Synthesis of 2′,3′-dideoxy-2′-monofluoromethyl azanucleosides

Article abstract of DOI:10.1016/j.bmc.2004.09.040

(2S,4S)-Methyl-N-tert-butoxycarbonyl-4-monofluoromethylpyroglutamate 6 was synthesized via a key dehydrofluorination followed by hydrogenation. Compound 6 was converted to (5S,3S)-N-benzyloxycarbonyl-5-tert-butyldimethylsilyloxymethyl- 3-monofluoromethyl-

Full text of DOI:10.1016/j.bmc.2004.09.040

Bioorganic & Medicinal Chemistry 13 (2005) 277–283
Synthesis of 20,30-dideoxy-20-monofluoromethyl azanucleosides
Xiao-Long Qiua and Feng-Ling Qinga,b,
*
aKey Laboratory of Organofluorine Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Science,
354 Fenglin Lu, Shanghai 200032, China
bCollege of Chemistry and Chemical Engineering, Donghua University, 1882 West Yanan Lu, Shanghai 200051, China
Received 5 September 2004; revised 20 September 2004; accepted 20 September 2004
Available online 12 October 2004
Abstract—(2S,4S)-Methyl-N-tert-butoxycarbonyl-4-monofluoromethylpyroglutamate 6 was synthesized via a key dehydrofluorina-
tion followed by hydrogenation. Compound 6 was converted to (5S,3S)-N-benzyloxycarbonyl-5-tert-butyldimethylsilyloxymethyl-3-
monofluoromethyl-2-pyrrolidone 12 over four steps in 62% yield, which was used as a precursor for the synthesis of 20,30-dideoxy-20-
monofluoromethyl azanucleosides 17–18.
ꢀ 2004 Elsevier Ltd. All rights reserved.
1. Introduction
of azanucleosides were summarized by Yokoyama and
Momotake.5 However, to the best of our knowledge,
few fluorinated azanucleosides have been synthesized14
and up to date there is no corresponding report on the
monofluorinated azanucleosides. Considering all these
aspects and in connection with our studies on fluori-
nated sugar nucleosides, we decided to synthesize mono-
fluorinated azanucleosides: 20,30-dideoxy-20-monofluo-
romethyl azanucleosides and investigate their biological
activities.
In the last two decades, nucleosides and nucleotides,
known to be DNA and RNA subunits, have become
an important subject of research in the field of pharma-
ceutical science. Modification of the ribose moiety and
base moiety of nucleosides exhibits two important ways
to new high bioactive nucleoside analogues.1 Recently,
many modified sugar nucleosides,2 including thionucleo-
sides,3 carbocyclic nucleosides,4 and azanucleosides5
were synthesized and studied. In connection with special
properties of fluorine, fluorinated nucleosides have re-
ceived a great interest for their biological and medical
applications.6 In fluorinated sugar nucleosides, fluorine
stabilizes the glycosidic bond toward hydrolysis by alter-
ation of the conformation of the sugar moiety.7 Some
highly bioactive fluorinated nucleosides have been syn-
thesized and used in cancer and herpes therapies, for
example, 20-deoxy-20,20-difluorocytidine (Gemcitabine)
has been approved as a drug for solid tumor treatment.8
Interestingly, sugar moieties of several high bioactive
fluorinated nucleosides FMAU,9 FLT,10 FIAC,9b
F-ddC,11 SFDC,12 and DFDT13 contain a fluorine
atom, which in some degree, reveals the special influ-
ences of monofluoro groups on the biological activities
of nucleosides (Fig. 1). Azanucleosides, in which the
oxygen atom of pyranose or furanose ring is replaced
by nitrogen atom, represent an important class of mod-
ified nucleosides. The synthesis and biological activities
2. Results and discussion
During the synthesis of 20,30-dideoxy-20-difluoromethyl
azanucleosides,14b we accidentally found that the
dehydrofluorination reaction occurred when the amino
group of 5-tert-butyldimethylsilyloxymethyl-3-difluoro-
methyl-pyrrolidin-2-one 1 was protected with tert-but-
oxycarbonyl group (Boc) (Scheme 1). The dehydro-
fluorinated compound 2 was obtained in 25% yield.
The dehydrofluorination was induced by the enhance-
ment of acidity of 3-H as a result of the protection of
the amino groups with electron-withdrawing group
(Boc). In our opinion, compound 2 could be used as a
precursor for the preparation of target molecules:
20,30-dideoxy-20-monofluoromethyl azanucleosides.
So, according to our previous reports,14b,15 the methyl
(2S)-N-tert-butoxycarbonyl-4-difluoromethylpyrogluta-
mate 4 were synthesized from the trans-4-hydroxy-L-
proline 3 in 22% yield over six steps (Scheme 2).
Dehydrofluorination of the compound 4 under the
Keywords: Azanucleosides; Fluorinated compounds.
*
Corresponding author. Tel.: +86 21 64163300; fax: +86 21
64166128; e-mail: flq@mail.sioc.ac.cn
0968-0896/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2004.09.040

278
X.-L. Qiu, F.-L. Qing / Bioorg. Med. Chem. 13 (2005) 277–283
I
CH3
H
N
NH2
O
O
O
O
O
O
N
N
N
NH
N
HO
HO
HO
Me
OH
O
O
HO
F
F
F
OH
FLT
O
FMAU
FIAC
CH3
NH2
NH2
O
O
O
N
N
N
N
N
NH
HO
HO
O
O
F
O
HO
CH2F
FH2C
SFDC
F-ddC
DFDT
Figure 1. Several high bioactive monofluorinated nucleosides.
Boc
N
Boc
N
Boc
N
H
N
Boc2O, Et3N
O
O
O
O
TBSO
+
TBSO
TBSO
+ TBSO
CH2Cl2, DMAP, r.t
CHF2
CHF2
CHF2
F
H
1
2 (25%)
Scheme 1.
