A new method for the synthesis of N2-alkylguanosines using mitsunobu reaction as a key step

Article abstract of DOI:10.1081/NCN-100105245

Peracetylated guanosine was reacted with POCl₃ to give an 2-acetamido-6-chloro-9H-purine derivative, which was condensed with primary or secondary alcohols to give N²-alkylated analogues. The products were treated with mercaptoethano

Full text of DOI:10.1081/NCN-100105245

This article was downloaded by: [Stanford University Libraries]
On: 10 October 2012, At: 08:57
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,
37-41 Mortimer Street, London W1T 3JH, UK
Nucleosides, Nucleotides and Nucleic Acids
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/lncn20
2
A NEW METHOD FOR THE SYNTHESIS OF N -
ALKYLGUANOSINES USING MITSUNOBU REACTION AS A
KEY STEP
a
a
b
Shigetada Kozai , Aya Yorikane & Tokumi Maruyama
a
Institute of Pharmacognosy, Faculty of Pharmaceutical Sciences, Tokushima Bunri
University, Yamashiro-cho, Tokushima, 770-8514, Japan
b
Institute of Pharmacognosy, Faculty of Pharmaceutical Sciences, Tokushima Bunri
University, Yamashiro-cho, Tokushima, 770-8514, Japan
Version of record first published: 17 Aug 2006.
2
To cite this article: Shigetada Kozai, Aya Yorikane & Tokumi Maruyama (2001): A NEW METHOD FOR THE SYNTHESIS OF N -
ALKYLGUANOSINES USING MITSUNOBU REACTION AS A KEY STEP, Nucleosides, Nucleotides and Nucleic Acids, 20:8, 1523-1531
To link to this article: http://dx.doi.org/10.1081/NCN-100105245
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to
anyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representation that the contents
will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should
be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims,
proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in
connection with or arising out of the use of this material.

NUCLEOSIDES, NUCLEOTIDES & NUCLEIC ACIDS, 20(8), 1523À1531 (2001)
A NEW METHOD FOR THE SYNTHESIS OF
2
N -ALKYLGUANOSINES USING MITSUNOBU
REACTION AS A KEY STEP
Shigetada Kozai, Aya Yorikane, and Tokumi Maruyama*
Institute of Pharmacognosy, Faculty of Pharmaceutical Sciences,
Tokushima Bunri University, Yamashiro-cho, Tokushima
770-8514, Japan
ABSTRACT
Peracetylated guanosine was reacted with POCl to give an 2-acetamido-
3
6
-chloro-9H-purine derivative, which was condensed with primary or
2
secondary alcohols to give N -alkylated analogues. The products were
treated with mercaptoethanol in the presence of sodium methoxide to
a€ord N -alkylguanosines.
2
INTRODUCTION
2
Recently, N -alkylguanosine has attracted the attention of many che-
mists since the discovery of this type of compound in cells. For instance, the 5 -
0
termini of nuclear RNAs involved a unique permethylated ribonucleoside of
1
2
0
0
2
,2,7-tri-N-methylguanosine (A) . An N -ethyl-2 -deoxyguanosine 3 -mono-
phosphate (B) moiety has been reported to be involved in the granulocyte and
lymphocyte DNA of alcohol abusers at a high level as the ultimate DNA
2
2
adduct of acetaldehyde . Robertson reported the formation of the N -sub-
stituent (C) by the reaction of deoxyguanosine with dehydroretronecine,
a carcinogenic metabolite of the pyrrolizidine alkaloid monocrotaline .
3
*
Corresponding author. Fax: ‡81-88-622-9611; E-mail: maruyama@ph.bunri-u.ac.jp
523
1
Copyright # 2001 by Marcel Dekker, Inc.
www.dekker.com

1524
KOZAI, YORIKANE, AND MARUYAMA
2
Also, interaction of N -substituted guanosine triphosphates with cellular and
oncogenic ras-p21 proteins has been reported .
