Palladium-catalyzed synthesis of nucleoside adducts from bay- and fjord-region diol epoxides

Article abstract of DOI:10.1021/jo070204z

(Chemical Equation Presented) Palladium-catalyzed C-N bond formation has been utilized to synthesize covalent 2′-deoxyadenosine (dA) and 2′-deoxyguanosine (dG) adducts of benzo[a]pyrene (BaP) series 1 (syn) and benzo[c]phenanthrene (BcPh) series 2 (anti)

Full text of DOI:10.1021/jo070204z

Palladium-Catalyzed Synthesis of Nucleoside Adducts from Bay-
and Fjord-Region Diol Epoxides
Elise Champeil,†,‡ Padmanava Pradhan,† and Mahesh K. Lakshman*,†
Department of Chemistry, The City College and The City UniVersity of New York, 138th Street at ConVent
AVenue, New York, New York 10031, and Department of Sciences, John Jay College of Criminal Justice,
899 Tenth AVenue, New York, New York 10019
lakshman@sci.ccny.cuny.edu
ReceiVed January 31, 2007
Palladium-catalyzed C-N bond formation has been utilized to synthesize covalent 2′-deoxyadenosine
(dA) and 2′-deoxyguanosine (dG) adducts of benzo[a]pyrene (BaP) series 1 (syn) and benzo[c]-
phenanthrene (BcPh) series 2 (anti) diol epoxides. For this, (()-10R-amino-7â,8R,9â-trisbenzoyloxy-
7,8,9,10-tetrahydro BaP and (()-1â-amino-2R,3R,4â-trisbenzoyloxy-1,2,3,4-tetrahydro BcPh were coupled
with 6-halo-9-[3,5-bis-O-(tert-butyldimethylsilyl)-â-D-erythro-pentofuranosyl]purine and O6-benzyl-3′,5′-
bis-O-(tert-butyldimethylsilyl)-2-bromo-2′-deoxyinosine, using a (()-BINAP-Pd complex and Cs2CO3.
For the synthesis of the dA adducts, both the 6-chloro- as well as the 6-bromopurine nucleoside derivatives
were analyzed for the C-N coupling reaction with the hydrocarbon amino tribenzoates. With the BaP
amino tribenzoate, the 6-chloronucleoside provided satisfactory results, whereas the 6-bromo analogue
proved to be superior with the BcPh amino tribenzoate. Overall, lower yields of the dA adducts were
obtained with the more hindered fjord-region BcPh amino tribenzoate as compared to the bay-region
BaP amino tribenzoate. In contrast to reactions leading to the dA adducts, the C-N reactions of both
BaP and BcPh amino tribenzoates with the 2-bromo-2′-deoxyinosine derivative proceeded in comparable
yields. This seems to indicate that such Pd-catalyzed adduct forming reactions at the C-6 position may
be influenced by steric constraints of the amine component, whereas those at the C-2 position are less
sensitive. Diastereomeric adduct pairs were separated and characterized by spectral methods and by
comparisons to adducts produced by direct displacement reactions as well as those formed from DNA
alkylation by diol epoxides.
Introduction
carcinogenic activity by alkylation of cellular DNA.5-7 This
reaction with DNA proceeds by C-O bond scission of the
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous
environmental pollutants that result from activities of a modern
society. Among the multiple metabolic pathways,1-4 many
PAHs that contain a bay- or a fjord-region undergo metabolic
activation to four diol epoxides4 that are thought to exert their
(1) Earlier studies on PAHs and carcinogenesis have been reviewed in:
(a) Polycyclic Aromatic Hydrocarbon Carcinogenesis: Structure-ActiVity
Relationships; Yang, S. K., Silverman, B. D., Eds.; CRC Press: Boca Raton,
FL, 1988; Vols. I and II. (b) Polycyclic Aromatic Hydrocarbons: Chemistry
and Carcinogenicity; Harvey, R. G., Ed.; Cambridge University Press:
Cambridge, 1991. Polycyclic Hydrocarbons and Carcinogenesis; Harvey,
R. G., Ed.; ACS Symposium Series 283: Washington, DC, 1985. (c) For
a detailed survey of the chemistry of polycyclic aromatic hydrocarbons,
please see: Polycyclic Aromatic Hydrocarbons; Harvey, R. G., Ed.; Wiley-
VCH: New York, 1997.
* Corresponding author. Tel.: (212) 650-7835; fax: (212) 650-6107.
† The City College (CCNY).
‡ John Jay College of Criminal Justice.
10.1021/jo070204z CCC: $37.00 © 2007 American Chemical Society
Published on Web 06/09/2007
J. Org. Chem. 2007, 72, 5035-5045
5035

Champeil et al.
SCHEME 1. Cis/Trans Ring Opening of Four Isomeric Diol Epoxides
oxirane, followed by cis and trans attack by the exocyclic amino
groups of the purine bases (Scheme 1).6,7
after appropriate functionalization, be incorporated into DNA
oligomers by solid-phase synthesis methods.8 Typically, only
fluorinated purine nucleosides possess sufficient reactivity to
undergo SNAr displacement reactions with the relatively un-
reactive amino derivatives of polycyclic aromatic hydro-
carbons.9b,10 However, syntheses of 6-fluoropurine-2′-deoxy-
riboside11 and 2-fluoro-2′-deoxyinosine12 are non-trivial, multi-
step procedures.
DNA alkylation upon metabolism of any PAH results in the
formation of 16 purine nucleoside adducts.6,7 To probe the
structural and biological properties of individual diol epoxide-
DNA lesions, access to site-specifically modified DNA contain-
ing stereochemically defined diol epoxide adducts is critical.
Thus, substantial effort has been directed to the development
of methods leading to diol epoxide adducted DNA.8,9 Reactions
of diol epoxides with nucleosides or nucleotides are not
productive avenues for the synthesis of these adducts.8a There-
fore, the total synthesis approach requires reversing the nucleo-
phile/electrophile roles of the nucleoside and the PAH. Reactions
of electrophilic purine nucleosides with amino PAH derivatives
lead to the covalent diol epoxide-nucleoside adducts that can,
Pd-catalyzed C-N bond formation is growing in significance
for the modification of nucleosides,13 and several biologically
important nucleoside adducts have been synthesized via its
application.14 Our interest in Pd-catalyzed synthesis of diol
epoxide-nucleoside adducts stemmed from several important
considerations, such as the cumbersome synthesis of reactive
fluorinated nucleosides usually required for displacement reac-
tions with the axially constrained and hindered PAH amines
and the fact that some displacement reactions leading to the
diol epoxide nucleoside adducts are not particularly efficient.
Access to chloro- and bromonucleosides is easier,11,14a,15,16 and
Pd-catalyzed C-N bond formation presents a potentially facile
approach to this important class of biologically relevant,
modified nucleosides.
(2) (a) Cavalieri, E. L.; Rogan, E. G. Xenobiotica 1995, 25, 677-688.
(b) Cavalieri, E. L.; Rogan, E. G. In The Handbook of EnVironmental
Chemistry, Vol 3J; Neilson, A. H., Ed.; Springer-Verlag: Heidelberg, 1998;
pp 81-117.
(3) (a) Penning, T. M.; Burczynski, M. E.; Hung, C.-F.; McCoull, K.
D.; Palackal, N. T.; Tsuruda, L. S. Chem. Res. Toxicol. 1999, 12, 1-18.
(b) Bolton, J. L.; Trush, M. A.; Penning, T. M.; Dryhurst, G.; Monks, T. J.
Chem. Res. Toxicol. 2000, 13, 135-160.
(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.
(5) Harvey, R. G.; Geacintov, N. E. Acc. Chem. Res. 1988, 21, 66-73.
(6) 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.
(7) Dipple, A. In DNA Adducts: Identification and Biological Signifi-
cance; Hemminki, K., Dipple, A., Shuker, D. E. G., Kadlubar, F. F.,
Sagerba¨ck, D., Bartsch, H., Eds.; Scientific Publication No. 125, Interna-
tional Agency for Research on Cancer: Lyon, France, 1994; pp 107-129.
(8) (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.; Jerina, D. M.
J. Org. Chem. 1992, 57, 3438-3443. (c) Lakshman, M. K.; Sayer, J. M.;
Yagi, H.; Jerina, D. M. J. Org. Chem. 1992, 57, 4585-4590. (d) Chaturvedi,
S.; Lakshman, M. K. Carcinogenesis 1996, 17, 2747-2752.
(9) (a) Cosman, M.; Ibanez, V.; Geacintov, N. E.; Harvey, R. G.
Carcinogenesis 1990, 11, 1667-1672. (b) Kim, S. J.; Harris, C. M.; Jung,
K.-Y.; Koreeda, M.; Harris, T. M. Tetrahedron Lett. 1991, 32, 6073-6076.
(c) Steinbrecher, T.; Becker, A.; Stezowski, J. J.; Oesch, F.; Seidel, A.
Tetrahedron Lett. 1993, 34, 1773-1774. (d) 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. (e) Pilcher, A. S.; Yagi, H.;
Jerina, D. M. J. Am. Chem. Soc. 1998, 120, 3520-3521. (f) Cooper, M.
