Modeling the formation and reactions of benzene metabolites

Article abstract of DOI:10.1016/j.cbi.2010.01.001

One or more of the muconaldehyde isomers is a putative product of benzene metabolism. As muconaldehydes are highly reactive dienals and potentially mutagenic they might be relevant to the carcinogenicity of benzene. Muconaldehydes may be derived through the action of a cytochrome P450 mono-oxygenase on benzene oxide-oxepin, which are established metabolites of benzene. Oxidation of benzene oxide-oxepin either by the one-electron oxidant cerium(IV) ammonium nitrate (CAN) or by iron(III) tris(1,10-phenanthroline) hexafluorophosphate in acetone at -78°C or acetonitrile at -40°C gave (E,Z)-muconaldehyde, which was a single diastereoisomer according to analysis by ¹H NMR spectroscopy. Reaction of toluene-1,2-oxide/2-methyloxepin with CAN gave (2E,4Z)-6-oxo-hepta-2,4-dienal. Similarly, the action of CAN on 1,6-dimethylbenzene oxide-2,7-dimethyloxepin gave (3Z,5E)-octa-3,5-diene-2,7-dione. In vivo, benzene oxide-oxepin could suffer one-electron oxidation by cytochrome P450 mono-oxygenase giving (E,Z)-muconaldehyde. The observations presented may be relevant to the toxicology of benzene oxide-oxepin and other arene oxide-oxepins as we have previously shown that (E,Z)-muconaldehyde, analogously to (Z,Z)-muconaldehyde, affords pyrrole adducts with the exocyclic amino groups of the DNA bases adenine and guanine. Independent of their possible toxicological significance, the experiments described provide preparatively useful routes to (E,Z)-muconaldehyde and its congeners. Methods are also described for the trapping and analysis of reactive benzene metabolites, e.g. using the Diels-Alder reaction with the dienophile 4-phenyl-1,2,4-triazoline-3,5-dione to trap arene oxides and with the diene 1,3-diphenylisobenzofuran to trap enals.

Full text of DOI:10.1016/j.cbi.2010.01.001

Chemico-Biological Interactions 184 (2010) 196–200
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Chemico-Biological Interactions
journal homepage: www.elsevier.com/locate/chembioint
Modeling the formation and reactions of benzene metabolites
Bernard T. Golding∗, Martine L. Barnes, Christine Bleasdale, Alistair P. Henderson,
Dong Jiang, Xin Li, Esra Mutlu, Hannah J. Petty, Majid M. Sadeghi
School of Chemistry, Bedson Building, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 11 January 2010
One or more of the muconaldehyde isomers is a putative product of benzene metabolism. As muconalde-
hydes are highly reactive dienals and potentially mutagenic they might be relevant to the carcinogenicity
of benzene. Muconaldehydes may be derived through the action of a cytochrome P450 mono-
oxygenase on benzene oxide–oxepin, which are established metabolites of benzene. Oxidation of
benzene oxide–oxepin either by the one-electron oxidant cerium(IV) ammonium nitrate (CAN) or by
iron(III) tris(1,10-phenanthroline) hexafluorophosphate in acetone at −78 ◦C or acetonitrile at −40 ◦C
gave (E,Z)-muconaldehyde, which was a single diastereoisomer according to analysis by 1H NMR spec-
troscopy. Reaction of toluene-1,2-oxide/2-methyloxepin with CAN gave (2E,4Z)-6-oxo-hepta-2,4-dienal.
Similarly, the action of CAN on 1,6-dimethylbenzene oxide-2,7-dimethyloxepin gave (3Z,5E)-octa-3,5-
diene-2,7-dione. In vivo, benzene oxide–oxepin could suffer one-electron oxidation by cytochrome P450
mono-oxygenase giving (E,Z)-muconaldehyde. The observations presented may be relevant to the tox-
icology of benzene oxide–oxepin and other arene oxide–oxepins as we have previously shown that
(E,Z)-muconaldehyde, analogously to (Z,Z)-muconaldehyde, affords pyrrole adducts with the exocyclic
amino groups of the DNA bases adenine and guanine. Independent of their possible toxicological signif-
icance, the experiments described provide preparatively useful routes to (E,Z)-muconaldehyde and its
congeners. Methods are also described for the trapping and analysis of reactive benzene metabolites,
e.g. using the Diels–Alder reaction with the dienophile 4-phenyl-1,2,4-triazoline-3,5-dione to trap arene
oxides and with the diene 1,3-diphenylisobenzofuran to trap enals.
