Synthesis and anti-human immunodeficiency virus activity of 4′-branched (±)-4′-thiostavudines

Article abstract of DOI:10.1021/jm060980j

Motivated by our recent finding that 4′-ethynylstavudine (4) is a promising anti-human immunodeficiency virus type 1 (HIV-1) agent, we synthesized its 4′-thio analogue, as well as other 4′-thiostavudines having a carbon substituent at the 4′-position, as

Full text of DOI:10.1021/jm060980j

J. Med. Chem. 2006, 49, 7861-7867
7861
Synthesis and Anti-Human Immunodeficiency Virus Activity of 4′-Branched
(()-4′-Thiostavudines
Hiroki Kumamoto,† Takahito Nakai,† Kazuhiro Haraguchi,† Kazuo T. Nakamura,† Hiromichi Tanaka,*,† Masanori Baba,‡ and
Yung-Chi Cheng§
School of Pharmaceutical Sciences, Showa UniVersity, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan, DiVision of AntiViral
Chemotherapy, Center for Chronic Viral Diseases, Graduate School of Medical and Dental Sciences, Kagoshima UniVersity,
Kagoshima 890-8544, Japan, and Department of Pharmacology, School of Medicine, Yale UniVersity, New HaVen, Connecticut 06520
ReceiVed August 14, 2006
Motivated by our recent finding that 4′-ethynylstavudine (4) is a promising anti-human immunodeficiency
virus type 1 (HIV-1) agent, we synthesized its 4′-thio analogue, as well as other 4′-thiostavudines having a
carbon substituent at the 4′-position, as racemates in this study. Methyl 3-oxo-tetrahydrothiophen-2-carboxylate
(5) was used as a starting material to construct the requisite 4-thiofuranoid glycal (13). Introduction of a
thymine base was carried out by an electrophilic addition reaction to 13 using N-iodosuccinimide (NIS) and
bis(trimethylsilyl)thymine. The desired â-anomer (16â) obtained as a major product in this reaction underwent
ready elimination with activated Zn to give the 4′-carbomethoxy derivative (18). By using 18 as a common
intermediate, 4′-carbon-substituted (CH2OH, CO2Me, CONH2, CHdCH2, CN, and CtCH) 4′-thiostavudines
were prepared. Among these six compounds, 4′-cyano (28) and 4′-ethynyl (29) analogues were found to
show inhibitory activity against HIV-1 with ED50 values of 7.6 and 0.74 µM, respectively. The activity of
29 was comparable to that of stavudine, but 29 was not as active as 4. Optical resolution of 29 was briefly
examined.
Introduction
Nucleosides in which the furanose ring oxygen is replaced
with a sulfur atom are called 4′-thionucleosides, and the first
report dealing with this class of nucleosides appeared in 1964
for the synthesis of 4′-thioadenosine (1).1 A renaissance of 4′-
thionucleosides began in 1991 when potent antiviral and
antitumor activities were found in 4′-thiothymidine (2) and 2′-
deoxy-4′-thiocytidine (3) (Figure 1).2 Extensive synthetic stud-
ies3 carried out since then have led to the finding of several
biologically interesting compounds.4-6
Meanwhile, our recent studies on the reaction of organo-
aluminum reagents with nucleosides bearing an epoxy-sugar
structure7,8 has disclosed that 2′,3′-didehydro-3′-deoxy-4′-
ethynylthymidine (4, Figure 2) is more potent against human
immunodeficiency virus (HIV) than the parent compound
stavudine (d4T) and much less toxic to various cells and also
to mitochondrial DNA synthesis.8,9 This compound has several
potential advantages as a promising anti-HIV agent: (1) it is a
better substrate for human thymidine kinase than d4T, (2) it is
very much resistant to catabolism by thymidine phosphorylase,
and (3) its activity improves in the presence of a major mutation,
K103N, known for nonnucleoside reverse transcriptase inhibitor
resistant HIV.9,10
Figure 1. 4′-Thionucleosides 1-3.
In this paper, as a study on the structure-activity relationship
regarding 4, we describe the synthesis and anti-HIV activity of
the (()-4′-thio-counterpart of 4, as well as other 4′-thiostavudine
analogues having carbon substituents at the 4′-position.
Figure 2. 4′-Ethynylstavudine (4).
analogues I with a variety of 4′-carbon substituents can be
prepared from II by manipulation of the 4′-carbomethoxy group.
Two possible approaches were envisioned for the preparation
of II: one is a Pd-catalyzed allylic substitution of IV, and the
other is an electrophilic glycosylation followed by elimination
of X and OR′ from III (IV f III f II). We anticipated that
the known tetrahydrothiophene derivative 5 could be used for
the preparation of IV.
Results and Discussion
A synthetic plan for the title compounds is depicted in Scheme
1 as a retrosynthetic analysis. The desired 4′-thiostavudine
* Corresopnding author: tel 81-3-3784-8186, fax 81-3-3784-8252, e-mail
hirotnk@pharm.showa-u.ac.jp.
† Showa University.
Compound 5 used as the starting material was prepared
according to the published procedure.11 An aldol reaction
between 5 and formaldehyde gave 6 (95%), which was then
‡ Kagoshima University.
§ Yale University.
10.1021/jm060980j CCC: $33.50 © 2006 American Chemical Society
Published on Web 12/06/2006

7862 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 26
Kumamoto et al.
Scheme 1. Retrosynthesis of 4′-Substituted 4′-Thiostavudine Analogues
O-silylated to yield 7 (89%) (Figure 3). Transformation of 7 to
the enone 8 (92%) was performed in CH2Cl2 by a Pummerer-
type reaction using N-chlorosuccinimide (NCS). Treatment of
8 with NaBH4/CeCl312 in MeOH/THF (-50 °C, 1 h) followed
by column chromatography gave a mixture of 9 and its epimer
with a ratio of ca. 10/1 (89% combined yield) along with a
minor byproduct (ca. 6%) that was assumed to be the 2-carb-
presence of N-iodosuccinimide (NIS) (1.5 equiv) as an elec-
trophile in CH3CN (at rt, overnight), a mixture of the â-anomer
(15â) and R-anomer (15R) [NOE data 15â, H-1′/H-3′ (7.8%)
and H-6/H-2′ (11.6%); 15R, H-2′/H-6 (12.3%) and H-2′/H-3′
(11.8%)]17 was formed in 40% combined yield. The diastereo-
meric ratio of 15â/15R ) 5/1 was determined on the basis of
1H NMR spectroscopy by comparing integration of H-2′. One
might expect that the presence of a more bulky acyl protecting
group would encourage the more efficient iodonium formation
at the R-face of the thioglycal 11, thus leading to a higher ratio
of the desired â-anomer. This appeared, however, not to be the
case. When the pivalate 12 was subjected to the glycosylation
under the same reaction conditions as described above, equal
amounts of 16â and 16R [NOE data 16â, H-2′/H-6 (13.9%)
and H-2′/H-5′ (1.7%); 16R, H-2′/H-6 (13.9%) and H-2′/H-3′
(10.3%)] were formed in 88% combined yield. The highest
â-selectivity (17â/17R ) 10/1) and combined yield (98%) were
seen in the case of the benzoate 13. Moreover, in this particular
case, the desired â-anomer (17â) was isolated from the anomeric
mixture simply by crystallization. The stereochemistry of 17â
was confirmed on the basis of its NOE data [H-2′/H-5′ (1.2%)
and H-3′/H-1′ (2.9%)], while that of the R-anomer (17R) was
determined by X-ray crystallographic analysis.18
1
aldehyde (10) based on its H NMR (δ 9.82, CHO) and FAB-
MS (m/z 437, M+ + K) spectra. The depicted stereochemistry
of 9 was confirmed by NOE experiment, as well as X-ray
crystallographic analysis, after introduction of thymine base.
