Pioglitazone impurities

Article abstract of DOI:10.1691/ph.2007.8.6720

Methods of preparation of API pioglitazone were discussed from the point of view of impurities occurrence. Four real impurities (I-IV) of pioglitazone were prepared and characterized by means of NMR spectroscopy.

Full text of DOI:10.1691/ph.2007.8.6720

ORIGINAL ARTICLES
Department of Technology of Organic Compunds1, Faculty of Chemical Technology, Univerzity of Pardubice, Zentiva a.s.2,
Praha, the Czech Republic
Pioglitazone impurities
1
2
2
1
ˇ
J. Richter , J. Jirman , J. Havl´ıcek , R. Hrdina
Received September 25, 2006, accepted December 28, 2006
Jindrich Richter, Univerzity of Pardubice, Faculty of Chemical Technology, Department of Technology of
Organic Compounds, TP Doubravice, Studentska´ 95, 532 10, Pardubice, Czech Republic
Jindrich.richter@zentiva.cz josef.jirman@zentiva.cz
Pharmazie 62: 580–584 (2007)
doi: 10.1691/ph.2007.8.6720
Methods of preparation of API pioglitazone were discussed from the point of view of impurities occur-
rence. Four real impurities (I–IV) of pioglitazone were prepared and characterized by means of NMR
spectroscopy.
1. Introduction
glitazone (Oakes et al. 1994) (4) (SmithKline Beecham).
Most successful on the market are pioglitazone and rosi-
glitazone. Metabolism of glitazones was studied recently
and metabolites of pioglitazone (Tanis et al. 1996) and ro-
siglitazone (Baldvin et al. 1999; Cox et al. 2000) are de-
scribed.
We are focused on the problem of impurities in pioglita-
zone, because there is a need to know the structure and
the quantity of all impurity in pharmaceutical ingredients.
Most of synthetic impurities have the basic thiazolidine
skeleton and we can suppose their biological activity. The
Glitazones, being derivatives of thiazolidine-2,4-dione are
used in the treatment of diabetes mellitus type II (non-in-
sulin-dependent diabetes mellitus, NIDDM). They influ-
ence insulin resistance and increase body sensitivity to in-
sulin. A large number of glitazone type antidiabetics were
developed and tested. Only some of them were used in
clinical practice: pioglitazone (1) (Sohda et al. 1990) (Ta-
keda Chemical Industries, Inc./Upjohn), troglitazone (2)
(Sankyo and Parke-Davis), englitazone (3) (Pfizer) or rosi-
Scheme 1
O
O
HO
NH
O
NH
S
S
O
N
O
O
1
2
O
O
NH
NH
S
N
N
S
O
O
O
O
3
4
Scheme 2 (a) NaH, DMF; (b) Pd-C, H2; (c) base; (d) NaNO2; (e) methylacrylate, HBr, Cu2O; (f) thiourea; (g) HCl
NHAc
a, b
NH2
c
NO2
+
+
N
N
OTs
HO
N
O
N
OH
F
6
7
8
5
O
O
O
f, g
d, e
NH2
NH
O
S
Br
O
N
O
N
O
6
9
1
580
Pharmazie 62 (2007) 8

ORIGINAL ARTICLES
Scheme 3 (a) base; (b) Pd––C, H2
O
+
O
O
O
a
b
NH
NH
NH
S
S
S
N
O
N
O
N
O
O
O
O
10
11
12
1
Scheme 4 (a) NaNO2, HBr; (b) thiourea; (c) HCl; (d) base
O
O
O
a, b, c
OH
d
+
NH
O
NH
O
NH2
S
S
N
OTs
HO
HO
N
O
13
14
15
1
Scheme 5
O
O
Br
NH
O
NH
S
S
HO
F
N
O
O
16
14
17
main group of impurities arises from intermediates and
products of side reactions during the preparation process.
The presence of a particular impurity in the final product
is often typical for the method of preparation.
Several methods for the preparation of glitazones are de-
scribed. Every method has also several modifications, pub-
lished mainly in the patent literature.
to the process of preparation but is a decomposition pro-
duct of pioglitazone.
