Synthesis of adducts of o-quinone metabolites of carcinogenic polycyclic aromatic hydrocarbons with 2′-deoxyribonucleosides

Article abstract of DOI:10.1021/ol0475358

(Chemical Equation Presented) The first syntheses of the adducts formed in the reactions of o-quinone metabolites of carcinogenic polycyclic aromatic hydrocarbons (BPQ and BAQ) at 2′-deoxyadenosine and 2′- deoxyguanosine sites in DNA are reported. These s

Full text of DOI:10.1021/ol0475358

ORGANIC
LETTERS
2005
Vol. 7, No. 6
999-1002
Synthesis of Adducts of o-Quinone
Metabolites of Carcinogenic Polycyclic
Aromatic Hydrocarbons with
2′-Deoxyribonucleosides
Qing Dai, Chongzhao Ran, and Ronald G. Harvey*
Ben May Institute for Cancer Research, The UniVersity of Chicago,
Chicago, Illinois 60637
rharVey@ben-may.bsd.uchicago.edu
Received December 1, 2004
ABSTRACT
The first syntheses of the adducts formed in the reactions of o-quinone metabolites of carcinogenic polycyclic aromatic hydrocarbons (BPQ
and BAQ) at 2 -deoxyadenosine and 2 -deoxyguanosine sites in DNA are reported. These syntheses entail Pd-catalyzed coupling of protected
amine derivatives of catechols with suitably protected halopurine analogues of 2 -deoxyribonucleosides.
′
′
′
Polycyclic aromatic hydrocarbons (PAHs), some of which
are potent carcinogens, are common environmental pollutants
produced in the combustion of organic matter.1,2 PAHs are
activated enzymatically to reactive metabolites that attack
DNA to form adducts that result in mutations and induction
of tumors.2-4 At least two mechanisms are operative. The
most studied pathway involves activation by cytochrome
P-450 (CYP) enzymes to diol epoxides, e.g., benzo[a]pyrene
anti-diol epoxide (anti-BPDE) (Figure 1).2,5 The alternative
pathway involves activation by aldo-keto reductase (AKR)
enzymes to catechols that enter into redox cycles with
quinones, e.g., benzo[a]pyrene-7,8-dione (BPQ), thereby
(1) International Agency for Research on Cancer. Monographs on the
Evaluation of the Carcinogenic Risk of Chemicals to Humans. Polynuclear
Aromatic Compounds, Part 1; IARC: Lyon, France, 1983; Vol. 32.
(2) Harvey, R. G. Polycyclic Aromatic Hydrocarbons: Chemistry and
Carcinogenicity; Cambridge University Press: Cambridge, U.K., 1991.
(3) Jeffrey, A. M.; Weinstein, I. B.; Jennette, K.; Grzeskowiak, K.;
Nakanishi, K.; Harvey, R. G.; Autrup, H.; Harris, C. Nature (London) 1977,
269, 348-350. Jennette, K.; Jeffrey, A. M.; Blobstein, S. H.; Beland, F.
A.; Harvey, R. G.; Weinstein, I. B. Biochemistry 1977, 16, 932-938.
(4) Dipple, A. In DNA Adducts: Identification and Biological Signifi-
cance; Hemminki, K., Dipple, A., Segerba¨ck, D., Kadulbar, F. F., Shuker,
D., Bartsch, H., Eds.; IARC: Lyon, France, 1994; Sci. Pub. no. 125, pp
107-129.
Figure 1. Active metabolites of benzo[a]pyrene (anti-BPDE, BPQ)
and structures of the BPQ-dG and BPQ-dA adducts.
(5) Conney, A. H. Cancer Res. 1982, 42, 4875.
10.1021/ol0475358 CCC: $30.25
© 2005 American Chemical Society
Published on Web 02/15/2005

