An efficient large-scale synthesis of gemcitabine employing a crystalline 2, 2-difluoro-α-ribofuranosyl bromide

Article abstract of DOI:10.1016/j.tet.2010.05.039

An efficient large-scale synthesis of gemcitabine was achieved without chromatography or fractional crystallization. The key steps include stereospecific conversion of a novel β-ribofuranosyl phosphate into a highly crystalline a-ribofuranosyl bromide and coupling of the α-ribofuranosyl bromide and trime- thylsilyl cytosine to produce a β-nucleoside. p-Phenylbenzoyl group was introduced for the protection of one of hydroxy groups in order to enhance the crystallinity of intermediates. Continuous removal of trimethylsilyl bromide, generated during the coupling reaction, by distillation from the reaction medium substantially enhanced the β-selectivity of the crucial coupling reaction.

Full text of DOI:10.1016/j.tet.2010.05.039

Tetrahedron 66 (2010) 5687e5691
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
An efficient large-scale synthesis of gemcitabine employing a crystalline
2,2-difluoro-
a
-ribofuranosyl bromide
,
Young-Kil Chang a b, Jaeheon Lee b, Gha-Seung Park b, Moonsub Lee b, Chul Hyun Park b,
,
Han Kyong Kim b, Gwansun Lee b, Bo-Young Lee a, Ju Yuel Baek a, Kwan Soo Kim a
*
a Center2010-05-15 for Bioactive Molecular Hybrids and Department of Chemistry, Yonsei University, Seoul 120-749, Republic of Korea
b Hanmi Research Center, Hanmi Pharmaceutical Co. Ltd., Dongtan-myeon, Hwaseong-si, Gyeonggi-do 445-813, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 April 2010
Received in revised form 10 May 2010
Accepted 11 May 2010
Available online 15 May 2010
An efficient large-scale synthesis of gemcitabine was achieved without chromatography or fractional
crystallization. The key steps include stereospecific conversion of a novel
a highly crystalline -ribofuranosyl bromide and coupling of the -ribofuranosyl bromide and trime-
thylsilyl cytosine to produce a -nucleoside. p-Phenylbenzoyl group was introduced for the protection of
b-ribofuranosyl phosphate into
a
a
b
one of hydroxy groups in order to enhance the crystallinity of intermediates. Continuous removal of
trimethylsilyl bromide, generated during the coupling reaction, by distillation from the reaction medium
Keywords:
Gemcitabine
Nucleoside
substantially enhanced the
b
-selectivity of the crucial coupling reaction.
Ó 2010 Elsevier Ltd. All rights reserved.
Ribofuranosyl bromide
Ribofuranosyl phosphate
1. Introduction
The first synthesis of gemcitabine (1) was accomplished by
Hertel and co-workers through coupling of tert-butyldime-
thylsilyl (TBDMS)-protected difluororibofuranosyl methanesulfo-
nate 2 and trimethylsilyl (TMS) cytosine 3 followed by removal of
protecting groups.5 Chou and co-workers reported a large-scale
synthesis of 1 by coupling of benzoyl (Bz)-protected difluoror-
ibofuranosyl methanesulfonate (OMs) 4 and 3.6 Although there
have been reports on the synthesis of 1 by using benzoyl-pro-
tected difluororibofuranoses bearing other leaving groups, such
as trifluoromethanesulfonate, p-toluenesulfonate, and iodide at
C-1,7 the procedure employing the coupling of the benzoyl-pro-
tected methanesulfonate 4 and the trimethylsilylated cytosine 3
appears to be better than others.6,8 Nevertheless, because the
stereoselectivity in the coupling reaction of 4 and 3 is not quite
Gemcitabine (20-deoxy-20,20-difluorocytidine, 1), the active
pharmaceutical ingredient of GemzarÒ,1 is a nucleoside antime-
tabolite2 that exhibits antitumor activity. It has shown that activity
against a number of human solid tumors including lung, bladder,
pancreatic, and non-small cell lung cancers.3 Gemcitabine is con-
verted intracellularly into active 50-diphosphate and 50-tri-
phosphate nucleosides by nucleoside kinases. The cytotoxicity of
gemcitabine was attributed to the combined action of the di-
phosphate and triphosphate nucleosides, which lead to inhibition
of DNA synthesis.4
NH2
N
satisfactory,6,8 there has been an effort to enhance the
tivity of the coupling reaction by employing the pure
of 4 instead of the anomeric mixture, 4.8c However, the isolation
b-selec-
a
-anomer
N
O
HO
F
F
of the pure a-anomer of 4 requires preparation of the a-anomer
O
enriched anomeric mixture of 4 at around ꢀ80 ꢁC followed by
fractional crystallization of the
a-anomer out of the anomeric
OH
mixture.9 Therefore, there still remains a need for development
of a more efficient large-scale synthesis of 1. In this paper, we
reported the preparation of stable crystalline p-phenylbenzoyl
1
(PhBz)-protected10 difluororibofuranosyl
a
-bromide
5
and
a highly stereospecific large-scale synthesis of 1 by the coupling
of 5 and 3.
