[O:1]=[C:2]1[C:14]2[C:13]3[C:12]([C:15]([O:17][CH3:18])=[O:16])=[CH:11][CH:10]=[CH:9][C:8]=3[NH:7][C:6]=2[CH2:5][NH:4][CH2:3]1.[BH3-][C:20]#N.[Na+].C=O.Cl>CO.O>[CH3:20][N:4]1[CH2:3][C:2](=[O:1])[C:14]2[C:13]3[C:12]([C:15]([O:17][CH3:18])=[O:16])=[CH:11][CH:10]=[CH:9][C:8]=3[NH:7][C:6]=2[CH2:5]1Methyl 4-oxo-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole-5-carboxylate (0.04 g, 0.016 mmol) and NaCNBH3 (2.4 mg, 0.04 mmol) were added to a round bottomed flask, which were then dissolved in MeOH (2 mL), and treated with 0.5 mL of a 27% solution of formaldehyde in water. This mixture was stirred for 2 h, after which, 2N HCl (2 mL) was added, followed by stirring for 15 min. The mixture was taken to pH=11 by addition of concentrated, aqueous NaOH and extracted with methylene chloride (3×10 mL). The combined organic layers were washed with brine, dried (Na2SO4), and concentrated. The crude product was used in the next step without further purification.
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