Effect of ionic state of 2'-deoxyguanosine and solvent on its aralkylation by benzyl bromide

Article abstract of DOI:10.1021/tx980012m

To extend studies of the aralkylation of nucleic acid components under a variety of solvent conditions, we determined product distributions from the reactions of benzyl bromide with 2'-deoxyguanosine and the anion of 2'- deoxyguanosine in 2,2,2-trifluoroethanol (TFE) and compared these distributions with those from the reaction of the anion with benzyl bromide in N,N-dimethylacetamide (DMA). 7-Benzylguanine was the only benzylated product detected in the reaction with the neutral nucleoside in TFE. In striking contrast, the reaction of the anion of 2'-deoxyguanosine with benzyl bromide in TFE produced N²-benzyl-2'-deoxyguanosine in significant yield and with high selectivity. The reaction of the anion of 2'-deoxyguanosine with benzyl bromide in DMA produced products derived only from reaction at the 1- and/or 7-position of the nucleoside. The weakly nucleophilic but protic polar solvent TFE and the iminolate tautomeric form of the 2'-deoxyguanosine anion appear to be essential for benzylation at the exocyclic N²-position.

Full text of DOI:10.1021/tx980012m

6
96
Chem. Res. Toxicol. 1998, 11, 696-702
Effect of Ion ic Sta te of 2′-Deoxygu a n osin e a n d Solven t
on Its Ar a lk yla tion by Ben zyl Br om id e
Ki-Young Moon and Robert C. Moschel*
Chemistry of Carcinogenesis Laboratory, ABL-Basic Research Program, NCI-Frederick
Cancer Research and Development Center, P.O. Box B, Frederick, Maryland 21702
Received J anuary 15, 1998
To extend studies of the aralkylation of nucleic acid components under a variety of solvent
conditions, we determined product distributions from the reactions of benzyl bromide with
2
′-deoxyguanosine and the anion of 2′-deoxyguanosine in 2,2,2-trifluoroethanol (TFE) and
compared these distributions with those from the reaction of the anion with benzyl bromide in
N,N-dimethylacetamide (DMA). 7-Benzylguanine was the only benzylated product detected
in the reaction with the neutral nucleoside in TFE. In striking contrast, the reaction of the
2
anion of 2′-deoxyguanosine with benzyl bromide in TFE produced N -benzyl-2′-deoxyguanosine
in significant yield and with high selectivity. The reaction of the anion of 2′-deoxyguanosine
with benzyl bromide in DMA produced products derived only from reaction at the 1- and/or
7
-position of the nucleoside. The weakly nucleophilic but protic polar solvent TFE and the
iminolate tautomeric form of the 2′-deoxyguanosine anion appear to be essential for benzylation
at the exocyclic N -position.
2
(10) could be used to produce improved yields for an N2-
substituted 2′-deoxyguanosine product, we examined the
product distributions for reactions between 7-(bromom-
ethyl)benz[a]anthracene and either the neutral or anionic
form of 2′-deoxyguanosine in TFE (8). These reactions
In tr od u ction
Several studies of the reaction of benzylic electrophiles
with guanine and adenine nucleosides have been carried
out in efforts to explain the site selectivity exhibited by
a wide variety of chemical carcinogens in their reactions
with DNA (1-9). These studies showed that product
distributions were markedly dependent on the reaction
solvent. For example, in dipolar aprotic solvents [e.g.,
2
produced substantial amounts of N -(benz[a]anthracen-
7
-ylmethyl)-2′-deoxyguanosine which is formed in only
very low yield under aqueous solvent conditions. These
observations prompted us to examine reactions between
1
N,N-dimethylacetamide (DMA) or N,N-dimethylforma-
-
the neutral (1) or anionic form (1 ) of 2′-deoxyguanosine
mide] reaction occurred primarily on ring nitrogen sites
(Scheme 1) and the simplest benzylating agent, benzyl
(
1
i.e., the 7-position on guanine nucleosides and the
-position in adenine nucleosides) (1, 2). In solvents of
greater ionizing power (e.g., aqueous organic solvent
bromide in TFE and DMA, to determine which system
2
might afford the highest yield of N -benzyl-2′-deoxygua-
nosine. We also compared these product distributions
with those obtained under similar conditions but in the
presence of silver nitrate. Our intent was to determine
if silver coordination with the departing bromide leaving
group could increase the ionic character of the benzylat-
ing agent and alter product distributions observed in the
absence of silver ions. Silver catalysis has been used
2
2
mixtures or H O) reaction at exocyclic sites (i.e., the N -
6
6
and O -positions on guanine nucleosides and the N -
position on adenine nucleosides) occurred in addition to
reaction at ring nitrogen sites (2). However, the pre-
ferred sites of benzylation of these nucleosides in aqueous
solvents depended on the benzylating agents’ leaving
group and/or para-substituent (1-6 ). Additionally, with
guanine nucleosides, sites of reaction also depended on
whether reaction occurred with the anionic or neutral
form of the guanine residue (4-7). Surprisingly, benzy-
4
4
previously to prepare O -isopropyl- (11) and O -ben-
zylthymidine (12) in reactions between thymidine anion
and isopropyl or benzyl bromide, respectively. In this
report we describe product distributions resulting from
a variety of reaction conditions and demonstrate that the
2
lation at the N -position on guanine nucleosides was
shown to increase substantially in aqueous reactions
involving the nucleoside anion compared to the neutral
nucleoside even though the exocyclic amino group is not
formally charged in the anion (4-7). Still, however, the
-
2
reaction of 1 with benzyl bromide in TFE provides N -
benzyl-2′-deoxyguanosine in high yield. The factors that
contribute to the efficient formation of this product
appear to be the polar but low nucleophilic character of
2
total yield of the N -substituted products was fairly low
the TFE solvent and the iminolate tautomeric form of
due to the high nucleophilicity of the aqueous solvents
which led to preferential hydrolysis of the benzylating
agents rather than to reaction with the nucleoside.
To test whether solvents of high ionizing power but
low nucleophilicity such as 2,2,2-trifluoroethanol (TFE)
-
1
.
Exp er im en ta l Section
Ultraviolet absorption spectra were determined on a Milton
1
Roy SLM-AMINCO 3000 diode array spectrophotometer.
H
1
NMR spectra were recorded on a Varian VXR 500S spectrometer
equipped with Sun 4/110 data stations or a Varian XL200
Abbreviations: DMA, N,N-dimethylacetamide; TFE, 2,2,2-trifluo-
roethanol.
