[NH2:1][C@H:2]([C:12]([OH:14])=[O:13])[CH2:3][C:4]1[CH:9]=[CH:8][C:7]([C:10]#[N:11])=[CH:6][CH:5]=1.Cl[C:16]([O:18][CH2:19][CH:20]=[CH2:21])=[O:17]>[OH-].[Na+]>[NH:1]([C:16]([O:18][CH2:19][CH:20]=[CH2:21])=[O:17])[C@H:2]([C:12]([OH:14])=[O:13])[CH2:3][C:4]1[CH:5]=[CH:6][C:7]([C:10]#[N:11])=[CH:8][CH:9]=15.7 g (30 mmol) of H-Phe(4-CN)—OH were dissolved in 100 ml of 1M NaOH with addition of 2M NaOH to pH=10 with ice cooling. With vigorous stirring, allyl chloroformate (7.5 ml) was slowly added (pH kept at 10 by 2M NaOH). The reaction mixture was stirred at 0° C. for 15 min and at RT for 30 min, acidified with HCI to pH=2, extracted with ethyl acetate (3 times), dried with MgSO4, and evaporated. The residue was recrystallized from ethyl acetate/hexane to give a white solid. Yield: 7.0 g (85%).
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