To a solution of 3-(3-benzylureido)propanoic acid (Compound VIII-1) 267 mg (1.20 mmol) in dichloromethane 5 ml, N-hydroxybenzotriazole 203 mg (1.50 mmol) and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride 288 mg (1.50 mmol) were added and the mixture was stirred at room temperature for 0.5 hr. (S)-benzyl 3-(4-(benzyloxy)phenyl)-2-(1-methylhydrazinyl)propanoate (Compound XVIII-1) 390 mg (1.00 mmol) and a solution of dimethylaminopyridine 61 mg (0.50 mmol) in dichloromethane 1 ml were added to the reaction mixture and the mixture was stirred at room temperature for 3 hrs. The reaction mixture was diluted with ethyl acetate 50 ml and washed with saturated sodium bicarbonate solution 50 ml twice, water 50 ml twice and brine 50 ml and the organic phase was dried over magnesium sulfate and filtered. The mother solution was concentrated in vacuo and the residue was purified on silica gel column chromatography (Merck 60N spherical, neutral elution by chloroform:methanol=100:0 to 95:5) to obtain the title compound 0.31 g (52.0%).
