Reaction of O6-methylguanosine with nitrite in the presence of carboxylic acid: Synthesis of the purin-2-yl carboxylate

Article abstract of DOI:10.1016/j.tetlet.2005.09.140

O6-Methylguanosine derivative was treated with sodium nitrite or isoamylnitrite in the presence of carboxylic acid to give the purin-2-yl carboxylate, an unusual product bearing a carboxylic group at the 2-position of the purine moiety.

Full text of DOI:10.1016/j.tetlet.2005.09.140

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 8225–8228
Reaction of O6-methylguanosine with nitrite in the presence
of carboxylic acid: synthesis of the purin-2-yl carboxylate
a,
b
a
b
*
Tokumi Maruyama, Nobuyasu Moriwaka, Yosuke Demizu and Masami Ohtsuka,
a
Faculty of Pharmaceutical Sciences at Kagawa Campus, Tokushima Bunri University, Shido 1314-1, Sanuki City,
Kagawa 769-2193, Japan
Faculty of Medical and Pharmaceutical Sciences, Kumamoto University, Ohe-Honmachi 5-1, Kumamoto 862-0973, Japan
b
Received 14 July 2005; revised 9 September 2005; accepted 16 September 2005
Available online 10 October 2005
Abstract—O6-Methylguanosine derivative was treated with sodium nitrite or isoamylnitrite in the presence of carboxylic acid to give
the purin-2-yl carboxylate, an unusual product bearing a carboxylic group at the 2-position of the purine moiety.
ꢀ
2005 Elsevier Ltd. All rights reserved.
It has been considered that alkylating agents are the
causative chemicals of cancer. Particularly important is
the alkylation of guanosine. In 1986, monoclonal anti-
body-based immunoanalytical methods for detection of
carcinogen-modified DNA components was developed
preservation, the effect of the nitrites on tumors has long
been discussed. Also nitric oxide overproduction has
6
been implicated in the pathogenesis of many disorders,
including artherosclerosis, neurodegenerative diseases,
inflammatory and auto-immune diseases as well as can-
0
7
and O6-alkyl-2 -deoxyguanosine in DNA was detected
cers. However, no report has described the reaction of
1
in cancer cells. Repair of nucleosides alkylated at the
O6-alkylguanosine with nitrites.
O6-guanine is mediated by an O6-alkylguanine–DNA
transferase (AGT) which removes only the alkyl group
and inhibition of enzymatic repair of O6-methyl-2 -deoxy-
We directed our attention to the aromaticity of the O6-
alkylguanosines. It is anticipated that O6-alkylation of
guanosine increases aromaticity of the purine moiety
since the 6-oxo form was abolished. The diazonium
ion prepared from O6-alkylguanosine could be stabi-
lized by resonance and receive substitution by nucleo-
0
guanosine enhances mutagenesis in rat liver epithelial
2
cells. Recently, Ziegel et al. reported that endogenous
5
-methylcytosine protects neighboring guanines from
N7 and O6-methylation and O6-pyridyloxobutylation
by the tobacco carcinogen 4-(methylnitrosamino)-1-
philes leaving N . Nair et al. have reported that the
2
3
(
3-pyridyl)-1-butanone. When oligodeoxynucleotides
reaction of 2-aminopurine nucleosides with the nitrite
ester in the presence of di-iodomethane gave 2-iodo-
0
modified site-specifically with O6-methyl-2 -deoxygua-
nosine (O6medG) were used as templates for DNA syn-
thesis in primer-extension reactions dTMP, accompanied
8
purine nucleosides. A nonaqueous diazotization–dedi-
azoniation method which introduces halogen at the 2
position of purine has been further revised by Robins
4
by small amounts of dCMP, was incorporated. These
9
0
miscodings during DNA synthesis predict the mutagenic
and co-workers. When 2 -deoxyguanosine was treated
0
0
potentialof O6-a lk y la tion of 2 -deoxyguanosine. Impor-
with HNO in the presence of NaCl, however, 2 -deoxy-
oxanosine and 2 -deoxyxanthosine were obtained in
2
0
tant alkylation agents such as N-alkyl-N-nitrosourea and
N-alkyl-N-nitrosoamine are formed endogeneously from
13.4% and 68.9% yield, respectively, and the 2-haloge-
5
10
amine or urea by the action of the nitrite ion. Since
nated product was obtained only in 3.3% yield. It is
nitrates and nitrites have been used as additives for food
also reported that the diazonium ion from an aromatic
compound reacts with carboxylic acid to give an acyl-
1
1
oxylated product. This background prompted us to
explore the reaction of O6-alkylguanosines with nitrite
in the presence of carboxylic acid. In this letter, we
describe the synthesis of purin-2-ylcarboxy al te, a new
type of nucleoside derivative.
