Aryl sulphonyl amides as potent agonists of the growth hormone secretagogue (ghrelin) receptor

Article abstract of DOI:10.1016/j.bmcl.2008.12.042

As part of an on-going lead optimisation effort, a cross screening exercise identified an aryl sulphonyl amide hit that was optimised to afford a highly potent series of ghrelin receptor agonists.

Full text of DOI:10.1016/j.bmcl.2008.12.042

Bioorganic & Medicinal Chemistry Letters 19 (2009) 684–687
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Aryl sulphonyl amides as potent agonists of the growth hormone
secretagogue (ghrelin) receptor
a
d
a
a
Jason Witherington a, , Lee Abberley , Benjamin R. Bellenie , Rio Boatman , Katharine Collis ,
David K. Dean a, Alessandra Gaiba a, N. Paul King a, Nicola Shuker a, Jon G. A. Steadman a, Andrew K. Takle a,
Gareth Sanger b, Sharon Butler c, Fiona McKay c, Alison Muir c, Kim Winborn c, Robert W. Ward a,
Tom D. Heightman d
*
a Department of Medicinal Chemistry & DMPK, Neurology & GI Centre of Excellence for Drug Discovery, GlaxoSmithKline, New Frontiers Science Park, Third Avenue,
Harlow, Essex CM19 5AW, UK
b Department of Biology, Neurology & GI Centre of Excellence for Drug Discovery, GlaxoSmithKline, New Frontiers Science Park, Third Avenue, Harlow, Essex CM19 5AW, UK
c Molecular Discovery Research, Department of Screening and Compound Profiling, GlaxoSmithKline, New Frontiers Science Park, Third Avenue, Harlow, Essex CM19 5AW, UK
d Molecular Discovery Research, Department of Medicinal Chemistry, GlaxoSmithKline, New Frontiers Science Park, Third Avenue, Harlow, Essex CM19 5AW, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
As part of an on-going lead optimisation effort, a cross screening exercise identified an aryl sulphonyl
amide hit that was optimised to afford a highly potent series of ghrelin receptor agonists.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 13 November 2008
Revised 9 December 2008
Accepted 9 December 2008
Available online 14 December 2008
Keywords:
Ghrelin
Growth hormone secretagogue receptor
(GHSR1a)
Cachexia
Post-operative Ileus
Motility disorders
Neurogenic and diabetic gastroparesis
High-throughput screening (HTS) lead
optimisation
Cross screening
Ghrelin, a 28-amino acid gastric hormone containing a unique
post translational modification on serine 3, exhibits a wide range
of biological activities via its postulated cognate receptor, the
growth hormone secretagogue receptor (GHSR1a). In humans as
well as in rodents, ghrelin stimulates pituitary growth hormone
(GH) secretion1 and in addition increases food intake and body
weight gain and regulates energy balance.2,3 Agents which mimic
the actions of ghrelin have potential not only in growth hormone
replacement therapy, but also in disorders requiring increased
nutritional intake, such as cancer-induced cachexia and post-oper-
ative ileus, and in motility disorders such as neurogenic and dia-
betic gastroparesis.4 Previously we described the systematic
optimisation of a high-throughput screening hit (HTS) to yield a
series of small molecule orally bioavailable ghrelin receptor
agonists (Scheme 1).5,6
As part of our on-going lead optimisation efforts, a routine cross
screening exercise of all newly prepared GSK compounds identified
(2) as a hit worthy of further investigation. Herein we report the
subsequent SAR optimisation and preliminary in vivo properties
of these compounds.
Our initial evaluation of the lead (2) focussed on understanding
the stereochemical preference at both asymmetric centres. Interest-
ingly, whilst the S-isomer of the pipecolinic acid was essential for
potency (cf 3 and 4 with 5 and 6) there was no stereochemical influ-
ence of the 3-aminopyrrolidinyl amine (cf 5 and 6) (Tables 1 and 2).
Given the structural similarity to the previously disclosed aryl
sulphonamide lead (1) we then sought to determine whether we
could exploit the previous SAR findings from this series. As in the
aryl sulphonamide series a biaryl moiety appeared essential for
high inhibitory potency (cf 6 and 7) and further optimisation of
this side chain afforded dramatic improvements in potency which
was also consistent with our original lead series (cf 8, 9 and 11).
The preferred furanyl substituent was confirmed to be an optimal
* Corresponding author. Tel.: +44 1279 627832; fax: +44 1279 627685.
E-mail address: Jason_Witherington@GSK.com (J. Witherington).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.12.042

