Novel substituted tetrahydrotriazaacenaphthylene derivatives as potent CRF1 receptor antagonists

Article abstract of DOI:10.1016/j.bmcl.2007.06.077

Corticotropin-releasing factor (CRF), a 41 amino acid peptide neurohormone synthesised by specific hypothalamic nuclei in the brain, is implicated in stress-related function. Antagonism of CRF₁ receptors is an attractive therapeutic approach fo

Full text of DOI:10.1016/j.bmcl.2007.06.077

Bioorganic & Medicinal Chemistry Letters 17 (2007) 5218–5221
Novel substituted tetrahydrotriazaacenaphthylene derivatives
as potent CRF1 receptor antagonists
a,
a
a
Gabriella Gentile,a,* Romano Di Fabio, Francesca Pavone, Fabio Maria Sabbatini,
*
Yves St-Denis,a Maria Grazia Zampori,a,ꢀ Giovanni Vitullia,ꢁ and Angela Worbyb
aPsychiatry Centre of Excellence for Drug Discovery, GlaxoSmithkline, Medicine Research Centre, Via Fleming 4, 37135 Verona, Italy
bGlaxoSmithkline, Screening & Compound Profiling, Harlow, Essex CM 19 5AW, UK
Received 31 May 2007; revised 22 June 2007; accepted 27 June 2007
Available online 30 June 2007
Abstract—Corticotropin-releasing factor (CRF), a 41 amino acid peptide neurohormone synthesised by specific hypothalamic nuclei
in the brain, is implicated in stress-related function. Antagonism of CRF1 receptors is an attractive therapeutic approach for the
treatment of depression and anxiety. Unsaturated tetrahydrotriazaacenaphthylenes of general structure 3 have been identified as
potent and selective CRF1 receptor antagonists with a suitable oral pharmacokinetic profile.
Ó 2007 Elsevier Ltd. All rights reserved.
The health burden of stress-related diseases, including
depression and anxiety disorders, is rapidly increasing,
requiring the identification of more efficacious pharma-
cotherapies exhibiting improved tolerability with respect
to current treatments.1 Recent findings support a major
role for neuropeptides in mediating the response to
stress and emotional behaviors. Corticotropin-releasing
factor (CRF), a 41 amino acid peptide synthesised by
specific hypothalamic nuclei in the brain, was originally
isolated by Wale and colleagues in 1981 from ovine
hypothalamus.2 This neuropeptide is known to be the
major physiological regulator of the basal and stress-
mediated release of adrenocorticotropic hormone
(ACTH) from the anterior pituitary. In addition CRF
has been recognised to coordinate many of the endo-
crine, autonomic and behavioral responses to stress via
activation of CRF1 receptors.
Therefore the identification of CRF1 antagonists is an
attractive therapeutic approach for the treatment of
depression and anxiety.3
Despite major efforts by many pharmaceutical compa-
nies and academic groups during the last decade, the dis-
covery of potent small molecule CRF1 receptor
antagonists has proved to be challenging.4
Compounds such as CP-154,5265 and DMP-6966
(Fig. 1) were amongst the first CRF-1 antagonists show-
ing high affinity along with interesting signs of in vivo
activity in animal models of anxiety and depression.
These molecules share common pharmacophoric fea-
tures: (a) a bicyclic heterocyclic core substituted in the
top region of the molecule with a lipophilic alkylamine
OMe
OMe
N
HN
N
Keywords: CRF1 antagonists; Anxiety; Depression; Corticotropin-rel-
easing factor.
N
N
N
N
*
N
N
Corresponding authors: Tel.: +39 0458219355; fax: +39 0458218196
Cl
(G.G.); tel.: +39 0458218879; fax: +39 0458218196 (R.D.F.); e-mail
addresses: gg87301@gsk.com; rdf26781@gsk.com
Present address: Pfizer, Ramsgate Road, Sandwich, Kent CT13 9NJ,
ꢀ
UK.
Present address: Department of Drug Metabolism and Pharmaco-
Cl
DMP-696
ꢁ
CP-154,526
Figure 1. Bicyclic CRF1 receptor antagonists.
kinetic, RI Centre of Excellence for Drug Discovery, Stevenage SG1
2NY, UK.
0960-894X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2007.06.077

