2,4-Diphenyl furan diamidines as novel anti-Pneumocystis carinii pneumonia agents

Article abstract of DOI:10.1021/jm990071c

Dicationic 2,4-bis(4-amidinophenyl)furans 5-10 and 2,4-bis(4- amidinophenyl)-3,5-dimethylfurans 14 and 15 have been synthesized. Thermal melting studies revealed high binding affinity of the compounds to poly(dA- dT) and to the duplex oligomer d(CGCGAATTC

Full text of DOI:10.1021/jm990071c

2260
J . Med. Chem. 1999, 42, 2260-2265
2,4-Dip h en yl F u r a n Dia m id in es a s Novel An ti-P n eu m ocystis ca r in ii P n eu m on ia
Agen ts
Iris Francesconi,† W. David Wilson,† Farial A. Tanious,† J ames E. Hall,‡ Brendan C. Bender,‡
Richard R. Tidwell,‡ Donald McCurdy,‡ and David W. Boykin*,†
Department of Chemistry and Center for Biotechnology and Drug Design, Georgia State University,
Atlanta, Georgia 30303-3083, and Department of Pathology, School of Medicine,
The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
Received February 10, 1999
Dicationic 2,4-bis(4-amidinophenyl)furans 5-10 and 2,4-bis(4-amidinophenyl)-3,5-dimethyl-
furans 14 and 15 have been synthesized. Thermal melting studies revealed high binding affinity
of the compounds to poly(dA-dT) and to the duplex oligomer d(CGCGAATTCGCG)2. All of the
new compounds were effective against Pneumocystis carinii pneumonia in the immunosup-
pressed rat model with up to 200-fold increase in activity compared to the control compound
pentamidine. No toxicity was noted for 5, 7-10 at the dose of 10 µmol/kg/d; however, the
isopropyl analogue 7 showed toxicity comparable to pentamidine at the dosage of 20 µmol/kg/
d. Dimethylation of the parent compound on the furan ring resulted in reduced activity and
increased toxicity.
In tr od u ction
and their biological evaluation against P. carinii pneu-
monia in the immunosuppressed rat model.
The primary goals of optimum pneumocystosis treat-
ment are immediate alleviation of symptoms, a micro-
bicidal effect on the organism, and prevention or mini-
mization of adverse drug reactions without causing a
reduction in efficacy. Efficacy and safety therefore play
a primary role in the selection of therapeutic agents.1
Pentamidine is an effective agent for the treatment of
Pneumocystis carinii pneumonia (PCP), but clinical
development of pentamidine-type molecules has been
severely limited not only by the toxicity of several of
the compounds but also by the lack of understanding of
their mechanisms of toxicity and action, pharmacoki-
netics, and structure-activity relationships. Recent
evidence from studies of various aromatic amidines
related to pentamidine supports the hypothesis of initial
binding of these drug candidates to AT-rich regions of
the minor groove of DNA and subsequent inhibition of
microbial enzymes. However, no quantitative correlation
has been established between DNA binding and biologi-
cal activity.
The broad anti-infective, in particular anti-PCP activ-
ity, reported for 2,5-bis(4-amidinophenyl)furan10 and its
low in vivo toxicity led to the design of a new set of
dicationic diphenyl furans. Modifications of the lead
compound were intended to increase nonbonding inter-
actions between the drugs and the minor groove of the
DNA. A change in the substitution pattern as well as
dimethylation of the central furan ring was assumed
to induce an out-of-plane twist, which could result in
enhanced isohelicity of these compounds with the inner
surface of the minor groove. Different positioning in the
minor groove could favor additional H-bonding as well
as electrostatic interactions. This report describes the
synthesis of 2,4-bis(4-amidinophenyl)furans, their rela-
tive binding affinity to the minor groove of AT-rich DNA,
Ch em istr y
The synthesis for target compounds 5-10 employed
a base-catalyzed condensation of 4-cyanobenzaldehyde
with 4-cyanoacetophenone (Scheme 1). Addition of
bromine to the R,â-unsaturated ketone 1 and subse-
quent treatment with sodium methoxide gave an enol
ether2-5 which was used for the next reaction step
without further identification or purification. The key
step for the furan formation employed highly reactive
dimethyl sulfonium methylide generated in dimethyl
sulfoxide.6 This insertion reaction gave a furanoid
product 3, readily identified as a 2,4-diarylfuran. The
classical Pinner method was employed to transform the
cyano into amidine groups.7 The imidate ester 4, gener-
ated as an intermediate product, was very hygroscopic
and tended to hydrolyze fairly rapidly if left exposed to
the atmosphere. However, immediate reaction with the
appropriate amine gave the desired amidines 5-10.8-11
The low solubility of free amidines with an extended
aromatic backbone in aqueous systems is a major reason
amidines are converted to salts prior to in vitro or in
vivo testing.
