(R)-ethyl 5-(benzyloxycarbonylamino)-2-(3-(4-(tert-butoxy-carbonylamino)benzyl)ureido)pentanoate (1 equivalent, 115 mg, 0.21 mmol) was dissolved in 50 ml of MeOH. The Pd/C (12 mg) and the acetic anhydride (3 equivalent, 60 μl, 0.63 mmol). The reaction mixture was stirred under hydrogen at room temperature for 4 h. Then the mixture was filtrated on celite and the filter was concentrated. the crude was washed by 30 ml NaHCO3 and extracted by 3×30 ml EtOAc. The organic phase was dried over Na2SO4, filtered and concentrated. The crude was purified by flash chromatography (CH2Cl2/MeOH) to afford the amide (84 mg, 78%) a colourless oil Rf=0.27 (CH2Cl2/MeOH 95/5). 1H NMR (200 MHz, CDCl3): δ 7.30 (d, J=8.6 Hz, 2H), 7.18 (d, J=8.6 Hz, 2H), 6.63 (broad s, 1H), 6.28-6.10 (m, 1H), 5.45 (d, J=7.6 Hz, 1H), 5.34-5.20 (m, 1H), 4.52-4.35 (m, 1H), 4.29 (d, J=5.8 Hz 2H), 4.15 (q, J=7.1 Hz, 2H), 3.32-3.12 (m, 2H), 1.94 (s, 3H), 1.90-1.36 (m, 4H) 1.50 (s, 9H), 1.25 (1, J=7.5 Hz, 3H).
