6-Methylangelicins: a new series of potential photochemotherapeutic agents for the treatment of psoriasis.

The possible presence of methylpsoralens as undesired inquinants in synthetic methylangelicins has been avoided through a synthetic pathway starting from umbelliferones carrying a methyl group in the 6-position. The new 6-methylangelicins show a high affinity toward DNA, forming in the dark a molecular complex; the complexed angelicins under UV-A irradiation photobind effectively to the macromolecule, forming only monoadducts. The new compounds show an evident antiproliferative activity by inhibiting DNA synthesis on Ehrlich cells; great differences, however, can be seen between the various compounds. All the compounds are lacking of skin erythemogenic activity. Some of the new 6-methylangelicins, evaluated in terms of mutagenic activity, demonstrate to be less effective than 8-methoxypsoralen (8-MOP), used for a comparison. On the basis of antiproliferative activity, lack of skin phototoxicity, and low mutagenicity, two compounds have been chosen for clinical evaluation. The compounds tested on seven psoriatic patients by topical application and UV-A irradiation proved to be more effective than 8-MOP, used in the same conditions.