Dialkylimidazole inhibitors of Trypanosoma cruzi sterol 14α-demethylase as anti-Chagas disease agents

Article abstract of DOI:10.1016/j.bmcl.2013.08.015

New dialkylimidazole based sterol 14α-demethylase inhibitors were prepared and tested as potential anti-Trypanosoma cruzi agents. Previous studies had identified compound 2 as the most potent and selective inhibitor against parasite cultures. In addition, animal studies had demonstrated that compound 2 is highly efficacious in the acute model of the disease. However, compound 2 has a high molecular weight and high hydrophobicity, issues addressed here. Systematic modifications were carried out at four positions on the scaffold and several inhibitors were identified which are highly potent (EC₅₀ <1 nM) against T. cruzi in culture. The halogenated derivatives 36j, 36k, and 36p, display excellent activity against T. cruzi amastigotes, with reduced molecular weight and lipophilicity, and exhibit suitable physicochemical properties for an oral drug candidate.

Full text of DOI:10.1016/j.bmcl.2013.08.015

Bioorganic & Medicinal Chemistry Letters 23 (2013) 6492–6499
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Dialkylimidazole inhibitors of Trypanosoma cruzi sterol
14a-demethylase as anti-Chagas disease agents
Praveen Kumar Suryadevara a, Kishore Kumar Racherla a, Srinivas Olepu a, Neil R. Norcross a,
Hari Babu Tatipaka a, Jennifer A. Arif b, Joseph D. Planer b, Galina I. Lepesheva d,
b,
a,
Christophe L. M. J. Verlinde c, , Frederick S. Buckner , Michael H. Gelb
⇑
⇑
⇑
a Department of Chemistry, University of Washington, Seattle, WA 98195, USA
b Department of Medicine, University of Washington, Seattle, WA 98195, USA
c Department of Biochemistry, University of Washington, Seattle, WA 98195, USA
d Department of Biochemistry, School of Medicine, Vanderbilt University, Nashville, TN, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
New dialkylimidazole based sterol 14a-demethylase inhibitors were prepared and tested as potential
Received 19 April 2013
Revised 24 July 2013
Accepted 5 August 2013
Available online 12 August 2013
anti-Trypanosoma cruzi agents. Previous studies had identified compound 2 as the most potent and selec-
tive inhibitor against parasite cultures. In addition, animal studies had demonstrated that compound 2 is
highly efficacious in the acute model of the disease. However, compound 2 has a high molecular weight
and high hydrophobicity, issues addressed here. Systematic modifications were carried out at four posi-
tions on the scaffold and several inhibitors were identified which are highly potent (EC50 <1 nM) against
T. cruzi in culture. The halogenated derivatives 36j, 36k, and 36p, display excellent activity against T. cruzi
amastigotes, with reduced molecular weight and lipophilicity, and exhibit suitable physicochemical
properties for an oral drug candidate.
Keywords:
Trypanosoma cruzi
Sterol 14-alpha demethylase
CYP51
Chagas disease
Dialkylimidazole
Ó 2013 Elsevier Ltd. All rights reserved.
Chagas disease (American Trypanosomiasis), caused by the
protozoan parasite Trypanosoma cruzi, is leading cause of
range.5 The activity of these compounds is due to inhibition of
the enzyme sterol 14
-demethylase6 (CYP51), essential for the bio-
a
a
heart failure in Latin America. The disease is endemic through-
out much of Mexico, Central and South America, with an
estimated
synthesis of ergosterol-like sterols, crucial components of the par-
asite membrane.7 In the acute mouse model of Chagas disease,
several dialkylimidazole compounds reduced parasitemia to
microscopically undetectable levels after oral administration.5,8
However, the compounds are relatively large, hence we attempted
to reduce the size of our original lead 2 while maintaining potency
to arrive at T. cruzi inhibitors like 3 with more drug-like physico-
chemical properties.
We previously reported a very simple and straightforward syn-
thetic route to arrive at dialkylimidazoles in good yields.5 Synthesis
requires the preparation of two fragments that are then coupled
under reductive amination conditions. Analogs 12a–l were ob-
tained according to Scheme 1. To generate the first fragment, trityl
protected imidazole carboxaldehyde 5 was treated with substi-
tuted benzylbromides and subsequent deprotection resulted in
substituted imidazole carboxaldehyde 6 in moderate to good yields
varied depending on substituents on alkyl bromide. The second
fragment 11 was derived from 7 using reported methods.5 Reduc-
tive coupling of key intermediates 11 and 6 provided the target
compounds 12a–l.
