(E)-3-{8-[2-(4-Isopropyl-1,3-thiazol-2-yl)ethyl]-2-morpholino-4-oxo-4H-pyrido-[1,2-a]pyrimidin-3-yl}-2-propenoic acid (222.7 mg, 0.49 mmol) dissolved in tetrahydrofuran (8 ml) was added with triethylamine (342 μl) and ethyl chloroformate (141 μl) at −20° C., then stirred at room temperature for 1 hour, and subsequently added with aqueous sodium borohydride (0.8 M, 4 ml) at room temperature. The aqueous sodium borohydride was occasionally added until the reaction was completed, and the completion of the reaction was confirmed by TLC. Then, the reaction solution was added with water and extracted with chloroform and chloroform:methanol=10:1, and the organic layer collected was dried over magnesium sulfate and concentrated under reduced pressure. The resulting residue was purified by silica gel column chromatography (chloroform→chloroform:methanol=100:1→60:1→30:1) to recover 81 mg (37%) of the title compound and 82 mg of the starting material.
