Synthesis, in vitro antimalarial activity and cytotoxicity of novel 4-aminoquinolinyl-chalcone amides

Article abstract of DOI:10.1016/j.bmc.2013.12.032

A series of 4-aminoquinolinyl-chalcone amides 11-19 were synthesized through condensation of carboxylic acid-functionalized chalcone with aminoquinolines, using 1,1′-carbonyldiimidazole as coupling agent These compounds were screened against the chloroquine sensitive (3D7) and chloroquine resistant (W2) strains of Plasmodium falciparum Their cytotoxicity towards the WI-38 cell line of normal human fetal lung fibroblast was determined All compounds were found active, with IC₅₀ values ranging between 0.04-0.5 μM and 0.07-1.8 μM against 3D7 and W2, respectively They demonstrated moderate to high selective activity towards the parasitic cells in the presence of mammalian cells However, amide 15, featuring the 1,6-diaminohexane linker, despite possessing predicted unfavourable aqueous solubility and absorption properties, was the most active of all the amides tested It was found to be as potent as CQ against 3D7, while it displayed a two-fold higher activity than CQ against the W2 strain, with good selective antimalarial activity (SI = 435) towards the parasitic cells During this study, amide 15 was thus identified as the best drug-candidate to for further investigation as a potential drug in search for new, safe and effective antimalarial drugs

Full text of DOI:10.1016/j.bmc.2013.12.032

Bioorganic & Medicinal Chemistry 22 (2014) 1128–1138
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis, in vitro antimalarial activity and cytotoxicity of novel
4-aminoquinolinyl-chalcone amides
a
b,
⇑
Frans J. Smit , David D. N’Da
a
Pharmaceutical Chemistry, School of Pharmacy, North-West University, Potchefstroom 2520, South Africa
Center of Excellence for Pharmaceutical Sciences, North-West University, Potchefstroom 2520, South Africa
b
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of 4-aminoquinolinyl-chalcone amides 11–19 were synthesized through condensation of carbox-
ylic acid-functionalized chalcone with aminoquinolines, using 1,1 -carbonyldiimidazole as coupling
agent. These compounds were screened against the chloroquine sensitive (3D7) and chloroquine resistant
Received 8 October 2013
Revised 2 December 2013
Accepted 12 December 2013
Available online 22 December 2013
0
(
W2) strains of Plasmodium falciparum. Their cytotoxicity towards the WI-38 cell line of normal human
fetal lung fibroblast was determined. All compounds were found active, with IC50 values ranging between
.04–0.5 M and 0.07–1.8 M against 3D7 and W2, respectively. They demonstrated moderate to high
0
l
l
Keywords:
Chalcone
selective activity towards the parasitic cells in the presence of mammalian cells. However, amide 15, fea-
turing the 1,6-diaminohexane linker, despite possessing predicted unfavourable aqueous solubility and
absorption properties, was the most active of all the amides tested. It was found to be as potent as CQ
against 3D7, while it displayed a two-fold higher activity than CQ against the W2 strain, with good selec-
tive antimalarial activity (SI = 435) towards the parasitic cells. During this study, amide 15 was thus iden-
tified as the best drug-candidate to for further investigation as a potential drug in search for new, safe and
effective antimalarial drugs.
4
-Aminoquinoline
Chloroquine (CQ)
Plasmodium falciparum
Malaria
Ó 2013 Elsevier Ltd. All rights reserved.
1
. Introduction
With over three billion people at risk and around 660,000
activity that are medically/therapeutically more effective than its
individual components.
6
Despite widespread chloroquine (CQ) resistance in the majority
of malaria endemic areas, quinoline based compounds remain an
important class of potential antimalarial drugs that require further
investigation, mainly as a result of their cheap synthetic cost and
1
deaths reported in 2011, malaria poses a major public health
2
threat, globally. Of these reported deaths, 91% were in the African
region and 86% were children under the age of five.1 Malaria is
commonly found in tropical and subtropical regions, such as Africa
7
,8
diverse applications. Additionally, resistance seems to be com-
pound specific and not related to changes in the structure of the
drug target. CQ resistance can thus be overcome by hybridization
of the parent molecule (quinoline) with other pharmacophores.9
Recent advents in genetic sequencing of the Plasmodium gen-
ome have identified several new unique targets, including the par-
asite induced permeation pathways and malarial cysteine
proteases. These can be specifically targeted with minimal toxicity
to the host. Cysteine protease mediates protein hydrolysis through
nucleophilic attack on a carbonyl of a susceptible peptide bond.
The main function of malarial cysteine protease is the hydrolysis
3
and Asia, and is endemic in 106 countries worldwide.
Although artemisinin combination therapies (ACTs) currently
are the preferred treatment method for both uncomplicated and
4
severe malaria, all of the shortcomings of the individual com-
pounds remain problematic, including resistance to the parent
molecule. Additionally, alarming reports of P. falciparum tolerance
to artemisinins in South-Asia and along the Cambodia-Thailand
1
,5
border, jeopardize the use of ACTs and signify the urgent need
for identifying and developing new therapies that can act on un-
ique targets. An alternative method that has been proposed to
overcome the development of resistance is the incorporation of a
second pharmacophore via a chemical bond, forming a hybrid drug
molecule. Hybrid molecules combine two drugs in a single mole-
cule, with the goal of creating a chemical entity with two or more
structural domains, having different biological functions and dual
1
0
of haemoglobin in the food vacuole. This enzyme is also pre-
sumed to be involved in the rupture of the erythrocyte
1
1
membrane.
A known cysteine protease inhibitor is E64 (Fig. 1), a natural
modified peptide, containing an active epoxide functional group.
Other inhibitors include natural compounds, such as chalcones
(1,3-diaryl propenone) and isatins. The first reported chalcone with
antimalarial activity was Licochalcone A (Fig. 1), a natural product
⇑
Corresponding author. Tel.: +27 18 299 2256; fax: +27 18 299 4243.
E-mail address: david.nda@nwu.ac.za (D.D. N’Da).
0
968-0896/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmc.2013.12.032

F. J. Smit, D. D. N’Da / Bioorg. Med. Chem. 22 (2014) 1128–1138
1129
O
O
O
O
O
NH
NH2
H
N
Ar
Ring A
Ar
HO
OH
HO
N
H
N
H
Ring B
O
O
General structure of
a chalcone
E64
Licochalcone A
Figure 1. General structure of a chalcone, cysteine protease inhibitor E64 and licochalcone A.
isolated from Chinese liquorice roots, with an IC50 value of 6.5
l
M
in vitro antimalarial activity and cytotoxicity of these novel
4-aminoquinolinyl-chalcone amides are reported.
1
2,13
against 3D7 clones.
Ever since, interest in these compounds
has ignited. Numerous chalcones have to date been prepared and
5
,12,14–17
screened for antiplasmodial activity with varying success.
2
2
. Materials and methods
.1. Materials
Several chalcone based hybrids have also been reported containing
a number of different pharmacophores, such as thiolactone-, isat-
1
8
19
20–22
23,24
in-, stilbene-, quinoline-,
ferrocene-
and endoperox-
2
5
ide-chalcone based hybrids.
4
,7-Dichloroquinoline, 4-formylbenzoic acid, 2-acetyl-5-meth-
In 2009, Sharma et al.22 synthesized some of the first reported,
substituted quinolinyl-chalcone based hybrids (Fig 2, (A) of which
the 4-amino linked compounds showed low to no activity against
the NF-54 strain of P. falciparum. This disappointing outcome cor-
roborated earlier reports by Chibale et al. (2000)26 that the length
of the methylene spacer between the two nitrogen groups in the
side chain of CQ analogues was a major determinant of their anti-
malarial activities against CQ resistant P. falciparum. Sashidhara
0
ylfuran, hydrochloric acid, sodium hydroxide, 1,1 -carbonyldiimid-
azole (CDI), ethylene diamine, propylene diamine, butylene
diamine, piperazine, 1,2-diamino propane, 1,6-diaminohexane,
0
N-methyl-1,3-propylene diamine, 2,2 -(ethylenedioxy)bis(ethyla-
mine), N-(3-aminopropyl)-N-methylpropane-1,3-diamine, magne-
sium sulphate and sodium bicarbonate were purchased from
Sigma–Aldrich (South-Africa). All solvents used were purchased
from Associated Chemical Enterprises (ACE, South Africa). All
chemicals and reagents were of analytical grade and were used
without further purification. Dichloromethane (DCM) was distilled
over calcium hydride and kept on molecular sieves (4 Å) prior to
use in reactions.
2
0,21
et al.
reported the synthesis and biological activity of a num-
ber of chloroquine–chalcone based hybrids. Of these keto-enam-
ine chloroquine–chalcone based hybrid compounds (Fig 2, (B)
several were equipotent to CQ against 3D7 strains. These com-
pounds also displayed antimalarial activity in vivo against the
MDR rodent malaria parasite, P. yoelii. Mechanistic studies done
2
.2. General procedures
by these authors had revealed that these compounds acted
through haem polymerisation targets.2
0,21
These findings inter alia
The 1H and 13C NMR spectra were recorded on a Bruker
formed the rationale underlying the design of the novel quinoli-
nyl-chalcone hybrids during this study. It also indicated that the
combination of chloroquine–chalcone based hybrids may become
leading compounds in the future design of more potent antima-
larial drugs. Additionally, since both the chalcone and CQ exert
their activities in the digestive vacuole, a synergistic effect might
be expected.
Avance™ III 600 spectrometer at
50 MHz, respectively, in deuterated dimethyl sulfoxide (DMSO-
), deuterated methanol (MeOD), or deuterated chloroform
CDCl ). Chemical shifts are reported in parts per million d (ppm)
with the residual protons of the solvent as reference. The splitting
pattern abbreviations are as follows: s (singlet), d (doublet), dd
a frequency of 600 and
1
d
6
(
3
(
doublet of doublet), t (triplet), q (quartet), p (pentet), and m (mul-
As part of our program focusing on the discovery of novel anti-
malarial compounds and in light of the above considerations, we
investigated amide compounds formed by conjugating chalcone
moiety (with a 5-methylfuran as ring B) to 7-chloroquinoline
pharmacophore through various linkers. It is argued that since
chalcones are cysteine inhibitors, which specifically target amide
bonds, thus, the incorporation of amide bond in the compounds
of this study might prove worthy. In this Letter, the synthesis,
tiplet). High Resolution Mass spectrometry (HRMS) was recorded
on a Bruker MicroTOF Q II mass spectrometer that had an APCI
or an ESI source set at 300 °C, or 180 °C, respectively, using Bruker
Compass DataAnalysis 4.0 software. A full scan, ranging between
5
0–1500 m/z, was generated at a capillary voltage of 4500 V, an
end plate offset voltage of ꢀ500 V and a collision cell RF voltage
of 100 Vpp.
Infrared (IR) spectra were recorded on a Bruker Alpha-P FTIR
instrument. Melting points (mp) were determined with a BÜCHI
melting point B-545 instrument and were uncorrected.
Thin layer chromatography (TLC) was performed using silica gel
plates (60F254), acquired from Merck.
R
O
A Shimadzu (Kyoto, Japan) DSC-60 instrument was used to gen-
erate DSC thermograms. Samples (3–5 mg) were accurately
weighed and sealed in aluminium crimp cells with pierced lids.
The samples were heated from 25–300 °C at a 10 C/min rate and
a nitrogen gas purge of 35 ml/min.
