Synthesis of ipratropium bromide-related compounds

Article abstract of DOI:10.1080/00397910601039119

Synthesis of ipratropium bromide metabolites is described. Copyright Taylor & Francis Group, LLC.

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Synthesis of Ipratropium Bromide–Related
Compounds
Irina Tsyskovskaia a , Mustapha Kandil a & Yves Beaumier a
a Pharmascience Inc. , Saint‐Laurent, Quebec, Canada
Published online: 06 Feb 2007.
To cite this article: Irina Tsyskovskaia , Mustapha Kandil & Yves Beaumier (2007) Synthesis of Ipratropium
Bromide–Related Compounds, Synthetic Communications: An International Journal for Rapid Communication
of Synthetic Organic Chemistry, 37:3, 439-446, DOI: 10.1080/00397910601039119
To link to this article: http://dx.doi.org/10.1080/00397910601039119
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Synthetic Communicationsw, 37: 439–446, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910601039119
Synthesis of Ipratropium Bromide–Related
Compounds
Irina Tsyskovskaia, Mustapha Kandil, and Yves Beaumier
Pharmascience Inc., Saint-Laurent, Quebec, Canada
Abstract: Synthesis of ipratropium bromide metabolites is described.
Keywords: ipratropium bromide, related compound, synthesis, HPLC
Ipratropium bromide, (endo, syn)-(+)-3-(3-hydroxy-1-oxo-2-phenyl-
propoxy)-8-methyl-8-(1-methylethyl)-8-azoniabicyclo [3.2.1] octane bromide
10, belongs to the group of tropane alkaloids. It is in fact a diastereomer of
the N-isopropyl quaternary salt of atropine 8S-ipratropium bromide 18. As
depicted in Fig. 1, the isopropyl group in ipratropium bromide 10 is axial,
whereas in 8S-ipratropium bromide 18, it is in the equatorial position. Both
compounds are active anticholerinergic agents, though the former displays
stronger activity and fewer clinical side effects.[1,2]
Synthesis of ipratropium bromide has been described by Banholzer
et al.[3–5] (Fig. 2). Accordingly, Robinson condensation of succindialdehyde
1, isopropylamine 2, and acetonedicarboxylic acid 3 provides N-isopropylnor-
tropinone 4, which is then catalytically hydrogenated to produce N-isopropyl-
nortropine 5. Transesterification with ethyl a-formylphenylacetate 7 followed
by sodium borohydride reduction yields N-isopropylnoratropine 9. Finally, the
product is N-alkylated with methylbromide to give ipratropium bromide 10.
The in vivo metabolism of ipratropium bromide generates different
products[6–9] (Fig. 3). Also, the preparation of ipratropium bromide is
accompanied by the formation of several by-products. Synthesis of these
by-products and metabolites are important to trace the generated impurities
Received in the USA May 18, 2006
Address correspondence to Yves Beaumier, Pharmascience Inc., 6625 Abrams,
Saint-Laurent, Quebec H4S 1X9, Canada. E-mail: ybeaumier@pharmascience.com
439

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I. Tsyskovskaia, M. Kandil, and Y. Beaumier
Figure 1. Isomers of methyl isopropyl derivatives of atropine.
in the final product, as, well as to study the pharmacokinetic and stability of
ipratropium bromide 10.
A number of procedures have been reported for this purpose. Herein, we
introduce an alternative route to some of these impurities and metabolites:
N-isopropylnoratropine 9, apo-ipratropium bromide 15, N-isopropylnortropine
methylbromide 17, and 3-(2-phenyl-acryloyloxy)-8-isopropyl-8-methyl-8-azo-
niabicyclo [3.2.1] octane bromide 16. The quantification and the purity of these
compounds are evaluated by high-performance liquid chromatography (HPLC).
There are numerous articles in the literature concerning the synthesis of
atropine from tropine and tropic acid.[10,11] We found that the one depicted
in Fig. 4 provides the most reliable route to the synthesis of N-isopropylnoratro-
pine 9. A modification of the procedure of Fodor et al. was used.[11] Thus, tropic
acid 11 was first protected by reaction with acetyl chloride. The product was
then converted by treatment with thionyl chloride to the corresponding
acid chloride 12. Condensation by heating with N-isopropylnoratropine 5
followed by hydrolysis provided N-isopropylnoratropine 9 in 30% overall
yield (Fig. 4). The required N-isopropylnortropine 5 was prepared by the
route presented in Fig. 2.
The synthesis of apo-ipratropium bromide 15 is depicted in Fig. 5. The
dehydratation of atropine 13 on treatment with sulfuric acid provided apoatro-
pine 14, which was then N-alkylated by isopropyl bromide[13] (Fig. 5).
The N-alkylation of apoatropine 14 proceeds diastereoselectively.[14] As
determined by a rule discovered by Fodor,[10] the substituent introduced last at
the nitrogen preferably becomes situated over the pyrrollidine ring. Thus the
apo-ipratropium bromide 15 and 3-(2-phenyl-acryloyloxy)-8-isopropyl-8-
methyl-8-azoniabicyclo [3.2.1] octane bromide 16 were obtained as a 1:9 dia-
stereoisomeric endo/exo mixture. Their stereochemistry was confirmed by 1H
NMR, 13C NMR, and correlation spectroscopy (COSY) spectroscopy.
The last compound of interest in this study was N-isopropylnortropine
methylbromide 17. This compound was obtained via the reaction of methyl
bromide with N-isopropylnortropine 5 (Fig. 6). NMR and MS spectroscopy
confirmed the expected structure.