Benzylidene intermediate 12 and its determination in bulk
and pharmaceutical formulations was described earlier
(Radhakrishna et al. 2002). Benzylidene intermediate 12 is
present in the commercial pioglitazone prepared by Kno-
venagel condensation (Scheme 3).
For pioglitazone three methods of preparation are most
famous.
2. Investigations, results and discussion
The oldest one is based on Meerwein arylation of sub-
stited 4-hydroxyaniline (6) and followed by closure of the
thiazolidindione ring. The key intermediate 6 can be pre-
pared by an older procedure starting from 4-fluoraniline
(Meguro and Fujita 1985) (5) or starting from the cheaper
N-(4-hydroxy-phenyl)acetamide (which is used also as an
active pharmaceutical ingredient) (Halama et al. 2002) (8)
(Scheme 2).
The second process is based on Knovenagel condensation
of aldehyde 10 with the thiazolidinedione (11) and follow-
ing benzylidene intermediate double bond reduction (12)
(Momose et al. 1991; Dolitzky 2003) (Scheme 3).
The third published process is starting from L-tyrosine
(13) (Halama et al. 2002) (Scheme 4).
Other processes for pioglitazone or glitazones preparation
have been patented. For example the process starting from
phenyllactic acid or process based on Darzens condensa-
tion of aromatic aldehyde and halogenacetic acid (Thijs
and Zhu 2005).
Three pioglitazone impurities 16, 17, 14 were described
besides of metabolites and their preparation was also pub-
lished (Kumar et al. 2004).
The content and nature of impurities in pioglitazone de-
pends on the method of preparation. In the pioglitazone
prepared by Meerwein arylation (Scheme 2) we can detect
and identify besides impurity 17 also set of impurities
with m/e 581. These compounds have practically the same
fragmentation in the MS spectra so they cannot be distin-
guished from each other. Therefore these impurities were
separated by preparative chromatography and structures
were determined by assigning of NMR signals (see later).
These isomeric impurities have structures I, II and III.
The remaining two possible isomers 18 and 19 were not
detected in the product. Also the presence of compound
20 was not confirmed. Standard of compound 20 has been
prepared from the disubstituted urea (21) (Scheme 8).
Pioglitazone prepared by the method starting from tyro-
sine (Scheme 4) contains the impurities 14 and IV. Com-
pound IV is formed by the consecutive alkylation of pio-
glitazone (1) by the alkylating agent 15 (Scheme 9).
All 1H and 13C NMR signals of compound I were as-
signed on the basis of 1D and 2D experiments, mainly
homonuclear g-COSY and heteronuclear H-13C g-HSQC
1
These compounds are typical for the oldest process of pio-
glitazone preparation starting from 4-fluoronitrobenzene
(5) (Scheme 2). Compound 14 in this case is not related
and 1H-13C g-HMBC experiments. These heteronuclear
2D experiments are inversion experiments. The resolution
in F1 domain in such NMR experiments is worse than
Pharmazie 62 (2007) 8
581

ORIGINAL ARTICLES
Scheme 6
O
2
5
14
16
1
3
15
17
6
7
13
18
33
NH
19
31
9
21
32
29
34
30
34
33
22
20
S
29
30
4 N
O 10 12
32
31
8
11
26
O
N
N 28
O 25
23
34
24
27
27
28
26
33
32
O
29
31
30
I
25
24
N
22
21
28
23
20
27
26
25
O
2
5
14
11
16
22
1
3
15
12
17
6
7
13
18
21
O
O
NH
9
2
5
14
11
16
S
1
3
4
15
12
17
6
13
10
18
19
N
O
4
10
20
24
8
8
23
9
NH
19
O
S
N
O
7
O
II
III
Scheme 7
N
O
N
O
NH
O
S
O
N
O
18
O
N
O
NH
O
O
N
O
S
N
O
S
N
O
19
20
Scheme 8 (a) CS2, EtOH; (b) compound (9), EtOH; (c) aqueous HCl
N
N
O
NH2
a
b
O
O
N
N
S
HS
N
O
N
O
NH
N
N
O
21
6
c
O
N
N
O
O
N
O
S
N
O
20
582
Pharmazie 62 (2007) 8

ORIGINAL ARTICLES
Scheme 9 (a) KOH, EtOH
O
O
NH
a
S
N
O
+
NH
O
Ts
S
a
1