A Shimadzu (Kyoto, Japan) TGA-60 instrument was used to
determine the percentage weight loss (%) of samples during
heating. Samples (3–5 mg) were accurately weighed into open
aluminium crucibles. The samples were heated from 25–300 °C
at a heating rate of 10 °C/min and a nitrogen gas purge of 35 ml/
min.
O
R
H
N
HN
N
R
HN
N
n
O
n = 0; 1
Cl
Cl
A
B
22
Figure 2. General structures of quinolinyl-chalcones synthesized by Sharma et al.
A) and Sashidhara et al.2 (B).
1
(

1
130
F. J. Smit, D. D. N’Da / Bioorg. Med. Chem. 22 (2014) 1128–1138
Accelrys Discovery Studio 3.1 was used to calculate ADMET
properties of compounds 10–19 and CQ. ACD/ChemSketch
2000), Version 4.54 was used to calculate logP values.
of each well with cold 50% trichloroacetic acid, washed, dried
and dyed by SRB. Unbound dye was removed and protein bound
dye was extracted with 10 mM Tris base for optical density deter-
mination at a wavelength of 540 nm, using a multiwell spectro-
photometer. Data analysis was performed using GraphPad Prism
software. 50% of cell growth inhibition (IC50) was determined by
non-linear regression. The results are summarized in Table 2.
(
2
2
.3. Biological evaluation
.3.1. In vitro antimalarial assay
The in vitro antimalarial activity of test samples against the 3D7
and W2 strains of the malaria parasite, P. falciparum, was measured
2.4. Synthesis
by assessing parasite survival after drug exposure, using the para-
2
7
site lactate dehydrogenase (pLDH) colorimetric enzyme assay.
2.4.1. 4-Amino-7-chloroquinolines, 1–9
3
0
Lactate dehydrogenase is an enzyme found in all the cells and
catalyses the formation of pyruvate from lactate by reducing the
co-enzyme, nicotinamide adenine dinucleotide (NAD+) to nicotin-
amide adenine dinucleotide hydrogenase (NADH).
A combined method, as described by Biot et al. and N’Da
3
1
et al. were used. 4,7-dichloroquinoline (15.1 mmol, 3 g, 1 equiv)
and diamine (0.15 mol, 10 equiv) were reacted for 3–6 h at
80–100 °C [Scheme 1, step (i)]. The reaction mixture was allowed
to cool and neutralized with an aqueous solution of 1 M NaOH.
The product was extracted with hot ethyl acetate, washed with
4
and evaporated to dryness under reduced
pressure to produce the desired pure compound in high yields
(51–85%), unless stated otherwise. In the reaction involving
piperazine and leading to 4-amino-7-chloroquinoline 9, acetoni-
trile was used as solvent. The yields, melting points, IR, NMR,
and HRMS data are reported.
In the pLDH assay, the NAD + analogue, 3-acetylpyridine ade-
nine nucleotide (APAD), is reduced to 3-acetylpyridine adenine
nucleotide hydrogenase (APADH) and in turn a yellow, nitro-blue
tetrazolium/phenazine ethosulphate (NBT/PES) reagent is con-
verted into purple, formazan crystals. The absorbance was re-
corded at 620 nm, using a multiwell spectrophotometer (Tecan
Infinite F500). Formazan formation is directly proportional to pLDH
activity, which in turn is indicative of the number of parasites in
the cultures following drug exposure. Assay specificity is ensured
by the inability of human LDH, found in the host red blood cells,
to use APAD as a co-factor. Compound inhibitory activity was
determined by preparing test samples in parasite culture medium
in transparent 96-well, flat bottom plates (Greiner Bio-one), with a
water, dried over MgSO
3
2
2.4.1.1. N-(2-Aminoethyl)-7-chloroquinolin-4-amine, 1.
reaction of ethylenediamine and 4,7-dichloroquinoline afforded an
off-white powder; yield: 85%; mp: 148–150 °C (lit. 143.5–
The
3
2
ꢀ1
145.4 °C), IR (ATR)
m
max/cm : 3352, 3298, 2956, 2927, 1610,
1
1
00
lM starting concentration in three-fold serial dilutions, to ob-
1579, 1541, 1426, 1321, 1140, 1082, 807, 770; H NMR (600 MHz,
MeOD) d (ppm): 8.35 (d, J = 5.6 Hz, 1H, H-2a), 8.10 (d, J = 9.0 Hz,
1H, H-5a), 7.76 (d, J = 2.2 Hz, 1H, H-8a), 7.39 (dd, J = 9.0, 2.2 Hz,
1H, H-6a), 6.55 (d, J = 5.6 Hz, 1H, H-3a), 3.44 (t, J = 6.4 Hz, 2H, H-
1 ), 2.97 (t, J = 6.4 Hz, 2H, H-2 ); C NMR (151 MHz, MeOD) d
(ppm): 152.82 (C-4a), 152.45 (C-2a), 149.66 (C-9a), 136.33 (C-7a),
127.60 (C-8a), 126.04 (C-6a), 124.32 (C-5a), 118.81 (C-10a), 99.70
(C-3a), 46.27 (C-1b), 40.82 (C-2b); HRMS (APCI) m/z [M+H]+
tain eleven (11) decreasing concentrations (n = 2 for each data
point). Parasitized red blood cells were added to a final concentra-
tion of 1% haematocrit, 2% parasitaemia and the plates incubated
for 48 h, before proceeding with the pLDH assay. Percentage para-
site survival in each well was calculated relative to control wells
that were not exposed to the drug.
Results are presented in Table 2 as the 50% inhibitory concen-
trations (IC50) of individual compounds calculated from fitted sig-
moidal dose-response curves.
0
0
13
3
222.0789 (Calcd for C11H13ClN : 222.0798).
2
.4.1.2. N-(3-Aminopropyl)-7-chloroquinolin-4-amine, 2.
reaction of propylenediamine and 4,7-dichloroquinoline afforded
max
an off-white powder; yield: 83%; mp: 127–129 °C; IR (ATR) m /
The
2
.3.2. In vitro cytotoxicity assay
The cytotoxic effects of the prepared amide compounds were
ꢀ1
tested by sulforhodamine B (SRB) assay on the WI-38 cell line.
The SRB assay was developed by Skehan et al.28 to measure drug
induced cytotoxicity and cell proliferation. Its principle is based
on the ability of the protein dye, sulforhodamine B (Acid Red 52),
to bind electrostatically in a pH dependent manner to basic protein
amino acid residues of trichloroacetic acid-fixed cells. Under mild
acidic conditions it binds to the fixed cellular protein, while under
mild basic conditions it can be extracted from cells and solubilised
for measurement. The SRB assay was performed at CSIR in accor-
dance with the protocol of the Drug Evaluation Branch, NCI, and
the assay has been adopted for the screening tests compounds of
this study.
cm : 3258, 2936, 2865, 2573, 2233, 1610, 1579, 1537, 1476,
1315, 1220, 1079, 899, 819, 799; H NMR (600 MHz, MeOD) d
1
(ppm): 8.33 (d, J = 5.6 Hz, 1H, H-8a), 8.06 (d, J = 9.0 Hz, 1H, H-5a),
7.76 (d, J = 2.2 Hz, 1H, H-8a), 7.37 (dd, J = 9.0, 2.2 Hz, 1H, H-6a),
0
6.51 (d, J = 5.8 Hz, 1H, H-3a), 3.41 (t, J = 7.1 Hz, 2H, H-1 ),
0
0
13
2.80 (t, J = 7.1 Hz, 2H, H-3 ), 1.96–1.81 (m, 2H, H-2 ); C NMR
(151 MHz, MeOD) d (ppm): 152.66 (C-4a), 152.42 (C-2a), 149.65
(C-9a), 136.27 (C-7a), 127.58 (C-8a), 125.95 (C-6a), 124.25 (C-5a),
2
9
118.76 (C-10a), 99.63 (C-3a), 41.69 (C-1b), 40.23 (C-3b), 31.97
+
(C-2b); HRMS (APCI) m/z [M+H] 236.0950 (Calcd for C12
H
15ClN
3
:
236.0955).
The WI-38 cell line (normal human fetal lung fibroblast) from
ECACC was routinely maintained as a monolayer cell culture at
2.4.1.3. N-(4-Aminobutyl)-7-chloroquinolin-4-amine, 3.
reaction of butylenediamine and 4,7-dichloroquinoline afforded an
The
32
3
7 °C, 5% CO
2
, 95% air and 100% relative humidity in EMEM con-
-glutamine and 50 g/ml
off-white powder; yield: 70%; mp: 123–125 °C (lit. 122–124 °C);
ꢀ1
taining 10% fetal bovine serum, 2 mM
L
l
IR (ATR)
1450, 1427, 1366, 1328, 1281, 1135, 1078, 848, 806; H NMR
(600 MHz, DMSO-d ) d (ppm): 8.37 (d, J = 5.4 Hz, 1H, H-2a), 8.30
mmax/cm : 3210, 3062, 2942, 2867, 1610, 1574, 1541,
1
gentamicin. For this screening experiment, the cells (21–50 pas-
sages) were inoculated in a 96-well microtiter plates at plating
densities of 10 000 cells/well and were incubated for 24 h. After
6
(d, J = 9.0 Hz, 1H, H-5a), 7.76 (d, J = 2.2 Hz, 1H, H8a), 7.42 (dd,
J = 9.0, 2.2 Hz, 1H, H-6a), 6.45 (d, J = 5.5 Hz, 1H, H-3a), 3.25 (t,
2
4 h the cells were treated with the experimental drugs, which
0
0
had previously been dissolved in DMSO and diluted in medium
to produce five concentrations. Neat cells served as control. The
blank contained complete medium without cells. Parthenolide
was used as a standard. The plates were incubated for 48 h after
addition of the compounds. Viable cells were fixed to the bottom
J = 6.9 Hz, 2H, H-1 ), 2.68 (t, J = 7.2 Hz, 2H, H-4 ), 1.68 (p, J = 7.0 Hz,
0
0
13
2H, H-2 ), 1.56 (p, J = 7.4 Hz, 2H, H-3 ); C NMR (151 MHz, DMSO-
) d (ppm): 151.92 (C-2a), 150.15 (C-4a), 149.09 (C-9a), 133.38
d
6
(C-7a), 127.44 (C-8a), 124.22 (C-6a), 123.99 (C-5a), 117.50 (C-10a),
98.67 (C-3a), 42.04 (C-1b), 39.08 (C-4b), 27.60 (C-2b), 25.01 (C-

F. J. Smit, D. D. N’Da / Bioorg. Med. Chem. 22 (2014) 1128–1138
1131
RH
5
a
4
a
O
6
'
6
a
(
i)
3a
5''
3
''
1'
4''
2''
1''
7
a
R
N
O
5'
4'
2
a
5a
2
Cl
N
4a
Cl
N
(iii)
3
8
a
6a
1
a
2'
3
a
3'
1
7
a
1-9
O
2a
Cl
8
a
1
a
1
1-19
6
'
1
'
5'
O
4'
O
3
'' 2''
2
3
2' 3'
O
(
ii)
4
''
1''
H
a
O
O
5''
1
HO
OH
1
0
Amides
R
Amides
16
R
1b
3b
1
b
b
NH
HN
N
1
1
1
1
2
3
HN
2b
4b
2
b
4b
1
3b
1b
1
5b
O
NH
17
18
HN
NH
HN
O
2b
2b
3b
3b
6b
6b
b
4b
1
b
3b
NH
HN
N
NH
HN
2b
5b
2
b
4b
7
b
1b
2b
NH
1
4
5
HN
N
2
b
3
b
6
19
1b
3b
b
1b
N
NH
1
HN
2b
4b
5b
Scheme 1. Multi-step synthesis of 4-aminoquinolinyl-chalcone amides 11–19. Reagents and conditions: (i) Liquid diamine/piperazine in acetonitrile, 3–6 h, 80–100 °C;
ii) 2-acetyl-5-methylfuran, MeOH, NaOH, 12 h, rt; (iii) 10, CDI, DCM, 3 h, rt then 1–9, DMF, 24 h.
