Synthesis and antiprotozoal properties of pentamidine congeners bearing the benzofuran motif

Article abstract of DOI:10.1021/jm9006406

Forty-eight cationically substituted pentamidine congeners possessing benzofuran rings were synthesized by a copper mediated heteroannulation of substituted o-iodophenols with phenyl acetylenes. Activities of compounds 1-48 against Trypanosoma brucei rhod

Full text of DOI:10.1021/jm9006406

J. Med. Chem. 2009, 52, 5763–5767 5763
DOI: 10.1021/jm9006406
Synthesis and Antiprotozoal Properties of Pentamidine Congeners Bearing the Benzofuran Motif
Stanislav A. Bakunov,† Svetlana M. Bakunova,† Arlene S. Bridges,† Tanja Wenzler,§ Todd Barszcz,‡ Karl A. Werbovetz,‡
Reto Brun,§ and Richard R. Tidwell*,†
†Department of Pathology and Laboratory Medicine, School of Medicine, The University of North Carolina, Chapel Hill, North Carolina
27599-7525, ‡Division of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, The Ohio State University, 500 West 12th Avenue,
Columbus, Ohio 43210, and §Department of Medical Parasitology and Infection Biology, Swiss Tropical Institute, CH-4002 Basel, Switzerland
Received May 14, 2009
Forty-eight cationically substituted pentamidine congeners possessing benzofuran rings were synthe-
sized by a copper mediated heteroannulation of substituted o-iodophenols with phenyl acetylenes.
Activities of compounds 1-48 against Trypanosoma brucei rhodesiense, Plasmodium falciparum, and
Leishmania donovani and cytotoxicities for mammalian cells were influenced by the nature of cationic
substituents, placement of the benzofuran fragment, and the length of the carbon linker between
aromatic moieties. Several dications exhibited superior antiplasmodial and antileishmanial potencies
compared to pentamidine.
Introduction
3-hydroxybenzoic acid, respectively, as previously descri-
bed.8 Synthesis of isomeric 1-ethynyl-3-methoxybenzene 51
and 1-ethynyl-4-methoxybenzene 52 was carried out follow-
ing the literature procedure.10
In recent years, the emergence of drug resistant pathogens
has led to treatment failures for many infectious diseases,
including malaria, human African trypanosomiasis (HATa or
sleeping sickness), and leishmaniasis. The aromatic diamidine
1,5-bis(4-amidinophenoxy)pentane (pentamidine) has been
used against early stage T. b. gambiense HAT,1,2 antimony-
resistant leishmaniasis,3 and Pneumocystis jiroveci (formerly
P. carinii) pneumonia.4 Additionally, the drug exhibited some
antimalarial potency,5,6 although it was never approved to
treat the disease. Despite its extensive use as an HAT prophy-
lactic, widespread resistance of trypanosomes to pentamidine
in the field has not been observed.6,7 However, there is
growing pentamidine resistance of leishmaniasis. Thus, while
pentamidine may be a viable starting point for novel anti-
microbial agents, there is an urgent need for novel classes of
compounds that are effective against these re-emerging infec-
tions.
The synthesis of the benzofurans 59-62 is outlined in
Scheme 1. Copper-mediated coupling of o-iodophenols 49
and 50 with phenylacetylenes 51 and 52 using the modified
Castro reaction11 afforded benzofurans 53-56 in 72-81%
yields. Esters 55 and 56 were directly converted to the
corresponding nitriles 57 and 58 in 68 and 69% yields,
respectively, by treatment with two-fold excess of Me2AlNH2
in hot xylene.12 Deprotection of the compounds 53, 54, 57,
and 58 with melted pyridine hydrochloride9 afforded cyano-
phenols 59-62 in 69-80% yields.
4-Bromoalkoxybenzonitriles13 63-66 were prepared by
alkylation of 4-cyanophenol with excess of appropriate di-
bromoalkane. Alkylation of the compounds 59-62 with 4-
bromoalkoxybenzonitriles 63-66 by treatment with K2CO3
in hot DMF afforded isomeric dinitriles 67-82 in 65-94%
yields (Scheme 2). Compounds 67-82 were converted to
imidate esters by the modified Pinner method,14 followed by
reaction with ethanolic solutions of ammonia, isopropyla-
mine, or ethylenediamine at ambient temperature to yield
dicationic benzofurans 1-48.