D.; Hodge, R. P.; Tamura, P. J.; Wilkinson, A. S.; Harris, C. M.; Harris, T.
M. Tetrahedron Lett. 2000, 41, 3555-3558.
We17 and others18 have independently reported Pd-catalyzed
synthesis of nucleoside adducts from the carcinogenic (()-BaP
(10) Lakshman, M.; Lehr, R. E. Tetrahedron Lett. 1990, 31, 1547-
1550.
(11) Robins, M. J.; Basom, G. L. Can. J. Chem. 1973, 51, 3161-3169.
(12) Zajc, B.; Lakshman, M. K.; Sayer, J. M.; Jerina, D. M. Tetrahedron
Lett. 1992, 33, 3409-3412.
(13) (a) Lakshman, M. K. J. Organomet. Chem. 2002, 653, 234-251.
(b) Lakshman, M. K. Curr. Org. Synth. 2005, 2, 83-112.
(14) For some examples of Pd-catalyzed C-N bond formation leading
to biologically important nucleoside derivatives, please see: (a) Harwood,
E. A.; Sigurdsson, S. T.; Edfeldt, N. B. F.; Reid, B. R.; Hopkins, P. B. J.
Am. Chem. Soc. 1999, 121, 5081-5082. (b) De Riccardis, F.; Bonala, R.
R.; Johnson, F. J. Am. Chem. Soc. 1999, 121, 10453-10460. (c) Wang, Z.;
Rizzo, C. J. Org. Lett. 2001, 3, 565-568. (d) Schoffers, E.; Olsen, P. D.;
Means, J. C. Org. Lett. 2001, 3, 4221-4223. (e) Gillet, L. C. J.; Sha¨rer, O.
D. Org. Lett. 2002, 4, 4205-4208. (f) Lakshman, M. K.; Ngassa, F. N.;
Bae, S.; Buchanan, D. G.; Hahn, H.-G.; Mah, H. J. Org. Chem. 2003, 68,
6020-6030. (g) Chakraborti, D.; Colis, L.; Schneider, R.; Basu, A. K. Org.
Lett. 2003, 5, 2861-2864. (h) Elmquist, C. E.; Stover, J. S.; Wang, Z.;
Rizzo, C. J. J. Am. Chem. Soc. 2004, 126, 11189-11201. (i) Stover, J. S.;
Rizzo, C. J. Org. Lett. 2004, 6, 4985-4988. (j) Dai, Q.; Ran, C.; Harvey,
R. G. Org. Lett. 2005, 7, 999-1002.
(15) Maruenda, H.; Chenna, A.; Liem, L.-K.; Singer, B. J. Org. Chem.
1998, 63, 4385-4389.
(16) Lakshman, M. K.; Keeler, J. C.; Hilmer, J. H.; Martin, J. Q. J. Am.
Chem. Soc. 1999, 121, 6090-6091.
5036 J. Org. Chem., Vol. 72, No. 14, 2007

Nucleoside Adducts of Bay- and Fjord-Region Diol Epoxides
SCHEME 2. Synthesis of BaP Amino Tribenzoate
FIGURE 1. Bay- and fjord-region diol epoxides of BaP and BcPh.
DE-2. Therefore, the current investigation focused on the
synthesis of adducts from the stereoisomeric (()-BaP DE-1 (a
bay-region derivative) and from (()-BcPh DE-2 (a fjord-region
compound; Figure 1), representing two structurally different
paradigms. This also provided an opportunity to understand on
a comparative basis the efficiency of catalysis reactions on
chloro- and bromonucleosides. Pd-catalyzed amination of a
trissilyl protected 6-chloropurine nucleoside with aliphatic
amines was reported to proceed in good yield, but reactions
with the less nucleophilic aryl amines were low-yielding.19 Prior
work has shown that the direct displacement reactions of
hindered PAH amines with 6-chloropurine nucleoside are
inefficient.9b,10 On the other hand, two PAH amines underwent
efficient Pd-catalyzed coupling with 6-chloro-9-[3,5-bis-O-(tert-
butyldimethylsilyl)-â-D-erythro-pentofuranosyl]purine,17 and both
chloro- and bromonucleosides were effective coupling partners
in C-N bond formation with azole nitrogens.20 On the basis of
these results, we decided to assess the effectiveness of 6-bromo-
and 6-chloro-9-[3,5-bis-O-(tert-butyldimethylsilyl)-â-D-erythro-
pentofuranosyl]purine for Pd-catalyzed C-N bond forming
reactions with bay- and fjord-region amino PAH derivatives.
In this paper, we discuss: (a) the efficiencies of 2′-deoxyad-
enosine adduct syntheses by C-N bond formation with the two
C-6 halopurine 2′-deoxyribonucleosides, (b) the synthesis of 2′-
deoxyguanosine adducts of the two PAH diol epoxides, (c) a
comparison of the various reactions, and (d) an assessment of
the stereochemical integrity in the Pd-catalyzed reactions.
SCHEME 3. Synthesis of BcPh Amino Tribenzoate
resulting crude material was directly converted to the azido
tribenzoate (()-3.21b Finally, the reduction of the azide moiety
with H2 and the Lindlar catalyst yielded the amino tribenzoate
(()-4 (use of excess catalyst was required for efficient conver-
sion; Pd-C could also be used but was less efficient and PtO2
was ineffective).
Synthesis of BcPh Amino Tribenzoate. Synthesis of the
BcPh amino tribenzoate (()-8 commenced from BcPh DE-2
[(()-(5)] (Scheme 3).24 Because of its low solvolytic reactivity,
as we had reported earlier,25 the ring opening of (()-5 was
conducted in THF-H2O. These conditions eliminate non-
benzylic ring opening by the azide, a feature that was observed
when DMF was used as a solvent.25 Conversion of the azidotriol
(()-6 to the triester (()-7 was accomplished with PhCOCN/
Et3N in DMF.21b Again, catalytic reduction with H2 and excess
Lindlar catalyst yielded the amino tribenzoate (()-8.
Results and Discussion
Synthesis of BaP Amino Tribenzoate. Many PAH amino
triols and amino triacyl derivatives that are suitable precursors
to the nucleoside-diol epoxide adducts can be stereoselectively
synthesized by ring-opening reactions of the diol epoxides
themselves.8,9b,10,21 As shown in Scheme 2, in the present case,
known bromohydrin (()-1 was synthesized via reaction of BaP
dihydrodibenzoate22 with NBS/NaOAc in ∼30% H2O-THF23
and cyclized to the epoxide (()-223 with NaH in dry THF (Cs2-
CO3 in THF can be used, but the ensuing reactions are not very
clean). Ring-opening of 2 to the azidotriol dibenzoate was
performed with LiN3 in DMF at room temperature, and the
Coupling of the BaP and BcPh Amino Tribenzoates with
C-6 Halo Purine 2′-Deoxyribosides. Once the amino triben-
zoates (()-4 and (()-8 were synthesized, the next step was the
analysis of their coupling with each of the halo nucleosides
6-chloro- and 6-bromo-9-[3,5-bis-O-(tert-butyldimethylsilyl)-
â-D-erythro-pentofuranosyl]purine (9 and 10). For this, we
selected conditions that we have successfully used previously
(17) Lakshman, M. K.; Gunda, P. Org. Lett. 2003, 5, 39-42.
(18) Johnson, F.; Bonala, R.; Tawde, D.; Torres, M. C.; Iden, C. R. Chem.
Res. Toxicol. 2002, 15, 1489-1494.
(19) Barends, J.; van der Linden, J. B.; van Delft, F. L.; Koomen, G.-J.
Nucleosides Nucleotides 1999, 18, 2121-2126.
(20) Lagisetty, P.; Russon, L. M.; Lakshman, M. K. Angew. Chem., Int.
Ed. 2006, 45, 3660-3663.
(21) (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.
(22) McCaustland, D. J.; Engel, J. F. Tetrahedron Lett. 1975, 16, 2549-
2552.
(24) Sayer, J. M.; Yagi, H.; Croisy-Delcey, M.; Jerina, D. M. J. Am.
Chem. Soc. 1981, 103, 4970-4972.
(25) Lakshman, M. K.; Yeh, H. J. C.; Yagi, H.; Jerina, D. M. Tetrahedron
Lett. 1992, 33, 7121-7124.
(23) Yagi, H.; Thakker, D. R.; Hernandez, O.; Koreeda, M.; Jerina, D.
M. J. Am. Chem. Soc. 1977, 99, 1604-1611.
J. Org. Chem, Vol. 72, No. 14, 2007 5037

Champeil et al.
TABLE 1. Coupling of Amino Tribenzoates (()-4 and (()-8 with the Two C-6 Halo Nucleosides 9 and 10a
a Reactions were conducted in PhMe at 85 °C. b Yield is of isolated, purified products and represents the combined yield of diastereomeric adduct pairs.
for the synthesis of BaP DE-2 adducts with 2′-deoxyadenosine.17
The C-N bond formation was conducted with 1.1 molar equiv
of amine with the combination of 10 mol % Pd(OAc)2/30 mol
% (()-BINAP/1.4 molar equiv of Cs2CO3 in toluene as the
solvent. The results of these reactions are compiled in Table 1.
