Preparation of Dolutegravir Intermediate Diastereomer

Article abstract of DOI:10.1002/jhet.3588

A convenient method was developed to prepare the diastereomer of dolutegravir tricyclic intermediate in the catalysis of EDCI/DMAP in up to 87% yield. Different solvents, temperature, and times were optimized. The synthesized diastereomer 6′ could be used as a standard for the industrial manufacture requirement of dolutegravir active pharmaceutical ingredient.

Full text of DOI:10.1002/jhet.3588

Month 2019
Preparation of Dolutegravir Intermediate Diastereomer
a
a
a
a
b
*
*
Liangye Long, and Yuhe Wang
Xianheng Wang, Song Chen, Changkuo Zhao,
aDepartment of Pharmacology and Key Laboratory of Basic Pharmacology of Ministry of Education, Zunyi Medical
University, No. 6 Xue Fu West Road, Zunyi 563003, China
bDepartment of Pharmacy, Zunyi Medical University Affiliated Hospital, No. 139 Dalian Road, Zunyi 563003, China
*E-mail: zck7103@hotmail.com; 1149076068@qq.com
Received December 8, 2018
DOI 10.1002/jhet.3588
Published online 00 Month 2019 in Wiley Online Library (wileyonlinelibrary.com).
A convenient method was developed to prepare the diastereomer of dolutegravir tricyclic intermediate in
the catalysis of EDCI/DMAP in up to 87% yield. Different solvents, temperature, and times were optimized.
The synthesized diastereomer 60 could be used as a standard for the industrial manufacture requirement of
dolutegravir active pharmaceutical ingredient.
J. Heterocyclic Chem., 00, 00 (2019).
INTRODUCTION
of intermediate 6 (Fig. 1). Herein, we described a
convenient preparation method for this compound.
AIDS became a serious global public health and social
problem for a long time [1]. It has been found that
integrase plays an important role in the replication of
HIV-1 virus because there is no functional analogue of
integrase in human body, and this enzyme has gradually
become an ideal target for anti-HIV drugs. In recently, a
number of integrase inhibitors including raltegravir,
elvitegravir, dolutegravir, cabotegravir, and bictegravir
have been launched or approved to enter into clinic
phases [2–5].
RESULTS AND DISCUSSION
A facile and direct process to prepare dolutegravir was
developed by Glaxo SmithKline, which was started from
4-methoxyacetoacetic acid methyl ester [12]. In this
modified process, the compound 4 was synthesized in a
total of 36% yield for a continuous four steps. Similarly,
without additional separation and purification of aldehyde
5, the key intermediate 6, (4S,12aR)-4-methyl-7-(meth
yloxy)-6,8 -dioxo-3,4,6,8,12,12a-hexahydro[1,3]oxazolo
Dolutegravir (trade name Tivicay), (4R,12aS)-N-(2,4-dif
luorobenzyl)-7-hydroxy-4-methyl-6,8-dioxo-3,4,6,8,12,12
a-hexahydro-2H-pyrido[10,20:4,5]pyrazino[2,1-b][1,3]oxaz
ine-9-carboxamide, was developed by Viiv Healthcare and
Glaxo SmithKline as a second generation of integrase
inhibitor [6], which was first approved by Food and Drug
Administration (FDA) in August 2013. Compared with the
first generation of integrase inhibitors, raltegravir and
elvitegravir, dolutegravir possesses a higher barrier for
developing resistance, as well as that the clinical efficacy
for AIDS treatment is better than raltegravir [7,8].
Recently, there is a great need for process research [9–15]
for the forthcoming industrial manufacture. Hence, an
efficient synthetic route of dolutegravir is urgently needed.
In this course, it was found that the existence of other
enantimers of dolutegravir contaminated the quality of
final product. Therefore, in order to meet the requirement
of API manufacture, it is necessary to prepare sufficient
amounts of dolutegravir enantimers for impurity profiling.
Among of these enantiomeric impurities, dolutegravir
diastereomer could be easily prepared from diastereomer
[3,2-a]pyrido[1,2-d]pyrazine-9-carboxylic
acid
was
smoothly obtained in a good yield upon treatment with
R-2-aminobutanol; and after the coupling with 2, 4-
difluorobenzylamine and de-methylation, the target
compound dolutegravir was obtained in a medium yield
(Scheme 1).
