A solution of 2-((3R,5R,6S)-1-((S)-1-tert-butoxy-1-oxobutan-2-yl)-5-(3-chlorophenyl)-6-(4-chlorophenyl)-3-methyl-2-oxopiperidin-3-yl)acetic acid (230 mg, 0.430 mmol; Example 67) in DMF (4.3 mL) was treated with N-(3-dimethyaminopropyl)-N′-ethylcarbodiimide hydrochloride (165 mg, 0.86 mmol), 1-hydroxy-7-azabenzotriazole (117 mg, 0.86 mmol) and NaHCO3 (72.3 mg, 0.861 mmol) successively. After being stirred at rt for 0.5 h, 7 M ammonia in methanol (6.2 mL, 4.30 mmol) was added dropwise and the reaction was stirred overnight. Then, the reaction was diluted (water), extracted (2×EtOAc), and washed (1×saturated NaHCO3, and 2×sat. aq. NaCl solution). The combined organic layers were dried (Na2SO4) and concentrated under reduced pressure. Purification by RP-HPLC (45 to 70% MeCN/H2O (0.1% TFA), a gradient elution) provided the title compound as a white solid.
