Discovery and evaluation of 2-anilino-5-aryloxazoles as a novel class of VEGFR2 kinase inhibitors

Article abstract of DOI:10.1021/jm049538w

A series of derivatives of 2-anilino-5-phenyloxazole (5) has been identified as inhibitors of VEGFR2 kinase. Herein we describe the structure-activity relationship (SAR) of this novel template. Optimization of both aryl rings led to very potent inhibitors at both the enzymatic and cellular levels. Oxazole 39 had excellent solubility and good oral PK when dosed as the bis-mesylate salt and demonstrated moderate in vivo efficacy against HT29 human colon tumor xenografts. X-ray crystallography confirmed the proposed binding mode, and comparison of oxazoles 39 and 46 revealed interesting differences in orientation of 2-pyridyl and 3-pyridyl rings, respectively, attached at the meta position of the 5-phenyl ring.

Full text of DOI:10.1021/jm049538w

1610
J. Med. Chem. 2005, 48, 1610-1619
Discovery and Evaluation of 2-Anilino-5-aryloxazoles as a Novel Class of
VEGFR2 Kinase Inhibitors
Philip A. Harris,* Mui Cheung, Robert N. Hunter III, Matthew L. Brown,† James M. Veal,† Robert T. Nolte,
Liping Wang, Wendy Liu,† Renae M. Crosby, Jennifer H. Johnson, Andrea H. Epperly, Rakesh Kumar,
Deirdre K. Luttrell,† and Jeffrey A. Stafford†
GlaxoSmithKline, Five Moore Drive, Research Triangle Park, North Carolina 27709
Received June 11, 2004
A series of derivatives of 2-anilino-5-phenyloxazole (5) has been identified as inhibitors of
VEGFR2 kinase. Herein we describe the structure-activity relationship (SAR) of this novel
template. Optimization of both aryl rings led to very potent inhibitors at both the enzymatic
and cellular levels. Oxazole 39 had excellent solubility and good oral PK when dosed as the
bis-mesylate salt and demonstrated moderate in vivo efficacy against HT29 human colon tumor
xenografts. X-ray crystallography confirmed the proposed binding mode, and comparison of
oxazoles 39 and 46 revealed interesting differences in orientation of 2-pyridyl and 3-pyridyl
rings, respectively, attached at the meta position of the 5-phenyl ring.
Introduction
The growth of solid tumors is dependent on the
formation of new capillaries from existing blood vessels.1
This process, known as angiogenesis, is facilitated by a
number of mitogenic endogenous proteins, of which
vascular endothelial growth factor (VEGF) is thought
to be key. VEGF is upregulated by tumors and induces
a mitogenic response on binding to the tyrosine kinase
receptor VEGFR2 (KDR/Flk-1) on nearby endothelial
cells.2 Inhibition of angiogenesis via blocking of this
pathway has attracted widespread interest as an ap-
proach to anticancer therapy.3 The first successful
clinical validation to this approach came recently from
phase III trials of bevacizumab (Avastin), a monoclonal
antibody to VEGF, which when combined with chemo-
therapy in metastatic colorectal cancer met its primary
endpoint of improving survivial.4 Other large-molecule
therapeutic approaches currently in clinical develop-
ment include neutralizing antibodies to VEGFR25 and
a soluble VEGF decoy-receptor.6 A number of orally
active small-molecule inhibitors of VEGFR2 are cur-
rently undergoing clinical evaluation, including the
anilinophthalazine (1) (PTK787/Vatalanib, Schering/
Novartis, phase III),7 the anilinoquinazoline (2) (ZD6474,
AstraZeneca, phase II),8 the indolinone (3) (SU11248/
Sutent, Pfizer, phase III),9 and the isothiazole (4) (CP-
547,632, Pfizer, phase I/II).10
induced proliferation of human umbilical vein endo-
thelial cells (HUVEC) with an IC50 of 3 µM. As a
measure of selectivity, 5 was found to only weakly
As part of our efforts to develop small molecule
inhibitors of the VEGFR2 kinase domain, screening of
our sample collection identified 2-anilino-5-phenylox-
azole (5) as an initial hit.11 This oxazole was an
attractive starting point, exhibiting moderate VEGFR2
enzyme potency (IC50 ) 1.2 µM) and inhibiting VEGF-
inhibit the basic fibroblast growth factor (b-FGF) in-
duced proliferation of HUVEC cells (IC50 ) 24 µM).
Herein, we report on the SAR of this series, the enzyme
binding mode as evidenced by X-ray structures and
initial in vivo efficacy.
Results and Discussion
* Corresponding author. Phone: 919-483-6239. Fax: 919-483-6053.
E-mail: Philip.A.Harris@gsk.com.
Initially we focused our investigation on the 2-anilino
portion of the template, since such substitutions were
easily accessible from known 2-chloro-5-phenyloxazole
(7) via condensation with commercial anilines. As shown
in Scheme 1, 2-aminoacetophenone was initially con-
verted to 2-mercapto-5-phenyloxazole (6) by reaction
† Current addresses. M.L.B.: Eli Lilly and Co., Lilly Corporate
Center, Indianapolis, IN, 46285. J.M.V.: Serenex, Inc., 323 Foster St.,
Durham, NC 27701. W.L.: Medtronic Vascular, 3576 Unocal Place,
Santa Rosa, CA 95403. D.K.L.: MUSC, 171 Ashley Av., Charleston,
SC 29425. J.A.S.: Syrrx, Inc., 10410 Science Center Drive, San Diego,
CA 92121.
10.1021/jm049538w CCC: $30.25 © 2005 American Chemical Society
Published on Web 02/09/2005

2-Anilino-5-aryloxazoles as VEGFR2 Kinase Inhibitors
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 5 1611
Scheme 1a
Scheme 2a
Reagents and conditions: (a) CS2, EtOH, Na2CO3 (aq), 80 °C;
i
(b) POCl3, Et3N, 100 °C; (c) PrOH, 80 °C.
a Reagents and conditions: (a) NaN3, MeOH; (b) bis(2-py-
ridyl)thiocarbonate, DCM or thiophosgene, NaHCO3, DCM/
acetone; (c) PPh3, DCM.
Table 1. Modification of the Aniline Ring
IC50, µM
VEGFR2a
HUVECb
Table 2. Modification of the Phenyl Ring
IC50, µM
compd
R
5
8
9
H
1.2
0.87
0.38
0.93
1.41
0.50
0.72
0.87
0.50
>10
0.14
0.17
0.10
0.023
0.050
3.0
14.4
3.26
7.6
2-CN
2-OMe
3-CN
3-OPh
compd
R
VEGFR2a
HUVECb
21
24
25
26
27
28
29
30
31
32
33
H
0.050
0.360
0.022
0.141
0.036
0.093
0.087
0.081
0.079
0.051
0.018
0.29
7.6
10
11
12
13
14
15
16
17
18
19
20
21
ndc
2-Cl
3-Cl
0.65
1.62
1.65
0.35
3.20
0.93
0.30
0.49
0.21
3-CH2OH
1.65
10.2
1.7
3-CN
3-MeO
3-F
3-SO2Et
3-Me
4-SO2NH2
4-OPh
3,4-di-OMe
3,5-di-OMe
3,4,5-tri-OMe
2-OMe, 5-SO2NEt2
2-OMe, 5-SO2Et
4.66
ndc
4-MeO
4-Cl
4-F
4-CN
4-CONH2
1.13
1.69
0.42
1.31
0.29
a Values are means of two or more experiments. b Inhibition of
VEGF-induced proliferation of HUVEC cells.
a Values are means of two or more experiments. b Inhibition of
VEGF-induced proliferation of HUVEC cells. c No data.
which readily cyclize to the oxazoles 24-33 (Scheme 2).
In general, ortho-substitution of the 5-phenyl ring was
not favorable, whereas meta- and para-substitutions of
the phenyl ring did not improve the inhibition profile
compared to unsubstituted oxazole 21, as shown in
Table 2.
A homology model of the VEGFR2 enzyme, based on
FGFR crystal structures, was used to predict the bind-
ing mode of the oxazole at the ATP binding site.15,16 The
Cys919 of the peptide backbone was thought to bind to
the inhibitor via hydrogen donor and acceptor bonds
with the anilino and oxazole nitrogens, respectively
(Figure 1). As predicted from the binding mode, intro-
duction of a methyl group at either the aniline nitrogen
or the 4 position on the oxazole ring removed all
VEGFR2 inhibition. The 2-methoxy-5-ethyl sulfone
aniline, as mentioned earlier, was thought to impart
increased potency by virtue of the methoxy substituent
sitting in a small hydrophobic pocket, coupled with a
sulfone oxygen accepting a hydrogen bond from the
backbone nitrogen of Asn 923.
In the model, the 5-phenyl group orientates toward
the back of the pocket. A vacant lipophilic pocket exists
at the rear of the binding site and it was predicted that
aromatic meta-substitution at the 5-phenyl ring would
access this site. This region has been previously ob-
served to be occupied by small molecule tyrosine kinase
inhibitors, and interactions in this region are capable
of affording distinct selectivity profiles to a given
inhibitor.15,18-20 A similar region is occupied by Gleevec
in its binding to the Abl kinase, as shown in Figure 1.17
The region to the center-right of the binding site, in the
vicinity of Val 848 and Lys 868 and typically occupied
by the ribose moiety of ATP, was also sterically acces-
with carbon disulfide under basic conditions,12 and
subsequent treatment with phosphorus oxychloride led
to 2-chloro-5-phenyloxazole (7).13
The SAR at both enzyme and cellular levels substi-
tuting off the aniline ring is exemplified in Table 1.