The results in Table 1 show some interesting features and
also provide meaningful comparisons between the reactions of
the two amines. In the case of the BaP amino tribenzoate (()-
4, the reactions appeared to be dependent upon the concentration
of the nucleoside (limiting reagent), and the coupling yield
increased with concentration (entries 1-3). When comparing
yields of 11a,b from the reactions of the two halo nucleosides,
as we had demonstrated in an earlier communication,17 chloro-
nucleoside 9 underwent C-N bond formation in comparable
yield to the bromo analogue 10 (entry 3 vs 4). In contrast to
these results, reactions with BcPh amino tribenzoate (()-8
appeared to be different. The nucleoside concentration had a
smaller influence on the product yield, and more notably,
reactions with bromonucleoside 10 provided superior results.
Yields of adducts 12a,b from the more hindered fjord-region
BcPh amino tribenzoate were lower than those from the bay-
region BaP derivative.
yguanosine adducts. Using the same catalyst composition
described previously for the synthesis of the 2′-deoxyadenosine
adducts, C-N bond formation between PAH amino tribenzoates
(()-4, (()-8, and 13 was conducted at a nucleoside concen-
tration of 0.1 M. The results from these experiments are shown
in Table 2.
The most noteworthy feature in Table 2 is the observation
that comparably good product yields were obtained from the
two amino benzoates. This contrasts with the results in Table 1
where the yield of the 2′-deoxyadenosine adducts from the more
hindered BcPh amino tribenzoate was lower than that from the
BaP amino tribenzoate. This result seems to imply that some
subtle influences, possibly steric features associated with the
PAH amines, come into play in C-N bond formation at the
C-6 position of purine nucleosides but that such effects do not
seem to influence C-N bond formation at the C-2 position.
Most impressively, good yields of both BaP and BcPh adducts
are realized via this method. Although these compounds can
be directly used for DNA assembly by methods we have
previously described,8d for reasons indicated later, unequivocal
structure confirmation was undertaken.
Structure Confirmation of the Synthetic PAH Diol
Epoxide-Nucleoside Adducts. In products 11a,b and 12a,b,
the benzoates in each pair of diastereomeric adducts were
cleaved with NH3/MeOH, and the resulting trihydroxy com-
pounds were acetylated (Scheme 4). In the case of 14a,b and
15a,b, the previously described acyl group interchange was
followed by removal of the O6-benzyl group by hydrogenolysis
(Scheme 4). Small amounts of the diastereomeric adducts were
Coupling of the BaP and BcPh Amino Tribenzoates with
O6-Benzyl-2-bromo-2′-deoxyinosine. Since we have faced
difficulties in the preparation of 3′,5′-bis-O-(tert-butyldi-
methylsilyl)-2-chloro-2′-deoxyinosine,26 the readily available
2-bromo analogue 1314a was used to synthesize the 2′-deox-
(26) Pottabathini, N.; Bae, S.; Pradhan, P.; Hahn, H.-G.; Mah, H.;
Lakshman, M. K. J. Org. Chem. 2005, 70, 7188-7195.
5038 J. Org. Chem., Vol. 72, No. 14, 2007

Nucleoside Adducts of Bay- and Fjord-Region Diol Epoxides
TABLE 2. Coupling of Amino Tribenzoates (()-4 and (()-8 with 3′,5′-Bis-O-(tert-butyldimethylsilyl)-2-bromo-2′-deoxyinosine 13a
a Reactions were conducted in PhMe at 85 °C at a 0.1 M concentration of the nucleoside. b Yield is of isolated, purified products and represents the
combined yield of diastereomeric adduct pairs.
SCHEME 4. Preparation of Adduct Triacetates for Characterization
separated by preparative TLC after these manipulations, and as
described in the next section, the disilyl triacetates 16a-19b
were analyzed in detail.
Evaluation of Stereochemical Integrity in the Adduct
Forming Reactions. The presence of a hydrogen atom R to
the amino group raises the possibility of a loss of stereochemical
integrity, and a loss of chirality in Pd-mediated C-N bond
formation via â-hydride migration has been documented in the
literature.27 The use of a bis-phosphine ligand provides ame-
lioration of this problem, possibly by closing open coordination
sites at the metal center.27 In the present cases, stereochemical
integrity is of utmost importance since loss of chirality at the
amine bearing carbon would alter the structure and conformation
of the biologically important adducts that are to be used for
structure-biological studies.
(27) Wagaw, S.; Rennels, R. A.; Buchwald, S. L. J. Am. Chem. Soc.
1997, 119, 8451-8458.
J. Org. Chem, Vol. 72, No. 14, 2007 5039

Champeil et al.
TABLE 3. Coupling Constants for Tetrahydro Ring Protons in the
Adductsa
FIGURE 2. Loss of stereochemical integrity would result in the cis
rather than the trans adducts.
In our preliminary communication where we had initially
disclosed studies on Pd-mediated C-N bond formation as a
route to carcinogen-nucleoside conjugates,17 we had addressed
this potential problem by comparison of the products to those
that were synthesized by displacement of fluoride from a
fluoronucleoside. In the present cases, chirality attrition would
result in a cis relative stereochemical arrangement of the
nucleoside and the adjacent acetoxyl group (Figure 2). Chiro-
optical methods alone would not be adequate to distinguish
between trans and cis products due to close similarities in their
CD spectra.28
Therefore, the coupling constants of the tetrahydro ring
protons in the adducts obtained by the Pd-catalyzed method
(Table 3) were compared to cis and trans adducts that are known
in the literature and/or have been unequivocally synthesized (see
the Supporting Information for this data). In the BaP case, the
trans ring-opened 2′-deoxyadenosine adducts (16a,b) synthe-
sized in this study showed J7,8 ) 5.8-6.0, J8,9 ) 6.6-6.9, and
J9,10 ) 3.9-4.2 Hz, and these are consistent with those for
adducts derived from 6-fluoro-9-[3,5-bis-O-(tert-butyldi-
methylsilyl)-â-D-erythro-pentofuranosyl]purine (J7,8 ) 6.2, J8,9
) 7.0, and J9,10 ) 4.0 Hz). The latter products are derived via
a SNAr mechanism, where chirality attrition is not a question.
Further, the J values of the trans adducts are quite different
from those of the isomeric cis compounds, where they are J7,8
) 7.9-8.0, J8,9 ) 11.5, and J9,10 ) 4.5 Hz.9e The coupling
constants for the trans ring-opened 2′-deoxyguanosine adducts
(18a,b) obtained in the present study were J7,8 ) 6.5-6.9, J8,9
) 6.5-7.0, and J9,10 ) 4.0-4.4 Hz. Not only are these values
very similar to those reported for the adducts obtained from
3′,5′-bis-O-(tert-butyldimethylsilyl)-2-fluoro-2′-deoxyinosine by
fluoride displacement (J7,8 ) 6.1-6.9, J8,9 ) 6.6-6.8, and J9,10
) 3.9-4.4 Hz),29 but again these are also markedly different
from those of the isomeric cis ring-opened adducts (J7,8 ) 8.2,
J8,9 ) 11.8, and J9,10 ) 2.2 Hz).30
a Data obtained at 500 MHz under ambient conditions. b Obtained in
acetone-d6. c Obtained in deacidified CDCl3. d Obtained in DMSO-d6.
data for the 2′-deoxyadenosine adducts (17a,b) were compared
to those reported for the products arising from fluoride displace-
ment chemistry25 as well as adduct peracetates obtained from
alkylation of DNA by (()-BcPh DE-2,31 and a very close match
was observed (see the Supporting Information for a compre-
hensive tabulation). Best comparisons for the 2′-deoxyguanosine
adducts (19a,b) were data for the peracetates of adducts derived
from DNA alkylation by (()-BcPh DE-2.31 The observed
coupling constants for 19a,b are J3,4 ) 8.5-8.9, J2,3 ) 2.6-
2.7, and J1,2 ) 4.3-4.4 Hz, and these match well with J3,4
)
8.4-8.5, J2,3 ) 1.6-2.6, and J1,2 ) 4.1-4.5 Hz reported for
the corresponding adduct peracetates (see the Supporting
Information).
These comparisons led us to the conclusion that chirality
scrambling was not a problem within the detection limits of
the analyses used. An interesting observation that stemmed from
these studies is that the BaP adducts 16a,b showed a solvent-
dependent conformational change that is reflected in the
coupling constants of the tetrahydro ring protons. The J7,8
)
5.8-6.0, J8,9 ) 6.6-6.9, and J9,10 ) 3.9-4.2 Hz observed in
acetone-d6 dramatically changed to J7,8 ) 3.1, J8,9 ) 3.3-3.6,
and J9,10 ) 2.9 Hz in CDCl3. Since the coupling constants
provide an understanding of the orientation of the substituents
in the tetrahydrobenzo ring, a decrease in the values is an
indication of substantially more axially disposed substituents
in CDCl3 as compared to acetone-d6.
