Indole-propionic acid derivatives as potent, S1P3-sparing and EAE efficacious sphingosine-1-phosphate 1 (S1P1) receptor agonists

Article abstract of DOI:10.1016/j.bmcl.2012.02.083

Novel indole-propionic acid derivatives were developed as sphingosine-1-phosphate (S1P) receptor agonists through a systematic SAR study. The optimized and S1P₃ selective S1P₁ agonist 9f induced peripheral blood lymphocyte reduction

Full text of DOI:10.1016/j.bmcl.2012.02.083

Bioorganic & Medicinal Chemistry Letters 22 (2012) 2794–2797
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Indole-propionic acid derivatives as potent, S1P3-sparing and EAE
efficacious sphingosine-1-phosphate 1 (S1P1) receptor agonists
Qinghua Meng, Baowei Zhao, Qiongfeng Xu, Xuesong Xu, Guanghui Deng, Chengyong Li, Linbo Luan,
Feng Ren, Hailong Wang, Heng Xu, Yan Xu, Haibo Zhang, Jia-Ning Xiang, John D. Elliott, Taylor B. Guo,
⇑
Yonggang Zhao, Wei Zhang, Hongtao Lu, Xichen Lin
Research and Development, GlaxoSmithKline Pharmaceuticals, 898 Halei Road, Zhangjiang Hi-tech Park, Pudong, Shanghai 201023, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel indole-propionic acid derivatives were developed as sphingosine-1-phosphate (S1P) receptor ago-
nists through a systematic SAR study. The optimized and S1P3 selective S1P1 agonist 9f induced periph-
eral blood lymphocyte reduction in vivo and has an excellent efficacy in mouse experimental
autoimmune encephalomyelitis (EAE).
Received 10 December 2011
Revised 8 February 2012
Accepted 24 February 2012
Available online 3 March 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Sphingosine-1-phosphate
Agonist
Lymphopenia
Experimental autoimmune
encephalomyelitis (EAE)
SAR
Sphingonsine-1-phosphate1 (S1P) induces a range of cellular re-
sponses by its interaction with the S1P family of G-protein coupled
receptors (GPCRs). A total of five S1P receptors are known: S1P1–
S1P5. The in vivo immunosuppressive efficacy of a non-selective
S1P receptor agonist has been evidenced by the numerous preclin-
ical and clinical studies of FTY720 (fingolimod, Fig. 1), which has
been recently approved for the treatment of remitting relapsing
multiple sclerosis (RRMS) by FDA.2 Recent studies have demon-
strated that S1P receptor agonists affect lymphocyte trafficking
and an interaction with S1P1 receptors on lymphocytes drives
the observed pharmacodynamics.3 On the other hand, fingolimod’s
S1P3 activity has been linked to mediate vascular side effects seen
in clinical trials.4 Hence, there is a need for S1P1 receptor agonist
compounds with selectivity over S1P3 which is expected to show
a reduced tendency to induce bradycardia and hypertension.4
The understanding of FTY720 unique mode of action has triggered
intensive effort towards the discovery of S1P1 agonists with in-
creased degree of selectivity versus S1P3.5 Herein, we report our ef-
forts to identify orally active S1P1, selective over S1P3.
1,3,4-oxadiazole and propanoic acids at the indole ring (5). As
showed in Scheme 1, treatment of the nitrile (5a) with hydroxyl-
amine provided N-hydroxylamidine (5b), which was coupled with
various benzoic acids followed by dehydration at elevated temper-
ature to afford the oxadiazole esters (5c). The esters were hydro-
lyzed to afford the desired acids (5). The indole derivatives and
benzoic acids used to prepare the new analogs were synthesized
based on literature precedents.7
A direct comparison of different substitution patterns of the
indole showed that pEC50 of the agonists varied depending on the
orientations of the indole in Tango assay8 (Table 1). The selectivity
over S1P3 is generally good as determined by S1P3 Ca2+ mobilization
in hS1P3 assay.9 In this set, 6c showed the best S1P1 potency and
S1P3 selectivity, therefore, was selected for further exploration.
OH
O
P
OH
O
OH
NH2
1
, sphingosine-1-phosphate, S1P
NH2
We recently identified 3-[4-(5-aryl-1, 2, 4-oxadiazol-3-yl)-1
H-indol-1-yl]propanoic acid series (4) (Fig. 2) are potent S1P1
receptor agonists without S1P3 activity.6 In order to fully under-
stand the SAR, we synthesized different substituent patterns of
OR
OH
2
, R = H,
FTY720
3
, R = PO(OH)2, FTY720 phosphate
⇑
Corresponding author. Tel.: +86 21 6159 0718; fax: +86 21 6159 0730.
E-mail address: Xichen.2.Lin@gsk.com (X. Lin).
Figure 1. Structure S1P (1), FTY720 (2), FTY720 phosphate (3).
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2012.02.083

