Synthesis of 2'-deoxy-2'-fluoroguanyl-(3',5')-guanosine.

Article abstract of DOI:10.1081/NCN-120016479

The protected analogue of 2-amnio-6-chloropurine arabinoside (3b) was subjected to reaction with diethylaminosulfur trifluoride (DAST) and subsequently treated with NaOAc in Ac2O/AcOH to give N2, O3', O5'-triacetyl-2'-deoxy-2'-fluoroguanosine (5a). After

Full text of DOI:10.1081/NCN-120016479

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SYNTHESIS of 2′-DEOXY-2′-FLUOROGUANYL-(3′,5′)-
GUANOSINE
Tokumi Maruyama a , Shigetada Kozai a , Kazuo Nakamura b & Masachika Irie c
a Tokushima Bunri University, Yamashiro-cho, Tokushima, 770-8514, Japan
b School of Pharmaceutical Sciences, Showa University, 1-5-8 Hatanodai, Shinagawa-ku,
Tokyo, 142-8555, Japan
c Department of Microbiology, Hoshi College of Pharmacy, Ebara 2-4-41, Shinagawa-ku,
Tokyo, 142-8501, Japan
Version of record first published: 31 Aug 2006
To cite this article: Tokumi Maruyama, Shigetada Kozai, Kazuo Nakamura & Masachika Irie (2002): SYNTHESIS of 2′-DEOXY-2′-
FLUOROGUANYL-(3′,5′)-GUANOSINE, Nucleosides, Nucleotides and Nucleic Acids, 21:11-12, 765-774
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NUCLEOSIDES, NUCLEOTIDES & NUCLEIC ACIDS
Vol. 21, Nos. 11 & 12, pp. 765–774, 2002
SYNTHESIS OF 20-DEOXY-20-FLUOROGUANYL-
(30,50)-GUANOSINE
Tokumi Maruyama,1,* Shigetada Kozai,1 Kazuo Nakamura,2
and Masachika Irie3
1Faculty of Pharmaceutical Sciences, Tokushima Bunri University,
Yamashiro-cho, Tokushima 770-8514, Japan
2School of Pharmaceutical Sciences, Showa University, 1-5-8
Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan
3Department of Microbiology, Hoshi College of Pharmacy, Ebara
2-4-41, Shinagawa-ku, Tokyo 142-8501, Japan
ABSTRACT
The protected analogue of 2-amnio-6-chloropurine arabinoside (3b) was
subjected to reaction with diethylaminosulfur trifluoride (DAST) and
0
0
subsequently treated with NaOAc in Ac2O=AcOH to give N2; O3 ; O5-
triacetyl-20-deoxy-20-fluoroguanosine (5a). After deacetylation of the
sugar moiety and protection of 50-OH by a 4,40-dimethoxytrityl group,
this nucleoside component was converted to 20-deoxy-20-fluoroguanyl-
(30,50)-guanosine (6c, GfpG).
Ribonucleases (RNases) are very important enzymes for RNA metabolism in
almost all organisms; they include those that hydrolyze only single-stranded
RNA, double-stranded RNA, and RNA hybridized with DNA. The mode of
hydrolysis is thought to be via a 20,30-cyclic phosphated intermediate at the
30-terminus of oligonucleotides, ultimately forming oligo- or mononucleotides
with a terminal 30-phosphated (transferase-type RNase). Recently, some
*Corresponding author. E-mail: maruyama@ph.bunri-u.ac.jp
765
DOI: 10.1081=NCN-120016479
Copyright # 2002 by Marcel Dekker, Inc.
1525-7770 (Print); 1532-2335 (Online)
www.dekker.com

766
MARUYAMA ET AL.
ribonucleases showed biological activity in addition to digestion of RNAs.
