Strategies for synthesis of adducts of o-quinone metabolites of carcinogenic polycyclic aromatic hydrocarbons with 2′-deoxyribonucleosides

Article abstract of DOI:10.1021/jo701667u

(Chemical Equation Presented) Polycyclic aromatic hydrocarbons (PAHs) are major environmental carcinogens produced in the combustion of fossil fuels, tobacco, and other organic matter. Current evidence indicates that PAHs are transformed enzymatically to

Full text of DOI:10.1021/jo701667u

Strategies for Synthesis of Adducts of o-Quinone Metabolites of
Carcinogenic Polycyclic Aromatic Hydrocarbons with
2′-Deoxyribonucleosides
Chongzhao Ran,† Qing Dai,† Qian Ruan,‡ Trevor M. Penning,‡ Ian A. Blair,‡ and
Ronald G. Harvey*,†
The Ben May Department for Cancer Research, The UniVersity of Chicago, Chicago, Illinois 60637, and
The Centers for Cancer Pharmacology and Excellence in EnVironmental Toxicology, UniVersity of
PennsylVania School of Medicine, Philadelphia, PennsylVania 19104
rharVey@ben-may.bsd.uchicago.edu
ReceiVed July 30, 2007
Polycyclic aromatic hydrocarbons (PAHs) are major environmental carcinogens produced in the combustion
of fossil fuels, tobacco, and other organic matter. Current evidence indicates that PAHs are transformed
enzymatically to active metabolites that react with DNA to form adducts that result in mutations. Three
activation pathways have been proposed: the diol epoxide path, the radical-cation path, and the quinone
path. The latter involves aldo-keto reductase mediated oxidation of PAH dihydrodiol metabolites to
catechols that enter into redox cycles with quinones. This results in generation of reactive oxygen species
(ROS) that attack DNA, and the PAH quinones also react with DNA to form adducts. Several strategies
for synthesis of the stable adducts formed by the o-quinone metabolites of carcinogenic PAHs with 2′-
deoxyribonucleosides were investigated and compared. The PAH quinones studied were benz[a]anthracene-
3,4-dione and its 7-methyl- and 7,12-dimethyl- derivatives. The parent PAHs represent a range of
carcinogenicity from inactive to highly potent. Two synthetic methods were devised that differ in the
catalyst employed, Pd(OAc)2 or CuI. The Pd-mediated method involved coupling a protected amino-
catechol PAH derivative with a halo-2′-deoxyribonucleoside. The copper-mediated method entailed reaction
of a halo-PAH catechol derivative with a 2′-deoxyribonucleoside. Adducts of benz[a]anthracene-3,4-
dione (and its 7-methyl- and 7,12-dimethyl- derivatives) with 2′-deoxyadenosine and 2′-deoxyguanosine
were prepared by these methods. Availability of adducts of these types through synthesis makes possible
for the first time biological studies to determine the role of these adducts in tumorigenesis. The copper-
mediated method offers advantages of economy, adaptability to large-scale preparation, utility for synthesis
of 13C- or 15N-labeled analogues, and nonformation of bis-adducts as secondary products.
Introduction
nogenic PAHs benzo[a]pyrene and dibenzo[def,p]chrysene5 have
been identified as components of tobacco smoke and vehicle
exhaust condensate,6,7 and current evidence suggests that they
may be involved in initiation of lung cancer.6,8,9
Polycyclic aromatic hydrocarbons (PAHs) are widespread
environmental pollutants produced in the combustion of fossil
fuels, tobacco, and other organic matter.1-3 They have recently
been designated human carcinogens by the WHO.4 The carci-
(1) International Agency for Research on Cancer. Monographs on the
Evaluation of the Carcinogenic Risk of Chemicals to Humans. Polynuclear
Aromatic Compounds, Part 1, Chemical, EnVironmental and Experimental
Data; IARC: Lyon, France 1983; Vol. 32.
† The University of Chicago.
‡ University of Pennsylvania School of Medicine.
10.1021/jo701667u CCC: $40.75 © 2008 American Chemical Society
Published on Web 01/09/2008
992
J. Org. Chem. 2008, 73, 992-1003

Adducts of o-Quinone Metabolites of Carcinogenic PAHs
FIGURE 1. Pathways of metabolic activation of benzo[a]pyrene.
FIGURE 2. Structures of adducts formed by reaction of BPQ at dGuo and dAde sites in DNA.
For PAHs to exert their carcinogenic effects, metabolic
activation is required. The most studied activation pathway
involves cytochrome P-450 (CYP)-mediated oxidation of PAHs
to diol epoxide metabolites, such as benzo[a]pyrene anti-diol
epoxide (anti-BPDE) (Figure 1).2,10 The PAH diol epoxides react
with DNA to form adducts11,12 that lead to mutations and
induction of tumors.
Two additional activation pathways have been proposed
(Figure 1). One of these entails aldo-keto reductase (AKR)-
mediated oxidation of a dihydrodiol metabolite (e.g., BP-7,8-
diol) to form a catechol that enters into a redox cycle with the
corresponding quinone (BPQ).13,14 In the process, O2 is con-
sumed and reactive oxygen species (ROS) are generated. The
ROS attack DNA, and the quinone reacts with DNA to form
stable and depurinated adducts.15,16 The AKR pathway parallels
AKR-mediated activation of estrogens.17 The third activation
pathway entails oxidation by CYP peroxidase to generate PAH
radical-cations that react with DNA to form depurinated
adducts.18
Determination of the relative importance of these pathways
for human cancer requires synthetic access to the adducts formed
by reactions of PAH metabolites with DNA. The structures of
the adducts formed by PAH diol epoxides with 2′-deoxygua-
nosine (dGuo) and 2′-deoxyadenosine (dAde) are well-
established,11,12 and methods for their synthesis have been
extensively investigated.3,19 In contrast, very little is known
concerning the synthesis or biological properties of the adducts
arising from reactions of PAH quinones with DNA. The
structures of the stable adducts of BPQ with dAde and dGuo
(BPQ-dA and BPQ-dG) (Figure 2) are consistent with their
origin via formal 1,4-Michael addition of the exocyclic amino
groups of the purine bases to BPQ followed by auto-oxidation
of the air-sensitive primary catechol intermediates.15 However,
attempts to synthesize these adducts by direct reaction of the
components (Figure 3, Method A) were not successful, and their
synthesis by Pd-catalyzed coupling of an amine derivative of a
PAH quinone, e.g., 10-amino-BPQ, with a halopurine (Method
(2) Harvey, R. G. Polycyclic Aromatic Hydrocarbons: Chemistry and
Carcinogenicity; Cambridge University Press: Cambridge, U.K., 1991.
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E. L.; Higginbotham, S.; RamaKrishna, N. S. V.; Devanesan, P. D.;
Todorovic, R.; Rogan, E. G.; Salmasi, S. Carcinogenesis 1991, 12, 1939-
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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.
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J. Org. Chem, Vol. 73, No. 3, 2008 993

Ran et al.
are formed as secondary products in the synthesis of the dAde
adducts (but not the dGuo adducts).20
We now report synthesis of the stable adducts of the
o-quinones of benz[a]anthracene (1a),21 7-methylbenz[a]an-
thracene (1b),21 and 7,12-dimethylbenz[a]anthracene (1c)21 with
dAde (2a-c) and dGuo (3a-c) (Figure 4). These adducts are
needed as standards for LC-MS-MS analysis of the adducts
formed in human cells. The parent PAHs, BA, MBA, and
DMBA, represent a range of carcinogenicity from inactive (BA)
to intermediate (MBA) to highly potent (DMBA).22
Results
Michael Addition (Method A). The potentially most straight-
forward synthetic route to the stable adducts of 1a with dAde
(2a) and dGuo (3a) is via direct reaction of the components
(Figure 3). However, it was shown previously15b that reactions
of simple PAH quinones, such as naphthalene-1,2-dione and
phenanthrene 3,4-dione, with dGuo in aqueous acetic acid take
a different course, furnishing instead depurinated adducts arising
from Michael addittion of the N7-atom of dGuo to the PAH
quinone. Attempts to react 1a with Ade in the presence of
various potential catalysts, such as CuBr2, PdCl4, PdCl2CN2,
CeCl3‚7H2O, AuCl3, and InCl3, were not successful, providing
neither 2a nor the depurinated adduct arising from reaction on
N7 of dAde.
Palladium-Mediated Coupling of Aminoquinones and
Aminocatechols with Halopurines (Methods B and C):
Synthesis of dAde Adducts. 1-Aminobenz[a]anthracene 3,4-
dione (5a) required as the starting compound for synthesis of
the stable adducts of 1a with dAde was prepared by addition
of azidotrimethylsilane (Me3SiN3) to BAQ (Scheme 1). The
unstable 1-azido-BA catechol product (4a) underwent loss of
nitrogen and auto-oxidation to 5a (92%).20,23 6-Bromo- and
6-chloro-9-(3,5-bis-O-acetyl-2-deoxy-â-D-erythro-pentofurano-
syl)purine (6a,b) were synthesized by published procedures.24a
Attempted coupling of 5a with 6a in the presence of Pd(OAc)2/
BINAP and Cs2CO3 failed to furnish adduct 2a. This was
consistent with the earlier finding that 10-aminobenzo[a]pyrene
7,8-dione did not couple with 6a.20 As in that case, the problem
was solved by conversion of the amino-quinone into a protected
amino-catechol derivative that readily underwent Pd-catalyzed
coupling with 6a. Pd-mediated coupling of arylamines with
arylhalides,25a including the halopurine derivatives 6a,b,25b-f is
a well-known reaction.
FIGURE 3. Strategies for synthesis of adducts of PAH o-quinones
with 2′-deoxyribonucleosides: (A) Michael addition of 2′-deoxyribo-
nucleoside to PAH quinone; (B) Pd-mediated coupling of amino
derivative of PAH quinone with a halopurine; (C) Pd-mediated coupling
of amino derivative of PAH catechol with a halopurine; (D) Cu-
mediated coupling of halo derivative of PAH catechol with 2′-
deoxyribonucleoside.
B) also failed. However, syntheses of BPQ-dAde and BPQ-
dGuo were successfully accomplished by Pd-catalyzed coupling
of a 10-amino-catechol derivative of BP (10-amino-7,8-dihy-
droxy-BP) with halopurine analogues of dAde and dGuo
(Method C).20
The failure of 10-amino-BPQ to react despite the fact that
the related amino-catechol derivative readily underwent coupling
is attributed to the weak nucleophilic character of the amino
group of the former due to the electron-withdrawing effect of
the carbonyl groups. Reduction of the quinone to a catechol
converted the carbonyl groups into electron-donating hydroxyl
groups. However, Method C has the limitation that 1:2 adducts
Reduction of 5a with hydrogen over a 5% Pd/C catalyst and
protection of the air-sensitive hydroxyl groups of the catechol
product by silylation with N-tert-butyldimethylsilyl-N-methyl-
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14, 475-482. (b) McCoull, K. D.; Rindgen, D.; Blair, I. A.; Penning, T.
