Discovery and Structural Optimization of Acridones as Broad-Spectrum Antimalarials

Article abstract of DOI:10.1021/acs.jmedchem.8b01961

Malaria remains one of the deadliest diseases in the world today. Novel chemoprophylactic and chemotherapeutic antimalarials are needed to support the renewed eradication agenda. We have discovered a novel antimalarial acridone chemotype with dual-stage activity against both liver-stage and blood-stage malaria. Several lead compounds generated from structural optimization of a large library of novel acridones exhibit efficacy in the following systems: (1) picomolar inhibition of in vitro Plasmodium falciparum blood-stage growth against multidrug-resistant parasites; (2) curative efficacy after oral administration in an erythrocytic Plasmodium yoelii murine malaria model; (3) prevention of in vitro Plasmodium berghei sporozoite-induced development in human hepatocytes; and (4) protection of in vivo P. berghei sporozoite-induced infection in mice. This study offers the first account of liver-stage antimalarial activity in an acridone chemotype. Details of the design, chemistry, structure-activity relationships, safety, metabolic/pharmacokinetic studies, and mechanistic investigation are presented herein.

Full text of DOI:10.1021/acs.jmedchem.8b01961

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Article
Discovery and Structural Optimization of
Acridones as Broad-Spectrum Antimalarials
Rozalia A. Dodean, Papireddy Kancharla, Yuexin Li, Victor Melendez, Lisa Read, Charles Bane, Brian
Vesely, Mara Kreishman-Deitrick, Chad Black, Qigui Li, Richard J. Sciotti, Raul Olmeda, Thu-Lan Luong,
Heather Gaona, Brittney Potter, Jason Sousa, sean marcsisin, Diana Caridha, Lisa Xie, Chau Vuong, Qiang
Zeng, Jing Zhang, Ping Zhang, Hsiuling Lin, Kirk Butler, Norma Roncal, Lacy Gaynor-Ohnstad, Susan E.
Leed, Christina Nolan, Stephanie J. Huezo, Stephanie A. Rasmussen, Melissa T. Stephens, John C. Tan,
Roland Cooper, Martin J. Smilkstein, Sovitj Pou, Rolf W. Winter, Michael K. Riscoe, and Jane X. Kelly
J. Med. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jmedchem.8b01961 • Publication Date (Web): 10 Mar 2019
Downloaded from http://pubs.acs.org on March 11, 2019
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Experimental Therapeutics
Butler, Kirk ; Walter Reed Army Institute of Research, Division of
Experimental Therapeutics
Roncal, Norma ; Walter Reed Army Institute of Research, Division of
Experimental Therapeutics
Gaynor-Ohnstad, Lacy ; Walter Reed Army Institute of Research,
Division of Experimental Therapeutics
Leed, Susan; Walter Reed Army Institute for Research, Experimental
Therapeutics
Nolan, Christina ; Walter Reed Army Institute of Research, Division of
Experimental Therapeutics
Huezo, Stephanie ; Dominican University of California, Department of
Natural Sciences and Mathematics
Rasmussen, Stephanie ; Dominican University of California, Department
of Natural Sciences and Mathematics
Stephens, Melissa ; University of Notre Dame , Genomics Core Facility
Tan, John ; University of Notre Dame, Genomics Core Facility
Cooper, Roland; Dominican University of California, Department of
Natural Sciences & Mathematics
Smilkstein, Martin; Portland Veterans Affairs Medical Center
Pou, Sovitj; Portland VA Medical Center
Winter, Rolf ; Portland State University, Department of Chemistry
Riscoe, Michael; VA Medical Center, Portland State Univ, Experimental
Chemotherapy Lab
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Kelly, Jane; Oregon Health and Science University,
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Discovery and Structural Optimization of Acridones
as Broad-Spectrum Antimalarials
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Rozalia A. Dodean†, §, ‡, Papireddy Kancharla , Yuexin Li , Victor Melendez , Lisa
†, ‡
†,§
#
#
#
#
#
#
#
Read , Charles Bane , Brian Vesely , Mara Kreishman-Deitrick , Chad Black , Qigui Li ,
#
#
#
#
#
Richard J. Sciotti , Raul Olmeda, Thu-Lan Luong , Heather Gaona , Brittney Potter ,
#
#
#
#
#
#
Jason Sousa , Sean Marcsisin , Diana Caridha , Lisa Xie , Chau Vuong , Qiang Zeng ,
#
#
#
#
#
Jing Zhang , Ping Zhang , Hsiuling Lin , Kirk Butler , Norma Roncal , Lacy Gaynor-
#
#
#

Ohnstad , Susan E. Leed , Christina Nolan , Stephanie J. Huezo , Stephanie A.


,

Rasmussen , Melissa T. Stephens , John C. Tan , Roland Cooper , Martin J.
§
§
†, §
†, §
†, §,
Smilkstein , Sovitj Pou , Rolf W. Winter , Michael K. Riscoe , and Jane X. Kelly
*
†Department of Chemistry, Portland State University, Portland, Oregon 97201, United
States
§Department of Veterans Affairs Medical Center, Portland, Oregon 97239, United States
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#Division of Experimental Therapeutics, Walter Reed Army Institute of Research, Silver
Spring, Maryland 20910, United States
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Department of Natural Sciences and Mathematics, Dominican University of California,
San Rafael, CA 94901, United States
Genomics Core Facility, University of Notre Dame, Notre Dame IN, 46556
Eck Institute for Global Health, University of Notre Dame, Notre Dame IN, 46556
KEYWORDS. Malaria, antimalarials, acridones, Plasmodium falciparum, multi-drug
resistance
ABSTRACT
Malaria remains one of the deadliest diseases in the world today. Novel
chemoprophylactic and chemotherapeutic antimalarials are needed to support the
renewed eradication agenda. We have discovered a novel antimalarial acridone
chemotype with dual stage activity against both liver stage and blood stage malaria.
