2-(2-Furanyl)-7-phenyl[1,2,4]triazolo[1,5-c]pyrimidin-5-amine analogs: Highly potent, orally active, adenosine A2A antagonists. Part 1

Article abstract of DOI:10.1016/j.bmcl.2005.05.086

The structure-activity relationship of this novel class of compounds based on 2-(2-furanyl)-7-phenyl[1,2,4]-triazolo[1,5-c]pyrimidin-5-amine, 1, and its analogs was evaluated for their in vitro and in vivo adenosine A_2A receptor antagonism. Several compounds displayed oral activity at 3 mg/kg in a rat catalepsy model. Specifically, compound 8g displayed an excellent in vitro profile, as well as a highly promising in vivo profile.

Full text of DOI:10.1016/j.bmcl.2005.05.086

Bioorganic & Medicinal Chemistry Letters 15 (2005) 3670–3674
2-(2-Furanyl)-7-phenyl[1,2,4]triazolo[1,5-c]pyrimidin-5-amine
analogs: Highly potent, orally active, adenosine
A2A antagonists. Part 1
Julius J. Matasi, John P. Caldwell, Hongtao Zhang, Ahmad Fawzi,
Mary E. Cohen-Williams, Geoffrey B. Varty and Deen B. Tulshian*
Department of Medicinal Chemistry—CV & CNS, Schering-Plough Research Institute,
2015 Galloping Hill Road, Kenilworth, NJ 07033, USA
Received 25 March 2005; revised 5 May 2005; accepted 11 May 2005
Available online 22 June 2005
Abstract—The structure–activity relationship of this novel class of compounds based on 2-(2-furanyl)-7-phenyl[1,2,4]-triazolo[1,5-
c]pyrimidin-5-amine, 1, and its analogs was evaluated for their in vitro and in vivo adenosine A2A receptor antagonism. Several com-
pounds displayed oral activity at 3 mg/kg in a rat catalepsy model. Specifically, compound 8g displayed an excellent in vitro profile,
as well as a highly promising in vivo profile.
Ó 2005 Elsevier Ltd. All rights reserved.
1. Introduction
kinsonian monkey without producing hyperactivity and
provoking dyskinesia.7 These results suggest that A2A
AR antagonists potentially represent a novel class of
Adenosine is a modulator of physiological functions
through activation of numerous cell surface receptors.
Four adenosine receptors (A1, A2A, A2B, and A3)
belonging to the family of G protein-coupled receptors
have been characterized according to their primary
sequences.1 A1 and A3 are coupled to inhibitory G pro-
tein while A2A and A2B are coupled to stimulatory G
protein. Adenosine A2A receptors (AR) are abundant
in specific regions of the brain, such as the striatum,
caudate-putamen, nucleus accumbens, and olfactory
tubercle.2 In the caudate-putamen A2A AR are localized
on several neurons and have been shown to modulate
the neurotransmission of c-aminobutyric acid acetylcho-
line and glutamate.3 These actions of the A2A AR could
contribute to motor behavior.4 For example, A2A AR
agonists have been shown to inhibit locomotor activity
and induce catalepsy in rodents.5 In contrast, A2A AR
antagonists prevent the motor disturbances seen in
dopamine D2 receptor null mice.6
anti-symptomatic drugs for the treatment of ParkinsonÕs
disease.
Several selective A2A AR antagonists of various struc-
tural classes have been developed.8 Based upon these
compounds SAR and our previous work, we proposed
to develop an SAR using structure 1 as a template to
identify novel A2A AR antagonists.9
The compounds shown in Table 1 were prepared using
the general procedures described in Scheme 1. Initially,
the Pd-catalyzed coupling of commercially available
2-amino-4,6-dichloropyrimidine with aryl boronic acids
yielded chlorides 2 which underwent displacement with
2-furoic hydrazide to produce 3. Dehydrative rear-
rangement10 of 3 in N0,O0-bis(trimethylsilyl)acetamide
Recently, KW-6002, an A2A AR antagonist, has been
reported to exhibit anti-parkinsonian activity in the par-
Keywords: Adenosine receptor; Antagonist; Arylindenopyrimidines.
*
Corresponding author. Tel.: +1 908 740 3505; fax: +1 908 740
7164; e-mail: deen.tulshian@spcorp.com
0960-894X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.05.086

