Discovery of 1,3-diethyl-7-methyl-8-(phenoxymethyl)-xanthine derivatives as novel adenosine A1and A2Areceptor antagonists

Article abstract of DOI:10.1016/j.bmcl.2016.10.086

Based on a previous report that a series of 8-(phenoxymethyl)-xanthines may be promising leads for the design of A₁adenosine receptor antagonists, selected novel and known 1,3-diethyl-7-methyl-8-(phenoxymethyl)-xanthine and 1,3,7-trimethyl-8-(phenoxymethyl)-xanthine analogs were synthesized and evaluated for their A₁and A_2Aadenosine receptor affinity. Generally, the study compounds exhibited affinity for both the A₁and A_2Aadenosine receptors. Replacement of the 1,3-dimethyl-substition with a 1,3-diethyl-substition pattern increased A₁and A_2Abinding affinity. Overall it was found that para-substitution on the phenoxymethyl side-chain of the 1,3-diethyl-xanthines decreased A₁affinity except for the 4-Br analog (4f) exhibiting the best A₁affinity in the submicromolar range. On the other hand A_2Aaffinity for the 1,3-diethyl-xanthines were increased with para-substitution and the 4-OCH₃(4b) analog showed the best A_2Aaffinity with a K_ivalue of 237?nM. The 1,3-diethyl-substituted analogs (4a, and 4f) behaved as A₁adenosine receptor antagonists in GTP shift assays performed with rat whole brain membranes expressing A₁adenosine receptors. This study concludes that para-substituted 1,3-diethyl-7-methyl-8-(phenoxymethyl)-xanthine analogs represent novel A₁and A_2Aadenosine receptor antagonists that are appropriate for the design of therapies for neurodegenerative disorders such as Parkinson's and Alzheimer's disease.

Full text of DOI:10.1016/j.bmcl.2016.10.086

Accepted Manuscript
Discovery of 1,3-diethyl-7-methyl-8-(phenoxymethyl)-xanthine derivatives as
novel adenosine A1 and A2A receptor antagonists
Rozanne Harmse, Mietha M. van der Walt, Jacobus P. Petzer, Gisella
Terre’Blanche
PII:
S0960-894X(16)31134-9
DOI:
http://dx.doi.org/10.1016/j.bmcl.2016.10.086
BMCL 24389
Reference:
Bioorganic & Medicinal Chemistry Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
12 September 2016
26 October 2016
28 October 2016
Please cite this article as: Harmse, R., van der Walt, M.M., Petzer, J.P., Terre’Blanche, G., Discovery of 1,3-
diethyl-7-methyl-8-(phenoxymethyl)-xanthine derivatives as novel adenosine A1 and A2A receptor antagonists,
Bioorganic & Medicinal Chemistry Letters (2016), doi: http://dx.doi.org/10.1016/j.bmcl.2016.10.086
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Discovery of 1,3-diethyl-7-methyl-8-
(phenoxymethyl)-xanthine derivatives as
novel adenosine A1 and A2A receptor
antagonists.
Rozanne Harmse a, Mietha M van der Walt b Jacobus P Petzer a,b and Gisella Terre’Blanche a,b*
aPharmaceutical Chemistry, School of Pharmacy, North-West University, Private Bag X6001, Potchefstroom 2520, South Africa
bCentre of Excellence for Pharmaceutical Sciences, School of Pharmacy, North-West University, Private Bag X6001, Potchefstroom 2520,
South Africa
Abstract
Based on a previous report that a series of 8-(phenoxymethyl)-xanthines may be promising leads for
the design of A1 adenosine receptor antagonists, selected novel and known 1,3-diethyl-7-methyl-8-
(phenoxymethyl)-xanthine and 1,3,7-trimethyl-8-(phenoxymethyl)-xanthine analogs were synthesized
and evaluated for their A1 and A2A adenosine receptor affinity. Generally, the study compounds
exhibited affinity for both the A1 and A2A adenosine receptors. Replacement of the 1,3-dimethyl-
substition with a 1,3-diethyl-substition pattern increased A1 and A2A binding affinity. Overall it was
found that para-substitution on the phenoxymethyl side-chain of the 1,3-diethyl-xanthines decreased
A1 affinity except for the 4-Br analog (4f) exhibiting the best A1 affinity in the submicromolar range.
On the other hand A2A affinity for the 1,3-diethyl-xanthines were increased with para-substitution and
the 4-OCH3 (4b) analog showed the best A2A affinity with a Ki value of 237 nM. The 1,3-diethyl-
substituted analogs (4a, and 4f) behaved as A1 adenosine receptor antagonists in GTP shift assays
performed with rat whole brain membranes expressing A1 adenosine receptors. This study concludes
that para-substituted 1,3-diethyl-7-methyl-8-(phenoxymethyl)-xanthine analogs represent novel A1
and A2A adenosine receptor antagonists that are appropriate for the design of therapies for
neurodegenerative disorders such as Parkinson’s and Alzheimer’s disease.
Keywords: Caffeine, 1,3-diethyl-7-methyl-8-(phenoxymethyl)-xanthines, 1,3,7-trimethyl-8-(phenoxymethyl)-xanthines, Adenosine A1 and
A2A receptor antagonists
*Corresponding author. Tel: +27 18 2992264; fax: +27 18 2994243; E-mail address: Gisella.Terreblanche@nwu.ac.za (G. Terre’Blanche).

The actions of adenosine may be mediated by four adenosine receptor (AR) subtypes [1], namely the
A1, A2A, A2B and A3 ARs [2], all of which couple to G proteins [3]. The A1 AR antagonists may
potentially find therapeutic relevance as drug targets for numerous diseases including asthma [4],
cardiovascular disorders [5], renal diseases [6] and cognitive deficits [7]. This wide range for
therapeutic potential may be contributed to the wide distribution of the A1 ARs throughout the human
body, eg. lungs [4], heart [8], kidneys [6] and brain [9]. The ARs mediate bronchoconstriction,
inflammation, increased endothelial cell permeability, and mucin production in the lung [4], while
these receptors mediate negative chronotropic, dromotropic, and inotropic effects in the heart [8] and
lead to vasoconstriction, reduction of glomerular filtration rate, inhibition of renin secretion, and
inhibition of neurotransmitter release after activation in the kidneys [6]. Furthermore, the A1 ARs are
widely expressed throughout the human brain, including the hippocampus and prefrontal cortex that is
important brain areas for cognitive function [10]. The A1 AR antagonists depolarize postsynaptic
neurons and presynaptically enhance the release of a number of neurotransmitters, e.g. acetylcholine,
glutamate, serotonin and norepinephrine. Antagonists of the A1 AR have been suggested as a potential
treatment of cognitive deficits in animal models [11] and this release of neurotransmitters could find
application in the treatment of cognitive deficits associated with Alzheimer’s disease (AD) and
Parkinson’ disease (PD).
The expression of A2A ARs are approximately 20 times greater in the basal ganglia, compared to the
rest of the brain [12], with the highest abundance found in the striatum [13,14]. Furthermore, the A2A
ARs are localized exclusively in the dopamine enriched areas of the brain and mediate inhibition of
locomotor activity [15]. PD is a neurodegenerative disorder and are pathologically defined by
neuronal loss in the substantia nigra pars compacta (SNpc), followed by the loss of striatal dopamine
content [16]. This dopamine deficiency within the basal ganglia, leads to the characteristic PD-
associated impaired motor functions [17]. For this reason it is suggested that A2A AR antagonists may
show promise as a novel treatment of PD-related motor symptoms [18]. Further evidence proposes
that A2A AR antagonists exhibit a lower risk of dyskinesia when used in conjunction with L-DOPA
[18]. In addition, these antagonists may also exhibit neuroprotective properties [19,20]. Therefore,
selective A2A AR antagonists present an attractive non-dopaminergic target to improve the PD-related
motor symptoms [18].
Xanthine derivatives represent an important class of naturally occurring (e.g. caffeine, 1) and/or
synthetic (e.g. CSC, KW-6002) compounds that consist of a fused six- and five-membered nitrogen
containing ring system. Some xanthine derivatives (e.g. caffeine, CSC and KW-6002) have previously
been evaluated in the treatment of AD and PD by acting as AR antagonists (Figure 1) [21,22,23].
Caffeine (1) is a well-known 1,3,7-trimethyl-substituted xanthine that acts as a non-selective A1 and
A2A AR antagonist (A1Ki = 55 μM; A2AKi = 50 μM) [24]. Substitution of caffeine at the C8 position
has previously shown to result in gained A1 and A2A AR affinity. For example, 8-phenylcaffeine
presented with an increased affinity for both the A1 and A2A ARs, with selectivity for the A1 AR over
the A2A isoform (A1Ki = 17 μM; A2AKi = 27 μM) [24]. Furthermore, C8 substitution with a
phenoxymethyl side-chain has resulted in 1,3,7-trimethyl-8-(phenoxymethyl)-xanthine (2a, A1Ki =
3.09 μM; A2AKi = 2.37 μM) [25] and displayed an approximate 17- and 21-fold enhancement towards
the A1 and A2A AR affinity, respectively, when compared to caffeine (1). In addition, the 1,3-diethyl-
substitution pattern, 1,3-diethyl-7-methyl-8-(phenoxymethyl)-xanthine (4a), lead to an approximate
63- and 26-fold increase towards A1 and A2A AR affinity (A1Ki = 0.874 μM; A2AKi = 1.91 μM) [25].

O
N
O
O
N
N
N
Cl
O
N
N
N
N
N
N
N
O
O
O
N
O
Caffeine
CSC
KW-6002
Figure 1. Xanthine structures of AR antagonists bearing 1,3-dimethyl-substitution (caffeine and CSC)
and 1,3-diethyl-substitution (KW-6002).
To further explore the influence of 1,3-dimethyl-substitution and gain insight into the structure
activity relationships, we compared 1,3-diethyl-7-methyl-xanthine (3) to its 1,3-dimethyl-substitution
counterpart, namely caffeine (1), as the 1,3-diethyl-substitution pattern is expected to enhance AR
affinity as shown by previously synthesized xanthine derivatives, CSC and KW-6002 (Figure 1)
[26,27]. Based on recent research suggesting that 1,3-diethyl-7-methyl-8-(phenoxymethyl)-xanthines
represent an interesting class of xanthine derivatives that possess affinity for the A1 and A2A ARs [25]
we synthesized and compared a series of para-substituted 1,3-diethyl-7-methyl-8-(phenoxymethyl)-
xanthine derivatives (4a–f) to their 1,3,7-trimethyl-8-(phenoxymethyl)-xanthine counterparts (2a–f)
as potential new A1 and/or A2A AR antagonists.
The starting materials, 1,3-dimethyl- and 1,3-diethyl-5,6-diaminouracil, was prepared as reported in
the literature [25,28]. The phenoxyacetic acids that were not commercially available were synthesized
as previously documented [29,30,31]. Overall, the desired target compounds were synthesized as
described elsewhere [25,32]. In short, 1,3-dialkyl-5,6-diaminouracil (5) was reacted with an
appropriately substituted phenoxyacetic acid (6) in the presence of the dehydrating reagent, N-(3-
dimethylaminopropyl)-N’-ethylcarbodiimide hydrochloride (EDAC) (Scheme 1). The obtained
intermediary amide was treated with aqueous NaOH (1 N) solution to yield the corresponding 1,3-
dimethyl-8-phenoxymethyl-7H-xanthinyl or 1,3-diethyl-8-phenoxymethyl-7H-xanthinyl analogs [32].
These intermediary 1,3-dialkyl-8-phenoxymethyl-7H-xanthinyl analogs (7) were subsequently
methylated in the presence of potassium carbonate and an excess iodomethane in order to obtain the
desired 7-methylated novel test compounds (2b, 2c, 4a–f). The target compounds (yields of 79–90%)
1
were purified by recrystallization from ethanol, and the structures and purities were verified by H
NMR, 13C NMR, and mass spectrometry analysis (see Supporting Information). The known test
compounds 2a [25], 2d–2f [33], 3 [32,34] and 4a [25] were prepared as described in literature.
O
O
O
H
N
R1
O
R1
O
R1
O
NH2
NH2
O
COOH
N
N
N
N
N
+
a,b
c
N
O
X
N
R3
N
R3
O
X
X
N
R3
6
7
5
2b,c
4a-f
X = H, OCH3, CH3,
F, Cl or Br
R1 = R3 = CH3 or
R1 = R3 = C2H5
Scheme 1: Synthetic pathway to 8-(phenoxymethyl)-xanthine analogs (2b, 2c, 4a-f). Reagents and
conditions: (a) EDAC, dioxane:H2O (1:1), room temperature; (b) NaOH (aq), reflux; (c) CH3I,
K2CO3, DMF.

The A1 and A2A AR affinities of all the test compounds were determined with radioligand binding
experiments (ethics number NWU-0035-10-A5) as described previously [25]. The A1 AR radioligand
binding assay was performed in the presence of the radioligand [3H]-8-cylcopentyl-1,3-
dipropylxanthine ([3H]DPCPX) with rat whole brain membranes expressing the A1 AR [25,35]. In
turn the A2A AR binding affinity was measured at rat striatal membranes with 5’-N-[3H]-
ethylcarboxamideadenosine ([3H]NECA) as radioligand [25,36]. Selected compounds were further
evaluated to assess if they act as agonists or antagonists of the A1 AR in GTP shift assays with rat
whole brain membranes in the absence and presence of 100 μM GTP [25]. The competition curves
were obtained by plotting the percentage binding vs. the logarithm of the test compound’s
concentrations (ranging between 0 and 100 µM) by using the Prism software package (GraphPad
Software Inc.). The radioligand binding assays were carried out in triplicate and the dissociation
constant values (Ki) are expressed as mean ± standard error of mean (SEM). The Ki values were
calculated by using the Kd values of 0.36 nM for [3H]DPCPX at rat whole brain membranes [25,35],
while 15.3 nM for [3H]NECA at rat striata membrane [25,36] were used. Furthermore, GTP shifts are
calculated by dividing the Ki value of a compound reported in the presence of GTP by the Ki value
obtained in the absence of GTP [37]. A compound with a calculated GTP shift of approximately 1 is
considered an antagonist, in turn the presence of GTP affects the competition curve of an agonist and
shifts the curve to the right [25,38]. The A1 and A2A AR affinity and GTP shift results of the test
compounds are summarized in Table 1.
Table 1
The dissociation constant values (Ki values) for the binding of the test compounds to rat adenosine A1
O
and A2A receptors.
O
N
N
N
N
R8
N
R8
N
O
N
O
N
1, 2a-f
3, 4a-f
Ki ± SEM (µM)a
Compd
R8
A1
A2A
A1 + GTPb
GTP
SId
(A2A/A1)
Shiftc
1,3,7-trimethyl-xanthine (caffeine)
-H
41e; 55f
43e; 50f
-
-
1.1
1
1,3,7-trimethyl-phenoxymethyl-xanthines
-CH2-O-C6H5
3.09g
2.37g
-
-
-
-
0.8
0.5
2a
-CH2-O-[4-OCH3-(C6H5)] 4.67 ± 0.39
2.40 ± 0.66
2b
-CH2-O-[4-CH3-(C6H5)]
-CH2-O-[4-F-(C6H5)]
-CH2-O-[4-Cl-(C6H5)]
- CH2-O-[4-Br-(C6H5)]
6.76 ± 1.11
9.19 ± 0.90
5.56 ± 0.69
3.69 ± 0.60
3.64 ± 0.09
2.57 ± 0.34
0.94 ± 0.23
1.73 ± 0.92
-
-
-
-
-
-
-
-
0.5
0.3
0.2
0.5
2c
2d
2e
2f
1,3,7-triethyl-xanthine
-H
5.61 ± 0.95
2.69 ± 0.29
-
-
0.5
3
1,3-diethyl-7-methyl-phenoxymethyl-xanthines
-CH2-O-C6H5
-CH2-O-[4-OCH3-(C6H5)] 1.22 ± 0.20
0.874g
1.91g
0.892 ± 0.05
1
-
-
-
-
2.2
0.2
0.9
0.7
1.1
4a
4b
4c
4d
4e
0.237 ± 0.06
1.30 ± 0.42
0.841 ± 0.24
1.04 ± 0.19
-
-
-
-
-CH2-O-[4-CH3-(C6H5)]
-CH2-O-[4-F-(C6H5)]
-CH2-O-[4-Cl-(C6H5)]
1.42 ± 0.08
1.23 ± 0.26
0.974 ± 0.21

-CH2-O-[4-Br-(C6H5)]
(A1 agonist)
0.264 ± 0.08
0.015 g
1.36 ± 0.16
-
0.267 ± .030
0.99 g
1
5.2
-
4f
6.48 g
CPA
a All Ki values determined in triplicate and expressed as mean ± SEM.
b GTP shift assay, where the 100 µM GTP was added to the A1 AR radioligand binding assay.
c GTP shifts calculated by dividing the Ki in the presence of GTP by the Ki in the absence of GTP.
d Selectivity index (SI) for the A1 receptor isoform calculated as the ratio of Ki (A2A)/Ki (A1).
e Literature values obtained from reference [39].
f Literature values obtained from reference [24].
g Literature values obtained from reference [25].
Caffeine (1) is a non-selective A1 and A2A AR antagonist with beneficial effects towards both motor
and non-motor symptoms associated with PD, but it is not considered as a treatment option due to its
poor A1 and A2A AR binding affinities (A1Ki = 41–55 μM; A2AKi = 43–50 μM) [24,40]. Previous
research [25] showed that substitution at position C8 of caffeine (1) with a phenoxymethyl side chain
(2a) improved affinity for both A1 and A2A AR (A1Ki = 3.09 μM; A2AKi = 2.37 μM)(Table 1, Figure
2). Furthermore, the current study investigated the influence of para-substitution on compound 2a.
Overall para-substitution seemed to decrease affinity for A1 AR as follow: 2f (4-Br) > 2b (4-OCH3) >
2e (4-Cl) > 2c (4-CH3) > 2d (4-F). Para-substitution only slightly decreased A2A AR affinity (2b, 2c,
2d) with the exception of compound 2e (4-Cl) and 2f (4-Br) where a slight increase was observed: 2e
(4-Cl) > 2f (4-Br) > 2b (4-OCH3) > 2d (4F) >2c (4-CH3) (Table 1).
The influence of the 1,3-diethyl-substitution pattern was investigated by comparing caffeine (1,3-
dimethyl-substitution, 1) to compound 3 (1,3-diethyl-substitution). 1,3-Diethyl-substitution improved
affinity for rat A1 and A2A ARs, with Ki values in the low micromolar range (A1Ki = 5.61 μM; A2AKi =
2.69 μM) and a slight selectivity towards the A2A AR isoform was observed. Thus, AR affinity seems
to be governed by replacement of the 1,3-dimethyl-substitution with a 1,3-diethyl-substitution pattern,
which support previous findings that 1,3-diethyl-substitution compared to 1,3-dimethyl-substitution
enhances A1 /A2A AR affinity [25,40].
Furthermore, C8 substitution of compound 3 (1,3-diethyl-7-methyl-xanthine) with a phenoxymethyl
side-chain, yielded 1,3-diethyl-7-methyl-8-(phenoxymethyl)-xanthine (4a), which showed the same
trend as its counterpart caffeine (1). Compared to compound 3, the 8-(phenoxymethyl)-xanthine
analog 4a showed a 6-fold enhancement in A1 AR affinity (A1Ki = 0.892 μM) and a slight increase
(1.4 fold) in A2A AR affinity (A2AKi = 1.91 μM) [25]. In order to further investigate the A1/A2A AR
structure-activity relationships (SARs) of the 1,3-diethyl-7-methyl-8-(phenoxymethyl)-xanthine
scaffold, a number para-substituted 1,3-diethyl-7-methyl-phenoxymethyl-xanthine analogs were
synthesized (4b, 4c, 4d, 4e, 4f) to compare with the 1,3,7-trimethyl-xanthine analogs (2b, 2c, 2d, 2e,
2f) (Table 1).
Generally para-substitution on the 1,3-diethyl-7-methyl-xanthine analogs (4a–f) showed the same
pattern as the 1,3,7-trimethyl-xanthine analogs on A1 AR affinity. Para-substitution decreased A1 AR
affinity with the exception of compound 4f (4-Br) which showed an increase in A1 AR affinity with a
submicromolar Ki value of 264 nM. Affinity for the A1 AR was in the following order: 4f (4-Br) > 4e
(4-Cl) > 4b (4-OCH3) > 4d (4-F) > 4c (4-CH3). In contrast to the 1,3,7-trimethyl analogs, para-
substitution to the 1,3-diethyl analogs increased A2A AR affinity overall with compound 4b showing
an 8-fold improved A2A AR affinity (4a vs. 4b) with a submicromolar Ki value of 237 nM. The order

of A2A binding affinity for the 1,3-diethyl-analogs (4a–4f) may be summarized as follow: 4b (4-
OCH3) > 4d (4-F) > 4e (4-Cl) > 4c (CH3) > 4f (4-Br) > 4a (4-H).
Comparing the 1,3,7-trimethyl-phenoxymethyl-xanthines to their counterparts, 1,3-diethyl-7-methyl-
8-(phenoxymethyl)-xanthines (1 vs 3; 2a vs 4a; 2b vs 4b; 2c vs 4c; 2d vs 4d; 2e vs 4e; 2f vs 4f), we
found an overall increase in both the A1 and A2A affinity (Table 1), thus concluding that AR affinity
may be governed by 1,3-diethyl-substitution at the xanthine core (Figure 2).
phenoxymethyl side-chain
increase A1 affinity
O
increase A2A affinity
R1
N
N
R1 = R3 = C2H5
increase A1 affinity
increase A2A affinity
N
O
O
N
R3
Figure 2: A general depiction showing the influence of 1,3-diethyl-substitution and C8-
phenoxymethyl-substitution at the xanthine core on the A1 and A2A AR affinity.
In order to demonstrate if the two compounds possessing the highest A1 AR binding affinity (4a and
4f) acted as antagonists or agonists, GTP shift experiments were performed. Compounds 4a and 4f
showed no significant shifts of the binding curves in the presence of GTP and these compounds may
be considered as antagonists of the A1 AR (Table 1, Figure 3).
Figure 3. The binding curves of compounds CPA (reference agonist) and 4a (test compound),
indicating their A1 AR agonist/antagonistic action as determined via GTP shift assays (with and
without 100 µM GTP) in rat whole brain membranes expressing A1 ARs with [3H]DPCPX as
radioligand. (A) GTP shift of 6.48 calculated for the A1 AR agonist CPA [25]. (B) GTP shift of 1.2
calculated for the A1 AR antagonist 4a.
The current study shows that the novel 8-(phenoxymethyl)-xanthines (2b, 2c, 4b–f) as well as the
previously synthesized 8-(phenoxymethyl)-xanthine derivatives (2d–f) exhibited potential as potent
AR antagonists with Ki values in the low micromolar to nanomolar range (A1Ki = 6.76 – 0.264 µM;
A2AKi = 2.40 – 0.237 µM). Replacement of the 1,3-dimethyl-substition with a 1,3-diethyl-pattern is
important for increased A1 and A2A binding affinity. Overall it was found that para-substitution on the
phenoxymethyl side-chain decreased A1 affinity except for the 4-Br (4f) analog which exhibited the

best and enhanced A1 affinity. On the other hand A2A affinity was increased with para-substitution
and compound 4b showed the best A2A affinity. Compounds 4a and 4f was characterized as
antagonists of the A1 AR and due to the structural similarity of the test compounds it is reasonable to
assume that the 1,3-diethyl-7-methyl-8-(phenoxymethyl)-xanthine (4b–f) and 1,3,7-trimethyl-8-
(phenoxymethyl)-xanthine (2b–e) derivatives may act as A1 AR antagonists. In conclusion,
compounds 4b and 4f was found to possess the highest A2A and A1 AR binding affinities respectively,
among the investigated compounds and therefore these 8-(phenoxymethyl)-xanthine analogs are ideal
drug candidates for future in vivo investigation as adenosine receptor antagonists in neurodegenerative
disorders, such as AD and PD.
Acknowledgements
We are grateful to Dr. J. Jordaan and Mr. A. Joubert of the SASOL Centre for Chemistry, North-West
University, for recording the NMR and MS spectra, respectively. We are also thankful to Prof. J. du
Preez for HPLC analysis. The financial assistance of the North-West University, the South African
Medical Research Council and the National Research Foundation towards this research is hereby
acknowledged. Opinions expressed and conclusions arrived at are those of the authors and are not
necessarily to be attributed to the NRF.
References
1.Sattin, A.; Rall, T.W. Mol. Pharmacol. 1970, 6, 13.
2. Fredholm, B.B.; Abbracchio, M.P.; Burnstock, G.; Daly, J.W.; Harden, T.K.; Jacobson, K.A.;
Legg, P.; Williams, M. Pharmacol. Rev. 1994, 46, 143.
3. Ralevic, V.; Burnstock, G. Pharmacol. Rev. 1998, 50, 413.
4. Brown, R.A.; Spina, D.; Page, C.P. Br. J. Pharmacol. 2008, 153, S446.
5. Shah, R.H.; Frishman, W.H. Cardiol. Rev. 2009, 17, 125.
6. Vallon, V.; Osswald, H. Handb. Exp. Pharmacol. 2009, 193, 443.
7. Suzuki, F.; Shimada, J.; Shiozaki, S.; Ichikawa, S.; Ishii, A.; Nakamura, J.; Nonaka, H.; Kobayashi,
H.; Fuse, E. J. Med. Chem. 1993, 36, 2508.
8. Fredholm, B.B.; IJzerman, A.P.; Jacobson, K.A.; Klotz, K.N.; Linden, J. Pharmacol. Rev. 2001, 53,
527.
9. Fastbom, J.; Pazos, A.; Probst, A.; Palacios, J.M. Neurosci. 1987, 22, 827.
10. Onodera, H.; Kogure, K. Brain Res. 1988, 458, 212.
11. Maemoto, T.; Tada, M.; Mihara, T.; Ueyama, N.; Matsuoka, H.; Harada, K.; Yamaji, T.;
Shirakawa, K.; Kuroda, S.; Akahane, A.; Iwashita, A.; Matsuoka, N.; Mutoh, S. J. Pharmacol. Sci.
2004, 96, 42.
12. Yuzlenko, O.; Kiec-Kononowicz, K. Curr. Med. Chem. 2006, 13, 3609.

13. Fink, J.S.; Weaver, D.R.; Rivkees, S.A.; Peterfreund, R.A.; Pollack, A.E.; Adler, E.M.; Reppert,
S.M. Mol. Brain Res. 1992, 14, 186.
14. Svenningsson, P.; Le Moine, C.; Kull, B.; Sunahara, R.; Bloch, B.; Fredholm, B.B. Neurosci.
1997, 80, 1171.
15. Ferre, S.; Von Euler, G.; Johansson, B.; Fredholm, B.B.; Fuxe, K. Proc. Natl. Acad. Sci. U.S.A.
1991, 88, 7238.
16. Dexter, D.T.; Jenner, P. Free Radic. Biol. Med. 2013, 62, 132.
17. Kalia, L.V.; Lang, A.E. Lancet. 2015, 386, 896.
18. Morelli, M.; Blandini, F.; Simola, N.; Hauser, R.A. Park. Dis. 2012, 2012, 489853.
19. Dall'Igna, O.P.; Porciúncula, L.O.; Souza, D.O.; Cunha, R.A.; Lara, D.R. Br. J. Pharmacol. 2003,
138, 1207.
20. Ikeda, K.; Kurokawa, M.; Aoyama, S.; Kuwana, Y. J. Neurochem. 2002, 80, 262.
21. Arendash, G.W.; Cao, C. J. Alzheimers Dis. 2010, 20, S117.
22. Postuma, R.B.; Lang, A.E.; Munhoz, R.P.; Charland, K.; Pelletier, A.; Moscovich, M.; Filla, L.;
Zanatta, D.; Romenets, S.R.; Altman, R.; Chuang, R.; Shah, B. Neurol. 2012, 79, 651.
23. Cunha, R.A. Purin, Signal. 2005, 1, 111.
24. Daly, J.W.; Padgett, W.; Shamim, M.T.; Butts-Lamb, P.; Waters, J. J. Med. Chem. 1985, 28, 487.
25. Van der Walt, M.M.; Terre’Blanche, G. Bioorg. Med. Chem. 2015, 23, 6641.
26. Jacobson, K.A.; Gallo-Rodriguez, C.; Melman, N.; Fischer, B.; Maillard, M.; Van Bergen, A.;
Van Galen, P.J.; Karton, Y. J. Med. Chem. 1993, 36, 1333.
27. Muller, C.E.; Jacobson, K.A. Biochim. Biopohys. Acta. 2011, 1808, 1290.
28. Blicke, F.F. Godt, H.C. J. Am. Chem. Soc. 1954, 76, 2798.
29. G. Zhao, T. Yu, R. Wang, X. Wang, Y. Jing, , Bioorg. Med. Chem. 13 (2005) 4056-62.
30. Koelsch, C.F. J. Am. Chem. Soc. 1931, 53, 304.
31. Buckles, R.E.; Wawzonek, S. J. Chem. Educ. 1948, 25, 514.
32. Van der Walt, M.M.; Terre'Blanche, G.; Petzer, A.; Lourens, A.C.; Petzer, J.P. Bioorg Chem.
2013, 49, 49.
33. Okaecwe, T.; Swanepoel, A.J.; Petzer, A.; Bergh, J.J.; Petzer, J.P. Bioorg Med Chem. 2012, 20,
4336.
34. Connell,R.; Goldmann, S.; Muller, U.; Lohmer, S.; Bischoff, H.; Denzer, D.; Grutzmann, R.;
Wohlfeil, S. U. S. Patent US5714494 A, 1998

35. Bruns, R.F.; Fergus, J.H.; Badger, E.W.; Bristol, J.A.; Santay, L.A.; Hartman, J.D.; Hays, S.J.;
Huang, C.C. Naunyn-Schmiedeberg's Arch. Pharmacol.1987, 335, 59.
36. Bruns, R.F.; Lu, G.H.; Pugsley, T.A. Mol. Pharmacol. 1986, 29, 331.
37. Van der Wenden, E.M.; Hartog-Witte, H.R.; Roelen, H.C.P.F.; Von Frijtag Drabbe Kunzel, J.K.;
Pirovano, I.M.; Mathot, R.A.A.; Danhof, M.; Van Aerschot, A.; Lidaks, J.M.; Ijzerman, A.P.;
Soudijn, W. Eur. J. Pharmacol.-Mol. Pharmacol. Sect. 1995, 290, 189.
38. Gutschow, M.; Schlenk, M.; Gab, J.; Paskaleva, M.; Wassam Alnouri, M.; Scolari, S.; Iqbal, J.;
Muller, C.E. J.Med. Chem. 2012, 55, 3331.
39. Muller, C.E.; Geis, U.; Hipp, J.; Schobert, U.; Frobenius, W.; Pawłowski, M.; Suzuki, F.;
Sandoval-Ramirez, J. J. Med. Chem. 1997, 40, 4396.
40. Shimada, J. Koike, N.; Nonaka, H.; Shiozaki, S.; Yanagawa, K.; Kanda, T.; Kobayashi, H.;
Ichimura, M.; Nakamura, J.; Kase, H.; Suzuki, F. Bioorg. Med. Chem. Lett. 1997, 18, 2349.

Discovery of 1,3-diethyl-7-methyl-8-(phenoxymethyl)-xanthine derivatives as novel
adenosine A1 and A2A receptor antagonists
R Harmse, MM van der Walt JP Petzer and G Terre’Blanche
Graphical abstract
O
O
N
N
N
N
N
vs
N
OCH
3
O
O
N
OCH
3
O
O
N
A2AKi = 2.40 µM
A2AKi = 0.237 µM

Discovery of 1,3-diethyl-7-methyl-8-(phenoxymethyl)-xanthine derivatives as
novel adenosine A1 and A2A receptor antagonists.
R Harmse, MM van der Walt JP Petzer and G Terre’Blanche
Highlights:




A1 receptors are considered drug targets for Alzheimer’s and Parkinson’s disease.
A2A receptors are considered drug targets for Alzheimer’s and Parkinson’s disease.
Novel 1,3-diethyl-7-methyl-8-(phenoxymethyl)-xanthines were synthesized.
1,3-diethyl-7-methyl-8-(phenoxymethyl)-xanthines possess A1 and A2A affinity.