Synthesis of nucleoside analogues bearing the five naturally occurring nucleic acid bases built on a 2-oxabicylo[3.1.0]hexane scaffold

Article abstract of DOI:10.1021/jo051047b

Hitherto unknown nucleoside analogues incorporating the five naturally occurring nucleic acid bases built on a 2-oxabicyclo[3.1.0]hexane template were synthesized. The synthesis of these new conformationally restricted nucleoside analogues involved the pr

Full text of DOI:10.1021/jo051047b

Synthesis of Nucleoside Analogues Bearing the Five Naturally
Occurring Nucleic Acid Bases Built on a 2-Oxabicylo[3.1.0]hexane
Scaffold†
Julien Gagneron, Gilles Gosselin, and Christophe Mathe´*
Laboratoire de Chimie Organique Biomole´culaire de Synthe`se, UMR 5625 CNRS-Universite´
Montpellier II, case courrier 008, Place Euge`ne Bataillon, 34095 Montpellier Cedex 05, France
cmathe@univ-montp2.fr
Received May 25, 2005
Hitherto unknown nucleoside analogues incorporating the five naturally occurring nucleic acid
bases built on a 2-oxabicyclo[3.1.0]hexane template were synthesized. The synthesis of these new
conformationally restricted nucleoside analogues involved the preparation of a suitable sugar
precursor bearing the 2-oxabicyclo[3.1.0]hexane scaffold. This sugar was readily obtained from
[(3aS,6aS)-2,2-dimethyl-3a,6a-dihydrofuro[2,3-d][1,3]dioxol-5-yl]methyl benzyl ether (4) following
a Simons-Smith-type cyclopropanation reaction. Finally, glycosylation reactions and deprotection
provided the nucleoside analogues. Using nucleoside 14 bearing thymine base as a model, we found
0
that the conformation of such nucleoside analogue was restricted toward a T1 conformation.
Introduction
polymerases. The sugar puckering of natural ribo- and
deoxy-ribonucleosides are known to exist in a dynamic
equilibrium between two major conformers, the North (N)
and the South (S) types (Figure 1).5 Conformational
studies of nucleosides in solution indicate that the North/
South interconversion is rapid on a NMR time scale;6
however, when a nucleoside or a nucleotide binds to an
activating enzyme or its pharmacological target, only one
form is expected to be present at the active site. Even if
the binding conformation is likely modified by the enzyme
to achieve optimal fitting,7 any conformation-activity
study would be very helpful in order to identify confor-
mational preferences of nucleoside- or nucleotide-convert-
ing enzymes and to study the interactions of the nucleo-
sides or nucleotides with the enzymatic targets. For these
reasons, conformationally restricted nucleosides have
drawn considerable attention because they can adopt a
determined conformation that can be useful tools in a
Over several decades, a large number of nucleoside
analogues have been synthesized, and some of them have
been shown to present potent antiviral or antitumoral
activities.1,2 To become active, such compounds, generally
have to be metabolized by cellular kinases to their 5′-
triphosphate forms, which finally interact with viral or
cellular polymerases. To discover new nucleoside deriva-
tives endowed with biological activities, modifications of
the base and/or sugar moiety of natural nucleosides can
be attempted.3,4 In recent years, the conformational
behavior of natural and modified nucleosides, and in
particular the sugar puckering, has been considered as
of great importance all along their metabolic pathway
as well as in the final interaction with the target
* To whom correspondence should be addressed. Phone: (+33) 4-67-
14-47-76. Fax: (+33) 4-67-04-20-29.
† This work has been presented in preliminary form at the Sixteenth
International Round Table on Nucleosides, Nucleotides and Nucleic
Acids, Sept. 12-16, 2004, Minneapolis, MN.
(5) Saenger, W. Principles of Nucleic Acid Struture; Springer: New
York, 1984.
(6) Altona, C.; Sundaralingam, M. J. Am. Chem. Soc. 1973, 95, 2333.
(7) Nicklaus, M. C.; Wang, S.; Driscoll, J. S.; Milne, G. W. A. Bioorg.
Med. Chem. 1995, 3, 411.
(1) De Clercq, E. J. Clin. Virol. 2004, 30, 115.
(2) Matsuda, A.; Sasaki, T. Cancer Sci. 2004, 95, 105.
(3) Herdewijn, P. Drug Discovery Today 1997, 2, 235.
(4) Ichikawa, E.; Kato, K. Curr. Med. Chem. 2001, 8, 385.
10.1021/jo051047b CCC: $30.25 © 2005 American Chemical Society
Published on Web 07/22/2005
J. Org. Chem. 2005, 70, 6891-6897
6891

Gagneron et al.
FIGURE 2. Retrosynthetic pathway. Pg ) variable protecting
group
protecting groups and the heterocyclic bases. For the
preparation of the sugar precursor a, a Simmons-Smith-
type cyclopropanation reaction18 should be straightfor-
ward from a furanose substrate b having a double bond
in position 3,4. The stereoselective control of the meth-
ylene insertion on the R face of b might be induced from
the steric hindrance of the 1,2-O-isopropylidene group on
the sugar â face. The unsaturated sugar b should be
easily synthesized following a â-elimination reaction from
1,2-O-isopropylidene L-xylose (Figure 2).
Chemical Synthesis. As an appropriate carbohydrate
precursor, commercially available L-xylose was chosen as
starting material. L-Xylose (1) was converted to 5-O-
benzyl-1,2-O-isopropylidene-R-L-xylofuranose (2) follow-
ing a similar protocol established in the literature for the
synthesis of the D-counterpart (Scheme 1).19
Compound 2 was reacted with triflic anhydride (Tf2O)
in a pyridine/dichloromethane mixture at -15 °C20 to
provide sugar 3, which was subjected to a â-elimination
reaction using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)
in acetonitrile under reflux. Compound (4) was obtained
in 93% yield after purification by silica gel column
chromatography. The cyclopropanation reaction of com-
pound 4 was accomplished via a Simmons-Smith-type
reaction following Furukawa’s procedure21,22 to afford a
mixture of compounds 5a and 5b. Separation was readily
achieved by silica gel column chromatography to provide
pure 5a and 5b, with 91% and 1.5% yield, respectively.
As expected, compound 5a with a methylene exo was
obtained as the major compound. Stereoselective control
of this reaction is obtained on a sterically constrained
substrate like compound 4 where the isopropylidene
group directs the methylene insertion on the R face, the
FIGURE 1. Conformational equilibrium. Nucleoside ana-
logues incorporating the five naturally occurring nucleic acid
bases built on a 2-oxabicyclo[3.1.0]hexane scaffold.
such evaluation. For instance, the use of conformationally
locked carbocyclic nucleosides built on a bicyclo[3.1.0]-
hexane template has demonstrated conformational pref-
erences for a number of enzymes8-11 and subtypes of
adenosine receptors.12-16 For our part, we chose to
introduce modifications on the sugar able of restricting
the dynamic equilibrium between the northern-type and
southern-type geometry that normally characterize the
sugar moiety of standard nucleosides in solution. In this
respect, we have synthesized new conformationally locked
nucleoside analogues built on a 2-oxabicyclo[3.1.0.]hexane
scaffold17 bearing purine and pyrimidine bases. Assuming
that the conformation and puckering of the glycon moiety
of nucleosides play a critical role in modulating biological
activity, such new conformationally restricted nucleoside
analogues, could be used to obtain further information
regarding the correlation between sugar ring conforma-
tion and biological activity. Herein, we will report on the
synthesis of such compounds (Figure 1).