J. Witherington et al. / Bioorg. Med. Chem. Lett. 19 (2009) 684–687
685
O
O
NH
O
O
NH
S
H
S
S
N
N
N
N
N
O
MeO
OMe
(1) GHSR pEC50 9.1 (1.0)
75% bioavailability in rats
SB-791016-A, GHSR pEC50 9.8 (0.9)
poor systemic exposure
Scheme 1. Identification of potent orally bioavailable ghrelin receptor agonists.
Table 1
Table 2
Stereo isomers of cross screening hit 2
Side chain SAR
O
S
O
N
N
S
R1
A
O
O
O
N
O
N
B
NH2
NH2
Compound
R/S
R1
GHSR pEC50 (IA)7
Compound
A (R/S)
B (R/S)
GHSR pEC50 (IA)7
7
8
9
R
R
R
R
R
S
S
S
S
S
4-Br-Ph
(2-Furanyl)-4-Ph
6.4 (0.7)
7.5 (1.2)
9.6 (1.3)
8.5 (0.9)
10.3 (1.3)
9.8 (1.3)
7.7 (1.1)
8.4 (1.3)
8.7 (1.3)
6.5 (0.6)
9.0 (1.2)
9.5 (1.2)
2
3
4
5
6
Racemic
7.5 (0.8)
<5.3
<5.3
8.1 (1.1)
7.8 (1.1)
R
R
S
S
S
R
S
R
(5-Me-2-furanyl)-4-Ph
(2-Furanyl)-4-(3-F-Ph)
(5-Me-2-furanyl)-4-(3-F-Ph)
(5-Me-2-furanyl)-4-(3-F-Ph)
PhCONH-4-Ph
(2-F-Ph)CONH-4-Ph
(3-MeO-Ph)CONH-4-Ph
(3-Pyridyl)-4-Ph
10
11
12
13
14
15
16
17
18
R
R
(2,5-diF-Ph)-4-Ph
(2,5-diCl-Ph)-4-Ph
substituent in both the R and S amino pyrrolidinyl amine series (11
and 12) but could also be replaced by a suitably functionalised aryl
moiety (e.g., 17 and 18). Consistent with the aryl sulphonamide
Table 3
Template SAR
O
R1
LINK
O
S
O
O
N
NH2
Compound
LINK
R1
clogP
GHSR pEC50 (IA)7
9.4 (1.2)
Compound
LINK
R1
cLogP
1.8
GHSR pEC50 (IA)7
9.3 (1.1)
OH
OH
N
19
F
3.4
22
F
N
N
N
20
21
F
2.4
2.6
7.8 (1.1)
8.9 (1.1)
23
24
F
F
1.8
2.0
8.3 (1.2)
9.7 (1.2)
NH
OH
N
N
H

