Synthesis of (±)-4′-ethynyl and 4′-cyano carbocyclic analogues of stavudine (d4T)

Article abstract of DOI:10.1081/NCN-200051900

The synthesis of (±)-4′-ethynyl (8) and 4′-cyano (9) carbocyclic analogues of the anti-HIV agent stavudine (5, d4T) is reported. The carbocyclic unit (16) was constructed from readily available β-keto ester 10. The ethynyl or cyano group of 8 and 9 were p

Full text of DOI:10.1081/NCN-200051900

Nucleosides, Nucleotides, and Nucleic Acids, 24 (2):73–83, (2005)
Copyright D 2005 Taylor & Francis, Inc.
ISSN: 1525-7770 print/ 1532-2335 online
DOI: 10.1081/NCN-200051900
SYNTHESIS OF ( )-4’-ETHYNYL AND 4’-CYANO CARBOCYCLIC
ANALOGUES OF STAVUDINE (d4T)
5
Hiroki Kumamoto, Kazuhiro Haraguchi, and Hiromichi Tanaka
School of
Pharmaceutical Sciences, Showa University, Tokyo, Japan
5
Takao Nitanda and Masanori Baba
Center for Chronic Viral Diseases, Division of
Human Retroviruses, Faculty of Medicine, Kagoshima University, Kagoshima, Japan
5
Ginger E. Dutschman and Yung-Chi Cheng
Department of Pharmacology, School of
Medicine, Yale University, New Haven, Connecticut, USA
5
Keisuke Kato
School of Pharmaceutical Sciences, Toho University, Chiba, Japan
5
The synthesis of (+)-4’-ethynyl (8) and 4’-cyano (9) carbocyclic analogues of the anti-HIV agent
ꢀ
stavudine (5, d4T) is reported. The carbocyclic unit (16) was constructed from readily available b-keto
ester 10. The ethynyl or cyano group of 8 and 9 were prepared, after the introduction of thymine base to
16, by manipulation of the ester function. Evaluation of the anti-HIV activity of 8 and 9 was also
carried out.
Keywords Stavudine, 4’-ethynyl-d4T, Carbocyclic Nucleoside
INTRODUCTION
The finding that thymidine derivatives bearing 4’-azido (1)[1] and 4’-cyano (2)[2]
substituents show significant inhibitory activity against HIV proliferation has
stimulated the synthesis of 4’-substituted nucleoside analogues. In fairy recent
studies along this line, 4’-ethynylnucleosides have also been shown to be promising
anti-HIV agents.[3–6]
On the other hand, carbocyclic nucleosides have attracted considerable attention
as antitumor and antiviral agents.[7–10] In particular, those having a cyclopentene
structure, such as carbovir (3) and its cyclopropylamino derivative abacavir (4), have
been known to act as potent anti-HIV (human immunodeficiency virus) agents.[11]
Received 21 September 2004, accepted 21 October 2004.
This work was financially supported in part by grants from the Japan Health Sciences Foundation (SA14718
to H. T.), Japan Society for the Promotion of Science (KAKENHI No. 15790075 to H. K., No. 15590100 to K. H.,
and No. 15590020 to H. T.), and NIH USA (RO1 AI 38204 to Y.-C. C.).
Address correspondence to Hiroki Kumamoto, School of Pharmaceutical Sciences, Showa University, 1-5-8
Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan; E-mail: kumamoto@pharm.showa-u.ac.jp
73
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H. Kumamoto et al.
In our recent studies on the C–C bond formation at the 4’-position of
nucleosides,[12–14] the synthesis of 4’-ethynyl (6)[13] and 4’-cyano (7)[14] analogues of
anti-HIV agent stavudine (5, d4T: 2’,3’-didehydro-3’-deoxythymidine) has been
executed. As a result of their antiviral evaluation, both compounds (6 and 7) were
found to be active against HIV, in particular the activity of 4’-ethynyl-d4T (6) was
higher than the parent compound d4T (5).[13] Furthermore, this compound was
found to be less toxic to CEM cell growth and less inhibitory to mitochondrial
DNA synthesis than d4T.[15] These findings prompted us to design and synthesize
the carbocyclic counterparts of 6 and 7. In this article, we report the synthesis of the
4’-ethynyl (8) and 4’-cyano (9) carbocyclic analogues of d4T as racemates.
RESULTS AND DISCUSSION
A synthetic method for 4’-alkylcarbovir derivatives has been reported from our
laboratory.[16,17] In this synthesis, alkyl substituents were introduced into the
cyclopentane ring by alkylation of the lithium enolate derived from the com-
mercially available methyl 2-oxocyclopentane-carboxylate (10). Since such an
approach was apparently not readily applicable to the introduction of ethynyl or
cyano groups, we considered the possibility of using the carbomethoxy group of
10 as precursor of our requisite 4’-substituents.
