Synthesis and conformation of 3′,4′-BNA monomers, 3′-O,4′-C-methyleneribonucleosides

Article abstract of DOI:10.1016/S0040-4020(02)00227-2

In order to develop novel 2′,5′-linked oligonucleotide analogues aimed for antivirus reagents and antisense/antigene oligonucleotides, novel nucleoside analogues, 3′-O,4′-C-methyleneribonucleosides (3′,4′-BNA monomers) were synthesized via two synthetic routes. The first route starting from uridine utilized a regioselective ring-closure reaction of the 4′-C-(p-toluenesulfonyl)oxymethyluridine derivative. The second route involved a coupling reaction of 1,2,3-tri-O-acetyl-4-C-(p-toluenesulfonyl)oxymethylribofuranose derivative with nucleobases followed by oxetan-ring formation to afford the 3′,4′-BNA monomers bearing all four nucleobases. By means of ¹H NMR, X-ray crystallography and computational analysis, the sugar puckering of the 3′,4′-BNA monomers was found to be restricted in S-conformation (C_1′-exo-C_2′-endo puckering mode).

Full text of DOI:10.1016/S0040-4020(02)00227-2

TETRAHEDRON
Pergamon
Tetrahedron 58 /2002) 3039±3049
Synthesis and conformation of 30,40-BNA monomers,
30-O,40-C-methyleneribonucleosides
Satoshi Obika, Ken-ichiro Morio, Daishu Nanbu, Yoshiyuki Hari, Hiromi Itoh
and Takeshi Imaniship
Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamadaoka, Suita, Osaka 565-0871, Japan
Received 25January 2002; accepted 18 February 2002
AbstractÐIn order to develop novel 20,50-linked oligonucleotide analogues aimed for antivirus reagents and antisense/antigene oligo-
nucleotides, novel nucleoside analogues, 30-O,40-C-methyleneribonucleosides /30,40-BNA monomers) were synthesized via two synthetic
routes. The ®rst route starting from uridine utilized a regioselective ring-closure reaction of the 40-C-/p-toluenesulfonyl)oxymethyluridine
derivative. The second route involved a coupling reaction of 1,2,3-tri-O-acetyl-4-C-/p-toluenesulfonyl)oxymethylribofuranose derivative
with nucleobases followed by oxetan-ring formation to afford the 30,40-BNA monomers bearing all four nucleobases. By means of 1H NMR,
X-ray crystallography and computational analysis, the sugar puckering of the 30,40-BNA monomers was found to be restricted in S-confor-
0
mation /C1 -exo±C2 -endo puckering mode). q 2002 Elsevier Science Ltd. All rights reserved.
0
1. Introduction
2±5A analogues have been synthesized to date.3 In addition,
oligonucleotide analogues having 20,50-phosphodiester
linkages were also synthesized by some groups,4 and it
was revealed that the 20,50-linked oligonucleotides have a
tendency to hybridize with their RNA complements rather
than DNA complements,4,5 and that they also have
resistance towards several types of nucleases.6 All of these
characters are quite favorable for antisense technology.
It is well known that nucleic acids /DNA and RNA) play
an important role in storage and transmission of genetic
information in a living cell. They are consisted of three
components, a nucleobase, a ribofuranose sugar and a
phosphodiester linkage. In most DNAs and RNAs, nucleo-
side units are connected via a 30-50 internucleoside
phosphodiester linkage. On the other hand, there are some
biologically active nucleic acids bearing a 20-50 internucleo-
side phosphodiester linkage. Studies on these `20,50-linked
nucleic acids' have focused on both their structural unique-
For isolation and enhancement of speci®c biological activi-
ties, conformational restraint of the parent compounds by
chemical modi®cation is well known to be effective. In
nucleosides, the ribofuranose ring is ¯exible and exists in
an equilibrium of some major sugar conformations, such as
N- and S-type conformations /Fig. 2).7 If the conformation
of the nucleoside for a 20,50-linked oligonucleotide is
restrained in a suitable form, the hybridization process
with ssRNA should pro®t from less negative entropy
changes during duplex formation. Furthermore, it would
contribute to the development of novel 2±5A analogues as
an effective antiviral reagent.
ness and characteristic biological activity /Fig. 1).1,2
A
20,50-linked oligoadenylate /2±5A) is well known to
enhance the activity of 2±5A-dependent RNaseL, which
plays an important role in prevention of virus infection.1
To develop an antiviral drug, various types of modi®ed
We have already accomplished the synthesis of 20-O,40-C-
methylene-bridged nucleic acids, 20,40-BNA8,9 /LNA),10
which have a strictly locked N-type sugar conformation
Figure 1. Structures of natural DNA, RNA and 20,50-linked nucleic acids.
Keywords: nucleic acid analogues; nucleosides; conformation; oxetanes.
Corresponding author. Tel.: 181-6-6879-8200; fax: 181-6-6879-8204;
p
Figure 2. N- and S-type conformation of nucleosides.
e-mail: imanishi@phs.osaka-u.ac.jp
0040±4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020/02)00227-2

3040
S. Obika et al. / Tetrahedron 58 +2002) 3039±3049
Scheme 2. Reagents and conditions: /i) 2TMS´T, TMSOTf, MeCN, rt,
88%.
Figure 3. Structures of 20,40-BNA /LNA) and 30,40-BNA monomers.
away to attack the 40-methylene carbon. Finally, the
50-dimethoxytrityl group of 4 was removed by 1% trichloro-
acetic acid in dichloroethane to give the desired 30,40-BNA
monomer 1a in 94% yield.
by a methylene bridging between 20-oxygene and 40-carbon
atoms in a ribonucleoside /Fig. 3). The effectiveness of
restraining the sugar puckering for hybridization with
ssDNA, ssRNA and dsDNA has also been demonstrated.8±11
Here, we describe the synthesis of another type of
BNA monomers, 30-O,40-C-methyleneribonucleosides 1
/30,40-BNA monomers), which have the ribofuranose
moiety conformationally restrained by a fused oxetane
ring.12±14 The conformational analyses of these nucleoside
analogues are also carried out.
To synthesize the cytidine analogue of 1, transformation of
the nucleobase from uracil to cytosine was examined
according to the literature.16 Acetylation of the 20-hydroxy
group in 4 by acetic anhydride±pyridine gave 5, quantita-
tively, and then 5 was treated with 4-chlorophenyl phos-
phorodichloridate and 1,2,4-triazole in pyridine to give the
4-triazolopyrimidine derivative 6 in 64% yield. The cytidine
analogue 7 was obtained by mild ammonolysis of 6 in 82%
yield. Deprotection of the 50-hydroxy group in 7 afforded
the 30,40-BNA cytosine monomer 1b.
2. Results and discussion
2.1. Synthesis of 30,40-BNA monomers, 30-O,40-C-methyl-
eneuridine and -cytidine, from uridine
2.2. Synthesis of 30,40-BNA monomers from d-glucose
At ®rst, we synthesized the 30,40-BNA monomers, 30-O,40-
C-methyleneuridine and -cytidine 1a and 1b, from
40-/p-toluenesulfonyl)oxymethyluridine 29 which was pre-
pared from uridine /Scheme 1). The primary hydroxy group
in 2 was selectively protected by a dimethoxytrityl group
to give 3 in 68% yield. Ring-closure reaction of 3 was
effectively accomplished under alkaline conditions to
yield the oxetane 4. The oxetane structure of 4 was
con®rmed by observation of the low-®eld shifts of the
oxetane-ring protons in its 1H NMR spectrum. Three proton
signals on the ring of 4 appeared at 4.52 and 4.83 ppm as an
AB-type quartet /Jˆ8 Hz) /for CH2) and at 5.11 ppm as a
doublet /Jˆ4 Hz) /for 30-H). The exclusive oxetane-ring
formation would be contributable to the predominant
To synthesize 30,40-BNA monomers containing all four
natural nucleobases, cytosine, adenine, guanine and
thymine, we investigated another synthetic route. Prelimin-
ary synthetic study for introduction of the thymine nucleo-
base into oxetane derivative 8 resulted in exclusive oxetane-
ring opening, yielding only 9 /Scheme 2). Considering this
®nding, we examined the oxetane-ring formation after intro-
duction of a nucleobase into 1,2,3-tri-O-acetyl-4-/p-tolue-
nesulfonyl)oxymethylribofuranose derivative 14 /Scheme
3). The starting material 10 was prepared from d-glucose
by a several-step sequence according to the literature.17
Selective desymmetrization of 10 was performed by
treatment with tert-butyldiphenylchlorosilane and triethyl-
amine in dichloromethane to give the desired compound 11
/67%) along with a small amount of its isomer. p-Toluene-
sulfonyl group was introduced into 11 to give 12 in 97%
yield. Acid-catalyzed removal of the isopropylidene group
in 12 and following acetylation gave the diacetate 13
in 86% yield as an anomeric mixture /a/bˆca. 1:4).
1
S-type sugar puckering of the diol 3. In the H NMR of 3,
0
0
the J1 ,2 value was 8 Hz, which indicates that the diol 3
exists in S-type conformation.15 In this conformation, only
the 30-hydroxy group in 3 seems to be located near the
40-carbon center, while the 20-hydroxy group is too far
Scheme 1. Reagents and conditions: /i) 4,40-dimethoxytrityl chloride, pyridine, rt, 68%; /ii) NaHMDS, THF, rt, 63%; /iii) 1%TCA in Cl2CH2CH2Cl2, rt, 94%;
/iv) Ac2O, pyridine, rt, 100%; /v) 1,2,4-triazole, 4-chlorophenyl phosphorodichloridate, pyridine, rt, 64%; /vi) aqueous NH3, 1,4-dioxane, rt, 82%;
/vii) 1%TCA in Cl2CH2CH2Cl2, rt, 100%.

S. Obika et al. / Tetrahedron 58 +2002) 3039±3049
3041
Scheme 3. Reagents and conditions: /i) TBDPSCl, Et3 N, CH2Cl2, rt, 67%; /ii) TsCl, Et3 N, DMAP, CH2Cl2, rt, 97%; /iii) AcOH, Ac2O, c. H2SO4, rt, 86%;
/iv) 10% Pd±C, H2, AcOEt, CHCl3, rt, then Ac2O, pyridine, rt, 91%; /v) sililated base, TMSOTf, ClCH2CH2Cl, rt, 70±82%; /vi) K2CO3, MeOH, rt, 63±100%;
/vii) NaHMDS, THF, rt, 82±100%; /viii) TBAF, THF, rt, 65±78%.