8
million persons infected.1 Additionally, recent
surveys suggest that 300,000 people in the United States,
mostly immigrants, have Chagas disease.2 The disease has an
acute and a chronic phase. In the latter the parasite can enter
and destroy heart muscle cells, eventually resulting in death
due to heart failure. The available drugs, benznidazole and
nifurtimox, have debilitating side effects and exhibit low efficacy
in the chronic stage of the disease.3 Hence, better drugs are
desperately needed to treat Chagas disease, one of the most
neglected tropical diseases.
The antifungal drug posaconazole (1 in Fig. 1), with an EC50 un-
der 1 nM against T. cruzi in culture, is currently in clinical trials for
Chagas disease, but if effective, high cost will likely limit wide-
spread use.4 We have previously reported on low-cost dialkylimi-
dazole compounds that kill T. cruzi amastigotes in the low nM
⇑
Corresponding authors. Tel.: +1 206 543 8865; fax: +1 206 685 1792
(C.L.M.J.V.); tel.: +1 206 598 9148; fax: +1 206 685 8681 (F.S.B.); tel.: +1 206 543
7142; fax: +1 206 685 8665 (M.H.G.).
Preparation of analogs 12r–v is described in Scheme 2. Phenol
derivatives 15 were reacted with alcohols in presence of DIAD
and TPP in THF to generate 16 in approximately 45–50% yields.
E-mail addresses: verlinde@ u.washington.edu (C.L.M.J. Verlinde), fbuckner@
u.washington.edu (F.S. Buckner), gelb@chem.washington.edu (M.H. Gelb).
0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2013.08.015

P. K. Suryadevara et al. / Bioorg. Med. Chem. Lett. 23 (2013) 6492–6499
6493
F
F
O
N N
O
HO
N
N
O
N
N
N
N
1
T. cruzi EC50 = < 1 nM
R3
R3
HN
R2
S
N
N
R2
HN
N
N
N
R1
H2N
3
H2N
R
R2 = -Cl; R = -CH3 = 0.6 nM (
)
3
36j
2
3
36k
R = -Cl; R = -H = 2.1 nM (
)
2
R2 = -F; R3 = -H = 1.1 nM (36p)
EC50 = 0.4-1.4 nM
Figure 1. Most potent T. cruzi Sterol-14
a
demethylase inhibitors.
CHO
(a)
N
N
N
(a)
(b)
CHO
CHO
N
N
H
N
Trt
5
4
6
R1
(b)
Br
(d)
(c)
(e)
O2N
NH2
O2N
Br
O2N
NH2
8
7
9
(f)
S
N
(g)
N
H
N
S
N
S
N
H2N
O2N
N
R1
12a-q
10
11
Scheme 1. Reagents and conditions: (a) TrtCl, Et3N, DMF, rt, 90–94%; (b) R1C6H4CH2Br, CH3CN, 60 °C, 24 h, 70–75%; (c) PhRB(OH)2, Ba(OH)2Á8H2O, Pd(PPh3)4, DME–H2O (5:1),
reflux, 90%; (d) NaNO2, H2SO4, AcOH, CuBr2, HCi, 71%; (e) Benzothiazole, Pd(PPh3)4, KOAc, DMAC, 160 °C, overnight, 32–35%; (f) SnCl2Á2H2O, EtOAc, reflux, 6 h, 76–80%; (g)
AcOH, 6, MeOH, 4 Å mol sieves, NaBH3CN, overnight, rt, 60–65%.
The intermediates were converted to the target compounds using
the procedure described in Scheme 1. Synthesis of halogenated
dialkylimidazole derivatives is depicted in Schemes 3 and 4. Com-
pound 21 was synthesized as a versatile intermediate for the prep-
aration of several analogs in this study. It was obtained in
considerable yield from 18 by Suzuki coupling followed by
bromination and further alkylation with 5.
compounds 24a–r in moderate to good yields. Similarly, all amino
analogues were prepared as described in Scheme 4.