Results and Discussion
Retrosynthetic Pathway. The synthesis of the target
nucleosides was achieved through glycosylation reactions
between a suitable sugar precursor a bearing appropriate
(8) Marquez, V. E.; Ezzitouni, A.; Russ, P.; Siddiqui, M. A.; Ford,
H., Jr.; Feldman, R. J.; Mitsuya, H.; George, C.; Barchi, J. J., Jr. J.
Am. Chem. Soc. 1998, 120, 2780.
(9) Marquez, V. E.; Ezzitouni, A.; Russ, P.; Siddiqui, M. A.; Ford,
H. J.; Feldman, R. J.; Mitsuya, H.; George, C.; Barchi, J. J., Jr.
Nucleosides Nucleotides 1998, 17, 1881.
(10) Marquez, V. E.; Russ, P.; Alonso, R.; Siddiqui, M. A.; Hernandez,
S.; George, C.; Nicklaus, M. C.; Dai, F.; Ford, H., Jr. Helv. Chim. Acta
1999, 82, 2119.
(16) Ravi, R. G.; Lee, K.; Ji, X. D.; Kim, H. S.; Soltysiak, K. A.;
Marquez, V. E.; Jacobson, K. A. Bioorg. Med. Chem. Lett. 2001, 11,
2295.
(17) For a recent example of nucleosides built on an oxabicyclo[3.1.0]-
hexane system, see: Comin, M. J.; Rodriguez, J. B.; Russ, P.; Marquez,
V. E. Tetrahedron 2003, 59, 295.
(11) Marquez, V. E.; Russ, P.; Alonso, R.; Siddiqui, M. A.; Shin, K.
J.; George, C.; Nicklaus, M. C.; Dai, F.; Ford, H., Jr. Nucleosides
Nucleotides 1999, 18, 521.
(12) Jacobson, K. A.; Ji, X.-D.; Li, A.-H.; Melman, N.; Siddiqui, M.
A.; Shin, K.-J.; Marquez, V. E.; Ravi, R. G. J. Med. Chem. 2000, 43,
2196.
(18) Simmons, H. E.; Smith, R. D. J. Am. Chem. Soc. 1958, 80, 5323.
(19) Tino, J. A.; Clark, J. M.; Field, A. K.; Jacobs, G. A.; Lis, K. A.;
Michalik, T. L.; McGeever-Rubin, B.; Slusarchyk, W. A.; Spergel, S.
H.; Sundeen, J. E.; Tuomari, A. V.; Young, M. G.; Zalher, R. J. Med.
Chem. 1993, 36, 1221.
(13) Kim, H. S.; Ravi, R. G.; Marquez, V. E.; Maddileti, S.; Wihlborg,
A.-K.; Erlinge, D.; Malsmjo, M.; Boyer, J. L.; Harden, T. K.; Jacobson,
K. A. J. Med. Chem. 2002, 45, 208.
(20) Liu, X.-G.; Binkley, R. W.; Yeh, P. J. Carbohydr. Chem. 1992,
11, 1053.
(14) Lee, K.; Ji, X. D.; Marquez, V. E.; Jacobson, K. A. Bioorg. Med.
Chem. Lett. 2001, 11, 1333.
(21) Furukawa, J.; Kawabata, N.; Nishimura, J. Tetrahedron Lett.
1966, 7, 3353.
(15) Nandanan, E.; Jang, S.-Y.; Moro, S.; Kim, H.; Siddiqui, M. A.;
Russ, P.; Marquez, V. E.; Busson, R.; Herdewijn, P.; Harden, T. K.;
Boyer, J. L.; Jacobson, K. A. J. Med. Chem. 2000, 43, 829.
(22) Furukawa, J.; Kawabata, N.; Nishimura, J. Tetrahedron 1968,
24, 53.
6892 J. Org. Chem., Vol. 70, No. 17, 2005

Synthesis of Nucleoside Analogues
SCHEME 1a
a Reagents and conditions: (a) Tf2O, pyridine/CH2Cl2, -15 °C; (b) DBU, CH3CN, 80 °C; (c) ZnEt2, CH2I2, toluene, 0 °C; (d) 4 N HCl/
dioxane, 0 °C; (e) (i) CrO3, Ac2O, pyridine/CH2Cl2, 0 °C, (ii) NaBH4/EtOH, rt; (f) Ac2O/pyridine, rt; (g) AcOH, Ac2O, H2SO4, 0 °C to rt.
and 7. In the case of R-methyl furanoside 6, H-3 signal
appears as a singlet while H-3 signal of compound 7
appears as a doublet with a coupling constant 3JH3-H4
)
5.8 Hz, confirming a ribo-like configuration for 7. Com-
pound 7 was converted into the suitable peracylated
sugar precursor 9 in a two-step procedure. First, an
acetylation reaction afforded 8, which was later reacted
with AcOH/Ac2O/H2SO4 to give, after purification by silica
gel column chromatography, an anomeric mixture (ratio
9R/9â, 9/91) of 3-(acetyloxy)-1-[(acetyloxy)methyl]-2-
oxabicyclo[3.1.0]hex-4-yl acetate with 81% yield. After-
ward, sugar 9 was used for the condensation reactions
with the heterocyclic bases and provided in each case only
the â anomers of the protected nucleosides owing to 4-O-
acyl-type participating group. The syntheses of the py-
rimidines 13-15 and purine 17 and 18 nucleosides are
depicted in Scheme 2.
Briefly, glycosylation reaction with uracil, thymine or
N4-benzoyl cytosine and sugar 9, under Vorbru¨ggen
conditions23 using (trimethylsilyl) trifluoromethane sul-
fonate (TMSOTf) as a catalyst in anhydrous acetonitrile
at 0 °C, afforded compounds 10-12. The target nucleo-
sides 13-15 were obtained from 10-12 following treat-
ment with methanolic ammonia after purification on
silica gel column chromatography. A glycosylation reac-
tion with adenine and 9 using tin(IV) chloride (SnCl4) as
a catalyst24 in anhydrous acetonitrile afforded protected
nucleoside 16, which upon treatment with sodium meth-
oxide in methanol gave the desired nucleoside 17 in 61%
yield after purification. To prepare the guanosine ana-
logue (18), a condensation reaction of 2-N-acetyl-6-O-
(diphenylcarbamoyl)guanine with 9 following Robins’
procedure25 was achieved. The crude coupling product
was directly treated with methanolic ammonia to give
nucleoside 18.