(
3
2
b); HRMS (APCI) m/z [M+H]+ 250.1104 (Calcd for C13
50.1111).
H
17ClN
3
:
with DCM:MeOH (9:1, v/v) then DCM:MeOH:NH
4
OH as eluent
32
(9:1:0.1, v/v/v); yield: 51%, mp: 135–138 °C (lit. 133–134 °C) ; IR
ꢀ
1
(
ATR) mmax/cm : 3270, 2918, 2849, 1611, 1574, 1537, 1487, 1367,
1
2
.4.1.4. N-(2-Aminopropyl)-7-chloroquinolin-4-amine, 4.
The
1133, 850, 817, 798; H NMR (600 MHz, MeOD) d (ppm): 8.31 (d,
reaction of 1,2-diamine propane and 4,7-dichloroquinoline afforded
J = 5.6 Hz, 1H, H-2a), 8.13 (d, J = 9.0 Hz, 1H, H-5a), 7.74 (d,
an off-white powder; yield: 74%; mp: charcoal at 240 °C; IR (ATR)
J = 2.3 Hz, 1H, H-8a), 7.37 (dd, J = 9.0, 2.2 Hz, 1H, H-6a), 6.48 (d,
ꢀ1
0
m
8
1
max/cm : 3257, 2961, 1610, 1575, 1539, 1450, 1368, 1136, 912,
46, 795; H NMR (600 MHz, MeOD) d (ppm): 8.34 (d, J = 5.6 Hz,
H, H-2a), 8.11 (d, J = 9.1 Hz, 1H, H-5a), 7.76 (d, J = 2.4 Hz, 1H,
J = 5.6 Hz, 1H, H-3a), 3.35 (2H, H-1 peak overlapping H
2.93–2.88 (m, 2H, H-6 ), 1.76 (p, J = 7.2 Hz, 2H, H-2 ), 1.68 (p,
2
O peak),
1
0
0
0
0
0
13
J = 7.5 Hz, 2H, H-5 ), 1.53–1.42 (m, 4H, H-3 and H-4 ); C NMR
(151 MHz, MeOD) d (ppm): 152.80 (C-4a), 152.07 (C-2a), 149.30
(C-9a), 136.33 (C-7a), 127.23 (C-8a), 125.93 (C-6a), 124.52 (C-5a),
118.65 (C-10a), 99.54 (C-3a), 43.79 (C-1b), 40.82 (C-6b), 29.11 (C-
H-8a), 7.38 (dd, J = 9.0, 2.2 Hz, 1H, H-6a), 6.55 (d, J = 5.6 Hz, 1H,
0
0
H-3a), 3.31 (dd, J = 3.7, 2.0 Hz, 1H, H-2 ), 3.29–3.26 (m, 1H, H-1 ),
1
1
0
13
.20 (d, J = 5.4 Hz, 2H, H-3 ); C NMR (151 MHz, MeOD) d (ppm):
52.81 (C-4a), 152.40 (C-2a), 149.66 (C-9a), 136.34 (C-7a), 127.59
2b), 28.95 (C-5b), 27.69 (C-3b), 27.26 (C-4b); HRMS (APCI) m/z
+
(
5
2
C-8a), 126.05 (C-6a), 124.31 (C-5a), 118.77 (C-10a), 99.86 (C-3a),
[M+H] 278.1406 (Calcd for C15
3
H21ClN : 278.1424).
+
1.56 (C-1b), 46.54 (C-2b), 20.90 (C-3b); HRMS (APCI) m/z [M+H]
36.0952 (Calcd for C12 15ClN : 236.0955).
H
3
2.4.1.6.
{3-[(7-Chloroquinolin-4-yl)amino]propyl}(methyl)
amine, 6.
The reaction of N-methyl-1,3-diamine and
2
.4.1.5. N-(6-Aminohexyl)-7-chloroquinolin-4-amine, 5.
The
4,7-dichloroquinoline afforded a yellow powder; yield: 62%; mp:
ꢀ1
reaction of hexylenediamine and 4,7-dichloroquinoline afforded a
yellowpowderafter purificationbycolumnchromatographyeluting
74–80 °C; IR (ATR)
mmax/cm : 3220, 3103, 3060, 2947, 1610,
1
1574, 1429, 1133, 853, 822, 772; H NMR (600 MHz, MeOD) d

1
132
F. J. Smit, D. D. N’Da / Bioorg. Med. Chem. 22 (2014) 1128–1138
(
7
6
ppm): 8.33 (d, J = 5.6 Hz, 1H, H-2a), 8.05 (d, J = 9.0 Hz, 1H, H-5a),
(60 ml) upon stirring at room temperature. Sodium hydroxide
solution, NaOH (1 M, 20 ml) was added and stirring was continued
for 12 h [Scheme 1, step (ii)]. The progress of the reaction was fol-
lowed by TLC. After completion, the pH of the solution was ad-
justed to 2 with HCl solution (1 M) upon which an off-white to
yellow precipitate formed. The precipitate was subsequently col-
lected by suction filtration and washed with water, then with a
10% MeOH solution, dried and recrystallized from MeOH to yield
2.30 g (90% yield) of the desired compound as an off-white to yel-
.75 (d, J = 2.2 Hz, 1H, H-8a), 7.37 (dd, J = 9.0, 2.2 Hz, 1H, H-6a),
0
.50 (d, J = 5.6 Hz, 1H, H-3a), 3.40 (t, J = 7.0 Hz, 2H, H-1 ), 2.72 (t,
0
0
J = 7.2 Hz, 2H, H-3 ), 2.42 (s, 3H, H-4 ), 1.94 (p, J = 7.2 Hz, 2H,
0
13
H-2 ); C NMR (151 MHz, MeOD) d (ppm): 152.63 (C-4a), 152.41
C-2a), 149.63 (C-9a), 136.28 (C-7a), 127.58 (C-8a), 125.97 (C-6a),
24.26 (C-5a), 118.75 (C-10a), 99.61 (C-3a), 50.19 (C-1b), 42.02
(
1
+
(
C-3b), 35.97 (C-4b), 28.65 (C-2b); HRMS (APCI) m/z [M+H]
2
3
50.1094 (Calcd for C13H17ClN : 250.1111).
ꢀ1
low powder; mp: 221–228 °C; IR (ATR)
mmax/cm : 3104, 3076,
2
.4.1.7. N-{2-[2-(2-Aminoethoxy)ethoxy]ethyl}-7-chloroquino-
2982, 2924, 2931, 1684, 1654, 1601, 1509, 1288, 1211, 1065,
0
1
lin-4-amine, 7.
The reaction of 2,2 -(ethylenedioxy)bis(ethyl-
1027, 845, 772, 754; H NMR (600 MHz, DMSO-d
6
) d (ppm):
0
0
amine) and 4,7-dichloroquinoline afforded a yellow oil; yield: 83%,
13.14 (s, 1H, H-a), 7.97 (d, J = 8.4 Hz, 2H, H-2 ), 7.94 (d, J = 8.4 Hz,
ꢀ1
00
0
IR (ATR)
331, 1101, 876, 804; H NMR (600 MHz, MeOD) d (ppm): 8.35
d, J = 5.6 Hz, 1H, H-2a), 8.09 (d, J = 9.0 Hz, 1H, H-5a), 7.77 (d,
m
max/cm : 3265, 2865, 1610, 1576, 1539, 1450, 1427,
2H, H-3 ), 7.80 (d, J = 3.5 Hz, 1H, H-3 ), 7.75 (d, J = 15.7 Hz, 1H,
1
0
1
(
H-1), 7.72 (d, J = 15.7 Hz, 1H, H-2), 6.44 (d, J = 3.3 Hz, 1H, H-4 ),
0
13
2.40 (s, 3H, H-6 ); C NMR (151 MHz, DMSO-d
6
) d (ppm): 175.46
0
0
0
0
J = 2.2 Hz, 1H, H-8a), 7.40 (dd, J = 9.0, 2.2 Hz, 1H, H-6a), 6.56 (d,
J = 5.6 Hz, 1H, H-3a), 3.78 (t, J = 5.5 Hz, 2H, H-2 ), 3.69–3.65 (m,
(C-3), 166.86 (C-5 ), 158.97 (C-2 ), 151.83 (C-5 ), 140.75 (C-1),
0
00
00
00
00
138.65 (C-4 ), 131.98 (C-1 ), 129.73 (C-3 ), 128.74 (C-2 ), 124.16
(C-2), 122.02 (C-3 ), 109.64 (C-4 ), 13.78 (C-6 ); HRMS (APCI) m/z
0
0
0
0
0
0
2
H, H-3 ), 3.65–3.61 (m, 2H, H-4 ), 3.56 (t, J = 5.5 Hz, 2H, H-1 ),
0
0
13
+
3
.49 (t, J = 5.3 Hz, 2H, H-5 ), 2.74 (t, J = 5.3 Hz, 2H, H-6 ); C NMR
13 4
[M+H] 257.0890 (Calcd for C15H O : 257.0814).
(
(
151 MHz, MeOD) d (ppm): 152.70 (C-4a), 152.43 (C-2a), 149.66
C-9a), 136.34 (C-7a), 127.62 (C-8a), 126.04 (C-6a), 124.28 (C-5a),
2.4.3. 4-Aminoquinolinyl-chalcone amides, 11–19
1
18.75 (C-10a), 99.81 (C-3a), 73.43 (C-5b), 71.49 (C-3b), 71.31
Chalcone 10 (3.9 mmol, 1 g, 1 equiv) and CDI (4.9 mmol, 0.8 g,
1.3 equiv) were added to anhydrous DCM (50 ml) and stirred for
3 h at room temperature. Afterwards, aminoquinoline 1–9
(
[
C-4b), 69.89 (C-2b), 43.81 (C-1b), 42.01 (C-6b); HRMS (APCI) m/z
M+H] 310.1323 (Calcd for C15H21ClN O : 310.1322).
3 3
+
(
5.9 mmol, 1.5 equiv) was added followed by DMF (10 ml) to en-
2
.4.1.8.