M. Chem. Res. Toxicol. 1999, 12, 237-246. (c) Penning, T. M.; Burczynski,
M. E.; Hung, C.-H.; McCoull, K. D.; Palackal, N. T.; Tsurudd, L. S. Chem.
Res. Toxicol. 1999, 12, 1-18.
(16) The stable adducts are formed by covalent bonding of the PAH
quinones to the exocylic amino groups of the purine bases; they are
stable in the sense that they remain attached to the DNA helix. The
depurinated adducts arise from reaction of the PAH quinones on the
N7 and N9 atoms of dG and dA in DNA with consequent loss of
2′-deoxyribose.
(19) Gunda, P.; Russon, L. M.; Lakshman, M. K. Angew. Chem. Int.
Ed. 2004, 43, 6372-6377. Lakshman, M. K.; Ngassa, F. N.; Bae, S.;
Buchanan, D. C.; Hahn, H.-D.; Mah, H. J. Org. Chem. 2003, 68, 6020-
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Res. Toxicol. 2002, 15, 1489-1494. Lakshman, M. K.; Hilmer, J. H.; Martin,
J. Q.; Keeler, J. C.; Dinh, Y. Q. V.; Ngassa, F. N.; Russon, L. M. J. Am.
Chem. Soc. 2001, 123, 7779-7787. Lee, H.; Ramesha, A. R.; Kroth, H.;
Jerina, D. M. Tetrahedron Lett. 2001, 1003-1005. Luna, E.; Hinz, M.;
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5604-5613.
(20) Dai, Q.; Ran, C.; Harvey, R. G. Org. Lett. 2005, 5, 999-1001.
(21) Harvey, R. G.; Dai, Q.; Ran, C.; Penning, T. M. J. Org. Chem.
2004, 69, 2024-2032.
(22) Huggins, C. B.; Pataki, J.; Harvey, R. G. Proc. Natl. Acad. Sci.
U.S.A. 1967, 58, 2253-2260.
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T. J. Chem. Res. Toxicol. 2000, 13, 135-160.
(18) Cavalieri, E. L.; Rogan, E. Xenobiotica 1995, 25, 677. The relevance
of the radical-cation mechanism has been disputed: Melendez-Colon, V.;
Luch, A.; Seidel, A.; Baird, W. Carcinogenesis 1999, 20, 1885.
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994 J. Org. Chem., Vol. 73, No. 3, 2008

Adducts of o-Quinone Metabolites of Carcinogenic PAHs
FIGURE 4. Structures of the quinone metabolites of BA, MBA, and DMBA (1a-c) and their adducts with dAde (2a-c) and dGua (2a-c).
SCHEME 1a
a Reagents and conditions: (i) Me3SiN3; (ii) H2/Pd/C; (iii) t-BuMe2SiN(Me)COCF3/K2CO3; (iv) Pd(OAc)2/BINAP, Cs2CO3; (v) TMG/KF/O2.
trifluoroacetamide gave 1-amino-3,4-bis-tert-butyldimethylsi-
lyloxy-BA (7a). This compound reacted with 6b in the presence
of Pd(OAc)2/BINAP/Cs2CO3 in toluene at 80 °C to furnish the
protected adduct (8a) (53%). It is worthy of note that the
6-bromo- and 6-chloro-2′-deoxyribonucleosides (6a and 6b)
exhibited essentially no difference in reactivity in these reactions.
This was unexpected in view of reports that 6-chloro-nucleosides
were more reactive than the 6-bromo- analogs in other related
Pd-catalyzed coupling reactions of 6-halo-2′-deoxyribonucleo-
sides with amines.26 Coupling of 7a with 6b also furnished a
1:2 adduct (9) (33%) formed by reaction of a second molecule
of 6b on the amino group of 8a. Formation of a 1:2 adduct was
observed earlier in the analogous synthesis of the BPQ-dAde
adduct by Pd-catalyzed coupling.20 Deacetylation of 8a with
N,N,N′,N′-tetramethylguanidine (TMG) followed by removal of
the TBDMS groups with KF furnished a catechol derivative
that underwent auto-oxidation to provide 2a.
(25) (a) Hartwig, J. F. Angew. Chem., Int. Ed. 1998, 37, 2046-2067.
(b) Lakshman, M. K.; Keeler, J. C.; Hilmer, J. H.; Martin, J. Q. J. Org.
Chem. 2005, 70, 7188-7195. (c) Bonala, R. R.; Shishkina, I. G.; Johnson,
F. Tetrahedron Lett. 2000, 41, 7281-7284. (d) Lakshman, M. K.; Keeler,
J. C.; Hilmer, J. H.; Martin, J. Q. J. Am. Chem. Soc. 1999, 121, 6090-
6091. (e) Lakshman, M. K.; Ngassa, F. N.; Bae, S.; Buchanan, D. C.; Hahn,
H.-D.; Mah, H. J. Org. Chem. 2003, 68, 6020-6030. (f) Johnson, F.; Bonala,
R.; Tawde, D.; Torres, M. C.; Iden, C. R. Chem. Res. Toxicol. 2002, 15,
1489-1494.
(26) Champeil, E.; Pradhan, P.; Lakshman, M. K. J. Org. Chem. Soc.
2007, 72, 5035-5045. Lakshman, M. K.; Gunda, P. Org. Lett. 2003, 5,
39-42.
J. Org. Chem, Vol. 73, No. 3, 2008 995

Ran et al.
SCHEME 2a
a Reagents and conditions: (i) Me3SiN3; (ii) H2/Pd/C; (iii) t-BuMe2-
SiN(Me)COCF3/K2CO3; (iv) Pd(OAc)2/BINAP, Cs2CO3; (v) TMG/KF/O2.
Synthesis of the analogous adduct of MBA 3,4-dione with
dAde (2b) was carried out by a similar reaction sequence
(Scheme 1). Reaction of 1b with Me3SiN3 and auto-oxidation
of the primary catechol product furnished 1-amino-7-methyl-
benz[a]anthracene 3,4-dione (5b) (90%). This was converted
into the catechol derivative 7b (80%) via hydrogenation
followed by silylation with N-tert-butyldimethylsilyl-N-meth-
yltrifluoroacetamide. Pd-catalyzed coupling of 7b with 6b gave
adduct 8b (40%) accompanied by an equal ratio of a 1:2 adduct.
Deprotection of 8b by deacetylation with TMG followed by
treatment with KF and auto-oxidation gave 7-methylbenz[a]-
anthracene 3,4-dione-dAde (2b).
Extension of this approach to synthesis of the related adduct
of DMBA 3,4-dione with dAde (2c) (Scheme 2) was compli-
cated by steric crowding in the bay region of DMBA. DMBA
has been shown to be distorted >23° from planarity as a result
of the steric interaction in this region.27 Although 1 equiv of
Me3SiN3 failed to react with 1c to give 5c, reaction took place
with a large excess of Me3SiN3 (10-20 equiv) to afford 4c
quantitatively.
Compound 4c, unlike the related adducts 4a and 4b, failed
to undergo spontaneous loss of nitrogen and auto-oxidation to
the corresponding amino-quinone product (5c). Transformation
of 4c into a TBDMS-protected amino-catechol derivative (7c)
was carried out by a procedure that did not involve 5c (Scheme
2). Thus, treatment of 4c with N-tert-butyldimethylsilyl-N-
methyltrifluoroacetamide and K2CO3 afforded a protected azido-
catechol derivative (10). Reduction of 10 with hydrogen over a
Pd/C catalyst furnished the amino-catechol derivative 8c in good
overall yield.
Synthesis of the DMBA 3,4-dione-dAde adduct (2c) was
carried out by the method used for synthesis of the related BA-
and MBA-3,4-dione-dAde adducts (Scheme 2). Pd-catalyzed
coupling of 7c with 6b took place readily to provide the
protected DMBA catechol-dAde adduct (8c) (46%). In contrast
to the analogous reactions of 7a and 7b, a 1:2 adduct was not
obtained as a byproduct. Repression of secondary adduct
formation is likely a consequence of increased steric crowding
in the bay region of the BA ring system of 7c due to the presence
of a methyl group in the C12-position that is lacking in 7a and
7b.
FIGURE 5. Structures of the isomers of the protected DMBA catechol-
dA adduct (8c1 and 8c2). The tautomeric structure 11 is ruled out by
the NMR data. Auto-oxidation of 8c affords an unstable product
tentatively assigned the 7,12-epidioxide structure (12).
Adduct 8c exhibited a strong tendency to undergo decom-
position. In spite of this difficulty, a pure sample of 8c was
obtained by flash chromatography on a silica gel column. HPLC
analysis (CH3CN/H2O, 4:1) showed only a single peak. The
mass spectrum of 8c was consistent with its structure, and the
1H NMR and 13C NMR spectra were also in general agreement
with this assignment, except that many of the signals appeared
as slightly shifted duplicate peaks. This suggested the presence
of conformationally restricted stereoisomers (8c1 and 8c2)
(Figure 5) formed as a consequence of the severe steric
interaction between the C12-methyl group and dAde. It is likely
that the bulky TBDMS protecting groups also contribute
importantly to the steric crowding responsible for this effect.
Formation of the methylene tautomer 1128,29 is ruled out by the
1H NMR and 13C NMR spectra, which exhibited none of the
characteristic signals expected for this structure.
Compound 8c also showed a strong tendency to undergo
oxidative decomposition on exposure to air and light. DMBA
itself is known to be highly susceptibile to photo-oxidation to
form a transannular bridged 7,12-epidioxide,30 and biological
experiments with this PAH are routinely conducted in subdued
light. It was not surprising, therefore, that a highly strained
derivative of DMBA, such as 8c, would also be susceptible to
photo-decomposition. The primary photo-oxidation product is
likely the DMBA 7,12-epidioxide (12); however, its character-
ization was prevented by its relative ease of decomposition.
Despite the facility of photo-oxidation of 8c, its conversion
to 2c (Scheme 2) was successfully accomplished by conducting
(28) Harvey, R. G. Polycyclic Aromatic Hydrocarbons; Wiley-VCH:
New York, NY, 1997.
(29) Cho, H.; Harvey, R. G.; Rabideau, P. W. J. Am. Chem. Soc. 1975,
97, 1140-1145.
(30) Wood, J. L.; Barker, C. L.; Grubbs, C. J. Chem.-Biol. Interact. 1979,
339-347.