FIGURE 3. NOE effects on compound 5a.
less hindered face of the compound, providing as a major
compound sugar 5a with a D-like configuration. Struc-
tural assignments were based upon 1H NMR spectra,
COSY homonuclear experiments, and NOE effects. In the
case of 5a, the H-4 signal appeared as a doublet with a
3
coupling constant JH4-H3 ) 4.1 Hz. In the case of 5b,
H-4 signal appeared as a pseudo-triplet with a coupling
3
3
constant JH4-H3 and JH4-H5 of 5.2 and 4.7 Hz, respec-
tively. Furthermore, using NOE-difference spectroscopy,
NOE effects were observed for 5a between the H-6
methylene protons and H-4 (8.8%) as well as H-6 meth-
ylene protons and H-3 (4.6%) (Figure 3).
No significant NOE effect was seen for compound 5b.
All of these observations are in agreement with a
methylene insertion mainly on the R face of sugar 4
during the cyclopropanation reaction. To obtain the
nucleoside analogues with the â-configuration and owing
to an anchimeric participation of a 4-O-acyl-type protec-
tive group during glycosylation reactions, compound 5a
with an arabino-like configuration has to be converted
to a sugar with a ribo-like configuration. In this regard,
hydrolysis of 5a with HCl in a dioxane-methanol mix-
ture afforded, as a single isomer, the R-anomer of methyl
furanoside 6 in a high yield. Later, a chromium-mediated
oxidation of 6 provided the corresponding ketone, which
was not isolated but directly reduced with sodium
boronhydride to give, after purification on silica gel
column chromatography, the sugar epimer 7 with 74%
yield. Inversion of configuration at C-4 was established
(23) Vorbru¨ggen, H. Acc. Chem. Res. 1995, 28, 509.
(24) Saneyoshi, M.; Satoh, E. Chem. Pharm. Bull. 1979, 27, 2518.
(25) Robins, M. J.; Zou, R.; Guo, Z.; Wnuk, S. F. J. Org. Chem. 1996,
61, 9207.
1
by taking account of H NMR spectra of compounds 6
J. Org. Chem, Vol. 70, No. 17, 2005 6893

Gagneron et al.
SCHEME 2a
Conclusion
Nucleoside analogues 13-15, 17, and 18 incorporating
the five naturally occurring nucleic acid bases built on
a 2-oxabicyclo[3.1.0]hexane scaffold were synthesized
through glycosylation reactions between heterocyclic
bases and a suitable sugar precursor bearing the 2-oxa-
bicyclo[3.1.0]hexane structure. Using compound 14 as
model, we found that the conformation of such nucleoside
analogue was restricted toward a 0T1 conformation.
Biological evaluations of nucleoside analogues 13-15, 17,
and 18 against a broad range of viruses are currently in
progress. These new nucleoside analogues built on a
2-oxabicyclo[3.1.0]hexane scaffold might find wider ap-
plicability to probe conformational preferences of nucleo-
side/nucleotide-converting enzymes and receptors.
Experimental Section
5-O-Benzyl-1,2-O-isopropylidene-r-L-xylofuranose (2).
Compound 2 was prepared in 75% yield from commercially
available L-xylose following a similar protocol established in
the literature for the synthesis of its D-counterpart:19 1H NMR
(CDCl3, 200 MHz) δ 7.37 (m, 5H), 6.01 (d, 1H, J ) 3.7 Hz),
4.68 (d, 1H, J ) 11.9 Hz), 4.59 (d, 1H, J ) 11.9 Hz), 4.54 (m,
1H), 4.28 (m, 2H), 3.97 (m, 2H), 3.66 (d, 1H, J ) 3.5 Hz), 1.37
(s, 3H), 1.23 (s, 3H). Compound 2 was directly used in the next
step without further purification.
5-O-Benzyl-1,2-O-isopropylidene-3-O-triflyl-r-L-xylo-
furanose (3). Compound 2 (58.7 g, 0.21 mol) was coevaporated
with dry pyridine and dissolved in a mixture of dry CH2Cl2
(500 mL) and dry pyridine (80 mL). The mixture was cooled
to -15 °C, then Tf2O (70.5 mL, 0.42 mol) in CH2Cl2 (500 mL)
was added dropwise, and the resulting mixture was stirred
for 1 h at room temperature. The mixture was poured into cold
saturated NaHCO3 solution and washed with water (3 × 200
mL). The organic phase was dried (Na2SO4) and the solvent
was removed under reduced pressure. The residue was dis-
solved in hot hexane, filtered, and coevaporated with dry
toluene to give compound 3 as a white solid: 1H NMR (CDCl3,
200 MHz) δ 7.32 (m, 5H), 6.02 (d, 1H, J ) 3.7 Hz), 5.31 (d,
1H, J ) 2.6 Hz), 4.76 (d, 1H, J ) 3.7 Hz), 4.64-4.54 (m, 3H),
3.86-3.65 (m, 2H), 1.52 (s, 3H), 1.36 (s, 3H); FAB-MS (>0)
m/z 413 (M + H)+. Compound 3 was directly used in the next
step without further purification.
[(3aS,6aS)-2,2-Dimethyl-3a,6a-dihydrofuro[2,3-d][1,3]-
dioxol-5-yl]methyl Benzyl Ether (4). DBU (59.8 mL, 0.4
mol) was added to a solution of compound 3 (82 g, 0.2 mol) in
dry CH3CN (1 L) and the mixture was heated under reflux 1
h. After cooling, the solution was carefully adjusted to pH
7.5-8 with 2 N HCl solution and dissolved in CH2Cl2 (300
mL). The organic phase was washed with water (3 × 100 mL)
and dried (Na2SO4) and the solvent was removed under
reduced pressure. The residue was purified by silica gel col-
umn chromatography using petroleum ether/ether (9:1) as
eluent to give compound 4 (48.5 g, 92%) as a yellow oil: 1H
NMR (CDCl3, 200 MHz) δ 7.37 (m, 5H), 6.11 (d, 1H, J ) 5.2
Hz), 5.33 (m, 1H), 5.26 (m, 1H), 4.62 (s, 2H), 4.08 (s, 2H), 1.50
(s, 3H), 1.47 (s, 3H); 13C NMR (CDCl3, 100 MHz) δ 159.1,
138-128.2, 112.6, 106.8, 100.3, 83.9, 73.5, 65.2, 28.5, 28.3;
FAB-MS (>0) m/z 263 (M + H)+. Anal. Calcd for C15H18O4: C,
68.68; H, 6.92. Found: C, 68.81; H, 6.98.
a Reagents: (a) silylated pyrimidine, TMSOTf, CH3CN, 0°; (b)
MeOH/NH3, rt; (c) adenine, SnCl4, CH3CN, rt; (d) (i) silylated 2-O-
acetyl-6-O-(diphenylcarbamoyl)guanine, BSA, toluene, 80 °C, (ii)
MeOH/NH3, rt; (e) MeONa/MeOH, rt.
