Compounds of formula I ##STR1## wherein A, X.sub.1, X.sub.2, X.sub.3, X.sub.4, Y, Z and R.sub.1 to R.sub.6 have the meanings given in the description, have valuable pharmaceutical properties and are effective especially against tumors. They are prepared in a manner known per se.
化合物的
化学式为I ##STR1## 其中A,X.sub.1,X.sub.2,X.sub.3,X.sub.4,Y,Z和R.sub.1到R.sub.6具有所述描述中给出的含义,具有有价值的药物特性,特别有效对抗肿瘤。它们的制备方法已经是众所周知的。