2-n-butyl-9-methyl-8-[1,2,3]triazol-2-yl-9H-purin-6-ylamine and analogues as A2A adenosine receptor antagonists. Design, synthesis, and pharmacological characterization

Article abstract of DOI:10.1021/jm058018d

Two types of adenosine receptor ligands were designed, i.e., 9H-purine and 1H-imidazo[4,5-c]pyridines, to obtain selective A_2A antagonists, and we report here their synthesis and binding affinities for the four adenosine receptor subtypes A

Full text of DOI:10.1021/jm058018d

J. Med. Chem. 2005, 48, 6887-6896
6887
2-n-Butyl-9-methyl-8-[1,2,3]triazol-2-yl-9H-purin-6-ylamine and Analogues as A2A
Adenosine Receptor Antagonists. Design, Synthesis, and Pharmacological
Characterization
Patrizia Minetti,*,‡ Maria Ornella Tinti,‡ Paolo Carminati,‡ Massimo Castorina,§ Maria Assunta Di Cesare,§
Stefano Di Serio,§ Grazia Gallo,‡ Orlando Ghirardi,§ Fabrizio Giorgi,‡ Luca Giorgi,† Giovanni Piersanti,†
Francesca Bartoccini,† and Giorgio Tarzia*,†
Istituto di Chimica Farmaceutica, Universita` degli Studi di Urbino “Carlo Bo”, Piazza del Rinascimento 6,
61029 Urbino (PU), and Italy, Dipartimento di Chimica and Dipartimento Sistema Nervoso Centrale e Periferico Sigma-Tau,
via Pontina Km 30,400, 00040 Pomezia (Roma), Italy.
Received March 29, 2005
Two types of adenosine receptor ligands were designed, i.e., 9H-purine and 1H-imidazo[4,5-
c]pyridines, to obtain selective A2A antagonists, and we report here their synthesis and binding
affinities for the four adenosine receptor subtypes A1, A2A, A2B and A3. The design was carried
out on the basis of the molecular modeling of a number of potent adenosine receptor antagonists
described in the literature. Three compounds (25b-d) showed an interesting affinity and
selectivity for the A2A subtype. One of them, i.e., ST1535 (2-n-butyl-9-methyl-8-[1,2,3]triazol-
2-yl-9H-purin-6-ylamine, 25b) (Ki A2A ) 6.6 nM, Ki A1/A2A ) 12; Ki A2B/A2A ) 58; Ki A3/A2A
>
160), was selected for in vivo study and shown to induce a dose-related increase in locomotor
activity, suggestive of an A2A antagonist type of activity.
Introduction
Adenosine is an endogenous modulator which, among
other effects, mediates a general depression of the
central nervous system, vasodilatation and inhibition
of platelet aggregation.1 It acts at specific membrane
G-protein receptors2 positively (A2A, A2B)1 or negatively
(A1, A3)1 linked to adenylate cyclase. The discovery of
selective ligands facilitated the defining of tissue dis-
tribution and the role of each receptor subtype. Recep-
tors A2A are densely distributed in the central nervous
system (striatum, nucleus accumbens and olfactory
tubercles) where they play an important role in the
regulation of mood and motor activity.1 Available evi-
dence provided the basis for the formulation of a theory
according to which selective A2A adenosine receptor
antagonists can be useful in the treatment of Parkin-
son’s disease.3
A number of potent and subtype selective A2A antago-
nists, of various structures, including xanthines and
nonxanthines, are reported in the literature.4 The most
important xanthine-based adenosine A2A receptor an-
tagonist is KW-6002 (((E)-1,3-diethyl-8-(3,4-dimethoxy-
styryl)-7-methyl-3,7-dihydro-1H-purine-2,6-dione, 1).5
SCH 58261 (5-amino-7-(2-phenylethyl)-2-(2-furyl)pyra-
zolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine, 2)6 and ZM
241385 (4-[2-[[7-amino-2-(2-furyl)[1,2,4]-triazolo[2,3-a]-
[1,3,5]triazin-5-yl]amino]ethyl]phenol, 3),7 which has
been derived from the prototype CGS 15943 (5-amino-
9-chloro-2-(furyl)-1,2,4-triazolo[1,5-c]quinazoline, 4) (Fig-
Figure 1. Reference compounds with different A1/A2A selec-
tivity.
* To whom correspondence should be addressed: (P.M.) Phone:
+39-06-91393906, Fax: +39-06-91393638. E-mail: Patrizia.Minetti@
sigma-tau.it. (G.T.) Phone: +39-0722-303325; Fax: +39-0722-2737.
E-mail: gat@uniurb.it.
Figure 2. General formula of series A-B.
ure 1)8 are considered as the reference ligands. Ade-
nosine receptor antagonists with a purine ring have also
been reported.9
† Universita` degli Studi di Urbino “Carlo Bo”.
‡ Dipartimento di Chimica Sigma-Tau.
§ Dipartimento Sistema Nervoso Centrale e Periferico Sigma-Tau.
10.1021/jm058018d CCC: $30.25 © 2005 American Chemical Society
Published on Web 10/01/2005

6888 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 22
Minetti et al.
Figure 3. Proposed alignment between: (A) SCH 58261 (orange) and CGS 15943 (light blue). (B). DPCPX (orange) and CGS
15943 (light blue). Heteroatoms are colored as atom type. Pharmacophoric features are highlighted as follows: red vectors are
H-bond acceptors, blue vectors are H-bond donors (as visualized using software Phase, Schrodinger Inc.), gray solids represent
steric clashes, respectively, in A1 and A2A receptors.
Figure 4. Pharmacophoric model visualized on SCH 58261.
Scheme 1a
The present paper describes a study aimed at gener-
ating new A2A antagonist ligands on the basis of the
available structure-activity knowledge for the A2A
receptor. We designed two different series (Figure 2):
series A (9H-purine derivatives), series B (1H-imidazo-
[4,5-c]pyridine derivatives). We report here the synthe-
sis of compounds of these series and their binding
affinities for the four adenosine receptor subtypes.
Series A was explored more extensively than B. In the
case of the former series we synthesized a number of
2-alkyl-substituted compounds and three of them (25b-
d) showed good affinity and a varying degree of selectiv-
ity for A2A adenosine receptor subtype.
a (i)EtOH, Bn2NH, iPr2EtN, rfx (80 °C), 20 h. (ii) DMF, K2CO3,
CH3I, rt, 12 h. (iii) MeOH, THF, sodium acetate buffer (pH 4),
Br2, rt, 20 h. (iv) DMF, NaH, 1H-1,2,3-triazole, rfx (100 °C). (v)
CH2Cl2, CF3SO3H, rfx (40 °C), 5 h.