4
2
The synthesis of N -alkylguanosine has been achieved by alkylation of
6
the O -silylated guanosine with 1,3-benzodithiolylium tetra¯uoroborate
5
2
(
BDTF) . In the case of N -ethyl-guanosine, one-step reaction of guanosine
6
with acetaldehyde and NaBH CN has been reported by Sako et al . Also,
3
reduction of the amide group of acyl nucleosides was performed with borane
7
to give the corresponding N-alkyl nucleosides . However, those methods are
limited to a primary alkyl group. For the synthesis of the guanosine analogue
bearing a secondary alkyl group, a nucleophilic displacement of inosine-2-
8
sulfonic acid or 2-halogeno-inosines has been used . Recently, the Mitsunobu
reaction has been employed as a method for N-alkylation of a heterocyclic
9
3
compound . We already reported a new method for the synthesis of N -alkyl-
5
10
-¯uorouracils . In this paper, a novel method to introduce a secondary as
2
well as a primary alkyl group onto the N position of guanosine using the
Mitsunobu reaction as a key step is described.
RESULTS
0
0
0
5
2
2
3
Peracetylation of guanosine (1a) gave N ,O ,O ,O -tetraacetyl-
guanosine (1b), which was treated with POCl (6.0 eq) in the presence of
3
1
1
N,N-dimethylaniline (1.0 eq) in CH CN
at re¯ux temperature for
3
3
0 min to a€ord 2-acetamido-6-chloro-9-(2,3,5-tri-O-acetyl-b-D-ribofur-
anosyl)purine (2) in 69% yield. Then, compound 2 (10 mmol) was treated
with 2-propanol (30 mmol), tributylphosphine (30 mmol) and 1,1 -azo-
0
ꢀ
1
2
bis(N,N-dimethylformamide) (30 mmol) in dry THF (200 mL) at 50 C for
3
h and separated by a column of silica gel. From the ®rst fraction 6-chloro-
2
2-(N -isopropyl)acetamido-9-(2,3,5-tri-O-acetyl-b-D-ribofuranosyl)purine
(
3a) was obtained in 61% yield. Change of the solvent to 1,4-dioxane
decreased the yield to 41%. When diisopropyl azodi-carboxylate and tri-
phenylphosphine were employed as a condensing agent, the imino ether 4
as well as the desired 3a was observed on thin-layer chromatography (tlc).

2
SYNTHESIS OF N -ALKYLGUANOSINES
1525
Scheme.
It is supposed that the bulky agents proceed the condensation of 2-pro-
panol with the imino form of 2, which is less susceptable to steric hin-
drance. A trial to convert 3a to the guanosine derivative was achieved by
13
the method of Lee et al . Thus, compound 3a (1 mmol) was re¯uxed with
-mercaptoethanol (0.3 ml, 4.3 mmol) and 0.06 M NaOMe in MeOH
50 mL, 3 mmol) under nitrogen atmosphere overnight. After work-up of
2
(
the solution, the mixture was separated by a column of silica gel to give 5a
and 6 in 65% and 19% yields, respectively. The major product (5a) showed
2
a similar absorption to that of N -methylguanosine on UV spectrum, and
correlation between Me CH- and C2 was observed on the HMBC spectrum
2
2
as shown in the Figure. Thus, compound 5a was proved to be N -iso-
propylguanosine. However, the H-NMR spectrum of the minor product
1
6
2
(
6) showed the methyl signals of O -CH and N -COCH , and HR-MS
3
3
suggested that the formula of 6 should be C H N O . Combined with
1
6
23
5
6
2
HMBC correlation, compound
6
was identi®ed as 2-(N -iso-
propyl)acetamido-6-methoxy-9-(b-D-ribofuranosyl)purine. When 3a was
treated with NaOMe alone, 6 was obtained as the sole product in quan-
titative yield. Next, we explored the reaction of 2 with ( Æ )-1-phenyletha-
nol. Thus, 2 (2 mmol) was condensed with ( Æ )-1-phenylethanol (6 mmol)
0
using tributylphosphine (6 mmol) and 1,1 -azobis(N,N-dimethylformamide)

1526
KOZAI, YORIKANE, AND MARUYAMA
Figure. HMBC correlations of the base moieties of compounds 4, 5a and 6.