(27) Glusker, J. P. In Polycyclic Hydrocarbons and Carcinogenesis;
Harvey, R. G., Ed.; ACS Symposium Series, No. 283; American Chemistry
Society: Washington, DC, 1985; pp 35-62.
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Adducts of o-Quinone Metabolites of Carcinogenic PAHs
SCHEME 3a
Synthesis of the related adduct of MBA-3,4-dione with dGuo
(3b) was carried out by an analogous sequence involving Pd-
mediated coupling of 7b with 13 (Scheme 3). The coupled
adduct 14b was obtained in good yield (82%) unaccompanied
by a 1:2 adduct. Debenzylation of 14b by transfer hydrogena-
tion, followed by deacetylation of the product with TMG,
removal of the TBDMS groups with KF, and auto-oxidation
furnished 3b in good overall yield (64%).
Extension of this approach to synthesis of the analogous
DMBA-3,4-dione-dGuo adduct (3c) was only partially success-
ful. Pd-catalyzed coupling of the protected 1-amino-catechol
derivative of DMBA (7c) with 13 took place smoothly under
the conditions employed in preceding examples to yield the
adduct of the protected DMBA catechol with dGuo (14c). Again,
a 1:2 adduct was not detected. However, 14c was highly
sensitive to oxidative decomposition. Its 1H NMR and 13C NMR
spectra, like those of the dAde adduct 8c, exhibited duplicate
peaks. Despite the instability of 14c, it was possible to
investigate its conversion to the target molecule by taking
appropriate precautions for exclusion of air and light. Under
these conditions, debenzylation of 14c and deacetylation of the
product proceeded normally. However, attempts to remove the
TBDMS protecting groups with KF led to rapid decomposition
and formation of complex product mixtures. It appears that the
DMBA-3,4-catechol-dGuo adduct and/or the DMBA-3,4-dione-
dGuo adduct (3c) formed by its auto-oxidation may be too
unstable to isolate and characterize.
Synthesis of dAde Adducts via Copper-Mediated Coupling
of Halo Derivatives of PAH Catechols with 2′-Deoxyribo-
nucleosides (Method D). A longer-range goal of these studies
was to develop methods for synthesis of 13C- and/or 15N-labeled
analogues of these adducts. Isotopically labeled analogues are
required as standards for isotope dilution liquid chromatography/
tandem mass spectrometric analysis of the adducts formed by
metabolites of carcinogenic PAHs in human cells. Progress in
the development of these new methodologies has recently been
reported.33-35
Copper-mediated coupling of halo-substituted PAH catechols
with nucleosides (Method D) offers significant potential ad-
vantages for synthesis of isotopically labeled analogues. Copper-
mediated coupling36 is tolerant of most substituents, and
protection of hydroxyl groups is not required. Methods for
copper-mediated regioselective N1- and N6-arylation of 2′-
deoxyribonucleosides have been reported.37,38
Synthesis of BA-3,4-dione-dAde (2a) via Method D (Scheme
4) requires a halo-substituted catechol, such as 1-bromo-3,4-
diacetoxy-BA (17a). Attempts to synthesize 17a from 4-bromo-
BA-3,4-dione (15) via addition of Me3SiBr to 1a were blocked
by failure of the inital step to take place. Although addition of
Me3SiBr appeared to occur, as evidenced by temporary loss of
a Reagents and conditions: (i) Pd(OAc)2/BINAP, Cs2CO3; (ii) Pd/
cyclohexadiene; (iii) TMG/MeOH; (iv) KF/O2.
operations in the absence of air in yellow light. Deacetylation
of 8c with TMG and removal of the TBDMS groups with KF
afforded a product that underwent auto-oxidation to yield adduct
2c (19%). The 1H NMR and 13C NMR spectra of 2c exhibited
only a single set of peaks, in good agreement with the structural
assignment. The loss of the multiplicity of the peaks evident in
the spectra of 8c is apparently indicative of the markedly
diminished internal steric strain in 2c as a consequence of
removal of the bulky protecting groups, allowing it to exist as
a single conformer.
Palladium-Mediated Coupling of Aminoquinones and
Aminocatechols with Halopurines (Methods B and C):
Synthesis of dGuo Adducts. Synthesis of the BA 3,4-dione-
dGuo adduct (3a) was carried out by a modification of the
method employed for synthesis of the corresponding dAde
adduct (2a). This entailed in the key step Pd-catalyzed coupling
of the protected 1-aminocatechol derivative of BA (7a) with
2-chloro-6-benzyloxy-9-[2′-deoxy-â-D-erythro-pentofuranosyl]-
purine (13) (Scheme 3). Compound 13 was synthesized as
previously described.20 Reaction of 7a with 13 took place in
the presence of Pd(OAc)2, BINAP, and Cs2CO3 to furnish the
expected adduct (14a) (84%), unaccompanied by the corre-
sponding 1:2 adduct. Debenzylation of 14a by hydrogenation
over a 5% Pd/C catalyst was complicated by partial hydrogena-
tion of the 5,6-bond of the BA ring (evidenced by the 1H NMR
spectrum of the product). Secondary hydrogenation of the PAH
ring system did not occur with the use of a Lindlar catalyst,
but conversion was low (<50%). Debenzylation was most
efficiently accomplished by transfer hydrogenation with 1,4-
cyclohexadiene and Pd black.31,32 Reaction took place at room
temperature to provide the debenzylated product quantitatively.
Deacetylation with TMG and removal of the TBDMS groups
by treatment with KF furnished the BA catechol adduct, which
underwent auto-oxidation to furnish BA-3,4-dione-dGuo (3a)
(65%).
(33) Jiang, H.; Gelhaus, S. L.; Mangal, D.; Harvey, R. G.; Blair, I. A.;
Penning, T. M. Chem. Res. Toxicol. 2007, 20, 1331-1341.
(34) Ruan, Q.; Gelhaus, S.; Penning, T. M.; Harvey. R. G.; Blair, I. A.
Chem. Res. Toxicol. 2007, 20, 424-431.
(35) Ruan, Q.; Kim, H. Y. H.; Jiang, H.; Penning, T. M.; Harvey, R.;
G.; Blair, I. A. Rapid Commun. Mass Spectrom. 2006, 20, 1369-1380.
(36) Kwong, F. Y.; Klapars, A.; Buchwald, S. L. Org. Lett. 2003, 4,
881-884. Kwong, F. Y.; Buchwald, S. L. Org. Lett. 2003, 4, 793-796.
Klapars, A.; Huang, X.; Buchwald, S. L. J. Am. Chem. Soc. 2002, 124,
7421-7428.
(31) Felix, A. M.; Heimer, E. P.; Lambros, T. J.; Tzovgraki, C.;
Meienhofer, J. J. Org. Chem. 1978, 43, 4194-4196.
(32) Harwood, E. A.; Hopkins, P. B.; Sigurdsson, S. T. J. Org. Chem.
2000, 72, 2959-2964.
(37) Ran, C.; Dai, C.; Harvey, R. G. J. Org. Chem. 2005, 70, 3724-
3726.
(38) Dai, C.; Ran, C.; Harvey, R. G. Tetrahedron 2005, 62, 1764-
1771.
J. Org. Chem, Vol. 73, No. 3, 2008 997

Ran et al.
SCHEME 4a
a Reagents and conditions: (i) H2/Pd/C/DM; (ii) Ac2O/K2CO3; (iii) t-BuONO; TMSBr, Bu4N/Br-; (iv) KOH/18-crown/BnBr/DMF; (v) Cul/DMEDA/
DMSO; (vi) Pd/cyclohexadiene; (vii) KF/DMF.
the intense purple color of the quinone, the bromocatechol
intermediate reverted rapidly to the unsubstituted quinone.
Attempted trapping of the bromocatechol intermediate by
trimethylsilylation was also unsuccessful. Similar behavior was
previously observed in the analogous reaction of Me3SiBr with
BPQ.20 Evidently, introduction of a Br atom into the bay regions
of PAH quinones is strongly disfavored by steric crowding.
Synthesis of 17a was successfully accomplished by an
alternative approach based on 1-amino-BA-3,4-dione (5a)
(Scheme 4). Thus, Pd-catalyzed reduction of 5a with hydrogen
over Pd/charcoal followed by acetylation of the catechol product
furnished the 1-amino-catechol diacetate 16a. Diazotization of
16a with t-BuONO and Me3SiBr in CH2Br2 at 0 to -35 °C
furnished 17a. This compound was unstable at higher temper-
atures, tending to undergo deacetylation. For this reason, 17a
was converted to the more stable dibenzyl derivative, 1-bromo-
3,4-dibenzyloxybenz[a]anthracene (18a), by treatment with
benzyl bromide, 18-crown-6 ether, and KOH. Attempts to
abbreviate this sequence by converting 16a to the dibenzyl
derivative prior to diazotization gave less satisfactory results.
Coupling of 18a with dAde took place smoothly in the
presence of CuI and N,N′-dimethylethylenediamine in DMSO
to furnish adduct 19a (60%). In contrast to the Pd-mediated
coupling, a 1:2 adduct was not obtained as a secondary product.
The yield of 19a was dependent on the concentrations of the
reactants. At low concentrations of dAde and 18a (10-5 M) only
low yields of adducts (<5%) were obtained, but at higher
concentrations (0.5 M) yields of 19a in the range of 60% were
attainable.
Adduct 19a was converted to the BA-3,4-dione-dAde adduct
(2a) via reductive debenzylation with Pd black and 1,4-
cyclohexadiene. The catechol adduct obtained underwent auto-
oxidation in the presence of KF/DMF to furnish 2a in excellent
yield (91%).
Synthesis of the MBA-3,4-dione-dAde adduct (2b) was
carried out by a similar reaction sequence (Scheme 4). 3,4-
Diacetoxy-1-amino-MBA (16b) was prepared from the corre-
sponding amino-quinone (5b) by reduction with H2 over Pd/C
followed by acetylation. Compound 16b was converted into the
bromocatechol derivative (17b) by diazotization with tert-
butylnitrite followed by reaction with Me3SiBr and n-Bu4NBr
at 0 °C. This was transformed into the more stable dibenzyl
derivative (18b) by treatment with benzyl bromide, 18-crown-6
ether, and KOH. Copper-mediated coupling of 18b by the
procedure employed for 18a furnished the coupled adduct 2b
in good yield (79%).
In the case of the DMBA-3,4-dione-dAde adduct, synthesis
of the bromocatechol diacetate derivative (17c) from 5c was
accomplished by a similar reaction sequence, but all attempts
to convert 17c to the dibenzyl derivative 18c provided intractable
mixtures. As a consequence, synthesis of the DMBA-3,4-dione-
dAde adduct could not be achieved.