In the BcPh case, the differences in the J values for the
isomeric cis and trans ring-opened adducts are smaller. Thus,
(28) Cheng, S. C.; Hilton, B. D.; Roman, J. M.; Dipple, A. Chem. Res.
Toxicol. 1989, 2, 334-340.
(29) See the Supporting Information to: Custer, L.; Zajc, B.; Sayer, J.
M.; Cullinane, C.; Phillips, D. R.; Cheh, A. M.; Jerina, D. M.; Bohr, V. A.;
Mazur, S. J. Biochemistry 1999, 38, 569-581.
(31) Agarwal, S. K.; Sayer, J. M.; Yeh, H. J. C.; Pannell, L. K.; Hilton,
B. D.; Pigott, M. A.; Dipple, A.; Yagi, H.; Jerina, D. M. J. Am. Chem. Soc.
1987, 109, 2497-2504.
(30) Kroth, H.; Yagi, H.; Seidel, A.; Jerina, D. M. J. Org. Chem. 2000,
65, 5558-5564.
5040 J. Org. Chem., Vol. 72, No. 14, 2007

Nucleoside Adducts of Bay- and Fjord-Region Diol Epoxides
FIGURE 3. Possible conformations of the 10S BaP DE-1 deoxyadenosine adduct 16a (generated via MacSpartan Pro V 1.0.3). For simplicity, the
saccharide of the nucleoside has been replaced with a hydrogen atom.
In evaluating the conformational equilibria of the BaP DE-1
adducts 16a,b, the NMR coupling constants were compared to
those of products obtained by a trans ring opening of BaP DE-1
with various nucleophiles.23 There are four principal conformers
that can be considered for 16a,b, and those for the 10S
diastereomer (16a) are shown in Figure 3. Among these, half-
chair conformer I was generated by imposing large dihedral
angles between vicinal protons, and the structure was optimized.
For conformers II-IV, possible dihedral angle constraints were
imposed based upon the observed J values, and the structures
were optimized followed by further minimization using semi-
empirical AM1. Conformer I that has all equatorial substituents
can be readily eliminated since this should display large coupling
constants between all the axial protons and would require a
quasi-equatorial orientation of the bay-region purine substituent
as well (for this reason, no further AM1 minimization was
considered). This analysis is comparable to that reported for
the ring-opening products of BaP DE-1.23 A half-chair con-
former II appears to be preferred in CDCl3, a solvent of lower
polarity, and dihedral angles (absolute values) after AM1
minimization are H7-C-C-H8 ) 55.3, H8-C-C-H9 ) 48.4,
and H9-C-C-H10 ) 54.6. A possible stabilizing feature in
such a conformer could be an intramolecular hydrogen bond
between the NH proton and the axial acyl group on the same
face. In analogy to the conformation of 16a, a C-10 anilino
adduct arising by a trans ring opening of BaP DE-1 has also
been proposed to exist in a conformation with all axial
substituents in CDCl3, possibly stabilized by an intramolecular
hydrogen bond.23 In the more polar acetone-d6, there are two
possible conformers that could account for the observed J values.
These are III, where the absolute values of the dihedral angles
in the minimized structure are H7-C-C-H8 ) 147.4, H8-
C-C-H9 ) 145.6, and H9-C-C-H10 ) 48.4, and IV with
dihedral angles H7-C-C-H8 ) 35.4, H8-C-C-H9 ) 144.7,
and H9-C-C-H10 ) 136.7. Both III and IV adopt a boat or
a flattened half chair conformation, and this analysis is again
comparable to that reported for the trans ring-opening products
of BaP DE-1.23 In conformer III, the C-7 and C-8 substituents
are diequatorially disposed, whereas in conformer IV, these are
diaxial. Between III and IV, the latter also has a quasi-equatorial
purine substituent in the sterically congested bay-region (quasi-
axial in III). These reasons render III more preferable to IV.
In the case of the BcPh adducts 17a,b, although small
differences in the coupling constants were observed in CDCl3
and acetone-d6, these were not as dramatic. Such an analysis
was not conducted with the 2′-deoxyguanosine adducts as a good
line shape for these is typically only observed in DMSO-d6 and
not in CDCl3.
Conclusion
In summary, our studies show that Pd-mediated amination
chemistry is an effective method leading to nucleoside adducts
J. Org. Chem, Vol. 72, No. 14, 2007 5041

Champeil et al.
1.28 mmol) and LiN3 (629.6 mg, 12.86 mmol) were allowed to
stir in DMF (15 mL) at room temperature overnight. The mixture
was diluted with EtOAc and washed with water. The organic layer
was dried over Na2SO4 and evaporated. This crude material was
directly benzoylated by the addition of dry DMF (30 mL) and dry
Et3N (1.5 mL, 10.7 mmol) followed by benzoyl cyanide (0.839 g,
6.4 mmol). The mixture was allowed to stir at room temperature
for 30 min, quenched with methanol, and diluted with EtOAc. The
mixture was washed twice with brine, and the organic layer was
dried over Na2SO4 and evaporated. The resulting yellow oil was
chromatographed on a silica gel column using CH2Cl2. The product
was washed twice with 1:1 Et2O-hexane to yield 513 mg (61%)
of (()-3 as a white powder.
(()-10r-Amino-7â,8r,9â-trisbenzoyloxy-7,8,9,10-tetrahy-
drobenzo[a]pyrene (4).21b To a suspension of Lindlar catalyst (875
mg) in 1:1 THF-EtOH (70 mL) was added the azidotribenzoate
(()-3 (175 mg, 0.27 mmol). The suspension was stirred under a
hydrogen balloon for 2 h and 20 min, at which time TLC indicated
that all starting material had been consumed. The mixture was
filtered through Celite, and the solvents were evaporated. The
resulting pinkish oil was chromatographed on a silica gel column
using 1:100 MeOH-CH2Cl2, and the resulting product was washed
twice with 1:1 Et2O-hexane to yield 121 mg (72%) of (()-4 as a
white powder.
(()-1â-Azido-2r,3r,4â-trihydroxy-1,2,3,4-tetrahydrobenzo-
[c]phenanthrene (6).25 BcPh diol epoxide (()-5 (244 mg, 0.876
mmol) and sodium azide (569.9 mg, 8.76 mmol) were stirred in
1:1 THF-H2O (100 mL) at 40 °C. TLC showed disappearance of
the starting material after 40 h. The mixture was extracted with
EtOAc. The aqueous layer was extracted one more time with
EtOAc, and the combined organic layers were washed with water,
dried over Na2SO4, and evaporated. The product was taken up in
the minimum volume of Et2O and added to hexane under sonication.
The precipitated product was isolated and treated in the same
manner one more time. The resulting white powder was dried to
yield 225 mg (80%) of (()-6.
of PAH diol epoxides. This method appears to be broadly
applicable to the synthesis of bay- and fjord-region diol
epoxide-nucleoside adducts and in the present case has led to
the synthesis of nucleoside adducts from BaP DE-1 and BcPh
DE-2. There are some interesting differences in these reactions.
The adduct forming reactions of the less hindered amino
tribenzoate derived from BaP DE-1 provided good yields of
the N6-2′-deoxyadenosine adducts, whereas corresponding reac-
tions with the more hindered amino tribenzoate derived from
BcPh DE-2 were lower yielding. This suggests that subtle
factors, possibly steric congestion, associated with the PAH
amino tribenzoates are at play in these reactions. Also, reactions
with the BaP amino tribenzoate proceeded well with the C-6
chloronucleoside, whereas those with the BcPh amino triben-
zoate proceeded better with the C-6 bromonucleoside. In each
case, the pure adduct diastereomers were separated after
replacement of the PAH benzoyl groups with acetyl esters. Quite
in contrast to reactions at the C-6 position, C-N bond-forming
reactions of both BaP and BcPh amino tribenzoates at the C-2
position of silyl protected O6-benzyl-2-bromo-2′-deoxyinosine
proceeded in comparably good yields. This seems to suggest
that structural factors associated with the PAH component are
not quite as critical in reactions at the C-2 position. Here again,
the benzoyl groups on PAH were replaced with acetyls, and
facile debenzylation delivered the PAH diol epoxide 2′-
deoxyguanosine adducts quite efficiently. The adduct diaster-
eomers were readily separated after the O6 deprotection. The
pure adduct diastereomers from each reaction were compared
with known compounds. On the basis of these comparisons, it
was rationalized that loss of chirality at the amine bearing carbon
does not compete with product formation. This factor is
important from the standpoint that these compounds are to be
used for structural and biochemical experimentation after
incorporation into DNA oligomers. Chemistry leading to site-
specific DNA modification by these diol epoxide-nucleoside
adducts is underway, and results are forthcoming.
