An improved preparation process for gemcitabine

Article abstract of DOI:10.1021/op800104r

An improved, cost-effective, and convenient process, using cinnamoyl as hydroxyl protective group and tosyl as the leaving group for gemcitabine (1) is described. The overall yield obtained from this newly developed process is around 10%, including two st

Full text of DOI:10.1021/op800104r

Organic Process Research & Development 2008, 12, 888–891
An Improved Preparation Process for Gemcitabine
Xiangrui Jiang,†,‡ Jianfeng Li,‡ Rongxia Zhang,‡ Yi Zhu,† and Jingshan Shen*,†,‡
Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zu Chong Zhi Road, Pudong,
Shanghai 201203, China, and Topharman Shanghai Co., Ltd., 1088 Chuansha Road, Pudong, Shanghai 201209, China
Abstract:
An improved, cost-effective, and convenient process, using cin-
namoyl as hydroxyl protective group and tosyl as the leaving group
for gemcitabine (1) is described. The overall yield obtained from
this newly developed process is around 10%, including two
stereospecific crystallizations, and the quality of the product
complies with the requirements of USP30.
Figure 1. Structures of gemcitabine and undesired isomer.
overall yield was at 5% from compound 2 over eight steps,
and the purity of the final product (98%) did not comply with
the requirement of USP30 (g99.8%).
Herein, we report a new process for producing gemcitabine
by using cinnamoyl as hydroxyl protective group and tosyl as
a leaving group. The improved process has some industrial
advantages such as economical material cost, convenient
operation, and relatively high yield, etc.
Introduction
Gemcitabine, 1 (Figure 1), is a nucleoside analogue of
cytidine with wide-ranging activity in a variety of solid tumors
such as nonsmall cell lung cancer (NSCLC), head and neck
cancer, genitourinary tract cancer.1,2 Gemzar, marketed by Eli
Lilly for intravenous use, contains gemcitabine, mannitol, and
sodium acetate as a sterile lyophilized powder.
The synthesis of gemcitabine was originally accomplished
by Hertel and co-workers, by using tert-butyldimethyl chlo-
rosilane as the protecting agent for the hydroxyl groups.3,4
However, this method was not suitable for large-scale produc-
tion, since the major product so obtained was undesired 1a (1:
1a ) 1:4). Several other syntheses of 1 have been reported with
relatively low yield.5-7
Chou and co-workers selected benzoyl as the protecting
group for the hydroxyls at C-3 and C-5 positions,8 and the ratio
of 1 and 1a was increased to 1:1 (Scheme 1). Therefore, benzoyl
is believed to be a qualified protective group in the process of
preparing gemcitabine. Nevertheless, Chou’s process suffered
from industrial inconveniences: (a) the impurities contained in
the oil form of intermediate 5a/b were not easy to get rid of,
and the remaining impurities not only decreased the yield of
subsequent coupling reaction but also consumed the expensive
trimethylsilyl trifluoromethanesulfonate (TMSOTf); (b) the
mixture of 6a/b (1:1) was used in following step, and the
undesired isomer, 6a, resulted in unnecessary material cost; (c)
Results and Discussion
Compound 8, 2-deoxy-2,2-difluoropentofuranos-1-ulose,3,9
was acylated by cinnamoyl chloride in the presence of pyridine
to give both isomers at C-3 position, 9a and 9b, in ethyl acetate
(Scheme 2). Workup of this reaction furnished the solution of
9a/b in toluene, which was cooled to ambient temperature
(5-10 °C) with stirring, and the desired 9a slowly crystallized
out as powder, in excellent purity (97.1%), ee (99.3%), and
yield (43%).
Compound 9a was reduced to get the hydroxyl intermediate
of 2-deoxy-2,2-difluoro-D-ribofuranose-3,5-dicinnamonate 10 by
lithium tri-tert-butoxyaluminohydride (LTBA), which was
prepared in situ by using tert-butanol and LiAlH4 in tetrahy-
drofuran (THF). Other reduction reagents, such as lithium
aluminohydride, lithium triacetoxyaluminohydride, and Vitride
solution also worked well with almost similar yields. The
hydroxyl intermediate 10, in a mixture of R and ꢀ isomers
(1:1), was used directly to the next step of tosylation without
further purification.
