Rapid synthesis of 2′,3′-dideoxy-3′β-fluoro- pyrimidine nucleosides from 2′-deoxypyrimidine nucleosides

Article abstract of DOI:10.1016/j.bioorg.2010.08.003

A rapid synthesis of 2′,3′-dideoxy-3′-fluoro-β-d- threo-nucleosides bearing the pyrimidine canonical bases of nucleic acids has been developed in order to discover new nucleoside derivatives as potential antiviral drugs. However, when evaluated for their antiviral activity in cell culture experiments, none of these compounds showed any significant antiviral activity.

Full text of DOI:10.1016/j.bioorg.2010.08.003

Bioorganic Chemistry 38 (2010) 271–274
Contents lists available at ScienceDirect
Bioorganic Chemistry
journal homepage: www.elsevier.com/locate/bioorg
Rapid synthesis of 20,30-dideoxy-30b-fluoro-pyrimidine nucleosides
from 20-deoxypyrimidine nucleosides
⇑
Ahmed Khalil, Christophe Mathé , Christian Périgaud
Institut des Biomolécules Max Mousseron (IBMM), UMR 5247 CNRS-UM 1-UM 2, Université Montpellier 2, cc1705, Place E. Bataillon, 34095 Montpellier cedex 5, France
a r t i c l e i n f o
a b s t r a c t
A rapid synthesis of 20,30-dideoxy-30-fluoro-b-
D-threo-nucleosides bearing the pyrimidine canonical bases
of nucleic acids has been developed in order to discover new nucleoside derivatives as potential antiviral
drugs. However, when evaluated for their antiviral activity in cell culture experiments, none of these
compounds showed any significant antiviral activity.
Article history:
Received 25 June 2010
Available online 7 September 2010
Keywords:
Nucleoside analogs
Antiviral agents
Ó 2010 Elsevier Inc. All rights reserved.
Fluorination reaction
Diethylaminosulfur trifluoride
1. Introduction
(similar polarity) that can exert a powerful influence on the stability
of the glycosyl bond on acid-sensitive nucleosides as well as on the
Nucleoside analogs are an important class of biologically active
compounds. Currently, nucleoside analogs are prominent drugs for
the treatment of several viral infections [1–3]. These nucleoside
analogs share a common mechanism of action. They are metabo-
lized by cellular kinases to their 50-triphosphate forms, which then
exert their biological effect as virus-specific polymerase competi-
tive inhibitors or chain terminators because they lack a hydroxyl
group at the C-30 position. In the search for new antiviral nucleo-
side analogs, structural modifications of the heterocyclic bases
and/or modifications on the sugar moiety of natural nucleosides
can be attempted. In the latter, the main modifications involved
sugar puckering. Such influences have been clearly established in
the case of b-FddA [9] and b-FddC [10] for increasing the stability
of the glycosyl bond. Furthermore, the presence of a fluorine atom
in position 20 or 30 of dideoxynucleosides, and in a particular config-
uration (up or down), can drive the puckering equilibrium toward a
specific distribution of the north/south [11].
In the present article, we describe the direct preparation of 20,30-
dideoxy-30b-fluoro-pyrimidine nucleosides 9–11 (Fig. 1) using as
model compounds their corresponding natural 20-deoxynucleoside
derivatives.
2. Experimental
changes in the D-ribofuranose or 2-deoxy-D-ribofuranose moiety
like inversion of hydroxyl group configurations, elimination lead-
ing to dideoxy- or dideoxy-didehydro-nucleosides, substitution/
functionalization by various synthetic groups [4].
