3
582 J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 17
Letters
are in progress in our lab to better describe the role of
the extracellular domain on the ligand recognition
process. For confirmation of the high potency of this
compound in a functional assay, the inhibition of cAMP26
generation by Cl-IB-MECA in membranes of CHO cells
stably transfected with the human A3 receptor was
evaluated.
(9) Brambilla, R.; Cattabeni, F.; Ceruti, S.; Barbieri, D.; Franceschi,
C.; Kim, Y.; J acobson, K. A.; Klotz, K. N.; Lohse, M. J .;
Abbracchio, M. P. Activation of the A
3
adenosine receptor effects
cell cycle progression and cell growth. Naunyn-Schmiedeberg’s
Arch. Pharmacol. 2000, 361, 225-234.
(
10) Baraldi, P. G.; Cacciari, B.; Romagnoli, R.; Merighi, S.; Varani,
3
K.; Borea, P. A.; Spalluto G. A Adenosine receptor ligands;
history and perspectives. Med. Res. Rev. 2000, 20, 103-128.
11) Baraldi, P. G.; Cacciari, B.; Romagnoli, R.; Spalluto, G.; Klotz,
K.-N.; Leung, E.; Varani, K.; Gessi, S.; Merighi, S.; Borea, P. A.
Pyrazolo[4,3-e]1,2,4-triazolo[1,5-c]pyrimidine derivatives as highly
potent and selective human A adenosine receptor antagonists.
3
J . Med. Chem. 1999, 42, 4473-4478.
12) Baraldi, P. G.; Cacciari, B.; Romagnoli, R.; Spalluto, G.; Moro,
S.; Klotz, K. N.; Leung, E.; Varani, K.; Gessi, S.; Merighi, S.;
Borea, P. A. Pyrazolo[4,3-e]1,2,4-triazolo[1,5-c]pyrimidine de-
(
Consistent with its binding affinity, 4 showed an IC50
value of 0.7 ( 0.06 nM, compared to an IC50 of 2.10 (
0
.21 nM for 1. A Schild analysis of the antagonism of
(
(
(
2
6
the effects of 4 on Cl-IB-MECA -induced inhibition of
forskolin-stimulated cAMP was carried out (Figure 2).
1
9
rivatives as highly potent and selective human A
receptor antagonists: Influence of the chain at N
3
adenosine
pyrazole
A KB value of 0.20 ( 0.03 nM was calculated, thus
demonstrating 4 to be the most potent antagonist of the
human A3 receptor ever reported.
8
nitrogen. J . Med. Chem. 2000, 43, 4768-4780.
13) Baraldi, P. G.; Cacciari, B.; Moro, S.; Spalluto, G.; Pastorin, G.;
Da Ros, T.; Klotz, K.-N.; Varani, K.; Gessi, S.; Borea, P. A.
Synthesis, Biological Activity, and Molecular Modeling Inves-
tigation of New Pyrazolo[4,3-e]1,2,4-triazolo[1,5-c]pyrimidine
Con clu sion s. The present study revealed a novel,
potent, selective, and most importantly, water-soluble
hA3 adenosine receptor antagonist. This derivative
featured a basic 4-pyridylcarbamoyl moiety at the N5
position of the pyrazolotriazolopyrimidine nucleus, and
the corresponding hydrochloride salt 4 displayed a Ki
value of 0.01 nM at the hA3 and selectivities versus the
other adenosine receptor subtypes ranging from 10 000
to 35 000. This increase of affinity compared to neutral
arylcarbamate derivatives could be attributed in recep-
tor modeling to strong electrostatic interactions between
the pyridinium moiety of 4 and the side chain carbonyl
oxygen atoms of Asn274 and Asn278, both located on
TM7. In view of the potency, selectivity, and water
solubility, 4 could be an ideal candidate for pharmaco-
logical and clinical investigation of the hA3 adenosine
receptor subtype.
3
Derivatives as Human A Adenosine Receptor Antagonists. J .
Med. Chem. 2002, 45, 770-780.
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spectra of some unsymmetric N,N′-dipyridyl ureas: spectral
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1
(
(
(
15) Curtius, T.; Mohr, E. Transformation of nicotinic acid to beta-
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18) Lohse, M. J .; Klotz, K.-N.; Lindernborn-Fotinos, J .; Reddington,
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(
19) Ongini, E.; Dionisotti, S.; Gessi, S.; Irenius, E.; Fredholm, B. B.
Comparison of CGS 15943 and SCH 58261 as antagonist at
3
human A adenosine receptors. Naunyn-Schmiedeberg’s Arch.
Pharmacol. 1999, 359, 7-10.
(
20) Varani, K.; Merighi, S.; Gessi, S.; Klotz, K. N.; Leung, E.; Baraldi,
Ack n ow led gm en t. We thank the Regione Friuli
Venezia Giulia and the University of Trieste for finan-
cial support.
3
P. G.; Cacciari, B.; Spalluto, G.; Borea, P. A. [ H]MRE3008-F20:
a novel antagonist radioligand for the pharmacological and
biochemical characterization of human A adenosine receptors.
3
Mol. Pharmacol. 2000, 57, 968-975.
(
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3
receptors is associated with enhancement of
125I]-1-[6-[[(4-amino-3-iodophenyl)methyl]amino]-
AB-MECA, [
2
+
9H-purin-9-yl]-1-deoxy-N-methyl-â-D-ribofuranuronamide; THF,
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embryonic kidney; MRE3008-F20, 5-[[(4-methoxyphenyl)amino]-
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J M020974X