34 mg of N-(piperidin-4-yl)-2-cyclopentyl-2-hydroxy-2-phenylacetamide obtained in Step 2 of Example 27, 50 mg of cycloheptanecarbaldehyde and 10 mg of acetic acid were dissolved in tetrahydrofuran. 70 mg of sodium triacetoxyborohydride was added thereto and the resulting mixture was stirred for 17 hours. After the addition of a saturated aqueous solution of sodium bicarbonate, the reaction mixture was extracted with chloroform. The organic layer was washed with a saturated aqueous solution of sodium chloride and then dried over anhydrous sodium sulfate. After the solvent was distilled off under reduced pressure, the resulting residue was purified by preparative thin layer chromatography (Kieselgel™, 60F254, Art 5744 (manufactured by E. Merck; developing solvent: chloroform/methanol=10/1) to obtain the title compound.