As an important scaffold of dolutegravir, compound 6
controls the optical purity of the drug. Therefore, on the
one hand, how to improve and optimize stereo-selectivity
of compound 6 is becoming a critical problem for the
whole industrial production (Scheme 1); on the other
hand, it seems that we can also easily obtain dolutegravir
intermediate diastereomer 60 in the same reaction.
In order to prepare diastereomer 60, the first thought
occurring to our mind is that diastereomer 60 could be
isolated from the cyclization reaction of compound 5
with (R)-3-amino-1-butanol, which theoretically can
produce two chiral centers and one pair of diastereomers
(Scheme 2). However, result shows that this reaction
produces enantiomer
6
stereo-selectively with
a
© 2019 Wiley Periodicals, Inc.

X. Wang, S. Chen, C. Zhao, L. Long, and Y. Wang
Vol 000
Figure 1. Structure of dolutegravir, intermediate 6 and 60.
Scheme 1. Synthetic route for dolutegravir [12].
Scheme 2. Preparation of intermediate 6 and diastereomer 60.
diastereoismer ratio >99:1. Only traces of diastereomer 60
can be detected by thin-layer chromatography (TLC).
More attention was then paid on the conversion of
intermediate 6. It was expected that the carboxylic acid
6 could undergo the ring-opening and ring-cycling
reaction in the proton acid condition, which will
finally lead to the formation for its diastereomer 60
(Scheme 3).
Scheme 3. Proposed synthetic route for diastereomer 60
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2019
Preparation of Dolutegravir Intermediate Diastereomer
Different coupling reagents, solvents, and reaction
temperature were then tried to optimize this reaction. And
the best result shows that the diastereomer 60 can be
prepared in up to 50% yield which is promoted by
EDCI/DMAP in a sealed tube reaction (Table 1, entry 7).
A mechanism was then proposed to explain this reaction
(Scheme 4). The acetal 6 was hydrolyzed in the acid
condition to form carbon cation 9. Consequently, the
carbon cation 9 will be attacked by OH-group from two
sides (a and b) to form configuration keeping and
conversing compound correspondingly.
400 MHz spectrometer (400 and 100 MHz, respectively)
using CDCl3, or DMSO-d6 as solvents with
tetramethylsilane as an internal standard. Chemical shifts
were reported as δ (ppm) and spin–spin coupling
constants as J (Hz) values. The mass spectra (MS) were
recorded on a Finnigan MAT-95 mass spectrometer. TLC
plates (GF 254) were bought from Branch Qingdao
Haiyang Chemical Plant. IR spectra were measured on
Fourier infrared spectrometer (Nicolet, USA, KBr tablet).
EXPERIMENTAL
MATERIALS AND METHODS
Synthesis of 1-[2,2-bis(methoxy)ethyl]-5-(methoxy)-6-
[(methoxy)-carbonyl]-4-oxo-1,4-dihydro-3-pyridinecarboxylic
acid 4.
Methyl 4-methoxyacetoacetate (8 m,
Melting points were taken on a Mettler Toledo FP62
melting point apparatus, uncorrected and reported in
61.80 mmol) and N,N-dimethylformamide dimethylacetal
(DMF-DMA, 9.6 mL, 72.26 mmol) were stirred at room
temperature for 1.5 h to form a brown mixture containing
1
degrees. H and 13C nuclear magnetic resonance (NMR)
spectra were recorded on a Varian Unity INOVA
Table 1
Optimization for the preparation of diastereomer 60.
Entry
Base
Solvent
Temp/Time
Yield (60)
Yield (6)
1
2
3
4
5
6
7
8
CH3SO3H
ECDI
ECDI
ECDI
-
ECDI
ECDI
CDI
-
-
DCM
DCM
DCM
Chloroform
Chloroform
Chloroform
Chloroform
Chloroform
Reflux/3 days
Reflux/3 days
Reflux/3 days
Reflux/3 days
Reflux/3 days
0
0
5%
0
100%
100%
95%
100%
100%
80%
DMAP
-
DMAP
DMAP
DMAP
DMAP
0
Reflux/3 days
20%
87%
0
70°C (sealed tube)/3 days
70°C (sealed tube)/3 days
13%
100%
Scheme 4. Proposed reaction mechanism for the formation of diastereomer 60. [Color figure can be viewed at wileyonlinelibrary.com]
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

X. Wang, S. Chen, C. Zhao, L. Long, and Y. Wang
Vol 000
the target compound 1 (Rf = 0.14, ethyl acetate/petroleum
ether = 5/1). The resulted mixture was added with
methanol (20 mL) and aminoacetaldehyde dimethyl
acetal (6.68 mL, 61.31 mmol). After stirring at room
temperature for 1 h, the solution turned reddish and TLC
showed a new point. Compound 2 (Rf = 0.56, ethyl
acetate). The reaction was stopped and evaporated to give
a red-brown oily liquid containing the crude product of
compound 2; 45.2 mL of methanol and 18.344 g
(155.34 mmol) of dimethyl oxalate were dissolved. After
the dimethyl oxalate was completely dissolved, the
temperature was controlled at 25 under an ice-water bath.
