Triethylamine (0.010 mL, 0.023 mmol) was added to a solution of (3R,6S)-3-amino-6-(2,3-difluorophenyl)-1-[2-(methylsulfonyl)ethyl]azepan-2-one (8 mg, 0.023 mmol) and 4-nitrophenyl chloroformate (4.6 mg, 0.023 mmol) in tetrahydrofuran (0.700 mL) at 0° C. After 15 min, 2-oxo-1-(4-piperidinyl)-2,3-dihydro-1H-imidazo[4,5-b]pyridine dihydrochloride (6.7 mg, 0.023 mmol) and triethylamine (0.040 mL, 0.092 mmol) were added and the mixture allowed to warm to ambient temperature. After 16 h, the mixture was concentrated. Purification by reverse phase HPLC (C-18, 95% water/acetonitrile→5% water/acetonitrile with 0.1% trifluoroacetic acid) gave the title compound. MS 591 (M+1).
