N-{[4-((2R,3R)-1-(4-Fluorophenyl)-3-{[2-(4-fluorophenyl)-2-oxoethyl]thio}-4-oxoazetidin-2-yl)phenoxy]acetyl}glycine (15.2 mg, 0.028 mmol) and N-methylmorpholine (15 μl, 0.14 mmol) were dissolved in DMF (2 ml). TBTU (10.5 mg, 0.033 mmol) was added and after 20 minutes (2R)-2-amino-4-(4-hydroxyphenyl)butanoic acid hydrobromide (9.2 mg, 0.033 mmol) was added. The reaction mixture was stirred for 1.5 h. The formation of the intermediate acid was confirmed. M/z: 718.3. MeOH (2 ml) and sodium borohydride (10.7 mg, 0.28 mmol) were added and the mixture was stirred for 20 minutes. Ammonium acetate (34 mg) was added and the methanol was removed under reduced pressure. The residue was purified with preparative HPLC on a C8 column. A gradient from 20% to 45% MeCN in 0.1M ammonium acetate buffer was used as eluent. After lyophilisation, the title compound was obtained as a white solid (9.6 mg, 47%). H-NMR (400 MHz, DMSO-d6): 1.75-1.86 (m, 1H), 1.89-1.98 (m, 1H), 2.41 (t, 2H), 2.81-2.98 (m, 2H), 3.78 (d, 2H), 3.97-4.05 (m, 1H), 4.27 (d, 0.5M), 4.31 (d, 0.5H), 4.53 (s, 2H), 4.67-4.76 (m, 1H), 5.02 (d, 0.5H), 5.05 (d, 0.5H), 6.62 (d, 2H), 6.91 (d, 2H), 6.98 (d, 2H), 7.05-7.16 (m, 4H), 7.20-7.25 (m, 2H), 7.30-7.39 (m, 4H), 7.87-7.97 (m, 1H), 8.30 (t, 1H), 8.91-9.30 (br, 1H). M/z: 718.0 (M−H).
