Synthesis and antiprotozoal activity of novel bis-benzamidino imidazo[1,2-a]pyridines and 5,6,7,8-tetrahydro-imidazo[1,2-a]pyridines

Article abstract of DOI:10.1016/j.bmc.2007.10.042

The key dinitrile intermediates 4a-d were synthesized by reaction of phenacyl bromide 1 and the appropriate 2-amino-5-bromopyridines to yield 3a-d. Suzuki coupling of 3a-d with 4-cyanophenylboronic acid yielded the 2,6-bis(4-cyanophenyl)-imidazo[1,2-a]pyridine derivatives 4a-d. The bis-amidoximes 5a-d, obtained from 4a-d by the action of hydroxylamine, were converted to the bis-O-acetoxyamidoximes which on catalytic hydrogenation in a mixture of ethanol/ethyl acetate gave the acetate salts of 2,6-bis[4-(amidinophenyl)]-imidazo[1,2-a]pyridines 7a-d. In contrast, catalytic hydrogenation of the bis-O-acetoxyamidoxime of 5a in glacial acetic acid gave the saturated analogue 2,6-bis[4-(amidinophenyl)]-5,6,7,8-tetrahydro-imidazo[1,2-a]pyridine 8. O-Methylation of the amidoximes 5a-d gave the N-methoxyamidines 6a-d. The diamidines showed strong DNA binding affinity, were very active in vitro against T. b. r. exhibiting IC₅₀ values between 7 and 38 nM, but were less effective against P. f. with IC₅₀ values between 23 and 92 nM. Two of the diamidines 7c and 7d were slightly more active than furamidine but less active than azafuramidine in the T. b. r. STIB900 mouse model. Only one prodrug 6b showed moderate activity in the same mouse model.

Full text of DOI:10.1016/j.bmc.2007.10.042

Available online at www.sciencedirect.com
Bioorganic & Medicinal Chemistry 16 (2008) 683–691
Synthesis and antiprotozoal activity of novel bis-benzamidino
imidazo[1,2-a]pyridines and 5,6,7,8-tetrahydro-
imidazo[1,2-a]pyridines
Mohamed A. Ismail,a Reem K. Arafa,a Tanja Wenzler,b Reto Brun,b
Farial A. Tanious,a W. David Wilsona and David W. Boykina,*
aDepartment of Chemistry and Center for Biotechnology and Drug Design, Georgia State University, Atlanta, GA 30303-3083, USA
bParasite Chemotherapy, Swiss Tropical Institute, Basel CH4002, Switzerland
Received 11 September 2007; revised 8 October 2007; accepted 12 October 2007
Available online 18 October 2007
Abstract—The key dinitrile intermediates 4a–d were synthesized by reaction of phenacyl bromide 1 and the appropriate 2-amino-5-
bromopyridines to yield 3a–d. Suzuki coupling of 3a–d with 4-cyanophenylboronic acid yielded the 2,6-bis(4-cyanophenyl)-imi-
dazo[1,2-a]pyridine derivatives 4a–d. The bis-amidoximes 5a–d, obtained from 4a–d by the action of hydroxylamine, were converted
to the bis-O-acetoxyamidoximes which on catalytic hydrogenation in a mixture of ethanol/ethyl acetate gave the acetate salts of 2,6-
bis[4-(amidinophenyl)]-imidazo[1,2-a]pyridines 7a–d. In contrast, catalytic hydrogenation of the bis-O-acetoxyamidoxime of 5a in
glacial acetic acid gave the saturated analogue 2,6-bis[4-(amidinophenyl)]-5,6,7,8-tetrahydro-imidazo[1,2-a]pyridine 8. O-Methyla-
tion of the amidoximes 5a–d gave the N-methoxyamidines 6a–d. The diamidines showed strong DNA binding affinity, were very
active in vitro against T. b. r. exhibiting IC50 values between 7 and 38 nM, but were less effective against P. f. with IC50 values
between 23 and 92 nM. Two of the diamidines 7c and 7d were slightly more active than furamidine but less active than azafuram-
idine in the T. b. r. STIB900 mouse model. Only one prodrug 6b showed moderate activity in the same mouse model.
ꢀ 2007 Elsevier Ltd. All rights reserved.
1. Introduction
tion of such diamidines is hypothesized to arise from
their binding to the minor groove of DNA at AT rich
sites.2,4–9 It has been further suggested that the DNA
binding leads to inhibition of DNA dependent enzymes
and possibly direct inhibition of transcription.9–13 At
least in part, the selectivity of the diamidines seems
likely due to involvement of amidine transporters for
uptake14 and strong binding to kinetoplast DNA once
in the parasite.1b
Dicationic diamidine derivatives have long been known
to exhibit broad-spectrum antiprotozoal activity.1 A sig-
nificant number of these compounds possesses effective-
ness against the protozoan diseases caused by
Trypanosoma brucei and Plasmodium sp.1 Despite this
fact, pentamidine (I) is the only compound of this class
to see clinical use.1 A prodrug of furamidine [2,5-bis(4-
amidinophenyl)furan] (IIa), pafuramidine [2,5-bis[4-
(methoxyamidino)phenyl]furan] (IIb), is currently in
two Phase III clinical trials as an oral drug versus hu-
man African trypanosomiasis (HAT) and against
Previous bis-benzamidine drug discovery efforts have fo-
cused on variations in the linker between the benzami-
dine units ranging from oxyalkyl groups for
pentamidine analogues to aryl/heteroaryl rings for
furamidine types. Extensive numbers of 5- and 6-mem-
bered ring systems have been investigated as a linker
for the bis-benzamidines of furamidine (replacement of
furan).1 However, larger linker units such as two fused
5-ring units or a fused 5–6-membered ring system does
not appear to have been investigated. Larger appropri-
ately designed linkers can be envisioned to be potent
minor groove binders and potentially show useful anti-
protozoan activity.15 As an initial effort to explore the
AIDS-related Pneumocystsis jiroveci pneumonia.1,2
closely related prodrug IId of the azafuramidine IIc is
effective in a model of late stage HAT and is under eval-
uation for clinical advancement.3 The antiparasitic ac-
A
Keywords: Diamidines; Antiprotozoal agents; Minor-groove binders;
Imidazo[1,2-a]pyridines; Prodrugs.
