Discovery of novel c-met inhibitors bearing a 3-carboxyl piperidin-2-one scaffold

Article abstract of DOI:10.3390/molecules19022655

A series of compounds containing a novel 3-carboxypiperidin-2-one scaffold based on the lead structure BMS-777607 were designed, synthesized and evaluated for their c-Met kinase inhibition and cytotoxicity against MKN45 cancer cell lines. The results indi

Full text of DOI:10.3390/molecules19022655

Molecules 2014, 19, 2655-2673; doi:10.3390/molecules19022655
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Discovery of Novel c-Met Inhibitors Bearing a 3-Carboxyl
Piperidin-2-one Scaffold
Wei Zhang 1, Jing Ai 2, Dakuo Shi 3, Xia Peng 2, Yinchun Ji 2, Jian Liu 1, Meiyu Geng 2,* and
Yingxia Li 1,*
1
School of Pharmacy, Fudan University, Shanghai 201203, China
2
Division of Antitumor Pharmacology, State Key Laboratory of Drug Research, Shanghai Institute
of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
3
School of Pharmacy, Ocean University of China, Qingdao 266003, China
* Authors to whom correspondence should be addressed; E-Mails: mygeng@simm.ac.cn (M.G.);
liyx417@fudan.edu.cn (Y.L.); Tel./Fax: +86-21-5198-0127 (Y.L.).
Received: 21 January 2014; in revised form: 13 February 2014 / Accepted: 14 February 2014 /
Published: 24 February 2014
Abstract: A series of compounds containing a novel 3-carboxypiperidin-2-one scaffold
based on the lead structure BMS-777607 were designed, synthesized and evaluated for
their c-Met kinase inhibition and cytotoxicity against MKN45 cancer cell lines. The results
indicated that five compounds exhibited significant inhibitory effect on c-Met with IC50
values of 8.6−81 nM and four compounds showed potent inhibitory activity against
MKN45 cell proliferation, with IC50s ranging from 0.57−16 μM.
Keywords: c-Met; synthesis; kinase inhibitor; 3-carboxypiperidin-2-one
1. Introduction
c-Met kinase is a transmembrane receptor tyrosine kinase (RTK). Upon binding of its endogenous
ligand hepatocyte growth factor (HGF, also known as scatter factor, SF), c-Met receptor undergoes
dimerization and in turn triggers signal transducers to mediate a variety of cellular responses such as
cell growth, invasion, migration and survival [1,2]. The normal c-Met/HGF pathway plays an
important role in embryogenesis and wound healing, but aberrant forms of this pathway (for example,
as a result of overexpression of c-Met and HGF) have frequently been observed in a variety of human
solid tumors and hematologic malignancies. Importantly, both increased levels of c-Met and HGF have

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been associated with poor clinical outcomes [3–5]. Therefore, c-Met has been pursued as an attractive
anticancer drug target for the past two decades [6,7]. Several approaches to inhibition of the HGF/c-Met
pathway in cancer cells have been reported, such as antagonistic ligands to c-Met, antibodies against
HGF or c-Met, and small molecule c-Met inhibitors [8–10].
During the development of small molecular c-Met kinase inhibitors, a compound disclosed by Kirin
Brewery Company in 2003 [11] could be regarded as a milestone (Figure 1). Structurally, this
compound (1) is composed of four moieties: a phenyl group (moiety A), a bridge moiety B, an
ortho-fluoro phenol and a 6,7-dimethoxyquinoline. Initiated by this discovery, numerous c-Met kinase
inhibitors bearing diverse chemical scaffolds have been reported. Generally, structural optimization
based on compound 1 mainly focused on moiety D and B. Replacement of the 6,7-dimethoxy-
quinoline moiety by various N-containing heterocycles, such as substituted quinoline [12],
thienopyridine [13–15], pyrrolopyridine [16], aminopyridine [17], thienopyrimidine [18],
furopyrimidine [18], imidazopyridine [19] or imidazopyridazine [19], has been investigated. The
bridge moiety B connecting moiety A and C was designed as linear [20–22] or cyclic [14,15,23–26],
bearing at least one amide bond with 5-atoms in the main chain [22,24] (i.e., six chemical bonds
distance between moiety A and C, Figure 1). However, there are little changes to moiety A and C,
except for phenyl ring or substituted phenyl ring modifications to the former.
Figure 1. Representative scaffolds used for the structural optimization of c-Met inhibitors.
A good example for these inhibitors is BMS-777067, which is now in phase 2 trial because of its
excellent in vivo efficacy and favorable pharmacokinetic and preclinical safety profiles [17]. Taking
BMS-777607 as leading compound, the design and synthesis of new derivatives with novel structures
are under study in our laboratory. Preliminary investigation indicated that 3-carboxypiperidin-2-one is
a promising scaffold for the design of new c-Met inhibitors. Herein we would like to report our efforts
in this respect (Figure 2).

Molecules 2014, 19
Figure 2. Scaffolds used for the structural optimization based on BMS-777607 in this paper.
2657
2. Results and Discussion
2.1. Chemistry
As shown in Scheme 1, saponification of isobutyl ester 2 with lithium hydroxide gave the piperidinone
3-carboxylic acid 3, which could be further brominated giving compound 4 in 92% yield. On the other
hand, deprotonation of compound 2 with sodium hydride, followed by treatment with an alkyl halide
(MeI, EtBr, or n-BuBr) led to the corresponding α-substituted piperidinones. Saponification of these
esters 5a–c gave the corresponding carboxylic acids smoothly. In this way, we had five carboxylic
acids (compounds 3, 4, 6a–c) in hand, which would be used in next coupling step.
Scheme 1. Synthesis of the piperidinone 3-carboxylic acids 3, 4 and 6a–c.
Reagents and conditions: (a) piperidin-2-one, CuI, K3PO4, DMF, 90%; (b) t-BuLi, isobutyl chloroformate,
82%; (c) LiOH, THF/MeOH/H2O, 87% for 3, 88% for 6a, 79% for 6b, 84% for 6c; (d) Br2/Et2O, 92%; (e)
NaH/MeI, 87% for 5a; NaH/EtBr, 76% for 5b; NaH/n-BuBr, 83% for 5c.
Deprotonation of 3,4-dichloropyridine (7) with lithium 2,2,6,6-tetramethylpiperidide (TMPLi)
followed by treated with trimethylsilyl isothiocyanate and acidic workup, gave 3,4-dichloropicolinamide

Molecules 2014, 19
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(8) in 40% yield (Scheme 2). This pyridyl chloride was coupled with 4-amino-2-fluorophenol in the
presence of potassium tert-butoxide to afford the aromatic amine 9 in 72% yield. Similarly, coupling
of phenol (10) with 4-chloro-7H-pyrrolo[2,3-d]pyrimidine and 4-chloro-6,7-dimethoxyquinoline
followed by conversion of the nitryl to an amino group gave amines 11 and 14, respectively. For the
preparation of substituted pyrimidine 13, the amino group was introduced to the C-2 position before
zinc-mediated reduction. Thus we had four aromatic amines (compounds 9, 11, 13 and 14) in hand,
which were subjected to the next step directly.
Scheme 2. Synthesis of aromatic amines 9, 11, 13 and 14.
Reagents and conditions: (a) TMPLi, trimethylsilyl isothiocyanate, −78 °C, 40%; (b) t-BuOK, 4-amino-2-
fluorophenol, 72%; (c) PhBr, 130 °C, 85%; (d) Zn, NH4Cl, 88% for 11, 69% for 13; 91% for 14; (e) K2CO3,
DMF; (f) 4-methoxybenzylamine, K2CO3, 68%.
Coupling of aromatic amines 9, 11, 13 or 14 with the 3-carboxypiperidin-2-one 3 in the presence of
1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC-HCl) and N,N-dimethyl-4-
amino pyridine (DMAP) gave the corresponding amides 15a, 17a, 18a or 20a, respectively (Scheme 3).
When bromide 4 was used as the carboxylic acid component, halo-exchanged products 15b, 17b, 18b,
20b were observed (confirmed by NMR and MS). The aminopyridine-containing products 16a–b were
achieved after Hoffman degradation and the aminopyrimidine derivates 19a–b were generated after
treatment of 18a–b with trifluoroacetic acid (TFA).

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Scheme 3. Synthesis of the newly designed c-Met inhibitors 15–20.
2659
Reagents and conditions: (a) EDC-HCl, DMAP, 76% for 15a, 68% for 15b, 31% for 17a, 42% for 17b, 69%
for 18a, 57% for 18b, 61% for 20a, 54% for 20b, 68% for 20c, 58% for 20d, 64% for 20e; (b) PhI(OAc)2,
72% for 16a, 76% for 16b; (c) TFA, 71% for 19a, 58% for 19b.
2.2. Evaluation of Biological Activity
As illustrated in Table 1, all of the compounds bearing a 3-carboxypiperidin-2-one scaffold exhibit
potent c-Met kinase inhibition activity. However, compounds lacking an α-substituent group (15a, 17a,
18a, 19a, 20a) only showed much less potent anti-c-Met kinase activity. When the α-proton was
substituted by chlorine, the activity generally increased (cf. 15b vs. 15a, 16b vs. 16a, 20b vs. 20a).
When alkyl groups (Me, Et, or n-Bu) were introduced to this position, the inhibitory effects were
greatly enhanced (20c, 20d and 20e vs. 20a). Among these three derivatives, the smallest methyl group
was the most favorable among the compounds exerting inhibitory activity against c-Met kinase activity
and c-Met-driven cell proliferation. Generally, 6,7-dimethoxyquinoline -containing analogues showed
more potency than the pyrropyridine, pyrimidine, or aminopyrimidine counterparts (20b vs. 15b, 16b,
17b, 18b, 19b) according to the biological activity results. The most potent analogue 20b exhibited
significant potency against c-Met kinase and c-Met-driven MKN45 cell proliferation, with IC50 values
of 8.6 nM and 0.57 μM, respectively. Other three analogues 20c–e with alkyl substitution in the piperidone
moiety are also promising, showing inhibitory activity against c-Met enzymatic activities with the IC50s of
11.2~64.0 nM and inhibiting MKN45 cell proliferation with IC50s of 0.65~16.0 μM, individually.