Recently, we discovered several cationic bisbenzofurans8
and 2-phenyl benzofurans9 exhibiting excellent antitrypano-
somal and antiplasmodial activities. To combine the rigidity
of 2-phenyl benzofurans with the flexibility of pentamidine
congeners, we incorporated the benzofuran ring into mole-
cules of pentamidine-related analogues. Here we report an
investigation of structure-activity relationships of novel pen-
tamidine congeners 1-48 bearing benzofuran motifs against
T. b. rhodesiense, P. falciparum, L. donovani, and for cyto-
toxicity against mammalian cells.
Results and Discussion
This study investigates the effects of the substitution on the
amidine groups, varying the placement of cationic moieties,
altering the overall geometry of molecules by changing the
position of the benzofuran fragment, and the elongation of
the aliphatic linker between aromatic rings from three to six
carbon atoms on antiprotozoal properties of novel pentami-
dine analogues 1-48. The results of the in vitro evaluation of
dications 1-48 against bloodstream form trypomastigotes of
T. b. rhodesiense (STIB900), chloroquine resistant P. falcipar-
um (K1), axenic amastigotes of L. donovani (MHOM/SD/62/
1S-CL2D), and their cytotoxicities against rat myoblast cells
Chemistry
4-Hydroxy-3-iodobenzonitrile 49 and methyl 3-hydroxy-4-
iodobenzoate 50 were prepared from 4-cyanophenol and
*To whom correspondence should be addressed. Phone: (919) 966-
4294. Fax: (919) 966-0704. E-mail: Tidwell@med.unc.edu.
a Abbreviations: HAT, human African trypanosomiasis; PMD, pen-
tamidine.
r
2009 American Chemical Society
Published on Web 08/10/2009
pubs.acs.org/jmc

5764 Journal of Medicinal Chemistry, 2009, Vol. 52, No. 18
Bakunov et al.
Scheme 1a
a Reagents and conditions: (i) Cu2O, pyridine, 100 °C, overnight; (ii) Me2AlNH2, o-xylene, 110-120 °C, 3 h; (iii) pyridine hydrochloride, 170-180 °C,
3 h.
Scheme 2a
a Reagents and conditions: (i) K2CO3, DMF, 80-100 °C, overnight.
(L6) are summarized in Tables 1 and 2 and compared to the
activity of pentamidine. To demonstrate the degree of selec-
tivity between parasite and mammalian cells, selectivity in-
dexes (SI) expressed as the ratio [IC50 (L6)/IC50 (parasite)]
were calculated for each tested parasite.
than 100 nM. None of the tested compounds demonstrated
a level of activity comparable to that of the standard trypano-
cidal medications. Thus, the most potent diamidine 37 (IC50=
25 nM) was 8-fold less active against T. b. rhodesiense than
pentamidine.
The antitrypanosomal properties of congeners 1-48 de-
pended on the nature and the placement of cationic moieties,
the position of the benzofuran ring, and the length of the
carbon linkers. Thus, bis(N-isopropyl)amidines possessing
one cationic group in the 5-position were more active against
the pathogen than diamidines and diimidazolines in all cases
except dications 11 and 29. There was no correlation between
the type of cationic moieties and activity of 6,30-disubstituted
congeners 13-24 versus T. b. rhodesiense. The antitrypano-
somal potency of 6,40-disubstituted dications 40-48 con-
nected by 4-6-carbon chains against the pathogen reduced
in the order Im > Am > i-PrAm, while the activity of the
dications with the propylene linker decreased as the sub-
stitution on the amidine group increased (Table 2).
Among the compounds with the benzofuran ring attached
to the 30-position (Table 1), 6,30-disubstituted cations con-
nected by the 3-, 5-, and 6-carbon chains were more active
versus T. b. rhodesiense than the corresponding 5,30-disub-
stituted congeners, except for bis(N-isopropyl)amidine 20.
