Synthesis of the first example of a nucleoside analogue bearing a 5′-deoxy-β-d-allo-septanose as a seven-membered ring sugar moiety

Article abstract of DOI:10.1016/j.carres.2008.12.019

The first example of a nucleoside analogue bearing a 5′-deoxy-β-d-allo-septanose as a seven-membered ring sugar moiety, namely 9-(5-deoxy-β-d-allo-septanosyl)-adenine, is reported. This compound was synthesized in 14 steps from the commercially available

Full text of DOI:10.1016/j.carres.2008.12.019

Carbohydrate Research 344 (2009) 448–453
Contents lists available at ScienceDirect
Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Synthesis of the first example of a nucleoside analogue bearing a
50-deoxy-b-D-allo-septanose as a seven-membered ring sugar moiety q
Gwenaëlle Sizun a, David Dukhan a, Jean-François Griffon a, Ludovic Griffe a, Jean-Christophe Meillon a,
Frédéric Leroy a, Richard Storer a, , Jean-Pierre Sommadossi b, Gilles Gosselin a,
*
a Idenix Pharmaceuticals, Medicinal Chemistry Laboratory, Cap Gamma, 1682 Rue de la Valsière, B.P. 50001, F-34189 Montpellier, France
b Idenix Pharmaceuticals, One Kendall Square, Building 1400, Cambridge, MA 02139, USA
a r t i c l e i n f o
a b s t r a c t
The first example of a nucleoside analogue bearing a 50-deoxy-b-
D-allo-septanose as a seven-membered
Article history:
Received 7 October 2008
Received in revised form 19 December 2008
Accepted 23 December 2008
Available online 3 January 2009
ring sugar moiety, namely 9-(5-deoxy-b-
thesized in 14 steps from the commercially available
D
-allo-septanosyl)-adenine, is reported. This compound was syn-
-glycero- -gulo-1,4-lactone. When evaluated in cell
D
D
culture experiments against a broad range of viruses, it did not exhibit any significant antiviral effect or
cytotoxicity.
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Septanose carbohydrates
Oxepane nucleosides
Synthesis
Antiviral evaluation
1. Introduction
bered sugar ring or acyclic derivatives11 have been approved as
antiviral drugs. Only few reports have appeared on derivatives
To date, septanoses (seven-membered ring sugars)2–7 have
not been extensively studied compared to the pyranose and
furanose systems. However,
interest in the biological studies of septanose derivatives have
been published these last years. The first observations were
published by Kuszmann and co-workers,8,9 who studied the
antithrombotic activity of a series of 4-substituted phenyl 1,6-
dithio-hexoseptanosides, all the compounds tested possessing
good activity. More recently, Peczuh and co-workers10 investi-
gated the ability of the jack bean lectin concanavalin A (ConA)
with four- and six-membered sugar rings.12
On the other hand, and to the best of our knowledge, only
six examples of nucleosides with a seven-membered carbohy-
drate moiety (called oxepane nucleosides according to Sabatino
and Damha)13 have been described in the literature (Chart 1).
The first one is a nucleoside containing a dihydro-oxepine ring
as the sugar moiety, which was unexpectedly obtained follow-
ing an unusual ring-expansion reaction in an attempt to synthe-
a few papers showing growing
size 40-
40- -formyl ribonucleoside derivatives.14
The second example comprises septanosyl-1,2,3-triazoles,
a-ethenyl ribonucleoside analogues via Wittig reaction of
a
to bind septanose monosaccharides. A series of methyl
a- and
b-septanosides–ConA complexes were measured, showing that
the lectin ConA selectively binds b-septanosides. This was the
first direct evidence of unnatural septanose sugars being bound
to a natural protein. Nucleoside analogues bearing a five-mem-
which were synthesized as potential glycosidase inhibitors.15 The
last four oxepane nucleoside examples were synthesized with
the goal either to be used as monomeric units of modified oligonu-
cleotides,13,16 or to impart some degree of conformational restric-
tion to the natural nucleosides.16,17
As part of an ongoing project aiming at designing new nucleo-
side analogues with potential antiviral activity, we embarked upon
the synthesis and study of novel series of oxepane nucleosides.18
q
Here, we report on the first example of a 50-deoxy-b-
D
-allo-septa-
nose nucleoside analogue.1 The title compound, namely 9-(5-
deoxy-b- -allo-septanosyl)-adenine (14), was synthesized in 14
steps from the commercially available -glycero- -gulo-1,4-lactone.
Presented in part at the Joint Symposium of ‘the 18th International Roundtable
Conference on Nucleosides, Nucleotides and Nucleic Acids (IRTXVIII) and the 35th
International Symposium on Nucleic Acids Chemistry (SNACXXXV)’, Kyoto, Japan,
September 8–12, 2008. For the Proceedings, see Ref. 1.