Conformational Analysis. Briefly, the definition of
the conformational behavior of natural and modified
nucleosides involves the determination of at least three
structural parameters.5 The glycosidic torsion angle ø
determines the syn or anti disposition of the base relative
to the sugar moiety (syn when the C-2 carbonyl of
pyrimidines or N-3 of purine lies over the sugar ring, anti
when these atoms are oriented in the opposite direction).
The torsion angle γ determines the orientation of the
5′-OH with respect to C-3′ as represented by the three
main rotamers γ+, γt and γ-. The conformation of the
furanose ring and its deviation from planarity are
described by the pseudorotational phase angle P and the
maximal puckering amplitude νmax. For conformational
studies, we chose as a model compound the nucleoside
14, and its conformation was analyzed by simple model-
ing. An ab initio calculation was performed on 14, i.e., a
geometry optimization at the 3-21 G level using basis set
as implemented in the HyperChem 7.5 software. A root-
mean-square gradient termination cutoff of 0.05 kcal Å-1
mol-1 was used for geometry optimization with the
Polak-Ribiere conjugate gradient algorithm. The torsion
angles γ and ø on the nucleoside structure were initially
located in the γ- and anti ranges, respectively. The
calculations provided a geometry optimized structure
close to a 0T1 conformation (P ) 107.2°) (ν2 ) -5.1°) and
νmax ) 17.2°. As established, the 2-oxabicyclo[3.1.0]hexane
scaffold seems to restrict the sugar moiety toward a
C1′-exo type of conformation according to the standard
conformational description of nucleosides. Such kind of
S-type conformation has been previously reported for
nucleoside analogues bearing various exo fused ring, such
as azetidine,26 oxetane,27 and propylene ring.28 However,
in our case, a flatter ring pucker was observed.
[(3aS,4aS,5aS,5bS)-2,2-Dimethyltetrahydro-4aH-
cyclopropa[4,5]furo[2,3-d][1,3]dioxol-4a-yl]methyl Ben-
zyl Ether (5a) and [(3aS,4aR,5aR,5bS)-2,2-Dimethyltet-
rahydro-4aH-cyclopropa[4,5]furo[2,3-d][1,3]dioxol-4a-
yl]methyl Benzyl Ether (5b). To a stirred solution of
(27) Obika, S.; Morio, K.-i.; Nanbu, D.; Hari, Y.; Itoh, H.; Imanishi,
T. Tetrahedron 2002, 58, 3039.
(28) Bjo¨rsne, M.; Szabo, T.; Samuelson, B.; Classon, B. Bioorg. Med.
Chem. 1995, 3, 397.
(26) Obika, S.; Andoh, J.-i.; Onoda, M.; Nakagawa, O.; Hiroto, A.;
Sugimoto, T.; Imanishi, T. Tetrahedron Lett. 2003, 44, 5267.
6894 J. Org. Chem., Vol. 70, No. 17, 2005

Synthesis of Nucleoside Analogues
4 (6.0 g, 22.9 mmol) in dry toluene (115 mL) at 0 °C
was added dropwise diethyl zinc [1 M in hexane] (60 mL,
60 mmol) and diiodomethane (4.8 mL, 59.6 mmol). After
15 min, the mixture was allowed to reach room temperature
and stirring was continued for 4 h. Saturated NH4Cl solu-
tion was carefully added and the resulting mixture was
extracted with CH2Cl2 (3 × 120 mL), washed successively with
a saturated NaHCO3 solution (100 mL) and water (100 mL),
and dried (Na2SO4) and the solvent was removed under
reduced pressure. The residue was purified by silica gel column
chromatography using petroleum ether/ether (4:1) as eluent
to give successively, as colorless oil, compound 5a (5.8 g, 91%)
138.5-128, 103.8, 74.1, 73.4, 71.9, 67.9, 56.6, 24.3, 15.3;
FAB-MS (>0) m/z 251 (M + H)+; FAB-MS (<0) m/z 249 (M -
H)-. Anal. Calcd for C14H18O4: C, 67.18; H, 7.25. Found: C,
67.04; H, 7.40.
(1S,3S,4R,5S)-1-[(Benzyloxy)methyl]-3-methoxy-2-
oxabicyclo[3.1.0]hex-4-yl Acetate (8). To a solution of the
compound 7 (380 mg, 1.52 mmol) in pyridine (7 mL) was added
acetic anhydride (1.4 mL, 14.8 mmol). After stirring for 2 h,
the solution was evaporated and coevaporated with toluene
and the crude product was purified by silica gel column
chromatography using petroleum ether/ether (3:2) as eluent
to give compound 8 (405 mg, 91%) as a colorless syrup: [R]20
D
and compound 5b (0.1 g, 1.5%). Compound 5a: [R]20 -50.9
+23.2 (c 0.86, DMSO); 1H NMR (CDCl3, 400 MHz) δ 7.30-7.2
(m, 5H), 5.22 (m, 1H), 5.06 (d, 1H, J ) 5.6 Hz), 4.57 (d, 1H, J
) 12.2 Hz), 4.53 (d, 1H, J ) 12.2 Hz), 3.75 (d, 1H, J ) 11.6
Hz), 3.52 (d, 1H, J ) 11.6 Hz), 3.26 (s, 3H), 2.03 (s, 3H), 1.64
(m, 1H), 1.50 (t, 1H, J ) 5.4 Hz), 0.61 (m, 1H); 13C NMR
(CDCl3, 100 MHz) δ 171.3, 138.5-128, 103.4, 76.1, 73.5,
71.7, 67.1, 56.8, 21.2, 15.9; FAB-MS (>0) m/z 293 (M + H)+;
FAB-MS (<0) m/z 291 (M - H)-. Anal. Calcd for C16H20O5: C,
65.74; H, 6.90. Found: C, 66.00; H, 7.03.