In our previous studies, inhibitors were potent but large and
highly hydrophobic.6 Hence we decided to produce simplified
and more drug-like analogues with reduced molecular weight
and lipophilicity (Table 1). We generated new structures by mod-
ifying 2 at four positions R, R1, R2 and R3 (Fig. 1). All the synthesized
analogs were tested against the clinically relevant amastigote
stages of T. cruzi.9
The second fragment was readily prepared from available nitro
derivatives. Fragments were coupled to generate the target

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P. K. Suryadevara et al. / Bioorg. Med. Chem. Lett. 23 (2013) 6492–6499
Br
(c)
(a)
(b)
O2N
OH
O2N
OH
O2N
OH
13
14
15
O
N
N
HN
R2
R2 =
(d)
(e)
O
O2N
R2
N
N
O
H2N
R2
12r-v
O
16
17
R1
N
Scheme 2. Preparation of dialkylimidazoles containing 2-ethoxy-morpholines and piperidines. Reagents and conditions: (a) NBS, FSO3H, 80%; (b) PhB(OH)2, Ba(OH)2Á8H20,
Pd(PPh3)4, DME–H2O (5:1), reflux, 60%; (c) DIAD, TPP, THF, R2, 45–50%; (d) SnCl2Á2H2O, EtOAc, reflux, 6 h, 76–80%; (e) AcOH, 6, MeOH, 4 Å mol sieves, NaBH3CN, overnight, rt,
60–65%.
(a)
Br
N
R
R
CHO
N
R
(a)
(b)
(c)
R
Br
18
21
19
20
R = F, Cl,H, OH, OCH3, CO2H
R3
(b)
N
H
N
R3
R3
R2
N
(d)
O2N
R2
(e)
H2N
R2
R = F, Cl,H, OH, OCH3,
CO2H
22
R2 = F, Cl, H
R3 = F, Cl, H, CH3, Ph
R
R2 = F, Cl, H
23
R3 = F, Cl, H, CH3, Ph
24
Scheme 3. Preparation of halogenated dialkylimidazoles. Reagents and conditions: (a) PhB(OH)2, Ba(OH)2Á8H2O, Pd(PPh3)4, DME–H2O (5:1), reflux, 90%; (b) NBS, CCl4,
benzoyl peroxide, reflux, 85%; (c) 5, CH3CN, 60 °C, 24 h, 70–75%; (d) SnCl2Á2H2O, EtOAc, reflux, 6 h, 76–80%; (e) AcOH, 21, MeOH, 4 Å mol sieves, NaBH3CN, overnight, rt, 60–
65%.
Initial modifications at R1 in compound 12 replaced the phenyl
group with various heterocycles like furan, pyridine and thiophene
(12a–c), which consequently, did little to modulate activity against
T. cruzi. However, introduction of polar functionality at the
2-position on R1 or lipophilic groups at the 4-position on R1
(12d–g) was less well tolerated.
at R3 for further modifications containing large, flexible linked
heterocycles.
Considering the dialkyl imidazole core, we began to focus our
attention on smaller functional groups at the R2 and R3 positions,
to try to further improve physicochemical properties, whilst
improving or at least, retaining potency against T. cruzi amastigotes
(Table 2). Furthermore, we investigated the importance of the –
NH2 group on the biphenyl rings of the imidazole subunit, for
activity against T. cruzi. Two of the most potent compounds from
previous studies6 both comprise an amino functionality at the
C-2 position of the biphenyl attached to the imidazole. The
introduction of the C-2 amino functionality to compound 12 to
afford compound 2 resulted in a 20-fold increase in potency. The
development of an in-house homology model of T. cruzi CYP51,
using the previously published Mycobacterium tuberculosis crystal
structure,10 has shown that this remarkable increase in activity
can be attributed to a key H-bond interaction of the aniline moiety
with a histidine residue in the active site of T. cruzi CYP51. How-
ever, replacement of the aniline moiety with other functional
groups such as –OMe (24n), –OH (24o) and –COOH (24q), led to
a >27-fold drop in potency, highlighting the importance of this
key amino/histidine interaction. Compounds such as 24a and
24o, without the aniline moiety, also exhibited sub-20 nM activity
against T. cruzi. Interestingly, compound 24a demonstrated that
We next investigated the effect of substitution on the R3 phenyl
system. Introduction of polar functional groups at the para position
on the terminal phenyl (R3) such as hydroxy and methoxy had little
effect on potency. However, the introduction of an amino group at
the 4-position on R3 (12k) dramatically inhibited the T. cruzi cul-
tures at low nanomolar level with >10-fold increase in potency
(EC50 = 1.6 nM) compared with compound 12.