* Corresponding author. Tel.: +33 4 99 64 27 31; fax: +33 4 67 63 73 26.
E-mail address: gosselin.gilles@idenix.com (G. Gosselin).
D
D
D
It was evaluated as a potential inhibitor of the replication of several
classes of viruses.
Present address: SUMMIT plc, 91 Milton Park, Abingdon, Oxfordshire OX14 4RY,
UK.
0008-6215/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2008.12.019

G. Sizun et al. / Carbohydrate Research 344 (2009) 448–453
449
minal acetal position is the easy cyclisation that occurs readily
afterwards. The primary hydroxyl function of 8 was selectively
protected by treatment with imidazole and tert-butyldimethylsilyl
chloride (TBDMSCl) to give the suitably protected septanose deriv-
ative 9.
The synthesis of the nucleoside analogue 14 from the septanose
derivative 9 is summarized in Scheme 2. To achieve the condensa-
tion of a carbohydrate with a base, a good leaving group is needed
at the anomeric position. In this context, we prepared the
trichloroacetimidate derivative of 9. Indeed, trichloroacetimidate
activation is currently one of the most frequently used alternative
strategies for glycoside bond formation.21–23 Treatment of 9 with
trichloroacetonitrile in the presence of catalytic amounts of 1,8-
diazabicyclo[5.4.0]undec-7-ene (DBU)24 afforded the correspond-
ing trichloroacetimidate derivative 10.
Trichloroacetimidate sugar 10 was then allowed to react with
the N-silylated derivative of 6-chloropurine in the presence of tri-
methylsilyl trifluoromethanesulfonate (TMSOTf) in toluene at re-
flux to give nucleoside 11 in 15% isolated yield after purification
by silica gel chromatography. The structure of compound 11 was
confirmed by nuclear Overhauser effect (NOE), which showed that
only the b anomer was obtained. Upon irradiation of the doublet at
d 6.58 (H-10), a reversible NOE was observed with the multiplet at
4.40 (H-60) (Fig. 1).
Performing the aminolysis at 100 °C provided 12 from 11.
Nucleoside 12 was then treated with BCl3 to remove the chloro-
benzyl-protecting group. Under the used conditions, cleavage of
the silyl-protecting group and partial deacetalization also oc-
curred. Thus, reaction of 12 with BCl3 concomitantly afforded the
partially protected nucleoside derivative 13 and the desired nucle-
oside 14.
NH2
N
N
N
R
HO
N
O
HO
N
O
O
OH
HO
OH
OH
Ref. 14.
HO
Ref. 15.
O
CH3
HO
O
OH
NH
HO
HO
N
N
O
N
N
O
N
NH2
Ref. 17.
HO
Ref. 13.
HO
O
O
NH
NH
O
N
N
O
O
O
HO
HO
Ref. 16.
Ref. 16.
2.2. Antiviral evaluations
Chart 1. Previously described nucleoside analogues containing a seven-membered
ring sugar.
9-(5-Deoxy-b-D-allo-septanosyl)-adenine 14 was evaluated in
cell-based assays (following methods described in Ref. 25) against
viruses representative of three genera of the ssRNA+ Flaviviridae
family: Pestivirus (Bovine Virus Diarrhoea Virus), Flavivirus (Yellow
Fever, Dengue and West Nile Viruses) and Hepacivirus (Hepatitis C
Virus, HCV), and against one genus of the ssRNA+ Picornaviridae
family, Enterovirus (Coxsackie Virus B2 and Poliovirus Sabin-1). It
was also tested against a virus of the ssRNA family, Retroviridae
(Human Immunodeficiency Virus, HIV-1), against two representa-
tives of a ssRNAꢀ family, Paramyxoviridae: Pneumovirus (Respira-
tory Syncytial Virus) and Morbillivirus (Measles Virus) and
against a virus representative of a dsDNA virus family, Poxviridae
(Vaccinia Virus). Unfortunately, against all these viruses, the new
nucleoside analogue 14 showed neither antiviral activity nor cyto-
2. Results and discussion
2.1. Synthesis
Our synthetic strategy to obtain the hitherto unknown nucle-
oside analogue 14 was based on the synthesis of a suitably pro-
tected septanose derivative 9, which was activated as its
trichloroacetimidate and reacted with 6-chloropurine.
Septanose derivative 9 (Scheme 1) was obtained from the com-
mercial D-glycero-D
-gulo-1,4-lactone through the known19 bis(eth-
ylidene)-protected talo derivative 1. Deoxygenation at C-5 was
achieved using the Barton–McCombie reaction;20 the free hydroxyl
group of 1 was activated for radical reduction with 1,10-thio-
carbonyldiimidazole. Reduction was performed using azobisisobu-
tyronitrile (AIBN) and tris(trimethylsilyl)silane as the reducing
agent, providing the deoxylactone 2.
toxicity at the highest concentration tested (generally 75 lM).
