[O:1]1[CH:5]=[CH:4][CH:3]=[C:2]1[CH2:6][N:7]([C:15]([O:17][CH2:18][CH3:19])=[O:16])[CH2:8][CH2:9][C:10]([O:12]CC)=[O:11].[OH-].[K+]>CO>[O:1]1[CH:5]=[CH:4][CH:3]=[C:2]1[CH2:6][N:7]([C:15]([O:17][CH2:18][CH3:19])=[O:16])[CH2:8][CH2:9][C:10]([OH:12])=[O:11]Ethyl 3-[(furan-2-ylmethyl) (ethoxycarbonyl)amino]-propionate (13.77 g) prepared in the step 3 was dissolved in 200 mL of methanol, 5.0 g of potassium hydroxide was added thereto and the mixture was heated to reflux for 3 hours. The solvent of the reaction solution was evaporated in vacuo and the residue was dissolved in methylene chloride. The resulting solution was slowly neutralized to pH 3 using 1N aqueous solution of hydrochloric acid (about 80 mL) with stirring. The organic layer was separated, washed with water and a saturated solution of sodium chloride successively and dried over anhydrous magnesium sulfate and the solvent was evaporated in vacuo therefrom to give 12.56 g of the objective compound as yellow liquid.
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