Keywords:
Muconaldehyde
Benzene oxide
Oxepin
One-electron oxidation
Diels–Alder reaction
© 2010 Elsevier Ireland Ltd. All rights reserved.
1. Introduction
ortho- and para-benzoquinone (p-BQ), (E,E)-muconaldehyde and
possibly other isomers, and benzene diol epoxide (Fig. 1). With
Benzene is designated a Group I carcinogen by the Interna-
tional Agency for Research on Cancer (Lyon, France), with acute
myeloid leukemia (AML) being a potential outcome for humans
who are chronically exposed to this substance [1–4]. The link
between benzene exposure and leukemia is based on extensive epi-
demiological data [5]. This data showed that AML arose in a small
number of persons who were occupationally exposed on a continu-
ous basis to much higher levels than recommended exposure limits.
Although there is no animal model for benzene-induced leukemia,
experiments with mice and rats have demonstrated that benzene
exposures cause tumors in a variety of organs [5].
The bewildering array of benzene metabolites and their
prospective biological targets has made the definition of the molec-
ular mechanism of benzene carcinogenesis an elusive goal. It is clear
that the metabolism of benzene, primarily by cytochrome P450 2E1,
gives several reactive metabolites including benzene oxide–oxepin,
respect to the muconaldehydes, previous studies by Ross and Witz
and their coworkers have focussed on the (E,E)-isomer and its
oxidative and reductive metabolism, e.g. to (E,E)-muconic acid [6]
and (E,E)-6-hydroxyhexa-2,4-dienal [7], respectively. And there are
perhaps additional unidentified reactive metabolites, e.g. a diepox-
ide derived by further oxidation of benzene oxide by cytochrome
P450. Recent studies suggest that the human metabolism of ben-
zene may be even more complex than hitherto realized: two
pathways were proposed dependent on dose [8].
All of the identified electrophilic metabolites form or are
expected to form adducts with glutathione, proteins and nucleic
acids, and are potentially genotoxic. The major problems to solve
are which of the metabolites and corresponding biomolecule
adducts is/are responsible for AML and what other cancers may
be initiated? Although benzene oxide is commonly regarded as a
reactive benzene metabolite this epithet may only strictly apply
to its facile rearrangement to phenol. Even so, the half-life of ben-
zene oxide in blood is ca. 8 min, whilst in deuterium oxide at pD 7.0
(pD = pH + 0.4) the half-life is ca. 34 min at 25 ◦C [9]. The capture of
benzene oxide by thiols [9] and other nucleophiles is a relatively
∗
Corresponding author.
E-mail address: b.t.golding@ncl.ac.uk (B.T. Golding).
0009-2797/$ – see front matter © 2010 Elsevier Ireland Ltd. All rights reserved.
doi:10.1016/j.cbi.2010.01.001

B.T. Golding et al. / Chemico-Biological Interactions 184 (2010) 196–200
197
2.2. General procedure for the synthesis of (E,Z)-muconaldehydes
To a solution of cerium(IV) ammonium nitrate (2.01 mole equiv.)
in acetone at −78 ◦C or acetonitrile at −40 ◦C was added the cor-
responding oxepin (1 mole equiv.) and the solution was stirred in
the dark for 1 h. The resulting mixture was diluted with ice-cold
diethyl ether. The ethereal solution was thrice washed with ice-
cold saturated brine, dried (MgSO4), filtered and concentrated to
give the muconaldehyde. A similar procedure was used for iron(III)
tris(1,10-phenanthroline) hexafluorophosphate acting on benzene
oxide–oxepin.
