Solid phase synthesis and antiprotozoal evaluation of di- and trisubstituted 5′-carboxamidoadenosine analogues

Article abstract of DOI:10.1016/j.bmc.2005.10.011

The rapid increase of resistance to drugs commonly used in the treatment of tropical diseases such as malaria and African sleeping sickness calls for the prompt development of new safe and efficacious drugs. The pathogenic protozoan parasites lack the cap

Full text of DOI:10.1016/j.bmc.2005.10.011

Bioorganic & Medicinal Chemistry 14 (2006) 1618–1629
Solid phase synthesis and antiprotozoal evaluation of
di- and trisubstituted 50-carboxamidoadenosine analogues
Boris Rodenko,a Remko J. Detz,a Victorine A. Pinas,a Catia Lambertucci,b Reto Brun,c
Martin J. Wannera and Gerrit-Jan Koomena,*
aVan ’t Hoff Institute for Molecular Sciences, Universiteit van Amsterdam, Nieuwe Achtergracht 129,
NL-1018 WS Amsterdam, The Netherlands
b
`
Dipartimento di Scienze Chimiche, Universita di Camerino, 62032 Camerino, Italy
cParasite Chemotherapy, Swiss Tropical Institute, Socinstrasse 57, CH-4002 Basel, Switzerland
Received 1 August 2005; revised 4 October 2005; accepted 6 October 2005
Available online 24 October 2005
Abstract—The rapid increase of resistance to drugs commonly used in the treatment of tropical diseases such as malaria and African
sleeping sickness calls for the prompt development of new safe and efficacious drugs. The pathogenic protozoan parasites lack the
capability of synthesising purines de novo and they take up preformed purines from their host through various transmembrane
transporters. Adenosine derivatives constitute a class of potential therapeutics due to their selective internalisation by these trans-
porters. Automated solid-phase synthesis can speed up the process of lead finding and we pursued the solid-phase synthesis of di-
and trisubstituted 50-carboxamidoadenosine derivatives by using a safety-catch approach. While efforts with KennerÕs sulfonamide
linker remained fruitless, successful application of the hydrazide safety-catch linker allowed the construction of two representative
combinatorial libraries. Their antiprotozoal evaluation identified two compounds with promising activity: N6-benzyl-50-N-phenyl-
carboxamidoadenosine with an IC50 value of 0.91 lM against Trypanosoma brucei rhodesiense and N6-diphenylethyl-50-phenylcarb-
oxamidoadenosine with an IC50 value of 1.8 lM against chloroquine resistant Plasmodium falciparum.
ꢀ 2005 Elsevier Ltd. All rights reserved.
1. Introduction
Plasmodium falciparum, the causative agent of the most
severe form of malaria in humans, is responsible for 1.5
million deaths per year, of which more than one million
occur in children under 5 years of age.4 Although che-
motherapy and prophylaxis are available, the rapidly
growing resistance against classical (and inexpensive)
drugs such as chloroquine and sulfadoxine–pyrimeth-
amine articulates the acute need for new efficacious
drugs.5
WHO estimates that tropical diseases such as malaria
and Human African Trypanosomiasis (HAT) are a daily
threat to more than 2 billion people.1 HAT or sleeping
sickness, which kills more than 50,000 people each year,
is caused by Trypanosoma brucei species.2 T. b. gamb-
iense is responsible for the chronic form of the disease,
taking months or even years to progress from the early
stage into the meningoencephalitic stage. T. b. rhodes-
iense causes the acute form of the disease, requiring just
a few weeks to reach this second stage. If left untreated,
late stage trypanosomiasis is fatal. Increasing resistance
to the common drugs3 and their cumbersome parenteral
administration combined with severe side effects highly
demand the development of new safer and more effective
drugs.
Protozoan parasites lack the capability of synthesising
purines de novo and therefore are solely dependent on
their host for purine uptake.6 Each genus of protozoan
parasite has a distinct and unique complement of purine
transporters and salvage enzymes that enable the para-
site to scavenge preformed purines from the host.7
Adenosine derivatives constitute a class of potential
therapeutics in the treatment of African trypanosomia-
sis8,9 and malaria 10 due to their selective internalisation.
Keywords: Solid phase synthesis; Safety-catch principle; Nucleosides;
Antiprotozoal activity.
Recently, we reported on a library of adenosine analogues
for the first time entirely prepared on a solid phase.11
The solid-phase sequence leading to 2,N6-disubstituted
*
Corresponding author. Tel.: +31 20 525 6933; fax: +31 20 525
5670; e-mail: gjk@science.uva.nl
0968-0896/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2005.10.011

B. Rodenko et al. / Bioorg. Med. Chem. 14 (2006) 1618–1629
1619
adenosine analogues involved anchoring of the nucleo-
Cl
Cl
N
side to the solid support by its riboside 50-hydroxyl func-
tionality, while subsequently diversity elements were
introduced on the purine skeleton. Antiprotozoal
screening of this library revealed adenosine analogues
with promising antitrypanosomal and antiplasmodial
activities.12 In our ongoing efforts to design solid-phase
mononucleoside syntheses allowing for the automated
preparation of these molecules, it was our desire to ex-
pand our methodology to the modification of the ribosyl
moiety. In the field of antiprotozoal research, 50-modi-
fied adenosine analogues are known as growth inhibi-
tors of multidrug resistant P. falciparum,13 inhibitors
of trypanosomal glycolytic enzymes14 and inhibitors
of enzymes involved in trypanosomal polyamine
synthesis.15
N
N
N
N
N
N
O
N
a
O
O
HO
HO
O
O
O
O
1
2
Scheme 2. Reagents: (a) TEMPO, iodobenzene diacetate, CH3CN,
H2O, 92%.
O O
S
Cl
N
NH2
H
N
N
N
N
O
2. Results and discussion
2.1. Chemistry
O
3
O
O
2
O
S
or
O
N
a
H
O
Our objective consisted of generating 50-carboxamidoad-
enosine analogues in a divergent way, thus allowing for
the introduction of pharmacophores not only on the pur-
ine 2 and N6 positions, as described previously,11 but also
on the ribosyl 50-position. Consequently, a procedure had
to be devised that granted both the attachment of the
nucleoside scaffold to a solid support and the introduction
of diversity elements on the three different positions. The
proposed strategy involving the safety catch principle16 is
outlined in Scheme 1. Suitably protected 6-chloropurine
riboside 50-carboxylic acid is coupled to the solid phase
via a dormant linker. Modifications can be realised on
the purine skeleton, while the linker remains intact. When
the ribosyl-protective groups (PGs) are removed and the
nucleoside is ready for cleavage, the linker is Ôswitched
on.Õ This sets the stage for combined cleavage and intro-
duction of the final diversity element, leading to the aimed
nucleoside carboxamide analogues. In this way, the 50-po-
sition serves both as the anchor to the solid support and
the reactive functionality in the final diversification/cleav-
age step.
O
O O
S
N
H
NH2
5
4
Scheme 3. Coupling attempts to KennerÕs linker. (a) For coupling
methods see Table 1.
2.1.1. Solid phase syntheses with KennerÕs sulfonamide
linker. Initial synthetic efforts towards substituted 50-
carboxamidoadenosine derivatives addressed the cou-
pling of 6-chloropurine riboside-50-carboxylic acid 2 to
KennerÕs sulfonamide linker,16 which has been success-
fully applied in peptide chemistry, solid-phase organic
synthesis and polymer-assisted solution phase synthe-
sis.19 KennerÕs benzenesulfonamide linker 3 (Scheme 3)
was selected for its complete stability towards strongly
basic/nucleophilic20 and strongly acidic conditions.16
At any desired point in the sequence the linker can be
activated towards nucleophilic release by alkylation of
the acylsulfonamide NH with diazomethane16 or iodo-
acetonitrile.21 Although it was noted that loading effi-
ciencies with KennerÕs original benzenesulfonamide
linker 3 were poor, especially with sterically demanding
carboxylic acids,21 this linker was at first preferred over
EllmanÕs alkanesulfonamide linker 4. The reactivity of
the NH2 in sulfonamide linkers has been compared to
To obtain the 50-carboxylic acid nucleoside precursor,
we applied the mild TEMPO–iodobenzene diacetate oxi-
dising system, reported for the 50-oxidation of common
20,30-protected nucleosides,17 to 20,30-isopropylidene-
protected 6-chloropurine riboside 1,18 which afforded
50-carboxylic acid 2 in excellent yield (Scheme 2).
Cl
6
NHR1
NHR1
N
N
N
N
N
N
N
N
1. modifications
on solid support
2
N
R2HN
'on'
N
O
R2HN
R3HN
N
O
N
O
5'
O
O
2. linker activation
O
'off'
OPG
OH
OH
linker
OPG
OH
OH
R3 NH2
Scheme 1. Proposed strategy involving the safety-catch principle.

1620
B. Rodenko et al. / Bioorg. Med. Chem. 14 (2006) 1618–1629
Table 1. Coupling methods used for loading KennerÕs linkera
Entry
Method
Base
Solvent
Result
1
2
3
4
5
6
Acid 2 (5 equiv), DIC (5 equiv), 1-MeImb (5 equiv)
Acid 2 (3 equiv), DIC (3 equiv), DMAP (0.4 equiv)
Acid 2 (3 equiv), CIP (3 equiv)
CH2Cl2
CH2Cl2
CH2Cl2
DMF
—
—
DIPEA (6 equiv)
DIPEA (6 equiv)
Pyridine (4 equiv)
DIPEA (5 equiv)
2–5%
—
—
Acid 2 (3 equiv), PyBOP (3 equiv)
Acid 2 (3 equiv), DBCc (3 equiv)
Symm. anhydride of 2 (5 equiv), DMAP (1 equiv)
DMF
CH2Cl2
2–5%
a Typical coupling times were 20–24 h.
b 1-MeIm = 1-methylimidazole, see Ref. 23.
c DBC = 2,6-dichlorobenzoylchloride.
that of an alcohol.21 Therefore, typical esterification re-
agents are to be used in the coupling procedure. How
ever, attachment of nucleoside 50-carboxylic acid 2 to
KennerÕs linker 3 offered significant problems (Scheme
3). The success of attachment to the resin can be as-
sessed by the appearance of a strong carbonyl vibration
at approximately 1735 cmꢀ1 in the infrared spectrum of
the immobilised nucleoside 50-carboxylic acid derivative.
