Truncated fluorocyclopentenyl pyrimidines as S-adenosylhomocysteine hydrolase inhibitors

Article abstract of DOI:10.1080/15257770903054316

On the basis of inhibitory activity of truncated cyclopentenyl cytosine against S-adenosylhomocysteine hydrolase (SAH), its fluorocyclopentenyl pyrimidine derivatives were efficiently synthesized from D-ribose via electrophilic fluorination as a key step.

Full text of DOI:10.1080/15257770903054316

Nucleosides, Nucleotides and Nucleic Acids, 28:601–613, 2009
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1525-7770 print / 1532-2335 online
DOI: 10.1080/15257770903054316
TRUNCATED FLUOROCYCLOPENTENYL PYRIMIDINES AS
S-ADENOSYLHOMOCYSTEINE HYDROLASE INHIBITORS
Yeon Hee Park, Won Jun Choi, Amol S. Tipnis, Kang Man Lee, and
Lak Shin Jeong
Department of Bioinspired Science and Division of Life and Pharmaceutical Sciences, College
of Pharmacy, Ewha Womans University, Seoul, Korea
On the basis of inhibitory activity of truncated cyclopentenyl cytosine against S-
2
adenosylhomocysteine hydrolase (SAH), its fluorocyclopentenyl pyrimidine derivatives were effi-
ciently synthesized from D-ribose via electrophilic fluorination as a key step. The final nucleosides
were evaluated for SAH inhibitory activity, among which the uracil derivative 9 showed significant
inhibitory activity (IC50 = 8.53 µM). They were also evaluated for cytotoxic effects in several
human cancer cell lines such as fibro sarcoma, stomach cancer, leukemia, and colon cancer, but
they did not show any cytotoxic effects up to 100 µM, indicating that 4ꢁ-hydroxymethyl groups are
essential for the anticancer activity.
Keywords Truncated nucleosides; S-adenosylhomocysteine hydrolase; electrophilic
fluorination
INTRODUCTION
The carbocyclic nucleoside,[1–4] whose furanose oxygen of the sugar
moiety is replaced by a methylene possesses inherent advantages such
as a stabilized glycosyl bond, resistance to phosphorylases, and increased
lipophilicity, but their syntheses have always been challenging because of
lengthy steps, low overall yields, and harsh reaction conditions. Recently,
thanks to several elegant syntheses of the carbocyclic moiety, several carbo-
cyclic nucleosides showing potent biological activities have been reported in
the literature.[5]
Received 3 March 2009; accepted 23 April 2009.
In honor of and in celebration of Morris J. Robins’ 70th birthday.
This work was supported by the Korea Research Foundation Grant (KRF-2008-E00304), the grant
from the World Class University (WCU) Project from Ministry of Education and Science, Korea (R31-
2008-000-10010-0).
Address correspondence to Lak Shin Jeong, Department of Bioinspired Chemistry and Division of
Life and Pharmaceutical Sciences, College of Pharmacy, Ewha Womans University, Seoul 120-750, Korea.
E-mail: lakjeong@ewha.ac.kr
601

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Y. H. Park et al.
FIGURE 1 Cyclopentenyl nucleosides showing potent inhibitory activity against SAH.
S-adenosylhomocysteine hydrolase (SAH) catalyzes the hydrolysis of
S-adenosylhomocysteine into adenosine and l-homocysteine.[6] Inhibition
of SAH leads to accumulation of S-adenosylhomocysteine in the cell,
resulting in the inhibition of S-adenosylmethionine (SAM) mediated
transmethylations.[6]
Because transmethylation is essential for replication of most animal
viruses, SAH has been a promising target for the development of broad-
spectrum antiviral agents.[7,8]
A naturally occurring carbocyclic nucleoside, neplanocin A (1)[9] is
one of the most potent inhibitors of SAH.[10] Unfortunately, compound
1 exhibited significant toxicity due to phosphorylation of the 5ꢁ-hydroxyl
group by cellular kinases (Figure 1).[10] Recently, we have reported its
fluoro analogue 2 as a new type of mechanism-based irreversible inhibitor of
SAH.[11] Compound 2 showed two times more potent SAH inhibitory activ-
ity than compound 1, but it was also cytotoxic.[11] In order to overcome the
cytotoxicity caused by the 5ꢁ-hydroxyl groups in compounds 1 and 2, their
truncated derivatives 3[12] and 4[13] were also synthesized. Both compounds
were also potent inhibitors of SAH although they were less potent than their
corresponding 4ꢁ-hydroxymethyl derivatives.[12,13] However, neither served
as a substrate for adenosine kinase nor adenosine deaminase, thus did not
show the toxicity associated with neplanocin A.[12] Interestingly, truncated
cytosine analogue 5 was also reported to show significant inhibitory activity
against SAH despite being a pyrimidine analogue, indicating that pyrim-
idines might serve as substrates for SAH in addition to adenine.[14]
The base-modified analogues of neplanocin A were also reported
to show potent biological activity (Figure 2). For example, the cytosine
derivative 6[15] showed potent antitumor activity by reducing cytidine-5ꢁ-
triphosphate (CTP) pools, resulting from the inhibition of CTP synthetase
and its 5-fluorocytosine analogue 7[16] exhibited potent antiviral activity

