Structure-activity relationship on the human EP3 prostanoid receptor by use of solid-support chemistry

Article abstract of DOI:10.1016/S0960-894X(01)00056-7

Potent and selective EP₃ receptor ligands were found by making a library using solid-support chemistry. These compounds can be obtained by a Suzuki coupling reaction of a solid-supported benzyl bromide using various boronic acids. The yields obtained for this reaction were in the range of 24-95% of arylmethyl cinnamic acid I after cleavage from the Wang resin,

Full text of DOI:10.1016/S0960-894X(01)00056-7

Bioorganic & Medicinal Chemistry Letters 11 (2001) 747±749
Structure±Activity Relationship on the Human EP3 Prostanoid
Receptor by Use of Solid-Support Chemistry
Helene Juteau,* Yves Gareau, Marc Labelle, Sonia Lamontagne, Nathalie Tremblay,
Marie-Claude Carriere, Nicole Sawyer, Danielle Denis and Kathleen M. Metters
Â
Merck Frosst Canada & Co., PO Box 1005, Pointe-Claire, Dorval, Quebec, Canada, H9R 4P8
Received 18 December 2000; accepted 23 January 2001
AbstractÐPotent and selective EP3 receptor ligands were found by making a library using solid-support chemistry. These com-
pounds can be obtained by a Suzuki coupling reaction of a solid-supported benzyl bromide using various boronic acids. The yields
obtained for this reaction were in the range of 24±95% of arylmethyl cinnamic acid 1 after cleavage from the Wang resin. # 2001
Published by Elsevier Science Ltd.
Recently, the eight known human prostanoid receptors
have been cloned and characterized.1 The ligand speci-
®city for a human prostanoid receptors can now be
determined and consequently, the correlation of a spe-
ci®c receptor with various pathologies could potentially
be established. Our search for a selective EP3 receptor
ligand was initiated by screening a large number of
compounds from our sample collection.2 One particular
class of compounds, namely the 2-(arylmethyl) cinnamic
acid (1) was identi®ed as a potential series. An e€ective
and rapid way to explore the ring A and study SAR
involved making a library using solid-phase synthesis.
biaryl methane core. Benzylic bromides have only been
used rarely for Suzuki coupling reaction in solution6a and
even more rarely on solid support.6b In this paper, we
report the preparation of a small library using a polymer-
supported benzyl bromide and various boronic acids to
®nd a potent and selective EP3 antagonist.
The benzyl bromide used in the Suzuki coupling reac-
tions was ®rst synthesized and then linked on a solid
support. The synthesis is outlined in Scheme 1. Starting
from 2-methylcinnamic acid, the ester 2 was obtained
under standard Fischer conditions. Benzylic bromina-
tion followed by hydrolysis and conversion of the car-
boxylic acid to the acyl chloride gave the intermediate 3
in 43% overall yield (three steps). Addition of the Wang
resin to 3 yielded 4 with a loading of 0.57 mmol/g
(Scheme 1).
With the polymer 4 in hand, we were ready to a€ect
Suzuki coupling reactions with boronic acids. Typically,
the reactions were performed using 3.0 equiv of boronic
acid, 6.0 equiv of CsF with 10 mol% of Pd(PPh3)4 in
DME at 100 ꢀCfor 10 h. The substrate was then cleaved
from the resin with either 20% TFA in CH2Cl2 for 10
min at room temperature or sodium hydroxide in THF/
MeOH.7 Under these conditions, 20 substituted aryl-
methyl cinnamic acids were rapidly obtained in 24±95%
yield but most importantly in high purity. Table 1 sum-
marizes the results of these reactions. The only major
impurity was determined to be 2-methylcinnamic acid,
which resulted from reduction of halide 4 and then
cleavage from the resin. This compound was found to
The preparation of small molecule libraries using solid-
phase organic chemistry is now routinely applied in phar-
maceutical research. For lead discovery and lead optimi-
zation, it has proven to be a powerful method.3 The
Suzuki coupling reaction4 using polymer-supported aryl
bromides with boronic acids to obtain biaryl adducts has
been widely used over the past few years.5 For our pur-
pose, a benzylic bromide instead of an aryl bromide would
be necessary in the Suzuki coupling reaction to achieve the
*Corresponding author. Fax: +1-514-428-4900; e-mail: helene_juteau@
merck.com
0960-894X/01/$ - see front matter # 2001 Published by Elsevier Science Ltd.
PII: S0960-894X(01)00056-7

