Dicyclohexylcarbodiimide → N-[2-chloro-4-[[[(3-hydroxyphenyl)methyl]amino]carbonyl]benzoyl]-3-[(9H-fluoren-9-ylmethoxy)carbonyl]amino-L-alanine, methyl ester

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A solution of N-[(1,1-dimethylethoxy)carbonyl]-3-[(9H-fluoren-9-ylmethoxy)carbonyl]amino-L-alanine, methyl ester (Example 62; 1.50 g, 3.4 mmol) was converted to crude 3-[(9H-fluoren-9-ylmethoxy)carbonyl]amino-L-alanine, methyl ester (1.30 g, 112% of the theoretical amount) by treatment with trifluoroacetic acid/dichloromethane (1:1). A portion of this material (0.50 g) was combined with 2-chloro-4-[[[(3-hydroxyphenyl)methyl]amino]carbonyl]benzoic acid (449 mg, 1.5 mmol), HOAT (219 mg, 1.6 mmol) and dicyclohexylcarbodiimide (363 mg, 1.8 mmol) in N,N-dimethylformamide (5 mL) and the reaction mixture was stirred at room temperature over the weekend. Water was added and the mixture was extracted three times with ethyl acetate. The combined organic layers were washed with water and brine, dried, filtered, evaporated, and chromatographed (2–10% methanol/dichloromethane) to give N-[2-chloro-4-[[[(3-hydroxyphenyl)methyl]amino]carbonyl]benzoyl]-3-[(9H-fluoren-9-ylmethoxy)carbonyl]amino-L-alanine, methyl ester (0.57 g, 62%) as a white solid.

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