An orally active corticotropin releasing factor 1 receptor antagonist from 8-aryl-1,3a,7,8-tetraaza-cyclopenta[a]indenes

Article abstract of DOI:10.1016/j.bmcl.2007.01.008

8-Aryl-1,3a,7,8-tetraaza-cyclopenta[a]indenes represent a novel series of high-affinity corticotropin-releasing factor-1 receptor (CRF1R) antagonists. Herein we report the synthesis and SAR around the tricyclic core and the anxiolytic activity of an orall

Full text of DOI:10.1016/j.bmcl.2007.01.008

Bioorganic & Medicinal Chemistry Letters 17 (2007) 2026–2030
An orally active corticotropin releasing factor 1 receptor antagonist
from 8-aryl-1,3a,7,8-tetraaza-cyclopenta[a]indenes
Xiaojun Han,* Rita Civiello, Sokhom S. Pin, Kevin Burris, Lynn A. Balanda, Jay Knipe,
Shelly Ren, Tracey Fiedler, Kaitlin E. Browman,à Robert Macci,
Matthew T. Taber, Jie Zhang§ and Gene M. Dubowchik
Pharmaceutical Research Institute, Bristol-Myers Squibb Company, 5 Research Parkway, Wallingford, CT 06492, USA
Received 30 November 2006; revised 6 January 2007; accepted 6 January 2007
Available online 13 January 2007
Abstract—8-Aryl-1,3a,7,8-tetraaza-cyclopenta[a]indenes represent a novel series of high-affinity corticotropin-releasing factor-1
receptor (CRF1R) antagonists. Herein we report the synthesis and SAR around the tricyclic core and the anxiolytic activity of
an orally dosed exemplary compound 9d (Ki = 8.0 nM) in a mouse canopy model.
Ó 2007 Elsevier Ltd. All rights reserved.
R1
N
R1
N
R1
N
Depression is a common and serious illness. In any given
1-year period, 9.5% of the population, or about 18.8 mil-
lion American adults, suffer from a depressive illness.1
The treatment of depression has evolved from tricyclic
antidepressants (TCA) in the 1970s to Selective Seroto-
nin Reuptake Inhibitors (SSRI) in the 1990s propelled
by the deeper mechanistic understanding of the disease.2
Although the SSRIs are better tolerated than their pre-
decessors, agents with increased efficacy, better side-ef-
fect profiles, and faster onset of action are still needed.
O
R2
R2
R2
R
F3C
R
N
N
N
N
N
X
N
X
N
Z
N
N
N
X
Z
Z
Y
I
Y
II
Y
III
Figure 1. The rational progression of CRF1R antagonist chemotypes.
The CRF is a 41-amino acid neuropeptide, secreted in
the hippocampus. It imposes its physiological effects
on depression and other neuropsychiatric disorders via
the hypothalamic–pituitary–adrenal (HPA) axis.3 The
CRF receptor, a G-protein coupled receptor, has two
well-characterized subtypes (CRF1 and CRF2).4 Com-
pelling clinical evidence3 supports the hypothesis that
over-production of CRF may underlie the pathology
of depression, anxiety, and stress-related disorders,
and that antagonists of CRF1R could be useful for
the treatment of depression.5
As a continuation of our work on 1-aryl-2,3-dihydro-
imidazoimidazoles (I),6 we have reported the synthesis
of 8-aryl-1,3a,8-triaza-cyclopenta[a]indenes (II).7 An
exemplified compound (X, Y, Z = Me, R1 = n-Pr,
R2 = c-PrCH2) had good microsomal stability, binding
affinity (Ki = 24 nM), and reasonable PK properties.
However, this compound is quite lipophilic
(clogP = 8.2)8 and poorly soluble in water (<0.01 lg/
mL).9 These unwanted properties were probably in part
due to the presence of the highly lipophilic CF3 group.
