Disclosed are cytotoxic tomaymycin derivatives of formula (I), wherein the substituents are as described within the specification. An example of a compound of formula (I) includes 4-(3,5-Bis-[(S)-2-eth-(E)-ylidene-7-methoxy-1,2,3,11a-tetrahydro-pyrrolo[2,1c] [1,4]benzodiazepin-5-one-8-yloxymethyl]-phenoxy)-butyric acid. Further disclosed is a conjugate comprising one or more compounds of formula (I) covalently linked to a cell binding agent through the linking group of the linker of the compound, wherein said cell binding agent is chosen from antibodies or a fragment of an antibody, lymphokines, hormones, growth factors, or nutrient-transport molecules, and the process for the preparation of said conjugate. Also disclosed is a pharmaceutical composition comprising said conjugate or a compound of formula (I), and the use of said conjugate or compound of formula (I) in the preparation of a medicament for the treatment of cancer.
