Synthesis and biological activity of a new series of N6-arylcarbamoyl, 2-(Ar)alkynyl-N6-arylcarbamoyl, and N6-carboxamido derivatives of adenosine-5'-N-ethyluronamide as A1 and A3 adenosine receptor a

Article abstract of DOI:10.1021/jm980147p

A new series of 1-(6-amino-9H-purin-9-yl)-1-deoxy-N-ethyl-β-D- ribofuranuronamide-bearing N-arylureas or N-arylcarboxamido groups at the purine 6 position and N-arylureas combined with halogens or alkynl chains at the 2 position have been synthesized and

Full text of DOI:10.1021/jm980147p

3174
J . Med. Chem. 1998, 41, 3174-3185
Syn th esis a n d Biologica l Activity of a New Ser ies of N6-Ar ylca r ba m oyl,
2-(Ar )a lk yn yl-N6-a r ylca r ba m oyl, a n d N6-Ca r boxa m id o Der iva tives of
Ad en osin e-5′-N-eth ylu r on a m id e a s A1 a n d A3 Ad en osin e Recep tor Agon ists
Pier Giovanni Baraldi,*,† Barbara Cacciari,† Maria J ose´ Pineda de Las Infantas,† Romeo Romagnoli,†
Giampiero Spalluto,† Rosaria Volpini,‡ Stefano Costanzi,‡ Sauro Vittori,‡ Gloria Cristalli,‡ Neli Melman,§
Kyung-Sun Park,§ Xiao-duo J i,§ and Kenneth A. J acobson§
Dipartimento di Scienze Farmaceutiche, Universita` di Ferrara, Via Fossato di Mortara 17-19, 44100 Ferrara, Italy,
Dipartimento di Scienze Chimiche, Universita` di Camerino, Via S. Agostino 1, 62032 Camerino, Italy, and
Molecular Recognition Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and
Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892
Received March 11, 1998
A new series of 1-(6-amino-9H-purin-9-yl)-1-deoxy-N-ethyl-â-D-ribofuranuronamide-bearing
N-arylureas or N-arylcarboxamido groups at the purine 6 position and N-arylureas combined
with halogens or alkynyl chains at the 2 position have been synthesized and tested for affinity
at A1 and A2A adenosine receptors in rat brain membranes and at cloned rat A3 receptors
expressed in CHO cells. The derivatives contained the 5′ substituent found in the potent,
nonselective agonist 1-(6-amino-9H-purin-9-yl)-1-deoxy-N-ethyl-â-D-ribofuranuronamide (NECA).
While the carboxamido derivatives (9-13) showed affinity for A1 receptors, the urea derivatives
(30-45) showed different degrees of affinity and selectivity for the A3 adenosine receptor
subtype. In particular the derivative bearing a p-sulfonamidophenyl-urea at the 6 position,
31 showed a high affinity (Ki ) 9 nM) and selectivity for the A3 receptors compared to that of
the reference compound 1-[6-[[(3-iodophenyl)methyl]amino]-9H-purin-9-yl]-1-deoxy-N-methyl-
â-D-ribofuranuronamide (IB-MECA). Furthermore, the importance of the stereochemistry in
the interaction of these ligands at the rat A3 adenosine receptors has been evaluated by
introducing a chiral chain at the 6 position. The introduction of halogens or alkynyl chains at
the purine 2 position of selected ureas did not give the expected enhancement of potency at
A2A and/or A3 receptors but rather showed a dramatic reduction of A2A affinity, resulting in
compounds with good A2A/A3 selectivity. For example, the 2-(3-hydroxy-3-phenyl-1-propyn-1-
yl)-6-(4-methoxyphenylurea) derivative 61 showed the capability to bind simultaneously to A1
and A3 receptor subtypes, excluding the A2A receptor. Compound 31 was shown to be an agonist,
9-fold more potent than NECA, at A3 receptors in rat RBL-2H3 mast cell membranes through
stimulation of binding of [35S]GTP-γ-S.
In tr od u ction
cloning of the A3 receptor from a rat brain cDNA li-
brary,4 recent efforts have been made in order to develop
selective agonist ligands24 as well as some selective
antagonists.25-28 The selective agonists, 1-[6-[[(3-io-
dophenyl)methyl]amino]-9H-purin-9-yl]-1-deoxy-N-meth-
yl-â-D-ribofuranuronamide (IB-MECA) 1, shows a Ki
Four subtypes of adenosine receptors (A1, A2A, A2B
,
and A3) have been cloned1-4 and characterized phar-
macologically with the use of potent agonists and
antagonists. The A1 and A2 receptor subtypes are linked
to inhibition and stimulation, respectively, of adenylyl
cyclase.5-7 A3 receptors are coupled both to the stimu-
lation of phospholipase C, as shown in rat RBL-2H3
mast cells8 and in rat brain slices,9 and to the inhibition
of adenylyl cyclase.4
Many selective agents have been developed for the
10-15
16-19
A1
and A2A
receptor subtypes. Some of these
seem promising as potential therapeutic agents in the
treatment of Parkinson’s disease,20 cognitive deficits,21
schizophrenia,22 epilepsy,23a and renal failure.23b Selec-
tive and/or high affinity agonists and antagonists for
the A2B receptor have not yet been reported. Since the
* To whom correspondence should be addressed: Prof. Pier Giovanni
Baraldi, Dipartimento di Scienze Farmaceutiche, Universita` di Fer-
rara, Via Fossato di Mortara 17-19, 44100 Ferrara, Italy. Tel: +39-
(0)532-291293. Fax: +39-(0)532-291296. E-mail: pgb@ifeuniv.unife.it.
† Universita` di Ferrara.
value of 1.1 ( 0.3 nM at rat A3 receptors and a 50-fold
selectivity vs either A1 or A2A receptors.29 The related
agonist,[125I]1-[6-[[(4-amino-3-iodophenyl)methyl]amino]-
9H-purin-9-yl]-1-deoxy-N-methyl-â-D-ribofuranuron-
‡ Universita` di Camerino.
§ National Institutes of Health.
S0022-2623(98)00147-2 CCC: $15.00 © 1998 American Chemical Society
Published on Web 07/22/1998

Derivatives of Adenosine-5′-N-ethyluronamide
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 17 3175
amide ([125I]AB-MECA),30 has become a useful radioli-
gand for the screening of new derivatives interacting
with cloned A3 receptors.
Sch em e 1
The A3 receptor mediates many processes such as
inflammation,31 hypotension,32 and mast cell degranu-
lation.33 Also, the A3 receptor apparently has a role in
the central nervous system. IB-MECA 1 induces be-
havioral depression34 and, upon chronic administration,
protects against cerebral ischemia.35 Furthermore, at
high concentrations A3 selective agonists were also
found to induce apoptosis in HL-60 human leukemia
cells.36
From the point of view of structure-activity relation-
ships, the ribose moiety of adenosine has to be main-
tained unchanged, with the exception of the 5′ position,
at which alkyluronamide groups are well tolerated.37
Furthermore, some substitutions at the purine 6 and/
or 2 positions modulates affinity and selectivity of aden-
osine agonists for the different receptor subtypes.24
Alkyl or aryl derivatives at the 6 position of the purine
nucleus are A1 selective, and many derivatives at the 2
position bearing C, N, or O substituents are A2A selec-
tive. 6-Benzyl analogues also containing the 5′-uron-
amide modification, such as 1, have been found to be
potent and selective A3 agonists.38 We have recently
reported a series of adenosine 5′-uronamide derivatives,
substituted at the purine 6 position, of general formula
2, which have shown high affinity at adenosine A3 recep-
tors. In particular, NECA derivatives containing at the
6-positon the 3-chloro-, 2-chloro-, or 4-methoxyphenyl-
carbamoyl moieties have shown affinity for A3 adenosine
receptors with 4-7 nM Ki values. However, while the
On the basis of the observation that 2-(1-hexyn-1-yl)-
1-(6-amino-9H-purin-9-yl)-1-deoxy-N-ethyl-â-D-ribofura-
nuronamide (HENECA), a potent A2A adenosine ago-
nist,16,40 also showed high affinity at rat A3 receptors,41
we combined ureido moieties at the purine 6 position,
that were favorable in A3 receptor binding, with the
substitution at the 2 position. Using results from a
previous work,39 we introduced the A3 receptor affinity
enhancing 4-methoxyphenyl-and 3-chlorophenyl-urea
groups at the purine 6 position, while substituting the
2 position with halogens (Cl, I) (52-55) and alkynyl
groups (56-62).
selectivity with respect to A2A receptors was high (A2A
/
A3 from 96 to 510), the discrimination between A1 and
A3 receptors was very low (A1/A3 from 4- to 10-fold).39
A new series of carboxamido and urea derivatives at
the 6 position of NECA (9-13, 30-45, and 52-62) have
Resu lts a n d Discu ssion
Ch em istr y. The preparation of N-acyl derivatives
of NECA, compounds 9-13, was performed following
the general synthetic strategy depicted in Scheme 1.
The amino group at the 6 position of NECA is not very
reactive; therefore, it was necessary to protect the
hydroxyl groups of the ribose moiety during selective
acylation. Reaction of 2′,3′-O-isopropylidene-protected
NECA (3) with the appropriate acyl chloride in the
presence of a catalytic amount of triethylamine at reflux
afforded the adducts 4-8 in a good yield, which were
in turn converted into the desired compounds (9-13)
by deprotection in aqueous 1 N HCl and dioxane at 65
°C. In a similar manner, derivatives 30-45 were pre-
pared by nucleophilic reaction of the appropriate isocy-
anate with 3 and then by deprotection of the ribosyl
moiety (Scheme 2).
been prepared to further explore the structural basis
for the selectivity for A3 vs A1 receptors. In particular,
we were interested in evaluating the influence of the
length of the acyl chain at the adenine N position on
the receptor affinity. We prepared some amide deriva-
tives of NECA (9-13), which are structurally related
to our previously reported series of urea derivatives.39
Also, some new urea derivatives at purine 6 position of
NECA (30-45) were synthesized to evaluate the phys-
icochemical parameters involved in the interaction with
A3 adenosine receptors. Furthermore, we introduced a
chiral center in compounds 33 and 34 to evaluate the
stereoselectivity of binding of the substituent at 6
position.
When not commercially available, the isocyanate was
prepared by reacting the corresponding substituted
anilines using trichloromethylchloroformate, as de-
scribed previously.42
Using 4-nitrophenyl isocyanate or 5-chloropyridin-2-
yl isocyanate under the conditions mentioned above, the

3176 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 17
Baraldi et al.
Sch em e 2
(9-13) was generally detrimental in terms of affinity
at rat A3 receptors, whereas several of these derivatives
(11 and 13) showed roughly 1 order of magnitude
increase in affinity for adenosine A2A receptor. Affinity
at A1 receptors was highly variable, ranging from 5.9
nM (biphenyl derivative, 9) to 1.2 µM. For example, the
o-chlorobenzoyl derivative (12) was 100-fold less potent
at A3 receptors and was 10-fold less potent at A1
receptors than the corresponding urea derivative.39 The
p-methoxybenzoyl derivative (11) was 127-fold less
potent at A3 receptors than the corresponding p-meth-
oxyphenyl urea derivative.39 These results suggested
that a small modification in the chain at the 6 position
could modulate the affinity for A1 or A3 receptors. In
the series of urea-derivatives (30-45), a substituted-
phenyl (31, 32, and 37) or substituted-benzyl (30, 33,
and 34) group led to higher affinity and selectivity at
A3 adenosine receptors. In fact, derivatives 31, 32, and
37 showed a high affinity (9.7-107 nM) at A3 receptors
with varying degrees of A1/A3 selectivity. In particular,
compound 31 was less active than IB-MECA (9.7 nM
vs 1.1 nM) but showed selectivity for A3 vs either A1 or
A2A receptors comparable to the reference compound.
In addition, it seemed necessary to have a free amino
group on the sulfonamido moiety, since its substitution
with some heteroaryl groups (e.g., compounds 41-43)
led to derivatives with modest affinity at rat A3 adeno-
sine receptors and low selectivity with respect to A1 and
A2A receptors.
