Synthesis and structure-activity relationships of 3,7-dimethyl-1- propargylxanthine derivatives, A(2A)-selective adenosine receptor antagonists

Article abstract of DOI:10.1021/jm970515+

A series of 8-substituted derivatives of 3,7-dimethyl-1- propargylxanthine (DMPX) was synthesized and investigated as A(2A) adenosine receptor antagonists. Different synthetic strategies for the preparation of DMPX derivatives and analogues were explored.

Full text of DOI:10.1021/jm970515+

4396
J . Med. Chem. 1997, 40, 4396-4405
Syn th esis a n d Str u ctu r e-Activity Rela tion sh ip s of
3,7-Dim eth yl-1-p r op a r gylxa n th in e Der iva tives, A2A-Selective Ad en osin e
Recep tor An ta gon ists†
Christa E. Mu¨ller,*,‡ Uli Geis,‡ J o Hipp,‡ Ulrike Schobert,‡ Wolfram Frobenius,‡ Maciej Pawłowski,‡,§
Fumio Suzuki,| and J esu´s Sandoval-Ram´ırez‡,
J ulius-Maximilians-Universita¨t Wu¨rzburg, Institut fu¨r Pharmazie und Lebensmittelchemie, Pharmazeutische Chemie,
Am Hubland, D-97074 Wu¨rzburg, Germany, and Pharmaceutical Research Laboratories, Kyowa Hakko Kogyo Co., Ltd.,
1188 Shimotogari, Nagaizumi, Sunto, Shizuoka 411, J apan
Received August 4, 1997X
A series of 8-substituted derivatives of 3,7-dimethyl-1-propargylxanthine (DMPX) was syn-
thesized and investigated as A2A adenosine receptor antagonists. Different synthetic strategies
for the preparation of DMPX derivatives and analogues were explored. A recently developed
synthetic procedure starting from 3-propargyl-5,6-diaminouracil proved to be the method of
choice for the preparation of this type of xanthine derivatives. The novel compounds were
investigated in radioligand binding studies at the high-affinity adenosine receptor subtypes
A1 and A2A and compared with standard A2A adenosine receptor antagonists. Structure-activity
relationships were analyzed in detail. 8-Styryl-substituted DMPX derivatives were identified
that exhibit high affinity and selectivity for A2A adenosine receptors, including 8-(m-
chlorostyryl)-DMPX (CS-DMPX, Ki A2A ) 13 nM, 100-fold selective), 8-(m-bromostyryl)-DMPX
(BS-DMPX, Ki A2A ) 8 nM, 146-fold selective), and 8-(3,4-dimethoxystyryl)-DMPX (Ki A2A
)
15 nM, 167-fold selective). These and other novel compounds are superior to the standard A2A
adenosine receptor antagonists KF17837 (4) and CSC (5) with respect to A2A affinity and/or
selectivity.
In tr od u ction
In addition to their A1 AR affinity, many xanthines
are also active at A2 AR.1,2,5 It has taken, however, quite
long until the first potent A2A-selective AR xanthines
were identified. In contrast to the wealth of A1 antago-
nists that are known, much fewer A2A AR antagonists
have been described in the literature so far, and
structure-activity relationship (SAR) studies of A2A
antagonists are limited (for a recent review see ref 10).
Potent and selective A2A AR antagonists, however, are
needed as pharmacological tools and have been proposed
as drugs, especially as a novel therapy for the treatment
of Morbus Parkinson.11
One of the first A2-selective AR antagonists described
in the literature was 3,7-dimethyl-1-propargylxanthine
(DMPX, 2, Chart 1).12 The compound was shown to
exhibit A2 selectivity in vitro as well as in vivo.13
Activity and selectivity of DMPX, however, is low. Later
on it was found that 7-methylation of 8-substituted
theophylline derivatives increased A2A selectivity.14 The
resulting caffeine derivatives, such as 8-cyclohexylcaf-
feine (3), showed A2A selectivity only in certain test
systems and relatively low affinity for the receptors.5,14
Nevertheless, that discovery eventually led to the
recent development of further xanthine derivatives
with increased A2A affinity and selectivity, such as
8-(3,4-dim et h oxyst yr yl)-1,3-dipr opyl-7-m et h ylxa n -
thine (KF17837, 4)15 and 8-(m-chlorostyryl)caffeine
(CSC, 5).16 Some non-xanthine A2A AR antagonists
have also been described, such as the triazoloquinazo-
line CGS15943 and various new, improved analogues,17
and the thiazoloquinazoline HTQZ and structurally
related tricyclic compounds.18
Adenosine receptors (AR) are currently subdivided
into four subtypes, all of which have been cloned from
different species including humans.1-4 The most thor-
oughly investigated subtypes are the high-affinity re-
ceptors A1 and A2A, both of which are activated by
adenosine in low, nanomolar, or at least submicromolar
concentrations, depending on the cell system investi-
gated.1 A variety of potent and selective agonists for
both subtypes has been developed, all structurally
derived from the physiological agonist adenosine.1,2
Antagonists for the A1 AR have also been identified.
Compounds derived from the alkaloid theophylline
bearing lipophilic substituents in the 8-position, such
as 8-phenyltheophylline and 1,3-dipropyl-8-cyclopen-
tylxanthine (DPCPX), are potent A1-selective AR an-
tagonists.5 Further structural classes, including ad-
enines,6 7-deazaadenines (pyrrolo[2,3-d]pyrimidines and
pyrimido[4,5-b]indoles),7 7-deaza-8-azapurines (pyra-
zolo[3,4-d]pyrimidines),8 and triazoloquinoxalines, as
well as related compounds,9 were identified and devel-
oped as A1 AR antagonists.
* Address correspondence to: Prof. Dr. Christa Mu¨ller, Institut fu¨r
Pharmazie und Lebensmittelchemie, Am Hubland, D-97074 Wu¨rzburg,
Germany. Phone: +49-(0)931-888-5440. Fax: +49-(0)931-888-5462.
E-mail: mueller@pharmazie.uni-wuerzburg.de.
† Preliminary results were presented at the 2nd European Congress
of Pharmaceutical Sciences in Berlin 1994 (abstract published in Eur.
J . Pharm. Sci. 1994, 2, 137) and the 10th Camerino-Noordwijkerhout
Symposium “Perspectives in Receptor Research”, 1995, in Camerino,
Italy.
‡ Universita¨t Wu¨rzburg.
§ M.P. was on leave from the J agiellonian University of Cracow,
Poland.
Despite its low affinity and A2A selectivity in vitro,
DMPX is still widely used as a standard A2A antagonist
in pharmacological studies, particularly in in vivo
experiments, due to its relatively high water solubility
| Kyowa Hakko Kogyo Co., J apan.
J . S.-R. was on leave from the Universidad Auto´noma de Puebla,
Mexico.
X Abstract published in Advance ACS Abstracts, December 1, 1997.
