[C:1]([O:5][C:6]([NH:8][CH2:9][CH2:10][C:11]([OH:13])=[O:12])=[O:7])([CH3:4])([CH3:3])[CH3:2].[CH2:14](O)[C:15]1[CH:20]=[CH:19][CH:18]=[CH:17][CH:16]=1>C(Cl)Cl>[C:1]([O:5][C:6]([NH:8][CH2:9][CH2:10][C:11]([O:13][CH2:14][C:15]1[CH:20]=[CH:19][CH:18]=[CH:17][CH:16]=1)=[O:12])=[O:7])([CH3:4])([CH3:2])[CH3:3]N-t-Butyloxycarbonyl-β-alanine (2.0 g, 10.6 mmol) in methylene chloride (50 mL) was treated with benzyl alcohol (1.66 mL, 26.0 mmol), N,N-dicyclohexylcarbodiimide (2.39 g, 11.6 mmol) and N,N-dimethylaminopyridine (1.42 g, 11.6 mmol) and the subsequent reaction mixture was stirred at room temperature for 54 h. The reaction mixture was filtered and evaporated at reduced pressure. The residue was purified using flash chromatography (silica gel, 50% ethyl acetate/hexane) to yield the title compound (25) (2.43 g, 82%). 1H NMR (CDCl3) ε 1.47 (s, 9H), 2.61 (t, 2H, J=6 Hz), 3.45 (q, 2H, J=7.5 Hz), 5.15 (br s, 1H), 5.27 (s, 2H), 7.43 (s, 5H).
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