Synthesis and examination of nucleoside adducts formed by alpha-hydroxy-N-nitrosomorpholine

N-nitrosomorpholine (NMOR) is a potent carcinogen and mutagen that has been shown to cause liver and esophageal tumors in rats and nasal tumors in hamsters. NMOR has been detected in smokeless tobacco, in many food products, in workplaces of tire, rubber, and leather industries, and in human urine. The metabolism of NMOR occurs in the liver by P-450 enzymes predominantly through alpha-hydroxylation. The resulting alpha-hydroxy-N-nitrosomorpholine readily decomposes in aqueous media with half-lives ranging from milliseconds to minutes to form a highly reactive diazonium ion. This diazonium ion can react with solvent water or alkylate DNA, producing 2-ethoxyacetaldehyde adducts. To date, there is only one report of attempts to examine the nucleoside adducts produced from alpha-hydroxy-N-nitrosomorpholine (HONMOR) exposure.;The primary aim of this research was to complete a full analysis of the purine nucleoside adducts that are generated from (HONMOR). This was accomplished with the use of a stable precursor, alpha-hydroperoxy-N-nitrosomorpholine (HOONMOR), and synthesized nucleoside standards. Initially, a model system was used to demonstrate that the (2-ethoxyacetaldehyde)-diazonium ion generated from HONMOR decay could be trapped by a model nucleobase, benzimidazole. Following this, experiments were conducted that exposed nucleosides and calf thymus DNA to HONMOR. In the reactions of nucleosides the yields of the 2-ethoxyacetaldehyde (EA) adducts are in order of N7-Gua > O6-Gua > N7-Ade > N1-Gua > N2-Gua > N3-Ade. In the reactions of DNA the yields of the EA adducts are in order of N7-Gua ≈ O6-Gua > N3-Ade > N7-Ade > N2-Gua.;The second aim of this research was to examine the aqueous stability of the EA fragment in various buffers, on nucleosides, and on duplex DNA to determine if EA could decay into a 2-hydroxyethyl (HE) fragment since a previous report described the isolation of a HE fragment at the N7 position of guanine in rats treated with NMOR. The results indicate that the EA fragment is stable in acidic media but readily decays in neutral and basic media. Further examination revealed that the EA decomposes into a HE fragment with its rate of decay stimulated by primary and secondary amines under physiological conditions.