Truncated Fluorocyclopentenyl Pyrimidines
603
FIGURE 2 Cyclopentenyl nucleosides showing antiviral and antitumor activities.
against West Nile virus. On the other hand, another cytosine analogue 8[17]
with fluorocyclopentenyl ring showed potent antitumor activity against most
human cancer cell lines.
Thus, on the basis of potent SAH inhibitory activity of the truncated
cyclopentenyl pyrimidine 5, it was of interest to synthesize its truncated
fluorocyclopentenyl pyrimidines 9 and 10 and to compare their biological
activity (Figure 3). It was also of interest to compare the antitumor activity
of truncated 9 and 10 with that of the cytosine derivative 8 showing potent
antitumor activity to determine if 4ꢁ-hydroxymethyl group is essential for
antitumor activity. Herein, we report the synthesis and biological activity of
the truncated fluorocyclopentenyl pyrimidines, 9 and 10.
RESULTS AND DISCUSSION
Synthesis started from d-ribose, as shown in Scheme 1. d-Ribose was ef-
ficiently converted to the key intermediate, d-cyclopentenone 10 according
to our previously reported procedure,[18] which was then converted to the
glycosyl donor 15.
FIGURE 3 Structures of the target nucleosides.

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Y. H. Park et al.
SCHEME 1 Reagents and conditions: a) l2, pyridine, CCl4, rt, 1.5 h; b) NaBH4, CeCl3–H2O, MeOH, 0◦,
40 min; c) TBDPSCl, imidazole, DMF, rt, overnight; d) NFSI, n-BuLi, THF, −78◦, 10 min; e) TBAF, THF,
rt, 1 h.
Our initial strategy to the introduction of the fluorine was to use
direct electrophilic fluorination on cyclopentenone 10, but this method
failed to give the desired fluorinated compound under various conditions.
Thus, we decided to utilize halogen-metal exchange reaction followed by
electrophilic fluorination. Treatment of 10 with iodine in pyridine gave
iodocyclopentenone 11. Reduction of 11 with NaBH4 in the presence of
cerium (III) chloride heptahydrate at 0◦C produced the iodocyclopentenol
12. Protection of the hydroxyl group in 12 with TBDPSCl in DMF afforded
TBDPS ether 13. Electrophilic fluorination reaction[11] was achieved by
adding n-BuLi to a solution of 13 and N -fluorobenzenesulfonimide (NFSI)
in THF at −78◦C to give an inseparable mixture of vinyl fluoride 14 and its
hydrogen derivative in 4/1 ratio in 89% yield. Treatment of 14 with tetra-n-
butylammonium fluoride afforded the glycosyl donor 15[13] in quantitative
yield.
Synthesis of the uracil derivative 9 from the glycosyl donor 15 was
achieved using a Mitsunobu reaction[19] as the key step, as illustrated in
Scheme 2. Condensation of 15 with N 3-benzoyluracil under the standard
Mitsunobu condition[19] gave N 3-Bz-uracil derivative 16, which was treated
with methanolic ammonia to afford the uracil derivative 17 (48% from 15).
Treatment of 17 with 50% aqueous trifluoroacetic acid (TFA) gave the final
uracil derivative 9.
For the synthesis of the cytosine derivative 10, two synthetic routes were
employed, as shown in Scheme 3. The first route began with the uracil
derivative 9. Compound 9 was treated with acetic anhydride in pyridine to
give triacetate 18 (63%). Treatment of 18 with 1,2,4-triazole, phosphorus
oxychloride, and triethyl amine (TEA) gave the N 4-triazole derivative, which
without purification, was reacted with aqueous ammonia in 1,4-dioxane