14
N
O
HO
25
O
O
28
N
2
5
16
21
1
3
15
12
17
6
7
13
18
14
15
22
26
24
N
19
27
20
S
23
4
N
O
10
9
8
11
O
IV
1
that direct detection experiments like H-13C HETCOR or
1H-13C COLOC. Nevertheless resolution in F1 domain
was so adequate to distinguish and assign even the
13C NMR signals of quaternary carbons C-10 and C-25
differs each other only 0.2 ppm. Signals of methyl groups
C-1 and C-34 were also unambiguously assigned on the
basis of combination of HSQC and HMBC optimized for
50% of compound I, ca 10% of compound II and ca 6% of compound
III. The rest comprised pioglitazone and several small and unknown impu-
rities. This material was chromatographed through column with reverse
phase silica gel in the mixture acetonitrile/formate buffer (55 : 45). Fraction
purity was monitored by TLC. Pioglitazone had Rf ¼ 0.74, comp. I had
Rf ¼ 0.51, comp. II had Rf ¼ 0.41 and comp. III had Rf ¼ 0.36. Fractions
containing compound I were combined, concentrated and residue extracted
with dichloromethane. The product received by dichloromethane evaporat-
ing was recrystallized from methanol. White compound I was yielded.
Melting point ¼ 122.5–124 ꢀC. MS m/e: 581. Anal. Calcd. for
3
three-bond coupling constant J(C, H) ¼ 8 Hz.
C
34H35N3O4S: C, 70.20; H, 6.06; N, 7.22; O, 11.00; S, 5.51 found: C,
The identification of pioglitazone impurities, when piogli-
tazone was prepared by Meerwein arylation, gives the op-
portunity for decreasing their content in the active pharma-
ceutical ingredient and consequently to fulfil the drug
authorities requirements for drug production.
69.85; H, 5.85; N, 6.95.
Other compounds II and III were received from other chromatographic
fractions by the similar manner. Compounds I, II and III have on TLC
different retention factors. The difference in retention factors of compounds
II and III is not suitable for quite a full separation on column chromato-
graphy described in this communication. We have got only the compound
II a little contaminated by compound III for NMR determination and the
small amount of compound III contaminated by compound II. For com-
pound I all 1D and 2D techniques for unambiguous assignment of all
NMR signals were used. For compound II only 1D 1H and 13C and H,H-
COSY techniques were used, so some signals are assigned tentatively and
assignment could be interchanged. For compound III only 1D and 2D
1H NMR spectra were measured (Table 1). Nevertheless the structures of
compounds II and III were proven.
3. Experimental
3.1. Chemicals and apparatus
Nuclear magnetic resonance was measured in CDCl3 solutions on BRUKER
AVANCE 500 spectrometer, (Bruker Analytische Messtechnik GmbH) at
500.13 MHz (1H) and 125.77 MHz (13C) respectively. 1D the experiments
were carried out using a 5 mm TXO probe. For the 2D experiments the
inverse TBI probe was used. All experiments were performed in the sol-
vent CDCl3. For the assignment the 1H-13C g-HSQC and 1H-13C g-HMBC
from Bruker library were used. The 1H-13C g-HSQC dataset consisting of
2K and 256 points in F2 and F1 dimensions, respectively was chosen. The
number of scans was 8 for each t1 increment. The time domain data was
zero-filled to 1024 and 2K data points in F1 and F2 dimensions, respec-
tively, and processed with sinusoidal squared sine-bell window function in
both the dimensions. The gradient-selected 1H-13C HMBC was performed
using 4K and 512 points in F2 and F1 dimensions, respectively. The num-
ber of scans was 32 for each t1 increment. The acquired data was zero-
filled to 1024 and 2K data points in F1 and F2 dimensions, respectively,
and processed with sinusoidal squared sine-bell window function in both
the dimensions.
