[C:1]1([CH2:7][O:8][C:9]([NH:11][C@H](C(O)=O)CC(C)C)=[O:10])[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=1.C[N:21]1[CH2:26][CH2:25][O:24]CC1.[CH2:27](OC(Cl)=O)[CH:28]([CH3:30])[CH3:29].N.CO>C(Cl)Cl>[C:1]1([CH2:7][O:8][C:9]([NH:11][C:25](=[O:24])[C@H:26]([CH2:27][CH:28]([CH3:30])[CH3:29])[NH2:21])=[O:10])[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=1To a solution of N-[(phenylmethoxy)carbonyl]-L-leucine (3 g., 11.3 mmol.) in 60 mL of methylene chloride at -20° under argon was added N-methylmorpholine (1.24 mL, 11.3 mmol.) followed by isobutylchloroformate (1.47 mL, 11.3 mmol.). The resulting suspension was stirred at -20° C. for 15 minutes at which time a solution of ammonia/methanol (about 5.6M, 20 mL, 113 mmol.) was added. After 30 minutes at -20° C., the reaction was quenched with water and warmed to room temperature. The layers were separated and the aqueous layer was extracted with methylene chloride (2 x). The combined organic extracts were dried (MgSO4) and evaporated to give 2.82 g. of the title A compound.
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