Tetrabutylammonium Fluoride → 2-amino-9-(2-hydroxyethyl)-9H-pyrido[2,3-b]indole-3-carboxamide

2-Amino-9-(2-(tert-butyldimethylsilyloxy)ethyl)-9H-pyrido[2,3-b]indole-3-carboxamide (xxv-a, 360 mg, 1.06 mmol) was dissolved in tetrahydrofuran (3 mL). A solution of tetrabutylammonium fluoride (1.0 M in THF, 1.3 mL, 1.4 mmol) was added. The resulting solution was stirred at room temperature 3 h. The solution was concentrated under reduced pressure. The residue was triturated with methylene chloride. The resulted solids were dissolved in tetrahydrofuran and washed with brine. The extracts were dried over sodium sulfate, filtered and concentrated under reduced pressure. The crude product was purified by silica gel chromatography (12 g silica, methylene chloride to 3% methanol in methylene chloride gradient). The product 9 was isolated as a yellow solid (30 mg, 10% for 2 steps). NH4OAc standard conditions. DAD retention time=5.02 min. M+H=271. 1H NMR (300 MHz, DMSO-d6): 8.66 (s, 1H), 7.73 (d, J=7.6 Hz, 1H), 7.59-7.50 (br s, 1H), 7.46 (d, J=8.2 Hz, 1H), 7.25 (ddd, J=1.7, 7.0, 8.2 Hz, 1H), 7.11 (dd, J=7.0, 7.0 Hz, 1H), 4.30-4.23 (m, 2H), 3.72-3.66 (m, 2H).