H
HF2C
O
F
HO
6 steps
Et3N, THF
75%
CO2Me
N
CO2H
22%
O
CO2Me
N
H
3
N
Boc
Boc
5
4
Pd-BaSO4,dioxane,
H2, 1atm
84%
H2FC
O
H2FC
O
i) TFA, CH2Cl2
ii) NaBH4
OTBDMS
CO2Me
N
iii) TBDMSCl / DMAP
67%
N
H
Boc
7
6
Scheme 2.
optimized condition (Et3N, THF) smoothly provided
the monofluoro olefin 5 in 75% yield. Hydrogenation
of the compound 5 with Pd–BaSO4 in dioxane gave
the desired product 6 in 84% yield. Then deprotection
of N-Boc group of 6 with trifluoroacetic acid in CH2Cl2
followed by reduction of the ester with NaBH4, and fur-
ther protection of the resulting hydroxyl group with
TBDMSCl afforded the compound 7 in 67% yield over
three steps.
9 in 81% yield. However, acetylation of compound 9
under two reaction conditions (Ac2O/DMAP/pyridine/
CH2Cl2 and AcCl/pyridine/CH2Cl2) failed to give the
desired compound 10. Protection of hydroxyl group of
9 with methyl group only gave the desired product 11
in 27% yield.16 In our opinion, the big block of the
tert-butoxycarbonyl group along with the existence of
monofluoromethyl group may be responsible for the
failure of the acetylation reaction and the low yield in
preparation of the compound 11.
Treatment of the lactam 7 with Boc2O/pyridine/CH2Cl2
under the catalyst of DMAP provided (5S,3S)-N-tert-
butoxycarbonyl-5-tert-butyldimethylsilyloxymethyl-3-
monofluoromethyl-2-pyrrolidione 8 in 90% yield and a
few defluorinated byproduct could be detected by TLC
(Scheme 3). Then, reduction of the compound 8 with Li-
BEt3H in THF at ꢀ78ꢁC yielded the desired compound
In view of above failure, the protection of the amino
group of compound 7 by benzyloxycarbonyl (Cbz)
group instead of Boc group was investigated. We were
pleased to find that treatment of 7 with CbzCl and
1.0equiv LHMDS in THF at ꢀ78ꢁC for 10min
smoothly gave the desired lactam 12 in 93% yield along

X.-L. Qiu, F.-L. Qing / Bioorg. Med. Chem. 13 (2005) 277–283
279
H2FC
O
H2FC
H2FC
HO
Boc2O, DMAP
LiBEt3H, THF
OTBDMS
OTBDMS
OTBDMS
O
N
H
Pyridine
90%
N
81%
N
Boc
Boc
7
8
9
HC(OMe)3, THF
27%
AcCl, CH2Cl2, Pyridine
or Ac2O, DMAP, CH2Cl2
H2FC
H2FC
AcO
OTBDMS
OTBDMS
MeO
N
N
Boc
11
Boc
10
Scheme 3.
H2FC
O
H2FC
O
LHMDS, CbzCl
THF
OTBDMS
OTBDMS
OTBDMS
+
O
N
H
N
N
Cbz
Cbz
7
12 (93%)
13 (4%)
Cbz
N
Cbz
N
Cbz
N
OH
O
OH
LiBEt3H, THF
TBDMSO
TBDMSO
TBDMSO
+
CH2F
CH2F
CH2F
12
15 (12%)
14 (81%)
Ac2O, DMAP
CH2Cl2,pyridine
R
O
R
O
Cbz
Cbz
N
O
Cbz
N
O
1 ) silylated uracil or silylated thymine
TMSOTf, CH3CN
N
OAc
TBDMSO
N
NH
N
NH
HO
+
HO
.
2 ) TBAF or HF Pyridine
CH2F
CH2F
CH2F
16 (92%)
17b R = H (20%)
18b R = CH3 (44%)
17a R = H (47%)
18a R = CH3 (15%)
Scheme 4.
with the dehydrofluorination product 13 in 4% yield
(Scheme 4).17 Similarly, reduction of lactam 12 with
LiBEt3H yielded two diastereoisomers 14 (81% yield)
and 15 (12% yield) (14/15 = 6.8:1.0). The two diastereo-
isomers could be separated on silica gel chromatography.
As we expected, O-acetylation of the major diastereo-
isomer 14 with Ac2O/DMAP/pyridine smoothly af-
forded the desired compound 16 in 92% yield. Finally,
coupling of 16 with silylated uracil and thymine under
Vorbruggenꢀs condition (glycosylation reaction)18 gave
¨
the silyl-protected azanucluosides. Deprotection of the
silyl protection groups with TBAF or HFÆpyridine af-
forded target molecules 17a, 17b, 18a, and 18b. The ratio
of 17a/17b and that of 18a/18b were different and oppo-
site. The absolute configuration of compound 17b was
confirmed by X-ray (Fig. 2).19
We investigated the biological activities of the target
molecules 17a, 17b, and 18b to the tumor cell U2OS.
The experiments were carried out in the effects of 17a,
17b, and 18b on the cell life cycle of U2OS. Mimosine
Figure 2. ORTEP drawing of the X-ray crystallographic structure of
17b.

280
X.-L. Qiu, F.-L. Qing / Bioorg. Med. Chem. 13 (2005) 277–283
Table 1. Effects of azanucleosides 17a, 17b, and 18b to the cell cycles of
U2OS
the mixture was hydrogenated at room temperature for
24h. Filtration and removal of the solvent gave a resi-
due, which was purified by silica gel chromatography
Cell cycles
Control Mimosine 17a
17b
18b
(hexane/ethyl acetate, 8:1 then 6:1) to give 6 as a white
Dip G1 (%)
Dip S (%)
46.20
43.23
Dip G2/M (%) 10.58
76.78
20.93
2.29
47.18 49.16 49.16
45.33 41.73 41.73
20
solid (871mg, 84%): mp 83–84ꢁC; ½aꢁ ꢀ29.3 (c
D
0.96, CHCl3); 1H NMR (300MHz, CDCl3) d 4.72
(ddd, J = 26.1, 6.0, 5.7Hz, 1H), 4.65–4.52 (m, 2H),
3.79 (s, 3H), 3.03–2.85 (m, 1H), 2.64–2.53 (m, 1H),
2.12–2.03 (m, 1H), 1.50 (s, 9H); 19F NMR (282MHz,
CDCl3) d ꢀ228.01 to ꢀ228.44 (m, 1F); 13C NMR
(75.5MHz, CDCl3) d 171.4, 171.2 (d, J = 8.8Hz),
148.9, 83.9, 81.7 (d, J = 170.1Hz), 57.2, 52.4, 43.7 (d,
J = 21.1Hz), 29.5, 27.7, 23.7 (d, J = 3.2Hz); IR (thin
film) 1776, 1745, 1702, 1339, 1296cmꢀ1; MS (EI) m/z
276 (M++1, <1), 260 (M+ꢀ15, <1), 57 (100); MS (ESI)
m/z 298 (M++Na); EI-HRMS m/z 260.09538
(M+ꢀCH3, C11H15FNO5 required 260.09343).
