Product ion studies of some novel arylamine adducts of deoxyguanosine by matrix-assisted laser desorption/ionization and post-source decay.

The product ions of the BH(2)(+) ions formed by the glycosidic cleavage of N-(deoxyguanosin-O(6)-yl)-2-methylaniline, 4-(deoxyguanosin-8-yl)-2-methylaniline, and N-(deoxyguanosin-1-yl)-2-methylaniline have been studied using matrix-assisted laser desorption/ionization (MALDI) and post-source decay (PSD) to identify fragment ions and pathways that may be used to differentiate their structures. All three isomers may be distinguished based on their PSD product ion spectra using only femtomole quantities of sample. N-(Deoxyguanosin-O(6)-yl)-2-methylaniline produces product ions at m/z 107 and 134 that are diagnostic for 2-methylaniline attachment to the O(6) position of guanine. The BH(2)(+) ion from 4-(deoxyguanosin-8-yl)-2-methylaniline yields a product ion formed by the consecutive losses of 17 and 42 u neutral fragments that may be regarded as specific for guanine-arylamine adducts that possess two primary amine groups. The BH(2)(+) ion from 4-(deoxyguanosin-8-yl)-2-methylaniline yields no product ions that correlate with specificity for guanine N1 substitution. However, the product ion abundance ratio of the protonated arylamine to that of the ammonia loss ion may be used to differentiate an adduct formed by N1 substitution from other arylamine adducts of guanine studied thus far.     

Development of fast atom bombardment mass spectral methods for the identification of carcinogen-nucleoside adducts

An analytical strategy using fast atom bombardment (FAB) ionization and tandem mass spectrometry has been developed to determine the molecular weight and major fragment ions, and to provide limited structural characterization of low picomole levels of carcinogen-nucleoside adducts. This strategy consists of three main components: (1) the sensitivity for analysis by FAB combined with mass spectrometry is increased via chemical derivatization; (2) the nucleoside adducts are selectively detected by using constant neutral loss scans; and (3) structurally characteristic fragments are obtained by using daughter ion scans. Trimethylsilyl derivatized arylamine-nucleoside adducts have been detected at levels as low as a few picomoles by using this approach. After experimental determination of the mass of the BH ₂ ⁺ fragment ion, daughter ion spectra have been used to probe the structure specificity associated with collision-activated decomposition of this fragment. With model C-8 substituted arylamine adducts [N-(deoxyguanosin-8-yl)-4-aminobiphenyl, N-(deoxyadenosin--yl)-4-aminobiphenyl, and N-(deoxyguanosin-8-yl)-2-aminofluorene], nucleoside-specific and carcinogen-specific fragmentation have been observed in daughter ion spectra.     

Development of an isotope dilution liquid chromatography/tandem mass spectrometry detection method for DNA adducts of selected aromatic amines

Polycyclic aromatic amines (arylamines) are a class of chemical carcinogens that are prevalent in environmental and industrial settings. They are metabolically activated to covalently bond to DNA, forming mutagenic adducts. In order to study the mechanisms of their toxicity, sensitive and selective quantitative LC/MS/MS detection methods were developed to measure the N-(adenin-8-yl)-benzidine adduct and N-(adenin-8-yl)-2-aminofluorene in total DNA extract samples. A novel synthetic method using a palladium catalyst was previously developed to prepare authentic and deuterated arylamine-adenine adducts to serve as standards. These standards were then used to develop an HPLC electrospray ionization tandem mass spectrometry, isotope dilution method. Sample detection limits in DNA samples were 22 pg on-column and 51 pg on-column for the N-(adenin-8-yl)-benzidine- and N-(adenin-8-yl)-2-aminofluorene-adenine adducts, respectively. This method has applications for the study of DNA adduct formation as a biological marker of exposure to carcinogens and for environmental and workplace monitoring of these aromatic amines.     