ꢀ
(
6 mmol) in dry THF (20 mL) at 50 C for 1 h and subsequent treatment
2
with mercaptoethanol and NaOMe a€orded N -(1-phenylethyl)-guanosine
5b) as a mixture of diastereomers in 60% overall yield from 2. However,
(
reaction of 2 with cyclohexanol gave the condensate (3c) only in 13% yield
and the reaction of 2 with tert-butanol was unsuccessful. These results
suggest the diculty to introduce a cycloalkyl and a tertiary alkyl group.
On the other hand, treatment of 2 with primary alcohols using the similar
conditions as described above gave 3dÀf. However, the yield of the pro-
ducts was in a range of 50À57%, which is less satisfactory compared with
5À8
the methods already established in the earlier report
.
2
As a conclusion, we have developed a method to obtain N -alkylgua-
nosine in 4 steps. It became possible to introduce an alcohol on exocyclic
amino of guanosine. It should be emphasized that the secondary alcohol is
possible to condense with 2. However, cyclic secondary alcohol such as
cyclohexanol was proved to be less reactive under the reaction condition,
indicating the diculty to prepare the guanosine derivative bearing a cyclic
secondary alkyl group.
EXPERIMENTAL
Melting points (mp) were determined using a Yanagimoto micro-
melting point apparatus (hot stage type) and are uncorrected. UV spectra
were recorded with a Shimadzu UV-190 digital spectrometer. Low resolution
mass spectra were obtained on a Shimadzu-LKB 9000B mass spectrometer in
the direct-inlet mode. High resolution mass spectra were obtained on a JMS
1
AX-500 spectrometer in the direct-inlet mode. H-NMR spectra were
recorded on either Varian UNITY 200 (200 MHz) or Varian UNITY 600
(
600 MHz) in CDCl3 (or dimethyl sulfoxide (DMSO)-d ) with tetra-
6
methylsilane as an internal standard. Merck Art 5554 plates precoated with
silica gel 60 containing ¯uorescent indicator F254 were used for thin-layer
chromatography and silica gel 60 (Merck 7734, 60À200 mesh) was employed
for column chromatography.

2
SYNTHESIS OF N -ALKYLGUANOSINES
1527
6
-Chloro-2-acetamido-(2,3,5-tri-O-acetyl-b-D-ribofuranosyl)purine (2). To a
0
0
0
5
2
2
3
solution of N ,O ,O ,O -tetraacetylguanosine (1b, 22.88 g, 63.8 mmol) in
acetonitrile (500 ml) was added N, N-dimethylaniline (8ml, 63.8mmol) and
phosporyl chloride (35 ml, 383 mmol) and the solution was re¯uxed for
30 min. Then the solution was concentrated to a small volume and the
residue was partitioned between CHCl (400 ml) and water (400 ml). The
3
organic layer was washed with 5% NaHCO (300 ml) and water (300 ml),
3
dried over MgSO , and chromatographed over a column of silica gel
4
(
6
5.0640 cm) using a 33À80% AcOEt in hexane to give a caramel (20.66 g,
‡
9%). HR-MS m=z: 469.0965 (M , C H ClN O requires 469.1001). UV
1
8
20
5
8
1
lmax (MeOH) nm: 288, 258. H-NMR (CDCl ) d: 8.25 (1H, br s, N-H), 8.13
3
0
0
(
5
1H, s, H8), 6.09 (1H, d, J ˆ 4.4 Hz, H1 ), 5.91 (1H, dd, J ˆ 4.4, 5.5 Hz, H2 ),
0
0
0
.76 (1H, dd, J ˆ 5.1, 5.5 Hz, H3 ), 4.40À4.55 (3H, m, H4 , H5 ), 2.46 (3H, s,
N-Ac), 2.16 (3H, s, Ac), 2.11 (3H, s, Ac), 2.10 (3H, s, Ac).
