Synthesis, Structure-Activity Relationships, and Mechanism of Drug Resistance of D- and L-β-3′-Fluoro-2′,3′ -unsaturated-4′-thionucleosides as Anti-HIV Agents

Article abstract of DOI:10.1021/jm0303148

Various D- and L-2′,3′-unsaturated 3′-fluoro-4′ -thionucleosides (D- and L-3′F-4′Sd4Ns) were synthesized for the studies of structure-activity relationships. The synthesized D-2′,3′-unsaturated 3′-fluoro-4′-thionucleosides did not show any significant ant

Full text of DOI:10.1021/jm0303148

J . Med. Chem. 2004, 47, 1631-1640
1631
Syn th esis, Str u ctu r e-Activity Rela tion sh ip s, a n d Mech a n ism of Dr u g
Resista n ce of D- a n d L-â-3′-F lu or o-2′,3′-u n sa tu r a ted -4′-th ion u cleosid es a s
An ti-HIV Agen ts
Wei Zhu,† Youhoon Chong,† Hyunah Choo,† J udy Mathews,‡ Raymond F. Schinazi,‡ and Chung K. Chu*,†
Department of Pharmaceutical and Biomedical Sciences, College of Pharmacy, The University of Georgia, Athens, Georgia
30602, and Emory University School of Medicine/ Veterans Affairs Medical Center, Decatur, Georgia 30033
Received J une 26, 2003
Various D- and L-2′,3′-unsaturated 3′-fluoro-4′-thionucleosides (D- and L-3′F-4′Sd4Ns) were
synthesized for the studies of structure-activity relationships. The synthesized D-2′,3′-
unsaturated 3′-fluoro-4′-thionucleosides did not show any significant antiviral activity against
HIV-1, while unnatural L-nucleosides such as cytosine 34 (EC50 ) 0.13 µM; EC90 ) 1.7 µM)
and 5-fluorocytosine 35 (EC50 ) 0.031 µM; EC90 ) 0.35 µM) derivatives exhibited potent anti-
HIV activity without significant toxicity. Molecular modeling study shows that the 3′-fluorine
atom of the D-2′,3′-unsaturated cytidine triphosphate (D-3′F-4′Sd4CTP) experiences unfavorable
electrostatic interaction with its own triphosphate moiety, resulting in the decreased binding
affinity to wild-type HIV-1 reverse transcriptase (RT), which may be one of the reasons for the
insensitivity of HIV-1 RT to these compounds. On the other hand, L-3′F-4′Sd4CTP binds to
the active site of wild-type HIV-1 RT without steric hindrance and there is a possible hydrogen
bonding between the 3′-fluorine atom and Asp185, which correlates with its potent anti-HIV
activity. However, L-3′F-4′Sd4C 34 and L-3′F-4′Sd4FC 35 showed high cross-resistance to 3TC-
resistant mutant (M184V) RT. Like other unnatural L-nucleosides, the unfavorable steric
hindrance of the sugar moiety of L-3′F-4′Sd4CTP with the side chain of Val184 explains its
significant cross-resistance to the M184V mutant.
In tr od u ction
ated 3′-fluoro-4′-thionucleosides were prepared and their
antiviral activity was evaluated against HIV in human
peripheral blood mononuclear (PBM) cells. To under-
stand the structure-activity relationships and the
mechanism of the cross-resistance against 3TC-resistant
(M184V) reverse transcriptase (RT), the binding modes
of D- and L-2′,3′-unsaturated 3′-fluoro-4′-thiocytidine
triphosphates to the wild type as well as the 3TC-
resistant (M184V) RT were investigated by molecular
modeling studies. Herein, we report the synthesis,
biological evaluation, and molecular modeling studies
of the D- and L-4′-thionucleosides.
There have been considerable interest in the modifi-
cation of nucleosides with a fluorine atom in the sugar
moiety because of the strong electronegativity of a
fluorine atom, which can influence the overall electronic
property of a nucleoside, resulting in the increased
chemical stability of fluorinated nucleosides.1 4′-Thio-
nucleosides with isosteric replacement of the 4′-oxygen
by a sulfur atom have been synthesized and biologically
evaluated as antiviral and antitumor agents2-6 because
4′-thionucleosides are known to be resistant to hydro-
lytic cleavage of a glycosyl linkage catalyzed by nucleo-
side phosphorylases,7 which deactivates several antivi-
ral nucleosides.8 However, among the 4′-thionucleosides,
only 2′,3′-unsaturated nucleoside analogues showed
potent antiviral activity against HIV.5,6 Recently, L-2′,3′-
unsaturated 3′-fluoronucleosides have been reported to
exhibit potent antiviral activity against HIV-1 without
significant cytotoxicity.9 Thus, it was of interest to
synthesize their corresponding 4′-thionucleosides.
Introduction of a fluorine atom into the 3′-position of
the 2′,3′-unsaturated sugar moiety has always been
challenging. There are limited examples to introduce the
3′-fluorine in 2′,3′-unsaturated nucleosides.9,10 In this
study, by adaptation of the synthetic protocol, which was
used in the synthesis of the L-2′,3′-unsaturated 3′-
fluorocytidine analogue,9 various D- and L-2′,3′-unsatur-
Resu lts a n d Discu ssion
Ch em istr y. Enantioselective synthesis of 3′-fluoro-
2′,3′-unsaturated nucleosides is extremely limited by the
lack of synthetic methodologies to introduce a fluorine
atom at the 3′-position of the 2′,3′ double bond. In this
study, the method in the synthesis of L-3′-fluoro-2′,3′-
unsaturated nucleosides,9 which introduced a 2′,3′
double bond by elimination of hydrogen fluoride (HF)
from a 2′,3′-dideoxy-3′,3′-difluoronucleoside, was adapted
to the synthesis of their corresponding 4′-thionucleo-
sides.
To synthesize the target compounds, L-â-3′-fluoro-
2′,3′-didehydro-2′,3′-dideoxy-4′-thio-nucleosides (L-3′F-
4′Sd4Ns), a versatile carbohydrate precursor 8 was used
as a key intermediate, which was obtained from com-
mercially available 2-deoxy-D-ribose (Scheme 1). The
conversion of 2-deoxy-D-ribose to its ketone 3 was
accomplished in three steps in 70% overall yield by the
reported method.11 Treatment of the ketone 3 with
* To whom correspondence should be addressed. Phone: (706) 542-
5379. Fax: (706) 542-5381. E-mail: dchu@rx.uga.edu.
† The University of Georgia.
‡ Emory University School of Medicine/Veterans Affairs Medical
Center.
10.1021/jm0303148 CCC: $27.50 © 2004 American Chemical Society
Published on Web 02/19/2004

1632 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 7
Sch em e 1. Preparation of the Key Intermediate 8a
Zhu et al.
a
Reagents and conditions: (a) H2SO4, MeOH, 0 °C to room temp; (b) Tol-Cl, pyr, 0-5 °C; (c) PDC, CH2Cl2, room temp; (d) DAST,
CH2Cl2; (e) BnSH, BF3‚OEt2, CH2Cl2, reflux; (f) Tf2O, 2,6-lutidine, CH2Cl2; (g) BaCO3, TBAI, CH3CN, heating; (h) Hg(OAc)2, Ac2O, AcOH.
(diethylamino)sulfur trifluoride (DAST) afforded the
difluorinated intermediate 4 in 55% yield.12 The ring-
opening reaction with benzyl mercaptan (BnSH) was
catalyzed by 0.5 equiv of BF3‚Et2O in CH2Cl2 at 40 °C
to give the thioacetal 5 in 94% yield.13 The 4-OH was
converted to the corresponding triflate 6, which was
cyclized to thiosugar 7 in 78% yield. The cyclization at
C-4 could also be accomplished under Mitsunobu condi-
tions with triphenylphosphine, iodine, and imidazole.14
Transglycosylation of compound 7 by the treatment with
mercury(II) acetate in acetic acid provided the key
intermediate 8 in 72% yield.15
A series of pyrimidine and purine nucleosides were
prepared by coupling the key intermediate 8 with
various silyl-protected bases in the presence of TMSOTf
(Scheme 2). Uracil and thymine nucleosides, 9 and 10,
were obtained in 67-71% yield as inseparable R/â
mixtures. The anomeric mixtures, 9 and 10, were
treated with NH3/MeOH at room temperature to give
free nucleosides 15-18, which were readily separated
by silica gel column chromatography (R/â ) 1:1, 90%
yield). Similarly, condensation of 8 with silylated N4-
isobutyrylcytosine and N4-benzoyl-5-fluorocytosine in
dry acetonitrile gave protected cytosine derivatives 11/
12 and 5-fluorocytosine derivatives 13/14, respectively.
These anomers were readily separated by silica gel
column chromatography. Deprotection of individual
anomers by ammonolysis using saturated methanolic
ammonia at room temperature afforded the free nucleo-
sides 19-22.
the silyl-protected 2-amino-6-chloropurine in 1,4-diox-
ane at 100 °C for 12 h. After removal of the 5′-toluoyl
protecting group, 2-amino-6-chloropurine derivatives 29/
30, were isolated by silica gel column chromatography.
The â-isomer 29 was then further transformed to the
guanine derivative 31 by heating under reflux in the
presence of 2-mercaptoethanol and sodium methoxide
in 60% yield.
The stereochemistry of these anomers was deter-
mined on the basis of nuclear Overhauser effect (NOE)
experiments of the thymine derivatives (17/18). NOE
(3%) was observed between the 6-H and 4′-H in the
R-thymine derivative 18 when the 6-H was irradiated,
whereas no NOE was observed between the correspond-
ing protons in â-analogue 17. This assignment was also
supported by lower field chemical shifts of the 4′-H (18,
R-form) compared to that of the 4′-H (17, â-form)
because of deshielding effects by heterocyclic bases.
The â-difluoronucleosides (15, 17, 19, 21, 25, 27, and
31) were converted to the target unsaturated nucleo-
sides (32-38) by treatment with potassium tert-butoxide
in THF. A careful control of the reaction was critical
because a longer reaction time usually resulted in
decomposition of the starting material and poor yield.
