Studies on the photoreactions (365 nm) between DNA and some methylpsoralens.

While many methyl derivatives of psoralen are very active as skin photosensitizers, others have a small activity or are practically inactive. This difference is not explicable in terms of different capacity ofphotobinding to deoxyribonucleic acid (DNA). Other factors are important, especially the ability to form cross linkings in DNA. As a result of a comparison of a group of methylpsoralen derivatives, a good correlation was found between the skin photosensitizing potencies of the various compounds, as evaluated by determining the minimum irradiation time necessary for the production of erythema on guinea pig skin, and the amounts of cross linking formed in DNA as a function of the time of irradiation.