After adding lithium hydride LiH 0.864 g (108.67 mmol)
in batches, the solution turns into a brownish-red
suspension. After addition, the reaction solution is placed
in an oil bath at 40°C for 14 h, and the solution changes
from a suspension to a brick red solution. A new spot
occurred in TLC (compound 3, Rf = 0.23, ethyl acetate).
The reaction solution was cooled to ꢀ5°C and anhydrous
lithium hydroxide (5.94 g, 123.8 mmol) was added while
the temperature was controlled at 3–5°C. The reaction
solution changed from brick red to orange-yellow
suspension and reacted for 2 h. The reaction was
quenched by the addition of 2N hydrochloric acid
(146.8 mL), and the reaction temperature was controlled
below 5°C in an ice-water bath. Add 180 mL of ethyl
acetate to the extraction, raise the temperature to 20°C,
filter the lower solid by filtration, and discard it; collect
the liquid phase and separate the liquid; add 90 mL of
water to the organic phase, concentrate under reduced
pressure, filter by suction, and the filter cake was
collected and dried in vacuo at 50°C to obtain compound
4 (6.93 g, 35.87%) as a colorless solid. Rf = 0.441
(dichloromethane/methanol = 20/1 with 0.5% glacial
acetic acid). The reaction solution was concentrated under
reduced pressure and a pale yellow solid precipitated;
25.5 mL of DCM was added and redissolved. After
adding 25.5 mL of 1N hydrochloric acid, the liquid was
separated and traced by TLC. The organic phase was
collected, and the aqueous layer was extracted twice with
25.5 mL of DCM and organic. Combine under reduced
pressure and concentrate. Add 7 mL of methanol and
evaporate to a light yellow solid. After adding 13 mL of
methanol and heating to reflux for 4 h, the reaction was
stopped, and the mixture was slowly cooled to 20°C and
allowed to stand for 15 h. After suction filtration, the
cake was collected and vacuum dried at 50°C to give
compound 6 (1.72 g, 52.12%) as a pale yellow solid.
Rf = 0.42 (dichloromethane/methanol = 20/1 with 0.5%
glacial acetic acid). [α]25 = ꢀ36.57 (c = 5.0, CH3OH). IR
(KBr) ν (cmꢀ1) = 3410, 2972, 2876, 1630, 1449, 1275,
1
1093, 775. H-NMR (400 MHz, CDCl3) δ = 15.02 (d,
J = 16.7 Hz, 1H), 8.42 (d, J = 11.8 Hz, 1H), 5.29 (dd,
J = 5.4, 3.9 Hz, 1H), 4.97 (q, J = 6.4 Hz, 1H), 4.52 (t,
J = 4.5 Hz, 1H), 4.43 (dd, J = 13.6, 3.5 Hz, 1H), 4.26
(dd, J = 13.6, 5.8 Hz, 1H), 4.13 (d, J = 4.5 Hz, 1H), 4.05
(d, J = 13.0 Hz, 2H), 3.98 (d, J = 2.2 Hz, 3H), 3.96 (d,
J = 2.9 Hz, 1H), 3.39 (s, 3H), 2.22–2.09 (m, 1H), 1.52
(dd, J = 13.9, 1.6 Hz, 1H), 1.35 (d, J = 7.0 Hz, 2H)13C-
NMR (100 MHz, CDCl3) δ = 173.23, 164.17, 162.24,
149.45, 144.64, 135.03, 130.77, 130.73, 130.67, 119.35,
111.34, 111.30, 111.13, 111.09, 103.81, 102.73, 60.78,
56.81, 55.72, 53.47, 36.60, 36.56. HRMS (ESI-TOF):
309.1166 [M + 1].