We, therefore, initiated the present study with the introduction of a
hydroxymethyl group to 10 (Scheme 1). Attempted reactions of the potassium
SCHEME 1 Preparation of the carbocyclic unit 16.

Synthesis of (+)-4’-Ethynyl and 4’-Cyano Carbocyclic Analogues of Stavudine
75
ꢀ
FIGURE 1 NOE correlations observed for 15.
salt of 10 with paraformaldehyde in variety of solvents (DMSO, DMF, HMPA, or
H2O) all met with failure. The desired alcohol 11 was obtained in 77% yield by
converting the potassium salt to its tin enolate (Bu3SnCl/HMPA-THF/0°C/0.5 h) and
then reacting with paraformaldehyde for 48 h at room temperature. It was found,
however, that direct treatment of 11 simply with 37% aqueous HCHO in the
presence of AcOH (at rt for 48 h) gave 11 in quantitative yield.
Conventional silylation of 11 with tert-butyldiphenylsilyl chloride gave 12
(77%). Introduction of a double bond to 12 was conducted by Pd-catalyzed
dehydrogenation through the corresponding silyl-enolate.[18] The enone 13 was
obtained in 88% yield by this procedure. The Luche reduction[19] of 13 fol-
lowed by acetylation gave the allyl acetate 14 in quantitative yield as a single
isomer, although its stereochemistry could not be determined at this stage. Com-
pound 14, upon Pd-catalyzed allylic rearrangement[20] followed by deacetylation,
gave the allyl alcohol 15 in 67% yield. The depicted stereochemistry of 15 came
from the results of NOE experiments given in Figure 1. The desired carbocyclic
unit 16 was prepared in 83% yield by the Mitsunobu inversion[21] of 15 and
subsequent deacetylation.
For the coupling reaction of 16 under the Mitsunobu conditions, N3-
benzoylthymine[22] was employed. The resulting reaction mixture was evaporated
and then treated with NaOMe in MeOH to give the carbocyclic nucleoside 17 in
52% yield (Scheme 2). The HMBC (heteronuclear multiple bond connectivity)
spectrum of 17 gave a cross peak between H-6 and C-1’, which confirmed the
depicted regiochemistry.
There are many methods available for the transformation of aldehydes to
alkynes.[2]a Reduction of the ester function of 17 was carried out with i-Bu2AlH.
However, it turned out that, even at low temperature (ꢀ70°C in CH2Cl2), only
a small amount of the desired aldehyde 19 was formed, the main product being
the hydroxymethyl derivative 18, as evidenced by TLC analysis (hexane/
EtOAc = 1/3). Compound 18 was, therefore, reoxidized with Dess-Martin
periodinane in CH2Cl2 and the aldehyde 19 formed was used for further trans-
formations without characterization.
aFor example, see Ref. [23].

76
H. Kumamoto et al.
SCHEME 2 (R = TBDPS) Synthesis of 4’-ethynyl and 4’-cyano carbocyclic d4T.
For the preparation of the 4’-ethynyl derivative (20), the method reported by
Agrofoglio and co-workers[24] was used. Thus, treatment of 19 with a
b
diazophosphonate CH3COC(N2)P(O)(OMe)2 in MeOH in the presence of
K2CO3 furnished 20 in 47% yield. Its 13CNMR spectrum showed the presence of
two 13C-resonances apparently derived from carbon atoms of the ethynyl group: d
71.1 (C ꢁ CH) and 84.8 (C ꢁ CH). In addition, an NOE enhancement (0.5%) was
observed between H-6 and CH2-6’ of 20, supporting the depicted stereochemistry.
The 4’-cyano derivative 22 was prepared in 81% yield through the oxime inter-
mediate 21, which underwent spontaneous elimination upon treatment with
MsCl in pyridine. In the 13C NMR spectrum of 22, the 4’-CN appeared at d 120.2,
which is typical for nitrile resonances.c Desilylation of 20 and 22 was carried out
by conventional procedure (Bu4NF in THF). The target compounds 8 (60%) and
9 (32%) were obtained after purification through the respective 6’-O-acetate.
Finally, 8 and 9 were assayed for their ability to inhibit the replication of HIV-1
in MT-4 cell culture, the results of which are summarized in Table 1 together with
the data of stavudine and 4’-ethynylstavudine (6). Unfortunately, both 8 and 9 did
not display any inhibitory activity.
