Synthesis and evaluation of 2-anilino-3-phenylsulfonyl-6-methylpyridines as corticotropin-releasing factor1 receptor ligands

Article abstract of DOI:10.1016/j.bmcl.2005.10.097

A novel series of 2-anilino-3-phenylsulfonyl-6-methylpyridines was synthesized and evaluated as corticotropin-releasing factor receptor ligands. Structure-activity relationship studies focused primarily on optimization of the 3-phenylsulfonyl group. Compo

Full text of DOI:10.1016/j.bmcl.2005.10.097

Bioorganic & Medicinal Chemistry Letters 16 (2006) 934–937
Synthesis and evaluation of
2-anilino-3-phenylsulfonyl-6-methylpyridines as
corticotropin-releasing factor1 receptor ligands
Richard A. Hartz,a,* Argyrios G. Arvanitis,a Charles Arnold,a
Joseph P. Rescinito,a Kimberly L. Hung,a Ge Zhang,b Harvey Wong,c
David R. Langley,a Paul J. Gilligana and George L. Trainora
aDiscovery Chemistry, Bristol-Myers Squibb Company, Pharmaceutical Research Institute,
5 Research Parkway, Wallingford, CT 06492, USA
bNeuroscience Biology, Bristol-Myers Squibb Company, Pharmaceutical Research Institute,
5 Research Parkway, Wallingford, CT 06492, USA
cDepartment of Metabolism and Pharmacokinetics, Bristol-Meyers Squibb Company, Pharmaceutical Research Institute,
5 Research Parkway, Waalingford, CT 06492, USA
Received 21 September 2005; revised 26 October 2005; accepted 28 October 2005
Available online 16 November 2005
Abstract—A novel series of 2-anilino-3-phenylsulfonyl-6-methylpyridines was synthesized and evaluated as corticotropin-releasing
factor receptor ligands. Structure–activity relationship studies focused primarily on optimization of the 3-phenylsulfonyl group.
Compounds within this series were identified which showed potent binding affinity for the CRF1 receptor. Selected compounds were
examined in a rat pharmacokinetic study and were found to have oral bioavailabilities ranging from 16 to 35%.
Ó 2005 Elsevier Ltd. All rights reserved.
Corticotropin-releasing factor (CRF), a 41 amino acid
neuropeptide, is an important regulator of the bodyÕs re-
sponse to stress via modulation of the hypothalamic–pi-
tuitary–adrenal (HPA) axis. CRF was first isolated from
ovine hypothalamus in 1981 and characterized by Vale
and coworkers.1 It was determined that the role of
CRF in the hypothalamic–pituitary–adrenal axis is to
act as an adrenocorticotropic hormone (ACTH) secreto-
gogue via the CRF1 receptors. ACTH in turn stimulates
the release of glucocorticoids, such as cortisol, from the
adrenal cortex. Elevated levels of glucocorticoids have
been shown to exert negative feedback on CRF secre-
tion at both the levels of the pituitary and
hypothalamus.
expressed primarily in the rat brain, whereas CRF2
receptors are found primarily in the rat periphery.
Experiments with CRF1 receptor knockout mice dem-
onstrated the involvement of CRF1 receptors in the
stress response mediated by the HPA axis.3 It was found
that in the presence of increasing CRF levels, ACTH
secretions do not increase in the pituitary cells of mice
lacking the CRF1 receptor.
Hypersecretion of CRF is associated with various endo-
crine and psychiatric disorders including depression,
anxiety, and post-traumatic stress disorder.2a,4 Clinical
studies have shown that plasma levels of cortisol were
elevated in a large number of depressed patients.4c
A
growing body of evidence continues to support the
hypothesis that CRF1 receptor antagonists offer signifi-
cant therapeutic potential in the treatment of diseases
resulting from elevated levels of CRF.5
CRF mediates its actions through two subtypes of 7-
transmembrane G-protein coupled receptors, designated
as CRF1 and CRF2 receptors.2 CRF1 receptors are
A variety of small molecule CRF1 receptor antagonists
have been reported in the literature.4a,6 Based on numer-
ous previously disclosed reports, the pharmacophore
model has been shown to include a required alkyl substi-
Keywords: Corticotropin-releasing factor; CRF; Phenylsulfone.
*
Corresponding author. Tel.: +1 203 677 7837; fax: +1 203 677
7702; e-mail: richard.hartz@bms.com
0960-894X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.10.097