We reasoned that if we could incorporate less hydropho-
bic electron withdrawing groups or elements into the
core to replace the CF3 group, we could lower clogP
and increase aqueous solubility. Therefore, 8-aryl-
1,3a,7,8-tetraaza-cyclopenta[a]indenes (III) (Fig. 1) were
proposed. We report here the SAR of this chemotype
along with detailed studies of compound 9d.
*
Corresponding author. Tel.: +1 203 677 7879; fax: +1 203 677
7702; e-mail: xiaojun.han@bms.com
Present address: Palatin Technologies Inc., 175 May St., Edison, NJ
08837, USA.
à
Present address: Abbott Laboratories, Department of R4N5, Bldg.
AP9A 100 Abbott Park Rd., Abbott Park, IL 60064-6125, USA.
Present address: Sanofi Aventis, 1041 Route 202-206, Bridgewater,
NJ 08807, USA.
§
0960-894X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2007.01.008

X. Han et al. / Bioorg. Med. Chem. Lett. 17 (2007) 2026–2030
2027
Cl
NO2
Ar NH NO2
DIBAL-H reduction of esters 7 and treatment of the
resulting alcohols with SOCl2 yielded chlorides 8. In a
parallel fashion, chlorides 8 were reacted with a series
of mainly secondary amines13 to afford amines 9.14
b,c
a
45 - 52%
70 - 80%
N
N
4
3
NH2
N
NH2
Br_
CRF1R binding affinities were determined as described
previously.15 We first studied the effect of different core
alkyl groups (R1) on binding affinity and aqueous solu-
bility. Since solubility assessments were performed on
amorphous TFA salts, the data are primarily useful in
gauging the effect of structural changes within a chemo-
type. As shown in Table 1, representative compounds
containing CF3, Et, and Me (9a–d) were nearly equipo-
tent. However, while CF3 substitution led to extremely
low aqueous solubility (<0.1 lg/mL), Me and Et substi-
tuted compounds showed excellent aqueous solubilities
(>50 lg/mL).9
Ar
e
d
N
Ar
N
N
CO2Et
80 - 90%
30 - 45%
N
N
5
6
Cl
EtO2C
R1
N
f,g
N
N
N
R1
N
85 - 90%
N
N
N
7
Ar
Ar
R3
8
R2
N
h
N
Next, a series of analogues where R1 = Me were pre-
pared to explore substitution of the amino side chains
(Table 2). As in our previous studies,6,7,17 2,4,6-trisubsti-
tuted pendant aryl groups were required for effective
binding to the CRF1R in our chemotypes. In order to
minimize molecular weight, only 2,4,6-trimethyl phenyl
and 2-chloro-4,6-dimethyl phenyl were chosen, and
resulting differences in receptor binding affinity were
small (<4-fold for all comparable examples). Tertiary
amines are clearly much more favored by the receptor
than secondary amines, such that both lipophilic (1-eth-
yl-propylamine, 9an) and polar (2-methoxy-1-meth-
oxymethyl-ethylamine, 9ao) secondary amines were
relatively inactive. Polar groups on the amino side
chains are not tolerated in this chemotype; the tertiary
amines derived from morpholine (9af) and di-methoxy-
ethyl amine (9am) showed very low affinities. For pyr-
idylmethyl and pyridylethyl containing compounds,
the different pyridyl substitution pattern (2-, 3- or 4-po-
sition) caused several fold changes in potency (>8-fold
for 9ai vs 9ag; >5-fold for 9al vs 9aj). In general, tertiary
amines containing one n-Pr group provided the most po-
tent examples (i.e., 9c, 9g, and 9r), with a variety of
hydrophobic (especially aromatic, vinylic or small cy-
clo-alkyl) groups favored on the opposing side. Excep-
tions were ethylamines (9d and 9w) where the large
phenethyl moiety presumably can compensate for the
removal of one methylene group. Historic SAR5 of a
N
35 -75%
R1
N
N
Ar
9
Scheme 1. Reagents and conditions: Ar = 2,4,6-trimethylphenyl or 2-
chloro-4,6-dimethylphenyl (a) 4.0 equiv aniline, 1.5 equiv KF, 130 °C,
16 h; (b) 1 atm H2, Pd/C, EtOAc, rt, 4 h, 80%; or Na2S2O4, THF/H2O/
concd NH4OH (1:1:1), rt, 70%; (c) 1.8 equiv BrCN, 1.8 equiv
NaHCO3, EtOH, 0 °C, 8 h, then 80 °C, 8 h; (d) 1.2 equiv
BrCH2CO2Et, acetone, 65 °C, 16 h; (e) 2.5 equiv R1CO2Na,
(R1CO)2O, 160 °C, 4 h; (f) 5 equiv i-Bu2AlH, PhMe, 0 °C, 1 h; (g) 2
equiv SOCl2, CH2Cl2, 0 °C, 1 h; (h) 5 equiv R2NHR3–HCl, 7 equiv i-
Pr2NEt (or 5 equiv R2NHR3, 2 equiv i-Pr2NEt), MeCN, rt, 1 h, then 8,
rt, 24 h.
