Abstract: Compounds of the formula ##STR1## or of the formula ##STR2## or the amides, esters or salts thereof, wherein: S.sup.x is S.dbd.O, O.dbd.S.dbd.O, S.dbd.NH, HN.dbd.S.dbd.O, Se.dbd.O, O.dbd.Se.dbd.O, Se.dbd.NH, HN.dbd.Se.dbd.O, S.sup.+ R.sup.3 wherein R.sup.3 is alkyl (1-6C) or O--C.dbd.O or HN--C.dbd.O;each R of R.sup.1, and R.sup.2 is independently H or a noninterfering substituent;wherein (conj) represents a conjugated system capable of transmitting electrons;n is 0 or 1;YCO is selected from the group consisting of .gamma.-Glu, .gamma.-Glu-Gly, Glu, Glu-Gly, .beta.Asp, .beta.-Asp-Gly, Asp and Asp-Gly;AA.sub.C is an amino acid linked through a peptide bond to the remainder of said compound of Formula 1; andN(Z) represents a reduced nitrogen-containing leaving group and L represents an electron-withdrawing leaving group,are useful as prodrugs and to generate active components released by the activity of glutathione S-transferase.