RNase A was demonstrated to show toxicity to tumor cells, both in vitro[1]
and in vivo.[2,3] Also, onconase, discovered from the Northern lieopard frog,[4]
has emerged as a promising cancer chemotherapeutic agent. To elucidate the
structure-function relationship of ribonucleases, X-ray crystallographic ana-
lysis of ribonucleases complexed with the analogues of dinucleoside mono-
phosphate was achieved in many laboratories,[5–8] An especially important
analogue is 20-deoxy-20-fluoroguanyl-(30,50)-cytidine (GfpC),[9] in which the
20-hydroxyl group (20-OH) of guanosine is replaced by a 20-fluorine atom
to prevent the transesterification step.
The synthesis of 20-deoxy-20-fluoronucleosides has been accomplished
by several routes including nucleophilic displacement of 20-O-trifluoro-
methanesulfonylarabinosides.[10,11] Recently, a method to introduce fluorine
into the sugar moiety of guanine nucleosides using diethylaminosulfur tri-
fluoride (DAST) has been developed.[12] However, problems still remain in
respect of the yields and the analogues modified at the base moiety. This
background prompted us to develop a new method to introduce fluorine at
the downside of the 20-carbon of guanosine. This paper reports a method
for the synthesis of 20-deoxy-20-fluoroguanosine in which treatment of the
protected 2-amino-6-chloropurine arabinoside with DAST was involved as
a key step.
An attempt at the conversion of 1a to the 20-O-acetyl arabinoside (2)
was made by application of the method of Fukukawa et al.[13] Thus,
treatment of 1a with 1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane afforded
the corresponding 30,50-O-(tetraisopropyldisiloxan-1,3-diyl) derivative 1b.[14]
Compound 1b was allowed to react with trifluoromethanesulfonyl chloride
in the presence of Et3N and 4-dimethylaminopyridine in THF to give the
20-O-triflate 1c. An SN2 displacement with the acetate anion at the 20-
position of 1c was employed to obtain the 20(S )(ara)-O-acetate 2a. At this
stage, the silyl protecting group should be changed to a group stable to the
fluoride anion. Desilylation of 2a with 2 equivalents of tetrabutyl-
ammonium fluoride in the presence of acetic acid at 0ꢀC for 15 min afforded
2b.[15] Since acyl protection causes neighboring group participation in the
nucleophilic substitution, ethereal groups were chosen as a protecting
group.[16] Reaction of 2b with trityl chloride in pyridine gave a ditrityl
derivative (3a), which was successively treated with 3,4-dihydro-2H-pyran
0
and ammonia in methanol to give the N2,O5 -ditrityl-2-amino-6-chloro-[3-O-
(tetrahydro-2-pyranyl)-9-b-D-arabinofuranosyl]-purine (3b). Then, 3b was
treated with DAST in the presence of pyridine in CH2Cl2 to afford the 20-
fluoride 4 in 60% yield, a key intermediate for the synthesis of base-
modified analogues. No spot other than 4 was observed on TLC. When the
DAST reaction was tried in the absence of pyridine, the protecting groups
were removed from 3b and 4 to give a complicated result. Reaction to
convert the 6-chloro atom of 4 to 6-oxo was carried out by treatment with

20-DEOXY-20-FLUOROGUANYL-(30,50)-GUANOSINE
767
Scheme 1.

768
MARUYAMA ET AL.
Figure 1. NOESY spectrum of 5b.
NaOAc in Ac2O-AcOH. Also, two trityl groups and the tetrahydro-2-pyr-
anyl group were removed in acidic medium, followed by acetylation with
30 50
Ac2O to afford N2,O ,O -triacetyl-20-deoxy-20-fluoroguanosine (5a). Com-
pound 5a was subjected to partial deacylation with 2M NaOH in MeOH at
1
0ꢀC to afford 5b. The H-NMR spectrum of 5b indicated that the 20-
fluorine caused a downfield shift of the 20-proton and a large H20-C-F
geminal coupling (52.7 Hz), and the nuclear Overhauser effect (NOE) was
observed between H20 and H30 in the two-dimensional NOE (NOESY)
spectrum of 5b (Fig. 1). Therefore, the structure of 5b was unequivocally
determined. Then, a 4,40-dimethoxytrityl group was introduced at 50-OH of
5b to give a nucleoside component 5c.