S0893-228x(98)00012-5 CCC: $15.00 © 1998 American Chemical Society
Published on Web 05/13/1998

Benzylation of 2′-Deoxyguanosine
Chem. Res. Toxicol., Vol. 11, No. 6, 1998 697
Sch em e 1
instrument interfaced to an Advanced data system. Samples
were dissolved in dimethyl-d sulfoxide, and chemical shifts are
nm (sh), λmin 262 nm, λmax 285 nm, pH 13 λmin 259 nm, λmax 282
nm; H NMR (of the hydrochloride salt) δ 12.10 (1H, s, 1-NH,
1
6
reported as δ values (ppm) downfield from tetramethylsilane
as an internal standard. Positive ion (+ve) fast atom bombard-
ment (FAB) and high-resolution electron impact (HREI) MS
were obtained with a reversed-geometry VG Micromass ZAB-
exchanges with D
exchange with D O), 7.32-7.43 (5H, m, C
CH ).
The pH of the filtrate was increased to 6.5 by the addition of
2
O), 8.95 (1H, s, 8-H), 7.64 (2H, s, NH
2
,
2
6 5
H
), 5.53 (2H, s,
C
6
H
5
2
2
F spectrometer interfaced to a VG 2035 data system.
A
0.1 N NaOH which led to the precipitation of guanine (70 mg,
19%) which was collected by filtration. The identification of
guanine was confirmed by comparison of its UV absorption
characteristics with those of an authentic sample. The filtrate
was loaded on a Sephadex LH-20 column (2.8 × 78 cm) eluted
mixture of dithiothreitol and dithioerythritol (1:1) was used as
the FAB matrix. Elemental analyses were performed by Gal-
braith Laboratories, Inc., (Knoxville, TN). Thin-layer chroma-
tography (TLC) was performed on Kodak silica gel (Eastman
Kodak Co., Rochester, NY) adsorbent with fluorescent indicator
2
with MeOH/H O (1:9) at 1 mL/min. UV absorption was
(
0.2-mm layer thickness, 2.5 × 7.5 cm), and visualization was
continuously monitored at 280 nm and fractions (10 mL) were
collected. Unreacted 2′-deoxyguanosine eluted in fractions 31-
37. Fractions 38-61 were pooled and evaporated to dryness.
accomplished by UV illumination. Sephadex LH-20 was pur-
chased from Pharmacia, Biotechnology AB (Uppsala, Sweden).
2
Louis, MO). O -Benzyl-2′-deoxyguanosine (7) (13) was prepared
as described previously (14). All other chemicals were from
Aldrich Chemical Co. (Milwaukee, WI).
Ben zyla tion of 2′-Deoxygu a n osin e (1) in TF E. To a
stirred suspension of 2′-deoxyguanosine (0.65 g, 2.43 mmol) in
′-Deoxyguanosine was purchased from Sigma Chemical Co. (St.
The resulting solid was dissolved in 25 mL of MeOH/H
95) and was loaded on a 2.8- × 78-cm Sephadex LH-20 column
eluted with MeOH/H O (5:95) at 0.8 mL/min. Under these
2
O (5:
6
2
conditions, unreacted 2′-deoxyguanosine eluted in fractions 54-
68. Guanine (6 mg) eluted in fractions 74-88. No other
products were observed.
1
3 mL of TFE was added benzyl bromide (0.28 mL, 2.32 mmol)
Ben zyla tion of 2′-Deoxygu a n osin e (1) in TF E Con ta in -
over a 2-min period. The reaction mixture was stirred for 72 h
at room temperature. The resulting white suspension was
in g AgNO
3
. To a stirred suspension of 2′-deoxyguanosine (0.65
(0.4
g, 2.43 mmol) in 13 mL of TFE was added ground AgNO
3
diluted with 120 mL of MeOH/H
2
O (1:9), was stirred for 30 min
g, 2.4 mmol) followed by the dropwise addition of benzyl bromide
(0.28 mL, 2.3 mmol) over a 2-min period. The reaction mixture
was stirred at room temperature for 72 h. The resulting purple
suspension was diluted with 120 mL of MeOH/H O (1:9) and
2
was stirred for 30 min at 55 °C to dissolve suspended solids
other than AgBr. The suspended AgBr was filtered (405 mg).
at 55 °C to dissolve nearly all suspended solids, and was allowed
to cool to room temperature. The precipitated solid that formed
was filtered. Crystallization of the filtered solid from 1 N HCl
afforded the hydrochloride salt of 7-benzylguanine (2) (15, 16)
(145 mg, 21%): UV pH 1 λmax 252 nm, 272 nm (sh), pH 6.9 244

6
98 Chem. Res. Toxicol., Vol. 11, No. 6, 1998
Moon and Moschel
4
1
On cooling to room temperature crude 7-benzylguanine (2)
precipitated. This was filtered and crystallized from 1 N HCl
to afford the hydrochloride salt of 7-benzylguanine (75 mg, 11%).
Increasing the pH of the filtrate to pH 6.0 with 0.1 N NaOH
caused precipitation of guanine (160 mg, 43%) which was
collected by filtration. Chromatography of the filtrate on a
1.168 × 10 ); H NMR δ 10.61 (1H, s, 1-H, exchanges with D
7.90 (1H, s, 8-H), 7.20-7.40 (5H, m, C ), 6.88 (1H, t, J CHNH
5.52 Hz, C CH NH, exchanges with D O), 6.14 (1H, t, J )
6.94 Hz, H-1′), 5.26 (1H, br s, OH-3′, exchanges with D O), 4.86
(1H, br s, OH-5′, exchanges with D O), 4.50 (2H, d, J CHNH
5.67 Hz, C CH NH changes to a singlet on addition of D
2
O),
)
6
H
5
6
H
5
2
2
2
2
)
6
H
5
2
2
O),
Sephadex LH-20 column (2.8 × 78 cm) eluted with MeOH/H
1:9) at 0.8 mL/min showed that the filtrate contained only
unreacted 2′-deoxyguanosine which eluted in fractions (10 mL)
2
O
4.33 (1H, br s, H-3′), 3.80 (1H, m, H-4′), 3.50 (2H, m, H-5′), 2.57
+
(
(1H, m, H-2′b), 2.16 (1H, m, H-2′a); FAB -MS m/z 358
+
+
([C17
H
19
19
N
5
O
4
4
+ H] ), 242 ([C12
11 5
H N O + H] ). Anal. Calcd for
4
4-65 and a trace of guanine in fractions 71-81.
C
17
H
2
N
5
O
: C, H, N.
2
Ben zyla tion of 2′-Deoxygu a n osin e (1) in TF E Con ta in -
N ,N -Dibenzyl-2′-deoxyguanosine (4) eluted in fractions
in g Na OH. To a stirred suspension of 2′-deoxyguanosine (1.3
g, 4.87 mmol) in 25 mL of TFE was added 0.23 g of NaOH (5.75
mmol) at room temperature. After stirring for 30 min, benzyl
bromide (0.55 mL, 4.63 mmol) was added dropwise over 3 min.