Truncated Fluorocyclopentenyl Pyrimidines
605
SCHEME 2 Reagents and conditions: a) N3-benzoyl-uracil, PPh3, DEAD, THF, rt, 2.5 h; b) NH3 in
MeOH, rt, overnight; c) 50% aq. TFA, rt, 3 h.
to afford the cytosine analogue 19 in only 14% yield. Deprotection of 19
with methanolic ammonia gave the final nucleoside 10 (34%). Because
of poor overall yield of the first route, the second route starting from
2,3-acetonide 17 was explored. Treatment of 17 with 1,2,4-triazole in the
presence of 4-chlorophenyldichlorophosphate in pyridine gave the triazole
derivative, which was then immediately treated with aqueous ammonia in
1,4-dioxane to give the cytosine derivative 20 in 66% yield. Removal of the
2,3-isopropylidene group in 20 using 50% aqueous TFA yielded the final
cytosine nucleoside 10 (42%). The second route turned out to be better
than the first route in view of number of steps and overall yields (27.7 vs.
2.6).
The final nucleosides 9 and 10 were assayed for SAH inhibitory activity.
Enzyme activity was measured using pure recombinant enzyme obtained
from human placenta.[11] The residual activity of the enzyme was de-
termined in the synthetic direction toward S-adenosylhomocysteine using
adenosine and L-homocysteine.[11] Both compounds were preincubated
with the enzyme at 100 µM for 5 minutes at 37◦C. Surprisingly, the uracil

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Y. H. Park et al.
SCHEME 3 Reagents and conditions: a) Ac2O, pyridine, rt, overnight; b) POCl3, 1,2,4-triazole, TEA,
CH3CN, rt, overnight; c) 1,4-dioxane: 28% NH4OH = 10 : 1, rt, overnight; d) NH3 in MeOH, rt,
overnight; e) 4-chlorophenyldichlorophosphate, 1,2,4-triazole, pyridine, rt, overnight; f) 1,4-dioxane:
28% NH4OH = 1 : 2, rt, 3 h; g) 50% aq. TFA, rt, 2.5 h.
derivative 9 exhibited potent inhibitory activity (IC50 = 8.53 µM) against
SAH, while the cytosine derivative 10 was inactive.
The growth inhibition of the final nucleosides 9 and 10 against a variety
of human tumor cells such as lung cancer, fibrosarcoma, stomach cancer,
leukemia, and colon cancer was also evaluated using the Sulforhodamine B
(SRB) method. Unlike the potent anticancer activity of compound 8, none
of the synthesized compounds showed anticancer activity, indicating that
4ꢁ-hydroxyl methyl group is essential for the anticancer activity.
In conclusion, we have accomplished the synthesis of novel fluorocy-
clopentenyl pyrimidines from d-ribose, using electrophilic fluorination and
Mitsunobu condensation as key steps. Among compounds tested, the uracil
derivative showed potent SAH inhibitory activity, indicating that pyrimidine
base can serve as a good template like a purine base. All synthesized
compounds showed no cytotoxic activity in several human cancer cell lines,