The data demonstrate the importance of a phenyl-
urea moiety at the purine 6 position for an interaction
with the A3 adenosine receptor subtype.46 When the
phenyl ring was replaced with various heterocycles (35,
36, and 40) both affinity and selectivity for A3 receptors
decreased.
bis adducts 44 and 45 were the only products isolated
from the reaction mixture.
Moreover, the disubstitution at the 6 position led to
derivatives (44-45) with diminished activity, in par-
ticular at A2A and A3 receptors. This could be explained
by the absence of one hydrogen atom at N6, which could
act as a hydrogen bond donor, already noted as a
requirement for binding at the A1 and A2A receptor
subtypes.47
The 2-chloro- and the 2-iodo-6-arylcarbamoyl deriva-
tives of NECA 52-55 were synthesized from 2′,3′-O-
isopropylidene-2-chloro-NECA (46)43 and 2′,3′-O-isopro-
pylidene-2-iodo-NECA (47),44 respectively (Scheme 3).
The reaction of 46 or 47 in dry THF with the
appropriate isocyanate to afford the protected nucleo-
sides 48-51 was carried out in a steel bomb at 110 °C
for 24 h. The nucleosides were deprotected in 1 N HCl
and dioxane at 65 °C to give the corresponding com-
pounds 52-55. The synthesis of the (ar)alkynyl deriva-
tives 56-62 was carried out by a modification of the
palladium-catalyzed cross-coupling reaction.40
The 2-iodo derivatives 54 and 55 in dry acetonitrile,
DMF, and triethylamine reacted with cuprous iodide,
bis(triphenylphosphine)palladium dichloride, and the
appropriate terminal alkyne, at room temperature for
several hours under an atmosphere of N2, to produce
the alkynyl derivatives 56-58 and 59-62, respectively
(Scheme 4).
The benzylic series (30, 33, and 34) showed a SAR
pattern comparable to the phenylic series. In fact, the
unsubstituted compound 30 showed affinity and selec-
tivity at A3 receptors very similar to those of the
previously reported phenyl derivative.39 Interestingly,
comparing the two diastereomers 33 and 34 in which
substituents at the purine 6 position are of opposite
configuration, the R-isomer (33) was more potent than
the S-isomer (34) at the rat A2A and A3 adenosine
receptor subtypes. The binding stereoselectivity of the
N6 substituent confirms the importance of the stereo-
chemistry at this subregion of the adenosine receptor
binding site, similar to that already observed for the A1
agonists R-PIA and S-PIA.48 A similar observation has
been made for the C2 subregion of the A2A subtype, both
with geometric isomers of 2-alkenyl-NECA49 and with
diastereomers of 2-alkynyl derivatives of NECA [R- and
S-PHPNECA].50
Biologica l Activity. All the synthesized compounds
(9-13, 30-45, and 52-62) were tested in radioligand
binding assays for affinity at the rat brain A1, A2A
,
and A3 receptors, and the results are summarized in
Table 1.45
In our previous studies, we demonstrated that the
6-substituted adenosine uronamides are full agonists in
inhibiting adenylate cyclase via rat A3 receptors.39
From the binding assays, it appeared that the pres-
ence of an amide vs urea functionality at the 6 position
The data also demonstrate the importance of chain
length at the 6 position and suggest that phenyl or
benzyl chains are the preferred substituents for the
interaction with the A3 adenosine receptor subtype.

Derivatives of Adenosine-5′-N-ethyluronamide
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 17 3177
Sch em e 3
Sch em e 4
Longer chains, with respect to the phenylic or benzylic
moieties, seemed not to improve the affinity at rat A3
receptors. Thus, compounds, 38 and 39, bearing 2-phen-
ylethyl and 3,4-dimethoxy-2-phenylethyl groups at the
purine 6 position, respectively, showed submicromolar
affinity but low selectivity at rat A3 receptors.
A functional assay indicated that compound 31 acted
as a full agonist at rat A3 receptors. The assay consisted
of agonist-induced stimulation of binding of a guanine
nucleotide to membranes of rat RBL-2H3 mast cells,
which contain a high density of A3 receptors.30 Figure
1 shows that the potent A3 agonists 1-[6-[[(4-amino-3-
iodophenyl)methyl]amino]-9H-purin-9-yl]-1-deoxy-N-
methyl-â-D-ribofuranuronamide (I-AB-MECA) and 2-chlo-
ro-1-[6-[[(3-iodophenyl)methyl]amino]-9H-purin-9-yl]-1-
deoxy-N-methyl-â-D-ribofuranuronamide (Cl-IB-MECA)
increased binding of [35S]GTP-γ-S in a dose-dependent
manner and with 9-fold greater potency than NECA,
as expected for A3 receptors.
A correlation between binding affinity and potency
in this functional assay has been demonstrated.52
Compound 31 was as efficacious as these two potent
agonists but approximately 1 order of magnitude less
potent, with an EC50 value of 1.15 µM.
The introduction of halogens at the 2 position of
selected urea derivatives at the purine 6 position led to
compounds 52-55, which show an A3 affinity ranging
from 17 nM (53) to 315 nM (54). For example, the
presence of a chlorine atom in the 2 position reduced
the affinity and selectivity with respect to the corre-
sponding 2-unsubstituted urea derivatives39 (52, Ki at
These results and our previous work39 seem to
indicate that the lipophilicity of the para substituents
of a phenyl ring plays a significant role in A3 affinity. A
quantitative correlation was not found, but compounds
31 (π SO2NH2 ) -1.82), 32 (π COCH3 ) -0.55), and
the previously reported 6-phenyl urea derivative sub-
stituted with a methoxy group at the para position (π
OCH3 ) -0.02), bearing the least lipophilic substitu-
ents, show some of the most favorable Ki values within
the series.51
Species differences, which are pronounced for antago-
nists but not for agonists, in binding of ligands to A3
receptors have been noted. The most interesting de-
rivative in the present study (31) showed affinity at
human A3 adenosine receptors (56.1 ( 9.1 nM) compa-
rable to that at rat A3 receptors, but there was 6-fold
more potency at rat receptors. This finding confirms,
as already observed, significant differences between rat
and human A3 adenosine receptor subtypes.28

3178 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 17
Baraldi et al.

Derivatives of Adenosine-5′-N-ethyluronamide
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 17 3179
selectivity vs that of either A1 or A2A with respect to
the reference compound IB-MECA.
Furthermore, a simultaneous substitution at the 6
and 2 positions does not improve affinity and selectivity
for A3. However, the 2-(3-hydroxy-3-phenyl-1-propyn-
1-yl) derivative 61 showed the capability to bind simul-
taneously to A1 and A3 receptor subtypes, excluding the
A2A receptor.
Exp er im en ta l Section
Ch em istr y. Reactions were routinely monitored by thin-
layer chromatography (TLC) on silica gel (precoated F254 Merck
plates), and products were visualized with iodine or aqueous
potassium permanganate. Infrared spectra (IR) were mea-
sured on a Perkin-Elmer 257 instrument. 1H NMR spectra
were determined in CDCl3 or DMSO-d6 solutions with a
Bruker AC 200 spectrometer, peak positions are given in parts
per million (δ) downfield from tetramethylsilane as internal
standard, and J values are given in Hz. Light petroleum ether
refers to the fractions boiling at 40-60 °C. Melting points
F igu r e 1. Effect of the adenosine agonists NECA, compound
31, Cl-IB-MECA, and I-AB-MECA on the binding of [35S]GTP-
γ-S to membranes of rat RBL-2H3 mast cells. EC50 values were
NECA (10.6 µM), compound 31 (1.15 µM), Cl-IB-MECA (174
nM), and I-AB-MECA (86.8 nM).
were determined on
a Buchi-Tottoli instrument and are
uncorrected. Chromatography was performed with Merck 60-
1
200 mesh silica gel. All products reported showed IR and H
A3 ) 77.6 nM vs 4.4 nM; 53, Ki at A3 ) 17 nM vs 6.6
NMR spectra in agreement with the assigned structures.
Organic solutions were dried over anhydrous magnesium
sulfate. Elemental analyses were performed by the microana-
lytical laboratory of Dipartimento di Chimica, University of
Ferrara, and were within (0.4% of the theoretical values for
C, H, and N.
53
nM), unlike data for various other 6-substituted A1
29
and A3 receptor agonists. Similarly, the presence of
an iodine atom further decreased affinity and selectivity
(54, Ki at A3 ) 315 nM; 55, Ki at A3 ) 251 nM).
The introduction of an alkynyl chains at the 2 position
of these 5′-carboxamide adenosine derivatives was
expected to enhance the potency at A3 receptors, con-
sistent with the high affinity demonstrated by HENECA
(Ki at A3 ) 25.6 nM).41 Surprisingly, the 2-alkynyl-
substituted N6-urea 5′-carboxamide derivatives (56-62),
in fact, showed a dramatic reduction of A2A affinity,
indicating the interdependence of substitution at the
purine 2 and 6 positions. The triple substitution
resulted in compounds with extremely high A3 vs A2A
receptor selectivity, 60 > 61 > 58 > 57 (in order of
selectivity). Thus, the most potent compounds in this
group, showing high selectivity versus the A2A subtype
and which also showed a comparable affinity for A1 and
A3 receptors, the 2-(3-hydroxy-3-phenyl-1-propyn-1-yl)
derivative 61, could be an interesting candidate for the
simultaneous stimulation of both A1 and A3 subtypes.
This could be interesting since an interaction between
these two subtypes has been demonstrated in the rat
hippocampus, in the presynaptic control of release of
glutamic acid.54 Since both the A1 and A3 receptors are
coupled to the inhibition of adenylate cyclase, it may
prove useful to have such pharmacological probes of
mixed A1 and A3 selectivity such that they would exert
a dual, simultaneous action on the same second mes-
senger system. Conversely, compound 62 showed very
high selectivity for the A3 versus the A1 subtype.
Gen er a l P r oced u r e for th e P r ep a r a tion of 1-Deoxy-1-
[6-[[(su bstitu ted)car bon yl]am in o]-9H-pu r in -9-yl]-N-eth yl-
2,3-O-(1-m eth yleth ylid en e)-â-D-r ibofu r a n u r on a m id e (4-
8). 2′,3′-O-Isopropylidene-NECA 3 (0.43 mmol) was dissolved
in freshly distilled dioxane (4 mL), and the appropriate acyl
chloride (1.3 equiv) and a catalytic amount of triethylamine
(2-3 drops) were added. The mixture was refluxed under
argon for 15 h. The solvent was then removed under reduced
pressure, and the residue was purified by flash chromatogra-
phy (CH2Cl2-EtOAc 20%) to afford the desired compound 4-8.
1-Deoxy-1-[6-[[(4-bip h en yl)ca r bon yl]a m in o]-9H-p u r in -
9-yl]-N-eth yl-2,3-O-(1-m eth yleth ylid en e)-â-D-r ibofu r a n u -
r on a m id e (4): yield 80%; pale yellow foam; IR (neat) cm-1
3445, 1720, 1640, 1575; 1H NMR (CDCl3) δ 0.84 (t, 3H, J ) 7),
1.39 (s, 3H), 1.62 (s, 3H), 3.02-3.11 (m, 2H), 4.71 (d, 1H, J )
2), 5.39-5.46 (m, 2H), 6.19 (d, 1H, J ) 2), 6.66 (t, 1H, J ) 2),
7.40-7.74 (m, 7H), 8.09-8.16 (m, 3H), 8.74 (s, 1H), 9.44 (bs,
1H). Anal. (C28H28N6O5) C, H, N.
1-Deoxy-1-[6-[[(2,4-d ich lor ob en zyl)ca r b on yl]a m in o]-
9H-p u r in -9-yl]-N-eth yl-2,3-O-(1-m eth yleth ylid en e)-â-D-r i-
bofu r a n u r on a m id e (5): yield 67%; white foam; IR (neat)
cm-1 3440, 1730, 1625, 1565, 1210; 1H NMR (CDCl3) δ 0.82 (t,
3H, J ) 7), 1.17 (s, 3H), 1.26 (s, 3H), 2.99-3.13 (m, 2H), 4.32
(s, 2H), 4.72 (d, 1H, J ) 1.8), 5.38-5.48 (m, 2H), 6.16 (d, 1H,
J ) 1.8), 6.56 (t, 1H, J ) 2), 7.20-7.32 (m, 3H), 7.41 (s, 1H),
8.20 (s, 1H), 8.67 (s, 1H). Anal. (C23H24Cl2N7O5) C, H, N.