(3-Aminopropyl)({3-[(7-chloroquinolin-4-yl)amino]
The reaction of N-(3-aminopro-
hance dissolution of the quinoline intermediate. The resulting
solution was stirred for an additional 24 h. The solution was
quenched with the addition of distilled water (50 ml). The organic
phase was separated and the aqueous phase was extracted 3 times
with DCM. The combined organic layers were washed with water
propyl})methylamine, 8.
pyl)-N-methylpropane-1,3-diamine and 4,7-dichloroquinoline
afforded a dark yellow oil after purification by column chromatog-
raphy, eluting successively with DCM:MeOH (9:1, v/v) and
DCM:MeOH:NH
4
OH (9:1:0.1, v/v/v); yield: 67%; IR (ATR)
cm : 3240, 2941, 2848, 2799, 1610, 1576, 1538, 1449, 1366,
136, 1077, 849, 804; 1H NMR (600 MHz, MeOD) d (ppm): 8.34
d, J = 5.6 Hz, 1H, H-2a), 8.03 (d, J = 9.0 Hz, 1H, H-5a), 7.77 (d,
m
max
/
(3 ꢁ 50 ml) and then with saturated NaHCO
3
solution (50 ml),
dried over MgSO , filtered and concentrated in vacuo. Purification
ꢀ
1
4
1
(
by column chromatography, eluting with DCM:MeOH (9:1, v/v)
afforded the pure amide. This procedure was used for the synthesis
of all amides 11–19. NMR, IR and HRMS data are reported below.
J = 2.1 Hz, 1H, H-8a), 7.40 (dd, J = 9.0, 2.2 Hz, 1H, H-6a), 6.51 (d,
J = 5.7 Hz, 1H, H-3a), 3.39 (t, J = 6.9 Hz, 2H, H-1 ), 2.64 (t,
J = 7.1 Hz, 2H, H-7 ), 2.54 (t, J = 7.2 Hz, 2H, H-3 ), 2.46–2.43 (m,
0
0
0
2.4.3.1.
(5-methylfuran-2-yl)-3-oxoprop-1-en-1-yl]benzamide,
11. During the extraction, a precipitate formed, which was fil-
N-{2-[(7-Chloroquinolin-4-yl)amino]ethyl}-4-[(1E)-3-
0
0
0
2
H, H-5 ), 2.28 (s, 2H, H-4 ), 1.93 (m, 2H, H-2 ), 1.70–1.62 (m, 2H,
0
13
H-6 ); C NMR (151 MHz, MeOD) d (ppm): 152.69 (C-4a), 152.47
C-2a), 149.66 (C-9a), 136.28 (C-7a), 127.62 (C-8a), 125.99 (C-6a),
24.23 (C-5a), 118.76 (C-10a), 99.58 (C-3a), 56.68 (C-3b), 56.57
C-5b), 42.64 (C-1b), 42.38 (C-4b), 40.95 (C-7b), 30.95 (C-6b),
(
1
(
tered, washed with water and then with cold methanol to yield
0.29 g (16%) of the desired pure compound as a light yellow pow-
ꢀ1
der; mp: 255.7–256.8 °C; IR (ATR)
1579, 1535, 1507, 1297, 1224, 1069, 848, 762;
(600 MHz, DMSO-d ) d (ppm): 8.82 (t, J = 5.7 Hz, 1H, amide), 8.41
d, J = 5.4 Hz, 1H, H-2a), 8.20 (d, J = 9.0 Hz, 1H, H-5a), 7.93 (d,
mmax/cm : 3338, 1643, 1608,
+
1
2
6.46 (C-2b); HRMS (APCI) m/z [M+H] 307.1667 (Calcd for C16
H
24-
H NMR
ClN : 307.1699).
4
6
(
0
0
00
2
.4.1.9. 7-Chloro-4-(piperazin-1-yl)quinoline, 9.
The reac-
J = 8.6 Hz, 2H, H-2 ), 7.90 (d, J = 8.5 Hz, 2H, H-3 ), 7.80 (d,
J = 3.5 Hz, 1H, H-3 ), 7.78 (d, J = 2.2 Hz, 1H, H-8a), 7.74 (d,
0
tion of piperazine and 4,7-dichloroquinoline afforded an off-white
powder; yield: 76%; mp: 117–121 °C (lit. 118-120 °C); IR (ATR)
J = 15.7 Hz, 1H, H-1), 7.71 (d, J = 15.7 Hz, 1H, H-2), 7.51 (t,
J = 5.6 Hz, 1H, N-H), 7.46 (dd, J = 9.0, 2.3 Hz, 1H, H-6a), 6.64 (d,
J = 5.4 Hz, 1H, H-3a), 6.45 (d, J = 3.4 Hz, 1H, H-4 ), 3.55 (q,
ꢀ1
m
max/cm : 3253, 2939, 2823, 2799, 2746, 1610, 1567,1422,
1
0
1
377, 1244, 1020, 865, 841, 820, 771; H NMR (600 MHz, MeOD)
d (ppm): 8.61 (d, J = 5.2 Hz, 1H, H-2a), 8.02 (d, J = 9.0 Hz, 1H,
H-5a), 7.89 (d, J = 2.2 Hz, 1H, H-8a), 7.48 (dd, J = 9.0, 2.2 Hz, 1H,
H-6a), 6.97 (d, J = 5.1 Hz, 1H, H-3a), 3.21 (dd, J = 6.3, 3.5 Hz, 4H,
J = 6.3 Hz, 2H, H-2b), 3.48 (q, J = 6.3 Hz, 2H, H-1b), 2.40 (s, 3H,
0
13
H-6 );
C NMR (151 MHz, DMSO-d
6
) d (ppm): 175.55 (C-3),
0
0
0
0
166.21 (C-5 ), 158.93 (C-2 ), 151.95 (C-2a), 151.85 (C-5 ), 150.12
(C-9a), 140.99 (C-1), 137.20 (C-1 ), 135.56 (C-4 ), 133.46 (C-7a),
128.61 (C-3 ), 127.73 (C-2 ), 127.54 (C-8a), 124.21 (C-6a), 123.95
(C-5a), 123.53 (C-2), 121.94 (C-3a), 117.49 (C-10a), 109.62 (C-4 ),
40.04 (C-1b), 37.97 (C-2b), 13.79 (C-6 ); HRMS (APCI) m/z [M+H]
460.1390 (Calcd for C26 23ClN : 460.1428).
0
0
13
00
00
H-1 ), 3.17–3.04 (m, 4H, H-2 ); C NMR (151 MHz, MeOD) d
0
0
00
(
(
(
ppm): 159.47 (C-4a), 152.85 (C-2a), 150.54 (C-9a), 136.42
C-7a), 128.28 (C-8a), 127.29 (C-6a), 127.09 (C-5a), 123.08
0
0
+
C-10a), 110.24 (C-3a), 54.03 (C-1b), 46.40 (C-2b); HRMS (APCI)
+
m/z [M+H] 248.0942 (Calcd for C13
3
H15ClN : 248.0955).
H
3 3
O
2
.4.2. 4-[(1E)-3-(5-Methylfuran-2-yl)-3-oxoprop-1-en-1-
yl]benzoic acid, 10
The chalcone 10 was synthesized by adopting a literature re-
2.4.3.2. N-{3-[(7-Chloroquinolin-4-yl)amino]propyl}-4-[(1E)-3-
(5-methylfuran-2-yl)-3-oxoprop-1-en-1-yl]benzamide,
12.
During the extraction, a precipitate formed which was fil-
1
4
ported method and described as follows: Formylbenzoic acid
10 mmol, 1.5 g, 1 equiv) and 2-acetyl-5-methylfuran (10.3 mmol,
.3 g, 1.2 ml, 1.03 equiv) were successively added to MeOH
tered, washed with water and then with cold methanol to yield
0.29 g (16%) of the desired pure compound as a light yellow pow-
(
1
ꢀ
1
der; mp: 122.1-122.2 °C; IR (ATR) mmax/cm : 3317, 1642, 1609,

F. J. Smit, D. D. N’Da / Bioorg. Med. Chem. 22 (2014) 1128–1138
1133
1
580, 1508, 1370, 1314, 1206, 1068, 792; 1H NMR (600 MHz,
DMSO-d ) d (ppm): 8.66 (s, 1H, amide), 8.38 (d, J = 5.3 Hz, 1H, H-
a), 8.26 (d, J = 9.1 Hz, 1H, H-5a), 7.91 (m, 4H, 3 and 4 ), 7.78
H-1 and H-2), 7.50 (t, J = 5.5 Hz, 1H, NH), 7.44 (dd, J = 9.0, 2.3 Hz,
1H, H-6a), 6.47 (d, J = 5.6 Hz, 1H, H-3a), 6.44 (d, J = 3.4 Hz, 1H,
H-4 ), 3.30–3.22 (m, 4H, H-6b and H-1b), 2.40 (s, 3H, H-6 ), 1.65
6
00
00
0
0
2
0
(
m, 2H, H-3 and H-5a), 7.72 (m, 2H, H-1 and H-2), 7.44 (d,
(p, J = 7.2 Hz, 2H, H-2b), 1.54 (p, J = 7.2 Hz, 2H, H-5b), 1.38 (m,
1
3
J = 8.9 Hz, 1H, H-6), 7.37 (s, 1H, N-H), 6.48 (d, J = 5.5 Hz, 1H, H-
3
2
4H, H-3b and H-4b); C NMR (151 MHz, DMSO-d
6
) d (ppm):
0
00
0
a), 6.44 (s, 1H, H-4 ), 3.72–3.17 (m, 16H, H-1b, H-3b and H
2
O),
175.63 (C-3), 165.55 (C-5 ), 158.99 (C-2 ), 151.89 (C-9a), 151.06
(C-2a), 150.71 (C-5 ), 148.03 (C-4a), 141.13 (C-1), 137.00 (C-1 ),
135.96 (C-4 ), 133.91 (C-7a), 128.61 (C-3 ), 127.72 (C-2 ), 126.63
(C-8), 124.34 (C-6a and C-5a), 123.41 (C-2), 121.99 (C-3 ), 117.29
(C-10a), 109.68 (C-4 ), 98.66 (C-3a), 42.50 (C-1b), 29.15 (C-6b),
27.78 (C-5b), 26.43 (C-2b), 26.37 (C-3b and C-4b), 13.84 (C-6 );
HRMS (APCI) m/z [M+H] 516.1997 (Calcd for C30
0
13
0
00
.40 (s, 3H, H-6 ), 1.93 (m, 2H, H-2b); C NMR (151 MHz, DMSO-
) d (ppm): 175.55 (C-3), 165.77 (C-5 ), 158.87 (C-2 ), 151.84 (C-
a), 150.07 (C-5 ), 148.99 (C-9a), 141.03 (C-1), 137.04 (C-1 ),
35.78 (C-4 ), 133.44 (C-7a), 128.56 (C-3 ), 127.68 (C-2 ), 127.44
00
0
00
00
00
d
2
1
6
0
00
0
00
00
00
0
0
0
(
C-8a), 124.10 (C-6a), 124.02 (C-5a), 123.43 (C-2), 121.88 (C-3 ),
0
+
1
17.48 (C-10a), 109.59 (C-4 ), 98.69 (C-3a), 40.16 (C-1b), 37.32
3
H31ClN O
3
:
0
+
(
C-3b), 27.81 (C-2b), 13.77 (C-6 ); HRMS (APCI) m/z [M+H]
516.2054).
4
74.1543 (Calcd for C27
3 3
H25ClN O : 474.1543).
2
.4.3.6. N-{3-[(7-Chloroquinolin-4-yl)amino]propyl}-N-methyl-
2
.4.3.3. N-{4-[(7-Chloroquinolin-4-yl)amino]butyl}-4-[(1E)-3-
4-[(1E)-3-(5-methylfuran-2-yl)-3-oxoprop-1-en-1-yl]benzam-
(
5-methylfuran-2-yl)-3-oxoprop-1-en-1-yl]benzamide,
ide, 16.
Yellow crystals; yield 0.70 g (37%); mp: 86.2-88.1 °C;
ꢀ1
1
1
1
(
(
3.
