Compounds of the general formula (I) or (IA) in which X is H, Y is a leaving group, R.sup.1 and optionally also R.sup.3 preferably being an aromatic DNA binding subunit are prodrug analogues of duocarmycin. The compounds are expected to be hydroxylated at the carbon atom to which X is joined, by cytochrome P450, in particular by CYP1B1, expressed at high levels in tumors. The prodrug is expected to be activated preferentially in tumor cells, where it will act as a DNA alkylating agent preventing cell division. ##STR00001##