Discovery and structure-activity relationships of urea derivatives as potent and novel CCR3 antagonists

Article abstract of DOI:10.1016/j.bmcl.2012.06.042

The synthesis and structure-activity relationships of ureas as CCR3 antagonists are described. Optimization starting with lead compound 2 (IC ₅₀ = 190 nM) derived from initial screening hit compound 1 (IC ₅₀ = 600 nM) led to the iden

Full text of DOI:10.1016/j.bmcl.2012.06.042

Bioorganic & Medicinal Chemistry Letters 22 (2012) 4951–4954
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Discovery and structure–activity relationships of urea derivatives as potent
and novel CCR3 antagonists
Aiko Nitta a, , Yosuke Iura a, Hiroki Tomioka a, Ippei Sato b, Koichiro Morihira b, Hirokazu Kubota b,
⇑
Tatsuaki Morokata b, Makoto Takeuchi b, Mitsuaki Ohta b, Shin-ichi Tsukamoto b, Takayuki Imaoka a,
Toshiya Takahashi a
a Pharmaceutical Research Laboratories, Toray Industries, Inc., 6-10-1 Tebiro, Kamakura, Kanagawa 248-8555, Japan
b Drug Discovery Research, Astellas Pharma Inc., 21 Miyukigaoka, Tsukuba-shi, Ibaraki 305-8585, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 February 2012
Revised 6 June 2012
Accepted 13 June 2012
Available online 20 June 2012
The synthesis and structure–activity relationships of ureas as CCR3 antagonists are described. Optimiza-
tion starting with lead compound 2 (IC50 = 190 nM) derived from initial screening hit compound 1
(IC50 = 600 nM) led to the identification of (S)-N-((1R,3S,5S)-8-((6-fluoronaphthalen-2-yl)methyl)-8-aza-
bicyclo[3.2.1]octan-3-yl)-N-(2-nitrophenyl)pyrrolidine-1,2-dicarboxamide 27 (IC50 = 4.9 nM) as a potent
CCR3 antagonist.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Allergic diseases
CCR3 antagonists
Urea derivatives
Proline moiety
The hallmark of allergic diseases such as asthma is selective
accumulation of eosinophils at inflammatory sites.1 Therefore,
eosinophils are thought to play an important role in the initiation
and progression of these diseases. CC chemokine receptor 3 (CCR3),
a member of the seven transmembrane G-protein coupled receptor
(GPCR) family, is the receptor for eotaxin and appears predomi-
nantly on eosinophils. Upon activation, eosinophils release lipid
mediators, cytotoxic proteins, oxygen metabolites and cytokines,
all of which have potential to produce the clinically observed
pathophysiology. A growing body of clinical studies and animal
models suggest that eotaxin and CCR3 play a major role in allergic
diseases and thus, a selective CCR3 antagonist that suppresses the
infiltration of eosinophils to inflammatory sites may have clinical
potential in allergic diseases.2–11
A series of potent amide-based CCR3 antagonists possessing
6-fluoronaphthalenyl methyl moiety in our joint research project
have been reported.12–14 During these studies, we also evaluated
a series of urea derivatives for CCR3 inhibitory activity that display
different structure–activity relationships from amides. In this Let-
ter, we detail our efforts to discover the urea series of CCR3
antagonists.
In our initial efforts to discover potential and selective CCR3
antagonists, screening of our corporate compound library yielded
several hit compounds, including compound 1 as shown in Figure
O
O
N
N
N
N
H
N
N
N
F
N
N
2: IC50 = 190 nM
1: IC50 = 600 nM
Figure 1. Screening hit compound 1 and modified lead compound 2.
⇑
Corresponding author. Tel.: +81 467 32 9659; fax: +81 467 32 9891.
E-mail address: Aiko_Nitta@nts.toray.co.jp (A. Nitta).
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2012.06.042