Truncated Fluorocyclopentenyl Pyrimidines
607
probably due to the absence of the 4ꢁ-hydroxylmethyl group, which may be
essential for phosphorylation by cellular kinases.
EXPERIMENTAL
General Methods
Melting points were measured and are uncorrected. UV spectra were
1
measured in methylene chloride or methanol. H NMR spectra (CDCl3,
CD3OD) were recorded on Varian Unity Inova 400 MHz NMR spectrom-
eters. Chemical shifts were reported in parts per million (δ) units relative
to the solvent peak. The 1H NMR data were reported as peak multiplicities:
s for singlet; d for doublet; dd for doublet of doublets; ddd for doublet
of doublet of doublets; t for triplet; pseudo t for pseudo triplet; br s for
broad singlet; and m for multiplet. Coupling constants were reported in
hertz. 13C NMR spectra (CDCl3, CD3OD) were recorded on Varian Unity
Inova 100 MHz. The chemical shifts were reported as ppm (δ) relative to
the solvent peak. FAB mass spectra were recorded on Jeol HX 110 spec-
trometer (Korea). Optical rotations were determined on Jasco III (Korea)
in methanol. Elementary analyses were measured on EA1110. Reactions
were checked with TLC (Merck precoated 60F254 plates, Korea). Spots were
detected by viewing under a UV light, colorizing with charring after dipping
in anisaldehyde solution with acetic acid and sulfuric acid and methanol.
Column chromatography were performed on silica gel 60 (230–400 mesh,
Merck). Reagents were purchased from Aldrich Chemical Company, Korea.
Solvents were obtained from local suppliers. All the anhydrous solvents were
distilled over CaH2, P2O5, or Na/benzophenone prior to the reaction.
5-Iodo-2,2-dimethyl-3a,6a-dihydro-cyclopenta[1,3]dioxol-4-one
(11)
To a stirred solution of 10 (9.81 g, 63.64 mmol) and iodine (56.53 g,
222.7 mmol) in carbon tetrachloride (200 mL) was added pyridine (5.15
mL, 63.64 mmol) under nitrogen atmosphere at 0◦C. The reaction mixture
was stirred at room temperature for 1.5 hours. The resulting mixture was
diluted with methylene chloride and water. The mixture was washed with
water, saturated solution of sodium thiosulfate and brine. The organic
layer was dried and filtered through a pad of celite. The filtrates were
concentrated in vacuo, and the residue was purified by silica gel column
chromatography (hexanes/ethyl acetate = 7 : 1) to afford 11 (14.48 g, 81%)
1
as a white solid: m.p. 80–82◦C; H NMR (400 MHz, CDCl3) δ 7.96 (d, J =
2.8 Hz, 1 H), 5.21 (dd, J = 2.8, 5.6 Hz, 1 H), 4.51 (d, J = 5.6 Hz, 1 H), 1.39
(s, 3 H), 1.36 (s, 3 H); 13C NMR (100 MHz, CDCl3) δ 197.7, 165.0, 115.9,

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Y. H. Park et al.
105.8, 79.8, 73.8, 27.4, 26.5; MS (FAB) m/z 281 [M + H]+; [α]23 +14.5 (c
D
0.53, MeOH).
5-Iodo-2,2-dimethyl-4,6a-dihydro-3aH-cyclopenta[1,3]dioxol-4-ol
(12)
To a stirred solution of 11 (14.0 g, 50.0 mmol) and cerium (III)
chloride heptahydrate (13.56 g, 55.0 mmol) in methanol (150 mL) was
added sodium borohydride (2.08 g, 55.0 mmol) at 0◦C. The reaction
mixture was stirred at 0◦C for 40 minutes. After adding water, the mixture
was evaporated, which was extracted with ethyl acetate and dried, filtered
through a pad of celite. The filtrates were concentrated in vacuo, and the
residue was purified by silica gel column chromatography (hexanes/ethyl
acetate = 6 : 1) to give 12 (13.7 g, 98%) as a white solid: m.p. 55–59◦C; 1H
NMR (400 MHz, CDCl3) δ 6.30–6.29 (m, 1 H), 4.91 (dd, J = 2.0, 5.6 Hz, 1
H), 4.67 (t, J = 5.6 Hz, 1 H), 4.41–4.40 (m, 1 H), 2.80 (br s, 1 H), 1.40 (s,
3 H), 1.38 (s, 3 H); 13C NMR (100 MHz, CDCl3) δ 139.8, 112.9, 107.6, 83.8,
78.6, 76.4, 27.7, 26.9; MS (FAB) m/z 283 (M + H+); [α]24 +1.05 (c 2.76,
D
MeOH).
tert-Butyl-(5-iodo-2,2-dimethyl-4,6a-dihydro-3aH-cyclopenta
[1,3]dioxol-4-yloxy)-diphenyl-silane (13)
To a stirred solution of 12 (13.68 g, 48.50 mmol) and imidazole (10.01
g, 145.5 mmol) in anhydrous N,N -dimethylformamide (100 mL) was added
tert-butyl diphenylchlorosilane (14.6 mL, 58.20 mmol) at room temperature
under nitrogen atmosphere. The reaction mixture was stirred at room
temperature overnight. After adding water, the mixture was evaporated,
which was extracted with ethyl acetate and dried, filtered through a pad of
celite. The filtrates were concentrated in vacuo, and the residue was purified
by silica gel column chromatography (hexanes/ethyl acetate = 30 : 1) to
1
give 13 (24.74 g, 98%) as a colorless oil; H NMR (400 MHz, CDCl3) δ
7.84–7.80 (m, 4 H), 7.44–7.26 (m, 6 H), 6.23–6.22 (m, 1 H), 4.61 (dd, J =
1.6, 5.2 Hz, 1 H), 3.91 (t, J = 6.0 Hz, 1 H), 1.40 (s, 3 H), 1.21 (s, 3 H), 1.16 (s,
9 H); 13C NMR (100 MHz, CDCl3) δ 139.7, 136.7, 136.2, 135.9, 134.0, 133.7,
129.9, 127.6, 127.4, 111.9, 107.1, 83.7, 79.5, 27.7, 27.2, 27.1, 26.9, 19.8; MS
(FAB) m/z 519 [M−H]+, 543 [M + Na]+; [α]24 −23.16 (c 1.87, MeOH).
D
tert-Butyl-(5-fluoro-2,2-dimethyl-4,6a-dihydro-3aH-cyclopenta
[1,3]dioxol-4-yloxy)-diphenyl-silane (14)
To a stirred solution of 13 (23.05 g, 44.29 mmol) and N -
fluorobenzenesulfonimide (21.60 g, 66.43 mmol) in tetrahydrofuran (400
mL) was slowly added a 1.6 M solution of n-butyllithium in hexanes (83 mL,