Monosubstitutions led only to marginal changes in
enzyme and cell potencies (oxazoles 8-16). Enhance-
ments in enzymatic activity were observed by addition
of methoxy groups, most prominently 3,4,5-trimethoxy-
anilino-5-phenyloxazole (19). However, significant im-
provements in enzyme potency were only observed from
anilines combining a 2-methoxy group with either a
5-diethylsulfonamide (oxazole 20) or 5-ethyl sulfone
(oxazole 21). Compared with the parent oxazole 5, 2-(5-
ethylsulfonyl-2-methoxyanilino)-5-phenyloxazole (21)
yielded 25- and 10-fold enhancements in enzyme and
cell potencies, respectively, and 5-ethylsulfonyl-2-meth-
oxyaniline became the preferred aniline for SAR explo-
ration of the 5-phenyl position. Oxazoles 9 and 13,
derived from o-methoxy and m-ethyl sulfone aniline,
respectively, were only slight improvements over the
parent and do not predict the efficacy of oxazole 21. Our
homology model, later supported by crystallographic
data, proposed that the methoxy group sits in a lipo-
philic pocket and acts to orientate the sulfone group to
bind to Asn 923.
To examine the SAR around the 5-phenyl ring, we
employed a synthetic route previously described by
Froeyen14 whereby a variety of 2-azido-acetophenones
22 (readily available from the corresponding bromide)
were converted in situ to their iminophosphoranes and
condensed with 2-methoxy-5-ethyl sulfone phenylisothio-
cyanate (23) to the corresponding â-keto carbodiimides,

1612 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 5
Harris et al.
Table 3. Substitution at the Meta Position of the Phenyl Ring
IC50, µM
compd
R
VEGFR2a
HUVECb
21
35
36
37
38
39
40
41
42
43
44
45
H
0.050
0.029
0.091
0.016
0.015
0.022
0.076
0.078
0.025
0.079
0.089
0.039
0.29
1.94
13.90
0.26
0.14
0.37
0.96
15
0.17
0.11
0.04
0.05
Et
COMe
2-thiophene
3-thiophene
2-pyridyl
3-pyridyl
4-pyridyl
5-(1-methylimidazole)
phenyl
2-F-phenyl
2-Cl-phenyl
a Values are means of two or more experiments. b Inhibition of
VEGF induced proliferation of HUVEC cells.
Figure 1. Predicted binding mode of oxazole 21 at the ATP
binding site of the VEGFR2 kinase. The binding mode of
Gleevec in Abl kinase is overlaid in yellow.17
Scheme 3a
a Reagents and conditions: (a) RSnBu3, Pd(PPh3)4, Bu4NCl,
CH3CN, 100 °C, sealed tube.
sible. This was potentially a favorable binding site for
smaller aliphatic or carbonyl groups, again via meta
substitition but in the alternative orientation. To explore
this a series consisting of aliphatic, carbonyl, and
aromatic substituents was prepared via Stille or Suzuki
palladium couplings of 5-(3-bromophenyl)oxazole 34
(Scheme 3).
Figure 2. Correlation between pIC50’s for the inhibition of
VEGFR2 enzyme and VEGF-induced HUVEC cellular prolif-
eration, r ) 0.63.
Small substitutions, as exemplified by ethyl and keto
derivatives 35 and 36, did not yield inhibitors with
favorable cellular activities (see Table 3). However,
aromatic substitution, particularly the o-fluoro- or o-
chloro-substituted phenyl groups (oxazoles 44 and 45),
resulted in inhibitors with a 7-fold increase in cellular
inhibition compared with compound 21. These oxazoles,
44 and 45, possess the best cellular potency in this
series, and evidence that their efficacy is driven by
VEGFR2 inhibition is shown by a >20-fold selectivity
for inhibiting VEGF- versus b-FGF-driven HUVEC
proliferation.
In general, there was a moderate correlation between
VEGFR2 enzyme inhibition and inhibition of HUVEC
cellular proliferation, as evidenced in Figure 2, with a
correlation coefficient of 0.63. A couple of outliers had
good enzyme potencies but were inactive in cells (ox-
azoles 36 and 41), while a couple more were somewhat
more active in cells than would have been predicted
from their enzyme inhibitions (oxazoles 44 and 45).
There does not appear to an easily identifiable reason
for this, as the outliers have lipophilicities similar to
those of others in this series and showed reasonable in
vitro cell permeabilites (Papp values >50 nm/s in
MDCK cells with good mass balance). The average
selectivity observed for VEGF- versus b-FGF-induced
proliferation of HUVEC cells for compounds in this
series was greater than 10-fold (see Figure 3).
Pharmacokinetics and in Vivo Efficacy. The
2-pyridyl-substituted oxazole 39 was selected on the
basis of its solubility and mouse pharmacokinetic profile
for in vivo evaluation in mouse xenografts. To obtain
optimal exposure via oral dosing, a salt screen was
conducted on oxazole 39. In 40% SBE-â-cyclodextrin in
0.05 M methanesulfonic acid at pH 2.3, the free base
had poor solubility (<1 mg/mL), which could be im-
proved by conversion to the citrate, hydrochloride,
sulfate, and tosylate salts (1-2 mg/mL). However,
conversion to the mono- and bis-mesylate salts gave the
best solubilities at >10 mg/mL. Oral administration to
mice of an aqueous solution of the bis-mesylate salt of
oxazole 39 at 100 mg/kg resulted in an AUC (0-8 h) of
102 µg h/mL with a Cmax at 4 h of 35 µM (average of
two mice). This represented an 8-fold increase in AUC
compared to the free base of oxazole 39 dosed as a
suspension in 0.5% HPMC with 0.1% Tween 80. The
pharmacokinetics of the bis-mesylate salt of oxazole 39

2-Anilino-5-aryloxazoles as VEGFR2 Kinase Inhibitors
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 5 1613
Table 5. Crystallographic Data
compound
39
46
space group
P212121
37.7
P212121
37.5
a (Å)
b (Å)
c (Å)
94.6
94.3
96.5
96.8
resolution range (Å)
Rmerge (outer shell)
completeness
19.8-2.1
4.7% (37.5)
99.78
36.6 (3.99)
6.63
16.6-2.1
4.5% (35.5)
99.67
42.9 (5.46)
6.79
I/σ(I) (outer shell)
average redundancy
no. unique reflections
R-factor
20720
19.8%
21.8%
2098
20768
19.4%
23.8%
2135
free R (%)
no. protein atoms
no. solvent atoms
ligand atoms
150
151
62
57
Wilson B-factor
average B-factor
rms bonded B-factor
rms bond lengths (Å)
rms bond angles (deg)
rms torsion angles (deg)
36.2
36.0
38.27
1.423
0.014
1.612
6.24
39.88
1.606
0.016
1.570
6.61
Figure 3. Correlation between pIC50’s for b-FGF- and VEGF-
induced HUVEC cellular proliferation, r ) 0.69.
Table 4. Pharmacokinetic Data for Bis-mesylate Salt of
Oxazole 39
PK parameter
rata
1.6
9
1032
11
dogb
3.5
18
3743
7
Table 6. Kinase Selectivity Data for Oxazoles 39, 44 and 45
selectivity (µM)a selectivity (µM)a
39 44 45
VEGFR2 0.022 0.089 0.039 CDK2
T1/2 (h)
Cl (mL/min/kg)
Vdss (mL/kg)
F (%)
kinase
kinase
39
1.7
44
nd
45
nd
>10
>10
>10
VEGFR3 0.010 0.055 nd CDK4
4.2 >10
a Average of three rats dosed at 3.5 mg/kg iv in 10% HP-â-
cyclodextrin in 0.05 M acetic acid and 10 mg/kg po in 0.5% HPMC
w/0.1% Tween 80. b Average of two dogs dosed at 1 mg/kg iv in
40% SBE-â-cyclodextrin and 1 mg/kg po in 0.5% HPMC w/0.1%
Tween 80.
VEGFR1 0.073 0.40
0.11 GSK3 >10
>10
>10
Src
0.017 0.26
0.29 P38
>10
>10
ITK
0.020 0.043 0.12 Tie-2
1.4
1.8
c-FMS
EphB4
0.14
0.66 nd
0.42
0.38
1.9
nd
EGFR >10
ErbB2 >10
>10
>10
nd
nd
nd
nd
PDGFR1â 1.6
0.93 PLK1 >10
was further characterized in the rat and dog. The PK
parameters are summarized in Table 4. Oxazole 39
showed reasonable in vitro metabolic stability data
(turnover in mouse and rat S9 liver fractions after 30
min at 1 µM was 2 and 29%, respectively); thus, the
low oral bioavailability is likely due to poor permeability
and/or solubility, although metabolism could be a con-
tributing factor.
a The concentration of ATP and kinase-specific biotinylated
peptide in each assay was below the apparent Km of the respective
substrate. Inhibitions of VEGFR1, -2, and -3, Src, PDGFR1â, and
Tie2 were evaluated by the homologous time-resolved fluorescence
(HTRF) format; inhibitions of CDK2, GSK3, PLK1, EphB4, EGFR,
and ErbB2 were evaluated by the scintillation proximity assay
format (SPA). Inhibitions of p38 and ITK were evaluated by the
fluorescence polarization (FP) binding assay. CDK4 and c-FMS
inhibitions were measured by plate capture and filtration binding,
respectively.
