Synthesis, antimalarial-, and antibacterial activity evaluation of some new 4-aminoquinoline derivatives

Article abstract of DOI:10.1007/s00044-012-0371-9

Some new 4-aminoquinoline derivatives were synthesized, characterized by their analytical and spectral data (IR, ¹HNMR, ¹³CNMR and MS), and screened for in vitro antimalarial activity against a chloroquine-sensitive strain of Plasmodium falciparum (3D7). Results clearly reveal that all the synthesized compounds possess in vitro antimalarial activity at the tested dose which, however, was considerably less than that of the standard reference drug, chloroquine. From results, it could be assumed that the presence of an aromatic bulky group with optimal lipophilicity at 1,3-thiazinan-4-one ring system might be an important requirement for the antimalarial activity of synthesized compounds, 6a-g. In addition to the evaluation of antimalarial activity, the synthesized compounds were also screened for antibacterial activity against six different strains of Gram-positive (Bacillus subtilis, Bacillus cereus, and Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae). All the compounds at the tested doses were found to be active against all the tested organisms, but were less active as compared to the standard drug, ofloxacin. Results of antibacterial study indicate that aromatic bulky substituents have greater contributing effect than the aliphatic non-bulky group toward the antibacterial activity of the prepared 4-aminoquinoline derivatives.

Full text of DOI:10.1007/s00044-012-0371-9

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2013) 22:3703–3711
DOI 10.1007/s00044-012-0371-9
ORIGINAL RESEARCH
Synthesis, antimalarial-, and antibacterial activity evaluation
of some new 4-aminoquinoline derivatives
•
Mithun Rudrapal Dipak Chetia Anil Prakash
•
Received: 7 August 2012 / Accepted: 14 November 2012 / Published online: 1 December 2012
Ó Springer Science+Business Media New York 2012
Abstract Some new 4-aminoquinoline derivatives were
synthesized, characterized by their analytical and spectral
Keywords 7-Chloro-4-aminoquinoline Á Antimalarial Á
Antibacterial Á Aromatic bulky substituent Á Lipophilicity
1
data (IR, HNMR, 13CNMR and MS), and screened for
in vitro antimalarial activity against a chloroquine-sensitive
strain of Plasmodium falciparum (3D7). Results clearly
reveal that all the synthesized compounds possess in vitro
antimalarial activity at the tested dose which, however, was
considerably less than that of the standard reference drug,
chloroquine. From results, it could be assumed that the
presence of an aromatic bulky group with optimal lipo-
philicity at 1,3-thiazinan-4-one ring system might be an
important requirement for the antimalarial activity of
synthesized compounds, 6a–g. In addition to the evaluation
of antimalarial activity, the synthesized compounds were
also screened for antibacterial activity against six different
strains of Gram-positive (Bacillus subtilis, Bacillus cereus,
and Staphylococcus aureus) and Gram-negative bacteria
(Escherichia coli, Pseudomonas aeruginosa, and Klebsi-
ella pneumoniae). All the compounds at the tested doses
were found to be active against all the tested organisms, but
were less active as compared to the standard drug, oflox-
acin. Results of antibacterial study indicate that aromatic
bulky substituents have greater contributing effect than the
aliphatic non-bulky group toward the antibacterial activity
of the prepared 4-aminoquinoline derivatives.
Introduction
Despite over a 100 years of drug development, malaria
remains one of the most devastating infectious diseases in
the world, both from the point of view of mortality and
morbidity and its worldwide occurrence in tropical and
subtropical regions. According to the World Health
Organization, it is estimated that approximately 40 % of
the world’s population lives in malaria endemic areas with
300–500 million clinical cases and 1.5–2.7 million deaths
per year globally, and up to 1 million of those deaths are
among children younger than 5-years old (Casteel, 2003;
Farooq and Mahajan, 2004; Gillies, 2000; Wiesner et al.,
2003). This life-threatening parasitic disease is caused by
protozoan parasites of the genus Plasmodium; P. falcipa-
rum, P. vivax, P. malariae, and P. ovale are four well-
known species of human malaria parasite (Chiang et al.,
2006; http://www.rbm.who.int/) and more recently another
species, P. knowlesi has been documented (White, 2008).