The fate of C5' radicals of purine nucleosides under oxidative conditions

The factors that influence the reactivity of C5' radicals in purine moieties under aerobic conditions are unknown not only in DNA, but also in simple nucleosides. 5',8-Cyclopurine lesions are the result of a rapid C5' radical attack to the purine moieties before the reaction with oxygen. These well-known lesions among the DNA modifications were suppressed by the presence of molecular oxygen in solution. Here we elucidate the chemistry of three purine-substituted C5' radicals (i.e., 2'-deoxyadenosin-5'-yl, 2'-deoxyinosin-5'-yl, and 2'-deoxyguanosin-5'-yl) under oxidative conditions using gamma-radiolysis coupled with product studies. 2'-Deoxyadenosin-5'-yl and 2'-deoxyinosin-5'-yl radicals were selectively generated by the reaction of hydrated electrons (e(aq)(-)) with 8-bromo-2'-deoxyadenosine and 8-bromo-2'-deoxyinosine followed by a rapid radical translocation from the C8 to the C5' position. Trapping these two C5' radicals with Fe(CN)6(3-) gave corresponding hydrated 5'-aldehydes in good yields that were isolated and fully characterized. When an oxygen concentration in the range of 13-266 microM (typical oxygenated tissues) is used, the hydrated 5'-aldehyde is accompanied by the 5',8-cyclopurine nucleoside. The formation of 5',8-cyclopurines is relevant in all experiments, and the yields increased with decreasing O2 concentration. The reaction of HO(*) radicals with 2'-deoxyadenosine and 2'-deoxyguanosine under normoxic conditions was also investigated. The minor path of C5' radicals formation was found to be ca. 10% by quantifying the hydrated 5'-aldehyde in both experiments. Rate constants for the reactions of the 2'-deoxyadenosin-5'-yl with cysteine and glutathione in water were determined by pulse radiolysis to be (2.1 +/- 0.5) x 10(7) and (4.9 +/- 0.6) x 10(7) M(-1) s(-1) at 22 degrees C, respectively.     

Reaction between isoprene and aniline on complex palladium catalysts

Isoprene and aniline have been reacted on the catalytic system Pd(acac)₂-Ph₃P to form a mixture of isomeric telomers: N-(dimethyloctadien-2,7-yl-1)anilines and N-(dimethyloctadien-1,7-yl-3)anilines but on the catalytic system Pd(acac)₂-Ph₃P-CF₃COOH the main product is a mixture of N-(methylbuten-2-yl)aniline adducts. The reaction between N-methylaniline and isoprene on the latter catalyst also gives a mixture of N-methyl and N-(methylbuten-2-yl)aniline adducts.A. N. Nesmeyanov Institute of Organoelemental Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1794–1798, August, 1992.     

Reduction and adduct formation from electrosprayed solutions of porphyrin salts

The solutions of four meso-tetrakis(N-alkylpyridinium-4-yl)porphyrin salts and of the p-toluenesulfonate salt of meso-tetrakis(4-trimethylammoniumphenyl)porphyrin, in methanol, were studied by electrospray mass spectrometry, in order to investigate the influence of the type of counter ion, the length of the substituent N-alkyl groups of the four (N-alkylpyridinium-4-yl)porphyrins and the presence of an aromatic (alkylpyridinium) or aliphatic (trimethylammonium) nitrogen, in ion formation.In our experimental conditions, adducts with the counter ions were formed only for the meso-tetrakis(4-trimethylammoniumphenyl)porphyrin and were not observed for the other porphyrins, even when the counter ion was the same. In contrast, formation of reduced species, such as the [M(4+) + e(-)]3+, [M(4+) + 2e(-)]2+, [M(4+) + 4e(-) + 2H(+)]2+, and [M(4+) + 5e(-) + 2H(+)]+ ions was observed only for the (N-alkylpyridinium-4-yl)porphyrins and the appearance of these species is apparently solvent related and may occur via counter ion/solvent adducts.     