D
1
(c 1.06, DMSO); H NMR (CDCl3, 300 MHz) δ 7.40-7.30 (m,
5H), 5.56 (d, 1H, J ) 4.1 Hz), 4.79 (d, 1H, J ) 4.1 Hz), 4.70 (d,
1H, J ) 12.1 Hz), 4.62 (d, 1H, J ) 12.1 Hz), 3.90 (d, 1H, J )
11.3 Hz), 3.76 (d, 1H, J ) 11.3 Hz), 1.78 (dd, 1H, J ) 5, 10
Hz), 1.61 (s, 3H), 1.4 (s, 3H), 0.83 (dd, 1H, J ) 5, 6.7 Hz), 0.54
(dd, 1H, J ) 6.7, 10 Hz); 13C NMR (CDCl3, 100 MHz) δ 138.6-
128, 114.5, 107.8, 84.5, 73.4, 71.5, 69.4, 28.7, 28.3, 23.8, 15.3;
FAB-MS (>0) m/z 277 (M + H)+. Anal. Calcd for C16H20O4: C,
69.54; H, 7.30. Found: C, 69.66; H, 7.37. Compound 5b: 1H
NMR (CDCl3, 200 MHz) δ 7.40-7.30 (m, 5H), 5.92 (d, 1H, J )
4.6 Hz), 4.93 (t, 1H, J ) 4.6 Hz), 4.58 (d, 1H, J ) 12.2 Hz),
4.52 (d, 1H, J ) 12.2 Hz), 3.79 (d, 1H, J ) 11.8 Hz), 3.39 (d,
1H, J ) 11.8 Hz), 1.72 (m, 1H), 1.47 (s, 3H), 1.40 (dd, 1H, J )
4.8, 6.1 Hz), 1.21 (s, 3H), 0.91 (dd, 1H, J ) 6.1, 9.8 Hz); 13C
NMR (CDCl3, 100 MHz) δ 138.2-127.5, 111.9, 110.6, 81.5,
74.1, 73, 71.7, 26.5, 26.5, 24.2, 18.3; FAB-MS m/z 277 (M +
H)+.
(1S,3R,4R,5S)-3-(Acetyloxy)-1[(acetyloxy)methyl]-2-
oxabicyclo[3.1.0]hex-4-yl Acetate (9r) and (1S,3S,4R,5S)-
3-(Acetyloxy)-1-[(acetyloxy)methyl]-2-oxabicyclo[3.1.0]-
hex-4-yl Acetate (9â). Acetic anhydride (1.2 mL, 12.7 mmol)
was added to a solution of compound 8 (356 mg, 1.22 mmol)
in acetic acid (6 mL) at 0 °C. Sulfuric acid (0.025 mL) was
then added dropwise. The reaction mixture was stirred at room
temperature overnight then diluted with a mixture of ice and
water. The aqueous phase was extracted with CH2Cl2 (3 × 30
mL). The combined extracts were successively washed with a
saturated NaHCO3 solution and water (3 × 30 mL) and dried
(Na2SO4) and the solvent was removed under reduced pres-
sure. The residue was purified by silica gel column chroma-
tography using petroleum ether/ether (3:2) as eluent to give
an anomeric mixture of compounds 9R/9â (269 mg, 81%, ratio
R/â, 9/91) as a colorless syrup: 1H NMR (CDCl3, 400 MHz) δ
6.35 (d, 1H, J ) 5.6 Hz), 5.84 (s, 1H), 5.43 (t, 1H, J ) 5.6 Hz),
5.25 (d, 1H, J ) 6.3 Hz), 4.38 (d, 1H, J ) 12.8 Hz), 4.34 (d,
1H, J ) 12.7 Hz), 4,19 (d, 1H, J ) 12.7 Hz), 4.15 (d, 1H, J )
12.8 Hz), 2.11 (m, 1H), 2.05-2.00 (m, 18H), 1.87 (m, 1H), 1.58
(dd, 1H, J ) 5.1, 6.8 Hz), 1.26 (t, 1H, J ) 5.6 Hz), 0.94
(dd, 1H, J ) 6.4, 9.6 Hz), 0.87 (m, 1H); 13C NMR (CDCl3, 100
MHz) δ 171.2-169.4, 105.5, 95.0, 79.8, 74.9, 73.3, 65.8, 65.4,
24.2, 21.4-20.9, 19.2, 16.2; FAB-MS (>0) m/z 273 (M + H)+;
FAB-MS (<0) m/z 271 (M - H)-. Anal. Calcd for C12H16O7: C,
52.94; H, 5.92. Found: C, 52.54; H, 6.26.
(1S,3S,4S,5S)-1-[(Benzyloxy)methyl]-3-methoxy-2-
oxabicyclo[3.1.0]hexan-4-ol (6). HCl (4 N) in dioxane (2.2
mL) was added to a solution of 5a (3.76 g, 13.6 mmol) in MeOH
(100 mL) at 0 °C. The mixture was allowed to reach room
temperature and stirring was continued overnight. The solu-
tion was neutralized with a saturated NaHCO3 solution and
then concentrated to dryness under reduced pressure. The
residue was purified by silica gel column chromatography
using petroleum ether/ether (1:1) as eluent to give compound
6 (3.05 g, 89%) as a colorless syrup: [R]20 +11.2 (c 1.07,
D
DMSO); 1H NMR (CDCl3, 400 MHz) δ 7.30-7.18 (m, 5H), 4.89
(s, 1H), 4.60 (d, 1H, J ) 12.1 Hz), 4.54 (d, 1H, J ) 12.1 Hz),
3.97 (s, 1H), 3.89 (d, 1H, J ) 11.6 Hz), 3.47 (d, 1H, J ) 11.6
Hz), 3.23 (s, 3H), 3.08 (br s, 1H), 1.40 (dd, 1H, J ) 5, 10 Hz),
1.12 (dd, 1H, J ) 5, 6.5 Hz), 0.62 (dd, 1H, J ) 6.5, 10 Hz);
13C NMR (CDCl3, 100 MHz) δ 138.3-128, 113.6, 77.9, 73.5,
71.8, 69.5, 55.8, 25.5, 15.4; FAB-MS (>0) m/z 251 (M + H)+;
FAB-MS (<0) m/z 249 (M - H)-. Anal. Calcd for C14H18O4: C,
67.18; H, 7.25. Found: C, 66.96; H, 7.41.
[(1S,3R,4R,5S)-4-(Acetyloxy)-3-(2,4-dioxo-3,4-dihydro-
1(2H)-pyrimidinyl)-2-oxabicyclo[3.1.0]hex-1-yl]methyl
Acetate (10). A mixture of uracil (350 mg, 3.12 mmol), HMDS
(15 mL), and a catalytic amount of ammonium sulfate was
refluxed for 14 h. The resultant clear solution was concentrated
to dryness under reduced pressure. TMSOTf (0.47 mL, 2.6
mmol) was added at 0 °C to a solution of compound 9 (380
mg, 1.40 mmol) and silylated base in dry acetonitrile (14 mL).