Unfortunately, the reaction did not proceed to comple-
tion, and only the adenine derivative 36 could be
separated from its starting material 25 with a normal
silica gel column chromatography. In the other deriva-
tives, final products could not be separated from their
corresponding difluoro starting materials by silica gel
column chromatography. Several other methods of
separation such as silver nitrate-silica gel column
chromatography and chiral auxiliaries were tried with-
out success. Therefore, after the reaction mixture was
stirred for 3-5 h at room temperature, the reaction was
stopped and, after purification, the recovered starting
material was recycled.
Condensation of 8 with silylated 6-chloropurine in dry
acetonitrile at 80 °C for 24 h gave inseparable 6-chlo-
ropurine nucleosides 23. After treatment with metha-
nolic ammonia in a steel bomb at 100 °C for 24 h,
anomeric mixtures of adenine derivatives (25/26) were
separated on a silica gel column. The hypoxanthine
derivatives (27/28) were also obtained from 6-chloropu-
rine nucleosides in 79% yield by refluxing with sodium
methoxide and 2-mercaptoethanol in MeOH. 5′-Toluoyl-
protected 2-amino-6-chloropurine derivatives (24) were
also obtained by the condensation of intermediate 8 with
The D-isomers (D-3′F-4′S-d4Ns) were also synthesized
under similar reaction conditions starting from the
opposite enantiomer, 2-deoxy-L-riboside (Scheme 3). The
key intermediate 39, the enantiomer of 8, was prepared

Thionucleosides as Anti-HIV Agents
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 7 1633
Sch em e 2. Synthesis of the Pyrimidine and Purine Nucleosidesa
a
Reagents and conditions: (a) BSA, pyrimidines or purines, CH3CN or 1,4-dioxane, TMSOTf, heat; (b) NH3/MeOH, room temp; (c)
t
NH3/MeOH, steel bomb, 100 °C; (d) 2-mercaptoethanol, NaOMe/MeOH, reflux; (e) BuOK/THF.
Sch em e 3. Synthesis of d-3′F-4′Sd4 Nucleosides
from 2-deoxy-L-ribose, which can be prepared from
L-arabinose in large quantity and high yield in six
steps.16 After coupling of 39 with the appropriately pro-
tected pyrimidine and purine bases, the final D-2′,3′-
unsaturated 3′-fluoro-4′-thionucleosides (40-46) were
obtained using the same procedure for L-isomers. During
syntheses of the final D-isomers (40-46), several reac-
tion conditions for the HF elimination were tried to
achieve completion of the reaction in a single operation.
The best result was obtained using a combination of
material and marginal decomposition. Presumably, de-
protonation of acidic protons such as the proton of the
5′-hydroxy group and the proton of an amide in the base
moiety with 2.2 equiv of a weaker base, NaOMe, fol-
lowed by the HF elimination by a stronger base, tBuOK,
at low temperature proceeds in a more controlled man-
ner.
Str u ctu r e-Activity Rela tion sh ip s. The antiviral
activity of the synthesized D- and L-nucleosides (32-38
and 40-46) was evaluated against HIV-1 in human
PBM cells in vitro, and the results are summarized in
Table 1. Among the tested nucleosides, L-cytosine 34
t
NaOMe and BuOK in DMF at 0°C, which afforded 2′,3′-
unsaturated nucleosides with no remaining starting

1634 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 7
Zhu et al.
Ta ble 1. Anti-HIV Activity of D- and
L-â-3′-Fluoro-2′,3′-unsaturated-4′-thionucleosides
Ta ble 2. Activity of Selected Nucleosides against
Lamivudine-Resistant Virus (HIV-1M184V) in Human PBM Cells
WT (xxBRU),a
EC90 (µM)
M184V,b
EC90 (µM)
compd
FIc
34 (L-cytosine)
35 (L-5-F-cytosine)
AZT
1.7
>100
>100
0.003
535
>58.8
>285.7
0.3
0.35
0.01
0.08
3TC
6688
HIV (PBM)
EC50 EC90
toxicity,
a
WT: wild type (drug-sensitive virus). b M184V: drug-resistant
IC50 (µM)
virus against 3TC. c FI: fold increase [EC90(HIVM184V)/EC90(HIV-
xxBRU)].
compd config
base
uracil
thymine
cytosine
5-F-cytosine
adenine
(µM) (µM) PBM CEM
Vero
1
32
33
34
35
36
37
38
40
41
42
43
44
45
46
AZT
L
L
L
L
L
L
L
D
D
D
D
D
D
D
>100 >100 >100 >100
>100 >100 >100 g100
0.13 1.7
>100
>100
>100
the drug resistance of 3′-fluoro-4′-thionucleosides toward
3TC-resistant mutant RT (vide infra).
>100 >100
0.031 0.35 >100 >100
14.9 57.0 >100 >100
88.1
Molecu la r Mod elin g. To investigate the character-
istic binding modes of D-3′F-4′Sd4C and L-3′F-4′Sd4C
as well as the mechanism of L-3′F-4′Sd4C’s high cross-
resistance to 3TC-resistant mutant (M184V) RT, mo-
lecular modeling studies were performed by using the
wild-type RT (PDB entry 1rtd)19 as well as the computer-
generated M184V HIV-1 RT complexed with D- and
L-3′F-4′Sd4C triphosphates (D- and L-3′F-4′Sd4CTPs).
The geometrically optimized conformation of L-3′F-
4′Sd4C, which was obtained by a quantum mechanical
calculation (RHF/6-31G**),6b,c was docked into the active
site of HIV-1 RT, and the resulting complex was
minimized20 until there was no significant change in
atomic coordinates. As other unnatural L-nucleosides,6c
L-3′F-4′Sd4CTP binds well in the active site of the wild-
type RT without any steric hindrance with the neigh-
boring enzyme residues, particularly the most adjacent
residue Met184 (Figure 1a). Interestingly, the 3′-fluorine
atom is within the hydrogen-bonding distance with the
amide backbone of Asp185, even though the distance
(∼2.2 Å) between the hydrogen-bonding donor (amide
backbone of Asp185) and the acceptor (3′F) is longer
than the normal distance (Figure 1a). However, because
of the long distance between the hydrogen-bonding pair
and relatively weak hydrogen-bonding ability of the
fluorine atom,21 the contribution of this interaction to
the binding affinity of the L-3′F-4′Sd4CTP to the active
site of RT is expected to be insignificant. In the M184V
RT‚L-3′F-4′Sd4CTP complex, the binding pocket of the
L-3′F-4′Sd4CTP tends to overlap with the bulky side
chain of Val184, which provides steric hindrance when
the L-3′F-4′Sd4CTP binds to the M184V RT (Figure 1b).
To circumvent this abortive binding mode, the M184V
RT‚L-3′F-4′Sd4CTP complex had to undergo significant
conformational change that resulted in a large decrease
in the calculated relative binding energy, reflecting the
high cross-resistance of L-3′F-4′Sd4C to M184V RT.
It is interesting to find that D-3′F-4′Sd4C 42 is
not active against HIV-1 in view of the fact that
D-2′F-4′Sd4C is active against HIV-1 with an EC50 of
1.3 µM.6b The quantum mechanically geometrically
optimized structures of D-3′F-4′Sd4C and D-2′F-4′Sd4C
show almost the same conformations, which implies that
the 3′-fluorine plays a role in the inactivity of D-3′F-
4′Sd4C to HIV-1. In our molecular modeling studies, the
3′-fluorine in D-3′F-4′Sd4CTP is located very close to the
â-phosphate of its own triphosphate moiety when it is
bound to the active site of HIV-1 RT (Figure 1c). The
two negatively charged moieties strongly repulse each
other to force a conformational change in the sugar
moiety. However, the possible steric hindrance between
the bulky 4′-sulfur atom of the sugar and Met184 does
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
hypoxanthine >100 >100 >100 >100
guanine
uracil
thymine
cytosine
5-F-cytosine
adenine
43.9 >100 >100 >100
>100 >100 >100 >100
>100 >100 >100 >100
>100 >100 >100 >100
>100 >100 >100 >100
>100 >100 >100 >100
hypoxanthine >100 >100 >100 >100
guanine 23.4 >100 >100 >100
0.004 0.01 >100 14.3
29.0
(EC50 ) 0.13 µM), L-5-fluorocytosine 35 (EC50 ) 0.031
µM), L-adenine 36 (EC50 ) 14.9 µM), and L-guanine 38
(EC50 ) 43.9 µM) derivatives showed moderate to potent
antiviral activity. Only the L-5-fluorocytosine derivative
35 showed marginal cytotoxicity (IC50 ) 88.1 µM) in
Vero cell, whereas no other compounds showed any
significant cytotoxicity up to 100 µM. Like L-â-3′Fd4N
nucleosides,9 there was a general trend of antiviral
activity throughout the series, in which the cytosine and
5-fluorocytosine derivatives exhibited the most potent
anti-HIV activity, which suggests that the two types of
nucleosides may have similar structural features and
can be recognized by the cellular kinases as well as viral
polymerases. However, the synthesized D-2′,3′-unsatur-
ated 3′-fluoro-4′-thionucleosides did not show any sig-
nificant antiviral activity against HIV-1. Only D-gua-
nosine analogue 46 showed marginal anti-HIV activity
(EC50 ) 23.4 µM) (vide infra for molecular modeling
studies)
An tivir a l Activity a ga in st La m ivu d in e-Resista n t
(HIV-1M184V) Mu ta n t Str a in . Treatment with 3TC
[lamivudine, (-)-â-2′,3′-dideoxy-3′-thiacytidine] rapidly
induces resistance in HIV-infected individuals. The
resistant isolates showed reduced susceptibility to lami-
vudine, and genotypic analysis showed that the resis-
tance was due to specific substitution mutation in HIV-1
RT at codon 184 within the YMDD motif.17 Therefore,
recent studies on anti-HIV nucleoside analogues have
been focused on the discovery of new drug candidates
active against the drug-resistant HIV strains, which
resulted in the recent approval of tenoforvir disoproxil
by the FDA.18 To access the anti-HIV activity, the most
potent compounds from our studies, the cytosine 34 and
5-fluorocytosine 35 derivatives along with two positive
controls AZT and 3TC, were evaluated against the
lamivudine-resistant mutant strain (HIV-1M184V) in
human PBM cells in vitro (Table 2). The results
indicated that both cytosine 34 and 5-fluorocytosine 35
derivatives are not active against 3TC-resistant mutant
(M184V) while AZT is still active against the mutant.
