5-CARBOXY-2'-DEOXYURIDINE, A NEW PHOTOOXIDATION PRODUCT OF THYMIDINE

In the present study, we have identified 5-carboxy-2'-deoxyuridine (Cd Urd; 5) as one of the main oxidation products of thymidine (1) upon me nadione photosensitization to UVA radiation. Anion-exchange chromatogr aphy and capillary zone electrophoresis allowed the isolation of this modified nucleoside which represents 19% of the initial product, after 3 h of irradiation. Mechanistic studies showed that CdUrd 5 results f rom UVA photooxidation of 5-formyl-2'-deoxyuridine (FdUrd; 4). The for mation of 5 may be rationalized in terms of autoxidation of the aldehy dic group of 4, according to a well established pathway. Thus, it was shown that FdUrd 4 could be oxidized into CdUrd 5 in the presence of a peracid in aqueous solution. Moreover, CdUrd 5 was also detected by c apillary electrophoresis upon far-UV photooxidation and gamma-irradiat ion of thymidine (1) in aerated aqueous solution. The presence of 5 wa s confirmed by mass spectrometry analysis of the products of the photo oxidized and gamma-irradiated solutions. (C) 1997 Elsevier Science S.A .