2.3. (E,Z)-Muconaldehyde 1b
Yellow solid, mp 57–59 ◦C, lit. 58.5–59 ◦C [17]. 1H NMR
(200 MHz, CD3CN) ı 6.21 (1H, dd, J1,2 7.4 and J2,3 11.1, H-2), 6.47
(1H, dd, J5,6 7.8 and J4,5 15.2, H-5), 7.28 (1H, dd, J2,3 11.9 and J3,4
11.6, H-3), 8.24 (1H, dd, J3,4 12.2 and J4,5 15.1, H-4), 9.77 (1H, d, J5,6
7.8, H-6), 10.34 (1H, d, J1,2 7.6, H-1).
2.4. (2E,4Z)-6-Oxo-hepta-2,4-dienal 3
Yellow solid, mp 42–44 ◦C, lit. 40 ◦C [18]. 1H NMR (200 MHz,
CD3CN) ı 2.12 (3H, s, Me), 6.29 (1H, dd, J1,2 7.8 and J2,3 15.6, H-2),
6.40 (1H, d, J4,5 11.4, H-5), 6.61 (1H, dd, J3,4 11.2 and J4,5 11.8, H-4),
8.13 (1H, dd, J3,4 11.2 and J2,3 15.6, H-3), 9.60 (1H, d, J1,2 7.8, H-6).
Fig. 1. Some reactive benzene metabolites.
inefficient process. Furthermore, benzene oxide may be an intrin-
sically unreactive epoxide because the diene ␲-system repels the
incoming nucleophile.
2.5. (3Z,5E,)-Octa-3,5-diene-2,7-dione 4
Orange solid, mp 123–125 ◦C, lit. 125 ◦C [19]. 1H NMR (200 MHz,
CD3CN) ı 2.10 (3H, s, Me), 2.13 (3H, s, Me), 6.20 (1H, d, J3,4 15.8, H-
3), 6.27 (1H, d, J5,6 11.4, H-6), 6.43 (1H, t, J4,5 and 5,6 11.3, H-5), 7.94
(1H, dd, J4,5 10.8 and J3,4 15.7, H-4); 13C NMR (50.3 MHz, CD3CN) ı
26.64, 38.48, 124.93, 136.69, 136.89, 140.25, 198.55, 198.94.
Several studies have focused on the role of quinones and the
related dihydroxybenzenes derived from metabolism of benzene.
p-Benzoquinone (p-BQ) accumulates in the bone marrow, the site
of the observed toxic effects of benzene, i.e. leukemogenicity and
myelotoxicity [10]. This quinone forms adducts with nucleosides,
nucleotides and DNA [11]. p-BQ, as well as hydroquinone (1,4-
dihydroxybenzene) and catechol (1,2-dihydroxybenzene), affect
the c-Myb oncoprotein, a transcription factor with an important
role in hematopoiesis [12]. It was suggested that these benzene
metabolites generate reactive oxygen species (ROS) that alter the
c-Myb signalling pathway. Hydroquinone induces endoreduplica-
tion in cells, and hence genomic instability and carcinogenesis, by
inhibiting topoisomerase II [13]. Others have focussed on ortho-
benzoquinone from catechol and have suggested that the formation
of depurinating adducts from DNA is linked to benzene leukemo-
genesis [14]. Another study suggested a role for nitric oxide and
peroxynitrite in DNA damage induced by hydroquinone and related
benzene metabolites [15].
(E,E)-Muconaldehyde has been shown to be an especially potent
inhibitor of gap junction intercellular communication, the abnor-
mal regulation of which is implicated in carcinogenesis and the
blocking of hematopoiesis [16]. Our research has been focused
on the isomeric muconaldehydes and benzene oxide–oxepin and,
using model studies to probe their reactivities towards bimolecules.
To assist the understanding of the roles of these molecules, we
are developing methods for their detection and analysis using the
Diels–Alder reaction.