* Corresponding author. Tel.: þ82
2
2123 2640; fax: þ82
2 365 7608;
e-mail address: kwan@yonsei.ac.kr (K.S. Kim).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.05.039

5688
Y.-K. Chang et al. / Tetrahedron 66 (2010) 5687e5691
10 in 70% yield, of which HPLC analysis indicated that it contained
NHTMS
N
only a trace (around 0.1%) of the threo-isomer. The present pro-
cedure for the separation of the erythro-isomer 10 from di-
astereomeric mixture by employing the PhBz-protecting group is
much more efficient and practical for the large-scale synthesis than
previous methods5,6 because it does not require chromatography or
fractional crystallization. In the Hertel’s procedure,5 the desired
erythro-isomer was separated by column chromatography from the
product mixture of the Reformatsky reaction, whereas Chou and
co-workers6 obtained the pure erythro-isomer only in 26% yield by
fractional crystallization in the later lactone stage.
RO
BzO
F
F
F
F
O
O
OMs
OTMS
N
Br
OR
PhBzO
2 R = TBDMS
4 R = Bz
5
3
PhBz: 4- Phenylbenzoyl
2. Results and discussion
Removal of the isopropylidene group of 10 and simultaneous
lactonization of the resulting hydroxy carboxylic acid under acidic
condition gave ribonolactone 11 as shown in Scheme 2. Benzoyla-
tion of the lactone 11, without purification, provided fully protected
ribonolactone 12 in 72% yield in two steps from 10 after re-
crystallization of the crude product. In this stage, HPLC analysis
indicated that the protected lactone 12 did not contain even a trace
amount of its threo-isomer. Reduction of 12 with lithium tri-tert-
butoxyaluminohydride provided 2-deoxy-2,2-difluororibofuranose
13 as a yellow syrup. Without purification of 13, phosphorylation of
the anomeric hydroxy group of the lactol 13 with diphenyl-
Synthesis started with Reformatsky reaction of (R)-2,3-O-iso-
propylideneglyceraldehyde (6)11 and ethyl bromodifluoroacetate
(7)12 according to the Hertel’s prodecure.5 Thus, coupling of 6 and 7
in the presence of activated Zn in THF followed by distillation of the
reaction mixture provided a diastereomeric mixture (3:1) of pen-
tonic acid ester 8 as a colorless liquid in 57% yield with an excess of
the desired erythro-isomer. Without separation of the di-
astereomeric mixture, the hydroxy group of the compound 8 was
protected with the p-phenylbenzoyl group, which was introduced
first in a prostaglandin synthesis for the preparation of a more
crystalline, more readily separable intermediate than other esters.9
Thus, reaction of 8 with p-phenylbenzoyl chloride in the presence
of triethylamine afforded PhBz-protected difluoroester 9 as a di-
astereomeric mixture in 98% yield as shown in Scheme 1. After
chlorophosphate afforded the anomeric mixture of desired
ribofuranosyl diphenyl phosphate 14 and a small amount of its
-anomer (
b-
a
a
/
b
¼1:10.8). Recrystallization of the anomeric mixture
of 14 and its anomer from isopropanol/water (3:1) gave pure b-
O
O
F
F
F
F
Zn
PhBzCl
O
O
O
OEt
OEt
BrF2CCO2Et
+
TEA, CH2Cl2
rt, 98%
TMSCl
H
O
THF, reflux
7
PhBzO
O
OH
O
8
9
O
57%
6
K2CO3, H2O
THF-MeOH, rt
70%
O
F
F
O-K+
O
O
PhBzO
10
Scheme 1. Synthesis of potassium erythro-pentonate 10.
O
HO
F
BzO
F
F
F
BzCl/Pyr.
12 N HCl
O-K+
O
11
O
O
O
O
O
EtOAc, rt
72% (in 2 steps)
CH3CN
reflux
O
F
PhBzO
PhBzO
10
F
PhBzO
12
LiAl(Ot-Bu)3H
THF, rt
F
O P(OPh)2
O
BzO
BzO
BzO
F
F
O
Cl P(OPh)2
O
O
OH
30% HBr/HOAc
rt, 82%
TEA
Br
F
PhBzO
F
F
PhBzO
PhBzO
14
Toluene, rt
13
5
77% (in 2 steps)
Scheme 2. Synthesis of crystalline
a-ribofuranosyl bromide 5.