N-(2-(5-(3-溴-1-(3-氯吡啶-2-基)-1H-吡唑-5-基)-1,3,4-噁二唑-2-基)-4-氯-6-甲基苯基)酰胺类新化合物的合成及生物活性

以N-吡啶基吡唑甲酸和2-氨基-3-甲基苯甲酸为起始原料,经由亲核加成、环化和酰化等多步反应合成了一系列结构新颖的N-(2-(5-(3-溴-1-(3-氯吡啶-2-基)-1H-吡唑-5-基)-1,3,4-噁二唑-2-基)-4-氯-6-甲基苯基)酰胺类化合物.测试了所合成化合物的杀虫及抑菌活性,结果表明,新化合物大多化合物在200 mg·L^-1浓度下对东方粘虫(Mythimna separataWalker)具有一定的杀虫活性,尤其是N-(2-(5-(3-溴-1-(3-氯吡啶-2-基)-1H-吡唑-5-基)-1,3,4-噁二唑-2-基)-4-氯-6-甲基苯基)乙酰胺(8a)和N-(2-(5-(3-溴-1-(3-氯吡啶-2-基)-1H-吡唑-5-基)-1,3,4-噁二唑-2-基)-4-氯-6-甲基苯基)-3-氯-2,2-二甲基丙酰胺(8e)致死率可达70%;部分化合物在50 mg·L^-1浓度下对油菜菌核病菌的抑菌活性相对较好(54.5%~63.6%),优于triadimefon和chlorantraniliprole;部分化合物如N-(2-(5-(3-溴-1-(3-氯吡啶-2-基)-1H-吡唑-5-基)-1,3,4-噁二唑-2-基)-4-氯-6-甲基苯基)-3,3-二甲基丁酰胺80和N-(2-(5-(3-溴-1-(3-氯吡啶-2-基)-1H-吡唑-5-基)-1,3,4-噁二唑-2-基)-4-氯-6-甲基苯基)-4-氟苯甲酰胺(8h)对苹果轮纹病菌具有中等抑菌活性.值得注意的是,化合物8e的杀粘虫活性和对油菜菌核病菌的抑菌活性都较为突出,可用作新农药创制研究的新型参考结构.     

Synthesis of 7-azabicyclo[2.2.1]heptane and 2-oxa-4-azabicyclo[3.3.1]non-3-ene derivatives by base-promoted heterocyclization of alkyl N-(cis(trans)-3,trans(cis)-4-dibromocyclohex-1-yl)carbamates and N-(cis(trans)-3,trans(cis)-4-dibromocyclohex-1-yl)-2,2,2-trifluoroacetamides

We have studied the base-promoted heterocyclization of alkyl N-(cis(trans)-3,trans(cis)-4-dibromocyclohex-1-yl)carbamates and N-(cis(trans)-3,trans(cis)-4-dibromocyclohex-1-yl)-2,2,2-trifluoroacetamides, investigating the effect of the nitrogen protecting group and the relative configuration of the leaving group at C3 and C4 on the outcome of this reaction. We have observed that the sodium hydride-promoted heterocyclization of alkyl N-(cis-3,trans-4-dibromocyclohex-1-yl)carbamates (10, 12, 14, 16, 18) is a convenient method for the synthesis of 7-azabicyclo[2.2.1]heptane derivatives. For instance, the reaction of tert-butyl N-(cis-3,trans-4-dibromocyclohex-1-yl)carbamate (10) with sodium hydride in DMF at room temperature provides 2-bromo-7-[(tert-butoxy)carbonyl]-7-azabicyclo[2.2.1]heptane (2) (52% yield), whose t-BuOK-promoted hydrogen bromide elimination affords 7-[(tert-butoxy)carbonyl]-7-azabicyclo[2.2.1]hept-2-ene (31) in 78% yield, an intermediate in the total synthesis of epibatidine (1). However, the NaH/DMF-mediated heterocyclization of alkyl N-(trans-3,cis-4-dibromocyclohex-1-yl)carbamates (11, 13) is a more structure dependent reaction, where the nucleophilic attack of the oxygen atom of the protecting group controls the outcome of the reaction, giving rise to benzooxazolone and 2-oxa-4-azabicyclo[3.3.1]non-3-ene derivatives, respectively, from low to moderate yields, in complex reaction mixtures. Conversely, the NaH/DMF heterocyclizations of N-(cis-3,trans-4-dibromocyclohex-1-yl)-2,2,2-trifluoroacetamide (40) or N-(trans-3,cis-4-dibromocyclohex-1-yl)-2,2,2-trifluoroacetamide (42) are very clean reactions giving 7-azabicyclo[2.2.1]heptane or 2-oxa-4-azabicyclo[3.3.1]non-3-ene derivatives, respectively, in good yields. Finally, a mechanistic investigation, based on DFT calculations, has been carried out to rationalize the formation of the different adducts.     