The stereoselectivity observed in 1,2-reduction of 8 has a
precedent in the case of methyl 1-methyl-2-oxo-3-cyclopentene-
carboxylate.13 Conventional acylation of 9 gave the respective
products (11-14).14
For the introduction of a thymine base, Pd-catalyzed allylic
substitution15 was first examined by using 11 as a substrate.
However, attempts made by changing the catalyst [Pd(Ph3P)4,
Pd2(dba)3/Ph3P, (η3-C3H5PdCl)2/Ph3P], the thymine derivative
(N3-benzoylthymine, bis(trimethylsilyl)thymine), or the solvent
(THF, DMSO/THF, DMF) resulted in the recovery of 11. The
desired glycosylated product was formed only upon reacting
the carbonate 14 with bis(trimethylsilyl)thymine in the presence
of Pd2(dba)3/Ph3P (in THF at 60 °C), but the yield was only
8%. These results led us to apply the second approach,
electrophilic glycosylation and subsequent elimination.
Electrophilic glycosylation using thiofuranoid glycals has
previously been reported from our laboratory.16 As shown in
Scheme 2, when the acetylated thiofuranoid glycal 11 was
reacted with bis(trimethylsilyl)thymine (1.5 equiv) in the
Compound 17â was found to readily undergo elimination with
activated Zn.19 Thus, treatment of 17â with the activated Zn in
THF/AcOH at rt for 1 h gave the 4′-carbomethoxy derivative
(18) of 4′-thiostavudine in 99% yield (Scheme 2). Attempted
direct transformation of 18 to its 4′-formyl derivative (e.g.,
i-Bu2AlH in CH2Cl2 or THF) all met with concomitant formation
of the 4′-hydroxymethyl derivative (19). Therefore, 18 was
converted to 19 (98%) by reacting with an excess amount of
NaBH4 in MeOH/THF, and then the resulting 19 was oxidized
with (CF3CO)2O/DMSO in CH2Cl2 at -80 °C to give the
aldehyde 20 in 97% yield.
Preparation of the 4′-ethynyl derivative (21) from 20 was
examined. The reaction between 20 and Me3SiCHN2/lithium
diisopropyl amide (LDA)20 gave several unknown byproducts,
and the desired 21 was isolated only in 20% yield. This result
presumably originates in the highly basic nature of LDA, which
is needed to generate an anionic species from Me3SiCHN2. In
fact, the use of dimethyl 1-diazo-(2-oxopropyl)phosphonate21
in combination with K2CO3 in MeOH gave 21 in a higher yield
of 85% (Scheme 2). To generate the Wittig reagent Ph3PdCH2
from methyltriphenylphosphonium bromide required for the
preparation of the 4′-vinyl derivative 22, methylsulfinyl car-
banion was found to be an appropriate base to give 22 in 98%
Figure 3. Compounds 6-14.

Synthesis and Anti-HIV ActiVity of 4′-ThiostaVudines
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 26 7863
Scheme 2. Electrophilic Glycosylation by Using Thiofuranoid Glycals 11-13 and Transformation of 17â to the 4′-Ethynyl Analogue
21
Table 1. Anti-HIV-1 Activity of 24-29 in MT-4 Cells
yield. When 20 was converted to its oxime and then reacted
with MsCl in pyridine, spontaneous formation of the 4′-cyano
derivative 23 was observed (Figure 4).
compound
4′-substituent
EC50a (µM)
CC50b (µM)
24
25
26
27
28
29
CH2OH
CO2Me
CONH2
CHdCH2
CN
CtCH
CtCH
CtCH
>100
>100
>100
>100
7.6
0.74
0.37
>20
>100
>100
>100
>100
>100
>100
>100
>100
The 4′-carbon-substituted derivatives thus far prepared were
deprotected to yield the corresponding free (()-4′-thiostavudines
(24-29). Compound 26, 4′-carbamoyl-4′-thiostavudine, was
prepared from 18 by a conventional reaction sequence: desilyl-
ation, acetylation, and ammonolysis. Table 1 summarizes anti-
HIV-1 activity and cytotoxicity of 24-29, together with those
of stavudine and 4′-ethynylstavudine (4). It is consistent with
our previous observation8,9,22,23 that only compounds having an
sp-hybridized 4′-carbon substituent (28 and 29) show inhibitory
activity against HIV-1. The fact that the 4′-ethynyl analogue
(29) is more inhibitory than the 4′-cyano analogue (28) also
follows our previous observation in the case of 4′-substituted
stavudines.22
Since (()-4′-ethynyl-4′-thiostavudine (29) was almost as
active as stavudine, its optical resolution was carried out. After
esterification of 29 with (-)-camphanic chloride, HPLC separa-
tion (CHCl3/MeOH ) 200/1) enabled us to isolate the two
diastereomers. Each diastereomer was then treated with K2CO3/
MeOH to give the respective optically active 29.24 From the
anti-HIV assay of the separated enantiomers, it was concluded
(-)-29
(+)-29
stavudine
0.51
>100
>100
4′-ethynyl-
0.060
stavudine (4)
a Inhibitory concentration required to achieve 50% protection of MT-4
cells against the cytopathic effect of HIV-1 IIIB. b Cytotoxic concentration
required to reduce the viability of mock-infected MT-4 cells by 50%.
that the observed activity of 29 derived from (-)-29. Although
the actual configuration of (-)-29 is not known at the moment,
it may be possible to assume that this compound has D-
configuration, since the L-isomer of stavudine has been reported
not to be inhibitory against HIV-1.25
Conclusion
Our recent finding that 4′-ethynylstavudine is a highly
promising anti-HIV agent led us to carry out the present study.
Synthesis of (()-4′-ethynyl-4′-thiostavudine (29) and its ana-
logues having a carbon substituent at the 4′-position was
accomplished based on stereoselective electrophilic addition of
NIS/bis(trimethylsilyl)thymine to the 4-thiofuranoid glycal 13.
The resulting major product (16â), upon reaction with activated
Zn, gave the elimination product 18 in almost quantitative yield.
Manipulation of the carbomethoxy group in 18 allowed the
preparation of other 4′-carbon-substituted 4′-thiostavudines.
Among six 4′-carbon-substituted (()-4′-thiostavudines synthe-
sized in the present study, the 4′-cyano (28) and 4′-ethynyl (29)
analogues showed inhibitory activity against HIV-1, suggesting
that the presence of an sp-hybridized carbon substituent at the
Figure 4. Compounds 22-29.