Molecular Modeling. The molecular design of the
new series of adenosine A2A antagonists was carried out
using 52 structures from the literature; in particular
we used three classes with different selectivity for A1
and A2A subtypes where the best compounds were
DPCPX (1,3-dipropyl-8-cyclopentylxanthine, 5)10 A1 se-
lective antagonist (Ki A1/A2A ) 2.1 10-3), CGS 15943 A1/
acceptors that represent the minimum requirement to
interact with both A1 and A2A receptors. An exclusion
zone, representing an unfavorable steric interaction in
the A2A active site, is visualized as a gray solid in Figure
3B. An additional exclusion zone, representing an
unfavorable steric interaction in the A1 active site, is
visualized as a gray solid in Figure 3A. Finally the furan
ring on both CGS 15943 and SCH 58261 represents an
additional pharmacophoric point (H-bond acceptor)
(Figure 3A) relative to DPCPX. In the case of CGS 15943
and SCH 58261 a variation of the position or type of
the heteroatom negatively modulates the potency but
does not modify the selectivity for the A1/A2A subtypes.
Figure 4 shows the final pharmacophoric model visual-
ized on SCH 58261. On the basis of previous consider-
ations, we planned some novel structures belonging to
two classes of compounds (Figure 2) that contain all
required pharmacophoric groups. In particular group D
A2A mixed antagonist (Ki A1/A2A ) 5.3) and SCH 58261
A2A selective antagonist (Ki A1/A2A ) 52.6) (Figure 1).
The reference molecules were built and optimized using
semiempirical quantomechanic method AM1 (ChemX
software, Chemical Design Ltd, Oxford Molecular Group,
the Magdalene Centre, Oxford Science Park, Oxford
OX4 4GA UK); we also obtained electrostatic potential
maps which we used to compare the electronic features
of the molecules and to invesigate the different align-
ments between compounds related or unrelated to the
xanthine ring system.1,11 In Figure 3A,B are shown our
proposed superimpositions between SCH 58261 (orange)
and CGS 15943 (light blue) (Figure 3A) and DPCPX
(orange) and CGS 15943 (light blue) (Figure 3B). These
alignments identified three common pharmacophoric
points showing one H-bond donor and two H-bond

A2A Adenosine Receptor Antagonists
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 22 6889
Scheme 2a
a (i) EtOH, Bn2NH, iPr2EtN, rfx (80 °C), 20 h. (ii) DMF, K2CO3, CH3I, rt, 12 h. (iii) THF, Al(CH3)3, PdCl2, PPh3, rfx (50 °C), 24 h. (iv)
NMP, Pd(PPh3)4, rfx (120 °C). (v) EtOH, H2, Pd/C, rt.
Scheme 3a
(Figure 4) is an alkyl or arylalkyl chain useful in
modulating selectivity versus A2A subtype receptor, and
group E (Figure 4) can be a 1,2,3 triazole or oxazole ring
useful for improving the solubility profile and for
providing one more H-bond acceptor relative to furan.
Chemistry. Synthesis of 9H-Purine Derivatives
(series A). The synthesis of 2-unsubstituted 9-methyl-
8-[1,2,3]triazol-2-yl-9H-purin-6-ylamine (11) is described
in Scheme 1. Dibenzyl-(9-methyl-9H-purin-6-yl)-amine
(8) was prepared by double substitution at the 6 and 9
positions of commercially available 6-chloro-9H-purine
(6) with dibenzylamine and methyl iodide.12 Selective
bromination of 8 with bromine in the presence of sodium
acetate buffer (pH 4) gave the bromo derivative 9,13
which, upon treatment with 1H-1,2,3-triazole, produced
a mixture of the two regioisomers 10a,b14 that were
separated by flash chromatography on silica gel. Finally,
acid-catalyzed debenzylation of 10a yielded 11,15 whereas
deprotection of compound 10b under the same condi-
tions yielded an untractable mixture of compounds.
The synthesis of the 2-alkyl-adenines (15a-f) is
described in Scheme 2. 2-Chloro-6-dibenzylamine-9-
methyl-9H-purine (14) was obtained by sequential
substitution with dibenzylamine and methylation of 2,6-
dichloro-9H-purine (12) according to the literature.12
Cross-coupling reaction of 14 with trimethylaluminum
in the presence of palladium catalyst (PdCl2) and
triphenylphosphine gave 15a.16 Instead, reductive de-
halogenation took place when triisopropylaluminum and
tributylaluminum were used (Scheme 3). Therefore,
compounds 15b,c and 16-19 were synthesized by
Stille’s reaction with the corresponding organostan-
nanes (Scheme 2).17 Catalytic hydrogenation of 16, 17
and 18 gave 15d, 15e and 15f, respectively (Scheme 2).
As described in Scheme 4 compounds 15a-f were
subsequently bromurated (22a-f)13 and substituted
a R ) CH(CH3)CH3 or CH2(CH2)2CH3.
Scheme 4a
a (i) MeOH, THF, sodium acetate buffer (pH 4), Br2, rt. (ii)
DMF,NaH or K2CO3, 1H-1,2,3-triazole, rfx (100 °C). (iii) CH2Cl2,
CF3SO3H, rfx (40 °C).
with 1H-1,2,3-triazole to give 23a-f and 24a-f.14,18 The
substitution reaction with commercially available 1H-
1,2,3-triazole provided in each case a mixture of regioi-
somers (N-1 and N-2 triazolyl derivatives). 23b and 24b
only were separated by flash chromatography on silica

6890 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 22
Minetti et al.
