Solvolysis of model compounds of .alpha.-hydroxylation of N'-nitrosonornicotine and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone: evidence for a cyclic oxonium ion intermediate in the alkylation of nucleophiles

Predecki

Thomson

et al. 2003

Chem. Res. Toxicol.

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4-Hydroxy-1-(3-pyridyl)-1-butanone (HPB) is a metabolite of the tobacco specific nitrosamines, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN). HPB is also a breakdown product of covalently bound pyridyloxobutyl adducts resulting from NNK and NNN exposure. HPB released from DNA or hemoglobin has been used as an important dosimeter of tobacco specific nitrosamine exposure in a variety of studies. This compound is not reactive with cellular nucleophiles under biological conditions. We have discovered that HPB reacts with nucleophiles under acidic conditions to form cyclic tetrahydrofuranyl reaction products. Dithiothreitol, 2-mercaptoethanol, and N-acetylcysteine all reacted with HPB under these reaction conditions. In addition, reactions were observed with buffer chemicals such as 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid and tris(hydroxymethyl)aminomethane. The resulting cyclic adducts were unstable at room temperature. Their half-lives were significantly longer under neutral conditions than under acidic conditions. NMR studies established that the cyclic form of HPB, 2-hydroxy-2-(3-pyridyl)-2,3,4,5-THF, is present at significant concentrations in acidic solutions. The observation of this cyclic compound suggests that the reaction with nucleophiles may occur via a cyclic oxonium ion intermediate. This reaction was significant in our biological samples; there was up to 40% conversion of [5-(3)H]HPB to cyclic DTT-derived compounds when acidic DNA repair reactions containing [5-(3)H]pyridyloxobutylated DNA were stored overnight at -20 degrees C. Therefore, long-term storage of acid hydrolysates of pyridyloxobutylated DNA or protein for the analysis of HPB-releasing adducts could result in an underestimation of HPB-releasing adduct in those samples. In addition, these observations provide a mild synthetic method to prepare large quantities of cyclic 2-(3-pyridyl)-2,3,4,5-THF adducts predicted to result from pyridyloxobutylation of important cellular nucleophiles as a result of NNK and/or NNN exposure.

Section: Discussionmentioning

confidence: 98%

Nucleophilic Reactions between Thiols and a Tobacco Specific Nitrosamine Metabolite, 4-Hydroxy-1-(3-pyridyl)-1-butanone

Predecki

Thomson

et al. 2003

Chem. Res. Toxicol.

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“…HPLC analyses were performed with a 11 by a modification of a previously published method for NNKOAc. 4 Upon conversion of 5-bromomyosmine (1.0 g, 4.4 mmol) to 4-amino-1-[3-(5-bromo)-pyridyl]-1-butanone dihydrochloride, it was combined with paraformaldehyde (135 mg, 4.4 mmol) in 40 ml glacial acetic acid and stirred at 658C for 3 h. Sodium nitrite (460 mg, 6.7 mmol) in water was added to the ice-cooled mixture over 30 min. After 30 min at room temperature, the acetic acid was removed under reduced pressure.…”

Section: Methodsmentioning

confidence: 99%

“…NNKOAc has been used in a variety of in vivo and in vitro assays as a model compound for the pyridyloxobutylation pathway. [3][4][5][6][7][8][9] Tritiated NNKOAc has been invaluable to studies investigating the carcinogenic properties of pyridyloxobutylating nitrosamines. 3,5,6 The previously reported synthesis started with H]myosmine and required several synthetic steps with an overall yield of less than 4% (Scheme 1).…”

Section: Introductionmentioning

confidence: 99%

An improved synthesis of radiolabeled 4‐(acetoxymethylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanone

Labelled Comp Radiopharmac

Spratt

Shan

et al. 2001

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SummaryThe synthesis of high specific activity tritium-labeled 4-(acetoxymethylnitrosamino)-1-(3-pyridyl)-1-butanone is reported. This compound was prepared by tritiation of 4-(acetoxymethylnitrosamino)-1-[3-(5-bromo)-pyridyl]-1-butanone (5-BrNNKOAc) in the presence of 10% Pd/C catalyst, yielding a product with a specific activity of 11.9 Ci/mmol. This pathway represents a major improvement over previously published methods.

“…Studies with model pyridyloxobutylating agents provide evidence for a reactive cyclic oxonium ion in the alkylation of nucleophiles by the pyridylxobutylating intermediate. 59 This cyclic oxonium ion was trapped with nucleophiles such as thiols. While there is no direct evidence for these adducts in DNA, they are expected to be unstable and release HPB under all DNA hydrolysis conditions.…”

Section: Chemistry and Toxicology Of Nnk-derived Dna Damagementioning

confidence: 99%

Context Matters: Contribution of Specific DNA Adducts to the Genotoxic Properties of the Tobacco-Specific Nitrosamine NNK

2016

Chem. Res. Toxicol.

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The tobacco specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a potent pulmonary carcinogen in laboratory animals. It is classified as a Group 1 human carcinogen by the International Agency for Cancer Research. NNK is bioactivated upon cytochrome P450 catalyzed hydroxylation of the carbon atoms adjacent to the nitrosamino group to both methylating and pyridyloxobutylating agents. Both pathways generate a spectrum of DNA damage that contributes to the overall mutagenic and toxic properties of this compound. NNK is also reduced to form 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) which is also carcinogenic. Like NNK, NNAL requires metabolic activation to DNA alkylating agents. Methyl hydroxylation of NNAL generates pyridylhydroxybutyl DNA adducts and methylene hydroxylation leads to DNA methyl adducts. The consequence of this complex metabolism is that NNK generates a vast spectrum of DNA damage, any of which can contribute to the overall carcinogenic properties of this potent pulmonary carcinogen. This article reviews the chemistry and the genotoxic properties of the collection of DNA adducts formed from NNK. In addition, it provides evidence that multiple adducts contribute to the overall carcinogenic properties of this chemical. Which adduct contributes to the genotoxic effects of NNK depends on the context, such as the relative amounts of each DNA alkylating pathway occurring in the model system, the levels and genetic variants of key repair enzymes and the gene targeted for mutation.