3.3. 1,3-Bis-{4-[2-(5-ethyl-pyridin-2-yl)-ethoxy]-phenyl}-isothiourea (21)
4-[2-(5-Ethylpyridin-2-yl)ethoxy]aniline (6) (40 g, 0.165 mol) and CS2
(25.2 g, 0.332 mol) were dissolved in absolute ethanol (65 ml). The reac-
tion mixture was maintained at 50 ꢀC for 2 h. After finishing the reaction
all residual solvents were removed. The residue was dissolved in dichloro-
methane. Dichloromethane solution was washed with 1 M solution of HCl
acid and dried over sodium sulfate. A slightly yellowish crude solid com-
pound was yielded. The crude product was recrystallized from ethanol to
give 17.8 g (42%) of pure compound (21). M.p. 84.5–86 ꢀC; 1H NMR
(CDCl3, 25 ꢀC) d 9.44 (s, 2), 8.38 (s, 2), 7.60 (dd, J ¼ 7.7, 1.6 Hz, 2),
7.31 (m, 6), 6.91 (d, J ¼ 7.5 Hz, 4), 4.33 (t, J ¼ 6.3 Hz, 4), 3.15
(t, J ¼ 6.3 Hz, 4), 2.52–2.65 (m, 4), 1.19 (t, J ¼ 7.5 Hz, 6); 13C NMR
(CDCl3, 25 ꢀC) d 180.3, 155.9, 155.7, 148.7, 136.9, 135.9, 132.5, 126.2,
123.3, 114.4, 67.1, 37.0, 25.2, 15.6.
Mass spectra were recorded on API 3000 LC MS/MS apparatus equipped
with E-spray ionization, (PE SCIEX).
Preparative column chromatography was made on silica gel 60 (Fluka) and
reverse phase of silica Lichroprep RP-18e (Merck).
Formate buffer was prepared by dissolving of 6.3 g of ammonium formate
in 1 L of distilled water. The pH was adjusted to 6 by the addition of
diluted (10%) formic acid.
Thin layer chromatography was made on FPKG60 F254 plates (Merck) in
the mixture CHCl3-methanol-NH4OH (25%) (30 : 15 : 0.5).
HPLC was made on Merck Hitachi LaChrom apparatus, endecaped (5 mm)
Purospher1STAR RP-18 column, detection Diode Array Detector L-
7450A.
3.4. 5-{4-[2-(5-Ethyl-pyridin-2-yl)ethoxy]benzyl}-3-{4-[2-(5-ethyl-pyridin-
2-yl)ethoxy] phenyl}-1,3-thiazolidine-2,4-dione (20)
Disubstituted thiourea 21 (11.5 g, 0.02 mol) and bromoester 9 (7.9 g,
0.02 mol) were dissolved in ethanol (125 ml). Reaction mixture was heated
for 7 h under reflux and then evaporated to dryness. The rest was extracted
three times with 40 ml of ethylacetate. Ethylacetate solution was evapo-
rated to dryness and the rest was heated for 5 h in 100 ml of 1 M HCl.
Then reaction mixture was cooled to the room temperature and extracted
three times with 50 ml of dichloromethane. Dichloromethane extract was
washed with a saturated aqueous solution of NaHCO3 (10%), dried over
sodium sulfate and concentrated. 6 g of brown solid was obtained after
evaporation of the solvent. A white product (20) was yielded by recrystalli-
zation from cyclohexane: M.p. 82.5–83.5 ꢀC; 1H NMR (CDCl3, 25 ꢀC) d
8.39 (s, 2), 7.45 (dd, J ¼ 7.7, 1.6 Hz, 2), 7.14–7.26 (m, 8), 6.86 (d,
J ¼ 7.5 Hz, 2), 4.54 (dd, J ¼ 8.3, 3.9 Hz, 1), 4.31–4.38 (m, 4), 3.23 and
3.42 (overlapped and dd, J ¼ 13.9, 3.9 Hz, 1), 3.23–3.28 (m, 4), 2.58–
2.67 (m, 4), 1.24 (t, J ¼ 7.5 Hz, 6); 13C NMR (CDCl3, 25 ꢀC) d 173.4,
170.5, 159.3, 158.4, 155.6, 155.4, 149.0, 149.0, 137.7, 137.1, 137.0,
135.7, 132.1, 130.6, 130.6, 128.3, 127.2, 125.2, 115.3, 114.8, 67.5, 67.3,
51.3, 37.8, 37.6, 37.4, 25.7, 15.3.