Many coupling procedures were employed, most of
them known from the attachment of amino acid residues
to the Kenner linker (Table 1). However, loading of
the resin, though quite insufficient, was only inferred
from experiments with the symmetrical anhydride
method or with 2-chloro-1,3-dimethylimidazolidinium
hexafluorophosphate (CIP), a coupling reagent known
to be particularly effective for sterically demanding
couplings.22 Model experiments in solution (DIC–
DMAP, EDC–DMAP and pentafluorophenylester) with
carboxylic acid 2 and linker analogue N-benzoyl-4-sul-
famoylbenzamide, also failed to produce the corre-
sponding acylsulfonamide.
The poor results on solid phase and even in solution
were partly ascribed to the moderate nucleophilicity of
the benzenesulfonamide linker. Therefore, attachment
of carboxylic acid 2 to EllmanÕs modified alkanesulfona-
mide linker 4 was attempted, a linker especially designed
for enhanced nucleophilicity.21 Concisely, all efforts
using the coupling methods mentioned before gave a
comparably poor outcome. From these results, we con-
cluded that steric hindrance combined with the moder-
ate nucleophilicity of the Kenner–Ellman linkers
frustrated immobilisation of the nucleoside 50-carboxyl-
ic acid and the sulfonamide strategy was suspended.
Remarkably, several months after we abandoned this
approach, a study appeared in the literature concerning
the coupling in solution of N6-benzoyl-20,30-isopropylid-
ene adenosine 50-carboxylic acid to various sulfona-
mides.24 Among the range of methods explored the
best results were reported with 1.1 equiv of DCC/
DMAP and 2 equiv of sulfonamide. Nevertheless, cou-
pling required stirring in dichloromethane for four days,
NHR1
Cl
N
N
N
N
O
N
O
N
N
N
O
c
b
O
O
H
H
N
NHR
N
N
N N
H
H
H
O
OR
NH
O
RO
6 R = Fmoc
7 R = H
8
9
R = >C(CH3)2
a
d
10 R = H
NHR1
NHR1
N
N
N
O
N
O
N
N
N
N
e
R2 NH2
O
O
N N
R2HN
OH
OH
HO
HO
11
12
Scheme 4. Reagents and conditions: (a) 20% piperidine in DMF; (b) 2, DIC, DMF; (c) R1-NH2, NMP, 50 ꢁC; (d) TFA–HO(CH2)2OH–CH2Cl2;
(e) 0.5 equiv Cu(OAc)2, R2-NH2, THF.

B. Rodenko et al. / Bioorg. Med. Chem. 14 (2006) 1618–1629
1621
Table 2. Yield and purity of disubstituted 50-carboxamidoadenosine
analoguesa
indicating the sluggishness of the reaction, which makes
it unsuitable for solid-phase applications.
A
B
CH3
F
2.1.2. Safety-catch approach with the arylhydrazide linker.
In the arylhydrazide safety catch linker,25 we found a
good alternative. Compared with the sulfonamide NH2
in KennerÕs linker, the hydrazine moiety is sterically much
less demanding and has superior nucleophilic properties.
The arylhydrazide linker was originally introduced in
1970 by Wieland et al. for the solid-phase synthesis of pep-
tides.26 The safety-catch concept relies on the fact that the
linker is acid and base stable and can be activated under
oxidative conditions to generate the reactive acyldiazene.
Subsequent attack by a nucleophile present releases nitro-
gen gas and produces carboxylic acids, esters or amides,
when water, alcohols or amines are used as nucleophiles.
Recent applications of this linker involve the synthesis of
(cyclic)27 peptides.28,29
NHR1
CH3CH2
I
N
N
N
C
D
N
O
O
G
H
R2HN
OH
Ph
Ph
HO
E
Compound
R1
R2
Yield (%)
Purity (%)
12a
12b
12c
12d
12e
12f
12g
12h
12i
C
C
C
C
E
A
B
43
37
28
32
50
46
45
30
54
44
50
34
54
50
36
42
31
32
25
19
>99
97
C
D
A
B
>99
99
The solid-phase synthesis of N50,N6-disubstituted 50-
carboxamidoadenosine analogues using the arylhydraz-
ide safety catch linker is depicted in Scheme 4. Follow-
ing removal of the Fmoc group from commercially
available 4-Fmoc-hydrazinobenzoyl AM resin 6 with
20% piperidine in DMF, 50-carboxylic acid 2 was cou-
pled to hydrazine resin 7 by using DIC as a coupling re-
agent to render hydrazide 8. Literature methods for the
acylation of resin 7 involve a diimide in combination
with an additive such as 1-hydroxybenzotriazole,
HOBt.27–29 In our system, we observed that HOBt dis-
places the chloroatom in the purine ring.30 Although
omission of this additive required a longer coupling peri-
od, effective loading of the resin was achieved as indicat-
ed by a bromophenol blue colour test.31 Introduction of
an amino substituent on the purine 6-position was effect-
ed in NMP at 50 ꢁC affording purine 9. Removal of the
20,30-isopropylidene group via transketalisation with a
cocktail of TFA, ethylene glycol and dichloromethane
(5:1:5) yielded resin-bound 10, which was now ready
for cleavage from the resin. The hydrazide linkage was
oxidised to acyldiazene 11 by the method of Lowe and
co-workers using 0.5 equiv of copper(II) acetate in the
presence of a nitrogen nucleophile.32 Under air atmo-
sphere, only catalytic quantities of copper(II) are re-
quired due to the rapid aerial oxidation of copper(I)
ions. Although 0.1 equiv of copper(II) suffices to effect
oxidation, we used 0.5 equiv to reduce reaction times.
The amine present in solution serves a triple goal; first,
deprotonation of the hydrazide, second, complexation
of the copper ions, thereby preventing them to precipi-
tate from solution, and finally, nucleophilic release
under formation of carboxamide 12. The copper salts
were easily removed by passing the solution of the crude
product over a silica gel cartridge.
>99
98
E
E
C
D
A
B
99
94
E
F
97
98
12j
F
12k
12l
F
C
D
A
B
>99
92
F
12m
12n
12o
12p
12q
12r
12s
12t
G
G
G
G
H
H
H
H
>99
99
C
D
A
B
98
94
97
95
C
D
99
99
a Overall yield and purity after HPLC purification.
purities (see Table 2). These final yields were comparable
to those obtained via an alternative procedure reported
during completion of our synthetic work.33
While disubstituted adenosine analogues 12a–t were
readily synthesised by application of the hydrazide resin,
our second goal was the preparation of trisubstituted
50-carboxamidoadenosine analogues, which required
nitration of the purine 2-position.34 Not surprisingly,
TBAN–TFAA nitration of hydrazide resin-bound 6-
chloropurine resulted in premature release of the nucle-
oside from the solid support by N-nitration or oxidation
of the hydrazide linkage and subsequent cleavage by
nucleophiles present. An alternative approach involving
the attachment of 2-nitro-6-chloropurine riboside 50-car-
boxylic acid to the hydrazine resin was not an option be-
cause of the high reactivity of the purine 6-position in
that system. Therefore, a different strategy was pursued
entailing a combined solution and solid-phase diversifi-
cation of the nucleoside. At first, 6-chloropurine 2 was
nitrated in solution as shown in Scheme 5. The carboxyl
group was protected in situ with TFAA under formation
of mixed anhydride 13, while subsequent addition of
TBAN to the reaction mixture resulted in efficient nitra-
tion of the purine ring at C2. Aqueous work-up in order
to liberate the carboxyl moiety gave 2-nitro-6-chloropurine
The construction of a 20-membered library validated the
developed solid-phase sequence. Purities after solid-
phase extraction using a silica gel cartridge ranged from
64% to 99%. Nevertheless, all compounds were subse-
quently purified by semi-preparative HPLC and isolated
by lyophilisation to allow for reliable antiprotozoal eval-
uation. Products 12a–t were obtained in reasonable
yields (19–54% over four solid-phase steps) and high

1622
B. Rodenko et al. / Bioorg. Med. Chem. 14 (2006) 1618–1629
Cl
N
Cl
NHR1
N
N
N
N
N
N
O
N
O
N
O
N
O2N
HO
N
c
O2N
HO
N
b
d
O
O
O
RO
a
O
O
O
O
O
O
2
R = H
14
15
13 R = COCF3
NHR1
NHR1
NHR1
N
N
N
N
N
N
N
N
N
X
N
R2HN
N
g
R2HN
R3HN
N
f
O
O
O
O
O
O
N
N
N
N
H H
H H
O
OH
OH
O
HO
HO
16 X = NO2
17 X = NHR2
19
18
e
Scheme 5. Reagents and conditions: (a) TFAA (3 equiv), CH2Cl2, 0 ꢁC; (b) add TBAN (2 equiv), then aqueous work-up, 94%; (c) R1-NH2, DIPEA,
CH2Cl2, rt; (d) 7, DIC, HOBt, DMF; (e) R2-NH2, DIPEA, NMP, 80 ꢁC; (f) TFA/HO(CH2)2OH/CH2Cl2, 5:1:5; (g) 0.5 equiv Cu(OAc)2, THF.