Target compounds 14 and 15 were prepared from bis-
(4-bromophenyl)furan (Scheme 2) by bromomethylation
with formaldehyde and HBr and subsequent reduction
using LAH to give 11.8 Substitution of the aromatic
bromo groups employing Cu(I)CN led to the cyano-
substituted intermediate 1212 which was transformed
into the amidine derivatives 14 and 15 employing the
Pinner method.7-11 The free amidine bases were pre-
cipited as HCl salts.
Biologica l Resu lts
Melting temperatures were measured for the com-
pounds 5-10 and 14-15 bound to poly(dA-dT)2 to
obtain a qualitative evaluation of the DNA binding
† Georgia State University.
‡ The University of North Carolina at Chapel Hill.
10.1021/jm990071c CCC: $18.00 © 1999 American Chemical Society
Published on Web 05/11/1999

Anti-Pneumocystis carinii Pneumonia Agents
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 12 2261
Sch em e 1
affinity of these drug candidates. The difference in Tm
values between the drug-DNA complexes and free
DNA in solution provides a useful tool to assess the
interaction strength of the molecules with DNA. Since
all compounds bound very strongly to poly(dA-dT)
(Table 1), the Dickerson-Drew dodecamer d(CGC-
GAATTCGCG)2, a DNA with different groove dimen-
sions, was employed. The reduced binding affinity of the
drugs to the dodecomer, reflected by the lower Tm values
of the drug-docedamer complexes (Table 1), allowed a
better relative comparison of the DNA binding affinity
of these minor groove binding compounds.
Docking experiments suggested that the compounds
5-10 fit well into the minor groove at the center of the
AT-rich region with the hydrogen on carbon 3 of the
central furan ring pointing toward the bottom of the
groove. Steric hindrance derived from the unfavorable
interaction of this hydrogen atom with the bottom of
the groove seemed to be responsible for a somewhat
decreased binding affinity to DNA of this set of 2,4-
substituted diphenylfuran diamidines in comparison to
a set of correspondingly substituted 2,5-diphenylfuran
diamidines, previously reported in the literature.10
Steric interactions between the phenyl ring on carbon
4 and the hydrogen atoms on the central furan ring of
compounds 5-10 seemed to induce an out-of-plane
twist, suggested also by preliminary crystal structure
data and by AM1 calculations performed on the inter-
mediate product 2,4-bis(4-bromophenyl)furan. A signifi-
cantly larger twist was expected for compounds 14 and
15 due to the methyl groups on carbon 3 and 5 of the
central furan ring, which may contribute to the lower
binding affinity of these compounds in comparison to
compounds 5-10. In the approach of the compounds 14
and 15 toward the bottom of the groove, the methyl
group on carbon 3 was not expected to contribute
additional steric hindrance compared to the hydrogen
atom of compounds 5-10, as according to unpublished
data on N-methyl-substituted pyrrole systems the minor
groove seemed to be able to accommodate methyl groups
quite well.
The amidine groups at the termini of the molecules
seemed to contribute significantly to the complex stabil-
ity between the dications and the DNA through H-
bonding and electrostatic interactions. Different posi-
tioning of the cationic groups due to a larger twist of
compounds 14 and 15 might have resulted in less
favorable interactions and therefore lower binding af-
finity of these compounds in comparison to compounds
5-10. The extended aromatic core region of the mol-
ecules 5-10 is expected to favor extensive contacts
between the compounds and the hydrophobic surface of
the groove. However, the suggested large twist of
compounds 14 and 15 might have had the opposite effect

2262 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 12
Francesconi et al.
Sch em e 2
Ta ble 1. Nucleic Acid Binding Results of
Ta ble 2. In Vivo anti-Pneumocystis carinii Pneumonia Activity
2,4-Bis(4-amidinophenyl)furans
of 2,4-Bis(4-amidinophenyl)furans
a
b
R
∆Tm (DNA)
∆Tm (oligomer)
dosage
(µmol/kg/d)
cyst/g of lunga
(% of control)
compound
toxicityb
pentamidine
12.6
19.0
16.8
17.6
23.2
20.4
20.4
17.0
12.5
4.8
9.1
7.2
10.9
10.9
9.3
13.6
6.5
saline
pentamidine
100.00 ( 22.28c
2.30 ( 1.08c
0.30 ( 0.24
0.00 ( 0.00
0.04 ( 0.02
0.08 ( 0.02
2.42 ( 1.00
110.50 ( 25.38
0.01 ( 0.00
0.16 ( 0.14
1.79 ( 0.61
0.89 ( 0.46
24.43 ( 10.68
5
6
7
8
22.0
10.0
20.0
10.0
5.0
++
0
++
0
0
0
0
0
0
0
+
0
5
7
9
10
14
15
1.0
0.25
10.0
10.0
1.0
10.0
10.0
5.4
8
Increase in thermal melting of poly(dA-dT)2.18 Increase in
10
a
b
thermal melting of d(CGCGAATTCGCG)2.19
14
15
and reduce favorable van der Waals interactions of the
aromatic rings with the walls of the groove. Alkyl
substitution on the amidino nitrogen of the compounds
7-10 resulted in higher affinity for DNA compared to
the unsubstituted parent compound 5. These results
were consistent with increased van der Waals interac-
tions between the alkyl groups and the walls of the
minor groove. The slightly reduced binding affinity of
the isobutyl compound 9 could be due to the greater
flexibility of this alkyl group. Entropic factors may have
also contributed to the stability of the complex. The
significantly reduced binding affinity of the isopropyl
derivative 15 could in part be due to unfavorable
positioning of the alkyl groups which probably resulted
in steric hindrance rather than in additional van der
Waals interactions.
