CHARACTERIZATION OF PHOTOCYCLOADDITION PRODUCTS FROM REACTION BETWEEN THYMIDINE and THE MONOFUNCTIONAL 3‐CARBETHOXYPSORALEN

Abstract
The photochemical reaction of 3‐carbethoxypsoralen. a monofunctional furocoumarin. with thymidine was investigated as a model system for its photoaddition to DNA. Near UV irradiation (320 nm > λ > 400 nm) of a mixture of thymidine and 3‐carbethoxypsoralen as a dry film gave rise to two main nucleoside diastereoisomers which were isolated by reverse phase high performance liquid chromatography. The structure of these products was assigned on the basis of UV absorption, fluorescence.‘H‐NMR and plasma desorption mass spectra analysis. The results are consistent with 1:1 C, cycloadducts involving the 5,6 double bond of thymine and the 4′, 5′double bond of 3‐carbethoxypsoralen. These two cycloadducts ofcis‐synstereoconfiguration show opposite circular dichroism suggesting a diastereoisomeric relationship.