2.1. General methods
Evaporation of solvents was carried out on a rotary evaporator
under reduced pressure. Melting points were determined in open
capillary tubes on a Gallenkamp MFB-595-010M apparatus and are
uncorrected. UV spectra were recorded on an Uvikon 931 (Kontron)
spectrophotometer. 1H NMR spectra were recorded at 300 MHz,
13C NMR spectra at 100 MHz and 19F NMR at 235 MHz in (CD3)2SO
at ambient temperature with a Brüker DRX 400. Chemical shifts (d)
are quoted in parts per million (ppm) referenced to the residual sol-
ventpeak((CD3)CD2H)SObeing setat d-H 2.49and d-C 39.5relativeto
tetramethylsilane (TMS). 19F chemical shifts are reported using tri-
chlorofluoromethane as external reference. Deuterium exchange
and COSY experiments were performed in order to confirm proton
assignments. Coupling constants, J, are reported in Hertz. 2D
1H–13C heteronuclear COSY were recorded for the attribution of
13C signals. Specific rotations were measured on a Perkin–Elmer
Among these functionalities, introduction of a fluorine atom into
the glycon moiety has been investigated in the search for nucleoside
analogs endowed with potent biological properties [5–7]. This
tremendous work led, for instance, to the discovery of 20,30-dide-
oxy-30-fluorothymidine [8]. The interest in the synthesis of fluorine
containing nucleoside analogs is derived from the stability of the
carbon–fluorine bond, chemically and enzymatically, and from the
strong electronegativity of fluorine which affect the stereoelectronic
properties of the whole molecule. Structural studies on glycon
fluorinated nucleosides have demonstrated the possibility to use
fluorineasa goodmimicofhydrogen(similarsize)orhydroxylgroup
⇑
Corresponding author. Fax: +33 (0)4 67 04 20 29.
E-mail address: christophe.mathe@univ-montp2.fr (C. Mathé).
0045-2068/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved.
doi:10.1016/j.bioorg.2010.08.003

272
A. Khalil et al. / Bioorganic Chemistry 38 (2010) 271–274
2.4. General procedure for the preparation of 1-(2,3-dideoxy-3-fluoro-
5-O-acetyl-b- -threo-pentofuranosyl)-3-nitro-uracil (5) and 1-(2,3-
D
dideoxy-3-fluoro-5-O-acetyl-b-
thymine (6)
D-threo-pentofuranosyl)-3-nitro-
To a stirred solution of nucleoside (3, 4) (1 mmol) in an anhy-
drous CH2Cl2/pyridine (20 cm3) mixture at ꢀ67 °C under argon
was added DAST (5 mmol). The reaction mixture was allowed to
warm up to room temperature and stirring was continued for
12 h. The reaction was quenched by addition of saturated aqueous
NaHCO3, washed with H2O. The organic phase was dried over
Na2SO4, concentrated to dryness and purified by silica gel chroma-
tography using ether as eluent to give the title compounds. (5)
Fig. 1. 20,30-Dideoxy-30b-fluoro-pyrimidine nucleosides.
(yield 45%): ½a 2D0
ꢁ
: +13 (c 1.00, DMSO). UV: (ethanol 95) kmax
260 nm, (e
9200). 1H NMR (DMSO-d6): d 7.75 (d, J = 8.1, 1H), 6.16
Model 241 spectropolarimeter (path length 1 cm), and are given in
units of 10ꢀ1 deg cm2 gꢀ1. Elemental analyses were carried out by
the Service de Microanalyses du CNRS, Division de Vernaison
(France). Thin layer chromatography was performed on precoated
aluminum sheets of Silica Gel 60 F254 (Merck, Art. 5554), visualiza-
tion of products being accomplished by UV absorbency followed
by charring with 5% ethanolic sulfuric acid and heating. Column
chromatography was carried out on Silica Gel 60 (Merck, Art.
9385). All moisture-sensitive reactions were carried out under rigor-
ous anhydrous conditions under an argon atmosphere using oven-
dried glassware. Solvents were dried and distilled prior to use and
solids were dried over P2O5 under reduced pressure.
(d, J = 6.9, 1H), 6.09 (d, J = 8.4, 1H), 5.90 (d, J = 53.42, 1H), 4.25–
4.47 (m, 3H), 2.87 (m, 1H), 2.46 (m, 1H), 2.07 (s, 3H). 13C NMR
(DMSO-d6):
d
170.1, 155, 145.3, 140.9, 100.4, 92.2 (d,
J = 178.4 Hz), 85.8, 81.3 (d, J = 18.1 Hz), 61.1, 38.3 (d, J = 20.2 Hz),
20.5. 19F NMR (DMSO-d6): ꢀ190.75 (dddd, J = 54.1, J = 43.2,
J = 31.3, J = 24.1 Hz). (6) (yield 43%): ½a D20
ꢁ
: +17 (c 1.00, DMSO).
