Highly diastereoselective synthesis of nucleoside adducts from the carcinogenic benzo[a]pyrene diol epoxide and a computational analysis

Article abstract of DOI:10.1021/ja063902u

A diastereoselective synthesis of the nucleoside adducts corresponding to a cis ring-opening of the carcinogen (±)-7β,8α-dihydroxy- 9α,10α-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BaP DE-2) by 2′-deoxyadenosine and 2′-deoxyguanosine is described. The key

Full text of DOI:10.1021/ja063902u

Published on Web 12/13/2006
Highly Diastereoselective Synthesis of Nucleoside Adducts
from the Carcinogenic Benzo[a]pyrene Diol Epoxide and a
Computational Analysis
Mahesh K. Lakshman,*,† John C. Keeler,§ Felix N. Ngassa,§, John H. Hilmer,†
Padmanava Pradhan,†,‡ Barbara Zajc,*,† and Kathryn A. Thomasson*,§
Contribution from the Department of Chemistry, The City College and The City UniVersity of
New York, 138th Street at ConVent AVenue, New York, New York 10031-9198, Department of
Chemistry, UniVersity of North Dakota, Abbott Hall Room 236, 151 Cornell Street Stop 9024,
Grand Forks, North Dakota 58202-9024, and Department of Chemistry, Grand Valley State
UniVersity, 1 Campus DriVe, Allendale, Michigan 49401-9403
Received June 14, 2006; E-mail: lakshman@sci.ccny.cuny.edu; kthomasson@chem.und.edu
Abstract: A diastereoselective synthesis of the nucleoside adducts corresponding to a cis ring-opening of
the carcinogen (()-7â,8R-dihydroxy-9R,10R-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BaP DE-2) by 2′-
deoxyadenosine and 2′-deoxyguanosine is described. The key intermediate (()-10R-amino-7â,8R,9R-
trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene was synthesized by a highly diastereoselective dihydroxylation
wherein phenylboronic acid was a water surrogate. The resulting boronate ester was converted to a tetraol
derivative in which two of the four hydroxyl groups (trans 7, 8) were protected as benzoate esters while the
remaining two (cis 9, 10) were free. The cis glycol entity was then subjected to a reaction with
1-chlorocarbonyl-1-methylethylacetate to yield an intermediate chloro monoacetoxy dibenzoate. Displace-
ment of the halide with azide, complete cleavage of the esters, and catalytic reduction of the azide yielded
the requisite amino triol. Fluoride displacement from appropriately protected nucleoside derivatives,
6-fluoropurine 2′-deoxyribonucleoside and 2-fluoro-2′-deoxyinosine, by the amino triol then yielded
diastereomeric pairs of diol epoxide-adducted 2′-deoxyadenosine (dA) and 2′-deoxyguanosine (dG)
nucleosides. Small aliquots of these adducts were separated for characterization purposes. The present
approach provides the first diastereoselective synthesis of the cis adducts of BaP DE-2 with 2′-
deoxyguanosine as well as the first synthesis of both dA and dG adducts from a common intermediate. An
1
informative analysis of the H NMR spectra of the cis adducts synthesized and comparisons to the trans
adducts are reported. To gain insight into the diastereoselectivity in the key dihydroxylation step, a
computational analysis, including molecular mechanics (MMFF94) and semiempirical AM1 geometry
optimizations, yielded results that are in fairly good agreement with the experimental observations.
upon the disposition of the benzylic hydroxyl and the oxirane.2
In the series 1 compounds these are on the same side of the
Introduction
Polycyclic aromatic hydrocarbons, products of activities in
modern society, are a class of compounds that are widely
prevalent in the environment. Several members of this class that
are alternant hydrocarbons, possessing a bay region, are potent
carcinogens.1 In mammalian systems, the biological activity of
these compounds stems from their metabolism wherein bay
region diol epoxides are formed by the combined actions of
cytochrome P450 and epoxide hydrolase. Thus, any given
hydrocarbon is converted to four isomeric diol epoxides that
are classified as series 1 (DE-1) and series 2 (DE-2), depending
molecule, whereas in the series 2 isomers these are on opposite
sides. Benzo[a]pyrene (BaP) is a hydrocarbon that has received
significant attention due to its environmental presence and the
high carcinogenicity of its diol epoxide metabolites. Figure 1
shows the structures of the series 1 and 2 diol epoxides of this
compound.
The mechanism of action of diol epoxides is attributed to
their electrophilic nature. In the presence of DNA, diol epoxides
covalently bind to the exocyclic amino groups of 2′-deoxyad-
enosine (dA) and 2′-deoxyguanosine (dG) via a putative
carbocation that is produced by protonation and ring-opening
of the oxirane.3 Such a reaction therefore produces a net 16
nucleoside adducts. Since the four isomeric diol epoxides have
markedly different potencies, with only the (+)-BaP DE-2 being
† The City College and The City University of New York.
‡ NMR Facility Manager, The City College of New York.
§ University of North Dakota.
Grand Valley State University.
(1) Reviewed in: Polycyclic Aromatic Hydrocarbon Carcinogenesis: Structure-
ActiVity Relationships; Yang, S. K., Silverman, B. D., Eds.; CRC Press:
Boca Raton, FL, 1988; Vols. I and II. Polycyclic Aromatic Hydrocarbons:
Chemistry and Carcinogenicity; Harvey, R. G., Ed.; Cambridge University
Press: Cambridge, U.K., 1991. Polycyclic Hydrocarbons and Carcino-
genesis; Harvey, R. G., Ed.; ACS Symposium Series 283; American
Chemical Society: Washington, DC, 1985.
(2) Thakker, D. R.; Levin, W.; Wood, A. W.; Conney, A. H.; Yagi, H.; Jerina,
D. M. In Drug Stereochemistry-Analytical Methods and Pharmacology;
Wainer, I. W., Drayer, D. E., Eds.; Marcel Dekker: Inc.: New York, 1988;
pp 271-296.