(()-1â-Azido-2r,3r,4â-trisbenzoyloxy-1,2,3,4-tetrahydro-
benzo[c]phenanthrene (7). The azido triol (()-6 (39.5 mg, 0.123
mmol) was dissolved in dry DMF (1.5 mL). Dry Et3N (171.5 µL,
1.23 mmol) and benzoyl cyanide (161.3 mg, 1.23 mmol) were
added, and the reaction mixture was allowed to stir for 45 min at
room temperature. The reaction was quenched with sat aq NaHCO3,
and the mixture was extracted with EtOAc. The organic layer was
washed with brine, dried over Na2SO4, and evaporated. The product
was chromatographed on silica gel using 2:1 toluene-CH2Cl2.
Finally, some minor impurities were removed by washing the
product twice with 1:1 Et2O-hexane. This process yielded 47 mg
(60%) of (()-7 as a white powder. Rf (SiO2/2:1 toluene-CH2Cl2)
Experimental Procedures
(()-7â,8r-Bisbenzoyloxy-9r-bromo-10â-hydroxy-7,8,9,10-
tetrahydrobenzo[a]pyrene (1).23 To a solution of (()-7â,8R-
bisbenzoyloxy-7,8-dihydrobenzo[a]pyrene22 (1.4 g, 2.8 mmol) in
THF-H2O (350 mL/140 mL) were added freshly recrystallized
N-bromosuccinimide (654 mg, 3.6 mmol) and NaOAc (695 mg,
8.4 mmol). The mixture was stirred under N2 gas at room
temperature under subdued light. TLC showed the reaction to be
complete after 18 h, and the solvents were evaporated. The residue
was dissolved in ethyl acetate and washed twice with water. The
organic layer was separated, dried over Na2SO4, and evaporated.
The resulting product was chromatographed on silica gel using
CH2Cl2, and product obtained was then washed twice with 1:1
ether-hexane to afford 1 g (60%) of (()-1 as a white powder.
(()-7â,8r-Bisbenzoyloxy-9â,10â-epoxy-7,8,9,10-tetrahydro-
benzo[a]pyrene (2).23 A stirring suspension of NaH (24 mg, 1
mmol) in THF (5 mL) was flushed with N2 gas and cooled in an
ice bath. Compound 1 (300 mg, 0.507 mmol) was added, and the
mixture turned brownish. After stirring at 0 °C for 1 h, the mixture
was allowed to warm to room temperature over 30 min. TLC
indicated the reaction to be complete. The mixture was diluted with
1:1 Et2O-EtOAc and washed twice with water. The organic layer
was dried over Na2SO4 and evaporated to leave a solid. This solid
was washed twice with 1:1 Et2O-hexane with sonication to yield
217 mg (84%) of (()-2 as a pinkish powder.
1
) 0.53. H NMR (600 MHz, CDCl3): δ 9.00 (d, 1H, Ar-H, J )
8.8), 8.14 (d, 2H, Ar-H, J ) 8.3), 8.01 (d, 1H, Ar-H, J ) 8.3),
7.97 (d, 2H, Ar-H, J ) 8.3), 7.82 (d, 1H, Ar-H, J ) 8.8), 7.79-
7.68 (m, 7H), 7.58 (t, 1H, Ar-H, J ) 7.7), 7.53 (t, 1H, Ar-H, J
) 7.4), 7.48 (t, 1H, Ar-H, J ) 7.4), 7.47 (d, 1H, Ar-H, J ) 7.8),
7.46 (d, 1H, Ar-H, J ) 7.8), 7.36 (t, 2H, Ar-H, J ) 7.8), 7.31 (t,
2H, Ar-H, J ) 7.4), 7.14 (d, 1H, H4, J ) 7.3), 6.35 (dd, 1H, H3,
J ) 7.3, 2.6), 6.18 (dd, 1H, H2, J ) 4.9, 2.6), 5.97 (d, 1H, H1, J
) 4.9). HRMS calculated for C39H31N4O6 (M+ + NH4): 651.2238,
found: 651.2239.
(()-1â-Amino-2r,3r,4â-trisbenzoyloxy-1,2,3,4-tetrahydro-
benzo[c]phenanthrene (8). The azido tribenzoate (()-7 (239 mg,
0.38 mmol) and Lindlar catalyst (1.195 g) were stirred in 1:1 THF-
EtOH (95 mL) under a hydrogen balloon for 2 h and 20 min while
protected from light. TLC showed a disappearance of the starting
material and the formation of a new spot. The mixture was filtered
through Celite, and the residue was washed twice with EtOAc. The
filtrate was dried over Na2SO4, and the solvents were evaporated.
The compound was purified by chromatography on a silica gel
column using 95:5 toluene-EtOAc. Finally, some minor contami-
nants were removed by washing the product with 1:1 Et2O-hexane
(()-10r-Azido-7â,8r,9â-trisbenzoyloxy-7,8,9,10-tetrahydro-
benzo[a]pyrene (3).21b The diol epoxide dibenzoate (()-2 (657 mg,
5042 J. Org. Chem., Vol. 72, No. 14, 2007

Nucleoside Adducts of Bay- and Fjord-Region Diol Epoxides
to provide 199 mg (87%) of (()-8 as a white powder. Rf (SiO2/
2.64 (app. quint, 1H, H2′, J ) 13.1, 5.4), 2.46 (ddd, 1H, H2′′, J )
13.1, 5.8, 4.5), 2.18, 2.11, 2.05 (3s, 9H, OCOCH3), 0.92, 0.86 (2s,
18H, tert-Bu), 0.11, 0.10, 0.05, 0.03 (4s, 12H, SiCH3). HRMS calcd
for C48H62N5O9Si2 (M+ + H) 908.4081, found 908.4090.
The more-polar diastereomer was the 10R isomer (16b) as
determined by the presence of a negative band at 282 nm in its
CD spectrum. 1H NMR (500 MHz, CDCl3): δ 8.62 (s, 1H, purine-
H2), 8.35 (d, 1H, Ar-H11, J ) 9.4), 8.21 (d, 1H, Ar-H1 or H3,
J ) 7.6), 8.17 (d, 1H, Ar-H3 or H1, J ) 7.6), 8.20 (s, 1H, Ar-
H6), 8.10 (d, 1H, Ar-H5, J ) 9.2), 8.06 (s, 1H, purine-H8), 8.08
(d, 1H, Ar-H4, J ) 9.2), 8.03 (d, 1H, Ar-H12, J ) 9.4), 8.02 (t,
1H, Ar-H2, J ) 7.6), 6.76 (br, 1H, H10), 6.67 (d, 1H, H7, J )
3.1), 6.46 (t, 1H, H1′, J ) 6.4), 6.22 (br d, 1H, NH, J ) 7.9), 5.69
(t, 1H, H8, J ) 3.6), 5.64 (t, 1H, H9, J ) 2.9), 4.62 (app. q, 1H,
H3′, J ) 4.3), 4.00 (app. q, 1H, H4′, J ) 3.7), 3.88 (dd, 1H, H5′,
J ) 11.4, 4.3), 3.77 (dd, 1H, H5′′, J ) 11.4, 3.0), 2.63 (app. quint,
1H, H2′, J ) 13.1, 6.2), 2.43 (ddd, 1H, H2′′, J ) 13.1, 6.0, 4.6),
2.18, 2.09, 2.04 (3s, 9H, OCOCH3), 0.91, 0.86 (2s, 18H, tert-Bu),
0.094, 0.092, 0.05, 0.04 (4s, 12H, SiCH3). HRMS calcd for
C48H62N5O9Si2 (M+ + H) 908.4081, found 908.4084.
1
95:5 toluene-EtOAc) ) 0.26. H NMR (600 MHz, CDCl3): δ
9.51 (d, 1H, Ar-H, J ) 8.6), 8.13 (d, 2H, Ar-H, J ) 7.8), 7.97
(d, 2H, Ar-H, J ) 7.8), 7.93 (t, 2H, Ar-H, J ) 7.6), 7.77 (d, 1H,
Ar-H, J ) 8.6), 7.75 (d, 2H, Ar-H, J ) 7.7), 7.72 (t, 2H, Ar-H,
J ) 8.3), 7.66 (d, 1H, Ar-H, J ) 8.1), 7.65 (t, 1H, Ar-H, J )
7.3), 7.57 (t, 1H, Ar-H, J ) 7.6), 7.50 (t, 1H, Ar-H, J ) 7.6),
7.47 (t, 1H, Ar-H, J ) 7.7), 7.46 (d, 1H, Ar-H, J ) 7.7), 7.44
(d, 1H, Ar-H, J ) 7.6), 7.35 (t, 2H, Ar-H, J ) 7.6), 7.30 (t, 2H,
Ar-H, J ) 7.7), 7.06 (d, 1H, H4, J ) 7.8), 6.65 (dd, 1H, H3, J )
7.8, 2.5), 6.04 (app. t, 1H, H2, J ) 3.5), 5.55 (d, 1H, H1, J ) 4.4).
HRMS calculated for C39H30NO6 (M+ + H): 608.2068, found:
608.2070.