J. J. Matasi et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3670–3674
Table 1. Optimization of C-7 arene substituents
3671
version of 4v to its corresponding chloride (7), fol-
lowed by displacement with the requisite amine, led
to compounds 8a-q as shown in Table 2. Requisite
amines that were not commercially available were pre-
pared as shown in Scheme 2. The appropriately
substituted bromophenols (9) were alkylated to form
their corresponding methoxyethoxyphenyl bromides
(10). Piperidines were prepared by the lithiation of
the aryl bromides 10 followed by addition to 4-oxo-pi-
peridine-1-carboxylic acid benzyl ester, deoxygenation,
and benzyl deprotection to yield piperidines 11. Piper-
azines (12) were prepared using a Pd-catalyzed amina-
tion with aryl bromides 10 and piperazine. All
compounds reported herein gave satisfactory analyti-
cal results.12
Compound
Ar
A2A Ki (nM)
A1/A2A
1
Ph
2-CH3-Ph
7.0
22.0
3.7
3
12
13
19
27
20
103
98
64
65
1
4a
4b
4c
4d
4e
4f
3-CH3-Ph
4-CH3-Ph
8.4
4.3
2-CH3O-Ph
3-CH3O-Ph
4-CH3O-Ph
2,4-(CH3O)2-Ph
3,4-(CH3O)2-Ph
2,5-(CH3O)2-Ph
2,6-(CH3O)2-Ph
2,3-(CH3O)2-Ph
3,4,5-(CH3O)3-Ph
2,3,4-(CH3O)3-Ph
2-Thiophene
4-Pyridine
5.0
7.3
4g
4h
4i
2.9
7.3
The in vitro results of the A2A AR binding assays13 are
expressed as inhibition constants (Ki, nM) and A1/A2A
describes the selectivity over the A1 AR. All assays were
performed in duplicate and reported as mean values.
These compounds were not tested against the other
known adenosine receptor subtypes, A3 and A2B. Re-
sults in Table 1 show that compound 1 had a high affin-
ity for A2A AR but was not selective over A1 AR. The
tolyl analogs (4a–c) retained the affinity for A2A AR
but failed to improve desired selectivity. The methoxy
phenyl analogs (4d–m) provided compounds with high
affinity for A2A AR with moderate to good selectivity
over A1 AR. One exception was compound 4j which
had very poor affinity for A2A AR, suggesting that
orthogonality between the arene and the triazolopyrim-
idine ring system was not tolerated. Heteroaromatic
analogs (4n–q) also retained single-digit nanomolar
potency for A2A AR with no improvement in selectivity
over the A1 AR.
4.5
4j
1700
21.7
4.5
4k
4l
27
69
17
15
66
65
34
31
82
11
14
135
4m
4n
4o
4p
4q
4r
4s
4t
4.5
4.4
1.9
6.6
3-Pyridine
2-Pyridine
3-(i-Pr)-Ph
3-(Ph)-Ph
1.4
4.7
5.5
5.0
3-(NH2)-Ph
3-(CN)-Ph
3-(CH2OH)-Ph
4u
4v
5.4
2.8
(BSA) produced structures of type 4. Alternatively, 2-
amino-4,6-dichloropyrimidine can be displaced with
2-furoic hydrazide to form 5 followed by the dehydra-
tive rearrangement to provide 6 as an advanced inter-
mediate.11 Subsequent Pd-catalyzed couplings of 6
with various aryl boronic acids yielded compounds
4a–v.
Meta-substituted compounds, 4r–v, retained single-
digit nanomolar A2A AR affinity and acceptable
selectivity over A1; particularly compound 4s, which
was 82-fold selective. Results of compound 4s demon-
strated the possibility of exploring the SAR via mod-
ifications of the side chains at the meta-position of
Synthesis of compounds shown in Table 2 originated
from the 3-(hydroxymethyl)phenyl analog (4v). Con-
Scheme 1. Reagents: (a) aryl boronic acid, Pd(PPh3)4, K2CO3, CH3CN/H2O (23–70%); (b) 2-furoic hydrazide, BuOH; (c) BSA (28%); (d) Et3N,
SOCl2, CH2Cl2; (e) KI, K2CO3, CH3CN, amine.