3.2. 5-{4-[2-(5-Ethyl-6-{4-[2-(5-ethylpyridin-2-yl)ethoxy]fenyl}pyrid-2-yl)-
ethoxy]benzyl}-1,3-thiazolidine-2,4-dione (I);
5-{4-[2-(5-ethyl-4-{4-[2-(5-ethylpyridin-2-yl)ethoxy]fenyl}pyrid-2-yl)-
ethoxy]benzyl}-1,3-thiazolidine-2,4-dione (II);
5-{6,40-bis-[2-(5-ethyl-pyridin-2-yl)ethoxy]biphenyl-3-ylmethyl}-
1,3-thiazolidine-2,4-dione (III)
Pioglitazone prepared by the procedure of Meerwein arylation was crystal-
lized from DMF/H2O (5/1). Mother liquor was concentrated and the resi-
due was extracted by toluene. The rest of pioglitazone was removed from
the mixture by concentration of toluene extract and filtration of solid. Eva-
poration of toluene filtrate finally yielded the solid material containing ca
Pharmazie 62 (2007) 8
583

ORIGINAL ARTICLES
Table: 1H and 13C chemical shifts of the compounds I–IV
C/H
(I)
(II)
(III)
1H (ppm);
(IV)
d
1H/13C (ppm);
d
1H/13C (ppm);
d
d
1H/13C (ppm);
(J(H,H) (Hz))
(J(H,H) (Hz))
(J(H,H) (Hz))
(J(H,H) (Hz))
1
2
3
1.11/15.1
2.62/25.3
134.7
1.09/15.3a
2.64/23.2
132.9
1.23
1.22/15.2a
2.59b/25.7
137.0
2.61a
4
5
6
7
8
9
10
11
12
13
14
15
16
157.8
8.44/155.7
155.2
7.06 (7.9)/114.7
149.4
3.26/37.3
4.35/67.3c
158.6d
6.85/114.8
7.13/129.6b
6.85/114.8
7.13/129.6b
127.8
8.36 (2.3)
7.37 (7.9, 2.3)
7.23 (7.9)
8.37(2.20)/149.0
7.42 (8.00, 2.20)/135.7
7.15 (8.06)/123.2
155.6
3.20/37.6
4.31/67.3
7.57 (7.9)/137.0
7.17 (7.9)/122.0
155.1
3.24/37.6
4.33/67.5
3.12b
4.30c
158.4
158.3
6.86/115.0
7.12/130.3
6.86/115.0
7.12/130.3
127.8
3.09 (14.1, 9.3), 3.43
(14.2, 4.0)/37.8
4.48 (9.3, 4.0)/53.8
174.4
6.80 (8.4)
7.07 (8.4, 2.3)
6.83/114.8
7.09/130.3
6.83/114.8
7.09/130.3
127.9
2.95 (overlapped);
3.39 (14.4, 4.0)/38.0
4.32/51.7
170.8
173.6
3.94/41.4
2.95/35.0
7.10 (2.3)
3.11 (14.1, 9.3); 3.42
(14.2, 4.0)/37.3
4.48 (9.3, 4.0)/53.7
174.6
3.09 (14.2, 9.4); 3.42
(14.1, 3.9)
4.48 (9.3, 3.9)
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
170.5
133.3
170.7
131.4
7.37/130.1
6.96/114.3
7.37/130.1
6.96/114.3
158.6
4.39/67.4
3.27/37.4
155.7
8.41 (2.0)/148.7
7.21 (7.9)/123.5
7.47 (7.8, 2.0)/136.1
137.2
2.64/25.7
1.25/15.3
7.20/130.2b
6.97/114.5
7.20/130.2b
6.97/114.5
158.2d
7.24
6.84
7.24
6.84
155.0
7.00 (8.00)/122.8
7.40 (8.00, 2.20)/135.7
8.36 (2.20)/149.1
137.2
4.41/67.4c
3.26/37.7
155.5
4.36c
3.23b
2.61b 25.7
1.20/15.3a
8.41 (2.0)/148.7
7.22/123.4
7.48/136.0
137.2
8.41 (2.2)
7.00 (7.9)
7.47 (7.9, 2.2)
2.64/25.7
2.62a
1.23
1.26/15.2a
a, b, c, d can be interchanged
3.5. 5-{4-[2-(5-Ethyl-pyridin-2-yl)ethoxy]benzyl}-3-[2-(5-ethyl-pyridin-
2-yl)ethyl]-1,3-thiazolidine-2,4-dione (IV)
Halama A, Hejtmankova L, Lustig P, Richter J, Srsnova L, Jirman J
(2002) Process for preparing 4-[2-(5-ethyl-2-pyridyl)ethoxy]aniline as an
intermediate for production of antidiabetic pioglitazone. WO022088120.