7864 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 26
Kumamoto et al.
Methyl 2-(tert-Butyldiphenylsilyloxy)methyl-(trans-3-hydroxy)-
2,3-dihydro-thiophen-2-carboxylate (9) and 2-(tert-Butyldiphen-
ylsilyloxy)methyl-(trans-3-hydroxy)-2,3-dihydrothiophen-2-carbalde-
hyde (10). A solution of 8 (9.0 g, 21.1 mmol) and CeCl3·7H2O
(7.76 g, 21.1 mmol) in MeOH (225 mL)/THF (75 mL) was cooled
to -50 °C under positive pressure of dry Ar. To this was added
NaBH4 (1.20 g, 31.6 mmol) by portions over 0.5 h. After being
stirred for 1.5 h, the reaction mixture was quenched by addition of
AcOH and acetone and then partitioned between CH2Cl2 and
saturated aqueous NaHCO3. Column chromatography of the organic
layer gave 9 (eluted with hexane/EtOAc ) 10/1, 7.92 g, 89%,
containing its epimer) and 10 (eluted with hexane/EtOAc ) 5/1,
500 mg, 6%). An analytically pure 9 was obtained by crystallization
from hexane-Et2O.
4′-position is crucial for the activity. It should be noted that
4′-thiostavudine itself has been reported not to be inhibitory
against HIV.26 The most active compound, (()-4′-ethynyl-4′-
thiostavudine (29), showed EC50 of 0.74 µM, which is almost
comparable to that of stavudine. Optical resolution of 29
revealed that its leVo-enantiomer is the active component.
Experimental Section
Chemistry. Melting points were determined on a Yanaco micro
melting point apparatus and are uncorrected. 1H NMR and 13C NMR
were measured on a JEOL JNM-LA 500 (500 MHz). Chemical
shifts are reported relative to Me4Si. Mass spectra (MS) were taken
in FAB mode with m-nitrobenzyl alcohol as a matrix on a JEOL
JMS-700. Ultraviolet spectra (UV) were recorded on a JASCO
V-530 spectrophotometer. Column chromatography was carried out
on silica gel (Micro Bead Silica Gel PSQ 100B, Fuji Silysia
Chemical Ltd.). Thin layer chromatography (TLC) was performed
on silica gel (precoated silica gel plate F254, Merck). Where
necessary, analytical samples were purified by high-performance
liquid chromatography (HPLC). HPLC was carried out on a
Shimadzu LC-6AD with a Shim-pack PREP-SIL (H)′KIT column
(2 cm × 25 cm).
1
Physical data for 9: mp 53-57 °C; H NMR (CDCl3) δ 1.04
(9H, s, SiBu-t), 2.48 (1H, d, J3,OH ) 6.1 Hz, OH), 3.72 (3H, s,
CO2Me), 4.18 and 4.26 (2H, each as d, Jgem ) 9.8 Hz, CH2OSi),
5.65 (1H, ddd, J3,OH ) 6.1 Hz, J3,4 ) 2.9 Hz, J3,5 ) 0.7 Hz, H-3),
5.76 (1H, dd, J4,5 ) 6.1 Hz and J3,4 ) 2.9 Hz, H-4), 6.25 (1H, dd,
J4,5 ) 6.1 Hz and J3,5 ) 0.7 Hz, H-5), 7.38-7.45 (6H, m, Ph),
7.63-7.67 (4H, m, Ph); 13C NMR (CDCl3) δ 19.2 (SiCMe3), 26.7
(SiCMe3), 52.7 (CO2Me), 64.3 (CH2OSi) 65.3 (C-2), 79.9 (C-3),
124.5 (C-4), 127.7 (C-5), 127.8, 130.0, 135.5 and 135.6 (Ph-
tertiary), 132.4 and 132.5 (Ph-quaternary), 172.1 (CO2Me); FAB-
MS (m/z) 467 (M+ + K). Anal. Calcd for C23H28O4SSi: C, 64.45;
H, 6.59. Found: C, 64.20; H, 6.61.
Physical data for 10: 1H NMR (CDCl3) δ 1.07 (9H, s, SiBu-t),
2.44 (1H, d, J3,OH ) 8.5 Hz, OH), 3.96 and 4.07 (2H, each as d,
Jgem ) 10.5 Hz, CH2OSi), 5.29 (1H, ddd, J3,OH ) 8.5 Hz and J3,4
) 2.4 Hz, J3,5 ) 1.5 Hz, H-3), 5.76 (1H, dd, J4,5 ) 6.0 Hz and J3,4
) 2.4 Hz, H-4), 6.26 (1H, dd, J4,5 ) 6.0 Hz and J3,5 ) 1.5 Hz,
H-5), 7.38-7.47 (6H, m, Ph), 7.63-7.69 (4H, m, Ph), 9.82 (1H, s,
CHO); FAB-MS (m/z) 437 (M+ + K).
Methyl 2-Hydroxymethyl-3-oxotetrahydrothiophen-2-car-
boxylate (6). A mixture of 5 (10.0 g, 62.4 mmol), 38% aqueous
solution of HCHO (60 mL, 759 mmol), and AcOH (7.15 mL, 125
mmol) was stirred at rt overnight. The reaction mixture was
partitioned between CH2Cl2 and saturated aqueous NaHCO3.
Column chromatography (hexane/EtOAc ) 1/1) of the organic layer
gave 6 (11.2 g, 95%) as an oil: 1H NMR (CDCl3) δ 2.74 (2H, m,
H-4 or H-5), 2.80 (1H, br, OH), 2.95 (1H, m, H-4 or H-5), 3.04
(1H, m, H-4 or H-5), 3.79 (3H, s, CO2Me), 4.04 (2H, m, CH2OH);
13C NMR (CDCl3) δ 23.7 (C-4 or C-5), 40.0 (C-4 or C-5), 53.1
(CO2Me), 62.8 (C-2), 64.0 (C-5), 170.3 (CO2Me) 209.2 (C-3); FAB-
MS (m/z) 191 (M+ + H). Anal. Calcd for C7H10O4S: C, 44.20; H,
6.07; N, 5.30. Found: C, 44.19; H, 6.00; N, 5.26.
Methyl 2-(tert-Butyldiphenylsilyloxy)methyl-3-oxotetrahydro-
thiophen-2-carboxylate (7). A mixture of 6 (500 mg, 2.62 mmol),
imidazole (269 mg, 3.94 mmol), and tert-butyldiphenylsilyl chloride
(TBDPSCl; 0.75 mL, 2.89 mmol) in DMF (5.0 mL) was stirred at
rt overnight. The reaction mixture was partitioned between CH2Cl2
and saturated aqueous NaHCO3. Column chromatography (hexane/
EtOAc ) 20/1) of the organic layer gave 7 (1.00 g, 89%) as a
solid. Crystallization from hexane-Et2O gave an analytical
sample: mp 85-88 °C; 1H NMR (CDCl3) δ 1.02 (9H, s, SiBu-t),
2.78 and 2.92 (2H, each as m, H-5), 3.16 (3H, s, CO2Me), 3.95
and 4.27 (2H, each as d, Jgem ) 10.3 Hz, CH2OSi), 7.37-7.45 (6H,
m, Ph), 7.66-7.73 (4H, m, Ph); 13C NMR(CDCl3) δ 19.2 (SiCMe3),
24.2 (C-4), 26.6 (SiCMe3), 40.7 (C-5), 52.9 (CO2Me), 64.0 (C-2),
64.9 (CH2OSi), 127.7, 127.8, 129.8, 129.9, 135.6 and 135.7 (Ph-
tertiary), 132.5 and 132.6 (Ph-quaternary), 169.6 (CO2Me) 208.9
(C-3); FAB-MS (m/z) 429 (M+ + H). Anal. Calcd for C23H28O4-
SSi: C, 64.45; H, 6.59. Found: C, 64.37; H, 6.55.
