Synthesis of N-pyrimidinyl-2-phenoxyacetamides as adenosine A2A receptor antagonists

Article abstract of DOI:10.1016/j.bmcl.2008.02.032

A series of N-pyrimidinyl-2-phenoxyacetamide adenosine A_2A antagonists is described. SAR studies led to compound 14 with excellent potency (K_i = 0.4 nM), selectivity (A₁/A_2A > 100), and efficacy (MED 10 mg/kg po

Full text of DOI:10.1016/j.bmcl.2008.02.032

Available online at www.sciencedirect.com
Bioorganic & Medicinal Chemistry Letters 18 (2008) 1778–1783
Synthesis of N-pyrimidinyl-2-phenoxyacetamides
as adenosine A2A receptor antagonists
Xiaohu Zhang,a,* Jaimie K. Rueter,a Yongsheng Chen,a Manisha Moorjani,a
Marion C. Lanier,a Emily Lin,a Raymond S. Gross,a John E. Tellew,a John P. Williams,a
Sandra M. Lechner,b Stacy Markison,b Tanya Joswig,b Siobhan Malany,c Mark Santos,c
d
d
d
d
´
Julio C. Castro-Palomino, Marıa I. Crespo, Maria Prat, Silvia Gual,
d
a
a
´
´
Jose-Luis Dıaz, John Saunders and Deborah H. Slee
aDepartment of Medicinal Chemistry, Neurocrine Biosciences, 12790 El Camino Real, San Diego, CA 92130, USA
bDepartment of Neuroscience, Neurocrine Biosciences, 12790 El Camino Real, San Diego, CA 92130, USA
cDepartment of Pharmacology and Lead Discovery, Neurocrine Biosciences, 12790 El Camino Real, San Diego, CA 92130, USA
`
´
Department of Almirall Research Center, Almirall, Ctra. Laurea Miro, 408-410, E-08980 St. Feliu de Llobregat, Barcelona, Spain
d
Received 13 December 2007; revised 12 February 2008; accepted 13 February 2008
Available online 16 February 2008
Abstract—A series of N-pyrimidinyl-2-phenoxyacetamide adenosine A2A antagonists is described. SAR studies led to compound 14
with excellent potency (Ki = 0.4 nM), selectivity (A1/A2A > 100), and efficacy (MED 10 mg/kg po) in the rat haloperidol-induced cat-
alepsy model for Parkinson’s disease.
Ó 2008 Elsevier Ltd. All rights reserved.
Adenosine is an important modulator of physiological
functions. Four adenosine receptors (A1, A2A, A2B
viation of Parkinson’s disease symptoms in human
clinical trials.7
,
A3) have been identified, all of which belong to the fam-
ily of seven trans-membrane G-protein coupled recep-
tors (GPCRs).1 In the central nervous system the A2A
receptor is highly expressed in the stratium, where it is
co-localized with dopamine D2 receptors on striatopalli-
dal output neurons.2 Several pharmacological studies
suggest that the A2A receptor is involved in motor activ-
ity. In particular, adenosine A2A receptor antagonists
have been demonstrated to restore the deficits caused
by degeneration of the striatonigral dopamine system,
and therefore offer a possible treatment for Parkinson’s
disease.3 Extensive work has been done to achieve po-
tent and selective adenosine A2A receptor antagonists
in the past decade.4 Examples (Fig. 1) include non-xan-
thine-based SCH 582615 and ZM 241385,6 and xan-
thine-based KW-6002 (istradefylline), which was
shown to be effective in Parkinson’s disease animal mod-
els. More recently, KW-6002 showed efficacy in the alle-
Efforts in our laboratory to develop non-xanthine-based
A2A antagonists led us to a series of pyrimidine-based
potent A2A antagonists.8 However, the initial com-
pounds suffered from a lack of selectivity over the aden-
osine A1 receptor9,10 as exemplified by compound 1
(A2A Ki = 0.6 nM, A1 Ki = 9.2 nM, 17-fold selectivity,
Fig. 2). Furthermore, we wanted to replace the furan
moiety in the molecule in view of the potential metabolic
liabilities.11 SAR studies showed that the right hand
acetamide can be changed with a little loss of potency.
When a fluorobenzyl group was appended to the acetyl
group, modest selectivity was observed (compound 2,
A2A Ki = 16 nM, A1 Ki = 410 nM, 26-fold selectivity).
Surprisingly, changing the benzylic carbon to an oxygen
resulted in a large gain in selectivity (compound 3, A2A
Ki = 7.5 nM, A1 Ki = 650 nM, 87-fold selectivity).
In order to explore the influence of the substituents on the
phenol ring, we prepared a focused library (Scheme 1).
Keywords: Parkinson’s disease; A2A adenosine receptor antagonists.
*
The results (Table 1) showed that substitutions are well
tolerated, with potency ranging from 7 to 36 nM.
Corresponding author. Tel.: +1 858 829 2234; e-mail:
litiger_99@yahoo.com
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.02.032

