Furan-side pyridopsoralens monoadducts to the thymine moiety of DNA

Isolation of the main cycloadducts formed in DNA by the UV-A (ultraviolet light of class A) photoreaction of 7-methyl-pyrido[3,4-c]psoralen (MePyPs) and 7-methyl-pyrido[4,3- c]psoralen (2N-MePyPs) was achieved by HPLC separation subsequent to enzymatic hydrolysis of DNA. The photoadducts have been quantified and their chemical structure assigned on the basis of spectroscopic measurements, including absorption and fluorescence spectroscopy, and circular dichroism as well as mass spectrometry analysis. They all present characteristics which are consistent with furan-side monoadducts resulting from a C4-cycloaddition of the psoralens to thymidine. The two major MePyPs-thymidine monoadducts formed in DNA exhibit a diastereoisomeric relationship and are likely to have a cis-syn stereochemistry.