P. falciparum is the most widespread and causing most
severe and potentially fatal form of malaria (Talisuna
et al., 2004). Chloroquine (CQ), Fig. 1 has remained the
drug of choice for the malaria chemotherapy for decades
because it is an effective, less toxic, and cheap drug
(Ridley, 2002). The emergence of resistance of malaria
parasite, especially P. falciparum toward currently avail-
able drugs, especially chloroquine, has become a major
health concern in the tropical and subtropical regions of
the world; therefore, the development of new chemo-
therapeutic agents is an urgent need to fight against
malaria.
M. Rudrapal (&) Á D. Chetia
Department of Pharmaceutical Sciences, Dibrugarh University,
Dibrugarh, India
e-mail: rs_rudrapal@yahoo.co.in
A. Prakash
Regional Medical Research Centre, I C M R, N E Region,
Dibrugarh, India
123

3704
Med Chem Res (2013) 22:3703–3711
small heterocyclic systems could modulate the antimalarial
activity. Based on this fact, proposed compounds were
designed by modifications at the C-2 position of a six-
membered 1,3-thiazinan-4-one ring attached at the terminal
propyl side chain of 7-chloro-4-aminoquinoline without
making alteration in 7-chloro-4-aminoquinoline nucleus
(Scheme 1).
N
HN
N
Cl
Fig. 1 Structure of chloroquine (CQ)
The incidence of microbial infections has been
increasing worldwide over the past few decades because of
widespread emergence of bacterial resistance toward the
currently available beta-lactam antibiotics, quinolones,
macrolides, etc. A matter of concern in the treatment of
microbial infection is the limited number of efficacious
antimicrobial agents, which clearly highlights the urgent
need of novel antimicrobial agents (Goker et al., 2002; He
et al., 2003). A large variety of synthetic compounds
having therapeutic use in some other ailments possess
antibacterial activities. On the basis of this premise, the
synthesized compounds tested for antimalarial activity
were also subjected to antibacterial activity screening.
In the present study, some new derivatives of 3-(3-(7-
chloroquinolin-4-ylamino)propyl)-2-substituted-1,3-thiaz-
inan-4-one were prepared and screened for antimalarial as
well as antibacterial activities.
The structure–activity relationship studies on 4-amino-
quinoline antimalarial compounds suggest that the
7-chloro-4-aminoquinoline nucleus is obligatory for anti-
malarial activity, which could be attributed mainly due to
prevention of heme polymerization into an insoluble
compound, hemozoin (malaria pigment) (Chou et al., 1980;
Dorn et al., 1995; Egan and Marques, 1999; Foley and
Tilley, 1998; Pandey et al., 2001; Sullivan et al., 1996) by
inhibiting parasitic enzyme, particularly heme polymerase.
This process ultimately leads to the death of parasite
(Tilley et al., 2001).
A new series of compounds with aromatic ring system at
the side chain of 7-chloro-4-aminoquinoline nucleus was
found active against P. falciparum (in vitro) and P. yoelli
(in vivo) because of their direct action on heme polymer-
ization target (Solomon et al., 2007). It has been observed
that three-carbon atoms in the side chain are appropriate for
the antimalarial activity of compounds with terminal six-
membered rings, while an increase or decrease in carbon
chain length results in the decrease in activity, which
indicates that the length of the side chain is crucial for the
activity of compounds, along with the size of the hetero-
cyclic ring. These findings have given impetus to the
concept that side chain modification is an attractive strat-
egy for the development of new antimalarial drugs with
desirable activity profile. Accordingly, we presumed that
selective modification at the pendent amino group with
Experimental
Materials and methods
All chemicals and reagents were procured from Sigma–
Aldrich Corporation (USA), Merck (Germany), or Spect-
rochem Pvt. Ltd. (India) and were used without further
purification unless otherwise stated. 4,7-dichloroquinoline
was obtained from M/s. Mangalam Drug & Organics,
Mumbai, India. Melting points (mp) were taken in open
Cl
HN
NH2
a
+
NH2
NH2
Cl
N
+
Cl
S
N
3
1
2
Cl
HN
NH2
HS
H
N
O
b
O
+
RCHO
OH
N
N
Cl
N
R
4
5
3
6
Scheme 1 Synthesis of compounds, 6a–g. Reagents and conditions a Reflux for 1 h at 80 °C and 9 h at 130 °C, b DCC, THF, rt, 1 h
123

Med Chem Res (2013) 22:3703–3711
3705
capillaries on a Veego-MPI melting point apparatus and are
uncorrected. The progress of reactions and purity of syn-
thesized compounds were checked on silica gel-G TLC plate
using various solvent combinations of different polarity. The
spots were detected with iodine vapors on UV-light
(254 nm). The UV–Visible spectra (kmax, nm) of the syn-
thesized compounds were obtained on Shimadzu UV-1700
UV–Visible spectrophotometer. Infrared (IR) spectra were
recorded on a FT-IR Perkin-Elmer Spectrum RX-I spec-
trometer. The 1HNMR and 13CNMR spectra were recorded
on a Bruker AC-F 300 FT-NMR spectrometer using CDCl3
as solvent. Chemical shifts (d in ppm) were reported with
tetramethylsilane (TMS) as an internal standard. Mass
spectra were undertaken using a LC–MS Water 4000 ZQ
instrument by atmospheric pressure ionization (API). Ele-
mental microanalyses (CHN) were performed on a Perkin
Elmer 2400 Series II CHNS/O analyzer.