generating reactive oxygen species that attack DNA.6,7 The
quinones combine with DNA to form stable and depurinating
adducts.8,9 This mechanism parallels AKR-mediated activa-
tion of estrogens.10
The PAH diol epoxides react at 2′-deoxyguanosine (dG)
and 2′-deoxyadenosine (dA) sites in DNA to afford adducts
whose structures are well-established.2-4,11 The stable adducts
of the PAH quinones are presumed to arise via 1,4-Michael
addition of the purines in DNA to the quinones followed by
auto-oxidation of the air-sensitive catechol intermediates.
However, the structures of the stable BPQ-dG and BPQ-dA
adducts (Figure 1)8b were not confirmed by independent
synthesis.
The aim of this investigation was to devise methods for
the synthesis of adducts of PAH quinones with dA and dG.
These adducts are urgently required for studies of the
mechanisms of PAH carcinogenesis. Syntheses of similar
adducts of a noncarcinogenic quinone, 1,2-naphthoquinone
(NQ), were reported,8,12 but attempted extension of the
methodology to the BPQ adducts was not successful.
Our synthetic approach entailed Pd-catalyzed coupling of
an amine derivative of a PAH quinone (or catechol) with a
halopurine analogue of a 2′-deoxyribonucleoside (Scheme
1). Initial studies were conducted with 4-amino-NQ (1),13
strong electron-withdrawing character of the carbonyl groups,
a protected catechol derivative (2) was prepared by reduction
of 1 with NaBH4 and reaction of the air-sensitive catechol
with TBDMS-Cl.16-18 Compound 2 reacted smoothly with
the bromo-dA analogue 3b in the presence of Pd(OAc)2,
BINAP, and Cs2CO3 at 80 °C overnight to furnish adduct 4
(47%).19 Similar reaction of the chloro-dA analogue 3c
required only 1 h for completion at 60 °C and gave 4 in
higher yield (85%). Treatment of 4 with TBAF in CH3CN
furnished the deprotected catechol, which underwent auto-
oxidation to the quinone and subsequent deacetylation with
TMG to yield NQ-dA (5c).
A similar strategy was adopted for synthesis of NQ-dG
(Scheme 2). Pd-catalyzed coupling of 2 with the benzyl ether
Scheme 2. Synthesis of NQ-dG Adduct
Scheme 1. Synthesis of NQ-dA Adduct
derivative of the chloropurine analogue of dG (6a) at 60 °C
for 1 h furnished 7 (88%). Hydrogenolysis of 7 over a Pd
catalyst followed by consecutive deacetylation with TMG
and removal of the TBDMS groups by treatment with TBAF
furnished NQ-dG.
Synthesis of the analogous BPQ-dG and BPQ-dA adducts
was carried out by similar methods (Scheme 3). Reaction of
BPQ20 with Me3SiN3 in DMF gave 10-amino-BPQ. This was
transformed to the aminocatechol derivative (8a) by reductive
hydrogenation over a Pd catalyst and treatment of the
aminocatechol product with N-methyl-N-TBDMS trifluoro-
acetamide. Pd-catalyzed coupling of 8a with 3c by the
procedure employed for synthesis of 5 furnished a bis-adduct
(11) Lee, H.; Luna, E.; Hinz, M.; Stezowski, J. J.; Kiselyov, A. S.;
Harvey, R. G. J. Org. Chem. 1995, 60, 5604-5613.
(12) Gopishetty, S. R.; Harvey, R. G.; Lee, S.-H.; Blair, I. A.; Penning,
T. M. In Aldo-Keto Reductases and Toxicant Metabolism; Penning, T. M.,
Petrash, J. M., Eds.; ACS Symposium Series 865; American Chemical
Society: Washington, DC, 2004; Chapter 9, pp 127-137.
(13) Husu, B.; Kafka, S.; Kadunc, Z.; Tisler, M. Monat. Chem. 1988,
119, 215-222.
but coupling of 1 with 3a failed to take place under various
conditions.14,15 Since this was likely a consequence of the
(6) Smithgall, T. E.; Harvey, R. G.; Penning, T. M. J. Biol. Chem. 1986,
261, 6184-6191; Cancer Res. 1988, 48, 1227-1232; J. Biol. Chem. 1988,
263, 1814-1820.
(7) Penning, T. M.; Onishi, S. T.; Onishi, T.; Harvey, R. G. Chem. Res.
Toxicol. 1996, 9, 84-92. Flowers, L.; Onishi, S. T.; Penning, T. M.
Biochemistry 1997, 36, 8640.
(8) (a) Shou, M.; Harvey, R. G.; Penning, T. M. Carcinogenesis 1993,
14, 475-482. (b) McCoull, K. D.; Rindgen, D.; Blair, I. A.; Penning, T.
M. Chem. Res. Toxicol. 1999, 12, 237-246.
(9) A third mechanism has been proposed that involves activation of
PAHs by CYP peroxidase to generate PAH radical-cations that combine
with DNA to form depurinated adducts: Cavalieri, E. L.; Rogan, E.
Xenobiotica 1995, 25, 677. Its relevance is disputed: Melendez-Colon, V.;
Luch, A.; Seidel, A.; Baird, W. Carcinogenesis 1999, 20, 1885.
(10) Bolton, J. I.; Trush, M. A.; Penning, T. M.; Dryhurst, G.; Monks,
T. J. Chem. Res. Toxicol. 2000, 13, 135-160.
(14) Fluoropurine 3a is known to react more readily with arylamines,
such as 1-aminopyrene, than its bromo- or chloro analogues.11
(15) Coupling of 1 with 3a also failed to take place in the presence of
the Pd catalyst system successfully employed for coupling 2 and 3b.
(16) Although PAH catechols are highly susceptible to air oxidation,
their diester or diether derivatives are relatively stable in air.
(17) Reagent abbreviations: TBDMS-Cl ) tert-butyldimethylsilyl chlo-
ride; BINAP ) 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl; TBAF )
tetrabutylammonium fluoride; TMG ) N,N,N′,N′-tetramethylguanidine.
(18) Cho, H.; Harvey, R. G. J. Chem. Soc., Perkin I 1976, 836-839.
(19) A bis-adduct with two 2′-deoxyribonucleoside groups attached to
the nitrogen atom of the aminocatechol was a minor product.
(20) Harvey, R. G.; Dai, Q.; Ran, C.; Penning, T. M. J. Org. Chem.
2004, 64, 2024-2032.
1000
Org. Lett., Vol. 7, No. 6, 2005