2.6. General procedure for the reaction of enals with
1,3-diphenylisobenzofuran
1,3-Diphenylisobenzofuran and the enal (1–2 mole equiv.) in
2,2,2-trifluoroethanol under nitrogen were heated at reflux with
exclusion of light until analysis by thin layer chromatography
showed completion of the reaction. The solvent was removed and
the residue was purified by medium pressure chromatography on
silica eluting with petrol–ethyl acetate (20:1, v/v) to give a mixture
of diastereoisomeric adducts. 1H NMR (200 MHz, CD3CN) [acrolein
adducts] ı 9.25 (d, CHO, isomer A), 8.94 (d, CHO, isomer B) [total
1H], 7.6 (m) 7.35 (m), 7.1 (m), 6.9 (m) [total 14H], 3.62 (m, CHCHO,
B), 3.04 (m, CHCHO, A) [total 1H], 2.65 (dd, CHH, B), 2.49 (dd, CHH,
A) [total 1H], 2.33 (m, CHH, A and CHH, B).
3. Conversion of benzene oxide–oxepin to muconaldehydes
One or more of the muconaldehyde isomers Z,Z, (1a; E,Z, 1b; E,E,
1c; Z = cis, E = trans) is a putative product of benzene metabolism
[20]. As muconaldehydes are highly reactive dienals [9,21–23] and
potentially mutagenic they may be relevant to the carcinogenicity
of benzene [2–4]. In the metabolism of benzene, muconaldehy-
des may be derived [24,25] through the oxidation of benzene
oxide–oxepin 2a, which are established metabolites of benzene
[26,27], by cytochrome P450 mono-oxygenase. To extend our ear-
lier investigations [21,22,24,28] of the toxicology of benzenoid
compounds and their metabolites, we have studied the oxidation
of benzene oxide–oxepin and methyl-substituted derivatives by
the one-electron oxidants cerium(IV) ammonium nitrate (CAN)
and iron(III) tris(1,10-phenanthroline) hexafluorophosphate [29].
2. Materials and methods
2.1. Safety precautions
All of the muconaldehydes and arene oxide/oxepins should be
regarded as potential carcinogens and were handled with protec-
tive clothing in an efficient hood.

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B.T. Golding et al. / Chemico-Biological Interactions 184 (2010) 196–200
Scheme 5. Reaction of benzene oxide–oxepin and toluene oxide-2-methyloxepin
with 4-phenyl-1,2,4-triazoline-3,5-dione (Cookson’s dienophile, 5a) and its
pentafluoro analogue 5b.
Scheme 1. Conversion of arene oxides–oxepins to (E,Z)-muconaldehydes
[CAN = cericum(IV) ammonium nitrate; Fe(III) = iron(III) tris(1,10-phenanthroline)
hexafluorophosphate].
of toluene-1,2-oxide/2-methyloxepin 2c/2d with CAN gave 6-oxo-
hepta-2,4-dienal 3, which was assigned as the (2E,4Z)-isomer, i.e.
the methyl group was attached to the (Z)-enone component, by
comparison of its 1H NMR data with that reported [18]. Reaction
of 1,6-dimethylbenzene oxide-2,7-dimethyloxepin 2e/2f with CAN
gave (3Z,5E)-octa-3,5-diene-2,7-dione 4, identified by its 1H and
13C NMR data [30]. The oxidations described are summarized in
Scheme 1.
It has been previously shown that benzene oxide–oxepin
2a/2b is converted into (Z,Z)-muconaldehyde 1a by oxida-
tion with perbenzoic acid [19] or dimethyldioxirane (DMDO)
[24], with the latter oxidant giving complete diastereoselec-
tivity (Scheme 2). (Z,Z)-muconaldehyde 1a was converted into
(E,Z)-muconaldehyde 1b by thermolysis [17,25] and into (E,E)-
muconaldehyde 1c by isomerization catalysed by triethylamine
[17] or glutathione [28] (Scheme 2). Similarly, treatment of
toluene-1,2-oxide/2-methyloxepin 2c/2d with DMDO gave (Z,Z)-
6-oxo-hepta-2,4-dienal, whilst 1,6-dimethylbenzene oxide/2,7-
dimethyloxepin 2e/2f afforded (Z,Z)-octa-3,5-diene-2,7-dione.