addition of 3-mercaptopropionic acid, 4 (3.0 mmol). After
5 min, DCC (1.2 mmol) was added to the reaction mixture
at 0 °C and the reaction mixture was stirred for an addi-
tional 60 min at room temperature. DCU (Dicyclohexyl-
urea) was precipitated out and removed by filtration. The
filtrate was concentrated under reduced pressure, and the
residue was taken up in chloroform. The organic layer was
successively washed with 5 % aqueous sodium hydrogen
carbonate and then finally with brine. The organic layer
was dried over sodium sulfate, and the solvent was
removed under reduced pressure to get the final product,
6a–g. The synthetic routes for 3 and 6a–g are outlined in
Scheme 1.
Antimalarial screening
All the synthesized compounds were evaluated for in vitro
antimalarial activity. Continuous culture of CQ-sensitive
strain of P. falciparum (3D7) was maintained in vitro in O?
human red blood cells diluted to 6 % hematocrit in RPMI
1,640 medium supplemented with 25 mM HEPES, 1 %
D-glucose, 0.23 % sodium bicarbonate, gentamycin (40 lg/
mL), amphotericin-B (0.25 lg/mL), and 10 % human
AB ? serum (Trager and Jensen, 1976). Incubations were
done at 37 °C and 5 % CO2 level in a modular incubator.
D-sorbitol synchronized (Lambros and Vanderberg, 1979)
1 % ring stage parasitemia in 3 % hematocrit was used for
antimalarial assays using 96-well microtitre plate. A stock
solution of 5 mg/mL of the test compound was prepared in
DMSO and subsequent dilutions were made with incomplete
RPMI in duplicate. All test compounds were assayed at a
fixed dose of 50 lg/mL. Each test well of the microtitre plate
contained 20 lL of the compound and 180 ll of 1 % ring
stage parasitaemia in 3 % hematocrit. In addition, drug-free
negative control to assess the parasite growth and chloro-
quine diphosphate, at predetermined 50 % inhibitory con-
centration (IC50) dose, as positive control to assess the
integrity of the assay were also maintained in duplicate in the
microtitre plate. After 40 h of incubation, the smears were
prepared from each well, stained with 3 % Giemsa, and
scanned under light microscope to ascertain percentage dead
rings and trophozoites by examining a minimum of 400
asexual parasites.
General method of synthesis, 6a–g
The reaction intermediate N1-(7-chloroquinolin-4-yl)-pro-
pane-1,3-diamine, 3 and target compounds, 6a–g were
prepared according to the following methods (Madrid
et al., 2004; Solomon et al., 2005):
Step-I
A mixture of 4,7-dichloroquinoline, 1 (5 g, 25.18 mmol)
and 1,3-diaminopropane, 2 (4.24 mL, 50.36 mmol) was
heated slowly from room temperature to 80 °C over 1 h with
stirring and subsequently at 130 °C for 9 h with continued
stirring to drive the reaction to completion. Then, the reac-
tion mixture was cooled to room temperature and taken up in
dichloromethane (80 mL). The resulting mixture was
washed with sodium hydroxide (1 M, 80 mL) and brine
(a concentrated solution of sodium chloride, 80 mL) to give
an aqueous layer, an organic layer, and a white coarse par-
ticulate precipitate. The organic layer was dried over
anhydrous sodium sulfate, and solvent was removed under
reduced pressure to obtain the product as a yellowish white
solid. The precipitate from the wash was filtered and
extracted in a Soxhlet extractor with dichloromethane for
24 h. The dichloromethane was then removed in vacuum to
yield a second crop of the product as a yellowish white solid.
