Product ion studies of diastereomeric benzo[ghi]fluoranthene tetraols by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and post-source decay.

The product ion formation characteristics of the four diastereomeric tetrahydroxy benzo[ghi]fluoranthene compounds formed by hydrolysis of the syn and anti diastereomers of trans-3,4-dihydroxy-5,5a-epoxy-3,4,5,5a-tetrahydrobenzo[ghi]fluoranthene are studied using matrix-assisted laser desorption/ionization and post-source decay (PSD) to determine a correlation between the fragmentation characteristics of these tetraols and the structures of the diol-epoxide diastereomers from which they are hydrolyzed. The tetraols formed by the trans ring opening of the diol epoxides during hydrolysis yield product ion spectra specific for the syn and anti configurations of their precursor diol epoxides. All four diastereomeric tetraols form product ions by the losses of one and/or two water molecules in varying proportions when lithium-cationized molecule ions (m/z 301) are selected for PSD product ion analysis. The differences in the PSD spectra of these four Li+-cationized molecules are rationalized in terms of a water loss mechanism that involves the 1,2 elimination of a hydrogen atom and hydroxyl group that are cis with respect to each other on adjacent carbons.

New syntheses of DNA adducts from methylated anilines present in tobacco smoke.

A new synthetic pathway for the formation of deoxyguanosine-monoarylamine adducts is described, involving the generation and use of arylnitrenes as electrophilic synthons. Photolysis of aryl azides, the most common method for generating arylnitrenes, was tested in the presence of 2'-deoxyguanosine. N-(2'-Deoxyguanosin-8-yl)monoarylamine (dG-C8-Ar) adducts were obtained, but the yields were typically low. Deoxygenation of nitro- and nitrosoarenes by triethyl phosphite in the presence of 2'-deoxyguanosine proved to be an effective method, by which dG-C8-Ar, (2'-deoxyguanosin-N1-yl)monoarylamine (dG-N1-Ar), and (2'-deoxyguanosin-O(6)-yl)monoarylamine (dG-O(6)-Ar) adducts were obtained in acceptable yields.

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.

Low energy tandem mass spectrometry of deoxynucleoside adducts of polycyclic aromatic hydrocarbon dihydrodiol-epoxides.

The use of fast-atom bombardment ionization-tandem mass spectrometry approaches, with collision energies on the order of 30-50 eV, was developed for the analysis of low picomole quantities of polycyclic aromatic hydrocarbon dihydrodiol-epoxide deoxynucleoside adducts. This strategy combines three experimental techniques: (1) product ion scans, (2) constant neutral loss scans, and (3) precursor ion scans. Product ion scans of the protonated molecule or the BH 2 (+) ion that results from loss of the deoxyribose were dominated by fragments associated with cleavage of the sigma bond between the dihydrodiol-epoxide moiety and the nucleobase. Constant neutral loss scans were based upon the loss of deoxyribose (116 u) or the combined loss of the deoxynucleoside, water, and carbon monoxide (313 u); precursor ion scans utilized the latter fragment. The formation of trimethylsilyl derivatives increased the sensitivity of analysis, which allowed the simultaneous detection of DNA adducts in a mixture.

Glucuronidation of N-hydroxy heterocyclic amines by human and rat liver microsomes.

The food-borne carcinogenic and mutagenic heterocyclic aromatic amines undergo bioactivation to the corresponding N-hydroxy (OH)-arylamines and the subsequent N-glucuronidation of these metabolites is regarded as an important detoxification reaction. In this study, the rates of glucuronidation for the N-OH derivatives of 2-amino-3-methylimidazo[4,5-f]-quinoline (IQ), 2-amino-1-methyl-6-phenylimidazo[4,5-b]-pyridine (PhIP), 2-amino-6-methyl-dipyrido[1,2-a:3',2'-d]imidazole (Glu-P-1) and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) by liver microsomal glucuronosyltransferase were compared to that of the proximate human urinary bladder carcinogen, N-OH-aminobiphenyl (N-OH-ABP) and the proximate rat colon carcinogen N-OH-3,2'-dimethyl-4-amino-biphenyl (N-OH-DMABP). Human liver microsomes catalyzed the uridine 5'-diphosphoglucuronic acid (UDPGA)-dependent glucuroidation of N-OH-IQ, N-OH-PhIP, N-OH-Glu-P-1 and N-OH-MeIQx at rates of 59%, 42%, 35% and 27%, respectively, of that measured for N-OH-ABP (11.5 nmol/min/mg). Rat liver microsomes also catalyzed the UDPGA-dependent glucuronidation of N-OH-PhIP, N-OH-Glu-P-1 and N-OH-IQ at rates of 30%, 20% and 10%, respectively of that measured for N-OH-DMABP (11.2 nmol/min/mg); activity towards N-OH-MeIQx was not detected. Two glucuronide(s) of N-OH-PhIP, designated I and II, were separated by HPLC. Conjugate II was found to be chromatographically and spectrally identical with a previously reported major biliary metabolite of PhIP in the rat, while conjugate I was identical with a major urinary metabolite of PhIP in the dog. Hepatic microsomes from rat, dog and human were found to catalyze the formation of both conjugates. The rat preferentially formed conjugate II (I to II ratio of 1:15), while the dog and human formed higher relative amounts of conjugate I (I to II ratio of 2.5:1.0 and 1.3:1.0 respectively). Fast atom bombardment mass spectrometry of conjugates I and II gave the corresponding molecular ions and showed nearly identical primary spectra. However, collision-induced spectra were distinct and were consistent with the identity of conjugates I and II as structural isomers. Moreover, the UV spectrum of conjugate I exhibited a lambda max at 317 nm and was essentially identical to that of N-OH-PhIP, while conjugate II was markedly different with a lambda max of 331 nm. Both conjugates were stable in 0.1 N HCl and were resistant to hydrolysis by rat, dog and human liver microsomal beta-glucuronidases.(ABSTRACT TRUNCATED AT 400 WORDS)

