Synthesis of bosutinib from 3-methoxy-4-hydroxybenzoic acid

Article abstract of DOI:10.3390/molecules15064261

This paper reports a novel synthesis of bosutinib starting from 3-methoxy-4-hydroxybenzoic acid. The process starts with esterification of the starting material, followed by alkylation, nitration, reduction, cyclization, chlorination and two successive amination reactions. The intermediates and target molecule were characterized by ¹H-NMR, ¹³C-NMR, MS and the purities of all the compounds were determined by HPLC.

Full text of DOI:10.3390/molecules15064261

Molecules 2010, 15, 4261-4266; doi:10.3390/molecules15064261
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Synthesis of Bosutinib from 3-Methoxy-4-hydroxybenzoic Acid
Xiao Jia Yin 1, Guan Hong Xu 1, Xu Sun 1, Yan Peng 1, Xing Ji 2, Ke Jiang 1 and Fei Li 1,*
1
School of Pharmacy, Nanjing Medical University, Nanjing 210029, China;
E-Mail: yinxiaojia@163.com (X.J.Y.)
2
Nanjing Children’s hospital, Nanjing Medical University, Nanjing 210008, China
∗ Author to whom correspondence should be addressed; E-Mail: kldlf@njmu.edu.cn;
Tel.: (+86)25-86862762.
Received: 9 April 2010; in revised form: 13 May 2010 / Accepted: 9 June 2010 /
Published: 11 June 2010
Abstract: This paper reports a novel synthesis of bosutinib starting from
3-methoxy-4-hydroxybenzoic acid. The process starts with esterification of the starting
material, followed by alkylation, nitration, reduction, cyclization, chlorination and two
successive amination reactions. The intermediates and target molecule were characterized
by 1H-NMR, 13C-NMR, MS and the purities of all the compounds were determined by HPLC.
Keywords: bosutinib; protein kinase inhibitors; 3-methoxy-4-hydroxybenzoic acid
1. Introduction
The Src family of non-receptor protein tyrosine kinases (SFKs) plays key roles in regulating signal
transduction, including cell growth, differentiation, cell shape, migration, and survival, and specialized
cell signals [1]. However, c-Src was also identified as a proto-oncogene based on decades of research
on an avian RNA tumor (sarcoma) virus. In some abnormal cases, such as mutation of the c-Src or
over-expression, these enzymes can become hyperactivated, resulting in uncontrolled cell proliferation
[2]. Bcr-Abl, the constitutively activated fusion protein product of the Philadelphia chromosome (Ph)
is the principal oncogene underlying the pathology of chronic myelogenous leukemia (CML). Abl
shares significant sequence homology with Src, and in its active conformation, bears remarkable
structural resemblance with most SFKs. As a result, ATP-competitive compounds originally developed
as Src inhibitors frequently exhibit potent inhibition of Abl kinase [3,4]. The second generation

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Bcr-Abl kinase inhibitors target both Src and Abl kinases to combat imatinib resistance, for example
the Wyeth drug bosutinib (10, SKI-606, Scheme 1) has been evaluated for the treatment of CML in a
Phase III clinical trial [5,6].
Several methods for the synthesis of bosutinib have been reported. Boschelli and Wang [5,7] started
the route with protection of the hydroxy group of methyl 4-hydroxy-3-methoxybenzoate. The
drawbacks are the facts that the cyclization reaction temperature (-78 ºC) is strict, and only gives a
47% yield. More important is that the overall yield is only 8.3%. Sutherland et al. [8] have designed a
novel method for synthesizing bosutinib starting from 2-methoxy-5-nitrophenol. The overall yield was
32.1%, but the raw materials of the route are costly, and the reaction time is long, especially the last
steps that required 66 h.
In this report, we present a novel approach to synthesizing bosutinib. Compared with Boschelli’s
route, it avoids the strict conditions of the cyclization reaction, and the overall yield is higher (21.7%).