Palladium-catalyzed hydrogenolysis of 13 gave a debenzyl-
ated product, which was then treated with acetic anhydride
in pyridine to give triacetate 14 in 91% yield.
monomers 1 to clarify their ribofuranose sugar confor-
mation. Generally, H NMR measurements of nucleoside
analogues give us useful conformational information. It is
well known that the nucleosides and their analogues exist in
an equilibrium between S- and N-type conformations based
1
Introduction of a nucleobase to triacetate 14 was accom-
plished under VorbruÈggen's conditions.18 Silylated nucleo-
base /2TMS´CBz, 2TMS´ABz, 3TMS´GBui or 2TMS´T) was
reacted with triacetate 14 in dichloroethane in the presence
of trimethylsilyltri¯ate. In this reaction, the desired cytidine,
adenosine or thymidine derivative 15b0,c and 15e was
yielded in 70±82% as the sole isomer, while the guanosine
analogue 15d was obtained as a mixture of N9- and
N7-regioisomer /72%, N9/N7ˆca. 3:1). Deprotection of the
acetyl group in 15 was performed with potassium carbonate
in methanol to give the corresponding diols 16, respectively,
in 63±100% yields. After this deprotection step, each
isomer of the guanosine derivative was easily separated
on their furanose-ring puckering. Altona and co-workers
1
reported H±1H coupling constants J1 2 , J2 3 and J3 4 had
a correlationship with ribofuranose ring conformation, and
several types of equations to predict the probability in
S-type conformation /S%) of the ribofuranose ring were
0
0
0
0
0 0
also proposed.15 In 30,40-BNA monomers 1, J3 4 is not
obtainable because these compounds have no hydrogen
atom at the C40 position. Therefore, the simplest equation
/Eq. /1)) was only available for 30,40-BNA monomers 1.
0
0
0
0
Observed coupling constant J1 2 values and calculated S%
values are summarized in Table 1. In our 1H NMR measure-
ments, natural ribonucleosides, uridine, cytidine, adenosine
1
0
0
by column chromatography. From an analysis of the H
and guanosine, showed various J1 2 values due to the
diversity of their ribofuranose ring puckering, and the calcu-
lated S% values of these ribonucleosides were 52, 26, 80 and
71%, respectively. On the other hand, all 30,40-BNA mono-
and 13C NMR spectra of these compounds, it was found
that the major isomer was the desired N9-isomer and the
minor one was the N7-isomer.19 Oxetane derivatives 17
were prepared in 82±100% yields by treatment of the
diols 16 with sodium hexamethyldisilazide. Finally,
deprotection of the tert-butyldiphenylsilyl group in 17
gave 30,40-BNA monomers 1 in 65±78% yields.
0
0
mers showed relatively large J1 2 values /7.3±7.6 Hz),
regardless of the type of nucleobase. The S% values of 1
ranged from 91 to 96%. These results indicate that the
furanose-ring conformation of 30,40-BNA monomers 1
was effectively restricted in S-type conformation by the
30-O,40-C-methylene bridge.
2.3. Conformational analysis of 30,40-BNA monomers
We performed the conformational analysis of 30,40-BNA
Sꢀ%† ˆ 100ꢀJ1 2 2 1†=6:9
ꢀ1†
0
0
Table 1. Coupling constants and S /%) values of nucleosides
Table 2. Selected torsion angles, pseudorotational phase angle P and
maximum torsion angle nmax of 1e determined from X-ray structure
0 0
J1 2 /Hz)
Nucleosides
S /%)
Uridine
Cytidine
Adenosine
Guanosine
1a
4.6
2.8
6.580
5.9
7.594
7.3
7.594
7.6
7.594
52
26
0
n0 /C4 ±O4 ±C1 ±C2 )
0
0
0
229.68
32.58
223.58
7.18
14.28
126.28
2108.08
74.18
136.38
32.58
0
n1 /O4 ±C1 ±C2 ±C3 )
0
0
0
0
n2 /C1 ±C2 ±C3 ±C4 )
0
0
0
71
91
96
0
n3 /C2 ±C3 ±C4 ±O4 )
0
0
0
0
n4 /C3 ±C4 ±O4 ±C1 )
0
0
0
1b0
0
d /C5 ±C4 ±C3 ±O3 )
0
0
0
1c
1d
1e
0
0
0
0
x /O4 ±C1 ±N1 ±C2 )
0
g /O5 ±C5 ±C4 ±C3 )
0
0
0
P
nmax
All 1H NMR data were measured in CD3OD.

3042
S. Obika et al. / Tetrahedron 58 +2002) 3039±3049
the oxetane-ring structure. These two energy barriers
0
0
existed for C3 -endo /Pˆca. 208) and C4 -endo /Pˆca.
2308) furanose puckering modes. The lowest energy state
0
0
was observed for the C1 -exo±C2 -endo /Pˆca. 1308) pucker
/Fig. 4/B)), and this result was in good agreement with that
from the X-ray crystallographic analysis. The energies for
0
0
C3 -endo and C4 -endo states were about 10 and 8 kcal/mol
0
0
above the energy calculated for C1 -exo±C2 -endo sugar
puckering, respectively. Thus, it was clearly demonstrated
that the sugar conformation of 30,40-BNA monomers
30-O,40-C-methyleneribonucleic acids, was effectively
0
restricted at the C1 -exo±C2 -endo state.
0
3. Conclusion
The conformationally restricted nucleoside analogues,
30-O,40-C-methyleneribonucleosides /30,40-BNA monomers
1) were effectively prepared by two synthetic approaches
using uridine or d-glucose as the starting materials. These
nucleoside analogues have a oxetane-fused ring consisting
of a methylene bridging between 30-oxygene and 40-carbon
atoms. From 1H NMR analysis, it was demonstrated that the
30,40-BNA monomers 1 preferred S-type sugar puckering.
Furthermore, the detailed conformation of 1 was studied by
X-ray crystallography and PM3 calculation, which revealed
0
that the sugar puckering of 1 was restricted in the C1 -exo±
0
C2 -endo state.
Figure 4. /A) Variation of heat of formation for 1e and 20-hydroxy-
thymidine with pseudorotational phase angle P. /B) The most stable confor-
mation of 1e /Pˆ1308).
4. Experimental
4.1. General considerations
Next, we carried out X-ray crystallographic analysis of
30,40-BNA monomer 1e.12b The selected torsion angles of
1e obtained from the X-ray crystallography are summarized
in Table 2. The conformation of the furanose ring can be
described by the pseudorotation phase angle /P) and the
maximum torsion angle /nmax) calculated from the endo-
cyclic sugar torsion angles.7 In the 30,40-BNA monomer,
the calculated P-value /136.38) showed that 1e existed in
All melting points were measured on a Yanagimoto micro-
1
melting point apparatus and are uncorrected. H and 13C
NMR spectra were recorded on a JEOL EX-270 /1H, 270
MHz; 13C, 67.8 MHz) or JEOL GX-500 /1H, 500 MHz)
spectrometer. IR spectra were recorded on a JASCO FT/
IR-200 spectrometer. Mass spectra were measured on
JEOL JMS-D300 or JMS-600 mass spectrometer. Optical
rotations were recorded on a JASCO DIP-370 instrument.
For column chromatography, Merck Kieselgel 60 /70±
200 mesh) or Fuji Silysia BW-127ZH /100±200 mesh)
was used.
0
0
C1 -exo±C2 -endo conformation, which was one of the
S-type conformations. In addition, the maximum torsion
angle nmax of 1e /32.58) was similar to that of typical nucleo-
sides. The dihedral angles n3 and n4 were smaller than those
of natural nucleosides, owing to the restrained structure of
the oxetane-fused furanose ring, whereas the value of other
dihedral angles n0, n1, n2, bond lengths and bond angles of
1e were comparable to those of natural nucleosides.7
4.1.1. 50-O--4,40-Dimethoxytrityl)-40-C--p-toluenesulfonyl)-
oxymethyluridine -3). Under N2 atmosphere, 4,40-dimeth-
oxytrityl chloride /242 mg, 0.71 mmol) was added to a
stirred solution of 29 /255 mg, 0.60 mmol) in pyridine
/5mL) at room temperature. After having been stirred for
14 h at the same temperature, the reaction mixture was par-
titioned with saturated NaHCO3 and the mixture was
extracted with CH2Cl2. Usual work-up and puri®cation by
SiO2 column chromatography /CHCl3/MeOH/Et3N, 30:1:1)
afforded 3 /297 mg, 0.41 mmol, 68%) as a white solid, mp
Finally, a PM3 semi-empirical calculation was carried out to
analyze the stable conformation of 30,40-BNA monomer 1.20
By using the X-ray structure of 1e, various initial structures
of 1e were generated, where the nmax-value was constrained
at 32.38 and the P-value was varied by changing the dihedral
angles n0±n4. The results of PM3 calculation are illustrated
in Fig. 4/A). In the case of 20-hydroxythymidine, only one
20
104±1058C /Et2O±hexane). [a]D ˆ215.3 /c 1.1, acetone).
