Exocyclic Deoxyadenosine Adducts of 1,2,3,4-Diepoxybutane: Synthesis, Structural Elucidation, and Mechanistic Studies

Abstract

Abstract1,2,3,4-Diepoxybutane (DEB)1 is considered the ultimate carcinogenic metabolite of 1,3-butadiene, an important industrial chemical and environmental pollutant present in urban air. Although it preferentially modifies guanine within DNA, DEB induces a large number of A → T transversions, suggesting that it forms strongly mispairing lesions at adenine nucleobases. We now report the discovery of three potentially mispairing exocyclic adenine lesions of DEB:. The structures and stereochemistry of the novel DEB-dA adducts were determined by a combination of UV and NMR spectroscopy, tandem mass spectrometry, and independent synthesis. We found that synthetic N 6 -(2-hydroxy-3,4-epoxybut-1-yl)-2′-deoxyadenosine (compound 1) representing the product of N 6 -adenine alkylation by DEB spontaneously cyclizes to form 3 under aqueous conditions or 2 under anhydrous conditions in the presence of organic base. Compound 3 can be interconverted with 4 by a reversible unimolecular pericyclic reaction favoring 4 as a more thermodynamically stable product. Both 3 and 4 are present in double stranded DNA treated with DEB in vitro and in liver DNA of laboratory mice exposed to 1,3-butadiene by inhalation. We propose that in DNA under physiological conditions, DEB alkylates the N-1 position of adenine in DNA to form N1- (2-hydroxy-3,4-epoxybut-1-yl)adenine adducts, which undergo an S N 2-type intramolecular nucleophilic substitution and rearrangement to give 3 (minor) and 4 (major). Formation of exocyclic DEB-adenine lesions following exposure to 1,3-butadiene provides a possible mechanism of mutagenesis at the A:T base pairs.

NanoHPLC-nanoESI+-MS/MS Quantitation of Bis-N7-Guanine DNA–DNA Cross-Links in Tissues of B6C3F1 Mice Exposed to subppm Levels of 1,3-Butadiene

“…20–25 DEB-specific bifunctional DNA adducts have been quantified in tissues of laboratory rats and mice that were exposed to 6.25–625 ppm of BD by inhalation. 26 Among DEB-DNA adducts, bis -N7G-BD were present at the highest concentration (3.95 ± 0.89 adducts/10 7 nucleotides (nts) in livers of mice exposed to 625 ppm BD), followed by N7G-N1A-BD(0.27 ± 0.07 adducts/10 7 nts) and 1,N 6 -HMHP-dA (0.044 ± 0.008 adducts/10 7 nts).…”

1,3-Butadiene-Induced Adenine DNA Adducts Are Genotoxic but Only Weakly Mutagenic When Replicated in Escherichia coli of Various Repair and Replication Backgrounds

“…9 These four adducts were detected when calf thymus DNA was allowed to react with BD epoxides, although only small amounts of N 6 , N 6 -DHB-dA were detected. 9, 22 1, N 6 -γ-HMHP-dA adducts have also been detected in tissues of laboratory mice treated with BD by inhalation. 24 …”

“…7, 11–14 The higher genotoxicity and mutagenicity of DEB have been hypothesized to be due to its bifunctional alkylating ability, which gives it the ability to form DNA–DNA crosslinks and exocyclic adducts. 9, 11, 15–17 One DEB-induced intrastrand crosslinked adduct has been shown to be genotoxic and mutagenic. 18, 19 …”

Novel Synthesis of 1-substituted meso-3,4-dihydroxypyrrolidines with a RuCl3-catalyzed Key Reaction

“…The organic phase was dried over Na 2 SO 4 than the solvent was evaporated in vacuum. The residual pale yellow crystals were recrystallized from dichloromethane (10 mL) to give the desired diol (6) as white crystals in 70 % yield. To the solution of aromatic amine (15 mmol; 1.40 g of 3a, 1.85 g of 3b, 1.67 g of 3c) in ethanol (40 mL) were added the dimethanesulfonate (6, 1.39 g, 5 mmol), dried KI (1.66 g, 10 mmol) and TEBACl (0.228 g, 1 mmol) and the reaction mixture was stirred under reflux for 48 h. After cooling the reaction mixture to room temperature, the salts were filtered off and the ethanol was removed under vacuum.…”