The synthesis of these compounds is outlined in Scheme
1. The reaction of 2-chloro-3-nitro-pyridine 3 with 2,4,6-
trisubstituted anilines afforded compound 4,10 which
was reduced to the corresponding diamines either by
11
hydrogenation (H2, Pd/C) or Na2S2O4 reduction.
After trying out various combinations of solvents, tem-
peratures, and bases, it was found that these diamines
could be reacted with BrCN in EtOH in the presence
of NaHCO3 at 80 °C to afford guanidines 5 in good
yield. Treatment of guanidines 5 with BrCH2CO2Et in
refluxing acetone afforded bromides 6, which were heat-
ed at reflux with acid salts RCO2Na in the correspond-
ing anhydrides, (RCO)2O, to produce esters 7.12
Table 1. The effect of R1 substitution on aqueous solubility of CRF1R antagonists 9a–d
R3
R2
N
N
N
Me
N
R1
N
Me
Me
Compound
R1
R2
R3
Aqueous solubilitya (lg/mL)
Ki (nM)
9a
9b
9c
9d
CF3
Et
c-PrCH2
n-Pr
n-Pr
n-Pr
Et
<0.1
52
16
17
c-BuCH2
c-BuCH2
PhCH2CH2
Me
Me
61
54
8.2
7.8
a Amorphous TFA salts. Solubilities were determined using a medium throughout assay at pH 6.5; see Ref. 10 for details. TFA, trifluoroacetic acid.

2028
X. Han et al. / Bioorg. Med. Chem. Lett. 17 (2007) 2026–2030
Table 2. hCRFR1 binding affinities of CRF1R antagonists 9e–ao
R3
N
R2
N
N
Me
N
R1
N
Me
Me
Compound
X
R2
R3
Ki (nM)
9e
Cl
Me
Cl
Cl
Cl
Me
Cl
Cl
Cl
Me
Me
Cl
Me
Cl
Cl
Me
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
c-PrCH2
c-PrCH2
n-Pr
n-Pr
n-Pr
n-Pr
n-Pr
n-Pr
n-Pr
n-Bu
Allyl
Allyl
c-PrCH2
n-Pr
n-Pr
n-Pr
Et
11
15
9f
9g
c-BuCH2
PhCH2
Allyl
6.0
9h
9i
28
11
41
15
18
28
26
23
15
43
9j
9k
Allyl
n-Pr
9l
n-Bu
Allyl
9m
9n
Allyl
c-PrCH2
9o
9p
c-PrCH2CH2
c-PrCH2CH2
PhCH2CH2
c-PrCH2
9q
9r
5.9
9s
36
93
20
50
9t
9u
c-PrCH2
Et
Et
c-BuCH2
c-PrCH2CH2
PhCH2CH2
n-Bu
9v
Et
Et
9w
9x
6.4
Et
Et
36
360
9y
9z
Et
3-Phenyl-pyrrolidinyl
2-Benzyl-pyrrolidinyl
2-Phenyl-pyrrolidinyl
3-Benzyl-pyrrolidinyl
8.4
9aa
9ab
9ac
9ad
9ae
9af
9ag
9ah
9ai
9aj
9ak
9al
9am
9an
9ao
48
580
700
700
3-Phenethyl-pyrrolidinyl
2-Phenethyl-pyrrolidinyl
Morpholinyl
1300
1400
1200
2700
>10,000
570
4-PyCH2
3-PyCH2
2-PyCH2
Me
Me
Me
Me
3-PyCH2CH2
2-PyCH2CH2
4-PyCH2CH2
MeOCH2CH2
2-Pentyl
Me
Me
2800
3200
4100
2900
5600
MeOCH2CH2
H
H
(MeOCH2)CH
large variety of CRF1R antagonists shows that the area
of the receptor in which these side chains bind is intoler-
ant of more than one polar atom, usually an ether oxy-
gen. It is tempting to see the need for highly lipophilic
side chains in our aminomethylene-containing antago-
nists as a compensation for the presence of the more