hydrolysis of the diastereomeric ethyl ester 9 with K2CO3 in THF/
MeOH/H2O at room temperature, when the volume of the reaction
mixture was reduced to one third by evaporation of the solvent,
solid potassium erythro-pentonate 10 precipitated while the threo-
isomer of 10 stayed in solution. Filtration followed by washing the
residue with Et2O afforded the pure potassium erythro-pentonate
phosphate 14 in 77% yield in two steps and HPLC analysis indicated
that it contained less than 2% of the -anomer. Treatment of the
phosphate 14 with 30% hydrogen bromide in acetic acid at room
temperature afforded a mixture of solid - and -ribofuranosyl
bromides with a large excess -anomer 5 (
¼10.8:1). Re-
crystallization of the anomeric mixture of the ribosyl bromides
a
b-
a
b
a/b
a

Y.-K. Chang et al. / Tetrahedron 66 (2010) 5687e5691
5689
from isopropanol provided pure
yield and HPLC analysis indicated that it contained less than 0.3% of
the -anomer. We, however, found that purification of the crude
phosphate 14 by recrystallization was unnecessary: bromination of
the crude -ribosyl phosphate 14 containing a small amount of its
-anomer provided the crystalline -bromide 5 in almost same
a
-ribofuranosyl bromide 5 in 82%
was not satisfactory, exhibiting the poor
mixture of 15 and its
with ammonia in methanol provided a crude mixture of gemcita-
bine 1 and its -anomer. Isolation of pure -nucleoside 1 as either
hemihydrate form or dihydrate form was possible just by extrac-
tion, evaporation, and crystallization from water. Cooling down the
warmed aqueous solution of the mixture of 1 and its anomer with
stirring to room temperature afforded pure gemcitabine 1 as
a hemihydrate form in 65% yield in two steps from 5. Cooling the
aqueous solution without stirring gave 1 as a dihydrate form. We
have, thus, found that the gemcitabine hemihydrate is also a stable
crystalline compound while the gemcitabine dihydrate was
known previously.5 Both gemcitabine hemihydrate and dihydrate
b
-selectivity. Finally, the
a
-anomer, without separation, was treated
b
a
b
b
a
a
purity and yield as the bromination of pure 14. The p-phenyl-
benzoyl-protecting group at O-3 of 5 was found to be essential for
the easy isolation of
5 from its anomeric mixture by re-
crystallization: we found that the ribofuranosyl bromide possess-
ing the benzoyl-protecting group at both O-3 and O-5 positions was
liquid.
Then, stage was set for coupling of a-ribosyl bromide 5 with
trimethylsilyl cytosine 3. However, the reaction of 5 and 3 was not
were found to contain less than 0.02% of its a-anomer based on
stereoselective at all, providing a mixture of almost an equal
HPLC analysis and their water contents were not changed on
standing or under humid condition in the prolonged time. Overall
yield of the present procedure (20%) from known compound 8 is
substantially higher than those of Hertel’s method (6%)5 and Chou’s
procedure (9%).6
amount of
b-nucleoside 15 and its
a
-anomer. Previously, Hertel and
co-workers reported that the
b/a ratio was 1:4 in the coupling
reaction of a ribosyl mesylate and the cytosine5 while Chou and co-
workers obtained almost an equal amount of the desired
oside and its
-anomer.6 The formation of the mixture of
-nucleosides from the pure -bromide 5 would be explained by
assuming the SN1-type reaction involving an oxocarbenium ion
intermediate and/or the SN2-type reaction of a mixture of the
b
-nucle-
a
a
- and
b
a
3. Conclusion
a
-
A highly efficient method for the large-scale synthesis of gem-
citabine has been developed. The pure erythro-isomer of potassium
salt of the pentonic acid, 10, was readily isolated from the mixture
of erythro- and threo-isomers by a filtration. The highly crystalline
bromide and the
anomerization of
b
-bromide, which might be generated by the
a
-bromide 5 during reaction. The anomerization
of the a-bromide 5 would be facilitated in the presence of bromide
sources, such as trimethylsilyl bromide (TMSBr) generated during
the reaction. We indeed observed formation of a small amount of
a
-ribofuranosyl bromide 5 was obtained by the reaction of
ribofuranosyl diphenyl phosphate 14 with HBr and readily purified
by recrystallization. The stereospecific coupling of an -ribofur-
b-
the
TMSBr. Because it is known that the
less stable but more reactive than its
amount of the -bromide in the present work would generate
a substantial amount of the -nucleoside. Based on the above result
and consideration, we envisioned that the -selectivity would be
enhanced by the SN2-like displacement of the -bromide 5 with the
b-anomer of 5, when the pure
a
-bromide 5 was treated with
-glycosyl halide is generally
-anomer,13 even a small
a
b
anosyl bromide 5 and trimethylsilyl cytosine 3 was possible by
conducting the reaction in the nonpolar solvent and by suppressing
the anomerization of 5. Thus, the coupling was carried out in oc-
tane/diphenyl ether by continuously removing TMSBr generated
during the reaction. Introduction of a p-phenylbenzoyl group as the
hydroxy-protecting group was essential for the easy purification of
compounds 5 and 10. The stable solid and crystalline intermediates,
higher overall yield, and stereospecific reactions including the
crucial coupling reaction of 5 and 3 make the present procedure
more efficient and practical than previous ones in the large-scale
synthesis of gemcitabine.