*
Corresponding author. Tel.: +1 404 413 5498; fax: +1 404 413
5505; e-mail: dboykin@gsu.edu
0968-0896/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2007.10.042

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M. A. Ismail et al. / Bioorg. Med. Chem. 16 (2008) 683–691
efficacy of triaryl bis-benzamidine molecules with larger
linkers we have elected to study a series of bis-benzam-
idine imidazo[1,2-a]pyridines. Imidazo[1,2-a]pyridine
units are important building blocks in both natural
and synthetic bioactive compounds16,17 and we have
found that an amidino imidazo[1,2-a]pyridine as a
replacement of one of the benzamidine units yields
highly effective antiprotozoan agents.18 All of these fac-
tors lead us to synthesize bis-benzamidino imidazo[1,2-
a]pyridine and 5,6,7,8-tetrahydroimidazo[1,2-a]pyri-
dines for evaluation of their DNA affinity and their anti-
protozoan activity. In addition, N-methoxy amidine
analogues were prepared as potential prodrugs for their
corresponding diamidines.
gen heterocycles further illustrates the importance of
solvent selection for this reaction.18,19 Nevertheless,
these hydrogenations are also quite sensitive to substrate
substituents since attempts to reduce bis-O-acetoxyami-
doximes of the analogues 5b–d by acetic acid aided cat-
alytic hydrogenation failed demonstrating that these
solvent effects are also quite sensitive to substrate
substituents.
Potential prodrugs, the N-methoxyamidines 6a–d, were
prepared by O-methylation of their corresponding bis-
amidoxime precursors 5a–d using dimethyl sulfate in
aqueous lithium hydroxide solution in reasonable yields
(Scheme 1). The hydrochloride salts of the 2,6-bis[4-(N-
methoxyamidinophenyl)]-imidazo[1,2-a]pyridine deriva-
tives 6a–d were obtained by passing hydrogen chloride
gas into ethanolic solutions of their free bases.
O
O
2.2. Biology
HN
NH
NH2
NH2
I
The results for the evaluation of the new diamidines
against Trypanosoma brucei rhodesiense (T. b. r.) and
Plasmodium falciparum (P. f.) and their DNA binding
affinities are shown in Table 1. For comparative pur-
poses the analogous data for furamidine (IIa) and an
azafuramidine (IIc) are also included in Table 1. The
DNA affinities for the diamidines 7a–d and 8 are repre-
sented by the DTm values for their complexes with
poly(dA-dT). The DTm values for 7a–d are shown as
>28 ꢁC which indicates that under the conditions of this
experiment the complexes are quite stable and did not
melt. Clearly, the interaction of 7a–d with DNA is quite
favorable as the affinity is greater than that of furami-
dine (DTm = 25 ꢁC). The interaction of 8 with DNA is
strong (DTm = 22.9 ꢁC) but not as favorable as that
for furamidine or 7a–d. The lower affinity for 8 which
contains a partially unsaturated linker is not unex-
pected as the non-planar linker would not be expected
to have as favorable van der Waals contacts as its pla-
nar counterparts 7a–d. These results demonstrate that
larger linkers when appropriately arrayed can lead to
potent DNA binders. CD spectra of 7a and 8 on titra-
tion into a solution of a polyd(A-T)2 DNA sequence
were monitored from 220 to 450 nm. At the maximum
absorption wavelength of the compounds, where the
DNA CD signals do not interfere, positive induced
CD signals were observed around 330 nm (Fig. 1). Nei-
ther 7a nor 8 has intrinsic CD signals and the signals
shown in Figure 1 are for the bound compound. Such
positive induced CD signals are generally a characteris-
tic of binding in the minor groove of DNA as observed
for other minor groove binding compounds.20,21 Pre-
sumably, the conjugated compound 7a shows a stron-
ger induced CD signal than 8 because it can slide
more deeply into the minor groove and interact better
with walls of the minor groove and the base pairs at
the floor of the groove. The CD results were obtained
at relatively high concentration, with respect to Kd, in
order to obtain satisfactory signals but they can still
be used to approximate Kd values. For 7a Kd
ꢀ20 nM with DNA concentration in base pairs and
for 8 Kd ꢀ250 nM, significantly less than for 7 in agree-
ment with DTm values. The CD results thus show that
NR
O
RN
H2N
X
NH2
IIa R = H; X = CH
IIb R = OMe; X = CH
IIc R = H; X = N
IId R = OMe; X = N
2. Results and discussion
2.1. Chemistry
As illustrated in Scheme 1, the key 2,6-bis(4-cyano-
phenyl)-imidazo[1,2-a]pyridine intermediates 4a–d were
prepared in two steps. The first step involves condensa-
tion between 4-cyanophenacyl bromide 1 and the appro-
priate 2-aminopyridine to yield, after cyclization, the
4-(6-bromo-imidazo[1,2-a]pyridin-2-yl)-benzonitriles
3a–d. In the second step, a Suzuki coupling reaction
between 3a–d and 4-cyanophenylboronic acid furnished
2,6-bis(4-cyanophenyl)imidazo[1,2-a]pyridine
deriva-
tives 4a–d in high yields. The dinitriles 4a–d were con-
verted to the corresponding bis-amidoximes 5a–d via
reaction with hydroxylamine in DMSO solution. There-
after, the acetate salts of the 2,6-bis[4-(amidin-
ophenyl)]imidazo[1,2-a]pyridine derivatives 7a–d were
obtained by transformation of the corresponding bis-
amidoximes 5a–d to their bis-O-acetoxyamidoxime
counterparts, without isolation, followed by catalytic
hydrogenation in a mixture of ethanol/ethyl acetate.
Interestingly, catalytic hydrogenation of the bis-O-acet-
oxyamidoxime of 5a in glacial acetic acid furnished the
saturated diamidine 2,6-bis[4-(amidinophenyl)]-5,6,7,8-
tetrahydroimidazo[1,2-a]pyridine 8 (Scheme 1). These
results indicate that proper choice of the hydrogenation
solvent(s) determines whether the product will be satu-
rated or unsaturated. A previous publication from our
laboratory as well as recent study of the effect of solvent
on the course of catalytic hydrogenation of other nitro-

M. A. Ismail et al. / Bioorg. Med. Chem. 16 (2008) 683–691
685
R1
R2
O
R2
Br
R1
Br
N
(i)
+
NC
Br
N
NC
H2N
N
2a-d
1
3a-d
R1
R2
N
(iii)
(ii)
NC
R2
N
CN
4a-d
R1
R1
R2
(iv)
N
N
HON
MeON
H2N
N
N
NOMe
NH2
H2N
NOH
NH2
5a-d
6a-d
(v)
(vi)
R1
R2
N
HN
N
N
NH
NH2
HN
H2N
N
7a-d
R2
H2N
NH
NH2
8
R1
2-7
a;
H
H
H
CH3
b;
c;
H
CH3
CH3 CH3
d;
Scheme 1. Reagents and conditions: (i) EtOH, reflux; (ii) 4-cyanophenyl boronic acid, Pd(PPh3)4; (iii) NH2OHÆHCl/K–O–t-Bu, DMSO; (iv) LiOH/
(CH3)2SO4; (v) (a) Ac2O/AcOH, (b) H2/Pd-C, EtOH (vi) (a) Ac2O/AcOH, (b) H2/Pd-C, AcOH.