polar basic amino group. A number of racemic,
phenyl-containing cyclic amines were prepared. It is
interesting to note that the compound derived from 3-
phenyl-pyrrolidine (9z) was much more potent than
the isomeric 2-phenyl-pyrrolidine (9ab), mirroring, to
some extent, the advantage of the acyclic phenethyl 9r
over the benzyl 9h. Limited flexibility in these phenyl-
substituted cyclic amines presumably makes substitution
position even more critical for potency.
groups of mice. The data are summarized in Table 3.
After iv dosing, the compound showed low whole body
clearance and a moderate elimination half-life. The low
(4%) bioavailability after po dosing may be reflective of
limited absorption and/or high first-pass metabolism by
the liver. That first-pass metabolism may be more sig-
nificant than poor absorption is suggested by the high
rate of metabolism of the compound in mouse liver
microsomes (0.30 nmol/min/kg). Despite the low bio-
availability, the serum concentrations are sufficient
for activity, as the dose used was in the efficacious
range (Fig. 2).
Compound 9d was assessed in a mouse canopy stretched
attend posture (SAP) model of anxiety, as previously
described.18 When dosed po at 30 and 60 mg/kg, 9d sig-
nificantly reduced SAPs in a dose-dependent manner in
comparison with vehicle-treated mice (Fig. 3).
To characterize the pharmacokinetics of compound 9d,
it was administered iv (tail vein) and by oral gavage to

X. Han et al. / Bioorg. Med. Chem. Lett. 17 (2007) 2026–2030
Table 3. Pharmacokinetic parameters of compound 9d in Balb/c mice
2029
References and notes
Parametersa
ivb 5.8 mg/kg
po 23 mg/kg
1. Psychiatric Disorders in America, The Epidemiological
Catchment Area Study; Robin, L. N., Regier, D. A., Eds.;
The Free Press: New York, 1990.
2. Wong, D. T.; Bymaster, F. P.; Engleman, E. A. Life Sci.
1995, 57, 411.
CL (mL/min/kg)
Vss (L/kg)
t1/2 (h)
5.2
—
—
0.48
3.0
—
AUC
(nM–h)
17794
—
—
2738
1189
0.5
4
0–t
Cmax (nM)
Tmax (h)
F (%)
3. (a) Contoreggi, C.; Ayala, A.; Grant, S.; Eckelman, W.;
Webster, E.; Rice, K. C. Drugs Future 2002, 27, 1093; (b)
—
´
Paez-Pereda, M.; Arzt, E.; Stalla, G. K. Expert Opin.
a Values are the averages calculated from three animals at six time
points through 8 h following dosing.
b Dosing vehicle: PEG400/ethanol (9:1, v/v).
Ther. Patents 2002, 12, 1537; (c) Dinan, T. G. Hum.
Psychopharmacol. Clin. Exp. 2001, 16, 89; (d) O’Brien, D.;
Skelton, K. H.; Owens, M. J.; Nemeroff, C. B. Hum.
