Discovery of 2-aminoimidazole and 2-amino imidazolyl-thiazoles as non-xanthine human adenosine A3 receptor antagonists: SAR and molecular modeling studies

Article abstract of DOI:10.1039/c7md00643h

A small-molecule combinatorial library of 24 compounds with 2-aminoimidazole and 2-aminoimidazolyl-thiazole derivatives was synthesized using a 2-chloro trityl resin. The generated compound library was tested against all the human adenosine receptors subt

Full text of DOI:10.1039/c7md00643h

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RESEARCH ARTICLE
Discovery of 2-aminoimidazole and 2-amino
imidazolyl-thiazoles as non-xanthine human
adenosine A3 receptor antagonists: SAR and
molecularmodeling studies†
Cite this: DOI: 10.1039/c7md00643h
Amit N. Pandya,a Arshi B. Baraiya,a Hitesh B. Jalani,a Dhaivat Pandya,a
c
Jitendra C. Kaila,a Sonja Kachler,b Veronica Salmaso,c Stefano Moro,
Karl-Norbert Klotzb and Kamala K. Vasu
*
a
A small-molecule combinatorial library of 24 compounds with 2-aminoimidazole and 2-aminoimidazolyl-
thiazole derivatives was synthesized using a 2-chloro trityl resin. The generated compound library was
tested against all the human adenosine receptors subtypes. The 2-aminoimidazole derivatives (6a–6l)
showed weak to moderate affinity towards the human adenosine receptors. Further modification to
2-aminoimidazolyl-thiazole derivatives (12a–12l) resulted in an improvement of affinity at adenosine A1, A2A
and A3 receptor subtypes. Compound 12b was the most potent and selective non-xanthine human adeno-
sine A3 receptor antagonist of this series. A receptor-based modeling study was performed to explore the
possible binding mode of these novel 2-aminoimidazole and 2-aminoimidazolyl-thiazole derivatives into
human adenosine A1, A2A and A3 receptor subtypes.
Received 22nd December 2017,
Accepted 27th February 2018
DOI: 10.1039/c7md00643h
rsc.li/medchemcomm
Many of these compounds are based on a xanthine structure
such as caffeine and theophylline which were the first antago-
Introduction
Adenosine is a modulator of multiple physiological processes,
including cardiovascular, neurological and respiratory func-
tions. In recent years the search for novel adenosine receptor
agonists or antagonists has intensified. Adenosine mediates
its effects through specific G-protein-coupled receptors ubiq-
uitously expressed in the body and classified as A1, A2A, A2B
and A3 (ARs).1,2 The A3 AR is able to inhibit forskolin- or
nists to be found for adenosine receptors. The problems asso-
ciated with the xanthine-based compounds, namely, poor re-
ceptor selectivity, poor solubility, and low bio-availability,
receptor-mediated
cAMP
accumulation,
to
increase
phosphatidylinositol-specific phospholipase C and D activity,
and to elevate IP3 and intracellular Ca2+ levels.1 Furthermore,
the A3 AR subtype has been subject to intensive investigation
as a potential therapeutic target in conditions such as inflam-
mation,3 neurodegeneration,4,5 ischaemia,6–8 asthma,9,10
glaucoma11–13 and cancer.14–17 Numerous compounds were
synthesized and tested as adenosine receptor antagonists.
a Department of Medicinal Chemistry, B. V. Patel Pharmaceutical Education and
Research Development (PERD) Centre, Sarkej-Gandhinagar Highway, Thaltej,
Ahmedabad 380e054, Gujarat, India. E-mail: kamalav@perdcentre.com,
kamkva@gmail.com
b Institut für Pharmakologie und Toxikologie, Julius-Maximilians-Universität
Würzburg, Germany
c Molecular Modeling Section (MMS), Dipartimento di Scienze Farmaceutiche,
Università degli Studi di Padova, via Marzolo 5, 35131 Padova, Italy
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c7md00643h
Fig. 1 Potent and selective adenosine receptor antagonist.
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necessitated the search for non-xanthine-like compounds.18
Thus compound KF26777 was found to be a potent and selec-
tive adenosine A3 receptor antagonist by Kyowa Hakko Kogyo
for the treatment of asthma19 while tricyclic compound OT-
7999 is a selective adenosine A3 receptor antagonist reported
by Otsuka Pharmaceutical Factory, Inc, investigated as a treat-
ment for glaucoma.11 Further, Novartis developed a series of
2-aminothiazole based compounds out of which CGH2466
was a potent ligand for adenosine A1 and A3 receptors, with
no binding activity at the A2A receptor.20 The QAF805 com-
pound was found to be an orally bioavailable dual adenosine
trig cyclization 4 to give resin bound aminoimidazole deriva-
tives 5. Cleavage of
5 from the solid support with
trifluoroacetic acid provides 2-aminoimidazoles 6 (Scheme 1).
Binding affinities of 2-aminoimidazole derivatives for human
adenosine receptors
All the synthesized compounds (6a–6l, Table S1 ESI†) were
tested in radioligand binding assays to determine their affin-
ity for the adenosine A1, A2A, and A3 receptor subtypes. The
data show that this series of compounds does not bind with
measurable affinity to A1and A2B receptors. No measurable
interaction with A2B receptors was observed in concentrations
up to 30 μM (Table S1†).
A2B/A3 receptor antagonist with therapeutic potential in
asthma and COPD21 (Fig. 1).
However, moderate affinity for A3 receptors (6e–6j). Com-
pound (2-amino-1-(4-(trifluoromethyl)phenyl)-1H-imidazol-5-
yl)IJ4-chlorophenyl) methanone (6g) showed the highest affin-
ity among aminoimidazole series of compounds. (Table S1†).