Methyl trans-3-Benzoyloxy-2-(tert-butyldiphenylsilyloxy)-
methyl-2,3-dihydro-thiophen-2-carboxylate (13). To a mixture
of 9 (3.43 g, 8.01 mmol), 4-dimethylaminopyridine (DMAP; 1.27
g, 10.41 mmol), and i-Pr2NEt (1.4 mL, 10.41 mmol) was added
BzCl (1.21 mL, 10.41 mmol) at rt. The reaction mixture was stirred
at rt overnight and partitioned between CH2Cl2 and saturated
aqueous NaHCO3. Column chromatography (hexane/EtOAc ) 4/1)
of the organic layer gave 13 (3.93 g, 94%) as an oil, which was
crystallized from Et2O-hexane: mp 111-114 °C; 1H NMR
(CDCl3) δ 0.94 (9H, s, SiBu-t), 3.73 (3H, s, CO2Me), 4.21 and
4.37 (2H, each as d, Jgem ) 9.7 Hz, CH2OSi), 5.90 (1H, dd, J4,5
)
5.7 Hz and J3,4 ) 2.9 Hz, H-4), 6.46 (1H, d, J4,5 ) 5.7 Hz, H-5),
6.74 (1H, dd, J3,4 ) 2.9 Hz, H-3), 7.07-7.10 (2H, m, Ph), 7.26-
7.31 (1H, m, Ph), 7.33-7.43 (7H, m, Ph), 7.55-7.58 (3H, m, Ph),
7.90-7.92 (2H, m, Ph); 13C NMR(CDCl3) δ 19.0 (SiCMe3), 26.5
(SiCMe3), 52.9 (CO2Me), 63.2 (CH2OSi) 66.3 (C-2), 79.1 (C-3),
121.9 (C-4), 131.1 (C-5), 127.5, 127.6, 128.4, 129.8, 130.0, 133.0,
135.4 and 135.7 (Ph-tertiary), 129.6, 132.5 and 132.6 (Ph-
quaternary), 165.0 (COPh), 171.4 (CO2Me); FAB-MS (m/z) 533
(M+ + K). Anal. Calcd for C30H32O5SSi: C, 67.64; H, 6.05.
Found: C, 67.51; H, 5.96.
Methyl 2-(tert-Butyldiphenylsilyloxy)methyl-3-oxo-2,3-dihydro-
thiophen-2-carboxylate (8). To a solution of 7 (2.66 g, 6.19 mmol)
in CH2Cl2 (12.5 mL) was added NCS (860 mg, 6.44 mmol) at 0
°C under positive pressure of dry Ar. The reaction mixture was
stirred at rt for 2.5 h and then partitioned between CH2Cl2 and
saturated aqueous NaHCO3. Column chromatography (hexane/
EtOAc ) 10/1) of the organic layer gave 8 (2.43 g, 92%) as a
solid. Crystallization from hexane-Et2O gave an analytical
sample: mp 102-106 °C; 1H NMR (CDCl3) δ 0.98 (9H, s, SiBu-
t), 3.71 (3H, s, CO2Me), 4.21 and 4.30 (2H, each as d, Jgem ) 10.3
Hz, CH2OSi), 6.19 (1H, d, J4,5 ) 5.7 Hz, H-4), 7.38-7.45 (6H, m,
1-[[(cis-3-Benzoyloxy)-[cis-2-(tert-butyldiphenylsilyloxy)methyl]-
(trans-4-iodo)-(trans-2-carbomethoxy)tetrahydrothiophen-5-yl]]-
thymine (17â) and 1-[[(trans-3-Benzoyloxy)-[trans-2-(tert-butyl-
diphenylsilyloxy)methyl]-(trans-4-iodo)-(cis-2-carbomethoxy)-
tetrahydrothiophen-5-yl]thymine (17R). A mixture of thymine
(1.78 g, 14.1 mmol), (Me3Si)2NH (150 mL), and (NH4)2SO4 (88
mg) was refluxed with stirring. After complete dissolution of the
thymine was confirmed (ca. 7 h), the mixture was evaporated to
remove excess (Me3Si)2NH. The resulting syrupy residue was
dissolved in CH3CN (50 mL). To this were added a solution of 13
(5.0 g, 9.39 mmol) in CH3CN (50 mL) and NIS (3.2 g, 14.1 mmol).
The reaction mixture was stirred at rt overnight and partitioned
between CH2Cl2 and aqueous NaHCO3 containing a small amount
of Na2S2O3. Column chromatography (hexane/EtOAc ) 1/1) of the
organic layer gave a mixture of 17â and 17R (7.29 g, 98%) as a
solid. Crystallization of this mixture from CH2Cl2-hexane gave
an analytically pure 17â. Compound 17R was isolated by HPLC
Ph), 7.62-7.63 (4H, m, Ph), 8.45 (1H, d, J4,5 ) 5.7 Hz, H-5); 13
C
NMR(CDCl3) δ 19.5 (SiCMe3), 26.5 (SiCMe3), 53.3 (CO2Me), 65.2
(CH2OSi) 47.5 (C-2), 121.8 (C-4), 127.7, 127.8, 129.9 and 135.6
(Ph-tertiary), 132.4 and 132.6 (Ph-quaternary), 163.3 (C-5), 166.7
(CO2Me), 199.3 (C-3); FAB-MS (m/z) 427 (M+ + H). Anal. Calcd
for C23H26O4SSi: C, 64.76; H, 6.14. Found: C, 64.60; H, 6.13.

Synthesis and Anti-HIV ActiVity of 4′-ThiostaVudines
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 26 7865
(hexane/EtOAc ) 1/1) purification and crystallized from Et2O-
hexane to give a sample for X-ray analysis.
6.23 (1H, dd, J2′,3′ ) 6.3 Hz and J1′,3′ ) 1.7 Hz, H-3′), 6.88 (1H,
d, J6,Me ) 1.1 Hz, H-6), 7.09 (1H, dd, J1′,2′ )2.3 Hz and J1′,3′ )1.7
Hz, H-1′), 7.38-7.47 (6H, m, Ph), 7.66-7.69 (4H, m, Ph), 9.19
(1H, br, NH); 13C NMR(CDCl3) δ 12.5 (5-Me), 19.3 (SiCMe3),
26.8 (SiCMe3), 66.5 (CH2OH), 66.9 (C-1′), 68.5 (C-5′), 72.4 (C-
4′), 112.1 (C-5), 129.2 (C-2′), 135.6 (C-6), 127.8, 127.9 and 135.5
(Ph-tertiary), 132.3 and 132.7 (Ph-quaternary), 138.4 (C-3′), 150.6
(C-2), 163.5 (C-4); FAB-MS (m/z) 509 (M+ + H). Anal. Calcd for
C27H32N2O4SSi: C, 63.75; H, 6.34; N, 5.51. Found: C, 63.67; H,
6.21; N, 5.47.