1-Deoxy-1-[6-[[(4-m eth oxyp h en yl)ca r bon yl]a m in o]-9H-
p u r in -9-yl]-N-eth yl-2,3-O-(1-m eth yleth ylid en e)-â-D-r ibo-
fu r a n u r on a m id e (6): yield 85%; white solid, mp 105-107 °C
(CH2Cl2-Et2O); IR (KBr) cm-1 3445, 1715, 1640, 1555, 1210;
1H NMR (CDCl3) δ 0.85 (t, 3H, J ) 7), 1.40 (s, 3H), 1.63 (s,
3H), 3.03-3.12 (m, 2H), 3.90 (s, 3H), 4.72 (d, 1H, J ) 2), 5.41-
5.49 (m, 2H), 6.16 (d, 1H, J ) 2), 6.61 (t, 1H, J ) 2), 7.01 (d,
2H, J ) 9), 8.02 (s, 2H, J ) 9), 8.10 (s, 1H), 8.74 (s, 1H), 9.09
(bs, 1H). Anal. (C23H26N6O6) C, H, N.
Con clu sion s
The present study provides useful information con-
cerning the structural requirements necessary for rec-
ognition by the A3 adenosine receptor. It appears that
a phenyl- or benzylcarbamoyl moiety at the purine 6
position seems favorable for A3 adenosine receptor
affinity and selectivity, while an arylcarboxamido group
enhances A1 affinity and selectivity. In particular, in
the urea series, compound 31 was shown to be less
potent but with approximately the same degree of A3
1-Deoxy-1-[6-[[(2-ch lor op h en yl)ca r b on yl]a m in o]-9H -
p u r in -9-yl]-N-eth yl-2,3-O-(1-m eth yleth ylid en e)-â-D-r ibo-
fu r a n u r on a m id e (7): yield 72%; white foam; IR (neat) cm-1
1
3435, 1720, 1620, 1550, 1230; H NMR (CDCl3) δ 0.83 (t, 3H,
J ) 7), 1.39 (s, 3H), 1.62 (s, 3H), 3.00-3.07 (m, 2H), 4.71 (d,
1H, J ) 2), 5.41-5.44 (m, 2H), 6.18 (d, 1H, J ) 2), 6.67 (t, 1H,
J ) 2), 7.30-7.44 (m, 3H), 7.71-7.76 (m, 1H), 8.16 (s, 1H),
8.69 (s, 1H), 10.24 (bs, 1H). Anal. (C22H23 Cl N7O5) C, H, N.

3180 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 17
Baraldi et al.
1-Deoxy-1-[6-[[(p h en yl)ca r b on yl]a m in o]-9H -p u r in -9-
yl]-N-et h yl-2,3-O-(1-m et h ylet h ylid en e)-â-D-r ib ofu r a n u -
r on a m id e (8): yield 90%; pale yellow oil; IR (neat) cm-1 3425,
1-Deoxy-1-[6-[[[(1,3,4-th ia d ia zol-2-yl)a m in o]ca r bon yl]-
am in o]-9H-pu r in -9-yl]-N-eth yl-2,3-O-(1-m eth yleth yliden e)-
â-D-r ibofu r a n u r on a m id e (20): yield 70%; yellow solid, mp
148 °C (CH2Cl2-Et2O); IR (KBr) cm-1 3430, 1730, 1615, 1560,
1240; 1H NMR (CDCl3) δ 0.86 (t, 3H, J ) 7), 1.44 (s 3H), 1.67
(s, 3H), 3.07-3.14 (m, 2H), 4.78 (d, 1H, J ) 1.8), 5.47-5.51
(m, 2H), 6.24 (d, 1H, J ) 1.8), 6.52 (t, 1H, J ) 2), 8.36 (s, 1H),
8.75 (s, 1H), 8.91 (bs, 1H), 9.40 (bs, 1H), 11.72 (bs, 1H). Anal.
(C18H21N9O5S) C, H, N.
1-Deoxy-1-[6-[[[(4-n -p r op yloxy-p h en yl)a m in o]ca r b o-
n yl]a m in o]-9H -p u r in -9-yl]-N-et h yl-2,3-O-(1-m et h ylet h -
ylid en e)-â-D-r ibofu r a n u r on a m id e (21): yield 70%; pale
yellow foam; IR (neat) cm-1 3440, 1725, 1620, 1555, 1220; 1H
NMR (CDCl3) δ 0.71 (t, 3H, J ) 7), 0.90 (t, 3H, J ) 7), 1.40 (s
3H), 1.62 (s, 3H), 1.81-2.03 (m, 2H), 2.95-3.01 (m, 2H), 3.90
(t, 2H, J ) 7), 4.71 (d, 1H, J ) 1.8), 5.46-5.51 (m, 2H), 6.19
(d, 1H, J ) 1.8), 6.51 (t, 1H, J ) 2), 6.89 (d, 2H, J ) 9), 7.48
(d, 2H, J ) 9), 8.25 (s, 1H), 8.56 (s, 1H), 8.80 (bs, 1H), 11.48
(s, 1H). Anal. (C22H25N7O5) C, H, N.
1
1730, 1640, 1555, 1240; H N:MR (CDCl3) δ 0.79 (t, 3H, J )
7), 1.39 (s, 3H), 1.61 (s, 3H), 2.91-3.03 (m, 2H), 4.71 (d, 1H, J
) 2), 5.45-5.52 (m, 2H), 6.18 (d, 1H, J ) 2), 6.40 (t, 1H, J )
2), 7.27-7.53 (m, 3H), 7.83-7.87 (m, 2H), 8.19 (s, 1H), 8.63
(s, 1H), 9.18 (bs, 1H). Anal. (C22H24N6O5) C, H, N.
Gen er a l P r oced u r e for th e P r ep a r a tion of 1-Deoxy-1-
[6-[[[(su b st it u t ed )a m in o]ca r b on yl]a m in o]-9H -p u r in -9-
yl]-N-et h yl-2,3-O-(1-m et h ylet h ylid en e)-â-D-r ib ofu r a n u -
r on a m id e (14-29). 2′,3′-O-Isopropylidene-NECA 3 (0.43
mmol) was dissolved in freshly distilled THF (4 mL), and then
the appropriate isocyanate (1.3 equiv) and a catalytic amount
of triethylamine (two drops) were added. The mixture was
refluxed under argon for 18 h. Next the solvent was removed
under reduced pressure, and the residue was purified by flash
chromatography (CH2Cl2-EtOAc 20%) to afford the desired
compound 14-29.
1-Deoxy-1-[6-[[[(b en zyl)a m in o]ca r b on yl]a m in o]-9H -
p u r in -9-yl]-N-eth yl-2,3-O-(1-m eth yleth ylid en e)-â-D-r ibo-
fu r a n u r on a m id e (14): yield 82%; white solid, mp 109-111
°C (CH2Cl2-Et2O); IR (KBr) cm-1 3440, 1740, 1610, 1550,
1210; 1H NMR (CDCl3) δ 0.76 (t, 3H, J ) 7), 1.21 (s, 3H), 1.63
(s, 3H), 2.96-3.03 (m, 2H), 4.64 (d, 2H, J ) 6), 4.71 (d, 1H, J
) 1.8), 5.44-5.48 (m, 2H), 6.16 (d, 1H, J ) 2), 6.52 (t, 1H, J )
2), 7.26-7.38 (m, 5H), 8.14 (s, 1H), 8.45 (s, 1H), 8.46 (s, 1H),
9.79 (bs, 1H). Anal. (C26H31N7O5) C, H, N.
1-Deoxy-1-[6-[[[(4-su lfon am idoph en yl)am in o]car bon yl]-
am in o]-9H-pu r in -9-yl]-N-eth yl-2,3-O-(1-m eth yleth yliden e)-
â-D-r ibofu r a n u r on a m id e (15): yield 60%; white solid, mp
207 °C (CH2Cl2-Et2O); IR (KBr) cm-1 3450-3250, 1730, 1610,
1565, 1360, 1230; 1H NMR (CDCl3) δ 0.57 (t, 3H, J ) 7), 1.35
(s, 3H), 1.54 (s, 3H), 2.96-3.03 (m, 2H), 4.60 (d, 1H, J ) 2),
5.47-5.50 (m, 2H), 6.47 (d, 1H, J ) 2), 6.60 (t, 1H, J ) 2),
7.26 (d, 2H, J ) 9), 7.74 (d, 2H, J ) 9), 8.60 (s, 1H), 8.64 (s,
1H), 9.22 (s, 1H), 10.47 (bs, 1H), 12.05 (s, 1H). Anal.
(C22H26N8O7S) C, H, N.
1-Deoxy-1-[6-[[[(2-ph en yleth yl)am in o]car bon yl]am in o]-
9H-p u r in -9-yl]-N-eth yl-2,3-O-(1-m eth yleth ylid en e)-â-D-r i-
bofu r a n u r on a m id e (22): yield 60%; pale yellow solid, mp
88-90 °C (EtOAc-light petroleum); IR (KBr) cm-1 3440, 1730,
1615, 1550, 1225; 1H NMR (CDCl3) δ 0.70 (t, 3H, J ) 7), 1.40
(s 3H), 1.62 (s, 3H), 2.94-3.23 (m, 4H), 3.67 (t, 2H, J ) 6.8),
4.71 (d, 1H, J ) 1.8), 5.46-5.51 (m, 2H), 6.18 (d, 1H, J ) 1.8),
6.49 (t, 1H, J ) 6), 7.24-7.32 (m, 5H), 8.25 (s, 1H), 8.30 (s,
1H), 9.48 (bs, 1H), 11.48 (s, 1H). Anal. (C24H29N7O5) C, H, N.
1-Deoxy-1-[6-[[[(3,4-d im eth oxy-2-p h en yleth yl)a m in o]-
ca r bon yl]a m in o]-9H-p u r in -9-yl]-N-eth yl-2,3-O-(1-m eth yl-
eth ylid en e)-â-D-r ibofu r a n u r on a m id e (23): yield 55%; yel-
low solid, 85-87 °C mp (EtOAc-light petroleum); IR (KBr)
cm-1 3440, 1724, 1623, 1554, 1225; 1H NMR (CDCl3) δ 0.73 (t,
3H, J ) 7), 1.23 (t, 2H, J ) 8), 1.41 (s 3H), 1.62 (s, 3H), 2.95-
3.07 (m, 2H), 3.85 (s, 3H), 3.87 (s, 3H), 4.71 (d, 1H, J ) 1.8),
5.47-5.51 (m, 2H), 6.17 (d, 1H, J ) 1.8), 6.51 (t, 1H, J ) 2),
6.60 (s, 1H), 6.62 (s, 2H), 8.23 (s, 1H), 8.36 (s, 1H), 8.71 (s,
1H), 9.46 (bs, 1H). Anal. (C26H33N7O7) C, H, N.
1-Deoxy-1-[6-[[[(4-acetylph en yl)am in o]car bon yl]am in o]-
9H-p u r in -9-yl]-N-eth yl-2,3-O-(1-m eth yleth ylid en e)-â-D-r i-
bofu r a n u r on a m id e (16): yield 77%; white solid, mp 204 °C
(CH2Cl2-Et2O); IR (KBr) cm-1 3430, 1740, 1730, 1630, 1545,
1240; 1H NMR (CDCl3) δ 0.83 (t, 3H, J ) 7), 1.42 (s, 3H), 1.64
(s, 3H), 2.61 (s, 3H), 2.99-3.08 (m, 2H), 4.74 (d, 1H, J ) 2),
5.47-5.55 (m, 2H), 6.21 (d, 1H, J ) 2), 6.47 (t, 1H, J ) 2),
7.74 (d, 2H, J ) 9), 7.98 (d, 2H, J ) 9), 8.21 (s, 1H), 8.63 (s,
1H), 8.67 (bs, 1H), 12.01 (s, 1H). Anal. (C21H27N7O6) C, H, N.