9
68
J. AM. CHEM. SOC. 2007, 129, 68-76
10.1021/ja063902u CCC: $37.00 © 2007 American Chemical Society

Synthesis of PAH Nucleoside Adducts
A R T I C L E S
Figure 1. Structures of the series 1 and series 2 diol epoxides of BaP.
oligomer via modified solid-phase synthesis procedures.10
Despite being somewhat labor intensive, it is more flexible and
versatile in providing access to any DNA oligomer so long as
synthetic routes are available to the individual diol epoxide-
nucleoside adducts. Although diol epoxides are good electro-
philes, the relatively low nucleophilicity of the nucleoside amino
groups prompts the nucleophile-electrophile role reversal in
our approach. Thus, diol epoxides are either directly converted
to amino triols via amminolysis10a or they are converted to azido
triols via reaction with azide anion, that are then peracylated
and reduced to yield amino triacyl derivatives.11,12 These amino
hydrocarbon derivatives are then coupled with electrophilic
nucleosides to produce the diol epoxide-nucleoside adducts.10
Studies by us and others have led to the understanding that
fluoro nucleosides possess sufficient reactivity to couple with
the sterically hindered, less reactive, bay-region amines.13 We
have used such an approach for the synthesis of DNA adducts
arising by a trans ring-opening of (()-BaP DE-1 and DE-2.14
In contrast to the relatively easy access to the amino triol
derivatives arising by a trans ring-opening of the diol epoxides,
synthesis of the isomeric cis ring-opened amino triols is less
trivial. The latter amino triols are key entities for the synthesis
of nucleoside adducts arising by a cis ring-opening of the diol
Figure 2. Structures of the eight nucleoside adducts (4dA + 4dG) formed
from (()-BaP DE-2.
highly tumorigenic,4 it is likely that the structural features
associated with each covalent adduct influence the biological
outcome. Figure 2 shows the structures of the eight nucleoside
adducts formed from (+)- and (-)-BaP DE-2.
To gain a greater insight into these structure-activity factors,
research has been directed toward the synthesis of DNA
fragments that contain site-specific modifications with stere-
ochemically defined diol epoxide lesions. Such site-specifically
modified DNA are valuable probes for structural studies by
NMR5 and biological experimentation.6 For the synthesis of diol
epoxide adducted DNA three approaches have been adopted:
(a) direct reaction of DNA oligomers with diol epoxides,7 (b)
reaction of DNA containing reactive nucleosides with stere-
ochemically defined hydrocarbon amino triols,8 and (c) synthesis
of individual nucleoside-diol epoxide adducts which are
subsequently introduced into DNA.9,10
(6) For some representative examples see: (a) Kramata, P.; Zajc, B.; Sayer, J.
M.; Jerina, D. M.; Wei, C. S.-J. J. Biol. Chem. 2003, 278, 14940-14948.
(b) Huang, X.; Kolbanovskiy, A.; Wu, X.; Zhang, Y.; Wang, Z.; Zhuang,
P.; Amin, S.; Geacintov, N. E. Biochemistry 2003, 42, 2456-2466. (c)
Xie, Z.; Braithwaite, E.; Guo, D.; Zhao, B.; Geacintov, N. E.; Wang, Z.
Biochemistry 2003, 42, 11253-11262. (d) Zou, Y.; Shell, S. M.; Utzat, C.
D.; Luo, C.; Yang, Z.; Geacintov, N. E.; Basu, A. K. Biochemistry 2003,
42, 12654-12661. (e) Khan, Q. A.; Kohlhagen, G.; Marshall, R.; Austin,
C. A.; Kalena, G. P.; Kroth, H.; Sayer, J. M.; Jerina, D. M.; Pommier, Y.
Proc. Natl. Acad. Sci. U.S.A. 2003, 100, 12498-12503. (f) Zou, Y.; Ma,
H.; Minko, I. G.; Shell, S. M.; Yang, Z.; Qu, Y.; Xu, Y.; Geacintov, N. E.;
Lloyd, R. S. Biochemistry 2004, 43, 4196-4205. (g) Zang, H.; Harris, T.
M.; Guengerich, F. P. Chem. Res. Toxicol. 2005, 18, 389-400. (h)
Baskunov, V. B.; Subach, F. V.; Kolbanovskiy, A.; Kolbanovskiy, M.;
Eremin, S. A.; Johnson, F.; Bonala, R.; Geacintov, N. E.; Gromova, E. S.
Biochemistry 2005, 44, 1054-1066.
We have been involved with method (c), the total synthesis
approach, wherein individual nucleoside adducts are synthesized
and subsequently introduced into specific sites of any DNA
(3) Jerina, D. M.; Chadha, A.; Cheh, A. M.; Schurdak, M. E.; Wood, A. W.;
Sayer, J. M. In Biological ReactiVe Intermediates IV; Witmer, C. M.,
Snyder, R., Jollow, D. J., Kalf, G. F., Kocsis, J. J., Sipes, I. G., Eds.; Plenum
Press: New York, 1991; pp 533-553.
(4) Jerina, D. M.; Sayer, J. M.; Agarwal, S. K.; Yagi, H.; Levin, W.; Wood,
A. W.; Conney, A. H.; Pruess-Schwartz, D.; Baird, W. M.; Pigott, M. A.;
Dipple, A. In Biological ReactiVe Intermediates III; Kocsis, J. J., Jollow,
D. J., Witmer, C. M., Nelson, J. O., Snyder, R., Eds.; Plenum Press: New
York, 1986; pp 11-30.
(7) (a) Cosman, M.; Ibanez, V.; Geacintov, N. E.; Harvey, R. G. Carcinogenesis
1990, 11, 1667-1672. (b) Mao, B.; Xu, J.; Li, B.; Margulis, L. A.; Smirnov,
S.; Ya, N.-Q.; Courtney, S. H.; Geacintov, N. E. Carcinogenesis 1995, 16,
357-365.
(8) (a) Kim, S. J.; Stone, M. P.; Harris, C. M.; Harris, T. M. J. Am. Chem.
Soc. 1992, 114, 5480-5481. (b) Harris, T. M.; Harris, C. M.; Kim, S. J.;
Han, S.; Kim, H.-Y.; Zhou, L. Polycyclic Aromat. Compd. 1994, 6, 9-16.
(c) DeCorte, B. L.; Tsarouhtsis, D.; Kuchimanchi, S.; Cooper, M. D.;
Horton, P.; Harris, C. M.; Harris. T. M. Chem. Res. Toxicol. 1996, 9, 630-
637. (d) Cooper, M. D.; Hodge, R. P.; Tamura, P. J.; Wilkinson, A. S.;
Harris, C. M.; Harris, T. M. Tetrahedron Lett. 2000, 41, 3555-3558.
(9) (a) Steinbrecher, T.; Becker, A.; Stezowski, J. J.; Oesch, F.; Seidel, A.
Tetrahedron Lett. 1993, 34, 1773-1774. (b) Lee, H.; Luna, E.; Hinz, M.;
Stezowski, J. J.; Kiselyov, A. S.; Harvey, R. G. J. Org. Chem. 1995, 60,
5604-5613.
(5) For a review see: Geacintov, N. E.; Cosman, M.; Hingerty, B. E.; Amin,
S.; Broyde, S.; Patel, D. J. Chem. Res. Toxicol. 1997, 10, 111-146. For
other recent representative examples, see: (a) Sayer, J. M.; Shah, J. H.;
Liang, C.; Xie, G.; Kroth, H.; Yagi, H.; Liu, X.; Yeh, H. J. C.; Jerina, D.
