On the other hand, trans-4-(t-butoxycarbonylaminomethyl)cyclohexyl carboxylic acid (203 g) was dissolved in dry tetrahydrofuran (80 ml) and triethylamine (1.19 ml) was added under ice-cooling to the solution, and the solution was stirred for 10 minutes. Subsequently, a solution of ethyl chlorocarbonate (0.85 g) in dry tetrahydrofuran (5 ml) was added and the mixture was further stirred for 20 minutes. The mixture was added to a mixture of the hydrochloride (II) previously obtained, triethylamine (1.19 ml), and N,N-dimethylformamide (5 ml) under ice-cooling, followed by stirring for 2 hours and again under room temperature for 2 hours. The solvent was evaporated under a reduced pressure, the residue was diluted with ice-water, and the precipitates were collected by filtration and washed with water. The product was washed with 10% aqueous citric acid and with water, followed by washing with 50% aqueous ethyl alcohol, 50% ethyl alcohol-ethyl ether, and dried to give N-[trans-4-(t-butoxycarbonylaminomethyl)cyclohexylcarbonyl]-L-phenylalanine methylamide (III) (2.57 g).