748
H. Juteau et al. / Bioorg. Med. Chem. Lett. 11 (2001) 747±749
Scheme 1. Synthesis of the solid-supported benzyl bromide 4.
Table 1. Suzuki coupling of boronic acids and benzyl bromide on solid support.
Entry
Boronic acid
Yield (%)a
Purity (%)b
Residual binding on EP3 (%)d
1
2
3
4
5
6
7
8
1-Naphthalene boronic acid
3,4-Dichlorobenzene boronic acid
3-Chlorobenzene boronic acid
67
48
90
92
76
67
49
62
77
33
38
72
87
24
41
95
51
21
94
57
96
90
48
8
90 (5)c
96
55
25
54
89
61
93
5
73
74
77
84
68
52
96
91
27
100
84
2,4-Dichlorobenzene boronic acid
3-(Tri¯uoromethyl)benzene boronic acid
2-(Tri¯uoromethyl)benzene boronic acid
Benzo[b]furan-2-boronic acid
2-Methoxybenzene boronic acid
2-Naphthalene boronic acid
2H-Benzo[d]1,3-dioxolene-5-boronic acid
Thiophene-2-boronic acid
Thiophene-3-boronic acid
89 (8)c
83 (11)c
95
74 (7)c
88
9
10
11
12
13
14
15
16
17
18
19
20
72 (13)c
93
94
3-(Hydroxymethyl)benzene boronic acid
2-[(2-Phenylethylthio)methyl]benzene boronic acid
3-[(2-Phenylethylthio)methyl]benzene boronic acid
2-(Methylthio)benzene boronic acid
2-Furan boronic acid
4-(Methylthio)benzene boronic acid
4-{[(tert-Butyl)amino]sulfonyl}benzene boronic acid
3,4-Dimethoxybenzene boronic acid
64 (30)c
59 (9)c
33 (32)c
95
60 (24)c
89
69
92
aIsolated yields from the crude reaction mixture (yields based on the original loading of the resin).
bPurities evaluated by HPLCat 275 nm.
cPercentage of 2-methylcinnamic acid.
dThe residual binding is the percentage of radiolabelled PGE2 bound on the receptor when the drug is present (evaluated at 1 mM).
Table 2. Full pro®le of potent EP3 antagonists.
Ki (mM)a
Entry
1
R
EP1
EP2
4.1
EP3
0.11
EP4
FP
63
DP
2.5
IP
31
TP
>100
>40
0.52
2
3
4
>100
63
43
13
12
0.080
0.032
0.020
>50
10
>83
41
4.1
>76
37
4.6
2.4
0.90
>100
3.1
69
0.53
>100
10
aData in Table 2 are an average value from at least two separate experiments.