TLC, melting point, and IR spectral analysis confirmed that
the two solids were identical and pure so they were com-
bined and used without further purification.
Antibacterial screening
All the synthesized compounds were screened for antibac-
terial activity by Kirby–Bauer disk diffusion method
(Hewitt, 2004; Collee et al., 1989) against six different
strains of Gram-positive and Gram-negative bacteria at two
different tested doses, viz., 25 and 50 lg/disk. Three strains
of Gram-positive bacteria—Bacillus subtilis [(ATCC
11774), Bacillus cereus (ATCC 10876), and Staphylococcus
Step-II
N-(3-aminopropyl)-7-chloroquinolin-4-amine, 3 (1.0 mmol)
and substituted aldehyde, 5 (2.0 mmol) were stirred in THF
under ice-cold condition for 5 min, followed by the
123

3706
Med Chem Res (2013) 22:3703–3711
aureus (ATCC BAA 1026), and three strains of Gram-neg-
ative bacteria—Escherichia coli (ATCC 10536)], Klebsiella
pneumoniae (ATCC 33495), and Pseudomonas aeruginosa
(ATCC 10662), were used for the study. All the bacterial
strains were obtained from the National Collection of
Industrial Microorganisms (NCIM), National Chemical
Laboratory (Council of Scientific & Industrial Research),
Pune, India. The cultures of bacteria were maintained in their
appropriate agar slants at 4 °C throughout the study and used
as stock cultures.
(chloroform), kmax (nm): 270, 366, 412.5. IR (KBR), t,
cm-1: 3422, 3382 (N–H str., –NH2); 3312 (N–H str.,[NH);
1352, 1286 (C–N str.); 1078 (Ar. C–Cl str). 1HNMR
(300 MHz, CDCl3), d (ppm): 1.82–1.86 (t, J = 9.6 Hz, 2H,
CH2); 2.71–2.81 (t, J = 19.2 Hz, 2H, CH2); 3.20–3.32 (dd,
J = 9.6, 25.2 Hz, 2H, CH2); 6.54–6.55 (d, J = 5.6 Hz, 1H,
quinoline-H3); 7.25 (bs, 2H, NH2), 7.51 (s, 1H, NH);
7.56–7.77 (dd, J = 18.0, 18.0 Hz, quinoline-H6); 7.89–7.90
(d, J = 6.0 Hz, 1H, quinoline-H5); 8.02–8.04 (d, J =
9.2 Hz, 1H, quinoline-H8); 8.22–8.29 (dd, J = 5.2, 6.4 Hz,
1H, quinoline-H2). 13CNMR (100 MHz, CDCl3), d (ppm):
27.65 (CH2), 39.38 (CH2), 44.67 (CH2); 109.54 (C-3, quin-
oline), 117.72 (C-4, quinoline); 124.48 (C-5, quinoline),
127.59(C-6, quinoline); 134.26(C-8, quinoline), 136.79(C-7,
quinoline C–Cl), 146.89 (C-8a, quinoline), 152.72 (C-2,
quinoline), 151.53 (C-4, quinoline). MS (API), m/z (%):
236.72 (100), [M?H]?. Anal. cacld. (%) for C12 H14 N3Cl:
C, 61.15; H, 5.99; N, 17.83; found (%): C, 61.42; H, 6.36; N,
12.99.
Freshly prepared and cooled (45–50 °C) medium of
about 25 mL was inoculated aseptically with each stan-
dardized inoculum (0.5–1.0 mL) in a laminar air flow unit.
The medium was then poured into previously sterilized
petri-plate to occupy a depth of 4 mm. The plates were left
at room temperature to allow solidification. Sterilized disk
(6-mm diameter) of Whatman filter paper No. 2 impreg-
nated with DMSO was used as negative control. Under
aseptic condition, empty sterilized disks were impregnated
with test drug solutions of two different doses (25–50 lg/
disk) and with vehicle control, DMSO. After solvent
evaporation, the dried disks were placed on the surface of
the agar medium and the plates were left undisturbed for an
hour at room temperature for pre-incubation diffusion to
minimize the effects of variation in time between the
applications of different solution. Ofloxacin was used as
reference standard drug. After incubation of the plates at
37 1 °C for 24 h, the diameters of the zones of complete
inhibition surrounding each of the disk were measured
including the diameter of the disk using a centimeter scale.
