To the compounds (I) (19.15 g) was added dry 1,4-dioxane (50 ml) and 4N hydrogen chloride/1,4-dioxane solution (250 ml), and the mixture was stirred under room temperature for 2 hours. The solvent was removed under a reduced pressure and toluene was added and reevaporated to give L-phenylalanine 4-carbamoylanilide hydrochloride (II) quantitatively as a white powder. On the other hand, trans-4-(t-butoxycarbonylaminomethyl)cyclohexylcarboxylic acid (13.36 g) was dissolved in dry tetrahydrofuran (500 ml), and triethylamine (7.80 ml) was added under ice-cooling, followed by stirring at the same temperature for 10 minutes. Subsequently, a solution of ethyl chlorocarbonate (5.64 g) in dry tetrahydrofuran (50 ml) was added dropwise under ice-cooling for 3 minutes, and the mixture was again stirred at the same temperature for 20 minutes. The above mixture was added to the suspension of the hydrochloride (II) previously obtained and triethylamine (8.53 ml) in N,N-dimethylformamide (150 ml) under ice-cooling, followed by stirring at the same temperature for 2 hours, and under room temperature for 6 hours. Ice-water (1.4 liter) was added and the insolubles were collected by filtration, thoroughly washed with water, and further washed with 10% aqueous citric acid, water 5% aqueous sodium hydrogen carbonate, followed by washing with water at 40° to 50° C., and drying, to give N-[4-trans-(t-butoxycarbonylaminomethyl)cyclohexylcarbonyl]-L-phenylalanine 4-carbamoylanilide (III) (24.63 g). The structure was confirmed by NMR.