Light yellow powder; yield 0.43 g (23%); mp: 161.5-
IR (ATR) mmax/cm : 3328, 2924, 1653, 1604, 1574, 1507, 1367,
1329, 1206, 1062, 800, 765; H NMR (600 MHz, CDCl ) d (ppm):
3
8.46 (d, J = 5.6 Hz, 1H, H-2a), 7.99 (d, J = 9.0 Hz, 1H, H-5a), 7.91
(d, J = 2.2 Hz, 1H, H-8a), 7.81 (d, J = 15.7 Hz, 1H, H-1), 7.68 (d,
J = 8.0 Hz, 2H, H-2 ), 7.45 (d, J = 7.9 Hz, 2H, H-3 ), 7.41 (d,
J = 15.7 Hz, 1H, H-2), 7.32 (dd, J = 9.0, 2.2 Hz, 1H, H-6a), 7.26
(d, J = 3.5 Hz, 1H, H-3 ), 6.92 (d, J = 6.2 Hz, 1H, N-H), 6.39
(d, J = 5.6 Hz, 1H, H-3a), 6.21 (d, J = 3.4 Hz, 1H, H-4 ), 3.67 (t,
J = 6.2 Hz, 2H, H-3b), 3.42 (t, J = 6.0 Hz, 2H, H-1b), 3.00 (s, 3H,
H-4b), 2.43 (s, 3H, H-6 ), 1.96 (p, J = 6.1 Hz, 2H, H-2b); C NMR
ꢀ1
1
69.1 °C; IR (ATR)
m
max/cm : 3386, 2930, 1641, 1608, 1586,
1
551, 1510, 1450, 1325, 1207, 1070, 808, 764;
) d (ppm): 8.65 (t, J = 5.7 Hz, 1H, amide), 8.43
s, 1H, H-8a), 8.42 (d, J = 4.1 Hz, 1H, H-2a), 8.22 (s, 1H, NH), 7.93–
H
NMR
600 MHz, DMSO-d
6
0
0
00
0
0
00
7
(
.89 (m, 4H, H-2 and H-3 ), 7.85 (d, J = 2.3 Hz, 1H, H-5a), 7.82
0
0
d, J = 3.4 Hz, 1H, H-3 ), 7.77–7.69 (m, 2H, H-1 and H-2), 7.55 (dd,
0
J = 9.0, 2.2 Hz, 1H, H-6a), 6.64 (d, J = 6.1 Hz, 1H, H-3a), 6.46 (d,
J = 3.4 Hz, 1H, H-4 ), 3.41 (q, J = 6.6 Hz, 2H, H-1b), 3.35 (q,
J = 6.4 Hz, 2H, H-4b), 2.41 (s, 3H, H-6 ), 1.77–1.63 (m, 4H, H-3b
and H-2b); C NMR (151 MHz, DMSO-d
1
(
1
(
0
0
0
13
1
3
00
6
) d (ppm): 175.55 (C-3),
(151 MHz, CDCl
3
) d (ppm): 176.80 (C-3), 171.94 (C-5 ), 158.49
00
0
0
0
0
65.53 (C-5 ), 158.88 (C-2 ), 152.17 (C-9a), 151.84 (C-5 ), 148.27
(C-2 ), 152.31 (C-5 ), 151.26 (C-2a), 150.18 (C-9a), 141.76 (C-1),
0
0
00
00
00
00
C-2a), 141.04 (C-1), 136.98 (C-1 ), 135.81 (C-4 ), 135.17 (C-7a),
137.22 (C-1 ), 136.39 (C-4 ), 135.13 (C-7a), 128.50 (C-3 ), 127.82
(C-8a), 127.43 (C-2 ), 125.45 (C-6a), 122.63 (C-5a), 122.16 (C-2),
119.97 (C-3 ), 117.51 (C-10a), 109.50 (C-4 ), 98.16 (C-3a), 44.42
(C-3b), 38.73 (C-1b), 37.47 (C-4b), 24.75 (C-2b), 14.20 (C-6 ); HRMS
00
00
00
28.54 (C-3 ), 127.66 (C-2 ), 125.08 (C-6a), 124.79 (C-8a), 124.12
0
0
0
0
C-5a), 123.40 (C-2), 121.91 (C-3 ), 116.65 (C-10a), 109.60 (C-4 ),
0
9
3
8.63 (C-3a), 42.44 (C-1b), 38.87 (C-4b), 26.69 (C-2b), 25.17 (C-
0
+
+
b), 13.78 (C-6 ); HRMS (APCI) m/z [M+H] 488.1691 (Calcd for C28-
(APCI) m/z [M+H] 488.1741 (Calcd for C28
H27ClN
3
O
3
: 488.1741).
3
H27ClN O
3
: 488.1741).
2
.4.3.7. N-[2-(2-{2-[(7-Chloroquinolin-4-yl)amino]ethoxy}eth-
2
.4.3.4.
N-{1-[(7-Chloroquinolin-4-yl)amino]propan-2-yl}-4-
oxy)ethyl]-4-[(1E)-3-(5-methylfuran-2-yl)-3-oxoprop-1-en-1-
[
(1E)-3-(5-methylfuran-2-yl)-3-oxoprop-1-en-1-yl]benzamide,
yl]benzamide, 17.
mp 80.1–80.9 °C; IR (ATR) mmax/cm : 3337, 2865, 1647, 1603,
1577, 1508, 1368, 1330, 1206, 1066, 876, 799, 764; H NMR
Dark yellow platelets; yield 1.36 g (64%);
ꢀ1
1
1
1
4.
Light yellow crystals; yield 0.39 g (21%); mp: 146.5-
ꢀ
1
1
48.0 °C; IR (ATR)
507, 1449, 1332, 1206, 1066, 847, 800, 767; H NMR (600 MHz,
m
max/cm : 3292, 2923, 1644, 1606, 1578,
1
(600 MHz, CDCl ) d (ppm): 8.40 (d, J = 5.3 Hz, 1H, H-2a), 7.85 (d,
3
0
0
MeOD) d (ppm): 8.33 (d, J = 5.7 Hz, 1H, H-2a), 8.04 (d, J = 9.1 Hz,
1
H-2), 7.75 (d, J = 6.3 Hz, 1H, H-2 ), 7.74 (d, J = 1.9 Hz, 1H, H-8a),
7
J = 9.0, 2.3 Hz, 1H, H-6a), 6.74 (d, J = 5.9 Hz, 1H, H-3a), 6.35 (d,
J = 3.3 Hz, 1H, H-4 ), 4.53 (hept, J = 6.8 Hz, 1H, H-2b), 3.60–3.42
J = 2.3 Hz, 1H, H-8a), 7.74–7.66 (m, 4H, H-1, H-2 and H-5a), 7.50
(d, J = 8.0 Hz, 2H, H-3 ), 7.32 (d, J = 15.7 Hz, 1H, H-2), 7.26 (d,
J = 3.5 Hz, 1H, H-3 ), 7.24–7.21 (m, 1H, H-6a), 6.97 (t, J = 5.6 Hz,
00
00
H, H-5a), 7.82 (d, J = 8.3 Hz, 2H, H-3 ), 7.76 (d, J = 8.6 Hz, 2H,
00
0
0
.59 (d, J = 8.3 Hz, 1H, H-1), 7.53 (d, J = 3.5 Hz, 1H, H-3 ), 7.39 (dd,
1H, amide), 6.27 (d, J = 5.4 Hz, 1H, H-3a), 6.20 (d, J = 3.4 Hz, 1H,
0
H-4 ), 5.74 (t, J = 5.1 Hz, 1H, N-H), 3.78 (t, J = 5.1 Hz, 2H, H-2b),
0
3.68 (m, 6H, H-3b, H-4b and H-5b), 3.65 (q, J = 5.2 Hz, 2H, H-6b),
3.39 (q, J = 4.9 Hz, 2H, H-1b), 2.41 (s, 3H, H-6 );
0
0
13
(
m, 2H, H-1b), 2.43 (s, 3H, H-6 ), 1.40 (d, J = 6.8 Hz, 3H, H-3b);
C NMR
1
3
00
00
C NMR (151 MHz, MeOD) d (ppm): 178.42 (C-3), 169.89 (C-5 ),
(151 MHz, CDCl
3
) d (ppm): 176.76 (C-3), 166.80 (C-5 ), 158.54
0
0
0
0
1
60.90 (C-2 ), 153.50 (C-5 ), 153.08 (C-9a), 151.81 (C-2a), 148.97
(C-2 ), 152.26 (C-4a), 151.50 (C-2a), 149.86 (c-9a), 148.61 (C-5 ),
00
00
00
00
(
C-4a)143.09 (C-1), 139.17 (C-1 ), 137.01 (C-4 ), 136.66 (C-7a),
141.60 (C-1), 137.59 (C-1 ), 135.54 (C-4 ), 134.95 (C-7a), 128.27
00
00
00
00
1
29.62 (C-3 ), 129.05 (C-2 ), 128.16 (C-8a), 127.11 (C-6a), 126.29
(C-3 ), 128.19 (C-8a), 127.44 (C-2 ), 125.28 (C-6a), 122.82 (C-2),
0
0
0
0
(
C-5a), 124.27 (C-5a), 122.77 (C-3 ), 118.53 (C-10a), 110.80 (C-4 ),
121.34 (C-5a), 120.12 (C-3 ), 117.16 (C-10a), 109.51 (C-4 ), 99.01
(C-3a), 70.20 (C-3b), 70.07 (C-4b), 69.78 (C-5b), 68.60 (C-2b),
42.62 (C-1b), 39.73 (C-6b), 14.19 (C-6 ); HRMS (APCI) m/z [M+H]
548.1942 (Calcd for C30 31ClN : 548.1952).
9
6
4
9.92 (C-3a), 49.68 (C-2b), 46.44 (C-1b), 18.09 (C-3b), 13.91 (C-
0
+
0
+
); HRMS (APCI) m/z [M+H] 474.1556 (Calcd for C27
74.1584).
3
H25ClN O
3
:
H
3 5
O
2
.4.3.5. N-{6-[(7-Chloroquinolin-4-yl)amino]hexyl}-4-[(1E)-3-
2.4.3.8.
N-[3-({3-[(7-Chloroquinolin-4-yl)amino]propyl}
(
5-methylfuran-2-yl)-3-oxoprop-1-en-1-yl]benzamide,
(methyl)amino)propyl]-4-[(1E)-3-(5-methylfuran-2-yl)-3-oxo-
1
1
1
1
5.
Light yellow powder; yield 0.5 g (25%); mp:177.1-
prop-1-en-1-yl]benzamide, 18.