The crude product from the reduction step was tosylated with
p-toluene sulfonyl chloride (TsCl) in ethyl acetate to give 11a/
b. The base used in this reaction had obvious effect on the ratio
of 11a and 11b (Figure 2), but the ratio did not affect the result
of the following coupling reaction.
The tosyl of 11a/b was replaced with mesyl to check which
one was better for large-scale preparation. It was found that
the tosylate easily crystallized in ethyl acetate/petroleum ether
with reasonable yield (63% based on 9a); nevertheless, the
mesylate was in oil form. Otherwise, the corresponding tosylate
of 5a/b was in solid form. This implied that 11a/b was in solid
form due to the effect of tosyl.
* Author for correspondence. Telephone: +86 21 50805891. Fax: +86 21
64319573. E-mail: jsshen@mail.shcnc.ac.cn.
‡ Shanghai Institute of Materia Medica, Chinese Academy of Sciences.
† Topharman Shanghai Co., Ltd.
(1) Van Moorsel, C. J.; Peters, G. J.; Pinedo, H. M. Oncologist 1997, 2,
127.
(2) Vogelzang, N. J. Semin. Oncol. 2002, 29 (1 Suppl. 3), 40.
(3) Hertel, L. W. U.S. Patent 4,808,614A1, 1989.
(4) Hertel, L. W.; Kroin, J. S.; Misner, J. W.; Tustin, J. M. J. Org. Chem.
1988, 53, 2406.
(5) Hertel, L. W.; Jones, C. D.; Kroin, J. S.; Mabry, T. E. U.S. Patent
5,480,992A1, 1996.
(6) Lee, J.; Park, G. S.; Lee, M.; Bang, H. J.; Lee, J. C.; Kim, C. K.; Choi,
C. J.; Kim, H. K.; Lee, H. C.; Chang, Y. K.; Lee, G. S. WO Patent
2006/071090A1, 2005.
(7) Shen, J. S.; Li, Y. F.; Kaspi, J. WO Patent 2007/027564A2, 2006.
(8) Chou, T. S.; Heath, P. C.; Patterson, L. E.; Poteet, L. M.; Lakin, R. E.;
Hunt, A. H. Synthesis 1992, 6, 565.
(9) Berton, C. P.; Laurens, A.; Henry, A. L. J. Am. Chem. Soc. 1950, 72,
2404.
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10.1021/op800104r CCC: $40.75
2008 American Chemical Society
Published on Web 08/21/2008

Scheme 1. Reported route for gemcitabinea
a Reagents and conditions: (a) benzoyl chloride, pyridine, N,N-dimethyl-4-amino-pyridine, 65 °C; (b) dichloromethane/heptane, 5-35 °C, 26%, over two steps; (c)
LTBA, ethyl ether, THF, -10 °C; (d) MsCl, Et3N, dichloromethane, 0 °C; (e) N-acetyl cytosine, HMDS, TMSOTf, DCE, reflux; (f) NH3, methanol, rt; (g) concd.
hydrochloric acid, i-PrOH, 70 °C, 49% over four steps; (h) acetone/H2O, 37%.
Scheme 2. Improved route for gemcitabinea
a Reagents and conditions: (a) cinnamoyl chloride, pyridine, ethyl acetate, 60 °C; (b) toluene, 43% over two steps; (c) LTBA, THF, -10 °C; (d) TsCl, Et3N, toluene,
-10 °C, 62% over two steps; (e) N-acetyl cytosine, HMDS, TMSOTf, DCE, reflux; (f) 5% sodium dicarbonate; (g) NH3, methanol, rt; (h) 1 N hydrochloric acid,
acetone, rt, 80% over two steps.