998 J. Org. Chem., Vol. 73, No. 3, 2008

Adducts of o-Quinone Metabolites of Carcinogenic PAHs
SCHEME 5a
a Reagents and conditions: (i) Nal/Cul/DMEDA/DMSO; (ii) Pd/cyclohexadiene/MeOH; (iii) KF/DMF.
SCHEME 6
Synthesis of dGua Adducts via Copper-Mediated Cou-
pling of Halo Derivatives of PAH Catechols with 2′-
Deoxyribonucleosides (Method D). Synthesis of the BA-3,4-
dione-dGua adduct (3a) via copper-mediated coupling of 18a
with derivatives of 2′-deoxyguanosine was also explored
(Scheme 5). Attempts to couple dGua with 18a in the absence
of a catalyst were unsuccessful, and analogous reaction of 2′-
deoxy-(6-benzyloxy)-guanosine (20) with 18a gave only a low
yield of adduct 21a. However, 20 coupled readily with 18a in
the presence of NaI/CuI and DMEDA in DMSO to yield 21a
(50%). It is likely that 18a is transformed to its more reactive
iodocatechol analogue under these conditions. Complete de-
benzylation of 21a was accomplished by treatment with 1,4-
cyclohexadiene and Pd black in MeOH. The primary catechol
product underwent auto-oxidation in the presence of KF in DMF
to provide 3a (88%).
Synthesis of the MBA-3,4-dione-dGua adduct (3b) via
analogous copper-mediated coupling of 18b with 20 was also
investigated, but the coupled adduct could not be obtained. It
appears the failure of coupling to occur is due to the relative
slow rate of coupling relative to the fast rate of decomposition
of the unstable bromocatechol (or iodocatechol) precursor. This
was confirmed by TLC monitoring, which showed relatively
rapid disappearance of the halobromocatechol under the condi-
tions employed.
involves in the key step coupling a protected aminocatechol,
such as 8a, with a halonucleoside (6a or 6b), and the latter
entails coupling a protected bromocatechol, such as 18a, with
dA or dG. These are the first methods for the synthesis of these
types of adducts to be reported.
The Pd-mediated method was employed successfully for
synthesis of the dAde adducts (2a,b,c) of all three quinones
(1a,b,c) as well as the dGua adducts (3ab,3b) of 1a and 1b.
This approach was shown previously to also provide convenient
synthetic access to the related adducts of BPQ with dAde and
dGua.20 However, attempted synthesis of the dGua adduct of
1c (3c) by this approach was not successful because of the
facility of decomposition of 3c and related compounds.
Cu-mediated coupling was explored because of its potential
advantages over the Pd-mediated method for synthesis of 13C-
and/or 15N-labeled adducts needed as standards for LC-MS-
MS analysis of PAH adduct formed in human cells.33,34
Synthesis of the dAde adducts 2a and 2b by the Cu-mediated
method required protected derivatives of the 1-bromo-BA- and
1-bromo-MBA-3,4-catechols (18a or 18b) as the starting
compounds. However, preliminary experiments strongly indi-
cated that PAH quinones or catechols containing a Br atom in
a bay region, such as 18a or 18b, would be unstable, if they
could be synthesized at all. Despite this, syntheses of 18a and
18b were successfully accomplished by diazotization of ami-
nocatechols 16a and 16b with tert-butylnitrite followed by
reaction with Me3SiBr and n-Bu4NBr and conversion of the
catechol products to dibenzyl ethers. Compounds 18a and 18b
were used directly as starting compounds for synthesis of
adducts 2a and 2b. The adducts were obtained in good yields,
and bis-adducts were not produced as byproducts.
Discussion
Two complementary methods were developed for synthesis
of the adducts formed by the quinone metabolites of carcino-
genic PAHs with 2′-deoxyribonucleosides, a Pd-catalyzed
method and a Cu-catalyzed method (Scheme 6). The former
J. Org. Chem, Vol. 73, No. 3, 2008 999

Ran et al.
FIGURE 6. Examples of PAH carcinogens. The sites of attachment of diol epoxide or quinone metabolites to DNA bases are indicated by arrows.
Attempts to extend the Cu-mediated method to synthesis of
the dAde and dGua adducts of DMBA-3,4-dione (2c and 3c)
were not successful due to decomposition of the products. The
instability of the DMBA-derived compounds is most likely due
to the severe steric crowding in the bay molecular regions of
the adducts.
these methods, whereas the adducts of DBC, BPA, and other
PAHs with a crowded fjord region are likely to be significantly
less stable.
Experimental Section
Both the Pd- and Cu-mediated methods appear to be general
in scope. The Pd method has the disadvantage that bis-adducts
(with two purines per PAH) are secondary products in the
synthesis of the dAde adducts (but not the dGua adducts). The
Cu-mediated method has the advantages that relatively inex-
pensive copper catalysts are used, protection and deprotection
of the sugar hydroxyl groups is not required, bis-adducts are
not obtained as secondary products, and 2′-deoxyribonucleosides
may be used directly in the coupling step (without conversion
to halides). The latter feature is important for synthesis of 15N5-
labeled adducts, because it allows retention of all five 15N-atoms
of the purine in the labeled adducts.
The utility of these methods for synthesis of analogous
adducts of quinone metabolites of other PAH carcinogens merits
comment. Not all PAHs are carcinogens. Some examples of
relatively potent PAH carcinogens are benzo[a]pyrene (BP),39
dibenzo[def,p]chrysene (DBC),40 dibenzo[a,h]anthracene (DBA),42
and benzo[c]phenanthrene (BPA)43 (Figure 6). Carcinogenic
PAHs are distinguished by possession of a bay or fjord region.
It is at these sites (indicated by an arrow) that adduct formation
takes place. Our findings indicate that adducts of PAH quinones
at unsubstituted bay region positions (BA, MBA, BP) are stable
and synthetically accessible by the methods reported, but
analogous adducts at a sterically restricted position (DMBA)
are unstable. We tentatively predict that adducts of the quinone
metabolites of DBA and other PAHs at unsubstituted bay region
positions are likely to be stable and synthetically accessible by
Caution: 7-Methylbenz[a]anthracene (MBA) and 7,12-dimeth-
ylbenz[a]anthracene (DMBA) are carcinogens and should be
handled with appropriate caution following the procedures recom-
mended in the publication NIH Guidelines for the Laboratory Use
of Chemical Carcinogens.
1-Aminobenz[a]anthracene-3,4-dione (5a). To a solution of
benz[a]anthracene-3,4-dione (1a) (0.30 g, 1.16 mmol) in DMF (1.0
mL) was added Me3SiN3 (0.20 g, 1.75 mmol). Caution: exothermic
reaction takes place vigorously with emission of nitrogen gas. The
mixture was stirred at room temperature for 1.5 h, then the solution
was cooled to room temperature and filtered, and the resulting dark
purple solid was washed with EtOAc to yield 5a (0.29 g, 92.0%),
mp >260 °C: 1H NMR (DMSO-d6) δ 5.83 (s, 1H), 7.65 (dd, 2H,
J ) 7.2, 7.2 Hz), 7.92 (d, 1H, J ) 8.4 Hz), 8.15 (d, 1H, J ) 8.0
Hz), 8.24 (d, 1H, J ) 8.0 Hz), 8.34 (d, 1H, J ) 8.4 Hz), 8.75 (s,
1H), 8.98 (br, 2H, NH2), 9.17 (s, 1H); 13C NMR (DMSO-d6) δ
99.44(C-2), 121.02 (C-1), 125.40, 127.08, 127.65, 128.01, 128.12,
128.52, 129.87, 129.97, 131.60, 132.21, 132.55, 132.66, 133.58,
161.39 (C-12), 174.76 (CdO), 183.09 (CdO); HRMS (M + Na+)
calcd for C18H11NO2Na 296.0687, found 296.0684.
1-Amino-7-methylbenz[a]anthracene-3,4-dione (5b). Yield )
1
91%; H NMR (DMSO-d6) δ 3.02 (s, 3H), 5.82 (s, 1H), 7.57 -
7.67 (m, 2H), 7.85 (d, 1H, J ) 9.0 Hz), 8.04 (br, NH2, 2H), 8.14
(d, 1H, J ) 8.0 Hz), 8.31 (d, 1H, J ) 8.6 Hz), 8.49 (d, 1H, J ) 9.1
Hz), 8.93 (s, 1H); 13C NMR (DMSO-d6) δ 14.5 (CH3), 99.5 (C-2),
120.6, 124.9, 125.3, 126.5, 127.0, 127.9, 128.8, 129.2, 130.8, 131.2,
131.7, 131.9, 161.4 (C-12), 174.7 (CdO), 183.1 (CdO); HRMS
(M+ + 1) calcd for C19H13NO2 288.1025, found 288.0998.
1-Amino-3,4-bis-O-TBDMS-benz[a]anthracene (7a). To a
solution of 5a (81.0 mg, 0.3 mmol) in DMSO (3.0 mL) was added
5% Pd/C (8.0 mg). Hydrogen gas was bubbled through the
suspension, and it was stirred at room temperature for 30 min. The
color changed from black to slightly yellow. The Pd/C catalyst was
filtered off and washed with DMSO (1.0 mL). To the filtrate was
added N-tert-butyldimethylsilyl-N-methyltrifluoramide (1.0 mL),
and the resulting mixture was stirred for 1.0 h. Then it was poured
into ice-water, extracted with EtOAc, dried over NaSO4, and
purified by chromatography on silica gel. Elution with hexanes/
EtOAc (30/1) gave 7a as a yellow solid (125.0 mg, 82.8%): 1H
NMR (CDCl3/D2O) δ 0.15 (s, 6H), 0.30 (s, 6H), 1.04 (s, 9H), 1.13
(s, 9H), 6.64 (s, 1H), 7.54 (dd, 2H, J ) 3.0, 6.5 Hz), 7.65 (d, 1H,
J ) 9.0 Hz), 7.93 (d, 1H, J ) 9.0 Hz), 8.01 (dd, 1H, J ) 3.5, 6.0
Hz), 8.30 (s, 1H), 9.60 (s, 1H); 13C NMR (CDCl3) δ -3.5, 18.6,
26.2, 110.5, 114.1, 124.2, 125.3, 125.4, 126.2, 126.3, 126.4, 127.3,
128.1, 128.5, 129.8, 130.7, 131.0, 131.8, 135.4, 139.7, 145.1; HRMS
(M + H+) calcd for C30H42NO2Si2 504.2793, found 504.2784.