a
Lower numbers of cysts/g of lung refer to higher activity
against Pneumocystis carinii pneumonia. Values below 1% of
control are within the experimental error and can be considered
as complete cure of the pneumonia infections in the immunosup-
pressed rats.13-15 Toxicity of the test compounds is evaluated
b
according to a five-level scale ranging from 0 to 5+. The toxicity
information reported in the in vivo studies should not be consid-
ered definitive and is mainly anectotal in nature. These values
though do allow for a comparison of the relative toxicities of the
compounds and of the control drug pentamidine.13-15 c Mean cyst
count for pooled controls: saline (n ) 46) 100.0 ( 22.28 cysts/g of
lung tissue; pentamidine (n ) 42) 2.30 ( 1.08.
pressed rat model.13-15 Except for 15, all test compounds
showed significantly higher anti-PCP activity than the
control compound pentamidine (Table 2). An investiga-
tion of the dose-response of the alkyl-substituted dia-
midines 7 and 10 showed an 11-fold decrease in the anti-
P. carinii activity of compound 10 and a 60-fold decrease
in activity of compound 7 when the dosage was reduced
from 10 to 1 µmol/kg/d. A qualitative evaluation of the
Four of the 2,4-diphenylfuran diamidines, 5, 7, 8, and
10, and the 3,5-dimethylated compounds 14 and 15 have
been evaluated on intravenous administration against
Pneumocystis carinii pneumonia in the immunosup-

Anti-Pneumocystis carinii Pneumonia Agents
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 12 2263
30 min. The clear orange solution was cooled to room temper-
ature and poured into 100 mL water. The aqueous suspension
was extracted with CH2Cl2, the organic phase was dried over
NaSO4, and the solvent was removed under reduced pressure
to give an oily orange residue. A suspension of 1.03 g (42.9
mmol) of NaH in 15 mL of dry DMSO was stirred at room
temperature for 30 min. Dry THF (30 mL) was added, and
the suspension was cooled in a salt/ice bath to 0 °C and treated
dropwise with a solution of 8.78 g (43.0 mmol) of trimethyl-
sulfonium iodide in 15 mL of dry DMSO. The suspension was
stirred for 5 min and treated with a solution of the crude enol
ether in 25 mL of dry THF. The dark suspension was stirred
at ice bath temperature for 15 min, the ice bath was removed,
and stirring was continued for 18 h. The mixture was poured
into 300 mL of water and extracted with CHCl3. The solvent
was evaporated, and the oily residue was passed through a
silica gel column to obtain an off-white crystalline solid.
toxicity in the same in vivo studies showed that the 2,4-
diphenylfuran diamidines 5, 7, 8, 10, and 15 caused no
toxic side effects at the administered dosages of 10 µmol/
kg/d or less. At a dosage of 20 µmol/kg/d compound 7
showed side effects comparable to those of the control
compound pentamidine; however, activity levels of these
two compounds were significantly different. Introduc-
tion of the methyl groups on the central furan ring as
seen in compound 14 and 15 resulted in reduced activity
and, for compound 14, in increased toxicity. A compari-
son of the 2,4-substituted furan diamidines 5, 7, 8, and
10 to a set of correspondingly substituted 2,5-bis(4-
amidinophenyl)furans showed that the correlation be-
tween DNA binding affinity and biological activity
previously reported for the symmetrical set of com-
pounds10 cannot be confirmed for the 2,4-diphenyl
derivatives. It is also noteworthy that despite weaker
interaction with DNA, the 2,4-substituted compounds
turned out to have higher biological activity against PCP
in the immunosuppressed rat model than the 2,5-
substituted analogues.10
Yield: 1.89 g (20%), mp 229-231 °C. IR (KBr): 2222 cm-1
.
1H NMR (CDCl3): δ 7.91 (s, 1 H), 7.81 (d, 2 H, J ) 8.8 Hz),
7.72 (d, 2 H, J ) 8.8 Hz), 7.71 (d, 2 H, J ) 8.8 Hz), 7.63 (d, 2
H, J ) 8.8 Hz), 7.12 (s, 1 H). 13C NMR (CDCl3): δ 153.9, 140.8,
136.5, 134.1, 133.0, 132.9, 127.8, 126.5, 124.5, 118.9, 111.5,
111.3, 106.5. Anal. (C18H10N2O) C, H, N.