One the other hand, the starting materials are cheaper than Sutherland’s route.
2. Results and Discussion
Our novel synthesis of bosutinib (Scheme 1) started from 3-methoxy-4-hydroxybenzoic acid (1).
This compound was esterified and then alkylated with 1-bromo-3-chloropropane to afford the
intermediate 3 in 90.0% yield. Nitration of 3 with nitric acid in acetic acid gave compound 4, which
was reduced by powdered iron and ammonium chloride to give compound 5 in satisfactory yield
(91.5%). In order to get a better reduction, Pd/C could be used to reduce compound 4 rather than
Fe/NH4Cl. However, Pd/C gave incomplete conversions (85% yield) even after long reaction times (18 h).
Scheme 1. Novel synthesis of bosutinib.
a) CH3OH; b) 1-bromo-3-chloropropane; c) HNO3; d) Fe/NH4Cl; e) 3,3-diethoxypropionitrile,
trifluoroacetic acid; f) NaOH; g) POCl3; h) 2,4-dichloro-5-methoxyaniline, pyridine hydrochloride;
i) NaI, N-methylpiperazine.
Compound 5 was reacted with 3,3-diethoxypropionitrile to obtain compound 6. In this step, 5 was
not directly reacted with 3,3-diethoxypropionitrile, but under the catalysis of trifluoroacetic acid,

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3,3-diethoxypropionitrile was converted to 3-oxopropanenitrile, and then the 3-oxopropanenitrile was
reacted with phenylamine 5 to form a Schiff's base. Because of the p-π conjugation, the Schiff's base
would switch to another conformation 6.
Cyclization of 6 with sodium hydroxide and chlorination with POCl3 afforded compound 8. The
final product was obtained after two reactions with different amines. Compared with other methods,
this new method is less costly because of the much cheaper starting materials used, consumes less time,
and gives high yields. These results reported here provide the possibility of industrial production.
3. Experimental
General
All reagents were purchased from commercial sources and used without further purification.
Melting points were measured in open capillaries and are uncorrected. 1H-NMR spectra were recorded
in CDCl3/DMSO-d6 on a Bruker Avance 300 spectrometer; chemical shifts (δ) are reported in parts per
million (ppm) relative to tetramethylsilane (TMS), used as an internal standard. Mass spectra (MS)
were obtained from Agilent 1100LC/MS Spectrometry Services. All compounds were routinely
checked by TLC with silica gel GF-254 glass plates and viewed under UV light at 254 nm. The
reported HPLC purity is the peak area calculated using Class-VP software on a Shimadzu 2010 instrument.
Methyl 4-hydroxy-3-methoxybenzoate (2). Thionyl chloride (30.0 g, 0.50 mol) was added dropwise at
room temperature to a solution of 3-methoxy-4-hydroxybenzoic acid (1, 44.3 g, 0.26 mol) in methanol
(500 mL). The mixture was stirred at room temperature for 2 h and the solvent was concentrated in
vacuo. The oil formed was resolved in ice-water (50 mL), and pH was adjusted to 7-8 with saturated
aqueous sodium bicarbonate solution. The solution was left standing in the refrigerator overnight, then
the precipitate was collected by filtration, and air dried to give as brown power (49.0 g, 98% yield,
1
97.2% HPLC purity); H-NMR (CDCl3): 3.89 (s, 3H), 3.91 (s, 3H), 6.09 (s, 1H), 6.92 (d, J = 8.4 Hz,
13
1H), 7.55 (s, 1H), 7.62 (d, J = 8.3 Hz, 1H); C-NMR (CDCl3): 51.94, 56.08, 111.75, 114.07, 122.24,
124.17, 146.16, 150.12, 166.88; MS (ES) m/z 183.1 (M+1).
