Bichromophoric Systems to Study the Base-Psoralen Photoreactions
The photosensitising properties of psoralens such as 1 and 2 have been generally related to their (2+2) photoaddition onto the pyrimidine bases of DNA. In recent years a number of results have been obtained regarding the photoaddition and the identification of the adducts formed in DNA (Hearst et al., 1984) and the photoreactions of psoralens with free thymine or thymidine in the solid phase (Vigny et al., 1985). However little is known about the photoreactivity in solution of the psoralen ring with the nucleic bases (due to the high tendancy of psoralens to photodimerise). In order to study 1/ the base-psoralen interactions 2/ the nature and the mechanism of the base-drug photoreaction in solution 3/ the influence of the complexation upon photoreactions, we have prepared model compounds 3, 4 and 5 in which a base is linked respectively to the 5-and 8-oxopsoralen rings by a flexible polymethylenic chain (models of 5M0P 1) and 8M0P 2). Such molecules can adopt folded conformations as a consequence of ring-ring stacking interactions. In dilute solution, for these models, the intramolecular psoralen-thymine photoaddition can occur and compete with the highly favoured photodimerisation of psoralen.
KeywordsHydrolysis DMSO Adduct Adenine Pyrimidine
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