Synthesis of 2,3-dideoxy-2,2-difluoro-L-glycero-pentofuranosyl nucleosides

Article abstract of DOI:10.1016/S0008-6215(97)00275-9

Various 2,3-dideoxy-2,2-difluoro-L-glycero-pentofuranosyl nucleosides were synthesized via the key intermediate, 5-O-benzoyl-2,3-dideoxy-2,2- difluoro-L-glycero-pentofuranose (6). 2,3-O-Isopropylidene-L-glyceraldehyde was coupled with ethyl bromodifluoroacetate under Reformatsky conditions to obtain the diastereomeric mixture of ethyl (4S)-3-hydroxy-3-(2,2-dimethyl- 1,3-dioxolan-4-yl)-2,2-difluoro propionate (1). Treatment of compound 1 with carbon disulfide, sodium hydride and methyl iodide followed by reduction afforded ethyl (4S)-3-(2,2-dimethyl-1,3-dioxolan-4-yl)-2,2-difluoro propionate (3). Compound 3 was treated with 5% HCl in ethanol, followed by refluxing in benzene under Dean-Stark conditions, to afford the lactone 4. The compound 4 was protected and reduced to afford the key intermediate 6. For the synthesis of pyrimidine derivatives 8-21, compound 6 was converted to the mesylate 7 and condensed with various silyl protected pyrimidine bases. The inosine and adenine derivatives 38-41 were obtained from compound 6 and 6-chloropurine using standard procedures. Compounds 22-35 and 38-41 were evaluated for their antiviral activity against HIV-1, HBV, HSV-1 and HSV-2, and for cellular toxicity. None of the synthesized compounds showed any significant activity or toxicity. Single-crystal X-ray structure of 1-(2,3- dideoxy-2,2-difluoro-β-L-glycero-pentofuranosyl)-5-iodocytosine (34) suggested a 2'-exo/3'-endo conformation for the carbohydrate moiety.

Full text of DOI:10.1016/S0008-6215(97)00275-9

Ž
.
Carbohydrate Research 306 1998 69–80
Synthesis of
2,3-dideoxy-2,2-difluoro-L-glycero-pentofuranosyl
nucleosides
a
b
a,)
Lakshmi P. Kotra , M. Gary Newton , Chung K. Chu
a
Department of Medicinal Chemistry, College of Pharmacy, The UniÕersity of Georgia, Athens, GA
30602-2352, USA
b
Department of Chemistry, The UniÕersity of Georgia, Athens, GA 30602-2352, USA
Received 9 May 1997; accepted 15 July 1997
Abstract
Various 2,3-dideoxy-2,2-difluoro-L-glycero-pentofuranosyl nucleosides were synthesized
Ž .
via the key intermediate, 5-O-benzoyl-2,3-dideoxy-2,2-difluoro-L-glycero-pentofuranose 6 .
2,3-O-Isopropylidene-L-glyceraldehyde was coupled with ethyl bromodifluoroacetate under
Ž
.
Ž
Reformatsky conditions to obtain the diastereomeric mixture of ethyl 4S -3-hydroxy-3- 2,2-
.
Ž .
dimethyl-1,3-dioxolan-4-yl -2,2-difluoro propionate 1 . Treatment of compound 1 with car-
bon disulfide, sodium hydride and methyl iodide followed by reduction afforded ethyl
Ž
.
Ž
.
Ž .
4S -3- 2,2-dimethyl-1,3-dioxolan-4-yl -2,2-difluoro propionate 3 . Compound 3 was treated
with 5% HCl in ethanol, followed by refluxing in benzene under Dean–Stark conditions, to
afford the lactone 4. The compound 4 was protected and reduced to afford the key
intermediate 6. For the synthesis of pyrimidine derivatives 8–21, compound 6 was converted
to the mesylate 7 and condensed with various silyl protected pyrimidine bases. The inosine
and adenine derivatives 38–41 were obtained from compound 6 and 6-chloropurine using
standard procedures. Compounds 22–35 and 38–41 were evaluated for their antiviral activity
against HIV-1, HBV, HSV-1 and HSV-2, and for cellular toxicity. None of the synthesized
compounds showed any significant activity or toxicity. Single-crystal X-ray structure of
X
Ž
.
Ž
.
1- 2,3-dideoxy-2,2-difluoro-b-L-glycero-pentofuranosyl -5-iodocytosine 34 suggested a 2 -
exor3X-endo conformation for the carbohydrate moiety. q 1998 Elsevier Science Ltd. All
rights reserved.
Keywords: 2,3-dideoxy-2,2-difluoro-L-glycero-pentofuranosyl nucleosides; X-ray structure; Nucleoside conforma-
tion
1. Introduction
X
X
X
Ž
In 1996, Gemzare 2 -deoxy-2 ,2 -difluorocyti-
) Corresponding author. Tel.: q1-706-542-5379; fax:
q1-706-542-5381; e-mail: dchu@rx.uga.edu.
.
dine, gemcitabine was approved for the treatment of
patients with inoperable pancreatic cancer and non-
0008-6215r98r$19.00 q 1998 Elsevier Science Ltd All rights reserved.

(
)
70
L.P. Kotra et al.rCarbohydrate Research 306 1998 69–80
w x
small-cell lung carcinoma 1 . This compound pos-
sesses a difluoro substitution at the 2X-position of
w x
cytidine and has D-configuration 2 . Recently, we
investigated the synthesis and anti-HIV activity of
2-deoxy-2,2-difluoro-L-ribofuranosyl nucleosides
w
x
3,4 . Among the synthesized compounds, the ade-
Ž
.
nine analogue Fig. 1A showed moderate activity
Ž
.
EC50 3.4 mM against HIV-1 without any toxicity
up to 100 mM in peripheral blood mononuclear
Ž
.
PBM , Vero and CEM cells. In view of the above
Fig. 1.
2X-Deoxy-2X,2X-difluoro-b-L-adenosine,
interesting discoveries and as part of our continuous
efforts to develop biologically active nucleosides, it
Ž .
A
Ž .
B
2X,3X-dideoxy-2X,2X-difluoro-L-nucleosides.
X
Ž .
Scheme 1. Synthesis of various pyrimidine derivatives 22–35. Reagents: a 1,1-thiocarbonyldiimidazole, Me2 NCHO, 50
Ž .
Ž
.
8C or carbon disulfide, NaH, iodomethane, Me2 NCHO, 0 8C; b tributyltin hydride Bu3SnH , AIBN, toluene, 90–100 8C;
Ž . Ž . Ž . Ž . Ž .
c
1 5% HCl, EtOH, 2 benzene, 80 8C, Dean–Stark apparatus; d benzoyl chloride, 2,6-lutidine, CH2Cl2 , rt; e lithiun
Ž
w
Ž
.
x
Ž .
Ž .
Ž .
tri tert-butoxyaluminum hydride Li tert-BuO AlH , tetrahydrofuran, y78 8C; f MsCl, Et3N, CH2Cl2; g silylated base,
3
sodium iodide, acetonitrile for compounds 8 and 9 or silylated base, Me3SiOTf, DCE, 90–100 8C; h ammonia or
methylamine, methanol, rt.

