New 2-(2'-phenyl-9'-benzyl-8'-azapurin-6'-ylamino)-carboxylic acid methylesters as ligands for A1 adenosine receptors.

Article abstract of DOI:10.1016/S0014-827X(01)01162-4

Synthesis of a series of new 2-phenyl-9-benzyl-8-azaadenines bearing on N6 an alkyl or aralkyl chain having a carbonyloxymethyl group on the carbon bound to N6 were reported. The ester group could assure to the molecule a better water-solubility than the 8-azaadenines 2, 6 and 9 substituted with lipophilic groups synthesised in the past. Compounds synthesised demonstrated only little capability of binding A1 adenosine receptors.

Full text of DOI:10.1016/S0014-827X(01)01162-4

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Il Farmaco 56 (2001) 929–931
New 2-(2%-phenyl-9%-benzyl-8%-azapurin-6%-ylamino)-carboxylic acid
methylesters as ligands for A1 adenosine receptors
Giuliana Biagi, Irene Giorgi *, Federica Pacchini, Oreste Livi, Valerio Scartoni
Dipartimento di Scienze Farmaceutiche, Uni6ersita` di Pisa, 6ia Bonanno, 6, 56100 Pisa, Italy
Received 15 February 2001; accepted 30 May 2001
Abstract
Synthesis of a series of new 2-phenyl-9-benzyl-8-azaadenines bearing on N6 an alkyl or aralkyl chain having a carbony-
loxymethyl group on the carbon bound to N6 were reported. The ester group could assure to the molecule a better water-solubility
than the 8-azaadenines 2, 6 and 9 substituted with lipophilic groups synthesised in the past. Compounds synthesised demonstrated
only little capability of binding A1 adenosine receptors. © 2001 Elsevier Science S.A. All rights reserved.
Keywords: A1 adenosine receptor antagonists; 8-Azaadenines
1. Introduction
2. Chemistry
In recent years we have synthesised a great number
of inhibitors of A1 adenosine receptors varying sub-
stituents in the positions 3, 6 and 9 of the nucleus of
8-azaadenine or adenine and some of these were very
effective having a Ki in the range of nanomolar [1–6].
All these compounds were characterised by a high
lipophilicity because the substituents on the bicyclic
nucleus were hydrophobic as alkyl, cycloalkyl or alkyl-
aromatic groups. This can make these compounds
nearly water-insoluble causing the determination of ac-
tivity in in vitro binding assays to be uncertain in some
cases. The scarce water-solubility also leads to a low
bioavailability of the compounds so that they are un-
suitable for in vivo studies.
The synthetic route (Scheme 1) employed known 1,3
dipolar addition reactions starting from benzylazide,
cyanoacetamide, ethyl benzoate to obtain the 2-phenyl-
9-benzyl-8-azahypoxanthine (1) [7]. The reaction of 1
with phosphorus oxychloride afforded 6-chloroaza-
purine (2) which, by nucleophilic displacement of chlo-
rine atom operated by suitable aminoesters [4], led to
N6-substituted-8-azaadenines.
3. Experimental
3.1. Biological e6aluation
Therefore we projected to obtain some A1 antago-
nists more water-soluble than the active antagonists
discovered in the past, introducing on the N6 a sub-
stituent having a polar function as a methoxycarbonyl
group.
The 8-azaadenines 3, 4, 5, 6, 7, 8, 9, 10 and 11 were
tested in radioligand binding assays for affinity at A1
adenosine receptors in bovine brain cortical mem-
branes. [3H]N6-cyclohexyladenosine (CHA) was used as
the radio-ligand. The experimental details were re-
ported in a previous paper [1].
3.2. Chemistry
Melting points were determined on a Kofler hot-
stage apparatus and are uncorrected. H NMR spectra
* Corresponding author.
E-mail address: igiorgi@farm.unipi.it (I. Giorgi).
1
0014-827X/01/$ - see front matter © 2001 Elsevier Science S.A. All rights reserved.
PII: S0014-827X(01)01162-4