The reaction mixture was stirred at room temperature for 72
h. The resulting white suspension was evaporated in vacuo to
give a crude solid. This solid was dissolved in 150 mL of MeOH/
115-170: TLC R
f
3
) 0.59 in MeOH/CHCl (2:8): UV pH 1 λmin
237 nm, λmax 266 nm, 289 nm (sh), pH 6.9 λmin 231 nm, λmax 263
1
nm, 281 nm (sh), pH 13 λmin 243 nm, λmax 268 nm; H NMR δ
10.98 (1H, s, 1-H, exchanges with D
7.38 (10H, m, 2C ), 6.16 (1H, t, J ) 6.9 Hz, H-1′), 5.26 (1H,
br s, OH-3′, exchanges with D O), 4.88 (1H, br s, OH-5′,
exchanges with D O), 4.86, 4.83, 4.81, and 4.78 (4H, ab, J ab
16.5 Hz, 2C CH ), 4.29 (1H, br s, H-3′), 3.79 (1H, m, H-4′),
3.49 (2H, m, H-5′), 2.55 (1H, m, H-2′b), 2.16 (1H, m, H-2′a);
2
O), 7.96 (1H, s, 8-H), 7.23-
6
H
5
2
2
)
H
2
O/NH
4
OH (50:50:3) and was loaded on a Sephadex LH-20
O/NH OH (50:50:3)
6
H
5
2
column (2.8 × 78 cm) eluted with MeOH/H
2
4
+
+
+
at 1 mL/min. UV absorption was monitored continuously at 280
FAB -MS m/z 448 ([C24
Anal. Calcd for C24
H
25
N
5
O
4
+ H] ), 332 ([C19
2
16 5
H N O + H] ).
nm, and fractions (10 mL) were collected. Fractions 30-62
H
25
N
5
O
4
‚0.5H O: C, H, N.
2
contained a mixture of 2′-deoxyguanosine, 3-benzylguanine, N -
Ben zyla tion of 2′-Deoxygu a n osin e (1) in TF E Con ta in -
in g Na OH a n d AgNO3. To a stirred suspension of 2′-deox-
yguanosine (1.3 g, 4.87 mmol) in 25 mL of TFE was added 0.23
g of NaOH (5.75 mmol) at room temperature. After the mixture
2
2
benzyl-2′-deoxyguanosine, and N ,N -dibenzyl-2′-deoxygua-
nosine. These fractions were pooled, evaporated, and rechro-
matographed (see below).
2
1
,N -Dibenzyl-2′-deoxyguanosine (6) eluted in MeOH/H
2
O/
3
stirred for 30 min, ground AgNO (0.78 g, 4.6 mmol) was added
NH
4
OH (50:50:3) fractions 75-91: UV pH 1 λmin 237 nm, λmax
followed by the dropwise addition of benzyl bromide (0.55 mL,
4.63 mmol) over 3 min. The reaction mixture was stirred at
room temperature for 72 h. The resulting pale-purple solution
was evaporated to dryness. The crude solid was stirred in 50
2
63 nm, 283 nm (sh), pH 6.9 λmax 258 nm, 279 nm (sh), pH 13
1
λ
max 259 nm, 279 nm (sh); H NMR δ 7.94 (1H, s, 8-H), 7.65
(
1H, t, J CHNH ) 5.4 Hz, C
6
H
5
CH
), 6.11 (1H, t, J ) 6.6 Hz, H-1′), 5.34
N) 5.26 (1H, br s, 3′-OH, exchanges with
O), 4.87 (1H, br s, 5′-OH, exchanges with D O), 4.51 (2H, d,
CH NH, changes to a singlet on addition
O), 4.29 (1H, br s, H-3′), 3.79 (1H, m, H-4′), 3.48 (2H, m,
H-5′), 2.53 (1H, m, H-2′b), 2.11 (1H, m, H-2′a); EI-MS m/z 447
2 2
NH, exchanges with D O),
7
.00-7.42 (10H, m, 2C
CH
6
H
5
2 4
mL of MeOH/H O/NH OH (50:50:3) at 55 °C and was filtered
(2H, br s, 1-C
6
H
5
2
to remove AgBr. This process was repeated a second time. The
pooled filtrates were then chromatographed as described above
D
J
of D
2
2
-
CHNH ) 5.2 Hz, C
6
H
5
2
for the separation of products derived from the reaction of 1
2
with benzyl bromide in the absence of AgNO
distribution and yields were essentially the same as those
observed for reactions in the absence of AgNO
3
. The product
+
+
(
[C24
H
25
N
5
O
4
] ), 331 ([C19
H
16
N
5
O] ); HREI-MS calcd for
3
.
C
24
H
25
N
5
O
4
447.1906, found 447.1956.
Ben zyla tion of 2′-Deoxygu a n osin e (1) in DMA Con ta in -
in g Na OH. To a stirred solution of 2′-deoxyguanosine (0.65 g,
2.43 mmol) in 13 mL of DMA was added NaOH (0.13 g, 3.2
mmol). When all sodium hydroxide had dissolved, benzyl
bromide (0.28 mL, 2.32 mmol) was added dropwise over a 2-min
period. The reaction mixture was stirred at room temperature
6
O -Benzyl-2′-deoxyguanosine (7) (16) eluted in fractions 98-
32.
1
2
6
N ,O -Dibenzyl-2′-deoxyguanosine (5) eluted in fractions
81-220: TLC R ) 0.83 in CHCl : UV pH 1 λmax 250 nm, λmin
72 nm, λmax 300 nm, pH 6.9 λmax 254 nm, λmin 271 nm, λmax 290
1
2
f
3
1
for 72 h. The resulting solution was diluted with MeOH/H O
nm, pH 13 λmax 254 nm, λmin 271 nm, λmax 290 nm; H NMR δ
.07 (1H, s, 8-H), 7.61 (1H, t, J CHNH ) 6.2 Hz, C CH NH,
exchanges with D O), 7.14-7.45 (10H, m, 2 C ), 6.21 (1H, t,
J ) 6.5 Hz, H-1′), 5.48 (2H, s, C CH O), 5.31 (1H, s, OH-3′,
exchanges with D O), 4.93 (1H, br s, OH-5′, exchanges with
O), 4.51 (2H, d, J CHNH ) 6.4 Hz, C CH NH, changes to a
singlet on addition of D O), 4.35 (1H, br s, H-3′), 3.81 (1H, m,
H-4′), 3.52 (2H, m, H-5′), 2.63 (1H, m, H-2′b), 2.18 (1H, m, H-2′a);
2
(1:1) to a final volume of 100 mL and was chromatographed on
a Sephadex LH-20 column (2.8 × 78 cm). The column was
8
6
H
5
2
2
6 5
H
H
5
2
2
eluted with MeOH/H O (1:1) at 1 mL/min. Fractions 19-60
6
contained a mixture of imidazole ring-opened 7-benzyl-2′-
deoxyguanosine (12), unreacted 2′-deoxyguanosine, and 1-ben-
zyl-2′-deoxyguanosine (10). These fractions were pooled, evapo-
rated to dryness, and rechromatographed (see below).