M. Polycyclic Aromat. Compd. 1999, 17, 95-104. (b) Suri, A. K.; Mao,
B.; Amin, S.; Geacintov, N. E.; Patel, D. J. J. Mol. Biol. 1999, 292, 289-
307. (c) Mao, B.; Gu, Z.; Gorin, A.; Chen, J.; Hingerty, B. E.; Amin, S.;
Broyde, S.; Geacintov, N. E.; Patel, D. J. Biochemistry 1999, 38, 10831-
10842. (d) Li, Z. I.; Kim, H.-Y.; Tamura, P. J.; Harris, C. M.; Harris, T.
M.; Stone, M. P. Biochemistry 1999, 38, 2969-2981. (e) Li, Z.; Kim, H.
-Y.; Tamura, P. J.; Harris, C. M.; Harris, T. M.; Stone, M. P. Biochemistry
1999, 38, 14820-14832. (f) Li, Z.; Kim, H.-Y.; Tamura, P. J.; Harris, C.
M.; Harris, T. M.; Stone, M. P. Biochemistry 1999, 38, 16045-16057. (g)
Volk, D. E.; Rice, J. S.; Luxon, B. A.; Yeh, H. J. C.; Liang, C.; Xie, G.;
Sayer, J. M.; Jerina, D. M.; Gorenstein, D. G. Biochemistry 2000, 39,
14040-14053. (h) Pradhan, P.; Tirumala, S.; Liu, X.; Sayer, J. M.; Jerina,
D. M.; Yeh, H. J. C. Biochemistry 2001, 40, 5870-5881. (i) Lin, C. H.;
Huang, X.; Kolbanovskii, A.; Hingerty, B. E.; Amin, S.; Broyde, S.;
Geacintov, N. E.; Patel, D. J. J. Mol. Biol. 2001, 306, 1059-1080. (j) Li,
Z.; Tamura, P. J.; Wilkinson, A. S.; Harris, C. M.; Harris, T. M.; Stone,
M. P. Biochemistry 2001, 40, 6743-6755. (k) Kim, H.-Y. H.; Wilkinson,
A. S.; Harris, C. M.; Harris, T. M.; Stone, M. P. Biochemistry 2003, 42,
2328-2338.
(10) (a) Lakshman, M. K.; Sayer, J. M.; Jerina, D. M. J. Am. Chem. Soc. 1991,
113, 6589-6594. (b) Lakshman, M. K.; Sayer, J. M.; Yagi, H.; Jerina, D.
M. J. Org. Chem. 1992, 57, 4585-4590. (c) Lakshman, M. K.; Sayer, J.
M.; Jerina, D. M. J. Org. Chem. 1992, 57, 3438-3443.
(11) (a) Lakshman, M.; Nadkarni, D. V.; Lehr, R. E. J. Org. Chem. 1990, 55,
4892-4897. (b) Lakshman, M. K.; Chaturvedi, S.; Lehr, R. E. Synth.
Commun. 1994, 24, 2983-2988.
(12) Steinbrecher, T.; Wameling, C.; Oesch, F.; Seidel, A. Angew. Chem., Int.
Ed. Engl. 1993, 32, 404-406.
(13) (a) Lakshman, M.; Lehr, R. E. Tetrahedron Lett. 1990, 31, 1547-1550.
(b) Kim, S. J.; Harris, C. M.; Jung, K.-Y.; Koreeda, M.; Harris, T. M.
Tetrahedron Lett. 1991, 32, 6073-6076.
(14) Chaturvedi, S.; Lakshman, M. K. Carcinogenesis 1996, 17, 2747-2752.
9
J. AM. CHEM. SOC. VOL. 129, NO. 1, 2007 69

A R T I C L E S
Lakshman et al.
Scheme 1
epoxides. Cis epoxide ring-opening of (()-BaP DE-2 7,8-bis-
O-TMS ether derivative by Ti(OiPr)4/TMSN3 in THF has been
reported.15,16 However, the factors leading to this unusual
stereochemical outcome are not known, and when the method
was applied to 7,8-bis-O-TMS ether derivative (()-BaP DE-1,
a 1.5:1 ratio of cis/trans ring-opening products was obtained.17
The synthetic challenges have therefore resulted in efforts that
circumvent the need for the amino triols. For example, adducts
corresponding to a cis ring-opening of (()-BaP DE-2 by dA
have been synthesized by an amino hydroxylation method
involving the exocyclic amino group of dA and the olefin (()-
trans-7,8-dihydroxy-7,8-dihydro BaP.17 Whereas this method
seems to work well for the synthesis of the cis dA adducts of
(()-BaP DE-2, no comparable chemistry has been reported for
the dG system. On the other hand, cis dG adducts of BaP DE-2
have been synthesized via a direct ring-opening of the racemic
diol epoxide with O6-allyl-3′,5′-bis-O-(tert-butyldimethylsilyl)-
2′-deoxyguanosine. In one such method the diol epoxide was
allowed to react with the protected dG derivative in N,N-
dimethylacetamide at 90-100 °C.18 This reaction produced a
mixture of trans and cis adducts in a ∼1:1.4 ratio, total 47%
yield after purification.18 This was followed by a report
involving a “solvent-free” reaction in which (()-BaP DE-2 was
mixed with the protected dG and a few drops of CH2Cl2 in a
mortar, which upon standing overnight produced a ∼6:1 mixture
of trans and cis adducts in a combined yield of 54%.19 More
recently, a direct reaction of (()-BaP DE-2 and protected dG
in trifluoroethanol was reported.20 This reaction yielded a
combined 43% of the trans and cis adducts in a 1.5:1 ratio.20 In
each of these methods, the trans adducts were separated from
the cis isomers by HPLC. Interestingly, when 3′,5′-bis-(O-tert-
butyldimethylsilyl)-2′-deoxyadenosine was allowed to react with
(()-BaP DE-2 under the various conditions the results were as
follows; under solvent-free conditions low (∼5%) yield of the
adducts was obtained,19 whereas in trifluoroethanol a 33% yield
of only the cis ring-opening product was observed.20
(()-10R-amino-7â,8R,9R-trihydroxy-7,8,9,10-tetrahydro BaP.
This amino triol when coupled with C-6 and C-2 fluoro purine
nucleosides afforded the corresponding dA and dG adducts of
(()-BaP DE-2. The basis of the high diastereoselection observed
in a critical synthetic step has also been evaluated by molecular
mechanic and semiempirical AM1 computations and these
results are in fairly good agreement with the experimental
observations.