Molecules 2014, 19
Table 1. SAR of the compounds bearing a 3-carboxypiperidin-2-one scaffold.
2660
c-Met IC50
(nM)
MKN45 a
c-Met IC50
(nM)
MKN45 a
Cmpd
15a
Ar
R
Compd
19a
Ar
R
IC50 (μM)
IC50 (μM)
59.1%@10 μM
27.5%@1 μM
H
63.9%@10 μM
NT b
H
NT
90.2%@10 μM
38.7%@1 μM
52.5%@10 μM
28.3%@1 μM
Cl
H
NT
NT
Cl
H
NT
NT
15b
16a
19b
20a
427.0 ± 6.1
81.0 ± 7.6
38.4%@10 μM
8.6 ± 1.6
Cl
H
NT
NT
NT
Cl
Me
Et
0.57 ± 0.04
0.65 ± 0.13
2.95 ± 0.12
16b
17a
17b
20b
20c
20d
70.7%@10 μM
41.9%@1 μM
11.2 ± 4.1
Cl 15.4%@10 μM
19.1 ± 4.5
H
28.4%@10 μM
NT
nBu
64.0 ± 10.8
16.0 ± 0.8
18a
20e
BMS-
Cl
10%@10 μM
NT
—
—
3.7 ± 1.3
0.29 ± 0.02
18b
777607
a: MKN45, human gastric cancer cell line that expresses elevated levels of constitutively active c-Met; b: NT,
Not tested.
2.3. Molecular Modeling
To further elucidate the binding mode of compounds, docking analysis was performed. In our study,
the co-crystal structure of BMS-777607 with c-Met kinase (PDB ID:3F82) was selected as the docking
model. The inhibitor was docked using the GLIDE docking algorithm [27] in the XP (extra precision)
mode. A binding model for (R)-20b in the ATP binding site is presented in Figure 3a. The resulting
model successfully identifies key hydrogen bond interaction and hydrophobic interactions between the
ligands and residues of the protein’s ATP binding pocket. The carbonyl oxygen of the

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3-carboxypiperidin-2-one and the nitrogen atom of the quinoline ring in 20b formed hydrogen bonding
interactions with Asp1222 and Met1160, respectively. π-π Interactions were formed between the
phenyl ring (moiety C) and Phe1223. In addition, hydrophobic interactions were formed between the
phenyl ring (moiety A) in 20b and Phe1134, Phe1200. A binding model for (S)-20b in the ATP
binding site is presented in Figure 3b. However, this compound failed to dock into the binding pocket,
as the orientation of the ligand in the binding model was opposite to that of BMS-777607. Therefore,
we postulate that the requisite chirality for these compound may be the R-configuration. We are now
seeking an efficient route to access the enantiomers, and the optical pure compounds will be
synthesized and evaluated in the due course.
Figure 3. Binding poses of compounds (R)-20b and (S)-20b with c-Met.
3. Experimental
3.1. General Information
All chemical reagents were used as supplied unless indicated. Solvents used in organic reactions
were distilled under an inert atmosphere. Unless otherwise noted, all reactions were carried out at room
temperature and performed under a positive pressure of argon. Flash column chromatography was
performed on silica gel (200–300 mesh, Qingdao Haiyang Chemical Co., Ltd, Qingdao, China).
Analytical thin layer chromatography (TLC) was performed on glass plates pre-coated with a 0.25 mm
1
thickness of silica gel. H-NMR and 13C-NMR spectra were taken on a Jeol JNM-ECP 600
1
spectrometer (Jeol Ltd., Tokyo, Japan) at room temperature. Chemical shifts of the H-NMR spectra
are expressed in ppm relative to the solvent residual signal 7.26 in CDCl3 or to tetramethylsilane
13
(δ = 0.00). Chemical shifts of the C-NMR spectra are expressed in ppm relative to the solvent signal
77.00 in CDCl3 or to tetramethylsilane (δ = 0.00) unless otherwise noted. Electrospray (ESI) mass
spectra were recorded on a Global Q-TOF mass spectrometer (Waters, Wilford, MA, USA).

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3.2. Synthesis
Isobutyl 1-(4-fluorophenyl)-2-oxopiperidine-3-carboxylate (2). 1-Fluoro-4-iodobenzene (2.22 g, 10 mmol)
and piperidin-2-one (1.2 g, 12 mmol) were added to dry DMF (30 mL), followed by the addition of
K3PO4 (6.36 g, 30 mmol) and CuI (190 mg, 0.1 mmol). The mixture was heated to 100 °C for 12 h
before filtering through Celite. After washing with ethyl acetate (3 × 10 mL), the combined organic
phase was concentrated and the residue was purified by column chromatography to give 1-(4-
fluorophenyl)piperidin-2-one (1.73 g, 90%) as a yellow solid. This N-arylpiperidin-2-one (386 mg,
2 mmol) was dissolved in dry THF (20 mL) and cooled to −78 °C. After the addition of tert-BuLi (1.4 mL,
1.6 M in THF, 2.2 mmol) and stirring at this temperature for 4 h, isobutyl chlorofomate (400 μL, 2 mmol)
was added. Ten min later, the reaction was quenched by addition of saturated aq. NH4Cl (2 mL). The
mixture was diluted with water (20 mL) and extracted with EtOAc (3 × 20 mL). The combined organic
layer was washed with brine, dried over Na2SO4, and concentrated in vacuo. The residue was purified
by column chromatography to give compound 2 (480 mg, 82%) as a yellow wax. 1H-NMR (600 MHz,
CDCl3) δ 7.25–7.20 (m, 2H, ArH), 7.09–7.03 (m, 2H，ArH), 3.99 (dd, 1H, J = 10.6, 6.7 Hz, CH), 3.83
(d, 1 H, J = 6.7 Hz, CHH), 3.70–3.61 (m, 1H, CHH), 3.58 (t, 1 H, J = 6.9 Hz, CH), 2.32–2.24 (m, 1H,
CHH), 2.23–2.16 (m, 1H, CHH), 2.12–2.04 (m, 1H, CHH), 2.02–1.87 (m, 2H, CH, CHH), 0.94 (d, 6 H,
J = 6.6 Hz, CH3); 13C-NMR (150 MHz, CDCl3) δ 171.0, 166.3, 162.1, 160.4, 138.8, 127.9, 116.2,
100.0, 71.5, 51.6, 49.6, 27.8, 25.3, 21.4, 19.1; HR-MS (ESI) Calcd for C16H21FNO3 [M + H]+
294.1506, Found 294.1518.
1-(4-Fluorophenyl)-2-oxopiperidine-3-carboxylic acid (3). To a solution of 2 (217 mg, 0.74 mmol) in
THF/MeOH/H2O (1/1/1, 3 mL in total) at 0 °C was added LiOH monohydrate (94 mg, 2.2 mmol). The
reaction mixture was warmed to room temperature and stirred for 5 h. The solution was acidified to pH
1 with 1 mol/L HCl and extracted with EtOAc (3 × 20 mL). The organic extracts were combined and
washed with brine (2 × 5 mL). Evaporation of the solvent gave the corresponding acid 3 (152 mg,
1
87%) as a white solid. H-NMR (600 MHz, CDCl3) δ 7.33–7.28 (m, 1H, ArH), 7.25–7.19 (m, 1H,
ArH), 3.69–3.55 (m, 2H, NCH2), 3.43 (dd, 1H, J = 8.2, 6.5 Hz, CH), 2.16–2.10 (m, 1 H, CHH), 2.08–2.02
13
(m, 1H, CHH), 1.98–1.91 (m, 1H, CHH), 1.91–1.83 (m, 1H, CHH); C-NMR (150 MHz, CDCl3) δ
174.3, 170.2, 161.3, 159.6, 138.7, 127.9, 115.6, 51.8, 50.3, 27.5, 21.6; HR-MS (ESI) Calcd for
C12H13FNO3 238.0880 [M + H]+, found 238.0910.
3-Bromo-1-(4-fluorophenyl)-2-oxopiperidine-3-carboxylic acid (4). To a solution of acid 3 (220 mg,
0.93 mmol) in Et2O (5 mL) was added liquid Br2 (48 μL, 0.93 mmol) at 0 °C. The reaction mixture
was stirred for 2 h before concentrated in vacuo. The residue was purified by column chromatography,
1
giving compound 4 (265 mg, 91%) as white solid. H-NMR (600 MHz, acetone-d6) δ 13.03 (s, 1H,
OH), 7.44–7.40 (m, 2H, ArH), 7.25–7.20 (m, 2H, ArH), 4.04 (td, 1H, J = 12.1, 4.6 Hz, NCHH), 3.82
(ddt, 1H, J = 13.0, 6.3, 2.4 Hz, NCHH), 2.77–2.69 (m, 1H, CHH), 2.62–2.56 (m, 1H, CHH), 2.53–2.43
(m, 1H, CHH), 2.19–2.12 (m, 1H, CHH); 13C-NMR (150 MHz, acetone-d6) δ 166.4, 162.5, 160.9,
140.6, 140.6, 129.0, 129.0, 116.2, 52.1, 32.3, 20.4.

