Cl[C:2](OC1C=CC([N+]([O-])=O)=CC=1)=[O:3].[C:14]([O:18][CH2:19][CH3:20])(=[O:17])[NH:15][NH2:16].C(N(CC)CC)C.Cl.[NH2:29][CH2:30][CH2:31][CH2:32][CH2:33][NH:34][C:35](=[O:44])[O:36][CH2:37][C:38]1[CH:43]=[CH:42][CH:41]=[CH:40][CH:39]=1>C1COCC1.O>[O:3]=[C:2]([NH:29][CH2:30][CH2:31][CH2:32][CH2:33][NH:34][C:35](=[O:44])[O:36][CH2:37][C:38]1[CH:39]=[CH:40][CH:41]=[CH:42][CH:43]=1)[NH:16][NH:15][C:14]([O:18][CH2:19][CH3:20])=[O:17]To 4-nitrophenyl chloroformate (1.008 g, 5.00 mmol) in THF (25.000 mL) at 0° C. was added ethyl carbazate (0.521 g, 5 mmol) and triethylamine (2.218 mL, 16.00 mmol). The mixture was stirred at 0° C. for 1 hour. Benzyl 4-aminobutylcarbamate hydrochloride (1.552 g, 6.00 mmol) was then added. The mixture was stirred at room temperature for 1 hour, water was then added, extracted twice with ethyl acetate, dried over MgSO4, filtered, and concentrated in vacuo. The crude product was purified by silica gel chromatography (40-100% ethyl acetate/heptane) giving ethyl 4,11-dioxo-13-phenyl-12-oxa-2,3,5,10-tetraazatridecan-1-oate (I-9a: 965 mg, 55%) as a white solid. LC-MS (M+1) 353.2, t=0.94 minute.
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