Methyl 4-(3-chloropropoxy)-3-methoxybenzoate (3). A mixture of methyl 4-hydroxy-3-methoxy-
benzoate (2, 48.0 g, 0.26 mol), 1-bromo-3-chloropropane (50.0 g, 0.32 mol), and potassium carbonate
(50.0 g, 0.36 mol) in DMF (125 mL) was heated at 70 ºC for 1 h. The reaction mixture was cooled to
room temperature, and then poured slowly into ice-water (1.5 L) while stirring constantly. The solid
formed was filtered off and washed with cold water. The off-white product was recrystallized from
1
ethyl acetate (120 mL) to afford 3 (61.3 g, 90% yield, 99.3% HPLC purity); H-NMR (CDCl3):
2.29–2.33 (m, 2H), 3.77 (t, J = 6.2 Hz, 2H), 3.89 (s, 3H), 3.91 (s, 3H), 4.22 (t, J = 6.0 Hz, 2H), 6.89 (d,
J = 8.5 Hz, 1H), 7.55 (d, J = 2.0 Hz, 1H), 7.67 (dd, J = 2.0 Hz, 1H); 13C-NMR (CDCl3): 32.02, 41.36,
51.93, 55.98, 65.41, 111.83, 112.46, 122.95, 124.43, 148.94, 152.16, 166.78; MS (ES) m/z 259.1 (M+1).
Methyl 4-(3-chloropropoxy)-5-methoxy-2-nitrobenzoate (4). Nitric acid (84.5 mL, 66%) was added
dropwise at room temperature to a solution of methyl 4-(3-chloropropoxy)-3-methoxybenzoate (3,
51.6 g, 0.20 mol) in a mixture of acetic acid (150 mL). This mixture was stirred at 60 ºC for 3–4 h.
Then the mixture was washed with ice-water (2 × 50 mL). The organic layer was washed with

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saturated sodium bicarbonate to neutrality. The oil formed was stirred till solidified and then collected
by filtration to afford the product as light yellow solid (54.0 g, 89% yield, 98.7% HPLC purity);
1H-NMR (CDCl3): 2.28–2.42 (m, 2H), 3.77 (t, J = 6.2 Hz, 2H), 3.91 (s, 3H), 3.96 (s, 3H), 4.24 (t, J = 6.0 Hz,
2H), 7.08 (s, 1H), 7.49 (s, 1H); 13C-NMR (CDCl3): 31.82, 41.00, 53.21, 56.54, 66.03, 108.32, 111.02,
121.89, 141.08, 149.54, 152.84, 166.25; MS (ES) m/z 304.1 (M+1).
Methyl 2-amino-4-(3-chloropropoxy)-5-methoxybenzoate (5). Powdered iron (5.6 g, 0.10 mol) and
ammonium chloride (8.4 g, 0.157 mol) were added to a mixture of methanol (70 mL) and water (30 mL).
The resulting suspension was heated at reflux for 10 min, then a solution of methyl
4-(3-chloropropoxy)-5-methoxy-2-nitrobenzoate (4, 9.1 g, 0.03 mol) in heated methanol (100 mL) was
added dropwise. The mixture was heated at reflux for 4 h. The catalyst was filtered, and the methanol
was evaporated from the filtrate. The residue was air dried to afford the product as white solid (7.5 g,
1
91.5% yield, 98.2% HPLC purity); H-NMR (CDCl3): 2.26–2.34 (m, 2H), 3.73 (t, J = 6.2 Hz, 2H),
13
3.80 (s, 3H), 3.85 (s, 3H), 4.15 (t, J = 6.0 Hz, 2H), 5.58(s, 2H), 6.18 (s, 1H), 7.31 (s, 1H); C-NMR
(CDCl3): 31.94, 41.43, 51.33, 56.70, 65.11, 100.58, 102.51, 113.65, 140.85, 146.97, 154.17, 168.10;
MS (ES) m/z 274.1(M+1).