At the same time, 5,30-disubstituted isomers possessing the
Biology
Cytotoxicity Study. Pentamidine congeners containing
benzofuran motifs exhibited cytotoxicities versus L6 cells
ranging from 0.8 to 82 μM. Bis(N-isopropyl)amidines were
generally less cytotoxic than diamidines and diimidazolines
apart from 5,40-disubstituted congener 35 and 6,40-disubsti-
tuted dications 41 and 47. Compounds bearing cationic
groups in the 6-position displayed lower cytotoxicity than
their 5-substituted counterparts in all cases except diamidine
4, bis(N-isopropyl)amidine 32, and diimidazolines 6 and 12,
which were more cytotoxic than the corresponding isomers
16, 44, 18, and 24. The elongation of the carbon linker
increased cytotoxicity of dications, especially those posses-
sing the benzofuran ring in the 30-position.
Antitrypanosomal Activity. All compounds 1-48 dis-
played antitrypanosomal activities in vitro with IC50 values
varying from 25 nM to 1.74 μM. Dications 26, 27, 37, 38 posses-
sing the trimethylene linker and the benzofuran ring attached
to the 40-position exhibited antitrypanosomal IC50 values less

Brief Article
Journal of Medicinal Chemistry, 2009, Vol. 52, No. 18 5765
Table 1. Cytotoxicity and in Vitro Antiprotozoal Activity of Congeners 1-24
T. b. rhodesiensec
P. falciparume
IC50 (μM) SIP
258
L. donovanig
d
f
h
compd
R
n
cytotoxicityb IC50 (μM)
IC50 (μM)
0.907
SIT
11
IC50 (μM)
SIL
1
Am
3
3
3
4
4
4
5
5
5
6
6
6
3
3
3
4
4
4
5
5
5
6
6
6
10.3
26.5
6.5
0.040
0.061
0.109
0.076
0.269
0.099
0.428
0.123
0.099
0.430
0.183
0.049
0.084
0.202
0.095
0.321
0.178
0.098
0.282
0.294
0.047
0.479
0.347
0.041
0.058
3.4
4.5
5.9
4.5
11
3
6
1
2
3
2
i-PrAm
Im
Am
0.547
1.17
48
6
434
60
3
4
8.1
0.779
0.537
1.17
10
68
8
107
136
96
5
i-PrAm
Im
Am
36.5
9.5
6
12
11
<1
<1
1
7
3.0
0.863
0.452
0.597
1.61
3
7
82
8
i-PrAm
Im
Am
10.1
2.6
22
4
6.9
17
9
26
<1
<1
1
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
PMDa
3.1
7.4
2
7
40
23
i-PrAm
Im
Am
1.16
6
7.0
1.9
11
2.5
0.996
0.327
0.483
1.08
26
61
170
9
51
1
19.8
82.3
10.1
7.6
236
407
106
24
2
i-PrAm
Im
Am
11
7
4.7
5.9
12
2
1.33
0.936
2.86
6
1
i-PrAm
Im
Am
46.5
5.8
50
2
261
59
4
7.4
5.7
8.9
17
<1
<1
2
4.1
0.531
0.911
0.442
1.22
8
15
68
i-PrAm
Im
Am
20.1
3.7
22
8
79
<1
<1
2
4.3
4
9
29
24
i-PrAm
Im
10.1
1.8
0.421
0.681
0.003
24
3
6.2
44
44
803
<1
25
46.6
15533
1.8
a PMD, pentamidine. b Cytotoxicity (L6). c T. b. rhodesiense (STIB900). d Selectivity index for T. b. rhodesiense (SIT) [IC50 (L6)/IC50 (T. b.
rhodesiense)]. e P. falciparum (K1). f Selectivity index for P. falciparum (SIP) [IC50 (L6)/IC50 (P. falciparum)]. g L. donovani (MHOM/SD/62/1S-CL2D)
axenic amastigotes. h Selectivity index for L. donovani (SIL) [IC50 (L6)/IC50 (L. donovani)].
butylene linker displayed better antitrypanosomal properties
compared to the 6,30-disubstituted analogues. In the series
of dications bearing benzofuran motifs in the 40-position,
5,40-disubstituted congeners were more active against the
pathogen than the corresponding 6,40-disubstituted iso-
mers apart from diamidines 25 and 31 and diimidazolines
33 and 36.
