Synthesis of deuterium-labelled etravirine

Article abstract of DOI:10.1002/jlcr.1882

This study describes the synthesis of deuterium-labelled etravirine. Etravirine labelled with six deuteriums was prepared in eight steps starting from phenol with excellent chemical purity and isotopic enrichment. It provides important internal standard f

Full text of DOI:10.1002/jlcr.1882

Research Article
Received 3 November 2010,
Revised 9 January 2011,
Accepted 10 January 2011
Published online 26 April 2011 in Wiley Online Library
(wileyonlinelibrary.com) DOI: 10.1002/jlcr.1882
Synthesis of deuterium-labelled etravirine
Ã
Wei Wang,a Wenchao Wu,b Zucheng Shen,a and Liqin Chenc
This study describes the synthesis of deuterium-labelled etravirine. Etravirine labelled with six deuteriums was prepared in
eight steps starting from phenol with excellent chemical purity and isotopic enrichment. It provides important internal
standard for the clinical studies of etravirine.
Keywords: deuterium; labelled; synthesis; etravirine
hydrogen had ceased, the mixture was stirred for 30 min at rt.
The cooled (01C) reaction mixture was treated with chloro-
Introduction
Etravirine, a second-generation non-nucleoside reverse transcrip-
tase inhibitor (NNRTI), is highly potent and effective against wild-
type and drug-resistant HIV-1 variants. It was granted accelerated
approval by the FDA (18 January 2008) and marketed under the
name IntelenceTM. In clinical development, etravirine has shown
durable efficacy and, with the exception of rash, a safety profile
similar to placebo. Furthermore, the nature and magnitude of
adverse events observed with etravirine suggest that the drug
may offer improved tolerability over first-generation NNRTIs.
In addition it could offer safety benefits over first-generation
NNRTIs in early experienced patients. Etravirine can be used in
combination with other antiretrovirals such as boosted protease
inhibitors and raltegravir with little potential for additional
toxicity. Therefore, given this favorable safety profile along with
its enhanced barrier to the development of resistance and
demonstrated efficacy, etravirine provides an important treat-
ment option for HIV-infected, treatment-experienced patients.
The safety of etravirine in treatment-naive patients is being
explored in ongoing clinical trials. New trials are also investigating
the safety and tolerability of etravirine in treatment-experienced
children and adolescents.1–5 To support the pharmacokinetic
and metabolism studies of etravirine, a stable isotope-labelled
standard was needed. This study describes the experimental
details for the preparation of etravirine labelled with six
deuteriums with high chemical purity and isotopic enrichment.
methylether (33.00 g, 409.9 mmol). It was stirred for overnight
at room temperature, before an ice-cooled saturated NH4Cl
solution (200 ml) was added. The mixture was extracted with
diethyl ether (3 ꢀ 200 ml). The combined organic layers were
washed with 1 M NaOH solution (100 ml), water (200 ml), brine
and dried over Na2SO4. After evaporation of the solvent, the
residue was purified by chromatography on silica gel (800 g)
column, eluting with petroleum ether, to give (2) as colorless oil
(20.00 g, 45.4%).
1H NMR (300 MHz, CDCl3):d 7.29 (m, 2H), 7.01 (m, 3H), 5.17
(s, 2H), 3.48 (s, 3H).
Synthesis of 1-(methoxymethoxy)-2-½2H3ꢁmethylbenzene (3)
To a solution of n-BuLi in hexane (24 ml 2.2 M, 52.8 mmol) under
nitrogen was added slowly TMEDA (6.14 g, 52.8 mmol) at room
temperature. The solution was then cooled in an ice bath and
(2) (5.00 g, 36.2 mmol) was added dropwise over 15 min. After
stirring for 1 h, CD3I (7.65 g, 52.8 mmol) was added dropwise.
After addition, the reaction mixture was allowed to warm to
room temperature over 1 h and then quenched with water
(20 ml). The solution was extracted with diethyl ether (200 ml).
The diethyl ether extracts were washed with 2 M HCl (50 ml),
water (3 ꢀ 200 ml), brine (200 ml) and dried over Na2SO4. After
concentration, it afforded crude (3) (5.50 g, 97.8%) as a light
yellow oil, which was used without further purification.
1 H NMR (300 MHz, CDCl3):d 7.14 (t, J = 6 Hz, 2H), 7.04
(d, J = 6 Hz, 1H), 6.91 (t, J = 9 Hz, 1H), 5.20 (s, 2H), 3.49 (s, 3H).
Experimental
General
All reagents were obtained from Sigma-Aldrich and CDN Isotope.
Mass spectra were recorded using a Quattro micro API mass
spectrometer. 1 H NMR spectra were recorded on a Bruker
300MHz instrument. Chemical purities were determined by an
Agilent 1200 HPLC with a XDB-C18 column, 5 mm, 4.6 ꢀ 150 mm.
aSchool of Pharmaceutical Sciences, Nanjing University of Technology,
5 Xinmofan Road, Nanjing, Jiangsu 210009, P. R. China
bSchool of Biotechnology and Pharmaceutical Engineering, Nanjing University
of Technology, 5 Xinmofan Road, Nanjing, Jiangsu 210009, P. R. China
cHi-Tech Research Institute and State Key Laboratory of Materials-Oriented
Chemical Engineering, Nanjing University of Technology, 5 Xinmofan Road,
Nanjing, Jiangsu 210009, P. R. China
Synthesis of (methoxymethoxy)benzene (2)
A 60% dispersion of sodium hydride in oil (15.00 g, 375.0 mmol
NaH) was suspended in dry DMF (50 ml) under nitrogen. The
cooled (01C) suspension was slowly treated with a solution of (1)
(30.00 g, 318.8 mmol) in dry DMF (50 ml). After the evolution of
*Correspondence to: Liqin Chen, Hi-Tech Research Institute and State Key
Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of
Technology, 5 Xinmofan Road, Nanjing, Jiangsu 210009, P. R. China.
E-mail: liqin_chen@hotmail.com
J. Label Compd. Radiopharm 2011, 54 371–373
Copyright r 2011 John Wiley & Sons, Ltd.