Several lead compounds generated from structural optimization of a large library of novel
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acridones exhibit efficacy in the following systems: 1) Picomolar inhibition of in vitro
Plasmodium falciparum blood stage growth against multi-drug resistant parasites; 2)
Curative efficacy after oral administration in erythrocytic P. yoelii murine malaria model;
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3) Prevention of in vitro P. berghei sporozoite-induced development in human
hepatocytes; and 4) Protection of in vivo P. berghei sporozoite-induced infection in mice.
This study offers the first account of liver stage antimalarial activity in acridone
chemotype. Details of the design, chemistry, structure-activity relationships, safety,
metabolic/pharmacokinetic studies, and mechanistic investigation are presented herein.
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INTRODUCTION
Malaria is an infectious disease caused by Plasmodium parasites, among which P.
falciparum is the most dangerous, with the highest rate of complications and mortality. It
remains one of the world’s deadliest diseases and the global effort to eradicate malaria
is compromised by lack of effective vaccine, emergence of artemisinin resistance1-5, as
well as the escalated burden of Plasmodium vivax6-10. Each year, malaria causes about
200 million clinical cases and claims nearly half a million lives, mostly children under the
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age of five and pregnant women . Although the burden of malaria is primarily borne by
those living in developing countries, dramatic increases in international travel now place
approximately 125 million Western travelers at risk of infection annually. More than 10000
of these are reported to acquire malaria each year11-14. In the absence of a clinically useful
vaccine15, 16, there will continue to be the need for new, low cost, effective and safe
malaria preventions and treatments, particularly for the most vulnerable populations:
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pregnant women and young children in endemic countries, as well as for non-immune
travelers into the areas of risk.
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Liver stage malaria is the first step of any natural infection, a symptomatically silent but
obligatory phase before the onset of the clinical symptoms of disease, which makes it an
attractive target for prophylactic antimalarial intervention strategies and the development
of an antimalarial vaccine17-22. Drugs targeting liver stage malaria (often referred to as
causal prophylactics) are highly sought after as they offer many advantages over drugs
19
that merely target the blood stage infection, but remain a formidable challenge .
Previously, we reported the discovery of dual-function acridones with both intrinsic
antimalarial activity and resistance-counteracting ability23,24,. We made modifications with
acridones lacking the (dialkylamino)alkyl moiety at N-10 position of the middle ring (Figure
1) and intriguingly they demonstrated broad-spectrum efficacy against both liver stage
and blood stage infection of malaria. Lead optimization effort followed, focusing on
structure–activity relationship (SAR) studies with various substituents on ring-A and ring-
B. The in vitro and in vivo blood stage and liver stage antimalarial activity/efficacy of
broad-spectrum acridones are described in this report, as well as safety profiles and
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metabolic/pharmacokinetic parameters. Notably, this study produced highly-potent drug
candidates with picomolar IC50 values against a panel of multidrug-resistant (MDR)
Plasmodium parasites, as well as full protection of liver stage infection at low oral doses
in animal model.
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Figure 1. Transition from dual-function acridone to broad-spectrum acridone chemotype.
RESULTS AND DISCUSSION
Chemistry. Initially, a series of acridones 7–15, 23 and 24 (Scheme 1 and Table 1) with
a substitution at the 3 position of ring-A and various (alkylamino)alkyl ethers at the 6
position of ring-B was synthesized starting with commercially available 2-chlorobenzoic
acid precursors 1a–d or methyl 4-methoxysalicylate (16). The copper-catalyzed
amination23, 25 of 1a–d with m-anisidine (2), and Buchwald-Hartwig cross coupling of
triflate 17 with 3-(trifluoromethyl)-aniline (18) yielded the corresponding anthranilic
26
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acid/ester intermediates 3a–d and 19, respectively. The Eaton’s acid-mediated cyclization
of 3a–d and 19 provided a mixture of corresponding methoxy-acridones 4a–d, 5a–d, and
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20, 21, which were separated by recrystallization using a mixture of DMF and MeOH in
4:1 ratio for 4a–d and 5a–d, and EtOAc and MeOH in 6:3 ratio for 20 and 21. The
compounds 5a–d and 21 were then demethylated either with HI/phenol or boron
tribromide (BBr ) to obtain the hydroxy-acridones 6a–d and 22, respectively, which when
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further treated with various 2-(dialkylamino)alkyl chlorides and K CO in dry acetone
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23
provided the desired acridones 7–15, 23 and 24 (Scheme 1) . Acridones 29 and 30, in
which ring-A is substituted with Cl at the 2 position and ring-B is substituted with
(dialkylamino)ethoxy moiety at the 6 position, were synthesized from triflate 17 and p-
chloroaniline (25), via the similar chemistry. The acridone 32 with (tert-
butylamino)propyloxy moiety at the 6 position of ring-B was obtained from
hydroxyacridone 28 via a two-step reaction sequence, in which 28 was first converted to
chloropropyloxy acridone 31 prior to amination with tert-butylamine in the presence of NaI
(Scheme 1, bottom panel).