UV: (ethanol 95) kmax 264 nm, (e
8700). 1H NMR (DMSO-d6): d
7.05 (s, 1H), 6.16 (dd, 1H, J = 8.04, 1.8 Hz), 5.4 (ddd, 1H, J = 54.2,
J = 4.3, J = 2.4 Hz), 4.42 (m, 2H), 4.3 (m, 1H), 2.74 (m, 1H), 2.43
(m, 1H), 2.07 (m, 3H), 1.94 (s, 3H). 13C NMR (DMSO-d6): d 170.1,
156.3, 145.1, 135.99, 109.1, 92.3 (d, J = 178.3), 85.4, 80.9 (d,
J = 18.25), 61.1, 38.1 (d, J = 20.2), 20.5, 12.3. 19F NMR (DMSO-d6):
ꢀ190.31 (dddd, J = 54.3, J = 42.2, J = 29.8, J = 24.9 Hz).
2.2. Synthesis of 20-deoxy-3-nitro-uridine (1) and 20-deoxy-3-nitro-
thymidine (2)
2.5. General procedure for the preparation of 1-(2,3-dideoxy-3-fluoro-
Compounds 1 and 2 were obtained from commercially available
20-deoxyuridine and 20-deoxythymidine following a procedure ini-
tially developed by Gorchs et al. [12]. The physico-chemicals prop-
erties were similar to those previously described. (1): 1H NMR
(DMSO-d6): d 8.13 (d, J = 8.4, 1H), 6.07–6.14 (m, 2H), 5.23 (br s,
2H), 4.26 (m, 1H), 3.86 (m, 1H), 3.60 (m, 2H), 2.32 (m, 2H).
13C NMR: d 155.4, 145.3, 141.5, 100.1, 88.0, 86.2, 69.7, 60.7, 39.9.
(2): 1H NMR (DMSO-d6): 7.98 (s, 1H), 6.11 (t, J = 6.5 Hz, 1H), 5.1–
5.4 (br s, 2H), 4.27 (m, 1H), 3.82 (m, 1H), 3.67–3.54 (m, 2H),
2.29–2.12 (m, 2H), 1.92 (s, 3H). 13C NMR (DMSO-d6): 155.3,
144.0, 135.9, 107.6, 86.7, 84.7, 68.7, 59.7, 38.6, 11.2.
5-O-acetyl-b-
fluoro-5-O-acetyl-b-
D
-threo-pentofuranosyl)uracil (7) and 1-(2,3-dideoxy-3-
-threo-pentofurano-syl)thymine (8)
D
A solution of nucleoside (5, 6) (1 mmol), Bu3SnH (1.1 mmol) and
AIBN (0.3 mmol) in anhydrous toluene (50 cm3) was heated at
100 °C for 2 h. The reaction mixture was cooled and the solvent
was removed under reduced pressure. The residue was purified
by silica gel column chromatography using as eluent CH2Cl2/Ace-
tone (8/2:v/v) to give the title compounds. (7) (yield 67%): M.p.:
167–168 °C. ½a 2D0
ꢁ
: +4.5 (c 1.00, DMSO). UV: (ethanol 95) kmax
260 nm (e
9100). 1H NMR (DMSO-d6): d 11.28 (s, 1H), 7.44 (d,
J = 8.1, 1H), 6.08 (d, J = 8.1, 1H), 5.62 (d, J = 8.1, 1H), 5.29 (ddd,
J = 54.6, J = 4.5, J = 2.4, 1H), 4.23 (m, 3H), 2.6 (m, 1H), 2.24 (ddd,
J = 27.4, J = 16.5, J = 2.5, 1H), 2.01 (s, 3H). 13C NMR (DMSO-d6): d
170.1, 163.1, 150.3, 139.7, 102.1, 92.5 (d, J = 178.1 Hz), 83.8, 80.3
(d, J = 18.0 Hz), 61.2, 38.1 (d, J = 20.2), 20.5. 19F (DMSO-d6): d
ꢀ190.23 (dddd, J = 54.9, J = 41.3, J = 31.9, J = 25.3 Hz). Anal. Calcd
for C11H13FN2O5: C, 48.53, H, 4.81, N, 10.29. Found: C, 48.33, H,
2.3. General procedure for the preparation of 50-O-acetyl-20-deoxy-3-
nitro-uridine (3) and 50-O-acetyl-20-deoxy-3-nitro-thymidine (4)