7.49
9.11
9.11
(500lM) was used as S phase block drug in control
experiment and the sample concentrations (17a, 17b,
and 18b) were 10mmol/L. The biological results were
summarized in Table 1. As shown in Table 1, the cell cy-
cles had no evident change after azanucleosides 17a,
17b, and 18b were injected. So, none of azanucleosides
17a, 17b, and 18b exhibited a significant biological effect
on the tumor cell U2OS.
In summary, we synthesized the novel fluorinated aza-
nucleosides: 20,30-dideoxy-20-monofluoromethyl azanu-
cleosides 17–18 from trans-4-hydroxy-L-proline via a
novel dehydrofluorination found accidentally. Active
tests shown that none of the synthesized azanucleosides
17a, 17b, and 18b had significant activity against U2OS.
The related modified fluorinated analogues are in inten-
sive synthesis and to be reported soon.
3.3. (5S,3S)-5-tert-Butyldimethylsilyloxymethyl-3-mono-
fluoromethylpyrolidin-2-one (7)
TFA (1.0mL) was added dropwise to a solution of 6
(813mg, 2.96mmol) in CH2Cl2 (30mL) at ꢀ78ꢁC. The
mixture was then warmed up to room temperature and
stirred overnight. The reaction mixture was cooled to
0ꢁC and quenched with saturated aqueous NaHCO3
(10mL). The organic phase was separated and the aque-
ous phase was extracted with CH2Cl2 (3 · 40mL). The
combined organic phases were washed with brine and
dried over anhydrous Na2SO4. After removal of the sol-
vent in vacuo, the residue was dissolved in MeOH
(30mL) and the solution was cooled to ꢀ78ꢁC. NaBH4
(145mg, 3.82mmol) was added. The mixture was then
warmed up to 0ꢁC and stirred for 1.5h. The reaction
was quenched with concentrated HCl. The mixture
was then filtered and concentrated to give a yellowish
3. Experimental
3.1. (2S)-Methyl-N-tert-butoxycarbonyl-4-[(Z)-fluorome-
thylidene]-pyroglutamate (5)
To a solution of 4 (3.162g, 10.79mmol) in CH3CN
(100mL), Et3N (7.0mL) was added dropwise at room
temperature. The mixture was stirred overnight at room
temperature. Removal of the solvent in vacuo gave a
residue and H2O (50mL) and CH2Cl2 (50mL) were
added. The organic phase was separated and the aque-
ous phase was extracted with CH2Cl2 (2 · 100mL).
The combined organic phases were washed with brine
and dried over anhydrous Na2SO4. After filtration and
removal of the solvent in vacuo, the resulting residue
was purified by silica gel chromatography (hexane/ethyl
acetate, 6:1) to give 5 as a white solid (2.082g, 75%):
solid. To
a cooled solution of DMAP (26mg,
0.21mmol) and imidazole (900mg, 13.24mmol) in
CH2Cl2 (50mL), a solution of above yellowish solid in
DMF (1mL) was added. Then, a solution of TBDMSCl
(2.0g, 13.27mmol) in CH2Cl2 (10mL) was added drop-
wise. After the mixture was stirred overnight at room
temperature, it was quenched with saturated aqueous
NH4Cl (10mL) in cooled ice-bath. The organic phase
was separated and the aqueous layer was extracted with
CH2Cl2 (3 · 40mL). The combined organic phases were
washed with brine and dried over anhydrous Na2SO4.
After removal of the solvent in vacuo, the resulting res-
idue was purified by flash chromatography (hexane/
ethyl acetate, 3:2) to give 7 as a clear oil (516mg,
20
D
1
mp 118–119ꢁC; ½aꢁ ꢀ8.6 (c 1.03, CHCl3); H NMR
(300MHz, CDCl3) d 7.46 (dt, J = 78.3, 2.7Hz, 1H),
4.66 (dd, J = 3.3, 3.6Hz, 1H), 3.80 (s, 3H), 3.11–3.00
(m, 1H), 2.76 (dq, J = 18.0, 3.0Hz, 1H), 1.51 (s, 9H);
19F NMR (282MHz, CDCl3) d ꢀ119.76 to ꢀ120.07
(dt, J = 78.5, 3.7Hz, 1F); 13C NMR (75.5MHz, CDCl3)
d 170.9, 165.0 (d, J = 19.3Hz), 154.9 (d, J = 276.1Hz),
149.0, 114.4 (d, J = 12.7Hz), 83.7, 55.8, 52.4, 29.4,
27.6, 22.7 (d, J = 1.5Hz). IR (thin film) 3109, 1790,
1747, 1706, 1687, 1288, 1152cmꢀ1; MS (ESI) m/z 296.0
(M++Na); Anal. Calcd for C12H16FNO5: C, 52.75; H,
5.86; N, 5.13. Found: C, 52.82; H, 5.89; N, 5.10.