It was the only compound that also bound with moderate af-
finity to the A2A receptor. The presence of 4-chloro in aryl ke-
tone (R2) and 4-trifluromethyl in N-aryl (R1) substituents in
(6g) of 2-aminoimidazole core was found to be important for
the affinity towards the A3 adenosine receptor. The presence
of a chloro substituent at 2 or 3 positions (6h, 6i) in N-aryl
(R1) was also found to be significant to enhance affinity to-
wards adenosine A3 receptor. However, the presence of 4-Me,
4-OMe, 4-SO2Me and 4-pyridyl substituents in aryl ketone (R2)
and 4-fluoro, 4-chloro substituents (6a–6e) in N-aryl (R1)
found to have deleterious effect on adenosine receptor affini-
ties. The 2-aminoimidazole series (Table S1†) did not show
Results and discussion
Chemistry and SAR of aminoimidazole and aminoimidazolyl-
thiazole derivatives
Our aim was to develop novel non-xanthine based antago-
nists for adenosine receptor subtypes. More specifically, our
efforts were based on small heterocyles like 2-aminothiazoles
and 2-aminoimidazoles derivatives since these five-member
heterocycles have been extensively used in the successful de-
sign of drugs/drug-like candidates. These rings can pack a
relatively large number of polarized bonds in a relatively
small molecular space and offer a convenient framework to
which various side chains can be attached. Recently, our
group has reported a series of 2-aminothiazole derivatives as
potent and selective adenosine receptor antagonist.22,23 In
fact, we have delineated the minimum structural features for
the compounds to be active against the adenosine receptors
by substituting 2-aminothiazole scaffold, with aroyl and
heteroaryl moiety at the 5 position. In continuation of our
findings, we herein report the structure–activity relationships
of novel 2-aminoimidazole and 2-aminoimidazolyl-thiazole de-
rivatives with high affinity and selectivity for A3 adenosine re-
ceptors. Initially, we synthesized a series of compounds with
a 2-aminoimidazole scaffold bearing an aroyl substitution in
5-position and investigated the pharmacological characteris-
tics in radio ligand binding studies at adenosine receptor
subtypes with the aim to obtain potent and selective adeno-
sine A3 receptor ligands. However, this series turned out to
possess only weak to moderate affinity. Further, the incorpo-
desired
affinity
as
their
previously
investigated
2-aminothiazole congeners22–24 but shows some good affinity
towards the A3 receptor (6e, 6h–j). We hypothesized that re-
placing the aryl/pyridyl (R2) group with substituted
2-aminothizoles at 5 position of 2-aminoimidazole leading to
aminoimidazolyl-thiazoles would be of therapeutic interest
and thus synthesized such molecules.
Series 2 – aminoimidazolyl-thiazole
In order to prepare 2-aminoimidazolyl-thiazole derivatives,
first step was the synthesis of (2-chloroacetyl) thiazoles (10).
Reaction of substituted isothiocynates 7 with amidines 8 was
carried out at room temperature to yield amidinothioureas 9
in good to high yields. 9 On further reaction with excess of
dichloroacetone gave (2-chloroacetyl) thiazoles 10 in good
yields (Scheme 2).
ration of
a
thiazolyl moiety at 5-position of the
2-aminoimidazole scaffold improved the affinity and selectiv-
ity towards the adenosine receptor subtypes.
To synthesize the desired compounds 12a–l, reaction of
(2-chloroacetyl) thiazoles 10 was carried out with resin bound
Series 1 – aminoimidazoles
The solid phase synthesis of 2-aminoimidazole library was
carried out using the 2-chlorotrityl chloride resin. The resin
amidinoguanidine
(Scheme 3).
3
to give 2-aminoimidazolyl-thiazole
was treated with amidinothiourea
1
in presence of
diisopropylethylamine (DIPEA) to give resin bound amidino-
thiourea 2. Guanylation of 2 with various arylamines using
Mukaiyama's reagent gave amidinoguanidines 3. The
amidinoguanidines 3 thus obtained on reaction with a series
of α-bromoketones undergo N-alkylation followed by 5-exo-
Binding affinities of 2-aminoimidazolyl-thiazole derivatives
for human adenosine receptors
The binding affinities for the 2-aminoimidazolyl-thiazole se-
ries are summarized in Table 1. In general, the replacement
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Scheme 1 Synthesis of 2-aminoimidazole derivatives.
Scheme 2 Preparation of (2-chloroacetyl) thiazoles 10.
Scheme 3 Synthesis of 2-aminoimidazolyl-thizole derivatives.
of aryl/pyridyl substituent (R2) (Scheme 1) to thiazole deriva-
tives (Scheme 2) at 5-position of the 2-aminoimidazole scaf-
fold significantly improved the affinity for A1, A2A and A3
adenosine receptors. No measurable interaction with A2B re-
ceptors was observed in concentrations up to 10 μM
(Table 1). Compounds 12a–c and 12f showed 20–40 fold se-
lectivity toward the A3 receptor. We identified compound 12b
as most potent and selective structure in this series with a Ki-
value of 0.19 μM at the A3 receptor. Compound 12b is be-
tween 40 and 200 fold selective compared to A2A and A1 re-
ceptors, respectively.
