Organic Process Research & Development
Article
Table 6. Detection of Mesityl Oxide in API
heated to the indicated temperature (25−45 °C). After stirring
over a preset time, each sample was taken from the mixture
and then quenched with acetonitrile (0.5% TEA) for HPLC
analysis.
sample class
number of batches mesityl oxide (ppm)
crude product from CH Cl
recrystallization product
2
3
20.4, 22.3
ND
2
2
a
(5-Methyl-2-oxo-1,3-dioxolen-4-yl)methyl 4-(1-Hydroxy-
a
Not detected. GC condition: carrier gas, nitrogen; split ratio, 5:1;
constant flow, 1.0 mL/min; oven program, 35 °C held for 0 min, 10
C/min increased to 150 °C without holding, 40 °C/min increased to
1-methylethyl)-2-propyl-1-[2′-(1H-tetrazol-5-yl)biphenyl-4-
yl]methyl-1H-imidazole-5-carboxylate (1). A three-neck flask
was charged with trityl-protected ester 9 (8.00 g, 9.92 mmol,
°
2
20 °C held for 2 min; FID temperature, 280 °C; injection
1
1
.0 equiv), suspended in acetone (16 mL). Then while stirring,
.56 M hydrochloric acid (16 mL) was added to the
temperature, 80 °C; interface temperature, 90 °C.
suspension. After being stirred at ambient temperature for 3
h, the complete conversion was indicated by TLC analysis
(50% AcOEt/petroleum ether). The reaction mixture was
CONCLUSIONS
■
In this study, NMR and mass spectroscopies were used to
characterize the newly discovered N-Alkyl impurity 10 in
olmesartan medoxomil API and a possible formation
mechanism was proposed. The process was optimized by
employing a QbD approach, and process-control strategies
were established. The multifactor screening was introduced to
ensure the robustness of the process in the design space. In the
synthesis of olmesartan medoxomil 1, we succeeded in
obtaining an almost quantitative deprotection yield while
effectively avoiding the formation of N-Alkyl impurity 10. The
application of headspace-GC also helped to determine that the
genotoxic impurity mesityl oxide in the crude product was
within the acceptable limit and was removed entirely in the
API during the recrystallization process.
In terms of the genotoxic impurities, this research is useful
for researchers developing reaction processes that contain
acetone and acidic environments, including acid salts (which
could lead to a stoichiometric amount of acid), where a mesityl
oxide GTI could occur both in the free form and the alkylated
substrate form. Notably, plenty of small-molecule drugs and
intermediates have nitrogen-containing moieties or nucleo-
philic functional groups; therefore, more attention should be
paid to impurities formed via Michael-type addition between
mesityl oxide and reactive substrates.
diluted with H
another 0.5 h. Triphenylmethanol was filtered and washed with
O (2 × 5 mL). The combined filtrate was diluted with
CH Cl (20 mL), followed by careful neutralization with
aqueous Na CO solution (0.2 g/mL) to adjust the pH to 5.5.
O (32 mL), cooled to 0 °C in an ice bath for
2
H
2
2
2
2
3
The organic layer was separated, and the aqueous layer was
extracted with CH Cl (3 × 10 mL). The combined organic
2
2
layer was washed with H O (30 mL), dried over Na SO , and
2
2
4
condensed in vacuo to afford an off-white solid. Recrystalliza-
tion from acetone afforded olmesartan medoxomil as a pure
white crystalline powder (4.38 g, 80.1% yield).
(5-Methyl-2-oxo-1,3-dioxol-4-yl)methyl 4-(2-Hydroxypro-
pan-2-yl)-1-((2′-(2-(2-methyl-4-oxopentan-2-yl)-2H-tetra-
zol-5-yl)-[1,1′-biphenyl]-4-yl)methyl)-2-propyl-1H-imida-
zole-5-carboxylate (10). To a three-neck flask, olmesartan
medoxomil (1.13 g, 2.02 mmol, 1.0 eq) and mesityl oxide
(2.98 g, 30.31 mmol, 15 equiv) were added. BF ·Et O (0.32 g,
3
2
2.23 mmol, 1.1 equiv) was added dropwise to the reaction
mixture. After being stirred at 50 °C for 5 h, the complete
conversion was indicated by TLC analysis (50% AcOEt/
petroleum ether). While stirring, H O (10 mL) was added
2
dropwise to the reaction mixture, followed by extraction with
ethyl acetate (3 × 10 mL). The organic layer was combined,
washed with brine (10 mL), dried over Na SO , and
2
4
EXPERIMENTAL SECTION
condensed in vacuo to afford a yellow oil. The crude product
was purified using short column chromatography (50%
AcOEt/petroleum ether) to eliminate the mesityl oxide. The
product was obtained as a light-yellow oil (1.10 g, 82.9%
yield).
■
HPLC Conditions. Analytical HPLC was performed on a
Thermo Fisher Vanquish Core 01 equipped with a VC-D40-A
VWD detector using a Waters Symmetry C8 (3.5 μm, 4.6 mm
100 mm) column or a Fortis Xi C18 (5 μm, 4.6 mm × 250
mm) column. Details of the exact method are given in Figure
×
2
.
ASSOCIATED CONTENT
■
GC Conditions. Headspace-GC was performed on a
*
sı Supporting Information
Shimadzu Nexis GC-2030 equipped with a HS-20 headspace
sampler using a SH-Rtx-1 30 m × 0.25 mm × 0.25 μm column.
Details of the exact method are given in Table 6.
1
5
15
N NMR Spectrum. N NMR was performed on a Bruker
Advance Neo operating at a proton-resonance frequency of
00.17 MHz. The relaxation delay was 10 s, the acquisition
MS, H NMR, 13C NMR, and 2D NMR of 10; 15
1
N
NMR of 4, 15 and 10; SCXRD of 4 and 15; NMR signal
assignments; screening DoE parameters; DoE ANOVA
tables; DoE residual diagnostics plots; and HPLC data
6
time was 0.5 s, 2000 scans were accumulated for 4 (400 mg
dissolved in 600 μL CDCl ) and 10 (425 mg dissolved in 600
μL CDCl ), and 4000 scans were accumulated for 15 (150 mg
3
3
dissolved in a mixture of 200 μL CDCl and 500 μL CH Cl ).
3
2
2
The standard was MeNO (80 μL dissolved in 600 μL CDCl ).
DoE Software. DoE analysis was carried out using Design
Expert (Version 11).
2
3
■
Corresponding Author
Syntheses. General Procedure of the DoE Experiment.
To each round-bottom flask was added trityl-protected ester 9
Taizhi Wu − State Key Lab of New Drug & Pharmaceutical
Process, Shanghai Institute of Pharmaceutical Industry,
(
0.50 g, 0.624 mmol, 1.0 equiv) and acetone (2−5 mL).
Hydrochloric acid with the indicated concentrations (1.04−7.8
M, 0.4−1.5 mL) was quickly added to the mixture, and then
1
120
Org. Process Res. Dev. 2021, 25, 1112−1122