Molecular modeling studies were conducted to explain

Thionucleosides as Anti-HIV Agents
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 7 1635
F igu r e 1. (a) L-3′F-4′Sd4CTP binds to the active site of HIV-1 RT without significant unfavorable steric hindrance with the
adjacent enzyme residues, particularly Met184. 3′-F is hydrogen-bonded to the -NH backbone of Asp185. (b) L-3′F-4′Sd4CTP
experiences strong steric hindrance with the bulky side chain of Val184 in M184V RT. (c) Negatively charged 3′-fluorine and
â-phosphate moieties (2.7 Å apart) strongly repulse each other to force a conformational change in the sugar moiety, but the
possible steric hindrance between the bulky 4′-sulfur atom of the sugar and Met184 does not allow the sugar moiety to escape
from the unfavorable electrostatic interaction. Rather, the minimized structure of D-3′-F-4′-Sd4CTP complexed with HIV-1 RT
shows a disrupted base-pairing with the complementary base in the template strand.
not allow the sugar moiety to escape from the unfavor-
able electrostatic interaction. Rather, the minimized
structure of D-3′F-4′Sd4CTP complexed with HIV-1 RT
shows a disrupted base-pairing with the complementary
base in the template strand (Figure 1c). Therefore,
under the assumption that D-3′F-4′Sd4C is phosphoryl-
ated to the corresponding triphosphate with the same
efficiency as its L-congener, our molecular modeling
study demonstrates that the repulsive electrostatic
interaction between the 3′-fluorine atom and the triph-
osphate moiety distorts the binding mode of D-3′F-
4′Sd4CTP to result in the loss of its binding affinity to
HIV-1 RT and thereby its inactivity against HIV-1.
In summary, various D- and L-3′F-4′Sd4 nucleosides
were prepared and their anti-HIV activity was evalu-
ated. Among the synthesized L-nucleosides, L-cytosine
(34, EC50 ) 0.13 µM) and L-5-fluorocytosine (35, EC50
) 0.031 µM) derivatives showed potent anti-HIV activity
against the wild-type HIV-1 RT. However, they failed
to show antiviral activity against the 3TC-resistant
mutant (M184V) RT. The synthesized D-isomers did not
show any significant anti-HIV activity presumably
because of the decreased binding affinity of the corre-
sponding triphosphates caused by the unfavorable
electrostatic interaction between the 3′-fluorine and its
own triphosphate moiety, resulting in the distruption
of the base-pairing.
Exp er im en ta l Section
Melting points were determined on a Mel-temp II apparatus
and were uncorrected. Nuclear magnetic resonance spectra
were recorded on a Bruker 400 AMX spectrometer at 400 MHz
for 1H NMR and at 100 MHz for 13C NMR with tetramethyl-
silane as the internal standard. Chemical shifts (δ) are
reported in parts per million (ppm), and signals are reported
as s (singlet), d (doublet), t (triplet), q (quartet), m (multiplet),
or br (broad singlet). UV spectra were recorded on a Beckman
DU-650 spectrophotometer. Optical rotations were measured
on a J asco DIP-370 digital polarimeter. Mass spectra were
recorded on
a Micromass Autospec high-resolution mass
spectrometer. TLC was performed on Uniplates (silica gel)
purchased from Analtech Co. Silica gel G (TLC grade, >440
mesh) was used for vacuum column chromatography as well
as for flash column chromatography. Elemental analyses were
performed by Atlantic Microlab Inc., Norcross, GA.
Meth yl-2-d eoxy-5-O-tolu oyl-D-fu r a n -3-u lose (3). Pyri-
dinium dichromate (159 g, 0.42 mol) and powder molecular
sieves (4 Å, 150 g) were added to a solution of 2 (75 g, 0.30
mol) in dry dichloromethane (1.5 L), and the mixture was
mechanically stirred at room temperature for 4 h. The suspen-

1636 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 7
Zhu et al.
1
sion was then filtered through a silica gel pad (eluting with
EtOAc). After concentration, the resulting residue was purified
by silica gel column chromatography (hexanes/EtOAc, 20:1 to
10:1) to give the ketone 3 (57 g, 0.22 mol, 73% yield) as a
colorless syrup: Rf ) 0.59 (hexanes/EtOAc, 3:1); 1H NMR
(CDCl3) δ 7.97-7.23 (m, 4H, Ar-H), 5.38 (m, 1H, H-1), 4.80-
4.28 (m, 3H, H-4, H-5), 3.49, 3.38 (2 × s, 3H, OCH3), 2.88-
2.49 (m, 2H, H-2), 2.41 (s, 3H, PhCH3). Anal. (C14H16O5) C, H.
(hexanes/EtOAc, 5:1); H NMR (CDCl3) δ 7.94-7.20 (m, 4H,
Ar-H), 6.07-6.00 (m, 1H, H-1), 4.68-4.03 (m, 3H, H-4, H-5),
2.87-2.71 (m, 2H, H-2), 2.37 (s, 3H, PhCH3), 2.06, 2.01 (2 ×
s, 3H, OAc). Anal. (C15H16F2O2S) C, H.
1-[(1S,4S)-2,3-Did eoxy-3,3-d iflu or o-4-th io- 5-O-tolu oyl-
r/â-L-r ibofu r a n osyl]u r a cil (9). N,O-Bis(trimethylsilyl)ac-
etamide (BSA, 4.4 mL, 18 mmol) was added at room temper-
ature to a mixture of compound 8 (1.65 g, 4.99 mmol) and
uracil (730 mg, 6.5 mmol) in anhydrous acetonitrile (40 mL),
and the resulting mixture was stirred under argon for 2 h at
50-60 °C to form a clear solution. After cooling to room
temperature, TMSOTf (1 mL, 5.5 mmol) was added and the
mixture was refluxed for 3 h under argon atmosphere. The
reaction mixture was cooled to room temperature and subse-
quently quenched with saturated aqueous NaHCO3 solution
(20 mL) and stirred until the evolution of CO2 ceased. The
resulting mixture was diluted with EtOAc (150 mL), washed
with brine (2 × 100 mL), dried over Na2SO4, filtered, and
concentrated. The residue was purified by silica gel column
chromatography (CH2Cl2/MeOH, 30:1) to give compound 9 (R/â
) 1, 1.28 g, 3.35 mmol, 67% yield) as a white foam: Rf ) 0.56
1-O-Meth yl-2,3-dideoxy-3,3-diflu or o-5-O-tolu oyl-D-fu r a-
n osid e (4). DAST (75 mL, 0.57 mol) was added to a solution
of ketone 3 (50 g, 0.19 mol) in CH2Cl2 (500 mL). The mixture
was stirred under N2 at room temperature for 24 h. The
reaction mixture was poured into cold saturated aqueous
NaCO3 solution (1 L) and extracted with CH2Cl2 (3 × 500 mL).
The organic layer was dried over Na2SO4, filtered, and
evaporated. The remaining residue was purified by silica gel
column chromatography (hexanes/EtOAc, 20:1 to 10:1) to give
compound 4 (30 g, 0.105 mol, 55% yield) as a colorless syrup
and recycle starting material 3 (15 g, 0.057 mol): Rf ) 0.75
1
(hexanes/EtOAc, 3:1); H NMR (CDCl3) δ 7.90-7.18 (m, 4H,
Ar-H), 5.10 (m, 1H, H-1), 4.54-4.29 (m, 3H, H-4, H-5), 3.31,
3.29 (2 × s, 3H, OCH3), 2.67-2.21 (m, 2H, H-2), 2.30 (s, 3H,
PhCH3). Anal. (C14H16F2O4) C, H.
1
(CH2Cl2/MeOH, 15:1); H NMR (CDCl3) δ 8.58 (br, 1H, NH),
7.93-7.29 (m, 5H, H-6 and Ar-H), 6.34-6.28 (m, 1H, H-1′),
5.85-5.63(m, 1H, H-5), 4.82-4.47 (m, 2H, H-5′), 4.26-4.06 (m,
1H, H-4′), 3.09-2.59 (m, 2H, H-2′), 2.44 (s, 3H, PhCH3). Anal.
(C17H16F2N2O4S) C, H, N.
2,3-Did eoxy-3,3-d iflu or o-5-O-tolu oyl-D-r ibose Diben zyl
Dith ioa ceta l (5). Benzyl mercaptan (47 mL, 0.4 mol) was
added to a solution of compound 4 (28.7 g, 0.100 mol) and boron
trifluoride etherate (6.3 mL, 0.05 mol) in CH2Cl2 (200 mL),
and the mixture was stirred at 40 °C for 2 h. The mixture was
diluted with saturated aqueous NaHCO3 solution (150 mL) and
extracted with CH2Cl2 (100 mL). The organic layer was
dissolved in EtOAc (300 mL), washed with brine (200 mL),
dried over Na2SO4, filtered, and evaporated. The residue was
purified by silica gel column chromatography to give dithio-
1-[(1S,4S)-2,3-Did eoxy-3,3-d iflu or o-4-th io-5-O-tolu oyl-
r/â-L-r ibofu r a n osyl]th ym in e (10). By use of the same
procedure as above, compound 8 (1.65 g, 4.99 mmol) was
condensed with thymine (820 mg, 6.5 mmol) to produce
compound 10 (R/â ) 1, 1.4 g, 3.53 mmol, 71% yield) as a white
foam: Rf ) 0.63 (CH2Cl2/MeOH, 15:1). 1H NMR (CDCl3) δ
10.34, 10.31 (2 × s, 1H, NH), 7.91-7.20 (m, 5H, H-6 and Ar-
H), 6.36 (m, 1H, H-1′), 4.78-4.00 (m, 3H, H-4′, H-5′), 3.03-
2.55 (m, 2H, H-2′), 2.39 (s, 3H, PhCH3), 1.94, 1.68 (2 × s, 3H,
5-CH3). Anal. (C18H18F2N2O4S) C, H, N.