20-Deoxy-20-fluoroguanyl-(30,50)-guanosine (6c) was prepared accord-
ing to the established phosphite-triester method.[17] Thus, 5c was treated
with N,N-diisopropyl-methylphosphonamidic chloride in the presence of
triethylamine in dry CH2Cl2. Monitoring the phosphitylating reaction by
thin-layer chromatography (TLC) revealed the appearance of the 30-O-
(N,N-diisopropylamino)phosphramidites as a mixture of diastereomers.
The products were converted to the monotetrazolides in situ and con-
densed with N2-acetyl-20,30-di-O-isobutyrylguanosine (7) to form the
dinucleotide phosphite triester. Mild oxidation and separation by silica gel
chromatography furnished the full-protected phosphate triester 6a as
a caramel in 55% overall yield from 5c. The product was deprotected
successively with CF3COOH in MeOH and ammonia in MeOH and
separated by DEAE-cellulose chromatography using 0–0.12 M triethyl-
ammonium bicarbonate (TEAB) as eluent. After removal of the solution,
the product was passed through a column of Amberlite IR120B (Naþ) to
give 20-deoxy-20-fluoroguanyl-(30,50)-guanosine (6c, Naþ salt) as a film in
34% overall yield from 5c. The structure of the product was determined
1
by the presence of two sets of sugar-protons in H NMR and FAB mass
spectroscopy (FAB-MS).
We are looking forward to obtaining the crystal structure of ribonu-
clease complexed with 20-deoxy-20-fluoroguanyl-(30,50)-guanosine.

20-DEOXY-20-FLUOROGUANYL-(30,50)-GUANOSINE
769
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
AX-500 spectrometer in the direct-inlet mode. 1H-NMR spectra were
recorded on either Varian UNITY 200 (200 MHz) or Varian UNITY 600
(600 MHz) in CDCl3 (or dimethyl sulfoxide (DMSO)-d6) with tetra-
methylsilane as an internal standard. Merck Ark 5554 plates precoated with
silica gel 60 containing fluorescent indicator F254 were used for thin-layer
chromatography and silica gel 60 (Merck 7734, 60–200 mesh) was employed
for column chromatography.
9-(2-O-Acetyl-3,5-O-tetraisopropyldisiloxan-1,3-diyl)-b-D-arabinofur-
anosyl)-2-amino-6-chloropurine (2a). 2-Amino-6-chloro-9-(3,5-O-tetraiso-
propyldisiloxan-1,3-diyl-b-D-ribofuranosyl)purine (1b) was prepared from
2-amino-6-chloro-purine riboside (1a) according to the published method.[14]
To an ice-cooled solution of 1b (19.4 g, 35.7 mmol), triethylamine
(8.8 mL), and 4-dimethylaminopyridine (7.1 g, 58 mmol) in CH2Cl2 (300 mL)
was added trifluoromethanesulfonyl chloride (7.1 mL, 66.7 mmol) and the
solution was kept at room temperature for 10 min, then water (200 mL) was
added. The organic layer was dried over MgSO4, and concentrated to a small
volume. The residual solution was chromatographed over a column of silica
gel G using 25% AcOEt in hexane. Evaporation of the fraction gave 1c as a
caramel, which was immediately dissolved in DMF (150 mL) and sodium
acetate (12 g, 146 mmol) was added. The solution was stirred at 50ꢀC for 10 h,
then partitioned between benzene (500 mL) and water (500 mL). The organic
layer was washed with water twice (500 mL), dried over MgSO4, and con-
centrated to a small volume. The residual solution was chromatographed
over a column of silica gel G using 20–33% AcOEt in hexane. Evaporation of
1
the fraction gave 2a as a caramel (13.4 g, 64%). H NMR (CDCl3) d 8.04
(1H, s, H8), 6.35 (1H, d, J ¼ 6.3 Hz, H10), 5.57 (1H, dd, J ¼ 6.3, 8.2 Hz, H20),
5.13 (2H, br s, NH2), 4.69 (1H, dd, J ¼ 8.2, 8.5 Hz, H30), 4.03–4.18 (2H, m,
H50), 3.88–3.92 (1H, m, H40), 1.78 (3H, s, Ac), 0.97–1.18 (28H, m, (CH3)2-
CH x 4); UV lmax (MeOH) nm: 249, 310; EI-MS m=z: 585, 587[Mþ].