S0022-2623(97)00515-3 CCC: $14.00 © 1997 American Chemical Society

Synthesis and SAR of DMPX Derivatives
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 26 4397
Ch a r t 1. Selection of A2 Adenosine Receptor Antagonists with Xanthine Structure
Sch em e 1. Synthesis of 8-Substituted DMPX
and bioavailability. The development of A2A antagonists
with enhanced potency, selectivity, and water solubility
is desirable.
Derivatives: Methods A and Ba
In the present study we have attempted to develop
new A2A AR antagonists with improved properties.
DMPX was selected as a lead structure. Our approach
was to introduce various substituents in the 8-position
of DMPX and/or to replace the substituents in the 1-,
3-, or 7-position of 8-substituted DMPX derivatives by
(ar)alkyl residues. Structure-activity relationships
were analyzed in detail. Various synthetic strategies
were developed and applied to obtain 8-substituted
DMPX derivatives and related xanthines with different
substituents in the 1-, 3-, 7-, and 8-positions.
Resu lts a n d Discu ssion
Ch em istr y. DMPX itself had been obtained by Daly
and co-workers by alkylation of theobromine (3,7-
dimethylxanthine) with propargyl bromide in ethanol/
water in the presence of sodium hydroxide as a base.12
For the preparation of 8-substituted DMPX deriva-
tives, the standard procedure for the synthesis of
xanthines bearing different substituents in the 1- and
3-position,19 namely alkylation of 6-amino-1-methyl-
uracil with propargyl bromide in the 3-position under
basic conditions, according to Papesch and Schroeder,20
had not been successful in our hands,21 probably due to
the high reactivity of the triple bond.22 An alternative
alkylation procedure after silylation of 6-amino-1-me-
thyluracil had provided the desired 6-amino-1-methyl-
3-propargyluracil only in relatively low yield.21 There-
fore, three alternative strategies, A, B, and C, were
investigated and applied for the synthesis of 8-substi-
tuted DMPX derivatives as depicted in Schemes 1 and
2.
a
(a) R8CHO, acetic acid, MeOH or EtOH; (b) FeCl3 in EtOH,
reflux, or SOCl2 at rt; (c) MeI, K2CO3, DMF; (d) R8COOH, EDC,
MeOH; (e) NaOH, H2O, MeOH, 60 °C.
Sch em e 2. Synthesis of 8-Substituted DMPX
Derivatives: Method Ca
(A) Following the procedure developed for the prepa-
ration of 1,8-disubstituted xanthines,21 3-propargyl-5,6-
diaminouracil (6)23,24 was condensed with the appropri-
ate aldehyde to yield the imines 7a -c. Compounds 7a
and 7b could subsequently be subjected to oxidative ring
closure using ferric chloride25 for the preparation of 8
and 9. The same reaction conditions lead to a degrada-
tion of styryl-substituted imine 7c. In this case ring
closure could be performed with thionyl chloride26 at
room temperature, which afforded 10 in short reaction
time and very pure form. 1,8-Disubstituted xanthines
8-10 were bismethylated using methyl iodide/potas-
sium carbonate in dimethylformamide (DMF) under
mild conditions. 8-Cyclohexyl as well as aryl (2-thienyl,
styryl) derivatives of DMPX were obtained in high yields
by this method (Scheme 1). The limited availability of
different aldehydes, however, prompted us to pursue yet
a different approach to 8-substituted DMPX derivatives,
in which the easily available carboxylic acids could be
employed. Another drawback of this method, with
regard to the preparation of analogues, is that substit-
a
(a) Br2; (b) CH3NH2; (c) R8COOH, EDC or R8COCl, pyridine;
(d) NaOH; (e) R1X; X ) Br, I.
uents in the 3- and 7-position have to be identical, since
selective alkylation is difficult to perform.
(B) Most DMPX derivatives investigated in the present
study were obtained by this alternative route which had
recently been developed in our group (Scheme 1).24
Thus, 5,6-diamino-3-propargyluracil (6) was condensed
with a carboxylic acid by means of a carbodiimide. The
5-amino group of 3-substituted 5,6-diaminouracils bear-
ing no substituent at the 1-position is particularly
reactive. Therefore, satisfactory to excellent yields of
various amides could be obtained. Uracil derivatives
unsubstituted in the 1-position, such as 14, can only be

4398 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 26
Mu¨ller et al.
cyclized under harsh basic or acidic conditions under
which the propargyl function is attacked.21,22 Therefore,
methylation in the 1-position of diaminouracil deriva-
tives 14 is required as the following step in order to
enhance the nucleophilicity of the 6-amino group for
subsequent alkaline ring closure of compounds 15 under
mild conditions.21 Final methylation of compounds 16
in the 7-position yielded the desired DMPX derivatives
17-22. 8-Styryl-DMPX derivatives bearing substitu-
ents on the phenyl ring and heterocyclic analogues of
8-styryl-DMPX were prepared. The synthesis of further
8-substituted DMPX derivatives and analogues (38-45)
has already been described elsewhere.24
our hands. We have now developed optimized ring
closure conditions for the preparation of 34 leading to
an increase in overall yield from 4%16 to 22%. Hydroly-
sis of the amide bond may also be the reason for the
low yields of the thienyl- and furylethenyl-substituted
xanthines 16d -f.
Yields, melting points, and elemental analyses data
for the majority of intermediate and all final products
are listed in Table 1. The compounds investigated were
further characterized by their 1H NMR spectra. For
selected compounds 13C NMR spectra were recorded
(Supporting Information).
(E)-Configurated cinnamic acid derivatives were used
as starting compounds for the preparation of 8-styryl-
substituted xanthines. The (E)-configuration was re-
tained during the course of the synthesis as documented
by the coupling constant of the vinylic protons (3J ca.
16 Hz).
The propargyl group in DMPX derivatives, which is
rather reactive and can be hydrated in strong acidic or
basic medium, remained intact under the applied reac-
tion conditions, as shown by the typical signals in the
1H NMR spectrum with a long-range coupling constant
of 2.3-2.4 Hz for the propargyl protons and the typical
signal for the propargyl carbon atoms in the 13C NMR
spectra (Supporting Information).
(C) A third method for the synthesis of 8-substituted
DMPX derivatives and analogues was investigated
(Scheme 2). Thus, 6-amino-1-methyl-5-(methylamino)-
uracil 25 was prepared essentially as described27 start-
ing from 1-methyl-6-aminouracil (23)20 via bromination
in the 5-position to 24, followed by nucleophilic dis-
placement of bromine by methylamine. Condensation
of the amino uracil 25 with a carboxylic acid chloride,
or a carboxylic acid by means of a carbodiimide, respec-
tively, and subsequent ring closure of compounds 26
under strong basic conditions afforded 8-substituted 3,7-
dimethylxanthines 27. It was observed that ring closure
of such uracil derivatives lacking a substituent in the
3-position required harder conditions compared to cor-
responding 1,3-disubstituted uracil derivatives. Thus,
a derivative of 26b bearing methoxy substituents in the
3- and 4-position of the styryl residue gave no ring-
closed product under a variety of ring closure conditions,
due to cleavage of the amide bond under the drastic
reaction conditions required. Such methoxy-substituted
6-amino-5-(cinnamoylamino)uracil derivatives appear to
hydrolyze particularly easily under basic conditions. If
a 3-substituent is lacking, the uracil derivative is
deprotonated under basic ring closure conditions, which
reduces its reactivity, and the labile amide bond of those
methoxy derivatives is hydrolyzed already under condi-
tions that are not yet sufficient for ring closure.