1-[(1S,4S)-2,3-Did eoxy-3,3-d iflu or o-4-th io-5-O-tolu oyl-
â-L-r ibofu r an osyl)-N4-isobu tylcytosin e (11) an d 1-[(1S,4S)-
2,3-Did eoxy-3,3-d iflu or o-4-th io-5-O-tolu oyl-r-L-r ibofu r a -
n osyl]-N4-isobu tylcytosin e (12). By use of the same procedure
as described for compound 9, compound 8 (1.65 g, 4.99 mmol)
was condensed with N4-isobutyrylcytosine (1.2 g, 6.6 mmol)
to give compound 11 (â anomer, 0.74 g, 1.64 mmol, 33% yield)
and compound 12 (R anomer, 0.79 g, 1.75 mmol, 35% yield) as
white foams.
acetal 5 (47 g, 0.094 mol, 94% yield) as a colorless syrup: Rf
1
) 0.70 (hexanes/EtOAc, 3:1); [R]22 +15.4 (c 2.9, CH2Cl2); H
D
NMR (CDCl3) δ 7.94-7.04 (m, 14H, Ar-H), 4.44 (dd, J ) 11.9,
2.5 Hz, 1H, H-5a), 4.35 (dd, J ) 11.9, 7.0 Hz, 1H, H-5b), 3.84-
3.70 (m, 6H, H-1, H-4, 2 × CH2Ph), 2.93 (d, J ) 6.0 Hz, 1H,
OH), 2.68-2.42 (m, 5H, H-2, PhCH3); MS (ESI) m/z 503 (MH+).
Anal. (C27H28F2O3S2) C, H.
Ben zyl-2,3-d id eoxy-3,3-d iflu or o-1,4-d ith io-5-O-tolu oyl-
L-fu r a n osid e (7). Trifluoromethanesulfonic anhydride (18 mL,
108 mmol) was slowly added to a solution of compound 5 (45
g, 90 mmol) and 2,6-lutidine (16.3 mL, 140 mmol) in CH2Cl2
(200 mL) over 10 min at -10 °C. After being stirred for an
additional 45 min at 0 °C, the reaction mixture was quenched
by adding MeOH (10 mL). After removal of the solvents, the
residue was purified by vacuum silica gel column chromatog-
raphy to afford compound 6 (50 g, Rf ) 0.59 (hexanes/EtOAc,
5:1)) as a colorless syrup, which was dissolved in anhydrous
acetonitrile (200 mL). BaCO3 (23 g, 118 mmol) and n-TBAI
(44 g, 118 mmol) were added, and the mixture was stirred for
3 h at 50-60 °C. After cooling to room temperature, the
reaction mixture was filtered and concentrated to give a
residue, which was participated between water and EtOAc.
After phase separation, the organic phase was dried over Na2-
SO4, filtered, concentrated, and purified by vacuum silica gel
column chromatography to afford compound 7 (27.6 g, 70
mmol, 78% yield from compound 5) as a colorless syrup: Rf )
Com p ou n d 11: Rf ) 0.33 (hexanes/EtOAc, 1:2); [R]23D -57.9
(c 1, CHCl3); 1H NMR (CDCl3) δ 9.03 (s, 1H, NH), 8.36 (d, J )
7.5 Hz, 1H, H-6), 7.89 (d, J ) 8.2 Hz, 2H, Ar-H), 7.41 (d, J )
7.5 Hz, 1H, H-5), 7.23 (d, J ) 8.2 Hz, 2H, Ar-H), 6.31 (dd, J
) 7.4, 3.3 Hz, 1H, H-1′), 4.79 (dd, J ) 11.8, 6.1 Hz, 1H, H-5a′),
4.63 (dd, J ) 11.8, 4.1 Hz, 1H, H-5b′), 4.09 (m, 1H, H-4′), 3.17-
2.65 (m, 3H, H-2′ and C(O)CHMe2), 2.40 (s, 3H, ArCH3), 1.19
(d, J ) 4.2 Hz, 6H, 2 × CH3). Anal. (C21H23F2N3O4S) C, H, N.
Com p ou n d 12: Rf ) 0.45 (hexanes/EtOAc, 1:2); [R]24D -46.8
(c 1, CHCl3); 1H NMR (CDCl3) δ 9.00 (s, 1H, NH), 8.31 (d, J )
7.5 Hz, 1H, H-6), 7.89 (d, J ) 8.1 Hz, 2H, Ar-H), 7.51 (d, J )
7.5 Hz, 1H, H-5), 7.24 (d, J ) 8.1 Hz, 2H, Ar-H), 6.31 (dd, J
) 7.5, 3.3 Hz, 1H, H-1′), 4.66 (dd, J ) 11.8, 5.7 Hz, 1H, H-5a′),
4.46 (dd, J ) 11.8, 6.1 Hz, 1H, H-5b′), 4.25 (m, 1H, H-4′), 3.10-
2.66 (m, 3H, H-2′ and C(O)CHMe2), 2.40 (s, 3H, ArCH3), 1.19
(d, J ) 4.2 Hz, 6H, 2 × CH3). Anal. (C21H23F2N3O4S) C, H, N.
1-[(1S,4S)-2,3-Did eoxy-3,3-d iflu or o-4-th io-5-O-tolu oyl-
â-L-r ibofu r a n osyl]-N4-ben zoyl-5-flu or ocytosin e (13) a n d
1-[(1S,4S)-2,3-Did eoxy-3,3-d iflu or o-4-th io-5-O-tolu oyl-r-
L-r ibofu r a n osyl)-N4-ben zoyl-5-flu or ocytosin e (14). By use
of the same procedure as described for compound 9, compound
8 (1.65 g, 4.99 mmol) was condensed with N4-benzoyl-5-
fluorocytosine (1.54 g, 6.6 mmol) to give compound 13 (â
anomer, 0.81 g, 1.61 mmol, 32% yield) and compound 14 (R
anomer, 0.83 g, 1.65 mmol, 33% yield) as white solids.
Com p ou n d 13: Rf ) 0.58 (hexanes/EtOAc, 1:1); mp 134-
1
0.66 (hexanes/EtOAc, 5:1); H NMR (CDCl3) δ 7.97-7.22 (m,
9H, Ar-H), 4.63-3.82 (m, 6H, H-1, H-4, H-5, CH2Ph), 2.49-
2.40 (m, 5H, H-2, PhCH3); MS (ESI) m/z 259 (M-OCOPhMe).
Anal. (C20H20F2O2S2) C, H.
1-O-Acetyl-2,3-d id eoxy-3,3-d iflu or o-4-th io-5-O-tolu oyl-
L-fu r a n ose (8). Compound 7 (25 g, 63.4 mmol) was treated
with a mixture of acetic acid (80 mL), acetic anhydride (20
mL), and mercuric acetate (30 g, 94 mmol) at room tempera-
ture for 24 h. The mixture was filtered through a Celite pad,
and the filtrate was diluted with EtOAc, which was washed
sequentially with water, saturated aqueous NaHCO3 solution,
and 5% NaCN aqueous solution, dried over Na2SO4, and
concentrated. Column chromatography of the crude product
in hexanes/EtOAc (30:1 to 10:1) gave the key intermediate 8
(15 g, 45.6 mmol, 72% yield) as a colorless syrup: Rf ) 0.46
136 °C; [R]25 -32.2 (c 1.7, CH2Cl2); 1H NMR (CDCl3) δ 13.07
(br, 1H, NH), 8.31-7.27 (m, 10H, H-6 and Ar-H), 6.28 (m,
1H, H-1′), 4.81 (dd, J ) 11.9, 5.8 Hz, 1H, H-5a′), 4.67 (dd, J )
D

Thionucleosides as Anti-HIV Agents
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 7 1637
11.9, 6.5 Hz, 1H, H-5b′), 4.13 (m, 1H, H-4′), 3.05-2.67 (m, 2H,
H-2′), 2.43 (s, 3H, ArCH3). Anal. (C24H20F3N3O4S) C, H, N.
silica gel column chromatography with 9% MeOH in CH2Cl2
to give 22 (372 mg, 1.32 mmol, 90% yield) as a white foam: Rf
) 0.32 (CH2Cl2/MeOH, 5:1); [R]24 -103.7 (c 1, MeOH); UV
Com p ou n d 14: Rf ) 0.79 (hexanes/EtOAc, 1:1); mp 95-97
D
1
°C; [R]24 -70.3 (c 0.8, CH2Cl2); H NMR (CDCl3) δ 13.06 (br,
(MeOH) λmax ) 241 nm (ꢀ ) 6886), 283 nm (ꢀ ) 5896); MS
D
(ESI) m/z 282 (MH+). Anal. (C9H10F3N3O2S‚0.2H2O) C, H, N.
1H, NH), 8.44-7.26 (m, 10H, H-6 and Ar-H), 6.31 (m, 1H,
H-1′), 4.66 (dd, J ) 11.7, 5.5 Hz, 1H, H-5a′), 4.48 (dd, J ) 11.7,
5.8 Hz, 1H, H-5b′), 4.24 (m, 1H, H-4′), 3.11-2.66 (m, 2H, H-2′),
2.42 (s, 3H, ArCH3). Anal. (C24H20F3N3O4S) C, H, N.
1-[(1S,4S)-2,3-Did eoxy-3,3-d iflu or o-4-th io-â-L-r ibofu r a -
n osyl]u r a cil (15) a n d 1-[(1S,4S)-2,3-Deoxy-3,3-d iflu or o-
4-th io-r-L-r ibofu r a n osyl]u r a cil (16). Compound 9 (R/â)
(1.15 g, 3.01 mmol) was treated with saturated methanolic
ammonia solution (20 mL) at room temperature for 8 h. Upon
completion of the reaction, the solvent was removed under
reduced pressure. The resulting syrup was purified by column
chromatography on silica gel (CH2Cl2/MeOH, 50:1) to afford
pure compound 15 (â anomer, 350 mg, 1.32 mmol, 44% yield)
and compound 16 (R anomer, 363 mg, 1.37 mmol, 46% yield)
in 90% overall yield.
6-Ch lor o-9-[(1S,4S)-2,3-d id eoxy-3,3-d iflu or o-5-O-t olu -
oyl-4-th io-r/â-L-r ibofu r a n osyl]p u r in e (23). By use of the
same procedure as described for compound 9, compound 8 (3.3
g, 10 mmol) was condensed with 6-chloropurine (2.0 g, 13
mmol) for 24 h to obtain compound 23 (2.4 g, 5.6 mmol, 56%
yield) as a white foam: 1H NMR (CDCl3) δ 8.74, 8.71 (2 × s,
1H, H-2), 8.50 (s, 1H, H-8), 7.90-7.20 (m, 4H, Ar-H), 6.32
(m, 1H, H-1′), 4.84-4.20 (m, 3H, H-4′, H-5′), 3.20-3.14 (m,
2H, H-2′), 2.39, 2.38 (2 × s, 3H, ArCH3). Anal. (C18H15
-
ClF2N4O2S) C, H, N.