The reaction mixture was stirred for 30 min, poured into a
saturated NaHCO3 solution, and filtered through Celite. The
resulting mixture was coevaporated, extracted with CH2Cl2
(3 × 30 mL), washed with water, dried (Na2SO4), and concen-
trated. The residue was purified by silica gel column chroma-
tography using dichloromethane/methanol (97:3) as eluent to
give the compound 10 (360 mg, 80%) as a white foam: UV
(1S,3S,4R,5S)-1-[(Benzyloxy)methyl]-3-methoxy-2-
oxabicyclo[3.1.0]hexan-4-ol (7). To
a mixture of dry
CH2Cl2 (150 mL) and dry pyridine (6 mL) at 0 °C were added
CrO3 (3.72 g, 37.2 mmol) and acetic anhydride (3.6 mL, 38.1
mmol). The resulting mixture was stirred for 30 min. A
solution of 6 (3 g, 12 mmol) in dry CH2Cl2 (30 mL) was added
and the solution was stirred for 4 h at room temperature. The
mixture was poured into cold ether and filtered through silica
with ether/pyridine (99:1). The filtrate was evaporated and
coevaporated with dry toluene. The resulting residue was
dissolved in absolute ethanol (90 mL) and NaBH4 (1.37 g, 36.2
mmol) in absolute ethanol (30 mL) was added dropwise. Then
the reaction mixture was neutralized with 2 N HCl solution,
extracted with CH2Cl2 (3 × 30 mL), and washed with water.
The organic layer was dried (Na2SO4) and the solvent was
removed under reduced pressure. The residue was purified by
silica gel column chromatography using petroleum ether/ether
(3:2) as eluent to give compound 7 (2.25 g, 74%) as a colorless
syrup: [R]20D +4.5 (c 1.1, DMSO); 1H NMR (CDCl3, 400 MHz)
δ 7.30-7.20 (m, 5H), 4.87 (d, 1H, J ) 5.8 Hz), 4.65-4.52
(m, 2H,), 3.71 (d, 1H, J ) 11.6 Hz), 3.49 (d, 1H, J ) 11.6 Hz),
3.34 (s, 3H), 2.67 (d, 1H, J ) 9.3 Hz), 1.63 (m, 1H), 1.33 (t,
1H, J ) 5.6 Hz), 0.55 (m, 1H); 13C NMR (CDCl3, 100 MHz) δ
(EtOH 95%) λmax ) 260 nm (ꢀ ) 9800); [R]20 -101 (c 1.00,
D
DMSO); 1H NMR (DMSO-d6, 300 MHz) δ 11.38 (br s, 1H), 7.66
(d, 1H, J ) 8.0 Hz), 5.71 (d, 1H, J ) 8.0 Hz), 5.61 (m, 2H),
4.39 (d, 1H, J ) 12.7 Hz), 4.28 (d, 1H, J ) 12.7 Hz), 1.93 (m,
7H), 1.30 (t, 1H, J ) 5.7 Hz), 1.00 (1H, dd, J ) 6.7, 9.2 Hz);
13C NMR (DMSO-d6, 100 MHz) δ 170.2, 163.0, 150.0, 142.0,
102.1, 90.7, 78.5, 69.5, 65.1, 21.7, 20.6, 14.2; FAB-MS (>0) m/z
325 (M + H)+; FAB-MS (<0) m/z 323 (M - H)-. Anal. Calcd
for C14H16N2O7: C, 51.85; H, 4.97; N, 8.64. Found: C, 51.69;
H, 5.05, N, 8.35.
J. Org. Chem, Vol. 70, No. 17, 2005 6895

Gagneron et al.
[(1S,3R,4R,5S)-4-(Acetyloxy)-3-(5-methyl-2,4-dioxo-3,4-
dihydro-1(2H)-pyrimidinyl)-2-oxabicyclo[3.1.0]hex-1-yl]-
methyl Acetate (11). A mixture of thymine (100 mg, 0.79
mmol), HMDS (5 mL), and a catalytic amount of ammonium
sulfate was refluxed for 14 h. The resultant clear solution was
concentrated to dryness under reduced pressure. TMSOTf
(0.08 mL, 0.44 mmol) was added at 0 °C to a solution of 9 (110
mg, 0.40 mmol) and silylated base in dry acetonitrile (4 mL).
The reaction mixture was stirred for 30 min, poured into a
saturated NaHCO3 solution, and filtered through Celite. The
resulting mixture was coevaporated, extracted with CH2Cl2
(3 × 30 mL), washed with water, dried (Na2SO4), and concen-
trated. The residue was purified by silica gel column chroma-
tography using dichloromethane/methanol (97:3) as eluent to
give the compound 11 (90 mg, 67%) as a white foam: UV
idinedione (14). A solution of 11 (150 mg, 0.45 mmol) in
methanolic ammonia (10 mL, previously saturated at -10 °C
and tightly stoppered) was stirred at room temperature for
15 h and then concentrated to dryness. The residue was
purified by silica gel column chromatography using chloroform/
methanol (9:1) as eluent and then lyophylizated from water
to give the compound 14 (101 mg, 88%) as a white powder:
UV (EtOH 95%) λmax ) 264 nm (ꢀ ) 9700); [R]20 -113.8 (c
D
1.01, DMSO); 1H NMR (DMSO-d6, 400 MHz) δ 11.30 (br s, 1H),
7.56 (s, 1H,), 5.51 (d, 1H, J ) 5.0 Hz), 5.40 (1H, d, J ) 6.7
Hz), 4.92 (1H, t, J ) 4.8 Hz), 4.55 (m, 1H), 3.80 (dd, 1H, J )
6.2, 12.5 Hz), 3.48 (dd, 1H, J ) 5.1, 12.5 Hz), 1.79 (s, 3H),
1.71 (m, 1H), 1.16 (t, 1H, J ) 5.6 Hz), 0.72 (dd, 1H, J ) 6.4,
9.1 Hz); 13C NMR (DMSO-d6, 100 MHz) δ 163.7, 150.4, 136.9,
109.9, 89.6, 75.9, 71.1, 62.2, 22.8, 12.1; FAB-MS (>0) m/z 255
(M + H)+. Anal. Calcd for C11H14N2O5‚0.65H2O: C, 49.68; H,
5.80 N, 10.53. Found: C, 50.01; H, 5.77, N, 10.27.
(EtOH 95%) λmax ) 263 nm (ꢀ ) 8600); [R]20 -101.9 (c 1.02,
D
DMSO); 1H NMR (DMSO-d6, 200 MHz) δ 11.38 (br s, 1H), 7.53
(d, 1H, J ) 1.2 Hz), 5.66 (d, 1H, J ) 4.5 Hz), 5.58 (t, 1H, J )
5.8 Hz), 4.40 (d, 1H, J ) 12.6 Hz), 4.30 (d, 1H, J ) 12.6 Hz),
2.08 (7H, m), 1.80 (d, 3H, J ) 1.2 Hz), 1.33 (t, 1H, J ) 5.4
Hz), 1.00 (dd, 1H, J ) 6.7, 9.0 Hz); 13C NMR (DMSO-d6, 100
MHz) δ 170.2, 163.6, 150.0, 137.1, 110.0, 89.3, 78.4, 69.1, 65.1,
21.5, 20.6, 14.0, 12.0; FAB-MS (>0) m/z 339 (M + H)+; FAB-
MS (<0) m/z 337 (M - H)-. Anal. Calcd for C15H14N2O7: C,
53.25; H, 5.36 N, 8.28. Found: C, 53.09; H, 5.36, N, 8.09.