Table 1. DNA affinities and in vitro anti-protozoan data
R
1
R
RN
2
N
N
H N
2
NR
NH
2
a
Code
Pyridine ring
R
R1
R2
DTm (ꢁC)
T. b. r. IC50 (nM)b
P. f. IC50 (nM)b
Cytotoxicity IC50 (lM)
IIa
IIc
8
NA
NA
NA
NA
H
NA
NA
H
NA
NA
H
25
4.3
6.5
14
15.5
6.5
85
6400
19.3
22.9
>28
77,900
8900
2500
Saturated
7a
6a
7b
6b
7c
6c
7d
6d
Unsaturated
Unsaturated
Unsaturated
Unsaturated
Unsaturated
Unsaturated
Unsaturated
Unsaturated
H
H
H
7.5
825
38
92
OMe
H
H
H
181
23
6900
7400
CH3
CH3
H
H
>28
>28
>28
OMe
H
H
2367
13
614
27
9500
6800
CH3
CH3
CH3
CH3
OMe
H
OMe
H
1739
15
880
63
17,000
4700
>146,800
CH3
CH3
7207
3249
a See Ref. 22.
b Average of duplicate determinations, see Ref. 22.
these compounds bind very strongly in the DNA minor
groove.
The diamidines 7a–d and 8 are very effective against
T. b. r., their IC50 values range from 7 to 38 nM,

686
M. A. Ismail et al. / Bioorg. Med. Chem. 16 (2008) 683–691
30
20
10
0
8
7a
-10
-20
250
300
350
400
250
300
350
400
450
Wavelength (nm)
Wavelength (nm)
Figure 1. Induced CD signals for 7a and 8 with the polyd(A-T)2 DNA duplex in MES 10 buffer at 25 ꢁC. Molar ratios of compounds to DNA base
pairs are 0, 0.05, 0.10, 0.15, 0.20, 0.25, and 0.30 for 7a, and 0.10, 0.20, 0.30, 0.40, 0.50, and 0.60 for 8.
however they are not quite as potent as furamidine
(IC50 = 4.3 nM). The activity of 7a–d and 8 against
P. f. is reduced from that against T. b. r. as the IC50
values range from 23 to 92 nM. These compounds are
Table 2 contains the results for evaluation of these com-
pounds in the STIB900 model for acute African trypan-
osomasis. To select and discriminate the compounds
with superior activity over the first generation com-
pound furamidine, it was decided to reduce the standard
screening dose for the diamidines to 5 mg/kg ip and
25 mg/kg po for prodrugs. This new condition makes
the model more stringent and enables better discrimina-
tion among active compounds. On intraperitoneal dos-
ing at 5 mg/kg all of the diamidines, 7a–d and 8,
extend the survival time of the treated animals 5 days
also less active against P. f. than furamidine (IC50
=
15.5 nM). As anticipated, the activities of the prodrugs
in the in vitro screens were low. The selectivity indices
for 7a–d and 8 are quite reasonable ranging from 194
to 635 based on their cytotoxicity to rat L-6 myoblast
cells. Based upon these results the compounds were ad-
vanced to an animal model for T. b. r.
Table 2. In vivo anti-trypanosomal activity of imidazo[1,2-a]pyridines and 5,6,7,8-tetrahydro-imidazo[1,2-a]pyridine analogues in the STIB900
mouse modela
R
1
R
RN
H N
2
N
N
2
NR
NH
2
Code
Pyridine ring
R
R1
R2
Dosage route
Dosageb (mg/kg)
Curesc
Survival (days)d
IIa
IIb
IIc
IId
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
ip
5
0/4
1/4
3/4
4/4
4/4
4/4
0/4
0/4
0/4
0/4
1/4
1/4
0/4
1/4
0/4
35.5
>60
po
ip
25
5
>54.5
>60
>60
po
25
5
8
Saturated
H
H
H
ip
20
5
>60
31.25
22
7a
6a
7b
6b
7c
6c
7d
6d
Unsaturated
Unsaturated
Unsaturated
Unsaturated
Unsaturated
Unsaturated
Unsaturated
Unsaturated
H
H
H
ip
20
25
5
OMe
H
H
H
po
ip
10.75
14.75
>20.25
>37.25
14.5
CH3
CH3
H
H
OMe
H
H
po
ip
25
5
CH3
CH3
CH3
CH3
OMe
H
OMe
H
po
ip
25
5
CH3
CH3
>39.5
15.5
po
25
a See Ref. 22 for details of STIB900 model.
b Dosage was for 4 days; ip, intraperitoneal; po, oral.
c Number of mice that survive and are parasite free for 60 days.
d Average days of survival; untreated control animals expire between day 7 and 9 post-infection.

M. A. Ismail et al. / Bioorg. Med. Chem. 16 (2008) 683–691
687
or more beyond that of untreated controls. Compounds
7c and 7d provide 1/4 cures at a dose of 5 mg/kg. Thus,
these two compounds are more effective in vivo than
furamidine which at this dosage provided no cures,
but not as effective as the azafuramidine IIc which yields
3/4 cures at the same dose. Compound 8 at a dosage of
20 mg/kg gave 4/4 cures, whereas 7a at the same dose
failed to provide cures. Only one of the prodrugs 6b pro-
vided 1/4 cures at the standard screening dose of 25 mg/
kg po. This result is comparable to that of pafuramidine
(IIb) which also gives 1/4 cures at this dosage but was
inferior to the prodrug of an azafuramidine IId which
provides 4/4 cures at both the screening dose and
remarkably at the low dose of 5 mg/kg po.
titrated into the same cuvette and the complexes
rescanned under same conditions. Changes in CD spec-
tra as a function of added compound concentration
were used to approximate Kd values for binding by using
published methods.24
3.5. Chemistry
Melting points were recorded using a Thomas-Hoover
(Uni-Melt) capillary melting point apparatus and are
uncorrected. TLC analysis was carried out on silica
gel 60 F254 precoated aluminum sheets and detected
under UV light. 1H and 13C NMR spectra were re-
corded employing a Varian Unity Plus 300 spectrome-
ter (Varian, Inc., Palo Alto, California), and chemical
shifts (d) are in ppm relative to TMS as the internal
standard. Mass spectra were recorded on a VG analyt-
ical 70-SE spectrometer (VG Analytical, Ltd., Man-
chester, United Kingdom). Elemental analyses were
obtained from Atlantic Microlab Inc. (Norcross, GA)
and are within 0.4 of the theoretical values. The
compounds reported as salts were frequently analyzed
correctly for fractional moles of water and/or ethanol
of solvation. In each case, proton NMR showed the
presence of indicated solvent(s). All chemicals and sol-
vents were purchased from Aldrich Chemical Co.,
Fisher Scientific, Frontier Scientific or Lancaster Syn-
thesis, Inc.
The strategy to replace the furan linker with the larger
imidazo[1,2-a]pyridine unit worked quite well as judged
by the high DNA affinities observed and by the fact that
these molecules were found to be effective antiprotozoal
agents on both in vitro and in vivo evaluation. The ob-
served DNA affinities for 7a–d are superior to that of
furamidine and their antiprotozoal activity is compara-
ble to that of furamidine. These results clearly suggest
that other linkers larger than single 5- or 6-ring systems
merit careful exploration.
3. Experimental
3.1. Biology
3.5.1.
4-(6-Bromo-imidazo[1,2-a]pyridin-2-yl)-benzoni-
trile (3a). A mixture of 2-amino-5-bromopyridine
(1.73 g, 10 mmol) and 4-cyanophenacyl bromide
(2.24 g, 10 mmol) in ethanol (50 mL) was heated at re-
flux for 24 h. The precipitated salt was filtered, sus-
pended in water, and neutralized with aqueous
NaHCO3 solution. The free base precipitate was fil-
tered and dried to furnish 3a in 62% yield, mp 218–
219 ꢁC (EtOH). 1H NMR (DMSO-d6); d 7.41 (d,
J = 8.7 Hz, 1H), 7.61 (d, J = 8.7 Hz, 1H), 7.90 (d,
J = 8.4 Hz, 2H), 8.15 (d, J = 8.4 Hz, 2H ), 8.53 (s,
1H), 8.92 (s, 1H). 13C NMR (DMSO-d6); d 143.5,
143.0, 137.9, 132.7, 128.5, 127.1, 126.1, 118.8, 117.9,
111.3, 110.0, 106.4. EIMS (m/z, rel. int.); 298 (M+,
100). Anal. Calcd for C14H8BrN3: C, 56.40; H, 2.70.
Found C, 56.33; H, 2.74.
3.2. Efficacy evaluations
In vitro assays with T. b. r. STIB 900 and P. f. K1 strain
as well as the efficacy study in an acute mouse model for
T. b. r. STIB 900 were carried out as previously
reported.22
3.3. Tm measurements
Thermal melting experiments were conducted with a
Cary 300 spectrophotometer. Cuvettes for the experi-
ment are mounted in a thermal block and the solution
temperatures are monitored by a thermistor in the refer-
ence cuvette. Temperatures were maintained under com-
puter control and are increased at 0.5 ꢁC/min. The
experiments were conducted in 1 cm path length quartz
curvettes in CAC 10 buffer (cacodylic acid 10 mM,
EDTA 1 mM, NaCl 100 mM with NaOH added to give
pH 7.0). The concentrations of DNA were determined
by measuring the absorbance at 260 nm. A ratio of
0.3 mole compound per mole of DNA was used for
the complex and DNA with no compound was used as
a control.23
3.5.2. 2,6-Bis(4-cyanophenyl)-imidazo[1,2-a]pyridine (4a).
To a stirred solution of 3a (2.98 g, 10 mmol) and tetra-
kis(triphenylphosphine) palladium (350 mg) in toluene
(20 mL) under a nitrogen atmosphere was added
10 mL of a 2 M aqueous solution of Na2CO3 followed
by 4-cyanophenylboronic acid (1.75 g, 12 mmol) in
10 mL of methanol. The vigorously stirred mixture
was warmed to 80 ꢁC for 24 h, then cooled, and the pre-
cipitate was filtered. The precipitate was partitioned be-
tween methylene chloride (500 mL) and 2 M aqueous
Na2CO3 (50 mL) containing 6 mL of concentrated
ammonia. The organic layer was dried (Na2SO4) and
then concentrated to dryness under reduced pressure
3.4. Circular dichroism (CD)
CD spectra were collected with a Jasco J-810 spectrom-
eter at different ratios of compound to DNA at 25 ꢁC in
MES 10 buffer. A DNA solution in a 1-cm quartz cuv-
ette was first scanned over a desired wavelength range.
Compounds 7a and 8 at increasing ratios were then
1
to afford 4a in 69% yield, mp 292–294 ꢁC (EtOH). H
NMR (DMSO-d6); d 7.70 (s, 2H), 7.88 (d, J = 7.8 Hz,
2H), 7.94 (s, 4H), 8.17 (d, J = 7.8 Hz, 2H), 8.55 (s,
1H), 9.02 (s, 1H). 13C NMR (DMSO-d6); d 144.4,

688
M. A. Ismail et al. / Bioorg. Med. Chem. 16 (2008) 683–691
1
143.2, 140.9, 138.0, 132.8, 132.6, 127.2, 126.1, 125.4,
125.0, 123.7, 118.8, 118.5, 117.0, 111.6, 110.2, 109.9.
EIMS (m/z, rel. int.); 320 (M+, 100), 293 (5), 191 (3),
179 (10), 160 (15). HRMS calcd for C21H12N4:
320.10620. Observed: 320.10640. Anal. Calcd for
C21H12N4: C, 78.73; H, 3.78. Found C, 78.46; H, 3.93.
with ether to give 7a in 76% yield mp 259–261 ꢁC. H
NMR (D2O/DMSO-d6); d 1.97 (s, 3· CH3), 7.67 (s,
2H), 7.77–7.88 (m, 6H), 8.07 (d, J = 8.4 Hz, 2H), 8.48
(s, 1H), 8.94 (s, 1H). Anal. Calcd for C21H18N6–
3.0AcOH–1.9H2O: C, 57.01; H, 5.98; N, 14.78. Found:
C, 56.68; H, 5.98; N, 15.02.
3.5.3. 2,6-Bis[4-(N-hydroxyamidinophenyl)]-imidazo[1,2-
a]pyridine (5a). A mixture of hydroxylamine hydrochlo-
ride (5.2 g, 75 mmol) in anhydrous DMSO (40 mL) was
cooled to 5 ꢁC under nitrogen and potassium t-butoxide
(8.4 g, 75 mmol) was added in portions. The mixture
was stirred for 30 min. This mixture was added to dinit-
rile 4a (2.40 g, 7.5 mmol). The reaction mixture was stir-
red overnight at room temperature. The reaction
mixture was then poured slowly onto ice-water. The pre-
cipitate was filtered and washed with water to afford 5a
(free base) in 95% yield, mp 251–253 ꢁC. 1H NMR
(DMSO-d6); d 5.88 (s, 2H), 5.91 (s, 2H), 7.67 (s, 2H),
7.75–7.83 (m, 6H), 8.00 (d, J = 8.4 Hz, 2H), 8.44 (s,
1H), 8.94 (s, 1H), 9.70 (s, 1H), 9.73 (s, 1H). 13C NMR
(DMSO-d6); d 150.6, 150.3, 144.4, 144.2, 136.8, 134.1,
132.55, 132.50, 126.0, 125.9, 125.7, 125.2, 124.8, 124.6,
124.0, 116.6, 109.8.
3.5.6. 2,6-Bis[4-(amidinophenyl)]-5,6,7,8-tetrahydro-imi-
dazo[1,2-a]pyridine acetate salt (8). To a solution of 5a
(386 mg, 1 mmol) in glacial acetic acid (10 mL) was
slowly added acetic anhydride (0.35 mL). After stirring
for overnight TLC indicated complete consumption of
the starting material, then the solvent was evaporated
under reduced pressure. To the formed product (the
product of acylation step) in glacial acetic acid
(20 mL) was added 10% palladium on carbon (80 mg),
then the mixture was placed on Parr hydrogenation
apparatus at 50 psi for 6 h at room temperature. The
reaction mixture was filtered through hyflo and the filter
pad washed with water. The filtrate was evaporated un-
der reduced pressure and the precipitate was collected
and washed with ether to give 8 in 84% yield, mp 234–
1
236 ꢁC. H NMR (D2O/DMSO-d6); d 1.75 (s, 3· CH3),
2.15 (br s, 3H), 2.95 (br s, 2H), 4.09 (br s, 1H), 4.27
(br s, 1H), 7.62 (m, 3H), 7.77–7.82 (m, 4H), 7.89–7.92
(m, 2H). Anal. Calcd for C21H22N6–3.0AcOH–1.9H2O:
C, 56.61; H, 6.65; N, 14.67. Found: C, 56.49; H, 6.30;
N, 14.58.
3.5.4. 2,6-Bis[4-(N-methoxyamidinophenyl)]-imidazo[1,2-
a]pyridine (6a). To a suspension of the amidoxime 5a
(386 mg, 1 mmol) in DMF (10 mL) was added LiOHÆ-
H2O (252 mg, 6 mmol, in 3 mL H2O) which was fol-
lowed by dimethylsulfate (630 mg, 5 mmol). The
reaction mixture was stirred overnight after which it
was poured onto ice/water and the precipitate was fil-
tered, washed with water, and chromatographed on sil-
ica gel using hexanes/EtOAc (50:50) to give compound
Free base of 8. Mp 254–255 ꢁC. 1H NMR (D2O/DMSO-
d6); d 2.13–2.20 (m, 3H), 2.91 (m, 1H), 3.34 (br s, 1H),
4.03 (m, 1H), 4.27 (m, 1H), 7.62 (m, 3H), 7.77–7.82
(m, 4H), 7.89–7.92 (m, 2H). 13C NMR (DMSO-d6); d
162.3, 144.2, 143.6, 138.7, 136.2, 126.8, 126.7, 123.4,
115.4, 99.4, 49.7, 27.6, 23.7. FABMS (m/z, rel. int., thi-
oglycerol); 359 (M++1, 75), 324 (100), 291(5), 273 (15),
237 (20). HRMS calcd for C21H23N6: 359.1984. Ob-
served: 359.1980.
1
6a in 73% yield, mp 192–194 ꢁC. H NMR (DMSO-
d6); d 3.75 (s, 3H), 3.76 (s, 3H), 6.08 (br s, 2H), 6.13
(br s, 2H), 7.64–7.66 (m, 2H), 7.73–7.81 (m, 6H), 7.98
(d, J = 7.8 Hz, 2H), 8.43 (s, 1H), 8.92 (s, 1H). 13C
NMR (DMSO-d6); d 150.7, 150.5, 144.3, 144.1, 137.2,
134.5, 131.6, 131.5, 126.1, 125.9, 125.8, 125.0, 124.6,
124.4, 123.8, 116.4, 109.7, 60.4, 60.3. Hydrochloride salt
3.5.7. 2-(4-Cyanophenyl)-6-bromo-8-methyl-imidazo[1,2-
a]pyridine (3b). The same procedure described for 3a
was used employing 4-cyanophenacyl bromide and
2-amino-3-methyl-5-bromopyridine. Yield 71%, mp
1
of 6a. Mp 236–238 ꢁC, H NMR (D2O/DMSO-d6); d
3.83 (s, 3H), 3.84 (s, 3H), 7.91–7.94 (m, 6H), 8.03 (d,
J = 8.7 Hz, 1H), 8.19 (d, J = 8.4 Hz, 2H), 8.28 (d,
J = 8.7 Hz, 1H), 8.84 (s, 1H), 9.34 (s, 1H). Anal. Calcd
for C23H22N6O2–3.0HCl–0.25H2O–0. 25C2H5OH: C,
52.28; H, 5.04; N, 15.56. Found C, 52.51; H, 4.98; N,
15.25.
1
209–210 ꢁC. H NMR (DMSO-d6); d 2.56 (s, 3H), 7.53
(s, 1H), 7.95 (d, J = 8.1 Hz, 2H), 8.14 (d, J = 8.1 Hz,
2H), 8.60 (s, 1H), 8.88 (s, 1H). 13C NMR (DMSO-d6);
d 143.3, 140.4, 133.3, 133.0, 128.1, 127.4, 127.0, 125.9,
119.2, 112.8, 111.2, 108.2, 16.7. MS (ESI) m/e (rel.
int.); 312 (M+, 10), 230 (100), 217 (60), 205 (50). Anal.
Calcd for C15H10BrN3: C, 57.71; H, 3.23. Found C,
57.93; H, 3.35.