a
b
a
b
a
nucleophilic base 3 if the anomerization of 5 is suppressed by re-
moving TMSBr as soon as it is generated and at same time if the
concentration of the oxocarbenium ion is kept as low as possible by
using nonpolar solvents. Removal of TMSBr in the present work was
carried out by continuous distillation of a mixture of TMSBr and
heptane as a carrier in a high boiling solvent with simultaneous
addition of heptane. Thus, the reaction of 5 and 3 was conducted in
octane/diphenyl ether (2:1, v/v) while adding heptane in a drop-
wise manner (around 300 mL per g of the bromide 5) and at same
time carrying out distillation by maintaining the reaction temper-
4. Experimental
4.1. General methods
ature at 140e150 ꢁC. The
creased substantially and a mixture of the
b
-selectivity of the reaction, indeed, in-
-nucleoside 15 and its
-anomer was obtained in 92% yield, with an excess of the
anomer ( ratio in the
All reagents were purchased from commercial suppliers and
used without further purification unless otherwise noted. Solvents
were purified and dried by standard methods prior to use. Thin-
layer chromatography (TLC) was performed using silica gel 60 F254
precoated plates (0.25 mm thickness) with a fluorescent indicator
to monitor the reactions. Visualization on TLC was achieved by UV
light (254 nm) and a typical TLC indication solution (cerium sulfate/
molybdic acid solution). Melting points are uncorrected. Optical
rotations were determined at 20 ꢁC with an automatic polarimeter.
b
a
b
b
/a
¼5.5:1) as shown in Scheme 3. The
b/a
coupling reaction of 5 and 3 employing the present protocol varied
from 4 to 8 depending on the equivalent of cytosine and the scale of
the reaction, whereas the
b/a ratio without distilling off TMSBr
during reaction remained 1.3e1.4. On the other hand, the reaction
in the distillation mode but without addition of the heptane carrier
NH2
NH2
NHTMS
N
N
N
O
N
F
O
N
HO
BzO
BzO
F
F
F
F
OTMS
N
7N NH3/MeOH
O
O
O
H2O, rt
71%
Octane/Heptane
Ph2O, 140~150oC
92%
Br
F
OH
PhBzO
PhBzO
1
15
5
Scheme 3. Synthesis of gemcitabine 1 by coupling of 5 and 3.

5690
Y.-K. Chang et al. / Tetrahedron 66 (2010) 5687e5691
1H NMR and 13C NMR spectra were recorded at 300 MHz spec-
trometer (300 MHz for 1H, 75 MHz for 13C). Chemical shifts are
solution (9.2 mL). The reaction mixture was heated to reflux for 6 h,
cooled down to room temperature, diluted with toluene (464 mL),
and concentrated in vacuo to dryness. The residue was dissolved in
EtOAc (232 mL) and insoluble KCl was filtered off. The filtrate was
concentrated in vacuo to afford ribonolactone 11 (30.1 g) as foamy
solid. This crude ribonolactone 11 was used for the next step
without further purification. A solution of 11 (30.1 g, 86.4 mmol)
and benzoyl chloride (15 mL, 129 mmol) in the presence of pyridine
(14 mL, 173 mmol) in EtOAc (375 mL) was stirred at room temper-
ature for 6 h and then the reaction was quenched with aqueous 1 N
HCl solution (210 mL). The organic layer was separated, washed
successively with H2O and saturated aqueous NaHCO3, dried over
MgSO4, and concentrated in vacuo to give a cream-color solid. The
solid was recrystallized from Et2O/hexane (300 mL, 5:1) to afford
reported as
d values in parts per million relative to tetramethylsi-
lane as an internal standard and J values are given in hertz (Hz).
4.1.1. Ethyl 2-deoxy-2,2-difluoro-
D-erythro,
D-threo-pentonate (8).
To a stirred suspension of zinc (13 g,198 mmol) and dibromoethane
(0.51 mL) in dry THF (26 mL) was added chlorotrimethylsilane
(0.76 mL) at 40 ꢁC. After being stirred for 10 min at 40 ꢁC, the re-
action mixture was heated to 60 ꢁC. A solution of (R)-2,3-O-iso-
propylideneglyceraldehyde
6
(30.8 g, 236 mmol) and ethyl
bromodifluoroacetate 7 (25.5 mL, 198 mmol) in THF (39 mL) was
added dropwise to the above solution and the resulting mixture
was heated to reflux for 30 min and then cooled down to room
temperature. After sequential addition of ice (260 g), Et2O (65 mL),
and aqueous 1 N HCl (260 mL) to the reaction mixture, it was stir-
red until the ice was completely melted. The resulting mixture was
extracted with Et2O (3ꢂ90 mL). The combined extracts were
washed successively with brine, saturated aqueous NaHCO3, dried
over MgSO4, and concentrated in vacuo. The residue was distilled at
130e134 ꢁC/10 Torr to afford the compound 8 (28.9 g, 57%, erythro/
compound 12 (28.4 g, 72% in two steps) as a white solid, mp
20
130e131 ꢁC; [
a
]
þ69.7 (c 1.0, DMF); IR (KBr) 1820, 1723, 1268,
D
1216, 1113, 743, 714, 690 cmꢀ1
4.69e4.76 (m, 2H), 5.00e5.03 (m, 1H), 5.74e5.81 (m, 1H),
7.42e7.71 (m, 10H), 8.01e8.04 (m, 2H), 8.11e8.14 (m, 2H); 13C NMR
(75 MHz, CDCl3) 62.4, 69.3, 69.7, 69.9, 78.5, 78.6, 108.2, 111.6, 111.7,
;
1H NMR (300 MHz, CDCl3)
d
d
115.1, 126.2, 127.4, 127.5, 128.7, 128.8, 129.2, 129.9, 130.9, 133.9,
139.6, 147.4, 162.2, 162.7, 163.1, 164.6, 165.8. HRMS (ESI) m/z calcd
for C25H18F2O6Na [MþNa]þ, 475.0969; found, 475.0967.