R. A. Hartz et al. / Bioorg. Med. Chem. Lett. 16 (2006) 934–937
935
R1
tuent linked to a mono- or bicyclic core ring system gen-
erally via an aniline nitrogen (e.g., the diethylamino
group in structure 1, Fig. 1). We were interested in
developing a novel chemotype by attempting to find a
suitable replacement for this alkyl group. As illustrated
in structure 2, it was anticipated that a group on the 3-
position of the pyridine ring could be designed as a suit-
able replacement for the dialkyl-amino group. It would
be essential for this group to be oriented properly to
achieve good binding affinity. A substituted phenylsulfo-
nyl group was chosen based on its potential ability to
achieve a favorable conformation due to hydrogen
bonding of the sulfone oxygen with the neighboring ani-
line hydrogen (Figs. 1 and 2). This report discloses the
synthesis, structure–activity relationships, and rat phar-
macokinetic data for a novel series of 3-phenylsulfonyl
pyridine-based compounds.
I
a
b,c
S
N
OH
N
OH
3
4
N
Cl
5
R1
R1
O
d
e
S
O
O
S
O
N
NH
N
Cl
6
7
Synthesis of the 2-anilino-3-phenylsulfonyl-6-methyl-
pyridine derivatives is illustrated in Scheme 1 below.
Commercially available 2-hydroxy-6-methylpyridine 3
was treated with powdered iodine in a water/CH2Cl2
mixture in the presence of NaHCO3 to give a 5:2:1:1 ra-
tio of 3-iodopyridine 4, starting material 3, 5-iodo, and
3,5-diiodopyridine, respectively. The mixture was
recrystallized from EtOAc to give the 3-iodoisomer (4)
in >95% purity. 3-Iodopyridine 4 was then coupled with
various substituted thiophenols in the presence of NaH
and 20% CuI in DMF at 120 °C to give the correspond-
ing sulfide. Subsequent treatment with POCl3 afforded
compound 5 in good yield. Compound 5 was oxidized
Scheme 1. Reagents and conditions: (a) I2/CH2Cl2, NaHCO3/H2O,
35–40%; (b) substituted thiophenol, NaH, CuI (20 mol %), DMF,
120 °C, 71–92%; (c) POCl3, 61–71%; (d) m-CPBA, CH2Cl2, 88–96%;
(e) 2,4,6-trimethylaniline (CH2OH)2, reflux, 33–69%.
to the corresponding sulfone (6) in high yield with
m-CPBA. Sulfone 6 was subsequently coupled with
2,4,6-trimethylaniline (6 equiv) in refluxing ethylene
glycol for 16 h to give the adduct 7, which was isolated
by chromatography.
Initially the SAR of a series of compounds with a 4,6-
dimethylpyridine core was studied7 (Table 1). CRF
receptor binding affinities were determined by displace-
ment of [125I]Tyr-o-CRF from rat frontal cortex homog-
enates by our test compounds.8 a-Helical CRF9–41 was
found to have a Ki = 7.6 0.8 nM (n = 3) in this assay.
The unsubstituted phenyl analog 7a and 2-methyl
R
N
N
O
S
O
H
N
N
N
Table 1. Structure–activity relationships of the R2 substituent and
phenylsulfone group
1
2
R1
R1
R1
Figure 1. Design of novel 3-phenylsulfonyl pyridine-based compounds.
R2
N
R2
N
R2
N
O
O
S
S
O
S
O
O
O
NH
NH
NH
7
8
9
Compound
R1
H
R2
Mean Ki (nM)a
Torsion
angle
7a
7b
7c
7d
7e
8
Me
Me
Me
Me
H
>10,000b
>10,000b
5170 160
1778 741
145 44
2-Me
3-Me
4-Me
4-Me
4-Cl
A
B
H
857 120
>10,000b
9
4-Me
H
a Data are averaged from a minimum of two replicates unless otherwise
noted. The standard deviation is also reported.
b Single determination.
Figure 2. Overlay of compounds 7d (magenta) and 7e (green) as
viewed from the front (left) and side (right). B is rotated 90° relative
to A.