It was interesting that a mixture of 13a and 13b (1:1) was
obtained, regardless of the ratio of 11a and 11b. The phenom-
enon indicates that the coupling reaction proceeds via SN1-like
pathway, which is consistent with the hypothesis of Chou’s
group.5 Excessive TMSOTf (1.5 equiv to 5a/b) was needed in
the reported procedure,8 as the impurities contained in 5a/b
consumed this expensive reagent. In the present procedure, pure
11a/b was used to reduce the consumption of TMSOTf to 1
equiv and improve the yield of this coupling step.
The unstable 12a/b was treated by 5% sodium carbonate
solution to give 13a/b in situ. Most of the 13a precipitated from
the mixture, thanks to its poor solubility in 1,2-dichloroethane
(DCE). Thereby, the undesired isomer 13a was simply removed
from the reaction mixture by filtration. This advantage reduces
the cost of materials in the following steps and makes the
process more efficient.
Crude 13b was treated with NH3/methanol at room temper-
ature to give crude gemcitabine base form in high yield. The
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Figure 2. Intermediates and byproduct of the improved procedure.
main byproduct of the deprotection were methyl cinnamate and
cinnamide, which can be removed by extraction with dichlo-
romethane during the workup step. The crude gemcitabine base
form 7b, containing a trace amount of R-isomer 7a, was
acidified with hydrochloric acid and crystallized in acetone/
H2O to give 1 of 99.9% purity and any individual impurity of
not more than 0.1%. The improved process showed a yield of
23% over the five steps from compound 9a to gemcitabine.
Comparatively, for the Chou’s process, the corresponding yield
was 18% from mesylate 3a.
Hz), 6.49 (d, 1H, J ) 16.0 Hz), 7.42 (m, 6H), 7.54 (m, 4H),
7.74 (d, 1H, J ) 16.0 Hz), 7.82 (d, 1H, J ) 16.0 Hz). 13C
NMR (100 MHz, CDCl3): δ 61.62, 68.85, 78.23, 111.52,
114.83, 116.17, 128.31, 128.48, 128.94, 129.06, 130.79, 131.28,
133.52, 133.87, 146.79, 162.41, 164.78, 165.90. EI-MS (m/z)
428 (M+).
2-Deoxy-2,2-difluoro-D-ribofuranose-3,5-dicinnamonate
(10a/b). The solution of 5.84 kg (78 mol) of tert-butanol in 2
L of THF was carefully added to the mixture of 8 L of absolute
THF and 1 kg (26 mol) of LiAlH4 at 10 °C. The reaction
mixture was stirred for 2 h and then concentrated to obtain 6.68
kg of off-white solid LTBA.
Conclusion
An improved process for gemcitabine, including two ste-
reoselective crystallizations, has been provided with the total
yield of 10% over six steps. Because of the affect of cinnamoyl
and tosyl, the resulting new intermediates have some industrially
favorable physical properties. For example, 9a and 13a can be
simply separated from their isomer mixtures, and the intermedi-
ate 11a/b can be purified conveniently. The advantages ensure
that the efficient, cost-effective, and industrially convenient
process will be employed for commercial production of
gemcitabine.
The suspension of 1 kg (2.3 mol) of 3a in 8 L of THF was
cooled to 10 °C, and the previously prepared reduction reagent
was added in portions. After the suspension became clear, the
reaction mixture was stirred for another 2 h, and 1 L of H2O
was carefully added to quench the reaction. The resulted mixture
was washed by 1 N hydrochloric acid and 5% sodium
bicarbonate, dried over Na2SO4, filtrated to obtain the filtration,
which was used directly in next step.
2-Deoxy-2,2-difluoro-D-ribofuranos-3,5-dicinnamonyl-1-
(4-methylbenzene) Sulfonate (11a/b). To the resulted filtration
of previous step, 480 mL (3.4 mol) of triethylamine was added
at 0 °C. The solution of 440 g (2.3 mol) of p-toluene sulfonyl
chloride in 500 mL of toluene was added to the resulted mixture
in 2 h, and stirred for 5 h more. The reaction mixture was
washed by 1 N hydrochloric acid and 5% sodium bicarbonate.