2,4-Bis(4-eth oxyim in oylp h en yl)fu r a n Dih yd r och lor id e
(4). Dinitrile 3 (0.50 g, 1.8 mmol) was suspended in 20 mL of
dry EtOH, and the solution was saturated with HCl gas at
ice bath temperature. The flask was sealed, and stirring was
continued at room temperature for another 3 d. The imidate
ester hydrochloride was precipitated with 20 mL of dry Et2O,
filtered, and dried under vacuum at room temperature. Yield:
0.80 g (99%). Because of its hygroscopic nature and limited
stability the imidate ester is used immediately for the forma-
tion of amidines without purification.
Exp er im en ta l Section
Melting points were determined in open capillary tubes with
a Thomas-Hoover and with a Mel-Temp 3.0 capillary melting
point apparatus and are uncorrected. IR spectra were recorded
on a Perkin-Elmer 2000 FT-IR spectrometer, 1H and 13C
nuclear magnetic resonance spectra were recorded on a Varian
Unity +300 and a Varian VRX 400 instrument. Mass spectra
were recorded on a VG Instruments 70-SE spectrometer by
Georgia Institute of Technology, Atlanta, GA. Elemental
analyses were performed on a Perkin-Elmer 2400 Series II C,
H, N organic elemental analyzer or by Atlantic Microlab,
Norcross, GA, and are within (0.4 of the theoretical values
unless otherwise noted. All chemical and solvents were
purchased from Aldrich Chemical Co., Fisher Scientific, or
Acros organics. In the cases where dry solvents were required,
MeOH and EtOH were distilled from Mg metal, THF and Et2O
were distilled from Na/benzophenone, and DMSO was distilled
from CaH2.
1,3-Bis(4-cya n op h en yl)p r op -2-en -1-on e (1). 4-Cyanoben-
zaldehyde (10.00 g, 76.3 mmol) and 4-acetylbenzonitrile (11.07
g, 76.3 mmol) were dissolved in 150 mL of dry MeOH and
heated to reflux. NaOH (1 N) was added dropwise until
precipitation occurred, and refluxing was continued for another
5 min. The suspension was cooled to room temperature, and
the bright yellow solid was filtered, washed with Et2O, and
dried over CaSO4 under vacuum. Yield: 12.89 g (65%), mp
2,4-Bis(4-a m id in op h en yl)fu r a n (5). A suspension of 0.80
g (1.8 mmol) of imidate ester hydrochloride 4 in 20 mL of dry
EtOH was cooled to 0 °C in an ice bath and saturated with
dry NH3 gas. The ice bath was removed, the flask was sealed,
and stirring was continued for 72 h. After addition of 20 mL
of 1 M NaOH, the white suspension was stirred for 1 h. The
solid was filtered, washed with water, and dried over CaSO4
under reduced pressure. For purification the crude product was
heated in dry EtOH for 30 min, again filtered, and dried over
CaSO4. A suspension of the free base in 20 mL of dry EtOH
was saturated with dry HCl gas at 0 °C, and stirring was
continued for 2 h at room temperature. The yellow solid was
precipitated with 20 mL of dry Et2O, filtered, and dried under
1
vacuum. Yield: 0.42 g (96%), mp > 346 °C decomposition. H
NMR (DMSO-d6:D2O 1:1): δ 8.33 (s, 1 H), 7.92 (d, 2 H, J )
8.4 Hz), 7.84-7.78 (m, 6 H), 7.60 (s, 1 H). 13C NMR (DMSO-
d6:D2O 1:1): δ 166.4, 166.3, 154.1, 142.9, 138.0, 135.6, 129.7,
129.7, 128.1, 127.4, 127.1, 127.1, 125.1, 107.9. MS: m/e 305
(M+) free base. Anal. Calcd for C18H16N4O‚.2HCl‚1H2O: C,
54.69; H, 5.10; N, 14.17. Found: C, 54.99; H, 4.98; N, 13.10.
113-115 °C, lit.16 mp 111-114 °C. IR (KBr): 2228, 1670 cm-1
.
1H NMR (DMSO-d6): δ 8.30 (d, 2 H, J ) 8.1 Hz), 8.10 (d, 2 H,
J ) 8.7 Hz), 8.09 (d, 1 H, J ) 15.3 Hz), 8.06 (d, 2 H, 7.5 Hz),
7.80 (d, 1 H, J ) 15.6 Hz). 13C NMR (DMSO-d6): δ 188.4, 142.8,
140.4, 138.8, 132.7, 132.6, 129.5, 129.1, 124.9, 118.4, 118.0,
115.2, 112.5. Anal. (C17H10N2O) C, H, N.
