Iminohydantoin Lesion Induced in DNA by Peracids and Other Epoxidizing Oxidants

Abstract

The oxidation of guanine to 5-carboxamido-5-formamido-2-iminohydantoin (2-Ih) is shown to be a major transformation in the oxidation of the single-stranded DNA 5-mer d(TTGTT) by m-CPBA and DMDO as a model for peracid oxidants and in the oxidation of the 5-base pair duplex d[(TTGTT)·(AACAA)] with DMDO. 2-Ih has not been reported as an oxidative lesion at the level of single/double-stranded DNA or at the nucleoside/nucleotide level. The lesion is stable to DNA digestion and chromatographic purification suggesting that 2-Ih may be a stable biomarker in vivo. The oxidation products have been structurally characterized and the reaction mechanism probed by oxidation of the monomeric species dGuo, dGMP and dGTP. DMDO selectively oxidizes the guanine moiety of dGuo, dGMP and dGTP to 2-Ih, and both peracetic and m-chloroperbenzoic acids exhibit the same selectivity. The presence of the glycosidic bond results in the stereoselective induction of an asymmetric center at the spiro carbon to give a mixture of diastereomers, with each diastereomer in equilibrium with a minor conformer through rotation about the formamido C-N bond. Labeling studies with 18O2-m-CPBA and H218O to determine the source of the added oxygen atoms have established initial epoxidation of the guanine 4-5 bond with pyrimidine ring contraction by an acyl 1,2-migration of guanine carbonyl C6 to form a transient dehydrodeoxyspiroiminodihydantoin followed by hydrolytic ring opening of the imidazolone ring. Consistent with the proposed mechanism, no 8-oxoguanine was detected as a product of the oxidations of the oligonucleotides or monomeric species mediated by DMDO or the peracids. The 2-Ih base thus appears to be a pathway-specific lesion generated by peracids and possibly other epoxidizing agents and holds promise as a potential biomarker.

Computational studies of electronic circular dichroism spectra predict absolute configuration assignments for the guanine oxidation product 5-carboxamido-5-formamido-2-iminohydantoin

“…S2). 18 The d2Ih nucleosides exhibit free rotation about the N -glycosidic bond and a number of bonds in the base (Scheme 2); therefore, to simplify the interpretation of the experimental ECD spectra by TDDFT methods removal of the sugar by cleavage of the glycosidic bond was first conducted (Scheme 2). Removing the 2-deoxyribose sugar eliminates many atoms and one freely rotatable bond that would need to be addressed via quantum mechanical calculations.…”

“…These results are in agreement with the structure proposed for the nucleosides based on NMR results, which also place the formyl group on N9. 18 Therefore, all further calculations on the 2Ih enantiomers were completed on only this isomer.…”

“…17 Subsequently, the structure for d2Ih was established by complementary NMR methods. 18 In addition, d2Ih has been observed during oxidation of 2′-deoxyguanosine by Mn-TMPyP/KHSO 5 , 16,19 NiCR/KHSO 5 , 20 dimethyldioxirane, 18 Cu(OAc) 2 /H 2 O 2 , 21 Pb(OAc) 2 /H 2 O 2 , 22 and CO 3 •− 23 . These studies highlight 2Ih , a two-electron oxidation product of guanine, as a possible primary oxidation product that might exist in the cellular context.…”

Porphyrins in complex with DNA: Modes of interaction and oxidation reactions

“…The first one is the guanine oxidation product 5-carboxamido-5-formamido-2-iminohydantoin (2Ih) [174][175][176][177][178], which forms through an initial epoxidation (intermediate 3 in Figure 17). The second one results from the oxidation of the 2- However, hydroxylation of the tertiary C1'-carbon is easier than that of the primary C5'-carbon.…”

Nucleotides and nucleic acids; oligo- and polynucleotides

“…223 Treatment of DNA containing guanine with peracids or dimethyldioxirane leads to the iminohydantoin lesion (51). 224 The exocyclic amino group of guanine is susceptible to reaction with a variety of environmental mutagens and drugs leading to analogues that are often mutagenic. Common lesions with guanine arise by reaction with aldehydes such as malondialdehyde, the latter giving rise to the mutagenic adduct (52), the mutagenicity of which is dependent on induction of the SOS response, and is due primarily to translesion synthesis.…”