Table 3. Yield and purity of trisubstituted 50-carboxamidoadenosine
14 in high yield. At this point, the first amino diversity
element was introduced in solution by 6-chloro displace-
ment furnishing substituted 6-aminopurines 15. Ensuing
attachment to hydrazine resin 7 was brought about un-
der standard acylation conditions, that is, DIC in com-
bination with HOBt. The use of additive HOBt was
allowed because in purine 15 no highly reactive electro-
philic positions were present. A bromophenol blue test31
confirmed quantitative formation of resin 16. Substitu-
tion of the 2-nitro group by nitrogen nucleophiles re-
quired gentle heating in NMP to obtain substituted
2,6-diaminopurines 17. Removal of the 20,30-isopropy-
lidene group under acidic conditions gave 18, which
was now fit for cleavage from the solid support. Cop-
per(II) mediated oxidation of the hydrazide linkage in
the presence of the final amino diversity element released
the desired 2,N50,N6-trisubstituted 50-carboxamidoade-
nosine analogues 19.
analoguesa
NHR1
N
N
R2HN
R3HN
N
N
O
O
OH
HO
Compound
R1
R2
R3
Yield (%)
Purity (%)
19a
19b
19c
19d
19e
19f
19g
19h
C
C
C
C
F
F
F
F
C
C
G
G
C
C
G
G
B
C
B
C
B
C
B
C
27
26
35
35
30
57
21
38
97
96
98
99
92
91
99
91
Again, a characteristic library was prepared, demon-
strating the efficiency of the developed solid-phase
route. After oxidative cleavage from the resin, the cop-
per salts were removed by filtration over a silica gel
cartridge, and products were obtained in 67–87% puri-
ty (Table 3). Subsequent semi-preparative HPLC and
lyophilisation afforded trisubstituted carboxamidoade-
nosine analogues 19a–h in high purity and 20–57%
yield over four solid-phase steps, ready for antiproto-
zoal screening.
a Overall yield and purity after HPLC purification.
rhodesiense (STIB 900 strain) and the chloroquine and
pyrimethamine resistant P. falciparum K1 strain are pre-
sented in Table 4. Whereas in our preliminary screening
of 2,N6-disubstituted adenosine analogues the cyclopen-
tyl substituted adenosine analogues belonged to the
most active and promising trypanocidal compounds,12
in the current series neither the introduction of a cyclo-
pentyl group on N2 nor on N6 leads to encouraging try-
panocidal activities. Nonetheless, for antiplasmodial
action the combination with a 50-cyclopentyl group ap-
pears to be optimal for the N6-benzyl and N6-m-iodoben-
zyl and N6-phenethyl substituted adenosine derivatives.
2.2. Biological activity
The results of the screening assays of the di- and trisub-
stituted carboxamidoadenosine analogues against T. b.

B. Rodenko et al. / Bioorg. Med. Chem. 14 (2006) 1618–1629
1623
Table 4. Antiprotozoal activity of di- and trisubstituted 50-carboxam-
idoadenosine analogues
ing structural leads for further antiprotozoal optimisa-
tion: N6-benzyl-50-N-phenylcarboxamidoadenosine 12h
with an IC50 value of 0.91 lM against T.b. rhodesiense
and N6-diphenylethyl-50-phenylcarboxamidoadenosine
12t with an IC50 value of 1.8 lM against multidrug resis-
tant P. falciparum.
Compound
T.b. rhodesiense
STIB 900 strain
IC50 (lM)
P. falciparum K1
strain IC50 (lM)
12a
12b
>75
>75
30.3
5.4
>10
>10
7.1
7.2
>10
9.7
3.0
4.6
6.4
3.4
2.7
3.6
>10
9.7
5.9
6.0
>10
>10
5.8
1.8
9.8
7.8
5.7
4.9
5.8
3.4
5.5
4.1
12c
12d
4. Experimental
12e
12f
37.2
9.7
4.1. General synthetic methods
12g
12h
4.1
0.91
5.1
All reagents and solvents were used as commercially
available, unless indicated otherwise. Peptide grade sol-
vents were used for solid-phase chemistry. 4-Fmoc-
12i
12j
4.0
4.9
12k
12l
hydrazinobenzoyl
AM
resin,
100–200
mesh,
5.4
0.98 mmol/g, was purchased from Novabiochem, N-(4-
sulfamoylbenzoyl)aminomethyl polystyrene 3, 200–400
mesh, 0.9 mmol/g, was purchased from Fluka, N-(4-sul-
famoylbutyryl)aminomethyl polystyrene 4, 200–400
mesh and 1.09 mmol/g, was a gift from Solvay Pharma-
ceuticals, Weesp, NL. Flash chromatography refers to
purification using the indicated eluents and Acros silica
gel 60 (0.030–0.075 mm). NMR spectra were determined
in the indicated solvent at 300 K using a Bruker ARX
400 (400 MHz) spectrometer. NH and OH signals were
identified after mixing the sample with a drop of D2O.
For the end-products 12 and 19 coupling constants
J = of H-20, H-30 and H-40 were determined after mixing
the sample with a drop of D2O. Infrared spectra of res-
ins were measured in KBr using a DRIFT module (Bru-
ker), vibrations m reported in cmꢀ1. Mass spectra and
accurate mass measurements were performed on a JEOL
JMS–SX/SX 102 A Tandem Mass Spectrometer using
Fast Atom Bombardment (FAB). A resolving power
of 10,000 (10% valley definition) for high resolution
FAB mass spectrometry was used. Analytical HPLC
was performed on a C18 column (Inertsil ODS-3, parti-
cle size 3 lm; 4.6 mm · 50 mm) using the following elu-
tion gradient: linear gradient of 5–95% aqueous CH3CN
containing 0.04% HCO2H over 5 min, then 95% aque-
ous CH3CN containing 0.04% HCO2H for 2 min at
2.0 mL minꢀ1. Semi-preparative HPLC was performed
on a C18 column (Polygosil 60 C-18, particle size
10 lm; 20 mm · 250 mm) using the following elution
gradient: linear gradient of 5–95% aqueous CH3CN con-
taining 0.04% HCO2H over 15 min, then 95% aqueous
CH3CN containing 0.04% HCO2H for 6 min at
7.0 mL minꢀ1. Products were detected at k = 254 nm.
12m
12n
>75
38.3
9.4
12o
12p
3.3
12q
12r
27.4
28.3
11.4
8.9
12s
12t
19a
19b
16.5
12.1
10.2
6.2
19c
19d
19e
19f
11.4
6.5
19g
19h
6.8
3.9
Melarsoprol
Artemisinin
0.0069
0.0051
On the other hand, we observed that, except for the N6-m-
iodobenzyl analogues, the combination with a 50-phenyl
group is most advantageous for trypanocidal activity;
N6-benzyl-50-N-phenylcarboxamidoadenosine 12h even
has submicromolar antitrypanosomal activity with an
IC50 value of 0.91 lM. Generally, a small 50-substituent,
such as methyl or ethyl, is not favourable for antiproto-
zoal activity. As also emerged from the previous screen-
ings,12 the N6-diphenylethyl derivatives display mainly
antimalarial activity. Especially, the combination with
an aromatic residue on the 50 position (12t) leads to
promising activity with an IC50 value of 1.8 lM. Judging
from the modest activities of the trisubstituted ana-
logues 19a–h, introduction of an additional substituent
on C2 does not improve antiprotozoal capacity.
4.1.1. General solid-phase procedures. Large-scale solid-
phase reactions (>200 mg of resin) were performed in
dried glass scintillation vessels, bubbling nitrogen gas
through the resin suspension. Small-scale solid-phase
reactions (100–200 mg of resin) were run under a nitro-
gen atmosphere in Radleys Carousel Reaction Sta-
tionTM using dried modified glass reaction tubes. The
tubes were fitted with a glass frit and luer tip to facil-
itate work-up on the IST VacMaster-20 Sample Pro-
cessing StationTM. Small-scale reactions were gently
stirred with a magnetic stirring bar. The modified tubes
were heated in a sand bath fitted in the Carousel Reac-
tion StationTM. Resins were suspended in 1 mL solvent/
3. Conclusions
By using the beneficial sterical and electronic properties
of the arylhydrazide linker we showed that the safety-
catch approach can be a practical synthetic tool leading
to di- and trisubstituted 50-carboxamidoadenosine deriv-
atives. As the arylhydrazide linker seemed incompatible
with our TBAN–TFAA nitration, the solid-phase
synthesis of trisubstituted 50-carboxamidoadenosine
analogues required a combined solution/solid-phase
diversification procedure. The biological evaluation of
two typical combinatorial libraries revealed two interest-

1624
B. Rodenko et al. / Bioorg. Med. Chem. 14 (2006) 1618–1629
100 mg resin. The resins were washed according to the
indicated sequence.
4.2.5. Fmoc removal from 2-Fmoc-hydrazinobenzoyl AM
resin 6 (7). A suspension of 2-Fmoc-hydrazinobenzoyl
AM resin 6 (1.0 g; 0.98 mmol) in DMF/piperidine 4:1
(10 mL) was mixed by nitrogen bubbling for 30 min.
Resin 7 was washed with DMF (3·), CH2Cl2 (3·),
MeOH, CH2Cl2, MeOH, Et2O, CH2Cl2, Et2O and
CH2Cl2 and dried in vacuo at 50 ꢁC.