Tautomerization in gas-phase ion chemistry of isomeric C-8 deoxyguanosine adducts from phenol-induced DNA damage

Collision-induced dissociation (CID) of 8-(4'-hydroxyphenyl)-2'-deoxyguanosine and 8-(2'-hydroxyphenyl)-2'-deoxyguanosine was investigated using sequential tandem mass spectrometry. These adducts represent biomarkers of DNA damage linked to phenolic radicals and were investigated to gain insight into the effects of chemical structure of a C-8 modification on fragmentation pathways of modified 2'-deoxyguanosine (dG). CID in MS(2) of the deprotonated molecules of both the isomers generated the same product ion having the same m/z values. CID in MS(3) of the product ion at m/z 242 and CID in MS(4) experiments carried out on the selected product ions at m/z 225 and m/z 218 afford distinct fragmentation patterns. The conformational properties of isomeric product ions from CID showed that the ortho-isomers possess the unique ability to tautomerize through an intramolecular proton transfer between the phenolic OH group and the imine nitrogen (N7). Tautomerization of ortho-isomers to their keto-tautomers led to differences in their system of conjugated double bonds compared with either their enol-tautomer or the para-isomer. The charge redistribution through the N-7 site on the imidazole ring is a critical step in guanosine adduct fragmentation which is disrupted by the formation of the keto-tautomer. For this reason, different reaction pathways are observed for 8-(4'-hydroxyphenyl)-2'-deoxyguanosine and 8-(2'-hydroxyphenyl)-2'-deoxyguanosine. We present herein the dissociation and the gas-phase ion-molecule reactions for highly conjugated ions involved in the CID ion chemistry of the investigated adducts. These will be useful for those using tandem mass spectrometry for structural elucidation of C-8 modified dG adducts. This study demonstrates that the modification at the C-8 site of dG has the potential to significantly alter the reactivity of adducts. We also show the ability of tandem mass spectrometry to completely differentiate between the isomeric dG adducts investigated.     

Adenine radicals in the gas phase: an experimental and computational study of hydrogen atom adducts to adenine

The elusive hydrogen atom adduct to the N-1 position in adenine, which is thought to be the initial intermediate of chemical damage, was specifically generated in the gas phase and characterized by neutralization-reionization mass spectrometry. The N-1 adduct, 1,2-dihydroaden-2-yl radical (1), was generated by femtosecond electron transfer to N-1-protonated adenine that was selectively produced by electrospray ionization of adenine in aqueous-methanol solution. Radical 1 is an intrinsically stable species in the gas phase that undergoes specific loss of the N-1-hydrogen atom to form adenine, but does not isomerize to the more stable C-2 adduct, 1,2-dihydroaden-1-yl radical (5). Radicals 1 that are formed in the fifth and higher electronically excited states of DeltaE > or = 2.5 eV can also undergo ring-cleavage dissociations resulting in expulsion of HCN. The relative stabilities, dissociation, and transition state energies for several hydrogen atom adducts to adenine have been established computationally at highly correlated levels of theory. Transition state theory calculations of 298 K rate constants in the gas phase, including quantum tunnel corrections, indicate the branching ratios for H-atom additions to C-8, C-2, N-3, N-1, and N-7 positions in adenine as 0.68, 0.20, 0.08, 0.03, and 0.01, respectively. The relative free energies of adenine radicals in aqueous solution point to the C-8 adduct as the most stable tautomer, which is predicted to be the predominating (>99.9%) product at thermal equilibrium in solution at 298 K.     