Truncated Fluorocyclopentenyl Pyrimidines
609
132.9 mmol) at −78◦C under nitrogen gas. The reaction mixture was stirred
at -78◦C for 10 minutes. After saturated solution of ammonium chloride was
added at 0◦C, the mixture was extracted with ethyl acetate and dried, filtered
through a pad of celite. The filtrates were concentrated in vacuo, and the
residue was purified by silica gel column chromatography (hexanes/ethyl
1
acetate = 30 : 1) to give 14 (16.24 g, 89%) as a colorless oil: H NMR (400
MHz, CDCl3) δ 7.82–7.79 (m, 2 H), 7.76–7.72 (m, 2 H), 7.46–7.26 (m, 6 H),
5.27 (br s, 1 H), 4.81–4.75 (m, 1 H), 4.40–4.37 (m, 1 H), 4.28–4.24 (m, 1 H),
1.53 (s, 3 H), 1.35 (s, 3 H), 1.11 (br s, 9 H); MS (FAB) m/z 411 [M−H]+,
435 [M + Na]+; [α]24D−59.93 (c 6.76, MeOH).
5-Fluoro-2,2-dimethyl-4,6a-dihydro-3aH-cyclopenta[1,3]
dioxol-4-ol (15)
To a stirred solution of 14 (30.18 g, 71.76 mmol) in tetrahy-
drofuran (400 mL) was added dropwise a 1.0 M solution of tetra-n-
butylammoniumfluoride in tetrahydrofuran (107.64 mL, 107.64 mmol) at
0◦C. The reaction mixture was stirred at room temperature for 1 hour. The
solvent was removed in vacuo, and the residue was purified by silica gel
column chromatography (hexanes/ethyl acetate = 4 : 1) to give 15 (12.74
1
g, 100%) as a colorless oil: H NMR (400 MHz, CDCl3) δ 5.27–5.26 (m, 1
H), 4.98–4.92 (m, 1 H), 4.72–4.68 (m, 1 H), 4.40 (br s, 1 H), 2.77 (br s, 1
H), 1.45 (s, 3 H), 1.36 (s, 3 H); 13C NMR (100 MHz, CDCl3, mixed with
5-hydrogenated compound) δ 165.2, 162.3, 136.5, 132.1, 112.5, 105.2, 83.7,
77.9, 76.9, 75.0, 69.1, 27.8, 27.7, 26.7, 26.4; MS (FAB) m/z 173 [M−H]+, 197
[M + Na]+; [α]25 +0.833 (c 1.20, MeOH); Anal. Calcd for C8H11FO3: C,
D
55.17; H, 6.37. Found C, 55.36; H, 6.53.
3-Benzoyl-1-(5-fluoro-2,2-dimethyl-4,6a-dihydro-3aH-cyclopenta
[1,3]dioxol-4-yl)-1H-pyrimidine-2,4-dione (16)
To a stirred solution of 15 (3.45 g, 19.84 mmol), N 3-benzoyl-uracil (8.58
g, 39.68 mmol), triphenylphosphine (13.00 g, 49.60 mmol) in tetrahydrofu-
ran (35 mL) was added dropwise diethyl azodicarboxylate (8.05 mL, 49.60
mmol) at 0◦C. The reaction mixture was stirred at room temperature for
2.5 hours. The solvent was removed in vacuo, and the residue was purified
by silica gel column chromatography (hexanes/ethyl acetate = 1.5 : 1) to
1
give 16 as a colorless oil: UV (MeOH) λmax 255.0 nm; H NMR (400 MHz,
CD3OD) δ 7.98–7.95 (m, 2 H), 7.74–7.70 (m, 1 H), 7.61 (d, J = 8.0 Hz, 1
H), 7.57–7.53 (m, 2 H), 5.86 (d, J = 8.4 Hz, 1 H), 5.67 (br s, 1 H), 5.33
(br s, 1 H), 5.28–5.25 (m, 1 H), 4.83–4.80 (m, 1 H), 1.44 (s, 3 H), 1.31 (s, 3
H); 13C NMR (100 MHz, CDCl3) δ 170.1, 164.2, 159.2, 156.4, 151.2, 144.8,
136.6, 132.9, 131.6, 130.6, 113.1, 112.9, 103.3, 82.5, 80.5, 67.6, 49.7, 48.5,