IR /KBr): 3396, 2937, 2737, 2675, 2493, 1691, 1474, 1397,
1
1173, 1035cm 21. H NMR /acetone-d6) d: 2.41 /3H, s),
0
large energy barrier was observed for the O4 -exo puckering
mode /Pˆca. 2708), which came from the steric repulsion
between the nucleobase and the 50-carbon atom.7,21 On the
contrary, 30,40-BNA monomer 1e had two large energy
barriers, both of which were attributable to the strain of
3.22, 3.33 /2H, ABq, Jˆ10 Hz), 3.79 /6H, s), 4.29 /1H,
dd, Jˆ6, 6 Hz), 4.34, 4.41 /2H, AB, Jˆ11 Hz), 4.40 /1H,
d, Jˆ6 Hz), 5.35 /1H, d, Jˆ8 Hz), 5.82 /1H, d, Jˆ6 Hz),
6.89 /4H, d, Jˆ9 Hz), 7.26±7.41 /7H, m), 7.43 /1H, d,

S. Obika et al. / Tetrahedron 58 +2002) 3039±3049
3043
Jˆ8 Hz), 7.70 /2H, d, Jˆ8 Hz). 13C NMR /acetone-d6) d:
21.6, 55.5, 64.6, 70.7, 72.7, 74.3, 85.8, 87.8, 88.9, 102.8,
114.0, 127.7, 128.7, 128.8, 130.7, 130.9, 131.0, 133.9,
141.1, 145.5, 151.4, 159.7, 163.3; MS /EI) m/z: 737
/M12OCH3, 11.0), 583 /11.5), 304 /100). Anal. calcd for
C38H38N2O11S´1/6H2O: C, 62.19; H, 5.26; N, 3.81; S, 4.15.
Found: C, 62.37; H, 5.26; N, 3.60; S, 4.15.
3200, 3062, 2953, 2836, 1697, 1610, 1508, 1456, 1380,
1250, 1178, 1040 cm21 1H NMR /acetone-d6) d: 2.04
.
/3H, s), 3.47, 3.61 /2H, AB, Jˆ10 Hz), 3.79 /6H, s), 4.53,
4.79 /2H, AB, Jˆ8 Hz), 5.19 /1H, dd, Jˆ7, 5Hz), 5.27 /1H,
d, Jˆ5 Hz), 5.54 /1H, d, Jˆ8 Hz), 6.60 /1H, d, Jˆ7 Hz),
6.90 /4H, d, Jˆ9 Hz), 7.30±7.49 /9H, m), 7.70 /1H, d,
Jˆ8 Hz), 10.10 /1H, br). 13C NMR /acetone-d6) d: 20.3,
55.5, 64.0, 76.4, 79.1, 84.6, 86.3, 87.3, 87.4, 103.5, 114.0,
127.7, 128.7, 128.9, 130.9, 136.3, 136.4, 141.1, 145.8,
151.4, 159.7, 170.4. MS /FAB) m/z: 601 /MH1). Anal.
calcd for C33H32N2O9´1/2H2O: C, 65.02; H, 5.36; N, 4.65.
Found: C, 65.02; H, 5.46; N, 4.60.
4.1.2. 50-O--4,40-Dimethoxytrityl)-30-O,40-C-methylene-
uridine -4). Under N2 atmosphere, sodium bis/trimethyl-
silylamide) /8.96 mmol, 1.0 M solution in THF) was
added to a stirred solution of 3 /735mg, 0.90 mmol) in
THF /11 mL) at room temperature. After having been
stirred for 48 h at the same temperature, the reaction mixture
was partitioned with saturated NaHCO3 and the mixture was
extracted with CHCl3. Usual work-up and puri®cation by
SiO2 column chromatography /CHCl3/MeOH/Et3N, 30:1:0,
4.1.5. 1-[2-O-Acetyl-5-O--4,40-dimethoxytrityl)-3-O,4-C-
methylene-b-d-ribofuranosyl]-4--1,2,4-triazol-1-yl)pyri-
midinone -6). Under N2 atmosphere, dichlorophenyl phos-
phorodichloridate /221 mg, 0.90 mmol) was added to a
stirred solution of 5 /118 mg, 0.20 mmol) in pyridine
/2 mL) at room temperature. After having been stirred for
3 min, 1,2,4-triazole /180 mg, 2.61 mmol) was added to the
reaction mixture at 08C. Stirring was continued for 10 h at
room temperature, and then the reaction mixture was
concentrated under reduced pressure. The remaining residue
was chromatographed on silica gel /AcOEt) to afford 6
/82 mg, 0.13 mmol, 64%) as a pale yellow solid, mp 78±
then 30:1:2) afforded 4 /311 mg, 0.56 mmol, 63%) as a
ˆ
21
white foam, mp 120±1218C /Et2O±hexane). [a]D
237.7 /c 1.1, acetone). IR /KBr): 3395, 3222, 3062, 2930,
1
1693, 1508, 1461, 1385, 1298, 1252, 1177, 1034 cm21. H
NMR /acetone-d6) d: 2.92 /1H, br), 3.47, 3.51 /2H, ABq,
Jˆ10 Hz), 3.85/6H, s), 4.36 /1H, dd, Jˆ8, 4 Hz), 4.52, 4.83
/2H, ABq, Jˆ8 Hz), 5.11 /1H, d, Jˆ4 Hz), 5.57 /1H, d,
Jˆ8 Hz), 6.51 /1H, d, Jˆ8 Hz), 6.96 /4H, d, Jˆ9 Hz),
7.39±7.41 /7H, m), 7.52 /2H, d, Jˆ5Hz), 7.71 /1H, d,
Jˆ9 Hz). 13C NMR /acetone-d6) d: 55.4, 64.1, 75.5, 79.0,
85.5, 86.2, 87.1, 88.8, 103.3, 113.7, 113.9, 127.6, 128.4,
128.6, 128.8, 129.9, 130.9, 131.1, 136.3, 136.4, 141.2,
22
808C /CH2Cl2±hexane). [a]D ˆ210.1 /c 1.5, acetone). IR
/KBr): 3860, 3122, 2048, 1746, 1682, 1548, 1509, 1281,
1
1249, 1062 cm21. H NMR /acetone-d6) d: 2.05/3H, s),
3.56, 3.70 /2H, ABq, Jˆ10 Hz), 3.76 /6H, s), 4.59, 4.84
/2H, ABq, Jˆ8 Hz), 5.31±5.36 /2H, m), 6.74 /1H, d,
Jˆ5Hz), 6.89 /4H, d, Jˆ9 Hz), 7.29±7.51 /9H, m),
8.24 /1H, s), 8.47 /1H, d, Jˆ7 Hz), 9.27 /1H, s). 13C
NMR /acetone-d6) d: 20.3, 55.5, 63.9, 78.0, 79.1, 85.1,
87.2, 87.5, 87.6, 88.2, 90.4, 95.5, 114.0, 127.7, 128.7,
128.8, 130.9, 136.2, 136.4, 144.2, 145.7, 147.8, 149.2,
154.7, 154.9, 159.6, 160.3, 170.5. MS /FAB) m/z: 65 2
/MH1).
1
145.7, 151.6, 159.6, 163.4. MS /EI) m/z: 5 5 8 /M, 2.2),
303 /64.1), 227 /8.7), 114 /100). Anal. calcd for
C31H30N2O8: C, 66.7; H, 5.41; N, 5.35. Found: C, 66.5; H,
5.43; N, 5.35.
4.1.3. 30-O,40-C-Methyleneuridine -1a). To a stirred
solution of 4 /107 mg, 0.21 mmol) in dichloroethane
/6.0 mL) was added 1% trichloroacetic acid in dichloro-
ethane /1.0 mL) at room temperature. After having been
stirred for 15min at the same temperature, the reaction
mixture was concentrated under reduced pressure. The
remaining residue was chromatographed on silica gel
4.1.6. 50-O--4,40-Dimethoxytrityl)-30-O,40-C-methylene-
cytidine -7). To a stirred solution of 6 /150 mg, 0.23
mmol) in 1,4-dioxane /6.5mL) was added NH 4OH /1 mL)
at room temperature. After having been stirred for 10 h at
the same temperature, the reaction mixture was concen-
trated under reduced pressure. The remaining residue was
chromatographed on silica gel /CHCl3/MeOH/Et3N, 30:2:3)
to afford 7 /107 mg, 0.19 mmol, 82%) as a white solid,
/CHCl3/MeOH, 10:1) to give 1a /85mg, 0.20 mmol, 94%)
17
as a white solid, mp 215±2168C /Et2O±hexane). [a]D
218.2 /c 1.2, acetone). IR /KBr): 3639, 1924, 1714, 1464,
ˆ
1134 cm21. H NMR /acetone-d6) d: 3.74, 3.82 /2H, ABq,
1
Jˆ12 Hz), 4.21 /1H, dd, Jˆ7, 5Hz), 4.42, 4.82 /2H, ABq,
Jˆ8 Hz), 5.05 /1H, d, Jˆ5Hz), 5.66 /1H, d, Jˆ9 Hz), 6.38
/1H, d, Jˆ7 Hz), 7.67 /1H, d, Jˆ9 Hz). 13C NMR /acetone-
d6) d: 62.3, 75.3, 78.3, 85.9, 86.9, 89.4, 103.4, 141.6, 151.7,
22
mp 139±1408C /Et2O±hexane). [a]D ˆ10.60 /c 0.34,
MeOH). IR /KBr): 3345, 3199, 2946, 1651, 1604, 1503,
1
1373, 1294, 1250, 1179, 1037 cm21. H NMR /CD3OD):
1
163.4. MS /EI) m/z: 25 6 /M , 2.1), 113 /100). Anal. calcd
for C10H12N2O6´1/2H2O: C, 45.29; H, 4.94; N, 10.56. Found:
C, 45.07; H, 4.82; N, 10.15.
d: 3.40, 3.50 /2H, ABq, Jˆ10 Hz), 3.76 /6H, s), 4.14 /1H,
dd, Jˆ7, 4 Hz), 4.48, 4.72 /2H, ABq, Jˆ7 Hz), 4.98 /1H, d,
Jˆ4 Hz), 5.79 /1H, d, Jˆ7 Hz), 6.56 /1H, d, Jˆ7 Hz), 6.85
/4H, d, Jˆ9 Hz), 7.21±7.42 /9H, m), 7.67 /1H, d, Jˆ7 Hz).
13C NMR /CD3OD) d: 55.7, 64.5, 76.8, 79.8, 86.2, 87.3,
87.8, 90.1, 97.0, 114.2, 128.1, 128.9, 129.3, 131.3, 136.8,
142.8, 146.1, 160.3, 167.3. MS /FAB) m/z: 558 /MH1).