936
R. A. Hartz et al. / Bioorg. Med. Chem. Lett. 16 (2006) 934–937
CH2OH
substituted analog 7b were inactive in the binding assay.
Movement of the methyl substituent to the 3- and 4-
positions however resulted in a progressive improve-
ment in binding affinity (7c and 7d). Replacement of
the methyl group at R2 with a hydrogen further
improved the binding affinity (7e, Ki = 145 nM).
Replacement of the 4-methylphenylsulfonyl group with
a 4-chlorobenzylsulfonyl group resulted in a decrease
in binding affinity (compare 7e with 8). In addition to
the 3-phenylsulfone structural motif, the 5-phenylsulf-
one structural motif was also examined. Attachment of
the benzenesulfone moiety at the 5-position (9) resulted
in loss of binding affinity to the CRF1 receptor.
O
OMe
CH2OH
a
O
S
O
b
O
O
S
O
S
N
NH
O
N
Cl
N
Cl
11
12
7m
Scheme 3. Reagents and conditions: (a) DIBAL, Et2O, 98%; (b) 2,4,6-
trimethylaniline, (CH2OH)2, reflux, 55%.
Modeling studies were conducted to better understand
these results. Figure 2 depicts the overlaid, minimized
structures of compounds 7d (magenta) and 7e (green).
The global minimum for each compound was identified
using a systematic grid search followed by CHARMM
minimization9 using the CFF98 force field.10 The results
show that the sulfone oxygen is capable of hydrogen
bonding with the neighboring aniline N-H. The mea-
sured distance between the sulfone oxygen and aniline
N-H is 1.77 A in structure 7d and 1.89 A in structure
7e. Possibly, the lack of binding affinity of compound
9 is due to the inability of the 5-phenylsulfone group
to be held in a favorable conformation by a hydrogen
bonding interaction. Furthermore, the presence of a
methyl group at the 4-position on the pyridine core of
7d apparently forces the neighboring 3-phenylsulfone
group in a suboptimal confirmation relative to com-
pound 7e. The torsion angle in compound 7d is 140°
versus 162° for compound 7e (Fig. 2).
Table 2. Structure–activity relationships of the R1 substituent
R1
O
S
O
N
NH
˚
˚
7
Compound
R1
Mean Ki (nM)a
7e
7f
4-Me
4-Et
145 44
52 22
198b
7g
7h
7i
4-OMe
4-Oallyl
119 18
32
4-OCH2Ph
4-OCF3
3
7j
268 50
635 39
In an attempt to enhance the binding affinity of this ser-
ies of compounds, an effort was made to further explore
the SAR on the phenylsulfonyl group. The primary fo-
cus of this effort was the preparation of analogs at the
4-position based on the initial results reported in Table
1. To this end, the methyl ether analogs of 7 (7g and
7u) were heated in 48% HBr at 110 °C for 24 h to fur-
nish, after washing with diethyl ether, the corresponding
phenols in excellent yield (Scheme 2). The phenols were
then alkylated under standard conditions (K2CO3, NaI,
and MeCN) to afford the desired products generally in
good yield. In addition, compound 7m was prepared
by DIBAL reduction of 11 followed by coupling with
2,4,6-trimethylaniline (Scheme 3).
7k
7l
4-OC3H6CN
4-OC4H8CN
4-CH2OH
395
1078 175
34
5
7m
7n
7o
7p
7q
7r
7s
7t
4-OCH2-(3,5-OMe2)Ph
4-OCH2-(3-OMe)Ph
4-OCH2-(2-OMe)Ph
4-OCH2-(3-CO2Me)Ph
4-OCH2-(3-CN)Ph
4-OCH2-(4-CN)Ph
4-OCH2-pyridin-2-yl
3-OMe
1
58 0.2
17 1.3
49 25
75 45
157
250 76
8
7u
7v
249
132b
4
3-OCH2Ph
a Data are averaged from a minimum of two replicates unless otherwise
noted. The standard deviation is also reported.
b Single determination.
R1
MeO
HO
Table 3. Rat pharmacokinetic parameters of selected 2-anilino-3-
phenylsulfonyl pyridines
O
O
O
a
b
S
S
S
O
7f
7i
7p
O
O
N
NH
N
NH
N
NH
iv (0.5 mg/kg)
CL (L/h/kg)
Vss (L/h)
5.2
25
5.1
4.7
10
3.5
8
t1/2 (h)
3
3.5
po (2.0 mg/kg)
AUC (nM h)
Cmax (nM)
F%
7g, 7u
10
7h-7l, 7n-7t, 7v
347
72
167
42
176
48
Scheme 2. Reagents and conditions: (a) HBr (48%), 110 °C, 90–97%;
35
18
16
(b) R1X, NaI, K2CO3, CH3CN, heat, 53–92%.

