The present invention relates to a new process for the preparation compounds of formula I ##STR1##

wherein R¹, R², R³ and n are as described in the description which process comprises reacting compounds of formula II ##STR2##

wherein R¹, R², R³, n and R⁴ are as described in the description, with a protease in an aqueous system containing an organic co-solvent. The compound of formula I are useful for the preparation of 1,5-benzothiazepines which are useful as enzyme inhibitors, such as protease, interleukin-1-converting enzyme, elastase or angiotensin converting enzyme, GPCR antagonists (cholecystokinin, angiotensin II receptor).