Preparation 2-(3-(tert-butylamino)-2-methylquinoxalin-5-yl)-5,6-dihydropyrrolo[3,4-b]pyrrol-4(1H)-one (334). To a 100-mL round-bottomed flask was added 2-(aminomethyl)-5-(3-(tert-butylamino)-2-methylquinoxalin-5-yl)-1H-pyrrole-3-carboxylic acid hydrochloride (334c) (0.21 g, 0.55 mmol), DCM (10 mL), DMF (10 mL), DIEA (0.29 mL, 1.65 mmol), and (benzotriazol-1-yloxy)tripyrrolidinophosphonium hexafluorophosphate (0.34 g, 0.66 mmol) (Sigma-Aldrich Chemical Company, Inc.). The reaction mixture was stirred at RT for 30 min, concentrated to half of its volume, and diluted with EtOAc (10 mL). The organic extract was washed with sat NaHCO3 (5 mL), dried over Na2SO4, and concentrated. The crude material was absorbed onto a plug of silica gel and purified by chromatography through a Redi-Sep pre-packed silica gel column (12 g), eluted first with 30% EtOAc in hexanes, and then with a gradient of 0-4% 2 M NH3/MeOH in DCM to provide 2-(3-(tert-butylamino)-2-methylquinoxalin-5-yl)-5,6-dihydropyrrolo[3,4-b]pyrrol-4(1H)-one (334) (97 mg, 52% yield) as a yellow solid. 1H NMR (400 MHz, DMSO-d6) δ 12.08 (br. s., 1H), 7.82 (d, J=7.24 Hz, 1H), 7.63 (d, J=8.02 Hz, 1H), 7.53 (s, 1H), 7.37 (t, J=7.73 Hz, 1H), 6.94 (s, 1H), 6.02 (s, 1H), 4.29 (s, 2H), 2.58 (s, 3H), 1.55 (s, 9H). m/z (ESI, +ve) 336.2 (M+H)+.