The mechanisms of the oxidations of arene oxides-oxepins
(2a–f) by CAN and iron(III) tris(1,10-phenanthroline) hexaflu-
orophosphate are presumed to be initiated by one-electron
oxidation of the oxepin component. In polar media, the rapidly
established equilibrium between benzene oxide and oxepin con-
tains predominantly oxepin, the double bonds of which possess a
greater nucleophilicity than those of benzene oxide [31]. Hence,
the oxidation is likely to involve oxepin, which could give a radi-
Scheme 2. Synthetic routes to isomeric muconaldehydes.
Surprisingly, the muconaldehydes obtained were exclusively the
(E,Z)-isomers.
Benzene oxide–oxepin 2a/2b and methyl-substituted deriva-
tives (2c/2d and 2e/2f) were prepared essentially as described [9].
Reactions of 2a–2f were performed either in acetone at −78 ◦C or
in acetonitrile at −40 ◦C. Reaction of 2a/2b with CAN gave (E,Z)-
muconaldehyde 1b (61%), which was a single diastereoisomer
according to analysis by 1H NMR spectroscopy. The same stere-
ochemical outcome was observed for the oxidation of 2a/2b by
iron(III) tris(1,10-phenanthroline) hexafluorophosphate. Reaction
Scheme 3. Putative mechanism of oxidation of 2a/2b by CAN or Fe(III) to 1b.
Scheme 4. Reaction of (Z,Z)-muconaldehyde with guanosine derivatives leading to pyrrole adducts (r = ribose or deoxyribose).

B.T. Golding et al. / Chemico-Biological Interactions 184 (2010) 196–200
199
Scheme 6. Reaction of 1,3-diphenylisobenzofuran with acrylamide.
cal cation that may be captured by adventitious solvent water to
5. Conclusions
afford the 2-hydroxy-2H-oxepin radical (Scheme 3). Ring-opening
of this species gives a radical corresponding in structure to (Z,Z)-
muconaldehyde. However, isomerization may occur to a radical
corresponding in structure to (E,Z)-muconaldehyde, which can
arise by further one-electron oxidation and deprotonation. The
proposed isomerization is analogous to that of the (E,E)- and
(E,Z)-pentadienyl radical. The (E,E)-isomer is more stable by ca.
10 kJ mol−1 with the two isomers being separated by an activation
energy of ca 40 kJ mol−1 at 370 K for the (E,Z) → (E,E) conversion
[32]. The mechanism outlined is speculative and requires further
validation.
Snyder’s review [4] concluded that bone marrow disease caused
by exposure to benzene could be due to one or more of the
following factors: covalent binding of benzene metabolites to
DNA or proteins; oxidative stress arising via several mecha-
nisms; specific effects of p-benzoquinone and muconaldehyde.
We have defined a number of possible routes to the muconalde-
hyde isomers and have demonstrated the propensity of the
(E,Z)- and (Z,Z)-isomer to form DNA adducts. It remains to prove
that (Z,Z)- and/or (E,Z)-muconaldehyde are derived from ben-
zene oxide–oxepin by metabolic oxidation and are precursors
of (E,E)-muconaldehyde. The contribution of a potential alter-
native pathway to (Z,Z)-muconaldehyde from dihydrocatechol
needs to be appraised. Pyrrole DNA adducts from (Z,Z)- and
(E,Z)-muconaldehyde (Scheme 4), still need to be evaluated as con-
tributors to benzene carcinogenesis. Whether benzene oxide forms
DNA and/or protein adducts also needs to be resolved for these
processes are predicted to be inefficient.
An intracellular one-electron oxidant converting benzene
oxide–oxepin directly to (E,Z)-muconaldehyde could be
a
cytochrome P450 mono-oxygenase, acting in a similar man-
ner to that shown by Sato and Guengerich for the oxidation of
1,2,4,5-tetramethoxybenzene [33]. The observations presented
may be relevant to the toxicology of benzene oxide–oxepin
and other arene oxide–oxepins as we have previously shown
that (E,Z)-muconaldehyde, analogously to (Z,Z)-muconaldehyde,
affords pyrrole adducts with primary amines and the exo-
cyclic amino groups of the DNA bases adenine and guanine
(Scheme 4) [21,22]. (E,E)-muconaldehyde, however, does not
form such adducts because this process requires at least one
double bond with Z-configuration. Irrespective of their pos-
sible toxicological significance, the experiments described
afford preparatively useful routes to (E,Z)-muconaldehyde 1b,
Conflict of interest
None.