6-Chloro-2-(N-isopropyl)acetamido-(2,3,5-tri-O-acetyl-b-D-ribofuranosyl)purine
(
3a). Method 1. To a mixture of 2 (4.7 g, 10 mmol) and 2-propanol (4.5 ml,
3
3
0 mmol) in dry THF (200 ml) was added tributylphosphine (7.5 ml,
0
0 mmol) and 1,1 -azobis(N,N-dimethylformamide) (5.16 g, 30 mmol) and
ꢀ
the solution was stirred at 50 C for 3 h, then concentrated to a small
volume. The residual solution was chromatographed over a column of
silica gel G (3.0660 cm) using a 25À66% AcOEt in benzene to give a
‡
caramel (3.10 g, 61%). HR-MS m=z: 511.1465 (M , C H ClN O requires
2
1
26
5
8
1
511.1470). UV lmax (MeOH) nm: 265. H-NMR (CDCl ) d: 8.33 (1H, s, H8),
3
0
0
6
.20 (1H, d, J ˆ 4.9 Hz, H1 ), 5.82 (1H, dd, J ˆ 5.2, 5.5 Hz, H2 ), 5.50 (1H, dd,
0
0
J ˆ 5.2, 5.5 Hz, H3 ), 4.97 (1H, q, J ˆ 6.9 Hz, CH), 4.49À4.51 (1H, m, H4 ),
0
4
2
.37À4.44 (2H, m, H5 ), 2.16 (3H, s, N-Ac), 2.14 (3H, s, Ac), 2.08(3H, s, Ac),
.07 (3H, s, Ac), 1.30 (3H, d, J ˆ 6.9 Hz, CH ), 1.28(3H, d, J ˆ 6.9 Hz, CH ).
3
3
Method 2. To a mixture of 2 (470 mg, 1 mmol) and 2-propanol (0.45 ml,
mmol) in dry THF (15 ml) was added triphenylphosphine (0.788 mg,
mmol) and diisopropyl azodicarboxylate (0.6 ml, 3 mmol) and the
solution was stirred at 50 C overnight, then concentrated to a small
volume. The residual solution was chromatographed over a column of
silica gel G (2.0635 cm) using a 25À75% AcOEt in hexane. Evaporation
of the ®rst fraction gave to N-[6-chloro-9-(2,3,5-tri-O-acetyl-b-D-
3
3
ꢀ
ribofuranosyl)purin-2-yl]-1-propoxyethylimine (4) as a caramel (94 mg,
‡
1
8%). HR-MS m=z: 511.1468(M , C H ClN O requires 511.1470). UV
2
1
26
5
8
1
lmax (MeOH) nm: 288. H-NMR (CDCl ) d: 8.15 (1H, s, H8), 6.25 (1H, d,
3
0
0
0
J ˆ 5.2 Hz, H1 ), 5.87 (1H, t, J ˆ 5.5 Hz, H2 ), 5.57À5.59 (1H, m, H3 ),
0
0
5
2
.29À5.33 (1H, m, CH), 4.34À4.45 (3H, m, H4 , H5 ), 2.15 (3H, s, Ac),
.14 (3H, s, Ac), 2.08(3H, s, Ac), 2.03 (3H, s, CH ), 1.35 (3H, d, J ˆ 6.3 Hz,
3
1
3
CH ), 1.34 (3H, d, J ˆ 6.3 Hz, CH ). C-NMR (150 MHz, DMSO-d ) d:
3
3
6
1
70.2, 169.5 and 169.3 (CˆO X 3), 165.8(C ˆN), 161.5 (C6), 152.9 (C4),

1528
KOZAI, YORIKANE, AND MARUYAMA
0
0
0
1
(
(
51.8 (C2), 141.9 (C8), 128.2 (C5), 85.9 (C1 ), 80.3 (C3 ), 73.0 (C2 ), 70.5
0
0
C5 ), 69.8(CH), 62.9 (C4 ), 21.68and 21.72 (CH X 2), 20.7, 20.5 and 20.4
3
CH CO X 3), 18.2 (CH CˆN). From the second fraction a mixture of 3a
3
3
and triphenylphosphine oxide was obtained.
