Synthesis of deuterium-labelled trantinterol

Article abstract of DOI:10.1002/jlcr.1796

Trantinterol, a selective β₂-adrenoceptor agonist, is currently in Phase II clinical trials for the treatment of asthma and bronchitis. The synthesis of deuterium-labelled trantinterol is described. The labelled trantinterol is used as an inter

Full text of DOI:10.1002/jlcr.1796

Research Article
Received 23 December 2009,
Revised 12 May 2010,
Accepted 18 May 2010
Published online 5 August 2010 in Wiley Online Library
(wileyonlinelibrary.com) DOI: 10.1002/jlcr.1796
Synthesis of deuterium-labelled trantinterol
Ã
Hongliang Wen,a Li Pan,b Yingdan Zhang,a Jiacheng Ma,a Liqiong Qin,a
and Maosheng Chengb
Trantinterol, a selective b2-adrenoceptor agonist, is currently in Phase II clinical trials for the treatment of asthma and
bronchitis. The synthesis of deuterium-labelled trantinterol is described. The labelled trantinterol is used as an internal
standard for the analysis and metabolic studies.
Keywords: deuterium; labelled; synthesis; trantinterol
(3) was brominated in acetic acid to give 4-amino-3-chloro-5-
trifluoromethyl-a-bromoacetophenone (4). The keto group of (4)
Introduction
b2-Adrenoceptor is
a surface-membrane bound, G-protein
was reduced with NaBH4 in MeOH/H2O to give 1-(4-amino-3-chloro-
5-trifluoromethylphenyl)-2-bromoethanol (5), which was converted
to 2-chloro-4-oxiran-2-yl-6-(trifluoromethyl)aniline (6) under basic
conditions. Aminolysis of 2-chloro-4-oxiran-2-yl-6-(trifluoromethyl)-
aniline (6) with [2H9]t-butylamine gave [2H9]trantinterol as a minor
isomer because the attack on the less hindered side of the
epoxide is preponderant. After purification of the free base by
flash chromatography, the hydrochloride of [2H9]trantinterol was
prepared.
coupled 7TM-receptor and distributes widely in human lung,
occurring not only in airway smooth muscle but also on other
cells such as epithelial and endothelial cells, type II cells, and
mast cells.1,2 When binding to b2-agonists, it carries out the
signal transduction to the interior of the cell by coupling to
heterotrimeric G proteins. The b2-adrenoceptor couples to the
stimulatory G protein termed G5, which acts to stimulate the
effector adenylyl cyclase catalyzing the conversion of adenosine
triphosphate to cyclic AMP (cAMP). cAMP acts as a classic
second messenger in the cell through its activation of protein
kinase A, which phosphorylates multiple targets.3 In the lung,
b2-adrenoceptor’s stimulation acts to relax airway smooth
muscle. b2-Adrenoceptor is an important target of drug
discovery efforts. Salbutamol, terbutaline, salmeterol, and
formoterol selectively activate b2-adrenoceptors in bronchioles
and result in the relaxation of airway smooth muscle.4–7
b2-Adrenoceptor agonists are the most effective and safe
bronchodilators currently available. Studies in this field led to
the discovery of trantinterol (2-(4-amino-3-chloro-5-trifluoro-
methyl-phenyl)-2-t-butylaminoethanol), which exhibited selective
b2-adrenoceptor agonist activity and potent bronchodilatation.8
Trantinterol is being evaluated in Phase II human clinical trials
for the treatment of asthma and bronchitis. To support the
pharmacokinetic and metabolism studies of trantinterol, a stable
isotopically labelled standard was needed. This report describes
the experimental details for the preparation of deuterium-
labelled trantinterol.
