A compound of formula I or a physiologically acceptable salt thereof
wherein X represents sulphur or methylene, R, represents hydrogen, amino or an acylated or carbamylated amino group, R2 represents hydrogen or an alkyl group and R3 represents an alkoxy group; preparation thereof by subjecting a tripeptide of formula III,
to the action of the enzyme isopenicillin N synthethase, and the tripeptide of formula III.
                            一种式Ⅰ的化合物或其生理上可接受的盐 其中X代表
硫或亚甲基,R代表氢、
氨基或酰化或
氨甲酰
氨基,R2代表氢或烷基,R3代表烷氧基;其制备方法是使式Ⅲ的三肽在异
青霉素N合成酶和式Ⅲ的三肽的作用下进行。