Anal. calcd for C31H31N3O7´2H2O: C, 62.72; H, 5.94; N,
7.08. Found: C, 63.01; H, 5.56; N, 7.08.
4.1.4. 20-O-Acetyl-50-O--4,40-dimethoxytrityl)-30-O,40-C-
methyleneuridine -5). Under N2 atmosphere, acetic
anhydride /41 mg, 0.40 mmol) was added to a stirred solu-
tion of 4 /188 mg, 0.34 mmol) in pyridine /3.5mL) at room
temperature. After having been stirred for 10 h at the same
temperature, the reaction mixture was concentrated under
reduced pressure. The remaining residue was chromato-
graphed on silica gel /AcOEt) to give 5 /203 mg, 0.34
mmol, 100%) as a white solid, mp 120±1218C /AcOEt±
4.1.7. 30-O,40-C-Methylenecytidine -1b). To a stirred solu-
tion of 7 /72 mg, 0.13 mmol) in dichloroethane /2 mL) was
added 1% trichloroacetic acid in dichloroethane /1 mL) at
room temperature. After having been stirred for 15min at
21
hexane). [a]D ˆ233.7 /c 0.91, acetone). IR /KBr): 3471,

3044
S. Obika et al. / Tetrahedron 58 +2002) 3039±3049
the same temperature, the reaction mixture was concen-
trated under reduced pressure. The remaining residue was
chromatographed on silica gel /CHCl3/MeOH, 10:1) to
afford 1b /33 mg, 0.13 mmol, 100%) as a white solid, mp
Bu, 50.1), 91 /100). Anal. calcd for C35H42N2O7Si: C,
66.64; H, 6.71; N, 4.44. Found: C, 66.63; H, 6.88; N, 4.41.
4.1.10.
3-O-Benzyl-5-O-tert-butyldiphenylsilyl-4-C-
23
224±2248C /iPrOH). [a]D ˆ132.6 /c 0.49, H2O). IR
hydroxymethyl-1,2-O-isopropylidene-a-d-erythro-pento-
furanose -11). Under N2 atmosphere, triethylamine /2.69 g,
26.6 mmol) and tert-butyldiphenylsilyl chloride /7.09 g,
25.8 mmol) were added to a stirred solution of 1017
/2.50 g, 8.1 mmol) in dichloromethane /50 mL) at room
temperature. After having been stirred for 11 h at the
same temperature, the reaction mixture was partitioned
with saturated NaHCO3 and the mixture was extracted
with CHCl3. Usual work-up and puri®cation by SiO2
column chromatography /hexane/AcOEt, 4:1 to 3:1)
afforded 11 /2.97 g, 5.4 mmol, 67%) as a white solid, mp
/KBr): 3348, 1653, 1494, 1374, 1286, 1125, 1042 cm21
.
1H NMR /CD3OD) d: 3.73, 3.81 /2H, ABq, Jˆ12 Hz),
4.16 /1H, dd, Jˆ7, 5Hz), 4.52, 4.81 /2H, ABq, Jˆ8 Hz),
5.04 /1H, d, Jˆ5Hz), 5.94 /1H, d, Jˆ7 Hz), 6.41 /1H, d,
Jˆ7 Hz), 7.68 /1H, d, Jˆ7 Hz). 13C NMR /D2O) d: 62.0,
74.6, 79.5, 86.39, 86.42, 89.3, 98.2, 142.8, 158.9, 167.1.
Mass /EI) m/z: 255 /M1, 1.9), 224 /0.9), 112 /100). Anal.
calcd for C10H13N3O5´1/3H2O: C, 45.98; H, 5.27; N, 16.09.
Found: C, 45.98; H, 5.02; N, 15.82.
22
4.1.8. Methyl 2-O-benzyl-5-O-tert-butyldiphenylsilyl-3-
O,4-C-methylene-b-d-ribofuranoside -8). Under N2
atmosphere, a solution of methyl 5-O-/tert-butyldiphenyl-
silyl)-3-O,4-C-methylene-b-d-ribofuranoside22 /143 mg,
0.34 mmol) in THF /2 mL) was added to a suspension of
hexane-washed NaH /60% in mineral oil /w/w), 17 mg,
0.41 mmol) in THF /1 mL) at 08C. After having been stirred
for 30 min at the same temperature, benzyl bromide /65mg,
0.38 mmol) was added to the reaction mixture at 08C.
Stirring was continued for 16 h at room temperature. After
addition of water, the mixture was extracted with AcOEt.
Usual work-up and puri®cation by SiO2 column chroma-
tography /hexane/AcOEt, 8:1) afforded 8 /147 mg, 0.29
98±998C /hexane). [a]D ˆ146.2 /c 0.92, CHCl3). IR
/KBr): 3553, 2936, 1463, 1379, 1107 cm21 1H NMR
.
/CDCl3) d: 1.13 /9H, s), 1.50 /3H, s), 1.78 /3H, s), 2.56
/1H, t, Jˆ7 Hz), 3.82, 3.92 /2H, ABq, Jˆ11 Hz), 3.94
/2H, m), 4.57 /1H, d, Jˆ5Hz), 4.64, 4.95/2H, ABq, Jˆ
12 Hz), 4.83 /1H, dd, Jˆ4, 5Hz), 5.95 /1H, d, Jˆ4 Hz),
7.44±7.55 /11H, m), 7.72±7.78 /4H, m). 13C NMR
/CDCl3) d: 19.2, 26.2, 26.5, 26.8, 63.2, 65.4, 72.5, 77.9,
79.1, 87.4, 104.4, 113.7, 127.6, 127.7, 128.0, 128.5, 129.5,
129.7, 132.9, 133.1, 134.7, 135.5, 137.2. Anal. calcd for
C32H41O6Si: C, 70.04; H, 7.35. Found: C, 70.19; H, 7.38.
4.1.11. 3-O-Benzyl-5-O-tert-butyldiphenylsilyl-1,2-O-iso-
propylidene-4-C--p-toluenesulfonyl)oxymethyl-a-d-
erythro-pentofuranose -12). Under N2 atmosphere,
triethylamine /286 mg, 2.83 mmol), p-toluenesulfonyl
chloride /133 mg, 0.073 mmol) and 4,40-dimethylamino-
pyridine /5.6 mg, 0.046 mmol) were added to a stirred
solution of 11 /250 mg, 0.46 mmol) in dichloromethane
/5mL) at room temperature. After having been stirred for
16 h at the same temperature, the reaction mixture was par-
titioned with saturated NaHCO3 and the mixture was
extracted with CHCl3. Usual work-up and puri®cation by
22
mmol, 85%) as a colorless oil. [a]D ˆ249.8 /c 1.65,
CHCl3). IR /KBr): 2934, 2860, 1111, 1010 cm21 1H
.
NMR /CDCl3) d: 1.01 /9H, s), 3.49 /3H, s), 3.66 /1H, dd,
Jˆ5, 5 Hz), 3.68, 3.74 /2H, AB, Jˆ11 Hz), 4.45, 4.88 /2H,
AB, Jˆ7 Hz), 4.62, 4.68 /2H, AB, Jˆ12 Hz), 5.01 /1H, d,
Jˆ5Hz), 5.37 /1H, d, Jˆ5Hz), 7.30±7.44 /11H, m), 7.63±
7.76 /4H, m). 13C NMR /CDCl3) d: 19.2, 26.8, 56.9, 63.5,
72.5, 78.4, 82.0, 83.9, 85.2, 108.9, 127.6, 127.7, 127.7,
127.9, 128.0, 128.4, 129.8, 132.9, 133.1, 135.6, 135.6,
137.5. MS /EI) m/z: 504 /M1, 0.1), 91 /100). Anal. calcd
for C30H36O5Si: C, 71.39; H, 7.19. Found: C, 71.45; H, 7.12.
SiO2 column chromatography /hexane/AcOEt, 1:6) afforded
12 /311 mg, 0.44 mmol, 97%) as a colorless oil. [a]D
23
ˆ
4.1.9. Methyl 2-O-benzyl-5-O-tert-butyldiphenylsilyl-4-
C--thymin-1-yl)methyl-b-d-ribofuranoside -9). Under
N2 atmosphere, silylated thymine /2TMS´T) /176 mg,
0.68 mmol) and trimethylsilyl tri¯uoromethanesulfonate
/0.773 M in dichloroethane, 0.34 mL, 0.26 mmol) were
added to a stirred solution of 8 /131 mg, 0.26 mmol) in
MeCN /2.5mL) at room temperature. After having been
stirred for 41 h, the reaction mixture was partitioned with
saturated NaHCO3, and the mixture was extracted with
AcOEt. Usual work-up and puri®cation by SiO2 column
chromatography /hexane/AcOEt, 2:1) afforded 9 /146 mg,
10.47 /c 1.76, CHCl3). IR /KBr): 2935, 1595, 1462, 1363,
1174 cm21. 1H NMR /CDCl3) d: 1.08 /9H, s), 1.40 /3H, s),
1.46 /3H, s), 2.48 /3H, s), 3.68, 3.83 /2H, ABq, Jˆ11 Hz),
4.45/2H, dd, Jˆ4, 5Hz), 4.62 /2H, ABq, Jˆ12 Hz), 4.64,
4.81 /2H, ABq, Jˆ12 Hz), 4.68 /1H, dd, Jˆ5Hz), 5.81 /1H,
d, Jˆ4 Hz), 7.32 /2H, d, Jˆ8 Hz), 7.42±7.72 /15H, m), 7.82
/2H, d, Jˆ8 Hz), 7.66 /4H, m), 7.72 /2H, d, Jˆ8 Hz). 13C
NMR /CDCl3) d: 19.1, 21.5, 26.1, 26.4, 26.7, 64.4, 70.0,
72.5, 78.1, 78.9, 85.4, 104.2, 113.6, 127.3, 127.7, 127.9,
128.0, 128.4, 129.6, 129.7, 129.8, 132.7, 132.8, 135.5,
137.2, 144.4. MS /EI) m/z: 646 /M12tert-Bu, 3.2), 91
/100). HRMS /EI) calcd for C35H37O8SSi /M12tert-Bu)
645.1978. Found: 645.1969.
0.23 mmol, 88%) as
a white solid, mp 62±658C.