Experimental
General
Melting points were determined on a XT4A microscopic digital
melting-point apparatus and are uncorrected. 1H-NMR
(400 MHz) and 13C-NMR (100 MHz) spectra were recorded on a
Bruker NMR spectrometer in CDCl3. Chemical shifts (d) are
reported in ppm and TMS as an internal standard. LC-MS Spectra
were obtained with a Thermo Scientific LTQ Orbitrap XLM mass
spectrometer. 4-Amino-3-chloro-5-trifluoromethylbenzoic acid
was obtained from Betapharma Co., Ltd (No. 17]-604. 830 Lane,
Maotai Road, Shanghai, China), thionyl chloride, diethyl ether,
and tetrahydrofuran were distilled before use. All other
chemicals were of analytical grade. [2H9]t-Butylamine was
purchased from CDN Isotopes (88 Leacock St., Pointe-Claire-
dorval; Quebec, Canada H9R 1H1) with isotopic purity of 99.4%.
All reactions were initially optimized using unlabelled
compounds.
Results and discussion
The procedures used for the preparation of [2H9]trantinterol were
modifications of the synthetic route developed by Cheng et al.9 As
shown in Scheme 1, 4-amino-3-chloro-5-trifluoromethylbenzoic
acid (1) reacted with thionyl chloride to give 4-amino-3-chloro-5-
trifluoromethylbenzoyl chloride (2), with no further purification (2)
reacted with diethyl malonate in the presence of magnesium
ethoxide in THF to afford 4-amino-3-chloro-5-trifluoromethylaceto-
phenone (3). The 4-amino-3-chloro-5-trifluoromethylacetophenone
aSchool of Chemical Engineering and Environment, Beijing Institute of
Technology, Beijing 100081, P. R. China
bSchool of Pharmaceutical Engineering, Shenyang Pharmaceutical University,
Shenyang 110016, P. R. China
*Correspondence to: Hongliang Wen, School of Chemical Engineering and
Environment, Beijing Institute of Technology, Beijing 100081, P. R. China.
E-mail: hongliang_wen@hotmail.com
J. Label Compd. Radiopharm 2010, 53 779–781
Copyright r 2010 John Wiley & Sons, Ltd.

H. Wen et al.
NH2
NH2
Cl
CF3
Cl
Cl
Cl
CF3
Mg(C2H5O)2
SOCl2
CH2(COOC2H5)2
COCl
COOH
2
1
NH2
NH2
Cl
CF3
CF3
NaBH4
Br2
CH3COOH
COCH2Br
COCH3
3
4
NH2
NH2
CF3
Cl
CF3
H2NC(CD3)3
OH-
H
C
OH
CH2Br
( 5 )
F3C
HC
CH2
O
6
F3C
NHC(CD3)3
NHC(CD3)3
HCl
H2N
C
H
CH2OH
HCl
H2N
C
H
CH2OH
Cl
Cl
7
8
Scheme 1. This paper describes the preparation of deuterium-labelled trantinterol, a selective b2-adrenoceptor agonist. 4-Amino-3-chloro-5-trifluoromethylbenzoic acid
reacted with thionyl chloride to give 4-amino-3-chloro-5-trifluoromethylbenzoyl chloride. With no further purification it reacted with diethyl malonate in THF to afford 4-
amino-3-chloro-5-trifluoromethylacetophenone. After bromination and reduction, 4-amino-3-chloro-5-trifluoromethylacetophenone was transferred to (4-amino-3-chloro-
5-trifluoromethylphenyl)-ethylene oxide. The reaction between [2H9]t-butylamine and (4-amino-3-chloro-5-trifluoromethylphenyl)-ethylene oxide gave [2H9]trantinterol.
After purification of the free base by flash chromatography, the hydrochloride of [2H9]trantinterol was prepared. The produced [2H9]trantinterol hydrochloride could be
used as a mass spectroscopic standard that was nine mass units separated from the original drug substance.
cold water, basified with 1 M NaOH, and washed with CHCl3
(30 mL). The combined organic fraction was dried over Na2SO4
4-Amino-3-chloro-5-trifluoromethylbenzoyl chloride (2)
4-Amino-3-chloro-5-trifluoromethylbenzoic acid (2.6g, 10.8mmol)
was added to thionyl chloride (10 mL, 140 mmol). The suspension
was heated until the solid dissolved and then refluxed for 2 h.