(E)-Methyl 4-(3-chloropropoxy)-2-(2-cyanovinylamino)-5-methoxybenzoate (6). 3,3-Diethoxy-
propionitrile (2 mL, 13.34 mmol), trifluoroacetic acid (4 mL) and water (1 mL) were stirred for 6 h at
5–10 ºC under an atmosphere of N2, and then a solution of methyl 2-amino-4-(3-chloro-
propoxy)-5-methoxybenzoate (5, 2.0 g, 7.32 mmol) in ethyl acetate (8 mL) was added. The mixture
was stirred for 10 min. The solid formed was filtered off and air dried to afford the product as light
yellow solid (2.0 g, 84.3% yield, 98.7% HPLC purity); 1H-NMR (CDCl3): 2.31–2.39 (m, 2H), 3.79 (t,
J = 6.2 Hz 2H), 3.85 (s, 3H), 3.90 (s, 3H), 4.26 (t, J = 6.0 Hz, 2H), 4.68(d, J = 6.8 Hz, 2H) ,6.58(s, 1H),
7.42 (s, 1H), 7.53 (t, J = 17.7 Hz, 1H), 10.55 (d, J = 6.5 Hz, 1H); 13C-NMR (CDCl3): 31.87, 41.15,
51.11, 56.37, 65.61, 71.96, 97.65, 105.26, 113.52, 117.41, 138.63, 142.95, 144.17, 153.94, 168.18; MS
(ES) m/z 324.9 (M+1).
7-(3-Chloropropoxy)-4-hydroxy-6-methoxyquinoline-3-carbonitrile (7). A solution of (E)-methyl
4-(3-chloropropoxy)-2-(2-cyanovinylamino)-5-methoxybenzoate (6, 1.5 g, 4.36 mmol) in ethanol (20 mL),
the pH was adjusted to 12–13 with sodium hydroxide. And then the solution was stirred at room
temperature for 6 h, the solution was adjusted to nurture with water. The solid formed was filtered off
and air dried to afford light yellow solid (1.16 g, 85.8% yield, 98.6% HPLC purity); 1H-NMR (CDCl3):
2.25–2.27 (m, 2H), 3.81 (t, J = 3.0 Hz, 2H), 3.88 (s, 3H), 4.20 (t, J = 3.7 Hz, 2H) ,7.09(s, 1H), 7.48 (s,
1H), 8.59 (t, 1H), 12.53 (s, 1H); 13C-NMR (CDCl3): 31.56, 41.17, 56.03 , 65.47, 93.78, 101.01, 104.89,
115.35, 119.99, 134.88, 144.49, 147.89, 152.14, 154.56; MS (ES) m/z 293.0 (M+1).
4-Chloro-7-(3-chloropropoxy)-6-methoxyquinoline-3-carbonitrile (8). A mixture of 7-(3-chloro-
propoxy)-4-hydroxy-6-methoxyquinoline-3-carbonitrile (7, 1.0 g, 3.42 mmol) and phosphorus
oxychloride (4.7 g, 30.10 mmol) in toluene (10 mL) was heated at reflux for 2 h. The solution was
concentrated, and the pH was adjusted to 7 with saturated aqueous sodium bicarbonate. The resultant
precipitate was collected by filtration to provide 8 (0.98 g, 92.4% yield, 98.1% HPLC purity); 1H-NMR
(CDCl3): 2.36–2.44 (m, 2H), 3.81 (t, J = 6.2 Hz, 2H), 4.06 (s, 3H), 4.37 (t, J = 6.0 Hz, 2H) ,7.42(s, 1H),

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13
7.46 (s, 1H), 8.78 (s, 1H), 12.53 (d, s, 1H); C-NMR (CDCl3): 31.69, 41.13, 56.35 , 65.62, 97.78,
102.06, 109.30, 113.57, 115.35, 142.96, 144.15, 148.19, 152.14, 154.64; MS (ES) m/z 311, 313 (M+1).