Results and Discussion
Synthesis and Compound Characterization. Our planned
synthesis of the key intermediate (()-10R-amino-7â,8R,9R-
trihydroxy-7,8,9,10-tetrahydro BaP dictated that the C-7 and
C-8 hydroxyls remain protected, and this task would be simplest
with a suitably protected dihydrodiol. Therefore, our synthesis
commenced from the readily available 7,8-bis-benzoyloxy-7,8-
dihydro BaP (1) that can be prepared on the multigram scale in
three steps from commercially available 7-hydroxy-7,8,9,10-
tetrahydrobenzo[a]pyren-7-ol.22 Dihydrodibenzoate 1 under
catalytic dihydroxylation conditions yielded a mixture of two
compounds that could be separated with some difficulty (4 and
6 in Scheme 1). The 1H NMR spectra of the separated
compounds after complete deprotection (NH3/MeOH, 50 °C)
and reacetylation (Ac2O/pyridine/DMAP) indicated that these
were two tetraol tetraacetates. Comparison of the NMR spectra
of the two products to reported data for 7â,8R,9â,10â-
tretraacetoxy-7,8,9,10-tetrahydro BaP (5) as well as 7â,8R,9R,-
10R-tetraacetoxy-7,8,9,10-tetrahydro BaP (7), that have been
independently prepared by hydrolysis reactions of BaP DE-1
and DE-2,23 showed that the major product from the dihydroxy-
lation of 1 was 6. To ascertain the ratio of the two products, in
one dihydroxylation reaction of 1, the mixture of tetraol
dibenzoate products 4 and 6 were debenzoylated and reacety-
lated. On the basis of the proton integrals of the mixture, the
ratio of 5:7 was determined to be ∼1:4.
Cis ring-opening of BaP DE-2 by the exocyclic amino group
of dG can be accomplished in direct reactions with DNA.
Although some control of cis versus trans ring-opening can be
exercised in these reactions by variation of reaction conditions,
the reactions typically produce both cis and trans ring-opening
products that need separation.21 There are to date no diastereo-
selective total syntheses of the adducts corresponding to a cis
ring-opening of (()-BaP DE-2 by dG. Herein we disclose a
novel, highly diastereoselective synthesis of a key intermediate
(15) Jhingan, A. K.; Meehan, T. J. Chem. Res. (S) 1991, 122-123.
(16) In our hands, the ring-opening of (()-BaP DE-2 7,8-bis-O-TMS ether with
Ti(OiPr)4/TMSN3 in THF (ref 15) led to the formation of two compounds
as observed by TLC, each containing TMS groups. We have also found
that cis ring-opening of (()-BaP DE-2 7,8-bis-O-TMS can be attained with
BF3‚Et2O/TMSN3 to yield the corresponding azido triol in about 30% yield.
(17) Pilcher, A. S.; Yagi, H.; Jerina, D. M. J. Am. Chem. Soc. 1998, 120, 3520-
3521.
(18) Kroth, H.; Yagi, H.; Seidel, A.; Jerina, D. M. J. Org. Chem. 2000, 65,
5558-5564.
(19) Ramesha, A. R.; Kroth, H.; Jerina, D. M. Org. Lett. 2001, 3, 531-533.
(20) Ramesha, A. R.; Kroth, H.; Jerina, D. M. Tetrahedron Lett. 2001, 42, 1003-
1005.
(21) (a) Cosman, M.; de los Santos, C.; Fiala, R.; Hingerty, B. E.; Ibanez, V.;
Luna, E.; Harvey, R.; Geacintov, N. E.; Broyde, S.; Patel, D. J. Biochemistry
1993, 32, 4145-4155. (b) Cosman, M.; de los Santos, C.; Fiala, R.;
Hingerty, B. E.; Singh, S. B.; Ibanez, V.; Margulis, L. A.; Live, D.;
Geacintov, N. E.; Broyde, S.; Patel, D. J. Proc. Natl. Acad. Sci. U.S.A.
1992, 89, 1914-1918. (c) Cosman, M.; Hingerty, B. E.; Luneva, N.; Amin,
S.; Geacintov, N. E.; Broyde, S.; Patel, D. J. Biochemistry 1996, 35, 9850-
9863. (d) Funk, M.; Ponte´n, I.; Seidel, A.; Jernstro¨m, B. Bioconjugate Chem.
1997, 8, 310-317. (e) Personal communication Dr. Monique Cosman
(Lawrence Livermore National Laboratories).
This direct dihydroxylation of 1 was unfortunately not ideal
due to the formation of two compounds that were not easily
separable. We therefore decided to analyze the dihydroxylation
of other protected dihydrodiol derivatives. For this we chose
the 7,8-bis-(tert-butyldimethylsilyl)ether derivative 3. This
compound was readily prepared from 1 by hydrolysis to the
dihydrodiol 2 and subsequent silylation with tert-BuMe2SiOTf
/Et3N (5 mol equiv each) in CH2Cl2 (92% yield). Dihydroxyl-
ation of 3 with OsO4 (1.1 mol equiv) in pyridine yielded, after
(22) McCaustland, D. J.; Engel, J. F. Tetrahedron Lett. 1975, 16, 2549-2552.
(23) Yagi, H.; Thakker, D. R.; Hernandez, O.; Koreeda, M.; Jerina, D. M. J.
Am. Chem. Soc. 1977, 99, 1604-1611.
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70 J. AM. CHEM. SOC. VOL. 129, NO. 1, 2007

Synthesis of PAH Nucleoside Adducts
A R T I C L E S
Table 1. Scalar Coupling Constants of the Tetrahydro Ring Protons of Compounds 1-3 in Different Solventsa
JH7,H8
JH7,H9
JH8,H9
JH8,H10
JH9,H10
solvent
1
2
3
1
2
3
1
2
3
1
2
3
1
2
3
CDCl3
7.5
7.4
7.7
7.0
7.5
11.0
11.2
11.2
11.5
11.3
9.9
8.5
8.0
8.6
9.0
0.0
0.9
0.0
0.0
0.0
0.0
1.0
0.0
0.0
0.0
0.0
0.9
0.0
0.0
0.0
3.6
3.7
3.4
3.7
2.1
1.9
2.3
2.3
2.0
3.7
2.4
3.1
3.1
2.9
2.8
1.3
1.5
2.0
1.2
1.2
1.9
1.5
2.4
2.3
2.6
2.1
1.8
1.5
1.5
1.4
10.2
10.3
10.1
10.1
10.2
10.0
10.1
10.1
10.1
10.1
10.2
9.9
9.4
10.3
9.9
CD2Cl2
(CD3)2CO
THF-d8
C5H5N
a Data was obtained at ambient temperature, at 500 MHz.
one recrystallization from MeOH, a single tetraol bis-silyl ether
8 (85% yield), the structure of which was confirmed by
desilylation and peracetylation to 7. These observations led us
to initially investigate the factors leading to the observed
diastereoselectivities in the dihydroxylation of 1 and 3. Although
the addition of OsO4 in these reactions occurred predominantly
from the same side as the allylic hydroxyl group, reminiscent
of the allylic hydroxyl-mediated epoxidation, we believe that
the facial selectivity of the dihydroxylation reactions was likely
not H-bonding driven. This rationale was based on the observa-
tion that dihydrodiol 2 and its bis-(tert-butyldimethylsilyl) ether
3 undergo the same facial addition by OsO4. We also reasoned
that the facial selectivity observed in the reactions of 1 and 3
was dependent on the conformation of the angular dihydro ring
as determined by the C-7, C-8 substituents. For this purpose
we briefly investigated the H-7 to H-8 coupling constants as a
function of solvent. This data as well as other coupling constants
are shown in Table 1.