Acknowledgements
We thank the United Kingdom Research Councils (BBSRC, EPSRC
and NERC) for support of this research.
(2E,4Z)-6-oxo-hepta-2,4-dienal
3
and (3Z,5E)-octa-3,5-diene-
2,7-dione 4. The latter compounds or their geometrical isomers
are potential minor metabolites of toluene and ortho-xylene,
respectively.
References
[1] International Agency for Research on Cancer, IARC Monographs, Lyons, Suppl.
7, 1987.
[2] B.T. Golding, W.P. Watson, Possible mechanisms of carcinogenesis after expo-
sure to benzene, in: B. Singer, H. Bartsch (Eds.), Exocyclic Nucleic Acid Adducts
in Carcinogenesis and Mutagenesis, International Agency for Research on Can-
cer, Issue 150, IARC Scientific Publications, Lyons, 1999, pp. 75–88 (Chapter 2).
[3] R. Snyder, Xenobiotic metabolism and the mechanism(s) of benzene toxicity,
Drug Metab. Rev. 36 (2004) 531–547.
[4] R. Snyder, Benzene’s toxicity: a consolidated short review of human and animal
studies by HA Khan, Hum. Exp. Toxicol. 26 (2007) 687–696.
[5] J. Huff, Benzene-induced cancers: abridged history and occupational health
impact, Int. J. Occup. Environ. Health 13 (2007) 213–221.
[6] L. Latriano, G. Witz, G.B.D. Goldstein, A.M. Jeffrey, Comparative metabolism
of benzene and (trans,trans)-muconaldehyde to (trans,trans)-muconic acid in
DBA/2N and C57BL/6 mice, Biochem. Pharmacol. 40 (1990) 1275–1280.
[7] D. Goon, X. Cheng, J.A. Ruth, D.R. Peterson, D. Ross, Metabolism of (trans,trans)-
muconaldehyde by aldehyde and alcohol dehydrogenase: identification of a
novel metabolite, Toxicol. Appl. Pharmacol. 114 (1992) 147–155.
[8] S.M. Rappaport, S. Kim, Q. Lan, R. Vermeulen, S. Waidyanatha, L.P. Zhang, G.L. Li,
S.N. Yin, R.B. Hayes, N. Rothman, M.T. Smith, Evidence that humans metabolize
benzene via two pathways, Environ. Health Perspect. 117 (2009) 946–952.
[9] A.P. Henderson, M.L. Barnes, C. Bleasdale, R. Cameron, W. Clegg, S.L. Heath, A.B.
Lindstrom, S.M. Rappaport, S. Waidyanatha, W.P. Watson, B.T. Golding, Reac-
tions of benzene oxide with thiols including glutathione, Chem. Res. Toxicol.
18 (2005) 265–270.
[10] S. Wilbur, D. Wohlers, S. Paikoff, L.S. Keith, O. Faroon, ATSDR evaluation of
health effects of benzene and relevance to public health, Toxicol. Ind. Health
24 (2008) 263–398 (and references cited therein).
[11] Z.W. Xie, Y.B. Zhang, A.B. Guliaev, H.Y. Shen, B. Hang, B. Singer, Z.G. Wang, The p-
benzoquinone DNA adducts derived from benzene are highly mutagenic, DNA
Repair 4 (2005) 1399–1409.
