To a solution of 8-(2-aminoethyl)-7-isopropyl-1,6,7,8-tetrahydro-2H-cyclopenta[d]furo[2,3-b]pyridin-8-ol (214 mg, 0.816 mmol) in tetrahydrofuran (8.2 mL) were added triethylamine (228 μL, 1.63 mmol) and acetic anhydride (92.5 μL, 0.979 mmol) under ice-cooling, and the mixture was stirred for 5 min. A saturated aqueous sodium hydrogen carbonate solution was added to the reaction solution, and the solvent was evaporated under reduced pressure. The residue was purified by silica gel column chromatography (methanol/ethyl acetate=0/100→15/85) and dissolved in toluene (10 mL). p-Toluenesulfonic acid monohydrate (478 mg, 2.52 mmol) and magnesium sulfate (900 mg) were added, and the mixture was stirred at 100° C. for 13 hr. The reaction solution was diluted with saturated aqueous sodium hydrogen carbonate solution, and the mixture was extracted with ethyl acetate. The extract was washed with saturated brine and dried over anhydrous sodium sulfate. The solvent was evaporated under reduced pressure and the residue was purified by silica gel column chromatography (methanol/ethyl acetate=0/100→10/90) to give the title compound (37.4 mg, yield 16%).