The 7-methyl group in 8-aryl- (compound 12) and
8-styryl-substituted compounds (13, 17-22) is shifted
downfield as compared to 8-alkyl- (11) or 8-unsubsti-
tuted xanthine derivatives21 from 3.8-3.9 to 4.0-4.1
ppm.
Biologica l Eva lu a tion
The compounds were tested in radioligand binding
assays for affinity to A1 and A2A adenosine receptors in
rat cortical membrane and rat striatal membrane
preparations, respectively. The A1-selective agonist
[3H]-N6-cyclohexyladenosine (CHA) was used as A1
ligand, and the A2A-selective agonist [3H]-2-[[[4-(car-
boxyethyl)phenyl]ethyl]amino]-5′-N-(ethylcarbonyl)ami-
no]adenosine (CGS21680) as A2A ligand. In addition,
some compounds were also tested versus another fre-
quently used A1 agonist radioligand, [3H]-N6-(R)-(phe-
nylisopropyl)adenosine (R-PIA). Before [3H]CGS21680
had become available as a radioligand, the nonselective
Alkylation of 27 in the 1-position under mild condi-
tions led to 8-phenyl-DMPX (29), which had been
synthesized before by method (A) starting from 8-phen-
yl-1-propargylxanthine.21 8-Phenylcaffeine (28), which
was required as a standard compound for comparison,
and 1-allyl-3-methyl-8-styrylxanthine (30) were ob-
tained analogously.
agonist
[3H]-5′-[(N-(ethylcarbonyl)amino]adenosine
(NECA) was generally used in A2A AR binding assays.
An A1-selective AR agonist, N6-cyclopentyladenosine
(CPA), was added in order to block A1 AR present in
striatal tissue. We tested some compounds versus both
radioligands, [3H]NECA and [3H]CGS21680 in order to
compare data.
The (3,4-dimethoxystyryl)-DMPX (18), which could
not be obtained by this method, was eventually obtained
by method B, which appears to be the method of choice
for the preparation of 8-substituted DMPX derivatives
and analogues.
Further 1,3,7,8-tetrasubstituted xanthines, including
8-(3,4-dimethoxystyryl)caffeine (34) and 7-methyl- and
7-propargyl-3-isobutyl-1-methyl-8-phenylxanthine (35
and 36), were prepared by standard procedures.19
Some standard compounds (1, 2, 4, 5, 28, 29, 31, 34)
were tested in our assay systems for comparison with
literature data. Our results were generally consonant
with data obtained by other groups, with few exceptions.
For CSC (5) a Ki value at A1 AR of 28 µM had been
determined using [3H]R-PIA as radioligand.16 In our
assay using [3H]CHA, we were not able to determine
an IC50 and a Ki value due to limited solubility of the
compound. We measured 17% inhibition of [3H]CHA
binding at a concentration of compound 5 of 1 µM.
Higher concentrations gave results indicating lacking
solubility of the compound. No sigmoidal curve could
be obtained. For compound 34, which was resynthe-
Compound 34 had been synthesized earlier by J acob-
son et al. in 4% overall yield in three steps starting from
1,3-dimethyl-5,6-diaminouracil.16 No yields for the
single steps were published. We found that the critical
step in that reaction sequence is the ring closure
reaction of 6-amino-1,3-dimethyl-5-((3,4-dimethoxycin-
namoyl)amino)uracil under basic conditions. Using the
published method,16 hydrolysis of the amide bond rather
than ring closure was observed as the main reaction in

Synthesis and SAR of DMPX Derivatives
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 26 4399
Ta ble 1. Yield, Melting Point, and Analytical Data of Intermediate and Final Products
elemental
analyses
compd.
yield (%)
mp (°C)
formula
7b
7c
9
10
11
12
13
78
96
64
87
63
72
93
96
50
71
82
29
45
71
45
85
24
53
68
59
56
78
24
24
37
34
60
74
67
72
60
66
70
73
69
85
88
80
242
266
299
>300
207
>270
232
268
>275
292
281
285
278
253
273
277
271
272
270
270
>270
>300
290
273
271
200
267
260
234
245
242
C12H10N4O
2
C,H,N,S
C,H,N
C,H,N,S
C,H,N
C,H,N
C,H,N
Ca,H,N
C,H,N
c
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
16H14N4O2
12H8N4O2S
16H12N4O2
16H14N4O2
14H12N4O2S
18H16N4O2
16H13N4O3Br
18H18N4O5
14a
14b
14c
14d
14e
14f
15a
15b
15c
15d
15e
15f
16a
16b
16c
16d
16e
16f
17
18
19
20
21
22
24
25
26a
26b
27a
27b
28
17H14N4O5
C,H,N
C,H,N,S
C,H,N,S
C,H,N
C,H,N
Ca,H,N
Ca,H,N
C,H,N,S
C,H,N,S
C,H,N
C,H,N
C,H,N
C,H,N
C,H,N,S
C,H,N,S
C,H,N
Ca,H,N
C,H,N
C,H,N
C,H,N,S
C,H,N,S
C,H,Nb
C,H,N
C,H,N
C,H,N
C,H,N
C,H,N
C,H,N
C,H,N
14H12N4N3S
14H12N4O3S
14H12N4O4
17H15N4O3Br‚H2O
19H20N4O5
18H16N4O5
15H14N4O3S‚H2O
15H14N4O3S
15H14N4O4
17H13N4O2Br
19H18N4O4‚1.25H2O
18H14N4O4
15H12N4O2S
15H12N4O2S
15H12N4O3
18H15N4O2Br‚H2O
20H20N4O4‚0.7H2O
19H16N4O4
16H14N4O2S
16H14N4O2S
16H14N4O3
>270 (lit.27 mp 286-288)
C5H6N3O2Br
C6H10N4O2
C13H14N4O3
243-244 (lit.27 mp 238-240)
>270 (lit.44 mp > 300)
>270
C
15H16N4O3
>270 (lit.44 mp > 300)
C13H12N4O2
>270
C
C
15H14N4O2
14H14N4O2
178
(lit.45 mp 186-188)
29
30
34
35
36
78
71
73
68
83
239 (lit.21 mp 237)
C16H14N4O2
18H18N4O2
C,H,N
C,H,N
C,H,N
C,H,N
C,H,N
206
C
236-238 (lit.16 mp 230-232)
C18H20N4O4‚0.5H2O
130
152
C
C
17H20N4O2
19H20N4O2
a
b
C found (calcd): 9, 52.9 (51.8); 13, 66.6 (65.6); 15b, 56.5 (57.0); 15c, 56.5 (56.0); 17, 52.9 (51.8). N found (calcd): 22, 17.4 (18.0).
c Not determined (intermediate product).
sized in our laboratory, we obtained an about 10-fold
higher A2A affinity than that described in the litera-
ture.16
receptor subtype (Table 2). The big breakthrough in the
development of A1-selective AR antagonists was, first,
the introduction of lipophilic substituents in the 8-posi-
tion of theophylline (31), such as phenyl and cycloalkyl
residues, and second, the exchange of the 1,3-methyl
groups for 1,3-dipropyl residues, as in 8-cyclopentyl-1,3-
dipropylxanthine (DPCPX).1,2,5
The caffeine analogue DMPX (2, 3,7-dimethyl-1-
propargylxanthine) is somewhat more potent than caf-
feine, particularly at A2A AR. DMPX exhibits A2A
selectivity up to 10-fold, depending on the test systems
that are being compared,12,13,29 while caffeine is nonse-
lective.