3.5.5. 2,6-Bis[4-(amidinophenyl)]-imidazo[1,2-a]pyridine
acetate salt (7a). To a solution of 5a (386 mg, 1 mmol)
in glacial acetic acid (10 mL) was slowly added acetic
anhydride (0.35 mL). After stirring for overnight TLC
indicated complete consumption of the starting mate-
rial, then the solvent was evaporated under reduced
pressure. To the formed product (the product of acyla-
tion step) in a mixture of ethanol/EtOAc (50 mL, 1:1)
was added 10% palladium on carbon (80 mg), then the
mixture was placed on Parr hydrogenation apparatus
at 50 psi for 4 h at room temperature. The reaction mix-
ture was filtered through hyflo and the filter pad washed
with water. The filtrate was evaporated under reduced
pressure and the precipitate was collected and washed
3.5.8. 2,6-Bis(4-cyanophenyl)-8-methyl-imidazo[1,2-a]pyri-
dine (4b). The same procedure described for 4a was used
1
starting with 3b. Yield 73%, mp 283–285 ꢁC. H NMR
(DMSO-d6); d 2.60 (s, 3H), 7.53 (s, 1H), 7.85–7.93 (m,
6H), 8.17 (d, J = 8.4 Hz, 2H), 8.53 (s, 1H), 8.87 (s,
1H). 13C NMR (DMSO-d6); d 144.9, 142.5, 141.1,
138.1, 132.6, 132.4, 127.0, 126.6, 126.0, 123.6, 123.3,
122.9, 118.6, 118.4, 111.9, 110.0, 109.7, 16.3. MS (ESI)
m/e (rel. int.); 335 (M++1, 100), 310 (30), 279 (20), 234
(40). Anal. Calcd for C22H14N4: C, 79.02; H, 4.22.
Found C, 78.68; H, 4.45.

M. A. Ismail et al. / Bioorg. Med. Chem. 16 (2008) 683–691
689
3.5.9. 2,6-Bis[4-(N-hydroxyamidino-phenyl)]-8-methyl-imi-
dazo[1,2-a]pyridine (5b). The same procedure described
for 5a was used starting with 4b. Yield 92%, mp
>300 ꢁC. 1H NMR (DMSO-d6); d 2.60 (s, 3H), 6.22
(s, 2H), 6.40 (s, 2H), 7.51 (s, 1H), 7.76–7.90 (m,
6H), 8.03 (d, J = 8.1 Hz, 2H), 8.44 (s, 1H), 8.80 (s,
1H), 9.93 (s, 2H). 13C NMR (DMSO-d6); d 152.0,
151.2, 144.7, 143.5, 137.5, 134.8, 131.6, 131.1, 126.2,
126.1, 125.3, 124.6, 123.5, 121.9, 110.5, 16.8. MS
(ESI) m/e (rel. int.); 401 (M++1, 75), 339 (20), 266
(10), 201 (100).
3.5.14. 2,6-Bis[4-(N-hydroxyamidino-phenyl)]-7-methyl-
imidazo[1,2-a]pyridine (5c). The same procedure de-
scribed for 5a was used starting with 4c. Yield 93%,
mp 187–189 ꢁC. H NMR (DMSO-d6); d 2.24 (s, 3H),
5.81 (s, 2H), 5.86 (s, 2H), 7.43–7.49 (m, 3H), 7.71–7.78
(m, 4H), 7.93 (d, J = 8.4 Hz, 2H), 8.32 (s, 1H), 8.40 (s,
1H), 9.66 (s, 1H), 9.71 (s, 1H). 13C NMR (DMSO-d6);
d 150.8, 150.7, 144.8, 144.1, 137.6, 134.5, 134.4, 132.7,
132.5, 129.4, 127.6, 125.8, 125.5, 125.3, 115.7, 109.0,
20.5. MS (ESI) m/e (rel. int.); 401 (M++1, 100), 386 (15).
1
3.5.15. 2,6-Bis[4-(N-methoxyamidinophenyl)]-7-methyl-
imidazo[1,2-a]pyridine (6c). The same procedure de-
scribed for 6a was used starting with 5c, the crude prod-
uct was chromatographed on silica gel eluting with
3.5.10. 2,6-Bis[4-(N-methoxyamidinophenyl)]-8-methyl-
imidazo[1,2-a]pyridine (6b). The same procedure de-
scribed for 6a was used starting with 5b, the crude prod-
uct was chromatographed on silica gel eluting with
hexanes/EtOAc (30:70). Hydrochloride salt of 6b. Mp
286–288 ꢁC. 1H NMR (D2O/DMSO-d6); d 2.80 (s,
3H), 3.85, 3.86 (2s, 6H), 7.93–7.98 (m, 6H), 8.18 (s,
1H), 8.32 (d, J = 8.4 Hz, 2H), 8.86 (s, 1H), 9.24 (s,
1H). 13C NMR (D2O/DMSO-d6); d 158.1, 157.0,
141.0, 139.6, 135.8, 132.3, 131.0, 129.2, 128.9, 128.6,
128.0, 127.6, 126.7, 124.8, 124.1, 113.8, 64.0, 63.7,
17.1. MS (ESI) m/e (rel. int.); 429 (M++1, 60), 240
(55), 215 (100). HRMS calcd for C24H25N6O2:
429.2039. Observed: 429.2043. Anal. Calcd for
C24H24N6O2–3.0HCl–1.5H2O: C, 51.02; H, 5.35; N,
14.87. Found: C, 50.92; H, 5.25; N, 14.50.
1
hexanes/EtOAc (30:70). Yield 85%, mp 112–114 ꢁC. H
NMR (DMSO-d6); d 2.24 (s, 3H), 3.75, 3.76 (2s, 6H),
6.05 (s, 2H), 6.12 (s, 2H), 7.44–7.49 (m, 3H), 7.71–7.77
(m, 4H), 7.94 (d, J = 8.4 Hz, 2H), 8.34 (s, 1H), 8.40 (s,
1H). 13C NMR (DMSO-d6); d 150.7, 150.6, 144.5,
143.9, 137.7, 134.7, 133.9, 131.6, 131.3, 128.9, 127.2,
125.7, 125.5, 124.9, 115.4, 108.7, 60.3, 19.9. Hydrochlo-
ride salt of 6c. Mp 133–135 ꢁC. 1H NMR (D2O/
DMSO-d6); d 2.42 (s, 3H), 3.83, 3.85 (2s, 6H), 7.65 (d,
J = 8.1 Hz, 2H), 7.91–7.95 (m, 5H), 8.21 (d,
J = 8.1 Hz, 2H), 8.85 (s, 1H), 8.87 (s, 1H). MS (ESI)
m/e (rel. int.); 429 (M++1, 100). HRMS calcd for
C24H25N6O2: 429.2039. Observed: 429.2026. Anal.
