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A mixture of L-tert-leucine (721 mg), sodium borohydride (189 mg) and tetrahydrofuran (25 ml) is refluxed under nitrogen atmosphere for three hours. The mixture is cooled to room temperature, and thereto is added tetrahydrofuran (25 ml). The mixture is cooled to -30° C., and thereto is added 2-(4-methoxyphenyl)-1,5-benzothiazepine-3,4(2H,5H)-dione (997 mg). Each 139 μl of conc. hydrochloric acid (1.67 mmole as hydrogen chloride) is added at 1, 3, 5 and 22 hours after the beginning of the reaction, and the reaction is carried out for 45 hours. After confirming by HPLC that the starting compound is completely consumed, the mixture is evaporated under reduced pressure to remove the solvent, and water (70 ml) is added to the residue. The mixture is stirred at room temperature for one hour, and the precipitated crystal is collected by filtration and dried. The resulting residue is suspended in isopropyl alcohol (13 ml), and the mixture is refluxed for one hour. The mixture is cooled to 5° C., and allowed to stand overnight. The precipitated crystal is collected by filtration, and washed with cold isopropyl alcohol, and dried to give (2S,3S)-3-hydroxy-2-(4-methoxyphenyl)-2,3-dihydro-1,5-benzothiazepin-4(5H)-one (842 mg).

1. temperatureis refluxed under nitrogen atmosphere for three hours
2. temperatureThe mixture is cooled to -30° C.
3. customafter the beginning of the reaction
4. customis completely consumed
5. customthe mixture is evaporated under reduced pressure
6. customto remove the solvent, and water (70 ml)
7. additionis added to the residue
8. filtrationthe precipitated crystal is collected by filtration
9. customdried
10. temperaturethe mixture is refluxed for one hour
11. temperatureThe mixture is cooled to 5° C.
12. waitto stand overnight
13. filtrationThe precipitated crystal is collected by filtration
14. washwashed with cold isopropyl alcohol
15. customdried