Analysis of the JH7,H8 data shown in Table 1 immediately
indicates that the dihydrodiol 2 exhibits a quasi-diequatorial
arrangement of the hydroxyls, almost to an extreme. Addition-
ally, the JH7,H8 in 2 is relatively independent of the solvent
polarity. These observations are consistent with the proposal
that in the dihydrodiol an intramolecular hydrogen bond exists
between the two hydroxyls.24 On the other hand, protection of
the hydroxyls in 1 and 3 removes the hydrogen bond, and greater
flexibility is observed along with a greater diaxial orientation
of the substituents. Among the two protected dihydrodiols, the
bis-silyl derivative 3 is more conformationally flexible and
exhibits a greater diequatorial orientation of the substituents than
dibenzoate 1. We believe that the greater the preference for the
diequatorial orientation of the substituents, the greater the
diastereoselection observed in the OsO4 dihydroxylation. Thus,
dihydrodiol 2 yields a single detectable tetraol diastereomer,
and a similar phenomenon is likely with the bis-silyl compound
3. On the other hand, in the case of dibenzoate 1 where a greater
preference for the diaxial substituents is seen compared to that
in 2 and 3, two tetraol dibenzoates are produced.
Figure 3. Plausible substituent interactions leading to the product distribu-
tion in the dihydroxylation.
side as the allylic C-8 OR substituent [Figure 3 pathway (b)].
Therefore, such a torsional steering25 is perhaps the origin of
the diastereoselectivities observed, rendering pathway (b) more
favorable than (a). Such a rationale as well as the data in Table
1 suggests that the greater the propensity for diequatorial
orientation of the substituents in the dihydrodiol, the greater
the contribution to the favored route.
Although these studies formed a basis for understanding
conformational influences leading to the diastereoselection, the
difficulty in separating 4 from 6 as well as the fact that 8 could
not be used for further reactions (explained later) raised the need
for a facile route to 6. Use of PhB(OH)2 as water surrogate in
OsO4-mediated dihydroxylation has been reported.26 It has also
been possible to influence the facial selectivity of dihydroxyl-
ation by this modified method.27 In the current context we
wondered about the course of the dihydroxylation of 1 in the
presence of PhB(OH)2. We reasoned that the short B-O bonds
in conjunction with the formation of fused 6- and 5-membered
ring systems in the product would likely increase the contribu-
tion of path (b).
As shown in Scheme 2, boronate 9 was obtained by the
reaction of 1 with catalytic OsO4/NMO/PhB(OH)2 in CH2Cl2.
This reaction, which was generally high yielding, could be
readily conducted on the multigram scale, with a simple
precipitation from hexanes sufficient to purify 9. Within the
detection limits of a 500 MHz instrument, the 1H NMR spectrum
of the product obtained via this procedure showed the presence
of a single boronate isomer. This boronate 9 was then oxidized
with 50% H2O2 in 2:1 acetone-EtOAc to yield a tetraol
dibenzoate also in generally good yield. Determination of the
facial selectivity in the conversion of 1 f 9 came at the stage
of boronate cleavage. The tetraol dibenzoate was completely
The observed diastereoselectivities can be rationalized on the
basis of the transition-state structures leading to the two
diastereomeric diol products in these cases. Inspection of
molecular models suggests that dihydroxylation from the
opposite side to the allylic C-8 OR substituent [Figure 3 pathway
(a)] would lead to eclipsing interactions between the substituents
on C-8 (shown in red) and those on C-9 (shown in blue). On
the other hand, the substituents at C-8 and C-9 would be in a
staggered conformation if the addition occurred from the same
(25) Martinelli, M. J.; Peterson, B. C.; Khau, V. V.; Hutchison, D. R.; Leanna,
M. R.; Audia, J. E.; Droste, J. J.; Wu, Y.-D.; Houk, K. N. J. Org. Chem.
1994, 59, 2204-2210.
(26) Iwasawa, N.; Kato, T.; Narasaka, K. Chem. Lett. 1988, 1721-1724. (b)
Sakurai, H.; Iwasawa, N.; Narasaka, K. Bull. Chem. Soc. Jpn. 1996, 69,
2585-2594.
(24) (a) Tierney, B.; Burden, P.; Hewer, A.; Ribeiro, O.; Walsh, C.; Rattle, H.;
Grover, P. L.; Sims, P. J. Chromatogr. A 1979, 176, 329-335. (b) Zajc,
B.; Grahek, R.; Kocijan, A.; Lakshman, M. K.; Kosˇmrlj, J.; Lah, J. J. Org.
Chem. 2003, 68, 3291-3294.
(27) Gypser, A.; Michel, D.; Nirschl, D. S.; Sharpless, K. B. J. Org. Chem.
1998, 63, 7322-7327.
9
J. AM. CHEM. SOC. VOL. 129, NO. 1, 2007 71

A R T I C L E S
Scheme 2
Lakshman et al.
hydrolyzed and peracetylated as before. The resulting tetraol
tetraacetate was identical to 7 whose structure had been
independently confirmed by comparison to the hydrolysis
products of (()-BaP DE-2.23 This indicated that the boronate
formation had occurred from the same side as the allylic
benzoate.
With the diastereoselectivity of the boronate formation
established, the next stages in the synthesis centered around the
selective conversion of the benzylic hydroxyl in 6 to an amino
functionality with an overall retention of stereochemistry. We
have reported that reaction of 1-aryl ethylene glycols with
1-chlorocarbonyl-1-methylethyl acetate (R-acetoxy-isobutyryl
chloride) yields reverse, trans chlorohydrin acetates, with a
benzylic halide.28 Application of this approach in the present
case should provide an intermediate with a benzylic chloride
that can then be manipulated to yield an amine. The overall
approach for the synthesis of (()-10R-amino-7â,8R,9R-trihy-
droxy-7,8,9,10-tetrahydro BaP is shown in Scheme 3.
compound 11 was isolated, purified, and characterized. Cleavage
of all ester linkages yielded azido triol 12. Finally, catalytic
reduction of the azide moiety provided amino triol 13 (the
corresponding salt could be obtained if the reduction was
performed in the presence of 6 M HCl).