In vivo efficacy was measured by the ability to inhibit
the growth of established HT29 human colon tumor
xenografts in nude mice. The bis-mesylate salt of oxazole
39 dosed orally once per day at either 30 or 100 mg/kg
(free base equivalent) in water resulted in 43 and 55%
smaller tumor, respectively, compared to vehicle control
following 26 days of dosing. There was no body weight
loss or other obvious signs of toxicity. By comparison,
in our hands anilinoquinazoline 2 resulted in 61 and
81% inhibition of tumor growth at 30 and 100 mg/kg in
the same model dosing orally once per day. As support
that the observed inhibition of xenograft growth is
working through an antiangiogenic rather than an
antitumor mechanism, oxazole 39 has low inhibitory
activity against the proliferation of HT29 cells in vitro
with an IC50 of 4.5 µM. Inhibition of additional targets
to VEGFR2 that might be contributing to the observed
antiangiogenic effects such as src cannot be ruled out,
although oxazole 39 is not potent against the angiogen-
esis-related kinases Tie-2, PDGFR, and EphB4 (see
Table 6).
the homology model, with clear density visible for the
core and aniline portions in both structures. The crystal
structure of oxazole 46, possessing a m-3-pyridine group,
showed the pyridyl group residing in the back lipophilic
pocket (Figure 4). The 3-pyridyl nitrogen is proximal to
the carboxylic acid of Glu885 at the rear of this pocket.
No water-mediated interactions were observed; thus, the
close distance implies a direct hydrogen bond via
protonation of either the glutamic acid side chain or the
pyridine nitrogen.
Interestingly, the crystal structure of oxazole 39 with
VEGFR2 (Figure 5) shows the same core interactions,
but the m-2-pyridine group, however, was found to be
orientated in multiple conformations, with no clear
density visible for this portion of the ligand. The m-2-
pyridine appears to exist in at least two conformations,
one toward the center-right position and a second
conformation that projects the group into the back
lipophilic pocket in a manner similar to that of oxazole
46 (Figure 4).
X-ray Crystal Structures. To confirm the binding
mode of the 2-anilino-5-phenyloxazoles, the crystal
structures of oxazoles 39 and 46 complexed with VEG-
FR2 were obtained (Table 5). The oxazole core and the
2-methoxy-5-ethyl sulfone aniline bind as predicted from
Given that the two X-ray structures also differ in the
sulfonamide side chain (ethyl versus cyclopropyl meth-
yl), the possibility that the m-3-pyridine group is driven
into the back of the binding site due to steric interfer-

1614 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 5
Harris et al.
Table 7. Comparison of Oxazoles with VEGFR2 Clinical
Candidates
IC50, µM
compd
VEGFR2a
v-HUVECb
b-HUVECc
1
2
0.16
0.009
1.2
0.022
0.039
0.10
0.40
3.0
0.37
0.05
25
1.2
24
5.8
1.1
5
39
45
a Values are means of two or more experiments. b Inhibition of
VEGF-induced proliferation of HUVEC cells. c Inhibition of basic
FGF-induced proliferation of HUVEC cells.
IC50’s for VEGFR2 inhibition of 22 and 38 nM, respec-
tively, indicating that the energy for both binding modes
is comparable. The activation loop is disordered between
residues 1046 and 1065 in both crystal structures,
indicating that residues beyond this region are not
contributing directly to the binding affinity of these
ligands. Asp1044 and Phe1045 are similarly positioned
in both structures with the phenylanine side chain
packing beneath the meta-substituted phenyl ring,
while the aspartate side chain is facing away from the
ligand, making no direct interactions.
Kinase and Cellular Selectivities. Oxazoles 39, 44,
and 45 serve as representative examples for this series
regarding selectivity against other kinases, with similar
potencies against both VEGFR2 and VEGFR3 and a
modest drop in potency for VEGFR1 (Table 6). Weak
activities were observed for EphB4 and PDGFR1â and
Tie-2, the other angiogenesis kinases assayed. Of the
other kinases examined, comparable activity was seen
for Src and ITK.
Evidence that cellular activity resulted from activity
at the desired target was showed by comparison of the
inhibition of VEGF- versus bFGF-induced proliferation
of HUVEC cells. A 10-fold or better window was typi-
cally observed for this oxazole class. For example,
oxazole 39 had IC50’s of 0.37 and 5.8 µM for VEGF- and
bFGF-induced HUVEC proliferation, respectively.
Figure 4. Crystal structure of oxazole 46 with VEGFR2.
Conclusions
We have identified 2-anilino-5-aryloxazole derivatives
as a novel class of potent VEGFR2 kinase inhibitors
with good enzymatic and cellular activities. Optimiza-
tion of both aryl rings yielded oxazole 45 with improved
enzymatic and cellular inhibitions compared with un-
substituted oxazole 5 of 30- and 60-fold, respectively,
and with an in vitro profile comparable to those of lead
VEGFR2 inhibitors 1 and 2 now in clinical trials (see
Table 7). Oxazole 39, as the bis-mesylate salt, possessed
good solubility and pharmokinetic profiles and showed
moderate efficacy in preliminary in vivo xenograft
studies. X-ray crystallography studies confirmed the
proposed binding mode at the ATP binding site. Com-
parison of oxazoles 39 and 46, differing only by a shift
in position of the nitrogen on a pyridine ring from ortho
to meta, revealed conformational differences in binding
of the pyridine rings.
Figure 5. Crystal structure of oxazole 39 with VEGFR2. Only
the conformation with the m-2-pyridine oriented to the center
right conformation is shown.
Experimental Section
All purchased starting materials were used without further
purification. 1H NMR spectra were recorded on a Varian VXR-
300, a Varian Unity-300, or a Varian Unity-400 instrument
as solutions in DMSO-d6. Chemical shifts are expressed in
parts per million (ppm, δ units). Coupling constants are in
ence with the larger cyclopropyl methyl group cannot
be ruled out. However, inspection of the structures
indicated that a forward conformation would be steri-
cally allowed. Both oxazoles 39 and 46 possess similar

2-Anilino-5-aryloxazoles as VEGFR2 Kinase Inhibitors
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 5 1615
units of hertz (Hz). Splitting patterns describe apparent
multiplicities and are designated as s (singlet), d (doublet), t
(triplet), q (quartet), m (multiplet), bs (broad singlet). Elemen-
tal analyses were carried out by Atlantic Microlabs Inc.,
Norcross, GA. Analytical HPLC. Method A was performed
with a Beckman 166 UV detector on a Rainin Dynamex-60A
column equipped with a Waters Lamda-Max 481 UV detector
monitoring at 254 nm. Elution was with H2O:MeCN:0.1%
trifluoroacetic acid, with a gradient of 5-100% MeCN over 40
min. Method B was performed on a Waters analytical HPLC
consisting of a 626 LC pump, 996 diode array, and a Gilson
233XL autosampler, eluting with H2O:MeCN:0.1% formic acid
with a gradient of 10-90% MeCN over 13 min, a 2 min column
wash, and reequilibration period for a total of a 15 min run
time (flow rate ) 1.5 mL/min). LCMS using electrospray
ionization were run on a Micromass ZMD mass spectrometer
equipped with a Waters 2790 LC system, Phenomenex Max-
RP column (4 µm, 150 × 4.60 mm), and a 996 DAD. Initial
conditions, 15% MeOH (0.075% formic acid), 85% H2O (0.1%
formic acid); flow rate ) 2.00 mL/min; gradient to 100% MeOH
(0.075% formic acid) over 12 min, hold for 3 min, 15 min total
run time.
90% MeCN over 15 min. 1H NMR: δ 11.0 (bs, 2H), 9.50 (s,
1H), 8.61 (d, J ) 8.3, 1H), 8.03 (t, J ) 7.4, 1H), 7.83 (d, J )
8.3, 1H), 7.77 (d, J ) 7.1, 2H), 7.69 (t, J ) 7.1, 1H), 7.63-7.55
(m, 4H). LCMS (ES+, m/z) ) 262 (MH)+ (tR 5.2 min). Anal.
(C16H11N3O·0.2HCO2H) C, H, N.
The following compounds 9-21 were similarly prepared
using the appropriate aniline. In most cases, the product
deposits as the hydrochloride salt; however, when the aniline
has phenoxy or sulfonamide substitution, the free base is
recovered.
N-(2-Methoxyphenyl)-5-phenyl-1,3-oxazol-2-amine Hy-
1
drochloride (9). Tan solid; yield 87%. H NMR: δ 9.94 (bs,
2H), 7.92 (bs, 1H), 7.60-7.55 (m, 3H), 7.42 (t, J ) 7.7, 2H),
7.27 (t, J ) 7.4, 1H), 7.06 (s, 2H), 6.99-6.92 (m, 1H), 3.82 (s,
3H). LCMS (ES+, m/z) ) 267 (MH)+ (tR 10.8 min). HPLC
(method A): 99.4% (tR 25.2 min).
N-(3-Cyanophenyl)-5-phenyl-1,3-oxazol-2-amine Hy-
drochloride (10). White solid; yield 50%. 1H NMR: δ 10.8
(bs, 1H), 8.08 (s, 1H), 7.9 (bs, 1H), 7.82 (dd, J ) 1.9, 8.3, 2H),
7.55 (d, J ) 7.5, 2H), 7.48 (t, J ) 8.1, 2H), 7.26-7.41 (m, 4H),
7.24 (t, J ) 7.4, 1H). LCMS (ES+, m/z) ) 262 (MH)+ (tR 10.2
min). Anal. (C16H11N3O·0.1H2O) C, H, N.
5-Phenyl-1,3-oxazole-2-thiol (6). A solution of sodium
carbonate (11.3 g, 91 mmol) in water (30 mL) was added slowly
to a mixture of phenacylamine hydrochloride (15 g, 87 mmol)
and carbon disulfide (13.3 g, 174 mmol) in ethanol (100 mL).