To study the minimum structural requirement of the com-
pounds to be selective for the A3 receptor, N-aryl (R6) substi-
tution of 2-aminoimidazole scaffold was kept constant as
Scheme 1 and systematic modification of aminothiazole moi-
ety was carried out. Diverse substituents like phenyl, benzoyl,
aryl, morpholine at the amino position of thiazole (R3) and
methyl, N,N-dimethyl, phenyl at thiazole (R4) were intro-
duced. All the compounds with phenyl substituent (12a–12c),
(12g), (12i), (12l) showed high affinity and selectivity towards
the adenosine A3 receptor compared all other subtypes. Fur-
ther, introduction of 4-chloro (12i–12j) and 4-methyl (12f)
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Table 1 Binding affinities of 2-aminoimidazolyl-thiazole derivatives for human adenosine receptors
Binding experiments Ki (μM)
Adenylyl cyclase activity Ki (μM)
a
b
c
d
Compound
R6
R4
R3
hA1
hA2A
hA3
hA2B
12a
4-OMe–C6H4
CH3
C6H5
48.6
(35.4–66.7)
39.2
(33.2–46.2)
6.71
(5.59–8.05)
25.4
(19.8–32.6)
19.7
(18.2–21.3)
37.5
(30.1–46.7)
3.67
(2.67–5.10)
>100
13.4
(9.24–19.4)
8.04
(6.45–10.0)
7.41
(4.33–12.7)
11.8
(7.70–18.1)
16.7
(11.9–23.5)
12.4
(8.84–17.5)
8.84
(6.64–11.8)
>100
0.574
(0.403–0.816)
0.190
(0.154–0.234)
0.305
(0.268–0.347)
4.32
(3.50–5.33)
4.92
(3.96–6.10)
0.487
(0.311–0.76)
0.326
(0.244–0.435)
13.0
(10.9–15.5)
0.871
0.825–0919
1.60
(1.54–1.65)
17.8
(15.4–20.6)
0.802
>10
>10
>10
>10
>10
>10
>10
>10
>10
>10
>10
>10
12b
12c
12d
12e
12f
12g
12h
12i
4-F–C6H4
CH3
Ph
C6H5
4-F–C6H4
C6H5
4-Cl–C6H4
4-CF3–C6H4
4-F–C6H4
NIJCH3)2
NIJCH3)2
CH3
Ph
COC6H4
COC6H4
4-Me–C6H4
C6H5
4-OMe–C6H4
4-OMe–C6H4
4-F–C6H4
Ph
—
CH3
CH3
Ph
4-Cl–C6H4
4-Cl–C6H4
—
19.8
(19.1–20.6)
33.3
(32.0–34.6)
>100
13.0
(11.8–14.3)
10.3
(8.07–13.1)
34.0
(24.1–48.0)
11.2
12j
4-OMe–C6H4
4-Me–C6H4
4-Cl–C6H4
12k
12l
CH3
C6H5
33.5
(33.3–33.7)
(8.82–14.2)
(0.673–0.958)
a
Data are expressed as geometric means, with 95% confidence limits in parentheses. Displacement of specific [3H]CCPA binding at human A1
b
c
receptors expressed in CHO cells. Displacement of specific [3H]NECA binding at human A2A receptors expressed in CHO cells. Displacement
of specific [3H]HEMADO binding at human A3 receptors expressed in CHO cells. Inhibition of NECA-stimulated adenylyl cyclase activity at
d
human A2B receptors expressed in CHO cells.
substitution to phenyl ring did not show significant improve-
ment in affinity towards A1, A2A and A2B receptors but decreases
selectivity towards the A3 receptor. Further, replacement by
benzoyl (12d, 12e) and morpholine (12h, 12k) group was also
found to significantly decrease selectivity for the A3 receptor.
ing those poses that minimize electrostatic and van der Waals
interaction values. Most favorable poses of all compounds on
A3, A2A and A1 ARs are shown in Videos SM1–SM3, included in
ESI.† With regard to the A1 AR, it was impossible to find a com-
mon binding mode for the various ligands, but this was not
surprising given the low affinity of the compounds for A1 AR.
Compound 12b was chosen as representative of the
2-aminoimidazolyl-thiazole series for a detailed description,
because of its pronounced selectivity toward A3 (0.19 μM)
over A2A (8.0 μM) and A1 (39.2 μM) receptors, as reported in
Table 1. The suggested binding mode to the A3 AR (Fig. 2,
panel A) shows compound 12b spanning the binding pocket
from top to bottom with the 2-phenyl-amino-thiazole portion
facing TM6, TM5 and TM7 and the 2-aminoimidazolyl portion
pointing toward TM7 and TM2. The compound realizes a
double hydrogen bond with Asn6.55, as anticipated by the
strong electrostatic contribution of that residue in the IEFs
reported in Fig. 2, panel B. The hydrogen bonds engage the
endocyclic nitrogen atom of thiazole as acceptor and the exo-
cyclic amine nitrogen as donor. The thiazole ring is stabilized
Molecular modeling study
A structure-based molecular modeling study was conducted
to rationalize the compounds' selectivity profile toward hu-
man A3 adenosine receptor (AR) over the other ARs subtypes,
using a very well consolidated in-house docking pipeline.25–29
The study was focused on human A1, A2A and A3 subtypes,
since no binding data were available for A2B. Functional data
from adenylyl cyclase experiments suggested that no detect-
able interaction of the studied compounds occurs with the
A2B AR. Docking was performed for all compounds on the
three receptors, and the resulting poses were evaluated
according to van der Waals and electrostatic interactions. For
each ligand one pose was selected by visual inspection, promot-
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Fig. 2 Panels A–E: Representation of the most favorable docking poses of compound 12b on A3, A2A and A1 adenosine receptors, respectively. The
compound is depicted by light-blue sticks, the backbone of the receptor is represented by a transparent light-gray ribbon and most relevant resi-
dues are rendered by gray sticks. Helix TM6 is not shown in order to make the visualization of the binding site more clear. The crystallographic
conformation of 4-(3-amino-5-phenyl-1,2,4-triazin-6-yl)-2-chlorophenol is reported and rendered by orange sticks. For A1 and A3 models, the
same ligand is obtained from the superimposition of A2A AR crystallographic structure (PDB ID: 3UZC) to the models. Panel B–F: Interaction energy
fingerprints (IEFs) of compound 12b on A3, A2A and A1 receptors, respectively. The upper heat map represents IEele fingerprints, with electrostatic
interactions strength rendered by blue to red colors for low to high potential values. The lower heat map represents IEhyd fingerprints, with hydro-
phobic interactions strength rendered by light to dark green colors for low to high potential values.
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by a π–π stacking interaction with Phe168IJEL2). The com-
pound is involved in a series of strong hydrophobic interac-
tions, as reported by IEFs in Fig. 2, panel B, among which
Phe168IJEL2) emerges as more intense. Phe168IJEL2),
Val169IJEL2), Leu6.51, Ile6.58, Val259IJEL3) and Leu7.35 form a
hydrophobic cleft which hosts the 1-(4-F-phenyl)-2-
aminoimidazolyl scaffold, while Val2.57, Leu2.60, Val2.64,
Leu3.32 and Ile7.39 define a pocket that could accommodate
thiazoles led to discovery of compound 12b with nanomolar
affinity against adenosine A3 receptor and 40 to 200-fold se-
lectivity versus the other adenosine receptor subtypes. The
molecular modelling study of compound 12b gave detailed
insight into receptor conformations for the lead optimiza-
tion, which will help to guide further development of the
2-aminoimidazolyl-thiazole series.
the 1-(4-F-phenyl)-2-aminoimidazolyl portion. A similar bind- Experimental
ing mode and interaction pattern is shared by further com-
pounds with sub-micromolar binding affinity for A3 AR, such
as compounds 12c, 12f, 12g, as can be noticed by Video
SM1.†
General remarks
All reagents were purchased from Sigma-Aldrich. All
chemicals were reagent grade and used without further puri-
1
fication. The H NMR and 13C NMR spectra were recorded on
Compound 12b presents a similar conformation within
the binding site of A2A receptor (Fig. 2, panel C). The 2-amino
thiazole scaffold is confirmed in its double hydrogen bond
interaction pattern with Asn6.55, while the 1-(4-F-phenyl)-2-
aminoimidazolyl portion is rotated by almost 90 degrees. For
both A2A and A3 receptors, the selected conformation of the
compound resembles the one assumed by 4-(3-amino-5-
phenyl-1,2,4-triazin-6-yl)-2-chlorophenol co-crystallized to A2A
AR (PDB ID: 3UZC), with the 2-amino-thiazole structure mim-
icking the 3-amino-trazine scaffold (Fig. 1, panel A and C).