(
)
L.P. Kotra et al.rCarbohydrate Research 306 1998 69–80
71
was of interest to synthesize 2,3-dideoxy-2,2-dif-
Ž
.
luoro-L-glycero-pentofuranosyl nucleosides Fig. 1B
as potential antiviral agents. This class of compounds
lacks the 2X- and 3X-OH groups. It was anticipated that
the presence of 2X-difluoro substitution in the absence
of 3X-OH would affect the conformation of 2X-deoxy-
X
X
w x
2 ,2 -difluoro nucleosides 2 resulting in a potentially
different biological profile. Herein, we wish to report
the synthesis and biological activities of 2,3-dideoxy-
2,2-difluoro-L-glycero-pentofuranosylpyrimidine and
purine nucleosides.
2. Synthesis
For the synthesis of the targetted nucleosides, 5-
O-benzoyl-2,3-dideoxy-2,2-difluoro-L-glycero-pento-
Ž .
furanose 6 was synthesized as the key intermediate
Ž
.
Scheme 1 . Compound 6 was synthesized from L-
gulono-g-lactone via 2,3-dideoxy-2,2-difluoro-L-
Fig. 2. X-ray structure of 5-iodocytosine analog 34.
Ž .
glycero-pentofurano-1,4-lactone 4 . 2,3-O-Isopro-
pylidene-L-glyceraldehyde was obtained from L-
w x
gulono g-lactone in two steps 5 and was reacted
carbon disulfide, sodium hydride and iodomethane to
give compound 2b, followed by the reduction with
tributyltin hydriderAIBN, afforded compound 3 in
with ethyl bromodifluoroacetate in the presence of
zinc under Reformatsky conditions to obtain the di-
astereomeric mixture 1 in 54% yield. Compound 1
Ž
. w x
fair yields 57% 6 . Compound 3 was treated with
5% HCl in ethanol for 3 h, followed by refluxing in
benzene at 95 8C in a Dean–Stark apparatus to afford
compound 4 in a 95% yield. Cyclization of com-
pound 3 as described above exclusively provided the
furanose ring isomer 4, whose structure was con-
X
was treated with 1,1-thiocarbonyldiimidazole in
Me2 NCHO, followed by reduction with tributyltin
hydride, to afford compound 3. The yields of reduc-
tion of the thiocarbonylimidazolide 2a to 3 were poor
Ž
.
20% and were not suitable for large-scale prepara-
X
1
tions. Additionally, 1,1-thiocarbonyldiimidazole is
too expensive to carry out the reaction on a multi-
gram scale. Thus, the treatment of compound 1 with
firmed by a triplet signal for the 5X-OH in the H
NMR spectrum. Compound 4 was protected by treat-
ment with benzoyl chloride and triethylamine in
Ž .
Scheme 2. Synthesis of adenine and hypoxanthine derivatives 38–41. Reagents: a DEAD, Ph3P, tetrahydrofuran, 8 h,
Ž . Ž .
argon; b ammonia, MeOH, steel bomb, 80–90 8C, 28 h; c 2-mercaptoethanol, NaOMe, MeOH, reflux.

(
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72
L.P. Kotra et al.rCarbohydrate Research 306 1998 69–80
Ž
.
Ž
.
Fig. 3. Stereo view of overlap of the X-ray structures of 34 green with L-FMAU red .
Ž
.
dichloromethane 62% followed by reduction with
The anomeric configuration of the final compounds
Ž
.
lithium tri tert-butoxy aluminum hydride in tetrahy-
were assigned based on the presencerabsence of a
X
drofuran at y78 8C to give compound 6 90% . For
the preparation of thymine derivatives 8 and 9, mesy-
late 7 was condensed with silylated thymine using
sodium iodide as a catalyst in acetonitrile, resulting in
cross-peak between H-1, H-4X in 2D NOESY experi-
Ž
.
ments or the by comparison of the chemical shifts of
the H-4X signals of the a and b anomers in 1D
experiments. The structure of compound 34 was also
Ž
.
poor yields a:br1:1, 15% of the products. Hence,
confirmed by single-crystal X-ray crystallography
1
Ž
.
Ž
Ž
.
for the synthesis of uracil 10–15 and cytosine 16–
21 derivatives, the mesylate 7 was condensed with
Fig. 2
.
.
various silyl-protected uracil and cytosine bases using
Me3SiOTf as a catalyst in dichloroethane at 90–100
3. Conformational aspects
The X-ray structures of compound 34 and 1- 2-de-
w x
8C 2 . In the condensation reactions, temperatures of
Ž
80–100 8C were critical for the condensation reac-
tion, and lower temperatures did not result in good
yields. Protected nucleosides were inseparable by
silica gel column chromatography; hence, the
anomeric mixture was used as such for the deprotec-
tion step. The free nucleosides 22–35 were obtained
by treatment of the corresponding protected nucleo-
sides with either methylamine or ammonia in MeOH
at room temperature. The deprotected anomeric mix-
ture was separated by silica gel column chromatogra-
phy into the individual anomers. 6-Chloropurine
analogs 36 and 37 were obtained by the condensation
of compound 6 with 6-chloropurine under Mitsunobu
.
Ž
oxy-2-fluoro-b-L-arabinofuranosyl thymine L-
.
w x
FMAU, Fig. 3 9 were compared to understand the
differences between these nucleoside conformations
Ž
.
Table 1 and the effect of difluoro substitution over
the monofluoro substitution. L-FMAU is a thymine
w
x
analog and exhibits potent anti-HBV activity 10 . Its
structure contains a fluorine atom at the 2X-position in
the arabino configuration. Compound 34 is a 5-iodo-
cytosine analog and contains two fluorine atoms at
the 2X-position. These molecules were compared by
overlapping 34 and L-FMAU using SYBYL molecu-
2
lar modeling software . Both structures possess the
b-L configuration. The compound 34 is in 3X-endo
Ž
. w x
conditions Scheme 2 7 . Compounds 36 and 37
were treated separately with ammonia in MeOH in a
steel bomb at 80–90 8C, followed by chromato-
graphic separation to obtain compounds 38 and 39.
Hypoxanthine analogs 40 and 41 were prepared by
the treatment of compounds 36 and 37 separately
with 2-mercaptoethanol and sodium methoxide in
1 Colorless prism crystal of orthorhombic system with
Ž .
Ž .
the lattice parameters: a, 4.989 3 A8, b, 7.595 1 A8, c,
30.857 2 A8, V, 1169.2 7 A8 3; space group P212121.
Ž .
Ž . Ž
.
2 Molecules were overlapped using ‘Fit Atoms’ module
in SYBYL Tripos Associates, St. Louis, MO on a Silicon
Graphics Indy workstation.
Ž
.
w x
MeOH, followed by chromatographic separation 8 .