686
J. Witherington et al. / Bioorg. Med. Chem. Lett. 19 (2009) 684–687
Table 4
Amine SAR
series, introduction of polarity led to a reduction in potency (cf 5
and 16) however the finding that a linker group was tolerated
between the two aryl rings was a surprising result (e.g., 14 and
15) given this was poorly tolerated in our initial lead series (data
not published).
O
R1
Having established the stereochemical preferences and side
chain SAR we turned our attention to establishing the role of
the central template in order to ascertain whether this part of
the molecule could be utilised to modulate the overall lipophic-
ity of the series which had previously been difficult to achieve
with our early lead series (SB-791016-A and 1 clogPs 4.1 and
4.9, respectively). Gratifyingly, whilst the six-membered pipeco-
linic acid moiety was confirmed as the optimal ring size (cf 11
with 19 and 20) (Table 3), a wide range of groups were tolerated
which potentially allows for the fine tuning of the physicochem-
ical properties of these molecules and the identification of com-
pounds with substantially lower clogPs than our initial lead
series (e.g., 19–20 cf SB-791016 and 1).
N
S
O
O
R2
O
Compound
11
R1
F
R2
GHSR pEC50 (IA)7
10.3 (1.3)
N
NH2
N
Having established the preliminary preferences of both the
side chain and the central core we sought to examine the struc-
tural requirements of the amine group. Previous SAR exploration
in the arylsulphonamide series had demonstrated that this part
of the molecule was highly sensitive to modification. Interestingly,
we again confirmed the cis-2,6-dimethylpiperazine moiety as hav-
ing good potency albeit this was not the optimal amine substitu-
ent (cf 28 and 11) (Table 4). In general this series was more
tolerant to changes in the amine functionality than in the aryl sul-
phonamide series.5
Given the initial promising SAR findings of this cross screening
hit we decided to profile one of our more potent compounds.
Whilst compound 19, displayed an encouraging profile following
iv dosing with low to moderate in vivo clearance the systemic
exposure was low following oral dosing and would need to be opti-
mised prior to further in vivo evaluation (Table 5).
25
26
27
28
H
H
H
F
8.2 (1.2)
8.0 (0.9)
8.1 (0.9)
8.6 (1.2)
NH
N
NHMe
N
N
N
H
NH
The pyrrolidinyl analogue 19 was obtained starting with the
coupling of the commercially available Cbz protected L-proline 29
and Boc protected (3R)-pyrrolidinyl amine 30 to afford, after
hydrogenolysis, the amine 31. Sulphonylation of the secondary
amine followed by Boc deprotection afforded the desired analogue
19 in good overall yield (Scheme 2).
In summary, having identified a hit from a cross screening exer-
cise, we have explored the initial structural requirements for opti-
mal potency. In common with our previously published aryl
sulphonamide series, and literature the SAR around the natural
ligand ghrelin, an appropriately placed lipophilic side chain is
essential for optimal potency. Furthermore, replacement of the
pipecolinic acid core and aminopyrrolidinyl side chain is well tol-
erated giving encouragement for further optimisation of the phar-
macokinetic properties of this series.
Table 5
Rat pharmacokinetic profile for compound 19 in male Sprague–Dawley rats
i.v. Bolus at 1 mg/kg
3 mg/kg po (n = 3, SD)
CLb (mL/min/kg)
Vss (L/kg)
25
3.5
0.762
2.4
Cmax (
l
M)
0.151 0.024
4.0 (4.0–4.1)
Tmax* ((h))
Cmax (
l
M)
AUC (0–t)/dose** (min kg/L)
5
1
t½ (h)
MRT (h)
2.4
*
Tmax expressed as median and range.
t for AUC (0 ? t) is 6 h or the time of the last quantifiable blood concentration.
**
O
F
HN
CbzN
c, d
a, b
47%
63%
NHBoc
N
OH
O
O
N
29
30
S
31
O
O
NH2
NHBoc
N
HN
O
19
Scheme 2. Reagents and conditions: (a) HOAt, EDC, DCM, 25 °C; (b) H2, Pd/C, EtOH, 25 °C; (c) (5-Me-2-furanyl)-4-(2-F-Ph)-SO2Cl, pyridine, DCM, 25 °C; (d) HClÁdioxane (63%,
two steps).

J. Witherington et al. / Bioorg. Med. Chem. Lett. 19 (2009) 684–687
687
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References and notes
6. Witherington, J.; Abberley, L.; Briggs, M. A.; Collis, K.; Dean, D. K.; Gaiba, A.; King,
N. P.; Kraus, H.; Shuker, N.; Steadman, J. G. A.; Takle, A. K.; Sanger, G.;
Wadsworth, G.; Butler, S.; McKay, F.; Muir, A.; Winborn, K.; Heightman, T. D.
Bioorg. Med. Chem. Lett. 2008, 18, 2203.
7. GHSR Agonist BACMAM FLIPR assay was used to determine the potency and
efficacy of the test compounds. Media is aspirated from cell plates using a cell
1. Takaya, K.; Ariyasu, H.; Kanamoto, N.; Iwakura, H.; Yoshimoto, A.; Harada, M.;
Mori, K.; Komatsu, Y.; Usui, T.; Shimatsu, A.; Ogawa, Y.; Hosoda, K.; Akamizu,
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4. (a) Binn, M.; Albert, C.; Gougeon, A.; Maerki, H.; Coulie, B.; Lemoyne, M.; Rabasa
Lhoret, R.; Tomasetto, C.; Poitras, P. Peptides 2006, 27, 1603; (b) Murray, C. D. R.;
Martin, N. M.; Patterson, M.; Taylor, S. A.; Ghatei, M. A.; Kamm, M. A.; Johnston,
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5. Heightman, T. D.; Scott, J. S.; Longley, M.; Dean, D. K.; Elliott, R.; Hutley,
G.; Witherington, J.; Abberley; Passingham, B.; Berlanga, M.; Frailes, M.;
Wise, A.; Powney, B.; Muir, A.; McKay, F.; Butler, S.; Winborn, K.; Gardner,
washer (leaving 10
ll of media). Cells are immediately loaded with loading buffer
(Tyrodes (Elga water + 145 mM NaCl + 5 mM KCl + 20 mM HEPES + 10 mM
glucose + 1 mM MgCl2) + 1.5 mM CaCl2 + 0.714 mg/ml Probenicid (predissolved
in 1 M NaOH) + 0.5 mM brilliant black + 2.5
37.5 °C for 1 h. Ten microliters from compound plates is then added immediately
to cell plates using FLIPR calcium imaging instrument. Fluorescence
lM Fluo 4 dye, and incubated at
a
3
measurements are then taken. Intrinsic activity (IA) expressed relative to
human ghrelin.