The interaction network reported for A2A AR by the IEFs
(Fig.2, panel D) confirms many of the interactions encoun-
tered for A3: these involve the conserved residues Leu6.51,
Ile7.39 and Phe168 (EL2) for hydrophobic interactions, and
Asn6.55 for electrostatic ones. However, some hydrophobic
interactions lack: positions of Val2.57, Val169IJEL2), Ile6.58,
Val259IJEL3), Leu7.35 are occupied by the less hydrophobic
Ala2.57, Glu169IJEL2), Thr6.58, Ala265IJEL3), Met7.35 on A2A
AR, respectively. This may support the drop of binding affin-
ity for A2A in comparison to A3, suggesting that these non-
conserved residues may play a role in driving binding selec-
tivity of compound 12b. Indeed, also in A1 AR, Val169IJEL2),
Ile6.58, Val259IJEL3), Leu7.35 are substituted by even more
polar residues, Glu172IJEL2), Thr6.58, Lys265IJEL3) and
Thr7.35, implying a general loss of the hydrophobic binding
contribution. With regard to A1 AR, among the poses pro-
posed by docking it was impossible to find a conformation
similar to the ones just described for the other receptor sub-
types. In the selected pose (Fig. 2, panel E), the conformation
of the compound within the binding site is driven by the
presence of Glu172 on EL2, which engages in a hydrogen
bond the exocyclic amine nitrogen atom at position 2 of
thiazole.
Bruker spectrometer (1H: 300 MHz, 13C: 75 MHz) using TMS
as an internal standard. Mass spectra were recorded on
Perkin Elmer Sciex API 165.
General procedure for preparation of solid phase synthesis
2-aminoimidazole derivatives (6a–6l)
2-Chlorotrityl resin (1 mmol) was loaded with DMF (10 mL)
and stirred. Monosubstituted thiourea 1 and DIPEA were
added and the stirring continued for 2 h. Repeated washing
of resin with DCM, DMF, THF (4 × 10 ml mmol−1) was carried
out in order to remove unbound monocondensed thiourea.
Further, guanylation of amidinothiourea with different
arylamines was carried out with Mukaiyama's reagent in
DMF and stirred for 30 minutes to generate resin bound
amidinoguanidine. Excess of reagent was removed by re-
peated washing of DCM, DMF, THF (4 × 10 ml mmol−1). Cy-
clization of resin bound amidinoguanidine was carried out
by phenacyl bromide in presence of DBU to give resin bound
2-aminoimidazole derivatives. The resin was cleaved using
10% TFA in DCM to give final compound with good to high
yield.
(2-Amino-1-(4-fluorophenyl)-1H-imidazol-5-yl)IJp-tolyl)-
methanone (6a). Yield: 70%, pale yellow solid, mp: 195–197
1
°C; H NMR (300 MHz, DMSO-d6, ppm) δ: 7.71–7.68 (m, 2H),
7.36–7.32 (m, 3H), 7.28–7.15 (m, 4H), 5.49 (s, 2H), 2.40 (s,
3H); 13C NMR (75 MHz, DMSO-d6, ppm) δ: 182.05, 164.0,
160.70, 153.79, 142.44, 140.54, 136.04, 131.71, 128.92, 127.83,
116.79, 116.48, 21.46; C17H14FN3O, exact mass 295.11; LC-ESI-
MS/MS: 296.6 [M + 1]+.
(2-Amino-1-(4-fluorophenyl)-1H-imidazol-5-yl)IJ4-methoxy-
phenyl)methanone (6b). Yield: 72%, pale yellow solid, mp:
1
178–180 °C; H NMR (300 MHz, DMSO-d6, ppm) δ: 7.83–7.77
(m, 2H), 7.39–7.33 (m, 3H), 7.26–7.17 (m, 2H), 6.95–6.92 (m,
2H), 4.94 (s, 2H), 3.87 (s, 3H); 13C NMR (75 MHz, DMSO-d6,
ppm) δ: 181.38, 164.12, 162.80, 160.81, 153.16, 140.0, 131.41,
130.94, 128.98, 116.91, 116.60, 113.59, 55.42; C17H14FN3O2.
Exact mass: 311.11; LC-ESI-MS/MS: 312.2 [M + 1]+.
Conclusions
In conclusion, the present study involves a synthesis of small
compound
library
of
24
2-aminoimidazole
and
2-aminoimidazolyl-thiazole derivatives using a 2-chloro trityl
resin to explore the SAR. All the compounds were tested for
their affinity at A1, A2A, A2B and A3 adenosine receptors. Com-
pounds with 2-aminoimidazole scaffold did not result in good
affinity. However, further modification to 2-aminoimidazolyl-
(2-Amino-1-(4-fluorophenyl)-1H-imidazol-5-yl)
(4-chlorophenyl)methanone (6c). Yield: 78%, pale yellow
solid, mp: 230–232 °C; H NMR (300 MHz, DMSO-d6, ppm) δ:
7.74–7.71 (m, 2H), 7.43–7.40 (m, 2H), 7.37–7.33 (m, 3H),
7.24–7.18 (m, 2H), 5.20 (s, 2H); 13C NMR (75 MHz, DMSO-d6,
1
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ppm) δ: 180.88, 164.21, 160.90, 153.88, 141.19, 138.14,
131.50, 130.10, 129.02, 127.73, 116.96, 116.68; C16H11ClFN3O
exact mass: 315.06; LC-ESI-MS/MS: 316.3 [M + 1]+.