4-Amino-1-[(1S,3R,4R,5S)-4-hydroxy-1-(hydroxymethyl)-
2-oxabicyclo[3.1.0]hex-3-yl]-2(1H)-pyrimidinone (15). A
solution of 12 (150 mg, 0.35 mmol) in methanolic ammonia
(10 mL, previously saturated at -10 °C and tightly stoppered)
was stirred at room temperature for 15 h and then concen-
trated to dryness. The residue was purified by silica gel column
chromatography using chloroform/methanol (97:3) as eluent
to give the compound 15 (71 mg, 85%). Analysis was made on
the corresponding chlorohydrate salt prepared from ethanol
[(1S,3R,4R,5S)-4-(Acetyloxy)-3-(4-(benzoylamino)-2-oxo-
1(2H)-pyrimidinyl)-2-oxabicyclo[3.1.0] hex-1-yl]methyl
Acetate (12). A mixture of N4-benzoyl cytosine (300 mg, 1.39
mmol), HMDS (7 mL), and a catalytic amount of ammonium
sulfate was refluxed for 14 h. The resultant clear solution was
concentrated to dryness under reduced pressure. TMSOTf (0.2
mL, 1.1 mmol) was added at 0 °C to a solution of 9 (160 mg,
0.59 mmol) and silylated base in dry acetonitrile (5.9 mL). The
reaction mixture was stirred for 30 min, poured into a
saturated NaHCO3 solution, and filtered through Celite. The
resulting mixture was coevaporated, extracted with CH2Cl2
(3 × 30 mL), washed with water, dried (Na2SO4), and concen-
trated under reduced pressure. The resulting yellow powder
was washed with ethanol to give compound 12 (190 mg, 75%)
as a white solid: mp 190-192 °C; UV (EtOH 95%) λmax ) 260
nm (ꢀ ) 27000); [R]20D -70.5 (c 0.61, DMSO); 1H NMR (CDCl3,
400 MHz) δ 8.86 (br s, 1H), 7.84-7.41 (m, 7H), 5.70 (d, 1H, J
) 3.5 Hz), 5.54 (dd, 1H, J ) 3.5, 6.1 Hz), 4.49 (d, 1H, J ) 12.9
Hz), 4.27 (d, 1H, J ) 12.9 Hz), 2.12 (m, 1H), 2.07 (s, 3H), 2.05
(s, 3H), 1.32 (dd, 1H, J ) 5.4, 6.7 Hz), 0.94 (dd, 1H, J ) 6.7,
9.4 Hz);13C NMR (CDCl3, 100 MHz) δ 171.0, 163.0, 154.7,
145.4, 133.7-128.1, 97.5, 93.8, 80.5, 72.0, 65.8, 23.3, 21.3, 16.1;
FAB-MS (>0) m/z 428 (M + H)+; FAB-MS (<0) m/z 426 (M -
H)-. Anal. Calcd for C21H21N3O7: C, 59.01; H, 4.95; N, 9.83.
Found: C, 59.11; H, 4.99, N, 9.93.
95% (0.5 mL) and 2 N HCl (0.25 mL): UV (EtOH 95%) λmax
)
270 nm (ꢀ ) 9500); [R]20 -80.3 (c 0.56, DMSO); 1H NMR
D
(DMSO-d6, 400 MHz) δ 9.80 (br s, 1H), 8.70 (br s, 1H), 8.12
(d, 1H, J ) 7.8 Hz), 6.18 (d, 1H, J ) 7.8 Hz), 5.52 (d, 1H, J )
4.2 Hz), 4.59 (m, 1H), 3.85 (d, 1H, J ) 12.6 Hz), 3.47 (d, 1H,
J ) 12.6 Hz), 1.79 (m, 1H), 1.19 (t, 1H, J ) 5.2 Hz), 0.77 (dd,
1H, J ) 6.3, 9.2 Hz); 13C NMR (DMSO-d6, 100 MHz) δ 160.3,
147.9, 146.0, 95.4, 93.0, 77.6, 73.8, 62.9, 24.1, 13.8; FAB-MS
(>0) m/z 240 (M - Cl)+. Anal. Calcd for C10H14ClN3O4: C,
43.28; H, 5.10; Cl, 13.41 N, 15.41. Found: C, 43.01; H, 5.05,
Cl, 13.55, N, 14.99.
[(1S,3R,4R,5S)-4-(Acetyloxy)-3-(6-amino-9H-purin-9-
yl)-2-oxabicyclo[3.1.0]hex-1-yl]methyl Acetate (16). Tin-
(IV) chloride (0.1 mL, 0.85 mmol) was added cautiously to a
stirred suspension of adenine (60 mg, 0.44 mmol) and com-
pound 9 (100 mg, 0.37 mmol) in dry acetonitrile (3 mL) at room
temperature. After 1 h, pyridine (1 mL) was added to the
resultant solution. The white precipitate was filtered and
washed with chloroform. The combined filtrates were washed
with saturated NaHCO3 solution (100 mL) and water (10 mL),
dried over sodium sulfate, and concentrated to dryness. The
residue was purified by silica gel column chromatography
using chloroform/methanol (96:4) as eluent to give the com-
pound 16 (78 mg, 61%), which was crystallized from acetoni-
trile: mp 109-111 °C; UV (EtOH 95%) λmax ) 260 nm (ꢀ )
13800); [R]20D -173.7 (c 0.98, DMSO); 1H NMR (DMSO-d6, 300
MHz) δ 8.31 (s, 1H), 8.17 (s, 1H), 7.34 (br s, 1H), 6.15 (1H, dd,
J ) 3.9, 6.0 Hz), 5.92 (1H, d, J ) 3.9 Hz), 4.32 (m, 2H), 2.33
(m, 1H), 2.05 (s, 3H), 1.94 (s, 3H), 1.40 (t, 1H, J ) 5.4 Hz),
1.09 (dd, 1H, J ) 6.5, 9.3 Hz); 13C NMR (DMSO-d6, 100 MHz)
δ 168.9, 154.9, 151.6, 147.8, 138.6, 117.7, 87.8, 77.0, 68.7, 63.7,
21.3, 19.4, 19.3, 13.7; FAB-MS (>0) m/z 348 (M + H)+;
FAB-MS (<0) m/z 346 (M - H)-. Anal. Calcd for C15H17N5O5:
C, 51.87; H, 4.93 N, 20.16. Found: C, 52.00; H, 4.99, N, 20.30.