4.2. Synthesis
4.2.1. 6-Chloro-(2,3-O-isopropylidene-5-carboxy-b-D-ribo-
furanosyl)-9H-purine (2). This compound was synthesised
according to a modified literature procedure.17 A mixture
of iodobenzene diacetate (6.72 g; 20.8 mmol), TEMPO
(296 mg; 1.90 mmol) and 20,30-isopropylidene-protected
6-chloropurine riboside 118 (3.10 g; 9.49 mmol) in water/
acetonitrile 1:1 (20 mL) was stirred for 4 h. The reaction
mixture was carefully poured into 0.5 M aqueous NaH-
CO3 (125 mL). After stirring for 10 min, the mixture was
washed with CH2Cl2 (3· 40 mL). The combined organic
layers were back-extracted with water (20 mL). The aque-
ous layers were combined, acidified with 1 M aqueous HCl
and extracted with CH2Cl2/EtOH 95:5 (4· 40 mL). Drying
with Na2SO4 and coevaporation with toluene gave 50-car-
boxylic acid 2 as a white solid (2.98 g; 8.74 mmol; 92%). 1H
NMR (DMSO-d6) d 12.92 (br s, 1H, COOH), 8.84and 8.78
(2· s, 2· 1H, H-2 and H-8), 6.52 (s, 1H, H-10), 5.64 (d,
J = 5.9, 1H, H-20), 5.58 (dd, J = 5.9 and 1.3, 1H, H-30),
4.80 (d, J = 1.3, 1H, H-40), 1.55 (s, 3H, CH3), 1.39 (s, 3H,
CH3). IR (KBr) m 3200, 1728.
4.2.6. Coupling of carboxylic acid 2 to hydrazinobenzoyl
AM resin 7 (8). To a suspension of hydrazinobenzoyl
AM resin 7 (0.78 g; 0.98 mmol) in DMF (10 mL) were
added carboxylic acid 2 (0.84 g; 2.45 mmol) and DIC
(384 lL; 2.45 mmol). The reaction was monitored with
a bromophenol blue test.31 After 16 h, the reaction
was complete and resin 8 was washed with DMF (3·),
CH2Cl2 (3·), MeOH, CH2Cl2, MeOH, Et2O, CH2Cl2,
Et2O and CH2Cl2, and dried in vacuo at 50 ꢁC.
4.2.7. General procedure for the amination by chloro
substitution of resin-bound 6-chloropurines 8 (9). A sus-
pension of resin-bound 6-chloropurine 8 (200 mg;
0.18 mmol) and the amine (0.71 mmol) in NMP
(2 mL) was gently stirred at 50 ꢁC. After 18 h, resin 9
was washed with NMP (3·), CH2Cl2 (3·), MeOH,
CH2Cl2, MeOH, Et2O, CH2Cl2, Et2O and CH2Cl2.
4.2.2. Attempted coupling of carboxylic acid 2 to sulfon-
amide resins 3 or 4. In a typical experiment to a suspen-
sion of the sulfonamide resin (100 mg; 0.09 mmol) in
1 mL DMF were added carboxylic acid 2 (153 mg;
0.45 mmol), DIC (70 lL; 0.45 mmol) and 1-methylimi-
dazole (36 lL; 0.45 mmol). After 20–24 h, the resulting
resin was washed with the solvent of the reaction (3·),
CH2Cl2 (3·), MeOH, CH2Cl2, MeOH, Et2O and
CH2Cl2, Et2O, CH2Cl2 and dried in vacuo at 50 ꢁC.
No coupling was observed judging from the absence of
a sulfonamide carbonyl vibration at ꢁ1735 cmꢀ1. For
other coupling conditions, see Table 1.
4.2.8. General procedure for removal of the 20,30-isopro-
pylidene group (10). In a typical experiment, resin-bound
isopropylidene-protected riboside 9 (0.18 mmol) was
washed with a solution of TFA/HO(CH2)2OH/CH2Cl2
5:1:5 (2 mL). After subjecting to this solution (2 mL)
for 18 h, resin 10 was washed with CH2Cl2 (3·),
CH2Cl2/DIPEA 9:1 (3·), CH2Cl2 (3·), MeOH, CH2Cl2,
MeOH, CH2Cl2, Et2O, CH2Cl2, Et2O and CH2Cl2.
4.2.9. General procedure for oxidative cleavage of the
nucleosides (12). In a typical experiment, a suspension of
resin 10 (0.18 mmol), amine (0.89 mmol) and Cu(OAc)2
(16 mg; 0.09 mmol) in THF (2 mL) was gently stirred
for 22 h under an air atmosphere. The resin was washed
with THF (3·), MeOH, THF, MeOH, THF, MeOH
and THF (2·). The combined washings were passed over
a silica gel cartridge (Supelco, 1 g of silica) and the sol-
vents were evaporated. The end products were purified
by semi-preparative HPLC and isolated by lyophilisation.
4.2.3. N-Benzyl-4-sulfamoyl-benzamide. A mixture of 4-
sulfamoyl-benzoic acid (5.0 g; 25 mmol), benzylamine
(5.57 mL; 50.0 mmol), EDC (5.75 g; 30.0 mmol) and
HOBt (4.05 g; 30.0 mmol) in DMA/CH2Cl2 1:1 (2 mL)
was stirred for 2 h. Et2O/EtOAc 1:1 (1 mL) and 5%
aqueous KHSO4 (1.5 mL) were added and after stirring
for 5 min the mixture was washed with water (3· 2 mL).
Drying with Na2SO4 and evaporation of the solvent
yielded N-benzyl-4-sulfamoylbenzamide as a white crys-
talline solid (4.86 g; 19.0 mmol; 76%). 1H NMR
(DMSO-d6) d 9.27 (t, J = 6.0, 1H, NH), 8.07 (d,
J = 8.4, 2H, HCOAr), 7.92 (d, J = 8.4, 2H, HCOAr),
7.50 (br s, 2H, NH2), 7.37–7.32 (m, 4H, HBn), 7.29–
7.27 (m, 1H, HBn), 4.52 (d, J = 6.0, 2H, CH2).
4.2.10. N6-Cyclopentyl-50-N-methylcarboxamidoadeno-
sine (12a). Yield: 28 mg; 0.077 mmol; 43%. H NMR
1
(DMSO-d6) d 8.98 (q, J = 4.5, 1H, CONH), 8.41 and
8.31 (2· s, 2· 1H, H-2 and H-8), 7.88 and 7.79 (2· d,
J = 5.0, 1H, N6-H rotamers), 5.98 (d, J = 7.5, 1H,
H-10), 5.77 (br s, 1H, OH), 5.57 (d, J = 5.8, 1H, OH),
5.12 and 4.53 (2· m, 1H, CH rotamers), 4.61 (dd,
J = 7.5 and 4.7, 1H, H-20), 4.34 (s, 1H, H-40), 4.16 (d,
J = 4.7, 1H, H-30), 2.74 (d, J = 4.5, 3H, CH3), 2.01–
1.93 (m, 2H, cyclopentyl), 1.77–1.72 (m, 2H, cyclopen-
tyl), 1.72–1.54 (m, 4H, cyclopentyl). m/z 363.1789
(M++H, C16H23N6O4 requires 363.1781).
4.2.4. Attempted coupling of carboxylic acid 2 to N-
benzyl-4-sulfamoylbenzamide. In a typical experiment,
a mixture of carboxylic acid 2 (80 mg; 0.23 mmol),
N-benzyl-4-sulfamoylbenzamide (50 mg; 0.20 mmol),
EDC (54 mg; 0.28 mmol) and DMAP (2.5 mg; 0.02 mmol)
in DMA/CH2Cl2 1:1 (2 mL) was stirred at rt. After 18 h,
still no reaction had taken place as indicated by TLC
analysis. After work-up of the reaction mixture, only
starting material was recovered.
4.2.11. N6-Cyclopentyl-50-N-ethylcarboxamidoadenosine
(12b). Yield: 25 mg; 0.067 mmol; 37%. 1H NMR
(DMSO-d6) d 8.94 (t, J = 5.3, 1H, CONH), 8.40 and
8.28 (2· s, 2· 1H, H-2 and H-8), 7.88 and 7.76 (2· d,

B. Rodenko et al. / Bioorg. Med. Chem. 14 (2006) 1618–1629
1625
J = 6.3, 1H, N6-H rotamers), 5.98 (d, J = 7.5, 1H,
H-10), 5.76 (d, J = 3.9, 1H, OH), 5.56 (d, J = 6.3, 1H,
OH), 5.12 and 4.55 (2· m, 1H, CH rotamers), 4.63 (dd,
J = 7.5 and 4.7, 1H, H-20), 4.32 (d, J = 1.3, 1H, H-40),
4.16 (dd, J = 4.7 and 1.3, 1H, H-30), 3.24 (dq, J = 7.0
and 5.3, 2H, CH2), 2.00-1.94 (m, 2H, cyclopentyl),
1.76–1.73 (m, 2H, cyclopentyl), 1.70–1.56 (m, 4H, cyclo-
pentyl), 1.10 (t, J = 7.0, 3H, CH3). m/z 377.1927 (M++H,
C17H25N6O4 requires 377.1937).
4.74 (2· m, 1H, CH2 rotamers), 4.65–4.62 (m, 1H, H-
20), 4.33 (d, J = 1.4, 1H, H-40), 4.17–4.08 (m, 2H, H-30
and CH), 1.92–1.84 (m, 2H, cyclopentyl), 1.73–1.67 (m,
2H, cyclopentyl) 1.62–1.39 (m, 4H, cyclopentyl). m/z
439.2116 (M++H, C22H27N6O4 requires 439.2094).
4.2.17. N6-Benzyl-50-N-phenylcarboxamidoadenosine (12h).
1
Yield: 24 mg; 0.054 mmol; 30%. H NMR (DMSO-d6) d
10.49 (s, 1H, CONH), 8.58 (br s, 1H, N6-H), 8.52 and 8.23
(2· s, 2· 1H, H-2 and H-8), 7.65 (d, J = 8.1, 2H, HAr),
7.41–7.29 (m, 6H, HAr), 7.24–7.22 (m, 1H, HAr), 7.15 (t,
J = 7.3, 1H, HAr), 6.08 (d, J = 7.0, 1H, H-10), 5.90 (br s,
1H, OH), 5.70 (br s, 1H, OH), 5.17 and 4.76 (2· m, 1H,
CH2 rotamers), 4.66–4.61 (m, 1H, H-20), 4.55 (d, J = 1.7,
H-40), 4.35 (dd, J = 4.5 and 1.7, 1H, H-30). m/z 447.1808
(M++H, C23H23N6O4 requires 447.1781).
4.2.12. N6-Cyclopentyl-50-N-cyclopentylcarboxamidoade-
nosine (12c). Yield: 21 mg; 0.050 mmol; 28%. H NMR
1
(DMSO-d6) d 8.55 (d, J = 7.0, 1H, CONH), 8.42 and
8.22 (2· s, 2· 1H, H-2 and H-8), 7.89 (br s, 1H, N6-H),
5.97 (d, J = 7.5, 1H, H-10), 5.74 (d, J = 4.3, 1H, OH),
5.56 (d, J = 6.4, 1H, OH), 5.09 and 4.62 (2· m, 1H, CH
rotamers), 4.72–4.68 (m, 1H, H-20), 4.32 (d, J = 1.6, 1H,
H-40), 4.15–4.08 (m, 2H, H-30 and CH), 2.00–1.81 (m,
4H, cyclopentyl), 1.77–1.32 (m, 12H, cyclopentyl). m/z
417.2247 (M++H, C20H29N6O4 requires 417.2250).
4.2.18. N6-(3-Iodobenzyl)-50-N-methylcarboxamidoadeno-
sine (12i). Yield: 37 mg; 0.073 mmol; 54%. 1H NMR
(DMSO-d6) d 8.89 (q, J = 4.7, 1H, CONH), 8.60 (br s,
1H, N6-H), 8.47 and 8.32 (2· s, 2· 1H, H-2 and H-8),
7.75 (s, 1H, HAr), 7.61 (d, J = 7.8, 1H, HAr), 7.39 (d,
J = 7.8, 1H, HAr), 7.13 (t, J = 7.8, 1H, HAr), 6.00 (d,
J = 7.5, 1H, H-10), 5.76 (d, J = 4.1, 1H, OH), 5.58 (d,
J = 6.2, 1H, OH), 5.15 and 4.70 (2· br s, 2H, CH2 rota-
mers), 4.62 (dd, J = 7.5 and 4.7, 1H, H-20), 4.34 (d,
J = 1.3, 1H, H-40), 4.17 (dd, J = 4.6 and 1.3, 1H, H-30),
2.73 (d, J = 4.7, 3H, CH3). m/z 511.0599 (M++H,
C18H20IN6O4 requires 511.0591).
4.2.13. N6-Cyclopentyl-50-N-phenylcarboxamidoadenosine
(12d). Yield: 24 mg; 0.057 mmol; 32%. 1H NMR (DMSO-
d6) d 10.52 (s, 1H, CONH), 8.47 and 8.23 (2· s, 2· 1H, H-2
and H-8), 7.91 (br s, 1H, N6-H), 7.65 (d, J = 7.7, 2H, HAr),
7.40 (t, J = 7.7, 2H, HAr), 7.16 (t, J = 7.7, 1H, HAr), 6.07(d,
J = 7.1, 1H, H-10), 5.87 (d, J = 4.3, 1H, OH), 5.67 (d,
J = 6.3, 1H, OH), 5.09 and 4.59 (2· m, 1H, CH rotamers),
4.63 (dd, J = 7.1 and 4.5, 1H, H-20), 4.54 (d, J = 1.9, H-40),
4.34 (dd, J = 4.5 and 1.9, 1H, H-30), 1.99–1.96 (m, 2H,
cyclopentyl), 1.75–1.70 (m, 2H, cyclopentyl), 1.67–1.59
(m, 4H, cyclopentyl). m/z 425.1908 (M++H, C21H25N6O4
requires 425.1937).
4.2.19. N6-(3-Iodobenzyl)-50-N-ethylcarboxamidoadeno-
sine (12j). Yield: 31 mg; 0.059 mmol; 46%. 1H NMR
(DMSO-d6) d 8.86 (t, J = 5.5, 1H, CONH), 8.61 (br s,
1H, N6-H), 8.46 and 8.29 (2· s, 2· 1H, H-2 and H-8),
7.75 (s, 1H, HAr), 7.61 (d, J = 7.8, 1H, HAr), 7.39 (d,
J = 7.8, 1H, HAr), 7.13 (t, J = 7.8, 1H, HAr), 6.00 (d,
J = 7.5, 1H, H-10), 5.77 (d, J = 4.1, 1H, OH), 5.59 (d,
J = 6.3, 1H, OH), 5.15 and 4.70 (2· m, 1H, CH2 rota-
mers), 4.63 (dd, J = 7.5 and 4.6, 1H, H-20), 4.33 (s, 1H,
H-40), 4.17 (d, J = 4.6, 1H, H-30), 3.23 (dq, J = 7.2 and
5.5, 2H, CH2), 1.09 (t, J = 7.2, 3H, CH3). m/z 525.0752
(M++H, C19H22IN6O4 requires 525.0747).
4.2.14. N6-Benzyl-50-N-methylcarboxamidoadenosine (12e).
1
Yield: 35 mg; 0.090 mmol; 50%. H NMR (DMSO-d6) d
8.92 (q, J = 4.6, 1H, CONH), 8.56 (br s, 1H, N6-H), 8.44
and 8.31 (2· s, 2· 1H, H-2 and H-8), 7.37–7.29 (m, 4H,
HAr), 7.23 (t, J = 7.4, 1H, HAr), 6.00 (d, J = 7.6, 1H, H-10),
5.77 (d, J = 4.0, 1H, OH), 5.59 (d, J = 6.3, 1H, OH), 5.19
and 4.74 (2· br s, 2H, CH2 rotamers), 4.62 (dd, J = 7.6
and 4.6, 1H, H-20), 4.34 (d, J = 1.1, 1H, H-40), 4.17 (dd,
J = 4.6 and 1.1, 1H, H-30), 2.73 (d, J = 4.6, 3H, CH3). m/z
385.1633 (M++H, C18H21N6O4 requires 385.1624).
4.2.20. N6-(3-Iodobenzyl)-50-N-cyclopentylcarboxamido-
adenosine (12k). Yield: 38 mg; 0.068 mmol; 50%. 1H
NMR (DMSO-d6) d 8.61 (br s, 1H, N6-H), 8.51 (d,
J = 7.1, 1H, CONH), 8.49 and 8.23 (2· s, 2· 1H, H-2
and H-8), 7.75 (s, 1H, HAr), 7.61 (d, J = 7.8, 1H, HAr),
7.39 (d, J = 7.8, 1H, HAr), 7.13 (t, J = 7.8, 1H, HAr),
6.00 (d, J = 7.4, 1H, H-10), 5.75 (d, J = 3.5, 1H, OH),
5.59 (d, J = 5.6, 1H, OH), 5.16 and 4.69 (2· m, 1H, CH2
rotamers), 4.65–4.62 (m, 1H, H-20), 4.33 (d, J = 1.4, 1H,
H-40), 4.17–4.08 (m, 2H, H-30 and CH), 1.98–1.80 (m,
2H, cyclopentyl), 1.74–1.69 (m, 2H, cyclopentyl) 1.58–
1.39 (m, 4H, cyclopentyl). m/z 565.1039 (M++H,
C22H26IN6O4 requires 565.1060).
4.2.15. N6-Benzyl-50-N-ethylcarboxamidoadenosine (12f).
Yield: 33 mg; 0.083 mmol; 46%. 1H NMR (DMSO-d6) d
8.90 (t, J = 5.6, 1H, CONH), 8.56 (br s, 1H, N6-H), 8.44
and 8.28 (2· s, 2· 1H, H-2 and H-8), 7.37–7.29 (m, 4H,
HAr), 7.23 (t, J = 7.2, 1H, HAr), 5.99 (d, J = 7.6, 1H, H-
10), 5.79 (d, J = 3.9, 1H, OH), 5.60 (d, J = 6.1, 1H, OH),
5.20 and 4.70 (2· m, 1H, CH2 rotamers), 4.63 (dd,
J = 7.6 and 4.7, 1H, H-20), 4.32 (d, J = 1.2, 1H, H-40),
4.16 (dd, J = 4.7 and 1.2, 1H, H-30), 3.24 (dq, J = 7.2
and 5.6, 2H, CH2), 1.09 (t, J = 7.2, 3H, CH3). m/z
399.1758 (M++H, C19H23N6O4 requires 399.1781).
4.2.16. N6-Benzyl-50-N-cyclopentylcarboxamidoadenosine
(12g). Yield: 35 mg; 0.081 mmol; 45%. 1H NMR (DMSO-
d6) d 8.57–8.52 (m, 2H, CONH and N6-H), 8.47 and 8.22
(2· s, 2· 1H, H-2 and H-8), 7.37–7.29 (m, 4H, HAr), 7.23
(t, J = 7.1, 1H, HAr), 5.99 (d, J = 7.4, 1H, H-10), 5.75 (d,
J = 4.2, 1H, OH), 5.58 (d, J = 6.3, 1H, OH), 5.18 and
4.2.21. N6-(3-Iodobenzyl)-50-N-phenylcarboxamidoadeno-
sine (12l). Yield: 26 mg; 0.046 mmol; 34%. 1H NMR
(DMSO-d6) d 10.47 (s, 1H, CONH), 8.61 (br s, 1H, N6-
H), 8.54 and 8.24 (2· s, 2· 1H, H-2 and H-8), 7.75 (s,
1H, HAr), 7.65 (d, J = 8.1, 2H, HNHAr), 7.61 (d, J = 7.8,
1H, HAr), 7.41–7.31 (m, 3H, HAr and HNHAr), 7.17–7.11

1626
B. Rodenko et al. / Bioorg. Med. Chem. 14 (2006) 1618–1629
(m, 2H, HAr and HNHAr), 6.09 (d, J = 7.0, 1H, H-10), 5.91
(br s, 1H, OH), 5.71 (br s, 1H, OH), 5.19 and 4.69–4.61 (2·
m, 2H, CH2 rotamers and H-20), 4.56 (d, J = 2.0, H-40),
4.35 (dd, J = 4.5 and 2.0, 1H, H-30). m/z 573.0770
(M++H, C23H22IN6O4 requires 573.0747).