(39) Benzo[a]pyrene is commonly employed as a standard for PAHs in
the environment. It is also implicated as a cancer-causative agents in tobacco
smoke.6-9
(40) Dibenzo[def,p]chrysene is the most potent PAH carcinogen currently
known based on rodent bioassays.5,37 Significant levels are present in
cigarette smoke, vehicle exhaust condensate, in the particulate matter formed
in combustion of smoky coal, and in soil and sediment samples: (a)
Reference 7. (b) Mumford, J. L.; Harris, D. B.; Williams, K.; Chuang, J.
C.; Cooke, M. EnViron. Sci. Technol. 1987, 21, 308-311. (c) Kozin, I. S.;
Gooijer, C.; Velthorst, N. H. Justus Liebigs Ann. Chem. 1995, 67, 1623-
1626.
(41) (a) Masuda, Y.; Kagawa, R. Chem. Pharm. Bull. 1972, 20, 2736-
2737. (b) Lacassagne, A.; Buu-Hoi, F.; Zajdela, F. A. Naturwissenschaften
1968, 55, 43.
(42) Dibenzo[a,h]anthracene was the first PAH shown to be carcinogenic.
It is moderately active, ranking between BA and BP in activity.3
(43) Although benzo[c]phenanthrene exhibits weak activity as a tumor
initiator in mouse skin, its bay region anti-diol epoxide shows exceptionally
high activity in rodent bioassays. This difference is apparently due to the
low efficiency of metabolic activation of BPA in mouse skin. Subsequently,
it was shown that the human mammary carcinoma cell line MCF-7 can
activate BPA to an anti-diol epoxide: (a) Levin, W.; Wood, A. W.; Chang,
R. L.; Ittah, Y.; Croisy-Delcey, M.; Yagi, H.; Conney, A. H.; Jerina, D. M.
Cancer Res. 1980, 3910-3914. (b) Einholf, H. J.; Amin, S.; Yagi, H.; Jerina,
D. M.; Baird, W. M. Carcinogenesis 1996, 2237-2244.
1-Amino-3,4-bis-O-TBDMS-7-methylbenz[a]anthracene (7b).
Yield ) 80%; 1H NMR (CDCl3) δ 0.17 (s, 6H), 0.32 (s, 6H), 1.06
(s, 9H), 1.16 (s, 9H), 3.08 (s, 3H), 4.26 (br, NH2, 2H), 6.63 (s,
1H), 7.51 - 7.58 (m, 2H), (dd, 2H, J ) 8.5, 8.5 Hz), 8.04 (d, 1H,
J ) 7.5 Hz), 8.27 (d, J ) 7.5 Hz), 9.52 (s, 1H); 13C NMR (CDCl3)
1000 J. Org. Chem., Vol. 73, No. 3, 2008

Adducts of o-Quinone Metabolites of Carcinogenic PAHs
δ -3.5, -3.6, 14.2, 14.4, 18.6, 18.7, 26.2, 26.3, 110.2, 114.4, 122.4,
122.9, 124.1, 124.9, 125.3, 127.6, 128.8, 129.2, 129.5, 129.6, 129.7,
131.2, 135.1, 139.7, 144.9; HRMS (M +) calcd for C31H43NO2Si2
517.2832, found 517.2822.
2.76 (s, 1.5H), 2.96-3.16 (m, 1H), 3.06 (s, 3H), 4.39-4.43 (m,
2H), 4.48-4.50 (m, 1H), 5.49-5.52 (m, 1H), 6.47 (dd, 0.5H, J )
6.5, 6.5 Hz), 6.51 (dd, 0.5H, J ) 6.5, 6.5 Hz), 7.57-7.64 (m, 2H),
7.82-7.91 (m, 3H), 8.10-8.13 (m, 1H), 8.33 (d, 1H, J ) 8.5 Hz),
8.59 (s, 1H); 13C NMR (CDCl3) δ -3.9, -3.6, -3.4, -3.3, 14.3,
18.7, 18.9, 20.8, 20.9, 21.0, 26.2 and 26.3, 37.2 and 37.6, 63.7 and
63.8, 74.4 and 74.5, 82.5 and 82.6, 84.4 and 84.7, 113.2, 117.0,
121.1, 121.5, 122.7, 124.9, 125.3, 125.4, 125.6, 125.7, 126.4, 127.2,
127.9, 128.4, 128.9, 130.5, 130.8, 131.9, 137.3, 138.4, 138.7, 145.7,
149.0, 151.9, 153.0, 170.3 and 170.4, 170.5 and 170.6; HRMS (M
+Na+) calcd for C46H59N5O7Si2Na 872.3851, found 872.3857.
N6-[1-(Benz[a]anthracene-3,4-dionyl)]-2′-deoxyadenosine (2a).
To a solution of 8a (24.0 mg, 0.03 mmol) in CH2Cl2 (3 mL) was
added a catalytic amount of tetramethylguandine/MeOH solution,
and the mixture was stirred at room temperature for 1.5 h. TLC
indicated reaction to be complete. The product was purified by
chromatography on silica gel. Elution with CH2Cl2/methanol (15:
1) gave the deacetylated product (19.0 mg, 90.7%), 1H NMR
(CDCl3/D2O) δ 0.21 (s, 6H), 0.34 (s, 6H), 1.01 (s, 9H), 1.15 (s,
9H), 2.39 (dd, 1H, J ) 5.0, 8.0 Hz), 3.21 (m, 1H), 3.82 (d, 1H, J
) 12.5 Hz), 4.03 (d, 1H, J ) 12.5 Hz), 4.28 (app s, 1H), 4.75 (app
s, 1H), 4.84 (d, 1H, J ) 5.0 Hz), 6.41 (dd, 1H, J ) 5.0, 9.0 Hz),
7.43 (t, 1H, J ) 8.0 Hz), 7.49 (t, 1H, J ) 8.0 Hz), 7.70 (d, 1H, J
) 10.0 Hz), 7.78 (d, 1H, J ) 10.0 Hz), 7.86 (s, 1H), 7.96 (d, 1H,
J ) 8.5 Hz), 7.98 (d, 1H, J ) 8.5 Hz), 8.01 (s, 1H), 8.31 (s, 1H),
8.45 (s, 1H), 9.49 (s, 1H).
The deacetylated product (16.0 mg, 0.022 mmol) was dissolved
in DMF/H2O (5:2) (3.5 mL), and to the solution was added KF
(5.1 mg, 0.088 mmol). The mixture was stirred at room temperature
for 30 min, and the solvent was evaporated. The dark colored
residue was dissolved in MeOH and purified by chromatography
on silica gel. Elution with CH2Cl2/MeOH (3:1) afforded 2a (10.0
mg, 92%): 1H NMR (CD3OD) δ 2.52 (m, 1H), 2.91 (ddd, 1H, J )
6.5, 6.5, 13.5 Hz), 3.79 (dd, 1H, J ) 3.0, 12.0 Hz), 3.88 (dd, 1H,
J ) 2.5, 12.0 Hz), 4.11 (d, 1H, J ) 2.5 Hz), 4.65 (s, 1H), 5.57 (s,
1H), 6.60 (dd, 1H, J ) 6.5, 6.5 Hz), 7.46 (dd, 1H, J ) 8.0, 8.0
Hz), 7.53 (dd, 1H, J ) 8.0, 8.0 Hz), 8.02 (dd, 2H, J ) 7.5, 7.5
Hz), 8.15 (d, 1H, J ) 8.0 Hz), 8.23 (d, 1H, J ) 8.0 Hz), 8.49 (s,
1H), 8.57 (s, 1H), 8.74 (s, 1H), 10.70 (s, 1H); 13C NMR (CD3OD)
δ 41.62, 63.5, 72.85, 86.92, 89.78, 104.51, 121.94, 125.90, 126.96,
127.73, 128.02, 128.70, 129.07, 130.83, 132.38, 133.02, 133.20,
133.58, 133.78, 134.29, 135.40, 144.47, 152.17, 153.41, 162.84,
165.80, 167.47, 188.92; HRMS (M + Na+) calcd for C28H21N5O5-
Na 530.1440, found 530.1456.
1-Amino-3,4-bis-O-TBDMS-7,12-dimethylbenz[a]an-
thracene (7c). To a solution of 1c (0.29 g, 1.0 mmol) in DMF (3
mL) was added Me3SiN3 (3.2 g, 10.0 mmol). The reaction mixture
was stirred at room temperature until the solution became clear,
and then excess Me3SiN3 was removed by high vacuum to give a
red residue. This was redissolved in DMF (3 mL), and N-tert-butyl-
dimethylsilyl-N-methyl-trifluoric amide (1.0 mL) was added. The
mixture was stirred at room temperature for 3.0 h and worked up
by evaporation of the solvent and flash chromatography on a silica
gel column eluted with hexane/EtOAc (30:1) to give a yellow solid
product (0.45 g). This was dissolved in CH2Cl2 (10 mL), 5% Pd/C
(∼50 mg) was added, and hydrogen gas was bubbled through the
suspension for 1.5 h. The Pd/C was removed by filtration, and the
solvent was evaporated off to give a yellow residue that was purified
by flash chromatography to afford 7c (0.40 g, 80%): 1H NMR
(CDCl3) δ 0.11 (s, 3H), 0.25 (s, 3H), 0.35 (s, 3H), 0.46 (s, 3H),
1.07 (s, 6H), 1.17 (s, 6H), 2.90 (s, 3H), 3.08 (s, 3H), 7.57 - 7.67
(m, 4H), 7.76 (s, 2H), 8.36 (d, 1H, J ) 5.5 Hz), 8.39 (d, 1H, J )
7.0 Hz); 13C NMR (CDCl3) δ -3.9, -3.7, -3.5, -3.3, 14.1, 18.6,
18.7, 20.6, 22.7, 26.2, 26.3, 31.6, 106.9, 113.3, 122.0, 122.2, 124.8,
124.9, 125.1, 125.4, 126.4, 127.4, 127.5, 128.0, 128.9, 130.4, 131.8,
133.4, 139.7, 146.2; HRMS (M + H +) calcd for C32H46NO2Si2
532.3062, found 532.3057.