(
)
L.P. Kotra et al.rCarbohydrate Research 306 1998 69–80
73
Table 1
Conformational parameters for the compounds 34 and L-FMAU
X
Compound
Pseudorotation
angle, P deg
Carbohydrate
conformation
Puckering
amplitude,
ymax
C-2–N-1–C-1 –O-4X x
C-3X–C-4X–C-5X–O-5Xg
Ž
.
34
194.48
190.28
y76.18
2X-exor3X-endo
2X-exor3X-endo
O4X-endo
34.6
36.9
46.6
143.48
156.58
150.58
y45.08
y42.78
y50.58
X
a
Ž
.
34- 3 -OH
L-FMAU
a
X
X
X
w x
2 -Deoxy-2 ,2 -difluoro-5-iodo-L-cytidine 2 .
conformation, whereas L-FMAU is in O-4X-endo con-
formation. The overlapped structures show the differ-
ences in the carbohydrate conformation as well as in
singlet , d doublet , t triplet , m multiplet , pd
Ž
Ž
.
Ž
.
Ž
.
Ž
.
.
Ž
.
Ž
pseudo doublet , pt pseudo triplet , bs broad sin-
.
glet . UV spectra were recorded on a Beckman DU-
650 spectrophotometer. Optical rotations were
recorded on a Jasco DIP-300 digital polarimeter.
Mass spectra were either obtained from the Biologi-
cal Sciences Mass Spectrometry facility at the Uni-
versity of Georgia or recorded on a Fison Autospec
high-resolution mass spectrometer. Elemental analy-
ses were performed by either Atlantic Microlab, Nor-
cross, GA or by Galbraith Laboratories, Knoxville,
TN. Standard workup procedure followed in the reac-
tions, where specified, was to wash the reaction
mixture with equal volumes of saturated NaHCO3
X
3
Ž . Ž
.
the 4 -hydroxymethyl torsion angle g Fig. 3
.
The influence of these differences in the carbohydrate
conformation of the 2X,3X-dideoxydifluoro nucleosides
on the lack of biological activity is not clear at this
Ž
.
time vide infra . It should be noted that when the
X-ray structure of 2X-deoxy-2X,2X-difluoro-5-iodo-L-
X
wŽ
Ž
.
.x w x
cytidine 34- 3 -OH , Table 1 2 was compared
with that of compound 34, similar conformational
features were observed despite the lack of a 3X-hy-
Ž
.
droxyl group in compound 34 figure not shown .
This close similarity between the conformations may
be due to the dominating effect of difluoro sub-
stituents on the carbohydrate conformation and indi-
cates that the 3X-OH did not have much influence on
the conformation of the ‘2X-deoxy-2X,2X-difluororibo-
syl’ moiety.
solution and brine and dry the organic layer
1
Na2SO4 . H and 13C NMR data are compiled in
Ž
.
Tables 2 and 3, respectively.
(
)
(
)
Ethyl 4S -3- 2,2-dimethyl-1,3-dioxolan-4-yl -2,2-
Ž .
difluoro - 3 - hydroxy propionate 1 .—Compound 1
was prepared from L-gulono-g-lactone as previously
described for the synthesis of 2-deoxy-2,2-difluoro-
4. Biological activity
w
x
L-glycero-pentofuranosyl nucleosides 2,3 .
(
)
(
)
Ethyl 4S -3- 2,2-dimethyl-1,3-dioxolan-4-yl -2,2-di-
Nucleoside derivatives 22–35 and 38–41 were
evaluated for their antiviral activity against HIV-1,
HBV, HSV-1 and HSV-2, and for cellular toxicity
(
)
Ž
.
fluoro-3- 1-imdazolthiocarbonyloxy propionate 2a .
Ž
.
Compound 1 10.3 g, 40.5 mmol in dry Me2 NCHO
70 mL was treated with 1,1-thiocarbonyldiimida-
zole 14.4 g, 80.9 mmol and stirred for 3 h at 50 8C.
X
Ž
.
w
x
11 . None of the synthesized compounds showed any
significant antiviral activity and toxicity.
Ž
.
The solvent was evaporated, and the crude brown oil
Ž
.
was purified in a flash column 5:95 EtOAc–CHCl3
Ž
.
to obtain pure compound 2a 11.6 g, 79.0% as a
yellow oil: Anal. Calcd for C14H18F2 N2O5S: C,
46.15; H, 4.98; N 7.68. Found: C, 46.32; H, 5.00; N,
7.50.
5. Experimental section
General methods.—Melting points were deter-
mined on a MelTemp-II melting point apparatus and
are uncorrected. NMR data were recorded on a Bruker
(
)
(
)
Ethyl 4S -3- 2,2-dimethyl-1,3-dioxolan-4-yl -2,2-di-
(
)
fluoro-3- methylthio-thiocarbonyloxy propionate
2b . A solution of compound 1 9.0 g, 35.4 mmol
and carbon disulfide 11.4 mL, 190.6 mmol in
Me2 NCHO 200 mL was stirred at room tempera-
Ž .
AMX 400 spectrometer, and the chemical shifts d
Ž
.
Ž
.
Ž .
were reported in ppm. Coupling constants J were
Ž
.
Ž
.
reported in hertz Hz . The abbreviations used are: s
Ž
.
ture for 15 min under nitrogen gas. The solution was
3 The X-ray structures of the nucleosides were overlaid
Ž
.
cooled in an ice bath, and sodium hydride 60%
X
using N-1, C-1 and C-4X atoms.
dispersion in mineral oil, 2.3 g, 57.2 mmol was

(
)
74
L.P. Kotra et al.rCarbohydrate Research 306 1998 69–80
d

(
)
L.P. Kotra et al.rCarbohydrate Research 306 1998 69–80
75
Table 3
13C NMR Data
a
Ž
.
Ž
.
Ž
.
2a 117.72, 115.24, 109.77, 70.28 dd, J 3.2 Hz , 69.67 C-5 , 63.31, 39.38 t, J 22.8 Hz , 27.03, 25.93, 14.23
Ž
.
Ž
.
.
3
4
117.72, 115.24, 109.77, 70.28 dd, J1 3.25, J2 6.17 , 69.67, 63.31, 39.38 t, J 22.88 , 27.03, 25.93, 14.23
Ž
.
Ž
.
Ž
.
171.24, 122.25 t, J 251.25 , 83.31 d, J 3.06 , 66.59, 37.32 t, J 21.83
16 166.08, 165.98, 155.11, 141.24, 141.17, 134.13, 129.78, 129.75, 129.61, 129.36, 127.47 dd, J1 250.26, J2 258.97 ,
95.16, 85.68 dd, J1 17.35, J2 20.80 , 73.92, 73.86, 65.09, 46.21, 35.61 t, J 23.69
22 163.79, 150.60, 135.67, 127.78 t, J 254.21 , 109.96, 84.50, 77.70 d, J 7.21 , 60.64, 33.75 d, J 22.68 , 12.51
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
24 162.91, 150.37, 139.88, 127.49 dd, J1 249.49, J2 259.41 , 102.07, 84.60 dd, J1 22.95, J2 44.32 , 77.57 d, J 7.10 ,
Ž
.
60.47, 33.56 t, J 23.15
.
25 163.36, 150.84, 141.28, 127.65 t, J 254.79 , 102.46, 85.28 dd, J1 21.03, J2 62.91 , 62.96, 34r81 t, J 22.94
Ž
.
Ž
.
Ž
Ž
.
Ž
.
Ž
.
Ž
.
26 157.33 d, J 26.31 , 149.40, 140.47 d, J 231.15 , 127.83 dd, J1 249.26, J2 259.94 , 124.44 d, J 35.70 ,
Ž
.
Ž
.
Ž
.
85.10 dd, J1 21.51, J2 44.38 , 78.43 d, J 7.33 , 60.64, 33.36 t, J 22.90
Ž
.
Ž
.
Ž
.
30 166.16, 155.29, 141.14, 128.07 dd, J1 249.03, J2 259.95 , 94.94, 85.42 dd, J1 38.10, J2 32.05 , 77.31 d, J 7.88 ,
Ž
.
61.08, 34.55 J 22.90
38 156.47, 153.29, 149.54, 138.99, 127.46 dd, J1 248.70, J2 260.14 , 118.86, 84.64 dd, J1 23.79, J2 44.28 ,
78.27 d, J 6.88 , 61.57, 33.86 t, J 22.67
39 157.11, 154.06, 150.16, 140.39, 127.96 t, J 255.01 , 119.49, 85.46 dd, J1 22.62, J2 42.20 , 80.42, 63.53,
35.46 t, J 22.82
40 156.81, 148.37, 146.89, 138.42, 127.38 dd, J1 248.99, J2 260.29 , 124.14, 84.76 dd, J1 23.80, J2 44.13 ,
78.60 d, J 7.15 , 61.36, 33.47 d, J 22.54
41 156.71, 148.35, 146.68, 139.20, 128.97, 126.99 t, J 263.0 , 85.12 dd, J1 22.80, J2 41.86 , 79.87, 62.64,
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
34.59 t, J 22.93
Ž .
of tributyltin hydride 17.2 g, 59.1 mmol and AIBN
644.0 mg, 3.9 mmol in toluene 196 mL was added
dropwise over a period of 10 min, with stirring. The
reaction mixture was stirred for an additional 5 min
and cooled to room temperature. The solvent was
evaporated and the crude product was purified in a
added slowly. The reaction mixture was stirred for 30
Ž
Ž
. Ž .
min at 0 8C and treated with iodomethane 6.5 g, 45.8
.
mmol . Stirring was continued for an additional 2 h.
The solvent was evaporated to dryness, and the crude
Ž
.
product was dissolved in EtOAc 300 mL and sub-
jected to the standard workup procedure. The organic
layer was concentrated to obtain crude compound 2b
Ž
.
flash column 3–5:97–95 EtOAc–hexane to obtain
Ž
.
Ž .
12.8 g . A small portion was purified in a flash
pure compound 3 6.9 g, 57.0% .
Ž
.
(
)
column 15:85 EtOAc–hexane for spectrometric
4S - 2, 3 - Dideoxy - 2, 2 - difluoro - L - glycero -
Ž .
Ž
analysis.
pentofurano-1,4-lactone 4 .—Compound 3 1.8 g,
(
)
(
)
.
Ž
Ethyl 4S -3- 2,2-dimethyl-1,3-dioxolan-4-yl -2,2-
7.5 mmol was treated with HClrEtOH 4 mL of
36% aqueous HCl dissolved in 16 mL of EtOH and
Ž .
.
difluoro propionate 3 .—Method 2a. A solution of
Ž
.
Ž
compound 2a 11.6 g, 31.9 mmol in toluene 125
mL was heated to 60 8C in an oil bath under argon
under refluxing conditions. Tributyltin hydride 34.4
mL, 128 mmol and AIBN 20 mg were added, and
the mixture was refluxed at 80 8C for 40 min. Then
the reaction mixture was cooled to room temperature
and the solvent was evaporated. The crude yellow oil
stirred at 40–50 8C for 3 h. The solvent was evapo-
rated, and the residual water was removed by reflux-
ing the syrup in benzene for 16 h at 95 8C using a
Dean–Stark apparatus. Excess benzene was evapo-
.
Ž
.
Ž
.
Ž
.
rated to obtain compound 4 1.1 g, 95.0% as a
y
colorless syrup: IR KBr : 1807.53 cm 1; Anal. Calcd
for C5H6F2O3 P0.55H2O: C, 37.06; H, 4.41. Found:
C, 37.07; H, 4.34.
Ž
.
Ž
.
was purified in a flash column 1:9 EtOAc–hexane
Ž
.
to obtain pure compound 3 1.8 g, 20.0% as a
colorless oil: Anal. Calcd for C10H16F2O4: C, 50.41;
H, 6.76. Found: C, 50.44; H, 6.70.
5-O-Benzoyl-2,3-dideoxy-2,2-difluoro-L-glycero-
Ž .
Ž
pentofurano-1,4-lactone 5 .—Compound 4 1.1 g,
.
Ž
.
7.1 mmol was dissolved in dry CH2Cl2 20 mL ,
Ž
.
Ž .
Method 2b. Compound 2b 12.8 g, 37.3 mmol was
and 2,6-lutidine 0.9 g, 8.2 mmol , followed by ben-
Ž
.
Ž
.
dissolved in toluene 196 mL and nitrogen gas was
bubbled into the solution for 15 min. The solution
was heated to 100 8C under nitrogen, and a solution
zoyl chloride 1.2 g, 8.2 mmol , were added slowly at
0–5 8C under argon. The reaction mixture was stirred
for 14 h at room temperature, and the solvent was

