NMR‐invisible nucleosides in adducts formed from carcinogenic nitrobenzo[a]pyrenes

Abstract

Anomalous 'H NMR spectra have been obtained for two related carcinogen-nucleoside adducts in which a 1-or 3-aminobenzo[a] pyrene ring is bound from its C-6 position to the N-2 position of 2'-deoxyguanosine. NOESY and COSY measurements at low temperature in methanol-d, revealed chemical exchange between a t least two forms. Large chemical shift differences exist between subspectra for all corresponding protons of the nucleoside moiety, whereas all such chemical shift differences are small for the protons of the benzolalpyrene moiety. Thus, at intermediate rates of exchange, the nucleoside resonances are broadened beyond recognition, whereas the aminobenzo l a ] pyrene resonances appear normal. This is linked with the large anisotropic ring-current field from the carcinogen ring system, and restricted internal rotation a t the site of attachment of the carcinogen to the nucleic acid base. The possibility of an absence of resonances from a nucleoside moiety can complicate structure elucidation of unknown carcinogen-nucleoside adducts and related compounds, especially in trace analysis. KEY WOKUS Chemical exchange Ring-current field 2'-Deoxyguanosine Nitrobenzo[a]pyrene Carcinogen-nucleoside adducts Polycyclic aromatic hydrocarbons Exchange spectroscopy 0749-I581/93/10093

Photoaddition of Ru(tap)2(bpy)2+to DNA: A New Mode of Covalent Attachment of Metal Complexes to Duplex DNA

“…These protons (asterisked in the formulae and denoted b Table ) point toward the modified tap ligand and are therefore sensitive to changes in its ring current caused by substitution. As observed previously for the Ru(tap) 3 2+ adduct with 5‘-GMP, the guanine H8 signals of both isomers are split into two components of equal intensity with slightly different chemical shifts; similar behavior has also been reported for aminobenzo[ a ]pyrene adducts with deoxyguanosine …”

Nitroreduction of 1- and 3-Nitro-7,8,9,10-tetrahydrobenzo[a]pyrene and 1-Nitrobenzo[a]pyrene Resulting in Formation of N2-deoxyguanosinyl Adducts through Long-Range Migration

“…The 500 MHz proton NMR spectrum is shown in Figure 3. Analogous to the previously published C6-substituted adduct of 3-nitro-BaP, 6-dG-3-amino-BaP (9,15), resonances for all the aromatic protons were observed except for H6 (Figure 3 and Table 1). The upfield shift of the…”

“…Its presence was inferred from signal intensities. We previously reported that when the 500 MHz proton NMR spectrum of dG-3-amino-BaP detected (15). The anomalous line broadening has been attributed to restricted internal rotation about the guanine C2-N2 bond (15).…”

Identification of a Novel, N7-Deoxyguanosine Adduct as the Major DNA Adduct Formed by a Non-Bay-Region Diol Epoxide of Benzo[a]pyrene with Low Mutagenic Potential

“…The sugar resonances for adduct 3 were not readily observable at ambient temperature due to the chemical exchange. A similar phenomenon has been described in an N2-substituted guanosine adduct of a pyrene derivative (Evans et al, 1993). The lack of a singlet referred to above is also inconsistent with peak 3 being due to a FAPY derivative.…”