[C:1](OC(=O)C)(=[O:3])C.[NH2:8][CH2:9][C:10]([N:12]1[CH2:16][C@H:15]([NH:17][C:18](=[O:25])[C:19]2[CH:24]=[CH:23][CH:22]=[CH:21][CH:20]=2)[CH2:14][C@H:13]1[C:26]([OH:28])=[O:27])=[O:11]>C(O)=O>[C:18]([NH:17][C@H:15]1[CH2:16][N:12]([C:10](=[O:11])[CH2:9][NH:8][CH:1]=[O:3])[C@H:13]([C:26]([OH:28])=[O:27])[CH2:14]1)(=[O:25])[C:19]1[CH:20]=[CH:21][CH:22]=[CH:23][CH:24]=1Acetic anhydride (Acros) (0.32 mL, 3.4 mmol, 10 equivalents) was added dropwise to a solution of (2S4R)1-(2-Amino-acetyl)-4-benzoylamino-pyrrolidine-2-carboxylic acid (Compound 2, 0.1 g, 0.34 mmol, 1 equivalent) in formic acid (J. T. Baker) (1 mL) at 0° C. After the addition was complete, the reaction mixture was allowed to warm to room temperature and stirred an additional 24 hours. The reaction mixture was monitored by TLC and LCMS. An additional amount of acetic anhydride (0.32 mL, 3.4 mmol, 10 equivalents) was added and the reaction mixture stirred for 24 hours at room temperature. Ice-water (1 mL) was added and the volatiles were removed in vacuo to yield an oily crude product that was further purified by HPLC (column: Waters Atlantis 19×150 mm) using 0.1% formic acid in H2O/MeOH 20-40% MeOH over 15 minute gradient to afford 0.031 g (29%) of the desired product.
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