9-(2-O-Acetyl-b-D-arabinofuranosyl)-2-amino-6-chloropurine (2b). To
a solution of 2a (13.53 g, 23.1 mmol) and AcOH (2.86 mL, 50 mmol) in dry
THF (50 mL) was added 1 M tetrabutylammonium fluoride (50 mL) and the
solution was stirred at room temperature for 2 h, ten concentrated to a small
volume. The residual solution was chromatographed over a column of silica
gel G with 0–17% EtOH in CHCl3. Evaporation of the fraction gave a

770
MARUYAMA ET AL.
caramel (7.36 g, 93%). 1H NMR (DMSO-d6) d 8.25 (1H, s, H8), 7.02 (2H, br
s, NH2), 6.30 (1H, d, J ¼ 5.5 Hz, H10), 5.87 (1H, br s, 30OH), 5.24 (1H, dd,
J ¼ 5.5, 5.8 Hz, H20), 5.07 (1H, br s, 50OH), 4.37 (1H, t, J ¼ 5.8 Hz, H30),
3.83–3.88 (1H, m, H40), 3.61–3.74 (2H, m, H50), 1.79 (3H, s, Ac); UV lmax
(MeOH) nm: 249, 310; EI-MS m=z: 343, 345 [Mþ]. HR-MS m=z: 343.0689
(Mþ, C12H14ClN5O5 requires 343.0684).
0
N2,O5 -Ditrityl-9-(2-O-acetyl-b-D-arabinofuranosyl)-2-amino-6-chloro-
purine (3a). To a solution of 2b (9.16 g, 26.7 mmol), 4-dimethylaminopyri-
dine (1.22 g, 10 mmol) and triethylamine (13.3 mL, 95 mmol) in dry DMF
(220 mL) was added trityl chloride (27.8 g, 100 mmol). The solution was
stirred at 50ꢀC overnight, then MeOH (50 mL) was added and stirring was
continued at room temperature for 1 h. The solvents were removed under
reduced pressure and the residue was partitioned between CHCl3 (300 mL)
and water (100 mL). The organic layer was washed with water (100 mL),
dried over MgSO4, and concentrated to a small volume. The residual solution
was chromatographed over a column of silica gel G using 25–50% AcOEt in
hexane. Evaporation of the fraction gave a caramel (15.34 g, 69%). 1H NMR
(CDCl3) d 7.77 (1H, s, H8), 7.18–7.45 (ca. 30H, m, Tr62), 6.63 (1H, br s,
H10), 5.71 (1H,br s, N2-H), 4.55 (1H, br s, 30OH), 4.16–4.18 (1H, m, H30),
3.98 (1H, q, J ¼ 4.9 Hz, H40), 3.35 (2H, d, J ¼ 4.9 Hz, H50), 2.72 (1H, d,
J ¼ 2.7 Hz, H20), 1.73 (3H, s, Ac); UV lmax (MeOH) nm: 259, 313; FAB-MS
m=z: 828 [Mþ], 850 [MþþNa].
0
N2,O5 -Ditrityl-2-amino-6-chloro-9-[3-O-(tetrahydro-2-phranyl)-b-D-ara-
binofuranosyl]purine (3b). To an ice-cooled solution of 3a (8.28 g, 10 mmol)
and 3,4-dihydro-2H-pyran (5 mL, 55 mmol) in dry DMF (50 mL) was added
p-toluenesulfonic acid (800 mg, 4.2 mmol), and the solution was kept at 4ꢀC
overnight, then neutralized with triethylamine. The solvents were removed
under reduced pressure and the residue was partitioned between benzene
(300 mL) and water (300 mL). The organic layer was washed with water twice
(300 mL), dried over MgSO4, and concentrated to a small volume. The
residual solution was chromatographed over a column of silica gel G using
17–25% AcOEt in hexane. Evaporation of the fraction gave a caramel, which
was dissolved in CH2Cl2 (150 mL). To the solution was added ammonia in
MeOH (100 mL), and the solution was kept at 4ꢀC overnight. The solvents
were removed under reduced pressure to give 3b as a caramel (6.99 g, 80%).