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3.2.1. General Procedure for the Synthesis of Isobutyl 1-(4-Fluorophenyl)-3-alkyl-2-oxopiperidine-3-
carboxylates 5a–c
To a solution of compound 2 (586 mg, 2 mmol) in dry THF (10 mL) at 0 °C was added NaH (72 mg,
80% suspension in mineral oil, 2.4 mmol) in portions. Thirty min later, alkyl halide (MeI, EtBr, or
n-BuBr, 2.6 mmol) was added slowly and the reaction mixture was stirred at this temperature for
another 5 h. When TLC showed all the starting material consumed, the reaction mixture was quenched
with 0.5 mol/L HCl, diluted with water (20 mL) and extracted with EtOAc (3 × 20 mL). The combined
organic layer was washed with brine, dried over Na2SO4 and concentrated. The residue was purified by
column chromatography to give the desired compound as pale yellow oil.
Isobutyl 1-(4-fluorophenyl)-3-methyl-2-oxopiperidine-3-carboxylate (5a). 87% yield; 1H-NMR (600 MHz,
CDCl3) δ 7.25–7.19 (m, 1 H, ArH), 7.12–7.01 (m, 1H, ArH), 4.06–3.88 (m, 2H, OCH2), 3.78–3.58 (m,
1H, CHH), 2.47–2.31 (m, 1H, CHH), 2.10–1.94 (m, 3H, CH2, CH), 1.94–1.84 (m, 1H, CHH), 1.57 (d,
3H, J = 2.4 Hz, CH3), 0.97 (d, 3H, J = 2.0 HzCH3), 0.96 (d, 3H, J = 2.1 Hz, CH3); 13C-NMR (150 MHz,
CDCl3) δ 173.8, 170.1, 161.9, 160.2, 139.3, 127.8, 116.0, 115.9, 71.5, 51.9, 51.3, 33.6, 27.8, 22.9,
20.4, 19.2; HR-MS (ESI) Calcd for C17H23FNO3 308.1662 [M + H]+, found 308.1599.
Isobutyl 3-ethyl-1-(4-fluorophenyl)-2-oxopiperidine-3-carboxylate (5b). 76% yield; 1H-NMR (600 MHz,
CDCl3) δ 7.24–7.18 (m, 2H, ArH), 7.08–7.03 (m, 2H, ArH), 4.01–3.90 (m, 2H, OCH2), 3.72–3.65 (m,
1 H, CHH), 3.63–3.56 (m, 1H, CHH), 2.31–2.24 (m, 1H, CHH), 2.16–2.09 (m, 1H, CHH), 2.10–2.04
(m, 1H, CHH), 2.02–1.91 (m, 4H, CH2), 0.98 (t, 3H, J = 7.4 Hz, CH3), 0.96 (d, 6H, J = 2.1 Hz, 2 × CH3);
13C-NMR (150 MHz, CDCl3) δ 173.6, 170.0, 161.8, 160.2, 139.3, 127.8, 116.0, 71.5, 51.9, 51.3, 33.6,
30.1, 27.8, 22.9, 20.4, 19.8; HR-MS (ESI) Calcd for C18H25FNO3 322.1819 [M + H]+, found 322.1830.
Isobutyl 3-butyl-1-(4-fluorophenyl)-2-oxopiperidine-3-carboxylate (5c). 83% yield; 1H-NMR (600 MHz,
CDCl3) δ 7.23–7.18 (m, 2H, ArH), 7.08–7.02 (m, 2H, ArH), 4.00–3.89 (m, 2H, OCH2), 3.72–3.66 (m,
1H, CHH), 3.61–3.56 (m, 1H, CHH), 2.32–2.26 (m, 1H, CHH), 2.10–1.86 (m, 6H), 1.46–1.38 (m, 1H,
CHH), 1.37–1.29 (m, 2H, CH2), 1.30–1.21 (m, 1H, CHH), 0.96 (d, 6H, J = 2.1 Hz, 2 × CH3), 0.90 (t, 3H,
J = 7.2 Hz, CH3); 13C-NMR (150 MHz, CDCl3) δ 173.5, 169.4, 161.8, 160.2, 139.4, 127.8, 115.9, 71.5,
54.9, 51.6, 35.7, 30.1, 27.0, 23.2, 20.7, 19.2, 14.1; HR-MS (ESI) Calcd for C20H29FNO3 350.2132,
[M + H]+, found 350.2122.
3.2.2. 1-(4-Fluorophenyl)-3-alkyl-2-oxopiperidine-3-carboxylic Acids 6a–c were Prepared by a
Procedure Similar to that of Compound 3.
3-Methyl-1-(4-fluorophenyl)-2-oxopiperidine-3-carboxylic acid (6a). White solid; 88% yield; 1H-NMR
(600 MHz, DMSO-d6) δ 12.59 (s, 1 H, OH), 7.31–7.25 (m, 2H, ArH), 7.24–7.17 (m, 2H, ArH), 3.65
(dt, 1H, J = 12.1, 6.1 Hz, NCHH), 3.59 (dt, 1H, J = 11.9, 5.8 Hz, NCHH), 2.25–2.18 (m, 1H, CHH),
1.95–1.87 (m, 2H, CH2), 1.87–1.80 (m, 1H, CHH), 1.37 (s, 3H, CH3); 13C-NMR (150 MHz, DMSO-d6)
δ 174.9, 169.7, 160.9, 159.3, 139.8, 128.2, 115.6, 51.2, 50.4, 32.8, 22.6, 19.8; HR-MS (ESI) Calcd for
C13H15FNO3 252.1036, [M + H]+, found 252.1040.

Molecules 2014, 19
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1
3-Ethyl-1-(4-fluorophenyl)-2-oxopiperidine-3-carboxylic acid (6b). white solid; 79% yield; H-NMR
(600 MHz, DMSO-d6) δ 12.79 (s, 1 H, OH), 7.26–7.23 (m, 2H, ArH), 7.16–7.12 (m, 2H, ArH), 3.92
(dt, J = 12.7, 6.5 Hz, 1H, NCHH), 3.74 (dt, J = 12.6, 6.4 Hz, 1H, NCHH), 2.56–2.50 (m, 1H, CHH),
2.20 (q, J = 6.7 Hz, 1H, CHH), 2.05–2.01 (m, 1H, CHH), 2.01–1.91 (m, 2H, CHH), 1.84 (dt, J = 12.3,
13
7.0 Hz, 1 H, CHH), 0.71 (t, J = 6.6 Hz, 3H, CH3); C-NMR (150 MHz, DMSO-d6) δ 174.8, 169.8,
161.2, 159.6, 139.5, 128.4, 115.8, 51.7, 50.9, 33.6, 29.7, 22.6, 18.8; HR-MS (ESI) Calcd for
C14H17FNO3 266.1193, [M + H]+, found 266.1201.
1
3-Butyl-1-(4-fluorophenyl)-2-oxopiperidine-3-carboxylic acid (6c). White solid; 84% yield; H-NMR
(600 MHz, DMSO-d6) δ 12.66 (s, 1H, OH), 7.25–7.20 (m, 2H, ArH), 7.14 (dd, 2H, J = 8.6, 7.0 Hz, ArH),
3.96–3.87 (m, 1H, CHH), 3.78–3.72 (m, 1H, CHH), 2.49–2.42 (m, 1H, CHH), 2.22 (dt, J = 19.0, 7.5 Hz,
2H, CH2), 2.03–1.91 (m, 3H, CHH, CH2), 1.38–1.21 (m, 4H, CH2CH2), 0.88 (t, 3 H, J = 6.4 Hz, CH3);
13C-NMR (150 MHz, DMSO-d6) δ 174.7, 169.5, 161.6, 160.0, 139.6, 127.9, 115.6, 54.6, 51.3, 35.4,
30.3, 23.2, 20.7, 14.2; HR-MS (ESI) Calcd for C16H21FNO3 294.1506, [M + H]+, found 294.1496.
3,4-Dichloropicolinamide (8). To a solution of 2,2,6,6-tetramethylpiperidine (1.56 g, 11 mmol) in dry
ether (20 mL) at 0 °C was added n-BuLi (4.4 mL, 2.5 M in THF, 11 mmol) slowly. The reaction
mixture was stirred at this temperature for 30 min before cooled to −78 °C. A solution of
3,4-dichloropyridine (1.48 g, 10 mmol) in dry ether (5 mL) was injected via syringe to the above
reaction mixture and stirred for 2 h before trimethylsilyl isothiocyanate (15 mmol) was added. After
warmed to room temperature, the reaction was quenched by the addition of HOAc (2 mL) and water
(10 mL), and then let to stir overnight. The suspension was filtered and washed with cold water, giving
1
the title compound as a gray solid (686 mg, 40%). H-NMR (DMSO-d6, 600 MHz) δ 8.50 (d, 1H,
J = 5.2 Hz, ArH), 8.12 (br s, 1H, CONH2), 7.83 (d, 1H, J = 5.2 Hz, ArH), 7.82 (br s, 1H, CONH2).
4-(4-Amino-2-fluorophenoxy)-3-chloropicolinamide (9). To a solution of 4-amino-2-fluorophenol (465 mg,
3.65 mmol) in DMF (10 mL) was added potassium tert-butoxide (440 mg, 3.95 mmol). Thirty min
later, 3,4-dichloropicolinamide (8) was added and the solution was heated to 50 °C. When TLC
showed all the starting materials consumed, the reaction mixture was diluted with EtOAc (50 mL),
washed with saturated NaHCO3, brine, and dried over Na2SO4. After concentration, the residue was
purified by column chromatography giving the title compound as a pale yellow solid (580 mg, 79%).
1H-NMR (DMSO-d6, 600 MHz) δ 8.29 (d, 1 H, J = 5.6 Hz, ArH), 7.00 (t, 1H, J = 8.8 Hz, ArH), 6.79
13
(d, 1H, J = 5.6 Hz, ArH), 6.63–6.55 (m, 2H, ArH); C-NMR (DMSO-d6, 150 MHz) δ 166.6, 160.8,
154.1, 153.9, 149.0, 148.7, 128.5, 123.7, 115.9, 110.1, 110.0, 101.3.
4-((7H-Pyrrolo[2,3-d]pyrimidin-4-yl)oxy)-3-fluoroaniline (11). The solution of 4-chloro-7H-pyrrolo-
[2,3-d]pyrimidine (1.0 g, 6.5 mmol) and 2-fluoro-4-nitrophenol (1.5 g, 9.5 mmol) in bromobenzene (5 mL)
was heated at 130 °C for 4 h in a sealed tube. After that, the reaction mixture was cooled to room
temperature, diluted with Et2O (5 mL) and filtered. Recrystallization in MeOH gave 4-(2-fluoro-4-
nitrophenoxy)-7H-pyrrolo[2,3-d]pyrimidine as a yellow solid (1.6 g, 85%), which was used for the next
step directly. To a solution of this nitro compound in THF (5 mL) and MeOH (5 mL) was added zinc
powder (130 mg, 2 mmol) and NH4Cl (270 mg, 5 mmol). The reaction mixture was stirred at room
temperature for 5 h before filtered through a Celite pad. The filtrate was diluted with EtOAc, washed