The geometry of the molecules defined by the placement of
the benzofuran ring also affected antitrypanosomal activities
of dications 1-48. For example, 40-substituted analogues
were more active against T. b. rhodesiense than the 30-
substituted congeners in all cases except bis(N-isopro-
pyl)amidines 29, 41, and 47, which were less potent than
the corresponding isomers 5, 17, and 23.
Dications 1-48 were selective for the Trypanosoma para-
site although none of the tested analogues reached the
selectivity of pentamidine.
Congeners possessing the propylene linker, except for
bis(N-isopropyl)amidine 2 and diimidazoline 3, exhibited
higher antitrypanosomal selectivity than those connected
by the 4- to 6-carbon chains. 5,40-Disubstituted bis(N-iso-
propyl)amidine 26, showing antitrypanosomal IC50 value of
41 nM, was the most selective compound in the group for T.
b. rhodesiense (SIT = 1112).
controls, although none provided cures to the infected mice
(data not shown).
Antiplasmodial Activity. Dications 1-48 displayed activ-
ities against P. falciparum with IC50 values ranging from 28
to 479 nM. Thirteen compounds (1, 12, 21, 24-27, 37-39,
42, 45, and 48) exhibited antiplasmodial properties superior
to those of pentamidine (IC50 = 58 nM). This group of
congeners included three diamidines (1, 25, and 37), two
bis(N-isopropyl)amidines (26 and 38), and eight diimidazo-
lines (12, 21, 24, 27, 39, 42, 45, and 48). Five compounds
(1, 12, 25-27) had one cationic group attached to the 5-
position of the benzofuran motif, and eight were 6-substi-
tuted isomers (21, 24, 37-39, 42, 45, and 48). Nine dications
(12, 25-27, 37-39, 42, 45, and 48) possessed benzofuran
fragment connected to the 40-position of the phenyl ring and
four (1, 12, 21, and 24) had it attached to the 30-position.
Seven of the 13 analogues (1, 25-27, 37-39), including
all diamidines and bis(N-isopropyl)amidines, possessed the
propylene linker. 6,40-Disubstituted diimidazoline 45 con-
nected by the 5-carbon chain was the most potent com-
pound in the series showing the antiplasmodial IC50 value of
28 nM.
The type and the placement of cationic groups, the posi-
tion of the benzofuran ring, and the length of the carbon
linkers influenced antiplasmodial properties of congeners
1-48. Diamidines joined by the propylene linkers exhibited
higher activities versus P. falciparum than bis(N-isopropyl)-
amidines and diimidazolines. However, among the congeners
Compounds 26-28, 37, and 39 have been evaluated in
vivo in the STIB900 acute mouse model of trypanosomiasis.
Administered for 4 days at 20 mg/kg daily, all of the tested
dications increased survival time compared to the untreated

5766 Journal of Medicinal Chemistry, 2009, Vol. 52, No. 18
Bakunov et al.
Table 2. Cytotoxicity and in Vitro Antiprotozoal Activity of Congeners 25-48
T. b. rhodesiensec
P. falciparume
L. donovanig
d
f
h
compd
R
n
cytotoxicityb IC50 (μM)
IC50 (μM)
0.451
SIT
16
IC50 (μM)
SIP
178
IC50 (μM)
SIL
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
PMDa
Am
3
3
3
4
4
4
5
5
5
6
6
6
3
3
3
4
4
4
5
5
5
6
6
6
7.3
0.041
0.042
0.043
0.141
0.302
0.064
0.313
0.193
0.060
0.263
0.063
0.116
0.044
0.037
0.042
0.166
0.139
0.046
0.268
0.074
0.028
0.280
0.052
0.032
0.058
0.78
1.6
NTi
0.61
3.0
9.2
5.1
2.1
39
9
i-PrAm
Im
Am
45.6
10.3
1.3
0.041
0.061
0.164
1.11
1112
169
8
1086
240
9
29
NTi
2
i-PrAm
Im
Am
6.9
2.9
6
23
45
2
0.374
0.369
0.302
0.338
0.368
0.211
0.360
0.025
0.088
0.144
1.06
8
<1
<1
10
<1
5
4.2
11
68
3
13
i-PrAm
Im
Am
20.5
0.9
106
15
3.3
0.8
9
13
13
0.65
5.4
3.3
0.78
3.2
0.48
3.2
4.5
13
i-PrAm
Im
Am
4
<1
<1
11
16
35
4
1.5
8.6
4
13
344
567
117
13
9
195
1349
400
85
i-PrAm
Im
Am
49.9
16.8
14.1
15.9
16.9
9.0
i-PrAm
Im
Am
1.74
114
367
34
4
0.942
0.313
0.557
0.262
0.416
0.884
0.224
0.003
18
29
19
12
19
6
1
2.9
1.4
10
NTi
2.6
15
3
i-PrAm
Im
Am
10.7
3.2
145
114
29
8
<1
NTi
2
8.0
4.9
i-PrAm
Im
94
3.4
46.6
15
15533
106
803
<1
25
1.8
a PMD, pentamidine. b Cytotoxicity (L6). c T. b. rhodesiense (STIB900). d Selectivity index for T. b. rhodesiense (SIT) [IC50 (L6)/IC50 (T. b.