N6-(3,4-bis-O-TBDMS-benz[a]anthracenyl)-3′,5′-bis-O-acetyl-
2′-deoxyadenosine (8a). To a Telfon sealing tube were added a
solution of (7a) (81.0 mg, 0.16 mmol) and 7a (47.2 mg, 0.13 mmol)
in anhydrous toluene (5 mL), Pd(OAc)2 (2.9 mg, 10%), BINAP
(24.2 mg, 30%), and Cs2CO3 (42.5 mg, 0.13 mmol). The resulting
mixture was purged with argon, sealed, heated to 80-90 °C, and
stirred for 24 h. The reaction was stopped, the solvent was
evaporated off, and the product was purified by chromatography
on silica gel. Elution with hexanes/EtOAc (3:2) gave 7a (38.0 mg)
and 8a (56.0 mg, 53.4%): 1H NMR (CDCl3) δ 0.23 (s,6H), 0.35
(s, 6H), 1.05 (s, 9H), 1.17 (s, 9H), 2.11 (s, 3H), 2.15 (s, 3H), 2.65
(ddd, 1H, J ) 2.2, 6.0, 14.0 Hz), 3.00-3.06 (m, 1H), 4.38-4.40
(m, 2H), 4.47 (dd, 1H, J ) 5.5, 13.4 Hz), 5.48 (dd, 1H, J ) 3.0,
3.0 Hz), 6.48 (dd, 1H, J ) 6.0, 6.0 Hz), 7.41 (dd, 1H, J ) 7.5, 7.5
Hz), 7.48 (dd, 1H, J ) 7.5, 7.5 Hz), 7.71 (d, 1H, J ) 9.0 Hz), 7.77
(d, 1H, J ) 9.0 Hz), 7.87 (s, 1H), 7.97(d, 1H, J ) 9.0 Hz), 7.98 (s,
NH, 1H), 8.02 (d, 1H, J ) 9.0 Hz), 8.30 (s, 1H), 8.37 (s, 1H), 8.48
(s, 1H), 9.57 (s, 1H); 13C NMR (CDCl3) δ -3.6, 18.6, 18.8, 20.8,
20.9, 26.2, 37.4, 63.7, 74.5, 82.5, 84.6, 119.9, 120.0, 121.2, 122.0,
125.0, 125.4, 125.8, 126.6, 126.7, 127.1, 128.0, 128.2, 128.5, 128.8,
131.0, 131.1, 131.8, 138.8, 140.2, 144.6, 149.5, 153.0, 153.3, 170.3,
170.5; HRMS (M + Na+) calcd for C44H55N5O7Si2Na 844.3538,
found 844.3535.
N6-[1-(3,4-bis-O-TBDMS-7-methylbenz[a]anthracenyl)]-3′,5′-
bis-O-acetyl-2′-deoxyadenosine (8b). Yield ) 40%; 1H NMR
(CDCl3) δ 0.24 (s,6H), 0.36 (s, 6H), 1.05 (s, 9H), 1.18 (s, 9H),
2.10 (s, 3H), 2.15 (s, 3H), 2.65 (ddd, 1H, J ) 2.0, 6.0, 14.5 Hz),
2.96-3.06 (m, 1H), 4.36-4.47 (m, 3H), 5.47 (dd, 1H, J ) 3.5, 3.5
Hz), 6.46 (dd, 1H, J ) 6.0, 6.0 Hz), 7.39 (dd, 1H, J ) 7.5, 7.5
Hz), 7.53 (dd, 1H, J ) 7.5, 7.5 Hz), 7.70 (d, 1H, J ) 8.5 Hz), 7.94
(s, 1H), 7.95 (s, 1H), 8.05 (dd, 2H, J ) 10.0, 10.0 Hz), 8.23 (d,
1H, J ) 8.5 Hz), 8.41 (br, 1H), 8.50 (s, 1H), 9.45 (s, 1H); 13C
NMR (CDCl3) δ -3.6, 14.4 (CH3), 18.6, 18.7, 20.7, 20.9, 26.2,
37.3, 63.7, 64.3, 74.5, 82.5, 84.5, 119.3, 120.0, 121.1, 121.8, 122.7,
123.7, 123.9, 124.9, 125.7, 127.5, 127.9, 128.5, 128.7, 129.6, 129.9,
130.1, 131.1, 138.8, 139.7, 144.5, 149.4, 152.8, 153.2, 170.3, 170.4;
HRMS (M+) calcd for C45H57N5O7Si2 835.3797, found 835.3806.
N6-[1-(3,4-bis-O-TBDMS-7,12-dimethylbenz[a]anthracenyl)]-
3′,5′-bis-O-acetyl-2′-deoxyadenosine (8c). Yield ) 46.0%; 1H
NMR (CDCl3/D2O) δ 0.18 (s, 3H), 0.30 (s, 3H), 0.38 (s, 3H), 0.46
(s, 3H), 1.09 (s, 6H), 1.18 (s, 6H), 2.12 (s, 1.5H), 2.14 (s, 1.5H),
2.18 (s, 1.5H), 2.19 (s, 1.5H), 2.66-2.68 (m, 1H), 2.75 (s, 1.5H),
N6-[1-(7-Methylbenz[a]anthracene-3,4-dionyl)]-2′-deoxyade-
nosine (2b). Yield ) 91%; 1H NMR (CD3OD) δ 2.50 (ddd, 1H, J
) 3.2, 6.1, 13.4 Hz), 2.86-2.92 (m, 1H), 3.11 (m, 3H), 3.77 (dd,
1H, J ) 3.2, 12.0 Hz), 3.88 (dd, 1H, J ) 3.2, 12.0 Hz), 4.09 (dd,
1H, J ) 3.2, 6.3 Hz), 4.63 (m, 1H), 5.55 (s, 1H), 6.58 (t, 1H, J )
6.8, 6.8 Hz), 7.43 (t, 1H, J ) 7.0, 7.0 Hz), 7.55 (t, 1H, J ) 8.0, 8.0
Hz), 8.00 (d, 1H, J ) 8.0 Hz), 8.16 (d, 1H, J ) 9.2 Hz), 8.29 (d,
1H, J ) 8.9 Hz), 8.56 (s, 1H), 8.56 (d, 1H, J ) 8.2 Hz), 8.71 (s,
1H), 10.56 (s, 1H); 13C NMR (DMSO) δ 14.5 (CH3), 48.9, 62.1,
70.1, 71.2, 84.2, 88.4, 103.5, 120.7, 124.9, 125.2, 126.2, 127.4,
127.5, 128.6, 129.9, 130.5, 130.7, 130.8, 131.9, 132.1, 132.8, 143.2,
151.4, 152.6, 160.9, 162.2, 163.3, 186.4; HRMS (M + Na+) calcd
for C29H23N5O5Na 544.1597, found 544.1603.
N6-[1-(7,12-Dimethylbenz[a]anthracene-3,4-dionyl)]-2′-deoxy-
1
adenosine (2c). Yield ) 19%; H NMR (DMSO-d6 + D2O) δ
2.29-2.32 (m, 1H), 2.70-2.74 (m, 1H), 3.02 (s, 6H), 3.48-3.61
(m, 2H), 3.87-3.90 (m, 1H), 4.40-4.47 (m, 1H), 5.34 (s, 1H),
6.38 (dd, 1H, J ) 6.8, 6.8 Hz), 7.52 (dd, 1H, J ) 7.0, 7.0 Hz),
7.59 (dd, 1H, J ) 7.0, 7.0 Hz), 7.84 (d, 1H, J ) 9.0 Hz), 8.14 (d,
1H, J ) 9.0 Hz), 8.32 (d, 1H, J ) 9.0 Hz), 8.37 (d, 1H, J ) 9.0
Hz), 8.40 (s, 1H), 8.54 (s, 1H); 13C NMR (DMSO-d6 + D2O) δ
14.3, 24.4, 61.9, 71.0, 84.1, 88.1, 98.1, 119.8, 125.1, 125.5, 125.9,
126.1, 127.0, 127.3, 127.5, 130.8, 131.0, 131.6, 131.8, 134.7, 139.2,
142.0, 151.0, 152.4, 161.9, 163.6, 168.5, 168.6, 186.7; HRMS (M
- H) calcd for C30H24N5O5 534.1777, found 534.1770.
J. Org. Chem, Vol. 73, No. 3, 2008 1001

Ran et al.
N2-[1-(3,4-bis-O-TBDMS-benz[a]anthracenyl)]-3′,5′-bis-O-
acetyl-O6-benzyl-2′-deoxyguanosine (14a). To a solution of 7a
(120.0 mg, 0.24 mmol) and 13 (106.0 mg, 0.24 mmol) in anhydrous
toluene (5 mL) in a sealing tube were added Pd(OAc)2 (5.4 mg,
0.024 mmol), BINAP (44.8 mg, 0.072 mmol), and Cs2CO3 (78.0
mg, 0.24 mmol) in order. The mixture was purged with argon and
then stirred at 85 °C for 48 h. The solvent was evaporated, and the
product was purified by chromatography on a silica gel column.
Elution with hexanes/EtOAc (3/2) afforded 7a (35.0 mg) and 14a
(129 mg, 84%, based on converted 7a): 1H NMR (CDCl3) δ 0.17
(s, 6H), 0.20 (s, 6H), 1.04 (s, 9H), 1.15 (s, 9H), 2.03 (s, 3H), 2.10
(s, 3H), 2.31 (m, 1H), 2.67 (m, 1H), 4.12 ∼ 4.22 (m, 3H), 5.20
(app s), 5.45 (s, 2H), 6.26 (dd, 1H, J ) 7.5, 7.5 Hz), 7.20 ∼ 7.36
(m, 5H), 7.38 (dd, 1H, J ) 8.0, 8.0 Hz), 7.45 (s, 1H), 7.48 (dd,
1H, J ) 7.5, 7.5 Hz), 7.68 (d, 1H, J ) 8.0 Hz), 7.74 (d, 1H, J )
8.0 Hz), 7.76 (s, 1H), 7.96 (d, 1H, J ) 8.0 Hz), 8.02 (d, 1H, J )
8.5 Hz), 8.29 (s, 1H), 9.62 (s, 1H); 13C NMR (CDCl3) δ -3.4,
18.8, 20.8, 21.1, 26.3, 26.34, 29.8, 36.7, 63.6, 68.0, 74.9, 82.3, 84.3,
116.6, 121.0, 121.4, 122.2, 125.4, 125.5, 125.9, 126.4, 126.8, 127.2,
128.0, 128.2, 128.4, 128.5, 128.7, 128.9, 130.3, 131.0, 131.1, 131.8,
136.4, 137.6, 140.4, 144.7, 153.7, 157.4, 161.1, 170.3, 170.5; HRMS
(M + H+) calcd for C51H62N5O8Si2 928.4137, found 928.4130.
N2-[1-(3,4-bis-O-TBDMS-7-methylbenz[a]anthracenyl)]-3′,5′-
bis-O-acetyl-O6-benzyl-2′-deoxyguanosine (134b). Yield ) 82%.