23
[a]D ˆ164.8 /c 0.80, CHCl3). IR /KBr): 2934, 1681,
1470, 1112, 1036 cm21. H NMR /CDCl3) d: 1.10 /9H, s),
1
1.92 /3H, s), 3.17 /3H, s), 3.63, 3.73 /2H, AB, Jˆ11 Hz),
3.67 /1H, d, Jˆ5Hz), 3.83, 4.28 /2H, AB, Jˆ15Hz), 4.06
/1H, dd, Jˆ5, 12 Hz), 4.44, 4.50 /2H, AB, Jˆ12 Hz), 4.58
/1H, s), 4.71 /1H, d, Jˆ12 Hz), 7.11 /1H, s), 7.24 /2H, d,
Jˆ7 Hz), 7.35±7.46 /9H, m), 7.64 /2H, d, Jˆ8 Hz), 7.68
/2H, d, Jˆ8 Hz). 13C NMR /CDCl3) d: 12.3, 19.4, 26.9,
46.8, 55.0, 69.3, 74.0, 86.5, 105.7, 127.8, 127.8, 128.2,
128.3, 128.4, 128.5, 129.9, 130.0, 132.8, 132.9, 135.6,
136.9, 142.7, 152.8, 163.5. MS /EI) m/z: 573 /M12tert-
4.1.12. 3-O-Benzyl-5-O-tert-butyldiphenylsilyl-1,2-di-O-
acetyl-4-C--p-toluenesulfonyl)oxymethyl-a- and -b-d-
erythro-pentofuranose -13). To a stirred solution of 12
/3.70 g, 5.3 mmol) in acetic acid /56 mL) were added acetic
anhydride /6 mL, 64 mmol) and concentrated sulfuric acid
/56 mL, 1.1 mmol). The solution was stirred at room
temperature for 2 h. Then the reaction mixture was poured
into ice-water /300 mL) and stirred for 30 min. Saturated
NH4Cl was added, and the mixture was extracted with

S. Obika et al. / Tetrahedron 58 +2002) 3039±3049
3045
CHCl3. Usual work-up and puri®cation by SiO2 column
chromatography /hexane/AcOEt, 1:2) afforded 13 /3.36 g,
4.5mmol, 86%) as a pale yellow oil. IR /KBr): 2934, 2863,
d, Jˆ6 Hz), 6.22 /1H, d, Jˆ6 Hz), 7.35±8.04 /22H, m). 13C
NMR /CDCl3) d: 19.1, 20.3, 21.6, 26.6, 26.8, 65.2, 67.5,
70.9, 73.9, 85.4, 87.7, 127.6, 127.8, 128.0, 128.1, 129.0,
129.8, 130.3, 131.5, 132.1, 132.3, 133.2, 135.4, 135.5,
135.6, 145.2, 168.9, 169.4. MS /FAB) m/z: 854 /MH1).
Anal. calcd for C44H47N3O11SSi´1/2H2O: C, 61.24; H,
5.61; N, 4.87; S, 3.72. Found: C, 61.01; H, 5.33; N, 4.62;
S, 3.89.
1
1751, 1365, 1217, 1106 cm21. H NMR /CDCl3) /major,
b-anomer) d: 1.02 /9H, s), 1.77 /3H, s), 1.98 /3H, s), 2.39
/3H, s), 3.61, 3.76 /2H, ABq, Jˆ11 Hz), 4.21±4.58 /5H, m),
5.26 /1H, d, Jˆ5 Hz), 5.94 /1H, s), 7.15±7.59 /13H,
m), 7.58±7.66 /4H, m), 7.72 /2H, d, Jˆ8 Hz). /minor,
a-anomer) d: 1.02 /9H, s), 1.98 /3H, s), 2.36 /3H, s),
3.48, 3.58 /2H, ABq, Jˆ11 Hz), 4.21±4.58 /5H, m), 5.12
/1H, dd, Jˆ5, 6 Hz), 6.33 /1H, d, Jˆ5Hz), 7.15±7.59 /13H,
m), 7.58±7.66 /4H, m), 7.72 /2H, d, Jˆ8 Hz). 13C NMR
/CDCl3) d: 14.2, 19.3, 20.5, 20.8, 21.6, 26.7, 26.8, 60.3,
64.8, 69.1, 73.6, 74.1, 78.6, 85.3, 97.4, 127.4, 127.6,
127.7, 127.8, 127.9, 128.0, 128.2, 128.3, 128.4, 129.5,
129.6, 128.98, 129.9, 132.4, 132.8, 132.9, 135.4, 135.5,
135.6, 136.9, 144.5, 168.7, 169.4. HRMS /FAB) calcd
for C40H46N2O10SSiNa /MH12Na) 769.2479. Found:
769.2484.
4.1.15. N6-Benzoyl-50-O-tert-butyldiphenylsilyl-20,30-di-
O-acetyl-40-C--p-toluenesulfonyl)oxymethyladenosine
-15c). Under N2 atmosphere, silylated N6-benzoyladenine
/2TMS´ABz) /0.5M solution in dichloroethane, 0.96 mL,
0.48 mmol) and trimethylsilyl tri¯uoromethanesulfonate
/76 mg, 0.32 mmol) were added to a stirred solution of 14
/250 mg, 0.32 mmol) in dichloroethane /5 mL) at room
temperature. After having been re¯uxed for 23 h, the reac-
tion mixture was cooled and partitioned with saturated
NaHCO3, and the mixture was extracted with CHCl3.
Usual work-up and puri®cation by SiO2 column chroma-
tography /hexane/AcOEt, 1:2 to 1:4) afforded 15c
/197 mg, 0.23 mmol, 70%) as a white foam, mp 84±868C.
4.1.13. 5-O-tert-Butyldiphenylsilyl-4--p-toluenesulfonyl)-
oxymethyl-1,2,3-tri-O-acetyl-a- and -b-d-erythro-pento-
furanose -14). Under H2 atmosphere, 10% Pd±C /1.0 g)
was added to a stirred solution of 13 /1.85g, 2.5mmol) in
AcOEt±CHCl3 /10:1, v/v, 220 mL) at room temperature.
After having been stirred for 16 h, the reaction mixture
was ®ltered, and the ®ltrate was concentrated. The residue
was dissolved in pyridine /10 mL), and acetic anhydride
/0.68 g, 6.7 mmol) was added at room temperature. After
having been stirred for 49 h, the reaction mixture was
concentrated under reduced pressure. The remaining residue
was chromatographed on silica gel /hexane/AcOEt, 2:1) to
afford 14 /1.58 g, 2.26 mmol, 91%) as a pale yellow oil. IR
/KBr): 2935, 1755, 1603, 1506, 1367, 1216 cm21. 1H NMR
/CDCl3) /major, b-anomer) d: 0.98 /9H, s), 1.79 /3H, s),
2.08 /6H, s), 2.41 /3H, s), 3.55, 3.78 /2H, ABq, Jˆ11 Hz),
4.21, 4.40 /2H, ABq, Jˆ10 Hz), 5.32 /1H, d, Jˆ5Hz), 5.51
/1H, d, Jˆ5Hz), 6.01 /1H, s), 7.25±7.26 /2H, m), 7.29±
7.43 /6H, m), 7.60 /4H, d, Jˆ7 Hz), 7.76 /2H, d, Jˆ8 Hz).
13C NMR /CDCl3) d: 14.1, 19.0, 20.3, 20.7, 20.9,
26.6, 55.1, 60.3, 65.4, 67.7, 72.1, 74.3, 84.3, 97.2,
113.5, 127.8, 128.0, 129.5, 129.7, 129.8, 132.2, 132.5,
132.6, 135.4, 135.5, 144.8, 168.6, 169.1. HRMS /FAB)
calcd for C35H42O11SSiNa /MH11Na) 721.2115. Found:
721.2122.
22
[a]D ˆ212.5/ c 1.03, CHCl3). IR /KBr): 2934, 1756,
1704, 1640, 1604, 1232, 1182, 1106 cm21 1H NMR
.
/CDCl3) d: 1.02 /9H, s), 2.04 /3H, s), 2.16 /3H, s), 2.40
/3H, s), 3.83, 3.89 /2H, ABq, Jˆ9 Hz), 4.30, 4.38 /2H,
ABq, Jˆ10 Hz), 5.94 /1H, d, Jˆ5Hz), 6.06 /1H, dd, Jˆ6,
5Hz), 6.12 /1H, d, Jˆ6 Hz), 7.24±7.57 /15H, m), 7.61 /2H,
d, Jˆ6 Hz), 7.73 /2H, d, Jˆ8.0 Hz), 8.02 /1H, s), 8.04 /1H,
s), 8.54 /1H, s). 13C NMR /CDCl3) d: 19.0, 20.2, 21.5, 26.6,
64.6, 67.3, 71.6, 72.8, 85.5, 86.1, 123.5, 127.2, 127.7, 127.8,
127.9, 128.4, 128.7, 129.7, 129.9, 130.0, 131.8, 132.0,
132.4, 132.7, 133.3, 135.35, 135.38, 141.6, 145.0, 149.6,
151.3, 152.6, 164.6, 169.0, 169.1. MS /FAB) m/z: 878
/MH1). Anal. calcd for C45H47N5O10SSi´1/10H2O: C,
61.43; H, 5.41; N, 7.96; S, 3.63. Found: C, 61.54; H, 5.60;
N, 7.81; S, 3.60.