Ipratropium Bromide-Related Compounds
441
Figure 2. Synthesis of ipratropium bromide.
EXPERIMENTAL
NMR spectra were recorded on a 400-MHz Bruker instrument. Mass spectra
were performed on a Micromass Autospec-TOF spectrometer. The microana-
lysis was performed on an EA 1108 CHNS model analyzer.

442
I. Tsyskovskaia, M. Kandil, and Y. Beaumier
Figure 3. In-vivo metabolism of ipratropium bromide.
High-Performance Liquid Chromatography
Liquid chromatography was performed using a HPLC system composed of an
Agilent model G1311A pump equipped with a ternary gradient controller and
a Agilent model G1315A diode array detector, wavelength 210 nm. The
computer is equipped with Agilent LC3D Chemstation for Analytical
program, Revision A:09.03.
Apoatropine
A 250 mm ꢀ 4.0 mm, 5-mm Lichrosphere 60 RP-Select column was used for
the determination of apoatropine. A mobile phase consisting of a water
solution (0.1% H3PO4) and acetonitrile was delivered at a rate of 1 mL/
min, holding the composition at 65:35 for 10 min.

Ipratropium Bromide-Related Compounds
443
Figure 4. Synthesis of the N-isopropylnoratropine.
Figure 5. Synthesis of apo-ipratropium bromide and its diastereoisomer.

444
I. Tsyskovskaia, M. Kandil, and Y. Beaumier
Figure 6. Synthesis of the N-isopropylnortropine.
Others
A 250 mm ꢀ 4.0 mm, 5-mm Lichrosphere 60 RP-Select column was used for
determination of degradation products. A mobile phase A consisting of a buffer
solution (50 mM of tetramethylamonium hydroxide, pH 3.0) and acetonitrile
was delivered at a rate of 1.5 mL/min, holding the composition at 92:8 for 40
min, then as a linear gradient to 50:50 in 10 min. A post time of 10 min is added.
N-Isopropylnoratropine 9
A mixture of acetyltropyl chloride (4.33 g, 16.9 mmol)[12] and N-isopropylnor-
tropine 5 (2.69 g, 16 mmol) was heated at 858C for 4 h. The mixture was cooled
and dissolved in chloroform (75 mL). The chloroform solution was poured into
an aqueous solution of 5% hydrochloric acid (250 mL). The two-phase mixture
was stirred vigorously for 18 h. The aqueous phase was extracted with
2 ꢀ 50 mL of chloroform, and the chloroform extracts were discarded. The
aqueous phase was adjusted to pH 10 with a saturated sodium carbonate
solution and extracted with 3 ꢀ 50 mL of chloroform. The combined chloro-
form extracts were washed with water, followed by a saturated sodium
chloride solution, and dried with sodium sulfate. Removal of solvent under
reduced pressure left a colored liquid (2.52 g, 50% crude yield). Crystallization
from acetone gave 0.89 g of a white solid. The yield evaluated by HPLC is 34%,
and the purity is 99.9%. H1 NMR (400 MHz, CD3OD) d: 7.3 (m, 5H); 5.0
(t, 1H); 4.15 (t, 1 H); 3.76 (m, 2H); 3.3 (1H); 2.74 (m, N-CH); 2.19–1.4
(m, 8H); 1.08 (d, J ¼ 16.6). MS m/z (Mþ) 318. C19H27NO3 calc. C,
71.89%; H, 8.57%; N, 4.41%; found C, 71.82%; H, 8.53%; N, 4.39%.
Apoatropine 14
Atropine(1.00 g, 3.45 mmol)wasdissolved in conc. H2SO4 (2.00 g, 14.4 mmol),
and the mixture was allowed to stand for 2 h at room temperature. Finely cracked