Scheme 5a
Scheme 7
was prepared from commercially available 4-hydroxy-
6-methyl-3-nitro-1H-pyridin-2-one (33) and POCl322 and
further treated with methylamine in refluxing ethanol
to give a mixture of regioisomers 35a,b,c (Scheme 7).23
The position of the amine substituent was established
by NOE experiments (Figure 5). Saturation of the signal
at 6.57 ppm (H-5 proton) of compound 35a resulted in
3% enhancement of the resonance at 2.42 ppm (methyl
in C-6) and 5.5% enhancement of the resonance at 3.10
ppm (methyl binding with NHCH3 in C-4), whereas
saturation of the signal at 6.48 ppm (H-5 proton) of
compound 35b resulted in 2% enhancement of the
resonance at 2.99 ppm (CH3 in C-6) and absence of NOE
effect between H-5 proton and NHCH3 in C-2. Reduction
of 35a with iron powder and further cyclization with
CH(OEt)3 produced 4-chloro-1,6-dimethyl-1H-imidazo-
[4,5-c]pyridine (37).21 Bromination of 37 with LDA/NBS
gave 38 (Scheme 6). Compound 41 was obtained by
using the same route and conditions described for 29
(Schemes 5, 6).
a (i) HCl 12 N, SnCl2‚2H2O, 90 °C, 1 h. (ii) DMF, CH(OEt)3, HCl
12 N, rt, 12 h. (iii) (1) THF, BuLi, -78 °C, 1 h (2) Br2, -65 °C, 2
h. (iv) DMF, K2CO3, 1H-1,2,3-triazole, rfx (100 °C), 20 h. (v)
BnNH2, MW 460 W, 5 min. (vi) CH2Cl2, CF3SO3H, rfx (40 °C), 1.5
h.
Scheme 6a
a (i) N,N-diethylaniline, POCl3, rfx (100 °C), 3 h. (ii) EtOH,
Na2CO3, MeNH2 (40% aq), rt, 24 h. (iii) MeOH, HCl 12 N, Fe, rt,
24 h. (iv) DMF, CH(OEt)3, HCl 12N, rt, 24 h. (v) THF, LDA, NBS,
-78 °C, 2 h. (vi) DMF, K2CO3, 1H-1,2,3-triazole, rfx (100 °C), 20
h. (vii) BnNH2, MW 460 W, 5 min. (viii) CH2Cl2, CF3SO3H, rfx
(40 °C), 2 h.
Figure 5. 1D- NOE experiments.
Results
Table 1 reports the affinity[Ki (nM)] values of the
studied compounds for the A1, and cloned human A2A
and A2B receptors (h-A2A, h-A2B), expressed in CHO-K1
(A1) and HEK-293 (A2A, A2B) cells (human embryo
kidney cells). Radioligand [3H]-DPCPX was used for
competition binding assays on receptors A1 and h-A2B,
gel and identified by 1H NMR spectra19 whereas 24a,c-f
were not isolated. 23a-f were deprotected (25a-f)
under the same conditions used for 10a.15
Synthesis of 1H-Imidazo[4,5-c]pyridine Deriva-
tives (series B). The synthesis of 1-methyl-2-[1,2,3]-
triazol-2-yl-1H-imidazo[4,5-c]pyrid-4-ylamine triflate (32)-
is described in Scheme 5. Methyl-(3-nitro-pyridin-4-
yl)amine (26) was prepared from commercially available
4-hydroxy-3-nitropyridine, using the literature proce-
dure.20 26 was reductively chlorinated to 2-chloro-N4-
methylpyridine-3,4-diamine (27) with stannous chloride
in hot 12 N HCl that after treatment with triethyl
orthoformate yielded 4-chloro-1-methyl-1H-imidazo[4,5-
c]pyridine (28).21 Selective bromination of 28 was car-
ried out by deprotonation with BuLi and subsequential
quenching with bromine. Substitution of 29 with 1H-
1,2,3-triazole gave a mixture of the two regioisomers
(30a,b),14 that were used in the next step without
further purification. Treatment of 30a,b with benzyl-
amine gave 4-benzyl-(1-methyl-2-[1,2,3]triazol-2-yl-1H-
imidazo[4,5-c]pyridin-4-yl)amine (31) that was depro-
tected under the same conditions used for 10a.15
The synthesis of 1,6-dimethyl-2-[1,2,3]triazol-2-yl-1H-
imidazo[4,5-c]pyridin-4-ylamine (41) is described in
Scheme 6. 2,4-dichloro-6-methyl-3-nitropyridine (34)
whereas [3H]-CGS21680 was used for h-A2A
.
Compounds 11 and 32 exhibit the same affinity
toward the adenosine A2A receptor but an appreciably
different selectivity toward A1; in particular 11 is 100
times more selective toward A1 while 32 is 20 times
more selective toward A2A. Moreover 25b-d exhibit
elevated affinity toward the adenosine A2A receptor. The
affinity of these compounds, relative to that of other
products with an adenine-type structure, denotes that
2-substitution of the adenine ring system with relatively
long (CH2)n-CH3, where n > 2 (see 25b and 25c) or bulky
(CH2)2-Ph, (see 25d) alkyl chains favors affinity toward
the A2A receptor, whereas relatively short (CH2)n-CH3,
(n e 2, see 25a and 25f) or branched alkyl chains (see
25e) are less effective. Reported in the same table are
affinity values with regard to the adenosine receptor
subtypes A2B and A1, of some of the synthesized com-
pounds and their selectivity ratios (Ki A1/A2A) and (Ki
A2B/A2A). It can be observed that compounds 25b-d and
32 possess, to a varying degree, significantly selective
affinity for A2A adenosine receptor. Compounds 25b-d

A2A Adenosine Receptor Antagonists
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 22 6891
Table 1. Affinity Ki (nM) and Selectivity for the Adenosine Receptors
affinitya Ki (nM)
A2B
compounds
R
A2A
A1
A1/A2A
0.01
0.15
11.92
7.84
17.02
4.72
3.18
A2B/A2A
11
25a
H
46.3
70.4
6.6
3.3
4.7
481.3
83.7
51.6
120.0
51.3
0.1
935.0
56
2.2
b
b
0.4
10.4
71.8
26.2
80.0
2270.0
266.0
CH3
25b (ST1535)
25c
(CH2)3CH3
(CH2)4CH3
(CH2)2Ph
CH(CH3)2
(CH2)2CH3
H
352.3
153.0
2330.0
b
58.53
45.81
495.74
25d
25e
25f
18.0
518.0
140.0
b
0.22
10.04
1.17
32
1056.3
340.0
20.48
2.83
41
CH3
CGS 21680
ZM 241385
alloxazine
DPCPX
KW600226
>10000
307.9
>100000
6.5
>1000
>1949
b
4430.7
3.8
>107.0
0.004
b
0.12
>454
a Ki values represent replicate determinations and SEM are tipically within (20%. b Not tested.