Calcd for C24H24N6O2–3.0HCl–2.8H2O–0. 75C2H5OH:
C, 49.17; H, 6.00; N, 13.49. Found: C, 49.53; H, 5.95;
N, 13.11.
3.5.11. 2,6-Bis[4-(amidinophenyl)]-8-methyl-imidazo[1,2-
a]pyridine acetate salt (7b). The same procedure de-
scribed for 7a was used starting with 5b. Yield 81%,
1
mp 241–243 ꢁC. H NMR (D2O/DMSO-d6); d 1.88 (s,
3.5.16. 2,6-Bis[4-(amidinophenyl)]-7-methyl-imidazo[1,2-
a]pyridine acetate salt (7c). The same procedure de-
scribed for 7a was used starting with 5c. Mp 241–
3· CH3), 2.63 (s, 3H), 7.53 (s, 1H), 7.89–8.00 (m, 5H),
8.07–8.18 (m, 3H), 8.53 (s, 1H), 8.86 (s, 1H). Anal. Calcd
for C22H20N6–3.0AcOH–1.7H2O: C, 58.06; H, 6.16; N,
14.51. Found: C, 57.90; H, 5.93; N, 14.76.
1
243 ꢁC. H NMR (D2O/DMSO-d6); d 1.72 (s, 3· CH3),
2.26 (s, 3H), 7.57 (s, 1H), 7.68 (d, J = 8.4 Hz, 2H),
7.85–7.92 (m, 4H), 8.14 (d, J = 8.4 Hz, 2H), 8.48 (s,
1H), 8.49 (s, 1H). MS (ESI) m/e (rel. int.); 369 (M+,
100). HRMS calcd for C22H21N6: 369.1828. Observed:
369.1826. Anal. Calcd for C22H20N6-3.0AcOH-
0.5H2O: C, 60.31; H, 5.96; N, 15.07. Found: C, 60.22;
H, 5.86; N, 15.08.
3.5.12. 2-(4-Cyanophenyl)-6-bromo-7-methyl-imidazo[1,2-
a]pyridine (3c). The same procedure described for 3a
was used employing 4-cyanophenacyl bromide and 2-
amino-4-methyl-5-bromopyridine. Yield 56%, mp
253–255 ꢁC. 1H NMR (DMSO-d6); d 2.49 (s, 3H),
7.61 (s, 1H), 7.89 (d, J = 8.4 Hz, 2H), 8.16 (d,
J = 8.4 Hz, 2H), 8.42 (s, 1H), 8.88 (s, 1H). 13C NMR
3.5.17. 2-(4-Cyanophenyl)-6-bromo-7,8-dimethyl-imi-
dazo[1,2-a]pyridine (3d). The same procedure described
for 3a was used employing 4-cyanophenacyl bromide
(DMSO-d6);
d 144.1, 142.7, 137.8, 134.7, 132.1,
126.4, 125.8, 118.3, 115.6, 110.0, 109.9, 109.6, 21.3.
MS (ESI) m/e (rel. int.); 312 (M+, 100), 293 (10). Anal.
Calcd for C15H10BrN3: C, 57.71; H, 3.23. Found: C,
57.94; H, 3.11.
and
2-amino-3,4-dimethyl-5-bromopyridine.
Yield
1
64%, mp 210–212 ꢁC. H NMR (DMSO-d6); d 2.35 (s,
3H), 2.56 (s, 3H), 7.87 (d, J = 8.1 Hz, 2H), 8.11 (d,
J = 8.1 Hz, 2H), 8.41 (s, 1H), 8.80 (s, 1H). 13C NMR
(DMSO-d6); d 144.6, 141.6, 137.6, 132.7, 131.7, 126.1,
124.5, 124.1, 118.9, 111.7, 111.0, 109.9, 18.4, 14.1. MS
(ESI) m/e (rel. int.); 326 (M+, 100), 241 (10). Anal. Calcd
for C16H12BrN3: C, 58.91; H, 3.71. Found: C, 58.73; H,
4.02.
3.5.13. 2,6-Bis(4-cyanophenyl)-7-methyl-imidazo[1,2-a]pyri-
dine (4c). The same procedure described for 4a was used
1
starting with 3c. Yield 94%, mp 220–222 ꢁC. H NMR
(DMSO-d6); d 2.21 (s, 3H), 7.53 (s, 1H), 7.66 (d,
J = 8.1 Hz, 2H), 7.85 (d, J = 8.1 Hz, 2H), 7.94 (d,
J = 8.1 Hz, 2H), 8.12 (d, J = 8.4 Hz, 2H), 8.45–8.47
(m, 2H). 13C NMR (DMSO-d6); d 144.9, 142.8, 141.8,
138.4, 134.5, 132.7, 132.3, 130.7, 126.9, 126.1, 125.9,
119.0, 118.7, 116.1, 110.8, 110.6, 109.7, 20.2. MS (ESI)
m/e (rel. int.); 335 (M++1, 100), 241 (5). Anal. Calcd
for C22H14N4: C, 79.02; H, 4.22. Found: C, 79.18; H,
4.13.
3.5.18. 2,6-Bis(4-cyanophenyl)-7,8-dimethyl-imidazo[1,2-
a]pyridine (4d). The same procedure described for 4a was
1
used starting with 3d. Yield 84%, mp 229–231 ꢁC. H
NMR (DMSO-d6); d 2.12 (s, 3H), 2.57 (s, 3H), 7.61
(d, J = 8.1 Hz, 2H), 7.84 (d, J = 8.1 Hz, 2H), 7.92 (d,
J = 8.1 Hz, 2H), 8.14 (d, J = 8.1 Hz, 2H), 8.31 (s, 1H),

690
M. A. Ismail et al. / Bioorg. Med. Chem. 16 (2008) 683–691
8.42 (s, 1H). MS (ESI) m/e (rel. int.); 349 (M++1, 100).
Anal. Calcd for C23H16N4: C, 79.29; H, 4.63. Found:
C, 78.96; H, 4.81.
Acid Complexes; Demeunynck, M., Bailly, C., Wilson, W.
D., Eds.; Wiley-VCH: New York, 2003; Vol. 2, pp 414–
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Mathis, A.; Hall, J. E.; Stephens, C. E.; Boykin, D. W.
Curr. Med. Chem.-Anti-Cancer Agents 2005, 5, 389; (c)
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Bouteille, B.; Oukem, O.; Bisser, S.; Dumas, M. Fundam.