Keywords: Carcinogenesis; Nucleic acid analogues; Nucleosides; Dia-
zonium ion.
*
Corresponding author. Tel.: +81 87 894 5111; fax: +81 87 894
181; e-mail: maruyama@kph.bunri-u.ac.jp
0
0040-4039/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.09.140

8226
T. Maruyama et al. / Tetrahedron Letters 46 (2005) 8225–8228
O6-Methylguanosine was prepared from 2-amino-6-
that N1–H of 5 was dissociated in alkaline condition
and the enolate ion was formed by resonance. In conclu-
sion, the structure of 4 is further enforced by the forma-
tion of 5. Next, we extended this reaction to benzoic
acid. Therefore, 2c was treated with isoamylnitrite
(2.4 equiv) in the presence of benzoic acid (2.1 equiv)
in CH Cl at room temperature for 1 h. TLC of the solu-
chloro-9-(2,3,5-tri-O-acetyl-b-D-ribofuranosyl)purine
1
2
(
1a) as follows. Compound 1a was deacylated with
ammonia in MeOH to give 2-amino-6-chloropurine
riboside (1b). However, when 1a was treated with 1 M
NaOH in MeOH, O6-methylguanosine (2a) was ob-
tained. Before treatment with the nitrite ion, the sugar-
OHs of 2a were protected to avoid undesired reaction.
A trialto introduce an acetylgroup using a conventional
method gave the tetra-acetate (3) as a major product
and the desired tri-O-acetate (2b) was obtained in only
2
2
tion showed the presence of four compounds. After
work-up of the solution and purification by silica gel
column chromatography using hexane–AcOEt as elu-
ants, the purin-2-ylbenzoate ( 6) was obtained in 38%
1
6
1
5% yield. It is supposed that the basicity of the 2-
yield. Also, 6-methoxy-9-[2,3,5-tris-O-(1,1-dimethyl-
1
7
NH group of 2a is increased compared with that of
ethyl)dimethylsilyl]-b-D-ribofuranosyl]purine (7a) and
2
1
8
guanosine. This makes it difficult to introduce an acetyl
group selectively at the sugar-OH of 2a. Therefore, 1b
was reacted with tert-butyldimethylsilyl (TBS) chloride
to afford tri-O-TBS derivative 1c in good yield. Then,
its 2-chloro congener (7b) were obtained in 5% and
24% yields, respectively. Another major by-product
was isolated from the last fraction in 32% yield and iden-
tified as O6-methylxanthosine 5. These results prompted
us to explore the reaction of 2c with an amino acid
derivative. Thus, compound 2c was treated with N-t-
Boc-L-valine in a similar manner to that of 6 to afford
1
c was subjected to the reaction with 1 M NaOH in
MeOH under mild conditions to give the O6-methyl-
1
3
guanosine derivative (2c) (Chart 1).
2
-tert-butoxycarbonyl-amino-3-methylbutyrate (8) in
1
9
Then, compound 2c was subjected to diazotization–sub-
stitution in the presence of acetic acid or an amino acid.
At first, an aqueous solution of sodium nitrite was
added to a solution of 2c in acetic acid and stirred at
room temperature for 30 min. After work-up of the
solution, the residue was chromatographed over a col-
umn of silica gel to give 4 in 79% yield as a colorless
49% yield. Undesired products, 5 and 7b were also
obtained in 22% and 19%, respectively. These results
indicate that acyloxy group could be introduced onto
2-position of O6-methylguanine nucleosides.