Adduct formation identification between phenyl glycidyl ether and 2'-deoxyadenosine and thymidine by chromatography, mass spectrometry and nuclear magnetic resonance spectroscopy

Thymidine and 2'-deoxyadenosine were reacted with phenyl glycidyl ether in order to study the formation of the corresponding 2'-deoxynucleoside adducts. Separation methods were elaborated using either reversed-phase high-performance liquid chromatography with photodiode-array detection, or centrifugal circular thin-layer chromatography. The adducts were isolated on a preparative scale and were fully characterized by UV spectroscopy, desorption chemical ionization and fast atom bombardment mass spectrometry and 270- and 360-MHz 1H NMR spectrometry. For thymidine the main adduct was characterized as N-3-(2-hydroxy-3-phenoxypropyl)thymidine. With 2'-deoxyadenosine, predominantly N-1-(2-hydroxy-3-phenoxypropyl)-2'-deoxyadenosine was formed. With longer reaction times, the formation of a minor amount of dialkylated 2'-deoxyadenosine was observed. These nucleoside adducts will be used as marker compounds for studies of DNA adduct formation.     

Formation of 2,3,4,5,6-pentafluorophenylcarbonimidoyl dichloride by copyrolysis of 2,3,4,5,6-pentafluoroaniline with chloroform

The pyrolysis of pentafluorophenyl 2-methylprop-2-enyl ether (XIII) at 310° gave 4-(2-methylprop-2-enyl)-2,3,4,5,6-pentafluoro-2,5-cyclohexadienone (XVI) (46%), while at 410° a mixture of 1-fluorovinyl 2,3,4-trifluoro-5-methylphenyl ketone (XVIII) (30%) and 2,5β,6,7,7aβ-pentafluoro-3aβ-methyl-3aβ,4,5,7a-tetrahydroinden-1-one (XXI) (22%) was formed from the possible internal Diels-Alder adducts (XVII) and (XX) respectively (Scheme 6). Pentafluorophenyl 2-methylbut-3-en-2-yl ether (XVI) decomposed under mild conditions (70°) to give pentafluorophenyl 3-methylbut-2-en-1-yl ether (XXII), pentafluorophenol and 2-methyl-1,3-butadiene possibly via an ion pair intermediate (Scheme 7).     

EXCITED STATE PROPERTIES OF THE N-(DEOXYGUANOSIN-8-YL)-2-AMINOFLUORENE ADDUCTS

The spectroscopic characteristics of adducts derived from the covalent binding of the carcinogen 2-aminofluorene to the C8 position of deoxyguanosine [N-(deoxyguanosin-8-yl)-2-amino-fluorene, dGuo-C8-AF], and from an adduct of similar structure formed with the synthetic polynucleotide poly(dG-dC).poly(dG-dC), were investigated. At 77 K both adducts are characterized by well-defined and rather narrow fluorescence emission spectra with maxima at 370 and 390 nm characteristic of the aromatic, monomolecular 2-aminofluorene (AF) residue. In contrast, at room temperature, the fluorescence is characterized by a broad, structureless emission band with a maximum at 460 nm in aqueous mixtures, shifting to 415 nm in solvents of lower polarity (100% propanol); the maxima are located at intermediate wavelengths in solutions of different propanol/water compositions, and this emission is attributed to an excited state complex (exciplex). The fluorescence quantum yield decreases when either the solvent polarity or the temperature are increased, varying from 5.4% (100% propanol) to 0.04-0.05% (100% H2O). The fluorescence decay profiles of dGuo-C8-AF adducts (measured at the National Synchrotron Light Source facility at the Brookhaven National Laboratory) can be roughly, but not exactly, modeled in terms of two exponential decay components in the range of about 0.3-1.0 ns with the propanol concentration greater than 60%; at lower propanol concentrations, a single short lifetime is observed and in 100% water solutions its value is 0.08 ns. The shorter lifetime, favored in solvent mixtures of higher polarities, is attributed to an exciplex with significant charge-transfer character.(ABSTRACT TRUNCATED AT 250 WORDS)     