(
)
76
L.P. Kotra et al.rCarbohydrate Research 306 1998 69–80
.
evaporated. The crude product was coevaporated with
mg, 8% as a white powder: compound 8: UV
Ž
.
Ž
Ž
.
Ž
.
toluene 2=25 mL , and the residue was purified
MeOH lmax 262.0, 225.0 nm; MS ESI 367.0
MH ; compound 9: UV MeOH lmax 262.0, 227.5
q
.
Ž
.
quickly by a flash silica gel column chromatography
q
Ž
.
Ž
Ž
.
Ž
.
3:7 EtOAc–hexane to obtain compound 5 1.1 g,
nm; MS ESI : 367.0 MH
.
.
(
62.0% as syrup. Upon drying, the syrup slowly
solidified: mp 39–42 8C. Anal. Calcd for
C12 H10F2O4 P0.1H2O: C, 55.86; H, 3.98; F, 14.72.
Found: C, 55.80; H, 4.27; F, 14.42.
1- 5-O-Benzoyl-2,3-dideoxy-2,2-difluoro-b-L-glycero
-pentofuranosyl uracil 10 and 1- 5-O-benzoyl-2,3-
dideoxy-2,2-difluoro-a-L-glycero-pentofuranosyl uracil
11 .—Uracil 281.0 mg, 2.5 mmol was reacted with
)
Ž
.
Ž
)
Ž
.
Ž
.
Ž
.
5-O-Benzoyl-2,3-dideoxy-2,2-difluoro-L-glycero-
1,1,1,3,3,3-hexamethyldisilazane HMDS, 10 mL
Ž .
Ž
Ž
.
Ž
.
pentofuranose 6 .—A solution of compound 5 1.1
and NH4 2SO4 10 mg under argon at 120–130 8C
for 3 h. After the suspension turned clear, the reac-
tion mixture was cooled to room temperature and
excess solvent was evaporated. Crude compound 7
was dissolved in anhydrous dichloroethane 30 mL
and added to the silylated uracil. Trimethylsilyl triflu-
oromethanesulfonate Me3SiOTf, 0.45 mL, 2.3 mmol
was added slowly, and the reaction mixture was
stirred at 90–100 8C for 8 h. Chloroform 50 mL
.
Ž
.
g, 4.1 mmol in 4:1 tetrahydrofuran–ether 15 mL
was cooled to y78 8C under argon and lithium
Ž
.
Ž
tri- tert-butoxy aluminum hydride 1 M solution in
. Ž
.
Ž
.
tetrahydrofuran 4.5 mL, 4.5 mmol was added drop-
wise. The reaction mixture was stirred for 1 h at y78
8C and was quenched by the slow addition of MeOH
Ž
.
Ž
.
1 mL . The reaction mixture was allowed to warm to
Ž
.
Ž
.
room temperature, ether 50 mL was added, and the
mixture was subjected to the standard workup proce-
dure. The organic layer was separated and concen-
trated to obtain chromatographically pure compound
was added to the reaction mixture and subjected to
standard workup procedure. The organic layer was
concentrated, and the crude product was purified by
Ž
.
Ž
.
6 950 mg, 90% as a colorless oil.
flash column chromatography 1:99 MeOH–CHCl3
5 - O - Benzoyl - 2, 3 - dideoxy - 2, 2 - difluoro - 1 - O -
to obtain an anomeric mixture of nucleosides. The
Ž .
methanesulfonyl-L-glycero-pentofuranose 7 .—Com-
anomeric mixture was separated on a flash column
Ž
Ž
.
Ž
.
Ž
pound 6 915.0 mg, 3.5 mmol was dissolved in
CH2CL2 12 mL under argon, and triethylamine
1.0 mL, 7.9 mmol and methanesulfonyl chloride
0.3 mL, 3.8 mmol were added slowly at room
temperature. The reaction mixture was stirred for 8 h,
diluted with 20 mL of CH2CL2, and subjected to
standard workup procedure. The organic layer was
concentrated to obtain crude compound 7 1.1 g ,
which was directly used in the subsequent reactions.
A small quantity was purified for spectroscopic iden-
tification.
9:11 EtOAc–hexane to obtain compound 10 121
.
.
Ž
.
mg, 18% and compound 11 198 mg, 29% : com-
pound 10: UV MeOH lmax 257.0, 230.0 nm; MS
Ž
Ž
Ž
.
.
Ž
.
q
.
Ž
.
Ž
.
ESI : 353.0 MH ; compound 11: UV MeOH
q
Ž
.
Ž
.
lmax 256.5, 230.0 nm; MS ESI : 353.0 MH
.
(
1- 5-O-Benzoyl-2,3-dideoxy-2,2-difluoro-b-L-glycero
)
(
.
Ž
-pentofuranosyl -5-fluorouracil 12 and 1- 5-O-
benzoyl - 2, 3 - dideoxy - 2, 2 - difluoro - a - L - glycero -
Ž
.
)
Ž
.
pentofuranosyl -5-fluorouracil 13 .—The condensa-
Ž
.
tion of 5-fluorouracil 376.0 mg, 2.9 mmol and
compound 7 was carried out as described above in
the presence of Me3SiOTf. The crude product was
(
1- 5-O-Benzoyl-2,3-dideoxy-2,2-difluoro-b-L-glycero
)
Ž
)
(
Ž
-pentofuranosyl thymine 8 and 1- 5-O-benzoyl-2,3-
dideoxy - 2, 2 - difluoro - a - L - glycero -
purified by flash column chromatography 1:99
.
MeOH–CHCl3 to obtain the anomeric mixture of 12
and 13 389 mg, 55% . The anomeric mixture was
used as such for the next reaction: UV MeOH lmax
)
Ž .
Ž
Ž
.
pentofuranosyl thymine 9 .—Thymine 375 mg, 2.97
mmol was suspended in acetonitrile 8 mL and
N,O-bis-trimethylsilylacetamide 1.1 mL, 4.5 mmol
was added under argon at room temperature and
.
Ž
.
Ž
.
q
Ž
.
Ž
.
Ž
.
263.5, 230.0 nm; MS ESI : 371.0 MH
.
(
1- 5-O-Benzoyl-2,3-dideoxy-2,2-difluoro-b-L-glycero
)
(
.
Ž
stirred for 1 h. After the suspension became clear,
- pentofuranosyl - 5 - iodouracil 14 and 1 - 5 - O -
benzoyl - 2, 3 - dideoxy - 2, 2 - difluoro - a - L - glycero -
Ž
.
crude compound 7 500 mg, 1.5 mmol dissolved in
Ž
.
Ž
)
Ž
.
acetonitrile 20 mL was added, followed by NaI 50
mg , and the mixture was stirred under refluxing
pentofuranosyl -5-iodouracil 15 .—The condensa-
.
Ž
.
tion of 5-iodouracil 459.0 mg, 1.9 mmol and com-
pound 9 in the presence of Me3SiOTf was carried out
as described above for compounds 10 and 11. The
crude product was purified by flash column chro-
matography 3:97 MeOH–CHCl3 to obtain the
anomeric mixture of 14 and 15 715 mg, 78% as a
conditions at 60 8C for 48 h. The reaction mixture
Ž
.
was cooled, EtOAc 75 mL was added, and the
standard workup procedure was carried out. The con-
centrated crude syrup was separated by prep TLC
Ž
.
Ž
.
Ž
.
3:1:96 dioxane–methanol–chloroform to obtain
Ž
.
Ž
pure compound 8 41 mg, 8% and compound 9 41
white foam. The anomeric mixture was used as such