20
1
67%). ½aꢁ +51.4 (c 1.29, CHCl3); H NMR (300MHz,
D
CDCl3) d 6.75 (br, 1H), 4.60 (ddd, J = 92.5, 4.2,
4.2Hz, 1H), 4.62–4.60 (m, 1H), 3.76–3.68 (m, 1H),
3.62 (dd, J = 3.9, 3.9Hz, 1H), 3.42 (dd, J = 7.8, 7.8Hz,
1H), 2.82–2.63 (m, 1H), 2.32 (ddd, J = 15.3, 7.2,
6.0Hz, 1H), 1.70 (ddd, J = 14.7, 7.5, 3.6Hz, 1H), 0.85
(s, 9H), 0.02 (2s, 6H); 19F NMR (282MHz, CDCl3) d
ꢀ228.52 to ꢀ228.96 (m, 1F); 13C NMR (75.5MHz,
CDCl3) d 175.4 (d, J = 7.5Hz), 82.3 (d, J = 169.7Hz),
66.7, 53.9, 42.6 (d, J = 21.7Hz), 25.7, 25.3 (d,
J = 3.2Hz), 18.1 (d, J = 0.5Hz), ꢀ5.6 (d, J = 0.8Hz);
IR (thin film) 3223, 1708, 1464, 1256, 1104cmꢀ1; MS
(EI) m/z 262 (M++1, 3), 260 (M+ꢀ1, <1), 246 (M+ꢀ
3.2. (2S,4S)-Methyl-N-tert-butoxycarbonyl-4-monofluoro-
methylpyroglutamate (6)
To a solution of compound 5 (1.028g, 3.77mmol) in
dioxane (60mL), Pd–BaSO4 (250mg) was added. Then,

X.-L. Qiu, F.-L. Qing / Bioorg. Med. Chem. 13 (2005) 277–283
281
15, 2), 110 (100); EI-HRMS m/z 246.13041 (M+ꢀCH3,
56.20; H, 9.37; N, 3.86. Found: C, 56.35; H, 9.71; N,
3.70.
C11H21FNO2Si required 246.13256).
3.4. (5S,3S)-N-tert-Butoxycarbonyl-5-tert-butyldimethyl-
silyloxymethyl-3-monofluoromethyl-2-pyrrolidone (8)
3.6. tert-Butyl (2R,3S,5S)-2-methoxy-5-tert-butyldimeth-
ylsilyloxy-3-monofluoromethylpyrrolidine-1-carboxylate
(11)
To a cooled solution of 7 (178mg, 0.68mmol), DMAP
(5mg, 0.04mmol), and pyridine (0.31mL) in CH2Cl2
(10mL), Boc2O (500mg, 2.29mmol) in CH2Cl2 (5mL)
was added dropwise. The mixture was warmed up to
room temperature and stirred for 3h. Then the reaction
was quenched with H2O and the organic phase was sep-
arated. The aqueous layer was extracted with CH2Cl2
(2 · 30mL) and the combined organic phases were
washed with diluted aqueous HCl, brine and dried over
anhydrous Na2SO4. After filtration and removal of the
solvent in vacuo, the resulting residue was purified by
˚
To a cooled mixture of 9 (86mg, 0.24mmol) and 4A MS
(131mg, powder) in Et2O (5mL), CH(OMe)3 (0.06mL)
was added dropwise followed by BF3ÆEt2O (10lL, 1M
in Et2O, 0.01mmol). The mixture was then stirred at
room temperature for 20min. The reaction was
quenched with H2O and extracted with Et2O. The com-
bined organic phases were washed with brine and dried
over anhydrous Na2SO4. Filtration and removal of the
solvent gave a residue, which was purified by flash chro-
20
matography to give 11 as an oil (24mg, 27%). ½aꢁ ꢀ59.3
D
flash chromatography (hexane/ethyl acetate, 7:1) to give
(c 0.87, acetone); 1H NMR (300MHz, acetone-d6) d 5.14
(br, 1H), 4.67–4.29 (m, 2H), 3.97–3.82 (m, 2H), 3.47 (br,
1H), 3.27 (2s, 3H), 2.51–2.34 (m, 1H), 2.15 (br, 1H),
1.74–1.63 (m, 1H), 1.46 (s, 9H), 0.89 (s, 9H), 0.07, 0.05
(2s, 6H); 19F NMR (282MHz, acetone-d6) d ꢀ221.04
to ꢀ221.63 (m, 1F); 13C NMR (75.5MHz, acetone-d6)
d 154.2 (d, J = 32.8Hz), 88.4 (d, J = 5.0Hz), 82.3 (d,
J = 162.0Hz), 79.5, 65.6, 64.8, 58.5, 54.6, 43.4, 27.6,
25.3, 17.8, ꢀ6.1; IR (thin film) 1705, 1473, 1381,
839cmꢀ1; MS (ESI) m/z 400.2 (M++Na); ESI-HRMS
m/z 400.22817 (M++Na, C18H36FNO4SiNa required
400.22898).
20
D
8 as a white solid (222mg, 90%): mp 65–66ꢁC; ½aꢁ
1
ꢀ53.2 (c 0.87, CHCl3); H NMR (300MHz, CDCl3) d
4.76 (ddd, J = 23.3, 5.1, 5.7Hz, 1H), 4.59 (ddd,
J = 22.5, 5.7, 5.4Hz, 1H), 4.18–4.11 (m, 1H), 3.92 (dd,
J = 4.8, 4.8Hz, 1H), 3.72 (dd, J = 2.4, 2.7Hz, 1H),
3.01–2.83 (m, 1H), 2.32 (ddd, J = 16.5, 8.9, 2.3Hz,
1H), 2.09 (ddd, J = 13.7, 5.1, 5.3Hz, 1H), 1.54 (s, 9H),
0.88 (s, 9H), 0.05 (2s, 6H); 19F NMR (282MHz, CDCl3)
d ꢀ226.23 to ꢀ226.65 (m, 1F); 13C NMR (75.5MHz,
CDCl3) d 172.3 (d, J = 10.1Hz), 150.0, 83.1, 83.0 (d,
J = 170.2Hz), 63.4 (d, J = 0.6Hz), 57.1, 43.9 (d,
J = 21.7Hz), 28.0, 25.8, 22.7 (d, J = 2.5Hz), 18.3, ꢀ5.5
(d, J = 0.8Hz); IR (thin film) 1765, 1689, 1473, 1369,
836, 779cmꢀ1; MS (EI) m/z 288 (M+ꢀC4H9O, 7), 248
(51), 204 (100); MS (ESI) m/z 384.2 (M++Na); ESI-
HRMS m/z 384.19792 (M++Na, C17H32FNO4SiNa re-
quired 384.19768).