Conversion of 3a to 5a. To a solution of 3a (512 mg, 1 mmol) in methanol
50 ml) was added 2-mercaptoethanol (0.3 ml, 4.3 mmol) and 28% sodium
(
methoxide in methanol (0.58ml, 3 mmol). The solution was stirred and
heated at re¯ux temperature under a nitrogen atmosphere overnight. Then
‡
the solution was chromatographed over Amberlite IR-120 (NH4 form)
(
10 ml) using a methanol, then concentrated to a small volume. The
residual solution was chromatographed over a column of silica gel G
2.0653 cm) using a 0À50% MeOH in AcOEt. First fraction was
evaporated to give 2-isopropylamino-6-methoxy-9-(b-D-
ribofuranosyl)purine (6) as a caramel (72 mg, 19%), HR-MS m=z: 381.1635
(
‡ ‡
M , C H N O requires 381.1649), 249.1235 (M -ribofuranosyl,
16 23 5 6
(
C H N O requires 249.1226). UV l
(MeOH) nm: 259, lmax (0.1 M
11
15
5
2
max
1
NaOH) nm: 258. H-NMR (CDCl ) d: 8.19 (1H, s, H8), 5.92 (1H, d,
3
0
0
0
J ˆ 6.6 Hz, H1 ), 5.23 (1H, d, J ˆ 8.5 Hz, 5 OH), 4.77À4.84 (3H, m, H2 ,
0
0
0
2
OH, CH), 4.45À4.46 (1H, m, H3 ), 4.31 (1H, br s, 3 OH), 4.29 (1H, q,
0
0
J ˆ 1.9 Hz, H4 ), 4.17 (3H, s, OCH ), 3.89À3.92 (1H, m, H5 a), 3.74À3.78
3
0
(
1H, m, H5 b), 1.93 (3H, s, Ac), 1.25 (3H, d, J ˆ 6.6 Hz, CH ), 1.18(3H, d,
3
13
J ˆ 6.9 Hz, CH ). C-NMR (150 MHz, DMSO-d ) d: 170.4 (CH (CO)-N),
3
6
3
0
1
(
(
61.5 (C6), 153.3 (C2), 151.3 (C4), 143.4 (C8), 121.4 (C5), 91.1 (C1 ), 87.1
0
0
0
0
C3 ), 74.3 (C2 ), 71.5 (C5 ), 62.7 (C4 ), 54.9 (OCH ), 48.5 (CH), 23.4
3
2
CH (CO)-N), 21.0 and 20.6 (CH X 2). From the second fraction N -
3
3
isopropylguanosine (5a) was obtained as white crystals (211 mg, 65%), mp
ꢀ
1
2
97.5À200 C. Anal Calcd for C H N O Á 0.3 H O: C, 47.21; H, 5.97; N,
1
3
19
5
5
2
‡
1.18. Found: C, 47.47; H, 5.95; N, 20.92. MS m=z: 193 (M -ribofuranosyl).
UV lmax (MeOH) nm: 256.5, lmax (0.1 M NaOH) nm: 260.5. H-NMR
DMSO-d )d: 10.32 (1H, br s, N -H), 7.94 (1H, s, H8), 6.30 (1H, d,
1
1
(
6
2
0
J ˆ 7.4 Hz, N -H), 5.70 (1H, d, J ˆ 6.0 Hz, H1 ), 4.52 (1H, t, J ˆ 5.5 Hz,
0
0
H2 ), 4.11 (1H, dd, J ˆ 3.6, 4.9 Hz, H3 ), 3.94À4.01 (1H, m, CH), 3.87 (1H,
13
0
0
dd, J ˆ 4.4, 8.0 Hz, H4 ), 3.62 (1H, dd, J ˆ 4.4, 11.8Hz, H5 a), 3.51 (1H, dd,
0
J ˆ 4.7, 11.8Hz, H5 b), 1.18(6H, d, J ˆ 6.3 Hz, CH X2). C-NMR
3
(
1
2
150 MHz, DMSO-d ) d: 156.5 (C6), 151.8(C2), 150.1 (C4), 136.2 (C )8 ,
6
0
0
0
0
0
16.7 (C5), 86.9 (C1 ), 85.2 (C3 ), 73.3 (C2 ), 70.5 (C5 ), 61.6 (C4 ), 42.3 (CH),
2.4 and 22.3 (CH X 2).