EXPERIMENTAL SECTION
1
Melting points are uncorrected. H NMR and 13C NMR were measured on a
JEOL JNM-LA 500 (500 MHz). Chemical shifts are reported relative to Me4Si. Mass
bFor the preparation of the diazophosphonate: Ref. [25].
cSynthesis of 4’-cyano-2’-deoxy purine nucleosides has recently been reported: Ref. [26].

Synthesis of (+)-4’-Ethynyl and 4’-Cyano Carbocyclic Analogues of Stavudine
77
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TABLE 1 Anti-HIV-1 Activity in MT-4 Cells
Compound
EC50 (mM)
CC50 (mM)
Stavudine
0.47
0.14
>100
>100
>100
>100
>100
>100
6
8
9
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 chro-
matography (HPLC). HPLC was carried out on a Shimadzu LC-6AD with a
Shim-pack PREP-SIL (H). KIT column (2 ꢂ 25 cm). THF was distilled from
benzophenone ketyl.
1-Hydroxymethyl-2-oxocyclopentanecarboxylic acid methyl
ester (11). A mixture of 10 (5.0 g, 35.2 mmol), 37% aqueous HCHO
(33 mL, ca. 370 mmol), and AcOH (4.03 mL, 70.3 mmol) was stirred for 23 h at rt.
The reaction mixture was partitioned between CH2Cl2 and aqueous NaHCO3.
The organic layer was dried (Na2SO4), and purified by column chromatography
1
(hexane/EtOAc = 1/1). This gave 11 (6.05 g, 100%) as an oil: HNMR (CDCl3) d
1.97–2.18 (2H, m, CH2), 2.21–2.25 (1H, m, CH2), 2.29–2.53 (3H, m, OH and
CH2), 2.62–2.66 (1H, m, CH2), 3.74 (3H, s, Me), 3.81 (1H, dd, J = 11.2 and 8.0
Hz, CH2OH), 3.89 (1H, dd, J = 11.2 and 4.4 Hz, CH2OH); FAB-MS m/z 173
.
(M++ H). Anal Calcd for C8H12O4 1/5H2O: C, 54.65; H, 7.11. Found: C, 54.54;
H 6.96.
1-(tert-Butyldiphenylsilyloxymethyl)-2-oxo-cyclopentanecar-
boxylic acid methyl ester (12). A mixture of 11 (10.35 g, 60.1 mmol),
imidazole (8.18 g, 120.2 mmol), and TBDPSCl (15.6 ml, 60.1 mmol) in DMF
(40 mL) was stirred for 16 h at room temperature under positive pressure of dry Ar.
The mixture was partitioned between EtOAc and sat. aqueous NaHCO3. The
organic layer was dried (Na2SO4) and evaporated. The resulting syrupy residue was
treated with MeOH (ca. 40 mL) to give the precipitated 12. This procedure was
repeated further three times to give 12 (18.97 g, 77%) as a white solid: mp 89–91°C;
1HNMR (CDCl3) d 1.02 (9H, s, SiBu-t), 2.03–2.11 (2H, m, CH2), 2.26–2.35 (1H, m,
CH2), 2.41–2.53 (3H, m, CH2), 3.65 (3H, s, Me), 3.87 (1H, d, J = 9.6 Hz, CH2OSi),
4.09 (1H, d, J = 9.6 Hz, CH2OSi), 7.37–7.46 (6H, m, Ph), 7.61–7.65 (4H, m, Ph);
FAB-MS m/z 411 (M++ H). Anal Calcd for C24H30O4Si ꢃ 1/10H2O: C, 69.90; H,
7.38. Found: C, 69.89; H, 7.43.

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H. Kumamoto et al.
1-(tert-Butyldiphenylsilyloxymethyl)-2-oxo-3-cyclopentene-
carboxylic acid methyl ester (13). To a stirring mixture of 12 (3.58 g,
8.72 mmol) and Et3N (6.1 ml, 43.6 mmol) was added Me3SiOSO2CF3 (2.56 mL, 13.0
mmol) at 0°C under positive pressure of dry Ar. The mixture was stirred for 30 min at
the same temperature and then partitioned between CH2Cl2 and sat. aqueous
NaHCO3. The organic layer was dried (Na2SO4) and evaporated. The residue
was dissolved in DMSO (12 mL). To this solution was added Pd(OAc)2 (98 mg,
0.44 mmol), and the mixture was stirred for 36 h under positive pressure of O2.