4.1.16. 50-O-tert-Butyldiphenylsilyl-20,30-di-O-acetyl-N2-
isobutyryl-40-C--p-toluenesulfonyl)oxymethylguanosine
-15d). Under N2 atmosphere, silylated N 2-isobutyrylgua-
nine /3TMS´GBui) /0.5M solution in dichloroethane,
0.96 mL, 0.48 mmol) and trimethylsilyl tri¯uoromethane-
sulfonate /76 mg, 0.32 mmol) were added to a stirred solu-
tion of 14 /250 mg, 0.32 mmol) in dichloroethane /5 mL) at
room temperature. After having been re¯uxed for 13 h, the
reaction mixture was cooled and partitioned with saturated
NaHCO3, and the mixture was extracted with CHCl3. Usual
work-up and puri®cation by SiO2 column chromatography
/CHCl3/MeOH, 33:1) afforded 15d /198 mg, 0.23 mmol,
72%, a mixture of N9- and N7-isomers, N9/N7ˆca. 3:1) as
a white foam, mp 83±848C. IR /KBr): 2936, 1751, 1685,
1608, 1561, 1368, 1244 cm21. 1H NMR /CDCl3) /major, N9-
isomer) d: 0.94 /9H, s), 1.14 /3H, d, Jˆ7 Hz), 1.15/3H, d,
Jˆ6 Hz), 2.05/3H, s), 2.08 /3H, s), 2.40 /3H, s), 2.53 /1H,
hep, Jˆ7 Hz), 3.73, 3.76 /2H, ABq, Jˆ6 Hz), 4.37 /2H, s),
5.93 /1H, d, Jˆ5Hz), 6.00 /2H, m), 7.21±7.74 /15H, m),
9.26 /1H, br), 12.20 /1H, br). 13C NMR /CDCl3) d: 18.8,
20.2, 21.5, 26.5, 36.1, 64.7, 67.4, 71.2, 72.6, 85.1, 85.4,
85.7, 96.0, 121.5, 127.6, 127.7, 127.8, 129.8, 129.9, 130.0,
131.8, 132.1, 132.5, 135.2, 135.3, 135.4, 135.5, 137.8,
145.1, 147.5, 148.0, 155.7, 169.1, 169.3, 178.4. MS /FAB)
m/z: 860 /MH1).
4.1.14. N4-Benzoyl-50-O-tert-butyldiphenylsilyl-20,30-di-
O-acetyl-40-C--p-toluenesulfonyl)oxymethylcytidine -15b0).
Under N2 atmosphere, silylated N4-benzoylcytosine
/2TMS´CBz) /0.5M solution in dichloroethane, 0.96 mL,
0.48 mmol) and trimethylsilyl tri¯uoromethanesulfonate
/76 mg, 0.32 mmol) were added to a stirred solution of 14
/250 mg, 0.32 mmol) in dichloroethane /5 mL) at room
temperature. After having been re¯uxed for 5h, the reaction
mixture was cooled and partitioned with saturated NaHCO3,
and the mixture was extracted with CHCl3. Usual work-up
and puri®cation by SiO2 column chromatography /CHCl3/
MeOH, 30:1) afforded 15b0 /225mg, 0.26 mmol, 82%) as a
23
white foam, mp 73±748C. [a]D ˆ125.4 /c 0.88, CHCl3).
IR /KBr): 3067, 2934, 1753, 1674, 1482, 1240, 1105 cm21
.
1H NMR /CDCl3) d: 1.19 /9H, s), 2.16 /3H, s), 2.20 /3H, s),
2.51 /3H, s), 3.87, 3.96 /2H, ABq, Jˆ11 Hz), 4.24, 4.34
/2H, ABq, Jˆ11 Hz), 5.63 /1H, dd, Jˆ6, 6 Hz), 5.79 /1H,

3046
S. Obika et al. / Tetrahedron 58 +2002) 3039±3049
4.1.17. 50-O-tert-Butyldiphenylsilyl-20,30-di-O-acetyl-5-
methyl-40-C--p-toluenesulfonyl)oxymethyluridine -15e).
Under N2 atmosphere, silylated thymine /2TMS´T) /0.5M
solution in dichloroethane, 0.96 mL, 0.48 mmol) and
trimethylsilyl tri¯uoromethanesulfonate /76 mg, 0.32
mmol) were added to a stirred solution of 14 /250 mg,
0.32 mmol) in dichloroethane /5mL) at room temperature.
After having been re¯uxed for 5h, the reaction mixture was
cooled and partitioned with saturated NaHCO3, and the
mixture was extracted with CHCl3. Usual work-up and
puri®cation by SiO2 column chromatography /hexane/
AcOEt, 1:2 to 1:4) afforded 15e /164 mg, 0.22 mmol,
/CDCl3) d: 19.1, 21.4, 26.7, 64.2, 68.7, 72.5, 74.2, 87.5,
89.0, 127.8, 127.9, 128.0, 128.8, 129.7, 130.0, 132.2,
132.4, 132.6, 133.0, 133.3, 135.4, 135.5, 141.9, 144.8,
149.2, 150.9, 152.0. MS /FAB) m/z: 794 /MH1). Anal.
calcd for C41H43N5O8SSi´1/4H2O: C, 61.67; H, 5.49; N,
8.77; S, 4.01. Found: C, 61.70; H, 5.59; N, 8.57; S, 3.88.
4.1.20. 50-O-tert-Butyldiphenylsilyl-N2-isobutyryl-40-C-
-p-toluenesulfonyl)oxymethylguanosine -16d) and its
N7-isomer. To a stirred solution of 15d /111 mg,
0.13 mmol) in MeOH /4 mL) was added K2CO3 /11 mg,
0.077 mmol). After having been stirred for 15min, the
reaction mixture was neutralized with concentrated HCl
and concentrated under reduced pressure. The remaining
residue was chromatographed on silica gel /CHCl3/MeOH,
25:1 to 20:1) to afford 16d /63 mg, 0.081 mmol, 63%) and
its N7-isomer /18 mg, 0.023 mmol, 18%) 16d: a white solid,
24
79%) as a white foam, mp 71±728C. [a]D ˆ15.7 /c
0.65, CHCl3). IR /KBr): 2934, 1753, 1695, 1465, 1369,
1
1236 cm21. H NMR /CDCl3) d: 1.09 /3H, s), 1.53 /3H,
s), 2.05/3H, s), 2.12 /3H, s), 2.40 /3H, s), 3.76 /2H, s),
4.02, 4.21 /2H, ABq, Jˆ10 Hz), 5.58 /1H, dd, Jˆ7, 6 Hz),
5.69 /1H, d, Jˆ6 Hz), 6.10 /1H, d, Jˆ7 Hz), 7.21±7.67
/15H, m), 9.28 /1H, br). 13C NMR /CDCl3) d: 11.8, 19.3,
20.3, 21.6, 26.9, 65.8, 67.3, 71.0, 72.1, 84.8, 85.5, 112.1,
127.8, 128.0, 128.1, 129.8, 130.2, 130.3, 131.4, 132.3,
135.0, 135.2, 135.5, 145.1, 150.5, 163.3, 169.1, 169.4. MS
/FAB) m/z: 765/MH 1). Anal. calcd for C38H44N2O11SSi´1/
10H2O: C, 59.53; H, 5.81; N, 3.65; S, 4.17. Found: C, 59.74;
H, 5.84; N, 3.37; S, 4.01.
22
mp 97±988C. [a]D ˆ18.5/ c 1.0, CHCl3). IR /KBr): 3164,
2933, 1678, 1606, 1564, 1363, 1182 cm21 1H NMR
.
/CDCl3) d: 0.92 /9H, s), 1.20 /6H, d, Jˆ7 Hz), 2.35/3H,
s), 2.96 /1H, hep, Jˆ7 Hz), 3.64, 3.80 /2H, ABq, Jˆ11 Hz),
4.50 /2H, s), 4.64 /2H, m), 5.87 /1H, d, Jˆ4 Hz), 7.20±7.75
/15H, m), 10.54 /1H, br), 12.36 /1H, br). 13C NMR /CDCl3)
d: 18.9, 19.1, 21.6, 26.7, 26.8, 29.7, 36.0, 64.4, 69.1, 72.3,
75.1, 87.5, 89.4, 96.1, 120.3, 127.7, 127.8, 127.9, 129.8,
129.9, 132.2, 132.7, 135.4, 135.5, 138.1, 144.8, 147.9,
148.3, 156.0, 180.5. MS /FAB) m/z: 776 /MH1). Anal.
calcd for C38H45N5O9SSi´H2O: C, 57.49; H, 5.97; N,
8.82; S, 4.13. Found: C, 57.59; H, 5.67; N, 8.41; S, 4.00.
4.1.18. N4-Benzoyl-50-O-tert-butyldiphenylsilyl-40-C--p-
toluenesulfonyl)oxymethylcytidine -16b0). To a stirred
solution of diacetate 15b0 /113 mg, 0.13 mmol) in MeOH
/4 mL) was added K2CO3 /11 mg, 0.079 mmol). After
having been stirred for 15min, the reaction mixture was
neutralized with concentrated HCl and concentrated under
reduced pressure. The remaining residue was chromato-
graphed on silica gel /CHCl3/MeOH, 25:1) to afford 16b0
/74 mg, 0.096 mmol, 73%) as a white solid, mp 97±988C.
N7-isomer: mp 87±888C. [a]D ˆ126.0 /c 1.2, CHCl3). IR
22
/KBr): 3164, 2932, 1682, 1608, 1369, 1105cm 21. 1H NMR
/CDCl3) d: 0.96 /9H, s), 1.28 /6H, d, Jˆ6 Hz), 2.37 /3H, s),
2.84 /1H, hep, Jˆ6 Hz), 3.68, 3.82 /2H, ABq, Jˆ11 Hz),
4.37 /2H, m), 4.45/2H, s), 6.03 /1H, d, Jˆ5Hz), 7.22±7.76
/14H, m), 7.98 /1H, s), 10.13 /1H, br), 12.54 /1H, br). 13C
NMR /CDCl3) d: 18.9, 21.4, 26.8, 29.7, 35.8, 36.2, 55.2,
64.2, 69.3, 72.5, 87.8, 91.7, 96.1, 111.0, 113.9, 127.9, 128.0,
129.7, 129.8, 129.9, 130.1, 132.0, 132.2, 132.5, 132.7,
135.5, 141.3, 144.8, 148.0, 180.3. MS /FAB) m/z: 776
/MH1). Anal. calcd for C38H45N5O9SSi´H2O: C, 57.49; H,
5.97; N, 8.82; S, 4.13. Found: C, 57.77; H, 5.87; N, 8.92; S,
4.22.
23
[a]D ˆ149.8 /c 0.16, CHCl3). IR /KBr): 3379, 1649,
1
1493, 1361 cm21. H NMR /CDCl3) d: 1.01 /9H, s), 2.38
/3H, s), 3.74 /2H, s), 4.24 /1H, dd, Jˆ5, 5 Hz), 4.33, 4.47
/2H, ABq, Jˆ11 Hz), 4.34 /1H, d, Jˆ5Hz), 5.72 /1H, d,
Jˆ5Hz), 7.22±7.74 /19H, m), 7.92±7.96 /2H, m). 13C
NMR /CDCl3) d: 19.1, 21.6, 26.8, 64.2, 69.1, 72.4,
76.9, 88.8, 92.5, 97.2, 127.3, 127.8, 128.0, 128.5, 128.9,
129.7, 130.2, 131.8, 132.0, 132.5, 132.6, 133.3, 135.4,
135.5, 144.1, 144.8, 162.8. MS /FAB) m/z: 770 /MH1).
