Structural characterization of the major adducts formed by reaction of 4,5-epoxy-4,5-dihydro-1-nitropyrene with DNA.

The only available marker of DNA adducts formed from 1-nitropyrene (1-NP) and DNA, N-(deoxyguanosin-8-yl)-1-aminopyrene, is derived from the nitroreduction pathway. Our studies, as well as those of others, have indicated that multiple DNA adducts are formed from 1-NP in vivo and in vitro. Thus the need for additional DNA adduct markers was apparent. Therefore, it was our goal to characterize the DNA adducts formed from 4,5-epoxy-4,5-dihydro-1-nitropyrene, a metabolite of 1-NP. The epoxide was incubated with calf thymus DNA (pH 5.4). The DNA was enzymatically hydrolyzed to deoxyribonucleosides which were analyzed by reverse phase HPLC. Three major peaks were obtained in yields less than 5%. The structural assignment of these adducts was made by comparison of their proton nuclear magnetic resonance spectra with those of cis- and trans-4,5-dihydro-4.5-dihydroxy-1-nitropyrene, and by long range coupling constants, decoupling experiments, D2O exchange, partitions and acid hydrolysis. Two adducts result from trans and one from cis addition of the N2-exocyclic amino group of deoxyguanosine to the C5-benzylic carbon of the epoxide ring. This is the first report that describes the structure of the DNA adducts formed with a ring-oxidized metabolite of 1-NP. On the basis of this finding we suggest that K-region oxides of 1-NP may be responsible for the formation of the putative 1-NP-DNA adducts in vivo.