1-Deoxy-1-[6-[[[((R)-1-ph en yleth yl)am in o]car bon yl]am i-
n o]-9H-p u r in -9-yl]-N-eth yl-2,3-O-(1-m eth yleth ylid en e)-â-
D-r ibofu r a n u r on a m id e (17): yield 65%; white solid, mp 110-
111 °C (CH2Cl2-Et2O); IR (KBr) cm-1 3430, 1730, 1620, 1555,
1230; 1H NMR (CDCl3) δ 0.68 (t, 3H, J ) 7), 1.41 (s, 3H), 1.63
(s, 3H), 1.64 (d, 3H, J ) 7), 2.87-2.96 (m, 2H), 4.71 (d, 1H, J
) 1.8), 5.16 (m, 1H), 5.48-5.51 (m, 2H), 6.16 (d, 1H, J ) 2),
6.52 (bs, 1H), 7.25-7.40 (m, 5H), 8.15 (s, 1H), 8.51 (s, 1H),
9.84 (bs, 1H), 10.94 (s, 1H). Anal. (C23H29N7O5) C, H, N.
1-Deoxy-1-[6-[[[((S)-1-ph en yleth yl)am in o]car bon yl]am i-
n o]-9H-p u r in -9-yl]-N-eth yl-2,3-O-(1-m eth yleth ylid en e)-â-
D-r ibofu r a n u r on a m id e (18): yield 82%; white solid, mp 107-
108 °C (CH2Cl2-Et2O); IR (KBr) cm-1 3445, 1725, 1615, 1560,
1230; 1H NMR (CDCl3) δ 0.85 (t, 3H, J ) 7), 1.40 (s, 3H), 1.63
(s, 3H), 1.64 (d, 3H, J ) 7), 3.00-3.09 (m, 2H), 4.72 (d, 1H, J
) 1.8), 5.17 (m, 1H), 5.39-5.50 (m, 2H), 6.14 (d, 1H, J ) 2),
6.57 (bs, 1H), 7.26-7.45 (m, 5H), 8.12 (s, 1H), 8.51 (s, 1H),
9.81 (bs, 1H), 10.87 (s, 1H). Anal. (C23H29N7O5) C, H, N.
1-Deoxy-1-[6-[[[(5-m eth yl-isoxazol-3-yl)am in o]car bon yl]-
am in o]-9H-pu r in -9-yl]-N-eth yl-2,3-O-(1-m eth yleth yliden e)-
â-D-r ibofu r a n u r on a m id e (19): yield 83%; pale yellow solid,
mp 120 °C (CH2Cl2-Et2O); IR (KBr) cm-1 3450, 1720, 1620,
1550, 1215; 1H NMR (CDCl3) δ 0.82 (t, 3H, J ) 7), 1.20 (s 3H),
1.41 (s, 3H), 2.44 (s, 3H), 3.00-3.07 (m, 2H), 4.74 (d, 1H, J )
2), 5.46-5.50 (m, 2H), 6.21 (d, 1H, J ) 2), 6.55 (t, 1H, J ) 2),
6.70 (s, 1H), 8.37 (s, 1H), 8.63 (s, 1H), 9.39 (bs, 1H), 12.34 (bs,
1H). Anal. (C20H24N8O6) C, H, N.
1-Deoxy-1-[6-[[[(fu r -2-yl-m eth yl)am in o]car bon yl]am in o]-
9H-p u r in -9-yl]-N-eth yl-2,3-O-(1-m eth yleth ylid en e)-â-D-r i-
bofu r a n u r on a m id e (24): yield 58%; yellow solid mp 90-93
°C (EtOAc-light petroleum); IR (KBr) cm-1 3445, 1727, 1620,
1550, 1222; 1H NMR (CDCl3) δ 0.72 (t, 3H, J ) 7), 1.40 (s,
3H), 1.62 (s, 3H), 2.84-2.99 (m, 2H), 4.6 (d, 2H, J ) 6), 4.71
(d, 1H, J ) 1.8), 5.45-5.55 (m, 2H), 6.19 (d, 1H, J ) 1.8), 6.30-
6.36 (m, 2H), 6.60 (s, 1H), 6.5 (t, 1H, J ) 6), 7.38 (d, 1H, J )
2), 8.32 (s, 1H), 8.49 (s, 1H), 9.00 (s, 1H), 9.84 (bs, 1H). Anal.
(C21H25N7O6) C, H, N.
1-Deoxy-1-[6-[[[(4-(p yr id in -2-yl-a m in osu lfon yl)p h en -
y l)a m in o ]c a r b o n y l]a m in o ]-9H -p u r in -9-y l]-N -e t h y l-
2,3-O-(1-m eth yleth ylid en e)-â-D-r ibofu r a n u r on a m id e (25):
yield 48%; yellow solid mp 168-170 °C (EtOAc-light petro-
1
leum); IR (KBr) cm-1 3450, 1730, 1625, 1550, 1350, 1220; H
NMR (CDCl3) δ 0.71 (t, 3H, J ) 7), 1.41 (s, 3H), 1.60 (s, 3H),
2.80-2.95 (m, 2H), 4.73 (d, 1H, J ) 1.8), 5.40-5.60 (m, 2H),
6.19 (d, 1H, J ) 1.8), 6.65 (t, 1H, J ) 6), 7.15-7.25 (m, 1H),
7.45 (d, 2H, J ) 9), 7.55-7.75 (m, 3H), 7.92 (d, 2H, J ) 9),
8.27 (s, 1H), 8.50 (s, 1H), 8.99 (s, 1H), 9.80 (bs, 1H), 11.02 (bs,
1H). Anal. (C27H29N9O7S) C, H, N.
1-Deoxy-1-[6-[[[(4-(5-m eth yl-isoxa zol-3-yl-a m in osu lfo-
n yl)p h en yl)a m in o] ca r bon yl]a m in o]-9H-p u r in -9-yl]-N-
e t h yl-2,3-O-(1-m e t h yle t h ylid e n e )-â-D -r ib ofu r a n u r on -
a m id e (26): yield 56%; yellow solid mp 157-159 °C (EtOAc-
light petroleum); IR (KBr) cm-1 3455, 1725, 1630, 1557, 1355,
1
1224; H NMR (DMSO-d6) δ 0.79 (t, 3H, J ) 7), 1.40 (s, 3H),
1.62 (s, 3H), 2.30 (s, 3H), 2.91-3.04 (m, 2H), 4.68 (d, 1H, J )
1.8), 5.40-5.48 (m, 2H), 6.11 (d, 1H, J ) 1.8), 6.39 (s, 1H),
7.06 (t, 1H, J ) 6), 7.63 (d, 2H, J ) 9), 7.85 (d, 2H, J ) 9),
8.44 (s, 1H), 8.59 (s, 1H), 9.07 (s, 1H), 9.62 (bs, 1H), 12.11 (bs,
1H). Anal. (C26H29N9O8S) C, H, N.
1-De oxy-1-[6-[[[(4-(p yr im id in -2-yl-a m in osu lfon yl)-
p h en yl)a m in o] ca r bon yl]a m in o]-9H-p u r in -9-yl]-N-eth yl-
2,3-O-(1-m eth yleth ylid en e)-â-D-r ibofu r a n u r on a m id e (27):
yield 53%; yellow solid mp 157-159 °C (EtOAc-light petro-

Derivatives of Adenosine-5′-N-ethyluronamide
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 17 3181
solid, mp 157-159 °C (EtOH); IR (KBr) cm-1 3500-3000, 1715,
leum); IR (KBr) cm-1 3450, 1722, 1633, 1552, 1350, 1220; H
NMR (DMSO-d6) δ 0.57 (t, 3H, J ) 7), 1.35 (s, 3H), 1.54 (s,
3H), 2.71-2.80 (m, 2H), 4.59 (d, 1H, J ) 1.8), 5.40-5.46 (m,
2H), 6.46 (d, 1H, J ) 1.8), 7.03 (t, 1H, J ) 6), 7.56 (m, 1H),
7.60 (d, 2H, J ) 9), 7.85 (d, 2H, J ) 9), 8.48 (s, 1H), 8.51 (s,
1H), 8.60 (d, 2H, J ) 7), 10.45 (bs, 1H), 11.71 (bs, 1H), 12.04
(s, 1H). Anal. (C26H28N10O7S) C, H, N.
1-Deoxy-1-[6,6-[[[bis-(4-n itr op h en yl)a m in o]ca r bon yl]-
am in o]-9H-pu r in -9-yl]-N-eth yl-2,3-O-(1-m eth yleth yliden e)-
â-D-r ibofu r a n u r on a m id e (28): yield 65%; yellow solid, mp
261 °C (CH2Cl2-Et2O); IR (KBr) cm-1 3430, 1730, 1620, 1555,
1350, 1210; 1H NMR (DMSO-d6) δ 0.56 (t, 3H, J ) 7), 1.34 (s,
3H), 1.54 (s, 3H), 2.67-2.83 (m, 2H), 4.61 (d, 1H, J ) 1.8),
5.47-5.50 (m, 2H), 6.47 (d, 1H, J ) 1.8), 7.61 (t, 1H, J ) 2),
7.71 (d, 2H, J ) 9), 7.91 (d, 2H, J ) 9), 8.22 (d, 2H, J ) 9),
8.24 (s, 1H), 8.64 (d, 2H, J ) 9), 9.72 (s, 1H), 10.63 (bs, 1H),
12.24 (s, 1H). Anal. (C29H28N10O10) C, H, N.
1
1
1630, 1535, 1260; H NMR (DMSO-d6) δ 1.03 (t, 3H, J ) 7),
3.16-3.19 (m, 2H), 3.74 (bs, 2H), 4.22 (bs, 1H), 4.36 (s, 1H),
4.51-4.63 (m, 1H), 6.13 (d, 1H, J ) 6.8), 7.48-7.59 (m, 3H),
8.04-8.11 (m, 2H), 8.52 (bs, 1H), 8.79 (s, 1H), 8.83 (s, 1H),
11.22 (s, 1H). Anal. (C19H20N6O5) C, H, N.
1-Deoxy-1-[6-[[[(b en zyl)a m in o]ca r b on yl]a m in o]-9H -
p u r in -9-yl]-N-eth yl-â-D-r ibofu r a n u r on a m id e (30): yield
70%;white solid, mp 184-186 °C (EtOH); IR (KBr) cm-1 3500-
3100, 1675, 1620, 1565, 1520, 1310; 1H NMR (DMSO-d6) δ 1.06
(t, 3H, J ) 7), 3.10-3.20 (m, 2H), 4.05 (bs, 2H), 4.17-4.20 (m,
1H), 4.36 (s, 1H), 4.47-4.50 (m, 2H), 4.55-4.65 (m, 1H), 6.05-
6.10 (m, 1H), 7.17-7.40 (m, 5H), 8.30-8.40 (m, 1H), 8.62 (s,
1H), 8.86 (s, 1H), 9.50-9.60 (m, 1H), 10.30 (bs, 1H). Anal.
(C20H24N7O5) C, H, N.
1-Deoxy-1-[6-[[[(4-su lfon am idoph en yl)am in o]car bon yl]-
a m in o]-9H-p u r in -9-yl]-N-eth yl-â-D-r ibofu r a n u r on a m id e
(31): yield 63%; white solid, mp 183-185 °C (EtOH); IR (KBr)
cm-1 3550-3050, 1715, 1630, 1545, 1370, 1250; 1H NMR
(DMSO-d6) δ 1.07 (t, 3H, J ) 7), 3.16-3.26 (m, 2H), 4.21 (bs,
1H), 4.36 (s, 1H), 4.63-4.69 (m, 1H), 5.62 (d, 1H, J ) 6.8),
5.78 (d, 1H, J ) 4), 6.11 (d, 1H, J ) 6.8), 7.31 (bs, 2H), 7.81 (s,
4H), 8.49 (bs, 1H), 8.75 (s, 1H), 8.89 (s, 1H), 9.69 (bs, 1H), 11.92
(bs, 1H). Anal. (C19H22N8O7S) C, H, N.