930
G. Biagi et al. / Il Farmaco 56 (2001) 929–931
Scheme 1.
were recorded on a Bruker AC 200 spectrometer in l
units from TMS as an internal standard; the com-
pounds were dissolved in chloroform-D1. Mass spectra
were performed on a Hewlett–Packard GC/MS System
5988A. TLC was performed on precoated silica gel F254
plates (Merck). Flash-column chromatographies were
performed using Merck Kieselgel 60 (230–400 mesh).
Microanalyses (C, H, N) were carried out on a Carlo
Erba elemental analyser (Model 1106) and were within
90.4% of theoretical values.
3.2.2. General procedure to prepare 6-aminosubstituted-
2-phenyl-9-benzyl-8-azaadenines (3–11)
In a well-stoppered flask a mixture of 2 (200 mg,
0.623 mmol), toluene (2 ml), the suitable amino ester
hydrochloride (1 mmol) (see Table 1) and N,N-diethyl-
aniline (0.1 ml, 0.67 mmol) were stirred at room tem-
perature for 24 h. Then the solution was evaporated at
reduced pressure, diluted with chloroform and washed
with 10% HCl and water. After evaporation of the
organic layer the residue was flash-chromatographed
using as eluent hexane–ethyl acetate 3:1. (see Tables 1
and 2).
3.2.1. General procedure to prepare aminoesters
hydrochloride
Aminoesters hydrochloride of (
nine, ( )-phenylalanine, ( )-phenylglicine, (
glutamic acid, )-methionine, )-norleucine,
)-norvaline, ( )-valine and ( )-histidine were
prepared starting from corresponding aminoacids. To a
solution of aminoacid in methanol, cooled at −18 °C,
an equimolar amount of SOCl2 was dropped slowly.
The mixture was refluxed for 12 h, then evaporated and
the residue was crystallised from methanol–ethyl ether.
D
,
L
)-alanine, b-ala-
D
,L
D
,L
D
,L
)-
4. Biological results and conclusions
(
D
,
L
(D,L
L
(D
,L
D
,
L
D
,
None of the compounds showed a significant activity
as A1 adenosine receptors ligands. Compounds 4, 7, 8,
9 and 11 showed a Ki included between 300 and 500
nM, while compounds 3, 5, 6 and 10 showed an inhibi-
tion B65% at 10 mM. Results demonstrated that for
2-phenyl-9-benzyl-8-azaadenines
a
carboxymethyl
Table 1
Reaction data for compounds 3–11
Comp.
Reagent
Yield (%)
m.p. (°C)
Formula (anal.)
3
4
5
6
7
8
9
10
11
NH2CH(COOCH3)CH3
NH2(CH2)2COOCH3
NH2CH(CH2C6H5)COOCH3
NH2CH(C6H5)COOCH3
NH2CH(CH2CH2COOCH3)COOCH3
NH2CH(CH2CH2SCH3)COOCH3
NH2CH(CH2CH2CH3)COOCH3
NH2CH(CH2CH2CH2CH3)COOCH3
NH2CH(COOCH3)CH(CH3)CH3
71
55
86
50
33
38
52
65
62
137–138
157–159
134–135
129–130
140–141
164–165
143–144
157–158
119–120
C21H20N6O2 (CHN)
C21H20N6O2 (CHN)
C27H24N6O2 (CHN)
C26H22N6O2 (CHN)
C24H24N6O2 (CHN)
C23H24N6O2S (CHN)
C23H24N6O2 (CHN)
C24H26N6O2 (CHN)
C23H24N6O2 (CHN)

