Process for preparing optically active 3-hydroxy-1,5-benzothiazepine derivative and intermediate therefor

A process for preparing an optically active cis-3-hydroxy-1,5-benzothiazepine compound (1) or an acid addition salt thereof, which comprises treating a racemic cis-3-hydroxy-1,5-benzothiazepine compound represented by the formula (1):

• ##STR8## wherein Ring A and Ring B are substituted or unsubstituted benzene rings and R.sup.1 and R.sup.2 are the same or different lower alkyl groups, or an acid addition salt thereof with an optically active d- or l-3-bromocamphor-9-sulfonic acid or a salt thereof in a solvent to form two diastereoisomeric salts of the formula (2):
• ##STR9## wherein the symbols are the same as defined above, separating and collecting a less-soluble optically active diastereoisomeric salt by utilizing difference in solubility between the resultant two diastereoisomeric salts, and converting the separated salt into a free base or an acid addition salt other than the diastereoisomeric salt of the formula (2).