threo¼3:1,) as
a
colorless liquid, 1H NMR (300 MHz, CDCl3)
d
1.34e1.47 (m, 9H), 2.18 (s, 1H), 2.93 (br s, 1H), 3.7e4.4 (m, 5H); 13
C
NMR (75 MHz, CDCl3)
d
13.3, 13.4, 24.5, 24.8, 25.7, 30.4, 62.6, 62.8,
65.1, 65.8, 70.4, 70.8, 71.2, 71.5, 71.8, 72.9, 109.2, 109.8, 110.1, 113.5,
116.9, 162.6.
4.1.5. Diphenyl
5-O-benzoyl-2-deoxy-2,2-difluoro-3-O-(p-phenyl-
benzoyl)- -ribofuranosyl phosphate (14). To a stirred solution of
b-D
lithium tri-tert-butoxyaluminohydride (338 g, 1.33 mol) in THF
(4.0 L) was added the ribonolactone 12 (500 g, 1.11 mol) in THF
(2.0 L) at ꢀ40 ꢁC. The reaction mixture was slowly warmed up to
room temperature, and stirred for further 2 h at room temperature.
Upon the completion of the reaction, aqueous 1 N HCl (5.5 L) so-
lution was added to the reaction mixture to quench the excess
lithium tri-tert-butoxyaluminohydride. The resulting mixture was
extracted with Et2O (5.5 L) and the extract was washed successively
with H2O, saturated aqueous NaHCO3, dried over MgSO4, and
concentrated to afford 2-deoxy-2,2-difluororibofuranose 13 (461 g)
as a yellowish syrup, which was used for the next step without
further purification. To a solution of 13 (461 g, 1.01 mol) and trie-
thylamine (168 mL, 1.20 mol) in toluene (3.7 L) was added a solu-
tion of diphenylchlorophosphate (311 mL, 1.50 mol) in toluene
(930 mL). The reaction mixture was stirred for 4 h at room tem-
perature and then quenched with aqueous 1 N HCl solution (1.2 L).
The organic layer was washed successively with H2O and saturated
aqueous NaHCO3, dried over MgSO4, and concentrated in vacuo to
4.1.2. Ethyl 2-deoxy-2,2-difluoro-3-O-(p-phenylbenzoyl)-
-threo-pentonate (9). A solution of compound
D
-erythro,
(50.0 g,
D
8
196 mmol), p-phenylbenzoyl chloride (51.1 g, 235 mmol), and trie-
thylamine (42 mL, 301 mmol) in CH2Cl2 (500 mL) was stirred for 6 h
at room temperature and then the reaction was quenched with
aqueous 1 N HCl (360 mL). The organic layer was separated, washed
successively with water, saturated aqueous NaHCO3, and brine,
dried over MgSO4, and concentrated in vacuo to afford compound 9
(83.7 g, 98%) as a bright yellowish liquid, [
a
]
20 þ8.85 (c 1.0, MeOH);
D
1H NMR (300 MHz, CDCl3)
d
1.25e1.74 (m, 9H), 4.11e4.19 (m, 2H),
4.30e4.36 (m, 2H), 4.56e4.58 (m, 2H), 5.78 (ddd,1Hꢂ1/3, J¼5.9, 7.7,
16.9 Hz), 5.95 (ddd, 1Hꢂ2/3, J¼5.7, 13.0, 12.8 Hz), 7.42e7.53 (m, 3H),
7.63e7.73 (m, 4H), 8.15e8.17 (m, 2H); 13C NMR (75 MHz, CDCl3)
d
13.8,14.1, 25.1, 25.3, 26.0, 26.1, 53.5, 63.3, 63.4, 65.6, 65.8, 70.6, 70.9,
71.1, 71.2, 71.5, 71.8, 72.4, 72.5, 109.5, 110.1, 110.2, 112.8, 112.9, 116.2,
116.3,127.0,127.2,127.2,127.4,127.5,128.3, 129.0,130.6,139.6,139.7,
146.5,146.6,161.7,162.1,162.5,164.5,164.7. HRMS (ESI) m/z calcd for
C23H24F2O6Na [MþNa]þ, 457.1439; found, 457.1440.
give a mixture of
a
- and
b-ribofuranosyl phosphates (
a/b
¼1:10.8)
as a solid. Recrystallization of the solid mixture from isopropanol/
4.1.3. Potassium 2-deoxy-2,2-difluoro-3-O-(p-phenylbenzoyl)-
D
-erythro-
water (3:1, v/v) afforded pure
b-phosphate 14 (584 g, two steps
pentonate (10). Aqueous 1.0 M K2CO3 (750 mL) solution was added
to a solution of compound 9 (83.8 g, 193 mmol) in THF/MeOH (2:3,
1.5 L). The reaction mixture was stirred for 30 min at room tem-
perature and evaporated until the volume is reduced to one third.