Physical data for 17â: mp 178-180 °C; UV (MeOH) λmax 265
1
nm (ꢀ 12 300), λmin 249 nm (ꢀ 8000); H NMR (CD2Cl2) δ 1.13
(9H, s, SiBu-t), 1.51 (3H, d, J6,Me ) 1.2 Hz, 5-Me), 3.84 (3H, s,
CO2Me), 4.27 (2H, s, H-5′), 5.29 (1H, t, J2′,3′ ) J1′,2′ ) 10.7 Hz,
H-2′), 6.19 (1H, d, J2′,3′ ) 10.7 Hz, H-3′), 6.64 (1H, d, J1′,2′ ) 10.7
Hz, H-1′), 7.32 (1H, d, J6,Me ) 1.2 Hz, H-6), 7.34-7.60 (1H, m,
Ph), 7.44-7.57 (6H, m, Ph), 7.70-7.78 (6H, m, Ph), 8.12-8.14
(2H, m, Ph), 9.83 (1H, br, NH); 13C NMR(CD2Cl2) δ 12.6 (5-Me),
20.1 (SiCMe3), 27.8 (SiCMe3), 28.1 (C-2′), 54.1 (CO2Me), 60.3
(C-1′), 62.0 (C-4′), 65.8 (C-5′), 81.5 (C-3′), 96.9 (C-5), 128.8, 128.9,
129.4, 130.9, 131.0, 131.1, 134.6, 136.1 and 136.3 (Ph-tertiary),
129.4, 132.7 and 133.6 (Ph-quaternary), 135.0 (C-6), 151.5 (C-2),
164.1 (C-4), 165.9 (COPh), 170.7 (CO2Me); FAB-MS (m/z) 785
(M+ + H). Anal. Calcd for C35H37IN2O7SSi: C, 53.57; H, 4.75;
N, 3.57. Found: C, 53.44; H, 4.64; N, 3.53.
(()-5′-O-(tert-Butyldiphenylsilyl)-2′,3′-didehydro-3′-deoxy-4′-
formyl-4′-thiothymidine (20). A mixture of DMSO (0.46 mL, 3.67
mmol), (CF3CO)2O (0.06 mL, 0.42 mmol), and CH2Cl2 (10.5 mL)
was stirred at -80 °C for 15 min under positive pressure of dry
Ar. To this was added a CH2Cl2 (7 mL) solution of 19 (933 mg,
1.83 mmol). The reaction mixture was stirred at at -80 °C for 1.5
h, quenched by adding Et3N (0.65 mL), and partitioned between
CH2Cl2 and saturated aqueous NaHCO3. Column chromatography
(hexane/EtOAc ) 1/1) of the organic layer gave 20 (901 mg, 97%)
as a solid. Crystallization from CH2Cl2-hexane gave an analytical
sample: mp 147-152 °C; UV (MeOH) λmax 271 nm (ꢀ 10 000),
Physical data for 17R: mp 221-223 °C; UV (MeOH) λmax 265
1
nm (ꢀ 12 500), λmin 249 nm (ꢀ 8000); H NMR (CD2Cl2) δ 0.93
(9H, s, SiBu-t), 1.93 (3H, d, J6,Me ) 1.2 Hz, 5-Me), 3.70 (3H, s,
CO2Me), 4.03 and 4.10 (2H, each as d, Jgem ) 10.0 Hz, H-5′),
5.03 (1H, dd, J1′,2′ ) 11.2 Hz and J 2′,3′ ) 2.9 Hz, H-2′), 6.53 (1H,
d, J2′,3′ )2.9 Hz, H-3′), 6.57 (1H, d, J1′,2′ ) 11.2 Hz, H-1′), 6.53-
6.58 (2H, m, Ph), 7.09 (1H, d, J6,Me ) 1.2 Hz, H-6), 7.22-7.35
(5H, m, Ph), 7.39-7.44 (1H, m, Ph), 7.50-7.56 (4H, m, Ph), 7.68-
7.72 (1H, m, Ph), 7.72-8.10 (2H, m, Ph), 8.70 (1H, br, NH); 13C
NMR (CD2Cl2) δ 13.1 (5-Me), 19.3 (SiCMe3), 26.9 (SiCMe3), 28.6
(C-2′), 53.8 (CO2Me), 64.5 (C-4′), 65.3 (C-5′), 66.2 (C-1′), 76.1
(C-3′), 113.7 (C-5), 128.0, 128.2, 129.4, 130.2, 130.5, 130.6, 134.4,
135.9 and 136.3 (Ph-tertiary), 129.6, 132.7 and 132.8 (Ph-
quaternary), 134.9 (C-6), 151.0 (C-2), 163.4 (C-4), 164.4 (COPh),
173.0 (CO2Me); FAB-MS (m/z) 785 (M+ + H). Anal. Calcd for
C35H37IN2O7SSi′1/3H2O: C, 53.16; H, 4.80; N, 3.54. Found: C,
53.17; H, 4.72; N, 3.45.
1
λmin 240 nm (ꢀ 3000); H NMR (CDCl3) δ 1.06 (9H, s, SiBu-t),
1.66 (3H, d, J6,Me ) 1.1 Hz, 5-Me), 4.12 and 4.16 (2H, each as d,
Jgem ) 10.9 Hz, H-5′), 6.02 (1H, dd, J2′,3′ ) 6.3 Hz and J1′,2′ )2.3
Hz, H-2′), 6.18 (1H, dd, J2′,3′ ) 6.3 Hz and J1′,3′ )1.7 Hz, H-3′),
6.95 (1H, d, J6,Me ) 1.1 Hz, H-6), 7.22 (1H, dd, J1′,2′ ) 2.3 Hz and
J1′,3′ ) 1.7 Hz, H-1′), 7.37-7.47 (6H, m, Ph), 7.66-7.71 (4H, m,
Ph), 8.19 (1H, br, NH), 9.32 (1H, s, CHO); 13C NMR (CDCl3) δ
12.4 (5-Me), 19.2 (SiCMe3), 26.7 (SiCMe3), 65.7 (C-5′), 67.5 (C-
1′), 76.5 (C-4′), 112.6 (C-5), 127.9 130.0, 130.1, 135.5 and 135.6
(Ph-tertiary), 132.2 and 132.5 (Ph-quaternary), 133.2 (C-3′), 133.3
(C-2′), 135.1 (C-6), 150.5 (C-2), 163.5 (C-4), 192.0 (CHO); FAB-
MS (m/z) 507 (M+ + H). Anal. Calcd for C27H30N2O4SSi: C, 64.05;
H, 5.97; N, 5.53. Found: C, 64.13; H, 6.03; N, 5.41.