Previously explored SAR of the benzothiazole moiety6 suggested
that benzothiazole is at the periphery of the active site, partially ex-
posed to solvent. Replacing it by a simple chloro retains the potency
against T. cruzi and, importantly, reduces the molecular mass by
100.6 By retaining –Cl at R2 position, we obtained an extra molecular
mass window within Lipinski space to explore R3 with a variety of
heterocyclic as well as saturated heterocyclic systems (12n–q).
However, associated modifications did not improve potency. In
addition, replacement of the benzothiazole moiety at R2 with alkoxy
and alkylamino linked heterocycles, (12r–v), displayed as much as a
10-fold drop in potency. These analogues suggest a limited tolerance

P. K. Suryadevara et al. / Bioorg. Med. Chem. Lett. 23 (2013) 6492–6499
6495
(a)
Br
N
NO2
NO2
CHO
N
NO2
(a)
(b)
(c)
O2N
Br
27
28
30
29
(b)
HO
R4
R4
B
OH
R2
R4
Br
(d)
(e)
+
O2N
R2
O2N
R2
H2N
31
32
R4
34
33
R4
R2 = F, Cl, H, CH3
N
N
H
N
N
H
N
R2
R2
(g)
(f)
N
N
R4 =
N
O2N
35
H2N
N
O
36
Scheme 4. Synthetic strategy for dialkylimidazole analogs bearing –NH2 at R. Reagents and conditions: (a) PhB (OH)2, Ba(OH)2Á8H2O, Pd(PPh3)4, DME–H2O (5:1), reflux, 90%;
(b) NBS, CCl4, benzoyl peroxide, reflux, 85%; (c) 5, CH3CN, 60 °C, 24 h, 70–75%; (d) Ba(OH)2Á8H2O, Pd(PPh3)4, DME–H2O (5:1), reflux, 90%; (e) SnCl2Á2H2O, EtOAc, reflux, 6 h,
76–80%; (f) AcOH, 30, MeOH, 4 Å mol sieves, NaBH3CN, overnight, rt, 60–65%; (g) SnCl2Á2H2O, EtOAc, reflux, 5–7 h, 75–82%.
Table 1
Activity of dialkylimidazoles with variations at R1, R2 and R3 against T. cruzi amastigotes
R3
R2
N
H
N
N
R1
12a-v
Compd No.
MWT
logP
PSA (Å2)
R1
R2
R3
T. cruzi EC50 (nM)
12
548
539
550
555
564
565
563
583
563
565
579
564
574
466
451
439
457
451
545
544
543
542
558
8.4
7.4
7.5
8.2
7.6
8.1
8.9
9.0
8.9
8.1
8.2
7.6
8.2
7.0
5.6
5.6
6.1
5.6
5.9
5.9
6.9
6.6
5.9
42.7
55.9
55.6
42.7
68.8
63.0
42.7
42.7
42.7
63.0
52.0
68.8
66.5
29.9
42.7
34.8
33.1
42.7
51.6
54.4
42.3
45.1
45.6
Phenyl
2-Furan
2-Pyridine
2-Thiophene
Benzb
Benz
Benz
Benz
Benz
Benz
Benz
Benz
Benz
Benz
Benz
Benz
Benz
Methyl
Chloro
Chloro
Chloro
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
20.0
21.2
19.3
11.1
75.4
123.2
50.0
48.5
12a
12b
12c
12d
12e
12f
12g
12h
12i
2-NH2-Ph
2-OH-Ph
4-Me-Ph
4-Cl-Ph
3-Me-Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Phenyl
5.4
4-OH-Ph
4-OMe-Ph
4-NH2-Ph
4-CN-Ph
2,6-Di-F-Ph
4-Pyridine
Pyrrole
Piperidine
3-Pyridine
Phenyl
11.0 (20,010)a
10.0
12j
12k
12l
1.6 (27,500)a
32.0
12m
12n
12o
12p
12q
12r
12s
12t
12u
12v
36.6
27.2
30.4
53.6
64.8
35.2
115.2
316.8
Chloro
–O(CH2)2-Morc
–NH(CH2)2-Mor
–O(CH2)2-Pipd
–NH(CH2)2- Pip
–O(CH2)2-4-Me-Pip
Phenyl
Phenyl
Phenyl
Phenyl
194.0 (10,700)a
97.4 (4,470)a
Ph
a
b
c
Host cell activity against CRL-8155 IC50 (nM).
