Ultraviolet Photoirradiation of Daunomycin and Dna–daunomycin Complexes

Daunomycin and daunomycin–DNA complexes have been irradiated with UV light for up to 1 h. The drug was degraded to a variety of precipitates, all of which were devoid of the sugar moiety and these precipitates were further degraded by photobleaching. The precipitates have been fractionated by HPLC. The major component (resulting from 10min irradiation of a deoxygenated drug solution) was characterized by proton NMR and field desorption mass spectrometry as a modified aglycone (ring A was aromatic and was de‐acetylated). The production of hydrogen peroxide, photobleaching and the formation of precipitate were all inhibited by the addition of DNA. All of these effects appear to depend on the free drug concentration in solution. In the absence of DNA, all of these effects were enhanced by the presence of oxygen and diminished if the solutions were deoxygenated with argon.