DIEA (0.0475 mL, 0.273 mmol) was added to a solution of 5-phenyl-4-(piperazin-1-yl)-1H-pyrazolo[3,4-b]pyridine dihydrochloride (0.030 g, 0.0681 mmol, See Example 1), (S)-2-((S)-1-(tert-butoxycarbonyl)-5,5-dimethylpyrrolidin-2-yl)-2-(4-chlorophenyl)acetic acid (0.0251 g, 0.0681 mmol, see Example D) and TBTU (0.0263 g, 0.0818 mmol) in DCM (1 mL) and stirred at room temperature for 16 hours. The mixture was directly loaded onto a silica column and purified by chromatography (hexane:ethyl acetate, 1:1) to give (S)-tert-butyl 5-((S)-1-(4-chlorophenyl)-2-oxo-2-(4-(5-phenyl-1H-pyrazolo[3,4-b]pyridin-4-yl)piperazin-1-yl)ethyl)-2,2-dimethylpyrrolidine-1-carboxylate as a solid. The solid was dissolved in DCM (1 mL), and TFA (0.2 mL) was added. The mixture was stirred at room temperature for 1 hour and then concentrated to dryness. The resulting residue was dissolved in DCM (0.5 mL), and HCl in ether (1 mL, 2N) was added. The resulting solid was collected by filtration to give (S)-2-(4-chlorophenyl)-2-((S)-5,5-dimethylpyrrolidin-2-yl)-1-(4-(5-phenyl-1H-pyrazolo[3,4-b]pyridin-4-yl)piperazin-1-yl)ethanone (0.019, 46%). MS APCI (+) m/z 529.3 detected.