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O
O
O
OMe
O
OH
ii
H N
OMe
+
2
OH
2
R1
NH
R1
R1
N
H
OMe
N
H
R1
i
Cl
4
a-d
5a-d
a: R1 = Cl
b: R1 = Br
c: R1 = F
1
1
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1
iii
MeO
O
3a-d
d: R1 = H
O
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R1
2
N
H
1
O-(CH ) -R
iv
2
n
R1
n = 2/3/5; R = Cl/Br/F/H
N
H
OH
2
R = (dialkylamino)-alkyl groups
6a-d
7
-15
O
CF3
O
O
O
MeO
HN
MeO
MeO
TfO
v
F3C
NH2
1
8
ii
HO
OMe
OMe
OMe
N
OMe
H
vi
1
6
17
20
19
O
F3C
+
O
O
R1
iv
N
R1
vii
F3C
N
O
H
F3C
N
H
OMe
1
1
F3C
O
N
H
OH
2
3: R = C H ; 24: R = n-C H
2
5
3
7
22
21
O
Cl
O
Cl
MeO
HN
MeO
TfO
NH2
ii
2
5
OMe
N
H
OMe
OMe
vi
17
27
2
6
iii
Cl
O
O
Cl
Cl
R1
iv
N
N
H
O
R1
N
H
OH
2
8
1
1
2
9: R = C H ; 30: R = n-C H
2
5
3
7
viii
O
O
Cl
Cl
ix
N
H
O
N
H
N
H
O
Cl
3
2
31
o
a
Reagents and conditions: (i) Cu powder, K CO , pentanol, reflux, 5 h; (ii) Eaton's acid, 90 C, 5-24 h; (iii) HI, phenol,
2
3
1
2
o
reflux, 3 h; (iv) Cl-(CH ) -R /R . HCl, K CO , acetone, reflux, 5-12 h; (v) Tf O, pyridine, CH Cl , 0 C-rt, 5 h; (vi)
2 n
2
3
2
2
2
o
o
Pd(dba) , DPPF, KOtBu, toluene, 100 C, 8-12 h; (vii) BBr , CH Cl , -78 C-rt, 12 h; (viii) Br-(CH ) -Cl, K CO ,
2
3
2
2
2 3
2
3
acetone, reflux, 24 h; (ix) tert-butylamine, NaI, DMSO, 145 °C, 2 h.
Scheme 1. Synthesis of acridones 7–15, 23, 24, and 29–32 with a substitution at the 2/3
position of ring-A and (dialkylamino)alkoxy/chloroalkoxy moiety at the 6 position of ring-
Ba
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To investigate the effect of disubstituent pattern at 1 and 3 positions of ring-A on
potency, a large number of acridones 38–55, 62 and 63 (Schemes 2, and Table 2) were
prepared. These have the ring-A is substituted either with Cl/F atoms or combination of
Cl and OMe groups, and ring-B substituted with a variety of (dialkylamino)alkyl/chloroalkyl
ethers at the 6 position. Acridones 38–55 were synthesized from the triflate 17 and 3,5-
dichloroaniline (33)/3,5-difluoroaniline (34), via the same chemistry as described in the
Scheme 1. Conversely, a different reaction strategy was designed and executed for the
synthesis of acridones 62 and 63 (Scheme 2, bottom panel), in which the
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(dipropylamino)ethoxy group was installed at the 6 position of ring-B before the Buchwald-
Hartwig cross coupling. Synthesis of 62 and 63 began with the coupling of methyl 2,4-
dihydroxybenzoate (56) with 1,2-dibromoethane in the presence of KI and K CO to
2
3
provide O-alkyl bromide 57, which was further converted into the dipropylamino-ethoxy
intermediate 58, by coupling with dipropylamine in the presence of KI and K CO . The
2
3
intermediate 58 was treated with triflic anhydride (Tf O) in the presence of pyridine to give
2
the triflate 59, which was further subjected to Buchwald-Hartwig cross coupling with 3-
chloro-5-methoxyaniline (60) to give the anthranilate intermediate 61. Eaton’s acid-
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mediated cyclization of 61 provided a mixture of two acridones 62 and 63, which were
separated by a column chromatography using a mixture of dichloromethane and MeOH
as mobile phase. It is noteworthy that our new strategy (Scheme 2, bottom panel) is
feasible to generate acridones that contain OMe group on ring-A and the
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(dialkylamino)alkyl ethers on ring-B.