Molecules 2014, 19
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with water, dried over Na2SO4 and concentrated. The residue was purified by column chromatography
giving compound 11 (115 mg, 69%) as a brown solid. 1H-NMR (600 MHz, DMSO-d6) δ 12.19 (s, 1H,
NH), 8.28 (s, 1H, CH), 7.44 (t, 1H, J = 3.1 Hz, ArH), 7.00 (t, 1H, J = 8.9 Hz, ArH), 6.48 (dd, 1H, J = 13.0,
2.6 Hz, ArH), 6.45 (dd, 1H, J = 3.4, 1.5 Hz, CH), 6.42–6.39 (m, 1H, CH), 5.35 (s, 2H, NH2).
2-Chloro-4-(2-fluoro-4-nitrophenoxy)pyrimidine (12). 2-Fluoro-4-nitrophenol (314 mg, 2 mmol), K2CO3
(304 mg, 2.2 mmoo) and 2,4-dichloropyrimidine (300 mg, 2 mmol) were dissolved in DMF (20 mL) and
heated at 100 °C for 2 h. the reaction mixture was concentrated, diluted with EtOAc (100 mL), washed
with water, brine, and concentrated in vacuo. The residue was purified by column chromatography
1
giving compound 12 (324 mg, 65%) as a white solid. H-NMR (600 MHz, DMSO-d6) δ 8.78 (d,
J = 5.7 Hz, 1H, ArH), 8.44 (dd, 1H J = 10.2, 2.7 Hz, ArH), 8.25 (ddd, 1H, J = 9.0, 2.7, 1.3 Hz, ArH),
7.82 (dd, 1H, J = 9.0, 7.7 Hz, ArH), 7.49 (d, 1H, J = 5.7 Hz, ArH).
4-(4-Amino-2-fluorophenoxy)-N-(4-methoxybenzyl)pyrimidin-2-amine (13). To the solution of compound
12 (239 mg 1mmol) and 4-methoxybenzylamine (192 mg, 1.4 mmol) in DMF (8 mL) was added
K2CO3 (152 mg, 1.1 mmol). The reaction mixture was heated at 100 °C for 1 h before concentrated in
vacuo. After diluted with EtOAc, the solution was washed with water and brine, and then concentrated.
The residue was purified by column chromatography giving a yellow solid (231 mg, 68%), which was
treated by zinc powder and NH4Cl as described for the preparation of compound 11. After workup and
purification, compound 13 was obtained as a brown solid (115 mg, 69%). 1H-NMR (600 MHz, CDCl3)
δ 8.06 (br s, 1H, ArH), 7.12 (br s, 2H, ArH), 6.92 (t, 1H, J = 8.6 Hz, ArH), 6.80 (d, 2H, J = 8.2 Hz,
ArH), 6.47 (dd, 1H, J = 11.8, 2.7 Hz, ArH), 6.45–6.39 (m, 1H, ArH), 6.15 (d, 1H, J = 5.8 Hz, ArH), 4.36
(br s, 2H, NH2), 3.92 (br s, 2H, CH2), 3.78 (s, 3H, CH3).
4-((6,7-Dimethoxyquinolin-4-yl)oxy)-3-fluoroaniline (14). The procedure used was similar to that used
for the synthesis of compound 11. Compound 14 was obtained as a brown solid in 76% yield.
1H-NMR (600 MHz, CDCl3) δ 8.47 (d, 1H, J = 5.1 Hz, ArH), 7.58 (s, 1H, ArH), 7.40 (s, 1H, ArH),
7.02 (t, 1H, J = 8.6 Hz, ArH), 6.55 (dd, 1H, J = 12.0, 2.7 Hz, ArH), 6.49 (dd, 1H, J = 8.9, 2.6 Hz, ArH),
6.40 (d, 1H, J = 5.0 Hz, ArH), 4.05 (s, 3H, OCH3), 4.03 (s, 3H, OCH3), 3.84 (br s, 2H, NH2).
3.2.3. General Procedure for the Preparation of 15a–b, 17a–b, 18a–b and 20a–b
EDC-HCl (1.2 g, 6.25 mmol) was added to a suspension of the carboxylic acid (2.5 mol of 3, 4, or
6a–c) and the amine (2.5 mmol of 9, 11, 13 or 14) in THF (25 mL) at 0 °C followed by DMAP (30 mg,
0.25 mmol). The reaction mixture was warmed to room temperature and stirred overnight. After
diluted with EtOAc (150 mL), the whole mixture was washed with 1 M HCl (3 × 10 mL), 5%
NaHCO3 (3 × 10 mL), and brine (3 × 10 mL), dried over Na2SO4, and concentrated in vacuo. The
residue was purified by column chromatography to give corresponding amide.
3-Chloro-4-(2-fluoro-4-(1-(4-fluorophenyl)-2-oxopiperidine-3-carboxamido)phenoxy)picolinamide
1
(15a, from 9 and 3): 76% yield; H-NMR (600 MHz, DMSO-d6) δ 10.56 (s, 1H, NH), 8.33 (d, 1H,
J = 5.5 Hz, ArH), 8.07 (s, 1H, NH), 7.91 (dd, 1H, J = 12.9, 2.4 Hz, ArH), 7.77 (s, 1H, NH), 7.44 (dd,
1H, J = 8.9, 2.4 Hz, ArH), 7.41 (t, 1H, J = 8.8 Hz, ArH), 7.36–7.32 (m, 2H, ArH), 7.26–7.20 (m, 2H,