Benzothiazole.
Morpholine.
Piperidine.
d

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P. K. Suryadevara et al. / Bioorg. Med. Chem. Lett. 23 (2013) 6492–6499
Table 2
Activity of halogenated dialkylimidazoles against T. cruzi amastigotes
N
R3
R2
H
N
N
R1
24a-r
R
Compd No.
MWT
logP
PSA (Å2)
R
R1
R2
R3
T. cruzi EC50 (nM)
12
2
548
564
451
375
380
409
393
331
335
317
408
405
426
409
469
480
465
564
592
579
8.4
7.6
6.5
4.8
5.3
5.4
5.0
3.8
3.5
3.3
5.7
5.8
5.9
5.4
6.6
6.6
6.5
8.0
7.2
8.2
42.7
68.8
29.9
29.9
29.9
29.9
29.9
29.9
29.9
29.9
29.9
29.9
29.9
29.9
29.9
39.1
50.1
63.0
80.0
52.0
H
NH2
F
F
F
F
F
F
F
F
Cl
Cl
Cl
Cl
H
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Fluoro
Fluoro
Fluoro
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Benzb
Benz
F
F
F
F
F
F
Phenyl
Phenyl
Phenyl
H
Methyl
Cl
20.0
1.0
12.0
70.2
53.0
49.0
46.0
272.0
212.0
354.0
83.2
24a
24b
24c
24d
24e
24f
24g
24h
24i
24j
24k
24l
24m
24n
24o
24p
24q
24r
F
Methyl
F
H
F
F
–Cl
F
F
F
F
Cl
Cl
H
Methyl
Cl
F
2,6-di-F-Phe
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
26.0
48.7
38.1
11.7 (17,460)a
35.1
OCH3
OH
OH
CO2H
OCH3
5.9 (21,500)
89.3
>1000
27.2
Benzb
Benz
Benz
a
Host cell activity against CRL-8155 IC50 (nM).
Benzothiazole.
b
the benzothiazole moiety at the R2 position could be replaced with
only an F atom, albeit with the aniline moiety also replaced with an
F atom. However, the changes highlighted by compound 24a com-
pared with compound 12, showed that small, lipophilic groups at
R2 were well tolerated, thus reducing molecular weight and logP
whilst retaining activity. In addition, desirable levels of potency
could be attained by the introduction of a combination of halogen
atoms at R, R1, R2 and R3, whilst still retaining sub-100 nM levels of
potency against T. cruzi.
human CYP’s but this series was discarded due to dramatic loss
in potency, highlighting the importance of the imidazole–nitrogen
binding interaction to the heme moiety in the T. cruzi CYP51 active
site for activity. Replacement of the biphenyl on the imidazole by
ethyl piperidines and indole derivatives (25e–h) was not tolerated.
These results also demonstrate the critical requirement of the
biphenyl system attached to the imidazole subunit. However, po-
tent analogues were also observed when the central phenyl ring
was replaced with pyridine. Replacement of pyridine and keeping
the biphenyl moiety on the imidazole (26b) showed activity at
12.5 nM against T. cruzi and further addition of an amino group
on biphenylimidazole (26c) led to an EC50 of 0.2 nM. Inhibition
of the proposed biological target by the dialkylimidazole series
was confirmed by spectrophotometric studies. Using recombinant
Also worthy of note is compound 24b in which the phenyl at R3
was replaced with hydrogen, resulting in less than fourfold drop in
potency compared with compound 12, against T. cruzi, supporting
the fact that smaller lipophilic groups were well tolerated at R2
and R3.
With this information in hand, a small set of chlorinated analogs
(24i–l) were designed and tested against T. cruzi cultures. The com-
parable potencies of analogues 24a–l suggest that all of these ana-
T. cruzi sterol 14a-demethylase, we have previously shown that
26c binds to the haem moiety in the CYP51 active site as character-
ized by a Soret Type II binding spectra (Fig. 2).6
logues adopt similar binding conformations. In addition,
a
Utilizing compound 26c as a reference point for further syn-
thetic modifications, we initially replaced the methoxy at R2 with
the metabolically more stable fluorine group (36n) to evaluate
the effects of further modifications at R3. Modifications at R3 with
the larger chlorine atom at the R2 position were also investigated
(Table 4).
combination of fluorine and chlorine atoms at R1, R2 and R3 could
be utilized to reduce molecular weight and logP, thus improving
physicochemical properties, whilst retaining activity against T. cruzi.