Studies were performed in triplicate; mean values with
standard deviation were calculated.
3-(3-(7-chloroquinolin-4-ylamino)propyl)-2-(2-
fluorophenyl)-1,3-thiazinan-4-one, 6a
Light yellow gummy solid, 73 % yield; Rf0.55 (chloro-
form:methanol = 3:1); UV–Visible spectrum (chloroform),
kmax (nm): 262.0, 364.5, 428.0. IR spectrum (chloroform), t,
cm-1: 3340 (N–H str.,[NH); 1698 (C=O str.); 1371, 1275
(C–N str.); 1097 (Ar. C–Cl str.). 1HNMR (300 MHz,
CDCl3), d (ppm): 1.73–1.85 (t, 2H, J = 17.4 Hz, CH2),
2.57–2.61 (t, 2H, J = 6.0 Hz, CH2); 2.67–2.84 (m, 2H,
CH2); 3.16–3.37 (m, 2H, CH2); 5.70 (s, 1H, NH), 6.22–6.23
(d, 1H, J = 4.5 Hz, quinoline-H3); 6.82 7.11 (m, 4H, C6H4–);
7.49–7.55 (dd 1H, J = 8.7 Hz, 5.1 Hz, quinoline-H6);
7.73–7.79 (dd 1H, J = 7.5, 4.8 Hz, quinoline-H5);
7.98–8.00 (d, 1H, J = 6.9 Hz, quinoline-H8); 8.23–8.24 (d,
1H, J = 4.5 Hz, 2H quinoline). 13CNMR (100 MHz,
CDCl3), d (ppm): 25.74 (CH2), 29.59 (CH2), 34.37 (CH2),
39.85 (CH2), 44.78 (CH2), 55.73 (CH), 115.85 (C-2, quino-
line), 116.58 (C-4a, quinoline), 123.07 (C-5, quinoline),
124.08, 124.64, 125.95, 126.63 (Ar–C), 127.63 (C-6, quin-
oline) 128.68 (Ar–C), 130.30 (C-8, quinoline), 132.67 (Ar–
C), 136.37 (C-7, quinoline, C–Cl), 148.16 (C-8a, quinoline),
151.94 (C-2, quinoline), 158.28 (C-4, quinoline), 160.76 (C–
F), 170.70 (C=O). MS (API), m/z (%): 430.2 (100), [M?H]?;
431.1 (25.67), 432.1 (36.45), 433.2 (10.35). Anal. cacld. (%)
for C22H21N3OSClF: C, 61.46; H, 4.92; N, 9.77; found (%):
C, 58. 59; H, 5.65; N, 5.28.
Results and discussion
In this study, new 3-(3-(7-chloroquinolin-4-ylamino)pro-
pyl)-1,3-thiazinan-4-one derivatives were synthesized. The
intermediate, 3, and target products, 6a–g, were obtained in
good yields and high purity. The purity of all compounds
was ascertained by TLC using various solvent combination
of different polarity. The purified compounds were there-
after characterized by IR, 1HNMR, 13CNMR and Mass
spectral data, and elemental analysis. The spectral data
(Silverstein and Webster 2005) are in good agreement with
the structure of the synthesized compounds.
Spectral and analytical data
3-(3-(7-chloroquinolin-4-ylamino)propyl)-2-(4-
N1-(7-chloroquinolin-4-yl)propane-1,3-diamine, 3
methoxyphenyl)-1,3-thiazinan-4-one, 6b
Yellowish white solid, 86 % yield, mp: 96–98 °C, Rf: 0.25
Light yellow gummy solid, 68 % yield; Rf: 0.52 (chloro-
(chloroform:methanol = 1:1);
UV–Visible
spectrum
form:methanol = 3:1); UV–visible spectrum (chloroform),
123

Med Chem Res (2013) 22:3703–3711
3707
3-(3-(7-chloroquinolin-4-ylamino)propyl)-2-(2-furyl)-1,3-
k
max (nm): 277.0, 368.0, 442.0. IR spectrum (chloroform), t,
cm-1: 3435 (N–H str.,[NH); 1734 (C=O str.); 1304, 1296
(C–N str.); 1161, 1046 (tas and tas C–O–C str.); 1080 (Ar.