After heating to 80 °C with stirring for 18 h, the reaction was
cooled, filtered and treated with glacial acetic acid (25 mL),
and stirred for an additional 15 min. The resulting deposited
copper colored solid was collected by vacuum filtration, rinsed
with ethanol, and air-dried to afford the title compound (10.84
g, 70%). 1H NMR δ 13.3 (bs, 1H), 7.84 (s, 1H), 7.57 (d, J ) 7.4,
2H), 7.42 (t, J ) 7.5, 2H), 7.33 (t, J ) 7.5, 1H); MS (ES-, m/z)
) 176 (M - H)-. HPLC (method A): 95% (tR 18.4 min).
N-(3-Phenoxyphenyl)-5-phenyl-1,3-oxazol-2-amine (11).
1
White solid; yield 8%. H NMR: δ 10.4 (s, 1H), 7.50 (d, J )
7.5, 2H), 7.36-7.41 (m, 6H), 7.28 (d, J ) 7.9, 2H), 7.23 (t, J )
7.4, 1H), 7.12 (t, J ) 7.4, 1H), 7.01 (d, J ) 7.9, 2H), 6.55 (dd,
J ) 2.2, 7.2, 1H). LCMS (ES+, m/z) ) 329 (MH)+ (tR 11.6 min).
HPLC (method A): 99.6% (tR 30.4 min).
N-(3-Hydroxymethylphenyl)-5-phenyl-1,3-oxazol-2-
amine Hydrochloride (12). White solid; yield 74%. 1H NMR
δ 10.44 (s, 1H), 7.58 (d, J ) 6.8, 2H), 7.55 (s, 1H), 7.38-7.48
(m, 4H), 7.3 (bs, 2H), 7.21-7.27 (m, 2H), 6.89 (d, J ) 7.5, 1H),
4.45 (s, 2H). LCMS (ES+, m/z) ) 267 (MH)+ (tR 9.0 min). HPLC
(method A): >99% (tR 17.6 min).
2-Chloro-5-phenyl-1,3-oxazole (7). To a suspension of
5-phenyl-1,3-oxazole-2-thiol (6) (11.0 g, 62 mmol) in phospho-
rus oxychloride (35 mL, 37.0 g, 372 mmol) cooled in an ice-
water bath and under nitrogen was slowly added dry trieth-
ylamine (9.5 mL, 6.9 g, 682 mmol). The mixture was then
heated to 100 °C overnight. The reaction mixture was cooled
to room temperature and poured onto crushed ice. The residue
was extracted with ethyl acetate (3 × 200 mL). The combined
organic layers were back-washed with water, saturated sodium
bicarbonate solution, and brine. The organic layer was dried
over anhydrous magnesium sulfate and evaporated to leave a
dark oil. The oil was purified by silica gel column chromatog-
raphy using 20% ethyl acetate in hexanes as an eluant to
afford the title compound (4.37 g, 39%) as an amber oil, which
N-(3-(Ethylsulfonyl)phenyl)-5-phenyl-1,3-oxazol-2-
amine (13). White solid; yield 37%. 1H NMR: δ 10.86 (s, 1H),
8.34 (s, 1H), 7.92 (dd, J ) 1.6, 8.0, 1H), 7.61-7.67 (m, 3H),
7.57 (s, 1H), 7.46-7.51 (m, 3H), 7.33 (t, J ) 7.3, 1H), 3.30 (q,
J ) 7.3, 2H), 1.16 (t, J ) 7.3, 3H). LCMS (ES+, m/z) ) 329
(MH)+ (tR 9.3 min). HPLC (method B): >99% (tR 10.5 min).
N-(3-Methylphenyl)-5-phenyl-1,3-oxazol-2-amine (14).
White solid; yield 14%; initially deposited as the hydrochloride
salt and converted to the free base by partitioning between
ethyl acetate and aqueous sodium bicarbonate. 1H NMR: δ
10.18 (s, 1H), 7.53 (d, J ) 7.5, 2H), 7.43-7.34 (m, 4H), 7.21 (t,
J ) 7.4, 1H), 7.13 (t, J ) 7.8, 1H), 6.92 (d, J ) 7.5, 1H), 2.24
(s, 3H). LCMS (ES+, m/z) ) 251 (MH)+ (tR 11.3 min). Anal.
(C16H14N2O) C, H, N.
1
solidified on standing. H NMR: δ 7.76 (s, 1H), 7.66 (d, J )
4-[(5-Phenyl-1,3-oxazol-2-yl)amino]benzenesulfona-
1
7.5, 2H), 7.46 (t, J ) 7.4, 2H), 7.38 (d, J ) 7.4, 1H). LCMS
(ES+, m/z) ) 180, 182 (MH)+ (tR 10.4 min). HPLC (method
B): >99% (tR 10.5 min).
mide (15). White solid; yield 64%. H NMR: δ 10.77 (s, 1H),
7.74 (s, 4H), 7.58 (d, J ) 7.5, 2H), 7.50 (s, 1H), 7.42 (t, J ) 7.7,
2H), 7.26 (t, J ) 7.4, 1H), 7.17 (s, 2H). LCMS (ES+, m/z) )
316 (MH)+ (tR 8.3 min). HPLC (method A): 99.0% (tR 21.1 min).
N-(4-Phenoxyphenyl)-5-phenyl-1,3-oxazol-2-amine (16).
White solid; yield 50%. 1H NMR: δ 10.38 (s, 1H), 7.64 (d, J )
9.1, 2H), 7.57 (d, J ) 7.4, 2H), 7.23-7.46 (m, 6H), 7.01-7.09
(m, 3H), 6.93 (d, J ) 7.9, 2H). LCMS (ES+, m/z) ) 329 (MH)+
(tR 11.6 min). Anal. (C21H16N2O2·0.5H2O) C, H, N.
N,5-Diphenyl-1,3-oxazol-2-amine (5). A mixture of 2-chlo-
ro-5-phenyl-1,3-oxazole (7) (0.5 g, 2.78 mmol) and aniline (1.0
g, 10.7 mmol) was heated to 100 °C for 5 min. Upon cooling,
the mixture was partitioned between ether (200 mL) and water
(100 mL). The organic phase was washed with 1 N hydrochloric
acid (3 × 50 mL) and then dried over anhydrous magnesium
sulfate and evaporated to afford a white solid. This was then
triturated with ether and filtered to yield the product as a
N-(3,4-Dimethoxyphenyl)-5-phenyl-1,3-oxazol-2-
amine Hydrochloride (17). White solid; yield 53%. 1H
NMR: δ 10.55 (s, 1H), 7.57-7.53 (m, 3H), 7.41 (t, J ) 7.8,
2H), 7.31-7.23 (m, 2H), 7.07 (dd, J ) 2.4, 8.6, 1H), 6.91 (d, J
) 8.8, 1H), 3.73 (s, 3H), 3.69 (s, 3H). LCMS (ES+, m/z) ) 297
(MH)+ (tR 9.6 min). HPLC (method A): >99% (tR 21.8 min).
N-(3,5-Dimethoxyphenyl)-5-phenyl-1,3-oxazol-2-
amine Hydrochloride (18). White solid; yield 43%. 1H
NMR: δ 10.27 (s, 1H), 7.52 (d, J ) 7.5, 2H), 7.42 (s, 1H), 7.38
(t, J ) 7.7, 2H), 7.22 (t, J ) 7.4, 1H), 6.83 (d, J ) 2.0, 2H),
6.08 (t, J ) 2.0, 1H), 3.68 (s, 6H). LCMS (ES+, m/z) ) 297
(MH)+ (tR 10.4 min). Anal. (C17H16N2O3·0.35H2O) C, H, N.
N-(3,4,5-Trimethoxyphenyl)-5-phenyl-1,3-oxazol-2-
amine hydrochloride (19). White solid; yield 17%. 1H
NMR: δ 10.23 (s, 1H), 7.52 (d, J ) 7.5, 2H), 7.43 (s, 1H), 7.38
(t, J ) 7.8, 2H), 7.22 (t, J ) 7.4, 1H), 6.96 (s, 2H), 3.71 (s, 6H),
1
white solid (0.18 g, 27%). H NMR: δ 7.61 (d, J ) 7.9, 2H),
7.55 (d, J ) 7.5, 2H), 7.45-7.37 (m, 3H), 7.31-7.21 (m, 3H),
6.92 (t, J ) 7.3, 1H). LCMS (ES+, m/z) ) 237 (MH)+ (tR 10.4
min). Anal. (C15H12N2O) C, H, N.
N-(2-Cyanophenyl)-5-phenyl-1,3-oxazol-2-amine Hy-
drochloride (8). A mixture of 2-chloro-5-phenyl-1,3-oxazole
(0.05 g, 0.28 mmol) and anthranilonitrile (0.033 g, 0.28 mmol)
in 2-propanol (1.5 mL) was heated to 80 °C for 18 h with
stirring. Upon cooling, a white solid precipitated out which
was filtered off, washed with 2-propanol, and dried. This was
then triturated with ether and filtered to yield the title
product, a white solid, as the hydrochloride salt (0.045 g, 62%).
Analytical purity was obtained by HPLC purification (method
B) eluting with H2O:MeCN: 0.1% formic acid; gradient 10-

1616 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 5
Harris et al.
3.56 (s, 3H). LCMS (ES+, m/z) ) 327 (MH)+ (tR 9.9 min). Anal.
(C18H18N2O4·0.1H2O) C, H, N.