The organic phase was concentrated to obtain the residue as a
yellow oil. The residue was dissolved in 4 L of ethyl acetate at
50 °C under reduced pressure, cooled to ambient temperature
(5-10 °C), and 3 L of petroleum ether was slowly added. The
resulted mixture was stirred for 3 h, and filtrated to obtain 850 g
of 11a/b, yield 62.3% of two steps, purity 97.31% of two
isomers on HPLC.
11b: mp 120-121 °C. 1H NMR (400 MHz, CDCl3): δ 2.37
(s, 3H), 4.12 (dd, 1H), 4.28 (dd, 1H), 4.39-4.44 (m, 1H), 5.68
(m, 1H), 6.01 (d, 1H, J 6.0 Hz), 6.34 (d, 1H, J ) 16.4 Hz),
6.46 (d, 1H, J ) 16.4 Hz), 7.27 (d, 1H, J ) 8.8 Hz), 7.39 (m,
8H), 7.52 (m, 5H), 7.67 (d, 1H, J ) 16.4 Hz), 7.76 (d, 1H, J
) 16.4 Hz), 7.80 (d, 1H, J ) 8.8 Hz). 13C NMR (100 MHz,
CDCl3): δ 21.63, 62.90, 69.31, 79.23, 98.55, 115.38, 116.92,
127.95, 128.21, 128.36, 128.90, 128.98, 129.90, 130.55, 131.02,
133.65, 133.74, 134.06, 145.74, 147.78, 164.98, 165.91. ESI-
MS (m/z) 607 (M + Na).
Experimental Section
Materials and Instruments. All commercially available
materials and solvents were used as received without any further
1
purification. H NMR spectra were recorded in CDCl3 or
DMSO-d6 at room temperature on a Bruker AMX-400/600 at
400 MHz using TMS as an internal standard. 13C NMR spectra
were obtained from a Gemini-300 spectrometer in CDCl3 or
DMSO-d6 at room temperature. The chemical-shift scale is
based on internal TMS. The mass spectrum was recorded on a
Finnigan MAT-95/711spectrometer. Melting points were mea-
sured on a Buchi-510 melting point apparatus, which are
uncorrected. TLC analyses were performed on Merck silica gel
60 F254 plate.
2-Deoxy-2,2-difluoro-D-erythropentofuranos-1-ulose-3,5-
dicinnamonate (9a). The solution of 2 kg (12 mol) of cinnamyl
chloride in 2 L of ethyl acetate was added to the mixture of 1
kg (6 mol) of 8 and 1.4 L (18 mol) of pyridine in 8 L of ethyl
acetate. The reaction mixture was heated to 30 °C for 3 h, cooled
to 5 °C, filtrated to obtain the wet cake, which was washed by
3 L of cooled toluene. The combined filtration was concentrated
under reduced pressure at 40 °C to obtain 5 L of residue, which
was slowly cooled to ambient temperature (5-10 °C), stirred
overnight, and filtrated to obtain the off-white powder; the solid
was washed by toluene, and oven-dried to obtain 1.1 kg of off-
white solid 9a; yield 43.0%, purity 97.1%, ee ) 99.3% (HPLC).
9a: mp 130-131 °C. 1H NMR (400 MHz, CDCl3): δ 4.59
(m, 2H), 4.87 (m, 1H), 5.64 (m, 1H), 6.45 (d, 1H, J ) 16.0
11a: 1H NMR (400 MHz, CDCl3): δ 2.42 (s, 3H), 4.09 (dd,
1H), 4.28 (dd, 1H), 4.35-4.37 (m, 1H), 5.31 (dd, 1H), 6.03 (d,
1H, J ) 7.2 Hz), 6.41 (d, 1H, J ) 16.4 Hz), 6.49 (d, 1H, J )
16.4 Hz), 7.34 (d, 1H, J ) 8.8 Hz), 7.39 (m, 6H), 7.52 (m,
4H), 7.70 (d, 1H, J ) 16.4 Hz), 7.78 (d, 1H, J ) 16.4 Hz),
7.85 (d, 1H, J ) 8.8 Hz). 13C NMR (100 MHz, CDCl3): δ
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21.63, 62.05, 69.31, 79.30, 99.72, 115.54, 116.76, 127.83,
128.21, 128.36, 128.90, 128.98, 129.84, 130.55, 131.02, 133.65,
133.74, 134.06, 145.58, 147.78, 164.98, 165.91. ESI-MS (m/z)
607 (M + Na).
