To a solution of (R)-6-(3-isopropyl-1-methyl-1H-pyrazol-5-yl)-2-(3-methyl-1-tosyl-1H-indol-4-yl)-4-(3-methyl-4-((2-nitrophenyl)sulfonyl)piperazin-1-yl)-5,6,7,8-tetrahydropyrido[4,3-d]pyrimidine (105 mg, 0.127 mmol) in DMF (3 mL) was added DBU (0.1 mL, 0.64 mmol) followed by 2-mercaptoacetic acid (0.018 mL, 0.255 mmol). The mixture was stirred for 3 hours and then diluted with water and dichloromethane. The layers were separated and the aqueous layer was extracted three additional times with dichloromethane. The organic layers were combined, dried over Na2SO4, filtered and concentrated. The resulting residue was purified via silica gel flash chromatography [4-25% (2 M NH3 in MeOH)/DCM] to provide (R)-6-(3-isopropyl-1-methyl-1H-pyrazol-5-yl)-2-(3-methyl-1-tosyl-1H-indol-4-yl)-4-(3-methylpiperazin-1-yl)-5,6,7,8-tetrahydropyrido[4,3-d]pyrimidine. MS (ESI+) m/z 639.4 (M+H)+.