(()-5′-O-(tert-Butyldiphenylsilyl)-2′,3′-didehydro-3′-deoxy-4′-
ethynyl-4′-thiothymidine (21). To a solution of 20 (210 mg, 0.414
mmol) in MeOH (2.1 mL) were added dimethyl 1-diazo-(2-
oxopropyl)phosphonate (142 mg, 0.75 mmol) and K2CO3 (115 mg,
0.83 mmol) under positive pressure of dry Ar. The reaction mixture
was stirred at rt for 1.5 h. Quenching of the reaction mixture with
saturated aqueous NH4Cl was followed by extraction with CH2Cl2.
Column chromatography (hexane/EtOAc ) 3/1) of the extract gave
21 (176 mg, 85%) as a solid. Crystallization from CH2Cl2-hexane
gave an analytical sample: mp 174-176 °C; UV (MeOH) λmax
271 nm (ꢀ 10 300), λmin 240 nm (ꢀ 3000); IR (neat) 3069 cm-1
(()-5′-O-(tert-Butyldiphenylsilyl)-4′-carbomethoxy-2′,3′-dide-
hydro-3′-deoxy-4′-thiothymidine (18). A mixture of 17â (2.27 g,
2.89 mmol) in THF (11.6 mL), AcOH (8.3 mL), and activated Zn,
prepared from Zn powder (537 mg, 8.24 mmol) according to the
published procedure,18 was stirred at rt for 1 h. The reaction mixture
was quenched by adding saturated aqueous NaHCO3, and filtered
through a Celite pad. The filtrate was partitioned between CH2Cl2
and saturated aqueous NaHCO3. Column chromatography (hexane/
EtOAc ) 3/1) of the organic layer gave 18 (1.55 g, 99%) as a
solid. Crystallization from CH2Cl2-hexane gave an analytical
sample: mp 184-185 °C; UV (MeOH) λmax 271 nm (ꢀ 10 000),
1
1
(CtCH); H NMR (CDCl3) δ 1.11 (9H, s, SiBu-t), 1.60 (3H, d,
λmin 240 nm (ꢀ 2900); H NMR (CDCl3) δ 1.06 (9H, s, SiBu-t),
J6,Me ) 1.1 Hz, 5-Me), 2.59 (1H, s, CtCH), 3.90 and 3.95 (2H,
each as d, Jgem ) 9.7 Hz, H-5′), 5.80 (1H, dd, J2′,3′ ) 6.0 Hz and
J1′,2′ ) 2.3 Hz, H-2′), 6.23 (1H, dd, J2′,3′ ) 6.0 Hz and J1′,3′ ) 1.7
1.68 (3H, d, J6,Me ) 1.2 Hz, 5-Me), 3.79 and 4.26 (2H, each as d,
Jgem ) 9.7 Hz, H-5′), 3.80 (3H, s, CO2Me), 5.83 (1H, dd, J2′,3′
)
6.3 Hz and J1′,2′ )2.4 Hz, H-2′), 6.55 (1H, dd, J2′,3′ ) 6.3 Hz and
J1′,3′ ) 1.9 Hz, H-3′), 6.78 (1H, d, J6,Me ) 1.2 Hz, H-6), 7.08 (1H,
dd, J1′,2′ ) 2.4 Hz and J1′,3′ ) 1.9 Hz, H-1′), 7.38-7.46 (6H, m,
Ph), 7.64-7.67 (4H, m, Ph), 8.91 (1H, br, NH); 13C NMR(CDCl3)
δ 12.5 (5-Me), 19.3 (SiCMe3), 26.6 (SiCMe3), 53.1 (CO2Me), 67.5
(C-1′), 69.8 (C-4′), 70.2 (C-5′), 112.2 (C-5), 129.3 (C-2′), 135.1
(C-6), 127.9, 130.1, 135.4 and 135.5 (Ph-tertiary), 132.2 and 132.7
(Ph-quaternary), 136.9 (C-3′), 150.3 (C-2), 163.2 (C-4), 171.3
(CO2Me); FAB-MS (m/z) 537 (M+ + H). Anal. Calcd for
C28H32N2O5SSi‚1/3H2O: C, 61.97; H, 6.07; N, 5.16. Found: C,
61.99; H, 6.00; N, 5.05.
Hz, H-3′), 6.93 (1H, d, J6,Me ) 1.1 Hz, H-6), 7.23 (1H, dd, J1′,2′
)
2.3 Hz and J1′,3′ ) 1.7 Hz, H-1′), 7.37-7.46 (6H, m, Ph), 7.68-
7.72 (4H, m, Ph), 8.61 (1H, br, NH); 13C NMR (CDCl3) δ 12.3
(5-Me), 19.5 (SiCMe3), 26.8 (SiCMe3), 61.0 (C-4′), 67.6 (C-1′),
71.4 (C-5′), 73.5 (CtCH), 82.7 (CtCH), 112.1 (C-5), 127.9, 130.0,
130.1 and 135.6 (Ph-tertiary), 128.9 (C-2′), 132.5 and 132.9 (Ph-
quaternary), 135.4 (C-6), 137.8 (C-3′), 150.3 (C-2), 163.2 (C-4);
FAB-MS (m/z) 503 (M+ + H). Anal. Calcd for C28H30N2O3SSi:
C, 66.90; H, 6.02; N, 5.57. Found: C, 66.96; H, 6.03; N, 5.57.
(()-2′,3′-Didehydro-3′-deoxy-4′-ethynyl-4′-thiothymidine (29).
To a THF (0.6 mL) solution of 21 (187 mg, 0.37 mmol) was added
Bu4NF (1 M in THF, 0.51 mL, 0.51 mmol). The reaction mixture
was stirred at rt for 1.5 h. Addtion of CH2Cl2 and saturated aqueous
NaHCO3 to the reaction mixture gave 29 (54 mg, 55%) as a
precipitate: mp 259-262 °C; UV (MeOH) λmax 271 nm (ꢀ 10 800),
(()-5′-O-(tert-Butyldiphenylsilyl)-2′,3′-didehydro-3′-deoxy-4′-
hydroxymethyl-4′-thiothymidine (19). To a solution of 18 (1.0
g, 1.86 mmol) in MeOH (10 mL) was added NaBH4 (2.8 g, 74.5
mmol) by portions at 0 °C. The reaction mixture was stirred at rt
for 3 h, quenched by adding AcOH, and then extracted with CH2Cl2.