C–Cl str.). 1HNMR (300 MHz, CDCl3, d (ppm): 1.73–1.88
(m, 2H, CH2), 2.59–2.64 (m, 2H, CH2), 2.66–2.78 (m, 2H,
CH2), 3.11–3.17 (m, 2H, CH2), 3.28–3.41 (m, 2H, CH2),
3.72 (s, 1H, OCH3), 5.43 (s, 1H, NH), 6.24–6.26 (d, 1H,
J = 4.2 Hz, quinoline-H3); 6.80–6.81 (m, 4H, C6H4–),
7.28–7.30 (d, 1H, J = 1.2, 1.2 Hz, quinoline-H6); 7.70–7.73
(d, 1H, J = 10.2 Hz, quinoline-H5); 7.89–7.91 (d, 1H,
J = 6.6 Hz, quinoline-H8); 8.34–8.36 (d, 1H, J = 4.2 Hz,
quinoline-H2). 13CNMR (100 MHz, CDCl3, d (ppm) 25.59
(CH2), 29.68 (CH2), 33.92 (CH2), 39.24 (CH2), 44.35
(CH2), 55.54 (OCH3), 61.76 (CH2), 113.95 (C-3, quinoline)
144.20 (2C), 117.49 (C-4a, quinoline), 122.20 (C-5, quino-
line), 127.77 (C-5, quinoline), 124.34 (C-8, quinoline),
129.83 (2C), 131.99 (Ar–C), 135.13 (C-7, quinoline, C–Cl),
148.52 (C-8a, quinoline), 151.20 (C-2, quionline), 157.17
(C-4, quinoline), 159.59 (Ar–C), 170.78 (C=O). MS (API),
m/z (%): 442.2 (100), [M?H]?; 443.1 (27.45), 444.3
(42.75), 445.2 (10.80). Anal cacld. (%) for C23H24N3O2SCl:
C, 62.50; H, 5.47; N, 9.51; found (%): C, 61.38; H, 6.94; N,
6.76.
thiazinan-4-one, 6d
Light yellow gummy solid, 65 % yield; Rf0.54 (chloro-
form:methanol = 3:1); UV–visible spectrum (chloroform),
k
max (nm): 257.0, 364.0, 426.0. IR spectrum (chloroform), t,
cm-1: 3432 (N–H str.,[NH); (C=O str.); 1375,1305, (C–N
1
str.); 1091 (Ar. C–Cl str.). HNMR (300 MHz, CDCl3, d
(ppm): 1.75–1.87 (m, 2H, CH2), 2.52–2.55 (t, 2H,
J = 4.8 Hz, CH2), 2.70–2.73 (m, 2H, CH2), 3.64–3.78 (m,
2H, CH2), 5.49 (s, 1H, NH), 6.18 (bs, 1H, CH), 6.09–6.12 (m,
2H, furan-2-yl); 6.22–623 (d, 1H, J = 1.2 Hz, quinoline-
H3); 7.25 (bs, 1H, furan–2–yl), 7.29–7.32 (d, 1H,
J = 8.4 Hz, quinoline-H6), 7.60–7.62 (d, 1H, J = 7.2 Hz,
quinoline-H5), 7.97–8.04 (d, 1H, J = 18.3 Hz, quinoline-
H8); (bs, 1H, quinoline-H2). 13CNMR (100 MHz, CDCl3, d
(ppm): 25.47 (CH2), 27.15 (CH2), 35.47 (CH2), 39.39 (CH2),
40.19 (CH2), 67.78 (CH2), 106.99 (C3, furan-2-yl), 110.60
(C4, furan-2-yl), 112.67 (C-3, quinoline); 119.78 (C-4a,
quinoline), 121.70 (C-5, quinoline), 127.17 (C-6, quinoline),
138.66 (C-7, quinoline, C–Cl), 142.33 (C5, furan-2-yl),
148.31 (C-8a, quinoline), 151.69 (C-2, quinoline), 152.25
(C2, furan-2-yl), 154.95 (C-4, quinoline), 170.67 (C=O). MS
(API), m/z (%): 402.1 (100), [M?H]?; 403.1 (24.30), 404.1
(41.40), 405.1 (9.00). Anal. cacld. (%) for C20H20N3O2SCl:
C, 59.77; H, 5.02; N, 10.46; found: C, 51.63; H, 6.11; N, 3.06.
