Tetrahydrofuran → N-[4-(t-butyloxycarbonyl)aminomethylbenzoyl]-4-benzyloxy-L-phenylalanine cyclohexylamide

The above compound (III) was suspended in dimethylformamide (10 ml)--tetrahydrofuran (10 ml) solution, and triethylamine (0.4 ml) and trans-4-(t-butyloxycarbonyl)aminomethylcyclohexylcarboxylic acid mixed acid anhydride were added under ice-cooling, followed by stirring for 30 minutes. Further, the reaction was carried out at room temperature for 3 hours. After a conventional post-treatment, N-[trans-4-(t-butyloxycarbonyl)aminomethylcyclohexylcarbonyl]-4-(3-cyanobenzyloxy)-L-phenylalanine 4-acetylanilide (IV) (1.31 g) was obtained. The above compound (IV) (1.31 g) was allowed to react with 4N-hydrogen chloride/dioxane solution (10 ml) for 1 hour, and the crystalline substance precipitated by addition of hexane was collected by filtration. The product was recrystallized from an ethanol-ether solution to obtain N-(trans-4-aminomethylcyclohexylcarbonyl)-4-(3-cyanobenzyloxy)-L-phenylalanine 4-acetylanilide hydrochloride (1.1 g).