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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
R1
O
O
MeO
NH2
R1
O
R2
MeO
TfO
1
2
HN
OMe
33: R = R = Cl
1
2
ii
3
4: R = R = F
OMe
R2
N
H
1
OMe
1
7
i
R1
R2
2
3
6a: R = R = Cl
1
2
1
2
3
3
5a: R = R = Cl
36b: R = R = F
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
5b: R = R = F
iii
R1
R1
O
O
iv
R2
R2
N
H
O-(CH ) -Cl
N
H
OH
2 n
1
2
1
2
1
2
37a: R = R = Cl
3
8: R = R = Cl, n = 2; 39: R = R = F, n = 2
1
2
1
2
1
2
37b: R = R = F
4
0: R = R = Cl, n = 3; 41: R = R = F, n = 3
1
2
R1
42: R = R = F, n = 4
O
v
vi
R2
3
N
H
O-(CH ) -R
2
n
4
2
3-55
1
n = 1-5; R = R = Cl/F
3
R = various aminoalkyl/alkyl groups
O
O
O
MeO
HO
viii
MeO
MeO
HO
vii
Br
N
OH
O
HO
O
5
6
57
5
8
Cl
ix
O
MeO
NH2
O
MeO
HN
6
0
N
MeO
TfO
O
i
N
61
O
59
Cl
OMe
ii
Cl
O
OMe O
+
N
N
MeO
N
H
O
Cl
N
H
O
6
2
63
a
o
o
Reagents and conditions: (i) Pd(dba) , DPPF, KOtBu, toluene, 100 C, 8-12 h; (ii) Eaton's acid, 90 C, 5-24 h; (iii)
2
HI, phenol, reflux, 3 h; (iv) Br-(CH ) -Cl, K CO , acetone, reflux, 24 h; (v) alkylamine, NaI, DMSO, 145 °C, 2 h;
2 n
2
3
3
(vi) Cl-(CH ) -R .HCl, K CO , acetone, reflux, 3-12 h; (vii) Br-(CH ) -Br, KI, K CO , acetone, reflux, 24 h; (viii)
2
n
2
3
2 2
2
3
o
dipropylamine, KI, K CO , acetone, reflux, 18 h; (ix) Tf O, pyridine, CH Cl , 0 C-rt, 5 h.
2
3
2
2
2
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Scheme 2. Synthesis of acridones 38–55, 62 and 63 with disubstitutions at the 1 and 3
positions of ring-A, and alkoxy/(dialkylamino)alkoxy/chloroalkoxy moiety at the 6 position
of ring-Ba
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
To investigate the effect of 1, 2- or 2, 3-disubstitution pattern of ring-A on potency, a
large number of acridones 70–86, 92, 93, 98 and 99 (Scheme 3, Table 3 and Table 4)
were generated. These acridones have the ring-A substituted either with Cl/F atoms or
combination of halogen and alkoxy groups at the 1 and 2 or 2 and 3 positions, and ring-
B substituted with a variety of (dialkylamino)alkoxy/chloroalkoxy moieties at the 6 position.
Acridones 70–86, 92 and 93, were synthesized from the triflate 17 and 3,4-dichloroaniline
(64)/3,4-difluoroaniline (87)/4-fluoro-3-methoxyaniline (88), via the same chemistry as
described in Scheme 2. The key acridone intermediates 66 and 67, obtained in 3:1 ratio,
respectively, from 65, were separated by recrystallization using a mixture of DMF and MeOH
(3:7). The acridones 98 and 99, which contain a F atom at the 2 position and OMe group
at the 3 position of ring-A, and (diethylamino)ethoxy and (diethylamino)ethyl-amino
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9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
groups at the 6 position of the ring-B, were synthesized from the methyl 2,4-
dihydroxybenzoate (56) and methyl 4-iodosalicylate (94), respectively. Coupling of 56
with 2-bromo-N,N-diethylethylamine in the presence of tetrabutylammonium chloride
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
TBAC)27 and K CO
provided compound 95a. Coupling of 94 with 2-
2
3
28
diethylaminoethylamine in the presence of CuI/Cs CO
and 2-acetylcyclohexanone
2
3
provided 95b. By treating with triflic anhydride, 95a–b were then transformed into the
corresponding triflates 96a–b, which when further subjected to Buchwald-Hartwig cross
29
coupling with 88, followed by Eaton’s acid-mediated cyclization gave acridones 98 and
99 (Scheme 3, bottom panel).
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9
Cl
Cl
O
O
MeO
Cl
O
O
NH2
MeO
TfO
Cl
Cl
6
4
HN
OMe
ii
+
OMe
i
N
H
OMe Cl
N
H
OMe
1
7
6
6
Cl
65
67
iii
iii
Cl
Cl
O
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Cl
O
O
Cl
iv
Cl
Cl
Cl
N
H
O-(CH ) -Cl
2 n
N
OH
N
H
OH
70: n = 2
1: n = 3
H
6
8
69
7
v
vi
iv
vi
Cl
O
O
O
Cl
Cl
Cl
Cl
v
1
O-(CH ) -R1
2 n
N
O-(CH ) -R
N
Cl
N
H
O-(CH ) -Cl
2 3
2
n
H
H
72-81
83-86
1
1
82
n = 2, 3; R = aminoalkyl substituents
n = 2, 3; R = aminoalkyl substituents
O
O
F
F
R1
O
MeO
R1
ii
NH2
MeO
TfO
1
1
HN
OMe
N
H
OMe
8
7: R = F; 88: R = OMe
1
1
90a: R = F
OMe
i
89a: R = F
iii
1
1
90b: R = OMe
8
9b: R = OMe
1
7
R1
O
F
O
F
F
vii
N
R1
2: R = F
N
H
O
R1
N
OH
H
1
1
N
9
9
3: R =
1
1
O
9
1a: R = F; 91b: R = OH
O
O
O
viii
x
MeO
MeO
HO
MeO
N
N
TfO
X
OH
HO
X
5
6
9
6a: X = O; 96b: X = NH
88, xi
9
5a: X = O; 95b: X = NH
O
ix
O
MeO
O
F
N
HN
X
ii
MeO
HO
N
MeO
N
H
X
97a: X = O
I
9
9
8: X = O
97b: X = NH
OMe
94
9: X = NH
F
a
o
o
Reagents and conditions: (i) Pd(dba) , DPPF, KOtBu, toluene, 100 C, 8-12 h; (ii) Eaton's acid, 90 C, 5-24 h; (iii) HI,
2
phenol, reflux, 3 h; (iv) Br-(CH ) -Cl, K CO , acetone, reflux, 24 h; (v) alkylamine, NaI, DMSO, 145 °C, 2 h; (vi)
2 n
2
3
Cl-(CH ) -R , K CO , acetone, reflux, 10-24 h; (vii) Cl-(CH ) -N(Et) .HCl, K CO , acetone, reflux, 10 h; (viii) Br-
2
n
1
2
3
2 2
2
2
3
(CH ) -N(Et) .HBr, TBAC, K CO , acetone, reflux, 4 h; (ix) NH -(CH ) -N(Et) , 2-acetylcyclohexanone, Cs CO ,
2
2
2
2
3
2
2 2
2
2
3
o
o
o
CuI, DMF, 100 C, 4 h; (x) Tf O, pyridine, CH Cl , 0 C-rt, 5 h; (xi) Pd(OAc) , XPhos, Cs CO , toluene, 110 C, 5-8 h.