Molecules 2014, 19
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ArH), 6.84 (dd, 1H, J = 5.5, 1.1 Hz, ArH), 3.76–3.68 (m, 1H, CH), 3.65–3.57 (m, 2H, CH2), 2.21–2.13
(m, 2H, CH2), 2.12–2.04 (m, 1H, CHH), 1.96–1.87 (m, 1H, CHH); 13C-NMR (150 MHz, DMSO-d6) δ
169.3, 166.5, 160.9, 160.0, 159.3, 154.2, 153.8, 152.2, 148.7, 139.4, 138.5, 138.4, 134.8, 134.7, 128.3,
128.2, 123.7, 116.3, 115.9, 115.6, 115.4, 110.6, 107.9, 107.8, 54.9, 51.2, 50.5, 48.6, 24.8, 21.2; MS
(ESI pos ion) m/z: calcd for C24H19ClF2N4O4 500.1, found 501.1 [M + H]+; HR-MS (ESI) Calcd for
C24H20ClF2N4O4 501.1141 [M + H]+, found 501.1160.
3-Chloro-4-(4-(3-chloro-1-(4-fluorophenyl)-2-oxopiperidine-3-carboxamido)-2-fluorophenoxy)-
1
picolinamide (15b, from 9 and 4) 68% yield; H-NMR (600 MHz, CDCl3) δ 10.11 (s, 1H, NH), 8.24
(d, 1H, J = 5.5 Hz, ArH), 7.80 (dd, 1H, J = 11.9, 2.5 Hz, ArH), 7.54 (d, 1H, J = 3.9 Hz, ArH), 7.33–7.22
(m, 3H, ArH), 7.18–7.11 (m, 3H, NH), 6.68 (dd, 1H, J = 5.5, 1.1 Hz, ArH), 6.15 (d, 1H, J = 3.4 Hz,
ArH), 3.85–3.78 (m, 1H, CHH), 3.73–3.68 (m, 1H, CHH), 2.96–2.87 (m, 1H, CHH), 2.65–2.56 (m,
1H, CHH), 2.45–2.34 (m, 1H, CHH), 2.17–2.07 (m, 1H, CHH); 13C-NMR (150 MHz, CDCl3) δ 166.8,
166.0, 164.9, 162.6, 161.8, 160.9, 154.7, 153.0, 148.3, 147.0, 137.9, 136.8, 136.8, 136.8, 127.9, 127.8,
123.4, 121.2, 116.7, 116.6, 116.5, 111.7, 109.8, 109.6, 64.4, 52.6, 33.8, 19.4; MS (ESI pos ion) m/z:
calcd for C24H18Cl2F2N4O4 534.1 found 535.1 [M + H]+; HR-MS (ESI) Calcd for C24H19Cl2F2N4O4
535.0752 [M + H]+, found 535.0764.
N-(4-((7H-pyrrolo[2,3-d]pyrimidin-4-yl)oxy)-3-fluorophenyl)-1-(4-fluorophenyl)-2-oxopiperidine-3-
carboxamide (17a, from 11 and 3): 31% yield, 1H-NMR (600 MHz, CDCl3) δ 11.02 (s, 1H, NH), 10.19
(s, 1H, NH), 8.87 (s, 1H, ArH), 8.54 (s, 1H, ArH), 8.13–7.93 (m, 1H, ArH), 7.81 (d, 1H, J = 11.6 Hz,
ArH), 7.42 (s, 1H, ArH), 7.31–7.20 (m, 2H, ArH), 7.16–7.03 (m, 2H, ArH), 6.92 (s, 1H, ArH), 3.74–3.59
(m, 2H, NCH2), 3.59–3.47 (m, 1H, CH), 2.63–2.51 (m, 1H, CHH), 2.26–2.16 (m, 1 H, CHH), 2.15–2.07
(m, 1 H, CHH), 2.08–1.98 (m, 1 H, CHH); 13C-NMR (150 MHz, CDCl3) δ 169.5, 168.3, 162.5, 160.9,
156.2, 155.9, 154.6, 152.4, 151.1, 139.8, 138.5, 134.5, 134.2, 128.2, 128.1, 126.2, 123.0, 116.9, 116.8,
116.7, 116.6, 115.8, 115.6, 109.4, 109.2, 100.3, 53.1, 47.8, 47.7, 29.7, 22.8, 21.6; MS (ESI pos ion)
m/z: calcd for C24H19F2N5O3 463.1, found 464.2 [M + H]+; HR-MS (ESI) Calcd for C24H20F2N5O3
464.1534 [M + H]+, found 464.1547.
N-(4-((7H-pyrrolo[2,3-d]pyrimidin-4-yl)oxy)-3-fluorophenyl)-3-chloro-1-(4-fluorophenyl)-2-oxo-
1
piperidine-3-carboxamide (17b, from 11 and 4): 42% yield; H-NMR (600 MHz, CDCl3) δ 8.25 (s,
1H, ArH), 7.89 (dd, J = 12.5, 2.5 Hz, 1H, ArH), 7.50 (d, J = 3.6 Hz, 1H, ArH), 7.48 (dd, J = 2.5, 1.3 Hz,
1H, ArH), 7.46–7.42 (m, 3H, ArH), 7.38 (t, J = 8.7 Hz, 1H, ArH), 7.25–7.19 (m, 2H, ArH), 6.64 (d,
J = 3.6 Hz, 1H, ArH), 3.98–3.88 (m, 1H. CHH), 3.84–3.78 (m, 1H. CHH), 2.96 (ddd, J = 14.8, 11.6,
3.2 Hz, 1H. CHH), 2.59–2.52 (m, 1H. CHH), 2.40–2.31 (m, 1H. CHH), 2.21–2.11 (m, 1H. CHH);
13C-NMR (150 MHz, CDCl3) δ 169.7, 168.5, 162.7, 160.9, 156.3, 155.9, 154.7, 152.4, 151.3, 139.8,
138.6, 134.7, 134.5, 128.4, 128.3, 126.4, 123.6, 117.0, 116.8, 116.7, 116.6, 115.9, 115.7, 109.6, 109.4,
100.6, 64.5, 53.5, 47.9, 47.7, 29.9, 22.8, 21.8; MS (ESI pos ion) m/z: calcd for C24H18ClF2N5O3 497.1,
found 498.0 [M + H]+; HR-MS (ESI) Calcd for C24H19ClF2N5O3 498.1145 [M + H]+, found 498.1155.
N-(3-fluoro-4-((2-((4-methoxybenzyl)amino)pyrimidin-4-yl)oxy)phenyl)-1-(4-fluorophenyl)-2-oxo-
1
piperidine-3-carboxamide (18a, from 13 and 3): 69% yield, H-NMR (600 MHz, CDCl3) δ 10.19 (s,
1H, NH), 8.06 (s, 1H, ArH), 7.75 (d, 1H, J = 12.2 Hz, ArH), 7.24–7.18 (m, 3H, ArH), 7.11 (t, 2H,

Molecules 2014, 19
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J = 8.3 Hz, ArH), 7.06 (t, 1H, J = 8.4 Hz, ArH), 7.00 (d, 1H, J = 8.6 Hz, ArH), 6.78 (s, 2H, ArH), 6.23
(s, 1H, ArH), 4.24 (s, 2H, CH2), 3.76 (s, 3H, OCH3), 3.71–3.62 (m, 2H, NCH2), 3.62–3.57 (m, 1H,
CH), 2.58–2.48 (m, 1H, CHH), 2.25–2.14 (m, 1H, CHH), 2.13–2.05 (m, 1H, CHH), 2.05–1.97 (m, 1H,
13
CHH); C-NMR (150 MHz, CDCl3) δ 169.3, 166.0, 162.4, 160.8, 159.0, 156.7, 154.8, 138.4, 129.3,
128.2, 128.1, 123.7, 116.6, 116.5, 115.3, 114.0, 55.4, 52.7, 47.7, 22.9, 21.7; MS (ESI pos ion) m/z:
calcd for C30H27F2N5O4 559.2, found 560.2 [M + H]+; HR-MS (ESI) Calcd for C30H28F2N5O4
560.2109 [M + H]+, found 560.2125.
3-Chloro-N-(3-fluoro-4-((2-((4-methoxybenzyl)amino)pyrimidin-4-yl)oxy)phenyl)-1-(4-fluorophenyl)-
1
2-oxopiperidine-3-carboxamide (18b, from 13 and 4):57% yield; H-NMR (600 MHz, CDCl3) δ 9.96
(s, 1H, NH), 8.12 (s, 1H, ArH), 7.69 (dd, J = 11.8, 2.5 Hz, 1H, ArH), 7.25–7.22 (m, 2H, ArH), 7.19
(dd, 1H, J = 8.9, 2.4 Hz, ArH), 7.15–7.08 (m, 4H, ArH), 6.80 (d, 2H, J = 8.0 Hz, ArH), 6.18 (d, 1H,
J = 5.7 Hz, ArH), 4.32 (s, 2H, CH2), 3.81–3.75 (m, 1H, CHH), 3.77 (s, 3H, OCH3), 3.69 (dt, 1H, J = 12.4,
4.9 Hz, CHH), 2.90 (ddd, 1H, J = 14.6, 11.3, 3.0 Hz, CHH), 2.63–2.54 (m, 1H, CHH), 2.41–2.31 (m,
1H, CHH), 2.15–2.06 (m, 1H, CHH); 13C-NMR (150 MHz, CDCl3) δ 166.9, 164.6, 162.6, 162.1,
160.9, 159.5, 158.9, 157.7, 155.3, 153.70, 138.0, 136.4, 136.3, 135.8, 135.8, 130.9, 129.1, 127.9,
127.8, 124.2, 116.7, 116.5, 115.7, 113.9, 64.4, 55.4, 55.3, 52.7, 45.0, 33.9, 19.5; MS (ESI pos ion) m/z:
calcd for C30H26ClF2N5O4 593.2, found 594.2 [M + H]+; HR-MS (ESI) Calcd for C30H27ClF2N5O4
594.1720 [M + H]+, found 594.1733.
N-(4-((6,7-dimethoxyquinolin-4-yl)oxy)-3-fluorophenyl)-1-(4-fluorophenyl)-2-oxopiperidine-3-carbox-
amide (20a, from 14 and 3): 61% yield; 1H-NMR (600 MHz, CDCl3) δ 10.30 (s, 1H, NH), 8.51 (s, 1 H,
ArH), 7.84 (dd, 1H, J = 12.1, 2.5 Hz, ArH), 7.69 (s, 1H, ArH), 7.59 (s, 1H, ArH), 7.29–7.26 (m, 1H,
ArH), 7.25–7.21 (m, 2H, ArH), 7.18 (t, 1H, J = 8.6 Hz, ArH), 7.12 (t, 2H, J = 8.5 Hz, ArH), 6.49 (d,
1H, J = 5.5 Hz, ArH), 4.08 (s, 3H, OCH3), 4.06 (s, 3H, OCH3), 3.75–3.60 (m, 2H, CHH), 3.58–3.49
(m, 1H, CH), 2.60–2.47 (m, 1H, CHH), 2.29–2.19 (m, 1H, CHH), 2.14–1.97 (m, 2H, CH2); 13C-NMR
(150 MHz, CDCl3) δ 169.3, 166.4, 154.6, 150.6, 145.7, 138.4, 128.1, 123.5, 116.6, 116.5, 116.2, 99.7,
56.7, 56.4, 52.7, 47.8, 29.8, 23.0, 22.8, 21.7; MS (ESI pos ion) m/z: calcd for C29H25F2N3O5 533.2,
found 534.2 [M + H]+; HR-MS (ESI) Calcd for C29H26F2N3O5 534.1841 [M + H]+, found 534.1850.
3-Chloro-N-(4-((6,7-dimethoxyquinolin-4-yl)oxy)-3-fluorophenyl)-1-(4-fluorophenyl)-2-oxopiperidine-
1
3-carboxamide (20b, from 14 and 4): 54% yield; H-NMR (600 MHz, CDCl3) δ 10.05 (s, 1H, NH),
8.48 (d, 1H, J = 5.4 Hz, ArH), 7.79 (dd, 1H, J = 12.0, 2.5 Hz, ArH), 7.57 (s, 1H, ArH), 7.44 (s, 1H,
ArH), 7.29–7.23 (m, 4H, ArH), 7.20 (t, 1H, J = 8.6 Hz, ArH), 7.13 (t, 2H, J = 8.4 Hz, ArH), 6.39 (d,
1H, J = 5.3 Hz, ArH), 4.05 (s, 3H, OCH3), 4.04 (s, 3H, OCH3), 3.80 (ddd, 1H, J = 14.5, 10.3, 4.7 Hz,
CHH), 3.74–3.66 (m, 1H, CHH), 2.97–2.83 (m, 1H, CHH), 2.67–2.56 (m, 1H, CHH), 2.45–2.34 (m,
1H, CHH), 2.15–2.07 (m, 1H, CHH); 13C-NMR (150 MHz, CDCl3) δ 166.9, 164.8, 162.6, 161.0,
160.2, 155.3, 153.6, 153.1, 149.8, 148.6, 146.7, 137.9, 137.7, 137.6, 136.3, 136.2, 127.9, 127.8, 123.8,
116.6, 116.5, 116.4, 115.6, 113.0, 109.8, 109.7, 109.6, 109.6, 107.8, 107.74, 99.5, 99.5, 64.3, 56.3,
56.2, 52.7, 33.8, 29.8, 19.5; MS (ESI pos ion) m/z: calcd for C29H24ClF2N3O5 567.1, found 568.1 [M + H]+;
HR-MS (ESI) Calcd for C29H25ClF2N3O5 568.1451 [M + H]+, found 568.1461.