To a solution of nucleoside (1, 2) (1 mmol) in dioxane (10 cm3)
were added PPh3 (1.5 mmol) and glacial acetic acid (9.9 mmol). The
resulting mixture was stirred at 60 °C, and a solution of diethyl
azodicarboxylate (1.5 mmol) in dioxane (1 cm3) was added drop-
wise. The solution was stirred at 60 °C for 1 h. After cooling to room
temperature and evaporation of the solvent, the oily residue was
purified by silica gel chromatography using as eluent CHCl3/Ace-
5.16, N, 9.99. (8) (yield 85%): M.p.: 142–143 °C. ½a D20
ꢁ
: +16.5 (c
1.00, DMSO). UV: (ethanol 95) kmax 265 nm, (e
8800). 1H NMR
(DMSO-d6): d 11.29 (s, 1H), 7.25 (s, 1H), 6.11 (dd, J = 8.7, 2.4 Hz,
1H), 5.29 (ddd, J = 54.6, J = 4.61, J = 2.42 Hz, 1H, H-30), 4.36–4.22
(m, 2H), 4.12 (m, 1H), 2.74 (m, 1H), 2.18 (ddd, J = 26.0, J = 16.1,
J = 2.8 Hz, 1H), 2.01 (s, 3H), 1.75 (s, 3H). 13C NMR (DMSO-d6): d
170.1, 163.6, 150.4, 135.1, 109.7, 92.5 (d, J = 178.2 Hz), 83.3, 79.9
(d, J = 17.9 Hz), 61.26, 37.9 (d, J = 20.17), 20.5, 12.3. 19F
tone (9/1:v/v) to give the title compounds. (3) (yield 75%): ½a D20
ꢁ
:
+35 (c 1.06, DMSO). UV: (ethanol 95) kmax 260 nm, (e
8700). 1H
NMR (DMSO-d6): d 7.86 (d, 1H, J = 8.4), 6.08–6.15 (m, 2H), 5.52
(s, 1H), 4.13–4.24 (m, 3H), 4.01 (m, 1H), 2.27–2.42 (m, 2H), 2.04
(s, 3H). 13C NMR (DMSO-d6): d 170.1, 155.5, 145.3, 141.7, 100.3,
86.4, 84.3, 69.7, 63.5, 38.9, 20.6. Anal. Calcd for C11H13N3O8: C,
41.91, H, 4.16, N, 13.33. Found: C, 41.66, H, 4.16, N, 13.08. (4) (yield
NMR(DMSO-d6):
d
ꢀ189.84 (dddd, J = 54.9, J = 41.4, J = 31.9,
J = 26.3 Hz). Anal. Calcd for C12H15FN2O5: C, 50.35, H, 5.28, N,
9.79. Found: C, 50.28, H, 5.40, N, 9.44.
74%): M.p.: 116–117 °C. ½a D20
ꢁ
: +17.5 (c 1.00, DMSO). UV: (ethanol
95) kmax 264 nm, (
e
9700). 1H NMR (DMSO-d6): d 7.65 (s, 1H),
2.6. General procedure for the preparation of 1-(2,3-dideoxy-3-fluoro-
6.13 (t, J = 6.5 Hz, 1H), 5.49 (d, 1H, J = 4.5 Hz), 4.28–4.16 (m, 3H),
3.96 (m, 1H), 2.39–2.12 (m, 2H,), 2.05 (s, 3H), 1.92 (s, 3H). 13C
NMR (DMSO-d6): 170.2, 156.4, 145.1, 136.9, 109.1, 85.8, 84.1,
69.7, 63.6, 38.6, 20.6, 12.1. Anal. Calcd for C12H15N3O8: C, 43.77,
H, 4.59, N, 12.76. Found: C, 44.15, H, 4.69, N, 12.47.
b-
D
-threo-pentofuranosyl)uracil (9) and 1-(2,3-dideoxy-3-fluoro-b-D-
threo-pentofuranosyl)thymine (10)
A solution of nucleoside (7, 8) (1 mmol) in methanolic ammonia
(20 cm3) (saturated beforehand at ꢀ10 °C and tightly stoppered)

A. Khalil et al. / Bioorganic Chemistry 38 (2010) 271–274
273
was stirred in a stainless-steel bombovernight at room temperature.
