To the compound S141C described in WO 06-059801A, that is, (6R)-2-chlorophenyl 6-(5-chloro-2-methoxybenzyl)-3,7-dioxo-4-(2,4,6-trimethoxybenzyl)-1,4-diazepane-1-carboxylate (395 mg) in an N,N-dimethylformamide (0.64 ml) solution, the compound S94 described in WO 06-059801A, that is, 1-(3-tert-butoxyisoxazol-5-yl)propylamine hydrochloride (150 mg), 4-dimethylaminopyridin (78 mg) and N,N-diisopropylethylamine (0.111 ml) were added at 0° C., and the mixture was stirred at that temperature for 15 hours. To the reaction solution, water was added, and the mixture was extracted with ethyl acetate. The extract was combined, successively washed with saturated aqueous potassium hydrogensulfate solution, saturated aqueous sodium hydrogencarbonate solution, and brine, dried over sodium sulfate, then concentrated. The residue was purified by flash column chromatography (silica gel, hexane/ethyl acetate=50/50 to 35/65) to obtain (6R)-6-(5-chloro-2-methoxybenzyl)-N-[(1R)-1-(3-tert-butoxyisooxazole-5-yl)propyl]-3,7-dioxo-4-(2,4,6-trimethoxybenzyl)-1,4-diazepane-1-carboxamide (189 mg) (compound S49a) and (6R)-6-(5-chloro-2-methoxybenzyl)-N-[(1S)-1-(3-tert-butoxyisooxazol-5-yl)propyl]-3,7-dioxo-4-(2,4,6-trimethoxybenzyl)-1,4-diazepane-1-carboxamide (compound S49b).
