Disclosed are a compound represented by formula (I) and a pharmaceutically acceptable salt thereof,wherein R1, R2, R3, R4, R5, W, n are defined as in the present application. Also disclosed is a method for treating cancer, comprising administering to a subject in need thereof a therapeutically effective amount of the compound represented by formula (I) or a pharmaceutically acceptable salt thereof. The compound and a salt thereof according to the present application possess good anticancer and/or antitumor activity, and good water solubility and stability, as well as good tolerance in animal bodies. Also disclosed is a process for preparing a compound represented by formula (I) of the present application, comprisingreacting a compound represented by formula (II) with a compound represented by formula (III) in the presence of a condensation agent to obtain a compound represented by formula (I).