1-Deoxy-1-[6-[[[(4-acetylph en yl)am in o]car bon yl]am in o]-
9H-pu r in -9-yl]-N-eth yl-â-D-r ibofu r an u r on am ide (32): yield
83%; white solid, mp 187 °C (EtOH); IR (KBr) cm-1 3550-
3100, 1740, 1720, 1630, 1525, 1215; 1H NMR (DMSO-d6) δ 1.08
(t, 3H, J ) 7), 2.55 (s, 3H), 3.16-3.23 (m, 2H), 4.18-4.20 (m,
1H), 4.21 (d, 1H, J ) 2), 4.45 (bs, 2H), 4.64-4.69 (m, 1H), 6.11
(d, 1H, J ) 7), 7.77 (d, 2H, J ) 9), 7.98 (d, 2H, J ) 9), 8.49 (bs,
1H), 8.76 (s, 1H), 8.88 (s, 1H), 10.62 (bs, 1H), 11.94 (bs, 1H).
Anal. (C21H23N7O6) C, H, N.
1-Deoxy-1-[6-[[[((R)-1-ph en yleth yl)am in o]car bon yl]am i-
n o]-9H-p u r in -9-yl]-N-eth yl-â-D-r ibofu r a n u r on a m id e (33):
yield 65%; white solid, mp 153-155 °C (EtOH); IR (KBr) cm-1
3550-3100, 1720, 1635, 1535, 1240; 1H NMR (DMSO-d6) δ 1.05
(t, 3H, J ) 7), 1.51 (d, 3H, J ) 8), 3.14-3.21 (m, 2H), 3.35-
3.41 (m, 1H), 4.20 (s, 1H), 4.36 (s, 1H), 4.93-5.00 (m, 3H), 6.09
(d, 1H, J ) 6.8), 7.25-7.39 (m, 5H), 8.48 (bs, 1H), 8.65 (s, 1H),
8.89 (s, 1H), 9.51 (bs, 1H), 10.38 (bs, 1H). Anal. (C21H25N7O5)
C, H, N.
1-Deoxy-1-[6-[[[((S)-1-ph en yleth yl)am in o]car bon yl]am i-
n o]-9H-p u r in -9-yl]-N-eth yl-â-D-r ibofu r a n u r on a m id e (34):
yield 72%; white solid, mp 151 °C (EtOH); IR (KBr) cm-1
3550-3100, 1725, 1630, 1525, 1240; 1H NMR (DMSO-d6) δ 1.06
(t, 3H, J ) 7), 1.49 (d, 3H, J ) 8), 3.15-3.21 (m, 2H), 3.28-
3.39 (m, 1H), 4.00 (bs, 2H), 4.35 (s, 1H), 4.61-4.66 (m, 1H),
4.94-5.01 (m, 1H), 6.07 (d, 1H, J ) 6.8), 7.24-7.39 (m, 5H),
8.48 (bs, 1H), 8.64 (s, 1H), 8.83 (s, 1H), 9.57 (bs, 1H), 10.12
(bs, 1H). Anal. (C21H25N7O5) C, H, N.
1-Deoxy-1-[6-[[[(5-m eth yl-isoxazol-3-yl)am in o]car bon yl]-
a m in o]-9H-p u r in -9-yl]-N-eth yl-â-D-r ibofu r a n u r on a m id e
(35): yield 58%; white solid, mp 197 °C (EtOH); IR (KBr) cm-1
3550-3050, 1715, 1620, 1535, 1240; 1H NMR (DMSO-d6) δ 1.06
(t, 3H, J ) 7), 2.40 (s 3H), 3.12-3.25 (m, 2H), 4.21-4.23 (m,
1H), 4.36 (d, 1H, J ) 2), 4.64-4.70 (m, 1H), 5.68 (m, 2H), 6.09
(d, 1H, J ) 6.8), 6.67 (s, 1H), 8.46 (t, 1H, J ) 6), 8.74 (s, 1H),
8.84 (s, 1H), 10.75 (bs, 1H), 12.19 (bs, 1H). Anal. (C17H20N8O6)
C, H, N.
1-Deoxy-1-[6-[[[(1,3,4-th ia d ia zol-2-yl)a m in o]ca r bon yl]-
a m in o]-9H-p u r in -9-yl]-N-eth yl-â-D-r ibofu r a n u r on a m id e
(36): yield 65%; white solid, mp 197 °C (EtOH); IR (KBr) cm-1
3450-300, 1720, 1635, 1515, 1240; 1H NMR (DMSO-d6) δ 1.06
(t, 3H, J ) 7), 3.15-3.22 (m, 2H), 3.72 (bs, 2H), 4.21-4.24 (m,
1H), 4.36 (d, 1H, J ) 2), 4.65-4.70 (m, 1H), 6.12 (d, 1H, J )
6.8), 8.45 (t, 1H, J ) 7), 8.80 (s, 1H), 8.89 (s, 1H), 9.19 (s, 1H),
10.35 (bs, 1H), 11.38 (bs, 1H). Anal. (C15H17N4O5S) C, H, N.
1-Deoxy-1-[6-[[[(4-n -p r op yloxy-p h en yl)a m in o]ca r b o-
n yl]a m in o]-9H -p u r in -9-yl]-N-et h yl-â-D-r ib ofu r a n u r on -
a m id e (37): yield 66%; white solid, mp 270 °C (EtOH); IR
(KBr) cm-1 3450-3050, 1720, 1630, 1535, 1240; 1H NMR
(DMSO-d6) δ 0.95 (t, 3H, J ) 7), 1.09 (t, 3H, J ) 7), 1.65-1.75
(m, 2H), 3.06-3.23 (m, 2H), 3.67 (bs, 2H), 3.89 (t, 2H, J ) 7),
1-Deoxy-1-[6,6-[[[bis-(5-ch lor o-p yr id in -2-yl)a m in o]ca r -
bon yl]a m in o]-9H-p u r in -9-yl]-N-eth yl-2,3-O-(1-m eth yleth -
ylid en e)-â-D-r ibofu r a n u r on a m id e (29): yield 60%; yellow
foam; IR (neat) cm-1 3440, 1710, 1630, 1540, 1220; H NMR
1
(DMSO-d6) δ 0.58 (t, 3H, J ) 7), 1.35 (s 3H), 1.54 (s, 3H), 2.71-
2.85 (m, 2H), 4.60 (d, 1H, J ) 2), 5.47-5.51 (m, 2H), 6.47 (d,
1H, J ) 2), 7.52 (t, 1H, J ) 2), 7.79-7.92 (m, 4H), 8.34-8.38
(m, 2H), 8.60 (s, 1H), 8.65 (s, 1H), 10.66 (bs, 1H), 12.22 (bs,
1H). Anal. (C27H26Cl2N8O6) C, H, N.
Gen er a l P r oced u r e for th e P r ep a r a tion of 1-Deoxy-1-
[6-[[(su bstitu ted)car bon yl]am in o]-9H-pu r in -9-yl]-N-eth yl-
â-D-r ibofu r a n u r on a m id e (9-13) a n d 1-Deoxy-1-[6-[[[(su b-
stitu ted )a m in o]ca r bon yl]a m in o]-9H-p u r in -9-yl]-N-eth yl-
â-D-r ib ofu r a n u r on a m id e (30-45). A solution of the iso-
propylidene derivative, 4-8 or 14-29, (0.084 mmol) in aqueous
1 N HCl (5 mL) and dioxane (5 mL) was stirred at 65 °C for 1
h. The solvent was then removed under reduced pressure, and
the residue was crystallized from ethanol to afford the desired
compound, 9-13 or 30-45.
1-Deoxy-1-[6-[[(4-bip h en yl)ca r bon yl]a m in o]-9H-p u r in -
9-yl]-N-eth yl-â-D-r ibofu r a n u r on a m id e (9): yield 65%; white
solid, mp 221 °C (EtOH); IR (KBr) cm-1 3500-3100, 1720,
1
1615, 1550; H NMR (DMSO-d6) δ 1.07 (t, 3H, J ) 7), 3.17-
3.24 (m, 2H), 4.23-4.25 (m, 1H), 4.36 (d, 1H, J ) 2), 4.71-
4.73 (m, 1H), 5.70 (d, 1H, J ) 8), 5.79 (d, 1H, J ) 4), 6.13 (d,
1H, J ) 8), 7.43-7.53 (m, 3H), 7.78-7.89 (m, 4H), 8.16 (d,
2H, J ) 11), 8.46 (t, 1H, J ) 4), 8.80 (s, 1H), 8.82 (s, 1H), 11.34
(bs, 1H). Anal. (C25H24N6O5) C, H, N.
1-Deoxy-1-[6-[[(2,4-d ich lor ob en zyl)ca r b on yl]a m in o]-
9H-pu r in -9-yl]-N-eth yl-â-D-r ibofu r an u r on am ide (10): yield
55%; off white solid, mp 132-134 °C (EtOH); IR (KBr)
cm-1 3450-3050, 1730, 1635, 1545, 1230; 1H NMR (DMSO-
d6) δ 1.08 (t, 3H, J ) 7), 3.18-3.25 (m, 2H), 3.34 (s, 2H), 4.12-
4.15 (m, 1H), 4.30 (s, 1H), 4.49-4.62 (m, 2H), 5.57 (d, 1H, J )
8), 5.77 (d, 1H, J ) 4), 5.95 (d, 1H, J ) 8), 7.44-7.51 (m, 3H),
8.19 (s, 1H), 8.39 (s, 1H), 8.95 (bs, 1H). Anal. (C20H20Cl2N6O5)
C, H, N.
1-Deoxy-1-[6-[[(4-m eth oxyp h en yl)ca r bon yl]a m in o]-9H-
p u r in -9-yl]-N-eth yl-â-D-r ibofu r a n u r on a m id e (11): yield
80%; white solid, mp 167-169 °C (EtOH); IR (KBr) cm-1
3550-3150, 1710, 1640, 1530, 1270; 1H NMR (DMSO-d6) δ 1.07
(t, 3H, J ) 7), 3.15-3.23 (m, 2H), 3.86 (s, 3H), 4.20-4.24 (m,
1H), 4.35 (d, 1H, J ) 2), 4.70-4.75 (m, 1H), 5.69 (d, 1H, J )
7), 5.77 (d, 1H, J ) 4), 6.11 (d, 1H, J ) 7), 7.08 (d, 2H, J ) 9),
8.04 (d, 2H, J ) 9), 8.44 (bs, 1H), 8.77 (s, 1H), 8.78 (s, 1H),
11.12 (s, 1H). Anal. (C20H22N6O6) C, H, N.
1-Deoxy-1-[6-[[(2-ch lor op h en yl)ca r b on yl]a m in o]-9H -
p u r in -9-yl]-N-eth yl-â-D-r ibofu r a n u r on a m id e (12): yield
78%; white solid, mp 179-180 °C (EtOH); IR (KBr) cm-1
3510-3050, 1720, 1660, 1510, 1250; 1H NMR (DMSO-d6) δ
1.06 (t, 3H, J ) 7), 3.15-3.22 (m, 2H), 4.22 (bs, 1H), 4.34 (s,
1H), 4.68-4.70 (m, 1H), 5.66 (d, 1H, J ) 7), 5.76 (d, 1H, J )
4), 6.10 (d, 1H, J ) 7), 7.43-7.61 (m, 4H), 8.44 (bs, 1H), 8.67
(s, 1H), 8.82 (bs, 1H), 11.53 (bs, 1H). Anal. (C19H19N6O5) C,
H, N.
1-Deoxy-1-[6-[[(p h en yl)ca r b on yl]a m in o]-9H -p u r in -9-
yl]-N-eth yl-â-D-r ibofu r a n u r on a m id e (13): yield 67%; white

3182 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 17
Baraldi et al.
4.18-4.20 (m, 1H), 4.33 (s, 1H), 4.51-4.61 (m, 1H), 6.05 (d,
1H, J ) 6.8), 6.91 (d, 2H, J ) 9), 7.52 (d, 2H, J ) 9), 7.92 (t,
1H, J ) 7), 8.22 (s, 1H), 8.52 (s, 1H), 9.65 (bs, 1H), 11.52 (bs,
1H). Anal. (C22H27N7O6) C, H, N.