After cooling to room temperature, the reaction mixture was
evaporated under vacuum and gave crude product 2 as a yellow
solid (2.46 g, 87.9%), m.p. 110–1131C (Lit. 110–1151C).9
and evaporated to give a white solid. Purified by flash
chromatography (petroleum ether:ethyl acetate = 8:1) afforded
3 as a white solid (9.94 g, 82.4%yield), m.p. 123–1251C (Lit.
120–1301C).9 1H-NMR (400 MHz, CDCl3)d: 2.54 (s, 3H), 5.13 (s, 2H),
8.01 (d, 1H, 4J = 1.76 Hz), 8.06 (d, 1H, 4J = 1.76 Hz); 13C-NMR
(100 MHz, CDCl3)d: 26.01, 120.35, 125.27, 126.35, 126.41, 126.62,
132.86, 144.60, 194.51. MS (ESI) m/z: 239 [M11].
4-Amino-3-chloro-5-trifluoromethylacetophenone (3)
4-Amino-3-chloro-5-trifluoromethyl-a-bromoacetophenone
(4)
To a solution of Mg(C2H5O)2 (6.21 g, 54.2 mmol) in anhydrous
THF (15 mL) a mixture of absolute ethanol (4.8 mL), diethyl
malonate (8.1 mL, 53.2 mmol), and THF (5.6 mL) was added
dropwise. The reaction mixture was refluxed for 2 h. A solution
of 2 (13.1 g, 50.8 mmol) in THF (40 mL) was added over 0.5 h and
the mixture was refluxed for another 2 h. After cooling to room
temperature, 2 M sulfuric acid was added dropwise to adjust pH
to 2. The organic phase was separated, evaporated under
reduced pressure to give a yellow oil. A mixture of glacial acetic
acid (45 mL), water (30 mL), and concentrated sulfuric acid
(5.7 mL) was added and refluxed for 5 h. After removal of the
solvent under reduced pressure, the residue was taken up in
Compound 3 (2.125 g, 8.9 mmol) was dissolved in glacial acetic
acid (20 mL). A solution of bromine (0.5 mL, 9.7 mmol) in glacial
acetic acid (4 mL) was added dropwise at 45–501C and kept at
this temperature for 0.5 h. After concentration under reduced
pressure, the residue was taken up in EtOAc (20 mL), washed
with 0.5M NaHCO3 (20 mL) and water (10 mL). The organic layer
was dried over Na2SO4 and evaporated to give a yellow solid.
Purification by flash chromatography (petroleum ether:ethyl
acetate = 10:1) produced 4 as a white solid (1.47 g, 51.9%
yield), m.p. 119–1201C (Lit. 113–1151C).9 1H-NMR (400 MHz,
www.jlcr.org
Copyright r 2010 John Wiley & Sons, Ltd.
J. Label Compd. Radiopharm 2010, 53 779–781

H. Wen et al.
2
2
CDCl3)d: 3.41 (d, 1H, J = 10.4 Hz), 3.50 (d, 1H, J = 10.4 Hz), 4.63 2-(4-Amino-3-chloro-5-trifluoromethylphenyl)-2-[2H9]-t-butyl-
(s, 2H), 7.32 (d, 1H, J = 1.2 Hz), 7.42 (d, 1H, J = 1.2 Hz); 13C-NMR
(100 MHz, CDCl3)d: 29.79, 120.61, 123.21, 127.26, 128.16, 128.62,
133.60, 145.35, 188.20. MS (ESI) m/z: 318 [M11].