rhodesiense)]. e P. falciparum (K1). f Selectivity index for P. falciparum (SIP) [IC50 (L6)/IC50 (P. falciparum)]. g L. donovani (MHOM/SD/62/1S-CL2D)
axenic amastigotes. h Selectivity index for L. donovani (SIL) [IC50 (L6)/IC50 (L. donovani)]. i NT, not tested.
with elongated carbon chains, diimidazolines displayed greater
antiplasmodial potency.
pyl)amidines 26 and 38, both connected by the propylene
linker, were more selective for P. falciparum than pentamidine.
Antileishmanial Activity. All tested compounds were active
in the L. donovani axenic amastigote assay demonstrating
activities ranging from 0.48 to 44 μM. Four diamidines (25,
28, 34, and 37), three bis(N-isopropyl)amidines (26, 32, and
44), and two diimidazolines (12 and 39) exhibited antileish-
manial IC50 values comparable to or lower than that of
pentamidine (IC50 = 1.8 μM). Out of nine dications, only
diimidazoline 12 had the benzofuran motif in the 30-position.
Among the eight congeners with the benzofuran fragment
connected to the 40-position of the phenyl ring, five com-
pounds (25, 26, 28, 32, and 34) contained their substituents in
the 5,40-positions and three (37, 39, and 44) were 6,40-
disubstituted isomers. Diamidine 28 and diimidazoline 39
were the most potent compounds versus L. donovani among
5- and 6-substituted congeners, respectively.
There was no obvious correlation between the position of
attachment of the cationic moieties to the benzofuran frag-
ment and the antileishmanial properties of 5,40- and 6,40-
disubstituted congeners. However, in the series of dications
bearing the benzofuran motif in the 30-position, 5,30-disub-
stituted diamidines and bis(N-isopropyl)amidines were more
active against L. donovani than 6,30-disubstituted analogues
apart from congeners 7 and 11. Concurrently, 6,30-disubsti-
tuted diimidazolines exhibited higher antileishmanial po-
tency than their 5,30-disubstituted counterparts, except for
congener 24. The placement of the benzofuran motif influenced
5,30-Disubstituted diamidines and bis(N-isopropyl)amidines
were more active than the corresponding 6,30-disubstituted
isomers except for congeners 5 and 7, while diimidazolines
15, 18, 21, bearing cationic groups in the 6,30-positions
exhibited superior antiplasmodial properties compared to
the 5,30-disubstituted analogues 3, 6, 9, and 12. Among the
dications possessing the benzofuran motif in the 40-position,
5,40-disubstituted diamidines were more potent against the
pathogen than the corresponding 6,40-disubstituted isomers
except diamidine 31. At the same time, 6,40-disubstituted
bis(N-isopropyl)amidines and diimidazolines were more
active versus P. falciparum than the comparable 5,40-disub-
stituted isomers.
All 6,40-disubstituted analogues 37-48 displayed higher
antimalarial activities than the corresponding 6,30-disubsti-
tuted congeners 13-24 while no correlation between the
position of the benzofuran ring and antiplasmodial proper-
ties of 5-substituted analogues was observed. All dications
1-48 were selective for P. falciparum and displayed selectiv-
ity indexes ranging from 7 to nearly 1350. Regardless of the
position of the cationic substituents and the length of the
carbon chains between the aromatic moieties, bis(N-isopro-
pyl)amidines and diimidazolines were more selective for the
parasite compared to diamidines.