3.7. (5S,3S)-N-Benzyloxycarbonyl-5-tert-butyldimethyl-
silyloxymethyl-3-monofluoromethyl-2-pyrrolidone (12)
and (5S)-N-benzyloxycarbonyl-5-tert-butyldimethylsilyl-
oxymethyl-3-methylene-2-pyrrolidone (13)
To a solution of 7 (516mg, 2.00mmol) in THF (20mL)
at ꢀ78ꢁC was added LHMDS (2.0mL, 1M in THF,
2.0mmol) dropwise. After the mixture was stirred for
10min, CbzCl (0.45mL, 3.16mmol) was added drop-
wise. The mixture was stirred for further 10min at
ꢀ78ꢁC and quenched with saturated aqueous NH4Cl
(5mL). The mixture was then warmed up to room tem-
perature and extracted with EtOAc (3 · 40mL). The
combined organic phases were washed with brine and
dried over anhydrous Na2SO4. After filtration and re-
moval of the solvent, the resulting residue was purified
by flash chromatography (hexane/ethyl acetate, 10:1)
to give 13 as a white solid (less polar, 28mg, 4%) and
3.5. tert-Butyl (2R,3S,5S)-5-tert-butyldimethylsilyloxy-
methyl-3-monofluoromethyl-2-hydroxypyrrolidine-1-carb-
oxylate (9)
To a solution of 8 (222mg, 0.62mmol) in THF (10mL)
at ꢀ78ꢁC was added LiBEt3H (1.70mL, 1M in THF,
1.70mmol) dropwise. The mixture was stirred at
ꢀ78ꢁC for 30min. The reaction was then quenched with
H2O (3mL) and warmed up to room temperature. H2O
(10mL) was added and the mixture was extracted with
CH2Cl2 (3 · 40mL). The combined organic phases were
washed with brine and dried over anhydrous Na2SO4.
After filtration and removal of the solvent, the resulting
residue was purified by flash chromatography (hexane/
12 as a white solid (more polar, 727mg, 93%). Com-
20
pound 12: mp 80–82ꢁC; ½aꢁ ꢀ57.2 (c 0.84, CHCl3);
D
ethyl acetate, 20:1, then 15:1) to give 9 as a clear
1H NMR (300MHz, CDCl3) d 7.50–7.32 (m, 5H),
5.34–5.23 (m, 2H), 4.76 (ddd, J = 28.1, 5.3, 5.0Hz,
1H), 4.61 (ddd, J = 27.2, 5.3, 5.4Hz, 1H), 4.24–4.17
(m, 1H), 3.90 (dd, J = 4.8, 4.8Hz, 1H), 3.70 (dd,
J = 2.7, 2.4Hz, 1H), 3.02–2.84 (m, 1H), 2.40–2.32 (m,
1H), 2.17–2.04 (m, 1H), 0.84 (s, 9H), ꢀ0.02, ꢀ0.03 (2s,
6H); 19F NMR (282MHz, CDCl3) d ꢀ226.31 to
ꢀ226.72 (m, 1F); IR (thin film) 2955, 1714, 1289,
834cmꢀ1; MS (ESI) m/z 418.2 (M++Na); Anal. Calcd
for C20H30FNO4Si: C, 60.76; H, 7.59; N, 3.54. Found:
20
D
oil (181mg, 81%). ½aꢁ ꢀ51.2 (c 1.05, acetone); 1H
NMR (300MHz, acetone-d6) d 5.44 (d, J = 12.6Hz,
1H), 4.61 (dt, J = 46.5, 8.1Hz, 1H), 4.40 (ddd,
J = 47.1, 5.7, 6.0Hz, 1H), 3.95–3.54 (m, 3H), 2.47–2.30
(m, 1H), 2.23–2.10 (m, 1H), 1.79–1.65 (m, 1H), 1.44 (s,
9H), 0.89 (s, 9H), 0.08, 0.07 (2s, 6H); 19F NMR
(282MHz, acetone-d6) d ꢀ221.72 to ꢀ222.34 (m, 1F);
13C NMR (75.5MHz, acetone-d6)
d
153.3 (d.,
J = 37.0Hz), 82.6 (d, J = 81.6Hz), 80.7 (d, J = 5.7Hz),
79.4, 65.4, 63.6, 57.9, 43.5, 27.7, 27.1, 25.4, 17.9. IR (thin
film) 3441, 1700, 1474, 1390, 839cmꢀ1; MS (ESI) m/z
386.2 (M++Na); Anal. Calcd for C17H34FNO4Si: C,
C, 60.70; H, 7.87; N, 3.40. Compound 13: mp 41–
20
D
43ꢁC; ½aꢁ
ꢀ33.8 (c 0.66, CHCl3); 1H NMR
(300MHz, CDCl3) d 7.47–7.32 (m, 5H), 6.16 (t,

282
X.-L. Qiu, F.-L. Qing / Bioorg. Med. Chem. 13 (2005) 277–283
J = 2.4Hz, 1H), 5.46 (t, J = 2.1Hz, 1H), 5.37–5.23 (m,
2H), 4.28–4.22 (m, 1H), 3.77 (dd, J = 4.8, 4.5Hz, 1H),
3.69–3.66 (dd, J = 2.4, 2.7Hz, 1H), 2.81–2.77 (m, 2H),
0.81 (s, 9H), ꢀ0.04, ꢀ0.07 (2s, 6H); 13C NMR
(75.5MHz, CDCl3) d 166.2, 152.1, 139.0, 135.4, 128.6,
128.3, 128.1, 119.3, 68.1, 63.7, 55.7, 27.8, 25.7, 18.1,
ꢀ5.7; IR (thin film) 2956, 2929, 1739, 1700, 1658,
1301, 1014, 838cmꢀ1; MS (ESI) m/z 376.2 (M++1);
ESI-HRMS m/z 398.17538 (M++Na, C20H29NO7SiNa
required 398.17581).
chromatography (hexane/ethyl acetate, 5:1) to afford 16
20
as a white solid (597mg, 92%): mp 74–76ꢁC; ½aꢁ ꢀ53.2
D
(c 0.98, acetone); 1H NMR (300MHz, acetone-d6) d
7.39–7.34 (m, 5H), 6.78 (d, J = 5.1Hz, 1H), 5.14 (br,
2H), 4.55 (dd, J = 4.2, 3.0Hz, 1H), 4.39 (dd, J = 3.6,
3.6Hz, 1H), 3.96–3.54 (m, 3H), 2.76–2.65 (m, 1H),
2.27–2.15 (m, 1H), 2.04–1.87 (m, 4H), 0.90 (s, 9H),
0.03 (s, 6H); 19F NMR (282MHz, acetone-d6)
d ꢀ223.55 to ꢀ223.87 (m, 1F); IR (thin film) 2937,
1736, 1716, 1401, 1213, 1086, 837cmꢀ1; MS (ESI) m/z
478.2 (M++K), 462.2 (M++Na); Anal. Calcd for
C22H34FNO5Si: C, 60.14; H, 7.74; N, 3.19. Found: C,
60.27; H, 7.73; N, 2.98.
