[C:1]([O:5][C:6]([N:8]1[CH2:12][CH2:11][C@@H:10]([C:13](=[NH:16])[NH:14][OH:15])[CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2].C1N=CN([C:22](N2C=NC=C2)=[O:23])C=1.Cl>O1CCOCC1.C(Cl)Cl>[C:1]([O:5][C:6]([N:8]1[CH2:12][CH2:11][C@@H:10]([C:13]2[NH:16][C:22](=[O:23])[O:15][N:14]=2)[CH2:9]1)=[O:7])([CH3:4])([CH3:2])[CH3:3]Crude (R)-3-(N-hydroxycarbamimidoyl)-pyrrolidine-1-carboxylic acid tert-butyl ester (887 mg, 3.86 mmol) and CDI (94 mg, 5.8 mmol) were dissolved in dioxane (30 mL) and heated to reflux. After 1 h, the reaction was concentrated in vacuo. The crude reaction mixture was dissolved in CH2Cl2 and the pH was adjusted to 3 by adding 1M HCl to the solution. The layers were separated and the aqueous layer was extracted with CH2Cl2. The combined organic layers were washed with water and brine, dried over MgSO4, filtered and concentrated in vacuo to yield 872 mg of crude (R)-3-(5-oxo-4,5-dihydro-1,2,4-oxadiazol-3-yl)-pyrrolidine-1-carboxylic acid tert-butyl ester.
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