Methyl (S)-1-((2S,4S)-2-(5-(4′-(2-((2S,4S)-1-((R)-(tert-butoxycarbonylamino)-2-phenylacetyl)-4-(methoxymethyl)pyrrolidin-2-yl)-1H-imidazol-5-yl)biphenyl-4-yl)-1H-imidazol-2-yl)-4-(methylthio)pyrrolidin-1-yl)-3-methyl-1-oxobutan-2-ylcarbamate (179 mg, 0.20 mmol) was dissolved in DCM (5 mL), MeOH (1 mL) and HCl (4 M in dioxane, 1 mL) was added. The reaction mixture was stirred for 20 h and then concentrated under reduced pressure. The crude residue was treated with cyclopropanecarboxylic acid (16 μL, 0.20 mmol), COMU (96 mg, 0.20 mmol) and DMF (5 mL), then DIPEA (0.17 mL, 1.0 mmol) was added dropwise. After 30 min, the mixture was diluted with 10% MeOH/EtOAc and washed successively with saturated aqueous NaHCO3 and brine. The organics were dried over MgSO4, filtered and concentrated under reduced pressure. The crude residue was purified by HPLC to afford methyl (S)-1-((2S,4S)-2-(5-(4′-(2-((2S,4S)-1-((R)-2-(cyclopropanecarboxamido)-2-phenylacetyl)-4-(methoxymethyl)pyrrolidin-2-yl)-1H-imidazol-5-yl)biphenyl-4-yl)-1H-imidazol-2-yl)-4-(methylthio)pyrrolidin-1-yl)-3-methyl-1-oxobutan-2-ylcarbamate (34 mg, 20%). LCMS-ESI+: calculated for C48H56N8O6S: 872.40; observed [M+1]+: 874.38.