G. Gentile et al. / Bioorg. Med. Chem. Lett. 17 (2007) 5218–5221
5219
R1
R1
N
The alkylation of 4 with the necessary alkyl bromides
occurred in high yields. Then, the formylation of the
C-3 position afforded the aldehyde intermediates 6,
which were homologated by Wittig-type reaction in
the presence of (methoxymethyl)triphenylphosphonium
chloride and BuLi, giving the corresponding methyl
enolethers 7 as mixture of the cis/trans isomers. Acid
hydrolysis generated the aldehyde derivative 8 in good
yield, after purification by flash chromatography. These
compounds were reduced to the corresponding alcohol 9
and then protected as TBS.
R1
N
N
N
N
N
N
N
N
N
N
R2
R2
R2
1
2
3
Figure 2. Tricyclic CRF1 receptor antagonists.
side chain; (b) an aromatic nitrogen acting as H-bond
acceptor7–9; (c) a pendant 2,4-disubstituted or 2,4,6-tri-
substituted aromatic moiety or heteroaromatic ring in
the bottom region of the molecule.
Intermediates 10 were reacted with the substituted ani-
lines using a Buchwald amination reaction,12 affording
compounds 11. The best conditions for this reaction used
Pd2(dba)3 (10%) as a catalyst, 2-(dicyclohexylphosphi-
no)-20-methylbiphenyl as a ligand, DME as a solvent
and K3PO4 as a base, under microwave irradiation
(150 W, T = 100 °C, P = 60 p.s.i., cooling, t = 20 min).
In the absence of microwave irradiation, reaction yields
reduced and conversion times increased. Also, the use
of different bases and solvents such as tBuOK and tolu-
ene significantly reduced yields.
As part of a broad chemical strategy aimed towards
the discovery of new series of CRF1 antagonists, the
tricyclic templates of general structures 1 and 2
have been designed and explored in detail9 in our
laboratories.
In this article, we report the preparation of the corre-
sponding tetrahydrotriazaacenaphthylenes of general
structure 3 (Fig. 2), suitably substituted in both the
top region of the molecule (R1) and in the bottom aro-
matic portion (R2).
After removal of the TBS, intermediates 11 afforded
alcohol derivatives 12. The final intramolecular cycliza-
tion reaction to give compounds 3a–j was successfully
carried out by refluxing the mesylates 13 in toluene in
the presence of triethylamine.
The synthetic route setup is described in Scheme 1.
Intermediates 8 (R1 = hept-4-yl or pent-3-yl) were pre-
pared in four steps starting from the azanidole 4.10,11
Alternatively, the mesylate derivatives 14, smoothly pre-
pared from alcohols 9, were transformed straight into
R1
N
R1
N
R1
HN
N
a
OMe
b
CHO
c
N
Cl
N
Cl
N
Cl
N
Cl
d
4
5
6
7
R1 = hept-4-yl or pent-3-yl
R1
R1
R1
R1
N
N
N
CH2OR
N
N
e
CHO
CH2OR
g
l
N
N
NH
N
Cl
N
Cl
R2
R2
8
3a-j
11 R = TBS
12 R = H
9
R = H
h
i
f
i
10 R = TBS
14 = Ms
13 R = Ms
g
Scheme 1. Reagents and conditions: (a) R1Br, NaH 80% oil, DMF, 75–81%; (b) DMF, POCl3, reflux, 70–75%; (c) (methoxymethyl)-
triphenylphosphonium chloride, 1.6 M BuLi/THF 0 °C 10 min, then compound 10, THF, rt, 68–70%; (d) 2N HCl, 0 °C during the addition, then
70 °C, 1.5 h, 67–70%; (e) NaBH4, MeOH, 0 °C, 1 h, 89–93%; (f) imidazole, TBSCl, DMAP, DMF, 0 °C, then rt overnight; (g) tris(dibenzylideneac-
etone)palladium(0), 2-(dicyclohexylphosphino)-20-methylbiphenyl, K3PO4 ArNH2, DME, rt, then microwave irradiation, 100 °C, 150 W, P = 60 p.s.i.,
20 min (cooling on), 84–88%; (h) Et3NÆ3HF, DMF, rt, overnight, 48–50%; (i) MsCl, Et3N, CH2Cl2, rt; (l) toluene, Et3N, reflux, 29–31% (two steps).