UV lmax (MeOH) nm: 255, 313; FAB-MS m=z: 870, 872 [Mþ], 892, 894
[MþþNa]. HR-MS m=z: 870.3436 (Mþ, C53H48ClN5O5 requires 870.3420).
0
N2,O5 -Ditrityl-2-amino-6-chloro-9-[2-deoxy-2-fluoro-3-O-(tetrahydro-2-
pyranyl)-b-D-ribofuranosyl]purine (4). To an ice-cooled solution of 3b
(13.52 g, 15.5 mmol) and pyridine (6.3 mL) in dry CH2Cl2 (200 mL) was
added diethylaminosulfur trifluoride (3.3 mL, 25 mmol), and the solution was

20-DEOXY-20-FLUOROGUANYL-(30,50)-GUANOSINE
771
stirred at 50ꢀC for 6 h. The whole was added dropwise to 5% NaHCO3
(500 mL) with stirring then the organic layer was diluted with CH2Cl2
(500 mL), washed water twice (500 mL), dried over MgSO4, and concentrated
to a small volume. The residual solution was chromatographed over a col-
umn of silica gel G using 15–40% AcOEt in hexane. Evaporation of the
fraction gave white crystals (8.12 g, 60%). mp 201–201.5ꢀC; UV lmax
(MeOH) nm: 260, 314; FAB-MS m=z: 872, 874 [Mþ], 894, 896 [MþþNa];
Anal Calcd for C53H47ClFN5O4: C, 72.97; H, 5.42; N, 8.03. Found: C, 72.78;
H, 5.52; N, 7.90.
30 50
N2,O ,O -Triacetyl-20-deoxy-20-fluoroguanosine (5a). A solution of 4
(4.73 g, 5.40 mmol) and sodium acetate (2.4 g, 30 mmol) in mixture of acetic
anhydride (50 mL) and acetic acid (50 mL) was stirred at 120ꢀC overnight.
Then the solvents were removed under reduced pressure and the residue was
dissolved in EtOH (30 mL). The solution was kept at room temperature for
3 hrs and concentrated to a small volume. The residue was partitioned
between CHCl3 (300 mL) and water (100 mL). The organic layer was washed
with 5% NaHCO3 (150 mL) and water (100 mL), dried over MgSO4, and
concentrated to a small volume. The residual solution was chromatographed
over a column of silica gel G using 0–10% EtOH in CHCl3. Evaporation of
the fraction and crystallization from MeOH gave white crystals (1.79 g,
1
80%). Mp 108–108.5ꢀC; H NMR (CDCl3) d 12.08 (1H, s, N1-H), 9.72 (1H,
S, N2-H), 7.78 (1H, s, H8), 6.04 (1H, m, H10), 5.56–5.68 (2H, m, H20, H30),
4.70 (1H, dd, J ¼ 4.7, 12.0 Hz, H50a), 4.48–4.50 (1H, m, H40), 4.25 (1H, dd,
J ¼ 5.5, 12.0 Hz, H50b), 2.32 (3H, s, Ac), 2.18 (3H, s, Ac), 2.07 (3H, s, Ac);
UV lmax (MeOH) nm: 259, 280; EI-MS m=z: 411 [Mþ]. HR-MS m=z:
411.1181 (Mþ, C16H18FN5O7 requires 411.1203).
