The Formamidopyrimidine Derivative of 7-(2-Oxoethyl)-2′-deoxyguanosine

Abstract

Vinyl chloride induces hepatic angiosarcomas, which are otherwise rare malignancies. The biochemical basis involves the formation of the epoxide, which reacts with DNA to give ~98% of the 7-(2-oxoethyl) adduct (4) of dGuo plus small amounts of the etheno derivatives of dGuo, dCyd, and dAdo. The carcinogenicity is generally ascribed to the etheno adducts, not 4, because 4 has been shown to disappear from cells rapidly and to have negligible mutagenicity, which argues against its biological importance, whereas etheno adducts are both persistent and mutagenic. It has also been shown that apurinic sites derived from 4 are unlikely to be crucial lesions. A confounding factor with regard to the etheno hypothesis is that etheno adducts arise in unexposed cells by reactions of various lipid peroxidation products. The present study explores the possibility that a major contributor to the carcinogenicity of vinyl chloride may be formamidopyrimidine (FAPy) 12, N-[2-amino-6-[(2-deoxy-β-D-erythro-pentofuranosyl)amino]-3,4-dihydro-4-oxo-5-pyrimidinyl]-N-(2-oxoethyl)-formamide, which can arise by ring opening of 4, although its formation has not been observed until the present study. N7 adduct 4 undergoes deglycosylation to give 7-(2-oxoethyl)-Gua (13) in acid and imidazolium ring-opening to 12 in base. At pH 7.4, both processes occur with the formation of 12 representing ~10% of the product mixture. FAPy 12 spontaneously cyclizes to 22, which upon mild acid treatment yields the deglycosylation product 2-amino-3,4,7,8-tetrahydro-7-hydroxy-4-oxopteridine-5(6H)-carbaldehyde (14). The structure of 14 has been established by NMR and mass spectroscopy and by independent synthesis. Reaction of the epoxide of crotonaldehyde with dGuo failed to give either 13 or 14, indicating that both compounds are unique products of the reactions of dGuo with the epoxides of vinyl monomers. Although FAPy 12 was found to be unstable, carbinolamine 22 arising from cyclization of 12 may be an important contributor to the carcinogenicity of vinyl chloride.

Chemical Structure and Properties of Interstrand Cross-Links Formed by Reaction of Guanine Residues with Abasic Sites in Duplex DNA

“…This is consistent with the observation that pyranose isomers of unprotected 2-deoxyribose and its arylamino-2-deoxyriboside analogues typically predominate in solution. 53–56 The chemical shifts of C1″ in the isomers of 9b at 76.5–82.9 ppm, along with HMBC correlations observed between H1″ and C4″ in the furanose isomers and between H5″ and C1″ in the pyranose isomers, were again consistent with the cyclic hydroxyalkylhemiaminal form. No evidence for a ring-opened imine isomer was seen in the NMR spectra.…”

“…This assessment was based upon the chemical shifts of C4″ in the two isomers of 14 at 86.7 and 87.0 parts per million (ppm), values consistent with a furanose sugar. 53 The major isomer showed a strong nuclear Overhauser efiect (NOE) cross-peak between guanine N 2 -H and H4″, consistent with the α -isomer, while the minor isomer showed a stronger NOE cross-peak between H1″ and H4″, consistent with the β -isomer (Figure 2). 44 The high-resolution mass spectrum was consistent with the molecular formula expected for 14 .…”

“…While this product has the potential to exist as either a ring-opened imine or a cyclic hydroxyalkylhemiaminal, the C1″ chemical shift at 83.6 ppm for this product was consistent with the cyclic structure of 14 . 53 The corresponding imine 13 C-chemical shift would be expected at approximately 160 ppm. 20 The observed HMBC correlation between H1″ and C4″ also was consistent with the ring-closed isomer of 14 .…”

“…As expected, the NMR spectrum of the deprotected material 9b was more complex than that of the starting material 14 because removal of the protecting groups from the 2-deoxyribose adduct enables interconversion between pyranose and furanose forms, each of which can exist as a mixture of α - and β -isomers (Scheme 5). 53–56 Two-dimensional NMR experiments provided evidence that the 2-deoxyribose adduct in 9b remained connected at the exocyclic N 2 -amino group of the guanine residue. As described above in the context of 14 , the 1 H– 1 H COSY spectrum of 9b in DMSO- d 6 showed a correlation between N 2 -H and H1″ of the 2-deoxyribose adduct (Figure 3).…”

Chemical Biology of N5-Substituted Formamidopyrimidine DNA Adducts

“…68 Acetoxyoxirane, an acetylated analogue of chlorooxirane, was used in many studies of DNA alkylation because it is more chemically stable than chlorooxirane, but generates the same types of DNA adducts. 69 Acetoxyoxirane can be readily prepared from vinyl acetate and dimethyldioxirane. 69 …”