3. Summary and conclusion
The hitherto unknown 9-(5-deoxy-b-
14 was synthesized as the first example of a nucleoside analogue
bearing -allo-septanose sugar
seven-membered 50-deoxy-b-
D-allo-septanosyl)-adenine
Complete reduction of 2 with sodium borohydride in methanol
afforded the polyol 5-deoxy-2,3:6,7-di-O-diethylidene-D-allo-hep-
a
D
tan-1-itol (3), which was treated as a crude with dimethoxytrityl
chloride (DMTrCl) to provide the protected compound 4. In this
case, only the primary alcohol group reacted due to the steric hin-
drance of the hydroxyl group at C4. Compound 5 was obtained
after successively treating 4 with NaH and with 4-chlorobenzyl
chloride. The primary alcohol of 5 was then selectively deprotected
using formic acid, and the free hydroxyl group was oxidized using
the convenient Dess–Martin periodinane reagent to afford the hep-
tose 7. Deprotection was achieved using formic acid in ether to
yield the cyclic sugar 8. The driving force of this reaction at the ter-
moiety. Unfortunately, when evaluated in cell culture experiments
against a broad range of viruses, this compound exhibited no sig-
nificant antiviral effect or cytotoxicity. Several factors could be
responsible for the inactivity of 9-(5-deoxy-b-D-allo-septanosyl)-
adenine 14, such as its inability to enter cells or to serve as a
substrate for intracellular enzymes catalyzing phosphorylation,
or perhaps a lack of inhibition of the viral polymerases by its
triphosphate.12,26 Further research would be needed to support
these hypotheses, and other results on new kinds of oxepane
nucleoside analogues will be reported in due course.

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G. Sizun et al. / Carbohydrate Research 344 (2009) 448–453
O
O
CH2OH
O
O
OH
H
CH2ODMTr
O
O
OH
H
O
O
O
O
a)
b)
c)
HO
O
O
D-glycero-D-gulo-1,4-lactone
H
H
O
O
O
O
O
O
O
O
4
1 (Ref. 19)
3
2
d)
TBDMSO
HO
CHO
O
O
CH2OH
O
O
CH2ODMTr
O
O
OBnCl
H
O
O
h)
O
g)
O
e)
OH
O
f)
OH
O
OBnCl
OBnCl
H
H
O
O
H
H
O
O
H
ClBnO
ClBnO
O
O
9
8
6
5
7
Scheme 1. Reagents and conditions: (a) (i) 1,10-thiocarbonyldiimidazole, 1,2-dichloroethane, reflux, (ii) (Me3Si)3SiH, AIBN, toluene, reflux; (b) NaBH4, MeOH, 0 °C to rt; (c)
DMTrCl, pyridine, rt; (d) (i) NaH, DMF, 0 °C, (ii) ClBnCl, 0 °C to rt; (e) HCOOH, Et2O, rt; (f) Dess–Martin periodinane, CH2Cl2, rt; (g) HCOOH, Et2O, rt; (h) TBDMSCl, imidazole,
pyridine, rt.
Cl
NH2
N
N
N
NH
CCl3
N
TBDMSO
TBDMSO
TBDMSO
TBDMSO
N
N
O
OH
O
O
O
O
O
N
N
a)
b)
c)
O
O
O
ClBnO
O
ClBnO
ClBnO
ClBnO
O
O
O
9
10
11
12
d)
NH2
N
NH2
N
N
N
HO
HO
N
N
O
O
N
N
+
O
OH
HO
HO
O
OH
13
14
Scheme 2. Reagents and conditions: (a) DBU, trichloroacetonitrile, CH2Cl2 rt; (b) (i) 6-chloropurine, BSA, 1,2-dichloroethane, reflux, (ii) TMSOTf, toluene, 80 °C; (c) MeOH/
NH3, 100 °C; (d) BCl3, CH2Cl2, ꢀ78 °C to rt.
with heating. Column chromatography was carried out on Silica
Gel 60 40–63 m (Merck, Art. 11567) or LiChoprep RP-18 (40–63 m,
4. Experimental
l
l
Merck 1.13900.0250). 1H (400 MHz) and 13C (100 MHz) spectra
were recorded on a Bruker DRX 400 or 400 Advance II spectrome-
ter using Me2SO-d6 or CDCl3 as solvent. 1H and 13C NMR chemical
shifts (d) are quoted in parts per million (ppm) referenced to the
residual solvent peak [Me2SO-d6] set at dH 2.49 ppm or [CDCl3]
set at dH 7.26 ppm. The accepted abbreviations are as follows: br,
broad; s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet.
