Reversible Photocycloaddition of a 4′,5′‐dihydropsoralen Derivative With Thymine

Abstract

The photocycloaddition reaction between a 4',5'-dihydropsoralen derivative and thymine was studied in solution using a synthetic bichromophoric model 8 in which the two rings are associated by a tetramethylene chain. In water this model molecule exhibits intramolecular ring-ring stacking interactions as evidenced by UV and NMR spectroscopies. Irradiation at 365 nm at usual concentrations (greater than or equal to 5.10(-4) M) leads exclusively to a regio- and stereo-selective dimerization reaction involving the 3,4 double bonds of the psoralen moities. Extreme dilutions (ca less than or equal to 2.10(-5) M) were necessary to observe the intramolecular reaction which results in the exclusive formation of a 3,4 cis-anti adduct. This reaction is completely reversed by irradiation at 254 nm. These results are discussed with regard to the behavior of the homologous models in which the furan part of the psoralen ring is not hydrogenated. These latter compounds also lead exclusively to a 3,4 cis-anti adduct. It appears that saturation of the furan ring increases strongly the quantum yield of the photoaddition at 365 nm (0.01----0.18) and that the triplet excited state of the 4',5'-dihydropsoralen is involved in the photoaddition.

Cross‐Reactions of Human Lupus Autoantibodies with 8‐Methoxypsoralen Photomodified DNA Fragments

“…Exposure of DNA to UVR results in the formation of photoproducts (UV-DNA) that are antigenic and can induce the formation of antibodies that react specifically with UV-DNA and not native DNA. Biological effects of furocoumarins (psoralens) are correlated to their capacity to photoreact with pyrimidine bases of native DNA and in particular to form interstrand crosslinkages (10,11,17). PUVA (psoralen plus UV-A light)-modified DNA may also play some role in the pathogenesis of SLE.…”