Anal. calcd for C40H43N3O9SSi´1/4H2O: C, 62.04; H,
5.66; N, 5.43; S, 4.14. Found: C, 62.03; H, 6.01; N, 5.42;
S, 3.99.
4.1.21.
50-O-tert-Butyldiphenylsilyl-5-methyl-40-C--p-
toluenesulfonyl)oxymethyluridine -16e). To a stirred
solution of 15e /35mg, 0.046 mmol) in MeOH /2 mL)
was added K2CO3 /4 mg, 0.028 mmol). After having been
stirred for 15min, the reaction mixture was neutralized with
concentrated HCl and concentrated under reduced pressure.
The remaining residue was chromatographed on silica gel
4.1.19. N6-Benzoyl-50-O-tert-butyldiphenylsilyl-40-C--p-
toluenesulfonyl)oxymethyladenosine -16c). To a stirred
solution of 15c /54 mg, 0.062 mmol) in MeOH /3 mL)
was added K2CO3 /3 mg, 0.019 mmol). After having been
stirred for 15min, the reaction mixture was neutralized with
concentrated HCl and concentrated under reduced pressure.
The remaining residue was chromatographed on silica gel
/CHCl3/MeOH, 15:1) to give the desired product 16c
/44 mg, 0.056 mmol, 90%) as a white solid, mp 94±958C.
/hexane/AcOEt, 1:2 to 1:4) to afford 16e /31 mg, 0.046
ˆ
22
mmol, 100%) as a white solid, mp 91±928C. [a]D
112.7 /c 0.84, CHCl3). IR /KBr): 3379, 3067, 2934,
1
1695, 1468, 1363, 1107 cm21. H NMR /CDCl3) d: 1.04
/9H, s), 1.56 /3H, s), 2.38 /3H, s), 3.72, 3.75 /2H, ABq,
Jˆ8 Hz), 4.26 /2H, s), 4.36 /2H, m), 5.84 /1H, d, Jˆ
6 Hz), 7.21±7.71 /15H, m), 9.74 /1H, br). 13C NMR
/CDCl3) d: 12.0, 19.3, 21.5, 26.9, 65.3, 69.0, 72.0, 74.9,
86.9, 88.6, 96.1, 111.3, 128.0, 129.8, 130.2, 131.8, 132.4,
135.3, 135.5, 144.9, 151.5, 163.7. MS /FAB) m/z: 681
/MH1). Anal. calcd for C34H40N2O9SSi´H2O: C, 58.43; H,
6.06; N, 4.01; S, 4.59. Found: C, 58.67; H, 6.26; N, 3.72; S,
4.59.
22
[a]D ˆ110.0 /c 1.2, CHCl3). IR /KBr): 3332, 2932, 1701,
1
1612, 1180, 1105cm 21. H NMR /CDCl3) d: 0.95/9H, s),
2.37 /3H, s), 3.72, 3.81 /2H, ABq, Jˆ11 Hz), 4.45/2H, s),
4.52 /1H, d, Jˆ5Hz), 4.86 /1H, dd, Jˆ5, 7 Hz), 5.90 /1H, d,
Jˆ7 Hz), 7.21±7.60 /17H, m), 7.75/2H, d, Jˆ8 Hz), 7.95
/2H, d, Jˆ7 Hz), 7.96 /1H, s), 8.46 /1H, s). 13C NMR

S. Obika et al. / Tetrahedron 58 +2002) 3039±3049
3047
4.1.22. N4-Benzoyl-50-O-tert-butyldiphenylsilyl-30-O,40-
C-methylenecytidine -17b0). Under N2 atmosphere, sodium
bis/trimethylsilylamide) /0.056 mL, 0.056 mmol, 1.0 M
solution in THF) was added to a stirred solution of 16b0
/43 mg, 0.056 mmol) in THF /2 mL) at room temperature.
After having been stirred for 1 h at the same temperature,
the reaction mixture was partitioned with saturated
NaHCO3, and the mixture was extracted with CHCl3.
Usual work-up and puri®cation by SiO2 column chroma-
tography /CHCl3/MeOH, 15:1) afforded 17b0 /34 mg,
0.056 mmol, 100%) as a white solid, mp 78±798C.
7.60±7.63 /4H, m), 7.90 /1H, s), 10.02 /1H, br), 12.21 /1H,
br). 13C NMR /CDCl3) d: 19.0, 19.3, 26.8, 29.7, 36.1, 63.4,
75.5, 78.1, 85.7, 86.0, 88.1, 96.1, 120.1, 127.9, 130.0, 132.5,
132.7, 135.4, 135.5, 138.0, 148.2, 155.4, 179.7. MS /EI)
m/z: 546 /M12tert-Bu, 29.6), 199 /100). Anal. Calcd. for
C31H37N5O6Si: C, 61.67; H, 6.18; N, 11.60. Found: C,
61.42; H, 6.22; N, 11.46.
4.1.25. 50-O-tert-Butyldiphenylsilyl-5-methyl-30-O,40-C-
methyleneuridine -17e). Under N2 atmosphere, sodium
bis/trimethylsilylamide) /0.18 mL, 0.18 mmol, 1.0 M solu-
tion in THF) was added to a stirred solution of 16e /52 mg,
0.077 mmol) in THF /3 mL) at room temperature. After
having been stirred for 1 h at the same temperature, the
reaction mixture was partitioned with saturated NaHCO3,
and the mixture was extracted with CHCl3. Usual work-up
and puri®cation by SiO2 column chromatography /CHCl3/
MeOH, 15:1) afforded 17e /38 mg, 0.074 mmol, 96%) as a
21
[a]D ˆ121.0 /c 0.17, CHCl3). IR /KBr): 3447,
1
1654 cm21. H NMR /CDCl3) d: 1.07 /9H, s), 3.96 /2H,
s), 4.11 /1H, dd, Jˆ6, 5Hz), 4.52, 4.76 /2H, ABq,
Jˆ8 Hz), 5.14 /1H, d, Jˆ5Hz), 6.44 /1H, d, Jˆ6 Hz),
7.38±7.96 /17H, m). 13C NMR /CDCl3) d: 19.2, 26.8,
63.3, 76.5, 77.9, 78.0, 85.7, 87.5, 91.9, 96.1, 97.5, 125.5,
127.3, 127.9, 128.0, 128.5, 128.9, 130.2, 132.2, 132.5,
132.7, 133.3, 135.4, 135.5, 144.5, 162.6. MS /FAB)
m/z: 598 /MH1). Anal. calcd for C33H35N3O6Si´1/4H2O:
C, 65.81; H, 5.94; N, 6.98. Found: C, 65.83; H, 5.57; N,
7.06.
25
white solid, mp 53±548C. [a]D ˆ18.1 /c 0.98, CHCl3). IR
/KBr): 3195, 3066, 2932, 1695, 1466, 1108 cm21. 1H NMR
/CDCl3) d: 1.09 /9H, s), 1.65/3H, s), 3.91, 3.94 /2H, ABq,
Jˆ12 Hz), 4.08 /1H, m), 4.56, 4.76 /2H, ABq, Jˆ9 Hz),
5.14 /1H, d, Jˆ4 Hz), 6.45/1H, d, Jˆ7 Hz), 7.16 /1H, s),
7.37±7.46 /4H, m), 7.63±7.70 /6H, m), 9.48 /1H, br). 13C
NMR /CDCl3) d: 12.0, 19.3, 21.4, 26.7, 26.9, 29.7, 63.5,
75.4, 78.3, 85.1, 85.5, 88.1, 96.1, 112.1, 127.8, 128.0,
130.1, 130.2, 132.2, 132.7, 135.2, 135.5, 151.1, 163.6. MS
4.1.23. N4-Benzoyl-50-O-tert-butyldiphenylsilyl-30-O,40-
C-methyleneadenosine -17c). Under N2 atmosphere,
sodium bis/trimethylsilylamide) /0.34 mL, 0.34 mmol,
1.0 M solution in THF) was added to a stirred solution of
16c /111 mg, 0.14 mmol) in THF /3 mL) at room tempera-
ture. After having been stirred for 3 h at the same tempera-
ture, the reaction mixture was partitioned with saturated
NaHCO3, and the mixture was extracted with CHCl3.
Usual work-up and puri®cation by SiO2 column chroma-
tography /AcOEt/EtOH, 20:1 to 10:1) afforded 17c
/76 mg, 0.13 mmol, 90%) as a white solid, mp 76±778C.
1
/EI) m/z: 45 1 /M2tert-Bu, 100). Anal. calcd for
C27H32N2O6Si´H2O: C, 61.58; H, 6.51; N, 5.32. Found: C,
61.81; H, 6.52; N, 5.42.
4.1.26. N4-Benzoyl-30-O,40-C-methylenecytidine -1b0). To
a stirred solution of 17b0 /24 mg, 0.040 mmol) in dry THF
/2 mL) was added to tetrabutylammonium ¯uoride
/0.048 mL, 0.048 mmol, 1.0 M solution in THF) at room
temperature. After having been stirred for 15min, the reac-
tion mixture was concentrated under reduced pressure.