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Y. H. Park et al.
27.7, 25.7; MS (FAB) m/z 373 [M + H]+, 395 [M + Na]+; [α]24 −137.26
D
(c 4.92, MeOH).
1-(5-Fluoro-2,2-dimethyl-4,6a-dihydro-3aH-cyclopenta[1,3]dioxol-
4-yl)-1H-pyrimidine-2,4-dione (17)
To 16 (5.9 g, impure) in a 25 mL of round bottom flask was added
methanolic ammonia (5 mL) rapidly. The reaction mixture was stirred
at room temperature overnight. The solvent was removed in vacuo, and
the residue was purified by silica gel column chromatography (methylene
chloride/methanol = 70: 1 to hexanes/ethyl acetate = 1 : 1) to give 17
(2.08 g, 48% for 2 steps) as a white solid: m.p. 105–110◦C; UV (MeOH) λmax
1
262.5 nm; H NMR (400 MHz, CD3OD) δ 7.46 (dd, J = 0.4, 8.0 Hz, 1 H),
5.70 (d, J = 8.0 Hz, 1 H), 5.31–5.28 (m, 1 H), 4.75–4.72 (m, 1 H), 1.45 (s, 3
H), 1.32 (s, 3 H); 13C NMR (100 MHz, CDCl3) δ 166.2, 159.7, 156.9, 152.5,
144.3, 113.1, 112.4, 103.4, 82.8, 80.7, 66.8, 27.7, 25.8; MS (FAB) m/z 269 [M
+ H]+, 291 [M + Na]+; [α]25 −199.59 (c 2.42, MeOH).
D
1-(2-Fluoro-4,5-dihydroxy-cyclopent-2-enyl)-1H-pyrimidine-2,
4-dione (9)
A solution of 17 (107 mg, 0.399 mmol) in 50% aqueous trifluoroacetic
acid solution (4 mL) was stirred at room temperature for 3 hours. The
solvent was removed in vacuo, and the residue was purified by silica gel
column chromatography (methylene chloride/methanol = 10 : 1) to give 9
(79.5 mg, 87%) as a white crystal: m.p. 138–140◦C; UV (MeOH) λmax 264.5
nm; 1H NMR (400 MHz, CD3OD) δ 7.48 (dd, J = 0.8, 8.0 Hz, 1 H), 5.73 (d,
J = 8.0 Hz, 1 H), 5.55–5.53 (m, 1 H), 5.43–5.39 (m, 1 H), 4.85–4.59 (m, 1
H), 4.27 (dt, J = 1.2, 6.0 Hz, 1 H); 13C NMR (100 MHz, CD3OD) δ 166.2,
162.3, 159.4, 152.9, 144.3, 110.3, 103.4, 75.7, 70.5, 65.1; MS (FAB) m/z 251
[M + Na]+; [α]25D −74.31 (c 5.59, MeOH); Anal. Calcd for C9H9FN2O4: C,
47.37; H, 3.98. Found C, 47.46; H, 4.03.
Acetic Acid 5-acetoxy-4-(2,4-dioxo-3,4-dihydro-2H-pyrimidin-1-yl)-
3-fluoro-cyclopent-2-enyl ester (18)
A solution of 9 (628 mg, 2.75 mmol) in pyridine (10 mL) was added
dropwise acetic anhydride (1.02 mL, 8.25 mmol) at 0◦C. The reaction mix-
ture was stirred at room temperature overnight under nitrogen atmosphere.
After removal of the solvent, the mixture was extracted with ethyl acetate
and dried, filtered through a pad of celite. The filtrates were concentrated
in vacuo, and the residue was purified by silica gel column chromatography
(hexanes/ethyl acetate = 1 : 2) to give 18 (540 mg, 63%) as a white solid:
m.p. 150–152◦C; UV (MeOH) λmax 260.5 nm; 1H NMR (400 MHz, CD3OD)