5220
G. Gentile et al. / Bioorg. Med. Chem. Lett. 17 (2007) 5218–5221
Table 1. In vitro potency of compounds 3a–l
OMe
OH
CO2Et
N
1
HN
N
R
a
b
N
N
N
X
N
Cl
N
Cl
16
N
Cl
N
N
N
4
15
2
2
R
R
c
3a-j
3k, 3l
OMe
OMe
Entry
R1
R2
X
pIC50
a
N
CP-154,526
DMP-696
7.8
7.4
7.5
7.0
7.8
8.4
7.3
6.9
7.4
7.9
7.9
7.3
7.1
6.9
7.6
7.2
7.4
6.8
N
1
Hept-4-yl
Hept-4-yl
Hept-4-yl
Hept-4-yl
Hept-4-yl
Hept-4-yl
Hept-4-yl
Pent-3-yl
Pent-3-yl
Pent-3-yl
Pent-3-yl
Pent-3-yl
Pent-3-yl
Pent-3-yl
—
2-Cl, 4-Cl
2,4-Bis-CF3
2,4-Bis-CF3
C
C
N
C
N
C
C
C
C
C
C
C
N
C
C
C
3a
2a
3b
2b
3c
3d
3e
3f
3g
3h
3i
N
N
N
Cl
2-CH3, 4-CN
2-CH3, 4-CN
2-CH3, 4-OCH3
3-F, 4-OCH3
2-CH3, 4-CN
2-CH3, 4-OCH3
3-F, 4-OCH3
2-CH3, 4-OCF3
2,4-Bis-CF3
2
R
5
3k-l
Scheme 2. Reagents and conditions: (a) ethyl 2-bromobutanoate, NaH
80% in oil, DMF, 0 °C to rt 1 h, 81%; (b) DIBAL-H, CH2Cl2, 0 °C,
then rt, 45 min, 42%; (c) NaH 80%/oil, MeI, THF, 0 °C to rt, 30 min,
79%.
2i
2,4-Bis-CF3
4-OCH3
the final unsaturated tetrahydrotriazaacenaphthylenes
via a Buchwald amination reaction in the presence of
the appropriately substituted anilines.
3j
3k
3l
2-CH3, 4-CN
2-CH3, 4-OCH3
—
a pIC50 = ꢀlogIC50
.
In order to prepare racemic compounds 3k and 3l, the
modified synthetic approach described in Scheme 2
was setup. Alkylation of the nitrogen on the azaindole
4 with ethyl 2-bromobutanoate gave intermediate 15,
which was subsequently reduced to the primary alcohol
16. This intermediate was smoothly transformed into the
corresponding methyl ether 5. Final compounds were
prepared from compound 5 as described in Scheme 1.
moderate-high plasma clearance (Clp = 54 mL/min/kg)
and low oral bioavailability (F = <5%). Compound 3d
showed similar plasma clearance but better bioavailabil-
ity (37%). Compounds 3a and 3i instead showed reduced
plasma clearance (Clp = 8 and 21 mL/min/kg, for 3a and
3i, respectively), leading to oral bioavailability of 71 and
28%, for 3a and 3i, respectively. Therefore 2,4-bis-CF3
substitution in the aromatic region of the molecule
proved to be a positive modulator of the metabolic sta-
bility and was associated to increased oral exposure,
thus allowing the progression of both compounds to
in vivo efficacy studies. Conversely the presence of meth-
oxy or cyano substituents in the pendant phenyl ring, as
in 3d and 3b, proved to increase plasma clearance and
distribution volume.
Compounds 3a–l were characterized in vitro by displace-
ment of 125I-CRF from recombinant human CRF recep-
tors expressed in CHO-cell membranes. Results are
presented in Table 1.13
Based on the results obtained the following conclusions
can be drawn: (a) moving from tetrahydrotetra-
zazaacenaphthylenes (2) to the corresponding tetrahydro-
triazaacenaphthylenes (3) a significant improvement of
in vitro potency was observed only for compound 3b,
which can be considered as one of the most potent
CRF1 antagonists identified to date (pIC50 = 8.4 vs.
7.8 for 3b and 2a, respectively), while 3a and 3i were less
active than the analogues 2a and 2i (pIC50 = 7.0 and 6.9
vs. 7.8 and 7.6, respectively); (b) different substituents on
the pendant phenyl ring allow modulation of in vitro
affinity; (c) replacement of one of the methyl groups
with a methoxy in the top chain of the molecule reduces
the affinity for CRF1 receptors (pIC50 = 7.9 and 7.4 for
3e and 3k, respectively).
In summary, the synthesis and the characterization of a
new series of unsaturated triazaacenaphthylene tem-
plates has been described. Several compounds exhibited
high affinity for the CRF1 receptor; in particular com-
Table 2. PK profile of compounds 3a, 3b, 3d and 3i in Sprague–
Dawley male rats
Parameters
3a
3b
3d
3i
Clp (mL/min/kg)
F (%)
8
71
54
47
37
21
28
<5
17
Vdss (L/kg)
T1/2 (h)
AUC (ngh/mL)a
2.5
5.3
1479
24
6.8
7.6
222
6.7
<15
8.6
131
Four compounds were selected for further PK charac-
terization14 namely 3a, 3b, 3d, and 3i.15 As shown in
Table 2, 3b, the most potent compound in vitro, showed
a AUC normalised by oral dose.

