Process improvements of prasugrel hydrochloride: An adenosine diphosphate receptor antagonist

Article abstract of DOI:10.1021/op200325u

An improved process for the synthesis of prasugrel hydrochloride with an overall yield of 58%, 99.9% purity, and meeting all other quality requirements is described.

Full text of DOI:10.1021/op200325u

Article
pubs.acs.org/OPRD
Process Improvements of Prasugrel Hydrochloride: An Adenosine
Diphosphate Receptor Antagonist†
Sampath Aalla,‡ Goverdhan Gilla,‡ Dattatray Shamrao Metil,‡ Raghupathi Reddy Anumula,‡
Prabhaker Reddy Vummenthala,*,§ and Pratap Reddy Padi⊥
‡Research and Development, Integrated Product Development, Dr. Reddy’s Laboratories Ltd., Survey No’s 42, 45, 46, and 54,
Bachupally, Qutubullapur, Ranga Reddy District-500 072, Andhra Pradesh, India
§Department of Chemistry, University College of Science, Osmania University, Hyderabad-500 007, Andhra Pradesh, India
⊥Research and Development, Macleods Pharmaceuticals Limited, G-2, Mahakali Caves Road, Shanthi Nagar, Andheri (E),
Mumbai-400 093, Maharashtra, India
ABSTRACT: An improved process for the synthesis of prasugrel hydrochloride with an overall yield of 58%, 99.9% purity, and
meeting all other quality requirements is described.
hydrochloride salt formation, examining all the disadvantages
associated with the reported processes.
INTRODUCTION
■
Prasugrel hydrochloride (5-[(1RS)-2-cyclopropyl-1-(2-fluoro-
phenyl)-2-oxoethyl]-4,5,6,7-tetrahydrothieno[3,2-c]pyridin-2-yl
acetate hydrochloride), is a novel platelet inhibitor developed
by Daiichi Sankyo & Co. for acute coronary syndrome (ACS).
The United States Food and Drug Administration (USFDA)
approved the use of prasugrel for the reduction of thrombotic
cardiovascular events (including stent thrombosis) in patients
with acute coronary syndrome who are to be managed with
percutaneous coronary intervention (PCI).1 Prasugrel is a
member of the thienopyridine class of adenosine diphosphate
(ADP) receptor inhibitors, like ticlopidine and clopidogrel.
These agents reduce the aggregation (“clumping”) of platelets
by irreversibly binding to P2Y12 receptors. Compared to
clopidogrel, prasugrel inhibits ADP-induced platelet aggrega-
tion more rapidly and more consistently in healthy volunteers
and in patients with coronary artery disease, including those
undergoing PCI.2
RESULTS AND DISCUSSION
■
Our improved process also starts with the N-alkylation using
commercially available materials, 2 and 3 (Scheme 1). The
initial experiments carried out for the reaction of 2 and 3 in
N,N-dimethylformamide using potassium carbonate resulted in
low yield and purity. These experiments indicated that the
solvent and the base are to play a major role in the N-alkylation
reaction.
Various solvents were examined for the reaction of 2 and 3
including acetonitrile, dichloromethane, acetone, isopropyl
alcohol, ethyl acetate, and N,N-dimethylformamide. Apart
from acetonitrile all other solvents furnished either lower
yield or less purity; experimental results are presented in Table
1. Hence, the use of acetonitrile would be appropriate for the
reaction of 2 and 3.
After selecting the acetonitrile as a solvent for the N-
alkylation reaction, another key parameter was studied by
screening of bases. Using sodium bicarbonate and potassium
bicarbonate, very little product formation was observed,
whereas triethylamine resulted in very low purity. On the
other hand higher yield and purity were obtained using sodium
carbonate as a base. On the basis of these results, sodium
carbonate was found to be the suitable base for the reaction of
2 and 3 (Table 2).
The solid byproduct was filtered after completion of the N-
alkylation reaction, and the filtrate was used without isolation of
compound 4 in the next reaction, acetylation. This reaction was
carried out using acetic anhydride in the presence of a base and
catalytic amount of 4-dimethylaminopyridine. Without 4-
dimethylaminopyridine, the rate of reaction is found to be
slow and requires more than 15 h for the completion of the
reaction, whereas the catalytic amount of 4-dimethylaminopyr-
idine completed the acetylation within 4 h. The reported
Though many synthetic schemes were reported for the
synthesis of prasugrel,3−7 N-alkylation of thienopyridine
derivative 2 with cyclopropyl ketone derivative 3 followed by
acetylation and hydrochloride salt formation is the convenient
and the most practiced route.8−14 Most of the reported
processes using this synthetic route involve isolation of the N-
alkylated compound 4 followed by acetylation with a low
overall yield. Moreover isolation of compounds 4 and 5
involves tedious workup process including extraction, evapo-
ration of the solvent followed by isolation of the solid product
using solvent and anti-solvent technique.8−10 In recently
reported processes11−14 acetylation was carried out without
isolation of the N-alkylated compound 4, but involved the
usage of a relatively expensive base, diisopropylethyl amine,
cumbersome workup process for the isolation of the solid
product, lower purity, and a moderate overall yield.