Differentiation of isomeric C8- and N (2)-deoxyguanosine adducts of 2-acetylaminofluorene by fast-atom bombardment and tandem mass spectrometry.

Product-ion studies of source-produced ions corresponding to acetylated and nonacetylated N (2)- and C8-substituted aminofluorene adducts of deoxyguanosine were conducted to identify specific fragmentation pathways differentiating the isomers and to determine the influence of the acetyl group on the fragmentation of the arylamide modified deoxyguanosine adducts. The collision-induced dissociation spectra of the BHZ 2 (+) ion and other significant source-produced ions showed no evidence to suggest that ketene loss (deacetylation) resulted in significant alteration of the structure of the adducts. However, other significant ion formation processes, particularly loss of water from the N (2)-substituted arylamide did appear to require rearrangement, likely involving bond formation between the carcinogen moiety (acetyl group) and the N1 or N2 position of the guanine base. The combined loss of ketene and water constitute a fragmentation pattern specific for the N (2)-arylamide, 3-(deoxyguanosin-N (2)-yl)-2-acetylaminofluorene.

Synthesis of 3-nitrobenzo[a]pyrene bay-region trans-7,8-diol anti-9,10-epoxide and the corresponding N2-deoxyguanosine adduct.

3-Nitrobenzo[a]pyrene (3-nitro-BaP) is a potent mutagenic environmental contaminant, and its biological activities have been intensively studied. It is significant to prepare its reactive metabolites and the corresponding modified DNA adducts for biological studies. The synthesis of its oxidized proximate metabolite trans-7,8-dihydro-3-nitrobenzo[a]pyrene (3-nitro-BaP-trans-7,8-dihydrodiol, 1), its oxidized ultimate metabolite trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydro-3- nitrobenzo[a]pyrene (3-nitro-BaP-DE, 2), and the corresponding DNA adduct 10-(deoxyguanosin-N2-yl)-7,8,9-trihydroxy-7,8,9,10-tetrahydro-3- nitrobenzo[a]pyrene is described.

Detection and characterization of DNA adducts at the femtomole level by desorption ionization mass spectrometry.

Current methodologies for the detection and isolation of carcinogen-DNA adducts have advanced beyond the capabilities of the methods used to elucidate their structures. This difficulty seriously limits the potential use of DNA-carcinogen adducts in human dosimetry. We have investigated two general strategies for the analysis of model arylamine-nucleoside adducts using desorption ionization mass spectrometry (MS). Using fast atom bombardment MS-MS with constant neutral loss scans, we can identify the protonated molecule of derivatized adducts in samples as small as 1 pmole, and then apply daughter ion MS-MS scans to obtain structure-specific fragmentation. Using this strategy we have differentiated adducts having the same carcinogen and different bases [e.g., N-(deoxyadenosin-8-yl)-4-aminobiphenyl and N-(deoxyguanosin-8-yl)-4- aminobiphenyl] or the same base and different carcinogens [e.g., N-(deoxyguanosin-8-yl)-4- aminobiphenyl and N-(deoxyguanosin-8-yl)-2-aminofluorene]. In the second approach we used laser desorption time-of-flight MS to obtain spectra from adduct samples as small as 20 fmole. These data indicate that MS can be used for the analysis of very low (picomole-femtomole) levels of nucleoside adducts, including isomers, and that desorption ionization MS and MS-MS have significant potential for applications in human dosimetry.

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.

Characterization of the mycotoxin fumonisin B1: comparison of thermospray, fast-atom bombardment and electrospray mass spectrometry.

The utility of thermospray mass spectrometry (TSMS), fast-atom bombardment mass spectrometry (FABMS), and electrospray mass spectrometry (ESMS) for the analysis of Fumonisin B1 is investigated. In addition, the analysis of two different standards of Fumonisin B1 as well as an inoculated corn culture extract that contained Fumonisin B1 is reported. The results of these efforts show that ESMS, as well as FABMS and a combination of FAB and tandem mass spectrometry (FABMS/MS), provide useful data for the characterization of Fumonisin B1. The detection limit was 50 pg for Fumonisin B1 when analyzed by full scan FABMS, and 5 pg when analyzed by single-reaction monitoring FABMS/MS.