3
2
N -(1-Phenylethyl)guanosine (5b). To a mixture of 2 (940 mg, 2 mmol)
and ( Æ )-1-phenyletanol (0.72 ml, 6 mmol) in dry THF (20 ml) was added
0
tributylphosphine (1.5 ml, 6 mmol) and 1,1 -azobis(N, N-dimethylformamide)
(
ꢀ
1.03 g, 6 mmol) and the solution was stirred at 50 C for 1 h. Then the
solution was concentrated to a small volume, and chromatographed over a

2
SYNTHESIS OF N -ALKYLGUANOSINES
1529
column of silica gel G (2.2650 cm) using a 25À75% AcOEt in benzene to
2
give
6-chloro-2-[N -(1-phenylethyl)acetamido]-9-(2,3,5-tri-O-acetyl-b-D-
ribofuranosyl)purine (3b) as a syrup. The product was dissolved in
methanol (100 ml) and 2-mercaptoethanol (0.6 ml, 8.6 mmol) and 28%
sodium methoxide in methanol (1.16 ml, 6 mmol) was added to the
solution. The solution was re¯uxed under a nitrogen atmosphere overnight,
‡
then passed through a column of Amberlite IR-120 (NH form) (20 ml). The
eluant and washing was concentrated to a small volume and the residual
4
solution was chromatographed over a column of silica gel G (2.6624 cm)
2
using a 0À50% EtOH in CHCl to give N -(1-phenylethyl)guanosine as a
3
‡
mixture of diastereomers. Caramel (462 mg, 60%). MS m=z: 255 (M -
ribofuranosyl). UV l
(MeOH) nm: 257, lmax (0.1 M NaOH) nm: 262.5.
max
1
1
H-NMR (DMSO-d ) d: 10.36 (0.46 H, br s, A: N -H), 10.35 (0.54 H, br s, B:
6
1
N -H), 7.92 (0.46 H, s, A: H8), 7.94 (0.54 H, s, B: H8), 7.24À7.41 (5H, m,
0
Ph), 6.92À6.95 (1H, m, N-H), 5.66 (0.46 H, d, J ˆ 5.8Hz, A: H1 ), 5.69 (0.54
0
0
H, d, J ˆ 5.5 Hz, B: H1 ), 5.01À5.16 (1H, m, CH), 4.40À4.48(1H, m, H2 ),
0
0
0
4
3
.09À4.11 (1H, m, H3 ), 3.84À3.88 (1H, m, H4 ), 3.52À3.58(1H, m, H5 a),
0
.37À3.41 (1H, m, H5 b), 1.47 (1.38H, d, J ˆ 3.8, Hz, A: CH ), 1.48(1.62 H,
3
d, J ˆ 3.8, Hz, B: CH ).
