To a stirred solution of N-({4-[(2R,3R)-3-{[2-(1,3-benzodioxol-5-yl)-2-hydroxyethyl]thio}-1-(4-fluorophenyl)-4-oxoazetidin-2-yl]phenoxy}acetyl)glycine (12.8 mg, 0.023 mmol) in DMF (2 ml) was added N-methylmorpholine (15 μl, 0.091 mmol). TBTU (8.8 mg, 0.027 mmol) was added and the reaction mixture was stirred at 30° C. for 1 hour. D-valine (4.5 mg, 0.038 mmol) was added and the mixture was stirred at ambient temperature overnight. The solution was purified with preparative HPLC on a C8 column, UV 240/260 nm. A gradient from 20 to 45% MeCN in 0.1M NH4OAc buffer was used as eluent. The pure fractions were collected and the MeCN was removed under reduced pressure. The remaining water solution was acidified to pH 1 with HCl (1M) and extracted with DCM. The organic phase was passed through a phase separator and concentrated under reduced pressure. The residue was dissolved in MeCN and water. After lyophilisation, the title compound was obtained. H-NMR (400 MHz, DMSO-d6): 0.80 (bs, 6H), 1.92-2.04 (m, 1H), 2.77-2.90 (m, 2H), 3.77 (bs, 2H), 3.94-4.10 (b, 1H), 4.22-4.30 (m, 1H), 4.49 (s, 2H), 4.56-4.64 (m, 1H), 4.99-5.03 (m, 1H), 5.90-5.94 (m, 2H), 6.70-6.79 (m, 2H), 6.82 (s, 1H), 6.96 (d, 2H), 7.09-7.15 (m, 2H), 7.18-7.24 (m, 2H), 7.34 (d, 2H), 8.23 (bs, 1H). M/z: 666.67 (M−1).
