The invention relates to compounds of the formula I wherein X1 and X2 independently represent a bond; a straight, branched and/or cyclic hydrocarbon diradical, optionally substituted with one or more hydroxy, halogen, nitro, amino, cyano, aminosulfonyl, alkylsulfonylamino, alkylcarbonyl, formyl, aminocarbonyl or alkylcarbonylamino; a heteroarylene or non-aromatic heterocyclic hydrocarbon diradical, all of which are optionally substituted with one or more straight, branched and/or cyclic non-aromatic hydrocarbon radical, hydroxyl, halogen, amino, nitro, cyano, aminosulfonyl, alkylsulfonylamino, alkylcarbonyl, formyl, aminocarbonyl or alkylcarbonylamino; Y1 and Y2 independently represent a bond, an ether diradical (R′—O—R″), an amine diradical (R′—N—R″), O, S, S(O), S(O)2, C(O), NH—CO, CO—NH, SO2—N(R′), methylene or N(R′)—SO2 wherein R′ and R″ independently represent straight or branched hydrocarbon diradicals containing up to 4 carbon atoms; Y3 represents O, O—C(O), C(O)—O, N(R8), R8 being hydrogen or C1-4alkyl R1 represents hydrogen or straight, branched and/or cyclic alkyl, optionally substituted with phenyl; or an aromatic hydrocarbon radical; R2 represents aryl, heteroaryl or a non-aromatic heterocyclic hydrocarbon radical, all of which are optionally substituted; tetrahydropyranyloxy, di-(C1-4 alkoxy)phosphinoyloxy or C1-4 alkoxycarbonylamino; R3 represents hydrogen; a straight, branched and/or cyclic hydrocarbon radical, optionally substituted with one or more amino, hydroxy, carboxy, halogen, nitro, cyano, alkoxy, aminocarbonyl, C1-4alkoxycarbonyl, C1-4alkoxycarbonylamino, sulfo, hydroxysulfonyloxy, dihydroxyphosphinoyloxy, phosphono, sulfamino, aminosulfonyl, aminoacylamino or dialkoxyphosphinoyl; heteroaryl or a non-aromatic heterocyclic hydrocarbon radical, all of which are optionally substituted with one or more straight, branched and/or cyclic hydrocarbon radical, amino, hydroxy, carboxy, halogen, nitro, cyano, alkoxy, aminocarbonyl, C1-4alkoxycarbonyl, C1-4alkoxycarbonylamino, sulfo, hydroxysulfonyloxy, dihydroxyphosphinoyloxy, phosphono, sulfamino, aminosulfonyl, aminoacylamino or dialkoxyphosphinoyl; wherein s is an integer from 1 to 200; R6 is hydrogen or an optionally substituted non-aromatic hydrocarbon radical; R7 is independently hydrogen or methyl; R4 and R5 independently represent hydrogen; a straight, branched and/or cyclic hydrocarbon radical, optionally substituted with halogen, hydroxyl, halogen, amino, nitro or cyano; A represents hydrogen, an optionally substituted, straight, branched and/or cyclic hydrocarbon radical, hydroxy, halogen, nitro, cyano, heteroaryl, heteroaralkyl or thiol; m and r are independently integers from 0 to 4; and n is 0 or 1; Z? is a pharmaceutically acceptable anion, such as chloride, bromide, iodide, sulfate, methanesulfonate, p-toluenesulfonate, nitrate or phosphate. The compounds are well suited as prodrugs in human and veterinary therapy.