2,4-Bis[4,5-d ih yd r o-1H-im id a zol-2-yl)p h en yl]fu r a n Di-
h yd r och lor id e (6). Dried and freshly distilled 1,2-diamino-
ethane (freshly distilled from KOH) (0.14 mL, 2.1 mmol) was
added to a suspension of 0.41 g (0.9 mmol) of imidate ester
hydrochloride 4 in 20 mL of dry EtOH, and under exclusion
of water the solution was refluxed for 16 h. The solvent was
removed under reduced pressure, the residue was suspended
in 20 mL of 1 N KOH, and the suspension was stirred for 30
min. The solid was filtered, washed with H2O, and dried in
vacuo. The free imidazoline base was suspended in 20 mL of
dry EtOH, and the solution was saturated with HCl gas at
ice bath temperature. After the solution was stirred for 2 h
the imidazoline salt was precipitated with 20 mL of dry Et2O,
filtered, and dried under vacuum. Yield: 0.22 g (49%), mp >
300 °C decomposition. 1H NMR (DMSO-d6): δ 8.21(s, 1 H),
7.90-7.78 (m, 8 H), 7.48 (s, 1 H), 3.96 (t, 8 H). 13C NMR
(DMSO-d6): δ 167.0, 166.9, 154.7, 143.7, 139.1, 136.6, 130.5,
128.7, 127.9, 125.8, 122.3, 122.0, 108.6, 46.0. Anal. (C22H20N4O‚
2HCl‚3H2O) C, H, N.
1,3-Bis(4-cya n op h en yl)-2,3-d ibr om op r op a n -1-on e (2).
Compound 1 (12.89 g, 49.9 mmol) was added to a solution of
2.6 mL of Br2 (50.5 mmol) in 150 mL of CHCl3. The suspension
was stirred at room temperature for 3 h. The solvent was
evaporated under reduced pressure, and the solid was filtered,
washed with Et2O, and dried over CaSO4 under reduced
pressure. Yield: 19.78 g (95%), mp 187-189 °C. IR (KBr):
2228, 1691 cm-1 1H NMR (CDCl3): δ 8.18 (d, 2 H, J ) 8.4
.
Hz), 7.87 (d, 2 H, J ) 8.8 Hz), 7.75 (d, 2 H, J ) 8.4 Hz), 7.64
(d, 2 H, J ) 8.0 Hz), 6.70 (d, 1 H, J ) 11.2 Hz), 5.62 (d, 1 H,
J ) 11.2 Hz). 13C NMR (CDCl3): δ 189.5, 142.9, 137.4, 133.1,
132.9, 129.5, 129.4, 118.2, 117.8, 117.7, 113.6, 47.5, 46.2. Anal.
(C17H10N2OBr2) C, H, N.
2,4-Bis(4-cya n op h en yl)fu r a n (3). A suspension of 15.00
g (35.9 mmol) of 2 in 150 mL of dry MeOH was heated to
reflux. Freshly prepared 3 M MeONa (2.49 g of Na in 36 mL
of MeOH) was added dropwise, and stirring was continued for
2,4-Bis[4-{N-(isop r op yla m id in o)p h en yl}]fu r a n (7). In
a sealed flask a mixture of 1.47 g (3.4 mmol) of imidate ester

2264 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 12
Francesconi et al.
hydrochloride 4 and 0.75 mL (8.8 mmol) of isopropylamine
(freshly distilled from KOH) in 20 mL of dry EtOH was stirred
at room temperature for 3 d. The solvent was removed under
reduced pressure, and the residue was suspended in 1 N
NaOH. After the mixture was stirred for 30 min, the white
solid was filtered, washed with water, and dried in vacuo. The
white solid was suspended in 30 mL of dry EtOH, and the
solution was saturated with HCl gas at ice bath temperature.
Stirring was continued for 2 h, and the yellow solid was
precipitated with 30 mL of dry Et2O, filtered, and dried under
(DMSO-d6): δ 163.6, 154.4, 142.6, 137.4, 135.2 129.9, 129.8,
128.7, 128.4, 128.3, 127.1, 125.1, 107.7, 55.7, 32.5 24.6. MS:
m/e 441 (M+) free base. Anal. Calcd for C28H34N4O‚2HCl‚5/
4H2O: C, 64.18; H, 7.02; N, 10.69. Found: C, 63.80, H, 6.51;
N, 10.47.