Table 2. Values of Affinity and Selectivity, Expressed as Ki (nM), for the Adenosine A3 Receptorsa
25b
25c
receptors
A3 (h)
1 µM
Ki (nM)
>1000
1 µM
Ki (nM)
reference compounds
IC50 (nM)
Ki (nM)
760
IB-MECA
NBTI
prazosin
yohimbine
atenolol
ICI 118551
diazepam
SCH 23390
(+)butaclamol
(+)butaclamol
clozapine
SCH 23390
muscimol
baclofen
nipecotic acid
L-glutamate
kainic acid
MK-801
R,â-MeATP
dATPR S
CGS 19755
pyrilamine
pirenzepine
methoctramine
4-DAMP
1.2
0.30
0.86
0.84
ADOtransporter
R1 (nonselective)
R2 (nonselective)
â1
24
34
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
b
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
95
1.770
2.3
â2
BZD (central)
D1
12
0.66
8.9
5.1
D2
D3
D4 (h)
D5 (h)
GABAa
GABA b
GABAtransporter
AMPA
kainate
PCP
156
0.61
16
50
10.100
613
77
2.0
14
22
967
P2X
P2Y
NMDA
H1 (central)
M1
1.3
22
34
M2
M3
3.5
1.9
2.0
M4
4-DAMP
4-DAMP
M5
cholinetransporter
hemicholinium-3
naloxone
8-OH-DPAT
ketanserin
mesulergine
MDL 72222
12
opiatec
1.6
0.66
2.7
1.9
9.3
5-HT1A
5-HT2A
5-HT2C (h)
5-HT3 (h)
5-HT4
5-HT5A (h)
5-HT6 (h)
NE transporter
DA transporter
5-HT transporter
serotonin
serotonin
protriptyline
GBR 12909
imipramine
79
421
1.1
5.0
4.4
a For the test compounds, the results are expressed as percent inhibition of control specific binding (mean values; n ) 2). b - Symbol
indicates an inhibition of less than 10%. c ) nonselective.
show a better affinity than compound 32 vs A2A receptor
and 25b,d are generally more selective than 25c. The
in vivo examination (locomotor activity, vide infra) was
restricted to 25b because of practical reasons related
to the synthesis of the two compounds. The overall yield
of 25b is in fact 11% vs 0.6% of 25d. Due to the number

6892 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 22
Minetti et al.
Column chromatography purifications were performed in flash
conditions using Merck 230-400 Mesh silica gel. Thin-layer
chromatography (TLC) was carried out with silica gel plates.
Elemental analyses were performed by REDOX, Milan, Italy,
and were within (0.4 of the theoretical values (C, H, N). The
solvents used for purification were purchased from Carlo Erba
(Italy) with the exception of DMF and dichloromethane that
were purchased from Fluka. All reactants were purchased from
Aldrich.
Dibenzyl-(9H-purin-6-yl)amine (7). Diisopropylethy-
lamine (1.2 mL, 7.15 mmol) and dibenzylamine (1.4 mL, 7.15
mmol) were added to a solution of 6 (1 g, 6.50 mmol) in
absolute ethanol (37 mL). The mixture was stirred at reflux
temperature for 20 h (after 1 h a white precipitate formed).
The solvent was removed under reduced pressure and the
residue washed with cold water. The solid was filtered and
dried under vacuum to yield 1.8 g (89%) of 7; mp 182 °C
Figure 6. Effect of 25b (1.25 mg/kg to 10 mg/kg po) on
spontaneous locomotor activity in rats. The mean ( SE of 12
rats for each treatment group are shown. ANOVA with
Student-Neuman-Keuls post hoc analysis: *: p < 0.01 and
**: p < 0.001 vs corresponding vehicle group.
1
(water); H NMR (CDCl3) δ 5.45 (br, 4H), 7.31 (s, 10H), 7.97
(s, 1H), 8.48 (s, 1H); MS (EI) m/e 316 (M + 1)+, 224, 91.
Dibenzyl-(2-chloro-9H-purin-6-yl)amine (13). The title
compound was obtained by the same procedure as for 7, with
12 as starting material. Yield 95%; mp 250-252 °C (water);
1H NMR (CDCl3) δ 4.94 (br, 2H), 5.55 (br, 2H), 7.32 (s, 10H),
7.89 (s, 1H); MS (EI) m/e 351-349 (M+), 260-258, 91.
Synthesis of Compounds 8 and 14. General Procedure.
K2CO3 (2.5 g, 17.94 mmol) was added to a solution of 7 or 13
(17.42 mmol) in hot DMF (45 mL). The solution was then
cooled to 0 °C and treated dropwise with CH3I (1.5 mL, 24.39
mmol). The mixture was stirred at room temperature for 12
h. The solvent was evaporated under reduced pressure. The
solid obtained was washed with water and collected by
filtration.
of animals to be observed it was not practical to proceed
with 25d although the profile of this compound com-
pares favorably with that of 25b.
Furthermore, the affinity of compounds 25b and 25c
for A3 adenosine receptors and an array of 35 unrelated
enzymes or receptors was evaluated (Table 2). In these
binding studies, compounds of interest were initially
tested at a concentration of 1 µM. Compounds that
displaced more than 50% of the specific radioligand were
evaluated at eight different concentrations to determine
their IC50 value. Compounds 25b and 25c displayed low
to negligible affinity for the A3 subtype and had no
affinity for the other receptors (IC50 > 1000 nM).
Effect on Locomotor Activity. Motor activity in-
creasing effects were observed in rats after A2A receptor
antagonists administration whereas an activation of
adenosine A2A receptors reduce locomotion.24 Rat loco-
motor activity was therefore studied to indirectly evalu-
ate the functional profile at adenosine A2A receptor of
selected compound. Rat spontaneous locomotor activity
was dose-relatedly and significantly increased by oral
administration of 25b (Figure 6). The increase in motor
activity is the protypic effect of adenosine receptor
antagonism due to an inhibition of central adenosine
A2A receptor; this effect and the selectivity for the A2A
receptor (Tables 1 and 2) suggest that the 25b binding
to adenosine A2A receptor is of the antagonistic type.
SAR Analysis. By comparing 11 and 32 we can
assume that A1 receptor needs the N3 atom as further
pharmacophoric determinant with respect to A2A recep-
tor. Moreover the elongation of the alkyl chain has the
same effect on both receptors, indicating a steric clash
with short or branched chains (25a, 25e and 25f) and a
more favorable interaction with long or bulky chains.