(2-Amino-1-(4-fluorophenyl)-1H-imidazol-5-yl)IJpyridin-4-yl)-
methanone (6l). Yield: 76%, yellow solid, mp: 236–239 °C; H
NMR (300 MHz, DMSO-d6, ppm) δ: 8.71–8.65 (m, 2H), 7.71–
7.68 (m, 2H), 7.61–7.57 (m, 2H), 7.45 (s, 1H), 6.98–6.87 (m,
2H), 5.27 (s, 2H); C15H11FN4O exact mass: 282.09; LC-ESI-MS/
MS: 283.4 [M + 1]+.
1
(2-Amino-1-(4-chlorophenyl)-1H-imidazol-5-yl)
(p-tolyl)-
methanone (6d). Yield: 68%, pale yellow solid, mp: 195–197
1
°C H NMR (300 MHz, DMSO-d6, ppm) δ: 7.71–7.69 (m, 2H),
7.49–7.45 (m, 2H), 7.36 (s, 1H), 7.31–7.29 (m, 4H), 5.30 (s,
2H), 2.41 (s, 2H); 13C NMR (75 MHz, DMSO-d6, ppm) δ:
182.04, 153.43, 142.56, 140.64, 135.96, 134.81, 134.35, 129.92,
128.98, 128.88, 128.33, 127.89, 21.51; C17H14ClN3O exact
mass: 311.08; LC-ESI-MS/MS: 312.3 [M + 1]+.
(2-Amino-1-(4-chlorophenyl)-1H-imidazol-5-yl)IJpyridin-4-yl)-
methanone (6e). Yield: 80%, brown solid, mp: 247 °C; decom-
poses; 1H NMR (300 MHz, DMSO-d6) δ: 8.77–8.75 (m, 2H),
7.59–7.57 (m, 2H), 7.54–7.50 (m, 2H), 7.34 (s, 1H), 7.33–7.26
(m, 2H), 4.76 (s, 2H); 13C NMR (75 MHz, DMSO-d6) δ: 180.16,
153.85, 150.36, 145.33, 142.63, 135.47, 133.76, 130.19, 128.40,
127.48, 122.20; C15H11ClN4O exact mass: 298.06; LC-ESI-MS/
MS m/z 299.4 [M + 1]+.
General procedure for preparation of solid phase synthesis
aminoimidazolyl-thiazole (12a–12l)
2-Chlorotrityl resin (1 mmol) was loaded and vortex it with
DMF (10 mL) to swell the resin, the monosubstituted thio-
urea 1 and DIPEA was added followed by stirring it for about
2 h, then repeated washing of resin with DCM, DMF, THF (4
× 10 ml mmol−1) was given to remove unbound mono con-
densed thiourea. Further, guanylation of amidinothiourea
with various arylamine was carried out with Mukaiyama's re-
agents in DMF and stirred for 30 minutes to generate resin
bound amidinoguanidine. Excess of reagents was removed by
repeated washing of DCM, DMF, THF (4 × 10 ml mmol−1). Cy-
clization of resin bound amidinoguanidine was carried out
by (2-chloroacetyl) thiazole derivatives in presence of DBU to
give resin bound aminoimidazolyl-thiazole derivatives. The
cleavage of resin was done by 10% TFA in DCM to give final
compound with good to high yield.
(2-Amino-1-phenyl-1H-imidazol-5-yl)IJ4-(methylsulfonyl)-
phenyl)methanone (6f). Yield: 62%, pale yellow solid, mp:
1
192–195 °C; H NMR (300 MHz, DMSO-d6, ppm) δ: 8.28–7.79
(m, 2H), 7.88–7.85 (m, 2H), 7.49–7.39 (m, 3H), 7.38–7.21 (m,
3H), 3.35 (s, 3H); 13C NMR (75 MHz, DMSO-d6, ppm) δ:
178.47, 155.76, 144.02, 143.51, 142.61, 135.94, 129.21, 129.12,
128.09, 127.22, 127.02, 126.84, 54.90; C17H15N3O3S exact
mass: 311.08; LC-ESI-MS/MS m/z 312.3 [M + 1]+.
(2-Amino-1-(4-(trifluoromethyl)phenyl)-1H-imidazol-5-yl)IJ4-
chlorophenyl)methanone (6g). Yield: 65%, yellow solid, mp:
190–194 °C; 1H NMR NMR (300 MHz, DMSO-d6, ppm) δ:
7.83–7.74 (m, 2H), 7.56–7.49 (m, 2H), 7.41 (s, 1H), 7.37–7.26
(m, 4H), 5.32 (s, 2H); C17H11ClF3N3O, exact mass: 365.05; LC-
ESI-MS/MS: 366.3 [M + 1]+.
(2-Amino-1-(4-methoxyphenyl)-1H-imidazol-5-yl)IJ4-methyl-
2-(phenylamino)thiazol-5-yl)methanone (12a). Yield: 64%,
1
brown solid, mp: 235–239 °C; H NMR (300 MHz, DMSO-d6,
ppm) δ: 10.58 (S, 1H) 7.61–7.58 (d, J = 9, 2H), 7.50 (s, 1H)
7.36–7.31 (m, 2H), 7.19–7.16 (d, J = 9, 2H), 7.02–6.97 (m, 3H),
6.14 (s, 2H), 3.79 (s, 3H), 2.49 (s, 3H); 13C NMR (75 MHz,
DMSO-d6, ppm) δ: 171.59, 163.90, 158.65, 155.04, 154.90,
140.32, 139.16, 129.12, 128.74, 128.60, 128.36, 122.26, 117.92,
117.73, 114.34, 55.33, 18.19; C21H19N5O2S exact mass: 405.13;
LC-ESI-MS/MS: 406.5 [M + 1]+.
(2-Amino-1-(2-chlorophenyl)-1H-imidazol-5-yl)IJp-tolyl)-
methanone (6h). Yield: 64%, pale yellow solid, mp: 163–165 °C;
1H NMR (300 MHz, DMSO-d6, ppm) δ: 7.81–7.78 (m, 2H), 7.69–
7.61 (m, 3H), 7.56–7.41 (m, 4H), 5.51 (s, 2H), 2.41 (s, 3H);
C17H14ClN3O, exact mass: 311.08; LC-ESI-MS/MS: 312.3 [M + 1]+.
