PHOTO-CHEMICAL INTERACTION BETWEEN XANTHYLETINE AND DNA

The interaction of calf thymus DNA with xanthyletin, a dimethyl-pyranocoumarin [from Hortia arborea] with a structural relationship to psoralen was studied. In the dark, xanthyletin forms a weak molecular complex with DNA, which is not of the intercalated type. Under irradiation at 365 nm, it binds covalently to DNA, with a much lower rate relative to psoralen. In this photobinding, it behaves as a pure monofunctional reagent, involving only its 3,4-double bond of the .alpha.-pyronic ring. 3-(.alpha.,.alpha.-Dimethyl-allyl)-xanthyletin, studied for a comparison, showed only a very low photoreactivity with DNA for covalent addition; this is attributed to the presence of a bulky group at position 3, which almost completely prevents the photoreaction of the 3,4-double bond. Because of the low capacity of photobinding with DNA and the inability to form cross-links, the photobiological effects of xanthyletin are accordingly reduced. Inhibition of DNA and RNA synthesis in mouse Ehrlich ascites tumor cells, killing of Escherichia coli bacterial cells and inactivation of T2 bacteriophage were observed. By contrast, it was inactive in producing erythema on guinea pig skin.