Psychopharmacol. Clin. Exp. 2001, 16, 81.
4. Hauger, R. L.; Grigoriadis, D. E.; Dallman, M. F.;
Plotsky, P. M.; Vale, W. W.; Dautzenberg, F. M.
Pharmacol. Rev. 2003, 55, 21.
100000.0
10000.0
5. (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.—Cent. Nerv. Syst. 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.
6. Han, X.; Michne, J. A.; Pin, S. S.; Burris, K. D.; Balanda,
L. A.; Fung, L. K.; Fiedler, T.; Browman, K. E.; Taber,
M. T.; Zhang, J.; Dubowchik, G. Bioorg. Med. Chem.
Lett. 2005, 15, 3870.
IV
PO
1000.0
100.0
10.0
1.0
0
1
2
3
4
5
6
7
8
9
7. Han, X.; Pin, S. S.; Burris, K.; Fung, L. K.; Huang, S.;
Taber, M. T.; Zhang, J.; Dubowchik, G. Bioorg. Med.
Chem. Lett. 2005, 15, 4029.
8. clogP was calculated using a licensed program from
Tripos.
Time (hr)
Figure 2. Serum levels after iv (5.8 mg/kg) and po (23 mg/kg)
administration of compd 9d to mice (Means SD of 3 mice/time
point).
9. Aqueous solubility was determined as follows: 10 mg/mL
stock solutions of each compound were prepared in neat
DMSO. The stock solutions were diluted 100-fold into a
96-well plate with 25 mM phosphate buffer, pH 6.5. The
plate was sealed and sonicated for 3 min. The plate was
shaken for 4 h at room temperature to allow the
compounds to equilibrate. Standards were prepared at
0.05 mg/mL from the DMSO stock by diluting 200-fold
into ACN:H2O (1:1). The plate was centrifuged for 30 min
to separate compound from solution. The supernatant and
standards were analyzed by HPLC to determine the
solubility.
10. Kulagowski, J. J.; Rees, C. W. Synthesis 1980, 215.
11. Redemann, C. T.; Redemann, C. E. Org. Syn. Coll. Vol.
1955, 3, 69.
12. (a) Spasov, A. A.; Larionov, N. P.; Sibiryakova, T. B.;
Verovskii, V. E.; Anisimova, V. A.; Dudchenko, G. P.;
Baldenkov, G. N.; Men’shikov, M. Y. Khim.-Farm. Zh.
1998, 32, 17; (b) Anisimova, V. A.; Kuz’menko, T. A.;
Spasov, A. A.; Bocharova, I. A.; Orobinskaya, T. A.
Pharm. J. Chem. 1999, 33, 361.
50
40
*
*
30
*
20
10
0
Vehicle
Buspirone
20 mg/kg
15 mg/kg
30 mg/kg
60 mg/kg
Figure 3. Canopy test results of compound 9d (po, 30% PEG400/70%
water, 15 min pretreatment). Data represent means SEM of 10 mice
(Balb/c) per group. Asterisks indicate significant difference from
vehicle-treated mice, p < 0.05 (Dunnett’s test).
13. Dubowchik, G. D.; Michne, J. A.; Zuev, D. Bioorg. Med.
Chem. Lett. 2004, 14, 3147.
In conclusion, we have discovered a novel class of potent
CRF1R antagonists, 8-aryl-1,3a,7,8-tetraaza-cyclopen-
ta[a]indenes. A representative compound, 9d, when dosed
orally in mice, showed significant, dose-dependent activi-
ty in a mouse canopy stretched attend posture model,
indicative of its potential use as an oral anxiolytic agent.