A reaction mechanism to provide purin-2ylcarboxy la tes
4, 6, and 8 was considered as follows. To receive substi-
tution similar to that of the Sandmyer reaction, a diazo-
nium ion should be stable. In the case of the diazonium
ion (I) derived from 2c, the positive charge delocalizes
by resonance as shown in Chart 2, in which structure
II contributes to stabilizing this ion. The intermediary
ion I receives nucleophilic attack of carboxylic acid to
afford the purin-2-ylderivatives. In the case of 4, a large
excess of nucleophile, and acetic acid, favors the forma-
1
oil. H NMR of compound 4 showed a signalattribut-
able to the 2-acetate (2.33 ppm) instead of the 2-NH2
group. The structure of 4, combined with data of
FAB-MS, UV, and IR spectra, was determined as 6-meth-
oxy-9-[2,3,5-tris-O-[(1,1-dimethyl-ethyl)dimethylsilyl]-b-
1
4
D-ribofuranosyl]purin-2-yl acetate. Since 4 was a new
type of nucleoside, the structure of 4 was further con-
firmed as follows. A solution of 4 in MeOH was treated
with aqueous ammonia at room temperature for 30 min
tion of S 2 product 4. However, compounds 6 and 8
N
1
5
to give the O6-methylxanthosine derivative 5. UV
spectra of 5 showed absorption maximum at 285 nm
in alkaline solution, almost 20 nm longer compared with
that in neutral condition. This result strongly indicates
were prepared by reaction of I with only 2.1 equiv of
benzoic acid or N-t-Boc-L-valine in CH Cl . Under the
2
2
conditions, two undesired products 7a,b were obtained
8
,9
by radical-substitution of the I. Formation of another
Cl
N
OMe
N
OMe
4
; R=Ac
N
N
N
N
N
N
N
N
O
6; R=C6H5
2
c
H
N
N
O
R 8; R=
NH2
N
NH2
O
O
O
O
Bu-t
RO
RO
TBSO
O
2
2
2
a; R=H
b; R=Ac
c; R=TBS
RO OR
RO OR
TBSO OTBS
1
a; R=Ac
1
1
b; R=H
OMe
N
OMe
OMe
N
c; R=TBS
N
N
N
NH
N
N
N
O
N
NHAc
N
O
N
X
O
O
AcO
TBSO
TBSO
AcO OAc
TBSO OTBS
TBSO OTBS
3
5
7a; R=H
7
b; R=Cl
Chart 1.

T. Maruyama et al. / Tetrahedron Letters 46 (2005) 8225–8228
8227
O6-Metylguanosine derivative
OCH3
OCH3
: OCH3
N
-N2
N
N
N
N
N
N
+
N +
O6-Methylxanthosine
N
N
+
N
N
N
–
derivative
N
+
N
Rf(TBS)3
N
5
Rf(TBS)3
I
Rf(TBS)3
+
+
OCH3
-H
RCOOH
N
N
N
+
+
+
OCH3
OCH3
OCH3
N
N
H O
C
2
C
C
RCOOH
N
N
N
Purine-2-yl
N
N
N
Rf(TBS)3
HN
C
N
H2N
carboxylates
lit. 20b
C
O
II
N
4
,6,8
N
N
RCOO
N
Rf(TBS)3
Rf(TBS)3
Rf(TBS)3
V
III
IV
O
N
N
HN
2
'-Deoxyguanosine
O
2'-Deoxy-
O
N
O
C
O
N
H
xanthosine
N
N
HN
HN
lit.20
N
N
2H2O
H O
N
dR
N +
N
-
2
+
N
+
N
N
+
N
N
–
N
O
dR
dR
dR
VII
N
VI
O
2'-Deoxy-
oxanosine
N
H N
N
2
dR
Chart 2.
undesired product 5 is explainable as follows. One
possibility is hydrolysis of the purin-2-yl carboxylates
PharmaceuticalSciences, for scientific discussion and
experimentalassistance.
6
and 8. Recently, it was shown that the deamination
0
0
of 2 -deoxyguanosine gave 2 -deoxyoxanosine and
2
proposed as the neutralkey intermediate.
0
10
-deoxyxanthosine and the cyanoimine VII has been
References and notes
2
0
Therefore,
1
. (a) Kyrtopoulos, S. A.; Vrotsou, B. Chem.–Biol. Interact.
981, 37, 191–197; (b) Wild, C. P.; Smart, G.; Saffhill, R.;
it is possible that the cyanoimine intermediate III was
formed from the diazonium ion I. When carboxylic
acids were added to III, the additive V could be formed
and subsequent ring closure affords purine-2-yl carboxy-
lates 4, 6 and 8. On the other hand, attack of water to
cyanoimine III affords undesired product 5 via IV. Like
1
Boyle, J. M. Carcinogenesis 1983, 4, 1605–1609; (c)
Adamkiewicz, J.; Ahrens, O.; Eberle, G.; Nehls, P.;
Rajewsky, M. F. In Role Cyclic Nucleic Acid Adducts
Carcinog. Mutagen; IARC Scientific Publications, 1986;
Vol. 70, pp 403–411.
0
the reaction of 2 -deoxyguanosine with nitrous acid,
however, the oxanosine derivative was not isolated by
2. (a) Alvi, N. K.; Foiles, P. G.; Williams, G. M. Mutation
Res. 1990, 230, 219–226; (b) Lyngdoh, R. H. D. J. Chem.