4
4
aminoethanol hydrochloride (8)
To a solution of compound 6 (0.134 g, 0.4 mmol) in diethyl ether
(10 mL) was added saturated HCl-isopropanol solution dropwise
at 01C until pH 2. The solution was stirred at this temperature for
0.5 h. The precipitate was collected by filtration, washed with
anhydrous ether, and dried under vacuum to afford 8 as a white
solid (0.133 g, 89.1% yield), m.p. 215–2171C (dec) (Lit. 205–2061C
for the unlabelled analogue).9
2-Chloro-4-oxiran-2-yl-6-(trifluoromethyl)aniline (6)
Compound 4 (1.5 g, 4.7 mmol) was dissolved in MeOH (10 mL)
and water (1 mL) was added. Sodium borohydride (0.258 g,
6.8 mmol) was added in small portions and the reaction mixture
was stirred at room temperature for 3 h, then acidified to pH = 2
with 2 M HCl at 01C. The reaction mixture was concentrated
and the residue was taken up in chloroform (15 mL), washed
Acknowledgements
with water to neutrality. The organic layer was dried over This work was supported by the National High Technology
Na2SO4, concentrated, and purified by flash chromatography Research and Development Program of China (863 Program)
(petroleum ether:ethyl acetate = 10:1) to give 6 as yellow oil (No. 2006AA020604). The authors thank Peking University
1
(0.324 g, 28.8% yield). H-NMR (400 MHz, CDCl3)d: 3.48 (m, 1H), Analytical Instrumentation Center for spectral data.
3.59 (m, 1H), 4.70 (s, 2H), 4.83 (m, 1H), 7.39 (d, 1H, J = 1.6 Hz),
4
7.49 (d, 1H, 4J = 1.6 Hz); 13C-NMR (100 MHz, CDCl3)d: 64.51,
72.62, 120.98, 123.07, 123.11, 125.61, 129.52, 130.57, 141.06.
MS (ESI) m/z: 475 [2M11].
References
[1] B. K. Kobilka, R. A. F. Dixon, T. Frielle, H. G. Dohlman, M. A. Bolanowski,
I. S. Sigal, T. L. Yang-Feng, U. Francke, M. G. Caron, R. J. Lefkowitz,
Proc. Natl. Acad. Sci. USA 1987, 84, 46–50.
[2] M. Johnson, In Beta-Agonists in the Treatment of Asthma
(Eds.: J. F. Costello, R. D. Mann), Parthenon, Carnforth, 1992,
pp. 27–42.
[3] R. J. Lefkowitz, J. Biol. Chem. 1998, 273, 18677–18680.
[4] V. A. Cullum, J. B. Farmer, D. Jack, G. P. Levy, Br. J. Pharmacol.
1969, 35, 141–151.
[5] P. R. Smith, A. E. Heurich, C. T. Leffler, M. M. Henis, H. A. Lyons,
Chest 1977, 71, 129–134.
[6] A. B. Becker, F. E. Simons, F. Estelle, J. Allergy. Clin. Immunol. 1989,
84, 891–895.
[7] D. Bhadoria, P. Bhadoria, J. Postgrad. Med. 1995, 41, 24–26.
[8] L. L. Gan, M. W. Wang, M. S. Cheng, L. Pan, Biol. Pharm. Bull. 2003,
26, 323–328.
2-(4-Amino-3-chloro-5-trifluoromethylphenyl)-2-[2H9]-t-butyl-
aminoethanol (7)
Compound 5 (0.342 g, 1.4 mmol) was dissolved in anhydrous
ethanol (8 mL) and [2H9]t-butylamine (0.164 g, 2 mmol) was
added. The mixture was refluxed for 13 h and concentrated. The
residue was purified by flash chromatography (chloroform:-
methanol = 25:1) to give 7 as a white solid (0.202 g, 44.1% yield),
m.p. 86–881C (Lit. 85–901C for the unlabelled analogue).9 1H-
NMR (400 MHz, CDCl3)d: 1.98 (brs, 2H, –OH, –NH) 3.26 (m, 1H),
4
3.53 (m, 1H), 3.78 (m, 1H), 4.60 (s, 2H), 7.29 (d, 1H, J = 1.4 Hz),
7.40 (d, 1H, 4J = 1.4 Hz); 13C-NMR (100 MHz, CDCl3)d: 57.45, 66.78,
120.82, 122.92, 123.41, 125.63, 131.18, 133.48, 139.89. MS (ESI)
m/z: 320 [M11].
[9] M. S. Cheng, L. Pan, L. Ji, L. Zhang, J. M. Shen, G. L. Song, Z. G. Li,
US 20040266867A1, 2004. Chem. Abstract 2004, 142, 316557.
J. Label Compd. Radiopharm 2010, 53 779–781
Copyright r 2010 John Wiley & Sons, Ltd.
www.jlcr.org