3
6-Chloro-2-(N-cyclohexyl)acetamido-9-(2,3,5-tri-O-acetyl-b-D-ribofuranosyl)
purine (3c). To a mixture of 2 (940 mg, 2 mmol) and cyclohexanol (0.63 ml,
6
mmol) in dry THF (20 ml) was added tributylphosphine (1.5 ml, 6 mmol)
0
and 1,1 -azobis(N,N-dimethylformamide) (1.03 g, 6 mmol) and the solution
was stirred at 50 C overnight, then concentrated to a small volume. The
residual solution was chromatographed over a column of silica gel
ꢀ
(
2.5643 cm) using a 25À80% AcOEt in hexane. From the second fraction,
‡
3
c was obtained as a caramel (147 mg, 13%), HR-MS m=z: 551.1807 (M ,
1
(MeOH) nm: 269. H-NMR
C H ClN O requires 551.1783). UV l
24
30
5
8
max
0
(
CDCl ) d: 8.33 (1H, s, H8), 6.19 (1H, d, J ˆ 5.1 Hz, H1 ), 5.83 (1H, dd,
3
0
0
J ˆ 5.1, 5.6 Hz, H2 ), 5.51 (1H, dd, J ˆ 5.1, 5.4 Hz, H3 ), 4.32À4.55 (4H, m,
0
0
H4 , H5 , one of cyclohexyl), 2.16 (3H, s, Ac), 2.14 (3H, s, Ac), 2.09 (3H, s,
Ac), 2.08(3H, s, Ac), 1.23 À1.93 (10H, m, ten of cyclohexyl). Fourth fraction
was evaporated to recover starting material in 52%. Also a small amount of
the unknown products were obtained from the ®rst and third fraction.
6-Chloro-2-(N-ethyl)acetamido-9-(2,3,5-tri-O-acetyl-b-D-ribofuranosyl)purine
(
3d). To a mixture of 2 (940 mg, 2 mmol) and ethanol (0.35 ml, 6 mmol) in
dry THF (20 ml) was added tributylphosphine (1.5 ml, 6 mmol) and 1,1 -
0
azobis(N,N-dimethylformamide) (1.03 g, 6 mmol) and the solution was
stirred at 50 C for 1 h, then concentrated to a small volume. The residual
ꢀ
solution was chromatographed over a column of silica gel G (2.2630 cm)
using a 25À75% AcOEt in benzene to give a caramel (498mg, 50%). HR-MS
‡
m=z: 497.1334 (M , C H ClN O requires 497.1373). UV l
(MeOH)
max
20
24
5
8

1530
KOZAI, YORIKANE, AND MARUYAMA
1
nm: 288.5, 262. H-NMR (CDCl ) d: 8.23 (1H, s, H8), 6.14 (1H, d,
3
0
0
J ˆ 4.8Hz, H1 ), 5.89 (1H, dd, J ˆ 4.8, 5.5 Hz, H2 ), 5.51 (1H, t, J ˆ 5.5 Hz,
0
0
0
H3 ), 4.37À4.49 (3H, m, H4 , H5 ), 4.16 (2H, q, J ˆ 7.0 Hz, CH ), 2.46 (3H, s,
2
N-Ac), 2.16 (3H, s, Ac), 2.12 (3H, s, Ac), 2.10 (3H, s, Ac), 1.23 (3H, t,
J ˆ 7.0 Hz, CH3).
6-Chloro-2-(N-propyl)acetamido-9-(2,3,5-tri-O-acetyl-b-D-ribofuranosyl)purine
(
3e). To a mixture of 2 (940 mg, 2 mmol) and n-propanol (0.45 ml, 6 mmol)
in dry THF (20 ml) was added tributylphosphine (1.5 ml, 6 mmol) and 1,1 -
0
azobis(N,N-dimethylformamide) (1.03 g, 6 mmol) and the solution was
stirred at 50 C for 1 h, then concentrated to a small volume. The residual
ꢀ
solution was chromatographed over a column of silica gel G (2.2640 cm)
using a 25À75% AcOEt in benzene to give a caramel (536 mg, 52%), HR-MS
‡
1
m=z: 511.1474 (M , C H ClN O requires 511.1471). UV l
(MeOH)
max
21
26
5
8
nm: 287.5, 263. H-NMR (CDCl ) d: 8.24 (1H, s, H8), 6.15 (1H, d,
3
0
0
J ˆ 4.8Hz, H1 ), 5.86 (1H, dd, J ˆ 4.8, 5.5 Hz, H2 ), 5.50 (1H, t, J ˆ 5.5 Hz,
0
0
0
H3 ), 4.38À4.51 (3H, m, H4 , H5 ), 4.04À4.11 (2H, m, CH ), 2.43 (3H, s, N-
2
Ac), 2.16 (3H, s, Ac), 2.13 (3H, s, Ac), 2.09 (3H, s, Ac), 1.58À1.70 (2H, m,
CH ), 0.90 (3H, dd, J ˆ 7.3, 7.7 Hz, CH ).