N6-[10-(7,8,9-Trisbenzoyloxy-7,8,9,10-tetrahydrobenzo[a]py-
renyl)]-3′,5′-bis-O-(tert-butyldimethylsilyl)-2′-deoxyadenosine
(11a,b). (a) Pd-Mediated Coupling of 9 and (()-4. Into an oven-
dried, screw-capped vial equipped with a stirring bar were placed
Pd(OAc)2 (4.6 mg, 20.5 µmol) and (()-BINAP (37.7 mg, 60.5
µmol). Toluene (2 mL) was added, and the mixture was stirred at
room temperature for 5 min. Cs2CO3 (92.0 mg, 0.282 mmol)
followed by (()-4 (140.0 mg, 0.222 mmol) and then chloronucleo-
side 9 (100.6 mg, 0.202 mmol) were added. The vial was flushed
with N2 gas, sealed with a Teflon-lined cap, and heated in a sand
bath that was maintained at 85 °C. The reaction was monitored by
TLC and judged to be complete after 5 h, at which time the mixture
was cooled, diluted with Et2O, and washed twice with brine. The
organic layer was dried over Na2SO4, and the solvent was
evaporated. Chromatography of the crude mixture on a silica gel
column using 4:40:56 acetone-hexane-CH2Cl2 yielded 161 mg
(73%) of the diastereomeric mixture of adducts 11a,b as a white
powder. Rf 11a,b (SiO2/4:40:56 acetone-hexane-CH2Cl2) ) 0.61.
(b) Pd-Mediated Coupling of 10 and (()-4. A similar C-N
reaction between bromonucleoside 10 (11.7 mg, 21.5 µmol) and
(()-4 (15.0 mg, 23.7 µmol) was conducted using Pd(OAc)2 (0.5
mg, 2.2 µmol), (()-BINAP (4.0 mg, 6.4 µmol), and Cs2CO3 (9.9
mg, 30.4 µmol) in toluene (0.21 mL). This reaction was complete
within 4 h and yielded, after purification, 13.4 mg (57%) of the
adduct diastereomers as a white powder.
Synthesis and Characterization of N6-[10-(7,8,9-Trisacetoxy-
7,8,9,10-tetrahydrobenzo[a]pyrenyl)]-3′,5′-bis-O-(tert-butyldi-
methylsilyl)-2′-deoxyadenosine (16a,b). The diastereomeric mix-
ture of adducts 11a,b (10 mg) was dissolved in MeOH saturated
with NH3 (2.5 mL). The reaction was allowed to proceed for 15 h
at 55 °C at which time TLC showed the reaction to be complete.
The mixture was cooled to room temperature and carefully
evaporated. The product was dried under vacuum to give 8 mg of
crude material. This crude material was taken in pyridine (100 µL)
and acetic anhydride (100 µL), and a few crystals of DMAP were
added, and the mixture was allowed to stir at room temperature
overnight. The reaction mixture was diluted with Et2O and washed
with 1 M aq HCl, sat aq NaHCO3, and twice with water. The
organic layer was dried over Na2SO4, and the mixture was
evaporated to yield 9 mg of a crude mixture of diastereoisomers
16a,b that was separated using preparative TLC (SiO2, 1 mm, 20
cm × 20 cm and elution with 92:8 CH2Cl2-EtOAc) to yield 3.2
mg of the less-polar adduct and 2.8 mg of the more-polar adduct
(combined yield of 72%).
N6-[1-(2,3,4-Trisbenzoyloxy-1,2,3,4-tetrahydrobenzo[c]phenan-
threnyl)]-3′,5′-bis-O-(tert-butyldimethylsilyl)-2′-deoxyadeno-
sine (12a,b). (a) Pd-Mediated Coupling of 10 and (()-8. Into an
oven-dried, screw-capped vial equipped with a stirring bar were
placed Pd(OAc)2 (5.4 mg, 24.1 µmol) and (()-BINAP (45.0 mg,
72.3 µmol). Toluene (2.4 mL) was added, and the mixture was
stirred at room temperature for 5 min. Cs2CO3 (109.9 mg, 0.337
mmol) followed by (()-8 (161.0 mg, 0.265 mmol) and then
bromonucleoside 10 (131.0 mg, 0.241 mmol) were added. The vial
was flushed with N2 gas, sealed with a Teflon-lined cap, and heated
in a sand bath that was maintained at 85 °C. The reaction was
monitored by TLC and judged to be complete after 4 h, at which
time the mixture was cooled, diluted with Et2O, and washed twice
with brine. The organic layer was dried over Na2SO4, and the
solvent was evaporated. Chromatography of the crude mixture on
a silica gel column using 99:1 CH2Cl2-EtOAc yielded 116 mg
(45%, 75% based upon recovered (()-8) of the diastereomeric
mixture of adducts 12a,b as a white powder. Rf 12a,b (SiO2/99:1
CH2Cl2-EtOAc) ) 0.37.
(b) Pd-Mediated Coupling of 9 and (()-8. A similar C-N
reaction between chloronucleoside 9 (13.4 mg, 26.8 µmol) and
(()-8 (17.9 mg, 29.5 µmol) was conducted using Pd(OAc)2 (0.6
mg, 2.7 µmol), (()-BINAP (5.0 mg, 8.0 µmol), and Cs2CO3 (12.2
mg, 37.4 µmol) in toluene (0.26 mL). This reaction was complete
within 4 h and yielded, after purification, 10.5 mg (36%, 39% based
upon recovered (()-8) of the adduct diastereomers as a white
powder.
Synthesis and Characterization of N6-[1-(2,3,4-Trisacetoxy-
1,2,3,4-tetrahydrobenzo[c]phenanthrenyl)]-3′,5′-bis-O-(tert-
butyldimethylsilyl)-2′-deoxyadenosine (17a,b).25 The diastereo-
meric mixture of adducts 12a,b (10 mg) was dissolved in MeOH
saturated with NH3 (2.5 mL). The reaction was allowed to proceed
for 15 h at 55 °C at which time TLC showed the reaction to be
complete. The mixture was cooled to room temperature and
carefully evaporated. The product was dried under vacuum to give
8.4 mg of crude material. This crude material was taken in pyridine
(100 µL) and acetic anhydride (100 µL), and a few crystals of
DMAP were added, and the mixture was allowed to stir at room
temperature overnight. The reaction mixture was diluted with Et2O
and washed with 1 M aq HCl, sat aq NaHCO3, and twice with
water. The organic layer was dried over Na2SO4, and the mixture
was evaporated to yield 8 mg of the mixture of diastereoisomers
17a,b that was separated using preparative TLC (SiO2, 1 mm, 20
cm × 20 cm and elution with 90:10 CH2Cl2-EtOAc) to yield 2.8
mg of the less-polar adduct and 2.9 mg of the more-polar adduct
(combined yield of 69%).
The less-polar diastereomer was the 10S isomer (16a) as
determined by the presence of a positive band at 282 nm in its CD
1
spectrum. H NMR (500 MHz, CDCl3): δ 8.63 (s, 1H, purine-
H2), 8.29 (d, 1H, Ar-H11, J ) 9.4), 8.21 (d, 1H, Ar-H1 or H3,
J ) 7.8), 8.18 (d, 1H, Ar-H3 or H1, J ) 7.8), 8.19 (s, 1H, Ar-
H6), 8.09 (d, 1H, Ar-H5, J ) 9.2), 8.08 (d, 1H, Ar-H4, J ) 9.2),
8.06 (s, 1H, purine-H8), 8.05 (d, 1H, Ar-H12, J ) 9.4), 8.02 (t,
1H, Ar-H2, J ) 7.8), 6.77 (dd, 1H, H10, J ) 9.1, 2.9), 6.67 (d,
1H, H7, J ) 3.1), 6.46 (t, 1H, H1′, J ) 6.3), 6.23 (d, 1H, NH, J )
9.1), 5.69 (t, 1H, H8, J ) 3.3), 5.64 (t, 1H, H9, J ) 2.9), 4.59
(app. q, 1H, H3′, J ) 4.9), 4.00 (app. q, 1H, H4′, J ) 3.7), 3.87
(dd, 1H, H5′, J ) 11.4, 4.2), 3.75 (dd, 1H, H5′′, J ) 11.4, 3.1),
The less-polar diastereomer was the 1S isomer (17a) as deter-
mined by the presence of a positive band at 248 nm in its CD
1
spectrum. H NMR (500 MHz, CDCl3): δ 8.66 (s, 1H, purine-
J. Org. Chem, Vol. 72, No. 14, 2007 5043

Champeil et al.
H2), 8.52 (d, 1H, Ar-H12, J ) 8.6), 8.09 (s, 1H, purine-H8),
7.98 (d, 1H, Ar-H6, J ) 8.3), 7.87 (dd, 1H, Ar-H9, J ) 8.1,
1.3), 7.78 (d, 1H, Ar-H8, J ) 8.7), 7.74 (d, 1H, Ar-H7, J ) 8.7),
7.54 (d, 1H, Ar-H5, J ) 8.3), 7.50 (t, 1H, Ar-H10, J ) 7.6),
7.23 (dd, 1H, Ar-H11, J ) 8.6, 7.8), 6.54 (br s, 1H, NH), 6.51 (t,
1H, H1′, J ) 6.3), 6.47 (d, 1H, H1, J ) 3.3), 6.39 (d, 1H, H4, J )
7.3), 6.30 (t, 1H, H2, J ) 2.9), 5.95 (dd, 1H, H3, J ) 7.3, 2.9),
4.61 (app. quint, 1H, H3′, J ) 4.3), 4.01 (app. q, 1H, H4′, J )
3.5), 3.86 (dd, 1H, H5′, J ) 11.3, 4.1), 3.77 (dd, 1H, H5′′, J )
11.3, 2.9), 2.62 (app. quint, 1H, H2′, J ) 13.3. 6.2), 2.48 (ddd,
1H, H2′′, J ) 13.3, 6.1, 4.3), 2.24, 2.02, 1.89 (3s, 9H, OCOCH3),
0.92, 0.89 (2s, 18H, tert-Bu), 0.12, 0.10, 0.07, 0.06 (4s, 12H,
SiCH3).