1-[(1S,3R,4R,5S)-4-Hydroxy-1-(hydroxymethyl)-2-
oxabicyclo[3.1.0]hex-3-yl]-2,4(1H,3H)-pyrimidinedione
(13). A solution of 10 (150 mg, 0.46 mmol) in methanolic
ammonia (10 mL, previously saturated at -10 °C and tightly
stoppered) was stirred at room temperature for 15 h, then
concentrated to dryness. The residue was purified by silica gel
column chromatography using dichloromethane/methanol (9:
1) as eluent to give the compound 13 (71 mg, 64%) as a white
foam that was crystallized from absolute ethanol: mp 169-
171 °C; UV (EtOH 95%) λmax ) 260 nm (ꢀ ) 8600); [R]20
D
-147.2 (c 0.92, DMSO); 1H NMR (DMSO-d6, 300 MHz) δ 11.4
(br s, 1H), 7.79 (d, 1H, J ) 8.0 Hz), 5.79 (d, 1H, J ) 8.0 Hz),
5.60 (d, 1H, J ) 4.8 Hz), 5.51 (d, 1H, J ) 5.5 Hz), 4.98 (t, 1H,
J ) 4.8 Hz), 4.65 (m, 1H), 3.91 (dd, 1H, J ) 5.9, 12.6 Hz), 3.57
(1H, dd, J ) 4.5, 12.6 Hz), 1.81 (1H, m), 1.27 (1H, t, J ) 5.3
Hz), 0.74 (1H, dd, J ) 6.3, 9.2 Hz); 13C NMR (DMSO-d6, 100
MHz) δ 165.2, 152.5, 143.6, 104.5, 92.5, 78.3, 73.6, 64.4, 25.0,
14.4; FAB-MS (>0) m/z 241 (M + H)+; FAB-MS (<0) m/z 239
(M - H)-. Anal. Calcd for C10H12N2O5: C, 50.00; H, 5.04; N,
11.66. Found: C, 49.89; H, 5.24, N, 11.42.
(1S,3R,4R,5S)-3-(6-Amino-9H-purin-9-yl)-1-(hydroxy-
methyl)-2-oxabicyclo[3.1.0]hexan-4-ol (17). To a solution
of compound 16 (935 mg, 2.69 mmol) in methanol (51 mL) was
added sodium methoxide (480 mg, 8.88 mmol). The reaction
mixture was stirred at room temperature overnight, neutral-
ized with a 2 N HCl solution, and then concentrated to dryness.
The residue was purified by silica gel column chromatography
using dichloromethane/methanol (88:12) as eluent to give the
compound 17 (432 mg, 61%), which was crystallized from
absolute ethanol: mp 213-215 °C; UV (EtOH 95%) λmax ) 260
1-[(1S,3R,4R,5S)-4-Hydroxy-1-(hydroxymethyl)-2-
oxabicyclo[3.1.0]hex-3-yl]-5-methyl-2,4(1H,3H)-pyrim-
nm (ꢀ ) 15600); [R]20 -140.4 (c 0.99, DMSO); 1H NMR
D
(DMSO-d6, 300 MHz) δ 8.33 (s, 1H), 8.14 (s, 1H), 7.28 (s, 2H),
6896 J. Org. Chem., Vol. 70, No. 17, 2005

Synthesis of Nucleoside Analogues
5.58 (d, 1H, J ) 4.8 Hz), 5.52 (d, 1H, J ) 5.0 Hz), 5.06 (m,
1H), 4.89 (1H, t, J ) 5.5 Hz), 3.75 (dd, 1H, J ) 5.5, 12.4 Hz),
3.58 (dd, 1H, J ) 5.5, 12.4 Hz), 1.87 (m, 1H), 1.28 (t, 1H, J )
5.3 Hz), 0.82 (dd, 1H, J ) 6.4, 9.9 Hz); 13C NMR (DMSO-d6,
100 MHz) δ 155.9, 152.6, 149.1, 139.7, 118.8, 89.9, 75.8, 71.5,
62.3, 23.0, 12.2; FAB-MS (>0) m/z 264 (M + H)+; FAB-MS (<0)
m/z 262 (M - H)-. Anal. Calcd for C11H13N5O3‚0.1H2O: C,
49.85; H, 5.02 N, 26.42. Found: C, 49.53; H, 5.00, N, 26.36.
2-Amino-9-[(1S,3R,4R,5S)-4-hydroxy-1-(hydroxymethyl)-
2-oxabicyclo[3.1.0]hex-3-yl]-1,9-dihydro-6H-purin-6-
one (18). BSA (0.56 mL, 2.3 mmol) was added to a suspension
of 2-N-acetyl-6-O-(diphenylcarbamoyl)guanine (340 mg, 0.88
mmol) in dry 1,2-dichloroethane (7.6 mL). After 1 h at reflux,
the clear solution was evaporated and compound 9 (200 mg,
0.73 mmol) and TMSOTf (0.23 mL, 1.27 mmol) were succes-
sively added to the residue in dry toluene (5 mL). The reaction
mixture was stirred at reflux for 2 h and then was allowed to
reach room temperature. Ethyl acetate (20 mL) was added and
the reaction mixture was quenched with saturated NaHCO3
solution, washed with water, dried (Na2SO4), and concentrated
to dryness. The crude product was directly treated with
methanolic ammonia (15 mL) for 48 h at room temperature.
After evaporation to dryness under reduced pressure, the
residue was subjected to reverse phase purification (C18) using
a stepwise gradient of acetonitrile (0-10%) in water. Ap-
propriate fractions were combined, evaporated, and lyophyl-
izated from water to give the compound 18 (40 mg, 20%) as a
white powder: UV (EtOH 95%) λmax ) 255 nm (ꢀ ) 11700);
1H NMR (DMSO-d6, 300 MHz) δ 10.67 (br s, 1H), 7.91 (s, 1H),
6.49 (br s, 2H), 5.53 (d, 1H, J ) 5.1 Hz), 5.37 (d, 1H, J ) 4.9
Hz), 4.90-4.80 (m, 2H), 3.70 (dd, 1H, J ) 5.1, 12.3 Hz), 3.56
(dd, 1H, J ) 5.5, 12.3 Hz), 1.82 (m, 1H), 1.20 (t, 1H, J ) 5.3
Hz), 0.77 (dd, 1H, J ) 6.4, 9.2 Hz); 13C NMR (DMSO-d6, 100
MHz) δ 156.9, 153.9, 151.2, 135.7, 116.4, 89.0, 76.0, 71.4, 62.3,
23.1, 12.2; FAB-MS (>0) m/z 280 (M + H)+; FAB-MS (<0) m/z
278 (M - H)-; HRMS (FAB >0, m/z) calcd for 280.1046, found
280.1045.
Acknowledgment. J.G. is particularly grateful to
the Ministe`re de l’Education Nationale, de la Recherche
et de la Technologie (France) for a doctoral fellowship.
Sidaction (France) is gratefully acknowledge for finan-
cial support (Grant 13022-02-00/AO14-2).
Supporting Information Available: Experimental de-
tails and 13C NMR spectra for compounds 4, 5a, 5b, 6-9,
13-15, 17, and 18. This material is available free of charge
via the Internet at http://pubs.acs.org.
JO051047B
J. Org. Chem, Vol. 70, No. 17, 2005 6897