7-Methyl and 4,7-dimethylallopsoralen: monofunctional photoreagents toward DNA as potential photochemotherapeutic agents in hyperproliferative conditions.

7-Methyl- (1 a) and 4,7-dimethylallopsoralen (1 b), prepared about ten years ago and till now considered non-photosensitizing agents, have been re-investigated for studying their photochemical and photobiological properties. They form a molecular complex with DNA in the ground state, undergoing intercalation between two base pairs of the macromolecule. By successive irradiation with U.V.-A they covalently photobind to DNA inducing only the formation of mono-adducts. They are not able to induce erythema on guinea pig skin, but show evident antiproliferative activity on various biological substrates. Compound (1 b) shows both photochemical and photobiological properties at a degree higher than that of compound (1 a).