(
)
L.P. Kotra et al.rCarbohydrate Research 306 1998 69–80
77
Ž
.
Ž
.
for the next reaction: UV MeOH lmax 277.5, 226.5,
202.5 nm.
10.39. Found: C, 44.73; H, 4.65; N, 10.16. MS ESI :
q
Ž
.
263.0 MH
.
(
(
1- 5-O-Benzoyl-2,3-dideoxy-2,2-difluoro-b-L-glycero
1 - 2, 3 - Dideoxy - 2, 2 - difluoro - a - L - glycero -
pentofuranosyl thymine 23 .—Compound 9 41 mg,
0.11 mmol was treated and purified in the same
manner as described for the preparation of compound
22 to obtain compound 23 23 mg, 80% as a white
q3.88 c 0.3,
MeOH ; UV MeOH lmax 263.0, 211.5; water
)
Ž
.
Ž
)
Ž
.
Ž
-pentofuranosyl cytosine 16 and 1- 5-O-benzoyl-2,3-
)
.
dideoxy-2,2-difluoro-a-L-glycero-pentofuranosyl cyto-
sine 17 .—Cytosine 321.6 mg, 2.9 mmol was sily-
lated and condensed with compound 7 in the pres-
ence of Me3SiOTf 0.75 mL, 3.86 mmol as de-
scribed above. The crude product was purified in a
flash column 1.5:4:94.5 Et3N–MeOH–CHCl3 to
obtain compound 16 99 mg, 28% and compound 17
94 mg, 27% : compound 16: mp 166–167 8C; UV
MeOH lmax 267.5, 230.0, 201.5 nm; MS ESI
352.0 MH ; compound 17: mp 75–79 8C; UV
Ž
.
Ž
.
Ž
.
25
D
Ž
.
w x
a
Ž
powder: mp 145–147 8C;
.
Ž
Ž
.
Ž
.
.
Ž
.
.
Ž
.
Ž
264.5 9197, 0.01 N HCl ; 264.5 9597 , 210.0 9835
Ž
.
Ž
.
Ž
.
Ž
. Ž
pH 7.0 ; 264. nm 6653 , 229.5 nm 6511 pH
Ž
.
.
11.0 . Anal. Calcd for C10H12 F2 N2O4 P0.2H2O: C,
45.18; H, 4.69; N, 10.53. Found: C, 45.43; H, 4.60;
Ž
.
Ž
.
q
q
Ž
.
Ž
.
Ž
.
N, 10.15. MS ESI : 263.0 MH
.
Ž
.
Ž
.
(
MeOH lmax 269.5, 230.5, 201.5 nm; MS ESI :
1 - 2, 3 - Dideoxy - 2, 2 - difluoro - b - L - glycero -
pentofuranosyl uracil 24 .—Compound 10 87 mg,
0.25 mmol was treated with saturated ammonia in
MeOH 10 mL , and the reaction mixture was stirred
for 24 h at room temperature. The solvent was evapo-
rated, the crude product was purified by flash column
chromatography 5:95 MeOH–CHCl3 , and the prod-
uct was freeze dried to obtain compound 24 61 mg,
q
Ž
.
)
Ž
.
Ž
352.0 MH
.
(
.
1- 5-O-Benzoyl-2,3-dideoxy-2,2-difluoro-b-L-glycero
-pentofuranosyl -5-fluorocytosine 18 and 1- 5-O-
benzoyl - 2, 3 - dideoxy - 2, 2 - difluoro - a - L - glycero -
pentofuranosyl -5-fluorocytosine 19 .—5-Fluorocy-
tosine 498.0 mg, 3.9 mmol was silylated and con-
densed with the compound 7 in the presence of
Me3SiOTf 0.75 mL, 3.9 mmol as described above.
The crude product was purified in a flash silica
column 4:96 EtOH–CHCl3 to obtain the anomeric
mixture of the compounds 18 and compound 19 358
)
Ž
.
Ž
Ž
.
)
Ž
.
Ž
.
Ž
.
Ž
25
Ž
.
.
w x
Ž
98% : mp 160.5–162.0 8C; a
y21.48 c 0.65,
MeOH ; UV water lmax 259.5 nm 10,320 , 206.5
nm 9873 pH 2.0 ; 258.5 nm 9958 , 208.5 nm
D
.
Ž
.
.
Ž
.
Ž
.
Ž
. Ž
Ž
.
Ž
Ž
. Ž
.
Ž
.
Ž
. Ž
8671 pH 7.0 ; 259.0 7416 , 231.5 6408 pH
.
Ž
.
.
mg, 50% : UV MeOH lmax 275.0, 230.5, 202.5
11.0 . Anal. Calcd for C9H10F2 N2O4: C, 43.55; H,
nm.
4.03; N, 11.29. Found: C, 43.46; H, 4.01; N, 11.21.
q
(
Ž
.
Ž
.
1- 5-O-Benzoyl-2,3-dideoxy-2,2-difluoro-b-L-glycero
-pentofuranosyl -5-iodocytosine 20 and 1- 5-O-
benzoyl - 2, 3 - dideoxy - 2, 2 - difluoro - a - L - glycero -
MS ESI : 249.0 MH
.
)
(
.
Ž
(
1 - 2, 3 - Dideoxy - 2, 2 - difluoro - a - L - glycero -
)
Ž
.
Ž
pentofuranosyl uracil 25 .—Compound 11 178 mg,
)
Ž
.
.
pentofuranosyl -5-iodocytosine 21 .—5-Iodocytosine
0.5 mmol was treated with saturated ammonia in
Ž
.
Ž
.
919 mg, 3.9 mmol was silylated and condensed
MeOH 15 mL , and the reaction mixture was stirred
for 24 h at room temperature. The solvent was evapo-
rated, the crude product was purified by flash column
Ž
with compound 7 in the presence of Me3SiOTf 0.75
mL, 3.9 mmol as described above. The crude prod-
uct was purified in a flash column 3:97 MeOH–
CHCl3 to obtain the anomeric mixture of the com-
.
Ž
Ž
.
chromatography 5:95 MeOH–CHCl3 , and the prod-
.
Ž
uct was freeze dried to obtain compound 25 51 mg,
41% : mp 70–73 8C; a
UV water lmax 259.0 nm 10,267 , 207.0 nm 9424
pH 2.0 ; 259.0 nm 9927 , 209.5 nm 8271 pH
25
Ž
.
.
Ž
w x
Ž
.
pounds 20 and compound 21 444 mg, 48% : UV
y3.08 c 0.49, MeOH ;
.
DŽ
.
Ž
. Ž
.
Ž
.
MeOH lmax 282.0, 226.0, 205.0 nm.
(
Ž
.
Ž
.
.
Ž
. Ž
1 - 2, 3 - Dideoxy - 2, 2 - difluoro - b - L - glycero -
pentofuranosyl thymine 22 .—Compound 8 41 mg,
0.1 mmol was treated with saturated ammonia in
MeOH 10 mL , and the reaction mixture was stirred
for 10 h at room temperature. Then the solvent was
evaporated, and the crude product was purified by
)
Ž
.
Ž
.
Ž
Ž
.
7.0 ; 259.5 nm 7660 , 233.5 nm 6216 pH 11.0 .
.
Anal. Calcd for C9H10F2 N2O4 P0.35H2O: C, 42.26;
Ž
.
H, 4.20; N, 11.01. Found: C, 42.10; H, 3.95; N,
q
Ž
.
Ž
.
11.35. MS ESI : 249.0 MH
.
(
1 - 2, 3 - Dideoxy - 2, 2 - difluoro - b - L - glycero -
Ž
.
)
Ž
.
Ž
flash column chromatography 5:95 MeOH–CHCl3
pentofuranosyl - 5 - fluorouracil 26 and 1 - 2, 3 -
Ž
.
)
to obtain pure compound 22 24 mg, 83% as a white
dideoxy-2,2-difluoro-a-L-glycero-pentofuranosyl -5-
fluorouracil 27 .—An anomeric mixture of com-
pounds 12 and 13 366 mg, 0.99 mmol was treated
with methylamine 40% aqueous solution, 0.43 mL,
25
w x
Ž
Ž
.
powder: mp 172–173 8C;
a
y14.68 c 0.46,
D
.
Ž
.
Ž
.
.
Ž
Ž
.
MeOH ; UV water lmax 264.0 8742, 0.01 N HCl ;
Ž
.
Ž
Ž
. Ž
.
Ž
263.0 7878 , 210.5 8208 pH 7.0 ; 264.5 5772 ,
Ž
.
.
.
Ž
.
228.5 nm 5723
pH 11.0 . Anal. Calcd for
4.95 mmol in MeOH 15 mL and stirred for 4 h.
C10H12 F2 N2O4 P0.4H2O: C, 44.58; H, 4.75; N,
The solvent was evaporated, and the crude product