G. Gentile et al. / Bioorg. Med. Chem. Lett. 17 (2007) 5218–5221
5221
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ever reported. The SAR associated with this chemical
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Acknowledgments
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coworkers for the NMR and IR spectra and Dr. Han-
dam and his coworkers for the MS spectra.
References and notes
14. PK profile was measured in Sprague–Dawley male rats
(n = 3), after po (1 mg/kg, dose) and iv (0.4 mg/kg dose)
administration. For experimental details, see Ref. 9.
15. 1H NMR, 3a: (400 MHz, CDCl3) d ppm 8.02 (s, 1H), 7.82
(d, 1H), 7.68 (d, 1H), 6.59 (s, 1H), 6.47 (s, 1H), 4.07 (m,
1H), 3.74 (t, 2H), 2.35 (s, 2H), 1.78 (m, 4H), 1.22 (m, 4H),
0.87 (t, 6H). 3b: (500 MHz, CDCl3) d ppm 7.57 (s, 1H),
7.53 (dd, 1H), 7.41 (d, 1H), 6.63 (s, 1H), 6.51 (s, 1H), 4.10
(m, 1H), 3.90 (t, 2H), 3.12 (t, 2H), 2.41 (s, 3H), 2.27 (s,
3H), 1.77 (m, 4H), 1.20 (m, 4H), 0.91 (t, 6H). 3d:
(500 MHz, CDCl3) d ppm 7.35 (dd, 1H), 7.20 (dd, 1H),
6.95 (t, 1H), 6.58 (s, 1H), 6.50 (s, 1H), 4.08 (m, 1H), 3.94
(t, 2H), 3.90 (s, 3H), 3.07 (t, 2H), 2.45 (s, 3H), 1.80 (m,
4H), 1.20 (m, 4H), 0.87 (t, 6H). 3i: (300 MHz, CDCl3) d
ppm 8.05 (d, 1H), 7.90 (d, 1H), 7.80 (dd, 1H), 6.57 (s, 1H),
6.49 (s, 1H), 3.89 (t, 2H), 3.87 (m, 1H), 3.08 (m, 2H), 2.43
(s, 3H), 1.85 (m, 4H), 0.81 (t, 6H).
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