[C:1]([O:5][C:6]([NH:8][C@H:9]([C:23]([OH:25])=O)[CH2:10][C:11]1[CH:16]=[CH:15][C:14]([O:17][CH:18]2[CH2:22][CH2:21][CH2:20][CH2:19]2)=[CH:13][CH:12]=1)=[O:7])([CH3:4])([CH3:3])[CH3:2].O[N:27]1[C:31]2C=CC=CC=2N=N1.CN>ClCCl>[CH3:31][NH:27][C:23](=[O:25])[C@H:9]([CH2:10][C:11]1[CH:16]=[CH:15][C:14]([O:17][CH:18]2[CH2:22][CH2:21][CH2:20][CH2:19]2)=[CH:13][CH:12]=1)[NH:8][C:6]([O:5][C:1]([CH3:4])([CH3:3])[CH3:2])=[O:7]To a cold (0°) solution of N-(Tertiarybutoxycarbonyl)-O-cyclopentyl-L-tyrosine (6.89 g, 20 mM) in dichloromethane (40 ml) was added 1-hydroxybenzotriazole (3.32 g, 21 mM) and dicyclohenylcarbodiimide (4.47 g, 21 mM). After 20 minutes at 0° a solution of methylamine (1.34 g, 40 mM) in dichloromethane (20 ml) was added and the reaction mixture was allowed to stir and warm to room temperature overnight. The reaction mixture after filtration and washing with water, dilute (1M) sodium hydroxide, 3N citric acid and water was dried and concentrated in vacuo to an oil. Recrystallisation from ethyl acetate/hexane gave the title compound as white crystals (1 g); m.p. 152°-154°; (Found: C, 66.77; H, 8.47; N, 7.83. C20H30N2O4 requires C, 66.27; H, 8.34; N, 7.73%); δ(CDCl3) 1.40 (9H, s, C(CH3)3); 1.5-2.0 (8H, CH-cyclopentyl); 2.72 (3H, d, J=5 Hz, CONHCH3); 2.95 (2H, m, CH2Tyr); 4.22 (1H, dd, J=7 and 15 Hz,α-CH); 4.72 (1H, br, O--CH (cyclopentyl)); 5.07 (1H, br, CONH); 5.75 (1H, br, CONH); 6.78 (2H, d, J=8 Hz, C6H4); 7.10 (2H, d, J=8 Hz, C6H4).
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