Elongation of the alkyl chains usually reduced the antiplas-
modial selectivity of the congeners 1-48. Thus, bis(N-isopro-

Brief Article
Journal of Medicinal Chemistry, 2009, Vol. 52, No. 18 5767
the antileishmanial properties of dications 1-48. Thus, regard-
less of the position of the cationic moieties, 40-substituted
congeners displayed higher activities versus L. donovani than
their analogues with the benzofuran fragment connected to the
30-position of the phenyl ring in all cases except for diimidazo-
lines 33, 36, and 42.
The antileishmanial selectivity of dications 1-48 de-
pended on the substitution on the amidine groups, the
placement of the benzofuran fragment, and the length of
the carbon linkers in the molecules. Bis(N-isopropyl)amidines
were more selective for L. donovani than diimidazolines and
diamidines. Compounds bearing the benzofuran motif con-
nected to the 40-position generally exhibited higher selectivity
for the pathogen compared to the 30-substituted isomers.
Elongation of the carbon linkers usually reduced the antil-
eishmanial selectivity of congeners 1-48. Diimidazoline 39
was not only the most potent compound in the series
exhibiting antileishmanial IC50 value of 0.48 μM but also
demonstrated the highest selectivity for L. donovani (SIL =
35), which was greater than that of pentamidine.
The imidate (0.51 g, 0.90 mmol) was suspended in dry EtOH
saturated with gaseous ammonia (11 mL) and was stirred at
room temperature. The reaction mixture was diluted with
diethyl ether (50 mL). A precipitate was separated, washed with
ether, dried and recrystallized from 1 M HCl/EtOH to give 1 as a
white solid (0.230 g, 51%): mp 175-178 °C. 1H NMR (DMSO-
d6) δ 9.41 (br s, 2H), 9.22 (br s, 2H), 9.12 (br s, 2H), 8.94 (br s,
2H), 8.19 (d, J = 1.8 Hz, 1H), 7.90 (d, J = 8.6 Hz, 1H), 7.85 (d, J
= 8.8 Hz, 2H), 7.78 (dd, J = 8.6 and 1.8 Hz, 1H), 7.70 (s, 1H),
7.57 (d, J = 7.8 Hz, 1H), 7.55 (m, 1H), 7.43 (dd, J = 7.8 and 7.8
Hz, 1H), 7.21 (d, J = 8.8 Hz, 2H), 7.07 (dd, J = 7.8 and 1.8 Hz,
1H), 4.36-4.16 (m, 4H), 2.30-2.18 (m, 2H). HPLC (method A)
tR = 7.91 min (100 area %). Anal. (C25H24N4O3 2HCl
3
3
1.4H2O) C, H, N, Cl.
Acknowledgment. This work was supported by the Bill and
Melinda Gates Foundation.
Supporting Information Available: Experimental details
and characterization data. This material is available free of
charge via the Internet at http://pubs.acs.org.
References
Conclusions
(1) Barrett, M. P.; Boykin, D. W.; Brun, R.; Tidwell, R. R. Human
African trypanosomiasis: pharmacological re-engagement with a
neglected disease. Br. J. Pharmacol. 2007, 152, 1155–1171.
(2) Burri, C.; Brun, R. Human African Trypanosomiasis. In Manson’s
Tropical Diseases; Cook, G. C., Zumla, A., Eds.; W. B. Saunders:
London, 2008; pp 1307-1325.
A series of pentamidine congeners 1-48 containing benzo-
furan fragments have been synthesized and tested in vitro
against T. b. rhodesiense, P. falciparum, and L. donovani, and
for cytotoxicity versus mammalian cells. The antiprotozoal
properties and cytotoxicities of dications 1-48 depended on
the nature of the cationic substituents, the placement of the
benzofuran motif, and the length of the carbon linker. The
cytotoxicities of tested compounds decreased with the sub-
stitution on cationic groups and increased with the elongation
of the carbon linker. Dications with the benzofuran motif
in the 40-position and connected by the propylene linker
demonstrated higher potency and were more selective
against T. b. rhodesiense, P. falciparum and L. donovani.