Low-resolution LC mass spectra (LR LCMS) were recorded on Q-
TOF Micromass, electrospray ionisation (ESI) mass spectrometer,
equipped with a Hypersil BDS C18 column (50 ꢁ 2.1 mm), eluting
with a gradient of 0–80% MeCN in water at a flow rate of
4.1. General methods
All reactions were performed with reagent-grade materials un-
der an atmosphere of nitrogen. All chemicals and solvents were of
reagent grade unless otherwise specified. D-Glycero-D-gulo-1,4-lac-
tone was from Aldrich. Evaporation of the solvent was carried out
in a rotary evaporator under reduced pressure. Thin layer chroma-
tography (TLC) was performed on precoated aluminium sheets of
Silica Gel 60 F254 (Merck, Art. 5554), visualization of products
being accomplished by UV absorbance at 254 nm and by charring
with a soln of (NH4)2SO4 (150 g) in 30:3:45 EtOH–H2SO4–water

G. Sizun et al. / Carbohydrate Research 344 (2009) 448–453
451
with water. The organic layer was dried over Na2SO4, and the sol-
vent was removed under diminished pressure. The crude residue
was subjected to silica gel chromatography, eluting with 30%
diethyl ether in petroleum ether + 1% triethylamine, to give 4 as a
yellow oil (0.53 g, 69%). Rf 0.58 (3:2 Et2O–petroleum ether). 1H
NMR (400 MHz, CDCl3): d 7.47–6.84 (m, 13H, DMTr), 4.50 (m, 1H,
H-2), 4.28 (m, 1H, H-6), 4.06–3.99 (m, 2H, H-3 and H-7a), 3.82
(6H under H2O signal, 2OCH3), 3.50–3.43 (m, 2H, H-4 and H-7b),
Cl
N
N
TBDMSO
N
O
N
H
H
O
O
2
ClBnO
3.38 (dd, 1H, H-1a, J1a–1b 9.8 Hz, J1a–2 4.0 Hz), 3.19 (dd, 1H, H-1b,
2J1b–1a 9.8 Hz, J1b–2 8.3 Hz), 2.81 (s, 1H, OH), 1.84–1.89 (m, 2H,
H-5a and H-5b), 1.67–1.60 (m, 8H, 4(CH2CH3)), 0.93–0.86 (m,
12H, 4(CH2CH3)). ESIMS (m/z): 657 [M+Na]+; 633 [MꢀH]ꢀ, 669
[M+Cl]ꢀ.
11
nOe effect
4.5. 4-O-(4-Chlorobenzyl)-5-deoxy-2,3:6,7-di-O-diethylidene-1-
O-dimethoxytriphenylmethyl-D-allo-heptan-1-itol (5)
Figure 1. 1D NOE correlations for compound 11.
Compound 4 (0.54 g, 0.85 mmol) was dissolved in anhyd
dimethylformamide (4.7 mL) and cooled to 0 °C. Sodium hydride
(54.4 mg, 1.36 mmol) was then added in separate portions to the
stirred mixture. Once the addition was completed, the resulting
mixture was stirred at 0 °C for 30 min. The reaction mixture was
then treated with 4-chlorobenzyl chloride (219 mg, 1.36 mmol)
at 0 °C. The mixture was allowed to warm to room temperature,
stirred for 2 h, and then diluted with EtOAc. The resulting soln
was washed thrice with water. The organic layer was dried over
Na2SO4 and evaporated to dryness to give 5 as a yellow oil
(0.75 g, quantitative yield). Rf 0.62 (3:2 Et2O–petroleum ether).
ESIMS (m/z): 793 [M+Cl]ꢀ, 1552 [2M+Cl]ꢀ.
0.2 mL minꢀ1. Mass spectra were recorded on a Q-TOF Micromass
mass spectrometer (ESIMS) or on a Jeol JMS DX 300 mass spec-
trometer (HRFABMS).