In this case affinity gain for the A2A is more evident than
for the A1 receptor.
Dibenzyl-(2-chloro-9-methyl-9H-purin-6-yl)amine (14).
Yield 78%, mp 144-146 °C (ethanol); 1H NMR (CDCl3) δ 3.81
(s, 3H), 4.93 (br, 2H), 5.50 (br, 2H), 7.31 (s, 10H), 7.67 (s, 1H);
MS (EI) m/e 365-363 (M+), 274-272, 91.
Dibenzyl-(2,9-dimethyl-9H-purin-6-yl)amine (15a). 2 M
trimethylaluminum in toluene (6 mL, 12 mmol), PdCl2 (27 mg,
0.15 mmol) and PPh3 (79 mg, 0.3 mmol) were added to a
solution of 14 (1.07 g, 2.94 mmol) in anhydrous THF (30 mL),
under nitrogen. The reaction mixture was refluxed for 48 h.
The excess of trialkylaluminum was destroyed by small
additions of water and ethanol. Aluminum hydroxide was
filtered through paper, and the liquid mixture was extracted
with dichloromethane. The organic phase was dried over
anhydrous sodium sulfate and evaporated under reduced
pressure. The residue was purified by flash chromatography
(cyclohexanes-ethyl acetate 1:1) afforded 900 mg (89%) of
desired compound (15a) in crystalline form: mp 117-118 °C
(cyclohexanes-ethyl acetate); 1H NMR (CDCl3) δ 2.62 (s, 3H),
3.81 (s, 3H), 5.31 (br, 4H), 7.30 (s, 10H), 7.65 (s, 1H); MS (EI)
m/e 343 (M+), 252, 91.
Synthesis of Compounds 15b,c and 16-18. General
Procedure. The appropriate alkyl-stannane (3.8 mmol) and
Pd(PPh3)4 (140 mg) were added to a solution of 14 (700 mg,
1.93 mmol), in anhydrous NMP (N-methylpyrrolidinone) (4
mL), under nitrogen. The reaction mixture was stirred at 120
°C (8 h for compounds 15b, 15c and 17, 2 h for 16 and 20 h
for 18). The reaction mixture was cooled, diluted with water
and extracted with dichloromethane. The organic phase was
washed with brine and dried over anhydrous sodium sulfate,
and the solvent was evaporated under reduced pressure, thus
obtaining a dark liquid. The residue was purified by flash
chromatography, (cyclohexanes-ethyl acetate 7:3) giving 15b,c
and 16-18 in the form of solid or oily material.
Experimental Section
Dibenzyl-(2-n-butyl-9-methyl-9H-purin-6-yl)amine (15b).
1
Instrumentation. 1H NMR and 13C NMR spectra were
recorded on a Bruker AC 200 spectrometer; chemical shifts (δ
scale) are reported in parts per million (ppm) relative to the
central peak of the solvent. Coupling constants (J values) are
given in Hertz (Hz). EI-MS spectra (70 eV) were taken on a
Fisons Trio 1000. Molecular ions (M+) and base peaks only
are given. Melting points were determined on a Bu¨chi SMP-
510 capillary melting point apparatus and are uncorrected.
Yield 90%; mp nondeterminable - rubber-like substance; H
NMR (CDCl3) δ 0.91 (t, 3H, J ) 8.0 Hz), 1.3-1.5 (m, 2H), 1.7-
1.9 (m, 2H), 2.88 (t, 2H, J ) 7.6 Hz), 3.84 (s, 3H), 5.27 (br,
4H), 7.30 (s, 10H), 7.65 (s, 1H); MS (EI) m/e 385 (M+), 294,
238, 91.
Dibenzyl-(9-methyl-2-styryl-9H-purin-6-yl)amine (16).
1
Yield 84%; mp nondeterminable - rubber-like substance; H
NMR (CDCl3) δ 4.26 (s, 3H), 5.14 (br, 2H), 5.62 (br, 2H), 7.36

A2A Adenosine Receptor Antagonists
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 22 6893
(br, 15H), 7.65 (s, 1H), 7.71 (s, 1H), 7.96 (s, 1H); MS (EI) m/e
431 (M+), 340, 91.
Dibenzyl-(2-n-butyl-9-methyl-8-[1,2,3]triazol-2-yl-9H-
purin-6-yl)amine (23b). Yield 30%, mp 114 °C (dichlo-
1
romethane-acetone); H NMR (CDCl3) δ 0.92 (t, 3H, J ) 8.0
Synthesis of Compounds 15d-f. General Procedure.
Alkyl derivatives (16-18) (0.27 mmol) were placed in an
autoclave with ethanol (5 mL). The mixture was heated until
complete dissolution, and then 10% palladium on graphite (50
mg) was added. The mixture was stirred overnight under 4
atm of H2. The catalyst was filtered through Celite, and the
residue was washed with dichloromethane. The organic phases
were dried over anhydrous sodium sulfate and evaporated
under reduced pressure, to yield 15d-f.
Dibenzyl-(9-methyl-2-phenethyl-9H-purin-6-yl)-
amine (15d). Quantitative yield; mp 144 °C (ethanol); 1H
NMR (CDCl3) δ 3.16 (s, 4H), 3.81 (s, 3H), 5.2 (br, 4H), 7.2-7.3
(m, 15H), 7.66 (s, 1H); MS (EI) m/e 433 (M+), 342, 91.
Synthesis of Compounds 9 and 22a-f. General Pro-
cedure. Bromine (0.7 mL, 13.6 mmol) was added dropwise,
at 0°, to 8 or 15a-f (1.6 mmol) dissolved in a mixture of MeOH
(7 mL), THF (7 mL) and acetate buffer pH)4 (7 mL) (obtained
by dissolving 4 g of sodium acetate in 100 mL of water and by
adjusting to pH 4 with glacial acetic acid). The reaction was
stirred at room temperature until the starting products
disappeared (about 12 h). Excess of bromine was eliminated
with sodium metabisulfite and the reaction brought to pH 8
by addition of saturated solution of Na2CO3. The aqueous
phase was extracted with dichloromethane. The organic phases
were dried over anhydrous sodium sulfate and evaporated
under reduced pressure, to give a residue that was used for
the following reaction without further purification.