2
D
2
6
H
5
2
2
+
+
EI-MS m/z 447 ([C24
calcd for C24
The white solid recovered from evaporation of MeOH/H
NH OH (50:50:3) fractions 30-62 (see above) was dissolved in
0 mL of MeOH/H
O (3:7) and was loaded on a 2.8- × 78-cm
Sephadex LH-20 column eluted with MeOH/H O (3:7) at 1 mL/
H
25
N
5
O
4
] ), 331 ([C19
H
16
N
5
O] ); HREI-MS
2
1,7-Dibenzylguanine (11) eluted in MeOH/H O (1:1) fractions
H
25
N
5
O
4
447.1906, found 447.1892.
65-100 (115 mg, 14.3%): UV pH 1 λmin 237 nm, λmax 255 nm,
277 nm (sh), pH 6.9 246 nm (sh), λmin 265 nm, λmax 287 nm, pH
2
O/
1
13 246 nm (sh), λmin 265 nm, λmax 286 nm; H NMR δ 8.14 (1H,
4
4
2
s, 8-H), 7.10-7.59 (10H, m, 2C
6
H
5
), 6.70 (2H, s, NH
2
2
, exchange
with D
2
O), 5.45 (2H, s, 7-C
6
H
5
CH ), 5.22 (2H, s, 1-C
6
H
5
CH
2
+
);
2
+
+
min. Under these chromatographic conditions, unreacted 2′-
deoxyguanosine (1) eluted in fractions 37-55.
FAB -MS m/z 332 ([C19
H
18
N
H
5
O + H] ), 242 ([C12
18
H
11
N
5
O + H] );
+
HRFAB -MS calcd for C19
N
5
O 332.1511, found 332.1550.
3
-Benzylguanine (8) eluted in fractions 57-75: UV pH 1 λmin
Rechromatography of pooled MeOH/H
2
O (1:1) fractions 19-
2
35 nm, λmax 263 nm, pH 6.9 234 nm (sh), λmin 249 nm, λmax 270
60 (see above) was on the 2.8 × 78-cm Sephadex LH-20 column
1
eluted with MeOH/H O (1:9) at 1 mL/min. The imidazole ring-
nm, pH 13 λmin 248 nm, λmax 274 nm; H NMR δ 7.84 (s, 1H,
-H), 7.20-7.38 (m, 5H, C ), 6.92 (s, 2H, NH , exchange with
O), 5.34 (s, 2H, C CH ); FAB -MS m/z 242 ([C12 O +
2
8
D
6
H
2
5
2
opened 7-benzyl-2′-deoxyguanosine (12) eluted in fractions (10
mL) 20-33 (14 mg, 1.5%): UV pH 1, 6.9 λmin 247, λmax 272 nm,
pH 13 λmin 247 nm, λmax 265 nm.
+
2
6
H
5
11 5
H N
+
+
H] ), 152 ([C
5
H
5
N
5
O + H] ).
N -Benzyl-2′-deoxyguanosine (3) eluted in fractions 83-111:
mp 219-220 °C; TLC R ) 0.15 in MeOH/CHCl (2:8): UV pH
2
Unreacted 2′-deoxyguanosine (1) eluted in fractions 36-56.
1-Benzyl-2′-deoxyguanosine (10) eluted in fractions 70-114
(50 mg, 5.8%): UV pH 1 λmin 234 nm, λmax 260 nm, 279 nm (sh),
pH 6.9 λmin 231 nm, λmax 257 nm, 272 nm (sh), pH 13 λmin 231
f
3
4
4
1
2
1
1
λ
min 234 nm (ꢀ ) 0.468 × 10 ), λmax 261 nm (ꢀ ) 1.31 × 10 ),
81 nm (sh) (ꢀ ) 0.825 × 10 ), pH 6.9 λmin 229 nm (ꢀ ) 0.513 ×
0 ), λmax 256 nm (ꢀ ) 1.315 × 10 ), 276 nm (sh) (ꢀ ) 0.950 ×
0 ), pH 13 λmin 239 nm (ꢀ ) 0.673 × 10 ), λmax 261 nm (ꢀ )
4
4
4
1
nm, λmax 257 nm, 271 nm (sh); H NMR δ 7.98 (1H, s, 8-H), 7.17-
4
4
6 5 2 2
7.34 (5H, m, C H ), 7.02 (2H, s, NH , exchange with D O), 6.14

Benzylation of 2′-Deoxyguanosine
Chem. Res. Toxicol., Vol. 11, No. 6, 1998 699
(
1H, t, J ) 6.04 Hz, H-1′), 5.24 (2H, s, 1-C
br s, OH-3′, exchanges with D O), 4.97 (1H, br s, OH-5′,
exchanges with D O), 4.35 (1H, m, H-3′), 3.82 (1H, m, H-4′),
.54 (2H, m, H-5′), 2.54 (1H, m, H-2′b), 2.22 (1H, m, H-2′a);
6
H
5
CH
2
N), 5.10 (1H,
mental Section) of the TFE reaction filtrate revealed the
presence of only unreacted 2′-deoxyguanosine and a trace
amount of guanine. No other products were present. In
contrast to these data, chromatographic analyses of
2
2
3
+
+
+
FAB -MS m/z 358 ([C17
HRFAB -MS calcd for C17
Ben zyla tion of 2′-Deoxygu a n osin e (1) in DMA Con ta in -
in g Na OH a n d AgNO . To a stirred solution of 2′-deoxygua-
nosine (0.65 g, 2.43 mmol) in 13 mL of DMA was added 0.13 g
of NaOH (3.2 mmol). When all the NaOH had dissolved, ground
silver nitrate (0.4 g, 2.4 mmol) was added followed by the
dropwise addition of benzyl bromide (0.28 mL, 2.32 mmol) over
a 2-min period. The reaction mixture was stirred at room
temperature for 72 h. The resulting solution was evaporated
to dryness to produce a crude solid. This solid was stirred twice
H
19
N
H
5
O
4
+ H] ), 242 ([C12
11 5
H N O + H] );
-
product mixtures derived from the reaction of 1 (pro-
+
20
N
5
O
4
358.1514, found 358.1500.