4. Trapping benzene metabolites
We have shown that benzene oxide can be efficiently
scavenged by 4-phenyl-1,2,4-triazoline-3,5-dione (5a, ‘Cookson’s
dienophile’) and even better (ca. 25-fold more reactive) by its
4-pentafluorophenyl analogue 5b [34] (Scheme 5). For the reac-
tion of 2a/2b with 5b in tetrahydrofuran the bimolecular rate
constant k = 700 dm3 mol−1 s−1 and ꢀ = 0.1 s [34]. These reagents
½
give stable Diels–Alder adducts (Scheme 5) that can be ana-
lyzed by high-performance liquid chromatography and mass
spectrometric techniques. 4-Phenyl-1,2,4-triazoline-3,5-dione was
developed for the trapping of toluene oxide in a system [35]
that models the atmospheric photo-oxidation of toluene. The
triazoline-3,5-diones 5a/5b could, in principle, be used to trap
arene oxides in metabolic systems. We have also studied the trap-
ping of ␣,␤-unsaturated carbonyl compounds [e.g. acrylamide,
acrolein and (Z,Z)-muconaldehyde] using the reactive diene 1,3-
diphenylisobenzofuran in Diels–Alder reactions (e.g. Scheme 6).
The adducts 6 undergo acid-catalyzed conversion into the relatively
stable naphthalene derivative 7, which ‘fixes’ an ␣,␤-unsaturated
carbonyl unit [36]. Investigation of this sequence for trapping and
characterizing enals is in progress.

200
B.T. Golding et al. / Chemico-Biological Interactions 184 (2010) 196–200
[12] J. Wan, L.M. Winn, Benzene’s metabolites alter c-MYB activity via reactive oxy-
gen species in HD3 cells, Toxicol. Appl. Pharmacol. 222 (2007) 180–189.
[13] Z.Y. Ji, L.P. Zhang, W.H. Guo, C.M. McHale, M.T. Smith, The benzene metabo-
lite, hydroquinone and etoposide both induce endoreduplication in human
lymphoblastoid TK6 cells, Mutagenesis 24 (2009) 367–372.
[25] C.W. Bock, P. George, A. Greenberg, J.P. Glusker, An ab-initio computa-
tional molecular–orbital study of the conformers of muconaldehyde, and the
possible role of 2-formyl-2H-pyran in bringing about the conversion of a (Z,Z)-
muconaldehyde structure into an (E,Z)-muconaldehyde structure, Chem. Res.
Toxicol. 7 (1994) 534–543.
[14] E.L Cavalieri, K.M. Li, N. Balu, M. Saeed, P. Devanesan, S. Higginbotham, J. Zhao,
M.L. Gross, E.G. Rogan, Catechol ortho-quinones: the electrophilic compounds
that form depurinating DNA adducts and could initiate cancer and other dis-
eases, Carcinogenesis 23 (2002) 1071–1077.
[15] A.A. Melikian, K.M. Chen, L. Heyi, R. Sodum, E. Fiala, K. El-Bayoumy, The role of
nitric oxide on DNA damage induced by benzene metabolites, Oncol. Rep. 19
(2008) 1331–1337.
[26] M.R. Lovern, M.J. Turner, M. Meyer, G.L. Kedderis, W.E. Bechtold, P.M. Schlosser,
Identification of benzene oxide as a product of benzene metabolism by mouse,
rat, and human liver microsomes, Carcinogenesis 18 (1997) 1695–1700.
[27] A.B. Lindstrom, K. Yeowell-O’Connell, S. Waidyanatha, T.A. McDonald, B.T.
Golding, S.M. Rappaport, Formation of hemoglobin and albumin adducts of
benzene oxide in mouse, rat, and human blood, Chem. Res. Toxicol. 11 (1998)
302–310.
[16] E. Rivedal, E. Leithe, The benzene metabolite trans,trans-muconaldehyde
blocks gap junction intercellular communication by cross-linking connexin43,
Toxicol. Appl. Pharmacol. 232 (2008) 463–468.
[17] B.T. Golding, G. Kennedy, W.P. Watson, Simple syntheses of isomers of
muconaldehyde and 2-methylmuconaldehyde, Tetrahedron Lett. 29 (1988)
5991–5994.
[18] W. Adam, M. Balci, Photo-oxygenation of 1,3,5-cycloheptatriene—
transformations of endoperoxides, J. Am. Chem. Soc. 101 (1979) 7542–7547.
[19] S.G. Davies, G.H. Whitham, Benzene oxide oxepin—oxidation to muconalde-
hyde, J. Chem. Soc., Perkin 1 (1977) 1346–1347.