5-(2-Chlorophenyl)-N-[5-(ethylsulfonyl)-2-methoxyphe-
nyl]-1,3-oxazol-2-amine (24). Yellow solid; yield 25%. 1H
NMR: δ 9.90 (s, 1H), 8.80 (s, 1H), 7.78 (d, J ) 7.7, 1H), 7.73
(s, 1H), 7.47-7.61 (m, 3H), 7.30-7.38 (m, 2H), 4.01 (s, 3H),
3.23 (q, J ) 7.3, 2H), 1.14 (t, J ) 7.3, 3H). LCMS (ES+, m/z)
) 393 (MH)+ (tR 10.1 min). HPLC (method B): >95% (tR 12.7
min).
N,N-Diethyl-4-methoxy-3-[(5-phenyl-1,3-oxazol-2-yl)-
amino]benzenesulfonamide (20). White solid; yield 40%.
1H NMR: δ 9.46 (s, 1H), 8.69 (d, J ) 2.2, 1H), 7.58 (d, J ) 7.3,
2H), 7.50 (s, 1H), 7.44-7.35 (m, 3H), 7.25 (t, J ) 7.4, 1H), 7.16
(d, J ) 8.6, 1H), 3.92 (s, 3H), 3.12 (q, J ) 7.1, 4H), 1.02 (t, J
) 7.1, 6H). LCMS (ES+, m/z) ) 402 (MH)+ (tR 10.5 min). HPLC
(method A): 99.5% (tR 28.6 min).
5-(3-Chlorophenyl)-N-[5-(ethylsulfonyl)-2-methoxyphe-
1
nyl]-1,3-oxazol-2-amine (25). Off-white solid; yield 3%. H
NMR: δ 9.77 (s, 1H), 8.72 (d, J ) 2.1, 1H), 7.63 (m, 2H), 7.51
(d, J ) 7.9, 1H), 7.45 (dd, J ) 2.2, 8.6, 1H), 7.41 (d, J ) 7.9,
1H), 7.28 (d, J ) 8.2, 1H), 7.22 (d, J ) 8.6, 1H), 3.93 (s, 3H),
3.15 (q, J ) 7.3, 2H), 1.06 (t, J ) 7.3, 3H). LCMS (ES+, m/z)
) 393 (MH)+ (tR 10.2 min). HPLC (method B): >95% (tR 11.5
min).
5-(3-Cyanophenyl)-N-[5-(ethylsulfonyl)-2-methoxyphe-
nyl]-1,3-oxazol-2-amine (26). Yellow solid; yield 1%. 1H
NMR: δ 9.80 (s, 1H), 8.71 (d, J ) 2.2, 1H), 8.01 (s, 1H), 7.84
(d, J ) 7.9, 1H), 7.69-7.63 (m, 2H), 7.61 (t, J ) 7.9, 1H), 7.46
(dd, J1)8.5, J2)2.2, 1H), 7.23 (d, J ) 8.5, 1H), 3.93 (s, 3H),
3.16 (q, J ) 7.3, 2H), 1.06 (t, J ) 7.3, 3H). LCMS (ES+, m/z)
) 384 (MH)+ (tR 8.6 min). HPLC (method B): >95% (tR 10.1
min).
5-(3-Methoxyphenyl)-N-[5-(ethylsulfonyl)-2-methoxy-
phenyl]-1,3-oxazol-2-amine (27). Off-white solid; yield 49%.
1H NMR: δ 9.71 (s, 1H), 8.74 (d, J ) 2.2, 1H), 7.53 (s, 1H),
7.46 (dd, J ) 2.2, 8.6, 1H), 7.32 (t, J ) 8.0, 1H), 7.24 (d, J )
8.6, 1H), 7.17 (d, J ) 7.7, 1H), 7.13 (s, 1H), 6.83 (dd, J ) 2.4,
8.2, 1H), 3.94 (s, 3H), 3.78 (s, 3H), 3.17 (q, J ) 7.3, 2H), 1.08
(t, J ) 7.3, 3H). LCMS (ES+, m/z) ) 389 (MH)+ (tR 9.5 min).
HPLC (method A): 95.6% (tR 24.4 min).
N-[5-(Ethylsulfonyl)-2-methoxyphenyl]-5-phenyl-1,3-
oxazol-2-amine (21). White solid; yield 26%. 1H NMR: δ 9.72
(s, 1H), 8.75 (d, J ) 2.2, 1H), 7.59 (d, J ) 7.5, 2H), 7.51 (s,
1H), 7.46 (dd, J ) 2.2, 8.4, 1H), 7.41 (t, J ) 7.8, 2H), 7.29-
7.22 (m, 2H), 3.94 (s, 3H), 3.17 (q, J ) 7.4, 2H), 1.08 (t, J )
7.4, 3H). LCMS (ES+, m/z) ) 359 (MH)+ (tR 9.3 min). HPLC
(method A): 98.6% (tR 25.1 min).
General Procedure for Preparation of 2-Azidoace-
tophenones (22). To a solution of the phenacyl bromide (73
mmol) in methanol (150 mL) was added sodium azide (5.42 g,
83 mmol) and the reaction stirred at room temperature for 90
min. The solvent was removed under reduced pressure and
the crude product was partitioned between ethyl acetate (200
mL) and water (100 mL). The organic layer was separated,
dried over anhydrous magnesium sulfate, and concentrated
under reduced pressure to afford the 2-azidoacetophenones 22.
4-(Ethylsulfonyl)-2-isothiocyanato-1-methoxyben-
zene (23). A solution of 5-(ethylsulfonyl)-2-methoxyaniline
(15.6 g, 72.5 mmol) in dichloromethane (100 mL) was added
dropwise over 1 h to a stirred solution of thiophosgene (9 g,
78.0 mmol) in dichloromethane (300 mL) at room temperature.
After the addition was complete, the reaction was stirred for
2 h. Subsequently, saturated aqueous sodium bicarbonate (200
mL) was added, and the reaction was stirred for an additional
1 h. The organic layer was separated, and the aqueous layer
was extracted with dichloromethane (2 × 100 mL). The
combined organic layers were dried over anhydrous magne-
sium sulfate, filtered, and concentrated under reduced pres-
sure to afford the title compound 23 (18.6 g, 72.4 mmol) as a
tan solid. 1H NMR: δ 7.78 (dd, J ) 2.2, 8.8, 1H), 7.71 (d, J )
2.2, 1H), 7.35 (d, J ) 8.8, 1H), 3.95 (s, 3H), 3.22 (q, J ) 7.4,
2H), 1.02 (t, J ) 7.3, 3H). Anal. (C10H11NO3S2) C, H, N, S.
General Procedure for the Preparation of 5-(Substi-
tuted-phenyl)-N-[5-(ethylsulfonyl)-2-methoxyphenyl]-
1,3-oxazol-2-amines (24-33). A solution of the 2-azidoace-
tophenone (22) (72.5 mmol) in dichloromethane (50 mL) was
added dropwise over 2 h to a stirred solution of the isothio-
cyanate 23 (18.6 g, 72.4 mmol) and triphenylphosphine (18.8
g, 73 mmol) in dichloromethane (100 mL) under nitrogen. The
reaction was kept cool during the addition by periodically
placing the flask in an ice water bath. After the addition was
complete, the reaction was stirred at room temperature for
an additional 2 h. Subsequently, oxalic acid (6.5 g, 72.0 mmol)
was added, and the reaction was briefly warmed with a heat
gun until the appearance of a precipitate. After cooling in ice
water, the precipitate was filtered, washed with dichlo-
romethane and diethyl ether, and partitioned between dichlo-
romethane (200 mL) and 1 M aqueous sodium hydroxide (100
mL). The organic layer was separated, and the aqueous layer
was extracted with additional dichloromethane (2 × 100 mL).
The combined organic layers were dried over anhydrous
magnesium sulfate, filtered, and concentrated under reduced
pressure to afford the desired compound. In cases where the
addition of oxalic acid did not yield a precipitate, the solution
was subsequently diluted with diethyl ether (100 mL) and
extracted with 6 N hydrochloric acid (100 mL). The aqueous
phase was separated, basified by addition of 5 N sodium
hydroxide solution, and extracted with ethyl acetate (3 × 100
mL). The combined organic layers were dried over anhydrous
magnesium sulfate, filtered, and concentrated under reduced
pressure to afford the crude compound. Purification was
achieved either by trituration with methanol, filtering off the
precipitate and washing with methanol, or by flash chroma-
tography on silica gel with hexanes/EtOAc.
5-(3-Fluorophenyl)-N-[5-(ethylsulfonyl)-2-methoxyphe-
nyl]-1,3-oxazol-2-amine oxalate (28). Off-white solid; yield
1
27%. H NMR: δ 9.75 (bs, 1H), 8.71 (d, J ) 2.2, 1H), 7.59 (s,
1H), 7.47-7.36 (m, 4H), 7.22 (d, J ) 8.6, 1H), 7.08-7.04 (m,
1H), 3.92 (s, 3H), 3.15 (q, J ) 7.3, 2H), 1.06 (t, J ) 7.3, 3H).
LCMS (ES+, m/z) ) 377 (MH)+ (tR 9.5 min). HPLC (method
B): >95% (tR 10.8 min).
5-(4-Methoxyphenyl)-N-[5-(Ethylsulfonyl)-2-methoxy-
phenyl]-1,3-oxazol-2-amine Hydrochloride (29). White
solid; yield 58%. 1H NMR: δ 9.68 (s, 1H), 8.72 (d, J ) 2.2,
1H), 7.46 (dd, J ) 2.2, 8.6, 1H), 7.35 (s, 1H), 7.22 (d, J ) 8.4,
1H), 6.99 (d, J ) 8.8, 2H), 5.0 (bs, 1H), 3.94 (s, 3H), 3.76 (s,
3H), 3.17 (q, J ) 7.3, 2H), 1.08 (t, J ) 7.4, 3H). LCMS (ES+,
m/z) ) 389 (MH)+ (tR 9.3 min). HPLC (method A): 92.7% (tR
25.1 min).