Hz), 1.3-1.4 (m, 2H), 1.7-1.9 (m, 2H), 2.84 (t, 2H, J ) 8.0
Hz), 3.97 (s, 3H), 5.01 (br, 2H), 5.45 (br, 2H), 7.29 (s, 10H),
7.94 (s, 2H); MS (EI) m/e 452 (M+), 361, 333, 91.
Dibenzyl-(2-n-butyl-9-methyl-8-[1,2,3]triazol-1-yl-9H-
purin-6-yl)amine (24b). Yield 50%; mp 139 °C (dichlo-
1
romethane-acetone); H NMR (CDCl3) δ 0.93 (t, 3H, J ) 8.0
Hz), 1.3-1.5 (m, 2H), 1.7-1.9 (m, 2H), 2.86 (t, 2H, J ) 8.0
Hz), 4.12 (s, 3H), 5.06 (br, 2H), 5.36 (br, 2H), 7.31 (s, 10H),
7.81 (d, 1H, J ) 0.8 Hz), 8.24 (d, 1H, J ) 0.8 Hz); MS (EI) m/e
452 (M+), 361, 333, 91.
Synthesis of Compounds 11, 25a-f, 32 and 41. General
Procedure. CF3SO3H (0.37 mL, 3.3 mmol) was added drop-
wise to a solution of 10a, 23a-f, 31 or 40 (0.33 mmol) in
anhydrous dichloromethane (3 mL), under nitrogen at 0 °C.
The mixture was refluxed for 6 h, then cooled and diluted with
water, basified (pH 10) with 30% NaOH and extracted with
dichloromethane. The organic phase was dried over anhydrous
sodium sulfate and evaporated under reduced pressure. The
residue was purified by flash chromatography (cyclohexanes-
ethyl acetate 3:7) to give a white solid that was crystallized
by ethanol.
2-n-Butyl-9-methyl-8-[1,2,3]triazol-2-yl-9H-purin-6-
ylamine (25b). Yield 55%; mp 182 °C (ethanol); 1H NMR
(CDCl3) δ 0.97 (t, 3H, J ) 7.25 Hz), 1.3-1.5 (m, 2H), 1.7-1.9
(m, 2H), 2.85 (t, 2H, J ) 7.9 Hz), 4.07 (s, 3H), 5.56 (br, 2H),
8.00 (s, 2H); MS (EI) m/e 272 (M+), 257, 243, 230. Anal.
(C12H16N8 ‚ 0.3 EtOH) C,H,N.
Dibenzyl-(8-bromo-2-n-butyl-9-methyl-9H-purin-6-yl)-
amine (22b). Quantitative yield; mp 89-87°C (dichlo-
9-Methyl-2-phenetyl-8-[1,2,3]triazol-2-yl-9H-purin-6-
ylamine (25d). Yield 5%; mp 164 °C (ethanol); 1H NMR
(CDCl3) δ 3.18 (s, 4H), 4.07 (s, 3H), 5.65 (br, 2H), 7.2-7.3 (m,
5H), 8.01 (s, 2H); MS (EI) m/e 320(M+), 303, 243, 216. Anal.
(C16H16N8) C,H,N.
1
romethane); HNMR (CDCl3) δ 0.90 (t, 3H, J ) 8.0 Hz), 1.2-
1.4 (m, 2H), 1.6-1.8 (m, 2H), 2.79 (t, 2H, J ) 8.0 Hz), 3.75 (s,
3H), 5.31 (s, 4H), 7.28 (s, 10H); MS (EI) m/e 465-463 (M+),
374-372, 91.
Dibenzyl-(8-bromo-9-methyl-2-phenethyl-9H-purin-6-
2-Chloro-N4-methyl-pyridine-3,4-diamine (27). A solu-
tion of 26 (10 g, 65.3 mmol), prepared according to the
literature,20 in 12 N HCl (50 mL) was heated to 90 °C. To this
hot solution was added SnCl2‚2H2O (72.5 g, 0.32 mmol) in five
portions over a 60-s period. This solution was stirred at 90 °C
for 1 h, cooled to 0 °C, diluted with 100 mL of water and
reduced in vacuo to dryness. The residue was dissolved in 100
mL of water and stirred in an ice bath whereas 2 N ammonia
solution was added dropwise until a precipitate formed. The
pH was adjusted to 8.5-9 and the resulting emulsion centri-
fuged. The solid residue was redissolved in water and centri-
fuged. The operation was repeated three times. The combined
solid residues were stirred overnight in 50 mL of dichlo-
romethane. The centrifuged aqueous phases were extracted
three times with dichloromethane, then the combined organic
phases were dried over anhydrous sodium sulfate and evapo-
rated under reduced pressure, yielding 6.2 g (60%) of desired
compound (27) (pink crystals); mp 165 °C (dichloromethane);
1H NMR (CDCl3) δ 2.92 (d, 3H, J ) 4.8 Hz), 3.45 (br, 2H),
4.26 (br, 1H), 6.45(d, 1H, J ) 5.3 Hz), 7.78 (d, 1H, J ) 5.3
Hz); MS (EI) m/e 159-157 (M+), 143-141, 116-114.
Synthesis of Compounds 28 and 37. General Proce-
dure. To a solution of 27 or 36 (15.2 mmol) in triethyl
orthoformate (97 mL) and DMF (added with stirring until the
turbidity disappeared) was added 12 N HCl solution (1.7 mL),
under nitrogen. The mixture was stirred at room temperature
for 12 h. The solvent was evaporated under reduced pressure
and the brown oily residue purified by flash chromatography
(cyclohexane-ethyl acetate 2:8) provided a white solid.
4-Chloro-1-methyl-1H-imidazo[4,5-c]pyridine (28). Yield
68%; mp 168-170 °C (cyclohexane- ethyl acetate); 1H NMR
(CDCl3) δ 3.91 (s, 3H), 7.33 (d, 1H, J ) 5.6 Hz), 7.98 (s, 1H),
8.24 (d, 1H, J ) 5.6 Hz); MS (EI) m/e 169-167 (M+), 132, 105.
2-Bromo-4-chloro-1-methyl-1H-imidazo[4,5-c]pyri-
dine (29). 2.5 M BuLi in hexane (8 mL, 20 mmol) was added
dropwise to a solution of 28 (1.5 g, 9 mmol) in anhydrous THF
(25 mL), under nitrogen at -78 °C. The solution was stirred
at this temperature for 1 h, then bromine (2 mL, 40 mmol)
was carefully added dropwise, over a period of 30 min. This
yl)amine (22d). Quantitative yield; mp nondeterminable -
1
rubber-like substance; H NMR (CDCl3) δ 3.15 (s, 4H), 3.78
(s, 3H), 4.99 (br, 2H), 5.41 (br, 2H), 7.2-7.3 (m, 15H); MS (EI)
m/e 422-420, 91.
