2-[(Morpholine-4-carbonyl)-amino]-3-phenylmethanesulfonyl-propionic acid (100 mg, 0.28 mmol), acetic acid 3-amino-4-oxo-azetidin-2-yl ester (52 mg, 0.36 mmol), EDC (100 mg, 0.52 mmol), and HOBt (100 mg, 0.64 mmol) were combined. Dichloromethane (2 mL) was added and then 4-methylmorpholine (0.2 mL). The mixture was stirred at ambient temperature for 2 h. After dilution with ethyl acetate (100 mL) the solution was washed with 1N aqu. HCl (30 mL), sat. aqu. NaHCO3 (30 mL) and brine (30 mL), dried with MgSO4 and evaporated under vacuum. The residue was subjected to flash chromatography on silica gel (ethyl acetate) to give acetic acid 3-{2-[(morpholine-4-carbonyl)-amino]-3-phenylmethanesulfonyl-propionylamino}-4-oxo-azetidin-2-yl ester (17 mg, 0.035 mmol). 1H NMR: (DMSO) 9.18 (s, 1H), 8.72 (d, J=6.4 Hz, 1H), 7.41–7.30 (m, 5H), 7.08 (m, 1H), 5.76 (s, 1H), 4.80–4.61 (m, 2H), 4.49 (s, 2H), 3.63–3.22 (m, 10H), 2.08 (s, 3H). MS: (M+H)+ 483.