5-(4-Chlorophenyl)-N-[5-(ethylsulfonyl)-2-methoxyphe-
nyl]-1,3-oxazol-2-amine (30). Off-white solid; yield 10%. 1H
NMR: δ 9.91 (bs, 1H), 8.69 (d, J ) 2.2, 1H), 7.85 (d, J ) 8.3
Hz, 2H), 7.77 (s, 1H), 7.70 (d, J ) 8.3, 2H), 7.47 (dd, J ) 2.2,
8.7, 1H), 7.23 (d, J ) 8.7, 1H), 3.92 (s, 3H), 3.16 (q, J ) 7.3,
2H), 1.06 (t, J ) 7.3, 3H). LCMS (ES+, m/z) ) 393 (MH)+ (tR
10.1 min). HPLC (method B): >95% (tR 11.5 min).
5-(4-Fluorophenyl)-N-[2-methoxy-5-(methylsulfonyl)-
phenyl]-1,3-oxazol-2-amine Hydrochloride (31). White
solid; yield 19%. 1H NMR: δ 9.8 (bs, 1H), 8.70 (d, J ) 2.2,
1H), 7.60-7.64 (m, 2H), 7.51 (s, 1H), 7.48 (dd, J ) 2.2, 8.6,
1H), 7.23-7.30 (m, 3H), 3.94 (s, 3H), 3.17 (q, J ) 7.3, 2H),
1.08 (t, J ) 7.3, 3H), LCMS (ES+, m/z) ) 377 (MH)+ (tR 9.4
min). HPLC (method A): >99% (tR 26.2 min).
5-(4-Cyanophenyl)-N-[5-(ethylsulfonyl)-2-methoxyphe-
1
nyl]-1,3-oxazol-2-amine (32). Off-white solid; yield 6%. H
NMR: δ 9.91 (bs, 1H), 8.69 (d, J ) 2.2, 1H), 7.85 (d, J ) 8.3,
2H), 7.77 (s, 1H), 7.70 (d, J ) 8.3, 2H), 7.47 (dd, J ) 2.2, 8.7,
1H), 7.23 (d, J ) 8.7, 1H), 3.92 (s, 3H), 3.16 (q, J ) 7.3, 2H),
1.06 (t, J ) 7.3, 3H). LCMS (ES+, m/z) ) 384 (MH)+ (tR 8.6
min). HPLC (method B): >95% (tR 10.0 min).
4-(2-{[5-(Ethylsulfonyl)-2-methoxyphenyl]amino}-1,3-
oxazol-5-yl)benzamide (33). 5-(4-Cyanophenyl)-N-[5-(ethyl-
sulfonyl)-2-methoxyphenyl]-1,3-oxazol-2-amine (32) (0.084 g,
0.22 mmol) was treated with concentrated hydrochloric acid
(4 mL) and stirred at room temperature overnight. The
reaction mixture was diluted with ethyl acetate and made
basic with 5 N sodium hydroxide solution. The aqueous layer

2-Anilino-5-aryloxazoles as VEGFR2 Kinase Inhibitors
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 5 1617
was extracted with ethyl acetate (3 × 10 mL). The combined
organic layers were dried over anhydrous magnesium sulfate,
filtered, and evaporated under reduced pressure to afford the
title compound (0.085 g, 97% yield) as a yellow solid. 1H
NMR: δ 9.78 (bs, 1H), 8.72 (d, J ) 2.1, 1H), 7.94 (s, 1H), 7.89
(d, J ) 8.2, 2H), 7.63-7.61 (m, 3H), 7.46 (dd, J ) 2.1, 8.6,
1H), 7.32 (s, 1H), 7.22 (d, J ) 8.6, 1H), 3.93 (s, 3H), 3.15 (q, J
) 7.3, 2H), 1.07 (t, J ) 7.3, 3H). LCMS (ES+, m/z) ) 402 (MH)+
(tR 7.1 min). HPLC (method B): >95% (tR 7.6 min).
Compounds 37-43 were prepared following the general
Stille coupling procedure described above.
N-[5-(Ethylsulfonyl)-2-methoxyphenyl]-5-(3-thien-2-
ylphenyl)-1,3-oxazol-2-amine (37). White solid; yield 20%.
1H NMR: δ 9.76 (s, 1H), 8.74 (d, J ) 2.2, 1H), 7.82 (s, 1H),
7.60 (s, 1H), 7.50-7.56 (m, 4H), 7.41-7.46 (m, 2H), 7.22 (d, J
) 8.5, 1H), 7.13 (t, J ) 3.8, 1H), 3.94 (s, 3H), 3.16 (q, J ) 7.4,
2H), 1.07 (t, J ) 7.3, 3H). LCMS (ES+, m/z) ) 441 (MH)+ (tR
11.0 min). HPLC (method B): >99% (tR 12.6 min).
5-(3-Bromophenyl)-N-[5-(ethylsulfonyl)-2-methoxyphe-
nyl]-1,3-oxazol-2-amine (34). The title compound was pre-
pared as described earlier in the general procedure for the
preparation of 5-(substituted-phenyl)-N-[5-(ethylsulfonyl)-2-
methoxyphenyl]-1,3-oxazol-2-amines; yellow solid, yield 36%.
1H NMR: δ 9.77 (s, 1H), 8.72 (d, J ) 2.2, 1H), 7.77 (s, 1H),
7.62 (s, 1H), 7.56 (d, J ) 7.9, 1H), 7.47-7.33 (m, 3H), 7.22 (d,
J ) 8.6, 1H), 3.93 (s, 3H), 3.17 (q, J ) 7.3, 2H), 1.06 (t, J )
7.3, 3H). LCMS (ES+, m/z) ) 437, 439 (MH)+ (tR 10.3 min).
Anal. (C18H17N2BrO4S) C, H, N, Br, S.
General Procedure for the Stille Coupling of 5-(3-
Bromophenyl)-N-[5-(ethylsulfonyl)-2-methoxyphenyl]-
1,3-oxazol-2-amine. In a Pyrex sealed tube, oxazole 34 (0.123
g, 0.28 mmol), the appropriate tributylstannyl reagent (1
mmol), tetrabutylammonium chloride (0.170 g, 0.61 mmol),
and tetrakistriphenylphosphine palladium(0) (0.02 g, 0.017
mmol) were suspended in dry acetonitrile (10 mL) and stirred
at 100 °C. After the reaction was determine to be complete by
TLC analysis, the reaction was cooled, diluted with ethyl
acetate (50 mL), quenched with 1 M aqueous potassium
fluoride solution (20 mL), and stirred for 3 h. The organic layer
was separated, dried over anhydrous magnesium sulfate,
filtered, and concentrated under reduced pressure. The crude
product was purified by column chromatography on silica gel
eluting with hexane:ethyl acetate to afford the desired com-
pound.
N-[5-(Ethylsulfonyl)-2-methoxyphenyl]-5-(3-thien-3-
ylphenyl)-1,3-oxazol-2-amine (38). Off-white solid; yield
52%. 1H NMR: δ 9.80 (bs, 1H), 8.81 (s, 1H), 7.98 (s, 2H), 7.60-
7.75 (m, 4H), 7.46-7.60 (m, 3H), 7.31 (d, J ) 8.6, 1H), 4.01 (s,
3H), 3.24 (q, J ) 7.4, 2H), 1.15 (t, J ) 7.3, 3H). LCMS (ES+,
m/z) ) 441 (MH)+ (tR 10.9 min). HPLC (method B): >99% (tR
12.4 min).
N-[5-(Ethylsulfonyl)-2-methoxyphenyl]-5-(3-pyridin-2-
ylphenyl)-1,3-oxazol-2-amine (39). White solid; yield 51%.
1H NMR: δ 9.79 (s, 1H), 8.76 (d, J ) 2.2, 1H), 8.65 (d, J ) 4.2,
1H) 8.32 (s, 1H), 7.98 (d, J ) 7.9, 1H), 7.94 (d, J ) 7.9, 1H),
7.88 (dt, J ) 1.6, 7.5, 1H), 7.65 (d, J ) 7.9, 1H), 7.60 (s, 1H),
7.51 (t, J ) 7.9, 1H), 7.45 (dd, J ) 2.2, 8.6, 1H), 7.36 (dd, J )
2.0, 7.1, 1H), 7.22 (d, J ) 8.6, 1H), 3.94 (s, 3H), 3.16 (q, J )
7.3, 2H), 1.07 (t, J ) 7.3, 3H). LCMS (ES+, m/z) ) 436 (MH)+
(tR 9.1 min). Anal. (C23H21N3O4S·0.25H2O) C, H, N, S.
N-[5-(Ethylsulfonyl)-2-methoxyphenyl]-5-(3-pyridin-3-
ylphenyl)-1,3-oxazol-2-amine (40). White solid; yield 49%.
1H NMR: δ 9.74 (s, 1H), 9.08 (s, 1H), 8.72 (s, 2H), 8.44-8.52
(m, 1H), 7.98 (s, 1H), 7.70-7.84 (m, 1H), 7.64-7.68 (m, 3H),
7.58 (d, J ) 7.5, 1H), 7.46 (d, J ) 8.2, 1H), 7.22 (d, J ) 8.6,
1H), 3.93 (s, 3H), 3.16 (q, J ) 7.3, 2H), 1.06 (t, J ) 7.3, 3H).