During evaporation white solids started to precipitate. The solid
77%) as a white crystal, mp 101e103 ꢁC; [
a
]
20 þ13.0 (c 1.0, DMF); IR
D
(KBr) 1740. 1721, 1490, 1292, 1272, 1190, 997, 963, 744, 715 cmꢀ1; 1H
NMR (300 MHz, CDCl3)
d 4.44e4.65 (m, 3H), 5.87e5.97 (m, 1H),
6.06 (t, 1H, J¼6.1 Hz), 7.18e7.37 (m, 16H), 7.61e7.69 (m, 4H), 8.00 (d,
2H, J¼8.4 Hz), 8.12 (d, 2H, J¼8.4 Hz); 13C NMR (75 MHz, CDCl3)
collected by filtration was washed with Et2O and dried to afford
d 63.7, 69.8, 70.0, 70.1, 70.3, 79.2, 79.3, 97.6, 97.7, 98.0, 98.1, 98.2,
20
pure erythro-compound 10 (60.1 g, 70%) as a white solid, [
a
]
98.5, 120.0, 120.1, 120.2, 120.3, 125.7, 125.9, 126.7, 127.27, 127.29,
127.6, 128.4, 128.5, 129.1, 129.3, 129.8, 129.9, 130.7, 133.3, 139.6,
146.8,150.0,150.05,150.09,150.1,164.8,165.8. HRMS (ESI) m/z calcd
for C37H29F2O9PNa [MþNa]þ, 709.1415; found, 709.1418.
D
þ43.51 (c 1.0, MeOH); 1H NMR (300 MHz, DMSO-d6)
d 1.07 (s, 3H),
1.22 (s, 3H), 4.00 (t, 1H, J¼7.6 Hz), 4.11 (t, 1H, J¼7.5 Hz), 4.49 (t, 1H,
J¼6.7 Hz), 5.88 (dd, 1H, J¼6.5, 21.2 Hz), 7.38e7.54 (m, 3H), 7.75 (d,
2H, J¼7.1 Hz), 7.85 (d, 2H, J¼8.5 Hz), 8.07 (d, 2H, J¼8.4 Hz); 13C NMR
(75 MHz, CDCl3)
d
25.1, 26.0, 63.6, 63.7, 71.0, 71.3, 71.6, 73.3, 73.4,
4.1.6. 5-O-Benzoyl-2-deoxy-2,2-difluoro-3-O-(p-phenylbenzoyl)-
a-
107.8, 111.1, 114.5, 117.9, 127.0, 127.1, 128.1, 128.5, 129.1, 130.1, 138.8,
145.1, 162.9, 163.2, 163.5, 164.6. HRMS (ESI) m/z calcd for
C21H19F2KO6K [MþK]þ, 483.1770; found, 483.1772.
D
-ribofuranosyl bromide (5). A solution of -phosphate 14 (500 g,
b
0.728 mol) in 30% HBr in acetic acid (1.8 L) was stirred for 6 h at
room temperature. The reaction mixture was diluted with CH2Cl2
(8.7 L) and poured onto ice. The organic layer was separated,
washed successively with H2O and saturated aqueous NaHCO3,
4.1.4. 5-O-Benzoyl-2-deoxy-2,2-difluoro-3-O-(p-phenylbenzoyl)-D-
ribonolactone (12). To a suspension of compound 10 (38.8 g,
dried over MgSO4, and concentrated to give a mixture of
a- and b-
87.3 mmol) in acetonitrile (232 mL) was added aqueous 12 N HCl
ribofuranosyl bromides (a/b¼10.8:1) as a solid. Recrystallization of

Y.-K. Chang et al. / Tetrahedron 66 (2010) 5687e5691
5691
the mixture from isopropanol afforded pure
a
-bromide 5 (308 g,
The precipitated solid was collected by filtration, washed with cold
water (150 mL), and dried to afford pure gemcitabine 1 (98.9 g, 71%)
82%) as a white crystal, mp 111e112 ꢁC; [
a]
20 þ140.6 (c 1.0, DMF); IR
D
20
(KBr) 1725. 1607, 1263, 1119, 1084, 860, 748, 709 cmꢀ1
;
1H NMR
as a white crystalline hemihydrate form, mp 198e202 ꢁC; [
a]
D
(300 MHz, CDC13)
d
4.68e4.87 (m, 3H), 5.60 (dd, 1H, J¼4.5, 4.2 Hz),
þ76.4 (c 1.0, MeOH); 1H NMR (300 MHz, DMSO-d6)
d 3.57e3.64 (m,
6.54 (d, 1H, J¼9.0 Hz), 7.41e7.73 (m, 10H), 8.05 (d, 2H, J¼9.0 Hz),
1H), 3.73e3.81 (m, 2H), 4.10e4.15 (m, 1H), 5.18 (t, 1H, J¼5.4 Hz),
5.77 (t, 1H, J¼7.5 Hz), 6.12 (t, 1H, J¼8.3 Hz), 6.21 (d, 1H, J¼6.4 Hz),
7.35 (d, 1H, J¼6.8 Hz), 7.67 (d, 1H, J¼7.5 Hz); 13C NMR (75 MHz,
8.19 (d, 2H, J¼8.4 Hz); 13C NMR (75 MHz, CDCl3)
d 62.2, 71.0, 71.2,
71.4, 71.7, 82.9, 84.7, 85.0, 85.2, 85.6, 118.4, 121.7, 122.0, 125.3, 126.9,
127.1, 127.3, 127.6, 127.7, 128.5, 128.78, 128.84, 129.1, 129.3, 129.5,
129.6, 129.8, 130.7, 133.4, 139.2, 139.6, 146.7, 164.9, 165.9. HRMS
(ESI) m/z calcd for C25H19BrF2O5Na [MþNa]þ, 539.0282; found,
539.0284.