2
3
6-Chloro-2-(N-butyl)acetamido-9-(2,3,5-tri-O-acetyl-b-D-ribofuranosyl)purine
(
3f). To a mixture of 2 (470 mg, 1 mmol) and n-butanol (0.27 ml, 3 mmol) in
dry THF (10 ml) was added tributylphosphine (0.75 ml, 3 mmol) and 1,1 -
0
azobis(N,N-dimethylformamide) (0.52 g, 3 mmol) and the solution was
stirred at 50 C overnight, then concentrated to a small volume. The
residual solution was chromatographed over a column of silica gel G
ꢀ
(
5
2630 cm) using a 25À80% AcOEt in hexane to give a caramel (536 mg,
‡
7%), HR-MS m=z: 525.1584 (M , C H ClN O requires 525.1627). UV
2
2
28
5
8
1
lmax (MeOH) nm: 288, 263. H-NMR (CDCl ) d: 8.24 (1H, s, H8), 6.16 (1H,
3
0
0
d, J ˆ 4.7 Hz, H1 ), 5.84 (1H, dd, J ˆ 4.9, 5.5 Hz, H2 ), 5.50 (1H, dd, J ˆ 5.2,
0
0
0
5
(
(
.5 Hz, H3 ), 4.35À4.49 (3H, m, H4 , H5 ), 4.11 (2H, t, J ˆ 7.4 Hz, CH ), 2.43
2
3H, s, N-Ac), 2.16 (3H, s, Ac), 2.14 (3H, s, Ac), 2.09 (3H, s, Ac), 1.55À1.62
2H, m, CH ), 1.29À1.36 (2H, m, CH ), 0.91 (3H, dd, J ˆ 7.4, 7.1 Hz, CH ).
2
2
3
ACKNOWLEDGMENT
0
We thank Professor Tetsuto Tsunoda for the supplement of 1,1 -azo-
bis(N,N-dimethyl-formamide) and helpful comments.
REFERENCES
1
2
.
.
Reddy, R.; Busch, H. Prog. Nucleic Acid Res. Molec. Biol. 1983, 30, 127À162.
Fang, J.-L.; Vaca, C.E. Carcinogenecis. 1997, 18, 627À632.

2
SYNTHESIS OF N -ALKYLGUANOSINES
1531
3
4
.
.
Robertson, K.A. Cancer Res. 1982, 42, 8À14.
Noonan, T.; Brown, N.; Dudycz, L.; Wright, G.J. Med. Chem. 1991, 34,
1302À1307.
5
6
7
.
.
.
Sekine, M.; Satoh, T.J. Org. Chem. 1991, 56, 1224À1227.
Sako, M.; Kawada, H.; Hirota, K.J. Org. Chem. 1999, 64, 5719À5721.
Sergueeva, Z.A.; Sergueeva, D.S.; Shaw, B.R. Nucleosides, Nucleotides &
Nucleic Acids 2000, 19, 275À282.
8
9
.
.
Yamazaki, A.; Okutsu, M.J. Heterocyclic Chem. 1978, 15, 353À358.
Mitsunobu, O. Synthesis, 1981, 1À28.
1
0. Kozai, S.; Fukagawa, T.; Maruyama, T.J. Chem. Soc., Prekin Trans. 1, 1998
(
19), 3145À3146.
1
1
1
1. Robins, M.J.; Uznanski, B. Can. J. Chem. 1981, 59, 2601À2607.
2. Tsunoda, T.; Otsuka, J.; Yamamiya, Y.; Ito, S. Chem. Lett. 1994, 539À542.
3. Lee, W.W.; Tong, G.L. SyntheticProceduresinNucleicAcidChemistry ; Zorbach,
W.W.; Tipson, R.S., Eds.; John Wiley & Sons: New York, 1968; 224À227.
Received July 12, 2000
Accepted July 2, 2001