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N-(4-((6,7-dimethoxyquinolin-4-yl)oxy)-3-fluorophenyl)-1-(4-fluorophenyl)-3-methyl-2-oxopiperidine-
1
3-carboxamide (20c, from 14 and 6a): 68% yield; H-NMR (600 MHz, CDCl3) δ 10.01 (s, 1H, NH),
8.47 (d, 1H, J = 5.3 Hz, ArH), 7.82 (dd, 1H, J = 12.2, 2.5 Hz, ArH), 7.58 (s, 1H, ArH), 7.42 (s, 1H,
ArH), 7.25–7.20 (m, 3H, ArH), 7.19 (t, 1H, J = 8.5 Hz, ArH), 7.15–7.11 (m, 2H, ArH), 6.38 (d, 1H,
J = 5.1 Hz, ArH), 4.06 (s, 3H, OCH3), 4.04 (s, 3H, OCH3), 3.71–3.62 (m, 2H, NCH2), 2.83–2.76 (m,
1H, CHH), 2.07–1.97 (m, 2H, CH2), 1.87–1.81 (m, 1H, CHH), 1.71 (s, 3H, CH3); 13C-NMR (150 MHz,
CDCl3) δ 173.7, 170.1, 162.4, 160.8, 160.2, 153.7, 153.0, 149.7, 148.9, 146.9, 138.7, 137.1, 128.2,
123.8, 116.6, 116.5, 116.0, 116.0, 115.6, 109.2, 107.9, 102.3, 99.5, 56.3, 56.2, 53.1, 50.5, 30.9, 27.7,
20.7, 14.3; MS (ESI pos ion) m/z: calcd for C30H27F2N3O5 547.2, found 548.2 [M + H]+; HR-MS (ESI)
Calcd for C30H28F2N3O5 548.1997 [M + H]+, found 548.2012.
N-(4-((6,7-dimethoxyquinolin-4-yl)oxy)-3-fluorophenyl)-3-ethyl-1-(4-fluorophenyl)-2-oxopiperidine-3-
carboxamide (20d, from 14 and 6b): 58% yield; 1H-NMR (600 MHz, CDCl3) δ 9.99 (s, 1H, NH), 8.47
(d, 1H, J = 5.4 Hz, ArH), 7.82 (dd, 1H, J = 12.1, 2.4 Hz, ArH), 7.58 (s, 1H, ArH), 7.44 (s, 1H, ArH),
7.24–7.16 (m, 4H, ArH), 7.15–7.11 (m, 2H, ArH), 6.39 (d, 1H, J = 5.2 Hz, ArH), 4.06 (s, 3H, OCH3),
4.05 (s, 3H, OCH3), 3.71–3.59 (m, 2H, NCH2), 2.81 (1H, ddd, J = 13.9, 6.4, 2.7 Hz, CHH), 2.22–2.14
(m, 1H, CHH), 2.12–1.93 (m, 4H, CH2CH3), 1.82–1.76 (m, 1H, CHH), 1.02 (t, 3H, J = 7.4 Hz,
CH2CH3); 13C-NMR(150 MHz, CDCl3) δ 173.3, 169.0, 165.8, 162.5, 160.4, 155.3, 153.7, 153.1,
149.7, 148.7, 146.8, 138.8, 137.1, 137.1, 137.0, 136.9, 128.3, 115.7, 107.8, 102.3, 99.6, 56.3, 55.2,
53.1, 33.8, 27.0, 20.8; MS (ESI pos ion) m/z: calcd for C31H29F2N3O5 561.2, found 562.2 [M + H]+;
HR-MS (ESI) Calcd for C31H30F2N3O5 562.2154 [M + H]+, found 562.2160.
N-(4-((6,7-dimethoxyquinolin-4-yl)oxy)-3-fluorophenyl)-3-butyl-1-(4-fluorophenyl)-2-oxopiperidine-3-
carboxamide (20e, from 14 and 6c): 64% yield; 1H-NMR (600 MHz, CDCl3) δ 9.98 (s, 1H, NH), 8.47
(d, 1H, J = 5.4 Hz, ArH), 7.82 (dd, 1H, J = 12.5, 2.6 Hz, ArH), 7.58 (s, 1H, ArH), 7.42 (s, 1H, ArH),
7.25–7.16 (m, 4H, ArH), 7.16–7.11 (m, 2H, ArH), 6.39 (d, 1H, J = 5.1 Hz, ArH), 4.06 (s, 3H, OCH3),
4.05 (s, 3H, OCH3), 3.71–3.59 (m, 2H, NCH2), 2.82 (ddd, 1H, J = 14.0, 6.1, 2.7 Hz, CHH), 2.13–1.92
(m, 4H, 2 × CH2), 1.84–1.77 (m, 1H, CHH), 1.42–1.28 (m, 4H, 2 × CH2), 0.95–0.89 (m, 3H, CH2CH3);
13C-NMR (150 MHz, CDCl3) δ 173.3, 169.1, 160.3, 153.0, 149.7, 148.9, 147.0, 138.8, 137.1, 128.3,
128.2, 123.8, 116.7, 116.5, 116.0, 115.7, 109.4, 108.0, 102.3, 99.6, 56.3, 56.3, 54.9, 53.1, 40.5, 27.5,
27.0, 23.0, 20.9, 14.1; MS (ESI pos ion) m/z: calcd for C33H33F2N3O5 589.2, found 590.2 [M + H]+;
HR-MS (ESI) Calcd for C33H34F2N3O5 590.2467 [M + H]+, found 590.2478.
3.2.4. Preparation of 16a and 16b
To amide 15a or 15b (0.2 mmol) in ethyl acetate (2 mL), acetonitrile (2 mL), and water (1 mL) at 0 °C
was added iodobenzene diacetate (82 mg, 0.26 mmol). After stirring at room temperature for 2 h,
saturated NaHCO3 (3 mL) was added, followed by 30 mL of ethyl acetate. The mixture was filtered,
and the filtrate was washed with brine (3 × 5 mL), dried over Na2SO4 and concentrated in vacuo. The
residue was purified by flash chromatography on silica gel to give compounds 16a–b.
N-(4-((2-amino-3-chloropyridin-4-yl)oxy)-3-fluorophenyl)-1-(4-fluorophenyl)-2-oxopiperidine-3-
1
carboxamide (16a). white solid; yield 72%; H-NMR (600 MHz, CDCl3) δ 10.00 (s, 1H, NH), 7.71