The solution was evaporated to dryness under reduced pressure and
co-evaporated several times with methanol. The residue was puri-
fied by silica gel column chromatography using as eluent
CH2Cl2:MeOH (9/1:v/v)) to afford the title compounds. (9) (yield
½
a 2D0
: +13.1 (c 1.00, DMSO). UV: (ethanol 95) kmax 260 nm (e
ꢁ
8800). 1H NMR (DMSO-d6): d 7.67 (d, J = 8.3 Hz, 1H), 6.13 (d,
J = 7.9 Hz, 1H), 6.09 (d, J = 8.4 Hz, 1H), 5.22 (ddd, J = 54.1, J = 3.99,
J = 2.4 Hz, 1H), 5.06 (t, J = 5.5 Hz, 1H), 4.06 (m, 1H), 3.79 (m, 2H),
2.79 (m, 1H), 2.43 (m, 1H). 13C NMR (DMSO-d6): d 155.4, 145.3,
140.9, 100.2, 91.8 (d, J = 178.1 Hz), 85.7, 84.7 (d, J = 18.8 Hz), 57.9,
38.5 (d, J = 20.5 Hz). 19F NMR (DMSO-d6): d ꢀ191.05 (dddd,
J = 54.2, J = 43.2, J = 31.1, J = 22.8 Hz). Anal. Calcd for C9H10FN3O6:
C, 39.28, H, 3.66, N, 15.27. Found: C, 39.63, H, 4.01, N, 15.02. (13)
74%). M.p.: 167 – 168 °C. ½a D20
ꢁ : ꢀ11.25 (c 0.8, DMSO). UV: (ethanol
95) kmax 260 nm, (e
8800). 1H NMR (DMSO-d6): d 11.34 (s, 1H),
7.48 (d, J = 8.15, 1H), 6.14 (d, J = 8.0 Hz, 1H), 5.69 (d, J = 8.12, 1H),
5.29 (ddd, J = 54.3, J = 4.2, J = 2.4 Hz, 1H), 5.01 br (s, 1H), 4.01 (m,
1H), 3.65–3.78 (m, 2H), 2.76 (m, 1H), 2.22 (ddd, J = 28.0, J = 16.4,
2.3 Hz, 1H). 13C NMR (DMSO-d6): d 163.1 (C-4), 150.4 (C-2), 139.7,
101.8 (C-5), 92.0 (d, J = 178.2 Hz), 83.9, 83.6 (d, J = 15.9 Hz), 58.1,
38.4 (d, J = 20.1 Hz). 19F NMR (DMSO-d6): d ꢀ190.51 (dddd,
J = 54.7, J = 43.0, J = 30.0, J = 25.4 Hz). Anal. Calcd for C9H11FN2O4:
C, 46.96, H, 4.82, N, 12.17. Found: C, 47.02, H, 4.92, N, 11.99. (10)
(yield 78%). The physico-chemicals properties of were similar to
(yield 71%): M.p.: 178–180 °C. ½a D20
ꢁ
: +3 (c 1.00, DMSO). UV: (etha-
nol 95) kmax 264 nm, (e
7000). 1H NMR (DMSO-d6): d 7.49 (s, 1H),
6.14 (dd, J = 7.9, 1.6 Hz, 1H), 5.32 (ddd, J = 54.3, J = 4.2, J = 2.5 Hz,
1H), 5.05 (t, J = 5.6 Hz, 1H), 4.06 (m, 1H), 3.71–3.84 (m, 2H), 2.78
(m, 1H), 2.41 (ddd, J = 23.6, J = 16.0, J = 2.0 Hz, 1H), 1.93 (s, 3H).
13C NMR (DMSO-d6):
d 156.3, 145.1, 136.1, 108.8, 91.8 (d,
J = 178.2 Hz), 85.2, 84.4 (d, J = 18.6), 57.9, 38.3 (d, J = 20.3 Hz),
12.4. 19F NMR (DMSO-d6): d ꢀ190.63 (dddd, J = 54.3, J = 42.5,
J = 30.5, J = 24.1 Hz). Anal. Calcd for C10H12FN3O6: C, 41.53, H,
4.18, N, 14.53. Found: C, 41.57, H, 4.32, N, 14.82.
those previously described. ½a D20
ꢁ : ꢀ21.2 (c 1.00, DMSO) UV: (ethanol
95) kmax 266 nm (e
10,500). 1H NMR (DMSO-d6): d 11.34 (s, 1H), 7.31
(s, 7.31), 6.16 (dd, J = 8.1, 2.1 Hz, 1H) 5.28 (ddd, J = 54.6, J = 4.5,
J = 2.4 Hz, 1H), 4.99 (s, 1H), 3.95 (m, 1H), 3.72 (m, 2H), 2.75 (m,
1H), 2.22 (ddd, J = 25.2, J = 15.9, J = 2.7 Hz, 1H), 1.78 (s, 3H). 13C
NMR (DMSO-d6): d 162.2, 148.9, 133.8, 108.0, 90.6 (d, J = 178.4 Hz),
82.1, 81.6 (d, J = 25.1), 56.7, 38.2 (d, J = 20.6), 12.39. 19F NMR
(DMSO-d6): d ꢀ190.12 (dddd, J = 54.5, J = 42.4, J = 30.8, J = 25.1 Hz).