(
)
78
L.P. Kotra et al.rCarbohydrate Research 306 1998 69–80
Ž
Ž
.
Ž
.
pH 11.0 . Anal. Calcd for
was purified on a flash silica column 5:95 MeOH–
238.5 nm 8122
C9H11F2 N3O3: C, 43.72; H, 4.45; N, 17.00. Found:
.
Ž
.
CHCl3 to obtain pure compound 26 100 mg, 38%
and compound 27 47 mg, 18% : compound 26: mp
y31.08 c 0.53, MeOH ; UV
water lmax 266.0 9140 , 207.0 9804 pH 2.0 ;
266.0 7686 , 210.0 9590 pH 7.0 ; 266.0 8830 ,
pH 11.0 . Anal. Calcd for
C9H9F3N2O4: C, 40.60; H, 3.38; N, 10.53. Found:
C, 40.48; H, 3.46; N, 10.47. MS ESI : 267.0 MH ;
compound 27: mp 152–153 8C; a q7.98 c 0.50,
MeOH ; UV water lmax 266.0 10,658 , 207.0
11,436 pH 2.0 ; 266.0 9138 , 210.0 11,296 pH
7.0 ; 266.5 8364 , 233.0 nm 8443 pH 11.0 . Anal.
Calcd for C9H9F3N2O4 P0.4H2O: C, 39.56; H, 3.59;
N, 10.25. Found: C, 39.54; H, 3.33; N, 10.04. MS
q
Ž
.
Ž
.
Ž
.
C, 43.48; H, 4.54; N, 16.87. MS ESI : 248.0 MH
1 - 2, 3 - Dideoxy - 2, 2 - difluoro - a - L - glycero -
pentofuranosyl cytosine 31 .—Compound 17 77.0
mg, 0.22 mmol was treated with methylamine 40%
aqueous solution, 0.36 mL, 4.4 mmol in MeOH 20
mL and stirred for 10 h. The solvent was evaporated,
and the residue was purified by flash column chro-
.
25
w x
Ž
.
(
117–118 8C; a
D
Ž
.
Ž
Ž
.
. Ž
Ž
. Ž
.
.
)
.
Ž
.
Ž
Ž
.
Ž
Ž
.
Ž
.
Ž
.
.
Ž
233.5 nm 8856
.
q
Ž
.
Ž
.
25
w x
Ž
Ž
.
matography 1:9 MeOH–CHCl3 to obtain com-
.
Ž
.
DŽ
.
Ž
.
pound 31 45 mg, 83% as a white powder: mp
24
D
Ž
. Ž
.
.
Ž
.
Ž
. Ž
w x .
Ž
.
Ž
77–80 8C; a q21.58 c 0.50, MeOH ; UV water
.
Ž
Ž
. Ž
.
Ž
.
.
Ž
. Ž
.
.
lmax 277.5 12,596 , 211.5 9967 pH 2.0 ; 269.0
Ž
Ž
.
.
Ž
Ž
. Ž
8416 , 232.0 7555 , 202.5 13,494 pH 7.0 ; 269.5
8744 , 237.5 nm 7592 pH 11.0 . Anal. Calcd for
C9H11F2 N3O3 P0.15H2O: C, 43.27; H, 4.52; N,
16.81. Found: C, 43.58; H, 4.89; N, 16.43. MS ESI :
Ž
. Ž
.
q
Ž
.
Ž
.
ESI : 267.0 MH
.
(
Ž
.
1 - 2, 3 - Dideoxy - 2, 2 - difluoro - b - L - glycero -
pentofuranosyl -5-iodouracil 28 and 1- 2,3-dideoxy-
q
)
Ž
.
Ž
Ž
.
248.0 MH
.
)
(
2,2-difluoro-a-L-glycero-pentofuranosyl -5-iodouracil
1 - 2, 3 - Dideoxy - 2, 2 - difluoro - b - L - glycero -
Ž
.
)
Ž
.
Ž
29 .—An anomeric mixture of compounds 14 and
pentofuranosyl - 5 - fluorocytosine 32 and 1 - 2, 3 -
Ž
.
)
15 704 mg, 1.5 mmol was treated with saturated
dideoxy-2,2-difluoro-a-L-glycero-pentofuranosyl -5-
Ž
.
Ž
.
ammonia in MeOH 30 mL and stirred at room
temperature for 20 h. The solvent was evaporated and
the crude product was purified on a flash column
fluorocytosine 33 .—An anomeric mixture of com-
Ž
.
pounds 18 and 19 351 mg, 0.95 mmol was treated
Ž
.
with saturated ammonia in MeOH 20 mL and stirred
at room temperature for 12 h. The solvent was evapo-
rated, and the crude product was purified in a flash
column 5:95 MeOH–EtOAc to obtain pure com-
pound 32 85 mg, 34% as a sticky solid and com-
Ž
.
3:97 EtOH–CHCl3 to obtain pure compound 28
177 mg, 32% and compound 29 101 mg, 18% as a
Ž
.
Ž
.
27
D
w x
Ž
.
white powder: compound 28: mp 210–212 8C; a
Ž
Ž
Ž
.
Ž
.
Ž
Ž
.
q2.18 c 0.27, MeOH ; UV MeOH lmax 279.5,
216.0; water 284.0 5544 , 216.5 8975 pH 2.0 ;
282.5 5214 , 216.0 9051 pH 7.0 ; 277.0 4240 ,
221.0 nm 10,847 pH 11.0 . Anal. Calcd for
C9H9F2 IN2O4: C, 28.90; H, 2.41; N, 7.49. Found: C,
29.04; H, 2.46; N, 7.26. FABMS: 275.0 MH
compound 29: mp 177.5–180 8C; a
0.21, MeOH ; UV MeOH lmax 279.5, 214.0; water
.
Ž
.
. Ž
Ž
.
. Ž
.
.
.
pound 33 85 mg, 34% as a white powder: com-
27
D
.
Ž
Ž
Ž
w x
Ž .
y60.08 c 0.22, MeOH ; UV
pound 32:
a
. Ž
.
Ž
Ž
Ž
.
Ž
.
MeOH lmax 280.0, 243.0, 203.0; water 282.0
.
.
Ž
. Ž
. Ž
.
.
Ž
.
8316 , 210.5 8960 pH 2.0 ; 278.0 7318 , 239
q
Ž
.
Ž
.
Ž
.
;
7957 , 207.0 8784 pH 7.0 ; 278.0 7347 , 239.0
27
D
w x
Ž
Ž
. Ž
y10.28 c
nm 7993 pH 11.0 . Anal. Calcd for C9H10F3N3O3:
C, 40.77; H, 3.77; N, 15.84. Found: C, 40.47; H,
3.75; N, 15.58. FABMS: 266.0 MH ; compound
33: mp 204–206 8C; a q37.78 c 0.24, MeOH ;
UV MeOH lmax 279.5, 243.0, 214.0; water 282.0
.
.
Ž
.
Ž
Ž
.
.
q
Ž
Ž
. Ž
Ž
. Ž
.
Ž
.
284.5 6862 , 215.5 10,245 pH 2.0 ; 283.5 6646 ,
213.5 11,532 pH 7.0 ; 276.5 5165 , 220.0 nm
27
. Ž
.
Ž
.
w x
Ž
.
D
Ž
.
Ž
.
Ž
.
11,483 pH 11.0 . Anal. Calcd for C9H9F2 IN2O4:
Ž
Ž
Ž
.
Ž
. Ž
. Ž
.
.
Ž
Ž
.
.
C, 28.90; H, 2.41; N, 7.49. Found: C, 28.93; H, 2.57;
9181 , 211.5 9697 pH 2.0 ; 278.5 7597 , 238.5
q
Ž
.
.
.
Ž
N, 6.94. FABMS 275.0 MH
8192 , 210.0 9064 pH 7.0 ; 279.0 7821 , 238.5
(
.
Ž
. Ž
.
1 - 2, 3 - Dideoxy - 2, 2 - difluoro - b - L - glycero -
8465 , 217.5 nm 8636 pH 11.0 . Anal. Calcd for
C9H10N3F3O3 PH2O: C, 38.18; H, 4.24; N, 14.83.
Found: C, 38.50; H, 4.18; N, 14.77. FABMS: 266.0
)
.
Ž
.
Ž
Ž
pentofuranosyl cytosine 30 .—Compound 16 83.0
mg, 0.2 mmol was treated with methylamine 40%
aqueous solution, 0.2 mL, 2.4 mmol in MeOH 10
mL and stirred for 2 h. The solvent was evaporated,
and the residue was purified by flash column chro-
matography 1:9 MeOH–CHCl3 to obtain com-
pound 30 41 mg, 70% as a white powder: mp
180–182 8C; a
q
.
Ž
Ž
.
MH
.
.
(
1 - 2, 3 - Dideoxy - 2, 2 - difluoro - b - L - glycero -
)
Ž
.
Ž
pentofuranosyl - 5 - iodocytosine 34 and 1 - 2, 3 -
Ž
.
)
dideoxy-2,2-difluoro-a-L-glycero-pentofuranosyl -5-
iodocytosine 35 .—An anomeric mixture of com-
pounds 20 and 21 430 mg, 0.9 mmol was treated
with saturated ammonia in MeOH 20 mL and stirred
at room temperature for 24 h. The solvent was evapo-
rated and the crude product was precipitated out from
Ž
.
Ž
.
24
w x
Ž .
Ž
.
y46.98 c 0.53, MeOH ; UV
D
Ž
Ž
.
Ž
.
Ž
.
MeOH lmax 269.0, 211.5; water 277.0 nm
12,882 , 211.5 10,383 pH 2.0 ; 269.0 8850 ,
.
Ž
. Ž
.
Ž
Ž
.
.
Ž
.
Ž
. Ž
.
234.0 7706 , 202.5 13,867 pH 7.0 ; 269.0 9232 ,

