[C:1]([O:5][C:6]([N:8]([O:19][CH2:20][CH2:21][NH:22]C(OCC1C=CC=CC=1)=O)[C:9]([NH:11][C:12]([O:14][C:15]([CH3:18])([CH3:17])[CH3:16])=[O:13])=[NH:10])=[O:7])([CH3:4])([CH3:3])[CH3:2]>C(O)C.O1CCCC1.[Pd]>[C:1]([O:5][C:6]([N:8]([O:19][CH2:20][CH2:21][NH2:22])[C:9]([NH:11][C:12]([O:14][C:15]([CH3:17])([CH3:16])[CH3:18])=[O:13])=[NH:10])=[O:7])([CH3:4])([CH3:3])[CH3:2]A mixture of [N,N'-di(tert-butoxycarbonyl)]2-(benzyloxycarbonylamino)ethoxyguanidine (730 mg, 1.5 mmol), as prepared in the preceding step, and 10% Pd/C (70 mg) in ethanol (20 mL) and tetrahydrofuran (20 mL) was hydrogenated under hydrogen (balloon) for 30 min. The catalyst was removed by filtration through Celite and the filtrate was concentrated in vacuo. The residue was purified by Waters Sep-Pak (10 g, 95:5 methylene chloride:methanol saturated with ammonia) to give the title compound as a colorless oil (290 mg, 61%). 1H-NMR (300 MHz, CDCl3) δ9.08 (br s, 1H), 4.08 (t, J=5.2 Hz, 2H), 2.99 (q, J=5.1 Hz, 2H), 1.50 (s, 9H), 1.48 (s, 9H).
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