Structural Differentiation of Diastereomeric Benzo[ghi]fluoranthene Adducts of Deoxyadenosine by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry and Postsource Decay

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The product ion formation characteristics of four diastereomeric deoxyadenosine adducts formed by the reaction of the syn and anti diastereomers of trans-3,4-dihydroxy-5,5a-epoxy-3,4,5,5a-tetrahydrobenzo[ghi]fluoranthene are studied by matrix-assisted laser desorption ionization and postsource decay (PSD) to determine fragmentation pathways that may permit differentiation of their structures. The two adducts derived from each diol-epoxide with DNA differ in structure based on the cis/trans arrangement of the 3′-hydroxyl group on the benzo[ghi]fluoranthene (B[ghi]F) and the adenine base bound to the B[ghi]F 5a carbon. The two adduct diastereomers with the cis adenine-3′-hydroxyl configuration produce product ions at m/z 394 and m/z 510 formed by the loss of water that are not observed in the PSD spectra of the two trans isomers. The data suggest a mechanism of water loss that is initiated by a hydrogen-bonding interaction between the charge-bearing proton on the N1 atom and the 3′-hydroxyl oxygen on the polycyclic aromatic hydrocarbon (PAH). Fragmentation is initiated by the transfer of the adenine N1 proton from the nitrogen to the PAH 3′-hydroxyl oxygen and inductive cleavage of the C3-O3 bond to form a benzylic carbocation on B[ghi]F. The proposed mechanism is supported by semiempirical molecular modeling calculations.

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Chemical Research in Toxicology