W. Wang et al.
Synthesis of 1-(methoxymethoxy)-2,6-½2H6ꢁdimethylbenzene (4)
1H NMR (300 MHz, CDCl3):d 6.97 (d, J = 9 Hz, 2H), 6.75
(t, J = 9 Hz, 1H), 4.60 (s, 1H).
To a solution of n-BuLi in hexane (23 ml 2.2 M, 50.6 mmol) under
nitrogen was added slowly TMEDA (5.88 g, 50.6 mmol) at room
temperature. The solution was then cooled in an ice bath and
crude (3) (5.34 g, 34.4 mmol) was added dropwise over 15 min.
After stirring for 1 h, CD3I (7.33 g, 50.6 mmol) was added drop-
wise. After addition, the reaction mixture was allowed to warm
to room temperature over 1 h and then quenched with water
(20 ml). The solution was extracted with diethyl ether (200 ml).
The diethyl ether extracts were washed with 2 M HCl (50 ml),
water (3 ꢀ 200 ml), brine (200 ml) and dried over Na2SO4. After
concentration, it afforded crude (4) (5.63 g, 95.0%) as a light
yellow oil, which was used without further purification.
Synthesis of 4-bromo-2,6-½2H6ꢁdimethylphenol (6)
To a solution of (5) (0.93 g, 7.3 mmol) in glacial acetic acid (5 ml)
cooled in an ice bath was added dropwise a solution of bromine
(1.16 g, 7.3 mmol) in glacial acetic acid (5 ml). The reaction
mixture was stirred for 20 min at room temperature, and then
poured into 10 ml of 1% NaHCO3 solution. The solution was
stirred for 10 min and extracted with diethyl ether (3 ꢀ 20 ml).
The combined organic layers were washed with water (50 ml),
brine (50 ml), and dried over Na2SO4. After concentration, it
gave (6) (1.33 g, 88.7%) as off-white solid.
1H NMR (300 MHz, CDCl3):d 7.10 (s, 2H), 4.61 (s, 1H).
Synthesis of 2,6-½2H6ꢁdimethylphenol (5)
Synthesis of 4-hydroxy-3,5-½2H6ꢁdimethylbenzonitrile (7)
A solution of crude (4) (5.80 g, 33.7 mmol) in methanol (200 ml) and
2 M HCl (75 ml) was heated at 901C for 4 h. TLC analysis showed A suspension of (6) (1.33 g, 6.4 mmol) and CuCN (0.66g, 7.4 mmol)
that the reaction was complete. Methanol was removed under in dry DMF (5ml) was stirred at 1541C for 5 h. TLC analysis
reduced pressure, and the residue was extracted with diethyl ether indicated that the reaction was complete. The reaction mixture
(3 ꢀ 100 ml). The combined diethyl ether extracts were washed was cooled to room temperature and then poured into a mixture
with water (3 ꢀ 100 ml), brine (100 ml) and dried over Na2SO4. of FeCl3 (1.60 g), concentrated HCl (0.66 ml) and water (5ml). The
After concentration, the residue was purified by chromatography resulting slurry was filtered, washed with water (5ml) and ethanol
on silica gel (50 g) column, eluting with petroleum ether, to give (5) (20ml). The filtrate was concentrated, and then 1 M NaOH solution
(1.26 g, 29.2%) as a colorless crystalline solid.
(50ml) was added. The resulting mixture was stirred at 501C for
NaH
n-BuLi
CD3I
n-BuLi
CD3I
CD3
ClCH2OCH3
OH
O
O
OCH3
OCH3
1
2
3
Br
HCl
Br2
CD3
D3C
CD3
D3C
D3C
CD3
CH3OH
AcOH
O
OH
OCH3
OH
4
5
6
CN
H
Cl
Br
N
N
CuCN
NMP
NaH
+
DMF
D3C
CD3
N
CN
OH
Cl
7
8
H
N
H
Cl
Br
N
O
H2N
Br
D3C
N
O
N
N
N
CN
CN
NH3/1,4-dioxane
D3C
CD3
CD3
CN
CN
9
10
Scheme 1.
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Copyright r 2011 John Wiley & Sons, Ltd.
J. Label Compd. Radiopharm 2011, 54 371–373