Molecules 2014, 19
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(dd, 1H, J = 12.6, 2.5 Hz, ArH), 7.24–7.18 (m, 3H, ArH), 7.17–7.10 (m, 3H, ArH), 7.02 (dt, 1H, J = 9.0,
1.8 Hz, ArH), 6.62 (t, 1H, J = 8.9 Hz, ArH), 5.01 (s, 2H, NH2), 3.65 (dq, 2H, J = 7.2, 4.3, 3.4 Hz,
NCH2), 3.54 (t, J = 6.3 Hz, 1H, CH), 2.59–2.49 (m, 1H, CHH), 2.21–2.15 (m, 1H, CHH), 2.10–2.05
(m, 1H, CHH), 2.04–1.98 (m, 1H, CHH); 13C-NMR (150 MHz, CDCl3) 169.4, 165.7, 162.5, 160.9,
155.6, 154.7, 151.1, 146.5, 139.9, 138.5, 134.5, 134.4, 128.2, 128.2, 123.3, 116.9, 116.8, 116.7, 116.6,
116.6, 115.3, 115.2, 109.4, 109.2, 108.9, 52.8, 47.6, 47.5, 29.8, 22.9, 21.8; MS (ESI pos ion) m/z: calcd
for C23H19ClF2N4O3 472.1, found 473.1 [M + H]+; HR-MS (ESI) Calcd for C23H20ClF2N4O3 473.1192
[M + H]+, found 473.1214.
N-(4-((2-amino-3-chloropyridin-4-yl)oxy)-3-fluorophenyl)-3-chloro-1-(4-fluorophenyl)-2-oxo-piperidine-
3-carboxamide (16b). white solid; yield 76%; 1H-NMR (600 MHz, CDCl3) δ 10.02 (s, 1H, NH), 7.77
(d, 1H, J = 5.8 Hz, ArH), 7.74 (dd, 1H, J = 12.0, 2.5 Hz, ArH), 7.26–7.23 (m, 2H, ArH), 7.23–7.20 (m,
1H, ArH), 7.16–7.11 (m, 3H, ArH), 5.99 (dd, 1H, J = 5.8, 1.0 Hz, ArH), 5.04 (br s, 2H, NH2),
3.84–3.74 (m, 1H, CHH), 3.74–3.66 (m, 1H, CHH), 2.94–2.82 (m, 1H, CHH), 2.63–2.57 (m, 1H,
CHH), 2.43–2.34 (m, 1H, CHH), 2.14–2.09 (m, 1H, CHH); 13C-NMR (150 MHz, CDCl3) δ 166.9,
164.8, 162.6, 161.0, 160.5, 156.6, 155.0, 153.3, 148.6, 147.8, 146.7, 137.9, 136.2, 127.8, 123.4, 116.7,
116.6, 116.2, 109.6, 109.4, 102.6, 102.1, 91.8, 64.2, 52.7, 33.8, 19.5; MS (ESI pos ion) m/z: calcd for
C23H18Cl2F2N4O3 506.1, found 507.1 [M + H]+; HR-MS (ESI) Calcd for C23H19Cl2F2N4O3 507.0802
[M + H]+, found 507.0816.
3.2.5. Preparation of 19a and 19b
Compound 18a or 18b (40 mg, 0.07 mmol) was dissolved in TFA and heated to reflux for 6 h. The
solvent was removed and the residue was purified by column chromatography, giving the title
compound 19a or 19b as a pale yellow solid.
N-(4-((2-aminopyrimidin-4-yl)oxy)-3-fluorophenyl)-1-(4-fluorophenyl)-2-oxopiperidine-3-carbox-
amide (19a). 71% yield; 1H-NMR (600 MHz, CDCl3) δ 10.20 (s, 1 H, NH), 7.95 (s, 1H, ArH), 7.75 (d,
1H, J = 11.8 Hz, ArH), 7.21 (dd, 2H, J = 8.7, 4.8 Hz, ArH), 7.18 (d, 1H, J = 8.6 Hz, ArH), 7.13 (t, 2H,
J = 8.2 Hz, ArH), 7.07 (t, 1H, J = 8.4 Hz, ArH), 6.49 (s, 1H, ArH), 5.77 (s, 1H, NH), 3.67 (q, 2H,
J = 6.0 Hz, NCH2), 3.57 (s, 1H, CH), 2.57–2.46 (m, 1H, CHH), 2.25–2.16 (m, 1H, CHH), 2.13–1.95
13
(m, 2H, CH2); C-NMR (150 MHz, CDCl3) δ 166.3, 162.5, 160.9, 154.4, 152.8, 138.4, 137.8, 134.1,
128.2, 128.1, 123.1, 116.7, 116.5, 115.6, 108.9, 108.7, 52.7, 47.7, 29.8, 23.0, 21.7; MS (ESI pos ion)
m/z: calcd for C22H19F2N5O3 439.1, found 440.1 [M + H]+; HR-MS (ESI) Calcd for C22H20F2N5O3
440.1534 [M + H]+, found 440.1528.
N-(4-((2-aminopyrimidin-4-yl)oxy)-3-fluorophenyl)-3-chloro-1-(4-fluorophenyl)-2-oxopiperidine-3-
carboxamide (19b). 87% yield; 1H-NMR (600 MHz, CDCl3) δ 10.04 (s, 1H, NH), 7.96 (d, 1H, J = 6.7 Hz,
ArH), 7.72 (dd, 1H, J = 11.8, 2.5 Hz, ArH), 7.25–7.18 (m, 3H, ArH), 7.16–7.06 (m, 3H, ArH), 6.47 (d,
1H, J = 6.7 Hz, ArH), 3.79 (ddd, 1H, J = 12.4, 10.1, 4.7 Hz, CHH), 3.69 (dt, 1H, J = 11.3, 4.5 Hz,
CHH), 2.88 (ddd, 1H, J = 14.9, 11.6, 3.1 Hz, CHH), 2.63–2.49 (m, 1H, CHH), 2.44–2.31 (m, 1H,
13
CHH), 2.15–2.05 (m, 1H, CHH); C-NMR (150 MHz, CDCl3) δ 171.2, 166.8, 164.9, 162.6, 161.0,
154.5, 152.8, 137.9, 137.9, 137.2, 137.1, 134.8, 134.7, 127.9, 127.9, 127.8, 123.3, 116.7, 116.6, 116.0,

Molecules 2014, 19
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109.3, 109.2, 109.1, 109.1, 100.0, 99.0, 64.4, 52.7, 33.8, 19.4; MS (ESI pos ion) m/z: calcd for
C22H18ClF2N5O3 473.1, found 474.0 [M + H]+; HR-MS (ESI) Calcd for C22H19ClF2N5O3 474.1145
[M + H]+, found 474.1151.
3.3. Biology
3.3.1. c-Met Kinase Assay
The effects of indicated compound on the activities of c-Met kinases were determined using
enzyme-linked immunosorbent assays (ELISAs) with purified recombinant proteins. Briefly,
20 μg/mL poly (Glu,Tyr)4:1 (Sigma, St. Louis, MO, USA) was pre-coated in 96-well plates as a
substrate. A 50-μL aliquot of 10 μmol/L ATP solution diluted in kinase reaction buffer (50 mmol/L
HEPES [pH 7.4], 50 mmol/L MgCl2, 0.5 mmol/L MnCl2, 0.2 mmol/L Na3VO4, and 1 mmol/L DTT)
was added to each well; 1 μL of various concentrations of indicated compound diluted in 1% DMSO
(v/v) (Sigma) were then added to each reaction well. DMSO (1%, v/v) was used as the negative
control. The kinase reaction was initiated by the addition of purified c-Met tyrosine kinase proteins
diluted in 49 μL of kinase reaction buffer. After incubation for 60 min at 37 °C, the plate was washed
three times with phosphate-buffered saline (PBS) containing 0.1% Tween 20 (T-PBS).
Anti-phosphotyrosine (PY99) antibody (100 μL; 1:500, diluted in 5 mg/mL BSA T-PBS) was then
added. After a 30-min incubation at 37 °C, the plate was washed three times, and 100 μL horseradish
peroxidase-conjugated goat anti-mouse IgG (1:2000, diluted in 5 mg/mL BSA T-PBS) was added. The
plate was then incubated at 37 °C for 30 min and washed 3 times. A 100-μL aliquot of a solution
containing 0.03% H2O2 and 2 mg/ml o-phenylenediamine in 0.1 mol/L citrate buffer (pH 5.5) was
added. The reaction was terminated by the addition of 50 μL of 2 mol/L H2SO4 as the color changed,
and the plate was analyzed using a multi-well spectrophotometer (SpectraMAX 190, Molecular
Devices, Sunnyvale, CA, USA) at 490 nm. The inhibition rate (%) was calculated using the following
equation: [1 − (A490/A490 control)] × 100%. The IC50 values were calculated from the inhibition
curves in two separate experiments.
3.3.2. Cell Proliferation Assay
Cells were seeded in 96-well tissue culture plates. On the next day, the cells were exposed to
various concentrations of compounds and further cultured for 72 h. Cell proliferation was then
determined using sulforhodamine B (SRB, Sigma, St. Louis, MO, USA). The IC50 values were
calculated by concentration-response curve fitting using the four-parameter method.
4. Conclusions
In summary, a series of compounds based upon the 3-carboxylpiperidin-2-one scaffold were
designed, synthesized and evaluated for their c-Met kinase inhibition and cytotoxicity against MKN45
cancer cell lines. Five compounds (16b, 20b–e) exhibited moderate to excellent activity against c-Met
kinase, with IC50 values ranging from 8.6–81 nM. Moreover, four compounds (20b–e) showed potent
inhibitory activity against MKN45 cell proliferation, with IC50s ranging from 0.57–16 μM. Further
structure-activity relationship studies are under way in our laboratory and will be reported in due course.