Proton affinity of uracil. A computational study of protonation sites

Relative stabilities of uracil tautomers and cations formed by gas-phase protonation were studied computationally with the B3LYP, MP2, QCISD, and QCISD(T) methods and with basis sets expanding from 6-31G(d,p) to 6-311+G(3df,2p). In accordance with a previous density functional theory study, the dioxo tautomer 1a was the most stable uracil isomer in the gas phase. Gibbs free energy calculations using effective QCISD(T)/6-311+G(3df,2p) energies suggested >99.9% of 1a at equilibrium at 523 K. The most stable ion isomer corresponded to N-1 protonated 2,4-dihydroxypyrimidine, which however is not formed by direct protonation of 1a. The topical proton affinities in 1a followed the order O-8 > O-7 > C-5 > N-3 > N-1. The thermodynamic proton affinity of 1a was calculated as 858 kJ mol⁻¹ at 298 K. A revision is suggested for the current estimate included in the ion thermochemistry database.     

SYNTHESIS OF NEW 8-METHOXY-4-METHYL-3-(N-[2′-AMINO-(1′,3′,4′)THIA/OXA-DIAZOL-5′-YL]-SUBSTITUTED METHYL)-AMINO THIOCOUMARINS

8-Methoxy-4-methyl-3-(N-[2′-amino-(1′, 3′,4′)thia/oxa-diazol-5′-yl] substituted methyl)-amino thiocoumarins 6(a–f) and 7(a–f), were synthesized by using the unreported 8-methoxy-4-methyl-3-[N-(2′-oxo-2′-methoxy-1′-substituted ethan-1′-yl) amino thiocoumarins as key intermediates.     

Novel approach to aminocarboranes by mild amidation of selected iodo-carboranes

A mild protocol for the palladium-catalyzed Buchwald-Hartwig amidation of icosahedral carboranes is described. Employing 2-dicyclohexylphosphino-2'-(N,N-dimethylamino)biphenyl (1) as a ligand and K(3)PO(4) as a base, benzamide, trifluoroacetamide, acetamide, and formamide were coupled to a series of mono- and di-iodo carboranes furnishing the respective carborane derivatives in good to excellent yields. Subsequent base-mediated saponification of the trifluoroacetamide derivatives was shown to provide the free aminocarboranes. The structures of N-(1,7-dicarba-closo-dodecaboran-9-yl)benzamide (8a), N-(1,7-dicarba-closo-dodecaboran-9-yl)trifluoroacetamide (8b), N-(1,12-dicarba-closo-dodecaboran-2-yl)benzamide (10a), N-(1,2-dicarba-closo-dodecaboran-9-yl)benzamide (12a), N-(1,2-dicarba-closo-dodecaboran-9-yl)acetamide (12c), N-(1,2-dicarba-closo-dodecaboran-9-yl)formamide (12d), N-(1,2-dicarba-closo-dodecaboran-3-yl)benzamide (13a), N,N'-(1,7-dicarba-closo-dodecaboran-9,10-diyl)dibenzamide (15a), and N,N'-(1,7-dicarba-closo-dodecaboran-9,10-diyl)bis(trifluoroacetamide) (15b) have been established through X-ray single-crystal diffraction studies.     

Combination of neural networks and DFT calculations for the comprehensive analysis of FDMPO radical adducts from fast isotropic electron spin resonance spectra

The 4-hydroxy-5,5-dimethyl-2-trifluoromethylpyrroline-1-oxide (FDMPO) spin trap is very attractive for spin trapping studies due to its high stability and high reaction rates with various free radicals. However, the identification of FDMPO radical adducts is a challenging task since they have very comparable Electron Spin Resonance (ESR) spectra. Here we propose a new method for the analysis and interpretation of the ESR spectra of FDMPO radical adducts. Thus, overlapping ESR spectra were analyzed using computer simulations. As a result, the N- and F-hyperfine splitting constants were obtained. Furthermore, an artificial neural network (ANN) was adopted to identify radical adducts formed during various processes (e.g., Fenton reaction, cleavage of peracetic acid over MnO(2), etc.). The ANN was effective on both "known" FDMPO radical adducts measured in slightly different solvents and not a priori "known" FDMPO radical adducts. Finally, the N- and F-hyperfine splitting constants of ·OH, ·CH(3), ·CH(2)OH, and CH(3)(C═O)O(·) radical adducts of FDMPO were calculated using density functional theory (DFT) at the B3LYP/6-31G(d,p)//B3LYP/6-31G++//B3LYP/EPR-II level of theory to confirm the experimental data.     