1H NMR (CDCl3) δ 0.19 (s,3H, Si-CH3), 0.22 (s,3H), 0.32 (s,
3H), 0.33 (s,3H), 1.05 (s, 9H), 1.17 (s, 9H), 2.02 (s, 3H), 2.11 (s,
3H), 2.28-2.32 (m, 1H), 2.65-2.70 (m, 1H), 3.08 (s, 3H), 4.08-
4.22 (m, 3H), 5.22 (app. br, 1H), 5.47 (s, 2H), 6.27 (dd, 1H, J )
6.5, 6.5 Hz), 7.25-7.53 (m, 8H), 7.69 (d, 1H, J ) 8.0 Hz), 7.76
(s, 1H), 8.07 (dd, 2H, J ) 10.0, 10.0 Hz), 8.22 (d, 1H, J ) 8.0
Hz), 9.54 (s, 1H); 13C NMR (CDCl3) δ -3.6, -3.5, 14.1, 18.6,
20.6, 20.8, 20.9, 26.1, 26.2, 36.5, 60.3, 63.4, 67.9, 74.7, 82.2, 84.2,
116.4, 120.5, 121.2, 121.9, 122.6, 123.8, 123.9, 124.9, 125.6, 127.5,
127.8, 128.2, 128.3, 128.7, 129.5, 129.6, 129.9, 130.1, 131.1, 136.2,
137.4, 139.8, 144.4, 153.5, 157.1, 160.9, 170.0, 170.3; HRMS (M+)
calcd for C52H63N5O8Si2 941.4215, found 941.4194.
Deacetylation. To a solution of the above residue (30 mg, 0.036
mmol) in MeOH (5 mL) was added tetramethylguandine (15.0 mg).
The mixture was stirred at room temperature for 1.5 h, and then
purified by chromatography on silica gel eluted with hexanes/
EtOAc/CH2Cl2/MeOH (5:5:5:2) to give the deacetylated product
(24.0 mg, 91%): 1H NMR (CD3OD) δ 0.24 (s, 6H), 0.36 (s, 3H),
0.37 (s, 3H), 1.07 (s, 9H), 1.19 (s, 9H), 2.02 (m, 1H), 2.33 (m,
1H), 3.44(dd, 1H, J ) 5.0, 12.0 Hz), 3.48 (dd, 1H, J ) 3.8, 12.0
Hz), 3.81 (d, 1H, J ) 3.6 Hz), 4.18 (t, 1H, J ) 3.0 Hz), 6.07 (t,
1H, J ) 6.6 Hz), 7.34 (s, 1H), 7.47 (dd, 1H, J ) 7.2, 7.2 Hz), 7.50
(dd, 1H, J ) 7.50, 7.50 Hz), 7.81 (d, 1H, J ) 9.4 Hz), 7.91 (d, 1H,
J ) 8.2 Hz), 7.94 (s, 1H), 8.00 (d, 1H, J ) 8.2 Hz), 8.05 (d, 1H,
J ) 8.2 Hz), 8.38 (s, 1H), 9.61 (s, 1H).
Removal of TBDMS. To a solution of the deacetylated product
(24 mg, 0.032 mmol) in DMF (5 mL) and water (2 mL) was added
KF (7.5 mg, 0.12 mmol), and the solution was stirred at room
temperature for 1.5 h. The solvent was evaporated off, and the
product was purified by chromatography on silica gel. Elution with
EtOAc/CH2Cl2 /MeOH (1/1/1) gave 3a (16 mg, 96%): 1H NMR
(CD3OD) δ 2.45 (ddd, 1H, J ) 3.0, 6.0, 13.0 Hz), 2.83 (ddd, 1H,
J ) 6.0, 6.0, 13.0 Hz), 3.71 (dd, 1H, J ) 4.0, 12.5 Hz), 3.84 (dd,
1H, J ) 2.5, 12.0 Hz), 4.02 (d, 1H, J ) 2.5 Hz), 4.55 (t, 1H, J )
3.0 Hz), 5.98 (s, 1H), 6.39 (t, 1H, J ) 7.0 Hz), 7.46 (dd, 1H, J )
8.0, 8.0 Hz), 7.51 (dd, 1H, J ) 8.0, 8.0 Hz), 7.98 (d, 1H, J ) 8.0
Hz), 8.08 (d, 1H, J ) 8.5 Hz), 8.09 (d, 1H, J ) 8.0 Hz), 8.15 (d,
1H, J ) 9.0 Hz), 8.17 (s, 1H), 8.43 (s, 1H), 10.55 (s, 1H);13 C
NMR (CD3OD) δ 40.19, 62.04, 71.37, 85.44, 88.12, 102.58, 120.04,
120.35, 125.44, 126.15, 126.51, 127.13, 127.32, 129.37, 130.85,
131.45, 131.68, 132.21, 132.77, 133.81, 138.26, 149.45, 158.34,
159.70, 166.87, 168.87, 178.89, 187.05; HRMS (M + Na+) calcd
for C28H21N5O6Na 546.1390, found 546.1410.
N2-[1-(7-Methylbenz[a]anthracene-3,4-dionyl)]-2′-deoxygua-
1
nosine (3b). H NMR (DMSO-d6) δ 2.18-2.28 (m, 1H), 2.64-
2.70 (m, 1H), 3.05 (s, 3H), 3.32-3.61 (m, 2H), 3.83 (br, 1H), 4.35
(br. 1H), 5.18 (br, 1H), 5.29 (br, 1H), 5.71 (s, 1H), 6.26 (t, 1H, J
) 4.2 Hz), 7.51 (t, 1H, J ) 7.5, 7.5 Hz), 7.60 (t, 1H, J ) 6.8, 6.8
Hz), 8.00 (d, 1H, J ) 9.0 Hz), 8.13 (s, 1H, Hguanine-8), 8.15 (d, 1H,
J ) 9.0 Hz), 8.31 (d, 1H, J ) 8.8 Hz), 8.50 (d, 1H, J ) 9.0 HZ),
10.44 (s, 1H, H-12); 13C NMR (DMSO-d6) δ 14.1 (CH3), 62.3,
71.3, 83.8, 88.3, 101.7 (?), 120.1, 120.9, 124.9, 125.8, 126.3, 127.4,
127.8, 130.1, 130.5, 130.6, 130.7, 131.0, 131.9, 132.0, 132.3, 134.4,
137.9, 150.1, 156.5, 157.9, 158.2, 165.4, 187.7; HRMS (M+) calcd
for C29H23N5O6 537.1648, found 537.1675.
N2-[1-(Benz[a]anthracene-3,4-dionyl)]-2′-deoxyguanosine (3a).
Debenzylation. Method A. To a solution of 14a (80 mg, 0.088
mmol) in MeOH (10 mL) was added Lindlar catalyst (5% Pd on
calcium carbonate, poisoned by lead, 10 mg). The suspension was
stirred at room temperature for 48 h under hydrogen. TLC indicated
that about half the 14a remained unreacted, but further conversion
failed to take place over longer time. Addition of more catalyst
did not improve the yield. The catalyst was removed by filtration,
and the product was purified by chromatography on a silica gel
column. Elution with hexanes/EtOAc/CH2Cl2/MeOH (5:5:5:1)
provided 14a (40.0 mg, conversion 50%) and the debenzylated
product (32.0 mg, 89%, based on converted 14a): 1H NMR (CD3-
OD) δ 0.18 (s, 3H), 0.25 (s, 3H), 0.34 (s, 3H), 0.40 (s, 3H), 1.07
(s, 9H), 1.17 (s, 9H), 1.72 (dd, 1H, J ) 5.2, 14.0 Hz), 2.17 (m,
1H), 3.36 (dd, 1H, J ) 5.1, 5.1 Hz), 3.74 (dd, 1H, J ) 5.7, 12.0
Hz), 3.91 (dd, 1H, J ) 5.5, 5.5 Hz), 4.74 (d, 1H, J ) 5.8 Hz), 5.85
(dd, 1H, J ) 6.2, 6.5 Hz), 7.29 (s, 1H), 7.40 (dd, 1H, J ) 7.0, 7.0
Hz), 7.46 (dd, 1H, J ) 8.5, 8.5 Hz), 7.65 (s, 1H), 7.80 (d, 1H, J )
9.4 Hz), 7.82 (d, 1H, J ) 8.6 Hz), 7.96 (d, 1H, J ) 8.1 Hz), 8.05
(d, 1H, J ) 9.4 Hz), 8.34 (s, 1H), 9.56 (s, 1H).
1-Amino-3,4-diacetoxybenz[a]anthracene (16a). Hydrogen gas
was bubbled through a solution of 5a (80 mg, 0.29 mmol) and 5%
Pd/C (10.0 mg) in DMF (5 mL) for 30 min (TLC indicated reaction
to be complete). To the resulting suspension were added Ac2O (59
mg, 0.58 mmol) and K2CO3, and the mixture was stirred at room
temperature for 30 min. Then it was poured into water (100 mL),
the Pd/C was filtered off, and the solution was extracted with
EtOAc. Purification by flash chromatography on a silica gel column
eluted with hexane/ EtOAc (3:1) gave 16a (86 mg, 82.3%): 1H
NMR (CDCl3) δ 2.37 (s, 3H), 2.47 (s, 3H), 4.50 (br, 2H), 6.86 (s,
1H), 7.46 (d, 1H, J ) 9.2 Hz), 7.57 (m, 2H), 7.64 (d, 1H, J ) 9.2
Hz), 8.03 (m, 2H), 8.23 (s, 1H), 9.54 (s, 1H); 13C NMR (CDCl3)
δ 20.3, 20.7, 109.8, 117.1, 119.2, 124.5, 125.8, 125.9, 126.9, 127.3,
127.5, 128.5, 129.0, 130.3, 130.6, 130.9, 131.8, 140.3, 144.3, 168.4,
169.0; HRMS (M + Na+) calcd for C22H17NO4Na 382.1055, found
382.1055.
1-Amino-3,4-diacetoxy-7-methyl-benz[a]anthracene (16b). Yield
1
) 83%; H NMR (CDCl3) δ 2.35 (s, 3H), 2.46 (s, 3H), 2.87 (s,
Method B. To a solution of 14a (80 mg, 0.088 mmol) in MeOH
(10 mL) was added 1,4-cyclohexadiene (1.0 mL) and Pd black.
The resulting suspension was stirred at room temperature for 1 h
(TLC indicated reaction was complete). Pd black was filtered off
(caution, may catch fire), and the filtrate was concentrated to give
the debenzylated product (65 mg, 90%) sufficiently pure for the
next step.
3H), 4.30 (br, 2H), 6.78 (s, 1H), 7.42 (d, 1H, J ) 9.7 Hz), 7.53 (t,
1H, J ) 6.8 Hz), 7.58 (t, 1H, J ) 6.8 Hz), 7.88 (d, 1H, J ) 9.6
Hz), 7.97 (d, 1H, J ) 8.1 Hz), 8.20 (d, 1H, J ) 8.5 Hz), 9.30 (s,
1H); 13C NMR (CDCl3) δ 14.3 (CH3), 20.5 (CH3CO), 20.9 (CH3-
CO), 109.7, 117.5, 118.9, 123.1, 124.2, 125.1, 125.4, 125.8, 126.9,
128.3, 128.4, 129.4, 129.9, 130.1, 130.4, 131.2, 140.3, 144.4, 168.6,
169.2; HRMS (M+) calcd for C23H19NO4 373.1314, found 373.1325.
