[C:1]([O:5][C:6]([N:8]1[CH2:12][CH2:11][C@@H:10]([C:13](=[NH:16])[NH:14]O)[CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2].N1([C:22](N2C=CN=C2)=[S:23])C=CN=C1.B(F)(F)F.CC[O:35]CC>C1COCC1.O>[C:1]([O:5][C:6]([N:8]1[CH2:12][CH2:11][C@@H:10]([C:13]2[NH:14][C:22](=[O:35])[S:23][N:16]=2)[CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2]
(R)-3-(N-Hydroxycarbamimidoyl)-pyrrolidine-1-carboxylic acid tert-butyl ester (0.54 g, 2.36 mmol) and di-imidazol-1-yl-methanethione (0.70 g, 3.53 mmol) were dissolved in THF (15 mL) and stirred for 30 min. The reaction was diluted with water (50 mL) and extracted with EtOAc (50 mL×3). The combined organic layers were dried by MgSO4 and concentrated in vacuo. The residue was dissolved in THF (20 mL) and BF3.Et2O (0.89 ml, 7.06 mmol) was added dropwise. After 1 h of stirring, the reaction was diluted with water (50 mL) and extracted with EtOAc (50 mL×3). The combined organic layers were dried with MgSO4 and concentrated in vacuo. The crude material was purified by flash chromatography on silica gel (20-50% EtOAc/Hexane) to give (R)-3-(5-oxo-4,5-dihydro-[1,2,4]thiadiazol-3-yl)-pyrrolidine-1-carboxylic acid tert-butyl ester (0.42 g, 1.55 mmol, 66%) as a white solid.
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