(
)
L.P. Kotra et al.rCarbohydrate Research 306 1998 69–80
79
Ž
.
Ž
. Ž
.
Ž
.
MeOH to obtain the anomeric mixture of nucleosides
as a white powder. The mixture was poorly soluble in
either MeOH or water. The anomeric mixture was
dissolved in hot MeOH and separated by prep TLC
256.0 8241 , 204.5 13,560 pH 2.0 ; 258.0 8217 ,
Ž
. Ž
.
Ž
. Ž
.
208.5 10,686 pH 7.0 ; 258.5 nm 8584 pH 11.0 .
Anal. Calcd for C10H11F2 N5O2: C, 44.28; H, 4.05;
N, 25.83. Found: C, 44.31; H, 4.09; N, 25.69. ES-
IMS: 272 MH
q
Ž
.
Ž
.
2.5:97.5 MeOH–EtOAc to obtain pure compound
.
Ž
.
(
34 25 mg, 7% as a white powder and compound 35
Ž
8C; a
293.5, 218.5, 203.0; water 303.0 6261 , 221.0
Ž
205.0 15,544 pH 7.0 ; 292.0 5067 , 222.0 nm
Ž
9 - 2, 3 - Dideoxy - 2, 2 - difluoro - a - L - glycero -
.
)
Ž
.
Ž
31 mg, 9% as a foam: compound 34: mp 210–211.6
pentofuranosyl adenine 39 .—Compound 37 150
mg, 0.38 mmol was treated with saturated ammonia
in MeOH 20 mL and stirred at 80–90 8C in a steel
bomb for 26 h. The solvent was evaporated and the
crude product was purified in a flash column 7:93
MeOH–CHCl3 to obtain pure compound 39 78 mg,
76% as a white powder: mp 184–187 8C; a
y35.08 c 0.71, MeOH ; UV MeOH lmax 258.0,
210.0; water 256.5 15,640 , 204.5 24,131 pH
2.0 ; 258.5 14,141 , 207.5 19,442 pH 7.0 ; 258.5
27
D
w x
Ž
.
Ž
Ž
.
.
14.98 c 0.13, MeOH ; UV MeOH lmax
Ž
.
.
Ž
Ž
.
. Ž
.
Ž
.
Ž
.
12,887 pH 2.0 ; 292.0 5080 , 219.0 13,886 ,
Ž
. Ž
. Ž
.
.
Ž
.
.
Ž
12,835 pH 11.0 . Anal. Calcd for C9H10F2 IN3O3:
27
D
.
w x
C, 28.98; H, 2.68; N, 11.26. Found: C, 29.00; H,
q
Ž
.
Ž
.
Ž
.
Ž
2.72; N, 10.83. FABMS: 375.0 MH ; compound
27
w x
Ž
.
Ž
.
Ž
.
Ž
.
. Ž
35: a y2.08 c 0.14, MeOH ; UV MeOH lmax
D
Ž
.
Ž
.
Ž
.
.
Ž
.
Ž
.
. Ž
.
292.0, 203.0; water 303.5 6831 , 221.5 13,725
Ž
Ž
Ž
.
Ž
.
Ž
Ž
.
Ž
.
Ž
pH 2.0 ; 292.0 5739 , 219.5 15,562 , 203.5
17,358 pH 7.0 ; 292.0 5414 , 222.5 nm 13,516
pH 11.0 . Anal. Calcd for C9H10F2 IN3O3 P0.2H2O:
nm 15,793
pH 11.0 . Anal. Calcd for
. Ž
.
.
Ž
.
C10H11F2 N5O2 P0.72H2O: C, 42.25; H, 4.38; N,
25.49. Found: C, 42.20; H, 4.27; N, 25.24. ESIMS:
272 MH
.
q
Ž
.
C, 28.70; H, 2.76; N, 11.15. Found: C, 28.97; H,
.
q
Ž
.
(
2.94; N, 10.76. FABMS: 375.0 MH
.
9 - 2, 3 - Dideoxy - 2, 2 - difluoro - b - L - glycero -
(
)
Ž
.
9- 5-O-Benzoyl-2,3-dideoxy-2,2-difluoro-b-L-glycero
pentofuranosyl hypoxanthine 40 .—Compound 36
81 mg, 0.2 mmol was treated with 2-mercapto-
ethanol 0.06 mL, 0.8 mL and NaOMe 95%, 43.2
mg, 0.8 mL in MeOH 10 mL . The mixture was
refluxed for 2 h under argon and cooled to room
temperature. The reaction mixture was neutralized
with glacial acetic acid and the solvent was evapo-
rated. The residue was purified in a flash silica
)
(
.
Ž
Ž
.
-pentofuranosyl -6-chloropurine 36 and 9- 5-O-
benzoyl - 2, 3 - dideoxy - 2, 2 - difluoro - a - L - glycero -
Ž
.
Ž
)
Ž
.
.
Ž
.
pentofuranosyl -6-chloropurine 37 .—A mixture of
Ž
.
Ž
compound 6 1 g, 3.9 mmol , 6-chloropurine 92 mg,
6 mmol and triphenylphosphine 1.6 g, 6.0 mmol in
dry tetrahydrofuran 25 mL was treated with diethyl
azodicarboxylate 0.99 mL, 6 mmol at room temper-
.
Ž
.
Ž
.
Ž
.
Ž
.
ature under argon. The orange-colored solution was
column 7:93 MeOH–CHCl3 to obtain pure com-
pound 40 32 mg, 59% : mp 208–211 8C;
21
D
Ž
Ž
.
w x
a
stirred at room temperature for 8 h, and EtOAc 25
.
Ž
.
Ž
.
mL was added to the reaction mixture. The organic
q10.08 c 0.21, MeOH ; UV MeOH lmax 244.0,
Ž
.
Ž
.
Ž
. Ž
.
layer was subjected to standard workup procedure
and concentrated. The crude product was purified by
203.5; water 247.0 9261 , 201.5 14294 pH 2.0 ;
Ž
.
Ž
. Ž
.
247.5 8870 , 203.0 11,561 pH 7.0 ; 252.5 nm
Ž
Ž
. Ž
.
flash column chromatography 1.5:98.5 MeOH–
10,223 pH 11.0 . Anal. Calcd for C10H10F2 N5O2:
C, 44.14; H, 3.68; N, 20.58. Found: C, 44.13; H,
3.65; N, 20.46. ESIMS: 273.0 MH
.
CHCl3 to obtain an anomeric mixture of nucleosides
q
Ž
.
.
that was further subjected to flash column chro-
Ž
.
(
matography 5% Et2O–CH2Cl2 to obtain compound
9 - 2, 3 - Dideoxy - 2, 2 - difluoro - a - L - glycero -
Ž
.
Ž
.
)
Ž
.
36 164 mg, 11% and compound 37 322 mg, 21% :
compound 36: UV MeOH lmax 263.5, 230.5, 204.5
nm; MS ESI : 394.7 MH ; compound 37: UV
MeOH lmax 263.5, 230.5, 203.5 nm; ESIMS: 394.7
pentofuranosyl hypoxanthine 41 .—Compound 37
147 mg, 0.37 mmol was treated with 2-mercapto-
ethanol 0.1 mL, 1.48 mmol and NaOMe 95%, 80
mg, 1.48 mmol in MeOH 15 mL and stirred at
refluxing conditions for 2 days. The mixture was
cooled and neutralized with glacial acetic acid. The
solvent was evaporated, and the residue was purified
Ž
.
Ž
.
q
Ž
.
Ž
.
Ž
.
Ž
Ž
Ž
Ž
.
.
.
.
q
.
MH
(
9 - 2, 3 - Dideoxy - 2, 2 - difluoro - b - L - glycero -
)
Ž
.
Ž
pentofuranosyl adenine 38 .—Compound 36 80 mg,
.
Ž
0.2 mmol was treated with saturated ammonia in
by flash column chromatography 7:93 MeOH–
.
Ž
.
MeOH and stirred at 80–90 8C in a steel bomb for 28
h. The solvent was evaporated, and the crude product
CHCl3 to obtain pure compound 41 21 mg, 21% :
21
D
Ž
.
w x
a
Ž
mp 213–215 8C dec. ;
y35.58 c 0.28,
Ž
.
.
Ž
.
Ž
.
Ž
was purified in a flash column 7:93 MeOH–CHCl3
MeOH ; UV water lmax 247.5 11,542 , 202.5
Ž
.
Ž
Ž
. Ž
.
.
Ž
. Ž
.
.
to obtain compound 38 36 mg, 66% as a white
18,064 pH 2.0 ; 247.5 10,955 , 204.5 12,401
pH 7.0 ; 252.5 nm 13,054 pH 11.0 . Anal. Calcd
for C10H10F2 N5O2 P0.55H2O: C, 42.59; H, 3.94; N,
27
D
w x
Ž
Ž
.
powder: mp 241–244 8C;
a
q8.08 c 0.14,
.
Ž
.
Ž
.
MeOH ; UV MeOH lmax 258.0, 209.0; water

