To solution of propionyl chloride (52.5 mg, 0.708 mmol) in DCM (7 mL) at 0° C. was added Et3N (0.2 mL, 1.47 mmol), HBTU (292 mg, 0.75 mmol), tert-butyl 5-amino-3-(6-(4-(tert-butoxycarbonylamino)piperidin-1-yl)pyrazin-2-yl)-1H-indole-1-carboxylate (300 mg, 0.59 mmol) The resulting reaction mixture was stirred at RT for 3 h. The reaction mixture was extracted with DCM (14 mL), washed with brine, dried over Na2SO4, and concentrated to dryness. The crude product was purified by column chromatography to obtain the title compound (150 mg, 45%) as an off white solid. MS (ESI, pos. ion) m/z: 565.2 (M+1).