N2-Acetyl-20-deoxy-20-fluoroguanosine (5b). To an ice-cooled solution
of 5a (1.40 g, 3.4 mmol) in MeOH (80 mL) was added 1 M NaOH (15 mL),
and the solution was stirred at 0ꢀC for 10 min. Then the solution was neu-
tralized with 1 M HCl and concentrated to a small volume. The residual
solution was crystallized from water (10 mL) to give white crystals (970 mg,
1
87%). Mp 235.5–237ꢀC; H-NMR (DMSO-d6) d 12.08 (1H, s, N1-H), 11.74
(1H, s, N2-H), 8.27 (1H, s, H8), 6.11 (1H, DD, J ¼ 2.5, 16.5 Hz, H10), 5.71
(1H, d, J ¼ 6.0 Hz, 30OH), 5.30 (1H, ddd, J ¼ 2.5, 4.1, 52.7 Hz, H20), 5.18 (1H,
t, J ¼ 5.2 Hz, 50OH), 4.38–4.44 (1H, m, H30), 3.95–3.97 (1H, m, H40), 3.75–
3.78 (1H, m, H50a), 3.59–3.63 (1H, m, H50b), 2.19 (3H, s, Ac); UV lmax
(MeOH) nm: 259, 280; Anal Calcd for C12H14FN5O5 ꢁ 0.2H2O: C, 43.56; H,
4.38; N, 21.17. Found: C, 43.58; H, 3.95; N, 21.01.
N2-Acetyl-50-O-(4,40-dimethoxytrityl)-20-deoxy-20-fluoroguanosine (5c). To
a solution of 5b (940 mg, 2.87 mmol) in pyridine (50 mL) was added

772
MARUYAMA ET AL.
4,40-dimethoxytrityl chloride (2.0 g, 6 mmol) and stirred at room temperature
for 3 h. Water (5 mL) was added to the solution and concentrated to a small
volume. The residue was partitioned between CHCl3 (150 mL) and water
(70 mL) and the organic layer was dried over MgSO4, then concentrated to a
small volume. The residue was evaporated azeotropically with toluene and
chromatographed over a column of silica gel G using 0–10% EtOH in
CHCl3. Evaporation of the fraction and crystallization from benzene gave
1
white crystals (1.39 g, 77%). Mp 164.5–165.5ꢀC; H NMR (DMSO-d6) d
12.08 (1H, s, N1-H), 11.68 (1H, s, N2-H), 8.12 (1H, s, H8), 6.77–7.37 (ca.13H,
m, phenyl of DMTr), 6.20 (1H, dd, J ¼ 1.4, 18.9 Hz, H10), 5.68 (1H, d,
J ¼ 7.1 Hz, 30OH), 5.41 (1H, ddd, J ¼ 1.4, 4.4 52.5 Hz, H20), 4.54–4.61 (1H,
m, H30), 4.11–4.13 (1H, m, H40), 3.723 (3H, s, OCH3), 3.719 (3H, s, OCH3),
3.26–3.33 (2H, m, H50), 2.18 (3H, s, Ac); UV lmax (MeOH) nm: 237, 281;
FAB-MS m=z: 630 [MþþH], 652 [MþþNa]. HR-MS m=z: 652.2178
(MþþNa,C33H32FN5O7 requires 652.2179).
20-Deoxy-20-fluoroguanyl-(30,50)-guanosine (6, Na+ salt). To a solution
of 5c (232 mg, 0.368 mmol) and triethylamine (0.1 mL) in CH2Cl2 (6 mL) was
added N,N-diisopropylmethylphosphonamidic chloride (0.11 mL, 0.57 mmol)
and the solution was stirred at room temperature under Ar atmosphere for
40 min, then concentrated to a small volume. The residue was partitioned
between AcOEt (12 mL) and water (2 mL) and the organic layer was washed
with water (2 mL), dried over MgSO4, and evaporated. The residue was
dissolved in CH3CN (6 mL) and 1H-tetrazole (64 mg, 0.91 mmol) and N2-
acetyl-20,30-di-O-isobutyrylguanosine (343 mg, 0.74 mmol) was added suc-
cessively to the solution. After stirring at room temperature overnight, the
solution was evaporated and the residue was partitioned between AcOEt
(15 mL) and water (1.5 mL). The organic layer was washed with water
(1.5 mL), dried over MgSO4, filtered to remove insoluble materials. To the
filtrate was added 3-chloroperbenzoic acid (300 mg, 1.7 mmol) and triethyl-
amine (0.15 mL), and the solution was stirred at room temperature for 3 h.