LCMS (ES+, m/z) ) 436 (MH)+ (tR 8.5 min). HPLC (method
B): >99% (tR 7.2 min).
N-[5-(Ethylsulfonyl)-2-methoxyphenyl]-5-(3-pyridin-4-
ylphenyl)-1,3-oxazol-2-amine (41). Tan solid; yield 34%. 1H
NMR: δ 9.73 (s, 1H), 8.74 (d, J ) 2.2, 1H), 8.63 (d, J ) 6.1,
2H) 7.97 (s, 1H), 7.71 (d, J ) 6.1, 2H), 7.64-7.68 (m, 3H), 7.55
(t, J ) 7.7, 1H), 7.44 (dd, J ) 2.2, 8.5, 1H), 7.23 (d, J ) 8.6,
1H), 3.93 (s, 3H), 3.17 (q, J ) 7.3, 2H), 1.07 (t, J ) 7.3, 3H).
LCMS (ES+, m/z) ) 436 (MH)+ (tR 7.9 min). HPLC (method
B): >99% (tR 6.1 min).
Preparation of 5-(3-Ethylphenyl)-N-[5-(ethylsulfonyl)-
2-methoxyphenyl]-1,3-oxazol-2-amine (35). 5-(3-Vinylphe-
nyl)-N-[5-(ethylsulfonyl)-2-methoxyphenyl]-1,3-oxazol-2-
amine was prepared by the Stille coupling procedure described
1
above as a red-brown solid in 73% yield. H NMR: δ 9.69 (s,
1H), 8.72 (d, J ) 2.2, 1H), 7.66 (s, 1H), 7.36-7.55 (m, 5H),
7.22 (d, J ) 8.6, 1H), 6.72 (dd, J ) 11.2, 17.5, 1H), 5.86 (d, J
) 17.6, 1H), 5.29 (d, J ) 11.2, 1H), 3.93 (s, 3H), 3.15 (q, J )
7.3, 2H), 1.06 (t, J ) 7.3, 3H). MS (ES+, m/z) ) 385 (MH)+ (tR
10.7 min). The solid (0.049 g, 013 mmol) was dissolved in ethyl
acetate (15 mL), and 10% palladium on carbon (0.018 g) added.
The reaction mixture was placed under hydrogen at 40 psi and
shaken for 3 h. The reaction mixture was filtered through
Celite and purified by flash chromatography on silica gel with
hexanes/EtOAc (2/1) to yield the title compound as an off-white
solid (0.035 g, 70%). 1H NMR: δ 9.68 (s, 1H), 8.73 (d, J ) 2.0,
1H), 7.44-7.48 (m, 3H), 7.40 (d, J ) 7.7, 1H), 7.32 (t, J ) 7.5,
1H), 7.23 (d, J ) 7.6, 1H), 7.10 (d, J ) 7.5, 1H), 3.94 (s, 3H),
3.18 (q, J ) 7.3, 2H), 2.60 (q, J ) 7.6, 2H), 1.18 (t, J ) 7.6,
3H), 1.08 (t, J ) 7.3, 3H). LCMS (ES+, m/z) ) 387 (MH)+ (tR
10.7 min). HPLC (method B): >99% (tR 11.8 min).
N-[5-(Ethylsulfonyl)-2-methoxyphenyl]-5-[3-(1-methyl-
1H-imidazol-5-yl)phenyl]-1,3-oxazol-2-amine (42). Off-
1
white solid; yield 28%. H NMR: δ 9.71 (s, 1H), 8.73 (d, J )
2.0, 1H), 7.68 (d, J ) 9.7, 2H), 7.59 (s, 1H), 7.55 (d, J ) 7.5,
1H), 7.45 (m, 2H), 7.35 (d, J ) 7.7, 1H), 7.22 (d, J ) 7.4, 1H),
7.07 (s, 1H), 3.93 (s, 3H), 3.67 (s, 3H), 3.15 (q, J ) 7.3, 2H),
1.06 (t, J ) 7.3, 3H). LCMS (ES+, m/z) ) 439 (MH)+ (tR 5.2
min). HPLC (method B): >95% (tR 5.1 min).
5-(1,1′-Biphenyl-3-yl)-N-[5-(ethylsulfonyl)-2-methoxy-
phenyl]-1,3-oxazol-2-amine (43). Off-white solid; yield 49%.
1H NMR: δ 9.72 (s, 1H), 8.74 (d, J ) 2.4, 1H), 7.85 (s, 1H),
7.67 (d, J ) 7.3, 2H), 7.61 (s, 1H), 7.44-7.58 (m, 6H), 7.37 (t,
J ) 6.2, 1H), 7.22 (d, J ) 8.6, 1H), 3.93 (s, 3H), 3.15 (q, J )
7.3, 2H), 1.06 (t, J ) 7.3, 3H). LCMS (ES+, m/z) ) 435 (MH)+
(tR 11.2 min). Anal. (C24H22N2O4S) C, H, N, S.
1-[3-(2-{[5-(Ethylsulfonyl)-2-methoxyphenyl]amino}-
1,3-oxazol-5-yl)phenyl]ethanone (36). 5-(3-Oxazole 34 (2 g,
4.6 mmol), 1-ethoxyvinyltribuyltin (2 g, 5.52 mmol), tetrabu-
tylammonium chloride (2.66 g, 9.6 mmol), and tetrakistriph-
enylphosphine palladium(0) (0.5 g, 0.43 mmol) were suspended
in DMF (50 mL) and stirred at 110 °C under nitrogen. After 1
h the reaction was cooled and evaporated under reduced
pressure. The crude residue was partitioned between 3:1
diethyl ether/dichloromethane (100 mL) and 1 N hydrochloric
acid (100 mL) and stirred for 1 h. The resulting precipitate
was filtered off, washed with diethyl ether followed by water,
and dried to yield the title compound as a tan solid (1.45 g,
N-[5-(Ethylsulfonyl)-2-methoxyphenyl]-5-(2′-fluoro-1,1′-
biphenyl-3-yl)-1,3-oxazol-2-amine (44). In a Pyrex sealed
tube, a mixture of oxazole 34 (0.1 g, 0.23 mmol), 2-fluorophe-
nylboronic acid (0.048 g, 0.34 mmol), anhydrous lithium
chloride (0.029 g, 0.68 mmol), (bistriphenylphosphine)palla-
dium(II) chloride (0.016 g, 0.023 mmol), and 2 M aqueous
sodium carbonate solution (0.29 mL, 0.58 mmol) was sus-
pended in 1:1 ethanol/dichloromethane (2 mL). The reaction
mixture was stirred at 100 °C for 16 h. The crude product was
partitioned between ethyl acetate (50 mL) and 1 N sodium
hydroxide (50 mL). The organic layer was separated, dried over
anhydrous magnesium sulfate, filtered, and concentrated
under reduced pressure. The product was purified by prepara-
tive plate chromatography eluting with hexane:ethyl acetate
(60-80%) to afford the title compound (0.045 g, 44%) as a
peach solid. An Analytical purity was obtained by HPLC
purification (method B) eluting with H2O:MeCN:0.1% formic
1
79%). H NMR: δ 9.90 (s, 1H), 8.81 (d, J ) 2.3, 1H), 8.18 (s,
1H), 7.90 (d, J ) 9.2, 2H), 7.72 (s, 1H), 7.63 (t, J ) 8.0, 1H),
7.52 (dd, J ) 2.3, 6.3, 1H), 7.31 (d, J ) 8.5, 1H), 4.01 (s, 3H),
3.24 (q, J ) 7.3, 2H), 2.66 (s, 3H), 1.15 (t, J ) 7.3, 3H). LCMS
(ES+, m/z) ) 401 (MH)+ (tR 8.8 min). Anal. (C20H20N2O5S·
0.4H2O) C, H, N, S.
1
acid, gradient 10-90% MeCN over 15 min. H NMR: δ 9.82

1618 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 5
Harris et al.
(s, 1H), 8.82 (d, J ) 2.1, 1H), 7.82 (s, 1H), 7.70-7.34 (m, 9H),
7.30 (d, J ) 8.6, 1H), 4.00 (s, 3H), 3.23 (q, J ) 7.3, 2H), 1.14
(t, J ) 7.3, 3H). LCMS (ES+, m/z) ) 453 (MH)+ (tR 10.7 min).
Anal. (C24H21FN2O4S·0.6HCO2H) C, H, N, S.
coated plate (Becton Dickinson). The plate was incubated at
37 °C overnight. The medium was removed by aspiration, and
test compounds were added to each well in a volume of 0.1
mL/well in serum-free M199 medium. Compound concentra-
tions ranged from 1.5 nM to 30 µM. The plate was incubated
for 30 min at 37 °C. Another 0.1 mL of serum-free M199
medium containing BSA and VEGF (or bFGF) was added to
give a final concentration of 0.1% BSA and 10 ng/mL VEGF
(0.3 ng/mL bFGF). The plate was incubated at 37 °C for 72 h.
BrdU was added to each well after the first 48 h to give a
concentration of 10 µM. The colorimetric ELISA assay was
performed according to manufacturer’s (Roche Molecular Sci-
ences) instructions, with detection by absorbance reading at
450 nm. Results were plotted as concentration of test com-
pound vs absorbance to give an IC50 value for inhibition of
BrdU incorporation.