1-De oxy-1-[6,6-[[[b is-(5-ch lor o-p yr id in -2-yl)a m in o]-
carbonyl]amino]-9H-purin-9-yl]-N-ethyl-â-D-ribofuranuron-
a m id e (45): yield 68%; white solid, mp 220 °C (EtOH); IR
(KBr) cm-1 3550-3100, 1725, 1630, 1525, 1250; 1H NMR
(DMSO-d6) δ 1.06 (t, 3H, J ) 7), 3.15-3.22 (m, 2H), 4.22-
4.24 (m, 1H), 4.36 (d, 2H, J ) 2), 4.64-4.69 (m, 1H), 5.95 (bs,
2H), 6.10 (d, 1H, J ) 6.8), 7.80-8.06 (m, 6H), 8.39 (t, 1H, J )
7), 8.76 (s, 1H), 8.93 (s, 1H), 10.39 (bs, 1H), 12.11 (bs, 1H).
Anal. (C24H22Cl2N8O6) C, H, N.
Gen er a l P r oced u r e for th e Syn th esis of 2-Ch lor o- a n d
2-Iod o-1-d eoxy-1-[6-[[[(su bstitu ted )a m in o]ca r bon yl]a m i-
n o]-9H-p u r in -9-yl]-N-eth yl-2,3-O-(1-m eth yleth ylid en e)-â-
D-r ibofu r a n u r on a m id e (48-51). The appropriate commer-
cially available isocyanate (2.1 mmol) was added to a solution
of 2′,3′-O-isopropylidene-2-chloro-NECA (46)43 or to 2′,3′-O-
isopropylidene-2-iodo-NECA (47)44 (0.42 mmol) and a catalytic
amount of triethylamine in THF (10 mL), and the mixture was
heated at 110 °C in a steel bomb for 24 h. After the mixture
was concentrated in vacuo, the residue was flash chromato-
graphed on a silica gel column eluting with CHCl3-MeOH (99:
1) to give the desired protected nucleosides 48-51.
1-Deoxy-1-[6-[[[(2-ph en yleth yl)am in o]car bon yl]am in o]-
9H-pu r in -9-yl]-N-eth yl-â-D-r ibofu r an u r on am ide (38): yield
82%; light brown solid, mp 166 °C (EtOH); IR (KBr) cm-1
3450-3000, 1725, 1610, 1560, 1210; 1H NMR (DMSO-d6) δ 1.04
(t, 3H, J ) 7), 2.84-2.95 (m, 2H), 3.01-3.23 (m, 2H), 4.15-
4.20 (m, 1H), 4.47 (s, 1H), 4.54-4.79 (m, 3H), 5.39-5.48 (m,
2H), 6.21 (d, 1H, J ) 1.8), 6.53 (t, 1H, J ) 6), 7.31-7.44 (m,
5H), 8.32 (s, 1H), 8.41 (s, 1H), 9.55 (bs, 1H), 11.18 (s, 1H). Anal.
(C21H25N7O5) C, H, N.
1-Deoxy-1-[6-[[[(3,4-d im eth oxy-2-p h en yleth yl)a m in o]-
ca r bon yl]a m in o]-9H-p u r in -9-yl]-N-eth yl-â-D-r ibofu r a n u -
r on a m id e (39): yield 68%; light brown solid, mp 120-122 °C
(EtOH); IR (KBr) cm-1 3540-3060, 1734, 1633, 1500, 1215;
1H NMR (DMSO-d6) δ 1.11 (t, 3H, J ) 7), 1.23 (t, 2H, J ) 8),
2.88-3.01 (m, 2H), 3.78 (s, 3H), 3.81 (s, 3H), 4.18-4.23 (m,
1H), 4.42 (s, 1H), 4.54-4.59 (m, 1H), 4.87-5.02 (bs, 2H), 5.47-
5.51 (m, 2H), 6.15 (d, 1H, J ) 1.8), 6.59 (t, 1H, J ) 2), 6.65 (s,
1H), 6.71 (s, 2H), 8.31 (s, 1H), 8.47 (s, 1H), 9.05 (s, 1H), 10.46
(bs, 1H). Anal. (C23H29N7O7) C, H, N.
2-Ch lor o-1-d eoxy-1-[6-[[[(3-ch lor op h en yl)a m in o]ca r -
bon yl]a m in o]-9H-p u r in -9-yl]-N-eth yl-2,3-O-(1-m eth yleth -
ylid en e)-â-D-r ibofu r a n u r on a m id e (48): yield 33%; white
solid, mp 98-100 °C dec (CH3CN-EtOH); IR (KBr) cm-1
3400-3050, 1685, 1650, 1520, 1235; 1H NMR (DMSO-d6) δ 0.66
(t, 3H, J ) 7.2 Hz), 1.37 (s, 3H), 1.56 (s, 3H), 2.74-2.92 (br m,
2H), 4.61 (s, 1H), 5.42 (s, 2H), 6.42 (s, 1H), 7.17 (d, 1H, J )
7.0 Hz), 7.32-7.42 (m, 2H),7.60-7.70 (m, 1H), 7.79 (s, 1H),
1-Deoxy-1-[6-[[[(fu r -2-yl-m eth yl)am in o]car bon yl]am in o]-
9H-pu r in -9-yl]-N-eth yl-â-D-r ibofu r an u r on am ide (40): yield
79%; brown solid mp 189-191 °C (EtOH); IR (KBr) cm-1
1
3500-3087, 1731, 1630, 1550, 1335, 1221; H NMR (DMSO-
d6) δ 1.06 (t, 3H, J ) 7), 2.94-3.05 (m, 2H), 4.20-4.24 (m,
1H), 4.38 (s, 1H), 4.56 (s, 2H, J ) 6), 4.61-4.67 (m, 1H),
4.96-5.04 (bs, 2H), 6.17 (d, 1H, J ) 1.8), 6.35-6.46 (m, 1H),
6.62 (s, 1H), 6.56 (t, 1H, J ) 6), 7.48 (d, 1H, J ) 2), 8.38 (s,
1H), 8.54 (s, 1H), 9.08 (s, 1H), 9.94 (bs, 1H). Anal. (C18H21N7O6)
C, H, N.
8.59 (s, 1H), 10.64 (s, 1H), 10.79 (s, 1H). Anal. (C22H23
Cl2N7O5) C, H, N.
-
2-Ch lor o-1-d eoxy-1-[6-[[[(4-m eth oxyp h en yl)a m in o]ca r -
bon yl]a m in o]-9H-p u r in -9-yl]-N-eth yl-2,3-O-(1-m eth yleth -
ylid en e)-â-D-r ibofu r a n u r on a m id e (49): yield 35%; vitreous
1-Deoxy-1-[6-[[[(4-(p yr id in -2-yl-a m in osu lfon yl)p h en -
yl)a m in o]ca r bon yl]a m in o]-9H-p u r in -9-yl]-N-eth yl-â-D-r i-
b ofu r a n u r on a m id e (41): yield 88%; brown solid mp
163 °C (EtOH); IR (KBr) cm-1 3500-3050, 1734, 1633, 1552,
1
solid; IR (KBr) cm-1 3450-3050, 1680, 1650, 1510, 1230; H
NMR (DMSO-d6) δ 0.67 (t, 3H, J ) 7.0 Hz), 1.38 (s, 3H), 1.56
(s, 3H), 2.76-2.94 (m, 2H), 3.76 (s, 3H), 4.61 (s, 1H), 5.42 (s,
2H), 6.41 (s, 1H), 6.93-7.03 (m, 2H), 7.41-7.53 (m, 2H), 7.65-
7.75 (m, 1H), 8.61 (s, 1H), 10.43 (s, 1H), 11.11 (s, 1H). Anal.
(C23H26ClN7O6) C, H, N.
1
1345, 1213; H NMR (DMSO-d6) δ 1.05 (t, 3H, J ) 7), 2.99-
3.18 (m, 2H), 4.23-4.26 (m, 1H), 4.42 (s, 1H), 4.54-4.62 (m,
1H), 4.91-5.15 (bs, 2H), 6.16 (d, 1H, J ) 1.8), 6.71 (t, 1H,
J ) 6), 7.18-7.31 (m, 1H), 7.57 (d, 2H, J ) 9), 7.63-7.71 (m,
3H), 7.95 (d, 2H, J ) 9), 8.37 (s, 1H), 8.78 (s, 1H), 9.05 (s,
1H), 10.15 (bs, 1H), 12.45 (bs, 1H). Anal. (C24H25N9O7S) C,
H, N.
2-Iodo-1-deoxy-1-[6-[[[(3-ch lor oph en yl)am in o]car bon yl]-
am in o]-9H-pu r in -9-yl]-N-eth yl-2,3-O-(1-m eth yleth yliden e)-
â-D-r ibofu r a n u r on a m id e (50): yield 62%; white solid, mp
127-130 °C (CH3CN-EtOH); IR (KBr) cm-1 3450-3050, 1690,
1
1650, 1520, 1240; H NMR (DMSO-d6) δ 0.66 (t, 3H, J ) 7.2
1-Deoxy-1-[6-[[[(4-(5-m eth yl-isoxa zol-3-yl-a m in osu lfo-
n yl)p h en yl)a m in o] ca r b on yl]a m in o]-9H -p u r in -9-yl]-N-
eth yl-â-D-r ibofu r a n u r on a m id e (42): yield 77%; pale yellow
solid mp 184 °C (EtOH); IR (KBr) cm-1 3550-3150, 1730, 1638,
Hz), 1.37 (s, 3H), 1.56 (s, 3H), 2.74-2.92 (br m, 2H), 4.61(s,
1H), 5.42 (s, 2H), 6.42 (s, 1H), 7.17 (d, 1H, J ) 7.0 Hz), 7.32-
7.42 (m, 2H), 7.56-7.66 (m, 1H), 7.79 (s, 1H), 8.50 (s, 1H),
10.64 (s, 1H), 11.33 (s, 1H). Anal. (C22H23ClIN7O5) C, H, N.
2-Iod o-1-d eoxy-1-[6-[[[(4-m eth oxyp h en yl)a m in o]ca r bo-
n yl]a m in o]-9H -p u r in -9-yl]-N-et h yl-2,3-O-(1-m et h ylet h -
ylid en e)-â-D-r ibofu r a n u r on a m id e (51): yield 70%; white
solid, mp 127-130 °C (CH3CN-EtOH); IR (KBr) cm-1 3450-
1
1550, 1350, 1210; H NMR (DMSO-d6) δ 1.08 (t, 3H, J ) 7),
2.30 (s, 3H), 3.17-3.20 (m, 2H), 4.22-4.23 (m, 1H), 4.36 (s,
1H), 4.40-4.95 (m, 3H), 6.11 (d, 1H, J ) 1.8), 6.15 (s, 1H),
6.68 (t, 1H, J ) 6), 7.37 (d, 2H, J ) 9), 7.84 (d, 2H, J ) 9),
8.42 (bs, 1H), 8.73 (s, 1H), 8.85 (s, 1H), 9.63 (bs, 1H), 11.37
(bs, 1H), 12.02 (s, 1H). Anal. (C23H25N9O8S) C, H, N.
1
3025, 1680, 1660, 1510, 1230; H NMR (DMSO-d6) δ 0.67 (t,
3H, J ) 7.0 Hz), 1.38 (s, 3H), 1.56 (s, 3H), 2.76-2.94 (m, 2H),
3.76 (s, 3H), 4.61 (s, 1H), 5.42 (s, 2H), 6.41 (s, 1H), 6.93-7.03
(m, 2H), 7.41-7.53 (m, 2H), 7.54-7.65 (m, 1H), 8.49 (s, 1H),
10.43 (s, 1H), 11.11 (s, 1H). Anal. (C23H26IN7O6) C, H, N.