Synthesis of (4S,12aS)-4-methyl-7-(methyloxy)-6,8-dioxo-
3,4,6,8,12,12a-hexahydro[1,3]oxazolo [3,2-a]pyrido [1,2-d]
pyrazine-9-carboxylic acid (60). A solution of compound
(dichloromethane/methanol
= 40/1, containing 0.5%
glacial acetic acid). 1H-NMR (400 MHz, CDCl3)
δ = 8.40–8.42 (m, 1H), 4.49–4.53 (m, 1H), 4.10–4.14 (m,
2H), 3.98 (s, 3H), 3.97 (s, 3H), 3.38 (s, 3H), 3.37 (s,
3H); 13C-NMR (100 MHz, CDCl3) δ = 174.86, 165.99,
161.60, 148.65, 145.47, 136.59, 116.53, 102.31, 60.97,
57.26, 55.97, 53.77.
6 (67.6 mg, 0.23 mmol), EDCI (155.5 mg, 0.81 mmol),
and DMAP (11.9 mg, 0.1 mmol) in chloroform (15 mL)
was stirred at 70°C in a sealed tube for 3 days. After
being cooled to the room temperature, the reaction
mixture was quenched with the addition of water (5 mL).
The separated aqueous phase was extracted with DCM (2
*20 mL) and the combined organic phases were dried
over MgSO4. The solvent was evaporated completely
under vacuo, and the residue was purified by
chromatography through a silical gel column using DCM:
CH3OH = 97: 3 as eluent to give the title product (60,
58.8 mg, 87%) as a pale yellow solid. Rf = 0.23 (DCM:
CH3OH = 97: 3). m.p. 86.2°C. [α]25 = ꢀ28.38 (c = 4.96,
Synthesis of (4S,12aR)-4-methyl-7-(methyloxy)-6,8-dioxo-
3,4,6,8,12,12a-hexahydro[1,3]oxazolo[3,2-a]pyrido[1,2-d]
pyrazine-9-carboxylic acid (6).
Compound 4 (3.38 g,
107.24 mmol) was dissolved in 33 mL of acetonitrile at
room temperature. To the solution was added acetic acid
(3 mL) and methanesulfonic acid (0.21 mL, 3.24 mmol).
The solution was heated to 60°C for 20 h. A solution of
R-3-amino-1-butanol (1.44 mL, 1.34 g) in acetonitrile
(2.25 mL) was slowly added to the previous reaction
solution. The reaction solution gradually changed from
light yellow to brownish yellow, and the solution was
white after the addition was completed. The suspension
was heated to 64°C and continued to stir for 18.5 h. TLC
1
CH3OH). H-NMR (400 MHz, CDCl3) δ = 7.97 (s, 1H),
5.20 (s, 1H), 4.97–4.81 (m, 1H), 4.33–4.10 (m, 3H), 3.99
(dd, J = 13.3, 6.1 Hz, 1H), 3.92 (s, 4H), 2.30 (d,
J = 9.5 Hz, 1H), 2.08 (dt, J = 11.6, 6.8 Hz, 1H), 1.27 (dt,
J = 9.3, 4.6 Hz, 5H). 13C-NMR (100 MHz, CDCl3)
δ = 172.29, 164.55, 155.84, 143.33, 128.06, 117.71,
76.10, 62.44, 60.88, 53.35, 44.35, 29.66, 15.98, 14.29.
showed
a new spot. Compound 5, Rf = 0.42
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2019
Preparation of Dolutegravir Intermediate Diastereomer
REFERENCES AND NOTES
CONCLUSIONS
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A convenient method was developed to prepare the
diastereomer of dolutegravir tricyclic intermediate
catalyzed by EDCI/DMAP in up to 50% yield. The
synthesized diastereomer 60 could be used not only as a
standard for the industrial manufacture requirement of
dolutegravir but also as a key building block for the
preparation of dolutegravir diastereomer derivatives.
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WO2011119566
AUTHOR CONTRIBUTIONS
Dr. Xianheng Wang designed the study and Dr.
Changkuo Zhao was responsible for the synthetic route
design. Mr. Song Chen validated the procedure and
prepared the sample. Ms. Liangye Long collected and
analyzed the data. Prof. Yuhe did some administration on
this project. All authors gave the approval for the final
submission.
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FUNDING
This research was funded by Guizhou Provincial
Department of Science and Technology, grant numbers
QKHSY [2015]3030 and QKHSY [2017]2844, and
Zunyi Medical University, grant number [2013] F-680.
[15] Gudisela, M. R.; Bommu, P.; Navuluri, S.; Mulakayala, N.
Chem Sel 2018, 3, 7152.
Acknowledgments. We thank for the financial support from
Science and Technology Department of Guizhou Province and
we are also grateful Dr. Yuqi He0s useful explanation on HPLC
and LC/MS spectra data.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet