Synthesis and pharmacological evaluation of novel 1,3,8- and 1,3,7,8-substituted xanthines as adenosine receptor antagonists

Article abstract of DOI:10.1016/j.bmc.2010.01.028

A number of novel xanthines bearing a variety of substituents at positions 1, 3, 7 and 8 were prepared and evaluated for their binding affinity to the human adenosine receptor A₁, A_2A, A_2B and A₃ subtypes. Several of the 1,3,8- and 1,3,7,8-substituted xanthines showed moderate-to-high affinity at human A_2B and A₁ receptors, with the most active compound (14q) having a pK_i of 7.57 nM for hA_2B receptors and a selectivity over hA_2A receptors of 8.1-fold and hA₁ receptors of 3.7-fold.

Full text of DOI:10.1016/j.bmc.2010.01.028

Bioorganic & Medicinal Chemistry 18 (2010) 2001–2009
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis and pharmacological evaluation of novel 1,3,8- and 1,3,7,8-substituted
xanthines as adenosine receptor antagonists
b
c,d
José Enrique Rodríguez-Borges a, Xerardo García-Mera b,c, , María Carmen Balo , José Brea
,
*
Olga Caamaño b,c, Franco Fernández b,c, Carmen López b,c, María Isabel Loza c,d, María Isabel Nieto e
a CIQ-Departamento de Química, Facultade de Ciencias, Universidade de Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal
b Departamento de Química Orgánica, Facultade de Farmacia, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Spain
c Instituto de Farmacia Industrial, Facultade de Farmacia, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Spain
d Departamento de Farmacología, Facultade de Farmacia, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Spain
e Departamento de Química Fundamental, Facultade de Química, Universidade de A Coruña, Campus da Zapateira, 15071, A Coruña, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
A number of novel xanthines bearing a variety of substituents at positions 1, 3, 7 and 8 were prepared and
evaluated for their binding affinity to the human adenosine receptor A1, A2A, A2B and A3 subtypes. Several
of the 1,3,8- and 1,3,7,8-substituted xanthines showed moderate-to-high affinity at human A2B and A1
receptors, with the most active compound (14q) having a pKi of 7.57 nM for hA2B receptors and a selec-
tivity over hA2A receptors of 8.1-fold and hA1 receptors of 3.7-fold.
Received 2 November 2009
Revised 11 January 2010
Accepted 12 January 2010
Available online 15 January 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Adenosine receptor antagonist
A1, A2A, A2B and A3 binding affinities
1,3,8- and 1,3,7,8-substituted xanthines
1. Introduction
Despite the fact that a number of high-affinity A2B-AdoR antag-
onists have been reported, very few have shown high affinity and
Adenosine is an endogenous non-selective agonist that acti-
vates all four subtypes of adenosine receptors (AdoR): A1, A2A
selectivity for A2B-AdoR relative to A1-, A2A- and A3-AdoR.8–11 The
xanthine-based A2B antagonists currently show the most promis-
ing combination of high affinity and selectivity12 and, as a result,
in recent years new and more selective high-affinity A2B antago-
nists with a xanthine scaffold have been developed. These com-
pounds include 3 (PSB-601),13 4 (PSB-603; first A2B antagonist
with subnanomolar affinity)14 and 5 (CVT-6883).15 Compound 5
is currently being evaluated for cardiopulmonary disease in a
phase I clinical study and is the first A2B antagonist in clinical
trials.15
Recently, we reported a series of a new 1,3,8-trisubstituted
xanthines (compounds 6 and 7; Fig. 2) some of which showed
interesting affinity values and selectivity for A2B-AdoR.16,17
The work reported here was carried out as part of a line of
investigation directed at finding a potentially selective, high
affinity A2B-AdoR antagonist through the preparation of a series
of xanthines bearing appropriate and/or more substituents in
several positions of the xanthine nucleus. The new adenosine
analogues of xanthine have structural variations at position 1
(alkyl or functionalized alkyl substituents), position 3 (alkyl or
functionalized alkyl or aryl or heteroaryl substituents), position
7 (unsubstituted or methyl substituent) and position 8 (aryl or
heteroaryl substituents) of the xanthine nucleus (Schemes 1
and 2).
,
A2B and A3.1 Adenosine receptors have been recognized as playing
an important role in chronic inflammatory airway conditions such
as asthma, chronic obstructive pulmonary disease and fibrosis.2,3
Experimental evidence, such as the increase in the adenosine con-
centration in hypoxia and cellular inflammation in the bronchoal-
veolar fluids of asthmatics and in plasma (upon contact with
allergens), has highlighted the key role that adenosine and its A2B
receptors play in asthma.4–6 Theophylline (1), which has a well-
established role in the therapy of asthma, selectively blocks the
AMP-induced bronchoconstriction in asthmatics. The bronchodi-
lating effect of theophylline and its structural analogue enprofyl-
line (2) has been attributed to a selective antagonism of the
A2B-AdoR.6 In addition, the recent discovery that A2B-AdoR are
functionally active on both human airway smooth muscle cells
and lung fibroblast cells provides further support for the role of
A2B-AdoR in inflammation and asthma.4,7 Therefore, antagonists
at the A2B-AdoR would provide a novel approach to the manage-
ment and treatment of asthma and chronic obstructive pulmonary
disease (Fig. 1).
* Corresponding author. Tel.: +34 981 563100x14939; fax: +34 981594912.
E-mail address: xerardo.garcia@usc.es (X. García-Mera).
0968-0896/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2010.01.028

2002
J. E. Rodríguez-Borges et al. / Bioorg. Med. Chem. 18 (2010) 2001–2009
O
N
O
H
N
H
N
1
5
4
7
HN
N
6
8
2
N
N
9
O
O
N
3
1. Theophylline
2. Enprophylline
O
O
N
H
N
O
H
O
N
N
N
S
N
N
N R
N
N
N
N
H
O
O
CF3
3
. PSB-601, R = benzyl
5. CVT-6883
4
. PSB-603, R = 4-chlorophenyl
Figure 1. Classic and prototypical xanthine-derived A2B receptor antagonists.
O
N
O
N
R3
R3
R1
O
R1
O
N
N
R2
N
N
R2
N
O
N
O
7
6
R1= methyl, ethyl, propyl, isobutyl, pentyl,
cyclopropylmethyl, prop-2-ynyl, allyl, 2-
methoxyethyl, 2-ethoxyethyl, 2-
(methylthio)ethyl,2-(ethylthio)ethyl, 2-
(ethylsulfinyl)ethyl, 2-(ethylsulfonyl)ethyl.
R2 = phenyl, furan-2-yl, thiophen-2-yl, 2,6-
difluorophenyl.
R1= ethyl, propyl, isobutyl, pentyl, 2-
methoxyethyl, 2-ethoxyethyl, 2-
(ethylthio)ethyl,2-(ethylsulfinyl)ethyl, 2-
(ethylsulfonyl)ethyl.
R2= phenyl, furan-2-yl, thiophen-2-yl,
biphenyl-4-yl, furfuryl, pyrrol-2-yl, cyclopentyl,
3-phenylpropyl.
R3= H, methyl.
R3= H, methyl.
Figure 2.
O
O
O
R1
O
NO
R1
O
ii
N
i
N
HN
O
N
H
9
NH2
N
H
8
NH2
N
H
NH2
iii
O
O
O
O
O
HN R3
HN R3
R1
O
R1
O
R1
O
NH2
NH2
v
iv
N
N
N
N
N
R2
12
NH2
N
NH2
N
H
10
H
11
vi
O
N
R2
14
O
H
CH3
N
R1
O
R1
O
N
vii
N
R3
R3
N
N
N
R2
13
Scheme 1. Reagents and conditions: (i) (a) HMDS, (NH4)2SO4, reflux, 2 h, (b) R1X, toluene, reflux, 90 min, (c) Na2S2O3, H2O, rt; (ii) NaNO2, 50% aq AcOH, 80 °C, 45 min; (iii)
Na2S2O4, 35% aq NH4OH, 60 °C, 1 h; (iv) R3CO2H, DIC, MeOH, rt, 1 h; (v) R2X, K2CO3, DMF, 50 °C, 48 h; (vi) NaOH, MeOH, reflux, 2 h; (vii) CH3I, K2CO3, DMF, 100 °C, 5 h.

J. E. Rodríguez-Borges et al. / Bioorg. Med. Chem. 18 (2010) 2001–2009
2003
O
N
O
N
O
N
H
N
H
N
H
N
R1
O
R1
O
R1
O
ii
N
N
N
i
R3
R3
R3
N
N
N
O
S
S
O
S
O
16c,R1 = propyl; R3 = phenyl
16d,R1 = propyl; R3 = benzyl
16g,R1 = ethyl; R3 = benzyl
16h,R1 = ethyl; R3 = pheny
15c,R1 = propyl; R3 = phenyl
15d,R1 = propyl; R3 = benzyl
15g,R1 = ethyl; R3 = benzyl
15h,R1 = ethyl; R3 = phenyl
13c,R1 = propyl; R3 = phenyl
13d,R1 = propyl; R3 = benzyl
13g,R1 = ethyl; R3 = benzyl
13h,R1 = ethyl; R3 = phenyl
Scheme 2. Reagents and conditions: (i) OxoneÒ, aliquat, CH3CN, H2O, CH2Cl2, rt. (ii) AcOH, 30% H2O2, rt.
A series of 8-methyl derivatives was prepared with the aim of
assessing the influence of methylation of the nitrogen at position
7 of the xanthine ring. The results indicate that methylation of po-
sition 7 has a different effect depending on the receptor. For exam-
ple, in the case of the A3 receptors a significant decrease in the
affinity levels was observed whereas the affinity values for the A1
receptors showed irregular behavior. This is exemplified by com-
pounds 14c and 14e (R1 = propyl), which showed extremely low
affinity in comparison to the demethylated analogues (13c and
13e), and compounds 14m, 14p, 14q and 14r (R1 = ethyl), for which
the affinity values showed a marked increase. For the A2B and A2A
receptors a significant increase in affinity levels was obtained
(14m, 14n, 14p, 14q and 14r). However, this increase in affinity
was accompanied by a significant decrease in A2B/A2A selectivity.
The best results were obtained for compound 14q (R1 = ethyl,
R2 = thiophen-2-ylmethyl, R3 = furfuryl, R4 = methyl), which
showed pKi values of 7.57 and 6.66 against A2B and A2A, respec-
tively, and had a Ki(A2B)/Ki(A2A) ratio of 8.1-fold, and compound
14n (R1 = ethyl, R2 = benzyl, R3 = furfuryl, R4 = methyl), which
showed pKi values of 6.55 and 5.76 against A2B and A2A, respec-
tively, and had a Ki(A2B)/Ki(A2A) ratio of 6.2-fold.
2. Chemistry
The synthesis of the target 1,3,8-trisubstituted-1H-purine-2,6-
(3H,9H)-diones, (13 and 14) is outlined in Scheme 1. Firstly, 3-
substituted 6-aminouracils, 8, were prepared by alkylation of sily-
lated 6-aminouracil with alkyl iodides in high yields via a silylated
intermediate.18 Standard nitrosation of compounds 8 with sodium
nitrite in acetic acid leading to compounds 9, was followed by
reduction with sodium dithionite to give 3-substituted 5,6-diami-
nouracils 10.19 These compounds were subsequently condensed
with the corresponding carboxylic acid to introduce the 8-substitu-
ent of the xanthines to afford compounds 11.20 Alkylation or aryl-
alkylation of uracil derivatives 11 was easily performed under mild
conditions in dimethylformamide using alkyl or arylalkyl bromides
or iodides and potassium carbonate.20 Finally, the imidazole ring
was cyclized by heating under reflux a mixture of compounds 12
and 2.5 N NaOH in MeOH to afford xanthines 13a–t.16,17,20
The 7-methylated derivatives 13c, 13e and 13m–r were ob-
tained by methylation of the corresponding xanthines with excess
methyl iodide in dimethylformamide in the presence of potassium
carbonate.16,17,20
Finally, oxidation of the sulfur atom of the 2-(ethylthio)ethyl
chain (13c, 13d, 13g and 13h) resulted in a significant decrease
in the affinity at all the AdoRs assayed (15c, 15d, 15g and 15h;
16c; 16d, 16g and 16h).
Oxidation of the corresponding xanthines to the sulfoxides 15c,
15d, 15g and 15h and sulfones 16c, 16d, 16g and 16h (Scheme 2)
was achieved by previously reported literature procedures.21
3. Results and discussion
4. Conclusions
The affinity (pKi or displacement percentage) values of the xan-
thine derivatives 13, 14, 15 and 16, at cloned human adenosine
receptors expressed in CHO (hA1), HeLa cells (hA2A and hA3) and
HEK-293 cells (hA2B), are given in Table 1.22 The radioligand
[3H]DPCPX was used for competition binding assays on A1 and
A2B receptors, [3H]ZM241385 was used for A2A receptors whereas
[3H]NECA was used for A3 receptors. The affinity values of com-
pounds that did not fully displace specific radioligand binding at
In summary, a set of novel xanthine derivatives (compounds
13a–t, 14c, 14e, 14m–r, 15c–d, 15g–h, 16c–d and 16g–h) has been
synthesized and their affinities for A1, A2A, A2B and A3 receptors
have been evaluated. These compounds showed moderate-to-low
affinity for all receptors with low levels of selectivity, with the
exception of compound 13p [1-ethyl-3,8-bis(thiophen-2-yl-
methyl)-1H-purine-2,6(3H,7H)-dione; A2A/A2B ratio = 28.9, A1/A2B
ratio = 4.9; A3/A2B ratio = 5.9]. The biological results also show that
the presence of an additional methyl group at position 7 (14m–n
and 14p–r) is beneficial for A1, A2B and A2A affinities. This result
confirms the trend found in previous studies carried out by our
group.17 Despite the moderate-to-low affinity results obtained for
these compounds, an important pool of new xanthine derivatives
has been synthesized, characterized an evaluated biologically.
1 lM are given only in terms of displacement percentage. These
compounds showed moderate-to-low affinity for expressed human
A1, A2A, A2B and A3 receptors. However, the results shown in Table
1 enable certain trends to be highlighted concerning the SAR in this
group of xanthines.
The 1,3,8-substituted xanthine derivatives (13a–t) showed mod-
erate-to-low affinity for A1 and A2B receptors and even lower affinity
for A3 and A2A receptors. The best results were obtained on introduc-
ing an ethyl group in position 1 of the xanthine ring, a thiophen-2-
ylmethyl or 2-(ethylthio)ethyl group in position 3 and an aromatic
substituent bonded directly or a heteroaromatic unit attached
through a methylene bridge to position 8 of the xanthine ring. Of
the 20 compounds prepared, only 13p (R1 = ethyl, R2 = R3 = thio-
phen-2-ylmethyl) had an interesting A2B/A2A selectivity level
(28.9), although the affinity values for both receptors are reasonably
low and in any case very similar for the different AdoRs assayed.
5. Experimental
All chemicals were of reagent grade and were obtained from Al-
drich Chemical Co. and used without further purification. Where
necessary, solvents were dried by standard techniques and dis-
tilled. All air-sensitive reactions were carried out under argon.
Flash chromatography was performed on silica gel (Merck 60,
230–240 mesh) and analytical TLC was carried out on pre-coated

2004
J. E. Rodríguez-Borges et al. / Bioorg. Med. Chem. 18 (2010) 2001–2009
Table 1
Chemical structures and binding affinitiesa at hA1, hA2A, hA2B and hA3 AdoRs of xanthine derivatives 13, 14, 15 and 16
R4
O
R1
N
N
R3
N
N
R2
O
General structure of compounds 13, 14, 15 and 16
Compound R1
R2
R3
R4
hA1
hA2A hA2B hA3
A2B selectivity
hA2A/hA2B hA1/hA2B hA3/hA2B
13a
13b
13c
13d
13e
13f
13g
13h
13i
Propyl
Ethoxyethyl
Ethoxyethyl
2-(Ethylthio)ethyl
2-(Ethylthio)ethyl
Tetrahydrofuran-2-ylmethyl Phenyl
Tetrahydrofuran-2-ylmethyl Benzyl
2-(Ethylthio)ethyl
2-(Ethylthio)ethyl
Cyclohexylmethyl
Cyclohexylmethyl
Phenyl
Benzyl
Phenyl
Benzyl
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
39%
22%
7.03 5.84
33% 8%
6.65 37%
2%
34%
6.83 12%
42% 11%
6.66 29%
6%
13%
24%
5%
47%
2%
6.93 7.6
—
—
—
—
0.5
—
—
—
—
0.3
—
—
—
—
—
—
—
4.9
—
—
—
—
—
0.6
—
—
—
—
0.9
—
—
—
—
—
—
—
5.9
—
—
—
—
—
—
—
—
—
—
—
—
0.4
—
—
—
—
—
—
—
Propyl
Propyl
Propyl
Propyl
Propyl
Ethyl
Ethyl
Methyl
Methyl
6.72
12%
64%
32%
5%
6.32
2%
34%
1%
10%
52%
34%
8%
6.86
30%
52%
22%
46%
26%
41%
6.43
6.55
48%
7.45
7.57
6.87
6.23
1%
1%
—
—
—
—
—
—
—
—
—
—
—
—
6.87
10%
10%
6.39
2%
41%
16%
2%
24%
0%
Benzyl
Phenyl
Thiophen-2-ylmethyl
Thiophen-2-yl
Thiophen-2-ylmethyl
Thiophen-2-yl
Thiophen-2-ylmethyl
Furfuryl
2,6-Difluorobenzyl
Thiophen-2-ylmethyl
Furfuryl
2,6-Difluorobenzyl
Biphenyl-4-yl
Biphenyl-4-yl
Phenyl
13j
13k
13l
Cyclohexylmethyl Cyclohexylmethyl
Cyclohexylmethyl Cyclohexylmethyl
4%
2%
50%
14%
6%
9%
1%
13m
13n
13o
13p
13q
13r
13s
13t
14c
14e
14m
14n
14o
14p
14q
14r
15c
15d
15g
15h
16c
16d
16g
16h
Ethyl
Ethyl
Ethyl
Ethyl
Ethyl
Ethyl
Ethyl
Ethyl
Propyl
Propyl
Ethyl
Ethyl
Ethyl
Ethyl
Ethyl
Ethyl
Propyl
Propyl
Ethyl
Ethyl
Propyl
Propyl
Ethyl
Ethyl
Benzyl
Benzyl
Benzyl
Thiophen-2-ylmethyl
Thiophen-2-ylmethyl
Thiophen-2-ylmethyl
2-(Ethylthio)ethyl
2-Ethoxyethyl
2-(Ethylthio)ethyl
Tetrahydrofuran-2-ylmethyl Phenyl
Benzyl
Benzyl
Benzyl
Thiophen-2-ylmethyl
Thiophen-2-ylmethyl
Thiophen-2-ylmethyl
2-(Ethylsulfinyl)ethyl
2-(Ethylsulfinyl)ethyl
2-(Ethylsulfinyl)ethyl
2-(Ethylsulfinyl)ethyl
2-(Ethylsulfonyl)ethyl
2-(Ethylsulfonyl)ethyl
2-(Ethylsulfonyl)ethyl
2-(Ethylsulfonyl)ethyl
22%
23%
23%
6.17 5.40
6.39 19%
28%
7%
19%
39%
30%
1%
6.09 28.9
42%
38%
17%
17%
1%
6.20
6%
14%
4%
—
—
—
—
—
—
2.1
6.2
—
3.5
8.1
1.3
—
—
—
—
—
21%
4%
28%
2%
—
—
—
1.1
—
Methyl 17%
Methyl 38%
25%
Thiophen-2-ylmethyl Methyl 6.41 6.12
Furfuryl
2,6-Difluorobenzyl
Thiophen-2-ylmethyl Methyl 7.02 6.91
Furfuryl
2,6-Difluorobenzyl
Phenyl
Benzyl
Benzyl
Phenyl
Phenyl
Benzyl
Benzyl
Methyl 29%
Methyl 21%
5.76
28%
—
1%
2.7
3.7
0.9
—
—
—
—
—
—
—
Methyl 7.00
Methyl 6.92 6.75
6.66
22%
20%
6.61
18%
3%
H
H
H
H
H
H
H
H
6.71 9%
10%
5%
29%
7.03 3%
15%
6%
35%
7%
0%
20%
0%
32%
39%
2%
55%
18%
0%
7.03
15%
6%
13%
1%
0%
—
—
—
Phenyl
35%
—
a
Binding affinity is expressed as pKi or displacement percentage at 1 lM where indicated. pKi and displacement percentage values have an SEM <10%.
silica gel plates (Merck 60 F254, 0.25 mm) type E. Chromatographic
spots were visualized by UV light or with Hanessian reagent.23
Melting points (uncorrected) were measured in glass capillary
tubes on a Stuart Scientific SMP3 electro thermal apparatus. Infra-
red spectra were recorded on a Perkin–Elmer 1640 FTIR spectro-
photometer. 1H NMR and 13C NMR spectra were recorded on a
Bruker AMX 300 spectrometer at 300 and 75.47 MHz, respectively,
using TMS as internal standard (chemical shifts in d values, J in
hertz). All of the observed signals are consistent with the proposed
structures. Chemical shifts (d scale) are reported in parts per mil-
lion (ppm) relative to the center of the solvent peak. Coupling con-
stants (J values) are given in hertz (Hz). Spin multiplicities are
given as s (singlet), d (doublet), dd (doublet of doublets), t (trip-
let), m (multiplet), br s (broad singlet), v s (virtual singlet), dt
(doublet of triplets), q (quartet), qt (quintet), sex (sextet). Elemen-
tal analyses were performed in a FISONS EA 1108 Elemental
Analyser at the University of Santiago Microanalysis Service;
all results shown are within 0.4% of the theoretical values
(C, N, H).
5.1. General procedure for the preparation of xanthines 13
The carboxamide 12 (3 mmol) was dissolved in a mixture of
MeOH (100 mL) and 20% aqueous NaOH (20 mL) and the mixture
was heated under reflux for 2 h. After cooling, the solution was
acidified to pH 4–5 with concentrated HCl. The resulting precipi-
tate was filtered off, washed with H2O, and air-dried under vacuum
to afford xanthines 13.
5.1.1. 3-(2-Ethoxyethyl)-8-phenyl-1-propyl-1H-purine-2,6-
(3H,9H)-dione, 13a
Yield 88%. White solid. Mp = 227–229 °C (H2O). IR (KBr)
m
(cmꢀ1) = 3166, 2967, 2880, 1695, 1654, 1555, 1523, 1470. 1H
NMR (DMSO): 13.62 (br s, 1H, D2O exchang. NH), 8.20–8.10 (m,
2H, ArH), 7.57–7.47 (m, 3H, ArH), 4.21–4.13 (t, J = 6.0 Hz, 2H, 1-
H2 Pr), 3.96–3.88 (t, J = 7.4 Hz, 2H, 10-H2), 3.78–3.70 (t, J = 6.0 Hz,
2H, 20-H2), 3.52–3.40 (q, J = 7.0 Hz, 2H, 40-H2), 1.66–1.56 (q,
J = 7.3 Hz, 2H, 2-H2 Pr), 1.12–1.08 (t, J = 7.0 Hz, 3H, 50-H2), 0.92–
0.88 (t, J = 7.4 Hz, 3H, CH3 Pr). Anal. Calcd for C18H22N4O3

J. E. Rodríguez-Borges et al. / Bioorg. Med. Chem. 18 (2010) 2001–2009
2005
(342.39): C, 63.14; H, 6.48; N, 16.36. Found: C, 63.35; H, 6.21; N,
16.11.
1.49 (m, 6H, 30-H2 + 40-H2 + 200-H2 Pr), 0.88–0.82 (t, J = 7.4 Hz, 3H,
CH3 Pr). Anal. Calcd for C20H24N4O3 (368.43): C, 65.20; H, 6.57; N,
15.21. Found: C, 64.96; H, 6.77; N, 15.49.
5.1.2. 8-Benzyl-3-(2-ethoxyethyl)-1-propyl-1H-purine-
2,6(3H,7H)-dione, 13b
5.1.7. 8-Benzyl-1-ethyl-3-(2-(ethylthio)ethyl)-1H-purine-
2,6(3H,7H)-dione, 13g
Yield 85%. White solid. Mp 165–166 °C (H2O). IR (KBr)
m
(cmꢀ1) = 3156, 2967, 2867, 1702, 1645, 1495. 1H NMR (DMSO):
13.66 (br s, 1H, D2O exchang. NH), 7.30–7.22 (m, 5H, ArH), 4.14–
4.09 (t, J = 6.0 Hz, 2H, 1-H2 Pr), 4.04 (s, 2H, CH2–Ph), 3.85–3.79 (t,
J = 7.4 Hz, 2H, 10-H2), 3.65–3.60 (t, J = 6.0 Hz, 2H, 20-H2), 3.46–
3.38 (q, J = 7.0 Hz, 2H, 40-H2), 1.58–1.52 (q, J = 7.3 Hz, 2H, 2-H2
Pr), 1.00–0.94 (t, J = 7.0 Hz, 3H, 50-H2), 0.88–0.82 (t, J = 7.4 Hz, 3H,
CH3 Pr). Anal. Calcd for C19H24N4O3 (356.42): C, 63.97; H, 6.73; N,
15.71. Found: C, 64.13; H, 6.51; N, 15.94.
Yield 79%. White solid. Mp 191–193 °C (DMF/H2O). IR (KBr) m
(cmꢀ1) = 3031, 2974, 1696, 1654, 1557, 1500. 1H NMR (DMSO):
13.54 (br s, 1H, D2O exchang. NH), 7.28–7.16 (m, 5H, ArH), 4.11–
4.06 (t, J = 7.3 Hz, 2H, 1-H2 Et), 4.04 (s, 2H, CH2–Ph), 3.91–3.84 (q,
J = 7.0 Hz, 2H, 10-H2), 2.80–2.75 (t, J = 7.3 Hz, 2H, 20-H2), 2.55–
2.47 (m, 2H, 40-H2), 1.14–1.05 (m, 6H, 50-H2 and CH3 Et). 13C
NMR and DEPT (DMSO): 153.98 (C8), 152.97 (C6), 150.70 (C2),
148.10 (C4), 137.38 (C4 Ph), 128.94 (C3 and C5 Ph), 126.97 (C2
and C6 Ph), 106.67 (C5), 42.45 (NCH2), 35.96 (CH2Ph), 34.60 (C1
Et), 28.22 (CH2CH2S), 24.88 (S–CH2), 14.77 (SCH2CH3), 13.48 (CH3
Et). Anal. Calcd for C18H22N4O2S (358.46): C, 60.31; H, 6.19; N,
15.63. Found: C, 60.17; H, 6.33; N, 15.41.
5.1.3. 3-(2-(Ethylthio)ethyl)-8-phenyl-1-propyl-1H-purine-
2,6(3H,7H)-dione, 13c
Yield 56%. White solid. Mp 223–225 °C (H2O). IR (KBr)
m
(cmꢀ1) = 3184, 2962, 1726, 1697, 1651, 1553, 1467. 1H NMR
(DMSO): 13.86 (br s, 1H, D2O exchang. NH), 8.12–8.09 (m, 2H, 2-
H and 6-H ArH), 7.50–7.48 (m, 3H, 3-H, 4-H and 5-H ArH), 4.23–
4.19 (t, J = 7.3 Hz, 2H, 1-H2 Pr), 3.88–3.83 (t, J = 7.3 Hz, 2H, 10-H2),
2.89–2.85 (t, J = 7.3 Hz, 2H, 20-H2), 2.66–2.59 (q, J = 7.3 Hz, 2H, 40-
H2), 1.61–1.54 (q, J = 7.3 Hz, 2H, 2-H2 Pr), 1.23–1.18 (t, J = 7.3 Hz,
3H, 50-H2), 0.89–0.84 (t, J = 7.3 Hz, 2H, CH3 Pr). 13C NMR and DEPT
(DMSO): 154.37 (C8), 150.93 (C6), 150.26 (C2), 148.41 (C4), 130.62
(C4 Ph), 129.31 (C3 and C5 Ph), 128.87 (C1 Ph), 126.72 (C2 and C6
Ph), 108.65 (C5), 54.15 (NCH2), 42.52 (C1 Pr), 28.20 (CH2CH2S),
24.88 (S–CH2), 21.18 (C2 Pr), 14.81 (SCH2CH3), 11.50 (CH3 Pr). Anal.
Calcd for C18H22N4O2S (358.46): C, 60.31; H, 6.19; N, 15.63. Found:
C, 60.15; H, 6.31; N, 15.82.
5.1.8. 1-Ethyl-3-(2-(ethylthio)ethyl)-8-phenyl-1H-purine-
2,6(3H,7H)-dione, 13h
Yield 72%. White solid. Mp 239–241 °C (DMF/H2O). IR (KBr)
m
(cmꢀ1) = 3154, 2975, 1706, 1649, 1466. 1H NMR (DMSO): 13.86
(br s, 1H, D2O exchang. NH), 8.12–8.09 (m, 2H, ArH), 7.52–7.43
(m, 3H, ArH), 4.23–4.18 (t, J = 7.4 Hz, 2H, 1-H2 Et), 3.97–3.90 (q,
J = 7.0 Hz, 2H, 10-H2), 2.89–2.85 (t, J = 7.3 Hz, 2H, 20-H2), 2.67–
2.59 (q, J = 7.4 Hz, 2H, 40-H2), 1.24–1.19 (t, J = 7.4 Hz, 2H, 2-H2 Et),
1.16–1.11 (t, J = 7.0 Hz, 2H, 50-H2). Anal. Calcd for C17H20N4O2S
(344.43): C, 59.28; H, 5.85; N, 16.27. Found: C, 59.57; H, 6.01; N,
15.98.
5.1.9. 3-(Cyclohexylmethyl)-1-methyl-8-(thiophen-2-
5.1.4. 8-Benzyl-3-(2-(ethylthio)ethyl)-1-propyl-1H-purine-
2,6(3H,7H)-dione, 13d
ylmethyl)-1H-purine-2,6(3H,7H)-dione, 13i
Yield 30%. White solid. Mp 232–233 °C (H2O). IR (KBr)
m
Yield 51%. White solid. Mp 256–258 °C (H2O). IR (KBr)
m
(cmꢀ1) = 2921, 2850, 1706, 1652, 1501, 1420. 1H NMR (DMSO):
13.12 (br s, 1H, D2O exchang. NH), 7.39–7.37 (m, 1H, C4H3S),
6.96–6.94 (m, 2H, C4H3S), 4.25 (s, 2H, CH2–C4H3S), 3.84–3.81 (d,
J = 7.3 Hz, 2H, N–CH2), 3.22 (s, 3H, CH3), 2.01–1.81 (m, 1H, Cyclo-
hex), 1.80–1.51 (m, 5H, Cyclohex), 1.21–0.90 (m, 5H, Cyclohex).
Anal. Calcd for C18H22N4O2S (358.46): C, 60.31; H, 6.19; N, 15.63.
Found: C, 60.58; H, 6.47; N, 15.38.
(cmꢀ1) = 3152, 2963, 1700, 1645, 1556, 1497. 1H NMR (DMSO):
13.52 (br s, 1H, D2O exchang. NH), 7.28–7.16 (m, 5H, ArH), 4.12–
4.07 (t, J = 7.4 Hz, 2H, 1-H2 Pr), 4.04 (s, 2H, CH2–Ph), 3.82–3.77 (t,
J = 7.3 Hz, 2H, 10-H2), 2.80–2.75 (t, J = 7.3 Hz, 2H, 20-H2), 2.55–
2.47 (q, J = 7.4 Hz, 2H, 40-H2), 1.58–1.46 (sext, J = 7.4 Hz, 2H, 2-H2
Pr), 1.14–1.09 (t, J = 7.4 Hz, 3H, 50-H2), 0.85–0.80 (t, J = 7.4 Hz, 2H,
CH3 Pr). 13C NMR and DEPT (DMSO): 154.21 (C8), 152.98 (C6),
150.91 (C2), 137.37 (C4), 128.95 (C4 Ph), 128.82 (C3 and C5 Ph),
126.99 (C2 and C6 Ph), 106.63 (C5), 42.43 (NCH2), 42.36 (C1 Pr),
34.61 (CH2Ph), 28.22 (CH2CH2S), 24.87 (S–CH2), 21.17 (C2 Pr),
14.76 (SCH2CH3), 11.48 (CH3 Pr). Anal. Calcd for C19H24N4O2S
(372.48): C, 61.27; H, 6.49; N, 15.04. Found: C, 61.41; H, 6.28; N,
15.19.
5.1.10. 3-(Cyclohexylmethyl)-1-methyl-8-(thiophen-2-yl)-1H-
purine-2,6(3H,7H)-dione, 13j
Yield 52%. White solid. Mp 317–319 °C (MeOH/H2O). IR (KBr)
m
(cmꢀ1) = 3134, 2922, 2851, 1700, 1661, 1534, 1484. 1H NMR
(DMSO): 13.17 (br s, 1H, D2O exchang. NH), 7.87–7.86 (d,
J = 3.5 Hz, 1H, C4H3S), 7.71–7.69 (d, J = 4.7 Hz, 1H, C4H3S), 7.20–
7.16 (m, 1H, C4H3S), 3.86–3.83 (d, J = 7.3 Hz, 2H, N–CH2), 3.24 (s,
3H, CH3), 1.90–1.85 (m, 1H, Cyclohex), 1.62–1.51 (m, 5H, Cyclo-
hex), 1.19–0.93 (m, 5H, Cyclohex). Anal. Calcd for C17H20N4O2S
(344.43): C, 59.28; H, 5.85; N, 16.27. Found: C, 59.59; H, 5.53; N,
15.98.
5.1.5. 8-Phenyl-1-propyl-3-((tetrahydrofuran-2-yl)methyl)-1H-
purine-2,6(3H,7H)-dione, 13e
Yield 90%. White solid. Mp 261–262 °C (H2O). IR (KBr)
m
(cmꢀ1) = 3188, 2962, 1699, 1655, 1520, 1470. 1H NMR (DMSO):
13.45 (br s, 1H, D2O exchang. NH), 8.14–8.11 (m, 2H, ArH),
7.52–7.50 (m, 3H, ArH), 4.35–3.62 (m, 6H, 20-H2 + 100-H2
Pr + +50-H2), 1.95–1.54 (m, 6H, 30-H2 + 40-H2 + 200-H2 Pr), 0.91–
0.85 (t, J = 7.3 Hz, 3H, CH3 Pr). Anal. Calcd for C19H22N4O3
(354.41): C, 64.39; H, 6.26; N, 15.81. Found: C, 64.07; H, 6.59;
N, 15.71.
5.1.11. 1,3-Bis(cyclohexylmethyl)-8-(thiophen-2-ylmethyl)-1H-
purine-2,6(3H,7H)-dione, 13k
Yield 49%. White solid. Mp 237–239 °C (EtOH/H2O). IR (KBr)
m
(cmꢀ1) = 2924, 2851, 1703, 1647, 1558, 1529. 1H NMR (DMSO):
13.47 (br s, 1H, D2O exchang. NH), 7.42–7.39 (m, 1H, C4H3S),
6.98–6.96 (m, 2H, C4H3S), 4.28 (s, 2H, CH2–C4H3S), 3.86–3.83 (d,
J = 7.0 Hz, 2H, N–CH2), 3.77–3.74 (d, J = 7.0 Hz, 2H, N–CH2),
1.94–1.80 (m, 1H, Cyclohex), 1.73–1.47 (m, 11H, Cyclohex),
1.13–0.96 (m, 10H, Cyclohex). Anal. Calcd for C24H32N4O2S
(440.60): C, 65.42; H, 7.32; N, 13.72. Found: C, 65.17; H, 7.12;
N, 14.01.
5.1.6. 8-Benzyl-1-propyl-3-((tetrahydrofuran-2-yl)methyl)-1H-
purine-2,6(3H,7H)-dione, 13f
Yield 74%. White solid. Mp 186–187 °C (H2O). IR (KBr)
m
(cmꢀ1) = 3033, 2965, 1701, 1653, 1557, 1500. 1H NMR (DMSO):
13.43 (br s, 1H, D2O exchang. NH), 7.31–7.22 (m, 5H, ArH), 4.27–
3.56 (m, 6H, 20-H2 + 100-H2 Pr + +50-H2), 4.04 (s, 2H, CH2Ph), 1.91–

2006
J. E. Rodríguez-Borges et al. / Bioorg. Med. Chem. 18 (2010) 2001–2009
5.1.12. 1,3-Bis(cyclohexylmethyl)-8-(thiophen-2-yl)-1H-purine-
2,6(3H,7H)-dione, 13l
156.07 (C8), 153.27 (C6), 150.85 (C2), 148.99 (C4), 138.10 and
137.95 (C2 C4H3S), 128.91, 127.49, 127.01, 126.81, 126.50 and
125.46 (C4H3S), 107.48 (C5), 41.63 and 37.45 (CH2C4H3S), 30.04
(CH2 Et), 13.71 (CH3 Et). Anal. Calcd for C17H16N4S2O2 (372.47): C,
54.82; H, 4.33; N, 15.04. Found: C, 55.13; H, 4.46; N, 14.93.
Yield 53%. Violet solid. Mp 313–315 °C (iPrOH/Et2O). IR (KBr)
m
(cmꢀ1) = 3119, 2923, 2851, 1695, 1649, 1531, 1484. 1H NMR
(DMSO): 13.85 (br s, 1H, D2O exchang. NH), 7.89–7.84 (m, 1H,
C4H3S), 7.72–7.70 (m, 1H, C4H3S), 7.20–7.17 (m, 2H, C4H3S),
3.86–3.83 (d, J = 7.0 Hz, 2H, N–CH2), 3.76–3.74 (d, J = 7.0 Hz, 2H,
N–CH2), 1.91–1.75 (m, 1H, Cyclohex), 1.73–1.44 (m, 11H, Cyclo-
hex), 1.12–0.89 (m, 10H, Cyclohex). Anal. Calcd for C23H30N4O2S
(426.58): C, 64.76; H, 7.09; N, 13.13. Found: C, 64.96; H, 7.31; N,
13.35.
5.1.17. 1-Ethyl-8-(furan-2-ylmethyl)-3-(thiophen-2-ylmethyl)-
1H-purine-2,6(3H,7H)-dione, 13q
Yield 38%. Beige solid. Mp 283–284 °C (iPrOH). IR (KBr)
m
(cmꢀ1) = 3094, 1703, 1653, 1558, 1498, 1458. 1H NMR (DMSO):
13.55 (s, 1H, D2O exchang. NH), 7.55 (s, 1H, 5-H C4H3O), 7.39–
7.38 (m, 1H, 3-H C4H3S), 7.09–7.08 (m, 1H, 5-H C4H3S), 6.94–6.91
(m, 1H, 4-H C4H3S), 6.39–6.38 (m, 1H, 4-H C4H3O), 6.24–6.23 (m,
1H, 3-H C4H3O), 5.26 (s, 2H, CH2–C4H3S), 4.12 (s, 2H, CH2–
C4H3O), 3.94–3.87 (q, J = 7.0 Hz, 2H, 1-H2 Et), 1.12–1.07 (t,
J = 7.0 Hz, 3H, 2-H2 Et). 13C NMR and DEPT (DMSO): 155.85 (C8),
151.25 (C6), 150.68 (C2), 149.39 (C4), 148.12 (C2 C4H3O), 142.63
(C5 C4H3O), 138.13 (C2 C4H3S), 128.83 (C4 C4H3S), 126.99 (C3
C4H3S), 126.47 (C5 C4H3S), 111.06 (C4 C4H3O), 108.01 (C3 C4H3O),
107.45 (C5), 41.61 (CH2C4H3S), 37.38 (CH2 Et), 28.83 (CH2C4H3O),
13.62 (CH3 Et). Anal. Calcd for C17H16N4O3S (356.40): C, 57.29; H,
4.52; N, 15.72. Found: C, 57.01; H, 4.89; N, 15.85.
5.1.13. 3-Benzyl-1-ethyl-8-(thiophen-2-ylmethyl)-1H-purine-
2,6(3H,7H)-dione, 13m
Yield 33%. White solid. Mp 236–237 °C (iPrOH). IR (KBr)
m
(cmꢀ1) = 3130, 2945, 1700, 1648, 1559, 1498. 1H NMR (DMSO):
13.53 (br s, 1H, D2O exchang. NH), 7.37–7.22 (m, 6H, ArH + 1H
C4H3S), 6.94–6.92 (m, 2H, C4H3S), 5.14 (s, 2H, CH2–C4H3S), 4.25
(s, 2H, CH2–Ph), 3.93–3.86 (q, J = 7.0 Hz, 2H, 1-H2 Et), 1.11–1.07
(t, J = 7.0 Hz, 3H, 2-H2 Et). 13C NMR and DEPT (DMSO): 154.21
(C8), 152.15 (C6), 150.86 (C2), 148.57 (C4), 138.94 (C1 C4H3S),
137.29 (C1 Ph), 128.74 (C3 and C5 Ph), 128.04 (C4 C4H3S), 127.71
(C2 and C6 Ph), 127.28 (C3 C4H3S), 126.54 (C4 Ph), 125.53 (C5
C4H3S), 107.93 (C5), 46.34 (CH2 Ph), 36.14 (CH2 Et), 29.12 (CH2
C4H3S), 13.51 (CH3 Et). Anal. Calcd for C19H18N4O2S (366.44): C,
62.28; H, 4.95; N, 15.29. Found: C, 62.55; H, 4.77; N, 15.41.
5.1.18. 8-(2,6-Difluorobenzyl)-1-ethyl-3-(thiophen-2-ylmethyl)-
1H-purine-2,6(3H,7H)-dione, 13r
Yield 36%. Beige solid. Mp 283–284 °C (iPrOH). IR (KBr)
m
(cmꢀ1) = 3031, 1702, 1648, 1627, 1558, 1499, 1471. 1H NMR
(CDCl3): 13.53 (br s, 1H, D2O exchang. NH), 7.41–7.34 (m, 2H, 4-
H ArH and 3-H C4H3S), 7.12–7.07 (m, 2H, 3-H and 5-H ArH), 6.98
(s, 1H, 5-H C4H3S), 6.89–6.88 (m, 1H, 4-H C4H3S), 5.17 (s, 2H,
CH2–C4H3S), 4.11 (s, 2H, CH2–ArH), 3.91–3.85 (q, J = 6.7 Hz, 2H,
1-H2 Et), 1.10–1.05 (t, J = 6.7 Hz, 3H, 2-H2 Et). 13C NMR and DEPT
(CDCl3): 160.21 (C2 and C6 C6H3F2), 153.75 (C8), 151.12 (C6),
150.46 (C2), 147.84 (C4), 138.55 (C2 C4H3S), 136.75 (C1 Ph),
129.42, 128.07, 126.90, 126.59, 112.01 and 111.68 (ArH and C2–
C3–C4–C5 C4H3S), 107.82 (C5), 40.92 (CH2C6H3F2), 36.08 (CH2 Et),
22.19 (CH2C6H3F2), 13.49 (CH3 Et). Anal. Calcd for C19H16F2N4O2S
(402.42): C, 56.71; H, 4.01; N, 13.92. Found: C, 58.03; H, 3.85; N,
14.14.
5.1.14. 3-Benzyl-1-ethyl-8-(furan-2-ylmethyl)-1H-purine-
2,6(3H,7H)-dione, 13n
Yield 25%. White solid. Mp 231–233 °C (iPrOH). IR (KBr)
m
(cmꢀ1) = 3034, 1700, 1652, 1559, 1506, 1457. 1H NMR (DMSO):
13.51 (br s, 1H, D2O exchang. NH), 7.54–7.53 (d, J = 1.0 Hz, 1H, 5-
H C4H3O), 7.32–7.20 (m, 5H, ArH), 6.38–6.36 (q, J = 2.9, 1.0 Hz,
1H, 4-H C4H3O), 6.21–6.20 (d, J = 2.9 Hz, 1H, 3-H C4H3O), 5.13 (s,
2H, CH2–C4H3O), 4.10 (s, 2H, CH2–Ph), 3.94–3.87 (q, J = 7.0 Hz,
2H, 1-H2 Et), 1.12–1.07 (t, J = 7.0 Hz, 3H, 2-H2 Et). 13C NMR and
DEPT (DMSO): 154.17 (C8), 150.88 (C6), 150.11 (C2), 149.37 (C2
C4H3O), 148.71 (C4), 142.60 (C5 C4H3O), 137.30 (C1 Ph), 128.74
(C3 and C5 Ph), 127.88 (C2 and C6 Ph), 127.66 (C4 Ph), 111.02
(C4 C4H3O), 107.60 (C3 C4H3O), 106.56 (C5), 46.32 (CH2Ph), 36.13
(CH2 Et), 27.93 (CH2C4H3O), 13.51 (CH3 Et). Anal. Calcd for
C19H18N4O3 (350.37): C, 65.13; H, 5.18; N, 15.99. Found: C, 62.86;
H, 5.45; N, 16.16.
5.1.19. 8-(Biphenyl-4-yl)-1-ethyl-3-(2-(ethylthio)ethyl)-1H-
purine-2,6(3H,7H)-dione, 13s
Yield 58%. White solid. Mp 277–281 °C (iPrOH). IR (KBr)
m
(cmꢀ1) = 3157, 1690, 1645, 1569, 1552, 1531, 1472. 1H NMR
(DMSO): 14.27 (br s, 1H, D2O exchang. NH), 8.19–8.15 (d,
J = 8.4 Hz, 2H, ArH), 7.81–7.77 (d, J = 8.4 Hz, 2H, ArH), 7.72–7.69
(d, J = 7.2 Hz, 2H, ArH), 7.48–7.36 (m, 3H, ArH), 4.22–4.16 (t,
J = 7.1 Hz, 2H, 1-H2 Et), 3.95–3.87 (q, J = 7.0 Hz, 2H, 10-H2), 2.8–
2.82 (t, J = 7.0 Hz, 2H, 20-H2), 2.66–2.57 (q, J = 7.5 Hz, 2H, 40-H2),
1.22–1.16 (t, J = 6.5 Hz, 3H, 50-H2), 1.13–1.08 (t, J = 6.8 Hz, 3H,
CH3 Et). 13C NMR and DEPT (DMSO): 154.20 (C8), 151.30 (C6),
150.82 (C2), 150.10 (C4), 142.33, 140.15 and 133.54 (C Biphenylyl),
129.10 (C5), 129.40, 129.38, 127.56, 127.51, 127.36, 127.09 and
126.56 (CH Biphenylyl), 66.81 (NCH2), 65.24 (CH2CH2S), 28.36
(CH2 Et), 25.07 (SCH2CH3), 14.93 (SCH2CH3), 13.58 (CH3 Et). Anal.
Calcd for C23H24N4O2S (420.53): C, 65.69; H, 5.75; N, 13.32. Found:
C, 65.33; H, 6.07; N, 13.41.
5.1.15. 3-Benzyl-8-(2,6-difluorobenzyl)-1-ethyl-1H-purine-
2,6(3H,7H)-dione, 13o
Yield 65%. White solid. Mp 296–299 °C (iPrOH). IR (KBr)
m
(cmꢀ1) = 3031, 1700, 1646, 1500, 1470. 1H NMR (DMSO): 1300
(br s, 1H, D2O exchang. NH), 7.44–7.09 (m, 8H, ArH), 5.06 (s, 2H,
CH2–Ph), 4.13 (s, 2H, CH2–PhF2), 3.94–3.88 (m, 2H, 1-H2 Et),
1.13–1.07 (m, 3H, 2-H2 Et). 13C NMR and DEPT (DMSO): 163.36
(C2 and C6 C6H3F2), 154.03 (C8), 150.98 (C6), 150.86 (C2), 148.16
(C4), 137.26 (C1 Ph), 129.88, 129.74, 128.64, 128.40, 127.76,
111.98 and 111.66 (ArH), 106.90 (C5), 46.32 (CH2 Ph), 36.18 (CH2
Et), 22.25 (CH2C6H3F2), 13.56 (CH3 Et). Anal. Calcd for
C21H18F2N4O2 (396.39): C, 63.63; H, 4.58; N, 14.13. Found: C,
63.92; H, 4.77; N, 14.41.
5.1.16. 1-Ethyl-3,8-bis(thiophen-2-ylmethyl)-1H-purine-
2,6(3H,7H)-dione, 13p
5.1.20. 8-(Biphenyl-4-yl)-3-(2-ethoxyethyl)-1-ethyl-1H-purine-
2,6(3H,7H)-dione, 13t
Yield 49%. White solid. Mp 234–235 °C (iPrOH). IR (KBr)
m
Yield 77%. White solid. Mp 271–273 °C (iPrOH). IR (KBr)
m
(cmꢀ1) = 3148, 1702, 1654, 1558, 1498. 1H NMR (DMSO): 13.54
(br s, 1H, D2O exchang. NH), 7.38 (m, 2H, C4H3S), 7.12 (m, 1H,
C4H3S), 6.96–6.94 (m, 3H, C4H3S), 5.27 (s, 2H, CH2–C4H3S), 4.27
(s, 2H, CH2–C4H3S), 3.91–3.88 (d, J = 6.3 Hz, 2H, 1-H2 Et), 1.11–
1.07 (t, J = 6.3 Hz, 3H, 2-H2 Et). 13C NMR and DEPT (DMSO):
(cmꢀ1) = 3164, 1691, 1645, 1597, 1551, 1531, 1472. 1H NMR
(DMSO): 14.23 (br s, 1H, D2O exchang. NH), 8.23–8.20 (d,
J = 8.1 Hz, 2H, ArH), 7.83–7.80 (d, J = 8.1 Hz, 2H, ArH), 7.76–7.73
(d, J = 7.4 Hz, 2H, ArH), 7.52–7.37 (m, 3H, ArH), 4.25–4.21 (t,
J = 6.8 Hz, 2H, 1-H2 Et), 3.98–3.92 (q, J = 6.5 Hz, 2H, 10-H2), 3.74–

J. E. Rodríguez-Borges et al. / Bioorg. Med. Chem. 18 (2010) 2001–2009
2007
3.70 (t, J = 6.5 Hz, 2H, 20-H2), 3.55–3.47 (q, J = 6.8 Hz, 2H, 40-H2),
1.17–1.12 (t, J = 6.5 Hz, 3H, CH3 Et), 1.07–1.02 (t, J = 6.8 Hz, 3H,
50-H2). 13C NMR and DEPT (DMSO): 154.25 (C8), 151.3410 (C6),
150.92 (C2), 150.04 (C4), 142.09, 139.58 and 133.79 (C Biphenylyl),
129.39 (C5), 128.34, 128.11, 127.56, 127.48, 127.10, 127.06 and
126.89 (CH Biphenylyl), 66.62 (CH2CH2O), 65.64 (OCH2CH3),
36.23 (NCH2), 35.94 (CH2 Et), 15.46 (OCH2CH3), 13.60 (CH3 Et).
Anal. Calcd for C23H24N4O3 (404.46): C, 68.30; H, 5.98; N, 13.85.
Found: C, 68.02; H, 6.16; N, 13.99.
Et), 32.51 (NCH3), 21.05 (CH2C4H3O), 13.70 (CH3 Et). Anal. Calcd for
C20H20N4O3 (364.40): C, 65.92; H, 5.53; N, 15.38. Found: C, 66.21;
H, 5.21; N, 15.51.
5.2.5. 3-Benzyl-8-(2,6-difluorobenzyl)-1-ethyl-7-methyl-1H-
purine-2,6(3H,7H)-dione, 14o
Yield 85%. White solid. Mp 159–161 °C (hexane). IR (KBr)
m
(cmꢀ1) = 3019, 1703, 1654, 1595, 1540, 1474, 1444. 1H NMR
(CDCl3): 7.48–7.44 (m, 2H, ArH), 7.34–7.21 (m, 4H, ArH), 6.99–
6.89 (m, 2H, ArH), 5.15 (s, 2H, CH2–Ph), 4.13 (s, 2H, CH2–PhF2),
4.07–4.00 (q, J = 7.0 Hz, 2H, 1-H2 Et), 3.95 (s, 3H, N–CH3), 1.22–
1.18 (t, J = 7.0 Hz, 3H, 2-H2 Et). 13C NMR and DEPT (DMSO):
163.12 (C2 and C6 C6H3F2), 155.09 (C8), 151.31 (C6), 150.23 (C2),
147.35 (C4), 137.05 (C1 Ph), 129.81, 129.65, 128.68, 128.09,
111.95 and 111.61 (ArH), 108.83 (C5), 46.72 (CH2 Ph), 36.80 (CH2
Et),32.14 (NCH3), 21.04 (CH2C6H3F2), 13.69 (CH3 Et). Anal. Calcd
for C22H20F2N4O2 (410.42): C, 64.38; H, 4.91; N, 13.65. Found: C,
64.61; H, 5.15; N, 13.33.
5.2. General procedure for the methylation of xanthines 13
To a suspension of K2CO3 (1.2 mmol) in dry DMF (10 mL) was
added the corresponding xanthine 13 (1 mmol) and the mixture
was shaken at room temperature for 15 min and at 60 °C for a fur-
ther 15 min. Once the mixture had reached room temperature CH3I
(1 mmol) was added. The reaction mixture was heated at 100 °C for
2 h and then allowed to cool down to room temperature. Water
was added and the resulting precipitate was filtered off, washed
with water and dried under vacuum.
5.2.6. 1-Ethyl-7-methyl-3,8-bis(thiophen-2-ylmethyl)-1H-
purine-2,6(3H,7H)-dione, 14p
5.2.1. 3-(2-(Ethylthio)ethyl)-7-metyl-8-phenyl-1-propyl-1H-
purine-2,6(3H,7H)-dione, 14c
Yield 81%. Beige solid. Mp 85–88 °C (hexane). IR (KBr) m
(cmꢀ1) = 2983, 1700, 1653, 1558, 1540, 1508, 1490. 1H NMR (CDCl3):
7.06–7.00 (m, 3H, C4H3S), 6.77–6.68 (m, 3H, C4H3S), 5.23 (s, 2H, CH2–
C4H3S), 4.14 (s, 2H, CH2–C4H3S), 3.90–3.81 (d, J = 7.0 Hz, 2H, 1-H2 Et),
3.67 (s, 3H. N–CH3), 1.05–1.00 (t, J = 7.0 Hz, 3H, 2-H2 Et). 13C NMR
and DEPT (DMSO): 156.11 (C8), 151.54 (C6), 150.87 (C2), 147.23
(C4), 138.39 and 137.40 (C2 C4H3S), 128.78, 127.52, 126.97,
126.47, 126.39 and 125.51 (C4H3S), 108.32 (C5), 41.11 and 36.85
(CH2C4H3S), 32.42 (NCH3), 28.43 (CH2 Et), 13.70 (CH3 Et). Anal. Calcd
for C18H18N4S2O2 (386.09): C, 55.94; H, 4.69; N, 14.50. Found: C,
55.66; H, 4.92; N, 14.77.
Yield 75%. Yellow solid. Mp 97–99 °C (cyclohexane/Et2O). IR
(KBr)
m
(cmꢀ1) = 2958, 2924, 2853, 1699, 1655, 1537, 1452, 1429.
1H NMR (CDCl3): 7.69–7.66 (m, 2H, ArH), 7.53–7.51 (m, 3H, ArH),
4.39–4.32 (q, J = 7.4 Hz, 2H, 100-H2 Pr), 4.06 (s, 3H, N–CH3), 4.02–
3.97 (t, J = 7.4 Hz, 2H, 10-H2), 2.97–2.92 (m, 2H, 20-H2), 2.72–2.65
(q, J = 7.4 Hz, 2H, 40-H2), 1.74–1.66 (q, J = 7.4 Hz, 2H, 200-H2 Pr),
1.32–1.27 (t, J = 7.4 Hz, 2H, 300-H2 Pr), 1.00–0.95 (t, J = 7.4 Hz, 2H,
50-H2). Anal. Calcd for C19H24N4O2S (372.48): C, 61.27; H, 6.49; N,
15.04. Found: C, 61.02; H, 6.68; N, 15.25.
5.2.2. 7-Methyl-8-phenyl-1-propyl-3-((tetrahydrofuran-2-
5.2.7. 1-Ethyl-8-(furan-2-ylmethyl)-7-methyl-3-(thiophen-2-
yl)methyl)-1H-purine-2,6(3H,7H)-dione, 14e
ylmethyl)-1H-purine-2,6(3H,7H)-dione, 14q
Yield 78%. White solid. Mp 220–224 °C (cyclohexane). IR (KBr)
m
Yield 86%. Yellow solid. Mp 121–123 °C (hexane). IR (KBr) m
(cmꢀ1) = 2958, 1692, 1536, 1451, 1428. 1H NMR (CDCl3): 7.65–7.61
(m, 2H, ArH), 7.49–7.46 (m, 3H, ArH), 4.54–4.49 (m, 2H, 20-H2),
4.32–4.23 (m. 2H, 100-H2 Pr), 4.00 (s, 3H, CH3), 4.03–3.72 (m, 4H, N–
CH2 + 50-H2), 2.05–1.62 (m, 6H, 30-H2 + 40-H2 + 200-H2 Pr), 0.96–0.94
(t, J = 7.4 Hz, 3H, CH3 Pr). Anal. Calcd for C20H24N4O3 (368.43): C,
65.20; H, 6.57; N, 15.21. Found: C, 65.49; H, 6.33; N, 15.57.
(cmꢀ1) = 3000, 2898, 1702, 1653, 1540, 1490, 1443. 1H NMR
(CDCl3): 7.16 (s, 1H, 5-H C4H3O), 7.07–7.00 (m, 1H, 3-H and 5-H
C4H3S), 6.73 (s, 1H, 4-H C4H3S), 6.15 (s, 1H, 4-H C4H3O), 5.98 (s,
1H, 3-H C4H3O), 5.22 (s, 2H, CH2–C4H3S), 4.00 (s, 2H, CH2–
C4H3O), 3.90–3.84 (q, J = 6.7 Hz, 2H, 1-H2 Et), 1.06–1.01 (t,
J = 6.7 Hz, 3H, 2-H2 Et). 13C NMR and DEPT (DMSO): 155.79 (C8),
151.15 (C6), 150.41 (C2), 149.51 (C4), 147.98 (C2 C4H3O), 142.65
(C5 C4H3O), 138.21 (C2 C4H3S), 128.71 (C4 C4H3S), 126.95 (C3
C4H3S), 126.37 (C5 C4H3S), 111.13 (C4 C4H3O), 108.15 (C3
C4H3O), 107.98 (C5), 41.10 (CH2C4H3S), 36.85 (CH2 Et), 32.45
(NCH3), 27.23 (CH2C4H3O), 13.70 (CH3 Et). Anal. Calcd for
C18H18N4O3S (370.43): C, 58.36; H, 4.90; N, 15.12. Found: C,
58.07; H, 4.70; N, 15.43.
5.2.3. 3-Benzyl-1-ethyl-7-methyl-8-(thiophen-2-ylmethyl)-1H-
purine-2,6(3H,7H)-dione, 14m
Yield 89%. Beige solid. Mp 108–110 °C (hexane). IR (KBr)
m
(cmꢀ1) = 3027, 1700, 1654, 1540, 1490, 1448, 1426. 1H NMR
(CDCl3): 7.48–7.45 (m, 1H, C4H3S), 7.26–7.13 (m, 5H, ArH), 6.89–
6.86 (m, 1H, C4H3S), 6.78–6.77 (m, 1H, C4H3S), 5.19 (s, 2H, CH2–
C4H3S), 4.25 (s, 2H, CH2–Ph), 3.99–3.93 (q, J = 7.0 Hz, 2H, 1-H2
Et), 1.17–1.12 (t, J = 7.0 Hz, 3H, 2-H2 Et). Anal. Calcd for
C20H20N4O2S (380.46): C, 63.04; H, 5.30; N, 14.73. Found: C,
62.87; H, 5.55; N, 14.96.
5.2.8. 8-(2,6-Difluorobenzyl)-1-ethyl-7-methyl-3-(thiophen-2-
ylmethyl)-1H-purine-2,6(3H,7H)-dione, 14r
Yield 91%. Brown solid. Mp 177–179 °C (hexane). IR (KBr)
m
(cmꢀ1) = 3031, 1705, 1654, 1628, 1595, 1540, 1474, 1444, 1324,
1265, 1230, 1207, 1060, 1019, 761. 1H NMR (CDCl3): 7.22–6.81
(m, 6H, ArH and C4H3S), 5.25 (s, 2H, CH2–C4H3S), 4.07 (s, 2H,
CH2–ArH), 3.99–3.96 (m, 2H, 1-H2 Et), 3.88 (s, 3H, N–CH3), 1.16–
1.10 (m, 3H, 2-H2 Et). Anal. Calcd for C20H18F2N4O2S (416.45): C,
57.68; H, 4.36; N, 13.45. Found: C, 57.91; H, 4.11; N, 13.63.
5.2.4. 3-Benzyl-1-ethyl-8-(furan-2-ylmethyl)-7-methyl-1H-
purine-2,6(3H,7H)-dione, 14n
Yield 88%. Yellow solid. Mp 118–120 °C (hexane). IR (KBr)
m
(cmꢀ1) = 3029, 1700, 1653, 1559, 1541, 1497, 1448. 1H NMR (CDCl3):
7.45–7.42 (m, 1H, 5-H C4H3O), 7.28–7.20 (m, 5H, ArH), 6.27–6.24 (m,
1H, 4-H C4H3O), 6.09–6.06 (m, 1H, 3-H C4H3O), 5.18 (s, 2H, CH2–
C4H3O), 4.10 (s, 2H, CH2–Ph), 4.02–3.94 (q, J = 7.0 Hz, 2H, 1-H2 Et),
3.84 (s, 3H, N–CH3), 1.17–1.12 (t, J = 7.0 Hz, 3H, 2-H2 Et). 13C NMR
and DEPT (CDCl3): 155.21 (C8), 151.03 (C6), 150.45 (C2), 149.17
(C2 C4H3O), 147.35 (C4), 142.37 (C5 C4H3O), 138.64 (C1 Ph), 129.59
(C3 and C5 Ph), 128.93 (C2 and C6 Ph), 126.85 (C4 Ph), 111.97 (C4
C4H3O), 111.64 (C3 C4H3O), 108.72 (C5), 40.82 (CH2Ph), 36.79 (CH2
5.3. General procedure for the oxidation of xanthines 13 to
sulfoxides 15
OxoneÒ (0.67 mmol) and aliquat (three drops) in a mixture of
H2O (6 mL) and CH2Cl2 (4 mL) were added to a solution of the cor-
responding xanthine 13 (1 mmol) in CH3CN (0.4 mmol) at 0 °C. The

2008
J. E. Rodríguez-Borges et al. / Bioorg. Med. Chem. 18 (2010) 2001–2009
reaction mixture was stirred at room temperature for 7 h. The reac-
tion mixture was then poured into EtOAc (100 mL) and the organic
layer was washed twice with H2O, dried (Na2SO4) and the solvents
evaporated under reduced pressure to leave a residue, which was
purified by recrystallization.
ature for 24 h. H2O (30 mL) was then added and the mixture was
extracted with CH2Cl2 (3 ꢁ 30 mL). The combined organic layers
were washed with H2O, dried (Na2SO4) and the solvents evapo-
rated under reduced pressure to leave a residue, which was puri-
fied by recrystallization.
5.3.1. 3-(2-(Ethylsulfinyl)ethyl)-8-phenyl-1-propyl-1H-purine-
2,6(3H,7H)-dione, 15c
5.4.1. 3-(2-(Ethylsulfonyl)ethyl)-8-phenyl-1-propyl-1H-purine-
2,6(3H,7H)-dione, 16c
Yield 89%. White solid. Mp 226–227 °C (CH3CN). IR (KBr)
m
Yield 80%. White solid. Mp 270–272 °C (EtOH/Et2O). IR (KBr)
m
(cmꢀ1) = 3173, 2963, 1694, 1654, 1467. 1H NMR (DMSO): 13.87
(br s, 1H, D2O exchang. NH), 8.13–8.10 (m, 2H, 2-H and 6-H
ArH), 7.52–7.44 (m, 3H, 3-H, 4-H and 5-H ArH), 4.45–4.40 (t,
J = 7.3 Hz, 2H, 1-H2 Pr), 3.87–3.82 (t, J = 7.3 Hz, 2H, 10-H2), 3.31–
3.02 (m, 2H, 20-H2), 2.94–2.66 (m, 2H, 40-H2), 1.63–1.51 (q,
J = 7.4 Hz, 2H, 2-H2 Pr), 1.19–1.14 (t, J = 7.4 Hz, 3H, 50-H2), 0.89–
0.84 (t, J = 7.4 Hz, 2H, CH3 Pr13C NMR and DEPT (DMSO): 153.97
(C8), 150.92 (C6), 150.15 (C2), 148.07 (C4), 130.61 (C4 Ph),
129.28 (C3 and C5 Ph), 128.99 (C1 Ph), 126.80 (C2 and C6 Ph),
108.04 (C5), 49.01 (NCH2), 44.91 (C1 Pr), 42.61 (CH2CH2SO),
38.00 (SOCH2), 21.19 (C2 Pr), 11.50 (CH3 Pr), 6.74 (OSCH2CH3).
Anal. Calcd for C18H22N4O3S (374.46): C, 57.74; H, 5.92; N, 14.92.
Found: C, 57.95; H, 5.81; N, 15.07.
(cmꢀ1) = 3167, 2968, 1702, 1655, 1519, 1467. 1H NMR (DMSO):
13.91 (br s, 1H, D2O exchang. NH), 8.14–8.11 (m, 2H, 2-H and 6-
H ArH), 7.54–7.50 (m, 3H, 3-H, 4-H and 5-H ArH), 4.49–4.44 (t,
J = 7.3 Hz, 2H, 1-H2 Pr), 3.88–3.83 (t, J = 7.3 Hz, 2H, 10-H2), 3.58–
3.53 (t, J = 7.3 Hz, 2H, 20-H2), 3.29–3.22 (q, J = 7.4 Hz, 2H, 40-H2),
1.64–1.52 (sex, J = 7.4 Hz, 2H, 2-H2 Pr), 1.27–1.22 (t, J = 7.4 Hz,
3H, 50-H2), 0.90–0.85 (t, J = 7.4 Hz, 2H, CH3 Pr). 13C NMR and DEPT
(DMSO): 154.25 (C8), 150.89 (C6), 149.45 (C2), 147.68 (C4), 131.43
(C4 Ph), 130.66 (C3 and C5 Ph), 129.32 (C1 Ph), 127.93 (C2 and C6
Ph), 107.91 (C5), 48.55 (NCH2), 46.72 (C1 Pr), 42.62 (CH2CH2SO2),
36.92 (SO2CH2), 21.16 (C2 Pr), 11.52 (CH3 Pr), 6.48 (SO2CH2CH3).
Anal. Calcd for C18H22N4O4S (390.46): C, 55.37; H, 5.68; N, 14.35.
Found: C, 55.55; H, 5.43; N, 14.19.
5.3.2. 8-Benzyl-3-(2-(ethylsulfinyl)ethyl)-1-propyl-1H-purine-
2,6(3H,7H)-dione, 15d
5.4.2. 8-Benzyl-3-(2-(ethylsulfonyl)ethyl)-1-propyl-1H-purine-
2,6(3H,7H)-dione, 16d
Yield 83%. White solid. Mp 186–189 °C (CH3CN). IR (KBr)
m
Yield 74%. White solid. Mp 216–217 °C (EtOH/Et2O). IR (KBr)
m
(cmꢀ1) = 3032, 2963, 1699, 1645, 1497. 1H NMR (DMSO): 13.48
(br s, 1H, D2O exchang. NH), 7.30–7.19 (m, 5H, ArH), 4.38–4.30
(m, 2H, 1-H2 Pr), 4.04 (s, 2H, CH2–Ph), 3.83–3.78 (t, J = 7.4 Hz, 2H,
10-H2), 3.18–2.98 (m, 2H, 20-H2), 2.85–2.64 (m, 2H, 40-H2), 1.57–
1.50 (q, J = 7.4 Hz, 2H, 2-H2 Pr), 1.15–1.13 (t, J = 7.4 Hz, 3H, 50-
H2), 0.86–0.84 (t, J = 7.5 Hz, 2H, CH3 Pr). 13C NMR and DEPT
(DMSO): 154.85 (C8), 153.71 (C6), 151.22 (C2), 136.89 (C4),
128.93 (C4 Ph), 128.8 (C3 and C5 Ph), 127.04 (C2 and C6 Ph),
106.95 (C5), 48.97 (NCH2), 44.85 (C1 Pr), 42.47 (CH2Ph), 34.65
(CH2CH2SO), 25.12 (SOCH2), 21.16 (C2 Pr), 11.52 (CH3 Pr), 6.65
(SOCH2CH3). Anal. Calcd for C19H24N4O3S (388.48): C, 58.74; H,
6.23; N, 14.42. Found: C, 58.55; H, 6.41; N, 14.27.
(cmꢀ1) = 3144, 3090, 3030, 2964, 1699, 1639, 1560, 1497, 1451.
1H NMR (DMSO): 13.83 (br s, 1H, D2O exchang. NH), 7.32–7.11
(m, 5H, ArH), 4.40–4.35 (t, J = 7.3 Hz, 2H, 1-H2 Pr), 4.07 (s, 2H,
CH2–Ph), 3.85–3.80 (t, J = 7.3 Hz, 2H, 10-H2), 3.50–3.45 (t,
J = 7.3 Hz, 2H, 20-H2), 3.22–3.15 (q, J = 7.4 Hz, 2H, 40-H2), 1.58–
1.50 (sex, J = 7.4 Hz, 2H, 2-H2 Pr), 1.22–1.16 (t, J = 7.4 Hz, 3H, 5’-
H2), 0.89–0.83 (t, J = 7.4 Hz, 2H, CH3 Pr). Anal. Calcd for
C19H24N4O4S (404.48): C, 56.42; H, 5.98; N, 13.85. Found: C,
56.15; H, 6.17; N, 14.14.
5.4.3. 8-Benzyl-1-ethyl-3-(2-(ethylsulfonyl)ethyl)-1H-purine-
2,6(3H,7H)-dione, 16g
Yield 72%. Pink solid. Mp 181–184 °C (EtOH/Et2O). IR (KBr)
m
5.3.3. 8-Benzyl-1-ethyl-3-(2-(ethylsulfinyl)ethyl)-1H-purine-
2,6(3H,7H)-dione, 15g
(cmꢀ1) = 3087, 3029, 2982, 1709, 1659, 1584, 1553. 1H NMR
(DMSO): 13.50 (br s, 1H, D2O exchang. NH), 7.36–7.19 (m, 5H,
ArH), 4.38–4.33 (t, J = 7.1 Hz, 2H, 1-H2 Et), 4.05 (s, 2H, CH2Ph),
3.92–3.85 (q, J = 7.1 Hz, 2H, 10-H2), 3.5843.41 (m, 2H, 20-H2),
3.21–3.13 (q, J = 7.1 Hz, 2H, 40-H2), 1.29–1.05 (m, 6H, 50-H2 + CH3
Et). Anal. Calcd for C18H22N4O4S (376.43): C, 55.37; H, 5.68; N,
14.35. Found: C, 55.51; H, 5.40; N, 14.29.
Yield 87%. White solid. Mp 192–193 °C (CH3CN). IR (KBr)
m
(cmꢀ1) = 3144, 3090, 3034, 2979, 1703, 1656, 1586, 1556, 1498. 1H
NMR (DMSO): 13.81 (br s, 1H, D2O exchang. NH), 7.16–7.07 (m,
5H, ArH), 4.24–4.15 (q, J = 7.1 Hz, 2H, 1-H2 Et), 3.90 (s, 2H, CH2Ph),
3.76–3.70 (q, J = 7.0 Hz, 2H, 20-H2), 3.07–2.86 (m, 2H, 1-H2 Et),
2.67–2.34 (m, 2H, 40-H2), 1.06–0.99 (m, 3H, 50-H2), 0.97–0.92 (q,
J = 7.0 Hz, 2H, CH3 Et). Anal. Calcd for C18H22N4O3S (374.46): C,
57.74; H, 5.92; N, 14.96. Found: C, 57.45; H, 5.77; N, 15.21.
5.4.4. 1-Ethyl-3-(2-(ethylsulfonyl)ethyl)-8-phenyl-1H-purine-
2,6(3H,7H)-dione, 16h
5.3.4. 1-Ethyl-3-(2-(ethylsulfinyl)ethyl)-8-phenyl-1H-purine-
2,6(3H,7H)-dione, 15h
Yield 75%. White solid. Mp 272–273 °C (hexane/Et2O). IR (KBr)
m
(cmꢀ1) = 3172, 2982, 1701, 1660, 1519. 1H NMR (DMSO): 13.92 (br
s, 1H, D2O exchang. NH), 8.14–8.10 (m, 2H, 2-H and 6-H ArH),
7.55–7.46 (m, 3H, 3-H, 4-H and 5-H ArH), 4.48–4.44 (t, J = 7.0 Hz,
2H, 1-H2 Et), 3.97–3.90 (q, J = 7.0 Hz, 2H, 10-H2), 3.58–3.53 (t,
J = 7.4 Hz, 2H, 20-H2), 3.29–3.22 (q, J = 7.4 Hz, 2H, 40-H2), 1.27–
1.22 (t, J = 7.4 Hz, 3H, 50-H2), 1.16–1.11 (t, J = 7.0 Hz, 2H, CH3 Et).
Anal. Calcd for C17H20N4O4S (376.43): C, 54.24; H, 5.36; N, 14.88.
Found: C, 53.89; H, 5.61; N, 14.69.
Yield 90%. White solid. Mp 246–247 °C (CH3CN). IR (KBr)
m
(cmꢀ1) = 3154, 2976, 1698, 1659, 1519, 1470. 1H NMR (DMSO):
13.91 (br s, 1H, D2O exchang. NH), 7.95–7.92 (m, 2H, 2-H and 6-
H ArH), 7.36–7.30 (m, 3H, 3-H, 4-H and 5-H ArH), 4.27–4.21 (t,
J = 7.0 Hz, 2H, 1-H2 Et), 3.79–3.70 (q, J = 7.0 Hz, 2H, 20-H2), 3.13–
2.87 (m, 2H, 1-H2 Et), 2.73–2.49 (m, 2H, 40-H2), 1.08–1.02 (t,
J = 7.4 Hz, 3H, 50-H2), 1.01–0.92 (q, J = 7.4 Hz, 2H, CH3 Et). Anal.
Calcd for C17H20N4O3S (360.43): C, 56.65; H, 5.59; N, 15.54. Found:
C, 56.91; H, 5.38; N, 15.26.
5.5. Biochemistry and pharmacology
5.4. General procedure for the oxidation of xanthines 13 to
sulfones 16
5.5.1. Radioligand binding assays
Radioligand binding competition assays were performed
in vitro using A1, A2A, A2B and A3 human receptors expressed in
A mixture of the corresponding xanthine 10 (0.35 mmol), AcOH
(0.18 mmol) and 30% H2O2 (0.24 mL) was stirred at room temper-
transfected CHO (hA1), HeLa (hA2A and hA3) and HEK-293 (hA2B
)
cells as previously described.24 A brief description is given below.

J. E. Rodríguez-Borges et al. / Bioorg. Med. Chem. 18 (2010) 2001–2009
2009
5.5.1.1. Human A1 receptors. Adenosine A1 receptor competition
Acknowledgments
binding experiments were carried out in membranes from
CHO-A1 cells (Euroscreen, Gosselies, Belgium) labeled with 2 nM
[3H]DPCPX. Non-specific binding was determined in the presence
of 10 lM (R)-PIA. The reaction mixture was incubated at 25 °C
for 60 min.
The authors thank Almirall Prodesfarma S.A. (Spain) for pro-
moting and financially supporting this work. J.B. thanks the Xunta
de Galicia for financial support under ‘Isabel Barreto Contract’. I.N.
thanks the Xunta de Galicia for financial support under ‘‘Programa
Isidro Parga Pondal”.
5.5.1.2. Human A2A receptors. Adenosine A2A receptor competi-
tion binding experiments were carried out in membranes from
HeLa-A2A cells labeled with 3 nM [3H]ZM241385. Non-specific
References and notes
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binding was determined in the presence of 50
lM NECA. The reac-
tion mixture was incubated at 25 °C for 30 min.
5.5.1.3. Human A2B receptors. Adenosine A2B receptor competi-
tion binding experiments were carried out in membranes from
HEK-293-A2B cells (Euroscreen, Gosselies, Belgium) labeled with
35 nM [3H]DPCPX. Non-specific binding was determined in the
6. Holgate, S. T. Br. J. Pharmacol. 2005, 145, 1009.
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presence of 400
lM NECA. The reaction mixture was incubated at
25 °C for 30 min.
5.5.1.4. Human A3 receptors. Adenosine A3 receptor competition
binding experiments were carried out in membranes from HeLa-A3
cells. Labeled with 30 nM [3H]NECA. Non-specific binding was
determined in the presence of 100 lM (R)-PIA. The reaction mix-
ture was incubated at 25 °C for 180 min. After each incubation time
samples were filtered and measured in a microplate beta scintilla-
tion counter (Microbeta Trilux, Perkin–Elmer, Madrid, Spain).
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5.5.1.5. Data analysis. The ꢀlog of the inhibition constant (pKi) of
each compound was calculated by the Cheng–Prusoff equation
Ki ¼ IC50=ð1 þ ½Lꢂ=KDÞ
where IC50 is the concentration of compound that displaces the
binding of radioligand by 50%, [L] is the free concentration of radi-
oligand and KD is the dissociation constant of each radioligand. IC50
values were obtained by fitting the data with non-linear regression
using Prism 2.1 software (GraphPad, San Diego, CA). For those com-
pounds that showed either little affinity or poor solubility a per-
centage of inhibition of specific biding at 1
Results are the mean of 3 experiments (n = 3) each performed in
duplicate.
Selectivity is defined by the ratio Ki A2A/Ki A2B
lM is reported.
23. Touchstone, J. In Advances in Thin-Layer Chromatography; Wiley: New York,
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.