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Castagnini, L. A.; Allen, J. A.; Umesh, L.; Gotuzzo, E.
Efficacy and Safety of DB289, A New Oral Drug for
Treatment of Pneumocystis carinii Pneumonia (PCP) in
AIDS Patients. Presented at the 43rd Annual Interscience
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Meeting, September 14–17, 2003, Chicago, IL.
3.5.19. 2,6-Bis[4-(N-hydroxyamidinophenyl)]-7,8-dimethyl-
imidazo[1,2-a]pyridine (5d). The same procedure de-
scribed for 5a was used starting with 4d. Yield 94%,
mp 180–181.5 ꢁC. 1H NMR (DMSO-d6); d 2.14 (s,
3H), 2.56 (s, 3H), 5.85 (s, 2H), 5.90 (s, 2H), 7.41 (d,
J = 8.1 Hz, 2H), 7.72–7.79 (m, 4H), 7.97 (d, J = 8.1
Hz, 2H), 8.26 (s, 1H), 8.31 (s, 1H), 9.65 (s, 1H), 9.71
(s, 1H). 13C NMR (DMSO-d6); d 150.7, 150.5, 145.2,
143.4, 138.3, 134.5, 132.4, 132.2, 130.1, 129.4, 127.9,
125.6, 125.3, 125.1, 123.1, 122.6, 109.3, 16.4, 13.5. MS
(ESI) m/e (rel. int.); 415 (M++1, 100), 281 (25), 208
(52). HRMS calcd for C23H23N6O2: 415.1882. Observed:
415.1873.
3. Ansede, J. H.; Voyksner, R. D.; Ismail, M. A.;
Boykin, D. W.; Tidwell, R. R.; Hall, J. E. Xenobiotica
2005, 35, 211.
3.5.20. 2,6-Bis[4-(N-methoxyamidinophenyl)]-7,8-dimethyl-
imidazo[1,2-a]pyridine (6d). The same procedure de-
scribed for 6a was used starting with 5d. Yield 59%,
mp 140–141 ꢁC. 1H NMR (DMSO-d6); d 2.14 (s,
3H), 2.57 (s, 3H), 3.75 (s, 6H), 6.06 (s, 2H), 6.13 (s,
2H), 7.42 (d, J = 8.4 Hz, 2H), 7.71–7.77 (m, 4H),
7.98 (d, J = 8.4 Hz, 2H), 8.26 (s, 1H), 8.33 (s, 1H).
Hydrochloride salt of 6d. Mp 230–232 ꢁC. 1H NMR
(D2O/DMSO-d6); d 2.26 (s, 3H), 2.64 (s, 3H), 3.82,
3.84 (2s, 6H), 7.62 (d, J = 8.1 Hz, 2H), 7.83–7.88 (m,
4H), 8.12 (d, J = 8.1 Hz, 2H), 8.66 (s, 1H), 8.70 (s,
1H) 13C NMR (D2O/DMSO-d6); d 157.4, 155.7,
142.0, 140.6, 140.3, 135.1, 132.2, 130.8, 130.0, 129.8,
128.5, 128.4, 127.4, 125.5, 121.0, 112.9, 63.7, 63.2,
17.6, 14.1. MS (ESI) m/e (rel. int.); 443 (M++1, 100),
295 (32). HRMS calcd for C25H27N6O2: 443.2195. Ob-
served: 443.2195. Anal. Calcd for C25H26N6O2–
3.0HCl–2.75H2O–0.25C2H5OH: C, 49.97; H, 5.91; N,
13.71. Found: C, 49.99; H, 5.84; N, 13.42.
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J. Med. Chem. 1998, 41, 124.
6. Francesconi, I.; Wilson, W. D.; Tanious, F. A., et al.
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9. Wilson, W. D.; Tanious, F. A.; Ding, D.; Kumar, A.;
Boykin, D. W.; Colson, P.; Houssier, C.; Bailly, C. J. Am.
Chem. Soc. 1998, 120, 10310.
10. Bailly, C.; Dassonneville, L.; Carrascol, C.; Lucasl, D.;
Kumar, A.; Boykin, D. W.; Wilson, W. D. Anti-Cancer
Drug Des. 1999, 14, 47.
11. Fitzgerald, D. J.; Anderson, J. N. J. Biol. Chem. 1999, 274,
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12. Dykstra, C. C.; McClernon, D. R.; Elwell, L. P.; Tidwell,
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Ismail, M. A.; Boykin, D. W.; Tidwell, R. R.; Hall, J. E.
Antimicrob. Agents Chemother 2006, 50, 2185.
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Groove Interactions of Antiparasitic Diamidines: Re-
evaluation of the Crescent-Shape Concept in Groove-
Binding. In Synthetic and Biophysical Studies of DNA
Binding Compounds. Lee, M., Strekows, L., Eds.; Trans-
world Research Network: Trivandrum, India, 2007;
Chapter 2.
3.5.21. 2,6-Bis[4-(amidinophenyl)]-7,8-dimethyl-imidazo[1,2-
a]pyridine acetate salt (7d). The same procedure described
for 7a was used starting with 5d. Mp 260–262 ꢁC. H
NMR (D2O/DMSO-d6); d 1.71 (s, 2.8· CH3), 2.14 (s,
3H), 2.55 (s, 3H), 7.58 (d, J = 8.4 Hz, 2H), 7.84 (m,
4H), 8.12 (d, J = 8.4 Hz, 2H), 8.26 (s, 1H), 8.38 (s,
1H). MS (ESI) m/e (rel. int.); 383 (M++1, 100). HRMS
calcd for C23H23N6: 383.1984. Observed: 383.2001.
Anal. Calcd for C23H22N6–2.8AcOH: C, 62.38; H,
6.07; N, 15.26. Found: C, 62.29; H, 5.97; N, 15.33.
1
Acknowledgments
We thank Guy Riccio of STI for the technical assistance
with the T. b. r. animal model. This work was supported
by the Bill and Melinda Gates Foundation and by NIH
Grants GM61587 and AI46365.
16. Hamdouchi, C.; Blas, J.; Prado, M.; Gruber, J.; Heinz, B.
A.; Vance, L. J. Med. Chem. 1999, 42, 50.
17. (a) Hamama, W. S.; Zoorob, H. H. Tetrahedron 2002, 58,
6143; (b) Sundberg, R.; Biswas, S.; Murthi, K. K.; Rowe,
D. J. Med. Chem. 1998, 41, 4317.
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