8.39 and 8.36 (2· s, 2· 1H, H-2 and H-8), 7.96 (br s,
1H, N6-H), 7.36 (d, J = 7.3, 4H, HAr), 7.30 (t, J = 7.3,
4H, HAr), 7.19 (t, J = 7.3, 2H, HAr), 7.20 (t, J = 7.2,
2H, HAr), 5.97 (d, J = 7.4, 1H, H-10), 5.77 (br s, 1H,
OH), 5.58 (br s, 1H, OH), 4.68–4.55 and 4.18–4.14 (2·
m, 5H, H-20, H-30, CH2 and CH rotamers), 4.33 (s,
1H, H-40), 2.74 (d, J = 4.7, 3H, CH3). m/z 475.2067
(M++H, C25H27N6O4 requires 475.2094).
4.2.22. N6-(2-Phenethyl)-50-N-methylcarboxamidoadeno-
sine (12m). Yield: 29 mg; 0.073 mmol; 54%. H NMR
1
(DMSO-d6) d 8.95 (q, J = 4.5, 1H, CONH), 8.42 and
8.36 (2· s, 2· 1H, H-2 and H-8), 8.05 (br s, 1H, N6-
H), 7.35–7.29 (m, 4H, HAr), 7.23–7.20 (m, 1H, HAr),
5.99 (d, J = 7.5, 1H, H-10), 5.76 (d, J = 4.2, 1H, OH),
5.57 (d, J = 6.4, 1H, OH), 4.61 (dd, J = 7.5 and 4.5,
1H, H-20), 4.33 (s, 1H, H-40), 4.17 (d, J = 4.5, 1H, H-
30), 4.10 and 3.75–3.72 (2· m, 2H, CH2 rotamers),
2.95 (t, J = 7.5, 2H, PhCH2), 2.74 (d, J = 4.5, 3H,
CH3). m/z 399.1774 (M++H, C19H23N6O4 requires
399.1781).
4.2.27. N6-(2,2-Diphenylethyl)-50-N-ethylcarboxamidoad-
enosine (12r). Yield: 28 mg; 0.058 mmol; 32%. H NMR
1
(DMSO-d6) d 8.90 (t, J = 5.6, 1H, CONH), 8.36 (s, 2H,
H-2 and H-8), 7.96 and 7.76 (2· br s, 1H, N6-H rota-
mers), 7.36 (d, J = 7.3, 4H, HAr), 7.32 (t, J = 7.3, 4H,
HAr), 7.19 (t, J = 7.3, 2H, HAr), 5.97 (d, J = 7.4, 1H,
H-10), 5.78 (br s, 1H, OH), 5.58 (br s, 1H, OH), 4.64–
4.54 and 4.17–4.13 (2· m, 5H, H-20, H-30, CH2 and
CH rotamers), 4.32 (s, 1H, H-40), 3.23 (dq, J = 7.2 and
5.6, 2H, CH2), 1.11 (t, J = 7.2, 3H, CH3). m/z 489.2241
(M++H, C26H29N6O4 requires 489.2250).
4.2.23. N6-(2-Phenethyl)-50-N-ethylcarboxamidoadeno-
sine (12n). Yield: 28 mg; 0.068 mmol; 50%. H NMR
1
(DMSO-d6) d 8.92 (t, J = 5.5, 1H, CONH), 8.42 and
8.32 (2· s, 2· 1H, H-2 and H-8), 8.56 and 7.94 (2· br s,
1H, N6-H rotamers), 7.33–7.28 (m, 4H, HAr), 7.23–7.20
(m, 1H, HAr), 5.99 (d, J = 7.6, 1H, H-10), 5.77 (d,
J = 4.1, 1H, OH), 5.58 (d, J = 6.4, 1H, OH), 4.63 (dd,
J = 7.6 and 4.6, 1H, H-20), 4.33 (d, J = 1.1, 1H, H-40),
4.17 (dd, J = 4.6 and 1.1, 1H, H-30), 4.10 and 3.77–3.73
(2· m, 2H, CH2 rotamers), 3.24 (dq, J = 7.2 and 5.5,
2H, CH2), 2.95 (t, J = 7.5, 2H, PhCH2), 1.11 (t, J = 7.2,
3H, CH3). m/z 413.1943 (M++H, C20H25N6O4 requires
413.1937).
4.2.28. N6-(2,2-Diphenylethyl)-50-N-cyclopentylcarboxam-
idoadenosine (12s). Yield: 24 mg; 0.045 mmol; 25%. H
1
NMR (DMSO-d6) d 8.52 (d, J = 7.2, 1H, CONH), 8.38
and 8.29 (2· s, 2· 1H, H-2 and H-8), 7.97 and 7.73 (2· br
s, 1H, N6-H rotamers), 7.35 (d, J = 7.4, 4H, HAr), 7.29 (t,
J = 7.4, 4H, HAr), 7.19 (t, J = 7.4, 2H, HAr), 5.96 (d,
J = 7.3, 1H, H-10), 5.73 (d, J = 4.3, 1H, OH), 5.55 (d,
J = 6.4, 1H, OH), 4.64–4.54 and 4.19–4.08 (2· m, 6H,
H-20, H-30, CH and CH2 and CH rotamers), 4.32 (s, 1H,
H-40), 1.97–1.82 (m, 2H, cyclopentyl), 1.73–1.69 (m, 2H,
cyclopentyl) 1.58–1.32 (m, 4H, cyclopentyl). m/z 529.2547
(M++H, C29H33N6O4 requires 529.2563).
4.2.24. N6-(2-Phenethyl)-50-N-cyclopentylcarboxamidoade-
nosine (12o). Yield: 22 mg; 0.049 mmol; 36%. H NMR
1
4.2.29. N6-(2,2-Diphenylethyl)-50-N-phenylcarboxamido-
adenosine (12t). Yield: 18 mg; 0.034 mmol; 19%. 1H
NMR (DMSO-d6) d 10.49 (s, 1H, CONH), 8.44 and
8.31 (2· s, 2· 1H, H-2 and H-8), 7.97 and 7.79 (2· br s,
1H, N6-H rotamers), 7.65 (d, J = 7.8, 2H, HNHAr),
7.42–7.28 (m, 10H, HNHAr and HAr), 7.21–7.10 (m, 3H,
HNHAr and HAr), 6.06 (d, J = 6.9, 1H, H-10), 5.88 (br s,
1H, OH), 5.68 (br s, 1H, OH), 4.70–4.60 (m, 2H, H-20
and CH), 4.54 (s, 1H, H-40), 4.34 (m, 1H, H-30), 4.18–
4.14 (m, 1H, CH2). m/z 537.2259 (M++H, C30H29N6O4
requires 537.2250).
(DMSO-d6) d 8.55 (d, J = 7.0, 1H, CONH), 8.43 and 8.26
(2· s, 2· 1H, H-2 and H-8), 8.05 and 7.97 (2· br s, 1H,
N6-H rotamers), 7.31–7.27 (m, 4H, HAr), 7.24–7.20 (m,
1H, HAr), 5.98 (d, J = 7.4, 1H, H-10), 5.77 (br s, 1H, OH),
5.59 (br s, 1H, OH), 5.18 and 4.74 (2·m, 1H, CH2 rotamers),
4.65–4.61 (m, 1H, H-20), 4.33 (s, 1H, H-40), 4.15 (d, J = 4.5,
1H, H-30), 4.17–4.09 (m, 1H, CH), 4.06 and 3.76–3.72 (2·m,
2H, CH2 rotamers), 2.95 (t, J = 7.4, 2H, PhCH2), 1.98–1.82
(m, 2H, cyclopentyl), 1.74–1.62 (m, 2H, cyclopentyl) 1.59–
1.36 (m, 4H, cyclopentyl). m/z 453.2255 (M++H,
C23H29N6O4 requires 453.2250).