2-Am in o-6-ch lor o-9-[(1S,4S)-2,3-d id eoxy-3,3-d iflu or o-5-
O-tolu oyl-4-th io-r/â-L-r ibofu r a n osyl]p u r in e (24). By use
of the same procedure as described for compound 9, compound
8 (3.3 g, 10 mmol) was condensed with 2-amino-6-chloropurine
(2.2 g, 13 mmol) in anhydrous 1,4-dioxane (60 mL) for 12 h at
100 °C to produce compound 24 (1.76 g, 4.00 mmol, 40% yield)
as a white foam: 1H NMR (CDCl3) δ 8.09, 7.95 (2 × s, 1H,
H-8), 7.92-7.22 (m, 4H, Ar-H), 6.13, 6.03 (m, 1H, H-1′), 5.40,
5.17 (2 × br, 2H, NH2), 5.07-4.47 (m, 3H, H-4′, H-5′), 3.42-
Com p ou n d 15: Rf ) 0.58 (CH2Cl2/MeOH, 9:1); mp 210-
212 °C; [R]22 +25.4 (c 0.3, MeOH); UV (MeOH) λmax ) 262
D
nm (ꢀ ) 10 805); MS (ESI) m/z 265 (MH+). Anal. (C9H10F2N2O3S)
C, H, N.
Com p ou n d 16: Rf ) 0.55 (CH2Cl2/MeOH, 9:1); foam; [R]24
D
-117.3 (c 0.3, MeOH); UV (MeOH) λmax ) 262 nm (ꢀ ) 10 487);
MS (ESI) m/z 265 (MH+). Anal. (C9H10F2N2O3S) C, H, N.
1-[(1S,4S)-2,3-Did eoxy-3,3-d iflu or o-4-th io-â-L-r ibofu r a -
n osyl]th ym in e (17) a n d 1-[(1S,4S)-2,3-Did eoxy-3,3-d if-
lu or o-4-th io-r-L-r ibofu r a n osyl]th ym in e (18). Conversion
of 10 (R/â) (1.20 g, 3.03 mmol) to 17/18 was accomplished using
the same procedure as described above. The resulting syrup
was purified on a silica gel column (CH2Cl2/MeOH, 50:1) to
afford pure compound 17 (â anomer, 370 mg, 1.33 mmol, 44%
yield) and compound 18 (R anomer, 380 mg, 1.37 mmol, 45%
yield) as white solids in 90% overall yield.
3.05 (m, 2H, H-2′), 2.40, 2.39 (2 × s, 3H, ArCH3). Anal. (C18H16
-
ClF2N5O2S) C, H, N.
9-[(1S,4S)-2,3-Did eoxy-3,3-d iflu or o-4-t h io-â-L-fu r a n o-
syl]a d en in e (25) a n d 9-[(1S,4S)-2,3-Did eoxy-3,3-d iflu or o-
4-th io-r-L-r ibofu r a n osyl]a d en in e (26). A solution of 23 (1.0
g, 2.35 mmol) in methanolic ammonia (60 mL) was heated at
100 °C for 24 h in a steel bomb. After the mixture was cooled,
the solvent was removed under reduced pressure and the
residue was purified by a silica gel column chromatography
(1% MeOH in CH2Cl2) to yield 25 (â anomer, 280 mg, 0.975
mmol, 41% yield) and 26 (R anomer, 290 mg, 1.01 mmol, 43%
yield) as white solids with 84% overall yield.
Com p ou n d 17: Rf ) 0.25 (CH2Cl2/MeOH, 15:1); mp 151-
153 °C; [R]25 +16.5 (c 2.2, MeOH); UV (MeOH) λmax ) 268
D
Com p ou n d 25: Rf ) 0.43 (CH2Cl2/MeOH, 10:1); mp >200
nm (ꢀ ) 8500); MS (ESI) m/z 279 (MH+). Anal. (C10H12F2N2O3S‚
°C; [R]23 +13.5 (c 0.5, MeOH); UV (MeOH) λmax ) 259.5 nm
D
0.9H2O) C, H, N.
(ꢀ ) 9300); MS (ESI) m/z 288 (MH+). Anal. (C10H11F2N5OS) C,
Com p ou n d 18: Rf ) 0.17 (CH2Cl2/MeOH, 15:1); mp 124-
H, N.
126 °C; [R]26 -90.4 (c 1.8, MeOH); UV (MeOH) λmax ) 267.5
D
Com p ou n d 26: Rf ) 0.33 (CH2Cl2/MeOH, 10:1); mp 187-
nm (ꢀ ) 8400); MS (ESI) m/z 279 (MH+). Anal. (C10H12F2N2O3S‚
191 °C; [R]24 -83.7 (c 0.5, MeOH); UV (MeOH) λmax ) 260
D
0.9H2O) C, H, N.
nm (ꢀ ) 8930); MS (ESI) m/z 288 (MH+). Anal. (C10H11F2N5-
1-[(1S,4S)-2,3-Did eoxy-3,3-d iflu or o-4-th io-â-L-r ibofu r a -
n osyl]cytosin e (19). Conversion of 11 (690 mg, 1.53 mol) to
19 was accomplished using the same procedure as described
for 15/16. The obtained residue was purified by flash silica
gel column chromatography with 9% MeOH in CH2Cl2 to give
19 (343 mg, 1.30 mmol, 85% yield) as a white solid: Rf ) 0.15
OS) C, H, N.
9-[(1S,4S)-2,3-Did eoxy-3,3-d iflu or o-4-th io-â-L-r ibofu r a -
n osyl]h yp oxa n th in e (27) a n d 9-[(1S,4S)-2,3-Did eoxy-3,3-
d iflu or o-4-th io-r-L-fu r a n osyl]h yp oxa n th in e (28). To a
solution of 23 (1.1 g, 2.59 mmol) in MeOH (20 mL), NaOCH3
(840 mg) and 2-mercaptoethanol (900 mg) were added. The
mixture was refluxed for 12 h, and the solvent was removed
under reduced pressure. The syrupy residue was purified by
silica gel column chromatography (3% MeOH in CH2Cl2) to
yield 27 (â anomer, 295 mg, 1.02 mmol, 39% yield) and
compound 28 (R anomer, 300 mg, 1.04 mmol, 40% yield) as
white solids in 80% overall yield.
(CH2Cl2/MeOH, 10:1); mp >200 °C; [R]23 +35.5 (c 1, MeOH);
D
UV (MeOH) λmax ) 273.5 nm (ꢀ ) 8057); MS (ESI) m/z 264
(MH+). Anal. (C9H11F2N3O2S) C, H, N.
1-[(1S,4S)-2,3-Did eoxy-3,3-d iflu or o-4-th io-r-L-r ibofu r a -
n osyl]cytosin e (20). Conversion of 12 (750 mg, 1.66 mmol)
to 20 was accomplished using the same procedure as described
for 15/16. The obtained residue was purified by a flash silica
gel column chromatography with 9% MeOH in CH2Cl2 to give
20 (379 mg, 1.44 mmol, 87% yield) as a white solid: Rf ) 0.15
Com p ou n d 27: Rf ) 0.71 (CH2Cl2/MeOH, 3:1); mp >200
°C; [R]24 +19.7 (c 0.25, MeOH); UV (MeOH) λmax ) 246.5 nm
D
(ꢀ ) 14 219); MS (ESI) m/z 289 (MH+). Anal. (C10H10F2N4O2S)
(CH2Cl2/MeOH, 10:1); mp 198-201 °C; [R]24 -118.8 (c 0.9,
D
C, H, N.
MeOH); UV (MeOH) λmax ) 273 nm (ꢀ ) 7101); MS (ESI) m/z
264 (MH+). Anal. (C9H11F2N3O2S) C, H, N.
Com p ou n d 28: Rf ) 0.57 (CH2Cl2/MeOH, 3:1); mp >200
°C; [R]23 -111.8 (c 0.14, MeOH); UV (MeOH) λmax ) 247 nm
D
1-[(1S,4S)-2,3-Did eoxy-3,3-d iflu or o-4-th io-â-L-r ibofu r a -
n osyl)-5-flu or ocytosin e (21). Conversion of 13 (740 mg, 1.47
mmol) to 21 was accomplished using the same procedure as
described for 15/16. The obtained residue was purified by flash
silica gel column chromatography with 9% MeOH in CH2Cl2
to give 21 (364 mg, 1.29 mmol, 88% yield) as a white foam: Rf
(ꢀ ) 10 912); MS (ESI) m/z 289 (MH+). Anal. (C10H10F2N4O2S)
C, H, N.
2-Am in o-6-ch lor o-9-[(1S,4S)-2,3-d id eoxy-3,3-d iflu or o-4-
th io-â-L-r ibofu r a n osyl]p u r in e (29) a n d 2-Am in o-6-ch lor o-
9-[(1S,4S)-2,3-d id eoxy-3,3-d iflu or o-4-th io-r-L-r ibofu r a n o-
syl]p u r in e (30). Conversion of 24 (1.5 g, 3.41 mmol) to 29/30
was performed using the same procedure as described for 15/
16. The obtained residue was purified by flash silica gel column
chromatography with 9% MeOH in CH2Cl2 to afford pure
compound 29 (â anomer, 475 mg, 1.47 mmol, 43% yield) and
compound 30 (R anomer, 480 mg, 1.49 mmol, 44% yield) as
white solids in 87% overall yield.
) 0.32 (CH2Cl2/MeOH, 5:1); [R]24 +21.4 (c 0.5, MeOH); UV
D
(MeOH) λmax ) 242 nm (ꢀ ) 7281), 283 nm (ꢀ ) 6362); MS
(ESI) m/z 282 (MH+). Anal. (C9H10F3N3O2S) C, H, N.
1-[(1S,4S)-2,3-Did eoxy-3,3-d iflu or o-4-th io-r-L-r ibofu r a -
n osyl]-5-flu or ocytosin e (22). Conversion of 14 (740 mg, 1.47
mmol) to 22 was accomplished using the same procedure as
described for 15/16. The obtained residue was purified by flash

1638 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 7
Com p ou n d 29: Rf ) 0.25 (CH2Cl2/MeOH, 15:1); mp >200
Zhu et al.