X. Zhang et al. / Bioorg. Med. Chem. Lett. 18 (2008) 1778–1783
1779
NH2
O
N
N
N
O
N
N
O
N
N
N
N
O
O
N
KW-6002
SCH58261
NH2
HO
N
N
O
N
N
N
N
H
ZM241385
Figure 1. Representative A2A antagonists.
Table 1. Focused phenoxy library binding affinities
N
N
N
H
N
H
H
N
R
N
N
O
S
S
O
N
N
O
O
F
N
N
O
O
N
N
O
1
2
a
b
Compound
R
Ki (nM) hA2A
Ki (nM) hA1
N
H
N
4
7.4
1100
650
O
S
O
F
N
N
O
3
5
6
7.5
F
3
11
2200
1300
Figure 2.
F
F
>10,000
N
H
N
Cl
S
O
N
N
HO
+
7
8
6.8
14
4300
1500
R
CN
Cl
O
N
H
N
O
S
R
K2CO3/TBAI
9
36
2100
O
N
N
O
DMF
a Displacement of specific [3H]-ZM241385 binding at human A2A
expressed in HEK293.
40-60%
b Displacement of specific [3H]-DPCPX binding at human A1 receptors
expressed in HEK293 cells. Data are expressed as geometric means of
at least three runs with a standard deviation less than or equal to 20%.
Scheme 1. Focused phenoxy library synthesis.

1780
X. Zhang et al. / Bioorg. Med. Chem. Lett. 18 (2008) 1778–1783
O
N
O
N
O
ii
i
O
S
S
iii
NH2
NH
R1
R1
N
A
S
R2
N
OH
Cl
N
O
N
N
N
N
iv, v, vi
R1
R1
vi
R1
R2
N
S
O
N
NH2
HO
=
=
N
vii
N
NH2
N
N
A
N
iv, viii
N
N
N
R1
R1
Scheme 2. Reagents and conditions: (i) NaOMe, (1.1 equiv), NH4Cl, MeOH, rt 6–12 h, 96%; (ii) diethyl carbonate (5 equiv), NaH, 80 °C, 12 h, 56%;
(iii) KOt-Bu, (1.5 equiv), t-BuOH, 90 °C, 12 h, 50%; (iv) POCl3, DIPEA, 90 °C, 3–12 h, 66%; (v) NH4OH, MeOH, 80 °C, 12 h, 53%; (vi) chloroacetyl
chloride, pyridine, DCM, rt, 2–12 h, 60–85%; (vii) ethyl cyanoacetate, NaOMe, EtOH, 67%; (viii) N2H4, EtOH, 90 °C; pentane-2,4-dione, 0–90 °C,
2 h, 72%.
However, the selectivity was best with substituents at the
meta position (compounds 5, 7).
pound 18), and selectivity was 100- to 230-fold. Lar-
ger amino groups (e.g., compound 17) gave slightly
decreased potency, but selectivity improved to 500-
fold. A variety of other modifications were tolerated,
including addition of a second meta-substituent (com-
pounds 19, 20, 21), extension of the methylene spacer
(compounds 22, 23), and migration of the aminoalkyl
group to the ortho position, with or without addi-
tional substituents in the para position (compounds
24, 25, 26, 28). For the ortho-aminoalkyl series, addi-
tion of a second ortho substituent did result in a slight
decrease in potency (compound 27). With the amino-
alkyl group in the para position, both the potency and
selectivity were excellent with or without additional
substitutions (compounds 29–31). Aromatic heterocy-
cles were also tolerated as phenyl replacements.
Pyrimidine 32 was potent but had somewhat
poorer selectivity than the better phenyl compounds.
Pyridine 33, however, showed excellent potency and
selectivity.
Next we chose to explore the variations of the two het-
erocycles at the pyrimidine C-2 and C-6 positions
(Scheme 2).
We chose not to use an unsubstituted furan because of
its potential metabolic liabilities. The 5-methyl-2-furyl
group was used in this exercise since the methyl substitu-
tion on the furan substantially decreases the likelihood
of oxidative metabolism of the furan ring.11 The results
(Table 2) showed that all the heterocyclic combinations
led to potent antagonists (Ki 1.8–12 nM); however, the
methylfuran/dimethylpyrazole combination provided
the best selectivity (compound 10, Ki 3.7 nM, 2600-fold
selectivity).
Compound 10, although potent and selective, had poor
solubility (0.08 mg/mL, pH 5.0), as did most of its close
analogs. In order to improve solubility, we explored the
option of appending a basic amine to the phenol ring
(Scheme 3).
Despite the generally high potency and selectivity for
this class of compounds, a number of deficiencies were
revealed upon screening through secondary assays. For
example, the para-substituted aminoalkyl compounds
(29, 30) were found to be cytotoxic in cellular assays,
while the ortho-substituted compounds and the hetero-
cycle-substituted compounds displayed CYP inhibition
(e.g., compound 26, CYP3A4 IC50 = 1600 nM; com-
pound 33, CYP3A4 IC50 = 1100 nM, CYP2D6
IC50 = 50 nM)). The ortho-substituted aminoalkyl com-
pounds showed significant hERG inhibition (compound
We were pleased to find that this exercise led to a group
of antagonists with retained excellent potency and selec-
tivity (Table 3).
For the mono meta-substituted benzyl amino com-
pounds, it was clear that small amino groups were
favorable for A2A activity. The binding affinity ranged
from 0.3 nM (compounds 15, 16) to 0.7 nM (com-