The more-polar diastereomer was the 1R isomer (17b) as
determined by the presence of a negative band at 248 nm in its
CD spectrum. 1H NMR (500 MHz, CDCl3): δ 8.65 (s, 1H, purine-
H2), 8.56 (d, 1H, Ar-H12, J ) 8.6), 8.03 (s, 1H, purine-H8),
7.98 (d, 1H, Ar-H6, J ) 8.3), 7.87 (dd, 1H, Ar-H9, J ) 8.0,
1.4), 7.78 (d, 1H, Ar-H8, J ) 8.7), 7.73 (d, 1H, Ar-H7, J ) 8.7),
7.55 (d, 1H, Ar-H5, J ) 8.3), 7.50 (t, 1H, Ar-H10, J ) 7.5),
7.25 (dd, 1H, Ar-H11, J ) 8.5, 7.8), 6.54 (br s, 1H, NH), 6.47 (t,
1H, H1′, J ) 6.6), 6.40 (d, 1H, H1, J ) 3.7), 6.39 (d, 1H, H4, J )
7.4), 6.29 (t, 1H, H2, J ) 3.7), 5.94 (dd, 1H, H3, J ) 7.4, 2.9),
4.63 (app. quint, 1H, H3′, J ) 3.8), 4.03 (app. q, 1H, H4′, J )
3.7), 3.89 (dd, 1H, H5′, J ) 11.2, 4.4), 3.79 (dd, 1H, H5′′, J )
11.2, 3.4), 2.69 (app. quint, 1H, H2′, J ) 13.2. 6.2), 2.44 (ddd,
1H, H2′′, J ) 13.2, 6.0, 3.7), 2.23, 2.02, 1.89 (3s, 9H, OCOCH3),
0.92, 0.89 (2s, 18H, tert-Bu), 0.12, 0.11, 0.07, 0.05 (4s, 12H,
SiCH3).
N2-[10-(7,8,9-Trisbenzoyloxy-7,8,9,10-tetrahydrobenzo[a]py-
renyl)]-O6-benzyl-3′,5′-bis-O-(tert-butyldimethylsilyl)-2′-deoxy-
guanosine (14a,b). Into an oven-dried, screw-capped vial equipped
with a stirring bar were placed Pd(OAc)2 (4.5 mg, 20.0 µmol) and
(()-BINAP (37.7 mg, 60.6 µmol). Toluene (2.0 mL) was added,
and the mixture was stirred at room temperature for 5 min. Cs2CO3
(92.0 mg, 0.282 mmol) followed by (()-4 (140.0 mg, 0.222 mmol)
and then bromonucleoside 13 (131.0 mg, 0.202 mmol) were added.
The vial was flushed with N2 gas, sealed with a Teflon-lined cap,
and heated in a sand bath that was maintained at 85 °C. The reaction
was monitored by TLC and judged to be complete after 16 h, at
which time the mixture was cooled, diluted with Et2O, and washed
twice with brine. The organic layer was dried over Na2SO4, and
the solvent was evaporated. Chromatography of the crude mixture
on a silica gel column using 4:40:56 acetone-hexane-CH2Cl2
yielded 176.2 mg (73%) of the diastereomeric mixture of adducts
14a,b as a white powder. Rf 14a,b (SiO2/4:40:56 acetone-hexane-
CH2Cl2) ) 0.54.
complete. The mixture was filtered through Celite and evaporated
to dryness. The two diastereoisomers were separated using prepara-
tive TLC (SiO2, 1 mm, 20 cm × 20 cm and elution with 35:40:25
acetone-hexane-CH2Cl2) to yield 3.1 mg of the less-polar adduct
and 3.2 mg of the more-polar adduct (combined yield of 43% over
the two steps).
The less-polar diastereomer was the 10S isomer (18a) as
determined by the presence of a positive band at 251 nm in its CD
spectrum. 1H NMR (500 MHz, DMSO-d6): δ 10.68 (s, 1H, guanine
ring NH), 8.35 (d, 1H, Ar-H3 or H1, J ) 7.8), 8.31 (d, 1H, Ar-
H1 or H3, J ) 7.8), 8.29 (d, 1H, Ar-H11, J ) 9.3), 8.24 (s, 2H,
Ar-H4 and H5), 8.23 (s, 1H, Ar-H6), 8.22 (d, 1H, Ar-H12, J )
9.3), 8.11 (t, 1H, Ar-H2, J ) 7.8), 7.95 (s, 1H, purine-H8), 7.30
(br s, 1H, exocyclic NH), 6.63 (d, 1H, H7, J ) 6.9), 6.24 (t, 1H,
H1′, J ) 7.1), 6.18 (dd, 1H, H10, J ) 7.5, 4.4), 5.85 (dd, 1H, H9,
J ) 7.0, 4.4), 5.42 (t, 1H, H8, J ) 6.9), 4.50 (dt, 1H, H3′, J ) 5.1,
4.6), 3.88 (dt, 1H, H4′, J ) 5.4, 4.3), 3.79 (dd, 1H, H5′, J ) 11.5,
5.3), 3.73 (dd, 1H, H5′′, J ) 11.5, 4.9), 2.55 (app. quint, 1H, H2′,
J ) 12.9, 6.4), 2.29 (ddd, 1H, H2′′, J ) 12.9, 6.6, 5.6), 2.27, 2.07,
1.98 (3s, 9H, OCOCH3), 0.87, 0.85 (2s, 18H, tert-Bu), 0.06, 0.05,
0.44, 0.04 (4s, 12H, SiCH3).
The more-polar diastereomer was the 10R isomer (18b) as
determined by the presence of a negative band at 250 nm in its
CD spectrum.1H NMR (500 MHz, DMSO-d6): δ 10.65 (s, 1H,
guanine ring NH), 8.35 (d, 1H, Ar-H3 or H1, J ) 7.8), 8.31 (d,
1H, Ar-H1 or H3, J ) 7.8), 8.29 (d, 1H, Ar-H11, J ) 9.3), 8.24
(s, 2H, Ar-H4 and H5), 8.23 (s, 1H, Ar-H6), 8.15 (d, 1H, Ar-
H12, J ) 9.3), 8.11 (t, 1H, Ar-H2, J ) 7.8), 7.96 (s, 1H, purine-
H8), 7.24 (br s, 1H, exocyclic NH), 6.63 (d, 1H, H7, J ) 6.5),
6.23 (t, 1H, H1′, J ) 6.7), 6.18 (dd, 1H, H10, J ) 7.8, 4.0), 5.80
(dd, 1H, H9, J ) 6.5, 4.0), 5.43 (t, 1H, H8, J ) 6.5), 4.45 (m 1H,
H3′), 3.83 (m, 1H, H4′), 3.75 (dd, 1H, H5′, J ) 10.8, 7.3), 3.71
(dd, 1H, H5′′, J ) 10.8, 4.4), 3.08 (app. quint, 1H, H2′, J ) 13.9,
6.6), 2.28 (ddd, 1H, H2′′, J ) 12.9, 7.2, 5.2), 2.25, 2.07, 1.99 (3s,
9H, OCOCH3), 0.87, 0.64 (2s, 18H, tert-Bu), 0.10, 0.08, -0.02,
-0.31 (4s, 12H, SiCH3).
N2-[1-(2,3,4-Trisbenzoyloxy-1,2,3,4-tetrahydrobenzo[c]phenan-
threnyl)]-O6-benzyl-3′,5′-bis-O-(tert-butyldimethylsilyl)-2′-deoxy-
guanosine (15a,b). Into an oven-dried, screw-capped vial equipped
with a stirring bar were placed Pd(OAc)2 (5.4 mg, 24.1 µmol) and
(()-BINAP (45.0 mg, 72.3 µmol). Toluene (2.4 mL) was added,
and the mixture was allowed to stir at room temperature for 5 min.
Cs2CO3 (109.9 mg, 0.337 mmol) followed by (()-8 (161.0 mg,
0.265 mmol) and then bromonucleoside 13 (156.0 mg, 0.24 mmol)
were added. The vial was flushed with N2 gas, sealed with a Teflon-
lined cap, and heated in a sand bath that was maintained at 85 °C.