G. Biagi et al. / Il Farmaco 56 (2001) 929–931
931
Table 2
Spectroscopic data of compounds 3–11
Comp. 1H NMR
Aromatic H
MS
Benzylic H
5.82 (s, 2H)
Aliphatic H
Exchang. H m/z (%)
3
4
5
6
7
8.50 (m, 2H); 7.53–7.48 (m,
5H), 7.36–7.32 (m, 3H)
8.50 (s, 2H); 7.49 (m, 2H); 7.31 5.80 (s, 2H)
(m, 2H)
8.49 (m, 2H); 7.49 (m, 5H);
7.39–7.22 (m, 8H)
8.50–8.45 (m, 3H); 7.61–7.27
(m, 12H)
5.18–5.05 (m, 1H, CH); 3.80 (s, 6.65 (1H)
3H, OCH3); 1.69 (d, 3H, CH3)
4.10 (t, 2H, CH2); 3.73 (s, 3H
OCH3); 2.83 (t, 2H, CH2)
5.40 (m, 1H, CH); 3.75 (s, 3H, 6.62 (1H)
CH3)
388 (M+, 2); 329 (8); 287 (1);
91 (100)
6.64 (1H)
388 (M+, 4); 329 (2); 91
(100)
5.80 (s, 2H);
3.37 (m, 2H)
6.05 (d, 1H);
5.81 (s, 2H)
5.83 (s, 2H)
464 (M+,0.5); 373 (13); 273
(18); 91 (100)
3.80 (s, 3H, OCH3)
7.11 (1H)
450 (M+, 2); 391 (7); 91
(100)
8.49 (m, 2H); 7.49 (m, 5H);
7.35 (m, 3H);
5.27 (m, 1H, CHN); 3.82 (s,
3H, OCH3); 3.65 (s, 3H,
OCH3); (t, 2H, CH2ꢀCO); 2.30
(m, 2H, CH2)
6.91 (1H)
460 (M+, 12); 387 (22); 287
(10); 91 (100)
8
8.52 (m, 2H); 7.52 (m, 5H);
7.35 (m, 3H)
5.83 (s, 2H)
5.82 (s, 2H)
5.82 (s, 2H)
5.83 (s, 2H)
5.33 (m, 1H, CH); 3.81 (s, 3H, 6.92 (1H)
OCH3); 2.68 (t, 2H, CH2ꢀS);
2.38 (m, 2H, CHꢀCH2); 2.12 (s,
3H, SꢀCH3)
5.15 (m, 1H, CH); 3.79 (s, 3H, 6.64 (1H)
OCH3); 1.98 (m, 2H, CH2);
1.50 (m, 2H, CH2); 0.99 (t, 3H,
CH3)
5.12 (m, 1H, CH); 3.79 (s, 3H, 6.66 (1H)
OCH3); 2.00 (m, 2H, CH2);
1.42 (m, 4H, CH2ꢀCH2); 0.91
(t, 3H)
374 (4); 287 (6); 91 (100); 61
(54)
9
8.51 (m, 2H); 7.50 (m, 5H);
7.35 (m, 3H)
357 (5); 302 (1); 91 (100)
371 (6); 302 (2); 91 (100)
357 (3); 302 (3.5); 91 (100)
10
11
8.51 (m, 2H); 7.51 (m, 5H);
7.35 (m, 3H)
8.51 (m, 2H); 7.50 (m, 5H);
7.35 (m, 3H)
5.14 (m, 1H, CHꢀN); 3.80 (s,
3H, OCH3); 2.42 (m, 1H, CH);
1.14 (d, 3H, CH3); 1.11 (d, 3H,
CH3)
6.66 (1H)
group on the carbon bound to N6 cannot give positive
interactions with the receptors.
azaadenines. Their affinity for A1 and A2 receptors. A compari-
son with the corresponding 2-phenyl-9-benzyl-8-azaadenosines,
Farmaco 50 (1995) 13–19.
[3] G. Biagi, I. Giorgi, O. Livi, V. Scartoni, A. Lucacchini, C.
Martini, P. Tacchi, N6-substituted 2-n-butil-9-benzyl-8-azaadeni-
nes. Affinity for A1 and A2 receptors. IV, Farmaco 49 (1994)
183–186.
Acknowledgements
[4] G. Biagi, I. Giorgi, O. Livi, V. Scartoni, A. Lucacchini, C.
Martini, P. Tacchi, N6-substituted 2-phenyl-9-benzyl-8-azaadeni-
nes. Affinity for A1 and A2 receptors. A comparison with 2-n-bu-
til analogous derivatives. V, Farmaco 49 (1994) 187–191.
[5] G. Biagi, I. Giorgi, O. Livi, V. Scartoni, C. Breschi, C. Martini,
R. Scatizzi, N6- or N(9)-substituted 2-phenyl-8-azaadenines:
affinity for A1 receptors, Farmaco 50 (1995) 659–667.
[6] G. Biagi, I. Giorgi, O. Livi, V. Scartoni, A. Lucacchini, N(9)-sub-
stituted 2-phenyl-N6-benzyl-8-azaadenines: A1 adenosine receptor
affinity. A comparison with the corresponding N6-substituted
2-phenyl-N(9)-benzyl-8-azaadenines, Farmaco 51 (1996) 395–399.
[7] P.L. Barili, G. Biagi, O. Livi, V. Scartoni, A facile ‘‘one pot’’
synthesis of 2,9-disubstituted 8-azapurin-6-ones (3,5-disubstituted
7-hydroxy-3-H-1,2,3-triazolo[4,5-d]pyrimidines), J. Heterocyclic
Chem. 22 (1985) 1607–1609.
This research was supported by the Ministero della
Ricerca Scientifica e Tecnologica (MURST).
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