Attempted reaction of the tetraol bis-silyl ether 8 with
1-chlorocarbonyl-1-methylethylacetate was not very promising.
This may be due either to the incompatibility of silyl groups to
HCl formed in the reaction or because the benzoate groups of
6 provide electronic stabilization of the benzylic chloro inter-
mediate 10 that the silyl groups do not offer.
In order to compare amino triol 13 with the diastereomeric
(()-10â-amino-7â,8R,9R-trihydroxy-7,8,9,10-tetrahydro BaP
(product of trans ring-opening of (()-BaP DE-2) as well as
other tetrahydro BaP derivatives, a small portion of 13 was
converted to the tetraacetate. Table 2 is a listing of key chemical
shifts and coupling constants in a series of different tetrahydro
BaP derivatives. Clearly, the greatest difference lies in the H7-
H8 coupling constant, with derivatives arising by a trans epoxide
opening displaying a predominantly diequatorial orientation of
the substituents (J7,8 ) 8.3-9.5 Hz). On the other hand, in the
products corresponding to a cis ring-opening the substituents
adopt a more diaxial orientation (J7,8 ) 3.4-4.0 Hz).
Scheme 3
With the synthesis of the amino triol and the relative
stereochemical assignment completed, the final stage in the
synthesis was the preparation of the dA and dG adducts.
Although we and others have developed metal-mediated reac-
tions for the assembly of carcinogen-nucleoside lesions,29 the
presence of free hydroxyl groups was a consideration. In order
to avoid unwanted problems, displacement of fluoride from
fluorinated nucleosides10,14,30 was the method chosen for the
present work. Reactions of 6-fluoro-9-(2-deoxy-3,5-bis-O-(tert-
butyldimethylsilyl)-â-D-erythropentofuranosyl)purine and 3′,5′-
bis-O-(tert-butyldimethylsilyl)-2-fluoro-2′-deoxyinosine with 13
were conducted in DMSO in the presence of N,N-diisopropyl-
Reaction of 6 with 1-chlorocarbonyl-1-methylethylacetate in
CH3CN yielded the putative intermediate 10. Since the benzylic
halide on such an extended aryl system was expected to be
highly labile, direct displacement of the chloride by azide was
performed immediately upon workup. The resulting azido triacyl
Scheme 4
9
72 J. AM. CHEM. SOC. VOL. 129, NO. 1, 2007

Synthesis of PAH Nucleoside Adducts
A R T I C L E S
Table 2. Chemical Shifts and Coupling Constants of the Tetrahydro Ring Protons in a Series of BaP Derivatives
ethylamine and hexamethyldisiloxane at 85-90 °C to yield the
corresponding 2′-deoxyadenosine and 2′-deoxyguanosine ad-
ducts, respectively (Scheme 4). Reactions leading to the dA
adduct pair 14a, 15a proceeded in good yield (65-70%),
whereas those leading to the dG adduct pair 16a, 17a were lower
yielding (∼30-40%).
Small amounts of pure diastereomers from each pair were
separated and characterized as their triacetates (14b-17b) via
NMR spectroscopy. Since the chemical shift differences between
the individual cis and trans ring-opened adducts could be
important in the analysis of DNA structures containing them, a
comparison of key chemical shift data is provided in Table 3.
The chemical shifts of the sugar and the tetrahydrobenzo ring
protons of the adducted mononucleotides were unequivocally
assigned from an analysis of corresponding 2-D NOESY and
COSY spectra. Of the two benzylic resonances (H-10 and H-7),
H-10 was easily identified from its coupling to both H-9 and
the amino NH. Assignment of H-10 was also confirmed from
NOE interaction with H-11. On the other hand, H-7 showed
NOE with H-6 singlet.
Good line shape and resolution for the dA adducts were
observed in CDCl3 (deacidified) or acetone-d6, and the NMR
spectra can be obtained conveniently in either. The dG adducts,
on the other hand, provided good line shape and resolution only
in DMSO-d6, and this appears to be the case with such
hydrocarbon adducts generally. As can be seen from Table 3,
among the pairs of dA adducts derived from a cis or trans
opening, the differences in chemical shifts of the protons shown
are relatively small (|δ∆| ) 0.01-0.09 ppm for both the cis
and trans ring-opened pairs). In contrast, among the pairs of
(28) (a) Lakshman, M. K.; Zajc, B. Tetrahedron Lett. 1996, 37, 2529-2532.
(b) Lakshman, M. K.; Chaturvedi, S.; Zajc, B.; Gibson, D. T.; Resnick, S.
M. Synthesis 1998, 1352-1356.
(29) (a) Reviewed, in Lakshman, M. K. Curr. Org. Synth. 2005, 2, 83-112.
(b) Johnson, F.; Bonala, R.; Tawde, D.; Torres, M. C.; Iden, C. R. Chem.
Res. Toxicol. 2002, 15, 1489-1494. (c) Lakshman, M. K.; Gunda, P. Org.
Lett. 2003, 5, 39-42.
(30) Zajc, B.; Lakshman, M. K.; Sayer, J. M.; Jerina, D. M. Tetrahedron Lett.
1992, 33, 3409-3412.
9
J. AM. CHEM. SOC. VOL. 129, NO. 1, 2007 73

A R T I C L E S
Lakshman et al.
Table 3. Chemical Shift Data for the Cis and Trans Ring-Opened
(()-BaP DE-2 Nucleoside Adducts
adducta
H-1′
H-2′â
H-2′R
H-7
H-8
H-9
H-10
2′-Deoxyadenosine Adducts via Cis Ring-Opening of BaP DE-2b,c
10S
10R
6.46
6.48
2.67
2.58
2.45
2.43
6.65
6.66
5.74
5.75
6.01
6.00
7.15
7.16
2′-Deoxyadenosine Adducts via Trans Ring-Opening of BaP DE-2b,d,e
10S
10R
6.47
6.43
2.61
2.70
2.45
2.43
6.78
6.76
5.90
5.91
6.15
6.14
6.58
6.59
2′-Deoxyguanosine Adducts via Cis Ring-Opening of BaP DE-2d,f
10S
10R
6.37
6.28
2.75
3.20
2.39
2.25
6.52
6.53
5.60
5.61
5.80
5.84
6.58
6.59
2′-Deoxyguanosine Adducts via Trans Ring-Opening of BaP DE-2d,e,f
10S
10R
6.37
6.26
2.66
3.32
2.37
2.17
6.68
6.67
5.75
5.76
5.96
5.90
6.01
5.98
Figure 5. Structures of diastereomeric tetraol dibenzoates and their boronate
esters with torsion angles (BaP1 is the major isomer 6 in Scheme 1 and
BaPB1 is isomer 9 isolated in Scheme 2).
a
R and S refer to the configuration at the point of attachment (C-10) of
the BaP moiety to the amino group of the nucleoside. b Obtained in CDCl3.
c
d
Acquired at 600 MHz.