[3H]R-PIA and [3H]CHA data were very similar (see
9, 10, 13, 38). A comparison of [3H]NECA and [3H]-
CGS21680 data, however, showed significant differ-
ences. Ki values determined with [3H]CGS21680 were
generally lower (up to 9-fold, see compound 9) compared
to data obtained with [3H]NECA for xanthines investi-
gated (see compounds 9, 10, 13, 38; also see standard
xanthines 1, 2, 28, and 31). Therefore, A2A selectivity
appears greater if CGS21680 is used as radioligand.
J arvis et al., who introduced CGS21680 as an A2A
-
specific radioligand, had observed similar differences for
some but not all xanthines that were compared.28 They
observed up to 7-fold higher Ki values for xanthines
when determined with NECA as compared to CGS21680
as a radioligand.
The introduction of certain 8-substituents into caf-
feine and 1,3-dipropyl-7-methylxanthine led to potent
A2A-selective antagonists, the most potent compounds
bearing a styryl residue as in 8-styrylxanthine deriva-
tives 4 and 5.15,16 In the present study we investigated
the effects of 8-substitution of the A2-selective AR
antagonist DMPX and compared 8-substituted DMPX
derivatives with corresponding caffeine derivatives.
Str u ctu r e-Activity Rela tion sh ip s
Com p a r ison : Ca ffein e-DMP X. Caffeine (1) is a
weak, nonselective AR antagonist. Theophylline (31)
is more potent but also shows low selectivity for either
8-Substitution of DMPX with cyclohexyl (11), phenyl
(29), 2-thienyl (12), and styryl residues (13, 17-22, 38)

4400 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 26
Mu¨ller et al.

Synthesis and SAR of DMPX Derivatives
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 26 4401
generally increased A1 and A2 AR affinity of DMPX
(Table 2). The same effect had been observed for
caffeine derivatives, with the exception of the 8-phenyl
derivative (28), which was equally active to caffeine at
both receptor subtypes.
The steric hindrance of a coplanar or nearly coplanar
conformation should be reduced if a substituent other
than methyl was located in the 7-position. As an
example we introduced a propargyl residue in the
7-position, which indeed has quite different effects than
the methyl substituent. At A1 AR 7-propargyl was
superior to a 7-methyl substituent (cf. 35/36, 38/44). The
same effect had been observed with the 8-unsubstituted
caffeine analogue 7-propargyl-1,3-diethylxanthine.5 At
A2A AR the effect depended on the 8-substituent. For
the 8-phenyl derivative, 7-propargyl was superior to
7-methyl (35/36), as had been seen with the 8-unsub-
stituted derivative.5 This effect, however, was reversed
in the 8-styryl derivatives (38/44): The propargyl
derivative was 5-fold less potent compared to the methyl
derivative. Steric hindrance may be needed to force the
styryl residue in a favorable conformation.
A comparison of four caffeine derivatives with corre-
sponding DMPX derivatives (3/11, 28/29, 33/13, 5/38)
shows that 8-substituted DMPX derivatives are at least
about 2-3-fold more potent AR antagonists than cor-
responding caffeine derivatives at both receptor sub-
types. One exception is, however, the 8-(3,4-dimethoxy-
styryl)-DMPX 18, which is virtually equipotent to the
corresponding caffeine derivative 34 at A2A AR but
slightly more potent at A1 AR, thus leading to a
reduction in selectivity. This result demonstrates that
subtle changes in the substitution pattern of the 8-styryl
substitutent can influence the structure-activity rela-
tionships of substituents in the xanthine 1- and 3-posi-
tions.
In analogy to the current standard A2A antagonist
8-chlorostyrylcaffeine (CSC, 5), we synthesized the 8-(m-
chlorostyryl)-DMPX (CS-DMPX, 38) and investigated
SAR of analogues with variations in the 1-, 3-, and
8-positions. So far, only two 8-styrylxanthine deriva-
tives with different substituents in the 1- and 3-posi-
tions (1-methyl-3-propylxanthines) have been described.31
Most derivatives investigated so far were 1,3-dimethyl-
or 1,3-dipropyl-substituted xanthines. Few 1,3-diethyl-
and 1,3-diallyl-8-styrylxanthines have also been de-
scribed.16
The 1,3-dipropyl-7-methyl analogue 4 (KF 17837)
exhibits increased affinity compared to the correspond-
ing DMPX derivative 18 and the caffeine derivative 34
at both receptor subtypes, about 2-fold at A2A AR, and
10-fold (compared to 18), or 37-fold (compared to 34),
at A1 AR, thus yielding a compound with high affinity
but low selectivity (31-fold for 5 versus more than 100-
fold for 18 and 34).
Th e 7-P osition . 7-Methylation of theophylline (31)
led to a decrease in A1 and A2A AR affinity, caffeine (1)
being about 2-fold less potent at A1 and A2A AR than
31. The same effect is observed in 1-propargyl-3-
methylxanthine (32).21 Methylation causes a 3-fold
decrease in A2A AR affinity, but the decrease is much
more pronounced at A1 AR (55-fold). Thus, the A1-
selective 1-propargyl-3-methylxanthine (32) is turned
into an A2A-selective compound (DMPX, 2) by 7-methy-
lation. The N7-hydrogen of xanthines has been shown
to be an important hydrogen bond donor in A1 and A2A
AR binding,30 but may be of greater importance for
binding to A1 AR for many xanthine derivatives.
Th e 1-P osition . CS-DMPX (38) bearing a propargyl
substituent in the 1-position was compared to the
1-methyl analogue CSC (5) and to an analogue in which
the propargyl residue was replaced by n-propyl (45).
Propargyl was the best substituent in this series (com-
pound 38) for high A2A affinity, the methyl-substituted
derivative 5 was about 3-fold less potent and equally
potent to the 1-propyl derivative 45. At A1 AR, however,
the 1-propyl derivative was the most potent compound,
and therefore, 45 exhibited the least selectivity of the
three derivatives.
In a series of 8-(3,4-dimethoxystyryl)-3,7-dimethyl-
xanthines, three different substituents in the 1-position
were compared: methyl (in caffeine derivative 34),
propargyl (in DMPX derivative 18), and allyl (in 30).
Again, propargyl was the best substituent with regard
to A2A affinity, but methyl was nearly equipotent. Allyl
substitution decreased A2A AR affinity about 4-fold
compared to propargyl.
