Bioreductive cytotoxic agents

A compound consisting of a proactive alkylating moiety containing an electron-withdrawing group, a bioreductive moiety containing at least two double bonds, and a linker joining the proactive alkylating moiety and the bioreductive moiety, wherein the linker is a methylene group, a C.sub.3 hydrocarbon chain containing a double bond, or a C.sub.5 hydrocarbon chain containing two alternate double bonds;

• the double bonds of the bioreductive moiety, either by themselves when the linker is a methylene group, or together with the double bond of the C.sub.3 linker or the double bonds of the C.sub.5 linker, form a conjugated system, which allows electrons to flow from the bioreductive moiety to the electron-withdrawing group of the proactive alkylating moiety upon reduction of the bioreductive moiety, thereby breaking the bond between the electron-withdrawing group and the linker and converting the proactive alkylating moiety into an active alkylating compound;
• or a salt thereof.