7-(3-Chloropropoxy)-4-(2,4-dichloro-5-methoxyphenylamino)-6-methoxyquinoline-3-carbonitrile (9).
A mixture of 2,4-dichloro-5-methoxyaniline (0.54 g, 2.80 mmol), pyridine hydrochloride (0.276 g,
2.44 mmol), and 4-chloro-7-(3-chloropropoxy)-6-methoxyquinoline-3-carbonitrile (8, 0.80 g, 2.56 mmol)
in 2-ethoxyethanol (10 mL) was heated at reflux for 2.5 h. The reaction mixture was partitioned
between ethyl acetate and saturated aqueous sodium bicarbonate. The organic layer was washed with
water, filtered, and concentrated in vacuo until a solid began to appear. This solid was collected by
1
filtration to provide an off-white solid (0.68 g, 60.2% yield, 99.0% HPLC purity); H-NMR
(DMSO-d6): 2.22–2.33 (m, 2H), 3.83 (t, J = 6.0 Hz, 2H), 3.86 (s, 3H), 3.95 (s, 3H), 4.29 (t, J = 6.0 Hz
2H), 7.34 (s, 1H), 7.37 (s, 1H), 7.75 (s, 1H), 7.85 (s, 1H), 8.42 (s, 1H), 9.64 (s, 1H); 13C-NMR (CDCl3):
31.75, 41.18, 55.52, 56.35, 65.62, 85.91, 102.06, 104.24, 109.30, 111.57, 116.57, 117.43, 132.34,
135.49, 144.92, 148.14, 150.16, 152.14, 154.64, 155.32 MS (ES) m/z 465.8, 467.8 (M+1).
4-(2,4-Dichloro-5-methoxyphenylamino]-6-methoxy-7-[3-(4-methylpiperazin-1-yl)propoxy]quinoline-
3-carbonitrile (10).
A
mixture of 7-(3-chloropropoxy)-4-(2,4-dichloro-5-methoxyphenyl-
amino)-6-methoxyquinoline-3-carbonitrile (9, 0.328 g, 0.7 mmol) and sodium iodide (0.11 g, 0.70 mmol)
in N-methylpiperazine (4 mL) was heated at 80 ºC for 12 h. The reaction mixture was concentrated in
vacuo and partitioned between ethyl acetate and saturated aqueous sodium bicarbonate. The organic
layer was washed with brine, dried over sodium sulfate, filtered, and concentrated in vacuo. The
residue was purified by column chromatography, eluting with 30% methanol in dichloromethane. The
fractions containing product were collected and concentrated in vacuo. Diethyl ether was added to the
residue, and the light pink solid was collected by filtration (0.28 g, 75% yield, 98.7% HPLC purity):
m.p. 116–120 ºC; 1H-NMR (DMSO-d6): 1.92–1.97 (m, 2H), 2.15 (s, 3H), 2.32–2.46 (m, 10H), 3.84 (s,
3H), 3.93 (s, 3H), 4.19 (t, J = 6.3 Hz, 2H), 7.31 (br s, 2H), 7.43 (s, 1H), 7.64 (s, 1H), 8.52 (s, 1H), 9.51
(s, 1H); 13C-NMR (CDCl3): 25.96, 45.68, 52.67, 52.67, 54.24, 54.72, 54.72, 56.01, 60.71, 66.87, 89.10,
101.66, 101.66, 109.12, 113.95, 117.17, 122.99, 122.99, 128.27, 137.88, 146.15, 148.13, 148.51,
149.50, 150.43, 153.03; MS (ES) m/z 530.2, 532.2 (M+1).
4. Conclusions
A novel synthesis of bosutinib starting from 3-methoxy-4-hydroxybenzoic acid has been established.
Compared with the existing methods, this new method is less costly because of the much cheaper
starting materials used, consumes less time, and gives higher yields. These results reported here offer
the possibility of industrial production.
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Sample Availability: Samples of the compounds are available from the authors.
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