The reaction was monitored by TLC and judged to be complete
after 16 h, at which time the mixture was cooled, diluted with Et2O,
and washed twice with brine. The organic layer was dried over
Na2SO4, and the solvent was evaporated. Chromatography of the
crude mixture on a silica gel column using 99:1 CH2Cl2-EtOAc
yielded 197 mg (70%) of the diastereomeric mixture of adducts
15a,b as a white powder. Rf 15a,b (SiO2/99:1 CH2Cl2-EtOAc) )
0.49.
Synthesis and Characterization of N2-[10-(7,8,9-Trisacetoxy-
7,8,9,10-tetrahydrobenzo[a]pyrenyl)]-3′,5′-bis-O-(tert-butyldi-
methylsilyl)-2′-deoxyguanosine (18a,b).29 (a) Step 1: Synthesis
of the Adduct Triacetate. The diastereomeric mixture of adducts
14a,b (18.9 mg) was dissolved in MeOH saturated with NH3 (2.5
mL). The reaction was allowed to proceed for 15 h at 55 °C, at
which time TLC showed the reaction to be complete. The mixture
was cooled to room temperature and carefully evaporated, and the
product was dried under vacuum. This crude material was taken in
pyridine (300 µL) and acetic anhydride (300 µL), and a few crystals
of DMAP were added, and the mixture was allowed to stir at room
temperature overnight. The reaction mixture was diluted with Et2O
and washed with 1 M aq HCl, sat aq NaHCO3, and twice with
water. The organic layer was dried over Na2SO4, and the mixture
was evaporated to yield 11.5 mg of the mixture of the triacetyl
adduct diastereoisomers that was purified by preparative TLC (SiO2,
1 mm, 20 cm × 20 cm and elution with 95:5 CH2Cl2-EtOAc).
This adduct mixture was used for the second step.
Synthesis and Characterization of N2-[1-(2,3,4-Trisacetoxy-
1,2,3,4-tetrahydrobenzo[c]phenanthrenyl)]-3′,5′-bis-O-(tert-butyl-
dimethylsilyl)-2′-deoxyguanosine (19a,b).32 (a) Step 1: Synthesis
of the Adduct Triacetate. The diastereomeric mixture of adducts
15a,b (23.1 mg) was dissolved in MeOH saturated with NH3 (2.5
mL). The reaction was allowed to proceed for 15 h at 55 °C, at
which time TLC showed the reaction to be complete. The mixture
was cooled to room temperature and carefully evaporated, and the
product was dried under vacuum. This crude material was taken in
pyridine (300 µL) and acetic anhydride (300 µL), and a few crystals
of DMAP were added, and the mixture was allowed to stir at room
temperature overnight. The reaction mixture was diluted with Et2O
(b) Step 2: Debenzylation. To a solution of the adduct mixture
(11.2 mg) in 1:1 THF-MeOH (0.12 mL) was added 5% Pd-C (5
mg). The reaction mixture was stirred under 1 atm H2 pressure
(balloon) for 5 h at which time TLC indicated the reaction to be
(32) Kroth, H.; Yagi, H.; Sayer, J. M.; Kumar, S.; Jerina, D. M. Chem.
Res. Toxicol. 2001, 14, 708-719.
5044 J. Org. Chem., Vol. 72, No. 14, 2007

Nucleoside Adducts of Bay- and Fjord-Region Diol Epoxides
1
and washed with 1 M aq HCl, sat aq NaHCO3, and twice with
water. The organic layer was dried over Na2SO4, and the mixture
was evaporated to yield 16.0 mg of the mixture of the triacetyl
adduct diastereoisomers that was purified by preparative TLC (SiO2,
1 mm, 20 cm × 20 cm and elution with 95:5 CH2Cl2-EtOAc).
This adduct mixture was used for the second step.
(b) Step 2: Debenzylation. To a solution of the adduct mixture
(16.0 mg) in 1:1 THF-MeOH (0.16 mL) was added 5% Pd-C (5
mg). The reaction mixture was stirred under 1 atm H2 pressure
(balloon) for 5 h, at which time TLC indicated the reaction to be
complete. The mixture was filtered through Celite and evaporated
to dryness. The two diastereoisomers were separated using prepara-
tive TLC (SiO2, 1 mm, 20 cm × 20 cm and elution with 35:35:30
acetone-hexane-CH2Cl2) to yield 4.4 mg of the less-polar adduct
and 7.0 mg of the more-polar adduct (combined yield of 64% over
the two steps).
The less-polar diastereomer was the 1S isomer (19a) as deter-
mined by the presence of a positive band at 257 nm in its CD
spectrum. 1H NMR (500 MHz, DMSO-d6): δ 10.16 (s, 1H, guanine
ring NH), 8.52 (d, 1H, Ar-H12, J ) 8.9), 8.18 (d, 1H, Ar-H9, J
) 8.4), 8.05 (d, 1H, Ar-H6, J ) 8.2), 8.04 (s, 1H, purine-H8),
7.95 (d, 1H, Ar-H7, J ) 8.8), 7.92 (d, 1H, Ar-H8, J ) 8.8), 7.64
(br d, 1H, exocyclic NH, J ) 6.5), 7.60 (t, 1H, Ar-H10, J ) 7.4),
7.58 (d, 1H, Ar-H5, J ) 8.2), 7.34 (t, 1H, Ar-H11, J ) 8.2),
6.43 (d, 1H, H4, J ) 8.5), 6.32 (t, 1H, H1′, J ) 6.6), 6.06 (dd, 1H,
H2, J ) 4.4, 2.7), 6.04 (dd, 1H, H1, J ) 6.5, 4.4), 5.74 (dd, 1H,
H3, J ) 8.5, 2.7), 4.50 (dt, 1H, H3′, J ) 6.0, 3.7), 3.86 (app. q,
1H, H4′, J ) 4.5), 3.77 (dd, 1H, H5′, J ) 11.3, 5.2), 3.72 (dd, 1H,
H5′′, J ) 11.3, 4.5), 2.68 (app. quint, 1H, H2′, J ) 13.4, 7.7), 2.35
(ddd, 1H, H2′′, J ) 13.4, 6.4, 4.0), 2.23, 1.99, 1.90 (3s, 9H,
OCOCH3), 0.89, 0.83 (2s, 18H, tert-Bu), 0.07, 0.06, 0.058, 0.054
(4s, 12H, SiCH3).
CD spectrum. H NMR (500 MHz, DMSO-d6): δ 10.24 (s, 1H,
guanine ring NH), 8.44 (d, 1H, Ar-H12, J ) 8.9), 8.19 (d, 1H,
Ar-H9, J ) 8.5), 8.06 (d, 1H, Ar-H6, J ) 8.1), 8.03 (s, 1H,
purine-H8), 7.97 (d, 1H, Ar-H7, J ) 8.9), 7.93 (d, 1H, Ar-H8,
J ) 8.9), 7.87 (br s, 1H, exocyclic NH), 7.61 (t, 1H, Ar-H10, J )
7.4), 7.57 (d, 1H, Ar-H5, J ) 8.1), 7.25 (t, 1H, Ar-H11, J )
8.3), 6.44 (d, 1H, H4, J ) 8.9), 6.23 (dd, 1H, H1′, J ) 9.2, 5.4),
6.10 (t, 1H, H2, J ) 3.5), 5.95 (dd, 1H, H1, J ) 6.4, 4.3), 5.75
(dd, 1H, H3, J ) 8.9, 2.6), 4.38 (d, 1H, H3′, J ) 5.1), 3.55 (t, 1H,
H4′, J ) 10.3), 3.76 (dd, 1H, H5′, J ) 10.3, 4.4), 3.46 (dd, 1H,
H5′′, J ) 10.3, 4.1), 3.23 (ddd, 1H, H2′, J ) 13.4, 9.2, 4.9), 2.12
(dd, 1H, H2′′, J ) 13.4, 5.4), 2.24, 2.00, 1.95 (3s, 9H, OCOCH3),
0.86, 0.52 (2s, 18H, tert-Bu), 0.08, 0.07, -0.54, -0.66 (4s, 12H,
SiCH3).
Acknowledgment. This work was supported in part by NIH
Grants S06 GM008168-24S1 and 2 S06 GM008168-27 (NIGMS)
and NSF Grant CHE-0314326 to M.K.L. P.P. (CCNY NMR
facility manager) acknowledges support via a PSC-CUNY 37
award. Acquisition of a mass spectrometer was funded by NSF
Grant CHE-0520963 (M.K.L.). Infrastructural support at CCNY
via NIH RCMI Grant G12 RR03060 is gratefully acknowledged.
Wavefunction, Inc. is thanked for their technical support.
Supporting Information Available: General experimental
methods; tabulation of the coupling constant data for the tetrahydro
ring protons in the BaP and BcPh adducts; CD spectra of adduct
pairs 16a/16b, 17a/17b, 18a/18b, and 19a/19b; and 1H NMR
spectra of (()-7, (()-8, 16a, 16b, 17a, 17b, 18a, 18b, 19a, and
19b. This information is available free of charge via the Internet at
http://pubs.acs.org.
The more-polar diastereomer was the 1R isomer (19b) as
determined by the presence of a negative band at 257 nm in its
JO070204Z
J. Org. Chem, Vol. 72, No. 14, 2007 5045