The mixture was partitioned between EtOAc and brine. Column chromatogra-
phy (hexane/EtOAc = 5/1) of the organic layer gave 13 (3.13 g, 88%) as a white
1
solid: mp 103–105°C; HNMR (CDCl3) d 0.97 (9H, s, SiBu-t), 2.99–3.05 (1H, m,
CH2), 3.21–3.26 (1H, m, CH2), 3.66 (3H, s, Me), 3.98 (1H, d, J = 10.0 Hz, CH2OSi),
4.18 ((1H, d, J = 10.0 Hz, CH2OSi),6.24–6.26 (1H, m, CH = CH), 7.37–7.45 (6H, m,
Ph), 7.58–7.62 (4H, m, Ph), 7.86–7.88 (1H, m, CH = CH); FAB-MS m/z 409 (M++ H).
Anal Calcd for C24H28O4Si ꢃ 1/10H2O: C, 70.24; H, 6.93. Found: C, 70.19; H, 6.94.
2-Acetoxy-1-(tert-butyldiphenylsilyloxy)methyl-3-cyclopent-
enecarboxylic acid methyl ester (14). A mixture of NaBH4 (628 mg,
16.6 mmol) and MeOH (50 mL) was cooled and stirred at ꢀ70°C. To this was added
a mixture of 13 (3.39 g, 8.3 mmol) and CeCl3ꢃ 7H2O (3.1 g, 8.3 mmol) in THF/
MeOH = 1/1 (50 mL) drop-wise for 15 min. The resulting suspension was stirred for
1 h at ꢀ70°C. The reaction was quenched by adding AcOH (ca. 1 mL). The reaction
mixture was evaporated. The residue was suspended in MeCN (15 ml). To this
suspension were added DMAP (1.02 g, 8.3 mmol), i-Pr2NEt (1.45 mL, 8.3 mmol) and
Ac2O (1.57 mL, 16.6 mmol). The mixture was stirred for 30 min at 0°C under
positive pressure of dry Ar and partitioned between CH2Cl2 and sat. aqueous
NaHCO3. Column chromatography (hexane/EtOAc = 4/1) of the organic layer
gave 14 (3.74 g, 100%) as an oil: 1HNMR (CDCl3) d 1.02 (9H, s, SiBu-t), 1.87 (3H, s,
Ac), 2.50–2.55 (1H, m, CH2), 2.91–2.97 (1H, m, CH2), 3.71 (3H, s, Me), 3.87 (1H, d,
J = 9.6 Hz, CH2OSi), 4.08 (1H, d, J = 9.6 Hz, CH2OSi), 5.76–5.78 (1H, m,
CH = CH), 5.99–6.00 (1H, m, CH = CH), 6.07–6.08 (1H, m, AcOCH), 7.29–7.45
(4H, m, Ph), 7.61–7.65 (4H, m, Ph); FAB-MS m/z 453 (M++ H). Anal Calcd for
C26H32O5Si ꢃ 1/2H2O: C, 67.65; H, 7.21. Found: C, 67.73; H, 7.03.
1-(tert-Butyldiphenylsilyloxy)methyl-(trans-4-hydroxy)-2-
cyclopentenecarboxylic acid methyl ester (15). A mixture of 14
(1.87 g, 4.13 mmol), PdCl2(MeCN)2 (106 mg, 0.41 mmol), and p-benzoquinone
(224 mg, 2.07mmol) in THF (17 mL) was refluxed for 3 h under positive pressure of
dry Ar. The mixture was partitioned between CH2Cl2 and sat. aqueous Na2S2O3.
The organic layer was dried (Na2SO4), and evaporated. The residue was dissolved
in MeOH (5 ml) and treated with K2CO3 (685 mg, 4.96 mmol) for 1 h with stirring.
The mixture was partitioned between CHCl3 and brine. Column chromatography
(hexane/EtOAc = 6/1) of the organic layer gave 15 (1.14 g, 67%) as an oil: 1HNMR

Synthesis of (+)-4’-Ethynyl and 4’-Cyano Carbocyclic Analogues of Stavudine
79
ꢀ
(CDCl3) d 1.02 (9H, s, SiBu-t), 1.87 (1H, dd, J = 14.4 and 2.4 Hz, CH2), 2.73 (1H,
dd, J = 14.4 and 7.2 Hz, CH2), 3.65 (3H, s, Me), 3.79 (1H, d, J = 9.6 Hz, CH2OSi),
3.85 (1H, d, J = 9.6 Hz, CH2OSi), 4.82–4.87 (1H, m, CHOH), 5.84–5.87 (1H, m,
CH = CH), 6.02–6.04 (1H, m, CH = CH), 7.38–7.44 (6H, m, Ph), 7.63–7.65 (4H,
m, Ph); FAB-MS m/z 411 (M++ H). Anal Calcd for C24H30O4Si ꢃ 1/10H2O: C,
69.90; H, 7.38. Found: C, 69.89; H, 7.40.