4952
A. Nitta et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4951–4954
1.15 Compound 1 showed unique structural features such as tricy-
suitable positions of right and left aromatics
clic imidazolo-quinazolone and diphenylmethyl piperidine moie-
ties and moderate inhibitory activity for CCR3 (IC50 = 600 nM). To
elevate CCR3 inhibitory activity and avoid synthetic difficulty and
low bioavailability of 1,16 various derivatives were synthesized.
As a result, tetrahydroisoquinoline urea derivative 2 (IC50 = 190
nM) was discovered as a lead compound. The inhibitory activity
of 2 against other CC chemokine receptors, CCR1, CCR2 and CCR5,
was also evaluated and it resulted in no effect on them at a concen-
suitable length but flexible linker
O
fluorine atom
F
N
N
H
N
2
tertiary amine
tration of 10 lM.
Toward optimization of the new lead compound 2, we decided
to modify the linker structure of 2, which showed a length suitable
for CCR3 inhibitory activity but was too flexible. To design a rigid
linker, the substructure of another lead compound 3 was utilized
for adjusting the positions of both terminal aromatics and central
tertiary amine.12 As shown in Figure 2, therefore, the diphenyl-
methyl propyl piperidine moiety of 2 was converted to 6-fluoro-
naphthyl methyl nortropane. Moreover, the tetrahydroisoquino-
line was replaced with various cyclic amines in the left part.
As shown in Scheme 1, the 6-fluoro-naphthyl methyl nortro-
pane derivatives were synthesized by activation of nortropane
amine 4 with 4-nitrophenyl chloroformate,13 followed by conden-
sation with commercially available or appropriate amines that
were prepared by common routes described in Scheme 2. 6-Flu-
oro-1,2,3,4-tetrahydroisoquinoline, a starting material for synthe-
sis of 5 was prepared as reported.17
O
N
N
H
F
rigid linker
3: IC50 = 20 nM
O
N
N
N
H
F
Figure 2. Important pharmacophores for CCR3 inhibitory activity and new com-
pound design.
O
a, b
The CCR3 inhibitory activity data for selected compounds are
listed in Table 1. Compound 5 (IC50 = 780 nM) possessing the sub-
structure of 2 was not effective with one-quarter of the potency of
2. As it seemed that the left aromatic ring of compounds 6
(IC50 = 59 nM) and 8 (IC50 = 52 nM) was located as the same
H2N
R
N
H
N
N
F
F
5-29
4
Scheme 1. Reagents and conditions: (a) ClCO2p-NO2Ph, NaHCO3, CHCl3; (b) amine,
Et3N, CHCl3.
NBn
NH
O
O
F
NBn
b, c
d
a
O2N
F
N
N
HN
HN
F
N
H
NO2
F
F
30
34
31
32
33
NH
O
NBn
F
O
CbzHN
NBn
O2N
N
e
a
b, c
HN
N
HN
N
H
NO2
35
NHCbz
N
H2N
37
CbzHN
g
36
O
O
HN
N
N
f
N
NH
R
R
Cl
Cl
38
39a: R=4-F
40a: R=4-F
39b: R=4-NH2
39c: R=2,6-diCl
40b: R=4-NH2
40c: R=2,6-diCl
40d: R=2-F,6-OH
40e: R=4-OH
39d: R=2-F,6-OH
39e: R=4-OH
39f: R=2-OH
40f: R=2-OH
O
O
O
R
R
h
i
HO
NFmoc
N
NFmoc
N
H
NH
H
41
43a: R=H
42a: R=H
43b: R=2-Br
43c: R=3-Br
43d: R=4-Br
43e: R=2-F
43f: R=2-Cl
43g: R=2-NO2
43h: R=2-OMe
43i: R=2-iPr
42b: R=2-Br
42c: R=3-Br
42d: R=4-Br
42e: R=2-F
42f: R=2-Cl
42g: R=2-NO2
42h: R=2-OMe
42i: R=2-iPr
Scheme 2. Reagents and conditions: (a) 1-benzylpiperidin-4-amine, K2CO3, DMF, 80 °C; (b) Fe, NH4Cl, THF/MeOH/water (1:2:2), 80 °C; (c) CDI, CH3CN; (d) 1-chloroethyl
chloroformate, 1,2-dichloroethane, quant.; (e) H2, Pd/C, THF, EtOH, AcOH, 91%; (f) benzoic acid, BOP, iPr2NEt, CH2Cl2; (g) H2, Pd/C, THF; (h) aniline, BOP, iPr2NEt, CH2Cl2; (i)
piperidine, DMF.