4.2.30. 2-Nitro-6-chloro-(2,3-O-isopropylidene-5-carboxy-
b-D-ribofuranosyl)-9H-purine (14). TFAA (1.27 mL;
9.0 mmol) was added to a suspension of 6-chloropurine
carboxylic acid 2 (1.07 g; 3.0 mmol) in dry CH2Cl2
(24 mL) at 0 ꢁC and the mixture was stirred until a clear
solution of 13 was obtained (30 min). TBAN (1.46 g;
4.8 mmol) was added and the reaction mixture was stirred
for an additional 2 h at 0 ꢁC. The reaction mixture was
divided between water (20 mL) and Et2O (75 mL) and
the organic layer was washed with water (3· 20 mL). The
combined water layers were extracted with EtOAc
(20 mL) and the EtOAc layer was washed with water
(10 mL).DIPEA(3.6 mL;20 mmol)wasaddedtothecom-
bined organic layers and they were extracted twice with
water (60 mL, 30 mL). Extra DIPEA (0.3 mL; 3 mmol)
was added to the organic layer, which was again washed
with water (30 mL). The combined water layers were
4.2.25. N6-(2-Phenethyl)-50-N-phenylcarboxamidoadeno-
sine (12p). Yield: 26 mg; 0.057 mmol; 42%. H NMR
1
(DMSO-d6) d 10.46 (s, 1H, CONH), 8.48 and 8.26 (2· s,
2· 1H, H-2 and H-8), 7.98 (br s, 1H, N6-H), 7.65 (d,
J = 7.5, 2H, HNHAr), 7.40 (t, J = 7.5, 2H, HNHAr), 7.34–
7.27 (m, 4H, HAr), 7.23–7.20 (m, 1H, HAr), 7.16 (t,
J = 7.5, 1H, HAr), 6.08 (d, J = 7.0, 1H, H-10), 5.81 (d,
J = 4.2, 1H, OH), 5.63 (d, J = 6.1, 1H, OH), 4.70 (dd,
J = 7.0 and 4.6, 1H, H-20), 4.55 (d, J = 2.0, 1H, H-40),
4.35 (dd, J = 4.6 and 2.0, 1H, H-30), 4.04 and 3.78–3.74
(2· m, 1H, CH2 rotamers), 2.96 (t, J = 7.5, 2H, PhCH2).
m/z 461.1953 (M++H, C24H25N6O4 requires 461.1937).
4.2.26. N6-(2,2-Diphenylethyl)-50-N-methylcarboxamido-
adenosine (12q). Yield: 26 mg; 0.056 mmol; 31%. 1H
NMR (DMSO-d6) d 8.93 (q, J = 4.7, 1H, CONH),

B. Rodenko et al. / Bioorg. Med. Chem. 14 (2006) 1618–1629
1627
washed with Et2O and the pH was adjusted to ꢂ2–3 with
oxalic acid (0.54 g; 6.0 mmol). After extraction of the car-
boxylic acid with EtOAc (40 mL, 15 mL and 15 mL) and
washing of the combined organic layers with water
(20 mL), the organic layer was dried with Na2SO4 and
the solvent was evaporated. Nitrated product 14 was ob-
washed with NMP (3·), CH2Cl2 (3·), MeOH, CH2Cl2,
MeOH, Et2O, CH2Cl2, Et2O and CH2Cl2.
4.2.35. General procedure for the removal of the 20,30-
isopropylidene group (18). See general procedure for 10.
1
tained as a yellow foam (1.09 g; 2.82 mmol; 94%). H
4.2.36. General procedure for oxidative cleavage of
the nucleosides from the resin (19). See general procedure
for 12.
NMR (DMSO-d6) d 12.97 (br s, 1H, OH), 9.20 (s, 1H, H-
8), 6.62 (s, 1H, H-10), 5.67 (d, J = 5.9, 1H, H-20), 5.63 (d,
J = 5.9, 1H, H-30), 4.77 (s, 1H, H-40), 1.57 (s, 3H, CH3),
1.40 (s, 3H, CH3).
4.2.37. 2-Cyclopentylamino-N6-cyclopentyl-50-N-ethylcarb-
oxamidoadenosine (19a). Yield: 20 mg; 0.043 mmol; 27%.
1H NMR (DMSO-d6) d 8.14 (br s, 1H, CONH), 8.00 (s,
1H, H-8), 7.18 (br s, 1H, N6-H), 6.16 (br s, 1H, 2-NH),
5.84 (d, J = 6.8, 1H, H-10), 5.59 (br s, 1H, OH), 5.51 (d,
J = 5.7, 1H, OH), 4.74–4.70 (m, 1H, H-20), 4.50–4.44 (m,
1H, N6-CH), 4.25 (s, 1H, H-40), 4.21–4.15 (m, 2H, 2-NHCH
and H-30), 3.27–3.23 (m, 1H, HCH), 3.22–3.11 (m, 1H,
HCH), 1.95–1.89 (m, 4H, cyclopentyl), 1.77–1.31 (m, 12H,
cyclopentyl), 1.03 (t, J = 7.0, 3H, CH3). m/z 460.2685
(M++H, C22H34N7O4 requires 460.2672).
4.2.31. 20,30-O-Isopropylidene-2-nitro-N6-cyclopentylade-
nosine 50-carboxylic acid (15a). To a solution of 2-nitro-6-
chloropurine 14 (1.09 g; 2.82 mmol) in CH2Cl2 (15 mL)
were added DIPEA (1.97 mL; 11.3 mmol) and cyclopen-
tylamine (0.36 mL; 3.67 mmol) and the solution was stir-
red for 18 h. The reaction mixture was divided between
water (75 mL) and Et2O (50 mL) and the organic layer
was extracted with water (2· 20 mL). The combined water
layers were washed with Et2O (25 mL) and the pH was
adjusted to ꢂ2–3 with oxalic acid. The acidic water layer
was extracted with EtOAc (3· 30 mL) and the combined
organic layers were washed with water (20 mL), dried
with Na2SO4 and coevaporated with toluene (3·). Tritur-
ation with CH2Cl2 furnished adenosine carboxylic acid
15a as a yellow solid (0.70 g; 1.61 mmol; 57%). 1H
NMR (DMSO-d6) d 12.78 (br s, 1H, OH), 8.80 (d,
J = 7.7, 1H, NH), 8.56 (s, 1H, H-8), 6.44 (s, 1H, H-10),
5.68 (dd, J = 5.8 and 1.5, 1H, H-30), 5.52 (d, J = 5.8, 1H,
H-20), 4.74 (d, J = 1.5, 1H, H-40), 5.13 and 4.50 (2· m,
1H, CH rotamers), 2.01–1.96 (m, 2H, cyclopentyl),
1.75–1.55 (m, 6H, cyclopentyl), 1.54 (s, 3H, CH3), 1.39
(s, 3H, CH3).
4.2.38. 2-Cyclopentylamino-N6-cyclopentyl-50-N-cyclopen-
tylcarboxamidoadenosine
(19b).
Yield:
21 mg;
1
0.042 mmol; 26%. H NMR (DMSO-d6) d 8.05 (s, 1H,
H-8), 7.88 (d, J = 7.1, 1H, CONH), 7.13 (br s, 1H, N6-
H), 6.21 (br s, 1H, 2-NH), 5.87 (d, J = 6.8, 1H, H-10),
5.53 (br s, 2H, 2· OH), 4.66–4.62 (m, 1H, H-20), 4.53–
4.45 (m, 1H, N6-CH), 4.27 (s, 1H, H-40), 4.22 (m, 1H,
H-30), 4.21–4.15 (m, 1H, 2-NHCH), 4.05–4.00 (m, 1H,
CONHCH), 1.94–1.33 (m, 24H, cyclopentyl). m/z
500.2982 (M++H, C25H38N7O4 requires 500.2985).
4.2.39. 2-(2-Phenethylamino)-N6-cyclopentyl-50-N-ethyl-
carboxamidoadenosine (19c). Yield: 28 mg; 0.056 mmol;
4.2.32. 20,30-O-Isopropylidene-2-nitro-N6-(3-iodobenzyl)aden-
osine 50-carboxylic acid (15b). This compound was pre-
pared by the method described for 15a. After trituration
with CH2Cl2, adenosine carboxylic acid 15b was obtained
35%. H NMR (DMSO-d6) d 8.11 (br s, 1H, CONH),
1
8.03 (s, 1H, H-8), 7.33–7.18 (m, 6H, N6-H and HAr),
6.35 (br s, 1H, 2-NH), 5.86 (d, J = 6.8, 1H, H-10), 5.60
(d, J = 3.6, 1H, OH), 5.51 (d, J = 5.7, 1H, OH), 4.75–
4.71 (m, 1H, H-20), 4.54–4.48 (m, 1H, N6-CH), 4.27 (s,
1H, H-40), 4.19 (m, 1H, H-30), 3.53–3.43 (m, 2H, 2-
NHCH2), 3.22–3.16 (m, 1H, HCH), 3.14–3.07 (m, 1H,
HCH), 2.89–2.86 (m, 2H, PhCH2), 1.99–1.96 (m, 2H,
cyclopentyl), 1.75–1.71 (m, 2H, cyclopentyl), 1.68–1.51
(m, 4H, cyclopentyl), 1.00 (t, J = 7.2, 3H, CH3). m/z
496.2686 (M++H, C25H34N7O4 requires 496.2672).
1
as a yellow solid (0.92 g; 1.58 mmol; 53%). H NMR
(DMSO-d6) d 12.81 (br s, 1H, OH), 9.36 and 9.24 (2 · t,
J = 6.1, 1H, NH rotamers), 8.60 (s, 1H, H-8), 7.85 and
7.78 (2· s, 1H, HAr rotamers) 7.64 (d, J = 7.7, 1H, HAr),
7.45 (d, J = 7.7, 1H, HAr), 7.16 (t, J = 7.7, 1H, HAr),
6.46 (s, 1H, H-10), 5.69 (dd, J = 5.9 and 1.5, 1H, H-30),
5.52 (d, J = 5.9, 1H, H-20), 4.75 (d, J = 1.5, 1H, H-40),
5.21 and 4.66 (2· d, J = 6.1, 2H, CH2 rotamers), 1.54 (s,
3H, CH3), 1.38 (s, 3H, CH3).
4.2.40. 2-(2-Phenethylamino)-N6-cyclopentyl-50-N-cyclo-
pentylcarboxamidoadenosine (19d). Yield: 30 mg;
1
4.2.33. General procedure for coupling of carboxylic acid
15 to hydrazinobenzoyl AM resin 7 (16). To a suspension
of hydrazinobenzoyl AM resin 7 (0.78 g; 0.98 mmol) in
DMF (5 mL) were added carboxylic acid 15 (1.47 mmol),
HOBt (198 mg; 1.47 mmol) and DIC (230 lL;
1.47 mmol). After 16 h, resin 16 was washed with DMF
(3·), CH2Cl2 (3·), MeOH, CH2Cl2, MeOH, Et2O,
CH2Cl2, Et2O and CH2Cl2 and dried in vacuo at 50 ꢁC.