14. All new compounds gave satisfactory analytical data.
See Scheme 1, in which Ar = 2,4,6-trimethylphenyl and
1
R = Me. For 4a: H NMR (CDCl3, 500 MHz) d 9.38 (s,
1H), 8.51 (d, J = 5.2 Hz, 1H), 8.38 (1H), 7.00 (s, 2H),
6.73 (s, 1H), 2.34 (s, 3H), 2.18 (s, 6H); 13C NMR
(CDCl3,125 MHz) d 156.2, 152.1, 137.2, 135.7, 135.4,
132.3, 129.1 (vs), 128.3, 112.8, 21.1, 18.5. For 5a: 1H
NMR (CDCl3, 500 MHz) d 7.95 (dd, J = 5.0, 1.5 Hz,
1H), 7.53 (dd, J = 8.0, 1.5 Hz, 1H), 7.03 (s, 2H), 7.00
(dd, J = 8.0, 5.0 Hz, 1H), 5.82 (br s, 2H), 2.32 (s, 3H),
1.99 (s, 6H); 13C NMR (CDCl3,125 MHz) d 154.3,
147.7, 140.1, 140.0, 137.3, 135.2, 129.9 (vs), 129.4, 128.0,
Acknowledgment
We thank Dr. Lawrence K. Fung for his help during the
preparation of the manuscript.

2030
X. Han et al. / Bioorg. Med. Chem. Lett. 17 (2007) 2026–2030
122.0, 117.8, 21.2, 17.8; mass spec.: 253.18 (MH)+. For
15. Membranes were prepared from IMR-32 cells as previ-
ously described16 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, 10 lg/
mL aprotinin, and 10 lg/mL leupeptin). Assays were
stopped by the addition of ice-cold buffer. Non-specific
binding was defined with 10 lM o-CRF. These com-
pounds are full antagonists of the CRF1R, as determined
by their ability to inhibit CRF stimulated cAMP produc-
tion in IMR-32 cells.
7a: 1H NMR (CDCl3, 500 MHz) d 8.77 (dd, J = 8.1,
1.2 Hz, 1H), 8.29 (dd, J = 4.9, 1.2 Hz, 1H), 7.23 (dd,
J = 8.1, 5.0 Hz, 1H), 7.04 (s, 2H), 4.48 (q, J = 7.1 Hz,
2H), 2.65 (s, 3H), 2.34 (s, 3H), 1.98 (s, 6H), 1.49 (t,
J = 7.1 Hz, 3H); 13C NMR (CDCl3,125 MHz) d 161.1,
152.1, 147.4, 147.0, 144.0, 139.8, 136.7, 129.7, 127.9,
123.9, 122.4, 120.0, 117.0, 60.4, 21.1, 17.9, 16.4, 14.7;
mass spec.: 363.30 (MH)+. For 9d: HCl:1H NMR
(DMSO-d6, 500 MHz) d 8.81 (d, J = 8.2 Hz, 1H), 8.37
(d, J = 4.9 Hz, 1H), 7.50 (dd, J = 8.2, 4.9 Hz, 1H),
7.37–7.32 (m, 4H), 7.28–7.25 (m, 1H), 7.16 (s, 2H), 5.09
(dd, J = 15.9, 3.3 Hz, 1H), 5.01 (dd, J = 15.9, 6.0 Hz,
1H), 3.54–3.46 (m, 2H), 3.42–3.36 (m, 2H), 3.27–3.22
(m, 2H), 2.49 (s, 3H), 2.37 (s, 3H), 1.98 (s, 3H), 1.92 (s,
3H), 1.39 (t, J = 7.3 Hz, 3H); 13C NMR (DMSO-d6,
125 MHz) d 145.5, 144.4, 142.8, 139.7, 137.1, 136.7,
136.5, 129.2, 128.61 (vs), 128.58 (vs), 127.0, 126.7, 122.1,
118.6, 117.9, 110.4, 66.3, 51.5, 46.2, 45.2, 28.7, 20.6,
17.4, 12.2, 8.6; Mass spec.: 452.32 (MH)+.
16. Dieterich, K. D.; DeSouza, E. B. Brain Res. 1996, 733,
113.
17. 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.
18. Grewal, S. S.; Shepherd, J. K.; Bill, D. J.; Fletcher, A.;
Dourish, C. T. Psychopharmacology 1997, 133, 29.