3.8. Benzyl (2R,3S,5S)-5-tert-butyldimethylsilyloxymeth-
yl-3-monofluoromethyl-2-hydroxypyrrolidine-1-carboxyl-
ate (14) and benzyl (2S,3S,5S)-5-tert-butyldimethylsilyl-
oxymethyl-3-monofluoromethyl-2-hydroxypyrrolidine-1-
carboxylate (15)
3.10. Benzyl (2S,3S,5S)-5-hydroxymethyl-2-[2,4-dioxo-
3,4-dihydro-pyrimidin-1(2H)-yl]-3-(monofluoromethyl)-
pyrrolidine-1-carboxylate (17a) and benzyl (2R,3S,5S)-5-
hydroxymethyl-2-[2,4-dioxo-3,4-dihydro-pyrimidin-
1(2H)-yl]-3-(monofluoromethyl)-pyrrolidine-1-carboxyl-
ate (17b)
To a solution of 12 (727mg, 1.84mmol) in THF (25mL)
at ꢀ78ꢁC was added LiBEt3H (6.0mL, 1M in THF,
6.0mmol) dropwise. The mixture was stirred at ꢀ78ꢁC
for 1h. The reaction was quenched with H2O (10mL)
and warmed up to room temperature. The mixture
was extracted with Et2O (3 · 40mL) and the combined
organic phases were washed with brine and dried over
anhydrous Na2SO4. After filtration and removal of the
solvent, the resulting residue was purified by flash chro-
matography (hexane/ethyl acetate, 5:1) to give 14 (less
Typical procedure: To a stirred solution of 16 (128mg,
0.29mmol) and uracil (96mg, 0.86mmol) in anhydrous
acetonitrile (30mL) was added N,O-bis(trimethylsil-
yl)acetamide (0.44mL, 1.33mmol). The reaction mix-
ture was stirred under reflux for 30min. After cooled
to 0ꢁC, TMSOTf (0.15mL, 0.72mmol) was added
dropwise and the solution was stirred at room temper-
ature for further 40min. The reaction was quenched
with cold saturated aqueous NaHCO3 (6mL) and the
resulting mixture was extracted with CH2Cl2
(3 · 40mL). The combined organic phases were washed
with brine and dried over anhydrous Na2SO4. After re-
moval of the solvent, the resulting residue was purified
by flash chromatography (hexane/ethyl acetate, 3:2) to
give two compounds, the less polar compound (75mg,
white foam) and more polar compound (34mg, white
foam). A stirred solution of above less polar compound
(42mg) in THF (4.5mL) was treated with 1.0M solu-
tion of TBAF (0.11mL, 0.11mmol) at 0ꢁC. After stir-
red at room temperature for 8.5h, the reaction was
quenched with H2O and the mixture was extracted with
CH2Cl2 (3 · 20mL). The combined organic phases were
washed with brine and dried over anhydrous Na2SO4.
After removal of the solvent, the resulting residue was
purified by flash chromatography (hexane/ethyl acetate,
1:3) to give 17a as a white foam (29mg, 47% from 16).
The more polar compound (34mg) was also treated
with TBAF under the same conditions to give 17b as
a white foam (22mg, 20% from 16). Deprotection of
the silyl protection groups was also conveniently
achieved using HFÆpyridine in CH2Cl2. Compound
polar) as a clear oil (589mg, 81%) and 15 (more
20
D
polar) as a clear oil (90mg, 12%). Compound 14: ½aꢁ
1
ꢀ48.1 (c 0.76, acetone); H NMR (300MHz, acetone-
d6) d 7.42–7.31 (m, 5H), 5.56 (t, J = 5.4Hz, 1H), 5.21–
5.05 (m, 2H), 4.75–4.34 (m, 3H), 4.02–3.90 (m, 2H),
3.78–3.56 (br, 1H), 2.51–2.42 (m, 1H), 2.27–2.15 (m,
1H), 1.82–1.70 (m, 1H), 0.90 (s, 9H), 0.08, 0.01 (2s,
6H); 19F NMR (282MHz, acetone-d6) d ꢀ221.99 to
ꢀ222.37 (m, 1F); IR (thin film) 3429, 2956, 1708,
1412, 1101, 838cmꢀ1; MS (ESI) m/z 380.2 (M+ꢀOH);
MS (MALDI) m/z 420.2 (M++Na); Anal. Calcd for
C20H32FNO4Si: C, 60.45; H, 8.06; N, 3.53. Found: C,
20
60.87; H, 8.20; N, 3.85. Compound 15: ½aꢁ ꢀ47.6 (c
D
0.47, acetone); 1H NMR (300MHz, acetone-d6) d
7.44–7.34 (m, 5H), 5.45–5.07 (m, 4H), 4.61–4.34 (m,
2H), 3.99–3.60 (m, 3H), 2.46–2.36 (m, 2H), 1.79 (br,
1H), 0.88 (s, 9H), 0.04 (s, 6H); 19F NMR (282MHz, ace-
tone-d6) d ꢀ218.77 to ꢀ220.47 (m, 1F); IR (thin film)
3426, 2956, 1710, 1409, 1101, 838cmꢀ1; MS (ESI) m/z
420.1 (M++Na), 398.3 (M++1), 380.2 (M+ꢀOH); Anal.
Calcd for C20H32FNO4Si: C, 60.45; H, 8.06; N, 3.53.
Found: C, 60.60; H, 8.37; N, 3.42.
