Dicyclohexylcarbodiimide → 4-Diethylaminobutyrate dihydrochloride

7-n-pentyl-4-[1-(2-naphthylmethyl)-1,2,5,6-tetrahydropyrid-4-yl]-2,2-dimethylchroman-5-ol monohydrate (4.57g., prepared as described in Examples 2 and 3), 4-diethylaminobutyric acid hydrochloride (1.96g.) and dicyclohexylcarbodiimide (2.10g.) were dissolved together in dry dichloromethane (150 ml.) and the solution was stirred for 5 days at ambient temperature. The resulting precipitate of dicyclohexylurea was removed by filtration and the filtrate was evaporated to dryness in vacuo. The residual amorphous foam was dissolved in the minimum of ethanol and dry ether was added causing an off-white solid to be precipitated. This solid (2.90g.) was filtered off and the filtrate was treated with ethereal hydrogen chloride to give another off-white precipitate (2.86g.) which was collected by filtration. These two solids were combined and recrystallised from ethanol-ether to yield the desired 4-diethylaminobutyrate dihydrochloride as hygroscopic, off-white microcrystals (3.79g.), mp 96°C upwards (vague).