1-(tert-Butyldiphenylsilyloxy)methyl-(cis-4-hydroxy)-2-cyclo-
pentenecarboxylic acid methyl ester (16). A mixture of 15 (1.08 g,
2.63 mmol) , Ph3P (897 mg, 3.42 mmol), and AcOH (301 mL, 5.26 mmol) in THF
(10 mL) was cooled to 0°C under positive pressure of dry Ar. To this was added
drop-wise diethyl azodicarboxylate (2.3 M solution in toluene, 1.49 mL, 3.42 mol).
After stirring for 30 min, the mixture was partitioned between CH2Cl2 and sat.
aqueous NaHCO3. The organic layer was dried (Na2SO4) and evaporated. The
residue was treated with K2CO3 (727 mg, 5.26 mmol) in MeOH (5 mL) for 1 h. The
mixture was partitioned between CHCl3 and brine. Column chromatography
(hexane/EtOAc = 4/1) of the organic layer gave 16 (892 mg, 83%) as an oil:
1HNMR (CDCl3) d 1.02 (9H, s, SiBu-t), 2.20–2.31 (3H, m, CH2 and OH), 3.70 (1H,
d, J = 9.6 Hz, CH2OSi), 3.71 (3H, s, Me), 3.87 (1H, d, J = 9.6 Hz, CH2OSi), 4.76–
4.81 (1H, m, CHOH), 5.88 (1H, d, J = 5.6 Hz, CH = CH), 6.03 (1H, dd, J = 5.6
and 2.4 Hz, CH = CH), 7.36–7.46 (6H, m, Ph), 7.61–7.65 (4H, m, Ph); FAB-MS
m/z 411 (M++ H). Anal Calcd for C24H30O4Si ꢃ 1/10H2O: C, 69.90; H, 7.38.
Found: C, 69.85; H, 7.46.
1-[cis-1-(tert-Butyldiphenylsilyloxy)methyl-trans-1-methoxy-
carbonyl-2-cyclopenten-4-yl]thymine (17). To a THF (30 mL) solution
of PPh3 (1.93 g, 7.35 mmol) was added drop-wise DEAD (2.3 M toluene solution,
3.08 mL, 7.08 mmol) at 0°C under positive pressure of dry Ar, and the mixture was
stirred for 0.5 h. To this was added a THF (45 mL) suspension containing 16 (1.16 g,
2.83 mmol) and N3-benzoylthymine (976 mg, 4.25 mmol), and the reaction mixture
was stirred for 45 h at room temperature. After evaporation of the solvent, the
residue was treated with 2M NaOMe in MeOH (5.5 mL) for 2 h with stirring. The
mixture was neutralized by adding AcOH (1.15 mL) and then partitioned between
CH2Cl2 and saturated aqueous NaHCO3. Column chromatography (hexane/
EtOAc = 1/1) of the organic layer gave 17 (758 mg, 52%) as a white foam: UV
(MeOH) lmax 272 nm (e 9800), lmin 240 nm (e 2200); 1HNMR (CDCl3) d 1.05 (9H,
s, SiBu-t), 1.74 (3H, d, J = 1.2 Hz, 5-Me), 1.75 (1H, dd, J = 14.0 and 6.8 Hz, H-5’),
3.01 (1H, dd, J = 14.0 and 8.4 Hz, H-5’), 3.70 (3H, s, CO2Me), 3.87 (1H, d, J = 10.0
Hz, H-6’), 3.90 (1H, d, J = 10.0 Hz, H-6’), 5.79 (1H, dd, J = 5.2 and 2.0 Hz, H-2’),
5.83–5.88 (1H, m, H-1’), 6.10 (1H, dd, J = 5.2 and 2.4 Hz, H-3’), 6.88 (1H, q, J = 1.2
Hz, H-6), 4.36–7.47 (6H, m, Ph), 7.61–7.64 (4H, m, Ph), 8.89 (1H, br, NH); FAB-MS
m/z 519 (M++ H). Anal Calcd for C29H34N2O5Si ꢃ 1/10H2O: C, 66.92; H, 6.62; N,
5.38. Found: C, 66.71; H, 6.59; N, 5.61.

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H. Kumamoto et al.