A. Nitta et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4951–4954
4953
Table 1
CCR3 inhibiting activity of urea derivatives 5–29
O
N
R
N
H
F
Compds
R
IC50 (nM) Compds
R
IC50 (nM) Compds
R
IC50 (nM)
Cl
F
O
O
O
N
N
N
N
N
5
780
59
13
14
62
51
21
22
240
13
N
H
N
N
F
Cl
O
O
N
N
H
HN
6
N
Br
OH
O
Cl
O
N
N
N
MeN
Br
Br
N
H
N
N
7
8
9
360
15
16
17
18
23
24
25
110
920
13
N
Cl
Cl
N
O
N
O
N
N
N
H
HN
52
1600
440
Cl
O
O
N
O
O
O
N
N
N
N
H
N
HN
44
F
HO
OH
F
O
N
O
N
N
N
N
H
N
HN
Cl
10
8.0
18
63
26
27
29
H2N
O
O
N
O
O
N
N
11
12
310
380
19
20
45
56
4.9
N
N
N
H
N
N
NO2
F
O
O
O
S
N
N
N
28
N
H
31
30
OMe
H2N
O
29
N
H
N
iPr
pharmacophore, these compounds showed the same value of IC50
.
derivatives 11–15 and 17–20 were obtained as potent CCR3 antag-
onists. It seemed that the ortho-substituent of the aromatic ring
was important for potency because benzamides 13 (IC50 = 62 nM),
14 (IC50 = 51 nM), and 18 (IC50 = 63 nM) were more effective than
para-substituents 11 (IC50 = 310 nM), 12 (IC50 = 830 nM), and 17
(IC50 = 440 nM). A replacement of the homopiperazine moiety of
13 with the piperazine (16: IC50 = 1600 nM) resulted in a decline
in inhibitory activity. The most potent homopiperazine derivative
An introduction of methyl substitution to the amide of 6 resulted
in compound 7 (IC50 = 360 nM) with one sixth of the potency of
6. The left aromatic ring of 7 seemed to be out of the pharmaco-
phore because of the methyl group. Substituents on the benzoim-
idazolone moiety were examined, and 5-amino derivative 37
showed sixfold potency compared with that of 8 (IC50 = 52 nM),
but 4-fluoro 9 (IC50 = 44 nM) equal potency. Next, homopiperazine