duced from 1 in TFE by the addition of NaOH) with
2
benzyl bromide indicated formation of N -benzyl-2′-
3
deoxyguanosine (3) in significant yield (45%) accompa-
2
2
nied by much lower yields of N ,N -dibenzyl-2′-deoxy-
2
6
2
guanosine (4), N ,O -dibenzyl-2′-deoxyguanosine (5), 1,N -
6
dibenzyl-2′-deoxyguanosine (6), O -benzyl-2′-deoxygua-
nosine (7), 3-benzylguanine (8), and 4-benzyl-5-guanidino-
1
-(â-D-2′-deoxyribofuranosyl)imidazole (9). No 7-benzyl-
guanine derivatives were detected in these reactions.
in 50 mL of MeOH/H
2
O (1:1) at 50 °C and was filtered to remove
2
The structure of N -benzyl-2′-deoxyguanosine (3)
undissolved AgBr. The combined filtrates were chromato-
graphed under the same conditions as described for the benzy-
lation of 2′-deoxyguanosine in DMA containing NaOH. The
product distribution was the same as that observed in the
(
Scheme 1) was established by comparison of its mass,
1
UV, and H NMR spectral characteristics with those of
2
1
the ribonucleoside, N -benzylguanosine (1). The H NMR
spectrum of 3 in DMSO-d showed an exchangeable one-
proton triplet at δ 6.88 coupled to a two-proton doublet
for the benzylic hydrogens at δ 4.50. On addition of D O,
3
absence of AgNO .
6
6
Ben zyla tion of O -Ben zyl-2′-d eoxygu a n osin e (7) in TF E
Con ta in in g Na OH or Tr ieth yla m in e. To a stirred solution
of 7 (178.57 mg, 0.5 mmol) in 3 mL of TFE was added 25 mg of
NaOH (0.6 mmol) or triethylamine (0.084 mL, 0.6 mmol) at room
temperature. Benzyl bromide (0.06 mL, 0.5 mmol) was added
dropwise to the reaction mixture which was stirred at room
temperature in the dark for 72 h. The resulting solution was
evaporated to a yellow solid which was redissolved in 15 mL of
2
the triplet disappeared and the benzylic hydrogens
appeared as a singlet. These findings were consistent
with attachment of the benzyl group through the benzylic
2
carbon to the exocyclic N -position on 2′-deoxyguanosine.
The mass spectral properties of products 4-6 indicated
that each was a dibenzylated nucleoside exhibiting a
molecular ion at m/z 477. The UV absorption spectrum
of 4 showed that the molecule could dissociate in alkaline
solution suggesting that the 1-position was unsubsti-
tuted. Additionally, the spectral characteristics were not
MeOH/H
2
O (1:1) and was loaded on a Sephadex LH-20 column
O (1:1) at 1 mL/min. UV
(
2.8 × 78 cm) eluted with MeOH/H
2
absorption was monitored at 280 nm, and fractions (10 mL) were
6
collected. Unreacted O -benzyl-2′-deoxyguanosine (7) eluted in
fractions 76-96.
6
6
consistent with substitution at either the O - or 7-posi-
O ,7-Dibenzylguanine (13) eluted in fractions 101-121 (17
mg, 10%): UV pH 1 λmin 259 nm, λmax 290 nm, pH 6.9 239 nm
tion. This suggested that both benzyl residues in the
product were attached to the exocyclic amino group of
(sh),_λmin 260 nm, λmax 286 nm, pH 13 239 nm (sh), λmin 260
1
1
nm, λmax 287 nm; H NMR δ 8.29 (1H, s, 8-H), 7.24-7.51 (10H,
m, 2C
C
the 2′-deoxyguanosine. The H NMR spectrum of 4 was
6
H
CH
5
), 6.17 (2H, s, NH
2
, exchange with D
2
+
O), 5.42 (2H, s,
consistent with this assignment since it showed the
presence of a normal 2-deoxyribose residue but failed to
exhibit any peaks for an exchangeable exocyclic amino
proton. Instead, it showed superimposed two-proton ab
quartets with resonances at δ 4.86, 4.83, 4.81, and 4.78
(J ab ) 16.5 Hz) for four benzylic protons. These data are
consistent with a structure having two benzyl groups
6
H
5
2
O), 5.37 (2H, s, 7-C
6
H
5
CH
2
); FAB -MS m/z 332
+
+
+
([C19
H
17
N
5
O + H] ), 242 ([C12
H
11
N
5
O + H] ); HRFAB -MS calcd
for C19
18 5
H N O 332.1511, found 332.1503.
Hydrolysis of this compound in 0.1 N HCl at 70 °C for 1 h
afforded a product with the same UV absorption characteristics
as 7-benzylguanine (2) (15). N ,O -Dibenzyl-2′-deoxyguanosine
2
6
(5) eluted in fractions 136-163 (30 mg, 13%).
2
attached to the exocyclic N -nitrogen of 2′-deoxygua-
Ben zyla tion of 1-Ben zyl-2′-d eoxygu a n osin e (10) in TF E
nosine. The UV absorption spectrum for compound 5
Con ta in in g Na OH. Benzylation of 10 and column chroma-
tography were carried out exactly as described for the benzy-
lation of 7 (see above). Fractions 35-70 contained a mixture
of imidazole ring-opened 1,7-dibenzyl-2′-deoxyguanosine (14)
and unreacted 10. These fractions were pooled and rechro-
matographed (see below). 1,7-Dibenzylguanine (11) eluted in
fractions 87-103 (10 mg, 6%). Rechromatography of pooled
fractions 35-70 on the Sephadex LH-20 column eluted with
6
resembled that for an O -substituted 2′-deoxyguanosine
although the various maxima appeared at longer wave-
length than those for 7. Overall, the UV spectral
characteristics for 5 most closely resembled those for
2
6
2
6
N ,O -dimethyl-2′-deoxyguanosine and N ,O -dimeth-
ylguanosine published previously (17, 18). No spectral
shifts in wavelength under alkaline conditions were
observed with 5 suggesting that the dissociable proton
2
MeOH/H O (1:9) provided the imidazole ring-opened 1,7-diben-
zyl-2′-deoxyguanosine (14) in fractions 41-60 (9 mg, 4%): UV
pH 1, 6.9, 13 λmin 250 nm, λmax 276 nm. Unreacted 1-benzyl-
1
at the 1-position was absent in the structure. The H
2
′-deoxyguanosine (10) eluted in fractions 70-115.