DMSO-d6)
d 58.9, 68.4, 68.7, 69.0, 80.3, 80.4, 83.1, 83.5, 83.9, 94.7,
119.6, 123.0, 126.5, 140.8, 154.8, 165.6. Anal. Calcd for
C9H11N3O4F2$0.5H2O: C, 39.51; H, 4.48; N, 14.36. Found: C, 39.58; H,
4.45; N, 15.07.
When the solution was cooled without stirring, filtration of the
precipitated solid, washing the solid with cold water, and drying
4.1.7. 1-(50-O-Benzoyl-20-deoxy-20,20-difluoro-3-O-(p-phenyl-
benzoyl)-
D
-ribofuranosyl)-4-aminopyrimidin-2-one (15). A mixture
provided pure gemcitabine 1 as a white crystalline dihydrate form,
20
of cytosine (951 g, 8.56 mol), hexamethyldisilazane (5.4 L,
25.9 mol), and ammonium sulfate (5.4 g, 0.041 mol) was heated to
reflux for 1.5 h. The resulting solution was diluted with toluene
(5.14 L) and refluxed for further 1 h. To the reaction mixture, which
mp 220e224 ꢁC; [
a
]
þ71.1 (c 1.0, MeOH); 1H NMR (300 MHz,
D
DMSO-d6)
d 3.57e3.64 (m, 1H), 3.73e3.81 (m, 2H), 4.10e4.15 (m,
1H), 5.18 (t, 1H, J¼5.4 Hz), 5.77 (t, 1H, J¼7.5 Hz), 6.12 (t, 1H,
J¼8.3 Hz), 6.21 (d, 1H, J¼6.4 Hz), 7.35 (d, 1H, J¼6.8 Hz), 7.67 (d, 1H,
was cooled down to 80 ꢁC, a solution of the
a
-bromide 5 (300 g,
J¼7.5 Hz); 13C NMR (75 MHz, DMSO-d6)
d 58.9, 68.4, 68.7, 69.0, 80.4,
0.58 mol) in octane (3.44 L) and diphenyl ether (1.72 L) was added.
Then, a mixture of diphenyl ether (860 mL) and heptane (85.7 L)
was added dropwise to the reaction mixture and at same time the
solvent and TMSBr were continuously removed by slow distillation
by maintaining the reaction temperature at 140e150 ꢁC for 10 h.
After addition of heptane (4.30 L) at once to the reaction mixture,
water (1.03 L) was added at 80 ꢁC. The resulting mixture was cooled
down and stirred for 1 h at room temperature. The precipitated
solid was collected by filtration and washed with heptane. The
80.4, 83.1, 83.5, 83.9, 94.7, 119.6, 123.0, 126.4, 140.8, 154.8, 165.6.
Anal. Calcd for C9H11N3O4F2$2H2O: C, 37.12; H, 4.88; N, 14.43.
Found: C, 36.78; H, 4.98; N, 14.01.
Acknowledgements
We wish to thank to colleagues from Hanmi Research Center for
analytical support, especially Cheol-kyung Kim, Jae-Chul Lee, Hyo-
Jeong Bang. We also wish to thank our colleagues from Hanmi Fine
Chemicals for supporting on the plant scale production of Gemci-
tabine. Support from Center for Bioactive Molecular Hybrids (R11-
2003-019-0000-0) of Yonsei University is also acknowledged.
solid, which contained a- and b-nucleosides and unreacted cyto-
sine, was mixed with CH2Cl2/MeOH (7.72 L, 5:1) and the mixture
was refluxed for 1 h. After filtration of the mixture, the residue was
washed with CH2Cl2/MeOH (3.60 L, 5:1). The combined filtrate was
concentrated in vacuo to afford a mixture of desired
15 and its -anomer (292 g, 92%,
¼5.5:1) as a white solid. This
anomeric mixture was used for the next step without further pu-
rification. For the identification of -nucleoside 15, the solid
b-nucleoside
References and notes
a
b/a
1. 2009 Physicians’ Desk ReferenceÒ
Montvale, NJ, 2008; p 1820.