Pharmacokinetics in Mouse, Rat, and Dog. Oxazole 39
was administered orally to male CD mice (n ) 2) and male
Sprague-Dawley rats (n ) 3) via oral gavage at a dose volume
of 10 mL/kg and by intravenous injection to rats at a dose
volume of 5 mL/kg. Oxazole 39 was administered orally to male
beagle dogs (n ) 2) via oral gavage and by intravenous
injection at a dose volume of 0.5 mL/kg. The blood samples
were placed on wet ice, and plasma was collected after
centrifugation. Plasma samples were stored frozen at -20 °C
until time of analysis. Plasma samples were prepared by
protein precipitation with four volumes of acetonitrile (200 µL)
per 50 µL of plasma sample. Samples were analyzed by high-
performance liquid chromatography (HPLC)/mass spectromet-
ric analysis. Pharmacokinetic parameters were determined by
PKCal 2.0.
Antitumor Activity against HT29 Colon Carcinoma
Xenograft Model. HT29 tumors were initiated by injection
of tumor cell suspension subcutaneously in 8-12 week old
female nude mice. Mice were randomized into groups of eight
prior to treatment when tumors reached a volume of 50-60
mm3 (9 days after implantation). Animals were treated with
oxazole 39 (30 or 100 mg/kg) or vehicle (in 0.5% HPMC, 0.1%
Tween 80 in sterile water), administered once daily by oral
gavage. Tumor volume was measured twice weekly by calipers,
using the formula (length × width2 × 0.5), where length was
the longest diameter across the tumor, and width was the
corresponding perpendicular. Tumor growth inhibition was
calculated by mean change in tumor volume of control and
treated groups. All animal studies were performed under
approved protocols from the institutional animal care and use
committee.
Crystallography of VEGFR2 Ligand Complexes. Pro-
tein expression and purification of human VEGFR2 was
carried out as described by McTigue et al.21,22 Protein-ligand
complexes were obtained by combining 100 µL of the protein
solution (VEGFR: 10 mg/mL, 10 mM Hepes, pH 7.5, 10 mM
DTT, and 10 mM NaCl) with 3 µL of a 50 mM compound in
DMSO and allowing the mixture to stand for 90 min at 20 °C.
Crystals of the complex were obtained using the hanging drop
method using drops composed of 1:l of the protein/ligand
complex and 4 µL of a reservoir solution (100 mM Hepes, pH
7.5, 2.1 M ammonium sulfate, and 2% PEG550). X-ray data
was collected from cryogenically preserved crystals using a
Mar165 detector at Sector 17 of the Advanced Photon Source.
Crystal structures were solved using the Amore molecular
replacement program23 with an unligand structure of VEGFR2
as the search model. The structures were built using the
program O,24 and initial refinement was carried out with the
CNX program.25 Map generation, density modification, and
final refinement was carried out using programs from the
CCP4 Suite.23
N-[5-(Ethylsulfonyl)-2-methoxyphenyl]-5-(2′-chloro-
1,1′-biphenyl-3-yl)-1,3-oxazol-2-amine (45). Following the
same procedure described for the preparation of 44, substitut-
ing 2-chloroboronic acid afforded the title compound (0.022 g,
1
21%) as an off-white solid. H NMR: δ 9.80 (bs, 1H), 8.81 (s,
1H), 7.69-7.49 (m, 9H), 7.37 (d, J ) 7.9, 1H), 7.30 (d, J ) 8.7,
1H), 4.00 (s, 3H), 3.22 (q, J ) 7.2, 2H), 1.13 (t, J ) 7.2, 3H).
LCMS (ES+, m/z) ) 469 (MH)+ (tR 10.9 min). Anal. (C24H21-
ClN2O4S 0.2 HCO2H) C, H, N, Cl, S.
N-(Cyclopropylmethyl)-4-methoxy-3-({5-[3-(3-pyridinyl)-
phenyl]-1,3-oxazol-2-yl}amino)benzenesulfonamide (46).
Following the procedure described for the preparation of
isothiocyanate 23, 3-amino-4-methoxybenzenesulfonyl fluoride
was converted to 3-isothiocyanato-4-methoxybenzenesulfonyl
1
fluoride in 94% yield. H NMR: δ 8.04 (m, 2H), 7.44 (d, J )
6.4, 1H), 4.01 (s, 3H). Following the general procedure
described for the preparation of oxazoles 24-33, 3-bromophen-
acyl azide and 3-isothiocyanato-4-methoxybenzenesulfonyl
fluoride were reacted to produce 3-{[5-(3-bromophenyl)-1,3-
oxazol-2-yl]amino}-4-methoxybenzenesulfonyl fluoride in 52%
yield. 1H NMR: δ 10.16 (s, 1H), 9.08 (d, J ) 2.4, 1H), 7.86 (s,
1H), 7.80 (dd, J ) 2.5, 8.5, 1H), 7.73 (s, 1H), 7.64 (d, J ) 7.6,
1H), 7.42-7.52 (m, 3H), 4.06 (s, 3H). LCMS (ES+, m/z) ) 428
(MH)+. Following the same general procedure for the Stille
couplings of oxazole 34, 3-{[5-(3-bromophenyl)-1,3-oxazol-2-yl]-
amino}-4-methoxybenzenesulfonyl fluoride was converted with
3-pyridyltributyltin to 4-methoxy-3-({5-[3-(3-pyridinyl)phenyl]-
1,3-oxazol-2-yl}amino)benzenesulfonyl fluoride in 30% yield.
1H NMR: δ 10.05 (s, 1H), 9.02 (d, J ) 2.4, 1H), 8.90 (d, J )
2.0, 1H), 8.57 (d, J ) 4.5, 1H), 8.08 (d, J ) 8.1, 1H), 7.93 (s,
1H), 7.72 (dd, J ) 2.3, 8.7, 1H), 7.67 (s, 1H), 7.62 (t, J ) 6.9,
2H), 7.55 (d, J ) 7.7, 1H), 7.48 (dd, J ) 4.8, 7.9, 1H), 7.33 (d,
J ) 8.8, 1H), 3.99 (s, 3H). LCMS (ES+, m/z) ) 426 (MH)+.
4-Methoxy-3-({5-[3-(3-pyridinyl)phenyl]-1,3-oxazol-2-yl}amino)-
benzenesulfonyl fluoride (0.07 g, 0.16 mmol) was dissolved in
(cyclopropylmethyl)amine (2 mL) and heated to 100 °C for 16
h in a sealed tube. On cooling, the excess amine was removed
on a rotavapor and the crude triturated with methanol to yield
the title compound as a white solid (0.04 g, 52%). 1H NMR: δ
9.57 (bs, 1H), 8.91 (s, 1H), 8.67 (d, J ) 1.9, 1H), 8.57 (d, J )
4.4, 1H), 8.09 (d, J ) 8.1, 1H), 7.92 (s, 1H), 7.62-7.46 (m, 6H),
7.37 (dd, J ) 1.9, 7.9, 1H), 7.15 (d, J ) 8.6, 1H), 3.90 (s, 3H),
2.59 (t, J ) 6.2, 2H), 0.70-0.81 (m, 1H), 0.29 (t, J ) 7.6, 2H),
0.03 (d, J ) 5.1, 2H). LCMS (ES+, m/z) ) 477 (MH)+ (tR 9.7
min).
VEGFR2 HTRF Assay. The assay was performed in 96-
well black plates. 10 nM hVEGFR2 was used to phosphorylate
0.36 µM peptide (Biotin-Ahx-EEEEYFELVAKKKK) in the
presence of 75 µM ATP, 5 mM MgCl2, 0.3 mM DTT, 0.1 mg/
mL BSA, and 0.1 M HEPES (pH 7.5). A 10 µL portion of 0.5
M EDTA was added to reactions as negative controls. The 50
µL kinase reaction with or without inhibitors in 5% DMSO
was carried out at room temperature for 45 min and then
stopped by 40 µL of 125 mM EDTA. Streptavidin-APC (2.4
µg/mL) and Eu-R-pY (0.15 µg/mL), in the presence of 0.1 mg/
mL BSA, 0.1 M HEPES (pH7.5), were added to a final volume
of 140 µL. The plate was incubated for 10 min at room
temperature and read on the Victor in the time-resolved
fluorescence mode by exciting at 340 nm and reading the
emission at 665 nm.
Human Umbilical Vein Endothelial Cell (HUVEC)
Proliferation Assay (BrdU Incorporation). HUVEC cells
and EGM-MV (endothelial cell growth mediumsmicrovascular)
were purchased from Clonetics (San Diego, CA). VEGF and
bFGF were purchased from R&D Systems (Minneapolis, MN).
Anti-BrdU antibody was obtained from Chemicon Interna-
tional (Temecula, CA). HUVECs were routinely maintained
in EGM-MV medium and were used within passage 7. HU-
VECs were plated at a density of 2500 cells/well in M199
medium containing 5% FBS (Hyclone) in a type I collagen-
Acknowledgment. We acknowledge Sue Kadwell
and Earnest Horne for generating the construct and
expression vectors used for protein production and
Warren Rocque and William Holmes for the production
of protein. X-ray data was collected at beam line 17-ID
in the facilities of the Industrial Macromolecular Crys-

2-Anilino-5-aryloxazoles as VEGFR2 Kinase Inhibitors
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 5 1619
A.; Schaeffer, T.; Whalen, P. M.; Roberts, W. G. Pharmacological
Characterization of CP-547,632, a novel vascular endothelial
growth factor receptor-2 tyrosine kinase inhibitor for cancer
therapy. Cancer Res. 2003, 63, 7301-7309.
tallography Association Collaborative Access Team
(IMCA-CAT) at the Advanced Photon Source. Use of the
Advanced Photon Source was supported by the U. S.
Departmentof Energy, Basic Energy Sciences, Office of
Science, under Contract No. W-31-109-Eng-38. We are
grateful to Peter Kitrinos and Amanda G. Alford for MS
and HPLC support, respectively.
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