Truncated Fluorocyclopentenyl Pyrimidines
611
δ 7.49 (dd, J = 0.8, 8.0 Hz, 1 H), 5.81–5.77 (m, 1 H), 5.69 (d, J = 8.0 Hz, 1
H), 5.59–5.56 (m, 2 H), 5.51–5.48 (m, 1 H), 2.04 (s, 3 H), 2.01 (s, 3H); 13C
NMR (100 MHz, CD3OD) δ 172.1, 171.7, 166.0, 162.9, 160.0, 152.7, 144.4,
107.1, 103.7, 74.0, 72.0, 63.6, 20.7, 20.4; MS (FAB) m/z 313 [M + H]+, 335
[M + Na]+; [α]24 −203.41 (c 0.82, MeOH).
D
Acetic Acid 5-acetoxy-4-(4-amino-2-oxo-2H-pyrimidin-1-yl)-3-
fluoro-cyclopent-2-enyl ester (19)
A solution of 1,2,4-triazole (0.27 g, 3.85 mmol) and phosphorus oxy-
chloride (0.32 mL, 3.50 mmol) in acetonitrile (3 mL) was treated with
triethylamine (0.44 mL, 3.15 mmol) and 18 (109 mg, 0.35 mmol) in
acetonitrile (2 mL). The reaction mixture was stirred at room temperature
overnight, followed by addition of triethylamine (0.54 mL, 3.85 mmol)
and water (0.54 mL), and then the reaction mixture was stirred at room
temperature for 10 minutes. After the addition of methylene chloride, the
mixture was washed with saturated solution of sodium bicarbonate and
brine. The organic layer was dried over anhydrous magnesium sulfate,
filtered through a pad of celite. The filtrates were concentrated in vacuo,
and the residue was used in the next step without further purification.
To a stirred solution of triazole derivative in 1,4-dioxane (10 mL) was
added 28% ammonium hydroxide (1 mL) at 0◦C, and the reaction mixture
was stirred at room temperature overnight. The solvent was removed in
vacuo, and the residue was purified by silica gel column chromatography
(methylene chloride/methanol = 10 : 1) to give 19 (23.5 mg, 14% for 2
steps) as a yellowish solid: m.p. 180◦C (decomp.); UV (MeOH) λmax 272.5
nm; 1H NMR (400 MHz, CD3OD) δ 7.52 (d, J = 8.0 Hz, 1 H), 5.91 (d, J =
7.2 Hz, 1 H), 5.84–5.80 (m, 1 H), 5.61–5.55 (m, 3 H), 2.07 (s, 3 H), 2.04
(s, 3H); 13C NMR (100 MHz, CD3OD) δ 172.2, 171.6, 167.9, 163.7, 160.9,
158.6, 148.1, 145.3, 106.2, 97.0, 74.1, 72.2, 20.7, 20.5; MS (FAB) m/z 312 [M
+ H]+, 334 [M + Na]+; [α]25 −154.31 (c 0.58, MeOH).
D
4-Amino-1-(2-fluoro-4,5-dihydroxy-cyclopent-2-enyl)-1H-
pyrimidin-2-one (10)
A solution of 19 (20 mg, 0.06 mmol) in saturated methanolic ammonia
(5 mL) was stirred at room temperature overnight. The solvent was removed
in vacuo, and the residue was purified by reverse phase silica gel column
chromatography using water as the eluent to give 10 (5.0 mg, 34%) as a
white crystal: m.p. 200◦C (decomp.); UV (MeOH) λmax 274.0 nm; 1H NMR
(400 MHz, CD3OD) δ 7.48 (d, J = 7.6 Hz, 1 H), 5.95 (d, J = 7.6 Hz, 1 H),
5.51–5.50 (m, 1 H), 5.39 (m, 1 H), 4.64–4.61 (m, 1 H), 4.32 (t, J = 5.2 Hz, 1
H); 13C NMR (100 MHz, CD3OD) δ 167.5, 163.0, 160.1, 158.7, 145.2, 109.7,
96.8, 75.8, 70.5, 66.4; MS (FAB) m/z 250 [M + Na]+; [α]25D −116.79 (c 1.96,

