Electrospray-mass spectrometry characterization and measurement of far-UV-induced thymine photoproducts

Far-UV-induced formation of dimeric pyrimidine photoproducts within DNA is a major cause of the carcinogenic effects of solar light. The chemical stru cture of this class of lesion has been mostly determined by studies on mode l compounds. The present work is aimed at providing mass spectrometry data on the thymine-thymine photoproducts, including the diastereoisomers of the cyclobutane dimer, the (6-4) adduct, the related Dewar valence isomer and the spore photoproduct. Fragmentation mass spectra of the modified bases, n ucleosides, dinucleoside monophosphates and dinucleotides were recorded fol lowing electrospray ionization with either triple-quadrupolar or ion-trap d etection. The results showed differences in fragmentation pattern between t he different types of photoproducts. In addition, a drastic effect of the d iastereoisometry was observed for the cyclobutane dimers. A sensitive detec tion technique has been developed for the analysis of dinucleoside monophos phate photoproducts by high-performance liquid chromatography associated wi th mass spectrometry in the negative mode with multiple reaction-monitoring detection. (C) 2000 Elsevier Science S.A. All rights reserved.