To a suspension of 866 mg (5.0 mmol.) of quinaldinic acid and 576 mg (5.0 mmol.) of 1-hydroxysuccinimide in 20 ml of ethyl acetate was dropwise added over a period of 5-10 min. under chilling with ice a solution of 1.09 g (5.0 mmol.) of N,N'-dicyclohexylcarbodiimide. After the addition was complete, the mixture was stirred for 2 hours at room temperature. To this mixture was dropwise added a solution of 1.09 g (5.0 mmol.) of 1-(3-amino-3-phenylpropyl)piperidine in 5 ml of ethyl acetate. After the addition was complete, the mixture was stirred overnight at room temperature. Precipitated insolubles were filtered off and then the insolubles were washed with ethyl acetate. The filtrate and the washings were combined and washed twice with a saturated aqueous sodium hydrogencarbonate solution and once with a saturated aqueous sodium chloride solution. The mixture was then dried over sodium sulfate, and was evaporated under reduced pressure to remove the solvent. The residue was purified by silica gel column chromatography (silica gel: 20 g, CHCl3 and CHCl3 /CH3OH (30:1)) to obtain 1.72 g (yield: 92%) of the subject compound as a pale yellow crystalline product.