Considering these disadvantages we intended to develop an
efficient and commercially viable process for prasugrel HCl, we
have subjected this synthetic route to further studies. In this
article, we describe an improved process with an overall yield of
58% for three steps including N-alkylation, acetylation, and
Received: November 12, 2011
Published: January 6, 2012
© 2012 American Chemical Society
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Scheme 1. Synthetic scheme for prasugrel hydrochloride
Table 1. Screening of solvents for the reaction of 2 and 3
significantly simplified by isolating the solid directly from the
reaction mixture by addition of water. Recrystallization from
the mixture of acetonitrile and water provided high-quality
prasugrel (>99.7% purity by HPLC).
a
entry
solvent
acetonitrile
purity (%)
yield (%)
1
2
3
4
5
6
90.1
83.3
63.8
65.2
75.0
82.6
85
74
75
70
61
80
acetone
Having achieved high purity of prasugrel, our next task was
to study the prasugrel hydrochloride salt formation. Preparation
of prasugrel hydrochloride according to the process reported8
using aqueous hydrochloric acid in acetone resulted in more
desacetyl prasugrel 4 (∼0.25%). This indicates that, prasugrel is
more susceptible to the desacetylation in aqueous hydrochloric
acid medium. Therefore, to control the desacetylation and
avoid the aqueous medium, isopropanolic hydrochloride was
used instead of aqueous hydrochloric acid. Applying this
modification, formation of desacetyl prasugrel 4 was signifi-
cantly reduced (<0.10%).
It was also observed that, the temperature of hydrochloride
salt formation reaction plays a major role on acetone content in
the final solid. At lower temperatures (≤40 °C) higher acetone
content was observed, while at higher temperatures (≥45 °C)
the acetone content was well within the limit (5000 ppm). It
was found that 50 °C would be optimum for the prasugrel
hydrochloride salt formation (Figure 2). 2-Chloropropane, the
dichloromethane
N,N-dimethylformamide
isopropyl alcohol
ethyl acetate
a
Isolated yield (solvent was evaporated to obtain the oily compound).
Table 2. Screening of base for the N-alkylation reaction
a
entry
base
purity (%)
yield (%)
1
2
3
4
5
triethylamine
55.6
−
94.7
90
−
95
b
sodium bicarbonate
sodium carbonate
b
potassium bicarbonate
−
91.0
−
84
potassium carbonate
a
b
Isolated yield. Product formation is very low, therefore not isolated.
processes involve the use of triethylamine10,11 and diisopropyl
ethylamine12,13 as a base. However, our experimental results
revealed that the use of N-methylmorpholine as a base would
increase the yield and the purity significantly (Figure 1).
Figure 2. Effect of temperature on residual solvents.
byproduct formed from the isopropanolic hydrochloride during
the salt formation reaction was observed around 12 ppm in the
prasugrel hydrochloride.
Figure 1. Selection of base for acetylation.
Further, it was identified that the concentration of
isopropanolic hydrochloride also had a significant influence
on the acetone content. The acetone content is higher when
the concentration of isopropanolic hydrochloride is high
(Figure 3). The reason for the higher content of acetone in
the solid may be explained by acetone being trapped in the
crystal lattice due to the fast crystallization when the higher
After studying the parameters of the key process, we focused
the attention on the workup process. In the processes reported,
after completion of the acetylation reaction, the product was
extracted with a solvent followed by evaporation of the solvent
and isolation of the solid using either a mixture of solvents10 or
a single solvent.11,13 This tedious workup process was
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filtrate was cooled to 0 °C. N-Methylmorpholine (7.39 kg,
73.0598 mol), 4-dimethylaminopyridine (49 g, 0.4011 mol),
and then acetic anhydride (5.6 kg, 54.8535 mol) were added at
0 °C and stirred for 4 h. Water was charged (49 L) and stirred
for 1 h at 0 °C; the precipitated solid was filtered and washed
with the mixture of acetonitrile (7 L) and water (7 L). The wet
solid was transferred into acetonitrile (35 L), heated to 50 °C,
and stirred for 10 min. The resulting clear solution was cooled
to 0 °C, and water (28 L) was added and stirred for 2 h. The
solid precipitate was filtered and washed with a mixture of
acetonitrile (35 L) and water (35 L). The wet solid was dried
for 6 h at 60 °C to furnish 9.0 kg (66.0%) of the title compound
with 99.8% purity by HPLC; DSC: 120−122 °C; Mass: 374 (M
+ H)+; IR (KBr, cm−1): 3085, 2989, 1758, 1703, 1585, 1493,
1368, 1193; 1H NMR (500 MHz, CDCl3): δ 7.47 (t, J = 7.5 Hz,
1H), 7.32 (m, 1H), 7.17 (t, J = 7.5 Hz, 1H), 7.11 (t, J = 9.0 Hz,
1H), 6.26 (s, 1H), 4.83 (s, 1H), 3.55 (d, J = 14.0 Hz, 1H), 3.48
(d, J = 14.0 Hz, 1H), 2.89 (m, 1H), 2.79 (m, 2H), 2.76 (m,
1H), 2.28 (m, 1H), 2.26 (s, 3H), 1.03 (m, 2H), 0.85 (m, 2H);
13C NMR (125 MHz, CDCl3): δ 207.6, 167.8, 162.5, 160.1,
149.5, 130.6, 129.2, 125.7, 124.4, 121.8, 115.9, 111.9,71.5, 50.5,
48.4, 24.9, 20.7, 18.4, 12.1, 11.5.