Soc., Perkin Trans. 2: Physical Organic Chemistry 1992,
deamination of 2c with nitrous acid or nitrite ester, sug-
0
1
173–1179.
gesting 1-oxygen of 2 -deoxyoxanosine comes from O6
0
3. Ziegel, R.; Shallop, A.; Upadhyaya, P.; Jones, R.; Tret-
of 2 -deoxyguanosine.
yakova, N. Biochemistry 2004, 43, 540–549.
4
5
. Shibutani, S.; Grollman, A. P. Cancer Lett. 1994, 83, 315–
22.
. (a) Stephanou, G.; Vlastos, D.; Vlachodimitropoulos, D.;
Demopoulos, N. A. Cancer Lett. 1996, 109, 109–114; (b)
Yoshida, K.; Yano, K.; Yano, Y. Nucleic Acids Sympos.
Series 1994, 31, 111–112.
We are looking forward to explore further reaction for
the synthesis of the 6-methoxypurine ribosides bearing
amino acids at the 2-position of purine moiety, a new
type nucleoside derivative.
3
6
. (a) Mensinga, T. T.; Speijers, G. J. A.; Meulenbelt, J.
Toxicol. Rev. 2003, 22, 41–51; (b) Boink, A.; Speijers, G.
Acta Horticult. 2001, 563, 29–36; (c) Walker, R. Royal
Soc. Chem. 1999, 237, 250–258.
Acknowledgements
The authors thank Dr. Shigetada Kozai of Tokushima
Bunri University, Faculty of Pharmaceutical Sciences
7
. Eu, J. P.; Liu, L.; Zeng, M.; Stamler, J. S. Biochemistry
2
000, 39, 1040–1047.
(
Tokushima Campus) and Dr. Tetsuo Yamasaki of
8. (a) Nair, V.; Young, D. A. J. Org. Chem. 1985, 50, 406–
408; (b) Nair, V.; Young, D. A. Synthesis 1986, 450–453;
Kyushu University of Health and Welfare, Faculty of

8228
T. Maruyama et al. / Tetrahedron Letters 46 (2005) 8225–8228
+
(
1
c) Nair, V.; Young, D. A.; DeSilvia, R., Jr. J. Org. Chem.
987, 52, 1344–1347.
262(sh), 254(sh), 235; ESI-MS(+) m/z: 767.2801 (M +Na);
1
ꢀ
FT-IR (cm ) 956, 2931, 2859, 1747, 1608, 1473.
1
9
. (a) Francom, P.; Janeba, Z.; Shibuya, S.; Robins, M. J. J.
Org. Chem. 2002, 67, 6788–6796; (b) Janeba, Z.; Francom,
P.; Robins, M. J. J. Org. Chem. 2003, 68, 989–992; (c)
Francom, P.; Robins, M. J. J. Org. Chem. 2003, 68, 666–
17. White crystals (5%); mp 97–98 ꢁC; H NMR (CDCl ) d :
3
8.52 (1H, s, 2-CH), 8.32 (1H, s, 8-CH), 4.18 (3H, s, OMe);
+
FAB-MS m/z: 626.2 (M +H); UV kmax (MeOH) nm: 248.
Anal. Calcd for C29H N O Si : C, 55.73; H, 9.03; N,
56 4 5 3
6
69.
8.96. Found: C, 55.51; H, 9.28; N, 9.02. These data were
identicalwith that of the sam pe l prepared from 6-
1
1
0. (a) Suzuki, T.; Yamaoka, R.; Nishi, M.; Ide, H.; Makino,
K. J. Am. Chem. Soc. 1996, 118, 2515–2516; (b) Suzuki,
T.; Ide, H.; Yamada, M.; Morii, T.; Makino, K. Bioorg.
Med. Chem. 2001, 9, 2937–2941.
chloropurine riboside by two steps.
1
18. Colorless oil (24%); H NMR (CDCl ): d 8.30 (1H, s);
3
+
FAB-MS m/z: 659, 661 (M +H); UV kmax (MeOH) nm:
1. (a) Huisgen, R.; Nakaten, H. Annals 1954, 586, 84–109; (b)
Franck, R. W.; Yanagi, K. J. Am. Chem. Soc. 1968, 90,
257, 266(sh).
19. Colorless oil (49%): H NMR (CDCl
1
3
): d 8.29 (1H, s, 8-
0
5814–5817; (c) Park, J. H.; Lee, Y. S.; Jung, S. H.; Park,
CH), 5.92–5.91 (1H, d, J = 4.2 Hz, 1 -CH), 5.03–5.01 (1H,
H. Bull. Korean Chem. Soc. 1995, 16, 489–492.
2. Robins, M. J.; Samano, V.; Zhang, W.; Balzarini, J.; De
Clercq, E.; Borchardt, R. T.; Lee, Y.; Yuan, C. S. J. Med.
d, J = 9.0 Hz, NH), 4.52–4.51 (1H, m, valine 2-CH), 4.49–
0
0
1
4.48 (1H, m, 2 -CH), 4.22–4.19 (1H, t, J = 4.2 Hz, 3 -CH),
0
4.07–4.03 (1H, m, OMe, 4 -CH), 3.95–3.90 (1H, dd,
0
Chem. 1992, 35, 2283–2293.