Acquired at 500 MHz. e Independently
Table 4. Monte Carlo Torsion Angles for the Tetraol Dibenzoates
and Their Boronate Esters (deg)
synthesized and analyzed. f Obtained in DMSO-d6.
angle
atoms
BaP1a
BaP2
BaPB1b
BaPB2
ø′R
ø′â
ø′1
ø′2
ø′3
ø′4
ø′5
H-O-C-H
H-O-C-H
CsC-B-O
C-B-O-C
B-O-C-H
B-O-C-H
C-B-O-C
-73.2
-71.1
-
73.8
96.8
-
-
-
-37.8
-107.2
-145.8
80.5
-
-
-24.7
119.1
137.2
-75.9
-144.6
-
-
-
-
-
-
-
-
132.1
a
b
The BaP1 isomer is favored by 86%. The BaPB1 isomer is favored
by 99%.
In a study of a large database of DNA chemical shifts,31 the
center of the shift distributions of the H-2′ protons in pyrimidines
is 2.0 ppm, and that of the purines is 2.6 ppm, with very little
overlap between them. The chemical shifts of the deoxyribose
ring protons, especially those at C-2′, are predicted to be affected
by the magnitude of glycosidic torsion angle that results from
ring current and the local magnetic anisotropy of their bases.32
In the case of the BaP adducts, the presence of the pyrene ring
can greatly affect the chemical shifts of the sugar protons due
to the ring current of the fairly large aromatic residue. A
preliminary examination of the spatial proximity of the BaP
ring to the sugar moieties in the dA and dG adducts has been
conducted by molecular modeling (MM2). As may be antici-
pated, in the case of the dG adducts the pyrene ring is closer to
the deoxyribose moiety, whereas in the case of the dA adducts
the pyrene ring is farther away. Consistent with this, the
chemical shifts of the 2′ protons of the dA adducts are influenced
to a lesser extent by the BaP residue than those of the dG.
For purposes of comparison Figure 4 shows the CD spectra
of BaP dA and dG adducts resulting from cis and trans ring-
opening. Although the literature amply documents CD spectra
of such PAH diol epoxide-nucleoside adducts, Figure 4
highlights some differences. Whereas the cis and trans ring-
opened dA adduct pair bear a nearly mirror image relationship,
the cis and trans ring-opened dG adduct pair show subtly
different CD spectra. Thus, these minor differences may be
related to the stereochemistry of the epoxide ring-opening.
However, the CD spectra are consistent with previously
published CD data of BaP-nucleoside adducts.33
Figure 4. Circular dichroism spectra (in MeOH) of four out of the eight
(()-BaP DE-2 dA and dG adducts. Panel A shows a pair of dA adducts:
blue ) 10S trans, red ) 10R cis. Panel B shows a pair of dG adducts: blue
) 10S trans, red ) 10R cis.
dG adducts these chemical shift differences become larger ((|δ∆|
) 0.01-0.45 ppm for the cis ring-opened pair and 0.01-0.66
ppm for the trans ring-opened pair). In terms of the magnitude
of the difference, the protons most affected are the H-2′â in
each case, followed by H-2′R and then H-1′. Among the dG
adducts, the 10R isomers show significantly downfield shifted
H-2′â, and this is more pronounced for the trans adduct. The
stereochemical disposition of the 2′-protons in the adducted
mononucleosides was obtained from the NOESY spectra of one
adduct from each pair. In this analysis the more upfield H-2′
displayed a stronger NOE with H-1′ and hence was labeled as
R. Correspondingly, the more downfield H-2′ was labeled â.
(31) van de Ven, F. J. M.; Hilbers, C. W. Nucleic Acids Res. 1988, 16, 5713-
5726.
(32) Wijmenga, S. S.; Kruithof, M.; Hilbers, C. W. J. Biomol. NMR 1997, 10,
337-350.
9
74 J. AM. CHEM. SOC. VOL. 129, NO. 1, 2007

Synthesis of PAH Nucleoside Adducts
A R T I C L E S
Table 5. AM1 Torsion Angles for the Tetraol Dibenzoates and
Their Boronate Esters (deg)
at the point of reaction and where the isomers differ in absolute
configuration are considered.
angle
atoms
BaP1a
BaP2
BaPB1b
BaPB2
The geometries resulting for the AM1 calculations (Table 5)
yield heats of formation (Table B in the Supporting Information)
that also favor the BaP1 and BaPB1 isomers. The standard
thermodynamic quantities computed at 298.15 K and 1.00 atm
also favor BaP1 and BaPB1 in both the enthalpic and entropic
contributions, but the enthalpic contributions dominate (Table
C in the Supporting Information). The energy difference and
Boltzmann weighting factors calculated using the solvation
potential energies (Table D in the Supporting Information) also
favor the BaP1 isomer.
ø′R
ø′â
ø′1
ø′2
ø′3
ø′4
ø′5
H-O-C-H
H-O-C-H
CsC-B-O
C-B-O-C
B-O-C-H
B-O-C-H
C-B-O-C
-69.3
-71.8
-
164.8
78.5
-
-
-
-
-
-5.6
179.2
121.0
-112.4
176.4
0.9
-
-
-178.7
-118.9
114.8
-178.6
-
-
-
-
-
-
a
b
The BaP1 isomer is favored by 95-96%. The BaPB1 isomer is
favored by 88%.
Computational Analysis. The potential energies of the
lowest-energy conformations obtained after the Monte Carlo
(MC) conformational searches for the compounds in Figure 5
show that for the BaP tetraol dibenzoate pair (BaP1 and BaP2),
BaP1 dominates, and for the pair of boronate esters (BaPB1
and BaPB2), BaPB1 dominates (Table A in the Supporting
Information). Of the flexible torsion angles in the tetraol
dibenzoates and their boronate esters (Table 4), there are two
torsion angles for each of the tetraol dibenzoate isomers and
five for each of their boroate esters. Only those torsion angles
For the tetraol dibenzoate and their boronate isomers,
compared to the torsion angles of the MC geometries, the torsion
angles of the AM1 geometries are more symmetrical for the
various isomers in which the angles are almost the same in
magnitude but differ in direction (Tables 4 and 5). Although
there are small variations in the energy differences (see the
Computational Analysis section in the Supporting Information),
all methods of determining equilibrium molecular geometries
Figure 6. Structures of the tetraol dibenzoates BaP1 (A), BaP2 (B), as well as the corresponding boronate analogues BaPB1 (C) and BaPB2 (D), resulting
from calculation of the electron density surface onto which the value of the electrostatic potential has been mapped. The different values of the electrostatic
potential at the surface are represented by different colors: red represents regions of most negative electrostatic potential, blue represents regions of most
positive electrostatic potential, and green represents regions of zero potential. Potential increases in the order red < orange < yellow < green < blue.