(2-Amino-1-(3-chlorophenyl)-1H-imidazol-5-yl)IJp-tolyl)-
(2-Amino-1-(4-fluorophenyl)-1H-imidazol-5-yl)IJ4-methyl-2-
(phenylamino)thiazol-5-yl)methanone (12b). Yield: 64%, yellow
1
solid, mp: 178–179 °C; H NMR (300 MHz, DMSO-d6, ppm) δ:
8.85 (s, 1H), 7.61 (s, 1H) 7.42–7.31 (m, 7H), 7.29–7.11 (m, 3H),
4.84 (s, 2H), 2.50 (s, 3H); 13C NMR (75 MHz, DMSO-d6, ppm) δ:
166.26, 164.16, 157.64, 139.37, 137.83, 131.55, 129.69, 128.93,
128.81, 127.92, 124.23, 119.19, 117.48, 117.08, 116.77, 18.26;
C20H16FN5OS exact mass: 393.11; LC-ESI-MS/MS: 394.3 [M + 1]+.
(2-Amino-1-(4-fluorophenyl)-1H-imidazol-5-yl)IJ4-phenyl-2-
(phenylamino)thiazol-5-yl)methanone (12c). Yield: 64%, yel-
low solid, mp: 230–231 °C; 1H NMR (300 MHz, DMSO-d6,
ppm) δ: 10.59 (s, 1H), 7.66–7.64 (d, J = 6, 2H), 7.57–7.55 (d, J
= 6, 2H), 7.40–7.34 (m, 5H), 7.32–7.24 (m, 4H), 7.15 (s, 1H),
7.02–6.67 (m, 1H), 6.31 (s, 2H); 13C NMR (75 MHz, DMSO-d6,
ppm) δ: 171.69, 163.05, 159.88, 155.02, 152.56, 142.40,
140.47, 135.14, 132.07, 129.54, 129.07, 128.30, 128.08, 127.62,
122.14, 119.86, 117.55, 116.22, 115.92; C25H18FN5OS exact
mass: 455.12; LC-ESI-MS/MS: 455.6 [M + 1]+.
1
methanone (6i). Yield: 78%, white solid, mp: 123–125 °C; H
NMR (300 MHz, DMSO-d6, ppm) δ: 7.82–7.79 (m, 2H), 7.71–
7.67 (m, 2H), 7.61–7.59 (m, 1H), 7.51–7.45 (m, 4H), 5.49 (s,
2H), 2.45 (s, 3H); C17H14ClN3O exact mass: 311.08; LC-ESI-
MS/MS: 312.2 [M + 1]+.
(2-Amino-1-(3-chloro-4-fluorophenyl)-1H-imidazol-5-yl)IJ4-
chlorophenyl)methanone (6j). Yield: 75%, yellow solid, mp:
1
220–224 °C; H NMR (300 MHz, DMSO-d6, ppm) δ: 7.81–7.78
(m, 2H), 7.72–7.68 (m, 2H), 7.65–7.58 (m, 1H), 7.57–7.46 (m,
2H), 5.47 (s, 2H); C16H10Cl2FN3O exact mass 349.02; LC-ESI-
MS/MS: 350.4 [M + 1]+.
(2-Amino-1-(4-(trifluoromethyl)phenyl)-1H-imidazol-5-yl)-
IJpyridin-4-yl)methanone (6k). Yield: 64%, brown solid, mp:
1
229–232 °C; H NMR (300 MHz, DMSO-d6, ppm) δ: 8.75–8.69
(m, 2H), 7.78–7.69 (m, 2H), 7.65–7.59 (m, 2H), 7.37 (s, 1H),
7.35–7.22 (m, 2H), 5.15 (s, 2H); C16H11F3N4O exact mass:
332.09; LC-ESI-MS/MS: 333.3 [M + 1]+.
N-(5-(2-Amino-1-(4-chlorophenyl)-1H-imidazole-5-car-
bonyl)-4-(dimethylamino)thiazol-2-yl)benzamide (12d). Yield:
64%, white solid, mp: 180–183 °C; 1H NMR (300 MHz,
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DMSO-d6, ppm) δ: 12.56 (s, 1H), 9.21 (s, 1H), 8.15–7.74 (m,
5H), 7.65 (s, 1H), 7.31–7.18 (m, 4H), 6.82 (s, 2H), 3.22 (s, 6H);
13C NMR (75 MHz, DMSO-d6, ppm) δ: 174.25, 166.15, 163.15,
162.19, 141.57, 140.7, 138.9, 136.96, 134.15, 133.07, 131.91,
129.20, 128.15, 126.57, 122.24, 41.15; C22H19ClN6O2S exact
mass: 466.1; LC-ESI-MS/MS : 467.3 [M + 1]+.
1H), 7.37–7.29 (m, 4H), 5.07 (s, 2H), 2.93 (s, 3H), 2.45 (s, 3H);
C21H18ClN5O2S exact mass: 439.09; LC-ESI-MS/MS: 439.9,
442.1 [M + 1]+.
(2-Amino-1-p-tolyl-1H-imidazol-5-yl)IJ2-morpholino-4-
phenylthiazol-5-yl)methanone (12k). Yield: 60%, brown solid,
1
mp: 230 °C decomposes; H NMR (300 MHz, DMSO-d6, ppm)
N-(5-(2-Amino-1-(4-(trifluoromethyl)phenyl)-1H-imidazole-
δ: 7.47–7.25 (m, 6H), 7.20–6.94 (m, 4H), 6.18 (s, 2H), 3.76–
3.71 (m, 4H), 3.52–3.35 (m, 4H), 2.56 (s, 3H); C24H23N5O2S;
exact mass: 445.16; LC-ESI-MS/MS: 446.3 [M + 1]+.
5-carbonyl)-4IJdimethylamino)thiazol-2-yl)benzamide
(12e).
Yield: 64%, white solid, mp: 230 °C decomposes; 1H NMR
(300 MHz, DMSO-d6, ppm) δ: 12.73 (s, 1H), 9.20 (s, 1H), 7.82
(s, 1H), 8.18–7.78 (m, 5H), 7.81 (s, 1H), 7.31–7.18 (m, 4H),
6.82 (s, 2H), 3.24 (s, 6H); 13C NMR (75 MHz, DMSO-d6, ppm)
δ: 174.28, 166.20, 163.09, 162.37, 141.61, 140.82, 138.9,
137.01, 134.20, 133.09, 131.94, 129.24, 128.20, 126.59, 122.26,
41.24; C23H19F3N6O2S; exact mass: 500.12; LC-ESI-MS/MS:
501.2 [M + 1]+.