Q. Meng et al. / Bioorg. Med. Chem. Lett. 22 (2012) 2794–2797
2795
Table 2
RO
RO
S1P1 and S1P3 pEC50 values for compounds (6c and 7a–7k)
X
X
HN
O
N
4
N
O
O
N
COOH
N
5
N
R3
R3
N
4
6
R
Compound
S1P1 pEC50
10.9
S1P3 pEC50
3
2
7
N
Cl
N
H
1
1
6c
<5.0
<5.0
COOH
O
Cl
5
COOH
4
Figure 2. General structures of 3-[4-(5-Aryl-1,2,4-oxadiazol-3-yl)-1H-indol-1-
yl]propanoic acid (4) series and the new scaffold (5).
7a
9.4
O
N
F3C
N
OH
7b
7c
7d
7e
7f
9.6
8.8
<5.0
<5.0
<5.0
<5.0
<5.0
<5.0
H2N
NC
R5
O
b
N
N
a
COOEt
COOEt
N
R5
N
R4
R4
5b
O
5a
MeO
R3
7.0
R3
O
O
N
O
O
N
N
c
N
N
COOH
8.5
COOEt
N
R5
N
O
O
R5
R4
R4
5
5c
5.9
Scheme 1. Synthesis of indole propanoic acids. Reagent: (a) NH2OHÁHCl, NaHCO3,
O
O
EtOH; (b) R3COOH, EDC, HOBt, TBAF, THF; (c) NaOH, MeOH, H2O and then HCl.
7g
<5.5
O
Table 1
O
S1P1 and S1P3 pEC50 values for compounds (6a–6e)
7h
7i
6.4
5.5
<5.0
<5.0
O
R1
Cl
O
O
O
7j
<5
<5
<5.0
<5.0
N
Cl
N
7k
OH
R2
N
H
O
As shown in (Tables 2 and 4) -isopropoxyl substituted aromatic
rings are crucial for the in vitro potency (6c and 7a–7c). Replace-
ments of the isopropoxyl group with other alkoxyl groups
(7e–7h) or aliphatic rings (7j–7k) yielded much less activity. The
4-isopropoxyl substituted phenyl ring (6c) is more potent than
its pyridine analogs (7a). Compounds with electron withdrawing
groups such as –Cl, –CF3, showed higher potency than that with
electron donating group such as –Me, –OMe. Based on these data,
3-chloro-4-isopropoxyl phenyl group was chosen as the moiety for
further investigation.
Among all carboxylic acids with various distances, the 3-indole-
propionic acid 6c was the most potent S1P1 agonist (Table 3). We
also evaluated carboxylic acid bioisosteres including the primary,
secondary amides and tetrazoles which provided similar potency.
As the final step, we focused on various substituents on the in-
dole moiety for further SAR study. Methylated indole ring 9a was
found to be optimal to enhance S1P1 potency. Depending on the
electron properties and position, other substituents on the indole
ring significantly affected the S1P1 pEC50. Electron withdrawing
groups are favorable over electron donating groups (9f vs 9e).
4- or 5-F substituted molecules gave much improved S1P1 potency
than 6-F substituted one (9f, 9g vs 9h).
Compound
Structure
S1P1 pEC50
S1P3 pEC50
<5.0
R1
6a
8.6
N
R2
6b
6c
6.4
<5.0
<5.0
R1
N
R2
R2
10.9
N
H
R1
R2
6d
6e
9.6
9.7
<5.0
<5.0
R1
R1
N
H
R2
N
H

2796
Q. Meng et al. / Bioorg. Med. Chem. Lett. 22 (2012) 2794–2797
Table 3
S1P1 and S1P3 pEC50 values for compounds (7c and 8a–8g)
3
vehicle
9f
R2
HN
N
O
Cl
O
fingolimod
2
N
Compound
R2
S1P1 pEC50
S1P3 pEC50
1
0
8a
8b
6c
8c
8d
–COOH
8.3
7.4
10.9
9.4
<5.0
<5.0
<5.0
<5.0
<5.0
Treatment
–CH2COOH
–(CH2)2COOH
–(CH2)3COOH
–(CH2)4COOH
0 2 4 6 8 10
15
20
25
30
10.3
Days post immunization
O
8e
8f
10.5
10.4
<5.0
<5.0
Figure 3. EAE results of compound 9f.
NH2
O
profile and whether the effects could be reversed upon time. The
lymphocyte count normalized at 24 h after the single dose. Com-
pared to fingolimod,11 9f showed much less severe and more tran-
sient lymphopenia effect (Table 5). Given the promising
lymphopenia data, we further evaluated 9f in CNS, PK and EAE
study. Mice CNS penetration assays demonstrated that 9f was able
to enter the CNS with a brain to blood ratio of 0.48. Pharmacokinet-
ics analysis of 9f in mice revealed a low systemic clearance, low
volume of distribution and high Cmax. Compound 9f also had good
oral bioavailability (100%) and a moderate terminal half-life
(3.83 h) (Table 5). On the basis of its S1P1 receptor agonist potency,
selectivity and pharmacokinetic profiles, 9f was evaluated in a
mouse experimental autoimmune encephalomyelitis (EAE) model
with a head-to-head comparation with fingolimod.12 As shown in
Figure 3, compound 9f showed a comparable in vivo efficacy to
fingolimod.
N
H
N
N
N
8g
10.1
<5.0
N
H
Table 4
S1P1 and S1P3 pEC50 values for compounds (9a–9h)
R4
N
N
O
COOH
Cl
O
4
N
R5
6
5
Compound
R4
R5
S1P1 pEC50
S1P3 pEC50
In conclusion, we conducted a systematic SAR analysis and
identified potent and selective S1P1 receptor agonists. Within the
set of indole compounds, 9f showed excellent PK profile and sim-
ilar efficacy to fingolimod. Details of further evaluation of 9f in
other preclinical studies and safety evaluation will be reported in
due course.
9a
9b
9c
9d
9e
9f
–Me
–Et
–Pr
–iPr
–Me
–Me
–Me
–Me
/
/
/
/
11.2
9.5
6.7
7.7
8.2
>11
>11
7.6
<5
<5
<5
<5
<5
<5
<5
<5
4-OMe
4-F
5-F
9g
9h
Acknowledgments
6-F
We thank Drs. Eric Y. Yang, Hong Lu, Zongping Zhang, and Jian-
song Yang for help for comments and suggestions.
Table 5
In vivo profile of 9f
References and notes
Assay
9f
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21%@4 h
114@24 h
0.35@1 h
0.48@2 h
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CLb (mL/min/kg)
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