J = 3.4, 11.5 Hz, 5 -CHH), 3.72–3.68 (1H, dd, J = 2.2,
11.6 Hz, 5 -CHH), 2.34–2.26 (1H, m, valine 3-CH), 1.38
1
0
1
3. Colorless oil (70%): H NMR (CDCl
3
): d 7.98 (1H, s, 8-
0
CH), 5.91–5.89 (1H, d, J = 5.0 Hz, 1 -CH), 4.78 (2H, s, 2-
(9H, s, t-Bu), 1.04–0.97 (6H, m, valine 4-CH
(9H, s, 2 -TBS t-Bu), 0.83 (9H, s, 3 -TBS t-Bu), 0.72 (9H,
3
· 2), 0.87
0
0
NH ), 4.06 (3H, s, OMe); UV k
(MeOH) nm: 282, 249;
2
max
+
0
0
0
MS m/z: 640.7 [M +H].
s, 5 -TBS t-Bu), 0.06 (3H, s, 2 -TBS CH ), 0.05 (3H, s, 2 -
3
1
0
1
1
1
4. Colorless oil (79%): H NMR (CDCl
3
): d 4.15 (3H, s,
TBS CH
5 -TBS CH
3
), ꢀ0.01 (6H, s, 3 -TBS CH
3
· 2), ꢀ0.09 (3H, s,
1
3
0
0
13
3
); C NMR
OMe), 2.33 (3H, s, COCH
3
); C NMR (CDCl
3
): d 21.0 (2-
3
), ꢀ0.12(3H, s, 5 -TBS CH
+
Ac CH ); FAB-MS m/z 683.4 (M +H); UV k
(MeOH)
(CDCl , 300 MHz): d 170.2 (valine C@O), 162.1 (Boc
3
max
3
ꢀ
1
nm: 262(sh), 253; FT-IR (cm ) 2930, 2858, 1780, 1606,
474.
5. Colorless oil (93%); H NMR (CDCl
C@O), 155.5 (4-C), 154.8 (2-C), 152.6 (6-C), 141.6 (8-CH),
0 0 0
120.5 (5-C), 88.5 (1 -CH), 85.0 (4 -CH), 79.9 (2 -CH), 76.2
1
1
0
0
3
): d 9.98 (1H, br s, 1-
(Boc C), 71.4 (3 -CH), 62.1 (5 -CH
2
), 58.3 (valine CH),
0
0
NH), 7.58 (1H, s, 8-CH), 4.15–4.10 (5H, m, 3 -CH, 4 -CH,
54.7 (OMe), 31.7 (valine CH), 28.3 (Boc CH ), 26.1, 25.8,
3
OMe); UV kmax (MeOH) nm: 267, 245, 238, kmax (0.02 M
25.7 (t-Bu CH
C), 17.4 (valine CH
(TBS CH3); TOF-MS m/z: 862.4 (M +Na), 878.5
3
), 18.9 (valine CH
3
), 18.5, 18.0, 17.8 (t-Bu
+
NaOH) nm: 285, 248; ESI-MS m/z: 663.2667 [M +Na];
3
), ꢀ4.39, ꢀ4.80, ꢀ4.91, ꢀ5.37, ꢀ5.43
ꢀ
1
+
FT-IR (cm ) 3226, 2955, 2931, 2860, 1667, 1630, 1473.
1
+
6. Colorless oil (38%): H NMR (CDCl ): d 8.31 (1H, s, 8-
(M +K); UV k
(MeOH) nm: 262(sh), 253.
3
max
CH), 8.23–8.21 (2H, d, J = 9.6Hz, Ph 2,6-CH), 7.67–7.63
20. (a) Rayat, S.; Glaser, R. J. Org. Chem. 2003, 68, 9882–
9892; (b) Rayat, S.; Majumdar, P.; Tipton, P.; Glaser, R.
J. Am. Chem. Soc. 2004, 126, 9960–9969.
(
1H, t, J = 8.0Hz, Ph 4-CH), 7.53–7.50 (2H, t, J = 7.8 Hz,
Ph 3,5-CH), 4.17 (3H, s, OMe); UV kmax (MeOH) nm: