Synthesis, structure-activity relationships, and anxiolytic activity of 7-aryl-6,7-dihydroimidazoimidazole corticotropin-releasing factor 1 receptor antagonists

Article abstract of DOI:10.1016/j.bmcl.2005.05.117

7-Aryl-6,7-dihydroimidazoimidazoles represent a novel series of high-affinity corticotropin-releasing factor 1 receptor antagonists. Here, we report their synthesis and SAR as well as behavioral activity of two exemplary compounds, 7b and 7k, in a mouse canopy model of anxiety.

Full text of DOI:10.1016/j.bmcl.2005.05.117

Bioorganic & Medicinal Chemistry Letters 15 (2005) 3870–3873
Synthesis, structure–activity relationships, and anxiolytic activity
of 7-aryl-6,7-dihydroimidazoimidazole
corticotropin-releasing factor 1 receptor antagonists
Xiaojun Han,a,* Jodi A. Michne,b Sokhom S. Pin,a Kevin D. Burris,c Lynn A. Balanda,a
Lawrence K. Fung,d Tracey Fiedler,a Kaitlin E. Browman,e Matthew T. Taber,a
Jie Zhangf and Gene M. Dubowchika,*
aPharmaceutical Research Institute, Bristol-Myers Squibb Company, 5 Research Parkway, Wallingford, CT 06492, USA
bAstraZeneca R&D Boston, Infection Discovery, 35 Gatehouse Park, Waltham, MA 02451, USA
cPalatin Technologies Inc., 4-C Cedar Brook Drive, Cranbury, NJ 08512, USA
dNeurogen Corp., 35 N.E. Industrial Road, Branford, CT 06405, USA
eAbbott Laboratories, Dept. R4N5, Building AP9A 100 Abbott Park Road, Abbott Park, IL 60064, USA
fSanofi Aventis, 1041 Route 202-206, Bridgewater, NJ 08807, USA
Received 31 March 2005; revised 24 May 2005; accepted 26 May 2005
Available online 28 June 2005
Abstract—7-Aryl-6,7-dihydroimidazoimidazoles represent a novel series of high-affinity corticotropin-releasing factor 1 receptor
antagonists. Here, we report their synthesis and SAR as well as behavioral activity of two exemplary compounds, 7b and 7k, in
a mouse canopy model of anxiety.
Ó 2005 Elsevier Ltd. All rights reserved.
Corticotropin-releasing factor (CRF), a 41-residue neu-
ropeptide, secreted in the hypothalamus, mediates stress
responses by stimulating the release of adrenocorticotro-
pic hormone (ACTH) from the pituitary. The resulting
secretion of ACTH initiates the release of adrenal gluco-
corticoids, which impose their pathophysiological effects
through the hypothalamic–pituitary–adrenal axis
(HPA).1–3 The clinical relevance of the HPA/stress/de-
pression hypothesis has been supported by the fact that
high CRF levels have been detected in the cerebrospinal
fluid in more than half of depressed patients, and that
treatment with antidepressants normalize these levels.4
These findings, along with the desire to target a new
antidepressant mechanism that might avoid problems
associated with current therapies, have inspired a num-
ber of groups to develop highly selective, small molecule
CRF1 receptor (CRF1R) antagonists. Initial clinical
work has shown promise for this target,5 but an opti-
mized compound, free of liabilities, has yet to appear.
The CRF receptor, a G-protein-coupled receptor (class
B), has two well-characterized subtypes, CRF1R and
CRF2R. The receptor is mainly expressed in the central
nervous system, primarily in the cortex, cerebellum, hip-
pocampus, amygdala, olefactory bulb, and pituitary.6
Nearly all known nonpeptidic CRF1R antagonists (e.g., 1
and 2) share the following structural features: a heteroa-
romatic core with an sp2-hybridized nitrogen, a small al-
kyl group on the atom next to that nitrogen, a branched
tertiary amine side-chain attached to this core, and an aryl
(or heteroaryl) ring also attached to it containing at least
one ortho substitution to reinforce the active, mutually
orthogonal conformation (Fig. 1).7 In this letter, we re-
port our efforts in the design, synthesis, binding studies
and behavioral efficacy of a novel series of 7-aryl-6,7-
dihydroimidazoimidazole CRF1R antagonists (7 and 8).
Keywords: Corticotropin-releasing factor 1 receptor antagonists; SAR;
Anxiolytic activity; Mouse canopy model.
*
Corresponding authors. Tel.: +1 203 677 7879; fax: +1 203 677 7702
(X.H.); e-mail addresses: xiaojun.han@bms.com; gene.dubowchik@
bms.com
The synthesis of imidazoles 7 and 8 is outlined in
Schemes 1 and 2. N-arylethylenediamines 3 were treat-
0960-894X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.05.117

X. Han et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3870–3873
3871
Figure 1. Small-molecule CRF1R antagonists.
ed with cyanogen bromide in ethanol at 150 °C with
the condenser open to the air, to give cyclic guanidines
4.8 These were alkylated with ethyl bromoacetate in
acetone at reflux. After acetone was removed, the resi-
dues were refluxed in either acetic (for R = Me) or pro-
pionic (for R = Et) anhydride, along with their
respective sodium salts to afford esters 6.9 Amidation
under Weinreb conditions10 with secondary amines
afforded amides 7.11 Finally, employment of the non-
Lewis acidic-reducing agent, Red-Al, to reduce amides
7 produced amines 8.11
N-arylethylenediamines 3 were prepared as shown in
Scheme 2. Reaction of 2,4,6-trimethylaniline with 2-
bromoethylamine-HBr in toluene at reflux afforded
diamine 3a.12 This methodology did not extend to ani-
lines containing electron-withdrawing groups. For a
wider study of aryl substitution, a new synthesis of
N-arylethylenediamines 3b–e was developed. Di- or
tri-substituted anilines 9 were acylated with chloroace-
tic anhydride to afford chlorides 10. Treatment of 10
with NaN3 gave azides 11 in high yields. Both the
amide and azide groups were smoothly reduced by
BH3-THF to afford diamines 3b–e following
methanolysis.
CRF1R-binding affinities were determined by displace-
ment of [125I]Tyr-o-CRF from hCRF1R endogenously
expressed on IMR-32 human neuroblastoma cells.13
We first looked at the requirements for alkyl substitu-
tion at the 2-position of the imidazole as well as the tol-
erance for amide or amine substitution at position 3.
The results for a series of N-cyclopropylmethyl-N-n-pro-
Scheme 1. Reagents and conditions: (a) BrCN, EtOH, 150 °C, 40 min.
(b) Bromoethyl acetate, acetone, reflux, 12 h. (c) (RCO)2O, RCO2Na,
170 °C, 8 h 15–30% for three steps. (d) R1NHR2, AlMe3, PhMe, 80 °C,
14 h, 70–90%. (e) Red-Al, PhMe, rt, 24 h, 40–70%.
Scheme 2. Reagents and conditions: (a) 2-bromoethylamine-HBr salt, PhMe, reflux, 14 h, 45%. (b) (ClCH2CO)2O, (ClCH2)2, rt, 1 h, 80–90%.
(c) NaN3, KI, DMF, 50 °C, 4 h, 60–90%. (d) BH3-THF, THF, reflux, 14 h, 70–88%.

3872
X. Han et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3870–3873
Table 2. hCRF1R-binding affinities of amides 7b–cc
pyl amides and amines are summarized in Table 1. In
contrast to the related series of aminothiazoles,15 tertia-
ry amides in this series were significantly more potent
than amines (7a, b, vs 8a, b). As reported for other series
of 5-membered bicyclic CRF antagonists,16 the ethyl
group in 7b conferred best activity.
Next, a series of 2-ethylimidazole-3-amides containing a
pendent 2,4,6-trimethylphenyl ring were prepared to ex-
plore SAR preferences for the amide side-chain. The
best activity was seen with compounds containing the
cyclopropylmethyl side-chain (7b and 7j–n) along with
a small alkyl (7b, 7j, and 7n) or fluorinated alkyl (7k–
m) chain. When cyclopropylmethyl was replaced by n-
propyl or n-butyl (7c, d), there was a modest loss of
affinity, while extension by one methylene group to give
cyclopropylethyl (7o–q) resulted in a >10-fold reduction
in potency. Benzyl, or substituted benzyl, derivatives
(7r–w) showed poor activity, but a single phenylethyl
example (7x vs 7r) was ca. 20-fold more potent, perhaps
because of greater conformational mobility. An attempt
to introduce polarity into the side-chain (7e) was unsuc-
cessful as were efforts to tie up the side-chains into 6-
membered rings (7z–cc). These results argue for a rela-
tively small, hydrophobic-binding pocket in which a
Ôpseudo-aromaticÕ group such as cyclopropylmethyl
binds well, either because of size or the restricted confor-
mation of the side-chain amide linkage, larger groups
such as benzyl do not (Table 2).
Compound R1
R2
Ki (nM)
7c
7d
7e
7f
nPr
nBu
nPr
Et
100
290
Me2NCH2CH2
Allyl
Allyl
Et
nPr
>10,000
740
7g
7h
7i
Allyl
nPr
3000
61
CF3CH2
CF3CH2CH2
cPrCH2
cPrCH2
nPr
nPr
220
42
7b
7j
Et
94
41
7k
7l
cPrCH2
cPrCH2
CF3CH2
CF3CF2CH2
CF3CH2CH2
cPrCH2
nPr
63
73
7m
7n
7o
7p
7q
7r
cPrCH2
cPrCH2
68
770
cPrCH2CH2
cPrCH2CH2
cPrCH2CH2
PhCH2
Et
610
650
CF3CH2CH2
nPr
nPr
4100
4200
3000
660
7s
m-F-PhCH2
p-Cl-PhCH2
PhCH2
7t
nPr
7u
7v
7w
7x
7y
7z
7aa
7bb
7cc
CF3CH2CH2
CF3CH2CH2
PhCH2
nPr
p-Cl-PhCH2
PhCH2
270
>10,000
220
Finally, a small selection of 2-ethylimidazole-3-cyclo-
propylamides containing four different pendent halo-ar-
omatic rings were prepared with either n-propyl or
trifluoroethyl side-chain (Table 3). While mono-bromin-
ation (7hh–ii) and mono- and di-chlorination (7dd–gg)
gave little-or-no potency advantage over corresponding
2,4,6-trimethyl analogues (7b and 7k), the loss of activity
seen with the 2-bromo-4-isopropylphenyl compounds
(7jj–kk) suggests the need for two ortho substituents in
this chemotype.
PhCH2CH2
Ph
H
>10,000
>10,000
>10,000
>10,000
>10,000
Morpholine
Piperazine
4-Acetylpiperazine
4-(2-F-phenyl)piperazine
Table 3. hCRF1R-binding affinities of amides 7dd–kk
Compounds 7b and 7k were chosen for further in vivo
study. Table 4 shows the results of a pharmacokinetic
study of 7b in rats. The compound showed a high-to-
moderate clearance with good oral bioavailability, but
a fairly low brain-to-plasma ratio.
Table 1. hCRF1R-binding affinities of amides 7a, b and amines 8a, b
Compound
X
Y
Z
R1
Ki (nM)
7dd
7ee
7ff
Cl
Cl
Cl
Cl
Br
Br
Br
Br
Me
Me
Cl
Me
Me
Me
Me
Me
Me
H
CF3CH2
nPr
41
94
CF3CH2
nPr
24
75
7gg
7hh
7ii
Cl
Me
Me
iPr
iPr
CF3CH2
nPr
26
126
270
1559
7jj
7kk
CF3CH2
nPr
H
Compound
R
W
Ki (nM)
7a
7b
8a
8b
Me
Et
O
220
42
O
We used the mouse canopy stretched attend posture
(SAP) model to determine the anxiolytic potential of
compounds 7b and 7k (Fig. 2).17 Behavioral efficacy is
Me
Et
H2
H2
6600
19,000

X. Han et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3870–3873
Table 4. Rat PK parameters for 7b (10 mg/kg, po; 2 mg/kg, iv)a
3873
7. (a) Kehne, J. H.; Maynard, G. D.; De Lombaert, S.;
Krause, J. E. Ann. Rep. Med. Chem. 2003, 38, 11; (b)
Grigoriadis, D. E.; Haddach, M.; Ling, N.; Saunders, J.
Curr. Med. Chem.—Central Nervous System Agents 2001,
1, 63; (c) Gilligan, P. J.; Robertson, D. W.; Zaczek, R. J.
Med. Chem. 2000, 43, 1641; (d) Keller, P. A.; Elfick, L.;
Garner, J.; Morgan, J.; McCluskey, A. Bioorg. Med.
Chem. 2000, 8, 1213.
Cl
Vd
35 mL/min/kg
5.7 L/kg
1524 ng h/mL
0.21
AUC0–24 h (plasma, po)
B/P (2 h)
Fpo
32%
250 ng/mL
4 h
Cmax (po)
Tmax (po)
8. Scherz, M. W.; Fialeix, M.; Fischer, J. B.; Reddy, N. L.;
Server, A. C.; Sonders, M. S.; Tester, B. C.; Webber, E.;
Wong, S. T.; Keana, J. F. W. J. Med. Chem. 1990, 33,
2421.
a Dosing vehicle was 10/10/80 Cremphor/DMSO/water. Dosing vol-
umes were 1 and 3 mL/kg for iv and po, respectively. Brain to plasma
concentration ratio (B/P) was determined after IV administration.
9. (a) Spasov, A. A.; Larionov, N. P.; Sibiryakova, T. B.;
Verovskii, V. E.; Anisimova, V. A.; Dudchenko, G. P.;
Baldenkov, G. N.; MenÕshikov, M. Y. Khim.-Farm. Zh.
1998, 32, 17; (b) Anisimova, V. A.; KuzÕmenko, T. A.;
Spasov, A. A.; Bocharova, I. A.; Orobinskaya, T. A.
Pharm. J. Chem. 1999, 33, 361.
10. Levin, J. I.; Turos, E.; Weinreb, S. M. Synth. Commun.
1982, 12, 989.
11. All new compounds gave satisfactory analytical data. For
7b: 1H NMR (CDCl3, 300 MHz) d 6.83 (s, 2H), 4.12–4.01
(m, 4H), 3.56 (t, J = 7.1 Hz, 2H), 3.35 (d, J = 6.8 Hz, 2H),
2.42 (q, J = 7.5 Hz, 2H), 2.21 (s, 3H), 2.17 (s, 6H), 1.59
(quint, J = 7.2 Hz, 2H), 1.11 (t, J = 7.5 Hz, 3H), 0.95–0.90
(m, 1H), 0.86 (t, J = 7.3 Hz, 3H), 0.51–0.49 (m, 2H), 0.17–
0.14 (m, 2H); 13C NMR (CDCl3, 75 MHz) d 164.1, 156.9,
147.6, 137.3, 136.9, 133.9, 129.6, 115.6, 53.6, 51.2, 48.1,
42.9, 22.6, 21.0, 20.9, 18.2, 13.7, 11.2, 10.0, 3.8; MS: 395.30
(MH)+. For 8b: 1H NMR (CDCl3, 300 MHz) d 6.86 (s,
2H), 4.13–3.97 (m, 4H), 3.47 (s, 2H), 2.45 (t, J = 7.2 Hz,
2H), 2.39 (q, J = 7.6 Hz, 2H), 2.31 (d, J = 6.5 Hz, 2H),
2.24 (s, 3H), 2.19 (s, 6H), 1.48–1.42 (m 2H), 1.32–26 (m,
1H), 1.06 (t, J = 7.4 Hz, 3H), 0.87 (t, J = 7.2 Hz, 3H),
0.50–0.46 (m, 2H), 0.09–0.07 (m, 2H); MS: 381.27 (MH)+.
12. Heidempergher, F.; Pillan, A.; Pinciroli, V.; Vaghi, F.;
Arrigoni, C.; Bolis, G.; Caccia, C.; Dho, L.; McArthur,
R.; Varasi, M. J. Med. Chem. 1997, 40, 3369.
13. Membranes were prepared from IMR-32 cells as previ-
ously described14 and incubated with [125I]Tyr-o-CRF
(100 pM) and increasing concentrations of test compound
for 100 min at 25 °C [assay buffer: 50 mM Tris (pH 7.2),
10 mM MgCl2, 0.5% BSA, 0.005% Triton X-100, 0.01 mg/
mL aprotinin, and 0.01 mg/mL leupeptin]. Assays were
stopped by addition of ice-cold buffer. Nonspecific binding
was defined with 0.01 mM o-CRF. These compounds are
full antagonists of the CRF1R, as determined by their
ability to inhibit CRF-stimulated cAMP production in
IMR-32 cells.14 Compounds 7b and 7k were also tested
against the CRF2R and found to have IC50Õs > 10 lM.18
14. Dieterich, K. D.; DeSouza, E. B. Brain Res. 1996, 733,
113.
Figure 2. Canopy test results in which a reduction in stretched attend
posture corresponds to putative anxiolytic activity. Data represent
means SEM of 10 mice (BALBc) per group. Asterisk indicate
significant difference from vehicle, p < 0.05 (DunnettÕs test).
indicated by a reduction in SAPs. Both compounds, giv-
en ip, significantly reduced SAPs in a dose-dependent
manner at 32 and 64 mg/kg, while compound 7k was
inactive at 16 mg/kg. Buspirone (2 mg/kg) was included
in the study as a positive control.
In summary, 7-aryl-6,7-dihydroimidazoimidazoles rep-
resent a novel series of high-affinity CRF1R antagonists.
Representative compounds show anxiolytic activity in a
mouse canopy model.
Acknowledgments
We thank Dr. John Macor and Dr. Joanne Bronson for
critical reading of the manuscript.
15. Dubowchik, G. M.; Michne, J. A.; Zuev, D.; Schwartz,
W.; Scola, P. M.; James, C. A.; Ruediger, E. H.; Pin, S. S.;
Burris, K.; Balanda, L. A.; Gao, Q.; Wu, D.; Fung, L.;
Fiedler, T.; Browman, K. E.; Taber, M. T.; Zhang, J.
Bioorg. Med. Chem. Lett. 2003, 13, 3997.
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