2
2
2
2
2
3
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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Scheme 3. Synthesis of acridones 70–86, 92, 93, 98 and 99 with disubstitutions at the 1
and 2 or the 2 and 3 positions of ring-A and (diethylamino)ethoxy/ethyl-
amino/chloroalkoxy at the 6 position of ring-Ba
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
To investigate the isomeric effect on potency, three dichloro-acridones 100–102 (Figure
2), which are isomeric to 45, 73 and 83 (Table 2–4), were prepared from triflate 17 and
the corresponding dichloroanilines, via the similar chemistry as described in Scheme 3.
Cl
O
O
O
Cl
N
N
N
N
H
O
N
H
O
Cl
N
H
O
Cl
100
Cl
Cl
101
102
Figure 2. Structures of 1,4/2,4/3,4-dichloro-acridones 100–102.
Next our attention was turned toward the synthesis of acridones that contain
(dialkylamino)alkyl ethers at the 7 position of ring-B. A series of acridones 109–113, 119,
120, 123 and 128 (Scheme 4), in which ring-A is substituted either with halogens or a
combination of halogen and alkoxy groups and ring-B is substituted with the
(alkylamino)alkyl ethers at the 7 position, was synthesized starting with commercially
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available precursors 103, 114 and 1d, via the same synthetic methods that were
employed in the previous Schemes.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
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8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
O
O
O
O
OH
O
O
O
MeO
i
ii
MeO
HO
N
MeO
HO
Cl
iii
MeO
TfO
N
HO
105
1
03
104
1
06
OMe
iv
34/60
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
F
NH2
N
R1
O
R2
107
O
O
O
O
N
+
N
O
MeO
HN
R2
N
H
R1
N
H
v
1
1
09: R1 = R2 = F
10: R1 = F, R2 = OMe
112: R1 = Cl, R2 = OMe
111: R1 = F, R = OMe
2
1
2
108a-c
113: R = Cl, R
= OMe
R1
R2
O
O
OMe
v
MeO
HN
Cl
O
O
OMe
MeO
64, iv
Cl
OMe Cl
OMe
+
Br
N
H
Cl
N
H
114
5, iv
Cl
116a
116b
2
Cl
O
115
vi
vi
O
Cl
O
O
v, vi
Cl
OH
OMe
Cl
OH
Cl
Cl
OH
MeO
HN
N
H
N
N
H
H
1
22
1
17
1
18
121
vii
viii
viii
Cl
O
Cl
O
O
Cl
O
Cl
O
Cl
Cl
O
N
N
N
N
H
N
N
H
1
23
1
19
H
120
O
OMe
O
OH
O
H N
2
OMe
OH
124
Cl
NH
v
ix
Cl
Cl
Cl
N
H
1d
126
OMe
25
vi
1
O
O
O
OH
N
vii
Cl
N
H
Cl
N
H
1
28
127
a
Reagents and Conditions: (i) Br-(CH ) -Cl, K CO , acetone, reflux, 10 h; (ii) dipropyl amine, NaI, DMSO, 145 °C, 3 h;
2 2
2
3
o
o
o
(iii) Tf O, pyridine, CH Cl , 0 C-rt, 5 h; (iv) Pd(OAc) , XPhos, Cs CO , toluene, 110 C, 5-8 h; (v) Eaton's acid, 90 C,
2
2
2
2
2
3
o
5-24 h; (vi) BBr , CH Cl , -78 C-rt, 12 h; (vii) Cl-(CH ) -N(Et) .HCl, K CO , acetone, reflux, 10 h; (viii) Cl-(CH ) -
3
2
2
2 2
2
2
3
2 2
N(Pr) .HCl, K CO , acetone, reflux, 10 h; (ix) Cu powder, K CO , pentanol, reflux, 5 h.
2
2
3
2
3
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Scheme 4. Synthesis of acridones 109–113, 119, 120, 123 and 128 with mono/di-
substitutions on ring-A and (dialkylamino)alkoxy moiety at the 7 position of ring-Ba
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Biological Activity. In this work, the structure–activity relationship (SAR) studies were
conducted with the focus on various substitutions at different positions on ring-A and ring-
B of the acridones. We have synthesized a large library of the acridones and evaluated
these for antimalarial blood stage and liver stage efficacy, safety, mode of action, and
metabolic/pharmacokinetic properties. The in vitro antimalarial blood stage activity of
acridone derivatives was tested against a panel of P. falciparum with different geographic
30
and genetic backgrounds using a SYBR Green based assay . Chloroquine (CQ) and
atovaquone (ATV) were used as reference drugs in all experiments. These acridones
exhibit potent activity against CQ sensitive and multi-drug resistant (MDR) parasites and
cross-resistance patterns against ATV-resistant parasites vary significantly between
positional isomers. The in vivo antimalarial blood stage efficacy was determined using a
well-established modified Thompson 4-day suppression rodent model against P. yoelii23,
31, 32.