Mechanism of direct conversion between C8 adducts and N7 adducts in carcinogenic reactions of arylnitrenium ions with purine nucleosides: a theoretical study

To validate the mechanism of direct formation of C8 adducts for a series of complicated and controversial carcinogenic reactions, in this study, we examine the key direct conversion process between N7 adducts and C8 adducts in some theoretical models. First, the mechanism of direct conversions between N7 adducts and C8 adducts suggested by some experiments is explored. For the first time, it is approved that direct conversion between N7 and C8 adducts does not proceed because of very high activation energy. Second, the relative stabilities of the N7 adducts and C8 adducts for these model reactions are evaluated by high-level calculations. Our results indicate that C8 adducts are more stable in aqueous solution. Third, on the basis of these findings, experimental phenomenon of rich C8 adducts and rare N7 adducts is well explained theoretically, and the correctness of the three different existing experimental schemes of these reactions is discussed. Finally, the mechanism of formation of C8 adducts by additions of arylnitrenium ions directly to C8 positions of nucleotide bases in DNA is supported.     

Photogenerated N-methyl-N-1-naphthylnitrenium ion: laser flash photolysis, trapping rates, and product study

N-Methyl-N-1-naphthylnitrenium ion (2) was generated through photolysis of 1-(N-methyl-N-(1-naphthyl)amino)-2,4,6-trimethylpyridinium tetrafluoroborate (1). Laser flash photolysis (LFP) with time-resolved UV-vis (TRUV) detection as well as photoproduct analysis verified that the expected nitrenium ion was formed cleanly and rapidly following photolysis. Consistent with an earlier study, which used competitive trapping methods (Novak, M. et al. J. Org. Chem. 1999, 64, 6023-6031), it is found that 2 reacts rapidly with a variety of nucleophiles. The high reactivity of 2 relative to other arylnitrenium ions is discussed in terms of steric and electronic effects.     

NanoLC/ESI+ HRMS3 Quantitation of DNA Adducts Induced by 1,3-Butadiene

Human exposure to 1,3-butadiene (BD) present in automobile exhaust, cigarette smoke, and forest fires is of great concern because of its potent carcinogenicity. The adverse health effects of BD are mediated by its epoxide metabolites such as 3,4-epoxy-1-butene (EB), which covalently modify genomic DNA to form promutagenic nucleobase adducts. Because of their direct role in cancer, BD-DNA adducts can be used as mechanism-based biomarkers of BD exposure. In the present work, a mass spectrometry-based methodology was developed for accurate, sensitive, and precise quantification of EB-induced N-7-(1-hydroxy-3-buten-2-yl) guanine (EB-GII) DNA adducts in vivo. In our approach, EB-GII adducts are selectively released from DNA backbone by neutral thermal hydrolysis, followed by ultrafiltration, offline HPLC purification, and isotope dilution nanoLC/ESI⁺-HRMS³ analysis on an Orbitrap Velos mass spectrometer. Following method validation, EB-GII lesions were quantified in human fibrosarcoma (HT1080) cells treated with micromolar concentrations of EB and in liver tissues of rats exposed to sub-ppm concentrations of BD (0.5–1.5 ppm). EB-GII concentrations increased linearly from 1.15?±?0.23 to 10.11?±?0.45 adducts per 10⁶ nucleotides in HT1080 cells treated with 0.5–10 μM DEB. EB-GII concentrations in DNA of laboratory rats exposed to 0.5, 1.0, and 1.5 ppm BD were 0.17?±?0.05, 0.33?±?0.08, and 0.50?±?0.04 adducts per 10⁶ nucleotides, respectively. We also used the new method to determine the in vivo half-life of EB-GII adducts in rat liver DNA (2.20?±?0.12 d) and to detect EB-GII in human blood DNA. To our knowledge, this is the first application of nanoLC/ESI⁺-HRMS³ Orbitrap methodology to quantitative analysis of DNA adducts in vivo.