(
)
80
L.P. Kotra et al.rCarbohydrate Research 306 1998 69–80
w x
4 L.P. Kotra, Y.J. Xiang, R.F. Schinazi, Y.-C. Cheng,
19.85. Found: C, 42.91; H, 3.87; N, 19.45. ESIMS:
q
M.G. Newton, and C.K. Chu, J. Med. Chem., submit-
Ž
.
273 MH
.
ted for publication.
w x
Ž
.
5 C. Hubschwerlen, Synthesis, 1986 962.
w x
6 Y. Chen, J.G. Bauman, and C.K. Chu, Nucleosides
Acknowledgements
Ž
.
Nucleotides, 11 1992 693–705.
w x
7 W.A. Szarek, C. Depew, H.C. Jarrell, and J.K.N.
We thank Dr. Michael Bartlett, UGA for providing
the mass spectral data. We thank Dr. R.F. Schinazi,
Emory University, VA Medical Center, and Dr. Y.-C.
Cheng, Yale University, for providing the anti-HIV
and anti-HBV data, respectively. We acknowledge
the financial support of the NIH grants AI 32351 and
AI 25899.
Ž
.
Jones, J. Chem. Soc., Chem. Commun., 1975 648–
649.
w x
8 L.S. Jeong, R.F. Schinazi, J.W. Beach, H.O. Kim, K.
Shanmuganathan, S. Nampalli, M.W. Chun, W.-K.
Chun, B.G. Choi, and C.K. Chu, J. Med. Chem., 36
Ž
.
1993 2627–2638.
w x
9 T. Ma, S.B. Pai, Y.L. Zhu, J.S. Lin, K. Shanmu-
ganathan, J.F. Du, C. Wang, H.B. Kim, M.G. New-
ton, Y.-C. Cheng, and C.K. Chu, J. Med. Chem., 39
Ž
.
1996 2835–2843.
w
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