The acridone derivatives (via oral administrations) exhibited excellent blood stage
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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
efficacy. The in vitro liver stage activity of acridone derivatives was assessed utilizing
luciferase-expressing P. berghei sporozoite infected human hepatocyte HepG2 cells33, 34
.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
A number of the acridone analogues exhibit potent activity (some superior to ATV) against
the liver stage parasite, without toxic effect to the host liver cells. The in vivo antimalarial
liver stage efficacy in rodent malaria model was conducted with real-time in vivo imaging
system (IVIS), utilizing transgenic bioluminescent parasites33, 35, 36. Several lead
compounds exhibited true causal prophylactic efficacy providing full protection and cure
in this animal model. Cytotoxicity test against human hepatic HepG2 cells indicates
favorable therapeutic index (>1000 for most compounds). In vitro cardiotoxicity and
mutagenicity were assessed as well, with lead acridone compounds demonstrating
feasible safety profiles. No overt clinical toxicity or behavior change was observed in mice
treated with acridones. The in vitro metabolic stability using mouse and human liver
microsomes, and in vivo pharmacokinetic (PK) studies in mice were are also conducted
for lead compounds. Observations from preliminary drug resistance selection studies
suggest a complex mode of action for broad spectrum acridones, including but not limited
to inhibition of the parasite electron transport chain.
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Page 21 of 122
Journal of Medicinal Chemistry
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3
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7
8
9
In Vitro Blood Stage Activity and SAR of Acridones with Mono-Substitution on Ring-A
23
and Ring-B. In our previous work , acridone 7, which is an intermediate of dual-function
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
novel antimalarial acridone T3.5, demonstrated excellent potency against a panel of CQ
sensitive and multi-drug resistant (MDR) P. falciparum parasites (Table 1). Our initial lead
optimizations focused on exploring substituents with the halogen and/or trifluoromethyl
moieties on the 2 and 3 positions of ring-A, and hydrophilic moieties such as
(
(dialkylamino)alkyl ethers) on the 6 position of ring-B. To probe the chlorine atom effect
on potency, we initially synthesized three acridones 8–10, in which the Cl atom at the 3
position of acridone 7 is replaced with bromine (Br), fluorine (F) and hydrogen (H) atoms,
respectively (Table 1), and examined for in vitro antimalarial activity.
It appears that acridone 8 with the Br atom at the 3 position of ring-A retained the
potency against all tested P. falciparum strains with great selectivity and was slightly more
potent than acridone 7. Replacing Cl by F atom as in 9 and H atom as in 10 led to
substantial decrease in the antimalarial activity (9 IC = 377 nM and 10 IC = 1347 nM
50
50
versus 7 IC = 32 nM against D6) against all P. falciparum strains (Table 1), suggesting
50
that halogen at the 3 position of ring-A is required for potent antimalarial activity and the
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Journal of Medicinal Chemistry
Page 22 of 122
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
size of the halogen also has impact on potency (potency order of substituents: Br ≥ Cl >
F >> H). We then investigated the effect of various substituents at the 6 position of ring-
B on antimalarial activities. A series of acridones 11–15, where the (diethylamino)ethoxy
group at the 6 position of acridone 7 is replaced with various (dialkylamino)alkoxy
moieties, was generated and tested for their in vitro antimalarial activity. Acridone 11 with
the (dimethylamino)ethoxy moiety at the 6 position on ring-B showed roughly 2-fold
decrease in activity as compared to 7 (11 IC = 56 nM versus 7 IC = 32 nM against
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
50
50
D6). In contrast, acridone 12 with the (dipropylamino)ethoxy moiety at the 6 position on
ring-B showed increased potency over 7 (12 IC = 2.5 nM versus 7 IC = 32 nM against
50
50
D6). Significant loss of potency was observed for acridones 13, 14 and 15, containing
ethoxypyrrolidin, (diethylamino)propoxy and (diethylamino)pentyloxy moieties,
respectively. These results demonstrate that the length and nature of the alkyl chain of
(dialkylamino)alkoxy moieties at the 6 position play a crucial role for antimalarial potency.
Replacing the chlorine atom of acridones 7 and 12 with trifluoromethyl (CF ) moiety as in
3
2
3 and 24 dramatically decreased the antimalarial activity (23 IC = 816 nM versus 7 IC
50
50
= 32 nM and 24 IC = 26 nM versus 12 IC = 2.5 nM against D6). This work suggested
50
50
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Page 23 of 122
Journal of Medicinal Chemistry
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7
8
9
that the bulky moiety (CF ) at the 3 position on ring-A had adverse effect on antimalarial
3
activity.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Investigations on the 2 position of ring-A produced acridones 29–32, where the chlorine
atom is shifted from the 3 position to the 2 position on ring-A. Interestingly, the effect of
varying the substituent on ring A depended to a degree on the ring B substituent. Thus
shifting the Cl atom from the 3 position to the 2 position as in 29, a positional isomer of 7,
led to reduced potency (29 IC50 = 212 nM versus 7 IC50 = 32 nM against D6), whilst
acridone 30, which is a positional isomer of 12, retained potency (30 IC = 3.6 nM versus
50
1
2 IC = 2.5 nM against D6). It is noteworthy that the activity was retained even after
50
replacing the (dialkylamino)alkoxy moieties at the 6 position of ring-B with chloropropoxy
moiety as in 31 (IC = 24 nM against D6). Significant loss of antimalarial potency was
50
observed when the Cl atom at the terminal carbon of acridone 31 was replaced with tert-
butylamine as in 32 (IC50 = 674 nM against D6). SAR analyses of these acridones
demonstrate that the nature of substituents on ring-A and the (dialkylamino)alkoxy
moieties on ring-B play a pivotal role for antimalarial potency.