Gen er a l P r oced u r e for th e Syn th esis of 2-Ch lor o- a n d
2-Iod o-1-d eoxy-1-[6-[[[(su bstitu ted )a m in o]ca r bon yl]a m i-
n o]-9H-p u r in -9-yl]-N-eth yl-â-D-r ibofu r a n u r on a m id e (52-
55). To a solution of 2′,3′-O-isopropylidene-2-chloro-6-ureas
(48-49) or 2′,3′-O-isopropylidene-2-iodo-6-ureas (50-51) (0.96
mmol) in dioxane (50 mL) was added 1 N HCl (50 mL), and
the mixture was heated at 65 °C for 1 h. After the mixture
was concentrated in vacuo, the residue was flash chromato-
graphed on a silica gel column eluting with CHCl3-MeOH (95:
5) to give the desired compounds 52-55.
Deoxy-1-[6-[[[(4-(p yr im id in -2-yl-a m in osu lfon yl)-p h en -
yl)a m in o] ca r bon yl]a m in o]-9H-p u r in -9-yl]-N-eth yl-â-D-
r ibofu r a n u r on a m id e (43): yield 80%; brown solid mp 184
°C (EtOH); IR (KBr) cm-1 3550-3100, 1720, 1630, 1555, 1355,
1200; 1H NMR (DMSO-d6) δ 1.08 (t, 3H, J ) 7), 3.17-3.23 (m,
2H), 4.22-4.25 (m, 1H), 4.37 (s, 1H), 4.64-4.70 (m, 1H), 4.90-
5.12 (bs, 2H), 6.11 (d, 1H, J ) 1.8), 6.60 (t, 1H, J ) 6), 7.03-
7.08 (m, 1H), 7.81 (d, 2H, J ) 9), 7.98 (d, 2H, J ) 9), 8.51 (d,
2H, J ) 6), 8.74 (s, 1H), 8.89 (s, 1H), 9.55 (bs, 1H), 11.19 (bs,
1H), 11.90 (s, 1H). Anal. (C23H24N10O7S) C, H, N.
1-Deoxy-1-[6,6-[[[bis-(4-n itr op h en yl)a m in o]ca r bon yl]-
a m i n o ]-9H -p u r i n -9-y l]-N -e t h y l-â-D -r i b o fu r a n u r o n -
a m id e (44): yield 52%; white solid, mp 213 °C (EtOH); IR
(KBr) cm-1 3500-3050, 1720, 1630, 1545, 1340, 1220; 1H NMR
(DMSO-d6) δ 1.07 (t, 3H, J ) 7), 3.12-3.23 (m, 2H), 4.21-
4.23 (m, 1H), 4.35 (d, 1H, J ) 2), 4.64-4.69 (m, 1H), 5.69 (bs,
2H), 6.09 (d, 1H, J ) 6.8), 7.68 (d, 2H, J ) 9), 7.91 (d, 2H, J
) 9), 8.18-8.29 (m, 4H), 8.83 (s, 1H), 9.69 (s, 1H), 10.68 (bs,
1H), 12.26 (bs, 1H). Anal. (C26H29N10O10) C, H, N.
2-C h lo r o -1-d e o x y -1-[6-[[[(3-c h lo r o p h e n y l)a m in o ]-
carbonyl]amino]-9H-purin-9-yl]-N-ethyl-â-D-ribofuranuron-
a m id e (52): yield 66%; white solid, mp 150-153 °C dec
(EtOH); IR (KBr) cm-1 3500-3000, 1690, 1640, 1530, 1240;
1H NMR (DMSO-d6) δ 1.07 (t, 3H, J ) 7.2 Hz), 3.13-3.31 (m,
2H), 4.25 (s, 1H,), 4.38 (d,1H, J ) 2.1 Hz), 4.67 (pq, 1H), 6.05

Derivatives of Adenosine-5′-N-ethyluronamide
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 17 3183
(d, 1H, J ) 6.7 Hz), 7.17 (d, 1H, J ) 5.2 Hz), 7.35-7.44 (m,
2H), 8.82 (s, 1H), 8.26-8.33 (m, 1H), 8.87 (s, 1H), 10.80 (s,
1H), 11.33 (s, 1H). Anal. (C19H19Cl2N7O5) C, H, N.
2-(1-H exyn -1-yl)-1-d eoxy-1-[6-[[[(4-m et h oxyp h en yl)-
a m in o]ca r bon yl]a m in o]-9H-p u r in -9-yl]-N-eth yl-â-D-r ibo-
fu r a n u r on a m id e (59): chromatography solvent, CHCl3-
C6H6-MeOH (81:10:9); yield 71%; white solid, mp 175-178
°C dec (EtOH); IR (KBr) cm-1 3500-3000, 2240, 1660, 1600,
2-Ch lor o-1-d eoxy-1-[6-[[[(4-m et h oxyp h en yl)a m in o]-
carbonyl]amino]-9H-purin-9-yl]-N-ethyl-â-D-ribofuranuron-
a m id e (53): yield 67%; white solid, mp 158-160 °C dec
(EtOH); IR (KBr) cm-1 3400-3050, 1680, 1660, 1520, 1240;
1H NMR (DMSO-d6) δ 1.02-1.14 (m, 3H), 3.12-3.30 (m, 2H),
3.75 (s, 3H), 4.20-4.30 (m, 1H), 4.37 (s,1H), 4.61-4.72 (m, 1H),
6.04 (d, 1H, J ) 6.8 Hz), 6.97 (d, 2H, J ) 8.9 Hz), 7.47 (d, 2H,
J ) 8.9 Hz), 8.22-8.35 (m, 1H), 8.85 (s, 1H), 10.51 (s, 1H),
10.62 (s, 1H). Anal. (C20H22ClN7O6) C, H, N.
1
1520, 1240; H NMR (DMSO-d6) δ 0.91-1.02 (m, 3H), 1.04-
1.17 (m, 3H), 1.43-1.70 (m, 4H), 2.50-2.61 (m, 2H), 3.18-
3.32 (m, 2H), 3.77 (s, 3H), 4.18-4.28 (m, 1H), 4.37 (d, 1H, J )
1.7 Hz), 4.66 (pq, 1H), 6.07 (d, 1H, J ) 7.3 Hz), 6.96 (d, 2H,
J ) 8.9 Hz), 7.48 (d, 2H, J ) 9.1 Hz), 8.40-8.51 (m, 1H),
8.82 (s, 1H), 10.31 (s, 1H), 11.49 (s, 1H). Anal. (C26H31N7O6)
C, H, N.
2-Iodo-1-deoxy-1-[6-[[[(3-ch lor oph en yl)am in o]car bon yl]-
a m in o]-9H-p u r in -9-yl]-N-eth yl-â-D-r ibofu r a n u r on a m id e
(54): yield 85%; white solid, mp 202-204 °C dec (EtOH); IR
(KBr) cm-1 3500-3000, 1700, 1640, 1530, 1240; 1H NMR
(DMSO-d6) δ 1.07 (t, 3H, J ) 7.2 Hz), 3.13-3.31 (m, 2H), 4.25
(s, 1H), 4.38 (d, 1H, J ) 2.1 Hz), 4.67 (pq, 1H), 6.05 (d, 1H, J
) 6.7 Hz), 7.17 (d, 1H, J ) 5.2 Hz), 7.35-7.44 (m, 2H), 8.82 (s,
1H), 8.13-8.23 (m, 1H), 8.79 (s, 1H), 10.66 (s, 1H), 11.33 (s,
1H). Anal. (C19H19ClIN7O5) C, H, N.
2-Iodo-1-deoxy-1-[6-[[[(4-methoxyphenyl)amino]carbonyl]-
a m i n o ]-9H -p u r i n -9-y l]-N -e t h y l-â-D -r i b o fu r a n u r o n -
a m id e (55): yield 89%; white solid, mp 214-218 °C dec
(EtOH); IR (KBr) cm-1 3375-3050, 1680, 1650, 1510, 1240;
1H NMR (DMSO-d6) δ 1.01-1.12 (m, 3H), 3.12-3.32 (m, 2H),
3.76 (s, 3H), 4.20-4.28 (m, 1H), 4.36 (s,1H), 4.60-4.73 (m, 1H),
6.04 (d, 1H, J ) 6.6 Hz), 6.93-7.04 (m, 2H), 7.44-7.56 (m,
2H), 8.11-8.21 (m, 1H), 8.76 (s, 1H), 10.45 (s, 1H), 11.09 (s,
1H). Anal. (C20H22IN7O6) C, H, N.
Gen er a l P r oced u r e for th e Syn th esis of 2-(Ar )a lk yn yl-
1-d eoxy-1-[6-[[[(su bstitu ted )a m in o]ca r bon yl]a m in o]-9H-
p u r in -9-yl]-N-eth yl-â-D-r ibofu r a n u r on a m id e (56-62). Cu-
prous iodide (0.12 mg), bis(triphenylphosphine)palladium
dichloride (1.7 mg) and the appropriate terminal alkyne (0.6
mmol) were added to a solution of 2-iodo-6-ureas (54 or 55)
(0.12 mmol) in a mixture of dry acetonitrile (4 mL), DMF (4
mL), and triethylamine (0.3 mL), and the mixture was stirred
at room temperature for 16 h in an atmosphere of N2. The
solvent was removed under vacuum, and the residue was
chromatographed on silica gel column, eluting with a suitable
mixture of solvents (see below) to give the desired alkynyl
derivatives 56-62.
2-(1-Hexyn -1-yl)-1-deoxy-1-[6-[[[(3-ch lor oph en yl)am in o]-
ca r b on yl]a m in o]-9H -p u r in -9-yl]-N -e t h yl-â-D -r ib ofu r -
a n u r on a m id e (56): chromatography solvent, CHCl3-MeOH
(92:8); yield 75%; white solid, mp 196-198 °C dec (EtOH); IR
(KBr) cm-1 3500-3150, 2235, 1680, 1660, 1545, 1260; 1H NMR
(DMSO-d6) δ 0.91-1.0 (m, 3H), 1.02-1.13 (m, 3H), 1.40-1.71
(m, 4H), 2.52-2.60 (m, 2H), 3.19-3.34 (m, 2H), 4.18-4.26 (m,
1H), 4.37 (d, 1H, J ) 2.2 Hz), 4.60-4.70 (m, 1H), 6.07 (d, 1H,
J ) 7.1 Hz), 7.11-7.22 (m, 1H), 7.41 (d, 2H, J ) 5.1 Hz), 7.74
(s, 1H), 8.40-8.50 (m, 1H), 8.84 (s, 1H), 10.56 (s, 1H), 11.80
(s, 1H). Anal. (C25H28ClN7O5) C, H, N.
2-(P h en yleth yn yl)-1-d eoxy-1-[6-[[[(4-m eth oxyp h en yl)-
a m in o]ca r bon yl]a m in o]-9H-p u r in -9-yl]-N-eth yl-â-D-r ibo-
fu r a n u r on a m id e (60): chromatography solvent, CHCl3-
C6H6-MeOH (80:10:10); yield 60%; white solid, mp 204-206
°C dec (EtOH); IR (KBr) cm-1 3400-3050, 2205, 1675, 1660,
1
1510, 1240; H NMR (DMSO-d6) δ 0.98-1.14 (m, 3H), 3.15-
3.34 (m, 2H), 3.77 (s, 3H), 4.20-4.30 (m, 1H), 4.39 (s, 1H),
4.65-4.75 (m, 1H), 6.12 (d, 1H, J ) 6.9 Hz), 6.99 (d, 2H, J )
8.8 Hz), 7.44-7.62 (m, 5H), 7.64-7.78 (m, 2H), 8.34-8.47 (m,
1H), 8.90 (s, 1H), 10.36 (s, 1H), 11.29 (s, 1H). Anal.
(C28H27N7O6) C, H, N.
2-(3-Hydr oxy-3-ph en yl-1-pr opyn -1-yl)-1-deoxy-1-[6-[[[(4-
m eth oxyp h en yl)a m in o]ca r bon yl]a m in o]-9H-p u r in -9-yl]-
N-eth yl-â-D-r ibofu r a n u r on a m id e (61): chromatography sol-
vent, CHCl3-C6H6-MeOH (80:10:10); yield 40%; yellow solid,
mp 218-220 °C dec (EtOH); IR (NaCl) cm-1 3450-3050, 2300,
1
1680, 1650, 1510, 1240; H NMR (DMSO-d6) δ 0.90-1.10 (m,
3H), 3.13-3.23 (m, 2H), 3.77 (s, 3H), 4.30-4.46 (m, 2H), 4.76-
4.89 (m, 1H), 6.19 (d, 1H, J ) 6.7 Hz), 6.88-7.02 (m, 2H),
7.43-7.83 (m, 5H), 8.03-8.30 (m, 4H), 8.92 (s, 1H), 10.30 (s,
1H), 11.32 (s, 1H). Anal. (C29H29N7O7) C, H, N.