We also examined other aromatic substituents to replace the
aniline moiety (24n–r) as described in Table 2. Compound 24o
showed considerable improvements in potency (EC50 of 5.9 nM)
compared with the compounds in the same series, which lack
the amino group on the biphenyl imidazole subunit, suggesting
that replacement of the amino group with alternative small,
hydrogen bond donors, may be tolerated. However, the larger polar
–COOH group (24q) was not tolerated. These studies suggest some
flexibility in the functionality placed at the R position, with a
preference for small H-bond donor groups.
Modification of the phenyl ring at R3 with saturated ring sys-
tems was poorly tolerated. However, direct replacement of the
phenyl ring at R3 with –Cl (36f), imidazole (36h) and pyrrole
(36i), also displayed sub10 nM levels of potency against T. cruzi.
The most potent analogues against T. cruzi were observed when
the phenyl at R3 was replaced with minimalistic groups such as
–CH3 (36j) and –H (36k). In addition, both examples indicate that
the size of groups at R3 can be significantly reduced, while still
retaining activity against T. cruzi amastigotes. Furthermore, similar
observations were made in the case of fluorinated analogs. It is
well known that incorporation of fluorine into a drug allows simul-
taneous modulation of electronic, lipophilic and steric parameters
Alternative functional groups were also investigated to try to
optimize the potency against T. cruzi (Table 3). Methylation at C-
2 position of the imidazole (25a–d) did not show activity even at
1
lM. The idea was to prevent the binding of the imidazole to

P. K. Suryadevara et al. / Bioorg. Med. Chem. Lett. 23 (2013) 6492–6499
6497
Table 3
Activity of dialkylimidazoles varied at X, R1, R2 and R3 positions and Pyridine based dialkylimidazoles against T. cruzi
N
R3
R2
H
N
R3
R2
N
H
N
N
X
N
X
N
R1
R1
25a-h
26a-c
Compd No.
MWT
404
logP
PSA (Å2)
x
R1
R2
R3
T. cruzi
EC50 (nM)
25a
4.1
55.8
55.8
55.8
55.8
Me
F
F
>1000
>1000
>1000
>1000
H2N
H2N
H2N
H2N
25b
25c
25d
400
420
386
4.5
4.6
4
Me
Me
Me
F
F
F
Me
Cl
H
25e
25f
396
412
4.8
5.2
45.6
45.6
H
H
F
Phenyl
Phenyl
333.0
333.0
HN
HN
Cl
25g
25h
26a
408
380
370
4.3
3.5
4.2
33
H
H
H
Cl
Phenyl
Phenyl
Phenyl
>1000 (17,400)a
>1000
N
41.8
52
Cl
NH
OMe
686.1
26b
26c
446
461
5.8
5.0
52
78
H
H
OMe
OMe
Phenyl
Phenyl
12.5
0.2 (>5000)a
H2N
a
Host cell activity against CRL-8155 IC50 (nM).
all of which can critically influence the pharmacokinetic properties
of drugs.11 In this context several fluorinated dialkylimidazole
phenyl group was removed completely, still exhibited high
potency of 1.1 nM.
based sterol 14
a
-demethylase inhibitors were synthesized and
As can be seen in Table 4, the majority of analogues prepared
were found to be extremely active with EC50 values of <1 nM. This
is a considerable improvement in potency in this series leading to
evaluated. All the synthesized fluoro analogues showed excellent
potency against T. cruzi. Remarkably, compound 36p, in which R3

6498
P. K. Suryadevara et al. / Bioorg. Med. Chem. Lett. 23 (2013) 6492–6499
anti-T. cruzi activity comparable to that of posaconazole (1). The
current SAR study clearly shows that 2-amino biphenyl as R-R1
system is superior for potency and also that halogens (–F, –Cl)
are well tolerated at the R2 position.
Twelve of the more potent compounds in this series were tested
for cytotoxicity to the mammalian lymphocytic cell line CRL-8155.
