| abstract |
A compound of formula I or a physiologically acceptable salt thereofn nwherein X represents sulphur or methylene, R, represents hydrogen, amino or an acylated or carbamylated amino group, R 2 represents hydrogen or an alkyl group and R 3 represents an alkoxy group; preparation thereof by subjecting a tripeptide of formula III,n to the action of the enzyme isopenicillin N synthethase, and the tripeptide of formula III. |