C⁸-Arylguanine and C⁸-Aryladenine Formation in Calf Thymus DNA from Arenediazonium Ions

Abstract

Arylhydrazides, arylhydrazines, and N-alkyl-N-arylnitrosamines are metabolized to arenediazonium ions which yield C8-arylpurine adducts in calf thymus and cellular DNA. The mechanism of adduct formation has not been fully elucidated. C8-Arylguanine adducts likely form from direct aryl radical (Ar*) addition to the C8 position of guanine. However, the amounts of C8-aryladenine adducts measured here are inconsistent with direct radical attack at the C8 position of adenine. An intermediate product, an aryltriazene, is likely formed which then decomposes to the C8-aryladenine adduct. We have demonstrated that N1-aryl-N3-purinyltriazene adducts are formed from a variety of para-substituted arenediazonium ions with adenine. Decomposition of the N1-aryl-N3-purinyltriazene, at high pH and elevated temperatures, has been shown to give C8-aryladenine derivatives, and a free radical mechanism for this process has been proposed. Here we show that this process can occur under physiological conditions and that the C8-aryladenine adduct can be quantitated by HPLC. ESR studies, in which DMPO was used as a spin trap, have been used to demonstrate the intermediacy of aryl radicals during the decomposition of the N1-aryl-N3-purinyltriazenes and to demonstrate that this process also occurs in calf thymus (ct) DNA treated with arenediazonium ions. These results suggest the involvement of an aryl radical in the formation of the observed DNA adducts. Finally, we have found that the treatment of ct DNA with arenediazonium ions produces a significant amount of depurination. Both the formation of C8-arylguanine and C8-aryladenine adducts and the generation of apurinic sites may contribute to the genotoxicity of arylhydrazides, arylhydrazines, N-alkyl-N-arylnitrosamines, and arenediazonium ions.

The cytotoxicity of (−)-lomaiviticin A arises from induction of double-strand breaks in DNA

“…16 The addition of nucleotides to benzenediazonium ions, and the decomposition of these adducts to aryl radicals, has been reported. 41,42 Thus, in the absence of thiol, DNA itself may behave as a nucleophile toward 1 . The sequence of steps, e.g., protonation then addition, or addition followed by protonation, is not known, although the latter seems more likely given the electron-deficient nature of 1 .…”

Formation and Reactions of N7-Aminoguanosine and Derivatives

“…The C 8 -guanyl adducts, once formed, are stable to depurination, even in DNA (12). Interestingly, reaction of DNA with arene diazonium ions has recently been reported to cause extensive depurination (10), and N 7 -purine adducts have been considered intermediates.…”

“…(2) [8-13 C]Guo. [8][9][10][11][12][13] C]Gua (120 mg in 80 mL of 1 N HCl, 10 mM) was added to 400 mL of 0.20 M Tris base and the pH adjusted to 7.0, followed by the addition of 300 mg of ribose 1-phosphate and 9 mg of purine nucleoside phosphorylase (31). HPLC analysis (25) indicated that the reaction was >90% complete in 1 h (23°C).…”

“…The C 8 -guanyl adducts are predominant, however, and more complex to explain (Scheme 1). The C8 atom of guanine is also a common site for radical reactions (Scheme 1d) (8,10), but the available evidence does not support a mechanism involving arylamine radicals (4). A caged electron transfer reaction (Scheme 1c) can also be considered but currently has no experimental support.…”

Dediazoniation of p-hydroxy and p-nitrobenzenediazonium ions in an aqueous medium: Interference by the chelating agent diethylenetriaminepentaacetic acid

“…In this context heterolytic dediazoniation has been reported to occur with methylbenzenediazonium and pnitrobenzenediazonium (pNO) ions in an aqueous medium (8,9), whilst other authors have interpreted their results as showing evidence of heterolytic and homolytic processes during the thermal and photochemical dediazoniation of several arenediazonium ions in trifluoroethanol and ethanol (10,11). Furthermore, in certain cases the reducing capacity of water has been sufficient to reduce arenediazonium to the aryl radical (12). It is obvious therefore that reaction conditions need to be chosen carefully when trying to establish the mechanisms involved in the decomposition of such versatile compounds as arenediazonium ions.…”