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Journal of Medicinal Chemistry
Page 24 of 122
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Table 1. In Vitro Blood Stage Antimalarial Activity and Cytotoxicity of Acridones (T3.5, 7–
15, 23, 24 and 29–32)
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
O
N
O
1
R1
N
Cl
O
3
R2
N
H
N
7-15, 23, 24 and 29-32
T3.5
blood stage IC50 (nM)a
vs P. falciparum
cytotoxicity
IC50 (nM)
vs HepG2
> 40000
selectivity
index (SI)
(D6)
a
b
compd
T3.5
7
R1
-
R2
D6
49
32
Dd2
7G8
Tm90-C2B
-
77
86
71
> 816
3-Cl
41
38
589
36389
> 40000
47872
1137
> 1600
127
N
N
N
N
O
O
O
O
8
9
3-Br
3-F
25
34
37
968
1669
2531
377
485
353
1
0
3-H
1347
1189
1187
96774
72
11
3-Cl
3-Cl
N
56
63
11
70
563
59023
40631
1054
O
1
2
2.5
9.1
1542
16252
N
O
13
3-Cl
3-Cl
529
272
781
254
959
294
1500
1890
25485
19653
48
72
N
O
O
1
4
N
2
15
23
3-Cl
540
511
517
1044
31279
58
N
4
O
O
3-CF
3-CF
3
816
26
555
0.44
351
1537
5.6
1394
1535
1163
38594
47
N
2
2
4
9
3
> 100000
> 100000
> 3846
> 473
N
O
2- Cl
212
304
N
O
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Page 25 of 122
Journal of Medicinal Chemistry
1
2
3
4
5
6
7
8
9
3
0
2- Cl
3.6
15
38
9.2
51
317
>100000
> 27777
N
O
O
31
2- Cl
2- Cl
O
Cl
24
371
> 100000
75225
> 4167
112
3
2
674
1023 > 2500
2135
N
H
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
ATV
CQ
-
-
-
0.10
15
0.10
163
0.20
171
8256
208
23160
37577
231600
2505
-
aIC50 values are the average of at least three determinations, each carried out in triplicate (±10%). In
order to compare results run on different days and with different batches of each stain, D6: CQ sensitive;
Dd2: MDR strain with Old World genetic background; 7G8: MDR strain with New World genetic background;
b
Tm90-C2B: Atovaquone resistant clinical isolate; ATV: Atovaquone; CQ: Chloroquine. SI (selectivity index)
=
IC50 (cytotoxicity)/IC50 (D6).
In Vitro Blood Stage Activity and SAR of Acridones with 1,3-Disubstitutions on Ring-A
and a 6-Substitution on Ring-B. Having determined the impact of substituents on the
antimalarial activity of acridones that contain a halogen either at the 2 or 3 position of
ring-A and an (alkylamino)alkyl ether at the 6 position of ring-B, we subsequently tested
a hypothesis that two halogens on ring-A might represent an opportunity to make more
potent and selective antimalarials. Therefore, we have generated a large number of
acridones 38–55, 62 and 63 with ring-A substituted either with two chlorine/fluorine atoms
or a combination of halogen and methoxy moieties at the 1 and 3 positions and ring-B
substituted with a variety of hydrophilic and/or hydrophobic moieties at the 6 position and
subsequently tested their antimalarial potentials against a panel of P. falciparum strains
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Journal of Medicinal Chemistry
Page 26 of 122
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
(
Table 2). Di-halogenated acridones 38–42 with various chloroalkyl ethers at the 6
position of ring-B exhibited excellent potency against all P. falciparum strains (IC =0.12–
50
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
4 nM against D6) with high selectivity index (Table 2). 1,3-Difluoro acridones 43 and 44,
where ring-B is substituted with trifluorobutoxy and hexyloxy moieties at the 6 position,
respectively, showed substantially higher potency (>10-fold) than that of the chloroalkyl
ether containing acridones 38–42 (Table 2). These results demonstrated that elongation
of the chloroalkyl/alkyl ethers chain at the 6 position of ring-B (from chloroethyl ether; 38
IC50 = 14 nM to hexyloxy ether; 44 IC50 = 0.026 nM against D6) led to increase in
antimalarial activity, regardless the di-chloro and/or di-fluoro substitutions on ring-A.