(2-Amino-1-(4-chlorophenyl)-1H-imidazol-5-yl)IJ4-methyl-2-
(phenylamino)thiazol-5-yl)methanone (12l). Yield: 65%, pale
1
brown solid, mp: 225–227 °C; H NMR (300 MHz, DMSO-d6,
ppm) δ: 8.96 (s, 1H), 7.59 (s, 1H), 7.40–7.32 (m, 5H), 7.30–
7.15 (m, 4H), 4.86 (s, 2H), 2.56 (s, 3H); 13C NMR (75 MHz,
DMSO-d6, ppm) δ: 166.24, 163.20, 159.70, 140.15, 137.91,
131.56, 129.70, 129.01, 128.89, 127.91, 124.98, 120.09, 117.51,
117.07, 116.98, 21.96; C20H16ClN5OS; exact mass: 409.08, LC-
ESI-MS/MS: 410.01 [M + 1]+.
(2-Amino-1-(4-fluorophenyl)-1H-imidazol-5-yl)IJ4-methyl-2-
(p-tolylamino)thiazol-5-yl)methanone (12f). Yield: 70%, yellow
1
solid, mp: 215–217 °C; H NMR (300 MHz, DMSO-d6, ppm) δ:
9.23 (s, 1H), 7.40–7.32 (m, 4H), 7.27–7.12 (m, 4H), 4.19 (s,
2H), 2.50 (s, 3H), 2.34 (s, 3H); 13C NMR (75 MHz, DMSO-d6,
ppm) δ: 166.21, 164.23, 163.21, 158.01, 140.15, 138.10,
131.61, 129.70, 128.94, 128.82, 127.92, 124.23, 119.20, 117.15,
117.01, 20.34, 18.26; C21H18FN5OS exact mass: 407.12; LC-ESI-
MS/MS: 408.2 [M + 1]+.
Biological assays
For radioligand binding studies (A1, A2A, and A3 receptor)
and measurement of adenylyl cyclase activity (A2B) mem-
branes were prepared from CHO cells stably transfected with
the respective human adenosine receptor subtype. For details
see ESI.†
(2-Amino-1-(4-methoxyphenyl)-1H-imidazol-5-yl)IJ4-phenyl-
2-(phenylamino) thiazol-5-yl)methanone (12g). Yield: 60%,
brown solid, mp: 175–178 decomp. °C; 1H NMR (300 MHz, Abbreviations
DMSO-d6, ppm) δ: 10.61 (s, 1H), 7.67–7.65 (d, J = 6, 2H), 7.60–
TM Transmembrane helix
EL Extracellular loop
AR Adenosine receptor
7.58 (d, J = 6, 2H), 7.49–7.30 (m, 5H), 7.24 (s, 1H), 7.23–7.16 (m,
2H), 7.03–6.95 (m, 3H), 6.20 (s, 2H), 3.79 (s, 3H); 13CNMR (75
MHz, DMSO-d6, ppm) δ: 171.73, 162.99, 158.78, 155.25, 155.07,
152.45, 143.49, 140.99, 140.52, 135.15, 129.47, 129.21, 128.44,
Author contributions
127.88, 127.68, 127.32, 120.45, 116.47, 113.33, 56; C26H21N5O2S
exact mass: 467.14; LC-ESI-MS/MS: 468.5 [M + 1]+.
The manuscript was written through contributions of all au-
(2-Amino-1-(4-methoxyphenyl)-1H-imidazol-5-yl)IJ2-
morpholino-4-phenylthiazol-5-yl)methanone (12h). Yield:
62%, white solid, mp: 178–180 °C; purification by column chro-
matography (ethyl acetate/hexane (3 : 7)) 1H NMR (300 MHz,
DMSO-d6, ppm) δ: 7.51–7.29 (m, 6H), 7.18–7.01 (m, 4H), 6.11
(s, 2H), 3.81 (s, 3H), 3.74–3.72 (m, 4H), 3.51–3.32 (m, 4H);
C24H23N5O3S exact mass 461.15; LC-ESI-MS/MS: 461.5 [M + 1]+.
(2-Amino-1-(4-fluorophenyl)-1H-imidazol-5-yl)IJ2-(4-chloro-
phenylamino)-4-methylthiazol-5-yl)methanone (12i). Yield:
74%, pale yellow solid, mp: 136–138 °C; purification by col-
umn chromatography (ethyl acetate/hexane (3 : 7)) 1H NMR
(300 MHz, DMSO-d6, ppm) δ: 10.15 (s, 1H), 7.51–7.45 (m,
4H), 7.37 (s, 1H), 7.29–7.14 (m, 4H), 4.81 (s, 2H), 2.45 (s, 3H);
13C NMR (75 MHz, DMSO-d6, ppm) δ: 167.62, 165.15, 158.16,
140.47, 139.19, 131.57, 129.72, 128.91, 128.74, 128.15, 124.29,
119.21, 117.45, 117.20, 117.15, 19.15; C20H15ClFN5OS; exact
mass: 427.07; LC-ESI-MS/MS: 428.4 [M + 1]+.
thors. All authors have given approval to the final version of
the manuscript.
Conflicts of interest
The authors declare no conflict of interests.
Acknowledgements
We thank Dr. Manish Nivsarkar, Professor Harish Padh and
Professor C. J. Shisoo, Directors, B. V. Patel PERD centre, for
their constant encouragement and support. A. N. P. thanks
PERD Centre for providing the doctoral fellowship. This work
was funded by DST through grant no. SR/S1/OC-83/2009. The
authors wish to thank DST for its financial support. The mo-
lecular modeling work coordinated by S. M. was carried out
with financial support from the University of Padova, Italy,
and the Italian Ministry for University and Research (MIUR),
Rome, Italy. S. M. is also very grateful to Chemical Computing
Group and to OpenEye for the scientific and technical
partnership.