Similarly, in 1-propargyl-8-(2-thienyl)xanthine (9)
introduction of methyl groups in the 3- and 7-positions
(compound 12) led to a decrease in A1 (5-fold) and A2A
(3-fold) AR affinity. In an 8-styryl derivative (10),
however, the same modification led to no change in A1
affinity, but an increase in A2A affinity (>10-fold). The
effect of methylation of 1-propargyl-3-(ar)alkyl-8-styryl-
xanthines could be observed in three compounds (37/
38, 40/41, 16c/19). The general finding was a decrease
in A1 AR affinity (2-10-fold), and at the same time an
increase in A2A affinity (3-9-fold). This effect appears
to be specific for styryl substituents.
Th e 3-P osition . Four different substituents in the
3-position were investigated. The 3-methyl group in CS-
DMPX (38) was exchanged for n-propyl (in 39), isobutyl
(in 41), or benzyl (in 43). The isobutyl derivative
showed similar A2A affinity as the methyl derivative,
but A1 affinity was increased 5-fold, leading to a
compound with lower A2A selectivity compared to the
DMPX derivative 38. A similar effect of a 3-isobutyl
substituent could be observed in a comparison of 8-phe-
nylcaffeine (28) and its 3-isobutyl analogue 35. The
latter was severalfold more potent than the methyl
derivative at A1 AR but not at A2A AR, where both
showed similar potency. A 3-benzyl residue decreased
A1 (2-fold) as well as A2A affinity (5-fold), and 43 was
therefore less potent and less selective than 38. The
most potent A2A antagonist investigated in the present
study was the 3-n-propyl analogue 39 of CS-DMPX (38)
with a Ki value of 5.1 nM. Exchange of methyl for
7-Methylation of 8-phenyl- and related 8-aryl-substi-
tuted xanthines will lead to a steric interaction between
the methyl hydrogen atoms and the phenyl ortho-
hydrogen atoms. This interaction may force the aryl
ring into an unfavorable (noncoplanar?) conformation.
For styryl and analogous 8-substituents in which the
aryl moiety is linked to the xanthine via an ethenyl
bridge, the situation is different. Coplanar conforma-
tion, for example, should be possible provided the (E)-
configurated double bond is in a cisoid conformation, in
which methyl hydrogen atoms and ethenyl hydrogen
atoms do not interact.

4402 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 26
Mu¨ller et al.
propyl in the 3-position of 38 increased A2A affinity 2.5-
fold, but at the same time, A1 affinity was increased
nearly 13-fold, leading to a decrease in selectivity.
Large substituents in the 3-position of xanthines in-
crease A1 selectivity in 8-phenyl- as well as in 8-styryl-
xanthines.
8-(m-chlorostyryl)-DMPX (38) for closer investigation of
the photoisomerization process. In fact, fast isomeriza-
tion was observed at normal daylight or when irradiated
with UV light (366 nm) in methanolic solution contain-
ing 0.1 mM 38, as measured by a decrease in UV
absorption at 356 nm, the absorption maximum of the
(E)-isomer. After 45 min the (E/ Z)-equilibrium of the
UV-irradiated solution was reached. HPLC analysis of
the products revealed that the stable mixture contained
ca. 57% (E)- and ca. 43% (Z)-isomer. The photoisomer-
ization process appeared to be somewhat slower in
DMSO solution as compared to methanol.
We conclude that all data for styrylxanthines in Table
2 represent results from stable mixtures of (E/ Z)-
isomers. Since the photoisomerization process is very
fast in dilute solutions most published data for styryl-
xanthine derivatives are probably results from (E/ Z)-
mixtures.15,16,31
Low -Affin ity Ad en osin e Recep tor Su btyp es. The
8-styrylxanthine derivatives 4 and 5 had been investi-
gated at the low-affinity A2B and A3 AR subtypes. Both
styrylxanthines showed low activity at A2B AR35,36 in
the micromolar concentration range. CSC (5) was
inactive at rat A3 AR in concentrations up to 10 µM.37
Preliminary results with BS-DMPX (17) at human
recombinant A2B and A3 AR indicate that 17 is inactive
at both receptor subtypes in high concentrations (10 µM;
Klotz, K.-N.; Mu¨ller, C. E., unpublished). Therefore it
appears that A2A-selective styryl-DMPX derivatives are
not only selective versus the high-affinity A1 AR, but
also exhibit a high degree of selectivity versus low-
affinity subtypes A2B and A3.
Th e 8-P osit ion . The largest set of compounds
investigated in the present study were DMPX deriva-
tives bearing different substituents in the 8-position.
8-Cyclohexyl- (11), 8-phenyl- (29), and 8-(2-thienyl)-
DMPX (12) were moderately potent at both receptor
subtypes in the low micromolar range and nonselective.
DMPX derivatives bearing a 2-(hetero)arylethenyl sub-
stituent in the 8-position (13, 17-22, 38) all exhibited
similar potency at A1 AR. Thus, the structure of the
8-substituent in DMPX derivatives had very little
influence on A1 AR affinity of the compounds, ranging
from ca. 1-4 µM. At A2A AR, however, 8-(2-arylethenyl)
substitution of DMPX led to a large increase in A2A AR
affinity (compounds 13, 17-22, 38) and subtle struc-
tural changes in the substituent pattern led to big
changes in receptor affinity.
We investigated different substituents on the phenyl
ring of 8-styryl-DMPX, namely the 3-chloro (38), the
3-bromo (17), the 3,4-dimethoxy (18), and the 3,4-
methylenedioxy (19) derivatives. Compound 19 was
similarly potent and A2A-selective as the parent com-
pound 8-styrylxanthine 13, but may be somewhat more
water-soluble due to polar substituents. 3-Halo substi-
tution increased A2A affinity, 2-fold for chlorine (in 38)
and 3-fold for bromine (in 17). Since A1 affinity re-
mained virtually unaltered, A2A selectivity was also
significantly increased. 8-(m-Bromostyryl)-DMPX (BS-
DMPX, 17) is about as potent at A2A AR as the standard
Exp er im en ta l Section
Syn th etic P r oced u r es. NMR spectra were performed on
a Bruker WP-80 (1H, 80 MHz; 13C, 20 MHz) or a Bruker AC-
250 spectrometer (1H, 250 MHz; 13C, 60 MHz), respectively.
DMSO-d6 was used as solvent. The chemical shifts of the
remaining protons of the deuterated solvent served as internal
standard: δ 1H, 2.50; 13C, 39.7. All compounds were checked
for purity by TLC on 0.2 mm aluminum sheets with silica gel
60 F254 (Merck); as eluent dichloromethane:methanol (9:1) was
used. Melting points were taken on a Bu¨chi 510 melting point
apparatus and are uncorrected. Elemental analyses were
performed by the Institute of Chemistry, University of Tu¨b-
ingen, or the Institute of Inorganic Chemistry, University of
Wu¨rzburg, respectively.
Standard compounds caffeine (1), DMPX (2), theophylline
(31), and 8-(m-chlorostyryl)caffeine (CSC, 5) were commercially
available. KF17837 (4) was synthesized as described.15 The
synthesis of xanthines 37-45 has been described elsewhere.24
6-Am in o-3-pr opar gyl-5-(2-th en yliden eam in o)u r acil (7b).
5,6-Diaminopropargyluracil 624 (0.53 g, 2.9 mmol) and thio-
phene-2-carbaldehyde (0.4 g, 3.6 mmol) are dissolved in EtOH
(10 mL). Acetic acid (1.5 mL) is added, and the mixture is
heated under reflux for 3 h. After cooling, H2O (20 mL) is
added to the solution, and the resulting precipitate is collected
by filtration: 1H NMR δ (ppm) 2.49 (t, 1H, propargyl CH), 4.46
(d, 2H, propargyl CH2), 6.44 (s, 2H, C6-NH2), 7.14 (dd, 1H,
C4′-H), 7.38, 7.53 (2 x dd, 2 × 1H, C3′-H, C5′-H), 9.73 (s, 1H,
NdCH), 10.90 (br s, 1H, N1-H); 13C NMR δ (ppm) 28.5
(propargyl CH2), 72.4 (propargyl CH), 79.9 (propargyl C2′), 97.9
(C5), 127.9, 128.7, 144.0, 145.5 (arom), 148.4, 151.7 (NdCH,
C2, C6), 157.4 (C4).
A
2A antagonist KF17837 (4), but its selectivity is much
greater (146-fold versus 31-fold). Compared with the
commercially available high-affinity A2A antagonist CSC
(5), 17 is several times more potent and at least as
selective as 5. 8-(3,4-Dimethoxystyryl)-DMPX (18)
showed about the same A2A affinity and selectivity as
8-(m-chlorostyryl)-DMPX (38)
In a further series of compounds, the phenylethenyl
(styryl) substituent was replaced by heteroarylethenyl
residues with furyl and thienyl as bioisosteric heter-
arylic replacements for the phenyl ring. 2-Furyl (in 22)
and 2-thienyl replacement (in 20) of phenyl (in 8-styryl-
DMPX, 13) led to compounds that were about 10-fold
less potent at A2A AR than 13, but still about 10-fold
more potent compared to 8-phenyl- (29) or 8-(2-thienyl)-
DMPX (12). The 3-thienylethenyl analogue (21) of
8-styryl-DMPX (13), however, was equally potent to 13.
It appears that the heteroatom in 21 is in vicinity to
the m-halogen atom in compounds 17 and 38.
(E/Z)-Isom er iza tion . Styryl derivatives are known
to undergo photoisomerization.32,33 8-Styrylxanthine
derivative 4, which had been investigated in this
respect, isomerized when irradiated by a fluorescent
lamp in dilute solution to yield a stable mixture of ca.
82% (Z) and ca. 18% (E)-configurated isomer.33 The (E)-
isomer was shown to be a much more potent AR
antagonist compared to the (Z)-isomer.33 The com-
mercially available styrylxanthine CSC (5) had also
been described to photoisomerize, but isomer ratios had
not been determined.34 We selected one of the most
potent and selective compounds of the present series,
(E)-6-Am in o-3-pr opar gyl-5-styr yliden eam in ou r acil (7c).
Compound 624 (0.7 g, 3.9 mmol) is dissolved in MeOH (30 mL).
(E)-Cinnamic aldehyde (0.5 mL, 3.8 mmol) and 3 drops of acetic
acid are added, and the solution is stirred at room temperature
for 30 min. After the addition of H2O (30 mL), the precipitated
yellow product is collected by filtration and washed with

Synthesis and SAR of DMPX Derivatives
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 26 4403
H2O: 1H NMR δ (ppm) 3.16 (t, 1H, propargyl CH), 4.56 (d,
2H, propargyl CH2), 6.70 (br s, 2H, NH2), 6.70-7.62 (m, 7H,
Hvinylic and H arom), 9.52 (br s, 1H, NdCH), 11.15 (br s, 1H,
N1-H); 13C NMR δ (ppm) 26.6 (propargyl CH2), 72.6 (propargyl
CH), 80.1 (propargyl C2′), 99.0 (C5), 126.8, 128.4, 128.9, 131.4,
136.6, 137.1 (arom), 148.6, 152.1 (NdCH, C2, C6), 157.2 (C4).
1-P r op a r gyl-8-(2-th ien yl)xa n th in e (9). Compound 7b
(0.57 g, 2.1 mmol) and anhydrous FeCl3 (0.40 g, 2.5 mmol) are
dissolved in anhydrous EtOH (10 mL). The mixture is refluxed
for 7 h. After cooling, H2O (20 mL) is added, and the product
is collected by filtration. The compound is dissolved in 1 N
NaOH (15 mL), insoluble material is removed by filtration,
and the product is precipitated by acidification of the solution
with concentrated HCl.
(E)-1-P r op a r gyl-8-st yr ylxa n t h in e (10). Compound 7c
(0.13 g, 0.44 mmol) is dissolved in SOCl2 (10 mL) and stirred
at room temperature for 1 h. SOCl2 is removed by distillation
in vacuo. The residue is treated with ice water, and the
precipitate is collected by filtration. The product is purified
by dissolution in DMF (5 mL) and subsequent precipitation
by the addition of H2O (20 mL).
Bism eth ylation of 1,8-Disu bstitu ted Xan th in es: P r epa-
r a tion of Com p ou n d s 11-13. 1,8-Disubstituted xanthine
(8,21 9, or 10, respectively; 1.5 mmol), K2CO3 (0.43 g, 3.1 mmol),
and MeI (1.9 mL, 60 mmol) are dissolved in dimethylforma-
mide (DMF, 10 mL) and stirred at room temperature for 12
h. The product is precipitated by the addition of H2O (20 mL),
collected by filtration, and washed with H2O. Purification is
achieved by dissolution in DMF and subsequent precipitation
by the addition of H2O. Starting products and monomethy-
lated derivatives can be extracted with 10% NaOH solution.
6-Am in o-3-p r op a r gyl-5-(ca r bon yla m in o)u r a cils (14a -
f). Gen er a l P r oced u r e. 3-Propargyl-5,6-diaminouracil24 (1,
0.7 g, 3.9 mmol) is dissolved in MeOH (30 mL), and the
appropriate carboxylic acid (1.1 equiv) and 1-(3-(dimethylami-
no)propyl)-3-ethylcarbodiimide hydrochloride (EDC, 0.822 g,
4.3 mmol) is added. The mixture is stirred at room temper-
ature for 24 h. Then, H2O (30 mL) is added to complete the
precipitation of the product which is collected by filtration and
washed with H2O.
6-Am in o-1-m e t h yl-3-p r op a r gyl-5-(ca r b on yla m in o)-
u r a cils (15a -f). Gen er a l P r oced u r e. Compound 14a -e
(3.0 mmol) is dissolved in DMF (30 mL). After the addition of
K2CO3 (0.50 g, 3.6 mmol) and MeI (4.0 mL, 64 mmol), the
suspension is stirred at room temperature for 24 h. The
product is precipitated by the addition of H2O (45 mL),
collected by filtration, and washed with H2O.
