[CH2:1]([O:3][C:4]([CH2:6][CH2:7][N:8]1[CH2:17][CH2:16][C:15]2[C:10](=[CH:11][C:12]([N+:18]([O-])=O)=[CH:13][CH:14]=2)[CH:9]1[CH3:21])=[O:5])[CH3:2].O.O.[Sn](Cl)(Cl)(Cl)Cl.C(=O)(O)[O-].[Na+]>C(O)C>[NH2:18][C:12]1[CH:11]=[C:10]2[C:15]([CH2:16][CH2:17][N:8]([CH2:7][CH2:6][C:4]([O:3][CH2:1][CH3:2])=[O:5])[CH:9]2[CH3:21])=[CH:14][CH:13]=10.90 g of 2-[2-(ethoxycarbonyl)ethyl]-1-methyl-7-nitro-1,2,3,4-tetrahydroisoquinoline was dissolved in 10 ml of ethanol, and 2.78 g of tin chloride dihydrate was added to the solution. The solution was heated under reflux with stirring for 2 hours. The resulting solution was neutralized with aqueous solution of sodium bicarbonate, and extracted with ethyl acetate. After washing with water and saturated aqueous solution of sodium chloride, the solution was dried with anhydrous sodium sulfate. The desiccant was separated by filtration, and the solvent was distilled off to obtain 0.69 g of 7-amino-2-[2-(ethoxycarbonyl)ethyl]-1-methyl-1,2,3,4-tetrahydroisoquinoline, which was an oily product. This product with no further purification was dissolved in 10 ml of DMF, and to this solution were added 0.92 g of separately synthesized 1-(benzyloxycarbonyl)-4-(carboxymethoxy)piperidine and 0.75 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide. The solution was stirred overnight at room temperature, and the resulting solution was extracted with ethyl acetate, washed with water, saturated aqueous solution of sodium bicarbonate, and saturated aqueous solution of sodium chloride, and dried with anhydrous sodium sulfate. After separating the desiccant by filtration, the filtrate was purified by silica gel column chromatography to obtain 1.00 g of 7-[1-(benzyloxycarbonyl)piperidine-4-yloxyacetylamino]-2-[2-(ethoxycarbonyl)ethyl]-1-methyl-1,2,3,4-tetrahydroisoquinoline, which was an oily product (yield: 71%).
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