(2S,4S)-tert-butyl 2-(7-(4-(2-((S)-1-((S)-2-(methoxycarbonylamino)-3-methylbutanoyl)pyrrolidin-2-yl)-1H-imidazol-5-yl)-2-(prop-1-ynyl)phenyl)-1H-naphtho[1,2-d]imidazol-2-yl)-4-(methoxymethyl)pyrrolidine-1-carboxylate (66 mg, 0.084 mmol) was dissolved in DCM (2 mL), MeOH (0.5 mL) and HCl (4 M in dioxane, 0.5 mL) was added. The reaction mixture was stirred for 2 h and then concentrated under reduced pressure. The crude residue was treated with (R)-2-(methoxycarbonylamino)-2-phenylacetic acid (18 mg, 0.084 mmol), COMU (40 mg, 0.084 mmol) and DMF (3 mL), then DIPEA (0.73 mL, 0.42 mmol) was added dropwise. After 15 h, 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 (R)-2-((2S,4S)-2-(7-(4-(2-((S)-1-((S)-2-(methoxycarbonylamino)-3-methylbutanoyl)pyrrolidin-2-yl)-1H-imidazol-5-yl)-2-(prop-1-ynyl)phenyl)-1H-naphtho[1,2-d]imidazol-2-yl)-4-(methoxymethyl)pyrrolidin-1-yl)-2-oxo-1-phenylethylcarbamate (16 mg, 21%). LCMS-ESI+: calculated for C50H54N8O7: 878.41; observed [M+1]+: 879.60.