X. Zhang et al. / Bioorg. Med. Chem. Lett. 18 (2008) 1778–1783
Table 2. Results of C-2 and C-6 heterocycle survey
1781
H
R2
N
O
X
O
N
N
R1
Compound
R1
R2
X
F
hA2A Ki
(nM)
hA1 Ki
(nM)
N
5
12
2200
O
O
O
O
N
N
S
N
7
CN
6.8
4300
9700
25,000
180
S
N
10
11
12
F
3.7
N
N
CN
>10,000
N
N
F
3.6
S
N
13
CN
1.8
87
S
See Table 1 footnotes.
28, hERG dofetolide competition binding assay
Ki = 180 nM).12 Ultimately, compound 14 demonstrated
the best overall profile for compounds in this series
(hERG patch-clamp IC50 = 1200 nM, CYP3A4 and
CYP2D6 IC50 > 6000 nM).13
dol-induced catalepsy model for Parkinson’s disease,
compound 14, dosed orally, showed significant inhibi-
tion of catalepsy with a minimum effective dose of
10 mg/kg.
In summary, we prepared a series of potent and selec-
tive adenosine A2A antagonists based on the N-pyri-
midinyl-2-phenoxyacetamide scaffold. The strategy of
introducing a solubilizing group onto the phenoxy moi-
ety succeeded in producing compounds with high po-
tency and selectivity, in addition to improved
solubility. The leading compound 14 was evaluated
in vivo and exhibited efficacy in the rat haloperidol-in-
duced catalepsy model with a minimum effective dose
of 10 mg/kg.
Compound 14 was chosen for further evaluation.
Compound 14 demonstrated improved solubility
(0.21 mg/mL, pH 5) compared with non-basic analogs
(e.g., compound 10), and was active at the rat A2A
receptor (Ki = 9.4 nM). When evaluated in a rat phar-
macokinetics study, it showed F% = 19%, Vd = 20 L/
kg and a half life of 0.8 h. Although plasma clearance
was rapid (330 mL/min kg), levels in the brain were
high, even after 4 h (360 ng/g). In the rat haloperi-