Synthesis of Compounds 10a, 23a, 23c-f, 30a,b and
39a,b. General Procedure. 1H-1,2,3-triazole (0.18 mL, 2.5
mmol) was added dropwise to a suspension of anhydrous DMF
(2 mL) and NaH (80% in paraffin, 92 mg, 2.5 mmol) under
nitrogen. The mixture was stirred for 1 h and to it was added,
dropwise, a solution of crude bromoderivatives (1.7 mmol) in
anhydrous DMF (5 mL) and stirred at 100 °C for 12 h. The
solvent was removed under reduced pressure, and water was
added to the residue. The aqueous phase was extracted with
dichloromethane, and the organic phases were dried over
anhydrous sodium sulfate and evaporated under reduced
pressure. The residue was purified by flash chromatography
(cyclohexanes-ethyl acetate). N-2-triazolyl derivatives of com-
pounds 10a, 23a and 23c-f were isolated by flash chroma-
tography whereas their regioisomers were not eluted under
the conditions used. 30a,b and 39a,b could not be separated
by chromatography and were used in the following reaction
as a mixture of the two regioisomers.
Dibenzyl-(9-methyl-2-phenethyl-8-[1,2,3]triazol-2-yl-
9H-purin-6-yl)amine (23d). Yield 20%; mp 173 °C (cyclohex-
anes-ethyl acetate); 1H NMR (CDCl3) δ 3.1-3.2 (m, 2H), 3.2-
3.3 (m, 2H), 4.10 (s, 3H), 5.00 (br, 2H), 5.53 (br, 2H), 7.2-7.3
(m, 15H), 7.96 (s, 2H); MS (EI) m/e 500 (M+), 409, 91.
Synthesis of Compounds 23b and 24b. K2CO3 (5.32 g,
28 mmol) and 1H-1,2,3-triazole (1.6 mL, 28 mmol) were added
to a solution of 22b (18 mmol) in anhydrous DMF (300 mL),
under nitrogen. The mixture was refluxed for 20 h at 100 °C.
The solvent was removed under reduced pressure, and water
was added to the residue. The aqueous phase was extracted
with dichloromethane, and the organic phases were dried over
anhydrous sodium sulfate and evaporated under reduced
pressure. The residue was purified by flash chromatography
(dichloromethane-acetone 98:2) giving 23b and 24b as white
solids.

6894 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 22
Minetti et al.
solution was stirred at -78 °C for 2 h and cooled slowly at 0
°C, and then a saturated solution of sodium metabisulfite was
added dropwise until the bromine was completely destroyed.
The solution was basified (pH 9) with 2 N Na2CO3. The
solution was extracted with dichloromethane. The combined
organic phases were washed with brine, dried over anhydrous
sodium sulfate and evaporated under reduced pressure. A
brownish solid was obtained which crystallized in water giving
1.4 g (64%) of desired compound (29) in the form of white
crystals: mp 207-209 °C (water); 1H NMR (CDCl3) δ 3.85 (s,
3H), 7.25 (d, 1H, J ) 6,1 Hz), 8.23 (d, 1H, J ) 6.1 Hz); MS
(EI) m/e 249-247-245 (M+), 212-210, 131, 105.
Synthesis of Compounds 31 and 40. General Proce-
dure. Crude 30a,b or 39a,b (5.5 mmol), in a flat-bottomed,
long-necked flask, was suspended in benzylamine (5 mL). The
reaction mixture was placed inside a microwave oven (fre-
quency of irradiation: 2.450 MHz) and irradiated at 460 W
until the benzylamine boiled (about 1-2 min) and then cooled
at r.t. The irradiation was repeated until the starting material
disappeared, as monitored by TLC. Cooling after the last cycle
yielded a yellow waxy mass that was purified by flash
chromatography [gradient: cyclohexanes-ethyl acetate 4:6
(100 mL), cyclohexanes-ethyl acetate 2:8 (100 mL), ethyl
acetate].
(s, 3H), 2.88 (d, 3H, J ) 5.2 Hz), 3.29 (br, 2H), 4.29 (br, 1H),
6.29 (s, 1H); MS (EI) m/e 173-171 (M+), 158-156, 143-141,
109-107.
2-Bromo-4-chloro-1,6-dimethyl-1H-imidazo[4,5-c]pyri-
dine (38). 2 M LDA (lithium diisopropylamide) in THF/
heptane/ethylbenzene (1.2 mL, 2.4 mmol) was added dropwise
to a solution of 37 (1.33 mmol) in anhydrous THF (3.3 mL),
under nitrogen at -78 °C. The solution was stirred at this
temperature for 30 min, then NBS (N-bromosuccinimide) (470
mg, 2.65 mmol) was added. This solution was stirred at room
temperature for 1 h, and then a saturated NH4Cl solution was
added. The mixture was extracted with dichloromethane, the
organic phases washed with brine and dried over anhydrous
sodium sulfate and then evaporated under reduced pressure.
The residue was purified by flash chromatography (ethyl
acetate) yielding 132 mg (38%) of desired compounds (38); mp
1
133-134 °C (ethyl acetate); H NMR (CDCl3) δ 2.60 (s, 3H),
3.76 (s, 3H), 7.02 (s, 1H); MS (EI) m/e 263-261-259 (M+),
248-246-244, 182-180.
Pharmacology. Compounds 11, 25a-f, 32 and 41 which
represent the two planned series A and B, were tested for their
affinity to human A1, A2A and A2B adenosine receptors. 25b
and 25c only were tested for their affinity to human A3
adenosine receptors.
Affinity toward the Adenosine A1 Receptor. The inter-
active capacity of each product toward the adenosine A1
receptor was evaluated using membranes from human recom-
binant CHO cells which stably express the human A1 subtype.
These membranes were incubated with [3H]-DPCPX at a
concentration of 1 nM in a buffer comprised of 50 mM Tris
(pH 7.4), 120 mM NaCl; 5 mM KCl; 10 mM MgCl2; 2 mM
CaCl2, 2 U/mL of adenosine deaminase for 60 min at 22 °C.
