stirred at room temperature for 2 h. The solution was then evaporated under reduced pressure. The resulting residue was dissolved in THF (10 mL), and di-tert-butyl dicarbonate (0.20 g, 0.92 mmol) in THF (5 mL) and triethylamine (0.37 g, 3.6 mmol) were added. The mixture was stirred at room temperature for 3 h. The reaction mixture was then diluted with EtOAc and the resulting solution was washed with aq. NaHCO3 and brine. The organic layer was then dried over Na2SO4 and concentrated under reduced pressure. The residue was purified by column chromatography on silica gel using CombiFlash® apparatus, eluting with 20 to 100% EtOAc in hexanes, to give 0.30 g (73%) of the sub-title compound. LCMS calc. for C24H33N6O3 (M+H)+: m/z=453.3. Found: 453.1.