4954
A. Nitta et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4951–4954
5. Varnes, J. G.; Gardner, D. S.; Santella, J. B., III; Duncia, J. V.; Estrella, M.; Watson,
P. S.; Clark, C. M.; Ko, S. S.; Welch, P.; Covington, M.; Stowell, N.; Wadman, E.;
Davies, P.; Solomon, K.; Newton, R. C.; Trainor, G. L.; Decicco, C. P.; Wacker, D.
A. Bioorg. Med. Chem. Lett. 2004, 14, 1645.
6. Dhanak, D.; Christmann, L. T.; Darcy, M. G.; Jurewicz, A. J.; Keenan, R. M.; Lee, J.;
Sarau, H. M.; Widdowson, K. L.; White, J. R. Bioorg. Med. Chem. Lett. 2001, 11,
1441.
was 15 (IC50 = 18 nM) possessing a 2,6-dichlorobenzyl moiety.
Lastly, benzamide proline moiety was examined. Introduction of
bromo substitution to the phenyl group of 21 (IC50 = 240 nM)
revealed most suitable substitution position for CCR3 inhibitory
activity is 2-position (22: IC50 = 13 nM). Among various 2-substitu-
tions (25–29) 2-nitrobenzamide proline derivative 27 was ob-
tained with an IC50 value of 4.9 nM. The 2-nitrobenzamide 27
has 50-fold inhibitory activity compared with that of 21 unsubsti-
tuted. The inhibitory activity of 27 against CCR1, CCR2 and CCR5
7. Gong, L.; Hogg, J. H.; Collier, J.; Wilhelm, R. S.; Soderberg, C. Bioorg. Med. Chem.
Lett. 2003, 131, 3597.
8. Ting, P. C.; Lee, J. F.; Wu, J.; Umland, S. P.; Aslanian, R.; Cao, J.; Dong, Y.; Garlisi,
C. G.; Gilbert, E. J.; Huang, Y.; Jakway, J.; Kelly, J.; Liu, Z.; McCombie, S.; Shah, H.;
Tian, F.; Wan, Y.; Shih, N. Y. Bioorg. Med. Chem. Lett. 2005, 15, 1375.
9. Anderskewitz, R.; Bauer, R.; Bodenbach, G.; Gester, D.; Gramlich, B.;
Morschhauser, G.; Birke, F. Bioorg. Med. Chem. Lett. 2005, 15, 669.
10. Wacker, D. A.; Santella, J. B., III; Gardner, D. S.; Varnes, J. G.; Estrella, M.;
DeLucca, G. V.; Ko, S. S.; Tanabe, K.; Watson, P. S.; Welch, P. K.; Covington, M.;
Stowell, N.; Wadman, E.; Davies, P.; Solomon, K.; Newton, R. C.; Trainor, G. L.;
Friedman, S. M.; Decicco, C. P.; Duncia, J. V. Bioorg. Med. Chem. Lett. 2002, 12,
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11. De Lucca, G. V.; Kim, U. T.; Johnson, C.; Vargo, B. J.; Welch, P. K.; Covington, M.;
Davies, P.; Solomon, K.; Newton, R. C.; Trainor, G. L.; Decicco, C. P.; Ko, S. S. J.
Med. Chem. 2002, 45, 3794.
12. Sato, I.; Morihira, K.; Inami, H.; Kubota, H.; Morokata, T.; Suzuki, K.; Hamada,
N.; Iura, Y.; Nitta, A.; Imaoka, T.; Takahashi, T.; Takeuchi, M.; Ohta, M.;
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resulted in no effect on them at 10 lM.
In conclusion, to improve the CCR3 inhibitory activity of the
lead compound 2 derived from the hit compound 1, a series of ur-
eas were identified. The conversion of diphenylmethyl propyl
piperidine moiety to 6-fluoronaphthyl methyl nortropane was
critical for potent activity. The ortho-substituent on the aromatic
ring of the left cyclic amine subunit was effective. Finally, the
introduction of a nitro substituent at the 2-position of the benzam-
ide moiety of the proline derivative led to the successful identifica-
tion of 27, which is a selective CCR3 antagonist and the most
potent in this series. We will report our additional efforts toward
potent, selective and bioavailable CCR3 antagonists in due course.
13. Sato, I.; Morihira, K.; Inami, H.; Kubota, H.; Morokata, T.; Suzuki, K.; Iura, Y.;
Nitta, A.; Imaoka, T.; Takahashi, T.; Takeuchi, M.; Ohta, M.; Tsukamoto, S.
Bioorg. Med. Chem. 2008, 16, 8607.
14. Sato, I.; Morihira, K.; Inami, H.; Kubota, H.; Morokata, T.; Suzuki, K.; Ohno, K.;
Iura, Y.; Nitta, A.; Imaoka, T.; Takahashi, T.; Takeuchi, M.; Ohta, M.; Tsukamoto,
S. Bioorg. Med. Chem. 2009, 17, 5989.
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