Nonspecific binding was measured in the presence of DPCPX
(8-cyclopentyl-1,3-dipropylxantine) at a concentration of 1 µM.
Affinity toward the Adenosine A2A Receptor. The
interactive capacity of each product toward the adenosine A2A
receptor was evaluated using membranes from human recom-
binant HEK 293 cells (human embryo kidney cells) stably
expressing the human A2A receptor subtype exclusively.
These membranes were incubated with [3H]-CGS21680 at
a concentration of 6 nM in a buffer comprised of 50 mM Tris
(pH 7.4), 120 mM NaCl; 10 mM MgCl2; 2 mM CaCl2, 2 U/mL
of adenosine deaminase for 90 min at 22 °C. Nonspecific
binding was measured in the presence of NECA (10 µM).
Affinity toward the Adenosine A2B Receptor. The
interactive capacity of each product toward the adenosine A2B
receptor was evaluated using membranes from human recom-
binant HEK 293 stably expressing the human A2B receptor
subtype exclusively.
4-Benzyl-(1-methyl-2-[1,2,3]triazol-2-yl-1H-imidazo[4,5-
c]pyridin-4-yl)amine (31). Yield 29%; mp 180-184 °C (ethyl
acetate); 1H NMR (CDCl3) δ 4.00 (s, 3H), 4.8 (br, 1H), 5.87
(br, 2H), 6.71 (d, 1H, J ) 5.9 Hz), 7.3-7.4 (m, 5H), 7.98 (s,
2H), 8.04 (d, 1H, J ) 5.9 Hz); MS (EI) m/e 305 (M+), 215, 200.
2,4-Dichloro-6-methyl-3-nitropyridine (34). 33 (1 g, 5.88
mmol) and diethylaniline (0.94 mL, 5.88 mmol) were heated
at reflux in POCl3 (4.5 mL) for 3 h. After cooling the solution
was poured into ice-water (50 mL) and stirred at room
temperature for 2.5 h. The mixture was extracted with ethyl
acetate, and the organic phases were washed with saturated
NaHCO3 solution and brine, dried over anhydrous sodium
sulfate and evaporated under reduced pressure. The residue
was dissolved in ethyl acetate and passed through a glass
funnel packed with a layer of silica gel (2 cm thick) and Celite
(2 cm thick). The filtrate was evaporated under reduced
pressure to give 1.2 g (98%) of desired compound (34) which
was used for the following reaction without further purifica-
tion: mp 74-75 °C (ethyl acetate); 1H NMR (CDCl3) δ 2.62 (s,
3H), 7.31 (s, 1H); MS (EI) m/e 210-208-206 (M+), 180-178-
176, 171, 164-162-160.
(4-Chloro-6-methyl-3-nitro-pyridin-2-yl)methyl-
amine (35a). To an ice-cooled mixture of 34 (600 mg, 2.90
mmol) in ethanol (6 mL) were added sodium carbonate (768
mg, 7.25 mmol) and a 40% w/w water solution of methylamine
(0.3 mL) dropwise. The resulting mixture was stirred at room-
temperature overnight. The solvent was evaporated, and water
was added to the residue. The aqueous phase was extracted
with ethyl acetate, and the organic phases were washed with
brine, dried over anhydrous sodium sulfate and evaporated
under reduced pressure. The residue was purified by flash
chromatography (cyclohexanes-ethyl acete 8:2) yielding 74 mg
(13%) of the desired compound (35a): mp 148-150 °C (cyclo-
hexanes-ethyl acetate); 1H NMR (CDCl3) δ 2.43 (s, 3H), 3.10
(d, 3H, J ) 4.8 Hz), 6.57 (s, 1H), 7.27 (br, 1H); MS (EI) m/e
203-201 (M+), 173-171, 166.
These membranes were incubated with [3H]-DPCPX at a
concentration of 5 nM in a buffer comprised of 50 mM Tris
(pH 7.4), 120 mM NaCl; 10 mM MgCl2; 2 mM CaCl2, 2 U/mL
of adenosine deaminase for 120 min at 22 °C. Nonspecific
binding was measured in the presence of NECA (100 µM).
Affinity toward the Adenosine A3 Receptor. For this
study, membranes from human recombinant HEK-293 cells,
which express the human A3 subtype, were used according to
the method described in the literature.25 Experimental condi-
tions required the use of [125I]AB-MECA as a radioligand at a
concentration of 0.1 nM, an incubation time of 90 min at a
temperature of 22 °C, and IB-MECA (1 µM) for the determi-
nation of nonspecific binding.
Spontaneous Locomotor Activity in Rats. The effect of
25b on motor performance was examined in 344 male Fischer
rats. The fasting animals (12 rats per group) were given either
25b (1.25, 2.5, 5 and 10 mg/kg po) or vehicle (0.3% Tween 80,
10% sucrose and saline). Rats were individually placed in
Plexiglas activity cage (40 × 40 cm) with photocells on the
walls. The photocells were connected through an interface to
a computer. The consecutive interruption of photocell beams
was taken as locomotion count. Rats were placed in the activity
cage for 30 min and then treated with either vehicle or test
compound. Locomotor activity was recorded for 90 min after
the administration of the test compound.
2-Chloro-6,N4-dimethylpyridine-3,4-diamine (36). Pow-
dered Fe (56 mg) was added to a solution of 35a (100 mg, 0.5
mmol) in MeOH (2 mL) and 1 N HCl solution (9.8 mL). The
mixture was stirred at room-temperature overnight and then
basified (pH 10) with 1 N NaOH solution and filtered through
a Celite cake, which was washed with several portions of ethyl
acetate and MeOH. The layers were separated, and the
aqueous phase was extracted with additional ethyl acetate.
The combined organic phases were washed with brine, dried
over anhydrous sodium sulfate and evaporated under reduced
pressure, to give a residue (36) that was used for the following
reaction without further purification.Yield 80%; mp nonde-
1
terminable - rubber-like substance; H NMR (CDCl3) δ 2.38

A2A Adenosine Receptor Antagonists
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Supporting Information Available: Spectroscopic data
of compounds 8, 9, 10a, 15c,e,f, 17, 18, 22a,c,e,f, 23a,c,e,f,
30a,b, 37, 39a,b, 40. Spectroscopic data and elemental analy-
sis of compounds 11, 25a,c,e,f, 32, 41. Elemental analysis of
compounds 25b,d. This material is available free of charge via
Internet at http://pubs.acs.org.
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