1.1 g (52%); mp: 83.4-85.7 °C; IR (ATR)
Dark yellow platelets; yield
ꢀ1
ꢀ1
81.5 °C; IR (ATR)
605, 1598, 1579, 1532, 1507, 1369, 1329, 1299, 1198, 1063,
014, 807, 769; H NMR (600 MHz, DMSO-d
mmax/cm : 3560, 3323, 2926, 2858, 1649,
m
max/cm : 3250, 2943,
2847, 2798, 1647, 1601, 1577, 1508, 1367, 1328, 1205, 1066,
1
1
6
) d (ppm): 8.57 (t,
843, 801, 766; H NMR (600 MHz, CDCl
3
) d (ppm): 8.39 (d,
J = 5.6 Hz, 1H, amide), 8.37 (d, J = 5.6 Hz, 1H, H-2a), 8.28 (d,
J = 5.4 Hz, 1H, H-2a), 7.83 (d, J = 2.0 Hz, 1H, H-8a), 7.77–7.70 (m,
3H, H-1 and H-2 ), 7.57 (dd, J = 11.2, 8.6 Hz, 3H, H-3 and H-5a),
7.40 (t, J = 5.7 Hz, 1H, amide), 7.33 (d, J = 15.8 Hz, 1H, H-2), 7.24
00
00
00
00
J = 9.0 Hz, 1H, H-5a), 7.92–7.85 (m, 4H, H-2 and H-3 ), 7.79 (d,
0
J = 3.5 Hz, 1H, H-3 ), 7.77 (d, J = 2.3 Hz, 1H, H-8a), 7.71 (m, 2H,

1
134
F. J. Smit, D. D. N’Da / Bioorg. Med. Chem. 22 (2014) 1128–1138
0
(
d, J = 4.0 Hz, 1H, H-3 ), 7.19 (dd, J = 8.9, 2.2 Hz, 1H, H-6a), 6.97 (t,
vent was removed and the residue was washed with water
(3 ꢁ 100 ml), then with cold 20% MeOH (2 ꢁ 10 ml) and dried to
yield 0.92 g (92%) of the desired pure compound as a brown pow-
J = 4.3 Hz, 1H, N-H), 6.21 (d, J = 5.6 Hz, 1H, H-3a), 6.20 (d,
J = 3.6 Hz, 1H, H-4 ), 3.50 (q, J = 6.3 Hz, 2H, H-6b), 3.31 (q,
J = 5.7 Hz, 2H, H-1b), 2.56 (t, J = 6.0 Hz, 2H, H-3b), 2.52 (t,
J = 6.8 Hz, 2H, H-4b), 2.41 (s, 3H, H-6 ), 2.32 (s, 3H, H-7b), 1.84
m, 4H, H-2b and H-5b); C NMR (151 MHz, CDCl
76.76 (C-3), 166.77 (C-5 ), 158.53 (C-2 ), 152.26 (C-4a), 151.85
C-2a), 150.20 (C-9a), 148.91 (C-5 ), 141.63 (C-1), 137.55 (C-1 ),
35.82 (C-4 ), 134.61 (C-7a), 128.36 (C-3 ), 128.32 (C-5a), 127.41
0
ꢀ1
der; mp: charcoal at 215 °C; IR (ATR) mmax/cm : 3347, 3180, 1649,
0
1
1595, 1507, 1067, 767; H NMR (600 MHz, DMSO-d
6
) d (ppm): 8.07
13
00
00
00
(
1
(
1
(
1
(
2
3
) d (ppm):
(d, J = 4.4 Hz, 1H, 6 -
a
), 7.94–7.90 (m, 4H, H-2 and H-3 ), 7.80 (d,
J = 3.5 Hz, 1H, H-3 ), 7.73 (d, J = 5.5 Hz, 2H, H-1 and H-2), 7.47 (d,
J = 5.9 Hz, 1H, 6 -b), 6.45 (d, J = 3.7 Hz, 1H, H-4 ), 2.40 (s, 3H, H-
6
6 ); C NMR (151 MHz, DMSO-d ) d (ppm): 175.53 (C-3), 167.21
(C-5 ), 158.86 (C-2 ), 151.84 (C-5 ), 141.02 (C-1), 137.13 (C-1 ),
135.50 (C-4 ), 128.50 (C-2 ), 127.96 (C-3 ), 123.45 (C-2), 121.90
00
0
0
0
00
00
0
00
00
0
13
0
0
0
00
0
0
00
C-2 ), 124.90 (C-6a), 122.78 (C-2), 121.58 (C-8a), 120.08 (C-3 ),
17.36 (C-10a), 109.50 (C-4 ), 98.50 (C-3a), 56.90 (C-3b), 56.42
C-4b), 43.01 (C-1b), 42.09 (C-7b), 39.09 (C-6b), 26.86 (C-5b),
0
00
00
00
0
0
0
+
(C-3 ), 109.58 (C-4 ), 13.77 (C-6 ); HRMS (APCI) m/z [M+H]
256.0969 (Calcd for C15 : 256.0973).
0
+
4.95 (C-2b), 14.19 (C-6 ); HRMS (APCI) m/z [M+H] 545.2303
34ClN : 545.2319).
H13NO
3
(
Calcd for C31
H
4 3
O
2
.4.4.2.
N-Butyl-4-[(1E)-3-(5-methylfuran-2-yl)-3-oxoprop-1-
Amide 21 was brought about as
2
.4.3.9. (2E)-3-(4-{[4-(7-Chloroquinolin-4-yl)piperazin-1-yl]car-
en-1-yl]-benzamide, 21.
bonyl}phenyl)-1-(5-methylfuran-2-yl)prop-2-en-1-one,
light yellow platelets in 55% yield (0.75 g) from chalcone 10 and
1
1
1
9.
Light brown powder; yield 0.65 g (34%); mp: 192.1–
n-butylamine (Scheme 2), similarly to compounds 11–19; mp:
ꢀ1
ꢀ1
95.4 °C; IR (ATR)
m
max/cm : 1656, 1631, 1601, 1574, 1511,
169.2-171.5 °C; IR (ATR)
m
max/cm : 3359, 2866, 1643, 1593,
1
1
426, 1380, 1247, 1207, 1125, 1061, 1008, 930, 812, 776;
) d (ppm): 8.72 (d, J = 4.9 Hz, 1H, H-2a),
.03 (d, J = 2.2 Hz, 1H, H-8a), 7.92 (d, J = 8.9 Hz, 1H, H-5a), 7.81
H
1536, 1069, 796; H NMR (600 MHz, CDCl
3
) d (ppm): 7.81–7.73
0
0
00
NMR (600 MHz, CDCl
8
3
(m, 3H, H-2 and H-1), 7.65–7.59 (m, 2H, H-3 ), 7.38 (d,
0
J = 15.8 Hz, 1H, H-2), 7.24 (d, J = 3.7 Hz, 1H, H-3 ), 6.36 (t,
00
00
0
(
d, J = 15.7 Hz, 1H, H-1), 7.68 (d, J = 8.1 Hz, 2H, H-2 ), 7.48 (d,
J = 5.8 Hz, 1H, H-6 ), 6.20 (d, J = 3.3 Hz, 1H, H-4 ), 3.42 (td, J = 7.2,
00
00
0
J = 8.1 Hz, 2H, H-3 ), 7.43 (d, J = 2.2 Hz, 1H, H-6a), 7.40 (d,
J = 15.7 Hz, 1H, H-2), 7.25 (d, J = 3.6 Hz, 1H, H-3 ), 6.82 (d,
J = 5.0 Hz, 1H, H-3a), 6.21 (d, J = 3.3 Hz, 1H, H-4 ), 3.38–3.03 (m,
5.6 Hz, 2H, H-7 ), 2.41 (s, 3H, H-6 ), 1.57 (tt, J = 7.7, 6.6 Hz, 2H, H-
0
00
00
00
8 ), 1.38 (h, J = 7.4 Hz, 2H, H-9 ), 0.92 (t, J = 7.3 Hz, 3H, H-10 );
0
13
00
C NMR (151 MHz, CDCl
3
) d (ppm): 176.81 (C-3), 166.70 (C-5 ),
0
13
0
0
00
4
H, H-1b), 2.42 (s, 3H, H-6 ); C NMR (151 MHz, CDCl
3
) d 176.77
158.48 (C-2 ), 152.30 (C-5 ), 141.78 (C-1), 137.49 (C-1 ), 136.12
(C-4 ), 128.39 (C-2 ), 127.43 (C-3 ), 122.74 (C-2), 119.98 (C-3 ),
00
0
00
00
00
0
(
C-3), 169.78 (C-5 ), 158.43 (C-2 ), 156.22 (C-4a), 152.32 (C-9a),
0
00
0
00
00
00
1
51.89 (C-2a), 150.08 (C-5 ), 141.74 (C-1), 136.74 (C-1 ), 136.49
109.47 (C-4 ), 39.87 (C-7 ), 31.64 (C-8 ), 20.12 (C-9 ), 14.17 (C-
0
0
00
00
0
00
+
(
C-4 ), 135.15 (C-7a), 129.02 (C-8a), 128.51 (C-3 ), 127.76 (C-2 ),
6 ), 13.75 (C-10 ); HRMS (APCI) m/z [M+H] 312.1589 (Calcd for
1
1
6
4
26.61 (C-6a), 124.62 (C-5a), 122.64 (C-2), 121.73 (C-10a),
C
19 3
H21NO : 312.1599).
0
0
19.90 (C-3 ), 109.48 (C-4 ), 109.34 (C-3a), 52.13 (C-1b), 14.19 (C-
0
+
3 3
); HRMS (APCI) m/z [M+H] 486.1545 (Calcd for C28H25ClN O :
2
.4.4.3. (2E)-1-(5-Methylfuran-2-yl)-3-{4-[(morpholin-4-yl)car-
Amide 22 was synthe-
86.1584).
bonyl]-phenyl}prop-2-en-1-one, 22.
sized as light yellow crystals in 71% (0.9), using chalcone 10 and
morpholine (Scheme 2), as for 21 above; mp:195.5–197.2 °C; IR
2
2
.4.4. Chalconyl amides, 20–22
.4.4.1.
4-[(1E)-3-(5-Methylfuran-2-yl)-3-oxoprop-1-en-1-
The amide 20 was synthesized using a
ꢀ1
1
(
(
ATR)
m
max/cm : 1656, 1634, 1603, 1507, 064, 834, 797; H NMR
) d (ppm): 7.66 (d, J = 15.7 Hz, 1H, H-1), 7.52 (d,
yl]benzamide, 20.
method by Fisher et al. and described as follows: To the chalcone
0 (3.9 mmol, 1 g, 1 equiv) in DCM (50 ml) and stirring at 0 °C, was
600 MHz, CDCl
3
3
3
00
00
J = 8.0 Hz, 2H, H-2 ), 7.32–7.20 (m, 3H, H-3 and H-2), 7.11 (d,
J = 3.2 Hz, 1H, H-3 ), 6.07 (d, J = 3.4 Hz, 1H, H-4 ), 3.73–3.21 (m,
H, H-6 and H-7 ), 2.28 (s, 3H, H-6 ); C NMR (151 MHz, CDCl )
3
d (ppm): 176.76 (C-3), 169.55 (C-5 ), 158.38 (C-2 ), 152.29 (C-5 ),
41.77 (C-1), 136.72 (C-1 ), 136.29 (C-4 ), 128.42 (C-2 ), 127.68
C-3 ), 122.50 (C-2), 119.84 (C-3 ), 109.42 (C-4 ), 66.76 (C-7 ),
), 42.49 (C-6 b), 14.15 (C-6 ); HRMS (APCI) m/z
M+H] 326.1381 (Calcd for C19
1
0
0
added oxalyl chloride (7.8 mmol, 0.99 g, 2 equiv) and 2 drops of
DMF. The solution was allowed to warm to room temperature
00
00
0
13
8
00
0
0
(
rt) over a period of 1 h, and the solvent was subsequently re-
moved. The residue was dissolved in DCM (50 ml), cooled to 0 °C
and an excess NH OH (33%) was added. The solution was allowed
to heat to rt and stirred for an additional 4 h (Scheme 2). The sol-
00
00
00
1
(
4
[
00
0
0
00
4
00
00
0
8.11 (C-6
a
+
4
H19NO : 326.1392).
6
'
3
. Results
1
'
5'
O
3
O
4'
2''
1
1
'
3
''
1''
2'
3.1. Chemistry
O
6'
3
'' 2''
1''
2
3
2' 3'
2
O
(i)/(ii)
O
5''
4
''
5'
3'
The aminoquinoline intermediates (1–9) were easily prepared
a
HO
O
4
''
5''
1
4'
R'
in high yields through nucleophillic aromatic substitution on the
4
th position of the quinoline ring by various diamines. In all in-
2
0-22
1
0
stances the presence of one chloride was confirmed by means of
the mass spectra having an M+2 ion peak being in a 4:1 height ratio
to the M peak. The chalcone intermediate 10 was attained by Cla-
Amide
R
2
Amide
22
R
2
+
7
'' 6''
6
''
isen-Schmidt condensation of 2-acetyl-5-methylfuran and 4-form-
ylbenzoic acid in basic methanolic water in high yields. Contrary,
compounds 11–19 were synthesized in low to moderate yields
through amide bond formation between the carboxylic acid of
the chalcone and the free amine of the aminoquinolines, using
CDI as coupling agent. The addition of different solvents (acetone
and acetonitrile) to the reaction mixture, to facilitate solubility
did not impact on the yields. The addition of DMF, however,
2
2
0
1
H N
O
N
2
9''
7''
6
NH
''
10''
8''
Scheme 2. Synthesis of chalconyl amides 20–22. Reagents and conditions:
i) oxalyl chloride, DCM/DMF, 0 °C to rt, 1 h then 33% NH OH (excess); (ii) CDI,
DCM, 3 h, rt then n-butylamine or morpholine, 24 h.
(
4

F. J. Smit, D. D. N’Da / Bioorg. Med. Chem. 22 (2014) 1128–1138
1135
substantially increased the yields of the final reaction. With short-
ened reaction times, a significant amount of chalcone was ex-
tracted during workup, with very low yields (<5%) of the desired
compound. Only after 24 h, the yields of the various hybrids
seemed to reach a plateau. Increasing the reaction times further
did not seem to impact on these yields.
determined using ACD/Chemsketch and Discovery studio. Preli-
minary ADMET calculations were performed in order to determine
the drug-likeness properties of the synthesized compounds and of
CQ and are summarized in Table 1.
The results show that the synthesized quinoline-chalcone
amides were all had the same level of calculated poor water solu-
bility, just like CQ at neutral pH value, which was consistent with
their high logP values recorded in the 4–6 range. They demon-
strated various absorption levels, for example good (11, 12, 16
and 19), moderate (13, 14, 17 and 18) and poor (15). None of them
showed better calculated solubility and intestinal absorption levels
than the intermediate chalcone 10 and the chalconyl amides 20–
22. Amide 15, which showed low solubility, was the most lipo-
philic (logP = 6) and the poorest absorbed of all of the amides,
while 19 was the least lipophilic, least soluble, but one of the best
absorbed compounds. Overall, the three chalconyl amides 20, 21
and 22 exhibited the best predicted drug-like properties.
3
.2. Physicochemical properties
Three different techniques were adopted to determine the
physicochemical properties of the prepared quinoline-chalcone
amides. Differential scanning calorimetry (DSC) was used to deter-
mine both the physical states of the compounds and their different
phase transitions. Thermogravimetric analysis (TGA) was em-
ployed to determine thermal stability. All the DSC and TGA ther-
mograms are presented as Supporting Information. The ADMET
properties, such as logP, solubility and absorption levels were
3
.3. In vitro antimalarial activity and cytotoxicity
Table 1
Calculated physicochemical properties of compounds 10–22 and CQ
The aminoquinoline-chalcone amides 11–19 and chalcone 10
Compound
Log Pa
ADMET solubility levelb
ADMET absorption levelc
were screened in vitro, alongside CQ and the equimolar CQ-10
combination, M, against the 3D7 and W2 strains of P. falciparum.
Their IC50 values are presented in Table 2. Compounds 11–19 were
1
1
1
1
1
1
1
1
1
1
2
2
2
0
1
2
3
4
5
6
7
8
9
0
1
2
2.9
4.4
4.7
5.1
4.8
6.0
4.3
4.4
5.1
3.8
1.8
3.5
0.9
3.1
3
2
2
2
2
2
2
2
2
1
3
2
3
2
0
0
0
1
1
2
0
1
1
0
0
0
0
0
found active, with IC50 values ranging between 0.04–0.53
.06–1.7 M against the 3D7 and W2 strains, respectively. Amide
15 showed the highest activity against 3D7 and W2 strains, with
an IC50 of 0.04 M and 0.06 M, respectively. Amides 11–15 and
8 showed activities comparable to that of CQ against the 3D7
lM and
0
l
l
l
1
strain, while 16, 17 and 19 had much lower activities of ten-, se-
ven- and five-fold less potent than CQ, respectively.
Amide 15 was found to be almost twice as potent against the
W2 strain as CQ. Amides 13 and 14 displayed equipotency to CQ,
while 12, 17 and 18 were two-fold less potent, whereas 16 was
four times less potent than CQ. Amides 11 and 19 were the least
active, being fifteen- and eleven-fold less potent than CQ, respec-
tively. The tertiary amides, 16, 19 and 22 displayed the lowest
activity against both the CQS and CQR strains.
CQ
a
Calculated with ACD/ChemSketch (2000), version 4.54.
ADMET aqueous solubility level (Log S ) at 25 °C and pH 7, values = 1, 2 and 3
w
b
indicate very low, low and good solubility, respectively, as determined using
Accelrys Discovery Studio 3.1.
c
ADMET human intestinal absorption, values = 0, 1 and 2 indicate good, mod-
erate and poor absorption, respectively, as determined using Accelrys Discovery
Studio 3.1.
All synthesized compounds had resistance index (RI) values
above 1, with amide 11 possessed the highest value of 17. They
Table 2
Antimalarial activity and cytotoxicity of screened amide compounds
Activity IC50a
(l
M)
W2
Resistance Index
RIb
Cytotoxicity, IC50c
WI-38 HFLFd
(lM)
Selectivity Index
SIe
Compound
3D7
1
1
1
1
1
1
1
1
1
1
2
2
2
0
1
2
3
4
5
6
7
8
9
0
1
2
18.4
0.11
0.07
0.05
0.08
0.05
0.37
0.26
0.09
0.54
10–30
10–30
>30
14.2
1.78
0.23
0.10
0.11
0.07
0.46
0.27
0.22
1.26
nd
0.8
16.7
3.4
2.1
1.4
1.5
1.2
1.1
2.4
2.3
nd
nd
nd
3.1
2.2
nd
>100
47.3
74.5
39.0
10.0
19.5
18.6
10.2
5.30
17.3
nd
nd
nd
20.9
nd
16.4
nd
446
1123
819
126.0
435
50
40
58
32
nd
nd
nd
1838.6
nd
nd
nd
nd
0.04
*
*
M
CQ
PTD
0.01
0.05 (0.02 )
nd
*
*
0.12 (0.04 )
nd
nd = not determined, M = equimolar combination of CQ and 10, parthenolide (PTD).
*
Expressed in lg/ml.
a
Minimum concentration of compound inducing 50% parasitic cells inhibition.
Resistance Index (RI) = IC50 W2/IC50 3D7.
Minimum concentration of compound inducing 50% of WI-38 HFLF cells inhibition.
WI-38 cell line of normal human fetal lung fibroblast.
b
c
d
e
Selectivity index (SI) = IC50 WI-38-HFLF/IC50 3D7.

1
136
F. J. Smit, D. D. N’Da / Bioorg. Med. Chem. 22 (2014) 1128–1138
were also found either moderately or highly cytotoxic to the mam-
malian cells, with selectivity index values varying between 30 and
temperatures ranging between 50–75 °C in most cases. Amides
13 and 17 had onset temperatures of 121 °C and 37 °C, respec-
tively, making them the extremities of the glass transition profile
of the series. The glass transitions were not evidently expressed
for amides 11, 12 and 15 and were referred to as ‘obscured’ glass
transitions, which could be readily elucidated by means of anneal-
1
4
4
000.
. Discussion
3
5
.1. Chemistry
ing. However, since a thorough physicochemical analysis of the
solid-state properties of the synthesized compounds, including
3
6
The IR spectra of intermediates 1–9 commonly showed the
strength and fragility parameters, was not the main objective
of this study, this aspect was not further investigated. The DSC
thermograms suggested that all of the compounds 11–19 pos-
sessed amorphous structures (see Supporting information).
Thermal stability plays a vital role in the storing of com-
pounds, especially when pharmaceuticals must withstand high
storage temperatures as in Sub-Saharan Africa, where cooling
facilities are limited. The TGA thermograms revealed weight
losses of between 2–8.5% for all these compounds when heated
to 300 °C. These endothermic events were characterized as glass
transitions during the DSC analyses, rather than desolvation endo-
therms, due to the nature of the weight loss. Indeed, in all cases,
the thermograms showed weight losses from the start of the
heating runs, which was consistent with the loss of solvent from
the surface of the solid, possibly due to adsorption. Although the
presence of solvent trapped within crystalline regions of the solid
could not be ruled out, the absence of a clear baseline before and
after the thermal events made it difficult to explain the exact
cause of the weight loss. Overall, all compounds showed a minor
weight loss, which indicated minimal to no thermal degradation,
therefore indicative of the ability to favourably withstand ordin-
ary drug storage conditions, typical of hot, malaria endemic
countries.
ꢀ1
presence of absorption frequencies in the 3350–3200 cm region,
which is associated with N–H stretching. The quinoline moiety was
clearly identified from the presence of four doublets and one dou-
blet of doublet, assigned to signals of the heterocyclic proton H-2a,
1
H-3a, H-5a, H-8a and H-6a, respectively, in the H spectra. Proton
H-8a, which in normal circumstances would be a singlet, coupled
weakly to H-6a to which the doublet of doublet (H-6a) could have
been ascribed to. The DEPT90 of each intermediate showed five dif-
ferent tertiary aryl carbons, which further supported the presence
of the quinoline moiety. Carbons of the various methylene linkers
1
3
were identified on C/DEPT135 between ca. 25–75 ppm, while the
1
protons were identified on H NMR at ca. 3.8–1.7 ppm.
The presence of the carboxylic acid of the chalcone 10 was con-
firmed by the signals of a highly deshielded proton at 13.07 ppm
and a carbon at 166 ppm. The conjugated ketone’s carbon was
shielded and was allocated the signal at 175 ppm. The IR spectra
ꢀ
1
showed a strong stretching band at 1654 cm , which is associated
with an unsaturated ketone. Additional evidence, such as six con-
jugated tertiary carbons (as determined with DEPT90) and six dou-
1
blets ( H NMR) were further indicative of the presence of the
chalcone. The integration of the two doublets at 7.9 ppm ac-
00
00
counted for four protons, which were assigned to H-2 and H-3 ,
indicating that the ortho- and meta portions were non-equivalent.
Due to the electronic effect of both the ketone and heterocyclic
Drug development is largely hampered by poor pharmacokinet-
3
7
ics and toxicity. It is therefore important to determine drug-like
properties during the early stages of the development of a drug.
