A mixture of 30.1 g of cis-(+)-2-(4-methoxyphenyl)-3-hydroxy-2,3-dihydro-1,5-benzothiazepine-4(5H)-one, 18.7 g of 2-(dimethylamino)ethyl chloride hydrochloride, 33.0 g of potassium carbonate and 240 ml of ethyl acetate is refluxed for 30 minutes under stirring. Then, 5 ml of water are added to the mixture, and the aqueous mixture is further refluxed for 6 hours under stirring. After cooling the reaction mixture, said mixture is washed with water. The ethyl acetate layer is separated and washed with water. The ethyl acetate layer is then evaporated under reduced pressure to remove ethyl acetate. The residue is dissolved in ethanol. After cooling the solution, said solution is acidified with 10% HCl/ethanol and then stirred at a temperature below 10° C. for 5 hours. The crystalline precipitates are collected by filtration, washed with ethanol and then dried. 37.9 g of cis-(+)-2-(4-methoxyphenyl)-3-hydroxy-5-[2-(dimethylamino)ethyl]-2,3-dihydro-1,5-benzothiazepine-4(5H)-one hydrochloride are thereby obtained. Yield: 92.7%