4.2. 5-Deoxy-2,3:6,7-di-O-diethylidene-D-allo-heptono-1,4-
lactone (2)
2,3:6,7-Di-O-diethylidene-D-glycero-L
-talo-heptono-1,4-lactone19
(1) (9.36 g, 27.18 mmol) was dissolved in 1,2-dichloroethane
(190 mL) and treated with 1,10-thiocarbonyldiimidazole (8.72 g,
48.92 mmol). The mixture was stirred at reflux overnight and con-
centrated under diminished pressure. The residue was dissolved in
anhyd toluene (190 mL) and treated with tris(trimethylsilyl)silane
(10.1 mL, 32.62 mmol) and AIBN (1.56 g, 9.51 mmol). The mixture
was stirred at reflux for 1 h, and then evaporated to dryness. The
residue was dissolved in EtOAc, and the soln was successively
washed with saturated aq NaHCO3 and saturated brine. The organ-
ic layer was dried over Na2SO4, and the solvent was removed under
diminished pressure. The crude residue was subjected to silica gel
chromatography, eluting with a gradient 2–30% diethyl ether in
petroleum ether, to give 2 as a yellow oil (9.36 g, 94%). Rf 0.40
(3:2 Et2O–petroleum ether). 1H NMR (400 MHz, Me2SO-d6: d 4.89
(d, 1H, H-3, J3–2 5.8 Hz), 4.65 (d, 1H, H-2, J2–3 5.8 Hz), 4.03–3.90
(m, 2H, H-6 and H-7a), 3.41 (t, 1H, H-7b, J7b–7a 7.5 Hz), 1.90–1.75
(m, 2H, H-5), 1.50–1.38 (m, 8H, 4 (CH2CH3)), 0.73–0.63 (m, 12 H,
4 (CH2CH3)). ESIMS (m/z): 329 [M+H]+, 657 [2M+H]+.
4.6. 4-O-(4-Chlorobenzyl)-5-deoxy-2,3:6,7-di-O-diethylidene-
D-
allo-heptan-1-itol (6)
To a soln of the crude protected alcohol 5 (0.85 mmol) in diethyl
ether (2.3 mL) was added formic acid (2.3 mL). The reaction mix-
ture was stirred at room temperature for 30 min and then diluted
with EtOAc. The resulting soln was washed with saturated aq NaH-
CO3. The organic layer was dried over Na2SO4 and the solvent was
removed under diminished pressure. The crude residue was
subjected to silica gel chromatography, eluting with a gradient
30–40% diethyl ether in petroleum ether, to give 6 as a pale yellow
oil (120 mg, 31%). Rf 0.43 (3:2 Et2O–petroleum ether). 1H NMR
(400 MHz, CDCl3): d 7.26–7.17 (m, 4H, C6H4Cl), 4.58 (d, 1H,
CH2C6H4Cl, J 11.1 Hz), 4.36 (d, 1H, CH2C6H4Cl, J 11.1 Hz), 4.37–
4.19 (m, 2H, H-2 and H-6), 4.12 (m, 1H, H-3), 4.01 (dd, 1H, H-7a,
J7a–6 5.9 Hz, J7a–7b 7.9 Hz), 3.79 (m, 1H, H-4), 3.63 (m, 2H, H-1),
3.40 (t, 1H, H-7b, J7b–7a 8.1 Hz), 2.01 (m, 1H, H-5a), 1.90 (m, 1H,
H-5b), 1.61–1.52 (m, 8 H, 4 (CH2CH3)), 0.87–0.79 (m, 12H, 4
(CH2CH3)). ESIMS (m/z): 457 [M+H]+; 913 [2M + H]+; 455 [MꢀH]ꢀ.
4.3. 5-Deoxy-2,3:6,7-di-O-diethylidene-D-allo-heptan-1-itol (3)
The lactone 2 (7.86 g, 23.93 mmol) was dissolved in anhyd
MeOH (168 mL) and cooled to 0 °C. Sodium borohydride (2.72 g,
71.80 mmol) was then added portion wise to the stirring mixture.
Once the addition was completed, the resulting mixture was stir-
red at room temperature for 4 h, quenched with an aq soln of
10% AcOH and evaporated to dryness. The residue was dissolved
in EtOAc, and the soln washed with saturated brine. The organic
layer was dried over Na2SO4, and the solvent was removed under
diminished pressure to give the title compound 3 as a pale yellow
oil (6.45 g, 80%). Rf 0.23 (3:2 Et2O–petroleum ether). ESIMS (m/z):
333 [M+H]+, 665 [2M+H]+.
4.7. 4-O-(4-Chlorobenzyl)-5-deoxy-2,3:6,7-di-O-diethylidene-
D-
allo-heptose (7)
The alcohol 6 (2.46 g, 5.38 mmol) was dissolved in anhyd
CH2Cl2 (68 mL) and treated with the Dess–Martin reagent (2.51 g,
5.92 mmol). The mixture was stirred at room temperature for 1 h
15, and diethyl ether was added. The precipitate was filtered over
successive layers of silica, MgSO4 and sand, and washed with
diethyl ether. The filtrate was concentrated under diminished pres-
sure. The crude residue was subjected to silica gel chromatogra-
phy, eluting with 30% diethyl ether in petroleum ether, to give 7
as a colourless oil (1.80 g, 73%). Rf 0.60 (3:2 Et2O–petroleum ether).