R. A. Hartz et al. / Bioorg. Med. Chem. Lett. 16 (2006) 934–937
937
The SAR of various alkyl and alkoxy groups (com-
References and notes
pounds 7e–i) indicates that, in general, the binding affin-
ity improves as the size of the alkyl or alkoxy group
increases within this set of compounds. However, ana-
logs with a polar group incorporated within R1 are less
potent (compounds 7j–m). This observation is not unlike
results noted in previously reported series of CRF1
receptor antagonists where it was found that polar func-
tionality, in particular very acidic or basic moieties, is
not well tolerated by the large lipophilic cavity of
CRF1 receptor.11
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1394.
2. (a) Gilligan, P. J.; Hartig, P. R.; Robertson, D. W.;
Zaczek, R. In Annual Reports in Medicinal Chemistry,
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41–50.; (b) DeSouza, E. B.; Grigoriadis, D. E. In
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Bloom, F. E., Kupfer, D. J., Eds.; Raven: New York,
1995; pp 505–517; (c) Kostich, W. A.; Chen, A.; Sperle,
K.; Largent, B. L. Mol. Endocrinol. 1998, 12, 1077; (d)
Chen, R.; Lewis, K. A.; Perrin, M. H.; Vale, W. W. Proc.
Natl. Acad. Sci. U.S.A. 1993, 90, 8967; (e) Perrin, M. H.;
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Endocrinology 1993, 133, 3058.
3. Smith, G. W.; Aubry, J.-M.; Dellu, F.; Contrarino, A.;
Bilezekijian, L. M.; Gold, L. H.; Chen, R.; Marchuk, Y.;
Hauser, C.; Bentley, C. A.; Sawchenko, P. E.; Koob, G.
F.; Vale, W.; Lee, K.-F. Neuron 1998, 20, 1093.
4. (a) Gilligan, P. J.; Robertson, D. W.; Zaczek, R. J. Med.
Chem. 2000, 43, 1641; (b) Nemeroff, C. B.; Widerlov, E.;
Bissette, G.; Wallens, H.; Karlsson, I.; Eklund, K.; Kilts,
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Since the highest affinity substituent was a benzyl ether
(7i, Ki = 32 nM), an investigation was conducted to
examine the SAR of various substituents on the benzyl
group. Several compounds are included in Table 2 to
illustrate the SAR trends observed. The 3,5-dimethoxy
substituted benzyl group (compound 7n) was somewhat
more potent than the 3-methoxybenzyl group (com-
pound 7o). Moving the methoxy group to the 2-position
(compound 7p), however, further improved the binding
affinity over 7n. A methyl ester at the 3-position pos-
sessed similar activity to the corresponding methoxy
group at this position (compare 7o with 7q). Replace-
ment of the phenyl group with a 2-pyridin-2-yl group
resulted in a decrease in binding affinity (compare 7t with
7i). The analog, where R1 is a benzyl ether at the 3-posi-
tion, was less potent than the corresponding analog at
the 4-position (compare 7u with 7g and 7v with 7i).
5. (a) Chen, Y. L.; Mansbach, R. S.; Winter, S. M.; Brooks,
E.; Collins, J.; Corman, M. L.; Dunaiskis, A. R.; Faraci,
W. S.; Gallaschun, R. J.; Schmidt, A.; Schultz, D. W. J.
Med. Chem. 1997, 40, 1749; (b) Mansbach, R. S.; Brooks,
E. N.; Chen, Y. L. Eur. J. Pharmacol. 1997, 323, 21; (c)
Arborelius, L.; Skelton, K. H.; Thrivikraman, K. V.;
Plotsky, P. M.; Schulz, D. W. J. Pharmacol. Exp. Ther.
Selected compounds were further assessed in a rat cas-
sette study to determine their pharmacokinetic profile.
Results of the rat pharmacokinetic studies are summa-
rized in Table 3.12 Examination of the iv data in Table
3 indicates that all three compounds have high clearance
and modest half-lives. The data from oral dosing show
that compounds 7f, 7i, and 7p possess oral bioavailabil-
ities of 35%, 18%, and 16%, respectively.
2000, 34, 171; (d) Zobel, A. W.; Nickel, T.; Kunzel, H. E.;
Ackl, N.; Sonntag, A.; Ising, M.; Holsboer, F. J. Psychi-
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¨
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7. Compounds with a 4,6-dimethylpyridine core analogous
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8. De Souza, E. B. J. Neurosci. 1987, 7, 88.
In conclusion, a novel series of 2-anilino-3-phenylsulfo-
nyl-6-methylpyridines was synthesized and investigated
as potential CRF1 receptor antagonists. Members of this
class of compounds were found to be potent ligands for
the CRF1 receptor. In addition, this study illustrates
that a novel phenylsulfonyl tether from the 3-position
of the pyridine core can serve as a replacement for the
dialkylamino group present in structure 1. Additional
efforts are required to further optimize binding affinity
and improve the pharmacokinetic profile of compounds
in this series.
9. Brooks, B. R.; Bruccoleri, R. E.; Olafson, B. D.; States, D.
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12. Compounds 7f, 7i, and 7p were co-administered intrave-
nously to Sprague–Dawley rats (n = 3) at a dose of
0.5 mg/kg for each compound. In addition, the same set
of compounds was administered to rats (n = 3) orally at a
dose of 2 mg/kg. Plasma samples were collected at 0, 0.1,
0.25, 0.5, 1, 2, 4, 6, 8, and 24 h post-dose for the
intravenous experiment, and at 0, 0.5, 1, 2, 4, 6, 8, and
24 h post-dose for the oral experiment. Drug concentra-
tions were determined in the plasma samples using LC/
MS/MS.
Acknowledgments
The authors gratefully acknowledge Anne Marshall and
Susan Keim forin vitro binding studies.