Anal. Calcd for C12H15FN2O5. 0.6H2O: C, 47.10, H, 5.61, N, 10.98.
Found: C, 46.96, H, 5.66, N, 10.63.
3. Results and discussion
So far, the 30b-fluoro-substituted nucleosides have been
synthesized through glycosylation reaction between pre-formed
3-deoxy-3-b-fluoro-
by introduction of a fluorine atom onto 20,30-anhydro-b-
anonucleosides [7]. The resulting 3-deoxy-3-b-fluoro-
D
-xylo-furanosides with heterocyclic bases or
-ribofur-
-xylo-
D
D
2.7. Synthesis of 1-(2,3-dideoxy-3-fluoro-b-
pentofuranosyl)cytosine (11)
D
-threo-
nucleosides were finally subjected to a Barton-type reductive
deoxygenation to afford the corresponding 20,30-dideoxy-30b-fluoro
nucleoside analogs. These methodologies have been used to syn-
thesize the nucleoside derivatives bearing adenine [13], guanine
[14] and thymine [14] as heterocyclic bases. In order to have a ra-
pid access to the hitherto unknown derivatives of uracil and cyto-
sine and evaluate their antiviral properties, we envisioned their
preparation from the corresponding natural 20-deoxynucleoside
derivatives. At this point, after selective protection in position 50,
a direct nucleophilic fluorination reaction using a fluorinating
agent such as diethylaminosulfur trifluoride (DAST) would not give
the corresponding C-30-b-fluoro pyrimidine nucleoside [15]. In-
stead, the formation of a 2,30-anhydro nucleoside would occur
due to the neighboring group participation of the C-2 carbonyl
function of the aglycon. Indeed, the intramolecular attack of the
C-2 carbonyl group of the nucleobase on C0-3, activated with a good
leaving group [C-O-SF2(NEt3)], of the sugar moiety precedes the
attack of a fluorine ion from the b-face of the nucleoside. Thus, to
produce the desired corresponding C-30b-fluoro pyrimidine nucle-
oside, anhydronucleoside formation has to be prevented. This un-
wanted side-reaction can be hindered by protection of the N-3
atom of the pyrimidine base. In this regard, Serra et al. reported
the use of nitro group as protective group for the N-3 position.
The use of such protective electron-withdrawing group prevented
the formation of anhydro nucleoside during nucleophilic substitu-
tions upon 20-O-triflyluridine [16] as well as 20,30-cyclic sulfate
pyrimidine nucleoside [17].
The synthesis began (Fig. 2) with the preparation of the appro-
priate 3-nitro 20-deoxynucleosides 1 and 2 which were obtained
from commercially available 20-deoxyuridine and thymidine fol-
lowing a reported procedure [12]. Regioselective 50-O-acylation
of 1 and 2 was achieved using a modified Mitsunobu procedure
[18] and gave the key intermediates 50-O-acetyl-20-deoxy-3-ni-
tro-uridine and -thymidine 3 and 4 after purification by silica gel
chromatography in 75% and 74%, respectively.
Reaction of DAST with 3 and 4 in an anhydrous dichlorometh-
ane/pyridine mixture provided the corresponding protected
C-30b-fluoro pyrimidine nucleosides 5 and 6. Removal of the nitro
group was attempted using iodide-mediated denitration process
Lawesson’s reagent (0.296 g, 0.73 mmol) was added under ar-
gon to a solution of compound (7) (0.2 g, 0.73 mmol) in anhydrous
1,2-dichloroethane (25 cm3) and the reaction mixture was stirred
under reflux for 6 h. The solvent was evaporated under reduced
pressure. The residue was purified by silica gel column chromatog-
raphy using as eluent CH2Cl2/Acetone (8/2:v/v) to give the 4-thio
intermediate (0.19 g). A solution of the 4-thio intermediate in
methanolic ammonia (16 cm3) (saturated beforehand at ꢀ10 °C
and tightly stoppered) was heated at 100 °C in a stainless-steel
bomb for 3 h, and then cooled to room temperature. The solution
was evaporated to dryness under reduced pressure and co-evapo-
rated several times with methanol. The residue was purified by sil-
ica gel column chromatography using as eluent CH2Cl2/MeOH (8/
2:v/v) to give the title compound (11) (0.13 g, overall yield 77%)
which was lyophilizated from water. ½a D20
ꢁ
: +10.8 (c 0.6, DMSO).
