To 3 mL of a dichloromethane solution containing 0.15 g of ethyl (2E)-3-(1-(2-(4-((tert-butoxycarbonyl)(2,3-dihydro-1,4-benzodioxin-6-ylmethyl)amino)piperidin-1-yl)ethyl)-7-methoxy-2-oxo-1,2-dihydroquinolin-5-yl)acrylate, 3 mL of trifluoroacetic acid was added and stirred at room temperature for 1 hour. The solvent was removed under reduced pressure, chloroform and water were added, and adjusted to pH 10 with 20% aqueous sodium hydroxide solution, under ice-cooling. The organic layer was separated, and the aqueous layer was extracted with chloroform. The organic layer and extracts were combined, washed sequentially with water and aqueous saturated sodium chloride solution, dried over anhydrous magnesium sulfate, and the solvent was removed under reduced pressure. To the residue thus obtained, hexane was added and the resulting solid was filtered to give 0.12 g of ethyl (2E)-3-(1-(2-(4-((2,3-dihydro-1,4-benzodioxin-6-ylmethyl)amino)piperidin-1-yl)ethyl)-7-methoxy-2-oxo-1,2-dihydroquinolin-5-yl)acrylate as a light brown solid.