1,3,8-Tr isu bstitu ted Xa n th in es (16a ,c-f). Gen er a l P r o-
ced u r e. Compound 15a , or 15c-f, respectively (2.0 mmol),
is suspended in a mixture of MeOH (155 mL) and H2O (22
mL). After the addition of an aqueous 10% NaOH solution
(66 mL), the yellow solution is heated to 60 °C for 3 h. Then
MeOH is distilled off. The aqueous solution is brought to pH
4 by the addition of concentrated HCl. The product precipi-
tates as a white solid which is collected by filtration and
washed with H2O. Purification is achieved by dissolution in
10% aqueous NaOH solution and subsequent precipitation
with HCl or, alternatively, by dissolution in DMF and pre-
cipitation by the addition of H2O.
1-P r op a r gyl-3-m e t h yl-8-(3,4-d im e t h oxyst yr yl)xa n -
th in e (16b). Compound 15b (0.38 g, 1 mmol) is suspended
in 120 mL of 0.5 N NaOH and 100 mL of EtOH and stirred at
60 °C for 18 h. After being cooled to room temperature, the
solution is acidified with 2 N HCl to pH 4, EtOH is evaporated,
and the remaining aqueous solution is cooled to 4 °C. The
precipitated product is collected by filtration and dried at 80
°C. Purification was achieved by column chromatography
(eluent MeOH:CH2Cl2 ) 1:9) followed by recrystallization from
95 mL of EtOH:H2O ) 50:50 (v/v): 1H NMR δ (ppm) 2.92 (t,
4J ) 2.4 Hz, 1 H, C-H), 3.47 (s, 3 H, N3-CH3), 3.75 (s, 3 H,
O-CH3), 3.89 (s, 3 H, O-CH3), 4.57 (d, 4J ) 2.4 Hz, 2H, CH2),
6.86 (d, J ) 16 Hz, 1H, Hvinylic), 6.9-7.2 (m, 6 H, Hvinylic+arom).
1,3,7,8-Tetr a su bstitu ted Xa n th in es (17-22 a n d 35, 36).
Gen er a l P r oced u r e. Xanthine derivative 16a -f (0.30 mmol,
for the preparation of 17-22), or 3-isobutyl-1-methyl-8-phe-
nylxanthine (8-phenyl-IBMX,38 0.30 mmol, for the preparation
of 35 and 36), respectively, is dissolved in DMF (7.0 mL). After
the addition of K2CO3 (0.070 g, 0.51 mmol) and MeI (0.2 mL,
3.29 mmol, for 17-22 and 35), or propargyl bromide (0.12 g,
1 mmol, for 36), the mixture is stirred for 24 h. The product
is precipitated by the addition of H2O (30 mL), cooled, and
collected by filtration. Purification of the product is achieved
by dissolution in DMF and precipitation by the addition of
H2O. Unreacted 7-unsubstituted xanthine can be extracted
with 10% aqueous NaOH solution.
6-Am in o-5-br om o-1-m eth ylu r a cil (24). A mixture of
6-amino-1-methyluracil (23)20 (3.44 g, 41 mmol), MeOH (40
mL), and NaHCO3 (3.41 g, 41 mmol) is cooled to 4 °C, and Br2
(6.55 g, 41 mmol) is added during a period of 30 min. The
reaction mixture is kept stirring for another 30 min at room
temperature and then cooled to 4 °C. The white precipitate
is filtered off and recrystallized from H2O: 1H NMR δ (ppm)
3.30 (s, 3H, CH3-N), 7.02 (br s, 2H, NH2), 10.90 (v br s, 1H,
H-N); 13C NMR δ (ppm) 29.9 (N7-CH3), 70.5 (C5), 149.9 (C2),
152.8 (C4), 158.2 (C6).
6-Am in o-1-m eth yl-5-(m eth yla m in o)u r a cil (25). Com-
pound 24 (3.52 g, 16 mmol) and 17 mL (160 mmol) of an
aqueous solution of methylamine (30%) are heated at 70 °C
for 4 h. Excess methylamine is evaporated, the residue
suspended in 20 mL of ethanol, and the pH of the solution
adjusted to 7 by the gradual addition of 2 N HCl solution. The
flask is allowed to stand for 5 h at 0 °C, during which time
the methylammonium bromide which had formed dissolves.
The product is filtered off and recrystallized from ethanol:
1H
NMR δ (ppm) 2.36 (s, 3H, N-CH3), 2.78 (br s, 1H, N-CH3),
3.21 (s, 3H, N-CH3), 6.38 (s, 2H, NH2), 10.48 (br s, 1H, N-H);
13C NMR δ (ppm) 34.1 (N1-CH3), 40.1 (N7-CH3), 104.0 (C5),
155.1 (C2), 157.5 (C4), 165.8 (C6).
6-Am in o -5-(N -b e n zo y l-N -m e t h y la m in o )-1-m e t h y l-
u r a cil (26a ). A suspension of 2.39 g (14 mmol) of 25 in 30
mL of dry pyridine is cooled to 0 °C, and 2.23 mL (16 mmol) of
benzoyl chloride is added dropwise with stirring. The mixture
is stirred overnight and then evaporated to dryness. The
residue is treated with 30 mL of H2O, collected by filtration,
and recrystallized from EtOH:H2O ) 50:50 (v/v) to give white
crystals: 1H NMR δ (ppm) 2.96 (s, 3H, N(CH3)CO), 3.33 (s,
3H, N1-CH3), 7.0-7.4 (m, 5H, Harom), 10.46 (v br s, 1H, N-H);
13C NMR δ (ppm) 28.9 (N1-CH3), 34.3 (N7-CH3), 96.0 (C5),
125.4, 127.1, 128.8, 137.4 (arom), 149.7, 152.6 (C2, C6), 159.0
(C4), 172.9 (CdO exocyclic).
(E)-6-Am in o-5-(N-cin n a m oyl-N-m eth yla m in o)-1-m eth -
ylu r a cil (26b). Compound 25 (0.85 g, 5 mmol), (E)-cinnamic
acid (0.72 g, 5.05 mmol), and EDC (0.98 g, 5.1 mmol) are
suspended in 40 mL of MeOH and stirred overnight. After
the addition of 60 mL of H2O the mixture is stirred for 3 h
and the precipitate filtered off, air-dried, dissolved in DMF
and precipitated by the addition of 40 mL of H2O to give 1.04
g of white crystals: 1H NMR δ (ppm) 2.95 (s, 3H, CH3), 3.27
(s, 3H, CH3), 6.74 (d, J ) 16 Hz, Hvinylic), 7.06 (s, 2H, NH2),
7.30-7.65 (m, 6 H, Harom+vinylic), 10.66 (s, 1 H, N-H); 13C NMR
δ (ppm) 29.1 (N-CH3), 34.3 (N1-CH3), 93.7 (C5), 108.9, 118.7
(vinylic), 127.8, 128.7, 129.3, 140.4 (arom), 150.2 (C6), 153.3
(C4), 159.5 (C2), 167.8 (CdO, exocyclic).