Ipratropium Bromide-Related Compounds
445
ice (5.00 g) was added carefully in small portions to this solution under
cooling. After regeneration with 10% KOH solution, apoatropine was
extracted with ether (50 mL) three times. The ether layers were washed with
sat. NaCl solution and dried with Na2SO4. Evaporation of the solvent gave a
colorless oil, which crystallized on standing, mp 608C. The yield evaluated by
HPLC is 86% and the purity is 94%. H1 NMR (400 MHz, CDCl3) d: 7.39–
7.26 (m, 5H); 6.35 (s, 1H); 5.87 (s, 1H); 5.14 (t, 1H); 3.08 (s, 2H); 2.27
(d, 3H); 2.18–1.73 (m, 8H). Ms m/z (Mþ) 272.2. C17H21NO2 calc. C,
75.25%; H, 7.80%; N, 5.16%; found C, 75.19%; H, 7.67%; N, 5.15%.
Apo-ipratropium Bromide 15
To the solution of apoatropine (0.7 g, 2.58 mmol) in acetonitrile (10 mL), iso-
propylbromide (0.97 mL, 0.01 M) was added under stirring. The resulting
mixture was heated under reflux for 5 days. After cooling, white precipitates
were collected on a filter. Recrystallization from chloroform gave a white
solid. The yield evaluated by HPLC is 6.4%, and the purity is 98%.
H1 NMR (400 MHz, CDCl3) d: 7.33 (s, 5H Ar); 6.38 (s, 1H); 5.91 (s, 1H);
5.27 (s, 1H); 4.1 (m, 2H); 3.68 (m, 1H); 2.85 (s, 3H); 2.75–1.99 (m, 8H); 1.4
(d, 6H, J ¼ 5.9). MS m/z (Mþ) 314 (100%). C20H28BrNO2 calc. C,
60.91%; H, 7.16%; N, 3.55%; Br, 20.26%; found C, 59.72%; H, 6.94%;
N, 3.22%.
3-(2-Phenyl-acryloyloxy)-8-isopropyl-8-methyl-8-azoniabicyclo
[3.2.1] octane bromide 16
This stereoisomer of apoipratropium bromide 15 was obtained in the same
reaction (Fig. 5). The yield evaluated by HPLC is 58%, and the purity is
99.2%. H1 NMR (400 MHz, CDCl3) d: 7.33 (s, 5H Ar); 6.38 (s, 1H); 5.83
(s, 1H); 5.26 (m, 1H); 4.1 (m, 2H); 3.68 (m, 1H); 3.0 (s, 3H); 2.75–1.99
(m, 8H); 1.4 (d, 6H, J ¼ 5.9). MS m/z (Mþ) 314 (100%). C20H28BrNO2
calc. C, 60.91%; H, 7.16%; N, 3.55%; Br, 20.26%; found C, 60.79%;
H, 7.09%; N, 3.41%.
N-Isopropylnortropine-methylbromide 17
To a solution of N-isopropylnortropine 5 (1.00 g, 6 mmol) in acetonitrile, a
solution of 2 N methylbromide (11.8 mL, 23.6 mmol) in ether was added.
This mixture was stirred for 5 days. The reaction was monitored by TLC
(butanol–H2O–AcOH 4:3:1). Removal of solvent under reduced pressure
resulted in a crude solid. Recrystallization from methanol left 1.45 g of a
white solid. The yield is 93%, and the purity is 98.6%. H1 NMR (400 MHz,

446
I. Tsyskovskaia, M. Kandil, and Y. Beaumier
CD3OD) d: 4.04 (q, 2H); 3.9 (m, 2H); 2.83 (s, 3H); 2.57–2.47 (m, 4H); 2.31–
2.28 (m, 4H); 1.88 (d, J ¼ 16.4 Hz, 2H); 1.32 (dd, J ¼ 6.4 Hz; 6H). C13 NMR
(400 MHz, CD3OD) d: 68.1 (C1/C5); 60.96 (C3); 57.03 (Cisopr); 40.5 (CCH3);
35.3 (C2/C4); 26.4 (C6/C7); 17.0 (CCH3-isopr); MS m/z (Mþ)184.1 (100%).
C11H22BrNO2 calc. C, 50.01%; H, 8.39%; N, 5.3%; Br, 30.24%; found C,
49.69%; H, 8.03%; N, 4.94%.
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