2,4-Bis(4-br om oph en yl)-3,5-dim eth ylfu r an (11).Paraform-
aldehyde (1.24 g, 41.3 mmol) was added to 35 mL of a 30%
solution of HBr in glacial acetic acid. 2,4-Bis(4-bromophenyl)-
furan17 (1.56 g, 4.1 mmol) was added, and the dark mixture
was stirred at room temperature for 2 d. The solution was
poured into 250 mL of H2O and stirred for 15 min. The light
green precipitate was filtered, washed with water, and dried
under vacuum. Without further purification the 2.20 g (3.90
mmol) of bis(4-bromophenyl)-3,5-dibromomethyl-2,4-furan was
added to a suspension of 0.59 g (15.5 mmol) of LAH in 30 mL
of dry Et2O. The suspension was stirred at room temperature
for 1 h, then slowly poured into 100 mL H2O. The precipitate
was filtered over Celite and thoroughly washed with Et2O, and
the two phases of the filtrate were separated. The organic
phase was washed with water, dried over Na2SO4, and reduced
under vacuum. Yield: 1.44 g (91%), mp 167-169 °C. 1H NMR
(CDCl3): δ 7.58-7.52 (m, 6 H), 7.17 (d, 2 H, J ) 8.4 Hz), 2.34
(s, 3 H), 2.16 (s, 3 H). 13C NMR (CDCl3): δ 147.9, 146.4, 132.6,
131.9, 131.5, 130.9, 126.9, 124.3, 121.2, 120.6, 117.0, 12.6, 10.9.
MS: m/e 406 (M+). Anal. Calcd for C18H14OBr2: C, 53.23; H,
3.47. Found: C, 53.72, H, 3.76.
1
vacuum. Yield: 0.73 g (47%), mp >305 °C decomposition. H
NMR (DMSO-d6): δ 8.31 (s, 1 H), 7.80-7.67 (m, 8 H), 7.54 (s,
1 H), 3.81 (m, 2 H), 1.14 (d, 12 H, J ) 4.8 Hz). 13C NMR
(DMSO-d6): δ 153.6, 139.6, 136.6, 136.1, 132.4, 130.6, 127.4,
126.9, 126.8, 124.8, 122.8, 104.9, 43.4, 22.8. Anal. (C24H28N4O‚
2HCl‚5/4H2O) C, H, N.
2,4-Bis[4-{N-(cyclop r op yla m id in o)p h en yl}]fu r a n (8).
In a sealed flask a mixture of 0.74 g (1.7 mmol) of imidate
ester hydrochloride 4 and 0.29 mL (4.1 mmol) of cyclopropy-
lamine (freshly distilled from KOH) in 15 mL of dry EtOH was
stirred at room temperature for 2 d. The suspension was
poured into 100 mL of water, and the free amidine base was
precipitated with 20 mL of 1 M NaOH. The suspension was
diluted with another 100 mL of water and stirred at room
temperature for 30 min. The beige precipitate was filtered,
washed with water, and dried in vacuo. The free base was
suspended in 10 mL of dry EtOH, and the solution was
saturated with HCl gas at ice bath temperature. Stirring was
continued for 2 h at room temperature, and the yellow
hydrochloric salt was precipitated with 50 mL of dry Et2O,
filtered, and dried under vacuum. Yield: 0.42 g (59%), mp >
2,4-Bis(4-cya n op h en yl)-3,5-d im eth ylfu r a n (12). To a
suspension of 3.31 g (36.9 mmol) of Cu(I)CN in 30 mL of
N-methylpyrrolidin-2-one was added 1.44 g (3.7 mmol) of 2,4-
bis(4-bromophenyl)-3,5-dimethylfuran 11. The suspension was
heated to reflux for 2.5 h. After cooling to room temperature
the suspension was poured into a solution of 41 mL of
concentrated NH4OH in 100 mL of water. The mixture was
stirred for 15 min, and the precipitate was filtered, washed
with water, and dried over CaSO4 under reduced pressure. The
dry precipitate was extracted with CHCl3 in a Soxhlet extrac-
tion apparatus for 3 d. The solvent was evaporated, and the
crude product was purified by column chromatography on
silica gel. Yield: 0.47 g (42%), mp 164-166 °C. IR (KBr): 2228
1
240 °C decomposition. H NMR (DMSO-d6:D2O): δ 8.36 (s, 1
H), 7.98 (d, 2 H, J ) 8.0 Hz), 7.88 (d, 2 H, J ) 7.2 Hz), 7.80 (d,
2 H, J ) 8.4 Hz), 7.78 (d, 2 H, J ) 8.0 Hz), 7.63 (s, 1 H), 2.79
(s, 2 H), 1.04 (d, 4 H, J ) 5.2 Hz), 0.85 (s, 4 H). 13C NMR
(DMSO-d6:D2O): 166.6, 166.4, 154.6, 142.9, 138.1, 135.8, 129.8,
129.8, 128.5, 128.1, 127.8, 127.5, 125.5, 108.0, 25.1, 7.6. Anal.
(C24H24N4O‚2HCl‚2/3H2O) C, H, N.
2,4-Bis[4-{N-(isobu tyla m id in o)p h en yl}]fu r a n (9). In a
sealed flask a mixture of 0.64 g (1.5 mmol) of imidate ester
hydrochloride 4 and 0.32 mL (3.2 mmol) of isobutylamine in
10 mL of dry EtOH was stirred for 2 d at room temperature.