This is a relatively sensitive cell line to the cytotoxic effects of
chemicals.12 The tested dialkylimidazoles were only cytotoxic at
relatively high concentrations in the range of 5–10
lM
demonstrating a selectivity margin over T. cruzi amastigotes of
>10,000-fold in many cases.
Overall in this study we synthesized 75 dialkylimidazole-based
inhibitors of sterol-14a-demethylase and evaluated them against
T. cruzi, the causative agent of Chagas disease. We previously re-
ported that, dialkylimidazole based inhibitors are well tolerated
in animals infected with acute stage of the disease. These new ana-
logues are structurally simple, display suitable physicochemical
properties for that of an oral drug candidate and can be efficiently
synthesized at low-cost. In addition, novel compounds reported
herein display excellent potency against T. cruzi amastigotes with
activity comparable to posaconazole and show potential as novel
therapeutics for the treatment of Chagas disease.
Acknowledgments
Mammalian cell cytotoxicity experiments were assisted by
Nicole A. Duster. This work was supported by grants from the
National Institutes of Health (NIH) AI070218, AI054384, and
GM067871. We appreciatively acknowledge the financial support
Figure 2. Spectral response of T. cruzi CYP51 to 26c. Titration curve and difference
binding spectra (inset). P450 concentration was 2.2
lM; 26c titration range 0.4–
7.6 M (titration steps of 0.4
l
l
M). Methods as described previously.6.
Table 4
In vitro anti-T. cruzi activities of highly potent dialkylimidazole analogs bearing –NH2 at R (Scheme 4)
N
R3
R2
H
N
N
R1
36a-x
R
Compd No.
MWT
logP
PSA (Å2)
R
R1
R2
R3
T. cruzi EC50 (nM)
26c
36a
36b
36c
36d
36e
36f
36g
36h
36i
461
534
550
449
508
480
423
472
454
453
386
388
484
388
448
390
372
480
ND
5.0
6.5
5.9
4.7
6.1
5.1
5
5.3
3.5
4.8
4.4
4.3
5.8
4.3
5.5
4
3.8
6.2
ND
5.1
ND
4.7
4.5
3.8
2.2
78
NH2
NH2
NH2
NH2
NH2
NH2
NH2
NH2
NH2
NH2
NH2
NH2
NH2
NH2
NH2
NH2
NH2
NH2
NH2
NH2
NH2
NH2
NH2
NH2
NH2
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
2-Pyridine
Cl
OMe
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
–F
F
F
F
Phenyl
2-Pyrroe-phe
2-Mor-phe
2-Pip-phe
2-N,N-Di-Me-Phe
4-NH2-Phe
Cl
0.2
87.0
24.5
20.8
59.1
68.3
68.7
59.1
81.8
55.8
59.1
73.7
60.8
55.8
55.8
55.8
55.8
55.8
55.8
55.8
55.8
ND
19.0
0.3 (12,900)a
9.0
Pipd
1.1 (>5000)a
5.0 (14,600)a
3.8
Imidazole
Pyrrole
Methyl
H
2,6-di-F -Phe
Cl
Phenyl
F
H
2,6-di-F-Phe
4-Cl-Phe
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl
F
36j
36k
36l
0.6 (12,900)a
2.1
0.4
1.2
36m
36n
36o
36p
36q
36r
36s
36t
36u
36v
36w
36x
0.8 (18,800)a
3.2
F
1.1
Methyl
0.4 (>5000)a
1.5
O(CH2)2-morb
572
ND
449
406
372
399
71.5
ND
68.7
55.8
55.8
68.3
O(CH2)2-4-Me pipc
5.8 (5270)a
1.4
Benzd
Methoxy
Cl
H
F
F
F
F
14.5
12.8
232.6
358.0
Morpholine
a
b
c
Host cell activity against CRL-8155 IC50 (nM).
Benzothiazole.
Morpholine.
Piperidine.
d
e
Pyrrolidine.

P. K. Suryadevara et al. / Bioorg. Med. Chem. Lett. 23 (2013) 6492–6499
6499
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for this project from Drugs for Neglected Diseases Initiative (DNDi).
For the work described in this paper, DNDi allocated non-
earmarked funding (Department for International Development
(DFID)/United Kingdom, Spanish Agency for International Develop-
ment Cooperation (AECID)/Spain, Médecins Sans Frontières
(Doctors without Borders)/International). The donors had no role
in study design, data collection and analysis, decision to publish,
or preparation of the manuscript.
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Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2013.08.
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