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X. Zhang et al. / Bioorg. Med. Chem. Lett. 18 (2008) 1778–1783
Table 3 (continued)
N
N
H
Compound
R
hA2A Ki
(nM)
hA1 Ki
(nM)
R
N
Cl
+
O
N
N
O
HO
H
O
R
17
1.2
600
N
O
N
H
i
N
N
O
H
O
N
N
O
O
18
0.7
73
NH2
R
F
N
H
N
N
Rb
19
0.5
140
O
N
ii
O
N
N
Ra
N
O
F
Scheme 3. Reagents: (i) DMF, K2CO3, TBAI, 40–60%; (ii) EtOH,
amine, BH3/pyridine, 60–90%.
20
0.5
120
N
Table 3. Binding affinities for aminoalkyl-substituted compounds
F
N
H
R
N
N
O
O
N
N
21
1.4
480
N
O
O
Compound
R
hA2A Ki
(nM)
hA1 Ki
(nM)
22
0.5
78
N
14
0.4
0.3
0.3
60
68
68
N
23
2.3
540
15
16
N
O
NH
24
1.0
270
N
N

X. Zhang et al. / Bioorg. Med. Chem. Lett. 18 (2008) 1778–1783
1783
Table 3 (continued)
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Compound
R
hA2A Ki
(nM)
hA1 Ki
(nM)
3. Suzuki, F.; Shimada, J. Adenosine Antagonist and
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25
1.0
270
N
N
O
26
0.9
200
6. (a) Vu, C. B.; Pan, D.; Peng, B.; Sha, L.; Kumarawel, G.;
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O
27
28
5.7
1.2
1400
1200
N
O
N
7. Jenner, P. Expert Opin. Investig. Drugs 2005, 14, 729.
8. (a) Slee, D. H.; Chen, Y.; Zhang, X.; Moorjani, M.;
Lanier, M. C.; Lin, E.; Rueter, J. K.; Gross, R. S.;
Williams, J. P.; Lechner, S. M.; Markison, S.; Malany, S.;
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M.; Malany, S.; Santos, M.; Ekhlassi, P.; Castro-Palo-
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N
29
30
0.3
0.2
120
100
N
O
9. Blockade of the adenosine A1 receptor could lead to
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A.; Skettino, S. L.; Beckman, E.; Belardinelli, L. Drug
Dev. Res. 1998, 45, 166; (b) Givertz, M.; Massie, B.;
Fields, T.; Pearson, L.; Ditrich, H. J. Am. Coll. Cardiol.
2007, 50, 1551.
N
31
0.3
150
O
10. Binding to the A2B and A3 receptors was not routinely
determined in this study.
N
32
33
3.7
0.7
95
11. (a) Dalvie, D. K.; Kalgutkar, A. S.; Khojasteh-Bakht, S.
C.; Obach, R. S.; O’Donnell, J. P. Chem. Res. Toxicol.
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3; (c) Kalgutkar, A. S.; Soglia, J. R. Expert Opin. Drug
Metab. Toxicol. 2005, 1, 91.
N
N
740
12. hERG activity is associated with an increased cardiovas-
cular safety risk: Jamieson, C.; Moir, E. M.; Rankovic, Z.;
Wishart, G. J. Med. Chem. 2006, 49, 5029.
See Table 1 footnotes.
Acknowledgments
13. hERG activity was routinely assessed using a dofetolide
competition binding assay. Key compounds were further
assayed in a patch clamp electrophysiology assay; for
details see: Slee, D. H.; Moorjani, M.; Zhang, X.; Lin,
E.; Lanier, M. C.; Chen, Y.; Rueter, J. K.; Lechner, S.
M.; Markison, S.; Malany, S.; Joswig, T.; Santos, M.;
Gross, R. S.; Williams, J. P.; Castro-Palomino, J. C.;
Crespo, M. I.; Prat, M.; Gual, S.; Jalali, K.; Sai, Y.;
Zuo, Z.; Yang, C.; Wen, J.; O’Brien, Z.; Petroski, R.;
Saunders, J. J. Med. Chem., in press.
We are indebted to Shawn Ayube, Chris DeVore, Paddi
Ekhlassi, and John Harman for analytical support.
References and notes
1. (a) Fredholm, B. B.; Abbraccio, M. P.; Burnstock, G.;
Daly, G. W.; Harden, T. K.; Jacobson, K. A.; Leff, P.;