NMR spectrum for 5 was confirmatory of structure since
it showed a singlet for one pair of benzylic hydrogens at
δ 5.48 (assignable to attachment of the benzyl carbon to
Resu lts a n d Discu ssion
6
the O -position) and a doublet (δ 4.51) for benzylic protons
2
The reaction of neutral 2′-deoxyguanosine (1) in TFE
coupled to a single exchangeable N -hydrogen (δ 7.61)
produced only 7-benzylguanine (2, 21% yield; Scheme 1)
which precipitated during the course of the reaction
together with guanine resulting from acid hydrolysis of
which appeared as a triplet (J CHNH ) 6.4 Hz). The UV
2
absorption spectra of 6 resembled that for N -benzyl-2′-
deoxyguanosine under acidic and neutral aqueous condi-
tions, although the spectrum for 6 in alkali was not
changed significantly from that in neutral solution. This
suggested that the two benzyl groups were attached to
1
. Compound 2 was crystallized as the hydrochloride
from dilute hydrochloric acid solution. Its chromato-
graphic and spectroscopic properties were identical to
those of authentic samples of 7-benzylguanine prepared
previously (15, 16). Chromatographic analysis (Experi-
2
1
the 1- and N -positions on 2′-deoxyguanosine. H NMR
data showed a singlet for one pair of benzylic hydrogens

7
00 Chem. Res. Toxicol., Vol. 11, No. 6, 1998
Moon and Moschel
at δ 5.34 (assignable to benzylic attachment to the
-position) and a doublet (δ 4.51) for the second pair of
Sch em e 2
1
2
benzylic protons coupled to a single exchangeable N -
proton which appeared as a triplet at δ 7.65 (J CHNH
.2 Hz). The chromatographic and spectroscopic proper-
)
5
6
ties of O -benzyl-2′-deoxyguanosine (7) were identical to
those of an authentic sample (13, 14). Compound 8 was
concluded to be 3-benzylguanine on the basis of its H
1
1
NMR and UV spectra. The H NMR spectrum showed a
two-proton singlet for the benzylic hydrogens at δ 5.34
and no protons assignable to a 2-deoxyribofuranosyl
residue. The UV absorption spectra agreed well with
those reported for 3-methylguanine (19) and 3-ben-
zylguanine described previously (20). Compound 9,
4
-benzyl-5-guanidino-1-(â-D-2′-deoxyribofuranosyl)imida-
zole, could be detected by thin-layer chromatography
after its color development with a nitroprusside-ferri-
cyanide-hydroxide spray reagent (3 ,4, 6, 7). However,
its very low yield did not permit a detailed spectroscopic
characterization.
for the benzylic hydrogens in the neutral form of 2 and
0 appear at δ 5.41 and 5.24, respectively. The structural
assignment for compound 12 was based on its UV
absorption characteristics which were the same as those
reported for the imidazole ring-opened form of other
1
-
Clearly, benzylation of 1 in TFE directs reaction away
2
from the 7-position and produces N -benzylguanine in
significant yield together with lesser amounts of a variety
2
of other products (many of which are derived from N -
7
-substituted guanine nucleosides (17, 18).
benzylation), while the benzylation of 1 in TFE leads only
to reaction at the 7-position. This site was previously
shown to be the major site of reaction of guanosine with
benzyl bromide in DMA (15). In contrast, the reaction
The presence of silver nitrate in these reaction solu-
tions had no effect on the product distributions in either
TFE or DMA. Thus, the major determinants of product
distributions were the ionic form of 2′-deoxyguanosine
and the reaction solvent. However, while the reaction
-
of 1 with benzyl bromide in DMA (Scheme 1) produced
products derived from reaction at the 1-position [i.e.,
-
of 1 in DMA resulted in formation of products derived
1
-benzyl-2′-deoxyguanonsine (10)], both the 1- and 7-po-
from reaction at the 1- and/or 7-position, the reaction of
sitions [1,7-dibenzylguanine (11)], and the 7-position [e.g.,
an imidazole ring-opened form of 7-benzyl-2′-deoxygua-
nosine (12)]. The mass spectrum for 10 indicated the
product was a monobenzylated nucleoside. Its UV spec-
tra in neutral and alkaline aqueous solvents were very
similar indicating that the purine portion of the nucleo-
side did not ionize in alkali which was consistent with
-
1
in TFE led primarily to reaction at the exocyclic amino
-
group. Since the iminolate tautomeric form of 1 (Scheme
) resembles the structure of O -benzyl-2′-deoxyguanine
6
1
(7) (21), we examined the reaction of 7 with benzyl
bromide in alkaline TFE solution (Scheme 2) and com-
pared the products formed with those produced in the
reaction of 1-benzyl-2′-deoxyguanosine (10) with benzyl
bromide under the same solvent conditions (Scheme 2).
The benzyl group at the 1-position in 10 locks the guanine
moiety in the predominant tautomeric form of the neutral
nucleoside, while the benzyl group in 7 locks the nucleo-
side in the iminol tautomeric form (21). Significantly,
1
substitution at the 1-position. The H NMR data for this
compound showed a singlet for the benzylic hydrogens
of 10 at δ 5.24 and no resonance for an exchangeable
1
-proton in the δ 10-11 range where the resonance for
2
the 1-proton on 2′-deoxyguanosine or on N -substituted
products appears (see Experimental Section). These data
were consistent with the 1-benzyl-2′-deoxyguanosine (10)
assignment and were consistent with the spectral prop-
erties exhibited by the ribonucleoside, 1-benzylguanosine
2
benzylation of 7 led to roughly equal amounts of N -
6
substituted and 7-substituted O -benzylguanine products
(i.e., 5 and 13), while the benzylation of 10 led only to
products derived from reaction at the 7-position (i.e., 11
and 14). The structures for 13 and 14 were assigned on
(1, 2). The mass spectrum for compound 11 suggested
that the molecule was a dibenzylated guanine derivative.