The remaining residue was chromatographed on silica gel
/AcOEt/EtOH, 20:1 to 10:1) to afford 1b0 /10 mg,
0.028 mmol, 70%) as a white solid, mp 150±1518C
22
[a]D ˆ15.6 /c 1.0, CHCl3). IR /KBr): 3283, 2932, 1702,
1
1613, 1458, 1250, 1109 cm21. H NMR /CDCl3) d: 1.07
/9H, s), 3.91 /2H, s), 4.64, 4.96 /2H, ABq, Jˆ8 Hz), 4.70
/1H, dd, Jˆ7, 5Hz), 5.30 /1H, d, Jˆ5Hz), 6.46 /1H, d,
Jˆ7 Hz), 7.33±7.65/13H, m), 8.03 /2H, d, Jˆ7 Hz), 8.14
/1H, s), 8.70 /1H, s). 13C NMR /CDCl3) d: 19.2, 26.7, 63.0,
75.8, 78.1, 85.3, 86.5, 88.3, 122.5, 127.3, 127.8, 127.9,
128.5, 128.7, 130.0, 131.9, 132.4, 132.5, 132.8, 133.1,
135.4, 135.5, 141.4, 149.2, 151.7, 152.7, 169.6. MS /FAB)
m/z: 622 /MH1). Anal. calcd for C34H35N5O5Si´3/4AcOEt:
C, 64.61; H, 6.01; N, 10.18. Found: C, 64.24; H, 5.70; N,
10.10.
22
/AcOEt). [a]D ˆ256.6 /c 0.35, CH3OH). IR /KBr):
1
3405, 1700 cm21. H NMR /CD3OD) d: 3.79, 3.87 /2H,
ABq, Jˆ12 Hz), 4.24 /1H, dd, Jˆ7, 5Hz), 4.55, 4.85/2H,
ABq, Jˆ8 Hz), 5 .10 /1H, d, Jˆ5Hz), 6.56 /1H, d,
Jˆ7 Hz), 7.52±7.67 /4H, m), 7.98±8.02 /2H, m), 8.20
/1H, d, Jˆ8 Hz). 13C NMR /CD3OD) d: 62.5, 77.0,
79.1, 86.9, 88.0, 91.4, 99.4, 129.18, 129.24, 129.4,
129.8, 130.7, 133.8, 134.2, 145.6, 147.2, 165.1.
MS /FAB) m/z: 360 /MH1). Anal. calcd for
C17H17N3O6´H2O: C, 54.11; H, 5.08; N, 11.14. Found: C,
54.22; H, 5.12; N, 11.31.
4.1.24.
50-O-tert-Butyldiphenylsilyl-N2-isobutyryl-30-
O,40-C-methyleneguanosine -17d). Under N2 atmosphere,
sodium bis/trimethylsilylamide) /0.041 mL, 0.041 mmol,
1.0 M solution in THF) was added to a stirred solution of
16d /13 mg, 0.017 mmol) in THF /2 mL) at room tempera-
ture. After having been stirred for 1 h at the same tempera-
ture, the reaction mixture was partitioned with saturated
NaHCO3, and the mixture was extracted with CHCl3.
Usual work-up and puri®cation by SiO2 column chroma-
4.1.27. N6-Benzoyl-30-O,40-C-methyleneadenosine -1c).
To a stirred solution of 17c /17 mg, 0.027 mmol) in THF
/2 mL) was added tetrabutylammonium ¯uoride /0.032 mL,
0.032 mmol, 1.0 M solution in THF) at room temperature.
After having been stirred for 15min, the reaction mixture
was concentrated under reduced pressure. The remaining
residue was chromatographed on silica gel /AcOEt/EtOH,
20:1 to 10:1) to afford 1c /7 mg, 0.018 mmol, 65%) as a
white solid, mp 228±2298C /iPrOH). IR /KBr): 3329,
tography /CHCl3/MeOH, 15:1) afforded 17d /8 mg,
25
0.014 mmol, 82%) as a white solid, mp 84±858C. [a]D
214.6 /c 0.97, CHCl3). IR /KBr): 3395, 3159, 2933, 1682,
ˆ
1609, 1564 cm21. H NMR /CDCl3) d: 1.04 /9H, s), 1.22
1
/6H, d, Jˆ7 Hz), 2.76 /1H, hep, Jˆ7 Hz), 3.86 /2H, s), 4.56,
4.83 /2H, ABq, Jˆ8 Hz), 4.63 /1H, dd, Jˆ7, 4 Hz), 5.23
/1H, d, Jˆ4 Hz), 6.38 /1H, d, Jˆ7 Hz), 7.32±7.41 /6H, m),
1
2923, 2856, 1705, 1613, 1459, 1250, 1107 cm21. H NMR
/CD3OD) d: 3.82, 3.86 /2H, ABq, Jˆ13 Hz), 4.64, 4.94

3048
S. Obika et al. / Tetrahedron 58 +2002) 3039±3049
/2H, ABq, Jˆ8 Hz), 4.80 /1H, dd, Jˆ8, 4 Hz), 5.22 /1H, d,
Jˆ4 Hz), 6.57 /1H, d, Jˆ8 Hz), 7.56±7.59 /2H, m), 7.64±
7.68 /1H, m), 8.08±8.10 /2H, m), 8.67 /1H, s), 8.73 /1H, s).
13C NMR /DMSO-d6) d: 60.8, 73.6, 77.4, 84.9, 86.3, 86.9,
125.8, 128.7, 128.9, 132.9, 133.5, 143.7, 150.7, 152.2,
152.8. MS /FAB) m/z: 384 /MH1). Anal. calcd for
C18H18N5O5´1/3H2O: C, 55.53; H, 4.57; N, 17.99. Found:
C, 55.77; H, 4.56; N, 17.74.
Acknowledgements
Part of this work was supported by a Grant for Research on
Health Sciences focusing on Drug Innovation from The
Japan Health Sciences Foundation, Industrial Technology
Research Grant Program in 2000 from New Energy and
Industrial Technology Development Organization /NEDO)
of Japan, a Grant-in-Aid from Japan Society for the
Promotion of Science, and a Grant-in-Aid from the Ministry
of Education, Science, and Culture, Japan. We thank JSPS
Research Fellowships for Young Scientists /Y. H.).
4.1.28. N2-Isobutyryl-30-O,40-C-methyleneguanosine -1d).
To a stirred solution of 17d /32 mg, 0.042 mmol) in THF
/3 mL) was added tetrabutylammonium ¯uoride /0.10 mL,
0.10 mmol, 1.0 M solution in THF) at room temperature.
After having been stirred for 15min, the reaction mixture
was concentrated under reduced pressure. The remaining
residue was chromatographed on silica gel /AcOEt/EtOH,
20:1 to 10:1) to afford 1d /20 mg, 0.033 mmol, 78%) as a
References
È
1. Schroder, H. C.; Suhadolnik, R. J.; P¯eiderer, W.; Charubala,
R.; MuÈller, W. E. G. Int. J. Biochem. 1992, 24, 55±63. Player,
M. R.; Torrence, P. F. Pharmacol. Ther. 1998, 78, 55±113.
2. Padgett, R. A.; Konarska, M. M.; Grabowski, P. J.; Hardy,
S. F.; Sharp, P. A. Science 1984, 225, 898±903.
23
white solid, mp 234±2358C /iPrOH). [a]D ˆ247.5/ c 0.13,
CH3OH). IR /KBr): 3316, 1688, 1607 cm21 1H NMR
.
/CD3OD) d: 1.23 /6H, d, Jˆ7 Hz), 2.67±2.77 /1H, hep,
Jˆ7 Hz), 3.76, 3.83 /2H, ABq, Jˆ12 Hz), 4.55, 4.65 /2H,
ABq, Jˆ8 Hz), 4.92 /1H, m), 5.15 /1H, d, Jˆ5Hz), 6.35
/1H, d, Jˆ8 Hz), 8.23 /1H, s). 13C NMR /CD3OD) d: 19.3,
37.0, 62.5, 75.9, 79.1, 86.8, 87.5, 88.4, 97.2, 121.4, 140.0,
150.0, 151.2, 181.7. MS /FAB) m/z: 366 /MH1). Anal. calcd
for C15H19N5O6´1/2H2O: C, 48.13; H, 5.38; N, 18.71. Found:
C, 48.32; H, 5.15; N, 18.24.
3. Kitade, Y.; Nakata, Y.; Hirota, K.; Maki, Y.; Pabuccuoglu, A.;
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Acta 1996, 79, 609±618. Wasner, M.; Suhadolnik, R. J.;
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4.1.29. 5-Methyl-30-O,40-C-methyleneuridine -1e). To a
stirred solution of 17e /32 mg, 0.062 mmol) in THF
/2 mL) was added tetrabutylammonium ¯uoride /0.075
mL, 0.075mmol, 1.0 M solution in THF) at room tempera-
ture. After having been stirred for 15min, the reaction
mixture was concentrated under reduced pressure. The
remaining residue was chromatographed on silica gel
/AcOEt/EtOH, 20:1 to 10:1) to afford 1e /12 mg,
0.044 mmol, 71%) as a white solid, mp 119±1208C
25
/AcOEt). [a]D ˆ263.1 /c 0.44, MeOH); IR /KBr): 4016,
3451, 1723 cm21. 1H NMR /CD3OD) d: 1.89 /3H, s), 3.75,
3.83 /2H, ABq, Jˆ12 Hz), 4.14 /1H, dd, Jˆ8, 5Hz), 4.51,
4.83 /2H, ABq, Jˆ8 Hz), 5.05 /1H, d, Jˆ5Hz), 6.42 /1H, d,
Jˆ8 Hz), 7.52 /1H, s). 13C NMR /CD3OD) d: 12.4, 62.5,
75.3, 79.1, 86.6, 86.9, 88.8, 112.4, 138.0, 152.8, 166.1. MS
/FAB) m/z: 277 /M1Li1). Anal. calcd for C11H14N2O6´H2O:
C, 45.83; H, 5.59; N, 9.72. Found: C, 45.81; H, 5.51; N,
9.71.
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4.2. Computation
Semi-empirical MO calculations of 1e and 20-hydroxy-
thymidine were carried out on an SGI O2 workstation
using Spartan version 5.1.20 All initial structures used for
the MO calculations were generated by reference to the
X-ray structures of 1e. Geometry optimization utilizing
the PM3 Hamiltonian was carried out with constraints on
torsion angles, n0±n4, x and g. The torsion angles x and g
were ®xed at 2108.08 and 74.18 for 1e and 2163.98 and
51.88 for 20-hydroxythymidine, respectively. The values of
endocyclic sugar torsion angles n0±n4 were determined to
vary the pseudorotation phase angle P every 108, and the
maximum torsion angles nmax were ®xed at 32.58 for 1e and
38.68 for 20-hydroxythymidine.
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