1H NMR (400 MHz, CDCl3): d 9.52 (t, 1H, CHO, JCHO–H2 1.4 Hz), 7.27–
7.16 (m, 4H, C6H4Cl), 4.53–4.45 (m, 2H, CH2C6H4Cl et H-2), 4.36–
4.26 (m, 2H, CH2C6H4Cl and H-6), 4.16 (m, 1H, H-30), 3.95 (dd,
1H, H-7a, J7a–7b 7.9 Hz, J7a–6 6.0 Hz), 3.72 (m, 1H, H-4), 3.39
4.4. 5-Deoxy-2,3:6,7-di-O-diethylidene-1-O-(4,40-
dimethoxytriphenylmethyl)-D-allo-heptan-1-itol (4)
Compound 3 (400 mg, 1.20 mmol) was dissolved in anhyd pyr-
idine (6 mL) and treated with 4,40-dimethoxytriphenylmethyl chlo-
ride (427.8 mg, 1.26 mmol). The resulting soln was stirred at room
temperature for two days, diluted with EtOAc and washed thrice

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G. Sizun et al. / Carbohydrate Research 344 (2009) 448–453
(t, 1H, H-7b, J7b–7a 7.9 Hz), 1.94 (m, 1H, H-5a), 1.75 (m, 1H, H-5b),
1.49–1.61(m, 8H, 4(CH2CH3)), 0.86–0.81 (m, 12H, 4(CH2CH3)).
ESIMS (m/z): 455 [M+H]+; 489 [M+Cl]ꢀ.
roacetimidate 10 (1.2 g, 1.86 mmol) in toluene (8.2 mL) was added.
The reaction mixture was treated with TMSOTf (431
2.23 mmol) and stirred at reflux for 5 h. More TMSOTf (200
l
L,
lL)
was added, and stirring was resumed at reflux for 2 h. The soln
was partitioned between EtOAc and satd aq NaHCO3. The organic
phase was washed with saturated brine, dried over Na2SO4 and
evaporated to dryness. The crude residue was subjected to silica
gel chromatography, eluting with a gradient 10–100% diethyl ether
in petroleum ether, to give 11 as a pale yellow oil (0.18 g, 15%). Rf
0.39 (3:2 Et2O–petroleum ether). 1H NMR (400 MHz, Me2SO-d6): d
8.82 (s, 1H, H-8), 8.32 (s, 1H, H-2), 7.38–7.45 (m, 4H, C6H4Cl), 6.58
4.8. 4-O-(4-Chlorobenzyl)-5-deoxy-2,3-O-diethylidene-D-allo-
septanose (8)
To a soln of the heptose 7 (1.77 g, 3.89 mmol) in diethyl ether
(17.5 mL) was added formic acid (17.5 mL). The reaction mixture
was stirred at room temperature for 1 h 15. The solution was par-
titioned between EtOAc and saturated aq NaHCO3. The organic
phase was washed with water, dried over Na2SO4 and evaporated
to dryness. The residue was purified over silica gel, eluting with
a gradient 0–4% MeOH in CH2Cl2, to give 8 as a colourless oil
(0.95 g, 63%). Rf 0.20 (19:1 CH2Cl2-MeOH). 1H NMR (400 MHz,
CDCl3): d 7.32–7.10 (m, 4H, C6H4Cl), 5.30 (d, 1H, H-1, J1–OH
7.5 Hz), 4.63 (d, 1H, CH2C6H4Cl, J 12.0 Hz), 4.49 (d, 1H, CH2C6H4Cl,
J 12.0 Hz), 4.08–4.02 (m, 2H, H-2 and H-3), 4.04–3.99 (m, 2H, H-6
and OH-1), 3.92 (d, 1H, H-4, J4–3 6.6 Hz), 3.50–3.39 m, 3H, H-7
and OH-7), 1.50–1.65 (m, 5H, H-5a and 2(CH2CH3)), 1.19 (m, 1H,
H-5b), 0.75–0.90 (m, 6H, 2(CH2CH3)). ESIMS (m/z): 387 [M+H]+;
421 [M+Cl]ꢀ.
(d, 1H, H-10, J1 –2 9.3 Hz), 5.04 (t, H-20, J2 –1 8.8 Hz, J2 –3 8.4 Hz),
0
0
0
0
0
0
4.90 (d, 1H, CH2C6H4Cl, 2J 12.3 Hz), 4.77 (d, 1H, CH2C6H4Cl, 2J
12.3 Hz), 4,52 (dd, 1H, H-30, J3 –4 2.9 Hz, J3 –2 7.8 Hz), 4.40 (m,
0
0
0
0
1H, H-60), 4.23 (dd, 1H, H-40, J4 –5 7.2 Hz, J4 –3 2.7 Hz), 3.65 (dd,
0
0
0
0
2
2
1H, H-70a, J7 a–7 b 10.7 Hz, J7 a–6 5.5 Hz), 3.54 (dd, 1H, H-70b, J7 b–7 a
0
0
0
0
0
0
10.6 Hz, J7 b–6 5.4 Hz), 2.14 (m, 1H, H-50a), 1.60–1.74 (m, 5H, H-
50b and 2CH2CH3), 0.78–0.95 (m, 15H, 2CH2CH3 and SiC(CH3)3),
0.00 (s, 6H, Si(CH3)2). LR LC/MS: tR = 23.92 min. ESIMS (m/z):
1275.5 (2M+H+), 637.2 (M+H+).
