The design and synthesis of some DNA binding ligands and novel radioprotection agents.

Polyammoniumcations have been used as DNA targeting ligands for a variety of DNA active reagents, for example radioprotectors and anti-tumour antibiotics, which do not rely on sequence specific binding for their activity. It is proposed that these ligands have a high affinity for DNA but exhibit an external (or loose) electrostatic binding interaction which enables them to remain mobile along DNA without dissociation of the drug: DNA complex. Polyammoniumcations based on the polytetraalkylammonium and polyprotonated ammonium salts of the naturally occurring polyamines spermine and spermidine were prepared. The synthesis of drug-ligand conjugates requires either selective mono-protection or mono-derivatisation of polyamines. These syntheses are problematic because of the combination of primary and secondary amine centres encountered and difficulties in handling the polyamines. Two strategies for achieving selective derivatisation were explored: the total synthesis of protected polyamines and selective protection of commercially available polyamines. Particularly successful were synthesis based on the successive cyanoethylation of benzylamine with protection of the intermediate amines and selective mono-derivatisation with tosylchloride, BOC-ON and episulphide. Model compounds were used to probe the nature of the polyammonium cation: DNA complex in solution by nmr and esr spectroscopy. Similar compounds were used to define the properties of the cellular polyamine active transport mechanism. These studies showed that. inter alia, mobility within the ligand: DNA complex was exhibited by polyprotonated as well as polyquaternary ammonium salts but that only the former were transported into cells. A second generation of polycationic ligands based on N(4)-derivatised spermidine was prepared which took account of the cellular uptake criteria determined. Biological data presented include in vitro testing results for a novel radioprotecting polyaminothiol and preliminary in vitro and in vivo evaluation of a spermidine-chlorambucil (nitrogen mustard) anti-tumour agent.