NaOH (10 mL, 1 M) was added to the light yellow suspension,
and stirring was continued for another 1.5 h. The mixture was
poured into 150 mL of H2O, and the off-white precipitation
was filtered, washed with H2O, and dried over CaSO4 under
vacuum. The crude product was recrystallized from EtOH/
Et2O. The free base was dissolved in 10 mL of dry EtOH, and
the solution was saturated with HCl gas at ice bath temper-
ature. Stirring was continued at room temperature for 2 h,
and the light yellow solid was precipitated with 10 mL of dry
Et2O, filtered, and dried under vacuum. Yield: 0.36 g (50%),
1
cm-1. H NMR (CDCl3): δ 7.75 (d, 4 H, J ) 7.6 Hz), 7.70 (d, 2
H, J ) 8.8 Hz), 7.40 (d, 2 H, J ) 8.4 Hz), 2.39 (s, 3 H), 2.23 (s,
3 H). 13C NMR (CDCl3): δ 150.0, 146.1, 138.2, 135.7, 132.7,
132.6, 130.4, 125.4, 124.6, 119.4, 119.2, 118.9, 111.2, 110.0,
12.8, 11.2. MS: m/e 298 (M+). Anal. Calcd for C20H14N2O: C,
80.52; H, 4.73; N, 9.39. Found: C, 79.63; H, 4.83; N, 9.23.
3,5-Dim eth yl-2,4-bis(4-eth oxyim in oylp h en yl)fu r a n Di-
h yd r och lor id e (13). 2,4-Bis(4-cyanophenyl)-3,5-dimethylfu-
ran 12 (0.30 g, 1.0 mmol) was suspended in 15 mL of dry
EtOH, and the solution was saturated with HCl gas at ice bath
temperature. The flask was sealed and stirring was continued
at room temperature for 1 d. The imidate ester hydrochloride
was precipitated with 50 mL of Et2O, filtered, and dried over
CaSO4 under vacuum. Yield: 0.37 g (79%). Because of its
hygroscopic nature and limited stability the imidate ester is
used immediately for the formation of amidines without
further purification.
2,4-Bis(4-a m id in op h en yl)-3,5-d im eth ylfu r a n (14). 3,5-
Dimethyl-2,4-bis(4-ethoxyiminoylphenyl)furan dihydrochloride
13 (0.62 g, 1.3 mmol) was suspended in 15 mL of dry EtOH,
and the solution was saturated with dry NH3 gas at ice bath
temperature. The flask was sealed, and the suspension was
stirred for 5 d. The solvent was removed under reduced
pressure, and the oily residue was suspended in 200 mL of
water. NaOH (30 mL, 1 M) was added to the clear solution,
and the mixture was stirred for 30 min at room temperature.
The precipitate was filtered, washed with water, and dried over
CaSO4 under vacuum. The free amidine base was dissolved
in 10 mL of dry EtOH, and the solution was saturated with
HCl gas at ice bath temperature. The suspension was stirred
at room temperature for 1 h, and the hydrochloric salt was
precipitated with 100 mL of dry Et2O, filtered, and dried over
CaSO4 under vacuum. Yield: 0.31 g (82%), mp > 285 °C
decomposition. 1H NMR (DMSO-d6:D2O 1:1): δ 7.80 (d, 6 H, J
) 8.4 Hz), 7.51 (d, 2 H, J ) 8.1 Hz), 2.30 (s, 3 H), 2.16 (s, 3 H).
1
mp > 278 °C decomposition. H NMR (DMSO-d6:D2O 1:1): δ
8.47 (s, 1 H), 7.95 (d, 2 H, J ) 8.0 Hz), 7.89 (d, 2 H, J ) 8.0
Hz), 7.81-7.74 (m, 5 H), 3.23 (t, 4 H), 2.00 (m, 2 H), 0.96 (m,
12 H). 13C NMR (DMSO-d6:D2O 1:1): δ 163.3, 163.2, 153.4,
142.3, 136.7, 134.4, 129.3, 129.2, 128.0, 127.7, 127.5, 126.2,
124.2, 107.3, 49.9, 27.3, 20.2. Anal. (C26H32N4O‚2HCl‚1H2O)
C, H, N.
2,4-Bis[4-{N-(cyclop en tyla m id in o)p h en yl}]fu r a n (10).
In a sealed flask a mixture of 0.53 g (1.2 mmol) of imidate
ester hydrochloride 4 and 0.27 mL (2.7 mmol) of cyclopenty-
lamine (freshly distilled from KOH) in 20 mL of dry EtOH was
stirred at room temperature for 24 h. NaOH (20 mL, 1 M) was
added, and stirring was continued for 30 min. The solid was
filtered, washed with H2O, and dried under reduced pressure.