The UV spectra for compound 11 under both neutral and
alkaline conditions resembled the spectrum for neutral
1
the basis of their H NMR and/or UV absorption proper-
ties. The spectroscopic properties for 13 were consistent
6
with data for several 7-substituted O -benzylguanine
7
-benzylguanine (2) suggesting that no alkali-dissociable
derivatives (22, 23). Thus, the product distribution
observed in the benzylation of 7 (Scheme 2) clearly
protons were present in the molecule. The similarity of
the UV absorption spectra for neutral 11 and neutral 2
suggested that one benzyl group was attached to the
6
indicates that the exocyclic amino group of O -benzyl-2′-
deoxyguanosine is more reactive than the amino group
7
-position. The lack of a spectral change in alkaline
of 1-benzyl-2′-deoxyguanosine toward benzyl bromide and
solution would be consistent with a second benzyl group
-
suggests that the iminolate anionic form of 1 probably
being attached to the 1-position in place of the dissociable
1
contributes to the enhanced nucleophilicity of the amino
1
1
-proton in a molecule such as 2. The H NMR data for
1 were consistent with this assignment since no peaks
-
group in 1 compared to that in 1.
for protons on a 2-deoxyribose residue were present. In
addition the spectra showed a peak for one set of benzylic
hydrogens at δ 5.45 assignable to benzyl group attach-
ment at the 7-position and a second set of benzylic
hydrogens at δ 5.22 resulting from attachment of the
benzyl group to the 1-position. The analogous resonances
We previously showed that the neutral form of 2′-
deoxyguanosine reacts with 7-(bromomethyl)benz[a]an-
thracene in TFE to produce N -(benz[a]anthracen-7-
ylmethyl)-2′-deoxyguanosine in reasonable quantity. We
interpreted this to be a result of the solvent’s ionizing
power which favored formation of a soft, stabilized ionic
2

Benzylation of 2′-Deoxyguanosine
Chem. Res. Toxicol., Vol. 11, No. 6, 1998 701
intermediate from 7-(bromomethyl)benz[a]anthracene
that reacted preferentially with the exocyclic amino group
on 2′-deoxyguanosine (8). Since benzyl bromide is not
able to ionize as readily as 7-(bromomethyl)benz[a]-
anthracene in TFE, its preferential reaction at the
Ack n ow led gm en t. This research was supported by
the National Cancer Institute, DHHS, under contract
with ABL.
Refer en ces
7
-position of neutral 2′-deoxyguanosine is not unexpected
since 7-substitution is favored with agents that react by
an S 2 mechanism, such as simple methylating agents
e.g., methyl iodide, dimethyl sulfate, or methyl meth-
(
1) Moschel, R. C., Hudgins, W. R., and Dipple, A. (1979) Selectivity
in nucleoside alkylation and aralkylation in relation to chemical
carcinogenesis. J . Org. Chem. 44, 3324-3328.
N
(
(2) Moschel, R. C., Hudgins, W. R., and Dipple, A. (1980) Aralkylation
of guanosine by the carcinogen N-nitroso-N-benzylurea. J . Org.
Chem. 45, 533-535.
anesulfonate) (24). Reaction at the 7-position of guanine
nucleosides is also favored in dipolar aprotic solvents
(
3) Moschel, R. C., Hudgins, W. R., and Dipple, A. (1981) A novel
product from the reaction of p-methylbenzyl chloride with gua-
nosine in neutral aqueous solution. Tetrahedron Lett. 22, 2427-
(
e.g., DMA) with both benzyl bromide and 7-(bromom-
ethyl)benz[a]anthracene (25) since these solvents en-
hance rates for S 2-type reactions and do not favor
2
430.
N
(
4) Moschel, R. C., Hudgins, W. R., and Dipple, A. (1981) Dissociation
aralkyl halide ionization. With 2′-deoxyguanosine anion
6
of O -(p-methoxybenzyl)guanosine in aqueous solution to yield
-
(
1 ) in DMA, benzylation at the 1-position accompanies
guanosine, p-methoxybenzylguanosines, and 4-(p-methoxybenzyl)-
5-guanidino-1-â-D-ribofuranosylimidazole. J . Am. Chem. Soc. 103,
5489-5494.
reaction at the 7-position since the nucleophilicity of the
-
1
-position in 1 is greatly enhanced compared to the same
(
5) Moschel, R. C., Hudgins, W. R., and Dipple, A. (1984) Substituent-
induced effects on the stability of benzylated guanosines: model
systems for the factors influencing the stability of carcinogen-
modified nucleic acids. J . Org. Chem. 49, 363-372.
site in the neutral nucleoside. On the basis of these data,
-
one might then expect that the benzylation of 1 in TFE
would also produce 1- and 7-benzyl-2′-deoxyguanosine
products (and perhaps some minor products) since the
ionizing power of the TFE solvent is probably not
adequate to produce an ionic intermediate from benzyl
(6) Moschel, R. C., Hudgins, W. R., and Dipple, A. (1986) Reactivity
effects on site selectivity in nucleoside aralkylation: a model for
the factors influencing the sites of carcinogen-nucleic acid interac-
tions. J . Org. Chem. 51, 4180-4185.
(7) Moschel, R. C., Hudgins, W. R., and Dipple, A. (1986) Electrophilic
attack at carbon-5 of guanine nucleosides: structure and proper-
ties of the resulting guanidinoimidazole products. In Role of Cyclic
Nucleic Acid Adducts in Carcinogenesis and Mutagenesis (Singer,
B., and Bartsch, H., Eds.) IARC Scientific Publication No. 70, pp
235-240, IARC, Lyon, France.
bromide. Surprisingly, however, the major site of ben-
zylation of the 1- in TFE was the N2-position. Only a
trace amount of a 1-substituted product and no 7-sub-
stituted products were detected (Scheme 1). Data for the
-
reaction of 7-(bromomethyl)benz[a]anthracene with 1 in
(
8) Pei, G. K., and Moschel, R. C. (1990) Aralkylation of 2′-deoxy-
guanosine: medium effects on sites of reaction with 7-(bromom-
ethyl)benz[a]anthracene. Chem. Res. Toxicol. 3, 292-295.
TFE was similar to that for the benzyl bromide reaction
2
since N -(benz[a]anthracen-7-ylmethyl)-2′-deoxyguanosine
was the major product, although reaction at the 1-posi-
tion was more readily detected in the 7-(bromomethyl)-
benz[a]anthracene reactions (8).
(
9) Moschel, R. C. (1994) Reaction of aralkyl halides with nucleic acid
components and DNA. In DNA Adducts: Identification and
Biological Significance (Hemminki, K., Dipple, A., Shuker, D. E.
G., Kadlubar, F. F., Segerb a¨ ck, and Bartsch, H., Eds.) IARC
Scientific Publication No. 128, pp 25-36, IARC, Lyon, France.
It is interesting to compare our data with those for the
methylation of 1 by N-methyl-N-nitrosourea in aqueous
solutions as a function of increasing pH (26). Under
neutral aqueous conditions, methylation occurred pri-
marily at the 7-position to produce 7-methyl-2′-deoxygua-
nosine and 7-methylguanine accompanied by lesser
(10) Bentley, T. W., and Schleyer, P. v. R. (1977) Medium effects on
the rates and mechanisms of solvolytic reactions. Adv. Phys. Org.
Chem. 14, 1-67.
(
11) Singer, B., and Kusmierek, J . T. (1983) Escherichia coli poly-
2
4
merase I can use O -methylthymidine or O -methylthymidine in
place of deoxythymidine in primed poly(dA-dT)•poly (dA-dT)
synthesis. Proc. Natl. Acad. Sci. U.S.A. 80, 4884-4888.
