To a solution of di-tert-butyldicarbonate (7.1 g) and dimethylaminopyridine (3.8 g) in acetonitrile (8 ml) cooled at −10° C., a solution of tert-butyl 4-((1R)-1-aminopropyl)-2-nitrobenzoate (8.7 g) in an acetonitrile (0.9 ml) was added at −10° C., and the mixture was stirred for 15 minutes. Next, the reaction solution was deaerated at an internal pressure of 60 to 100 mmHg for 1 hour, and then (6S)-6-(5-chloro-2-methoxybenzyl)-1-(2,4,6-trimethoxybenzyl)-1,4-diazepan-2,5-dione (1.3 g) was added. Next 1N solution of potassium tert-butoxide in tetrahydrofuran (0.53 ml) was dropwisely added to the mixture. After the end of the addition, acetic acid (2 ml) was added to the reaction solution, the mixture was concentrated in vacuo. Ethyl acetate was added to the obtained residue, and the mixture was washed with water. Then the organic layer was dried over anhydrous magnesium sulfate, and the solvent was distilled off in vacuo. The concentrated residue was purified with silica gel chromatography to obtain the title compound (17.4 g) as an oily substance. The 1H-NMR data matches those of Example 329.