1-[cis-1-(tert-Butyldiphenylsilyloxy)methyl-trans-1-hydroxy-
methyl-2-cyclopenten-4-yl]thymine (18). To a CH2Cl2 (30 mL)
solution of 17 (2.1 g, 4.05 mmol) was added drop-wise i-Bu2AlH (1.01 M in
toluene, 16 mL, 16.2 mmol) at ꢀ70°C under positive pressure of dry Ar. After
stirring for 40 min, the reaction was quenched by adding AcOH, and the mixture
was partitioned between CHCl3 and aqueous NH4Cl. Column chromatography
(CHCl3/MeOH = 20/1) of the organic layer gave 18 (1.75 g, 88%) as a foam: UV
(MeOH) lmax 272 nm (e 9300), lmin 240 nm (e 1800); 1HNMR (CDCl3) d 1.07 (9H,
s, SiBu-t), 1.50 (1H, dd, J = 14.0 and 6.8 Hz, H-5’), 1.75 (3H, d, J = 0.8 Hz, 5-Me),
1.90 (1H, t, J = 5.8 Hz, OH), 2.43 (1H, dd, J = 14.0 and 8.6 Hz, H-5’), 3.58–3.64 (2H,
m, CH2OH), 3.67 (1H, d, J = 10.0 Hz, H-6’), 3.71 (1H, d, J = 10.0 Hz, H-6’), 5.72–
5.76 (2H, m, H-1’ and H-2’), 6.09 (1H, dd, J = 5.6 and 2.2 Hz, H-3’), 6.88 (1H, q,
J = 0.8 Hz, H-6), 7.36–7.47 (6H, m, Ph), 7.63–7.65 (4H, m, Ph), 8.26 (1H, br, NH);
FAB-MS m/z 491 (M++ H). Anal. Calcd for C28H34N2O4Si ꢃ H2O: C, 66.11; H, 7.13;
N. 5.51. Found: C, 66.48; H, 6.92; N, 5.50.
1-[cis-1-(tert-Butyldiphenylsilyloxy)methyl-trans-1-ethynyl-2-
cyclopenten-4-yl]thymine (20). To a solution of 18 (66 mg, 1.35 mmol)
in CH2Cl2 (20 mL) was added Dess-Martin periodinane (1.15 g 2.70 mmol). After
stirring for 1.5 h, the reaction mixture was partitioned between CH2Cl2 and
saturated aqueous NaHCO3. The organic layer was dried (Na2SO4) and evap-
orated to give the crude aldehyde 19, which was dissolved in MeOH (30 mL).
After adding K2CO3 (747 mg, 5.40 mmol), the MeOH solution of 19 was reacted
with dimethyl (1-diazo-2-oxopropyl)phosphonate (648 mg, 3.38 mmol) at room
temperature for 2 h. The reaction mixture was partitioned between EtOAc and
saturated aqueous NaHCO3. Column chromatography (hexane/EtOAc = 1/1) of
the organic layer gave 20 (305 mg, 47%) as a foam: UV (MeOH) lmax 271 nm
(e 9600), lmin 238 nm (e 1800); 1HNMR (CDCl3) d 1.07 (9H, s, SiBu-t), 1.71 (3H, d,
J = 1.2 Hz, 5-Me), 2.02 (1H, dd, J = 13.2 and 7.6 Hz, H-5’), 2.20 (1H, s, C ꢁ CH),
2.70 (1H, dd, J = 13.2 and 8.0 Hz, H-5’), 3.69 (1H, d, J = 9.6 Hz, H-6’), 3.83 (1H, d,
J = 9.6 Hz, H-6’), 5.76 (1H, dd, J = 5.2 and 2.0 Hz, H-2’), 5.91–5.95 (1H, m, H-1’),
6.02 (1H, dd, J = 5.2 and 2.4 Hz, H-3’), 6.98 (1H, q, J = 1.2 Hz, H-6), 7.37–7.48
(6H, m, Ph), 7.63–7.66 (4H, m, Ph), 8.20 (1H, br, NH); 13C NMR (CDCl3) d 12.3
(5-Me), 19.5 (CMe3), 26.9 (CMe3), 40.2 (C5’), 49.2 (C4’), 60.6 (C1’), 67.7 (C6’), 71.1
(C ꢁCH), 84.8 (Cꢁ CH), 111.3 (C5), 127.9, 130.0 135.5 and 135.6 (Ph-tertiary),
130.8 (C2’), 132.8 (Ph-quaternary), 136.3 (C6), 139.6 (C3’), 150.7 (C2), 163.4 (C4);
FAB-MS m/z 485 (M++ H). Anal. Calcd for C29H32N2O3Si ꢃ 3/4H2O: C, 69.91; H,
6.78; N, 5.62. Found: C, 70.10; H, 6.73; N, 6.02.
