Triethylamine (0.015 mL, 0.109 mmol) was added to a solution of (2S,6R)-6-amino-4-(cyclopropylmethyl)-2-phenyl-1,4-oxazepan-5-one (27 mg, 0.104 mmol) and 4-nitrophenyl chloroformate (22 mg, 0.109 mmol) in tetrahydrofuran (2 mL) at 0° C. After 0.5 h, diisopropylethylamine (0.072 mL, 0.415 mmol), 2-oxo-1-(4-piperidinyl)-2,3-dihydro-1H-imidazo[4,5-b]pyridine dihydrochloride (36 mg, 0.124 mmol), and dichloromethane (2.5 mL) were added and the mixture warmed to ambient temperature. After 18 h, the mixture was concentrated. Purification by silica gel chromatography (100% dichloromethane→95% dichloromethane/methanol) gave the title compound (45 mg). MS 505.2559 (M+1).