Kumar YR, Reddy AR, Eswaraiah S, Mukkanti K, Reddy MSN, Suryanar-
ayana MV (2004) Structural characterization of impurities in pioglita-
zone. Pharmazie 59: 836–839.
Meguro K, Fujita T (1985) Thiazolidinedione derivatives and their use. EP
193256.
Momose Y, Meguro K, Ikeda H (1991) Studies on antidiabetic agents.
Synthesis and biological activities of pioglitazone and related com-
pounds. Chem Pharm Bull 39: 1440–1445.
Oakes ND, Kenedy CJ, Jenkins AB, Laybutt DR, Chisholm DJ, Kraegen
EW (1994) A new antidiabetic agent, BRL 49653, reduces lipid avail-
ability and improves insulin action and glucoregulation in the rat. Dia-
betes 43: 1203–1210.
Radhakrishna T, Rao DS, Reddy GO (2002) Determination of pioglitazone
hydrochloride in bulk and pharmaceutical formulations by HPLC and
MEKC methods. J Pharm Biomed Anal 29: 593–607.
Pioglitazone (1) (10 g, 28 mmol) was treated with KOH (1.6 g, 28 mmol)
in DMF (18 ml) for 30 min at laboratory temperature. To this solution was
slowly added dropwise 4-toluenesulfonyl ester of 2-(5-ethyl-pyridin)ethanol
(15) (8.6 g, 28 mmol) in DMF (10 ml) and the mixture was stirred at
45 ꢀC for 2 h. Separated potassium 4-toluenesulfonate was filtered off after
cooling to 15 ꢀC. The filtrate was concentrated on oily residue. This resi-
due was dissolved in toluene and washed with 1 M NaOH. Toluene solu-
tion was then dried with sodium sulfate and evaporated to dryness. The
received honey like sticky matter was dissolved in boiling cyclohexane,
filtered through the bed of carborafine and left to crystallize. 7.3 g (53%)
of white product (IV) were received. M.p. ¼ 92.6–93.3 ꢀC. MS m/e: 489.
Anal. Calcd. for C28H31N3O3S: C, 68.68; H, 6.38; N, 8.58; O, 9.80; S,
6.55 found: C, 68.12; H, 6.18; N, 7,93.
1H and 13C NMR signals of compound IV were assigned the similar way
like those of compound I (Table 1).
Sohda T, Momose Y, Meguro K, Kawamatsu Y, Sugiyama Y, Ikeda H (1990)
Studies on antidiabetic agents. Synthesis and hypoglycemic activity of 5-
[4-(pyridylalkoxy)-benzyl]-2,4-thiazolidinediones. Arzneim-Forsch./Drug
Res. 40: 37–42.
Tanis SP, Parker TT, Colca JR, Fisher RM, Kletzein RF (1996) Synthesis
and biological activity of the antidiabetic, antihyperglycemic agent pio-
glitazone. J Med Chem 39: 5053–5063.
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