(-)-1-[(1R,4R)-2,3-Did eoxy-2,3-d id eh yd r o-3-flu or o-4-
°C; [R]24 +18.6 (c 0.5, MeOH); UV (MeOH) λmax ) 309.5 nm
th io-â-D-r ibofu r a n osyl]cytosin e (42): mp 182-190 °C; [R]22
D
D
(ꢀ ) 9430). Anal. (C10H10ClF2N5OS) C, H, N.
-230.5° (c 0.17, MeOH); UV λmax ) 276.0 nm (ꢀ ) 11 990) (pH
2), 267.5 nm (ꢀ ) 8010) (pH 7), 264.5 nm (ꢀ ) 8060) (pH 11).
Anal. (C9H10FN3O2S‚0.4H2O) C, H, N.
Com p ou n d 30: Rf ) 0.17 (CH2Cl2/MeOH, 15:1); mp 183-
185 °C; [R]25 -74.2 (c 1.5, MeOH); UV (MeOH) λmax ) 309.5
D
nm (ꢀ ) 9169). Anal. (C10H10ClF2N5OS) C, H, N.
(-)-1-[(1R,4R)-2,3-Did eoxy-2,3-d id eh yd r o-3-flu or o-4-
th io-â-D-r ibofu r a n osyl]-5-flu or ocytosin e (43): mp 172-174
°C; [R]25D -228.4° (c 0.14, CH3OH); UV (H2O) λmax ) 292.0 nm
(ꢀ ) 10 178, pH 2), 283.0 nm (ꢀ ) 7192, pH 7), 283.0 nm (ꢀ )
6290, pH 11). Anal. (C9H9F2N3O2S) C, H, N.
9-[(1S,4S)-2,3-Did eoxy-3,3-d iflu or o-4-th io-â-L-r ibofu r a -
n osyl]gu a n in e (31). To a solution of 29 (400 mg, 1.24 mmol)
in MeOH (20 mL), NaOCH3 (420 mg) and 2-mercaptoethanol
(450 mg) were added. The mixture was refluxed for 12 h, and
the solvent was removed under reduced pressure. The syrupy
residue was purified by silica gel column chromatography with
3% MeOH in CH2Cl2 to yield 31 (226 mg, 0.745 mmol, 60%
yield) as a white solid: Rf ) 0.71 (CH2Cl2/MeOH, 3:1); mp >200
(-)-9-[(1R,4R)-2,3-Did eoxy-2,3-d id eh yd r o-3-flu or o-4-
th io-â-D-r ibofu r a n osyl]a d en in e (44): mp >200 °C; [R]22
D
-34.6° (c 0.10, CH3OH); UV (H2O) λmax ) 260.0 nm (ꢀ ) 10 497,
pH 2), 259.5 nm (ꢀ ) 7322, pH 7), 259.0 nm (ꢀ ) 11 275, pH
11). Anal. (C10H10FN5OS) C, H, N.
°C; [R]25 -8.5 (c 0.3, MeOH); UV (MeOH) λmax ) 255.5 nm (ꢀ
D
) 10 105); MS (ESI) m/z 304 (MH+). Anal. (C10H11F2N5O2S‚
(-)-9-[(1R,4R)-2,3-Did eoxy-2,3-d id eh yd r o-3-flu or o-4-
th io-â-D-r ibofu r a n osyl]h yp oxa n th in e (45): mp >200 °C;
1.4H2O) C, H, N.
[R]23 -27.7° (c 0.10, CH3OH); UV (H2O) λmax ) 244.0 nm (ꢀ )
Gen er a l P r oced u r e for Elim in a tion Rea ction s. â-Dif-
luoronucleosides (15, 17, 19, 21, 25, 27, and 31) were sus-
pended or dissolved in anhydrous THF, and then 2-3 equiv
of 1 M potassium tert-butoxide solution in THF was added at
0 °C. After being stirred at 0 °C for 12 h, the slurry suspension
was quenched by adding MeOH. After removal of the solvent
under reduced pressure, the residue was purified by silica gel
column chromatography with 8% MeOH in CH2Cl2. The whole
process was repeated several times to get the pure final
compounds (32-38) in 30-40% yield.
D
24 252, pH 2), 249.0 nm (ꢀ ) 21 430, pH 7), 253.5 nm (ꢀ )
22 487, pH 11). Anal. (C10H9FN4O2S) C, H, N.
(-)-9-[(1R,4R)-2,3-Did eoxy-2,3-d id eh yd r o-3-flu or o-4-
t h io-â-D-r ibofu r a n osyl]gu a n in e (46): mp >220 °C; [R]24
D
-66.9° (c 0.06, CH3OH); UV (H2O) λmax ) 248.5 nm (ꢀ ) 18 111,
pH 2), 251.5 nm (ꢀ ) 17 481, pH 7), 260.0 nm (ꢀ ) 19 537, pH
11). Anal. (C10H10FN5O2S) C, H, N.
An tivir a l Assa y. Human peripheral blood mononuclear
(PBM) cells (obtained from Atlanta Red Cross) were isolated
by Ficoll-Hypaque discontinuous gradient centrifugation from
healthy seronegative donors. Cells were stimulated with
phytohemagglutinin A (Difco, Sparks, MD) for 2-3 days prior
to use. HIV-1LAI obtained from the Centers for Disease Control
and Prevention (Atlanta, GA) was used as the standard
reference virus for the antiviral assays. The molecular infec-
tious clones HIV-1xxBru and HIV-1M184Vpitt were obtained from
Dr. J ohn Mellors (University of Pittsburgh). Infections were
done in bulk for 1 h, either with 100 TCID50/1 × 107 cells for
a flask (T25) assay or with 200 TCID50/6 × 105 cells per well
for a 24-well plate assay. Cells were added to a plate or flask
containing a 10-fold serial dilution of the test compound. Assay
medium was RPMI-1640 supplemented with heat inactivated
16% fetal bovine serum, 1.6 mM L-glutamine, 80 IU/mL
penicillin, 80 µg/mL streptomycin, 0.0008% DEAE-dextran,
0.045% sodium bicarbonate, and 26 IU/mL recombinant in-
terleukin-2 (Chiron Corp, Emeryville, CA). AZT was used as
a positive control for the assay. Untreated and uninfected PBM
cells were grown in parallel at equivalent cell concentrations
as controls. The cell cultures were maintained in humidified
5% CO2-air at 37 °C for 5 days, and supernatants were
collected for reverse transcriptase (RT) activity.
(+)-1-[(1S,4S)-2,3-Did eoxy-2,3-d id eoxy-3-flu or o-4-th io-
â-L-r ibofu r a n osyl]u r a cil (32): foam; [R]22 +135.0 (c 0.1,
D
MeOH); UV (MeOH) λmax ) 263.5 nm (ꢀ ) 9357); MS (ESI)
m/z 245 (MH+). Anal. (C9H9FN2O3S) C, H, N.
(+)-1-[(1S,4S)-2,3-Dideoxy-2,3-dideh ydr o-3-flu or o-4-th io-
â-L-r ibofu r a n osyl]th ym in e (33): mp 195-197 °C; [R]23
D
+77.3 (c 0.4, MeOH); UV (MeOH) λmax ) 269 nm (ꢀ ) 7025);
MS (ESI) m/z 259 (MH+). Anal. (C10H11FN2O3S) C, H, N.
(+)-1-[(1S,4S)-2,3-Dideoxy-2,3-dideh ydr o-3-flu or o-4-th io-
â-L-r ibofu r a n osyl]cytosin e (34): mp 192-195 °C; [R]23
D
+225.1 (c 0.5, MeOH); UV (MeOH) λmax ) 275.5 nm (ꢀ ) 6825);
MS (ESI) m/z 244 (MH+). Anal. (C9H10FN3O2S) C, H, N.
(+)-1-[(1SR,4S)-2,3-Did eoxy-2,3-d id eh yd r o-3-flu or o-4-
th io-â-L-r ibofu r a n osyl]-5-flu or ocytosin e (35): mp 174-176
°C; [R]24 +223.1 (c 0.22, MeOH); UV (MeOH) λmax ) 284.5
D
nm (ꢀ ) 9247), 240.5 nm (ꢀ ) 10 500); MS (ESI) m/z 262 (MH+).
Anal. (C9H9F2N3O2S) C, H, N.
(+)-9-[(1S,4S)-2,3-Dideoxy-2,3-dideh ydr o-3-flu or o-4-th io-
â-L-r ibofu r a n osyl]a d en in e (36): mp >200 °C; [R]24 +32.2
D
(c 0.5, MeOH); UV (MeOH) λmax ) 259.5 nm (ꢀ ) 8703); MS
(ESI) m/z 268 (MH+). Anal. (C10H10FN5OS) C, H, N.
(+)-9-[(1S,4S)-2,3-Dideoxy-2,3-dideh ydr o-3-flu or o-4-th io-
â-L-r ibofu r a n osyl]h yp oxa n th in e (37): mp >200 °C; [R]23
D
Supernatants were centrifuged at 12000 rpm for 2 h to pellet
the virus. The pellet was solubilized with vortexing in 100 µL
of virus solubilization buffer (VSB) containing 0.5% Triton
X-100, 0.8 M NaCl, 0.5 mM phenylmethylsulfonyl fluoride,
20% glycerol, and 0.05 M Tris, pH 7.8. An amount of 10 µL of
each sample was added to 75 µL of RT reaction mixture (0.06
M Tris, pH 7.8, 0.012 M MgCl2, 0.006 M dithiothreitol, 0.006
mg/mL poly(rA)n oligo(dT)12-18, 96 µg/mL dATP, and 1 µM of
+29.5 (c 0.08, MeOH); UV (MeOH) λmax ) 246.5 nm (ꢀ ) 8917);
MS (ESI) m/z 269 (MH+). Anal. (C10H9FN4O2S‚0.5H2O) C, H,
N.
(+)-9-[(1S,4S)-2,3-Dideoxy-2,3-dideh ydr o-3-flu or o-4-th io-
â-L-r ibofu r a n osyl]gu a n in e (38): mp >200 °C; [R]25 +64.9
D
(c 0.11, MeOH); UV (MeOH) λmax ) 256 nm (ꢀ ) 10 169); MS
(ESI) m/z 284 (MH+). Anal. (C10H10FN5O2S‚H2O) C, H, N.