W. Wang et al.
30 min. The solid was filtered and washed with water (20ml). 1 M with same procedure produced 1-(methoxymethoxy)-2,6-[2H6]di-
HCl was added to the filtrate until no more precipitate was methylbenzene (4). We tried to make (4) from (2) in one step
formed. The precipitate was filtered and dried over P2O5 under through using excess reagents. It was not successful. The reaction
vacuum overnight to afford (7) (0.57 g, 58.5%) as yellow solid.
1H NMR (300 MHz, CDCl3):d 7.29 (s, 2H), 5.20 (s, 1H).
only formed a small amount of compound (4). The major product
was compound (3). After standard hydrolysis of (4) with 2 M HCl in
methanol, the key intermediate 2,6-[2H6]dimethylphenol (5) was
Synthesis of 4-(5-bromo-6-chloro-2-(4-cyanophenylamino)- obtained in over 99% deuterium enrichment and 27% overall
pyrimidin-4-yloxy)-3,5-½2H6ꢁdimethylbenzonitrile (9)
yield from (2) over the three steps. Bromination of (5) with
bromine in glacial acetic acid gave 4-bromo-2,6-[2H6]dimethyl-
To a sealed tube containing a solution of (7) (0.36 g, 2.4 mmol) in
phenol (6).12 Treatment of compound (6) with CuCN at reflux in
1,4-dioxane (2.2 ml), was added sodium hydride (0.10 g,
DMF, and then quenching with a solution of FeCl3 generated
2.5 mmol). The mixture was stirred at rt for 2 min. NMP (2.20 g,
4-hydroxy-3,5-[2H6]dimethylbenzonitrile (7).12 The reaction of
22.2 mmol) was added, and the resulting mixture was stirred
compound (7) and commercially available 4-(5-bromo-4,6-dichlor-
for an additional 10 min at room temperature. Compound (8)
opyrimidin-2-ylamino)benzonitrile (8) in the presence of sodium
(0.74 g, 2.2 mmol) was added to the mixture, and the vessel was
hydride and 1-methyl-2-pyrrolidinone (NMP) produced 4-(5-
sealed and heated to 1551C for a period of 6 h. After cooling to
bromo-6-chloro-2-(4-cyanophenylamino)pyrimidin-4-yloxy)-3,5-
room temperature, the mixture was diluted with water (15 ml)
[2H6]dimethylbenzonitrile (9).6 Efforts were made to improve the
and the crude product was filtered off and washed with
yield for this step through optimizing reaction temperature and
additional water (10 ml). The crude solid was purified by
time. The best yield of 83% was obtained by heating the reaction
chromatography on silica gel (100 g) column, eluting with
at 1551C for 6 h. The ammoniation of compound (9) with 0.5 M
CH2Cl2/Hexane (1:1), to afford (9) (0.83 g, 83.6%) as white solid.
NH3/1,4-dioxane in a sealed tube afforded [2H6]etravirine (10) in
1H NMR (300 MHz, DMSO-d6):d 10.60 (s, 1H), 7.82 (s, 2H), 7.50
41% yield.13 It was observed that if NH3 was allowed to leak out of
(d, J = 6 Hz, 2H), 7.37 (d, J = 6 Hz, 2H).
the reaction, a significantly reduced yield was obtained.
After purification by flash chromatography and recrystalliza-
Synthesis of ½2H6ꢁetravirine (10)
tion, the desired product (10) was obtained with over 97%
Compound (9) (0.41 g, 0.9 mmol) was dissolved in 0.5 M NH3/1,4- chemical purity and over 99% deuterium enrichment, which
dioxane solution(15 ml, 7.5 mmol) in a sealed tube. The vessel provided an excellent internal standard for LC-MS-MS studies.
was heated to 1501C for a period of 24 h. After cooling to room
temperature, the reaction mixture was concentrated in vacuo, Acknowledgements
and purified by chromatography on silica gel (50 g) column,
eluting with CH2Cl2, to afford desired product, which was
recrystallized from CH3OH/THF (20 ml, 1:1) to yield (10) (0.16 g,
41.0%) as white solid.
This work is financially supported by the San Chuang Joint
Project of Nanjing University of Technology and Nanjing
New&High Technology Industry Development Zone.
1H NMR (300 MHz, DMSO-d6):d 9.58 (s, 1H), 7.74 (s, 2H), 7.54
(d, J = 9 Hz, 2H), 7.42 (d, J = 9 Hz, 2H), 7.11 (s, 2H). MS-EI (m/z):
439.1 (95), 440.1 (22), 441.1 (100), 442.0 (22). HPLC (XDB-C18,
CH3OH/10 mmol/l CH3COONH410.03% TEA = 76/24, 1.0 ml/min):
tR 4.8 min (497.7%). Isotopic enrichment determined by NMR
spectroscopy was over 99.0%.
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J. Label Compd. Radiopharm 2011, 54 371–373
Copyright r 2011 John Wiley & Sons, Ltd.
www.jlcr.org