[20] L. Latriano, B.D. Goldstein, G. Witz, Formation of muconaldehyde, an open-ring
metabolite of benzene, in mouse-liver microsomes—an additional pathway for
toxic metabolites, Proc. Natl. Acad. Sci. U.S.A. 83 (1986) 8356–8360.
[21] C. Bleasdale, B.T. Golding, G. Kennedy, J.O. MacGregor, W.P. Watson,
Reactions of muconaldehyde isomers with nucleophiles including tri-
acetylguanosine—formation of 1,2-disubstituted pyrroles from reactions of the
(Z,Z)-isomer with primary amines, Chem. Res. Toxicol. 6 (1993) 407–412.
[22] B.T. Golding, C. Bleasdale, J.O. MacGregor, J. Nieschalk, K. Pearce, W.P. Wat-
son, Chemistry of muconaldehydes of possible relevance to the toxicology of
benzene, Environ Health Perspect. 104 (1996) 1201–1209.
[28] A.P. Henderson, C. Bleasdale, K. Delaney, A.B. Lindstrom, S.M. Rappaport, S.
Waidyanatha, W.P. Watson, B.T. Golding, Evidence for the formation of Michael
adducts from reactions of (E,E)-muconaldehyde with glutathione and other
thiols, Bioorg. Chem. 33 (2005) 363–373.
[29] C.J. Schlesener, C. Amatore, J.K. Kochi, Kinetics and mechanism of aromatic
oxidative substitutions via electron-transfer—application of Marcus theory to
organic processes in the endergonic region, J. Am. Chem. Soc. 106 (1984)
3567–3577.
[30] H. Hopf, U. Hamann, G. Zimmermann, M. Remmler, The propargyl-Cope rear-
rangement of meso and dl-3,4-dimethyl-1,5-hexadiyne-3,4-diol, Chem. Ber.
127 (1994) 959–963.
[31] E. Vogel, H. Günther, Benzene oxide–oxepin valence tautomerism, Angew.
Chem. Int. Ed. Engl. 6 (1967) 385–401.
[32] R.C. Fort, D.A. Hrovat, W.T. Borden, Ab initio calculations of the stabilization
energy of pentadienyl radical from rotational barriers and from lowering of
bond-dissociation energies, J. Org. Chem. 58 (1993) 211–216.
[33] H. Sato, F.P. Guengerich, Oxidation of 1,2,4,5-tetramethoxybenzene to a cation
radical by cytochrome P450, J. Am. Chem. Soc. 122 (2000) 8099–8100.
[34] A.P. Henderson, E. Mutlu, A. Leclercq, C. Bleasdale, W. Clegg, R.A. Henderson, B.T.
Golding, Trapping of benzene oxide–oxepin and methyl-substituted deriva-
tives with 4-phenyl-and 4-pentafluorophenyl-1,2,4-triazoline-3,5-dione,
Chem. Commun. (2002) 1956–1957.
[23] S.A. Kline, Q. Xiang, B.D. Goldstein, G. Witz, Reaction of (E,E)-muconaldehyde
and its aldehydic metabolites, (E,E)-6-oxohexadienoic acid and (E,E)-6-
hydroxyhexa-2,4-dienal, with glutathione, Chem. Res. Toxicol.
578–583.
[24] C. Bleasdale, R. Cameron, C. Edwards, B.T. Golding, Dimethyldioxirane converts
benzene oxide/oxepin into (Z,Z)-muconaldehyde and sym-oxepin oxide: mod-
eling the metabolism of benzene and its photooxidative degradation, Chem.
Res. Toxicol. 10 (1997) 1314–1318.
6
(1993)
[35] J.F. Hamilton, A.C. Lewis, C. Bloss, V. Wagner, A.P. Henderson, B.T. Golding, K.
Wirtz, M. Martin-Reviejo, M.J. Pilling, Measurements of photo-oxidation prod-
ucts from the reaction of a series of alkyl-benzenes with hydroxyl radicals
during EXACT using comprehensive gas chromatography, Atmos. Chem. Phys.
3 (2003) 1999–2014.
[36] J.F. Taylor, D. Zhang, R. Ghai, M. Törnqvist, B.T. Golding, unpublished results.