UV: (ethanol 95) kmax 272 nm, (e
8100). 1H NMR (DMSO-d6): d
7.5 (d, J = 7.4, 1H), 7.14 (br d, 2H), 6.09 (d, J = 7.8 Hz, 1H), 5.75 (d,
J = 7.4, 1H), 5.25 (ddd, J = 54.3, J = 4.0, J = 2.4 Hz, 1H), 4.99 (t,
J = 5.4 Hz, 1H), 4.00 (m, 1H), 3.78–3.69 (m, 2H), 2.69 (m, 1H),
2.09 (ddd, J = 26.4, J = 15.8, J = 2.1 Hz, 1H). 13C NMR (DMSO-d6): d
165.3, 154.7, 139.9, 93.6, 91.8 (d, J = 177.9) 84.1, 83.6 (d,
J = 18.8 Hz), 57.9, 39.1 (d, J = 19.9) 19F NMR (DMSO-d6):
d
ꢀ190.99 (dddd, J = 54.5, J = 43.2, J = 30.4, J = 24.0 Hz). Anal. Calcd
for C9H12FN3O3. 0.9H2O: C, 44.05, H, 5.67, N, 17.12. Found: C,
44.24, H, 5.38, N, 16.87.
2.8. General procedure for the preparation of 1-(2,3-dideoxy-3-fluoro-
b-D-threo-pentofuranosyl)-3-nitro-uracil (12) and 1-(2,3-dideoxy-3-
fluoro-b-
D
-threo-pentofuranosyl)-3-nitro-thymine (13)
Treatment of nucleoside (5, 6) (0.5 mmol) with HCl/MeOH
(0.17 M, 25 cm3) for 12 h at room temperature. The solution was
evaporated to dryness under reduced pressure and co-evaporated
several times with toluene. The residue was purified by silica gel
column chromatography using as eluent CH2Cl2/Acetone (7:3) to
give the title compounds. (12) (yield 75%): M.p.: 168–169 °C.

274
A. Khalil et al. / Bioorganic Chemistry 38 (2010) 271–274
the potential antiviral activity of the fluorinated nucleosides ob-
tained during the synthesis of compounds 9–11, the 3-nitro fluori-
nated intermediates
5 and 6 were deprotected following a
treatment with methanolic HCl and provided the 20,30-dideoxy-
30b-fluoro-3-nitro-uridine (12) and -thymidine (13).
4. Conclusion
A rapid synthesis of 2030-dideoxy-30b-fluoro-nucleosides bear-
ing the pyrimidine canonical bases of nucleic acids has been devel-
oped in order to discover new nucleoside derivatives as potential
antiviral drugs. However, when the nucleosides 9, 11–13 were
evaluated against DNA and several RNA viruses (including HIV)
in cell culture experiments, none of the nucleoside derivatives
showed any antiretroviral activity nor cytotoxicity at the highest
concentration tested (usually 100 lM).
Acknowledgments
A.K. is particularly grateful to the Egyptian government for a
doctoral fellowship. We gratefully acknowledge Pr. J. Balzarini
(Laboratory of virology and chemotherapy, Katholieke Universiteit,
Leuven) for the biological results.
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presence of
a,
a0-azoisobutyronitrile (AIBN) under reflux gave the
protected nucleoside derivatives 7 and 8. Removal of the acetyl
group with methanolic ammonia afforded the desired dideoxynu-
cleosides 9 and 10 after purification on silica gel column. The struc-
tures of compounds 9 and 10 were fully established from 1H, 13C
and 19F NMR spectra. In particular, the physicochemical properties
of compound 10 were identical to those previously reported by
Gosselin et al. [14] for the 20,30-dideoxy-30b-fluoro-nucleoside
derivative of thymine. Compound 7 was converted into the corre-
sponding cytidine derivative 11 via the formation of a 4-thioamide
intermediate followed by aminolysis. Finally, in order to evaluate