3,7-Dim eth yl-8-p h en ylxa n th in e (27a ). Compound 26a
(1.65 g, 6 mmol) is refluxed in 13 mL of 2 N NaOH and 4 mL
of ethanol for 1 h. The hot solution is allowed to cool to 4 °C,
diluted with 17 mL of water, and acidified with acetic acid to
form a white precipitate, which is collected by filtration: 1H
NMR δ (ppm) 3.39 (s, 3H, N3-CH3), 3.97 (N7-CH3), 7.44-
7.83 (m, 5H, Harom), 11.16 (v br s, 1H, N-H); 13C NMR δ (ppm)
28.4 (N3-CH3), 33.5 (N7-CH3), 128.2, 128.7, 129.0, 130.1
(arom), 149.1 (C4), 150.8 (C8), 151.0 (C2), 155.0 (C6).
(E)-3,7-Dim eth yl-8-styr ylxan th in e (27b). Compound 26b
(0.54 g, 1.8 mmol) is refluxed in 2 mL of 2 N NaOH and 4 mL
of EtOH for 1 h. After being cooled to 4 °C, the solution is
acidified with 2 N HCl, and the white precipitate is collected
by filtration and recrystallized from H2O:EtOH ) 50:50 (v/v):
1H NMR δ (ppm) 3.35 (s, 3H, N3-CH3), 3.85 (s, 3H, N7-CH3),
3
6.74 (d, J ) 16 Hz, 1 H), 7.35-7.85 (m, 6H, Hvinylic+arom), 11.1
(s, 1H, N-H).
8-P h en ylca ffein e (28). To a mixture of 27a (0.154 g, 0.6
mmol) and K2CO3 (0.1 g, 0.73 mmol) in DMF (30 mL) is added

4404 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 26
Mu¨ller et al.
dropwise MeI (60 µL, 9.5 mmol). The mixture is stirred at
room temperature for 48 h. The product is precipitated by
the addition of H2O (60 mL). After the mixture is cooled to 4
°C, the precipitate is collected by filtration and washed with
H2O.
3,7-Dim eth yl-8-p h en yl-1-p r op a r gylxa n th in e (29). To a
solution of 27a (0.154 g, 0.6 mmol) and K2CO3 (0.1 g, 0.73
mmol) in DMF (30 mL) is added dropwise MeI (68 µL, 9 mmol).
The mixture is stirred at room temperature for 48 h. The
product is precipitated by the addition of H2O (70 mL). After
the mixture is cooled to 4 °C, the precipitate is collected by
filtration and washed with H2O.
support by the Fonds der Chemischen Industrie and the
Industrie- und Handelskammer Wu¨rzburg-Schweinfurt.
M.P. and J .S.-R. were supported by scholarships of the
Deutsche Forschungsgemeinschaft (DFG) and the Deut-
scher Akademischer Austauschdienst (DAAD), respec-
tively.
Su p p or tin g In for m a tion Ava ila ble: 1H and selected 13C
NMR data of final products (4 pages). Ordering information
is given on any current masthead page.
(E)-1-Allyl-3,7-d im eth yl-8-styr ylxa n th in e (30). To a
solution of 27b (0.27 g, 1 mmol) and K2CO3 (0.2 g, 1.5 mmol)
in DMF (10 mL) is added allyl bromide (0.18 g, 1.5 mmol).
The mixture is stirred at 50 °C for 3 h. The product is
precipitated by the addition of H2O (30 mL). After the mixture
is cooled to 4 °C the precipitate is collected by filtration and
washed with H2O.
Refer en ces
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8-(3,4-Dim eth oxystyr yl)ca ffein e (34). 6-Amino-5-[(3,4-
dimethoxycinnamoyl)amino]-1,3-dimethyluracil16 (0.36 g, 1
mmol) is suspended in 120 mL of 0.5 N NaOH and 100 mL of
EtOH and stirred at 60 °C for 18 h. After being cooled to room
temperature, the solution is acidified to pH 4 by the addition
of 2 N HCl. After evaporation of the EtOH, the aqueous
solution is cooled to 4 °C. The precipitate is collected by
filtration and dried at 80 °C. Purification is achieved by
column chromatography (eluent MeOH:CH2Cl2 ) 1:9) followed
by recrystallization from 80 mL of EtOH:H2O ) 50:50 (v/v) to
yield 0.18 g (53%) of 8-(3,4-dimethoxystyryl)theophylline (mp
>250 °C): 1H NMR δ (ppm) 3.19 (s, 3 H, N-CH3), 3.41 (s, 3
H, N-CH3), 3.75 (s, 3 H, O-CH3), 3.81 (s, 3 H, O-CH3), 6.86
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3
(d, J ) 16 Hz, 1 H, Hvinylic), 6.9-7.3 (m, 4 H, Hvinylic+arom).
8-(3,4-Dimethoxystyryl)theophylline (0.1 g, 0.3 mmol) is
dissolved in 5 mL of DMF. After the addition of 0.1 g (7.3
mmol) of K2CO3 followed by 60 mL (0.9 mmol) of MeI, the
mixture is stirred at room temperature for 12 h. The precipi-
tation of the product is completed by the addition of 10 mL of
H2O. The product is collected by filtration and dried in an
oven at 80 °C overnight.
P h otoisom er iza tion of 38. A solution of 38 (0.1 mM) in
MeOH, or DMSO, is irradiated by UV light (366 nm). Samples
are taken at time intervals of 5-10 min, and UV spectra are
immediately recorded. A methanolic solution of 38, treated
as described above, which had reached its equilibrium, is
subjected to HPLC separation with UV detection at 280 nm,
using an RP18 column and acetonitrile: H2O ) 60:40 as eluent,
essentially as described.33,39 Retention times were 6.18 min
for the (E)- and 5.37 min for the (Z)-isomer.
Ad en osin e Recep tor Assa ys. Inhibition of binding of
[3H]-N6-cyclohexyladenosine (CHA) to A1 adenosine receptors
of rat cerebral cortical membranes and inhibition of [3H]-2-
[[[4-(carboxyethyl)phenyl]ethyl]amino]-5′-[N-(ethylcarbonyl)-
amino]adenosine (CGS21680) to A2 adenosine receptors of rat
striatal membranes were assayed as described.28,40 2-Chloro-
adenosine (10 µM) was used to define nonspecific binding.
Inhibition of the receptor-radioligand binding was determined
by a range of five or six concentrations of the compounds in
triplicate in at least three (A1) or two (A2A) separate experi-
ments. The Cheng-Prusoff equation41 and KD values of 1 nM
for [3H]CHA and 14 nM for [3H]CGS21680 were used to
calculate the Ki values from the IC50 values, determined by
the nonlinear curve fitting program InPlot, Version 4.03
(GraphPad, San Diego, CA). For selected compounds, ad-
ditional A1AR binding studies with [3H]-N6-(R)-phenylisopro-
pyladenosine ([3H]R-PIA) as A1 radioligand42 and [3H]NECA
as A2A radioligand in the presence of 50 nM N6-cyclopentyl-
adenosine43 were performed as described. A KD value of 1 nM
for [3H]PIA and 8.5 nM for [3H]NECA was used for the
calculation of Ki values.
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J M970515+