Diethyl azodicarboxylate (790 μL, 5.0 mmol) was added to a solution of triphenylphosphine (1.31 g, 5.0 mmol), methyl 2-bromo-7-hydroxy-5H-pyrido[3,2-b]indole-4-carboxylate (800 mg, 2.49 mmol) and 2-morpholinoethanol (610 μL, 5.0 mmol) in dry THF (12 mL) at room temperature under nitrogen. After 1 hr, the reaction was partitioned between EtOAc and water and the organic phase was washed with brine and dried over sodium sulfate. The solvent was removed and the residue was taken up in a 1:1 mixture of DCM:MeOH and the product was captured on a SCX cartridge and released with a 1:1 mixture of 2 N NH3 in MeOH:DCM. The solvent was removed and the product was purified by radial chromatography (step gradient elution with DCM containing 0 to 3% MeOH) to afford methyl 2-bromo-7-(2-morpholinoethoxy)-5H-pyrido[3,2-b]indole-4-carboxylate (577 mg, 1.33 mmol, 53% yield) as a tan solid. MS (ESI) m/z 434.0 (M+H). 1H NMR (400 MHz, chloroform-d) δ ppm 9.48 (1H, s), 8.21 (1H, d, J=9.32 Hz), 7.88 (1H, s), 6.89-7.00 (2H, m), 4.22 (2H, t, J=5.67 Hz), 4.04 (3H, s), 3.70-3.80 (3H, m), 3.69-3.81 (4H, m), 2.86 (2H, t, J=5.67 Hz), 2.55-2.65 (4H, m).