1-(tert-Butyldiphenylsilyloxy)methyl-trans-4-(thymin-1-yl)-2-
cyclopentenecarbaldehyde oxime (21). To a solution of 18 (1.7 g,
3.46 mmol) in CH2Cl2 (45 mL) was added Dess-Martin periodinane (2.93 g, 6.93
mmol). After stirring for 1.5 h, the mixture was partitioned between CH2Cl2 and

Synthesis of (+)-4’-Ethynyl and 4’-Cyano Carbocyclic Analogues of Stavudine
81
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saturated aqueous NaHCO3. The organic layer was dried (Na2SO4) and evap-
orated to give the crude aldehyde 19, which was dissolved in pyridine (50 mL)
containing NH2OH.HCl (482 mg, 6.93 mmol). After stirring for 20 h at room
temperature, the reaction mixture was partitioned between CH2Cl2 and brine.
Column chromatography (hexane/EtOA = 1/2) of the organic layer gave 21 (1.18
1
g, 68%) as a foam: UV (MeOH) lmax 272 nm (e 9300), lmin 240 nm (e 2400); H
NMR (CDCl3) d 1.08 (9H, s, Bu-t), 1.80 (3H, d, J = 1.0 Hz, 5-Me), 1.81 (1H dd,
J = 13.2 and 8.8 Hz, H-5’), 2.92 (1H, dd, J = 13.2 and 7.8 Hz, H-6’), 3.79 (1H, d,
J = 10.2 Hz, H-6’), 5.76–5.80 (2H, m, H-1’ and H-2’), 6.10 (1H, dd, J = 5.8 and 2.4
Hz, H-3’), 7.00 (1H, q, J = 1.0 Hz, H-6), 7.37–7.47 (7H m, CH = NOH and Ph),
7.61–7.65 (4H, m, Ph), 9.05 (1H, br, NH), 9.32 (1H, br, CH = NOH); FAB-MS m/z
504 (M++ H). Anal. Calcd for C28H33N3O4Si: C, 66.77; H, 6.60; N, 8.34. Found: C,
66.68; H, 6.78; N, 8.15.
1-[cis-1-(tert-Butyldiphenylsilyloxy)methyl-trans-1-cyano-2-
cyclopenten-4-yl]thymine (22). To a pyridine (10 mL) solution contain-
ing 21 (1.0 g, 1.99 mmol) and DMAP (366 mg, 3.0 mmol) was added MsCl (461 mL,
5.96 mmol) at 0°C. After stirring for 30 h at room temperature, the reaction mixture
was partitioned between CH2Cl2 and brine. Column chromatography (hexane/
EtOAc = 1/2) of the organic layer gave 22 (787 mg, 81%) as a foam: UV (MeOH)
l
max 271 nm (e 9900), lmin 238 nm (e 2000); 1H NMR (CDCl3) d 1.09 (9H, s, Bu-t),
1.75 (3H, d, J = 1.2 Hz, 5-Me), 1.88 (1H, dd J = 14.4 and 7.2 Hz, H-5’), 2.96 (1H,
dd, J = 14.4 and 8.4 Hz, H-5’), 3.78 (1H, d, J = 10.0 Hz, H-6’), 3.83 (1H, d, J = 10.0
Hz, H-6’), 5.86–5.91 (1H, m, H-1’), 5.97 (1H, dd, J = 5.2 and 2.0 Hz, H-2’), 6.08 (1H,
dd, J = 5.2 and 2.0 Hz, H-3’), 6.76 (1H, q, J = 1.2 Hz, H-6), 7.38–7.49 (6H, m, Ph),
7.61–7.65 (4H, m, Ph), 8.28 (1H, br, NH); 13C NMR (CDCl3) d 12.4 (5-Me), 19.4
(CMe3), 26.8 (CMe3), 38.4 (C5’), 49.9 (C4’), 60.3 (C1’), 66.9 (C6’), 111.7 (C5), 120.2
(CN), 128.0 130.2, 130.3, 135.5, and 135.6 (Ph-tertiary), 132.0 and 132.1 (Ph-
quaternary), 134.3 (C2’), 134.5 (C3’), 135.4 (C6), 150.4 (C2), 163.1 (C4); FAB-MS m/z
486 (M++ H). Anal. Calcd for C28H31N2O3Si ꢃ 1/4H2O: C, 68.61; H, 6.48; N, 8.57.
Found: C, 68.42; H, 6.46; N, 8.35.
1-(trans-1-Ethynyl-cis-1-hydroxymethyl-2-cyclopenten-4-yl)thy-
mine (8). A mixture of 20 (101 mg, 0.21 mmol) and Bu4NF (1M solution in
THF, 230 mL, 0.23 mmol) in THF (3 mL) was stirred for 2 h at room temperature.