catalyzed coupling of 8a with 6a took place smoothly at 60
°C to furnish an adduct (10a) (82%). Removal of the benzyl
groups of 10a by Pd-catalyzed hydrogenolysis was ac-
companied by partial reduction of the aromatic ring system.
To obviate this problem, the p-nitrophenylethyl ether ana-
logue (6b) was substituted for 6a.11,21 Analogous coupling
of 8a with 6b gave (10b) in good yield (88%). Deacetylation
of 10b with TMG at room temperature, followed by removal
of solvents under vacuum and allowing the solution to stand
overnight, afforded an equal mixture of BPQ-dG and its
p-nitrophenylethyl ether (11). Transformation of 11 to BPQ-
dG was complete with longer reaction time. It is convenient
that all three protecting groups may be removed by treatment
with a single reagent.
Scheme 3. Synthesis of BPQ-dA Adduct
This synthetic approach was extended successfully to
synthesis of the analogous adducts of benz[a]anthracene-
3,4-dione (BAQ) with both dA and dG (Figure 2). The
plus a small amount of the desired mono-adduct (9a). A more
favorable product ratio resulted from use of the dibenzoate
ester (8b) in place of 8a. Pd-catalyzed reaction of 8b with
3d afforded 9b and a bis-adduct in 2:1 ratio. Debenzoylation
of 9b with TMG provided the corresponding catechol, which
underwent oxidation in air to yield BPQ-dA as its TBDMS
derivative (9a). Treatment of 9a with TBAF furnished BPQ-
dA.
Figure 2. Structures of the BAQ-dG and BAQ-dA adducts.
adducts (BAQ-dA and BAQ-dG) were obtained in excellent
overall yields. It is worthy of note that in the synthesis of
BAQ-dA a bis-adduct was not detected as a significant
product.22
In related studies, Balu et al.23 have recently identified
several adducts formed in low yields in the reactions of BPQ
with dG and dA in DMF-phosphate buffer solutions (pH
7.5) at 50-60 °C.5 Reaction of BPQ with dG gave a mixture
of two pairs of diastereomeric adducts in 2.5-3.5% yield
each. One of these pairs of adducts was assigned a structure
corresponding to a product of hydration of BPQ-dG. There
is currently no evidence that supports formation of these
types of adducts in vivo.
Synthesis of BPQ-dG was accomplished by modification
of the procedure for preparation of NQ-dG (Scheme 4). Pd-
Scheme 4. Synthesis of BPQ-dG Adduct
In summary, we have reported the first syntheses of the
dA and dG adducts of o-quinone metabolites of carcinogenic
PAHs (BPQ and BAQ) (Figures 1 and 2). The structures of
these adducts correspond to those proposed8,10,24 for the stable
adducts formed by the reactions of PAH quinones at dA and
(21) Lee, H.; Hinz, M.; Stezowski, J. J.; Harvey, R. G. Tetrahedron Lett.
1990, 31, 6773-6776.
(22) Full details of the syntheses of BAQ-dA and BAQ-dG will be
reported separately.
(23) Balu, N.; Padgett, W. T.; Lambert, G. R.; Swank, A. E.; Richard,
A. M.; Nesnow, S. Chem. Res. Toxicol. 2004, 17, 827-838.
(24) Penning, T. M.; Palackal, N. T.; Lee, S.-L.; Blair, I.; Yu, D.; Berlin,
J. A.; Field, J. M.; Harvey, R. G. In Aldo-Keto Reductases and Toxicant
Metabolism; Penning, T. M., Petrash, J. M., Eds.; ACS Symposium Series
865; American Chemical Society: Washington, DC, 2004; Chapter 6, pp
83-99.
Org. Lett., Vol. 7, No. 6, 2005
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dG sites in DNA in vivo.6 In principle, this general
methodology is applicable to synthesis of similar adducts of
other carcinogenic and noncarcinogenic PAH quinones, as
well as to the synthesis of analogous adducts of estrogenic
quinones.10 The BPQ-dG adduct may also be expected to
serve as a convenient synthetic precursor of the hydrated
BPQ-dG adducts formed by reaction of BPQ with dG in
phosphate buffer solution.23
dG adducts have also been accomplished, and these com-
pounds have been furnished to Dr. Blair as standards for
LC-MS-MS studies to develop methods for the screening
and detection of these types of adducts in human tissues.
Acknowledgment. This investigation was supported by
a grant (CA 92537) from the National Cancer Institute,
DHHS.
The BPQ-dA and BPQ-dG adducts have been provided
to Dr. Trevor Penning and Dr. Ian Blair at the University of
Pennsylvania for investigations to elucidate the role of these
adducts in the mechanism(s) of PAH carcinogenesis. Syn-
theses of the N15-labeled analogues of the BPQ-dA and BPQ-
Supporting Information Available: Experimental details
and spectroscopic data. This material is available free of
charge via the Internet at http://pubs.acs.org.
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