Molecules 2014, 19
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Acknowledgments
This work was supported by the funds from National Program on Key Basic Research Project of
China (2012CB910704), the National Natural Science Foundation (91229205, 81102461), and
National S&T Major Projects (2012ZX09301001-007).
Conflicts of Interest
The authors declare no conflict of interest.
References
1. Gherardi, E.; Birchmeier, W.; Birchmeier, C.; Vande Woude, G. Targeting MET in cancer:
Rationale and progress. Nat. Rev. Cancer 2012, 12, 89–103.
2. Benvenuti, S.; Comoglio, P.M. The MET receptor tyrosine kinase in invasion and metastasis.
J. Cell. Physiol. 2007, 213, 316–325.
3. Cappuzzo, F.; Marchetti, A.; Skokan, M.; Rossi, E.; Gajapathy, S.; Felicioni, L.; del Grammastro, M.;
Sciarrotta, M.G.; Buttitta, F.; Incarbone, M.; et al. Increased MET gene copy number negatively
affects survival of surgically resected non-small-cell lung cancer patients. J. Clin. Oncol. 2009,
27, 1667–1674.
4. Okuda, K.; Sasaki, H.; Yukiue, H.; Yano, M.; Fujii, Y. Met gene copy number predicts the
prognosis for completely resected non-small cell lung cancer. Cancer Sci. 2008, 99, 2280–2285.
5. Toiyama, Y.; Miki, C.; Inoue, Y.; Okugawa, Y.; Tanaka, K.; Kusunoki, M. Serum hepatocyte
growth factor as a prognostic marker for stage II or III colorectal cancer patients. Int. J. Cancer
2009, 125, 1657–1662.
6. Corso, S.; Comoglio, P.M.; Giordano, S. Cancer therapy: Can the challenge be MET? Trends Mol.
Med. 2005, 11, 284–292.
7. Birchmeier, C.; Birchmeier, W.; Gherardi, E.; Vande Woude, G.F. Met, metastasis, motility and
more. Nat. Rev. Mol. Cell Biol. 2003, 4, 915–925.
8. Christensen, J.; Burrows, J.; Salgia, R. c-Met as a target for human cancer and characterization of
inhibitors for therapeutic intervention. Cancer Lett. 2005, 225, 1−26.
9. Abidoye, O.; Murukurthy, N.; Salgia, R. Review of clinic trials: Agents targeting c-Met. Rev.
Recent Clin. Trials 2007, 2, 143−147.
10. Eder, J.P.; Vande Woude, G.F.; Boerner, S.A.; LoRusso, P.M. Novel therapeutic inhibitors of the
c-Met signaling pathway in cancer. Clin. Cancer Res. 2009, 15, 2207−2214.
11. Fujiwara, Y.; Senga, T.; Nishitoba, T.; Osawa, T.; Miwa, A.; Nakamura, K. Quinoline Derivative
and Quinazoline Derivative Inhibiting Self-phosphorylation of Hepatocytus Proliferator Receptor,
and Medicinal Composition Containing the Same. WO03000660 A1, 3 January 2003.
12. Mannoin, M.; Raeppel, S.; Claridge, S.; Zhou, N.; Savedra, O.; Isakovic, L.; Zhan, L.; Gaudette, F.;
Raeppel, F.; Déziel, R.; et al. N-(4-(6,7-Disubstituted-quinolin-4-yloxy)-3-fluorophenyl)-2-oxo-3-
phenylimidazolidine-1-carboxamides: A novel series of dual c-Met/VEGFR2 receptor tyrosine
kinase inhibitors. Bioorg. Med. Chem. Lett. 2009, 19, 6552–6556.

Molecules 2014, 19
2672
13. Claridge, S.; Raeppel, F.; Granger, M.-C.; Bernstein, N.; Saavedra, O.; Zhan, L.; Llewellyn, D.;
Wahhab, A.; Deziel, R.; Rahil, J.; et al. Discovery of a novel and potent series of thieno[3,2-
b]pyridine-based inhibitors of c-Met and VEGFR2 tyrosine kinases. Bioorg. Med. Chem. Lett.
2008, 18, 2793–2798.
14. Raeppel, S.; Claridge, S.; Saavedra, O.; Gaudette, F.; Zhan, L.; Mannion, M.; Zhou, N.;
Raeppel, F.; Granger, M.-C.; Isakovic, L.; et al. N-(3-Fluoro-4-(2-arylthieno[3,2-b]pyridin-7-
yloxy)phenyl)-2-oxo-3-phenylimidazolidine-1-carboxamides: A novel series of dual c-Met/VEGFR2
receptor tyrosine kinase inhibitors. Bioorg. Med. Chem. Lett. 2009, 19, 1323–1328.
15. Raeppel, S.; Gaudette, F.; Mannion, M.; Claridge, S.; Saavedra, O.; Isakovic, L.; Déziel, R.;
Beaulieu, N.; Beaulieu, C.; Dupont, I.; et al. Identification of a novel series of potent RON
receptor tyrosine kinase inhibitors. Bioorg. Med. Chem. Lett. 2010, 20, 2745–2749.
16. Kim, K.S.; Zhang, L.; Schmidt, R.; Cai, Z.-W.; Wei, D.; Williams, D.K.; Lombardo, L.J.;
Trainor, G.L.; Xie, D.; Zhang, Y.; et al. Discovery of pyrrolopyridine−pyridone based inhibitors
of Met kinase: Synthesis, X-ray crystallographic analysis, and biological activities J. Med. Chem.
2008, 51, 5330–5341.
17. Schroeder, G.M.; An, Y.; Cai, Z.W.; Chen, X.T.; Clark, C.; Cornelius, L.A.; Dai, J.;
Gullo-Brown, J.; Gupta, A.; Henley, B.; et al. Discovery of N-(4-(2-amino-3-chloropyridin-4-
yloxy)-3-fluorophenyl)-4-ethoxy-1-(4-fluorophenyl)-2-oxo-1,2-dihydropyridine-3-carboxamide
(BMS-777607), a selective and orally efficacious inhibitor of the Met kinase superfamily. J. Med.
Chem. 2009, 52, 1251−1254.
18. Zhao, A.; Gao, X.; Wang, Y.; Ai, J.; Wang, Y.; Chen, Y.; Geng, M.; Zhang, A. Discovery of
novel c-Met kinase inhibitors bearing a thieno[2,3-d]pyrimidine or furo[2,3-d]pyrimidine
scaffold. Bioorg. Med. Chem. 2011, 19, 3906–3918.
19. Matsumoto, S.; Miyamoto, N.; Hirayama, T.; Oki, H.; Okada, K.; Tawada, M.; Iwata, H.;
Nakamura, K.; Ymasaki, S.; Miki, H.; et al. Structure-based design, synthesis, and evaluation of
imidazo[1,2-b]pyridazine and imidazo[1,2-a]pyridine derivatives as novel dual c-Met and
VEGFR2 kinase inhibitors. Bioorg. Med. Chem. 2013, 21, 7686–7698.
20. Schroeder, G.M.; Chen, X.-T.; Williams, D.K.; Nirschl, D.S.; Cai, Z.-W.; Wei, D.; Tokarski, J.S.;
An, Y.; Sack, J.; Chen, Z.; et al. Identification of pyrrolo[2,1-f][1,2,4]triazine-based inhibitors of
Met kinase. Bioorg. Med. Chem. Lett. 2008, 18, 1945–1951.
21. Gaudette, F.; Raeppel, S.; Nguyen, H.; Beaulieu, N.; Beaulieu, C.; Dupont, I.; Macleod, A.R.;
Besterman, J.M.; Vaisburg, A. Identification of potent and selective VEGFR receptor tyrosine kinase
inhibitors having new amide isostere headgroups. Bioorg. Med. Chem. Lett. 2010, 20, 848–852.
22. Qi, B.; Mi, B.; Zhai, X.; Xu, Z.; Zhang, X.; Tian, Z.; Gong, P. Discovery and optimization of
novel 4-phenoxy-6,7-disubstituted quinolones possessing semicarbazones as c-Met kinase
inhibitors. Bioorg. Med. Chem. 2013, 21, 5246–5260.
23. Williams, D.K.; Chen, X.-T.; Tarby, C.; Kaltenbach, R.; Cai, Z.-W.; Tokarski, J.S.; An, Y.;
Sack, J.S.; Wautlet, B.; Gullo-Brown, J.; et al. Design, synthesis and structure-activity
relationships of novel biarylamine-based Met kinase inhibitors. Bioorg. Med. Chem. Lett. 2010,
20, 2998–3002.

Molecules 2014, 19
2673
24. Li, S.; Zhao, Y.; Wang, K.; Gao, Y.; Han, J.; Cui, B.; Gong, P. Discovery of novel 4-(2-
fluorophenoxy)quinoline derivatives bearing 4-oxo-1,4-dihydrocinnoline-3-carboxamide moiety
as c-Met kinase inhibitors. Bioorg. Med. Chem. 2013, 21, 2843–2855.
25. Norman, M.H.; Liu, L.; Lee, M.; Xi, N.; Fellows, I.; D’Angelo, N.D.; Dominguez, C.; Rex, K.;
Bellon, S.F.; Kim, T.-S.; et al. Structure-based design of novel class II c-Met inhibitors: 1.
Identification of pyrazolone-based derivatives. J. Med. Chem. 2012, 55, 1858–1867.
26. D’Angelo, N.D.; Bellon, S.F.; Booker, S.K.; Cheng, Y.; Coxon, A.; Dominguez, C.; Fellows, I.;
Hoffman, D.; Hungate, R.; Kaplan-Lefko, P.; et al. Design, synthesis, and biological evaluation of
potent c-Met inhibitors. J. Med. Chem. 2008, 51, 5766–5779.
27. Friesner, R.A.; Murphy, R.B.; Repasky, M.P.; Frye, L.L.; Greenwood, J.R.; Halgren, T.A.;
Sanschagrin, P.C.; Mainz, D.T. Extra precision glide:ꢀ Docking and scoring incorporating a model
of hydrophobic enclosure for protein−ligand complexes. J. Med. Chem. 2006, 49, 6177−6196.
Sample Availability: Samples of the compounds 15–20 are available from the authors.
© 2014 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article
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(http://creativecommons.org/licenses/by/3.0/).