To this mixture were added 4-dimethylaminopyridine (51 mg, 0.42 mmol), i-Pr2NEt
(73 mL, 0.42 mmol), and Ac2O (80 mL, 0.84 mmol). The reaction mixture was
stirred for 30 min, and then partitioned between CH2Cl2 and sat. aqueous
NaHCO3. Column chromatography (EtOAc) of the organic layer gave the acetate
(52 mg) as a solid. This acetate was treated with NH3/MeOH (35 ml) below 0°C for
12 h. During evaporation of the solvent, precipitation occurred. The precipitate was
washed with hot benzene (50 mL) to give an analytically pure sample of 8 (31 mg,
60%) as a solid: mp 205–208°C; UV (MeOH) lmax 272 nm (e 10,300), lmin 237 nm

82
H. Kumamoto et al.
1
(e 1600); HNMR (DMSO-d6) d 1.73 (3H, d, J = 0.8 Hz 5-Me), 1.89 (1H, dd,
J = 14.0 and 6.2 Hz, H-5’), 2.46 (1H, dd, J = 14.0 and 8.8 Hz, H-5’), 3.09 (1H, s,
C ꢁ CH), 3.41 (1H, dd, J = 10.8 and 6. Hz, H-6’), 4.58 (1H, dd, J = 10.8 and 5.4
Hz, H-6’), 5.22–5.25 (1H, m, OH), 5.60–5.63 (1H, m, H-1’), 5.77–5.79 (1H, m, H-2’),
5.93–5.95 (1H, m, H-3’) 7.31 (1H, q, J = 0.8 Hz, H-6) 11.2 (1H, br, NH); 13C NMR
(DMSO-d6) d 12.2 (5-Me), 39.8 (C5’), 49.1 (C4’), 59.9 (C1’), 66.4 (C6’), 72.8
(C ꢁ CH), 86.5 (C ꢁ CH), 108.8 (C5), 130.7 (C2’), 137.3 (C6), 139.0 (C3’), 150.8
(C2), 163.8 (C4). Anal. Calcd for C13H14N2O3ꢃ 1/5 H2O : C, 62.49; H, 5.81; N,
11.21. Found: C, 62.57; H, 5.65; N, 11.22.
1-(trans-1-Cyano-cis-1-hydroxymethyl-2-cyclopenten-4-yl)thy-
mine (9). A mixture of 22 (251 mg, 0.52 mmol) and Bu4NF (1M solution in
THF, 579 mL, 0.57 mmol) in THF (7 mL) was stirred for 2 h at room temperature.
To this mixture were added 4-dimethylaminopyridine (128 mg, 1.04 mmol), i-
Pr2NEt (181 mL, 1.04 mmol), and Ac2O (196 mL, 2.08 mmol). The reaction mixture
was stirred for 30 min, and then partitioned between CH2Cl2 and sat. aqueous
NaHCO3. Column chromatography (EtOAc) of the organic layer gave the acetate
(98 mg) as a solid. This acetate was treated with NH3/MeOH (20 ml) below 0°C for
12 h. During evaporation of the solvent, precipitation occurred. The precipitate was
washed with hot benzene (50 ml) to give an analytically pure sample of 9 (41 mg,
32%) as a solid: mp 228–230°C; UV (MeOH) lmax 271 nm (e 10,000), lmin 240 nm
1
(e 1700); H NMR (DMSO-d6) d 1.74 (3H, d, J = 0.8 Hz, 5-Me), 1.90 (1H, dd,
J = 14.4 and 6.4 Hz, H-5’), 2.73 (1H, dd, J = 14.4 and 8.8 Hz, H-5’), 3.62 (1H, dd,
J = 10.8 and 6.0 Hz, H-6’), 3.65 (1H, dd, J = 10.8 and 5.6 Hz, H-6’), 5.61–5.66 (2H,
m, H-1’ and OH), 6.06–6.11 (2H, m, H-2’ and H-3’), 7.23 (1H, q, J = 0.8 Hz, H-6),
11.31 (1H, br, NH); 13C NMR (DMSO-d6) d 12.1 (5-Me), 37.8 (C5’), 49.9 (C4’), 60.0
(C1’), 65.1 (C6’), 109.2 (C5), 121.8 (CN), 133.5 (C3’), 134.6 (C2’), 137.1 (C6), 150.8
(C2), 163.1 (C4); FAB-MS m/z 248 (M++ H). Anal. Calcd for C12H13N3O3: C,
58.29; H, 5.30; N, 17.00. Found: C, 58.27; H, 5.22; N, 16.71.
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