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J. J. Matasi et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3670–3674
Table 2. Receptor affinity and in vivo activity of side chain variants
Compound
R
A2A Ki (nM)
A1/A2A
135
Anti-cataleptic activity 1 h/4 h
NT
8a
3.6
8b
8c
8d
4.6
7.4
8.9
69
115
202
NT
20/20
0/0
8e
8f
4.6
10.5
2.8
69
3
NT
NT
8g
8h
601
115
40/65
29/53
4.0
8i
8j
2.7
2.9
642
204
20/0
12/15
8k
8l
3.3
2.7
3.6
1.1
134
72
33/39
NT
8m
8n
85
NT
314
14/9

J. J. Matasi et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3670–3674
3673
Table 2 (continued)
Compound
R
A2A Ki (nM)
A1/A2A
Anti-cataleptic activity 1 h/4 h
8o
6.4
71
NT
8p
8q
2.2
2.4
338
192
28/47
20/10
Scheme 2. Reagents: (a) CH3OCH2CH2Br, K2CO3, acetone (80%); (b) i—n-BuLi, THF, ii—4-oxo-piperidine-1-carboxylic acid benzyl ester; (c)
Et3SiH, TFA, CH2Cl2 (72%); (d) 10% Pd/C, H2, EtOAc/EtOH (99%); (e) Pd(OAc)2, NaOtBu, Pd(tBu)3, toluene.
compound 1. The result of this work is summarized
in Table 2.
oral activity at 3 mg/kg in a rat catalepsy model. Among
these compounds, 8g displayed optimum binding, selec-
tivity, and anti-cataleptic activity.
Side chain modifications (Table 2) produced several
compounds with high affinity for A2A AR and excel-
lent selectivity over A1 AR. Substitution of the
meta-position of the phenyl with either 4-(phenyl)-pi-
peridine (8b–d) or 4-(phenyl)-piperazine derivatives
(8e–q) was well tolerated. The incorporation of the
methoxethoxy substituent, as in 8g (A1/A2A = 601)
and 8h (A1/A2A = 115), seemed particularly beneficial
in terms of selectivity over A1 when compared with
phenylpiperazine analog 8e (A1/A2A = 69).
2. Catalepsy procedure
The rodent model for ParkinsonÕs Disease is the rat
catalepsy assay where the dopamine D2 receptor
antagonist, haloperidol (1 mg/kg, subcutaneous), is
administered. After 30 min, rats were placed facing up-
wards on a wire screen inclined at 60°. The time taken
for the rat to move one limb was measured, with a
cut-off time of 120 s. Rats showing >75 s of immobility
(catalepsy) were used for subsequent A2A antagonist
studies. Test compounds were administered orally and
catalepsy was retested at 1 and 4 h after administration.
Male CD rats (Charles River Laboratories) weighing
200–240 g were used for all studies. Upon arrival at
our holding facility, rats were housed 4 per cage, with
food and water available ad libitum. Rats were main-
tained on a 12-h light/dark cycle (light on 07:00; lights
off 19:00). All studies were carried out in accordance
with the National Institute of Health Guide for the Care
and Use of Laboratory Animals.
Several compounds from Table 2 were assessed for their
bioavailability and anti-cataleptic activity in the rat at
an oral dose of 3.0 mg/kg. In general, piperazine analogs
displayed better bioavailability than piperidine analogs.
Many of these compounds showed modest to high activ-
ity in the rat catalepsy assay at a 3 mg/kg dose. Brain
concentration of some of these compounds was mea-
sured at 6 h and found to be in 40–50 ng range. Gener-
ally, there was no apparent correlation between their
bioavailability and anti-cataleptic activity. Receptor
occupancy studies are planned to understand this
discrepancy.
The exploration of SAR of 2-(2-furanyl)-7-phen-
yl[1,2,4]triazolo[1,5-c]pyrimidin-5-amine analogs result-
ed in a novel class of A2A AR antagonists. Compared
to compound 1, several analogs with high selectivity
for A1 AR with retention of A2A binding affinity were
identified. Several of these compounds demonstrated
Acknowledgment
We thank Dr. William Greenlee for his support of this
work. We would also like to thank Lisa Silverman and
Zheng Tan for their help in the preparation of the
manuscript.

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J. J. Matasi et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3670–3674
(c) Vu, C. B.; Pan, D.; Peng, B.; Sha, L.; Kumaravel, G.; Jin,
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