Column chromatography (hexane/EtOAc ) 1/1) of the extract gave
19 (933 mg, 98%) as a solid. Crystallization from CH2Cl2-hexane
gave an analytical sample: mp 166-171 °C; UV (MeOH) λmax
272 nm (ꢀ 9700), λmin 240 nm (ꢀ 2800); 1H NMR (CDCl3) δ 1.08
(9H, s, SiBu-t), 1.70 (3H, d, J6,Me ) 1.1 Hz, 5-Me), 2.36 (1H, dd,
J5′,OH ) 8.0 and J) 5.2 Hz, OH), 3.85-3.95 (4H, m, H-5′ and
CH2OH), 5.75 (1H, dd, J2′,3′ ) 6.3 Hz and J1′,2′ ) 2.3 Hz, H-2′),
1
λmin 239 nm (ꢀ 3000); IR (neat) 3051 cm-1 (CtCH); H NMR
(DMSO-d6) δ 1.71 (3H, d, J6,Me ) 1.2 Hz, 5-Me), 3.46 (1H, s,
CtCH), 3.58 and 3.79 (2H, each as dd, Jgem ) 11.3 Hz and J5′,OH
) 6.1 Hz, H-5′), 5.75 (1H, t, J5′,OH ) 6.1 Hz, OH), 5.91 (1H, dd,
J2′,3′ ) 6.1 Hz and J1′,2′ ) 2.7 Hz, H-2′), 6.08 (1H, dd, J2′,3′ ) 6.1
Hz and J1′,3′ ) 2.0 Hz, H-3′), 6.93 (1H, dd, J1′,2′ ) 2.7 Hz and J1′,3′
) 2.0 Hz, H-1′), 7.69 (1H, d, J6,Me ) 1.2 Hz, H-6), 11.33 (1H, br,

7866 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 26
Kumamoto et al.
NH); 13C NMR (DMSO-d6) δ 12.2 (5-Me), 61.6 (C-4′), 67.4 (C-
1′), 68.0 (C-5′), 75.9 (CtCH), 82.8 (CtCH), 109.6 (C-5), 129.1
(C-2′), 136.8 (C-6), 138.0 (C-3′), 150.5 (C-2), 163.6 (C-4); FAB-
MS (m/z) 265 (M++H). Anal. Calcd for C12H12N2O3S: C,54.53;
H, 4.58; N, 10.60. Found: C, 54.56; H, 4.39; N, 10.81.
Anti-HIV-1 Assay. MT-4 cells27 were maintained in RPMI 1640
medium supplemented with 10% heat-inactivated fetal bovine serum
(FBS), 100 U/mL penicillin G, and 100 µg/mL streptomycin. The
IIIB strain of HIV-1 was used throughout the experiment. The virus
was propagated and titrated in MT-4 cells. Virus stocks were stored
-80 °C until use.
The anti-HIV-1 activity of the test compounds was determined
by the inhibition of virus-induced cytopathogenicity in MT-4 cells.28
Briefly, MT-4 cells (1 × 105 cells/mL) were infected with HIV-1
at a multiplicity of infection (MOI) of 0.02 and were cultured in
the presence of various concentrations of the test compounds. After
a 4-day incubation at 37 °C, the number of viable cells was
monitored by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetra-
zolium bromide (MTT) method.29 The cytotoxicity of the com-
pounds was evaluated in parallel with their antiviral activity, based
on the viability of mock-infected cells as determined by the MTT
method.
(10) Nitanda, T.; Wang, X.; Kumamoto, H.; Haraguchi, K.; Tanaka, H.;
Cheng, Y.-C.; Baba, M. Anti-human immunodeficiency virus type
1 activity and resistance profile of 2′,3′-didehydro-3′-deoxy-4′-
ethynylthymidine in vitro. Antimicrob. Agents Chemother. 2005, 49,
3355-3360.
(11) Woodward, R. B.; Eastman, R. H. Tetrahydrothiophene (“thiophane”)
derivatives. J. Am. Chem. Soc. 1946, 68, 2229-2235.
(12) (a) Luche, J.-L. Selective 1,2-reduction of conjugated ketones. J. Am.
Chem. Soc. 1978, 100, 2226-2227. (b) Luche, J.-L.; Rodriguez-Hahn,
L.; Crabbe´, P. Reduction of natural enones in the presence of cerium
trichloride. J. Chem. Soc., Chem. Commun. 1978, 601-602.
(13) Kato, K.; Suzuki, H.; Tanaka, H.; Miyasaka, T.; Baba, M.; Yamagu-
chi, K.; Akita, H. Stereoselective synthesis of 4′-a-alkylcarbovir
derivatives based on an asymmetric synthesis or chemoenzymatic
procedure. Chem. Pharm. Bull. 1999, 47, 1256-1264.
(14) During 3-O-acylation of 9, formation of a small amount of epimer
was observed. NMR data of the epimeric isomer of 13: 1H NMR
(CDCl3) δ 1.04 (9H, s, SiBu-t ), 3.77 (3H, s, CO2Me), 3.82 and 4.24
(2H, each as d, Jgem ) 9.5 Hz, CH2OSi), 6.14 (1H, dd, Hz, J3,4
)
2.7 Hz and J4,5 ) 6.3 Hz, H-4), 6.65 (1H, d, J4,5 ) 6.3 Hz, H-5),
6.90 (1H, d, J3,4 ) 2.7 Hz, H-3), 7.32-7.45 (8H, m, ph), 7.53-7.57
(1H, m, Ph), 7.61-7.64 (4H, m, Ph), 7.90-7.92 (2H, m, Ph); 13C
NMR (CDCl3) δ 19.3 (SiCMe3), 26.6 (SiCMe3), 52.8 (CO2Me), 69.5
(C-2), 71.3 (CH2OSi), 85.8 (C-3), 127.7, 128.4, 129.7, 129.8, 133.3
and 135.6 (Ph-tertiary), 129.4, 132.7 and 133.0 (Ph-quaternary ),
129.2 (C-4), 137.5 (C-5), 165.9 (COPh), 171.4 (CO2Me).
(15) For a review article, see: Trost, B. M. Asymmetric alkylation, an
enabling methodology. J. Org. Chem. 2004, 69, 5813-5837.
(16) (a) Haraguchi, K.; Takahashi, H.; Shiina, N.; Horii, C.; Yoshimura,
Y.; Nishikawa, A.; Sasakura, E.; Nakamura, K. T.; Tanaka, H.
Stereoselective synthesis of the â-anomer of 4′-thionucleosides based
on electrophilic glycosidation to 4-thiofuranoid glycals. J. Org. Chem.
2002, 67, 5919-5927. (b) Haraguchi, K.; Takahashi, H.; Tanaka,
H. Stereoselective entry to 1′-C-branched 4′-thionulcosides from
4-thiofuranoid glycals: synthesis of 4′-thioangustmycin C. Tetra-
hedron Lett. 2002, 43, 5657-5660. (c) Haraguchi, K.; Shiina, N.;
Yoshimura, Y.; Shimada, H.; Hashimoto, K.; Tanaka, H. Novel
stereoselective entry to 2′-â-carbon-substituted 2′-deoxy-4′-thio-
nucleosides from 4-thiofuranoid glycals. Org. Lett. 2004, 6, 2645-
2648. (d) Haraguchi, K.; Takahashi, H.; Tanaka, H.; Hayakawa, H.;
Ashida, N.; Nitanda, T.; Baba, M. Synthesis and antiviral activities
of 1′-carbon-substituted 4′-thiothymidines. Bioorg. Med. Chem. 2004,
12, 5309-5316.