After establishing the optimal di halogen substituents pattern at the 1 and 3 positions
on ring-A and chloroalkyl/alkyl ethers at the 6 position of ring-B, we focused further on
exploring hydrophilic moieties at the 6 position of ring-B. A set of di-halogenated
acridones 45–49, where ring-B is substituted with various (dialkylamino)ethoxy moieties
at the 6 position, were generated and screened for their antimalarial activity. Notably, di-
halogenated acridones 45–49 were highly potent (IC values as low as 0.00030 nM
50
against D6, Table 2) compared to mono-halogenated acridones 7, 8 and 12 (Table 1) and
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Page 27 of 122
Journal of Medicinal Chemistry
1
2
3
4
5
6
7
8
9
di-halogenated acridones 38–42 (Table 2). Specifically, acridones 47–49 with
(dipropylamino)ethoxy and (di-trifluoropropylamino)ethoxy moieties showed the highest
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
potencies with picomolar IC values. These results demonstrate that dipropylamine as
50
part of hydrophilic moiety at the 6 position of ring-B plays a vital role in enhancing
antimalarial potency. We also sought to explore the elongation of the alkyl chain between
oxygen and dialkylamine as a part of hydrophilic moiety at the 6 position preparing three
di-halogenated acridones 50–52 (Table 2). Although acridones 50–52 maintained
relatively good activity against all P. falciparum strains (IC50 < 32 nM against D6),
analogues 50–52 showed a significant decline in activity (50 IC = 19 nM versus 45 IC
50
50
= 8.2 nM; 51 IC = 32 nM versus 46 IC = 7.8 nM; 52 IC = 0.35 nM versus 48 IC =
50
50
50
50
0.00030 nM against D6) comparing with their homologous acridones 45, 46 and 48.
Together these results again demonstrate that the length of alkyl chain between oxygen
and dialkylamine as in a part of hydrophilic moiety at the 6 position plays an important
role and it appears that two carbon chain length is optimal for antimalarial potency. We
next investigated the effect of (monoalkylamino)alkoxy moieties at the 6 position.
Replacement of (dialkylamino)alkoxy moieties with the (monoalkylamino)alkoxy moieties
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Journal of Medicinal Chemistry
Page 28 of 122
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
as in 53–55 led to reduced potency in general (Table 2). The biggest potency loss
occurred when we introduced methoxy (OMe) group either at the 1 or 3 position on ring-
A as in 62 and 63. It appears that the OMe group on ring-A has an adverse effect,
specifically at the 1 position (62 IC = 0.65 nM versus 47 IC = 0.0050 nM; and 63 IC
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
50
50
50
=
251 nM versus 47 IC = 0.0050 nM against D6). In general, SAR analyses demonstrate
50
that di-halogen substitutions at the 1 and 3 positons of ring-A and (dialkylamino)ethoxy
moieties at the 6 position of ring-B are well tolerated (Table 1 and 2).
Table 2. In Vitro Blood Stage Antimalarial Activity and Cytotoxicity of Acridones (38–55,
61 and 63)
R1
O
R2
N
H
R3
38-55, 62 and 63
a
blood stage IC50 (nM) vs
cytotoxicity
IC50 (nM)
selectivity
index (SI)
(D6)
a
b
P. falciparum
compd
R1
Cl
F
R2
Cl
F
R3
D6
14
Dd2
7G8
Tm90-
C2B
409
vs HepG2
> 100000
> 200000
> 100000
> 100000
> 100000
> 200000
Cl
Cl
3
3
4
4
4
4
8
9
0
1
2
3
O
O
12
44
> 7143
> 40000
> 45454
> 71428
>100000
> 200000
5.0
7.0
22
46
70
89
40
40
Cl
F
Cl
F
O
Cl
2.2
2.9
6.6
O
Cl
1.4
0.30
0.16
0.033
1.9
Cl
F
F
O
0.12
0.027
0.50
0.50
F
F
O
CF3
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Page 29 of 122
Journal of Medicinal Chemistry
1
2
3
4
5
6
7
8
9
4
4
4
5
F
F
O
0.026
8.2
0.041
22
0.050
21
5.4
> 100000
13365
> 100000
1630
Cl
Cl
465
N
N
O
4
4
6
7
F
F
7.8
16
12
1979
153
77586
37194
9947
O
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Cl
Cl
0.0050
0.0030
0.0060
7438
N
O
4
8
F
F
F
F
0.00030
0.0020
0.00030 0.00030
6.8
2.0
42821
> 100000
> 100000
N
O
CF3
CF3
49
0.015
45
0.016
114
44
> 100000
N
O
5
5
5
0
1
2
Cl
F
Cl
F
19
32
228
705
440
130000
38601
61461
6842
1206
N
2
O
7.8
N
2
O
F
F
0.35
0.49
2.1
175602
N
O
2
5
5
3
4
Cl
F
Cl
F
O
N
101
115
186
8.9
294
627
82
11087
41492
110
361
H
2500
O
N
H
H
55
F
Cl
F
OMe
Cl
N
75
265
4.2
14
6.2
251
> 2500
81
101000
> 200000
45000
1346
> 307692
179
O
6
6
2
3
0.65
251
N
O
OMe
184
> 2500
N
O
ATV
CQ
-
0.10
15
0.10
163
0.20
171
8256
208
23160
37577
231600
2505
-
aIC50 values are the average of at least three determinations, each carried out in triplicate (±10%). In
order to compare results run on different days and with different batches of each stain, D6: CQ sensitive;
Dd2: MDR strain with Old World genetic background; 7G8: MDR strain with New World genetic background;
b
Tm90-C2B: Atovaquone resistant clinical isolate; ATV: Atovaquone; CQ: Chloroquine. SI (selectivity index)
=
IC50 (cytotoxicity)/IC50 (D6).
In Vitro Blood Stage Activity and SAR of Acridones with 1,2-Dichloro-Substitutions on
Ring-A and 6-Substitution on Ring-B. Exploration of the SARs on ring-A and ring-B of
ACS Paragon Plus Environment
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