, 63rd ed.; Physicians’ Desk Reference:
b
2. (a) Heinemann, V.; Hertel, L. W.; Grindey, G. B.; Plunkett, W. Cancer Res. 1988,
48, 4024; (b) Sunkara, P. S.; Lippert, B. J.; Snyder, R. D.; Jarvi, E. T.; Farr, R. A. Proc.
Am. Assoc. Cancer Res. 1988, 324; (c) Plunkett, W.; Chubb, S.; Novak, B.; Hertel, L.;
Grindey, G. B. Proc. Am. Assoc. Cancer Res. 1988, 352.
anomeric mixture was recrystallized from MeOH to afford pure b-
20
nucleoside 15, mp 252e253 ꢁC; [
(300 MHz, DMSO-d6)
a]
ꢀ5.4 (c 0.5, MeOH); 1H NMR
D
d
3.33 (s, 1H), 4.67e4.78 (m, 3H), 5.78 (d, 2H,
J¼7.5 Hz), 5.84 (s, 1H), 6.39 (s, 1H), 7.46e7.55 (m, 6H), 7.76 (d, 2H,
3. (a) Grunewald, R.; Kantarjian, H.; Da, M.; Faucher, K.; Tarassoff, P.; Plunkett, W.
J. Clin. Oncol. 1992, 10, 406; (b) Lund, B.; Hansen, O. P.; Theilade, K.; Hansen, M. J.
Natl. Cancer Inst. 1994, 86, 1530; (c) Casper, E. S.; Green, M. R.; Kelsen, D. P.;
Heelan, R. T.; Brown, T. D.; Flombaum, C. D. Invest. New Drugs 1994, 12, 29; (d)
Sandler, A.; Ettinger, D. S. Oncologist 1999, 4, 241.
4. (a) Bouffard, D. Y.; Momparler, L. F.; Momparler, R. L. Anti-Cancer Drugs 1991, 2,
49; (b) Matsuda, M. A.; Sasaki, T. Cancer Sci. 2004, 95, 105.
5. Hertel, L. W.; Kroin, J. S.; Misner, J. W.; Tustin, J. M. J. Org. Chem. 1988, 53, 2406.
6. Chou, T. S.; Heath, P. C.; Patterson, L. E.; Poteet, L. M.; Lakin, R. E.; Hunt, A. H.
Synthesis 1992, 565.
7. (a)Chou, T. S. U.S. Patent 5,594,124,1997. (b) Chou, T. S.; Grossman, C. S.; Hertel, L. W.;
Holmes, R. E.; Jones, C. D.; Mabry, T. E. U.S. Patent 5,744,597, 1998.
8. (a) Chou, T. S. U.S. Patent 5,371,210, 1994. (b) Kjell, D. P. U.S. Patent 5,426,183,
1995. (c) Chou, T. S.; Poteet, L. M.; Kjell, D. P. U.S. Patent 5,606,048, 1997.
9. (a) Chou, T. S. U.S. Patent 5,401,861, 1995. (b) Chou, T. S.; McCarthy, T. J. U.S.
Patent 5,256,797, 1993.
J¼7.5 Hz), 7.87 (d, 2H, J¼8.3 Hz), 7.96 (d, 2H, J¼7.4 Hz), 8.11 (d, 2H,
J¼8.2 Hz); 13C NMR (75 MHz, CDCl3)
d 64.0, 72.0, 72.3, 72.6, 76.2,
95.6, 122.4, 125.9, 127.4, 127.6, 129.2, 129.3, 129.7, 129.7, 129.8, 130.9,
134.2, 139.2, 142.5, 146.2, 155.0, 164.8, 166.0, 166.4. HRMS (ESI) m/z
calcd for C29H23F2N3O6Na [MþNa]þ, 570.1453; found, 570.1451.
4.1.8. 20-Deoxy-20,20-difluorocytidine (1). To a stirred solution of 2 N
NH3 in MeOH (8.12 L) was added the mixture of
b-nucleoside 15
and its -anomer (290 g, 0.53 mol,
a
b/a
¼5.5:1). The reaction mix-
ture was stirred at room temperature for 12 h and concentrated in
vacuo. The residue was dissolved in water (3.24 L) and EtOAc
(2.14 L) with stirring and the organic phase was extracted with
water (1.07 L). The combined aqueous extract was washed with
Et2O (1.07 L) and concentrated to dryness. The residue was mixed
with water (670 mL) and stirred by heating to 50 ꢁC. The solution
was cooled down to room temperature and stirred for further 2 h.
10. Corey, E. J.; Albonico, S. M.; Koeliker, U.; Schaaf, T. K.; Varma, L. K. J. Am. Chem.
Soc. 1971, 93, 1491.
11. (a) Chittenden, G. F. Carbohydr. Res. 1980, 87, 219.
12. Morel, D.; Darwans, F. Tetrahedron 1977, 33, 1445.
13. Lemieux, R. U.; Hendriks, K. B.; Stick, R. V.; James, K. J. Am. Chem. Soc. 1975, 97,
4056.