6
amounts of 1- and O -methyl-2′-deoxyguanosine (26).
(
12) Pegg, A. E., Boosalis, M., Samson, L., Moschel, R. C., Byers, T.
L., Swenn, K., and Dolan, M. E. (1993) Mechanism of inactivation
However, reactions under more alkaline conditions with
-
1
produced substantial increases in the amounts of 1-
6
6
of human O -alkylguanine-DNA alkyltransferase by O -ben-
zylguanine. Biochemistry 32, 11998-12006.
6
and O -methyl-2′-deoxyguanosine relative to 7-substitut-
ed products (26). Benzylation of anionic guanosine in
water was shown to favor reaction primarily at the N -
(13) Robins, M. J ., and Robins, R. K. (1969) Purine nucleosides. XXIV.
A new method for the synthesis of guanine nucleosides. The
preparation of 2′-deoxy-R- and -â-guanosines and the correspond-
2
position, although lower amounts of products derived
2
ing N -methyl derivatives. J . Org. Chem. 34, 2160-2163.
6
from reaction at the 7-, 1-, and O -positions were detected
(14) Pauly, G. T., Powers, M., Pei, G. K., and Moschel, R. C. (1988)
6
(3-6). Thus, these data emphasize major differences
Synthesis and properties of H-ras DNA sequences containing O -
substituted 2′-deoxyguanosine residues at the first, second, or both
positions of codon 12. Chem. Res. Toxicol. 1, 391-397.
between nucleoside aralkylation and alkylation as ex-
emplified by methylation. Although details of the mecha-
nistic differences between benzylation and methylation
(
15) Brookes, P., Dipple, A., and Lawley, P. D. (1968) The preparation
and properties of some benzylated nucleosides. J . Chem. Soc.
2026-2028.
-
of 1 are not completely understood, they reflect the
(
16) Rogers, G. T., and Ulbricht, T. L. V. (1968) 7-Benzylguanine. In
Synthetic Procedures in Nucleic Acid Chemistry Vol. 1 (Zorbach,
W. W., and Tipson, R. S., Eds.) pp 15-17, Wiley-Interscience, New
York.
reactivity differences exhibited by alkylating (24, 27)
versus aralkylating carcinogens (9, 28) in neutral aque-
ous DNA reactions. It is well-known that the alkylating
agents react with DNA guanine residues at the 7- and
(17) Farmer, P. B., Foster, A. B., J arman, M., and Tisdale, M. J . (1973)
The alkylation of 2′-deoxyguanosine and of thymidine with
diazoalkanes. Biochem. J . 135, 203-213.
6
O -positions (24, 26, 27), while the aralkylating carcino-
2
gens primarily react at the N -position (9, 28). It remains
(
18) Singer, B. (1975) UV spectral characteristics and acidic dissocia-
tion constants of 280 alkyl bases, nucleosides and nucleotides.
In Handbook of Biochemistry and Molecular Biology, Vol. 1,
Nucleic Acids, 3rd ed. (Fasman, G. D., Ed.) pp 409-447.
to be determined if the reaction between 2′-deoxygua-
nosine anion and more complex alkylating agents (e.g.,
isopropylating or tert-butylating agents) in TFE provides
2
(19) Townsend, L. B., and Robins, R. K. (1968) 3-methylguanine. In
Synthetic Procedures in Nucleic Acid Chemistry, Vol. 1 (Zorbach,
W. W., and Tipson, R. S., Eds.) pp 18-21, Wiley-Interscience, New
York.
a general route to N -alkylated products. This could be
2
very useful since N -alkylated guanine nucleosides are
not available by alkylation of the neutral nucleoside.

7
02 Chem. Res. Toxicol., Vol. 11, No. 6, 1998
Moon and Moschel
(
20) Miyaki, M., and Bunji, S. (1970) NfN alkyl and glycosyl migra-
tion of purines and pyrimidines. III. NfN alkyl and glycosyl
migration of purine derivatives. Chem. Pharm. Bull. 18, 1446-
acids, polynucleotides, and nucleosides. Biochemistry 10, 4323-
4330.
(
26) Golding, B. T., Bleasdale, C., McGinnis, J ., M u¨ ller, S., Rees, H.
T., Rees, N. H., Farmer, P. B., and Watson, W. P. (1997) The
mechanism of decomposition of N-methyl-N-nitrosourea (MNU)
in water and a study of its reactions with 2′-deoxyguanosine, 2′-
deoxyguanosine 5′-monophosphate and d(GTGCAC). Tetrahedron
1
456.
(21) Shapiro, R. (1968) The chemistry of guanine and its biologically
significant derivatives. Prog. Nucleic Acid Res. Mol. Biol. 8, 73-
1
12.
(
22) Moschel, R. C., McDougall, M. G., Dolan, M. E., Stine, L., and
Pegg, A. (1992) Structural features of substituted purine deriva-
5
3, 4063-4082.
6
(27) Shuker, D. E. G., and Bartsch, H. (1994) DNA adducts of
nitrosamines. In DNA Adducts: Identification and Biological
Significance (Hemminki, K., Dipple, A., Shuker, D. E. G., Kad-
lubar, F. F., Segerb a¨ ck, and Bartsch, H., Eds.) IARC Scientific
Publication No. 128, pp 73-89, IARC, Lyon, France.
tives compatible with depletion of human O -alkylguanine-DNA
alkyltransferase. J . Med. Chem. 35, 4486-4491.
(
(
(
23) Chae, M.-Y., McDougall, M. G., Dolan, M. D., Swenn, K., Pegg,
6
A. E., and Moschel, R. C. (1994) Substituted O -benzylguanine
6
derivatives and their inactivation of human O -alkylguanine-DNA
alkyltransferase. J . Med. Chem. 37, 342-347.
24) Lawley, P. D. (1984) Carcinogenesis by alkylating agents. In
Chemical Carcinogens, 2nd ed. (Searle, C. E., Ed.) ACS Mono-
graph 182, Vol. 1, pp 325-484, American Chemical Society,
Washington, DC.
(28) Dipple, A. (1994) Reactions of polycyclic aromatic hydrocarbons
with DNA. In DNA Adducts: Identification and Biological
Significance (Hemminki, K., Dipple, A., Shuker, D. E. G., Kad-
lubar, F. F., Segerb a¨ ck, and Bartsch, H., Eds.) IARC Scientific
Publication No. 128, pp 107-129, IARC, Lyon, France.
25) Dipple, A., Brookes, P., Mackintosh, D. S., and Rayman, M. P.
(1971) Reaction of 7-bromomethylbenz[a]anthracene with nucleic
TX980012M