Acknowledgment. Financial supports from the Japan Society
for the Promotion of Science (KAKENHI, Grant No. 18790090
to H.K., No. 17590093 to K.H., and No. 17590094 to H.T.)
and the Japan Health Sciences Foundation (Grant SA 14804 to
H.T.) are gratefully acknowledged. The authors are also grateful
to Ms. K. Shiobara and Y. Odanaka (Center for Instrumental
Analysis, Showa University) for technical assistance with NMR,
MS, and elemental analyses.
Supporting Information Available: Synthetic procedures and
characterization data for 11, 12, 14, 15â, 15R, 16â, 16R, 22-26,
and 28, procedures for optical resolution of 29, and ORTEP drawing
of 17R. This material is available free of charge via the Intermet at
http://pubs.acs.org.
(17) NMR assignments of 15-17 are given according to the numbering
of usual nucleosides.
References
(18) For ORTEP drawing and X-ray crystallographic data of 17R, see
supporting information.
(1) Reist, E. J.; Gueffroy, D. E.; Goodman, I. Synthesis of 4-thio-D- and
-L-ribofuranose and the corresponding adenine nucleosides. J. Am.
Chem. Soc. 1964, 86, 5658-5663.
(2) (a) Secrist, J. A., III; Tiwari, K. N.; Riordan, J. M.; Montgomery, J.
A. Synthesis and biological activity of 2′-deoxy-4′-thio pyrimidine
nucleosides. J. Med. Chem. 1991, 34, 2361-2366. (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.
(3) For a review, see: Yokoyama, M. Synthesis and biological activity
of thionucleosides. Synthesis 2000, 1637-1655.
(4) 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.
(5) Miura, S.; Yoshimura, Y.; Endo, M.; Machida, H.; Matsuda, A.;
Tanaka, M.; Sasaki, T. Antitumor activity of a novel orally effective
nucleoside, 1-(2-deoxy-2-fluoro-4-thio-â-D-arabinofuranosyl)cytosine.
Cancer Lett. 1998, 129, 103-110.
(6) Jeong, L. S.; Jin, D. Z.; Kim, H. O.; Shin, D. H.; Moon, H. R.;
Gunaga, P.; Chun, M. W.; Kim, Y.-C.; Melman, N.; Gao, Z.-G.;
Jacobson, K. A. N6-substituted D-4′-thioadenosine-5′-methyluron-
amides: potent and selective agonists at the human A3 adenosine
receptor. J. Med. Chem. 2003, 46, 3775-3777.
(19) Mansuri, M. M.; Starrett, J. E., Jr.; Wos, J. A.; Tortolani, D. R.;
Brodfuehrer, P. R.; Howell, H. G.; Martin, J. C. Preparation of 1-(2,3-
dideoxy-â-D-glycero-pent-2-enofuranosyl)thymine (d4T) and 2′,3′-
dideoxyadenosine (ddA): General methods for the synthesis of 2′,3′-
olefinic and 2′,3′-dideoxy nucleoside analogs active against HIV. J.
Org. Chem. 1989, 54, 4780-4785.
(20) Miwa, K.; Aoyama, T.; Shioiri, T. Extension of the Colvin re-
arrangement using trimethylsilyldiazomethane, a new synthesis of
alkynes. Synlett 1994, 107-108.
(21) Ohira, S. Methanolysis of dimethyl (1-diazo-2-oxopropyl)phos-
phonate: Generation of dimethyl (diazomethyl)phosphonate and
reaction with carbonyl compounds. Synth. Commun. 1989, 19, 561-
564.
(22) Haraguchi, K.; Itoh, Y.; Takeda, S.; Honma, Y.; Tanaka, H.; Nitanda,
T.; Baba, M.; Dutschman, G. E.; Cheng, Y.-C. Synthesis and anti-
HIV activity of 4′cyano-2′,3′-didehydro-3′-deoxythymidine. Nucleo-
sides, Nucleotides Nucleic Acids 2004, 23, 647-654.
(23) Kumamoto, H.; Haraguchi, K.; Tanaka, H.; Nitanda, T.; Baba, M.;
Dutschman, G. E.; Cheng, Y.-C.; Kato, K. Synthesis of (()-4′-ethynyl
and 4′-cyano carbocyclic analogues of stavudine (d4T). Nucleosides,
Nucleotides Nucleic Acids 2005, 24, 73-83.
(24) Specific rotation: (-)-29, [R]2D0 -150.0 (c 0.10, MeOH); (+)-29,
[R]2D0 +153.3 (c 0.10, MeOH).
(25) Mansuri, M. M.; Farina, V.; Starrett, J. E., Jr.; Benigni, D. A.;
Brankovan, V.; Martin, J. C. Preparation of the geometric isomers
of DDC, DDA, D4C and D4T as potential anti-HIV agents. Bioorg.
Med. Chem. Lett. 1991, 1, 65-68.
(26) 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.
(27) Miyoshi, I.; Taguchi, H.; Kubonishi, I.; Yoshimoto, S.; Ohtsuki, Y.;
Shiraishi, Y.; Akagi, T. Type C virus-producing cell lines derived
from adult T cell leukemia. Gann Monogr. Cancer Res. 1982, 28,
219-228.
(7) Haraguchi, K.; Kubota, Y.; Tanaka, H. Ring opening of nucleoside
1′,2′-epoxides with organoaluminum reagents: stereoselective entry
to ribonucleosides branched at the anomeric position. J. Org. Chem.
2004, 69, 1831-1836.
(8) Haraguchi, K.; Takeda, S.; Tanaka, H.; Nitanda, T.; Baba, M.;
Dutschman, G. E.; Cheng, Y.-C. Synthesis of a highly active new
anti-HIV agent 2′,3′-didehydro3′-deoxy-4′ethynylthymidine. Bioorg.
Med. Chem. Lett. 2003, 13, 3775-3777.
(9) Dutschman, G. E.; Grill, S. P.; Gullen, E. A.; Haraguchi, K.; Takeda,
S.; Tanaka, H.; Baba, M.; Cheng, Y.-C. Novel 4′-substituted stavudine
analog with improved anti-human immunodeficiency virus activity
and decreased cytotoxicity. Antimicrob. Agents Chemother. 2004, 48,
1640-1646.

Synthesis and Anti-HIV ActiVity of 4′-ThiostaVudines
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 26 7867
(28) Baba, M.; De Clercq, E.; Tanaka, H.; Ubasawa, M.; Takashima, H.;
Sekiya, K.; Nitta, I.; Umezu, K.; Nakashima, H.; Mori, S.; Shigeta,
S.; Walker, R. T.; Miyasaka, T. Potent and selective inhibition of
human immunodeficiency virus type 1 (HIV-1) by 5-ethyl-6-
phenylthiouracil derivatives through their interaction with the HIV-1
reverse transcriptase. Proc. Natl. Acad. Sci. U.S.A. 1991, 88, 2356-
2360.
(29) Pauwels, R.; Balzarini, J.; Baba, M.; Snoeck, R.; Schols, D.;
Herdewijn, P.; J. Desmyter, J.; De Clercq, E. Rapid and automated
tetrazolium-based colorimetric assay for the detection of anti-HIV
compounds. J. Virol. Methods 1988, 20, 309-312.
JM060980J