Improved antileishmanial activities of select congeners com-
pared to pentamidine warrant further investigation of these
compounds as potential leads for antileishmanial chemo-
therapy.
(3) Croft, S. L.; Yardley, V. Chemotherapy of leishmaniasis. Curr.
Pharm. Des 2002, 8, 319–342.
(4) Goa, K. L.; Campoli-Richards, D. M. Pentamidine isethionate. A
review of its antiprotozoal activity, pharmacokinetic properties
and therapeutic use in Pneumocystis carinii pneumonia. Drugs
1987, 33, 242–258.
(5) Stead, A. M.; Bray, P. G.; Edwards, I. G.; DeKoning, H. P.; Elford,
B. C.; Stocks, P. A.; Ward, S. A. Diamidine compounds: selective
uptake and targeting in Plasmodium falciparum. Mol. Pharmacol.
2001, 59, 1298–1306.
(6) Bray, P. G.; Barrett, M. P.; Ward, S. A.; de Koning, H. P.
Pentamidine uptake and resistance in pathogenic protozoa: past,
present and future. Trends Parasitol. 2003, 19, 232–239.
(7) Fairlamb, A. H. Chemotherapy of human African trypanosomia-
sis: current and future prospects. Trends Parasitol. 2003, 19, 488–
494.
(8) Bakunova, S. M.; Bakunov, S. A.; Wenzler, T.; Barszcz, T.;
Werbovetz, K. A.; Brun, R.; Hall, J. E.; Tidwell, R. R. Synthesis
and in vitro antiprotozoal activity of bisbenzofuran cations. J.
Med. Chem. 2007, 50, 5807–5823.
Experimental Section
(9) Bakunov, S. A.; Bakunova, S. M.; Wenzler, T.; Barszcz, T.;
Werbovetz, K. A.; Brun, R.; Tidwell, R. R. Synthesis and anti-
protozoal activity of cationic 2-phenylbenzofurans. J. Med. Chem.
2008, 51, 6927–6944.
(10) Dulog, L.; Korner, B.; Heinze, J.; Yang, J. Synthesis and electro-
chemical properties of 4-phenyl-1-buten-3-yne-1,1,2-tricarboni-
triles and tricyanoacrylates. Liebigs Ann. Chem 1995, 1663–1671.
(11) Doad, G. J. S.; Barltrop, J. A.; Petty, C. M.; Owen, T. C. A versatile
and convenient synthesis of benzofurans. Tetrahedron Lett. 1989,
30, 1597–1598.
(12) Wood, J. L.; Khatri, N. A.; Weinreb, S. M. A direct conversion of
esters to nitriles. Tetrahedron Lett. 1979, 20, 4907–4910.
(13) Berg, S. S.; Newbery, G. The search for chemotherapeutic ami-
dines. Part X. Substituted 4,4’-diamidino-Rω-diphenoxyalkanes
and -diphenyl ethers. J. Chem. Soc. 1949, 642–648.
(14) Dox, A. W.; Whitmore, F. C. Acetamidine hydrochloride. In
Organic Syntheses, 2nd ed.; Blatt, A. H., Ed. John Wiley and Sons:
New York, 1941; Vol. 1, pp 5-7.
Fullexperimental details and characterization data are given in
the Supporting Information. All tested compounds are >95%
purebyelementalanalysis and HPLC. Proton NMRspectra were
recorded on a Varian Gemini 2000 spectrometer (300 MHz) with
tetramethylsilane as an internal standard.
General Procedure for Syntheses of Cationic Benzofurans 1-
48. 2-(3-(3-(4-Carbamimidoylphenoxy)propoxy)phenyl)benzofu-
ran-5-carboxamidine Dihydrochloride (1). A mixture of anhy-
drous ethanol (10 mL) and 1,4-dioxane (30 mL) was saturated
with gaseous HCl at 0-5 °C. 2-(3-(3-(4-Cyanophenoxy)propoxy)-
phenyl)benzofuran-5-carbonitrile (67) (1.00 g, 2.54 mmol) was
added and the sealed mixture was stirred at room temperature.
The reaction mixture was diluted with dry ether. A precipitate
was separated under Ar and dried under high vacuum over
KOH to give an imidate ester as a white solid (1.42 g, 100%).