612
Y. H. Park et al.
MeOH); Anal. Calcd for C9H10FN3O3: C, 47.58; H, 4.44. Found C, 47.46; H,
4.53.
4-Amino-1-(5-fluoro-2,2-dimethyl-4,6a-dihydro-3aH-cyclopenta
[1,3]dioxol-4-yl)-1H-pyrimidin-2-one (20)
To a stirred solution of 17 (380 mg, 1.415 mmol) in pyridine
(9 mL) was added dropwise 4-chlorophenyldichlorophosphate (0.92 mL,
5.66 mmol) at room temperature, following by addition of 1,2,4-triazole
(0.39 g, 5.66 mmol), the reaction mixture was stirred at room temperature
overnight. After removal of the solvent, the mixture was extracted with
saturated solution of sodium bicarbonate and ethyl acetate, dried, and
filtered through a pad of celite. The filtrates were concentrated in vacuo,
and the residue was used without further purification for the next step. To a
stirred solution of triazole derivative in 1,4-dioxane (4 mL) was added 28%
ammonium hydroxide (2 mL) at 0◦C, and the reaction mixture was stirred at
the same temperature for 3 hours. The solvent was removed in vacuo, and
the residue was purified by silica gel column chromatography (methylene
chloride/methanol = 50: 1 to 10: 1) to give 20 (250 mg, 66% for 2 steps)
as a yellowish solid: m.p. 240◦C (decomp.); UV (MeOH) λmax 272.5 nm; 1H
NMR (400 MHz, CD3OD) δ 7.46 (d, J = 7.2 Hz, 1 H), 5.90 (d, J = 7.2 Hz, 1
H), 5.61 (s, 1 H), 5.31–5.27 (m, 2 H), 4.71–4.68 (m, 1 H), 1.45 (s, 3 H), 1.31
(s, 3 H); 13C NMR (100 MHz, CD3OD) δ 168.0, 160.4, 158.5, 157.6, 145.1,
112.8, 111.8, 96.7, 83.1, 80.8, 68.3, 27.2, 25.8; MS (FAB) m/z 268 [M + H]+,
290 [M + Na]+; [α]25 −46.90 (c 2.42, MeOH).
D
4-Amino-1-(2-fluoro-4,5-dihydroxy-cyclopent-2-enyl)-1H-
pyrimidin-2-one (10)
A solution of 17 (250 mg, 0.935 mmol) in 50% aqueous trifluoroacetic
acid solution (4 mL) was stirred at room temperature for 2.5 hours.
The solvent was removed in vacuo, to the mixture was added toluene
(3 mL) then evaporated. Several times this work was replayed. And the
residue was purified by silica gel column chromatography (methylene
chloride/methanol = 10: 1 to 5: 1) to give 10 (110 mg, 42%) as a white
crystal: All the analytical data was identical to 10 obtained from the previous
aminolysis reaction.
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