Ben zoic acid 5-acetoxy-3,3-diflu or otetr ah ydr oth ioph en -
2-ylm eth yl ester (39): 1H NMR (CDCl3) δ 7.99-7.94 (m, 2H),
7.53-7.49 (m, 1H), 7.40-7.36 (m, 2H), 6.02, 6.02-5.55 (m, 1H),
4.64 (dd, 0.5H, J ) 11.2, 6.6 Hz), 4.56 (dd, 0.5H, J ) 11.7, 6.1
Hz), 4.45 (dd, 0.5H, J ) 11.2, 6.1 Hz), 4.35 (dd, 0.5H, J ) 11.7,
6.1 Hz), 4.02-3.98 (m, 0.5H), 3.95-3.86 (m, 0.5H), 2.87-2.63
(m, 0.5H), 2.03 (s, 3H), 1.99 (s, 3H). Anal. (C14H14F2O4S) C, H.
(-)-1-[(1R,4R)-2,3-Did eoxy-2,3-d id eoxy-3-flu or o-4-th io-
â-D-r ibofu r a n osyl]u r a cil (40): mp 150-152 °C; [R]25D -133.1
° (c 0.19, MeOH); UV (H2O) λmax ) 265.0 nm (ꢀ ) 19 598, pH
2), 266.0 nm (ꢀ ) 18 721, pH 7), 265.0 nm (ꢀ ) 15 542, pH 11).
Anal. (C9H9FN2O3S) C, H, N.
3
0.08 mCi/mL H-thymidine triphosphate (Moravek Biochemi-
cals, Brea, CA)) and incubated at 37 °C for 2 h. The reaction
was stopped by the addition of 100 µL of 10% trichloroacetic
acid containing 0.05% sodium pyrophosphate. The acid-
insoluble product was harvested onto filter paper using a
Packard harvester (Meriden, CT), and the RT activity was read
on a Packard direct â counter (Meriden, CT). The RT results
were expressed in counts per minute (cpm) per milliliter. The
antiviral 50% effective concentration (EC50) and 90% effective
concentration (EC90) were determined from the concentration-
response curve using the median effect method.22
Cytotoxicity Assa ys. The compounds were evaluated for
their potential toxic effects on uninfected PHA-stimulated
human PBM cells and in CEM (T-lymphoblastoid cell line
obtained from American Type Culture Collection, Rockville,
MD.) and Vero (African green monkey kidney) cells. PBM cells
were obtained from the whole blood of healthy seronegative
(-)-1-[(1R,4R)-2,3-Did eoxy-2,3-d id eh yd r o-3-flu or o-4-
th io-â-D-r ibofu r a n osyl]th ym in e (41): mp 188-190 °C (dec);
[R]26 -72.6° (c 0.29, CH3COCH3); UV (MeOH) λmax ) 268.5
D
nm (ꢀ ) 17 606) (pH 2), 269.0 nm (ꢀ ) 10 094) (pH 7), 265.0
nm (ꢀ ) 9977) (pH 11). Anal. (C10H11FN2O3S) C, H, N.

Thionucleosides as Anti-HIV Agents
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 7 1639
timicrob. Agents Chemother. 1996, 40, 380-386. (d) Lee, K.;
Choi, Y.; Gullen, E.; Schlueter-Wirtz, S.; Schinazi, R. F.; Cheng,
Y.-C.; Chu, C. K. Synthesis and anti-HIV and anti-HBV activities
of 2′-fluoro-2′,3′-unsaturated L-nucleosides. J . Med. Chem. 1999,
42, 1320-1328. (e) Chun, B. K.; Schinazi, R. F.; Cheng, Y.-C.;
Chu, C. K. Synthesis of 2′,3′-dideoxy-3′-fluoro-L-ribonucleosides
as potential antiviral agents from D-sorbitol. Carbohydr. Res.
2000, 328, 49-59.
donors (HIV-1 and hepatitis B virus) by single-step Ficoll-
Hypaque discontinuous gradient centrifugation. Log phase
Vero, CEM, and PHA-stimulated human PBM cells were
seeded at densities of 5 × 103, 2.5 × 103, and 5 × 104 cells/
well, respectively. All of the cells were plated in 96-well cell
culture plates containing 10-fold serial dilutions of the test
drug. The cultures were incubated for 3, 4, and 5 days for Vero,
CEM, and PBM cells, respectively, in humidified 5% CO2-air
at 37°C. At the end of incubation, MTT tetrazolium dye
solution (Cell titer 96, Promega, Madison, WI) was added to
each well and incubated overnight. The reaction was stopped
with stop solubilization solution (Promega, Madison, WI). The
plates were incubated for 5 h to ensure that the formazan
crystals were dissolved. The plates were read at a wavelength
of 570 nm using an ELISA plate reader (Bio-tek instruments,
Inc., Winooski, VT, model EL 312e). The 50% inhibition
concentration (IC50) was determined from the concentration-
response curve using the median effect method.22
(2) (a) Reist, E. J .; Gueffroy, D. E.; Goodman, L. Synthesis of 4-thio-
D- & L-ribofuranose and corresponding adenine nucleosides. J .
Am. Chem. Soc. 1964, 86, 5658-5663. (b) Reist, E. J .; Fisher,
L. V.; Gueffroy, E.; Goodman, L. Neighboring-group participa-
tion. Preparation of dithiopentose sugars via a thioacylonium
ion intermediate. J . Org. Chem. 1968, 33, 189-192.
(3) (a) Whistler, R. L.; Doner, L. W.; Nayak, U. G. 4-Thio-D-
arabinofuranosylpyrimidine nucleosides. J . Org. Chem. 1971, 36,
108-110. (b) Bobek, M.; Bloch, A.; Parthasarathy, R.; Whistler,
R. L. Synthesis and biological activity of 5-fluoro-4′-thiouridine
and some related nucleosides. J . Med. Chem. 1975, 18, 784-
787. (c) Ototani, N.; Whistler, R. L. Preparation and antitumor
activity of 4′-thio analogs of 2,2′-anhydro-1-â-D-arabinofurano-
sylcytosine. J . Med. Chem. 1974, 17, 535-537. (d) Fu, Y.-L.;
Bobek, M. In Nucleic Aicd Chemistry; Townsend, L.; Tipson, R.
S., Eds.; J ohn Wiley & Sons: New York, 1978; pp 317-323.
(4) (a) Dyson, M. R.; Coe, P. L.; Walker, R. T. The synthesis and
antiviral properties of E-5-(2-bromovinyl)-4′-thio-2′-deoxyuridine.
J . Chem. Soc., Chem. Commun. 1991, 741-742. (b) Dyson, M.
R.; Coe, P. L.; Walker, R. T. The synthesis and antiviral activity
of some 4′-thio-2′-deoxy nucleoside analogs. J . Med. Chem. 1991,
34, 2782-2786. (c) Secrist, J . A.; Tiwari, K. N.; Riordan, J . M.;
Montgomery, J . A. Synthesis and biological activity of 2′-deoxy-
4′-thiopyrimidine nucleosides. J . Med. Chem. 1991, 34, 2361-
2366. (d) Uenishi, J .; Motoyama, M.; Nishiyama, Y.; Wakaba-
yashi, S. Stereocontrolled preparation of cyclic xanthatesA novel
synthetic route to 4-thiofuranose and 4′-thionucleoside. J . Chem.
Soc., Chem. Commun. 1991, 1421-1422. (e) Uenishi, J .; Taka-
hashi, K.; Motoyama, M.; Akashi, H.; Sasaki, T. Syntheses and
antitumor activities of D-2′-deoxy-4′-thio and L-2′-deoxy-4′-thio
pyrimidine nucleosides. Nucleosides Nucleotides 1994, 13, 1347-
1361. (f) Secrist, J . A.; Riggs, R. M.; Tiwari, K. N.; Montgomery,
J . A. Synthesis and anti-HIV activity of 4′-thio-2′,3′-dideoxy-
nucleosides. J . Med. Chem. 1992, 35, 533-538. (g) Secrist, J .
A.; Tiwari, K. N.; Shortnacy-Fowler, A. T.; Messini, L.; Riordan,
J . M.; Montgomery, J . A. Synthesis and biological activity of
certain 4′-thio-D-arabinofuranosylpurine nucleosides. J . Med.
Chem. 1998, 41, 3865-3871. (h) Yoshimura, Y.; Watanabe, M.;
Satoh, H.; Ashida, N.; Ijichi, K.; Sakata, S.; Machida, H.;
Matsuda, A. A facile, alternative synthesis of 4′-thioarabino-
nucleosides and their biological activities. J . Med. Chem. 1997,
40, 2177-2183. (i) Yoshimura, Y.; Kitano, K.; Yamada, K.; Satoh,
H.; Watanabe, M.; Miura, S.; Sakata, S.; Sasaki, T.; Matsuda,
A. A novel synthesis of 2′-modified 2′-deoxy-4′-thiocytidines from
D-glucose. J . Org. Chem. 1997, 62, 3140-3152. (j) Parks, R. E.,
J r.; Stoeckler, J . D.; Cambor, C.; Savarese, T. M.; Crabtree, G.
W.; Chu, S.-H. In Molecular Actions and Targets for Cancer
Chemotherapeutic Agents; Sartorelli, A. C., Lazo, J . S., Bertino,
J . R., Eds.; Academic Press: New York, 1981; pp 229-252.
(5) Young, R. J .; Shaw-Ponter, S.; Thomson, J . B.; Miller, J . A.;
Cumming, J . G.; Pugh, A. W.; Rider, P. Synthesis and antiviral
evaluation of enantiomeric 2′,3′-dideoxy- and 2′,3′-didehydro-
2′,3′-dideoxy-4′-thionucleosides. Bioorg. Med. Chem. Lett. 1995,
5, 2599-2604.
Molecu la r Mod elin g Stu d y. (a ) Con for m a tion a l An a ly-
sis. The initial conformations of D- and l-3′F-4′Sd4C were
constructed by a builder module in Spartan 5.1.1 (Wavefunc-
tions, Inc., Irvine, CA). The initial conformations were cleaned
up and geometrically optimized through quantum mechanical
ab initio calculations using the RHF/6-31G** basis in Spartan
5.1.1.
