A solution of [4-((2R,3R)-1-(4-fluorophenyl)-3-{[2-(4-fluorophenyl)-2-oxoethyl]thio}-4-oxoazetidin-2-yl)phenoxy]acetic acid (0.200 g, 0.414 mmol), glycylglycine methyl ester hydrochloride (0.090 g, 0.493 mmol) and N-methylmorpholine (0.150 ml) in DCM (5 ml) was stirred for 10 min. TBTU (0.170 g) was added and the mixture was stirred for 20 h. The formation of the ester was confirmed. M/z: 612.0. The solvent was removed under reduced pressure. The residue was dissolved in a mixture of MeOH (5 ml), water (1 ml) and Et3N (0.5 ml). The solution was stirred at 50° C. for 18 h. DBN (0.050 ml, 0.405 mmol) was added and the mixture was stirred for 2 h at 50° C. Ammonium acetate buffer (0.1 M, 3 ml) was added and the mixture was concentrated. The residue was purified by preparative HPLC, using a gradient of 20-50% MeCN in 0.1M ammonium acetate buffer as eluent. After freeze-drying, the title product (0.094 g, 38% yield) was obtained as a white solid. M/z: 598.2. 1H NMR (DMSO, 400 MHz): 3.50 (d, 2H), 3.75 (d, 2H), 4.32 (d, 1H), 4.35 (ABq, 2H), 4.46-4.53 (m, 2H), 5.15 (d, 1H), 6.94-7.00 (m, 2H), 7.10-7.25 (m, 4H), 7.29-7.39 (m, 4H), 7.68-7.81 (m, 1H), 7.98-8.04 (m, 2H), 8.30-8.36 (m, 1).