0
0
4.12. 9-[4-O-(4-Chlorobenzyl)-5-deoxy-2,3-O-diethylidene-7-O-
tert-butyldimethylsilyl-b-D-allo-septanosyl]-adenine (12)
4.9. 4-O-(4-Chlorobenzyl)-5-deoxy-2,3-O-diethylidene-7-O-tert
-butyldimethylsilyl-
D
-allo-septanose (9)
Nucleoside 11 (411 mg, 0.65 mmol) was treated with ammonia-
saturated MeOH (80 mL) in a sealed reactor at 100 °C for 3 h, then
concentrated under diminished pressure to give 12 as a pale yellow
oil used in the next stage without purification. LR LC/MS:
tR = 19.91 min. ESIMS (m/z): 618.3 (M+H+).
To a soln of the septanose derivative 8 (0.95 g, 2.46 mmol) in an-
hyd pyridine (21 mL) were added imidazole (251 mg, 3.68 mmol)
and tert-butyldimethylsilyl chloride (407 mg, 2.70 mmol). The soln
was partitioned between EtOAc and aq HCl 1 M. The organic phase
was washed with saturated brine, dried over Na2SO4 and evapo-
rated to dryness. The crude residue was subjected to silica gel chro-
matography, eluting with a gradient 10–40% diethyl ether in
petroleum ether, to give 9 as a colourless oil (0.82 g, 67%). Rf 0.65
(3:2 Et2O–petroleum ether). 1H NMR (400 MHz, CDCl3): d 7.21–
7.26 (m, 4H, C6H4Cl), 5.28 (m, 1H, H-10), 4.62 (d, 1H, CH2C6H4Cl, 2J
12.1 Hz), 4.53 (d, 1H, CH2C6H4Cl, 2J 12.1 Hz), 4.13–4.19 (m, 2H, H-
20 and H-30), 3.93–3.95 (m, 2H, H-40 and H-60), 3.64 (dd, 1H, H-70a,
4.13. 9-(5-Deoxy-2,3-O-diethylidene-b-
D-allo-septanosyl)-
adenine (13) and 9-(5-deoxy-b- -allo-septanosyl)-adenine (14)
D
To a soln of the crude nucleoside 12 (0.65 mmol) in anhyd
CH2Cl2 (6.3 mL) at ꢀ78 °C was added boron trichloride (1 M in
CH2Cl2, 1.29 mL, 1.29 mmol). The reaction mixture was stirred at
ꢀ78 °C for 1 h 30, then allowed to warm to ꢀ40 °C and stirred
for 1 h 30. The reaction was quenched by addition of 1:1 MeOH–
CH2Cl2 and stirred at ꢀ20 °C for 30 min, then neutralised at 0 °C
with aq ammonia and stirred at room temperature for 15 min.
The mixture was filtered through a pad of Celite and washed with
1:1 MeOH–CH2Cl2. The filtrate was concentrated under diminished
pressure, and the resulting residue was purified by reverse phase
(C18) silica gel column chromatography eluting with a gradient
0–100% MeCN in water to give the partially protected nucleoside
13 (11 mg, 4.5%, white lyophilised powder) and the desired com-
pound 14 (11 mg, 5.5%, white lyophilised powder).
2
2
J7 a–7 b 10.3 Hz, J7 a–6 5.5 Hz), 3.43 (dd, 1H, H-70b, J7 b–7 a 10.3 Hz,
0
0
0
0
0
0
J7 b–6 6.3 Hz), 2.89 (d, 1H, OH, JOH–1 4.7 Hz), 2.00 (m, 1H, H-50a),
1.56–1.72 (m, 4H, 2CH2CH3), 1.32 (m, 1H, H-50b), 0.82–0.90 (m,
15H, 2CH2CH3 and SiC(CH3)3), 0.00 (s, 6H, Si(CH3)2). ESIMS (m/z):
501 [M+H]+; 1001 [2M+H]+; 499 (MꢀH)ꢀ.