3.9. Benzyl (2R,3S,5S)-2-acetyloxy-5-tert-butyldimethyl-
silyloxymethyl-3-monofluoromethylpyrrolidine-1-carb-
oxylate (16)
20
D
1
17a: ½aꢁ ꢀ5.3 (c 0.66, CHCl3); H NMR (300MHz,
MeOH-d4) d 8.46 (br, 1H), 7.29 (br, 5H), 6.44 (d,
J = 7.2Hz, 1H), 5.56 (d, J = 7.8Hz, 1H), 5.21–5.17
(m, 1H), 5.10–4.97 (br, 1H), 4.56 (ddd, J = 25.0, 4.2,
4.2Hz, 1H), 4.47–4.34 (m, 2H), 3.92 (t, J = 9.0Hz,
1H), 3.66 (d, J = 11.4Hz, 1H), 2.93–2.74 (m, 1H),
2.33–2.18 (m, 1H), 2.10–2.00 (m, 1H); 19F NMR
(282MHz, MeOH-d4) d ꢀ228.87 to ꢀ229.45 (m, 1F);
13C NMR (75.5MHz, MeOH-d4) d 166.3, 156.5,
152.9, 144.0, 137.4, 129.6, 129.3, 128.9, 101.9, 82.1 (d,
J = 168.1Hz), 72.2, 68.7, 61.8, 61.0, 43.5 (d,
To a mixture of 14 (589mg, 1.48mmol), DMAP (16mg,
0.13mmol), pyridine (2.0mL, 24.56mmol) in CH2Cl2
(25mL) was added Ac2O (1.30mL, 13.89mmol). After
the mixture was stirred overnight at room temperature,
the reaction was quenched with H2O (10mL) and ex-
tracted with CH2Cl2 (3 · 30mL). The combined organic
phases were washed with dilute HCl, brine and dried
over anhydrous Na2SO4. After filtration and removal
of the solvent, the resulting residue was purified by flash

X.-L. Qiu, F.-L. Qing / Bioorg. Med. Chem. 13 (2005) 277–283
283
J = 19.5Hz), 27.8; IR (thin film) 3448, 3199, 1685,
Acknowledgements
1466, 1400, 1275cmꢀ1; MS (EI) m/z 266 (M+ꢀuracil,
14), 222 (16), 91 (100); MALDI-HRMS m/z 400.1319
We thank the National Natural Science Foundation of
China and Ministry of Education of China for funding
this work.
(M++Na, C18H20N3O5FNa required 400.1279). Com-
20
D
pound 17b: ½aꢁ
ꢀ25.2 (c 0.65, CHCl3); 1H
NMR (300MHz, MeOH-d4) d 7.54–7.23 (m, 6H), 5.86
(br, 1H), 5.42–5.30 (m, 1H), 5.11 (br, 1H), 4.84–4.80
(m, 1H), 4.62–4.59 (m, 1H), 4.47–4.44 (m, 1H), 4.22
(br, 1H), 3.99–3.79 (m, 1H), 3.67–3.63 (m, 1H), 2.73
(br, 1H), 2.48–2.37 (m, 1H), 1.88–1.75 (m, 1H); 19F
NMR (282MHz, MeOH-d4) d ꢀ222.53 to ꢀ222.65
(m, 1F); 13C NMR (75.5MHz, MeOH-d4) d 166.0,
155.2, 151.9, 143.5, 137.2, 129.7, 129.6, 129.5, 102.9,
84.6 (d, J = 170.3Hz), 75.8, 68.7, 62.8, 61.8, 46.1 (d,
J = 18.5Hz), 28.5; IR (thin film) 3510, 3152, 3033,
1677, 1627, 1461, 1402, 1262, 699cmꢀ1; MS (EI) m/z
346 (M+ꢀCH2OH, <1), 266 (M+ꢀuracil, 17), 222
(16), 91 (100); MALDI-HRMS m/z 400.1301
(M++Na, C18H20N3O5FNa required 400.1279).
References and notes
1. Ferrero, M.; Gotor, V. Chem. Rev. 2000, 100, 4319.
2. (a) Ichikawa, E.; Kato, K. Curr. Med. Chem. 2001, 8, 385;
(b) Ferrier, R. J. Carbohydr. Chem. 2001, 32, 256.
3. Yokoyama, M. Synthesis 2000, 1637.
4. For carbocyclic nucleosides reviews, see: (a) Crimmins, M.
T. Tetrahedron 1998, 54, 9229; (b) Borthwick, A. D.;
Biggadike, K. Tetrahedron 1992, 48, 571; (c) Agrofoglio,
L.; Suhas, E.; Farese, A.; Condom, R.; Challand, S. R.;
Earl, R. A.; Guedj, R. Tetrahedron 1994, 50, 10611; (d)
Marquez, V. E.; Lim, M.-U. Med. Res. Rev. 1986, 6, 1; (e)
Vine, R.; Akella, L. B. Med. Res. Rev. 1996, 52, 2789.
5. Yokoyama, M.; Momotake, A. Synthesis 1999, 1541.
6. For fluoronucleosides reviews, see: (a) Flurorine Containing
Moleculars, Structure, Reactivity, and Applications; Berg-
strom, D. E., Swartling, D. J., Libeman, J. F., Greenberg,
A., Jr., Dolbier, W. R., Jr., Eds.; VCH: New York, 1988;
pp 259–308; (b) Herdewijn, P.; Van Aerschot, A.; Kerre-
mans, L. Nucleosides/Nucleotides 1989, 8, 65; (c) Pan-
kiewicz, K. W.; Watanabe, K. A. J. Fluorine Chem. 1993,
64, 15; (d) Pankiewicz, K. W. Carbohydr. Res. 2000, 327,
87.