116.51, 128.26, 128.39, 128.94, 128.99, 130.72, 131.05, 133.68,
133.90, 144.67, 146.51, 147.85, 154.69, 163.39, 164.89, 166.16,
170.86. ESI-MS (m/z) 588 (M + Na).
2′-Deoxy-2′,2′-difluorocytidine, Monohydrochloride (Gem-
citabine, 1). The mixture of 250 g (440 mmol) of 13b and 2.5
L of 11% ammonia in methanol was stirred overnight and
concentrated to obtain an oily residue. The residue was dissolved
in 2 L of 1 N hydrochloric acid and washed by dichloromethane
two times. The aqueous layer was concentrated to 300 mL, 1.0
L of acetone was added; the mixture stirred for 12 h and was
filtrated to obtain 106 g of pure gemcitabine 1 (99.8%, initial
impurity no more than 0.1%), yield 80%.
1: mp 271-273 °C dec. [R]20D ) (+) 49.3 (c 1.0, H2O). 1H
NMR (400 MHz, DMSO-d6): δ 3.60 (dd, 1H, J ) 12.8, 4.0
Hz), 3.76 (d, 1H, J ) 12.0 Hz), 3.89 (dd, 1H, J ) 5.6, 1.8 Hz),
4.17 (m, 1H), 6.05 (m, 1H,), 6.25 (d, 1H, J ) 8.0 Hz), 8.15 (d,
1H, J ) 8.0 Hz), 8.91 (s, 1H), 10.07 (s, 1H). 13C NMR (100
MHz, CDCl3): δ 58.69, 68.12, 81.59, 83.80, 94.76, 143.38,
146.98, 159.58. ESI-MS (m/z) 298 (M - H).
N-1-Acetyl-2-deoxy-2,2-difluorocytidine-3,5-dicinna-
monate (13b). The mixture of 500 g (3.3 mol) of acetyl
cytosine, 1.36 L (6.5 mol) of hexamethyldisilazane (HMDS),
8.7 g (66 mmol) of ammonium sulfate, and 5 L of 1,2-
dichloroethane was heated to reflux for 4 h, concentrated to
obtain a white solid, 774 g. Another 8 L of DCE, 770 g (1.3
mol) of 11a/b and 470 mL of TMSOTf was added, and the
resulted mixture was heated to reflux for 12 h; the reaction
mixture was washed by 3 L of 5% sodium bicarbonate, filtrated
to obtain 320 g of 13a as off-white solid, purity at 93.4%; no
13b was found by HPLC. The filtration was washed by
saturated brine, dried over Na2SO4, and concentrated under
reduced pressure to obtain 340 g of 13b as a buff solid, yield
46.5%, ee ) 90%.
13b: mp 205-207 °C. 1H NMR (400 MHz, CDCl3): δ 2.29
(s, 3H), 4.51 (m, 1H), 4.63 (m, 1H), 5.49 (m, 1H), 6.45 (d, 1H,
J ) 6.6 Hz), 6.51 (d, 1H, J ) 6.6 Hz), 6.57 (m, 1H), 7.40 (m,
6H), 7.54 (m, 4H), 7.74-7.86 (m, 3H). 13C NMR (100 MHz,
CDCl3): δ 24.89, 62.16, 71.24, 78.55, 84.00, 97.42, 115.40,
Received for review April 26, 2008.
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