9
J. AM. CHEM. SOC. VOL. 129, NO. 1, 2007 75

A R T I C L E S
Lakshman et al.
consistently agree on which isomer is dominant. Indeed, the
predictions are borne out experimentally as well.
more significant when considering the minor DNA adducts
formed. For instance, in a direct reaction of (7R,8S,9S,10R)-
BaP DE-2 with DNA, of the total nucleoside adducts formed,
the cis ring-opened dA and dG adducts are only ∼1% each.35
With (7S,8R,9R,10S)-enantiomer, within detection limits, no cis
ring-opened dA adducts were observed.35 Since minor or
undetected adducts could play a disproportionate role in
carcinogenesis, the present synthesis allows access to the
unstudied, cis ring-opened BaP DE-2 adduct.5c In the course
of this synthesis we have also uncovered factors that control
facial selectivity of addition to BaP dihydrodiol and its
derivatives. To understand these, computational techniques have
been utilized. The results from the computation parallel quite
closely the observed facial selectivities in the key OsO4
dihydroxylation leading to either the tetraol dibenzoates or the
boronate esters. Although computational approaches have been
used to understand conformational aspects of diol epoxide-
nucleoside adducts and their impact on biochemical processes,36
a computation-based understanding of the chemistry of PAH
derivatives has been lacking. The combination of molecular
mechanics with quantum mechanics offers a useful approach
in the computational evaluation of flexible organic molecules,
and could offer insight into other reactions of PAH derivatives
that may assist in developing chemical syntheses such as those
described here.
Structures resulting from the calculation of electron density
surfaces (Figure 1 A-D in the Supporting Information) and
calculation of electron density surfaces onto which the value
of the electrostatic potential is mapped (Figure 6 A-D) depict
the conformational arrangement of the major and minor isomers.
The electrostatic potential is the hypothetical energy of a positive
test charge at some location around a molecule. The electrostatic
potential is positive in a region of excess positive charge, and
charge-molecule interaction is repulsive. Similarly, in a region
of excess negative charge, the electrostatic potential is negative,
and the charge-molecule interaction is attractive. The electro-
static potential is shown by mapping it onto a surface of electron
density, which depicts the size of the molecule, obtained from
quantum mechanical calculation. An electrostatic potential map
is a good indication of the size and shape of a molecule, the
charge distribution, and the site of chemical reactivity.
Experimental Section
Synthesis and Compound Characterization. For space consider-
ations all synthetic procedures and compound characterization details
are provided in the Supporting Information.
Computational Analysis. A computational search of the isomeric
tetraol derivatives of BaP (Figure 5) was performed with the molecular
modeling package PC SPARTAN Pro (Wavefunction, Inc.) using a
Monte Carlo (MC) method plus the MMF94 force field. The minimum
energy structures were next subjected to a semiempirical quantum
mechanical geometric optimization using AM1. Following AM1
calculation, the energy due to solvation for the tetraol dibenzoate
isomers was calculated using the SM5.4 model of Chambers et al.
(Table D in the Supporting Information).34 Details of the computational
procedures can be found in the Supporting Information.
Acknowledgment. This paper is dedicated to Prof. Roland
E. Lehr (1942-2003), a mentor and colleague. Support of this
work by NIH Grants 1R15 CA094224-01 (NCI) and S06
GM008168-24S1 (NIGMS) to M.K.L., ND EPSCoR Grant to
K.A.T., ND EPSCoR Doctoral Dissertation Fellowship to F.N.N.
Support via NIH RCMI Grant 5G 12 RR03060-20 at CCNY is
gratefully acknowledged. Dr. M. Cosman is thanked for useful
discussions and S. Patil for performing one adduct-forming
reaction.
Conclusions
In conclusion, we have developed an efficient, highly
diastereoselective synthesis of (()-10R-amino-7â,8R,9R-trihy-
droxy-7,8,9,10-tetrahydrobenzo[a]pyrene, a key component for
preparing nucleoside adducts of the carcinogen BaP DE-2
corresponding to a cis ring-opening of the oxirane in the
metabolite. This amino triol was used for the synthesis of the
nucleoside conjugates, and in this process good yields of the
dA adducts were realized. Although the yields leading to the
dG adducts were modest, we are currently considering methods
wherein the described chemistry can be modified and coupled
with Pd-catalysis, methodology that has proven to be highly
effective for the synthesis of these types of adducts.29 The
chemical syntheses of carcinogen-nucleoside adducts becomes
Supporting Information Available: Complete experimental
details including those for the computational analysis; 1H NMR
spectra for the BaP derivatives 3, 6, 8, 9, 11-13, and nucleoside
adducts 14b-17b. This material is available free of charge via
the Internet at http://www.pubs.acs.org.
JA063902U
(35) Szeliga, J.; Dipple, A. Chem. Res. Toxicol. 1998, 11, 1-11.
(36) For examples see: (a) Xie, X.-M.; Geacintov, N. E.; Broyde, S. Chem.
Res. Toxicol. 1999, 12, 597-609. (b) Xie, X.-M.; Geacintov, N. E.; Broyde,
S. Biochemistry 1999, 38, 2956-2968. (c) Tan, J.; Geacintov, N. E.; Broyde,
S. Chem. Res. Toxicol. 2000, 13, 811-822. (d) Kozack, R.; Seo, K.-Y.;
Jelinsky, S. A.; Loechler, E. L. Mutat. Res. 2000, 450, 41-59. (e) Seo,
K.-Y.; Jelinsky, S. A.; Loecher, E. L. Mutat. Res. 2000, 463, 215-246. (f)
Ruan, Q.; Zhuang, P.; Li, S.; Perlow, R.; Srinivasan, A. R.; Lu, X.-J.;
Broyde, S.; Olson, W. K.; Geacintov, N. E. Biochemistry 2001, 40, 10458-
10472. (g) Yan, S. F.; Wu, M.; Geacintov, N. E.; Broyde, S. Biochemistry
2004, 43, 7750-7765.
(33) Cheng, S. C.; Hilton, B. D.; Roman, J. M.; Dipple, A. Chem. Res. Toxicol.
1989, 2, 334-340.
(34) Chambers, C. C.; Hawkins, G. D.; Cramer, C. J.; Truhlar, D. G. J. Phys.
Chem. 1996, 100, 16385-16398.
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76 J. AM. CHEM. SOC. VOL. 129, NO. 1, 2007