0
0
0
4.10. Trichloroacetimidoyl 4-O-(4-chlorobenzyl)-5-deoxy-2,3-O-
diethylidene-7-O-tert-butyldimethylsilyl-D-allo-septanoside (10)
To a soln of septanose 9 (210 mg, 0.42 mmol) in CH2Cl2 (9.7 mL)
were added successively trichloroacetonitrile (92 L, 0.92 mmol)
and DBU (26 L, 0.16 mmol). The reaction mixture was stirred at
room temperature for 2 h, and more trichloroacetonitrile (46 L,
0.46 mmol) and DBU (13 L, 0.08 mmol) were added. The mixture
Compound 13: 1H NMR (400 MHz, Me2SO-d6): d 8.47 (s, 1H,
H-8), 8.20 (s, 1H, H-2), 7.57–7.65 (m, 2H, NH2), 6.35 (d, 1H, H-10,
l
J1 –2 9.40 Hz), 5.30 (br s, 1H, OH-70), 5.11 (t, 1H, H-20, J2 –1 9.1 Hz,
0
0
0
0
l
0
0
0
0
0
0
l
J2 –3 8.1 Hz), 4.34 (dd, 1H, H-30, J3 –2 7.8 Hz, J3 –4 2.5 Hz), 4.19–4.24
(m, 2H, H-40 and H-60), 3.87 (s, 1H, OH-40), 3.24–3.34 (m, 2H, H-70),
1.94 (m, 1H, H-50a), 1.51–1.61 (m, 5H, H-50b and 2CH2CH3), 0.76
(t, 6H, 2CH2CH3, JCH3–CH2 7.4 Hz). HRFABMS: calcd for C17H26O5N5
380.1934 [M+H+]; found (m/z): 380.1937.
l
wasstirredatroomtemperatureforanadditionalhour, thenconcen-
trated under diminished pressure. The resulting residue was filtered
through a silica gel plug, eluting with CH2Cl2 and evaporated to dry-
ness to give the septanoside 10 as a dark brown oil (270 mg, quant.
yield). Rf 0.83 (3:2 Et2O–petroleum ether). ESIMS (m/z): 647 [M+H]+.
Compound 14: 1H NMR (400 MHz, Me2SO-d6): d 8.25 (s, 1H,
H-8), 8.11 (s, 1H, H-2), 7.21 (s, 2H, NH2), 5.61 (d, 1H, H-10, J1 –2
0
0
12.0 Hz), 5.19 (d, 1H, OH-30, JOH-3 4.2 Hz), 5.01 (d, 1H, OH-20,
0
JOH-2 7.0 Hz), 4.67–4.70 (m, 2H, OH-40 and OH-70), 4.23(m, 1H, H-20),
0
4.11. 9-[4-O-(4-Chlorobenzyl)-5-deoxy-2,3-O-diethylidene-7-O-
tert-butyldimethylsilyl-b-
D-allo-septanosyl]-6-chloropurine (11)
3.91–4.05 (m, 3H, H-30, H-40 and H-60), 3.23 (m, 2H, H-70), 1.91
2
(ddd, 1H, H-50a, J5 a–5 b 13.6 Hz, J5 a–6 6.9 Hz, J5 a–4 2.8 Hz), 1.69
0
0
0
0
0
0
2
(ddd, 1H, H-50b, JH5 b–H5 a 13.4 Hz, JH5 b–H4 8.0 Hz, J5 b–6 2.2 Hz). 13C
NMR (100 MHz, Me2SO-d6): d 156.4 (C-4), 152.9 (C-2), 150.2 (C-6),
139.9 (C-8), 119.1 (C-5), 85.0 (C-10), 78.9–77.6 (2C, C-30 and C-60),
71.5 (C-20), 68.3 (C-40), 65.1 (C-70), 33.9 (C-50). HRFABMS: calcd for
C12H18O5N5 312.1308 [M+H+]; found (m/z) 312.1311.
0
0
0
0
0
0
N,O-Bis(trimethylsilyl)-acetamide (606
l
L, 2.48 mmol) was
added to a suspension of 6-chloropurine (191.5 mg, 1.24 mmol)
in 1,2-dichloroethane (16.4 mL). The reaction mixture was stirred
at reflux for 2 h and evaporated to dryness. The resulting residue
was dissolved in anhyd toluene (8.2 mL), and a soln of the trichlo-

G. Sizun et al. / Carbohydrate Research 344 (2009) 448–453
453
8. Bozo, E.; Medgyes, A.; Boros, S.; Kuszmann, J. Carbohydr. Res. 2000, 329,
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Acknowledgements
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This work is part of the Ph.D. of Gwenaëlle Sizun, who is partic-
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ation Nationale de la Recherche Technique (ANRT) for a doctoral
‘CIFRE’ fellowship (Grant No. 901/2004). We gratefully acknowl-
edge Dr. Michel Liuzzi (Idenix Senior Director Virology, Laboratory
Cooperativo Idenix-Universita di Cagliari, Italy) for the biological
results. We are indebted to Dr. Claire Pierra (Idenix Principal
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