2-(5-P h en yl-1-p en tyn -1-yl)-1-d eoxy-1-[6-[[[(4-m eth oxy-
p h en yl)a m in o] ca r bon yl]a m in o]-9H-p u r in -9-yl]-N-eth yl-
â-D-r ib ofu r a n u r on a m id e (62): chromatography solvent,
CHCl3-MeOH (94:6); yield 77%; white solid, mp 210-212 °C
dec (EtOH); IR (NaCl) cm-1 3450-3050, 2240, 1680, 1660,
1
1510, 1240; H NMR (DMSO-d6) δ 1.02-1.16 (m, 3H), 1.86-
2.04 (m, 2H), 2.49-2.64 (m, 2H), 2.73-2.88 (m, 2H), 3.16-
3.32 (m, 2H), 3.71 (s, 3H), 4.18-4.29 (m, 1H), 4.37 (s, 1H), 4.66
(pq, 1H), 6.07 (d, 1H, J ) 7.0 Hz), 6.84 (d, 2H, J ) 8.1 Hz),
7.17-7.38 (m, 5H), 7.41-7.54 (m, 2H), 8.39-8.52 (m, 1H),
8.83 (s, 1H), 10.32 (s, 1H), 11.50 (s, 1H). Anal. (C31H33N7O6)
C, H, N.
Meth od s for Recep tor Bin d in g Assa ys. Procedures for
preparation of rat brain membranes and CHO cell membranes
were reported previously.30,38,55 For binding experiments,
membrane homogenates were frozen and stored at -20 °C for
e2 months. Adenosine deaminase (ADA) was from Boehringer
Mannheim (Indianapolis, IN). [3H]R-PIA was from Amersham
(Arlington Heights, IL), and [3H]CGS 21680 was from DuPont
NEN (Boston, MA).
[
125I]-AB-MECA was prepared as de-
scribed by Olah et al.30
2-(P h en ylet h yn yl)-1-d eoxy-1-[6-[[[(3-ch lor op h en yl)-
a m in o ]c a r b o n y l]a m in o ]-9H -p u r in -9-y l]-N -e t h y l-â-D -
r ibofu r a n u r on a m id e (57): chromatography solvent, CHCl3-
MeOH (92:8); yield 59%; white solid, mp 210-214 °C dec
(EtOH); IR (KBr) cm-1 3450-3050, 2210, 1680, 1670, 1550,
1270; 1H NMR (DMSO-d6) δ 1.02-1.13 (m, 3H), 3.17-3.34 (m,
2H), 4.20-4.29 (m, 1H), 4.39 (s, 1H), 4.63-4.74 (m, 1H), 6.13
(d, 1H, J ) 7.0 Hz), 7.17 (d, 1H, J ) 7.2 Hz), 7.36-7.59 (m,
5H), 7.69-7.79 (m, 3H), 8.35-8.44 (m, 1H), 8.92 (s, 1H), 10.61
(s, 1H), 11.65 (s, 1H). Anal. (C27H24ClN7O5) C, H, N.
2-(3-Hydr oxy-3-ph en yl-1-pr opyn -1-yl)-1-deoxy-1-[6-[[[(3-
ch lor op h en yl)a m in o]ca r bon yl]a m in o]-9H-p u r in -9-yl]-N-
eth yl-â-D-r ibofu r a n u r on a m id e (58): chromatography sol-
vent, CHCl3-cC6H12-CH3CN-MeOH (73:10:5:12); yield 43%;
yellow solid, mp 214-216 °C dec (EtOH); IR (KBr) cm-1 3450-
3050, 2325, 1700, 1640, 1540, 1250; 1H NMR (DMSO-d6) δ
0.96-1.14 (m, 3H), 3.04-3.30 (m, 2H), 4.30-4.45 (m, 2H),
4.78-4.90 (m, 1H), 6.19 (d, 1H, J ) 6.6 Hz), 7.12-8.34 (m,
Binding of [125I]-AB-MECA to CHO cells stably transfected
with the rat A3 receptor clone or to HEK-293 cells stably
expressing the human A3 receptor was performed essentially
as described.28,30,38,55 Assays were performed in 50 mM Tris/
10 mM MgCl2/1 mM EDTA buffer (adjusted to pH 8.26 at 5
°C) in glass tubes containing 100 µL of the membrane
suspension, 50 µL of [125I]-AB-MECA (final concentration 0.3
nM), and 50 µL of inhibitor. Inhibitors were routinely dis-
solved in DMSO. Concentrations of DMSO in incubations
never exceeded 1%, at which concentration [125I]-AB-MECA
binding was not affected. Incubations were carried out in
duplicate for 1 h at 37 °C and were terminated by rapid
filtration over Whatman GF/B filters, using a Brandell cell
harvester (Brandell, Gaithersburg, MD). Tubes were washed
three times with 3 mL of buffer. Radioactivity was determined
in a Beckman gamma 5500B γ-counter. Nonspecific binding
was determined in the presence of 200 µM NECA. Ki values
were calculated according to Cheng-Prusoff56 assuming a Kd
for [125I]-AB-MECA of 1.48 nM.
11H), 8.94 (s, 1H), 10.51 (s, 1H), 11.47 (s, 1H). Anal. (C28H26
ClN7O6) C, H, N.
-

3184 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 17
Baraldi et al.
Binding of [3H]R-PIA to A1 receptors from rat cortical
membranes and of [3H]CGS 21680 to A2A receptors from rat
striatal membranes was performed as described previously.57
Adenosine deaminase (2 units/mL) was present during the
preparation of brain membranes. Additional deaminase was
not added during incubation with the radioligand.
(9) Abbracchio, M. P.; Brambilla, R.; Ceruti, S.; Kim, H. O.; von
Lubitz, D. K. J . E.; J acobson, K. A.; Cattabeni, F. G-protein-
dependent activation of phospholipase C by adenosine A3 recep-
tors in rat brain. Mol. Pharmacol. 1995, 48, 1038-1045.
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in brain membranes: binding of N-cyclohexyl[3H] adenosine and
1,3-diethyl-8[3H] phenylxanthine. Proc. Natl. Acad. Sci. U.S.A.
1980, 77, 5547-5551. (b) J acobson, K. A.; van Rhee, A. M.
Development of selective purinoceptor agonists and antagonists.
In Purinergic Approaches Experimental Therapy; J acobson, K.
A., J arvis, M. F., Eds; Wiley-Liss Publisher: New York, 1997;
pp 101-128.
(11) Olsson, R. A.; Kusachi, S.; Thompson, S. D.; Ukena, D.; Padgett,
W.; Daly, J . W. N6-substituted N-alkyladenosine-5′-urona-
mides: bifunctional ligands having recognition groups for A1 and
A2 adenosine receptors. J . Med. Chem. 1986, 29, 1683-1689.
(12) J acobson, K. A.; Nikodijevic, O.; J i, X. D.; Berkich, D. A.; Eveleth,
D.; Dean, R. L.; Hiramatsu, K.; Kassel, N. F.; van Galen, P. J .
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Bin d in g of [35S]GTP -γ-S. The binding of [35S]GTP-γ-S
(Amersham, Chicago, IL, specific activity 1275 Ci/mmol) was
carried out using rat RBL-2H3 mast cell membranes by the
general method of Lorenzen et al.58 Membranes (approxi-
mately 5 µg) were suspended in a buffer containing 50 mM
Tris (pH 7.4), 3 units/mL adenosine deaminase, 1 mM EDTA,
1 mM DTT, 10 µM GDP, 100 mM NaCl, and 10 mM MgCl2.
[35S]GTP-γ-S was added to a final concentration of 0.1 nM in
a total volume of 125 µL, and the mixture was incubated for
2 h at 30 °C. Nonspecific binding was determined in the
presence of 10 µM GTP-γ-S (Sigma, St. Louis, MO). Incubation
of the reaction mixture was terminated by filtration over GF/B
glass filter using a Brandell cell harvester and washed twice
with the same buffer.
Abbreviations: [125I]AB-MECA, [125I]1-[6-[[(4-amino-3-iodo-
phenyl)methyl]amino]-9H-purin-9-yl]-1-deoxy-N-methyl-â-D-ribo-
furanuronamide; HENECA that 2-(1-hexyn-1-yl)-1-(6-amino-
9H-purin-9-yl)-1-deoxy-N-ethyl-â-D-ribofuranuronamide; CHO
cells, Chinese hamster ovary cells; CGS 21680, 2-[4-[(2-car-
boxyethyl)phenyl]ethyl-amino]1-(6-amino-9H-purin-9-yl)-1-deoxy-
N-ethyl-â-D-ribofuranuronamide; Cl-IB-MECA, 2-Chloro-1-[6-
[[(3-iodophenyl)methyl]amino]-9H-purin-9-yl]-1-deoxy-N-meth-
yl-â-D-ribofuranuronamide; R-PIA, 1-[6-[[(phenylisopropyl]ami-
no]-9H-purin-9-yl]-1-deoxy-â-D-ribofuranose; DMSO, dimeth-
ysulfoxide; EDTA, ethylenediaminotetraacetate, I-AB-MECA,
1-[6-[[(4-amino-3-iodophenyl)methyl]amino]-9H-purin-9-yl]-
1-deoxy-N-methyl-â-D-ribofuranuronamide; IB-MECA, 1-[6-
[[(3-iodophenyl)methyl]amino]-9H-purin-9-yl]-1-deoxy-N-meth-
yl-â-D-ribofuranuronamide; Ki, equilibrium inhibition constant;
NECA, 1-(6-amino-9H-purin-9-yl)-1-deoxy-N-ethyl-â-D-ribo-
furanuronamide; PHPNECA, 2-(3-hydroxy-3-phenyl-1-propyn-
1-yl)-1-(6-amino-9H-purin-9-yl)-1-deoxy-N-ethyl-â-D-ribofur-
anuronamide; THF, tetrahydrofuran; Tris, tris(hydroxy-
methyl)aminomethane.
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[
125I]-labelled 8-phenylxanthine derivatives: antagonist radio-
ligands for adenosine A1 receptors. J . Med. Chem. 1988, 31, 745-
751.
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Padgett, W.; Pfleiderer, W.; Kirk, K. L.; Neumeyer, J . L.; Daly,
J . W. 8-substituted xanthines as antagonists at A1 and A2
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5′-N-ethyluronamide as selective agonists at A2 adenosine recep-
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Pharmacol. Exp. Ther. 1989, 251, 888-893.
(18) Shimada, J .; Suzuki, K.; Nonaka, H.; Ishii, A.; Ichikawa, S. (E)-
1,3-dialkyl-7-methyl-8-(3,4,5-trimethoxystyryl)xanthines: potent
and selective adenosine A2 antagonists. J . Med. Chem. 1992, 35,
2342-2345.
(19) (a) J acobson, K. A.; Gallo-Rodriguez, C.; Melman, N.; Fischer,
B.; Maillard, M.; van Bergen, A.; van Galen, P. J . M.; Karton,
Y. Structure-activity relationship of 8-styrylxanthines as A2-
selective adenosine antagonists. J . Med. Chem. 1993, 36, 1333-
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L.; Zocchi, C.; Dionisotti, S.; Ongini, E. Synthesis and activity
of new pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c] pyrimidine and 1,2,3-
triazolo[4,5-e]1,2,4-triazolo[1,5-c]pyrimidine displaying potent
and selective activity as A2A adenosine receptor antagonist.
Bioorg. Med. Chem. Lett. 1994, 4, 2539-2544. (c) Baraldi, P. G.;
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Ack n ow led gm en t. This work was partially sup-
ported by Consiglio Nazionale delle Ricerche (CNR),
Ministero della Ricerca Scientifica e Tecnologica
(MURST, grant 40 and 60%).
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