H. Juteau et al. / Bioorg. Med. Chem. Lett. 11 (2001) 747±749
749
be inactive on the EP3 receptor. The residual binding8 of
PGE2 on the EP3 receptor is also reported in Table 1.
From these results, we found four compounds that
showed high anity for this receptor with less than 30%
of residual binding (entries 2, 4, 9, and 18).
Slipetz, D. M.; Metters, K. M.; Abramovitz, M. J. Biol. Chem.
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2. Biological assays: Abramovitz, M.; Adam, A.; Boie, Y.;
Godbout, C.; Lamontagne, S.; Rochette, C.; Sawyer, N.;
Tremblay, N. M.; Belley, M.; Gallant, M.; Dufresne, C.; Gar-
eau, Y.; Ruel, R.; Juteau, H.; Labelle, M.; Ouimet, N.; Met-
ters, K. M. Biochim. Biophys. Acta 2000, 1483, 285.
3. Hermkens, P. H. H.; Ottenheijm, H. C. J.; Rees, D. C.
Tetrahedron 1996, 52, 4527. Hermkens, P. H. H.; Ottenheijm,
H. C. J.; Rees, D. C. Tetrahedron 1997, 53, 5643. Fruchtel,
J. S.; Jung, G. Angew. Chem., Int. Ed. Engl. 1996, 35, 17.
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Des. 1995, 2, 269. Thompson, L. A.; Ellman, J. A. Chem. Rev.
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4. Suzuki, A. Acc. Chem. Res. 1982, 15, 178. Martin, A. R.;
Yang, Y. Acta Chem. Scand. 1993, 47, 221.
These compounds were then prepared by standard
solution-phase chemistry, puri®ed and fully character-
ized.9 They all have activities equal to or less than 110
nM on the EP3 receptor (Table 2). The best activity was
achieved when R was 3,4-dichlorophenyl and 2-naph-
thyl with Ki values of 32 nM and 20 nM, respectively
(entries 3 and 4). These two compounds were also selec-
tive over the EP receptors by a factor of at least 155 and
by a factor of 30 over the other prostanoid receptors.
In conclusion, we have reported the preparation of an
arylmethyl cinnamic acid library using a solid-supported
benzyl bromide and various boronic acids in a Suzuki
type reaction. The benzylcinnamic acids reported herein
constitute a novel series of EP3 selective ligands. The
SAR from the library indicated that substitution with 2-
naphthyl and 3,4-dichlorophenyl were the most potent
and selective EP3 antagonists with activities on EP3 of 20
nM and 32 nM. The pharmacology studies and further
optimization of these leads will be disclosed elsewhere.
5. For Suzuki coupling on solid support: Frenette, R.; Frie-
sen, R. W. Tetrahedron Lett. 1994, 35, 9177.
6. (a) For Suzuki coupling using benzyl bromide: Pernia, G. J.;
Kilburn, J. D.; Essex, J. W.; Mortishire-Smith, R. J.; Rowley,
M. J. Am. Chem. Soc. 1996, 118, 10220. Pernia, G. J.; Kilburn,
J. D.; Rowley, M. J. Chem. Soc., Chem. Commun. 1995, 305.
Waymark, C. P.; Kilburn, J. D.; Gillies, I. Tetrahedron Lett.
1995, 36, 3051. Snieckus, V.; Sharp, M. J. Tetrahedron Lett.
1985, 26, 5997. Chowdhury, S.; Georgihiu, P. E. Tetrahedron
Lett. 1999, 40, 7599. (b) For Suzuki coupling on solid support
using benzyl bromide: Han, Y.; Giroux, A.; Lepine, C.; Lali-
berte, F.; Huang, Z.; Perrier, H.; Bayly, C. I.; Young, R. N.
Tetrahedron 1999, 55, 11669.
References and Notes
7. Typical procedure for the Suzuki coupling reaction on solid
support: To a suspension of the resin (300 mg, 0.57 mmol/g,
0.17 mmol) in 1.5 mL of DME was added the boronic acid
(0.51 mmol), cesium ¯uoride (156 mg, 1.03 mmol) (Na2CO3 aq
2 M may also be used) and Pd(PPh3)4 (20 mg, 10 mol%). The
reaction mixture was stirred at 95 ꢀCfor 10 h and cooled to rt.
The mixture was then ®ltered and successively washed with
THF/H2O (1:1) (2Â), THF (2Â), CH2Cl2 (2Â) and MeOH
(2Â) and dried under high vacuum for 1 h. Cleavage: to the
resin was added 5 mL of a solution of 20% TFA in CH2Cl2.
The mixture was stirred 10 min at rt, ®ltered and evaporated
to dryness.
1. EP1: Funk, C. D.; Furci, L.; FitzGerald, G. A.; Gry-
gorczyk, R.; Rochette, C.; Bayne, M. A.; Abramovitz, M.;
Adam, M.; Metters, K. M. J. Biol. Chem. 1993, 268, 26767.
EP2: Regan, J. W.; Bailey, T. J.; Pepperl, D. J.; Pierce, K. L.;
Bogardus, A. M.; Donello, J. E.; Fairbairn, C. E.; Kedzie,
K. M.; Woodward, D. F.; Gil, D. W. Mol. Pharmacol. 1994,
46, 213. EP3: Adam, M.; Boie, Y.; Rushmore, T. H.; Muller,
G.; Bastien, L.; McKee, K. T.; Metters, K. M.; Abramovitz,
M. FEBS Lett. 1994, 338, 170. EP4: Bastien, L.; Sawyer, N.;
Grygorczyk, R.; Metters, K. M.; Adam, M. J. Biol. Chem.
1994, 269, 11873. DP: Boie, Y.; Sawyer, N.; Slipetz, D. M.;
Metters, K. M.; Abramovitz, M. J. Biol. Chem. 1995, 270,
18910. FP: Abramovitz, M.; Boie, Y.; Nguyen, T.; Rushmore,
T. H.; Bayne, M. A.; Metters, K. M.; Slipetz, D. M.; Gry-
gorczyk, R. J. Biol. Chem. 1994, 269, 2632. IP: Boie, Y.;
Rushmore, T. H.; Darmon-Goodwin, A.; Grygorczyk, R.;
8. The residual binding is the percentage of radiolabelled
PGE2 bound on the receptor when the drug is present.
9. All new compounds reported herein were characterized
(1H NMR, and MS) and gave satisfactory elemental analysis.