1002 J. Org. Chem., Vol. 73, No. 3, 2008

Adducts of o-Quinone Metabolites of Carcinogenic PAHs
1-Bromo-3,4-diacetoxybenz[a]anthracene (17a). To a solution
of 16a (36 mg, 0.01 mmol) in CH2Br2 (25 mL) in a dry ice bath
(-35 °C) was injected by syringe a solution of t-BuONO (31 mg,
0.03 mmol) in CH2Br2 (2 mL) (2.0 mL) followed by addition of a
solution of TMSBr in CH2Br2 (2.0 mL). The resulting mixture was
stirred at -35 °C for 1.0 h, then allowed to warm to 0 °C, and
poured into saturated sodium bicarbonate solution. Extraction with
CH2Cl2 followed by flash chromatography on a silica gel column
eluted with hexane/EtOAc (5:1) gave 17a (22 mg, 53%): 1H NMR
(CDCl3) δ 2.40 (s, 3H), 2.52 (s, 3H), 7.63 (m, 3H), 7.86 (d, 1H, J
) 9.2 Hz), 7.95 (s, 1H), 8.05 (d, 1H, J ) 9.0 Hz), 8.18 (d, 1H, J
) 9.0 Hz), 8.36 (s, 1H), 10.50 (s, 1H).
5.18 (s, 2H), 5.29 (s, 2H), 6.52 (dd, 1H, J ) 6.0, 6.0 Hz), 7.34-
7.56 (m, 13H), 7.62 (s, 1H), 7.73 (d, 1H, J ) 9.5 Hz), 7.94 (d, 1H,
J ) 8.5 Hz), 8.00 (d, 1H, J ) 9.5 Hz), 8.13 (s, 1H), 8.28 (s, 1H),
8.50 (s, 1H), 9.61 (s, 1H); 13C NMR (CD3OD) δ 41.7, 63.7, 72.4,
73.1, 76.9, 87.3, 90.0, 117.4, 121.8, 123.0, 126.4, 126.8, 127.1,
127.8, 128.3, 129.1, 129.2, 129.3, 129.4, 129.5, 129.6, 129.8, 132.4,
132.6, 132.7, 133.3, 138.4, 139.0, 143.9, 150.8, 153.5; HRMS (M
+ H+) calcd for C42H36N5O5 690.2716, found 690.2738.
N6-[1-(3,4-Dibenzyloxy-7-methylbenz[a]anthracenyl)]-2′-deoxy-
1
adenosine (19b). Yield ) 79%; H NMR (DMSO-d6) δ 2.28-
2.32 (m, 1H), 2.75-2.79 (m, 1H), 3.01 (s, 3H), 3.52-3.55 (m,
1H), 3.62-3.65 (m, 1H), 3.90 (br, 1H), 4.43 (br, 1H), 5.18 (s, 2H),
5.20 (d, 1H, J ) 5.5 Hz), 5.31 (s, 2H), 5.34 (d, 1H, J ) 3.5 Hz),
6.41 (t, 1H, J ) 7.0 Hz), 7.35-7.58 (m, 13 H), 7.62 (s, 1H), 8.02
(d, 1H, J ) 9.8 Hz), 8.07 (s, 1H), 8.17 (d, 1H, J ) 9.8 Hz), 8.27
(d, 1H, J ) 8.8 Hz), 8.55 (s, 1H), 9.67 (s, 1H), 10.41 (s, 1H); 13C
NMR (DMSO) δ 14.5 (CH3), 62.3, 70.8, 71.3, 75.4, 84.4, 88.4,
120.8, 122.3, 124.7, 128.3, 128.5, 128.7, 128.8, 128.9, 129.4, 129.9,
130.1, 131.1, 137.2, 137.8, 141.7, 149.0, 152.6, 154.3; HRMS (M
+ Na+) calcd for C43H37N5O5Na 726.2692, found 726.2697.
N2-[1-(3,4-Dibenzyloxybenz[a]anthracenyl)]-2′-deoxy-(6-ben-
zyloxy)-guanosine (21a). To a solution of 18a (2.6 mg, 0.005
mmol) and 2′-deoxy-(6-benzyloxy)-guanosine (20) (1.8 mg, 0.007
mmol) were added Cs2CO3 and DMEDA (0.2 mg, 0.001 mmol),
and the solution was stirred at 100 °C under argon for 4.0 h. The
solution was cooled to ambient temperature, and water (10 mL)
and NH4OH (1.0 mL of 40% solution) were added. The resulting
blue solution was extracted with EtOAc, and the extracts were
combined, concentrated, and purified by flash chromatography on
a silica gel column. Elution with CH2Cl2/MeOH (8:1) gave 21a
(2.3 mg, 57%): 1H NMR (DMSO) δ 2.08-2.32 (m, 2H), 3.77 (m,
1H), 4.20 (m, 1H), 4.80 (m, 1H), 5.17 (s, 2H), 5.22 (m, 1H), 5.33
(s, 2H), 6.20 (m, 1H), 7.18-7.51 (m, 10 H), 7.57 (d, 1H, J ) 7.5
Hz), 7.63 (d, 1H, J ) 7.5 Hz), 7.68 (s, 1H), 7.82 (d, 1H, J ) 10
Hz), 7.97 (d, 1H, J ) 10 Hz), 8.02 (d, 1H, J ) 8.0 Hz), 8.11 (s,
1H), 8.42 (s, 1H), 9.67 (s, 1H), 9.74 (s, 1H); 13C NMR (DMSO-
d6) δ 62.1, 67.1, 62.1, 70.8, 71.2, 75.4, 75.4, 83.6, 88.2, 116.3,
121.0, 125.6, 127.5, 128.1, 128.2, 128.3, 128.4, 128.5, 128.6, 128.7,
128.8, 128.9, 129.0, 129.1, 130.9, 131.6, 136.7, 137.3, 137.7, 149.3,
157.6, 160.2; HRMS (M + H+) calcd for C49H42N5O5 796.3130,
found 796.3138.
1-Bromo-3,4-diacetoxy-7-methylbenz[a]anthracene (17b). 1H
NMR (CDCl3) δ 2.40 (s, 3H), 2.51 (s, 3H), 3.02 (s, 3H), 7.50-
7.63 (m, 3H), 8.07 (d, 1H, J ) 8.5 Hz), 8.14 (d, 1H, J ) 10.0 Hz),
8.27 (d, 1H, J ) 8.5 Hz), 8.69 (d, 1H, J ) 9.0 Hz), 8.95 (s, 1H).
1-Bromo-3,4-dibenzyloxybenz[a]anthracene (18a). To a solu-
tion of 17a (21 mg, 0.05 mmol) in DMF (5.0 mL), a catalytic
amount 18-crown-6, and benzyl bromide (171 mg, 0.1 mmol) under
argon was added KOH (5.7 mg, 1.0 mmol). The reaction mixture
was stirred at room temperature for 1.0 h and then poured into
ice-water (50 mL). The resulting yellow precipitate was collected
by filtration to give 18a (25 mg, 95.0%) pure enough for the next
step: 1H NMR (CDCl3) δ 5.20 (s, 2H), 5.31 (s, 2H), 7.38-7.60
(m,12H), 7.73 (d, 1H, J ) 12.0 Hz), 7.76 (s, 1H), 8.00 (d, 1H, J )
10.0 Hz), 8.03 (dd, 1H, J ) 2.8, 6.5 Hz), 8.15 (dd, 1H, J ) 2.8,
6.5 Hz), 8.30 (s, 1H), 10.42 (s, 1H); 13C NMR (CDCl3) δ 71.5,
75.7, 114.3, 120.2, 121.8, 123.7, 125.6, 126.0, 126.2, 126.3, 127.1,
127.6, 127.8, 128.1, 128.2, 128.4, 128.5, 128.6, 128.8, 129.0, 130.0,
130.9, 131.0, 131.4, 136.2, 137.1, 143.1, 148.9; HRMS (M + Na+)
calcd for C32H23BrO2Na 541.0774, found 541.0770.
1-Bromo-3,4-dibenzyloxy-7-methylbenz[a]anthracene (18b).
Yield ) 91%; 1H NMR (CDCl3) δ 3.07 (s, 3H), 5.28 (s, 2H), 5.31
(s, 2H), 7.39-7.57 (m, 12H), 7.73 (s, 1H), 8.00 (d, 1H, J ) 10.0
Hz), 8.08 (d, 1H, J ) 10.0 Hz), 8.12 (d, 1H, J ) 8.0 Hz), 8.28 (d,
1H, J ) 8.0 Hz), 10.18 (s, 1H); 13C NMR (CDCl3) δ 14.4 (CH3),
71.5 (CH2), 75.7 (CH2), 114.3, 119.9, 121.8, 124.1, 124.3, 124.8,
124.9, 125.3, 126.1, 127.5, 127.6, 128.1, 128.2, 128.5, 128.6, 129.3,
129.6, 129.7, 130.3, 130.4, 136.3, 137.2, 142.9, 148.9; HRMS (M
+ H+) calcd for C33H26BrO2 533.1116, found 533.1132.
N6-[1-(3,4-Dibenzyloxybenz[a]anthracenyl)]-2′-deoxyadenos-
ine (19a). To a solution of 18a (5.2 mg, 0.01 mmol) in DMSO
(20.0 µL) were added adenine hydrate (2.7 mg, 0.01 mmol), CuI
(0.4 mg, 0.002 mmol), N,N′-dimethylethylenediamine (0.2 mg,
0.002 mmol), and Cs2CO3 (3.3 mg, 0.01 mmol). The flask was
flushed with argon, and the solution was heated at 110 °C for 8 h.
After completion of the reaction, the mixture was diluted with
EtOAc and subjected to silica gel flash chromatography with
EtOAc/CH2Cl2/MeOH (6/6/1) to give 19a (5.6 mg, 82%): 1H NMR
(CD3OD) 2.47 (m, 1H), 2.88 (m, 1H), 3.78 (dd, 1H, J ) 3.5, 7.8
Hz), 3.89 (dd, 1H, J ) 3.5, 7.8 Hz), 4.12 (m, 1H), 4.62 (m, 1H),
Acknowledgment. This investigation was supported by NIH
Grants (P01 CA 92537, R01 CA039504, R01 ES015857, and
P30 ES3508).
Supporting Information Available: 1H and 13C NMR spectra
of reported compounds. This material is available free of charge
via the Internet at http://pubs.acs.org.
JO701667U
J. Org. Chem, Vol. 73, No. 3, 2008 1003