(2-Amino-1-(4-methoxyphenyl)-1H-imidazol-5-yl)IJ2-(4-
chlorophenylamino)-4-methylthiazol-5-yl)methanone
Yield: 70%, white solid, mp: 123–125 °C; H NMR (300 MHz,
DMSO-d6, ppm) δ: 10.28 (s, 1H), 7.61–7.54 (m, 4H), 7.43 (s,
(12j).
1
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Notes and references
18 L. Chang, J. Brussee and A. P. IJzerman, Chem. Biodiversity,
2004, 1, 1591.
1 B. B. Fredholm, A. P. IJzerman, K. A. Jacobson, K.-N. Klotz
and J. Linden, Pharmacol. Rev., 2001, 53, 527.
19 M. Saki, H. Tsumuki, H. Nonaka, J. Shimada and M.
Ichimura, Eur. J. Pharmacol., 2002, 444, 133.
2 B. B. Fredholm, G. Arslan, L. Halldner, B. Kull, G. Schulte
20 A. Trifilieff, T. H. Keller, N. J. Press, T. Howe, P. Gedeck, D.
Beer and C. Walker, Br. J. Pharmacol., 2005, 144, 1002.
21 N. J. Press, T. H. Keller, P. Tranter, D. Beer, K. Jones, A.
Faessler, R. Heng, C. Lewis, T. Howe, P. Gedeck, L. Mazzoni
and J. R. Fozard, Curr. Top. Med. Chem., 2004, 4, 863.
22 A. B. Scheiff, S. G. Yerande, A. El-Tayeb, W. Li, G. S.
Inamdar, K. K. Vasu, V. Sudarsanam and C. Muller, Bioorg.
Med. Chem., 2010, 18, 2195.
23 G. S. Inamdar, A. N. Pandya, H. M. Thakar, V. Sudarsanam,
S. Kachler, D. Sabbadin, S. Moro, K.-N. Klotz and K. K. Vasu,
Eur. J. Med. Chem., 2013, 63, 924.
24 D. H. Pandya, J. A. Sharma, H. B. Jalani, A. N. Pandya, V.
Sudarsanam, S. Kachler, K. N. Klotz and K. K. Vasu, Bioorg.
Med. Chem. Lett., 2015, 25, 1306.
25 M. Floris, D. Sabbadin, R. Medda, A. Bulfone and S. Moro,
Adenosiland: Walking through adenosine receptors
landscape, Eur. J. Med. Chem., 2012, 58, 248–257.
26 M. Floris, D. Sabbadin, A. Ciancetta, R. Medda, A. Cuzzolin
and S. Moro, Implementing the “Best Template Searching”
tool into Adenosiland platform, In Silico Pharmacol.,
2013, 20, 1–25.
27 A. Ciancetta, A. Cuzzolin and S. Moro, Alternative Quality
Assessment Strategy to Compare Performances of GPCR-
Ligand Docking Protocols: The Human Adenosine A2A Re-
ceptor as a Case Study, J. Chem. Inf. Model., 2014, 54,
2243–2254.
and
W.
Wasserman,
Naunyn-Schmiedeberg's
Arch.
Pharmacol., 2000, 362, 364.
3 E. Baharav, S. Bar-Yehuda, L. Madi, D. Silberman, L. Rath-
Wolfson, M. Halpren, A. Ochaion, A. Weinberger and P.
Fishman, J. Rheumatol., 2005, 32, 469.
4 K. A. Jacobson, H. O. Kim, S. M. Siddiqui, M. E. Olah, G. L.
Stiles and D. K. J. E. Von Lubitz, Drugs Future, 1995, 20, 689.
5 Y. Kohno, X. D. Ji, S. D. Mawhorter, M. Koshiba and K. A.
Jacobson, Blood, 1996, 88, 3569.
6 K. A. Jacobson, Trends Pharmacol. Sci., 1998, 19, 184.
7 D. K. J. E. Von Lubitz, R. C. S. Lin, P. Popik, M. F. Carter and
K. A. Jacobson, Eur. J. Pharmacol., 1994, 263, 59.
8 J. Rivo, E. Zeira, E. Galun and I. Matot, Anesthesiology,
2004, 101, 1153.
9 R. A. Brown, D. Spina and C. P. Page, Br. J. Pharmacol.,
2008, 153, 446.
10 D. Marx, C. I. Ezeamuzie, K. Nieber and I. Szelenyi, Drug
News Perspect., 2001, 14, 89.
11 T. Okamura, Y. Kurogi, K. Hashimoto, S. Sato, H. Nishikawa, K.
Kiryu and Y. Nagao, Bioorg. Med. Chem. Lett., 2004, 14, 3775.
12 U. Schlotzer-Schrehardt, M. Zenkel, U. Decking, D. Haubs,
F. E. Kruse, A. Junemann, M. Coca-Prados and G. O.
Naumann, Invest. Ophthalmol. Visual Sci., 2005, 46, 2023.
13 M. Y. Avila, R. A. Stone and M. M. Civan, Invest. Ophthalmol.
Visual Sci., 2002, 43, 3021.
14 S. Gessi, K. Varani, S. Merighi, E. Cattabriga, A. Avitabile, R.
Gavioli, C. Fortini, E. Leung, S. Mac Lennan and P. A. Borea,
Mol. Pharmacol., 2004, 65, 711.
15 G. Ohana, S. Bar-yehuda, F. Barer and P. Fishman, J. Cell.
Physiol., 2001, 186, 19.
28 A. Cuzzolin, M. Sturlese, I. Malvacio, A. Ciancetta and S.
Moro, DockBench: An Integrated Informatic Platform
Bridging the Gap between the Robust Validation of Docking
Protocols and Virtual Screening Simulations, Molecules,
2015, 20, 9977–9993.
16 P. G. Baraldi and P. A. Borea, Trends Pharm. Sci., 2000, 21, 456.
17 S. Merighi, P. Mirandola, K. Varani, S. Gessi, E. Leung, P. G.
Baraldi, M. A. Tabrizi and P. A. Borea, Pharmacol. Ther.,
2003, 1001, 31.
29 A. Ciancetta, D. Sabbadin, S. Federico, G. Spalluto and S.
Moro, Advances in Computational Techniques to Study
GPCR-Ligand Recognition, Trends Pharmacol. Sci., 2015, 36,
878–890.
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