Then the solvents were concentrated to a small volume and chromatographed
over a column of silica gel G using 0–10% MeOH in AcOEt. Evaporation of
the fraction gave full-protected GfpG 6a as a caramel (237 mg, 55% from
5c). UV lmax (MeOH) nm: 254, 277; FAB-MS m=z: 1193 [MþþNa], 1209
[MþþK]. The product 6a (212 mg, 0.178 mmol) was dissolved in a mixture of
MeOH (6 mL) and CH2Cl2 (2 mL), then trifluoroacetic acid (0.1 mL) was
added. The solution was stirred at room temperature for 3 h, and neutralized
with triethylamine. The solvents was removed under reduced pressure, and
the residue was chromatographed over a column of silica gel G using 0–10%
EtOH in CHCl3. Evaporation of the fraction gave the partially deprotected
product as a white powder 6b (112 mg, 72%). UV lmax (MeOH) nm: 260,
277; FAB-MS m=z: 869 [MþþH], 891 [MþþNa]. A part of the product
(80 mg, 92 mmol) was dissolved in MeOH (15 mL) and the solution was

20-DEOXY-20-FLUOROGUANYL-(30,50)-GUANOSINE
773
saturated with ammonia at 0ꢀC. The solution was stirred at room tempera-
ture overnight and concentrated to a small volume. The residue was chro-
matographed over a column of DEAD-cellulose (2620 cm) using 0–0.12 M
TEAB (1 L). The main fraction was evaporated under reduced pressure and
the residue was evaporated azeotropically with water. The residue was dis-
solved in water (2 mL) and passed through the column of Amberlite IR 120
(Naþ form, 10 mL). Evaporation of water (50 mL) gave 6 as a filmy substance
1
(6c, 51 mg, 78.2 mmol, 85%). H NMR (D2O, a series; protons of 50-Gf, b
series; protons of G-30) d 7.94 (1H, s, H8), 7.85 (1H, s, H8), 6.10 (1H, dd,
J ¼ 3.0, 17.0 Hz, H10a), 5.87 (1H, d, J ¼ 5.5 Hz, H10b), 5.48 (1H, ddd, J ¼ 3.6,
4.1, 51.4 Hz, H20a), 4.86–4.97 (1H, m, H30a), 4.70 (1H, t, J ¼ 5.2 Hz, H20b),
4.49 (1H, dd, J ¼ 4.7, 4.9 Hz, H30b), 4.33 (1H, br s, H40b), 4.28 (1H, br s,
H40a), 4.15–4.25 (2H, m, H50b), 3.76–3.89 (2H, m, H50a); UV lmax (MeOH)
nm: 252; FAB-MS m=z: 651 [Mþ-H].
N2-Acethyl-20,30-di-O-isobutyrylguanosine (7). This compound was
prepared from 50-O-trityl-N2-acetylguanosine by successive treatment with
1
isobutyryl chloride and acid treatment in 76% yield. H NMR (CDCl3) d
12.20 (1H, s, N1-H), 9.54 (1H, s, N2-H), 7.74 (1H, s, H8), 5.88–5.97 (2H, m,
H10, H20), 5.67 (1H, dd, J ¼ 2.7, 5.2 Hz, H30), 4.26 (1H, d, J ¼ 2.2 Hz, H40),
3.95 (1H, dd, J ¼ 2.2, 12.6 Hz, H50a), 3.82 (1H, dd, J ¼ 1.6, 12.6 Hz, H50b),
2.47–2.68 (2H, m, CH x2), 2.33 (3H, s, Ac), 1.08–1.23 (12H, m, CH364); UV
lmax (MeOH) nm: 257, 280; EI-MS m=z: 465 [Mþ].
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Received February 20, 2002
Accepted April 15, 2002