3.11. Benzyl (2S,3S,5S)-5-hydroxymethyl-2-[5-methyl-
2,4-dioxo-3,4-dihydro-pyrimidin-1(2H)-yl]-3-(monofluoro-
methyl)-pyrrolidine-1-carboxylate (18a) and benzyl
(2R,3S,5S)-5-hydroxymethyl-2-[5-methyl-2,4-dioxo-3,4-
dihydro-pyrimidin-1(2H)-yl]-3-(monofluoromethyl)-pyrr-
olidine-1-carboxylate (18b)
Compounds 18a (27mg, 15%) and 18b (78mg, 44%)
were prepared as white foams from compound 16
(119mg, 0.45mmol) and thymine (178mg, 1.41mmol)
7. Marquez, V. E.; Lim, B. B.; Barchi, J. J.; Nicklaus, M. C.
In Nucleosides and Nucleotides as Antitumor and Antiviral
Agents; Plenum Press: New York, 1993; p 265.
using the same conditions as described for compounds
8. (a) Kotra, L. P.; Xiang, Y.; Newton, M. G.; Schinazi, R.
F.; Cheng, Y.-C.; Chu, C. K. J. Med. Chem. 1997, 40,
3635; (b) Hertel, L. W.; Kroin, J. S.; Misner, J. W.; Tustin,
J. M. J. Org. Chem. 1988, 53, 2406.
9. (a) Chu, C. K.; Ma, T.; Shanmuganathan, K.; Wang, C.;
Xiang, Y.; Pai, S. B.; Yao, G. Q.; Sommadossi, J. P.;
Cheng, Y. C. Antimicrob. Agents Chemother. 1995, 39,
979; (b) Watanabe, K. A.; Reichman, U.; Hirota, K.;
Lopez, C.; Fox, J. J. J. Med. Chem. 1979, 22, 21.
10. (a) Etzold, G.; Hintsche, R.; Kowollik, G.; Langen, P.
Tetrahedron 1971, 27, 2463; (b) Balzarini, J.; Baba, M.;
Pauwells, R.; Hetdewijn, P.; De Clercq, E. Biochem.
Pharmacol. 1988, 37, 2847.
20
17a and 17b. Compound 18a: ½aꢁ +9.4 (c 0.72,
D
CHCl3); 1H NMR (300MHz, MeOH-d4) d 8.41 (br,
1H), 7.28 (br, 5H), 6.43 (d, J = 5.1Hz, 1H), 5.23–4.99
(m, 2H), 4.60–4.33 (m, 3H), 3.90 (t, J = 9.0Hz, 1H),
3.66 (d, J = 11.7Hz, 1H), 2.93–2.74 (m, 1H), 2.34–
2.22 (m, 1H), 2.10–2.01 (m, 1H), 1.79 (s, 3H);
19F NMR (282MHz, MeOH-d4)
d
ꢀ229.95 to
ꢀ230.72 (m, 1F); 13C NMR (75.5MHz, MeOH-d4) d
166.5, 156.3, 153.0, 139.9, 137.5, 129.6, 129.3, 128.8,
110.7, 82.1 (d, J = 168.1Hz), 71.8, 68.6, 61.8, 60.8,
43.5 (d, J = 19.6Hz), 27.7, 12.4; IR (thin film) 3448,
3192, 3064, 1685, 1472, 1404, 1273cmꢀ1; MS (EI) m/z
391 (M+, <1), 266 (M+ꢀthymine, 16), 222 (18),
91 (100); MALDI-HRMS m/z 414.1468 (M++Na,
C19H22N3O5FNa required 414.1436). Compound
11. Okabe, M.; Sun, R.-C.; Zenchoff, G. B. J. Org. Chem.
1991, 56, 4392.
12. Yoshimura, Y.; Saitoh, K.; Ashida, N.; Sakata, S.;
Matsuda, A. Bioorg. Med. Chem. Lett. 1994, 4, 721–724.
13. Lin, T.-S.; Zhu, J.-L.; Dutschman, G. E.; Cheng, Y.-C.;
Prusoff, W. H. J. Med. Chem. 1993, 36, 353–362.
14. (a) Qing, F.-L.; Yu, J.; Fu, X.-K. Collect. Czech. Chem.
Commun. 2002, 67, 1267; (b) Qiu, X.-L.; Qing, F.-L.
Synthesis 2004, 334.
15. (a) Qiu, X.-L.; Qing, F.-L. J. Org. Chem. 2002, 67, 7162;
(b) Qiu, X.-L.; Qing, F.-L. J. Org. Chem. 2003, 68, 3614.
16. Rassu, G.; Zanardi, F.; Battistini, L.; Gaetani, E.;
Casiraghi, G. J. Med. Chem. 1997, 40, 168.
20
D
1
18b: ½aꢁ ꢀ24.7 (c 0.62, CHCl3); H NMR (300MHz,
MeOH-d4) d 7.27 (m, 5H), 7.07 (br, 1H), 5.83 (br,
1H), 5.35–5.31 (d, J = 11.4Hz, 1H), 4.78–4.75 (m,
1H), 4.60–4.55 (m, 1H), 4.44–4.43 (m, 1H), 4.24
(br, 1H), 3.99–3.95 (m, 1H), 3.79–3.63 (m, 1H), 2.72
(br, 1H), 2.47–2.37 (m, 1H), 1.86–1.64 (m, 4H); 19F
NMR (282MHz, MeOH-d4) d ꢀ220.83 to ꢀ223.35
(m, 1F); 13C NMR (75.5MHz, MeOH-d4) d166.2,
155.2, 152.0, 139.2, 137.1, 129.7, 129.6, 129.5, 111.8,
84.5 (d, J = 169.7Hz), 76.7, 75.5, 68.6, 62.7, 46.0 (d,
J = 18.6Hz), 28.6, 12.4; IR (thin film) 3440, 3188,
3038, 1689, 1470, 1404cmꢀ1; MS (EI) m/z 391 (M+,
<1), 266 (M+ꢀthymine, 19), 222 (21), 91 (100); MAL-
DI-HRMS m/z 414.1474 (M++Na, C19H22N3O5FNa
required 414.1436).
17. Li, H.; Sakamoto, T.; Kato, M.; Kikugawa, Y. Synth.
Commun. 1995, 25, 4045.
18. (a) Vorbruggen, H.; Krolikiewicz, K.; Bennua, B. Chem.
¨
¨
Ber. 1981, 114, 1234; (b) Vorbruggen, H.; Ho¨fle, G. Chem.
Ber. 1981, 114, 1256.
19. The crystal structure has been deposited at the Cambridge
Crystallographic Data center and allocated the deposition
number CCDC 240681.