0.056 mmol; 35%. H NMR (DMSO-d6) d 8.09 (s, 1H,
H-8), 7.91 (d, J = 7.0, 1H, CONH), 7.31–7.20 (m, 6H,
N6-H and HAr), 6.41 (br s, 1H, 2-NH), 5.89 (d, J = 5.7,
1H, H-10), 5.53 (br s, 2H, 2· OH), 4.67–4.63 (m, 1H, H-
20), 4.53–4.49 (m, 1H, N6-CH), 4.29 (s, 1H, H-40), 4.21
(m, 1H, H-30), 4.04–4.00 (m, 1H, CONHCH), 3.59–3.44
(m, 2H, 2-NHCH2), 2.88–2.84 (m, 2H, PhCH2), 1.97–
1.94 (m, 2H, cyclopentyl), 1.83–1.24 (m, 14H, cyclopen-
tyl). m/z 536.2975 (M++H, C28H38N7O4 requires
536.2985).
4.2.34. General procedure for the amination by nitro
substitution of resin-bound 2-nitropurines 16 (17). A sus-
pension of resin-bound 2-nitropurine 16 (200 mg;
0.16 mmol) and the amine (0.71 mmol) in NMP (2 mL)
was gently stirred at 80 ꢁC. After 24 h, resin 17 was
4.2.41. 2-Cyclopentylamino-N6-(3-iodobenzyl)-50-N-eth-
ylcarboxamidoadenosine (19e). Yield: 30 mg; 0.045 mmol;
30%. 1H NMR (DMSO-d6) d 8.15–7.99 (m, 3H, CONH,

1628
B. Rodenko et al. / Bioorg. Med. Chem. 14 (2006) 1618–1629
H-8 and N6-H), 7.77 (s, 1H, HAr), 7.59 (d, J = 7.7, 1H,
HAr), 7.40 (d, J = 7.7, 1H, HAr), 7.13 (t, J = 7.7, 1H,
HAr), 6.20 (br s, 1H, 2-NH), 5.86 (d, J = 6.8, 1H, H-10),
5.45 (br s, 2H, 2· OH), 4.70 (dd, J = 6.8 and 5.5, 1H, H-
20), 4.63-4.59 (m, 2H, N6-CH2), 4.26 (d, J = 2.0, 1H, H-
40), 4.20 (dd, J = 5.5 and 2.0, 1H, H-30), 4.14–4.11 (m,
1H, 2-NHCH), 3.24–3.10 (m, 1H, CONHCH2), 1.91–
1.84 (m, 2H, cyclopentyl), 1.68-1.60 (m, 2H, cyclopentyl),
1.52–1.43 (m, 4H, cyclopentyl), 1.03 (t, J = 7.2, 3H, CH3).
m/z 608.1456 (M++H, C24H31IN7O4 requires 608.1482).
Ten microlitres of Alamar Blue (12.5 mg resazurin dis-
solved in 100 mL distilled water) was then added to each
well and incubation was continued for a further 2–4 h.
The plate was then read in a Spectramax Gemini
XS microplate fluorometer (Molecular Devices
Cooperation, Sunnyvale, CA, USA) using an excitation
wavelength of 536 nm and an emission wavelength of
588 nm.36 Fluorescence development was measured
and expressed as percentage of the control. Data were
transferred into the graphic program Softmax Pro
(Molecular Devices) which calculated IC50 values.
4.2.42. 2-Cyclopentylamino-N6-(3-iodobenzyl)-50-N-cyclo-
pentylcarboxamidoadenosine
(19f).
Yield:
55 mg;
4.3.2. Plasmodium falciparum. Antiplasmodial activity
was determined using the K1 strain of P. falciparum
(resistant to chloroquine and pyrimethamine). A mod-
ification of the [3H]hypoxanthine incorporation assay
was used.37 Briefly, infected human red blood cells in
RPMI 1640 medium with 5% Albumax II were exposed
to serial drug dilutions in microtitre plates. After 48 h
of incubation at 37 ꢁC in a reduced oxygen atmo-
sphere, 0.5 lCi [3H]hypoxanthine was added to each
well. Cultures were incubated for a further 24 h before
they were harvested onto glass-fibre filters and washed
with distilled water. The radioactivity was counted
using a BetaplateTM liquid scintillation counter (Wallac,
Zurich, Switzerland). The results were recorded as
counts per minute (cpm) per well at each drug concen-
tration and expressed as percentage of the untreated
controls. From the sigmoidal inhibition curves, IC50
values were calculated. Assays were run in duplicate
and repeated once.
1
0.086 mmol; 57%. H NMR (DMSO-d6) d 8.10 (s, 1H,
H-8), 7.99 (br s, 1H, N6-H), 7.87 (d, J = 6.9, 1H, CONH),
7.75 (s, 1H, HAr), 7.59 (d, J = 7.8, 1H, HAr), 7.38 (d,
J = 7.8, 1H, HAr), 7.13 (t, J = 7.8, 1H, HAr), 6.30 (d,
J = 7.3, 1H, 2-NH), 5.87 (d, J = 6.5, 1H, H-10), 5.52–5.49
(m, 2H, 2· OH), 4.65–4.59 (m, 3H, H-20 and N6-CH2),
4.27 (s, 1H, H-40), 4.22 (m, 1H, H-30), 4.14–4.10 (m, 1H,
2-NHCH), 4.09–4.00 (m, 1H, CONHCH), 1.84–1.25 (m,
16H, cyclopentyl). m/z 648.1769 (M++H, C27H35IN7O4
requires 648.1795).
4.2.43. 2-(2-Phenethylamino)-N6-(3-iodobenzyl)-50-N-eth-
ylcarboxamidoadenosine (19g). Yield: 20 mg; 0.032 mmol;
21%. 1H NMR (DMSO-d6) d 8.14–8.00 (m, 3H, CONH,
H-8 and N6-H), 7.77 (s, 1H, HAr), 7.60 (d, J = 7.8, 1H,
HAr), 7.39 (d, J = 7.8, 1H, HAr), 7.28 (t, J = 7.3, 2H,
HPh), 7.24–7.10 (m, 4H, HAr and HPh), 6.49 (br s, 1H, 2-
NH), 5.89 (d, J = 6.9, 1H, H-10), 5.51 (br s, 2H, 2· OH),
4.72–4.62 (m, 3H, H-20 and N6-CH2), 4.29 (d, J = 2.1,
1H, H-40), 4.21 (m, 1H, H-30), 3.51–3.33 (m, 2H, 2-
NHCH2), 3.23–3.16 (m, 1H, HCHCH3), 3.14–3.08 (m,
1H, HCHCH3), 2.81 (t, J = 7.0, 2H, PhCH2), 1.00 (t,
J = 7.2, 3H, CH3). m/z 644.1458 (M++H, C27H31IN7O4
requires 644.1482).
References and notes
1. World Health Report 2002; http://www.who.int/whr/
2002/en.
2. Barrett, M. P.; Burchmore, R. J. S.; Stich, A.; Lazzari, J.
O.; Frasch, A. C.; Cazzulo, J. J.; Krishna, S. Lancet 2003,
362, 1469–1480.
3. Matovu, E.; Seebeck, T.; Enyaru, J. C. K.; Kaminsky, R.
Microbes Infect. 2001, 3, 763–770.
4. World Malaria Report 2005: http://rbm.who.int/wmr2005/.
5. Attaran, A.; Barnes, K. I.; Curtis, C.; dÕ Alessandro, U.;
Fanello, C. I.; Galinski, M. R.; Kokwaro, G.; Looa-
reesuwan, S.; Makanga, M.; Mutabingwa, T. K.; Talis-
una, A.; Trape, J. F.; Watkins, W. M. Lancet 2004, 363,
237–240.
4.2.44. 2-(2-Phenethylamino)-N6-(3-iodobenzyl)-50-N-cyclo-
pentylcarboxamidoadenosine
(19h).
Yield:
39 mg;
0.057 mmol; 38%. 1H NMR (DMSO-d6) d 8.14 (s, 1H, H-
8), 8.06 (br s, 1H, N6-H), 7.92 (d, J = 7.3, 1H, CONH),
7.75 (s, 1H, HAr), 7.59 (d, J = 7.7, 1H, HAr), 7.38 (d,
J = 7.7, 1H, HAr), 7.30 (t, J = 7.1, 2H, HPh), 7.20–7.09 (m,
4H, HAr and HPh), 6.47 (br s, 1H, 2-NH), 5.90 (d, J = 6.7,
1H, H-10), 5.54 (m, 2H, 2· OH), 4.68–4.62 (m, 3H, H-20
and N6-CH2), 4.29 (d, J = 2.0, 1H, H-40), 4.22 (m, 1H,
H-30), 4.05–4.01 (m, 1H, CONHCH), 3.45-3.33 (m, 2H, 2-
NHCH2), 2.81–2.77 (m, 2H, PhCH2), 1.81–1.76 (m, 2H,
cyclopentyl), 1.60–1.25 (m, 6H, cyclopentyl). m/z 684.1805
(M++H, C30H35IN7O4 requires 684.1795).
6. Berens, R. L.; Krug, E. C.; Marr, J. J. In Purine and
Pyrimidine Metabolism; Marr, J. J., Muller, M., Eds.;
¨
Academic Press: New York, 1995; pp 89–117.
7. De Koning, H. P.; Bridges, D. J.; Burchmore, R. J. S.
FEMS Microbiol. Rev. 2005, 29, 987–1020.
4.3. Antiprotozoal activity
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