The aqueous solubility of any compound largely influences its abil-
ity to be absorbed when taken orally. Poor water solubility is gen-
erally associated with high lipophilicity, while hydrophilic
compounds generally show poor permeability and hence low
absorption, which to a large extent influence the drug’s bioavail-
ability. These two properties are thus of high importance when
designing new drugs.
0
oxygen in the furan ring, the quaternary carbon C-2 was deshield-
ed and was assigned the peak at 158 ppm. The presence of the
methyl group was indisputably assigned to the only aliphatic sig-
nal at 13 ppm.
The IR spectra of all target compounds 11–18 had a weak
ꢀ1
absorption frequency near 3300 cm , assignable to N–H stretch-
ing. Further confirmation of this group was obtained by the pres-
ence of triplets/singlets in the 1H-spectra between 6.9–8.8 ppm,
as well as the coupling to the CH
spectra. Additionally, H NMR displayed ten doublets and one dou-
blet of doublet between 6–8.5 ppm, which could have been cred-
2
of the linker displayed in COSY
In order for drug uptake to occur through biological mem-
branes, the drug must possess a limiting aqueous solubility and
be neither too lipophilic, nor too hydrophilic. Lipophilic drugs
show poor aqueous solubility and tend to be taken up in fatty glob-
ules in the intestine. Once they reach the blood stream, they may
be absorbed into tissue. Their slow release may exacerbate toxicity,
such as neurotoxicity. Contrary, hydrophilic drugs may be excreted
directly by the kidneys, or should they be able to penetrate a cell
membrane, become entrapped in intracellular aqueous media. An
ideal drug must therefore possess balanced lipophilic/hydrophilic
properties to both permeate biological membranes and be taken
up in the systemic circulation. The n-octanol/water partition coef-
ficient (LogP) offers a reliable measure of this balance, with values
between 1 and 5 being targeted, and values between 1 and 3 being
1
ited to the chalcone together with the quinoline-H in compounds
1
1
1–19, except for 12. An interesting observation from the
H
NMR of 12 was the number of singlet peaks. So long as the chem-
ical shift difference in hertz (d ) is higher than the coupling con-
stant (J), a simple splitting pattern appears, but within some
compounds d /J is very small, resulting in multiplets to be
displayed as singlets, such as the case with amide 12. The signals
m
m
3
4
1
3
at 176 and 166 ppm in C NMR were attributed to the ketone and
amide of the hybrids, respectively. Supplementary information,
such as signals at 99, 109 and 141 ppm, corresponding to C-3a,
0
C-4 and C-1, respectively, further indicated the presence of both
3
8,39
chalcone and quinoline moiety in the structures of these amides.
ideal.
In all cases (except 19), the theoretical number of CH
2
groups in
A combined analysis of the predicted solubility, absorption lev-
els and logP values revealed amides 11, 12 and 16 to be the most
drug-likeable compounds, similarly to CQ and they were thus ex-
pected to display the best biological profile. Compound 15, how-
ever, appeared as the least drug-likeable, based upon its high
lipophilicity, low solubility and poor absorption. Amides 20, 21
and 22, which also possessed favourable drug-like properties, were
expected to demonstrate good antimalarial activity. Compound 19,
a tertiary amide, like 16, had a predicted logP value in the target
the linker was in accordance with the one from DEPT135 spectra.
In the case of 19, only C-1b was displayed on 13C NMR, although
the HRMS confirmed the correct molecular ion.
4
.2. Physicochemical properties
All compounds 11–19 displayed small endothermic phase tran-
sitions, which were consistent with glass transitions, with onset

F. J. Smit, D. D. N’Da / Bioorg. Med. Chem. 22 (2014) 1128–1138
1137
range, poor solubility, but good absorption and were they both
therefore expected to show moderate activity.
combination’s activity. The most active quinoline-chalcone amide,
that is 15 was found to be as potent as CQ against both strains. No
synthesized compound in this study therefore possessed over-
whelmingly higher activity than CQ. This suggested that the chal-
cone moiety antagonized the antimalarial action of quinoline
pharmacophore in most cases. The need for a better partner should
thus be identified if one wishes to achieve synergism, using this
quinoline based hybrid type.
4
.3. In vitro antimalarial activity and cytotoxicity
The P. falciparum 3D7 strain, a line cloned from NF54, is of Afri-
can origin and is CQ susceptible. It has frequently been used to
evaluate in vitro antigametocytes activity of trial antimalarial
4
0
The tertiary amides, 16 and 19, despite their predicted favour-
able drug-like properties, demonstrated the lowest activity against
both the CQS and CQR strains, which suggested that the tertiary
amide bond was not conducive to increased antimalarial activity
for this compound type. Since the 7-chloro-4-aminoquinoline moi-
ety is a well-established antimalarial pharmacophore, this lower
activity observed among these amides could only have been as a
result of the presence of the chalcone portion in their structures.
In order to validate this statement, basic chalconyl amides 20–22
were synthesized and screened against the 3D7 clones at three dif-
compounds. In contrast, the Indochina/Laos clone W2 is a mul-
ti-drug resistant strain. It is known to be the most resistant of all
P. falciparum strains and has shown resistance against all
traditional antimalarial drugs, including chloroquine, cycloguanil,
pyrimethamine and sulfadoxine.41 Both strains were used to deter-
mine the in vitro antiplasmodial activity of the synthesized target
compounds.
Since the amides prepared during this study were tested in vitro
and not metabolized by metabolic enzymes, they would act as new
entities and not as prodrugs. The observed IC50 values were there-
fore most likely to be those of the hybrids, rather than that of any
active metabolite.
ferent concentrations that is 3, 10 and 30
lM. Compounds 20 and
2
1, bearing a primary and secondary amide, respectively, showed
activities between 10–30 lM, while amide 22 with a tertiary
amide showed no activity, even at the highest concentration of
Compared to the IC50 of 6.5 lM of Licochalcone A against 3D7
1
3
clone, chalcone 10 was found inactive against both the 3D7
and W2 strains. Chalcones, containing electron withdrawing
groups on ring A and a heterocyclic ring B, had been reported to
30 l
M. Compounds 16, 19 and 22 as tertiary amides, were de-
pleted of hydrogen bonds, while all active amides had one hydro-
gen bond, involving N–H of the amide functional group. This
emphasised the significance of hydrogen bonds as part of the
parameters that influence the absorption of drugs or molecules
and thus their antimalarial activity in this study.
42
show overall better antimalarial activities,
which was con-
tradicted by the performance of chalcone 10 against the 3D7 strain
in this study.
Due to the limited number of compounds prepared during this
study, an accurate structure activity relationship (SAR) could not
be drawn. However, the observations made with regards to SAR
from these results may be useful in the design of future studies,
which included:
Compared to the quinoline-chalcone ketones of Sharma et al.22
(Fig. 2), the incorporation of methylene spacer between both moi-
eties in this study, imparted the resulting conjugates with in-
creased activity, as was observed throughout the series of amide
compounds investigated. The amides had RI values above 1, an
indication of a loss of activity against the CQR, and no compound
were thus able to overcome the resistance of the W2 strain against
CQ.
With the exception of 11 and 12, all other amides showed
moderate to high cytotoxicity against human fetal lung fibroblast
WI-38 cells, compared to parthenolide. However, analysis of the
selectivity index (SI), which is indicative of the effectiveness of a
drug to clear only parasitic cells and not healthy cells, enabled
the reaching of the following conclusions: (i) amides 16–19 had
relatively low SI values, suggesting that their activities were
generally that of toxicity rather than any other mechanism; (ii)
compounds 11–15, however, showed high SI values, demonstrative
of their activities being intrinsic, hence not exerted by cytotoxicity,
but rather through other mechanisms.
Amides 11–18 had the same solubility levels and a comparison
of their lipophilicity properties could therefore be made based on
their logP values. In this Letter, the more lipophilic (higher logP va-
lue of 5–6) compounds, that is 13, 15 and 18 happened to be more
active, while the more hydrophilic (lower logP values of 3–4), that
is 11, 14, 16, 17 and 19 displayed lower activity against both
strains. ADMET predicted amides 11, 12 and 16 would be drug-
likeable, whereas their activities showed the opposite. Contrary,
amide 15, predicted as the least drug-likeable, was found the most
active. These outcomes indicated that the predicted absorption lev-
els did not corroborate their antimalarial activity, resulting from
their real absorption. These findings suggested that other proper-
ties, or other properties in combination with the predicted ones,
may have been involved in the real absorption of these com-
pounds. This was in accordance with a previous report that the
properties, such as hydrogen bonding, molecular size and shape,
polarity, flexibility and the charge/ionization of a compound/drug
molecule as a whole (rather than a single property), affect absorp-
tion through membranes.43
Compounds 11–15 were furthermore found in the following
increasing order of linker chain length: 11 < 12 = 14 < 13 < 15,
which was congruent with their lipophilicity and activity against
both strains. In this sub-series of amides, featuring methylene
chain linkers, the activity was found to be directly proportional
to the chain length, hence as the length increased, so did the activ-
ity against the CQS and CQR strains. Compound 11 showed the
highest RI value of 16, which might have been a result of the de-
creased flexibility of this short chain amide. As the chain increased
the RI index decreased, indicating the importance of flexible linkers
to overcome resistance.
5. Conclusion
In this Letter, a series of novel 4-aminoquinolinyl-chalcone
amides, 11–19, were synthesized in a three-step process involving
amino-functionalizing quinolines, a carboxylic acid-functionalized
0
chalcone and 1,1 -carbonyldiimidazole as coupling reagent. Rou-
tinely used techniques, such as NMR, HRMS and IR served to con-
firm their structures. DSC and TGA analyses were used to reveal
their amorphous structures and thermal stabilities, respectively,
while ADMET served to predict their drug-like properties. Antima-
larial screens, alongside CQ, showed that all of these amides proved
to be active with IC50 values ranging between 0.05–0.53
lM and
0.07–1.8 M against the 3D7 and W2 strains of P. falciparum,
l
respectively. The amides displayed a loss of activity against the
CQR strain, compared to that of the CQS, which resulted in resis-
tance index values exceeding the unit thus no resistance to CQ
was overcome in this study. They also demonstrated moderate to
The combination M was as potent as CQ against 3D7 and W2,
suggesting that the activity of M was in fact equal to that of CQ,
since the inactive chalcone 10 had no contribution to this

1
138
F. J. Smit, D. D. N’Da / Bioorg. Med. Chem. 22 (2014) 1128–1138
high selective toxicity towards the mammalian cells in the pres-
ence of the parasitic ones. During this study, the antimalarial activ-
ity of the amides was found to increase as the lipophilicity and the
linker chain length increased. The tertiary amides were the least
active, which emphasized the significance of hydrogen bonding
on the activity of this compound type. Amide 15, featuring 1,6-
diaminohexane linker was found the most active of all, being as po-
tent as and two-fold more potent than CQ against the 3D7 and W2
strains, respectively, despite its predicted unfavourable high lipo-
philicity, low solubility and poor absorption properties. The above
results generated necessitate the need for the inclusion of the
intermediate amino-functionalized quinolines, as well as the
aminoquinolines in a 1:1 molar ratio with the chalcone and to
evaluate the interaction of these combinations against various P.
falciparum cell lines. These results would have provided a more
definitive conclusion about the role of the chalcone. Additionally
the in vivo evaluation of amide 15 must also be investigated.
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Any opinion, findings and conclusions or recommendations ex-
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