(b) Bin d in g Affin ity Stu d y to HIV-1 Rever se Tr a n -
scr ip ta se. All molecular modeling of the enzyme-substrate
complexes was carried out using Sybyl 6.7 (Tripos Associates,
St. Louis, MO) on a Silicon Graphics Octane2 workstation. The
enzyme site of the enzyme-ligand complex was constructed
on the basis of the X-ray structure of the covalently trapped
catalytic complex of HIV-1 RT with TTP and primer-template
duplex (PDB entry 1rtd). A model of the NRTI binding site
was constructed that consisted of residues between Lys1 and
Pro243 in the p66 subunit, and a 7:4 (template-primer)
duplex. The geometrically optimized structures of each inhibi-
tor, obtained from the geometry optimization study, were used
as the initial Cartesian coordinates. The heterocyclic moiety
of the (n + 1)th nucleotide in the template overhang was
modified to the base complementary to the incoming NRTIs.
Thus, the adenine moiety that was in the original X-ray
structure (1rtd) was modified to guanine. The inhibitor triph-
osphates were manually docked to the active site of the enzyme
by adjusting the torsional angles to those found in the X-ray
structure. Ga¨steiger-Hu¨ckel charge was given to the enzyme-
ligand complex with formal charges (+2) on two Mg atoms in
the active site. Then, Kollman all-atom charges were loaded
onto the enzyme site from the biopolymer module in Sybyl.
To eliminate local strains resulting from merging inhibitors
and/or point mutations, residues inside 6 Å from the merged
inhibitors and mutated residues were annealed until energy
change from one iteration to the next was less than 0.05 kcal/
mol. The annealed enzyme-inhibitor complexes were mini-
mized by using the Kollman all-atom force field until the
iteration number reached 5000.
(6) (a) Choi, Y.; Choo, H.; Chong, Y.; Lee, S.; Olgen, S.; Schinazi, R.
F.; Chu, C. K. Synthesis and potent anti-HIV activity of L-2′,3′-
didehydro-2′,3′-dideoxy-2′-fluoro-4′-thiocytidine. Org. Lett. 2002,
4, 305-307. (b) Chong, Y.; Choo, H.; Lee, S.; Choi, Y.; Schinazi,
R. F.; Chu, C. K. Stereoselective synthesis and antiviral activities
of D-2′,3′-didehydro-2′,3′-dideoxy-2′-fluoro-4′-thionucleosides. J .
Med. Chem. 2002, 45, 4888-4898. (c) Choo, H.; Chong, Y.; Choi,
Y.; Mathew, J .; Schinazi, R. F.; Chu, C. K. Synthesis, anti-HIV
activity, and molecular mechanism of drug resistance of L-2′,3′-
didehydro-2′,3′-dideoxy-2′-fluoro-4′-thionucleosides. J . Med. Chem.
2003, 46, 389-398.
(7) Parks, R. E., J r.; Stoeckler, J . D.; Cambor, C.; Savarese, T. M.;
Crabtree, G. W.; Chu, S.-H. In Molecular Actions and Targets
for Cancer Chemotherapeutic Agents; Sartorelli, A. C., Lazo, J .
S., Bertino, J . R., Eds.; Academic Press: New York, 1981; pp
229-252.
Ack n ow led gm en t. This research was supported by
the U.S. Public Health Service Grants AI32351 and
AI25899 from the National Institutes of Health and the
Department of Veterans Affairs.
Su p p or tin g In for m a tion Ava ila ble: 1H and 13C NMR
data for compounds 15-22 and 25-38. This material is
available free of charge via the Internet at http://pubs.acs.org.
Refer en ces
(8) (a) Desgranges, C.; Razaka, G.; Rabaud, M.; Bricaud, H.;
Balzarini, J .; De Clercq, E. Phosphorolysis of (E)-5-(2-bromovi-
nyl)-2′-deoxyuridine (BVDU) and other 5-substituted-2′-deox-
yuridines by purified human thymidine phosphorylase and intact
blood-platelets. Biochem. Pharmacol. 1983, 32, 3583-3590. (b)
Samuel, J .; Gill, M. J .; Iwashina, T.; Tovell, D. R.; Tyrrell, D.
L.; Knaus, E. E.; Wiebe, L. I. Pharmacokinetics and metabolism
of E-5-(2-[I-131]iodovinyl)-2′-deoxyuridine in dogs. Antimicrob.
Agents Chemother. 1986, 29, 320-324.
(1) (a) Owen, G. R.; Verheyden, J . P. H.; Moffatt, J . G. 4′-Substituted
nucleosides. 3. Synthesis of some 4′-fluorouridine derivatives.
J . Org. Chem. 1976, 41, 3010-3017. (b) Marquez, V. E.; Tseng,
C. K.-H.; Mitsuya, H.; Aoki, S.; Kelley, J . A.; Ford, H., J r.; Roth,
J . S.; Broder, S.; J ohns, D. G.; Driscoll, J . S. Acid-stable 2′-fluoro
purine dideoxynucleosides as active agents against HIV. J . Med.
Chem. 1990, 33, 978-985. (c) Pai, S. B.; Liu, S.-H.; Zhu, Y.-L.;
Chu, C. K.; Cheng, Y.-C. Inhibition of hepatitis B virus by a novel
L-nucleoside, 2′-fluoro-5-methyl-â-L-arabinofuranosyluracil. An-

1640 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 7
Zhu et al.
(9) (a) Gunima, G.; Schinazi, R. F.; Chu, C. K. Synthesis and potent
anti-HIV activity of L-3′-fluoro-2′,3′-unsaturated cytidine. Org.
Lett. 2001, 3, 4177-4180. (b) Chong, Y.; Gumina, G.; Mathew,
J .; Schinazi, R. F.; Chu, C. K. L-2′,3′-Didehydro-2′,3′-dideoxy-3′-
fluoronucleosides: Synthesis, Anti-HIV Activity, Chemical and
Enzymatic Stability and the Mechanism of Resistance. J . Med.
Chem., in press.
nucleosides. J . Med. Chem. 1998, 41, 3865-3871. (b) Tiwari, K.;
Montgomery, J . A.; Secrist, J . A., III. The synthesis and biological
of 1-(2′-deoxy-4′-thio-R-L-threo-pentofuranosyl)thymine. Nucleo-
sides Nucleotides 1993, 12, 841-846.
(15) Bellon, L.; Barascut, J .-L.; Imbach, J .-L. Efficient synthesis of
4-thio-D-ribofuranose and some 4′-thioribonucleosides. Nucleo-
sides Nucleotides 1992, 11, 1467-1479.
(16) Chong, Y.; Chu, C. K. Efficient synthesis of 2-deoxy-L-erythro-
pentose (2-deoxy-L-ribose) from L-arabinose. Carbohyd. Res.
2002, 337, 397-402.
(17) Schinazi, R. F.; Lloyd, R. M.; Nguyen, M.-N.; Cannon, D. L.;
McMillan, A.; Ilksoy, N.; Chu, C. K.; Liotta, D. C.; Bazmi, H. Z.;
Mellors, J . W. Characterization of human immunodeficiency
viruses resistant to oxathiolane-cytosine nucleosides. Antimicrob.
Agents Chemother. 1993, 37, 875-881.
(18) FDA talk paper available at http://www.fda.gov/bbs/topics/
ANSWERS/2001/ANS01111.html.
(19) Huang, H.; Chopra, R.; Verdine, G. L.; Harrison, S. C. Structure
of a covalently trapped catalytic complex of HIV-1 reverse
transcriptase: Implications for drug resistance. Science 1998,
282, 1669-1675.
(10) (a) Van Aerschot, A. V.; Herdewijn, P.; Balzarini, J .; Pauwels,
R.; De Clercq, E. 3′-Fluoro-2′,3′-dideoxy-5-chlorouridine: most
selective anti-HIV-1 agent among
a series of new 2′- and
3′-fluorinated 2′,3′-dideoxynucleoside analogs. J . Med. Chem.
1989, 32, 1743-1749. (b) Koshida, R.; Cox, S.; Harmenberg, J .;
Gilljam, G.; Wahren, B. Structure-activity relationships of
fluorinated nucleoside analogs and their synergistic effect in
combination with phsophonofornate against human immunode-
ficiency virus type 1. Antimicrob. Agents Chemother. 1989, 33,
2083-2088.
(11) (a) Serra, C.; Dewynter, W.; Montero, J .-L.; Imbach, J .-L. 3′-C-
Phosphonates as nucleotide analogues synthesis starting from
original C-phosphonosugars (in ribo- and deoxyribo-series).
Tetrahedron 1994, 50, 8427-8444. (b) Wierenga, W.; Skulnick,
H. I. Stereochemical control as a function of protecting group
participation in 2-deoxy-D-erythro-pentofuranosyl nucleosides.
Carbohyd. Res. 1981, 90, 41-52.
(12) (a) Middleton, W. J . New fluorinating reagents: dialkylamino-
sulfur fluorides. J . Org. Chem. 1975, 40, 574-578. (b) Tewson,
T. J .; Welch, M. J . New approaches to the synthesis of 3-deoxy-
3-fluoro-D-glucose. J . Org. Chem. 1978, 43, 1090-1092.
(13) J eong, L. S.; Moon, H. R.; Choi, Y. J .; Chun, M. W.; Kim, H. O.
A short and efficient synthesis of L-thioarabinose derivative: a
versatile synthon for the synthesis of L-2′-deoxy-2′,2′-disubsti-
tuted-4′-thionucleosides. J . Org. Chem. 1998, 63, 4821-4825.
(14) (a) Secrist, J . A., III; Tiwari, K. N.; Shortnacy-Fowler, A. T.;
Messini, L.; Riordan, J . M.; Montgomery, J . A. Synthesis and
biological activity of certain 4′-thio-D-arabinofuranosylpurine
(20) (a) Chong, Y.; Borroto-Esoda, K.; Furman, P. A.; Schinazi, R.
F.; Chu, C. K. Molecular mechanism of DAPD/DXG against
zidovudine- and lamivudine-drug resistant mutants: a molecular
modeling approach. Antiviral Chem. Chemother. 2002, 13, 115-
128. (b) Lee, K.; Chu, C. K. Molecular modeling approach to
understanding the mode of action of L-nucleosides as antiviral
agents. Antimicrob. Agents Chemother. 2001, 45, 138-144.
(21) Dunitz, J . D.; Taylor, R. Organic fluorine hardly ever accepts
hydrogen bonds. Chem.sEur. J . 1997, 3, 89-98.
(22) Belen’kii, S. M.; Schinazi, R. S. Multiple drug effect analysis with
confidence interval. Antiviral Res. 1994, 25, 1-11.
J M0303148