Figure 3. Effect of isopropanolic HCl concentration on residual
solvents.
concentration of isopropanolic hydrochloride is used. The
experimental results indicates that, 5% isopropanolic hydro-
chloride is preferable for the preparation of prasugrel
hydrochloride.
Finally, the redesigned process furnished the prasugrel
hydrochloride with an overall yield of 58% (from three steps,
N-alkylation, acetylation, and hydrochloride salt formation),
around 99.9% purity and meeting other quality parameters
(Table 3).
Prasugrel Hydrochloride. To a solution of prasugrel base,
5 (6 kg, 16.0668 mol) in acetone (60 L) was added
isopropanolic hydrochloride (11.16 L, assay 5.0%, 15.2876
mol) slowly at 50 °C and stirred for 1 h. The reaction mixture
was cooled to room temperature and filtered. The wet solid was
washed with acetone (6 L) and dried under reduced pressure at
70 °C to furnish 5.8 kg (88.0%) of the title compound with
99.91% purity by HPLC; DSC: 191.8 °C. Residual solvents:
acetonitrile: ND, acetone: 1973 ppm, isopropyl alcohol: 278
ppm, 2-chloropropane: 8 ppm. Mass: 374 (M + H)+; IR (KBr,
cm−1): 3086, 2957, 2436, 2387, 1758, 1690, 1593, 1493, 1326,
CONCLUSION
■
In conclusion, we have developed an efficient and commercially
viable process for the synthesis of prasugrel hydrochloride,
meeting all the quality requirements with an overall yield of
58% and high purity (∼99.9% by HPLC).
EXPERIMENTAL SECTION
■
1
1213; H NMR (500 MHz, CDCl3): δ 8.0 (m, 1H), 7.55 (m,
A liquid chromatograph equipped with variable wavelength UV
detector and integrator was used in recording HPLC. Mass
spectra were obtained using a 4000-Q-trap LC−MS/MS mass
spectrometer. 1H NMR and 13C NMR were recorded in CDCl3
at 500 and 125 MHz, respectively, on Unity INOVA (Varian
500 MHz) FT NMR spectrometer, the chemical shifts are
reported in δ ppm relative to TMS (δ 0.00 ppm) and CDCl3 (δ
77.00 ppm). IR spectra were recorded on a Perkin-Elmer FT IR
instrument (KBr pellet method). The thermal analysis was
carried out on DSC Q1000 TA. The thermogram was recorded
from 40 to 220 °C under the nitrogen flow of 50 mL/min at a
heating rate of 10 °C/min. The solvents and reagents were
used without further purification.
1H), 7.37 (t, J = 8.0 Hz, 1H), 7.25 (t, J = 9.0 Hz, 1H), 6.40 (br,
1H), 5.72 (br, 1H), 4.65−2.88 (m, 6H), 2.30 (s, 3H), 1.82 (br,
1H), 1.30−0.89 (m, 4H); 13C NMR (125 MHz, CDCl3): δ
200.2, 167.2, 161.0, 151.3, 133.3, 132.6, 126.1, 123.2, 122.4,
116.5, 115.2, 110.9, 66.4, 49.5, 47.6, 22.2, 20.6, 19.8, 13.2.
AUTHOR INFORMATION
■
Corresponding Author
*To whom correspondence should be addressed. E-mail:
vummenthalapv@yahoo.co.in. Fax: +91-40-44346285. Tele-
phone: +91-9849210408.
5-[(1RS)-2-Cyclopropyl-1-(2-fluorophenyl)-2-oxoeth-
yl]-4,5,6,7-tetrahydrothieno[3,2-c]pyridin-2-yl acetate
(Prasugrel base). To a suspension of 3 (10.55 kg, 89%
assay, 36.5208 mol), sodium carbonate (8.5 kg, 80.1887 mol) in
acetonitrile (35 L) was added 2 (7.0 kg, 36.5192 mol) at 25−35
°C. The resulting reaction mixture was stirred for 10 h at 25−
35 °C. The solid byproduct was filtered off, and the obtained
Notes
†Dr. Reddy’s Communication number IPDO-IPM-00292.
ACKNOWLEDGMENTS
■
We are thankful to the management of Dr. Reddy’s
Laboratories Ltd. for supporting this work. Co-operation
Table 3. Final quality data of prasugrel hydrochloride
residual solvents (ppm)
a
entry
purity (%)
acetone
isopropanol
acetonitrile
2-chloropropane
yield (%)
1
2
3
99.91
99.90
99.91
1973
2675
2763
278
347
381
ND
ND
ND
8
9
58.1
58.0
57.8
12
a
Overall isolated yield; ND = not detected.
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from colleagues of analytical research and development is
highly appreciated.
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