Triethylamine (0.054 mL, 0.389 mmol) was added to a solution of (3R,6S)-3-amino-6-(2,3-difluorophenyl)-1-(2-hydroxy-2-methylpropyl)azepan-2-one (54 mg, 0.173 mmol) and 4-nitrophenyl chloroformate (40 mg, 0.199 mmol) in tetrahydrofuran (15 mL) at 0° C. After 30 min, 2-oxo-1-(4-piperidinyl)-2,3-dihydro-1H-imidazo[4,5-b]pyridine dihydrochloride (151 mg, 0.519 mmol), triethylamine (1.04 mmol) and chloroform (15 mL) were added and the mixture allowed to warm to ambient temperature. The reaction was then heated to 50° C. for 2 h, concentrated, diluted with saturated aqueous sodium bicarbonate and extracted with dichloromethane (2×). The organic layer was washed with water, saturated brine, dried over magnesium sulfate, filtered and concentrated. Purification by silica gel chromatography (1.5%→11% methanol/dichloromethane) gave the title compound (70 mg). MS 557.2653 (M+1). 1H NMR (500 MHz, CDCl3) δ 8.03 (d, J=4.8 Hz, 1H), 7.34 (d, J=7.7 Hz, 1H), 7.1 (m, 2H), 7.0-6.9 (m, 2H), 6.17 (d, J=5.1 Hz, 1H), 4.84 (dd, J=10.9, 5.0 Hz, 1H), 4.5 (m, 1H), 4.3 (br dd, 2H), 4.02 (dd, J=10.1, 15.1 Hz, 1H), 3.76 (d, J=14.1 Hz, 1H), 3.42 (d, J=15.1 Hz, 1H), 3.31 (d; J=14.1 Hz, 1H), 3.15-2.95 (m, 4H), 2.3-1.9 (m, 8H), 1.26 (s, 3H), 1.24 (s, 3H).