The free amidine base was suspended in 20 mL of dry EtOH,
and the solution was saturated with HCl gas at ice bath
temperature. After the mixture was stirred for 5 h, the yellow
solid was precipitated with 20 mL of dry Et2O, filtered, and
dried under vacuum. Yield: 0.43 g (69%), mp > 302 °C
decomposition. 1H NMR (DMSO-d6): δ 8.25 (s, 1 H), 7.87 (d, 2
H, J ) 8.0 Hz), 7.77 (d, 2 H, J ) 8.0 Hz), 7.67 (t, 4 H), 7.52 (s,
1 H), 4.00 (m, 2 H), 2.00 (m, 8 H), 1.62 (m, 8 H).13C NMR

Anti-Pneumocystis carinii Pneumonia Agents
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 12 2265
13C NMR (DMSO-d6:D2O 1:1): δ 166.9, 151.4, 146.5, 139.5,
137.2, 131.3, 129.7, 129.4, 127.2, 126.2, 125.0, 120.8, 13.3, 11.6.
Anal. (C20H20N4O‚2HCl‚1/2H2O) C, H, N.
(6) Harris, C. M.; Cleary, J . J .; Harris, T. M. Condensations of Enol
Ethers of beta-Dicarbonyl Compounds with Dimethylsulfonium
Methylide and Dimethyloxosulfonium Methylide. J . Org. Chem.
1974, 39, 72-77.
(7) Dox, A. W.; Whitmore, F. C. In Organic Synthesis, 2nd ed.;
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1, p 5-7.
(8) Das, B. P.; Boykin, D. W. Synthesis and Antiprotozoal Activity
of 2,5-Bis(4-guanylphenyl)furans. J . Med. Chem. 1976, 20, 531-
536.
(9) Boykin, D. W.; Kumar, A.; Spychala, J .; Zhou, M.; Lombardy,
R. J .; Wilson, W. D.; Dykstra, C. C.; J ones, S. K.; Hall, J . E.;
Tidwell, R. R.; Laughton, C.; Nunn, C. M.; Neidle, S. Dicationic
Diarylfurans as Anti-Pneumocystis carinii Agents. J . Med. Chem.
1995, 38, 912-916.
(10) Boykin, D. W.; Kumar, A.; Xiao, G.; Wilson, W. D.; Bender, B.
C.; McCurdy, D. R.; Hall, J . E.; Tidwell, R. R. 2,5-Bis[4-(N-
alkylamidino)phenyl]furans as Anti-Pneumocystis carinii Agents.
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(11) Weller, T.; Alig, L.; Beresini, M.; Blackburn, B.; Bunting, S.;
Hadvary, P.; Huerzeler-Mueller, M.; Knopp, D.; Levet-Trafit, B.;
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Solvent in Preparing Nitriles from Aryl Halides and Cuprous
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C. A.; Berger, B. J .; Hall, J . E. Development of Pentamidine
Analogues as New Agents for the Treatment of Pneumocystis
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K. A.; Reddy, V. V.; Geratz, J . D.; Tidwell, R. R. Novel
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2,4-Bis[4-{N-(isop r op yla m id in o)p h en yl}]-3,5-d im eth yl-
fu r a n (15). In a sealed flask a mixture of 0.61 g (1.3 mmol) of
3,5-dimethyl-2,4-bis(4-ethoxyiminoylphenyl)furan dihydrochlo-
ride 13 and 0.27 mL (3.2 mmol) of isopropylamine in 10 mL of
dry EtOH was stirred at room temperature for 2 d. The solvent
was removed under reduced pressure, and the oily residue was
suspended in 200 mL of water. NaOH (10 mL, 1 M) was added
to the clear solution, and the mixture was stirred at room
temperature for 30 min. The light yellow precipitate was
filtered under nitrogen atmosphere and dried under vacuum
over CaSO4. The free amidine base was dissolved in 10 mL of
dry EtOH and the solution was saturated with HCl gas at ice
bath temperature. The solution was stirred at room temper-
ature for 2 h, and the hydrochloric salt was precipitated with
100 mL of dry Et2O, filtered under nitrogen atmosphere, and
dried over CaSO4 under vacuum. Yield: 0.54 g (85%), mp 284-
1
286 °C. H NMR (DMSO-d6:D2O 1:1): δ 7.79-7.68 (m, 6 H),
7.48 (d, 2 H, J ) 8.1 Hz), 3.89 (m, 2 H), 2.30 (s, 3 H), 2.15 (s,
3 H), 1.26 (s, 3 H), 1.26 (s, 3 H), 1.24 (s, 3 H), 1.24 (s, 3 H). 13
C
NMR (DMSO-d6:D2O 1:1): δ 163.4, 163.2, 151.3, 146.7, 139.0,
136.7, 131.3, 129.7, 129.4, 128.6, 127.7, 126.3, 125.2, 120.6,
46.9, 22.0, 13.4, 11.7. Anal. (C26H2N4O‚2HCl‚9/4H2O) C, H, N.
Ack n ow led gm en t. This work was supported by
NIH Grant NIAID AI-33363 (D.W.B.) and the Fulbright
Commission (I.F.). An award by the Chemical Instru-
mental Program of NSF (CHE 8409599) and the Georgia
Research Alliance provided partial support for acquisi-
tion of the NMR spectrometers used in this work.
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