3-(3-(7-chloroquinolin-4-ylamino)propyl)-2-(3-
hydroxyphenyl)-1,3-thiazinan-4-one, 6c
3-(3-(7-chloroquinolin-4-ylamino)propyl)-2-ethyl-1,
Light yellow gummy solid, 62 % yield; Rf0.51 (chloro-
3-thiazinan-4-one, 6e
form:methanol = 3:1); UV–Visible spectrum (chloroform),
kmax (nm): 264.5, 388.0, 416.0. IR spectrum (chloroform), t,
cm-1: 3530 (O–H str., bonded OH); 3430 (N–H str.,[NH);
1310, 1283, (C–N str.), 1215 (C–O str.); 1083 (Ar. C–
Cl.str.). 1HNMR (300 MHz, CDCl3, d (ppm): 1.73–1.81 (m,
2H, CH2), 2.63–2.66 (t, 2H, J = 48 Hz, CH2), 2.67–2.77 (m,
2H, CH2), 3.62–3.66 (t, 2H, J = 72 Hz, CH2), 5.35 (s, 1H,
NH), 6.20–6.21 (d, 1H, J = 4.5 Hz, quinoline-H3);
6.57–6.59 (d, 1H, J = 5.7 Hz, C6H4–), 6.75–6.77 (d, 1H,
J = 6.0 Hz, C6H4–), 7.20–7.22 (d, 1H, J = 3.9 Hz, quino-
line-H6), 7.78 (s, 1H, OH), 7.88–7.90 (d, 1H, J = 6.6 Hz,
quinoline-H5), 8.19–8.20 (d, 1H, J = 4.2 Hz, quinoline-H8),
8.46 (bs, 1H, quinoline-H2). 13CNMR (100 MHz, CDCl3, d
(ppm): 24.85 (CH2), 29.66 (CH2), 33.74 (CH2), 39.96 (CH2),
45.13 (CH2), 62.25 (CH2), 113.86 (C-3, quinoline); 115.47
(2C), 116.58 (C-4a, quinoline) 121.75 (Ar–C), 122.48 (C-5,
quinoline), 126.29 (C-5, quinoline), 129.90 (C-8, quinoline),
130.10 (Ar–C), 136.94 (C-7, quinoline, C–Cl), 139.80
(Ar–C), 147.58 (C-8a, quinoline), 152.41 (C-2, quinoline),
153.76 (C-4, quinoline), 158,14 (Ar–C), 171.25 (C=O). MS
(API), m/z (%): 428.2 (100), [M?H]?; 429.2 (27.45 %),
433.2 (40.50), 433.1 (10.75). Anal. cacld. (%) for
C22H21N3O2SCl: C, 61.74; H, 5.18; N, 9.82; found (%):
C, 62.67; H, 7.16; N, 4.43.
Light yellow gummy solid, 74 % yield; Rf0.49 (chloro-
form:methanol = 3:1); UV–visible spectrum (chloroform),
kmax (nm): 255.0, 350.0, 419.0. IR spectrum (chloroform),
t, cm-1: 3422 (N–H str., [NH); 1719 (C=O str.); 1398,
1283 (C–N str.); 1074 (Ar. C–Cl str.). 1H NMR (300 MHz,
CDCl3), d (ppm): 0.96–0.98 (t, 3H, J = 2.1 Hz, CH3),
1.75–1.79 (m, 2H, CH2), 1.91-1.96 (dd, 2H, J = 5.1,
4.8 Hz, CH2), 2.54–2.59 (m, 2H, CH2), 2.60–2.77 (m, 2H,
CH2), 3.07–3.12 (dd, 2H, J = 4.8, 4.8 Hz, CH2), 3.65–3.68
(t, 2H, J = 4.8 Hz, CH2), 4.26–4.30 (t, 1H, J = 5.4 Hz,
CH), 6.35–6.37 (d, 1H, J = 5.1 Hz, quinoline-H3); 6.77
(bs, 1H, NH), 7.24–7.32 (dd, 1H, J = 6.6, 17.7 Hz, quin-
oline-H6); 7.88 (d, 1H, J = 0.9 Hz, quinoline-H5),
8.06–8.09 (d, 1H, J = 6.9 Hz, quinoline-H8); 8.28–8.30 (d,
1H, J = 4.8 Hz, quinoline-H2). 13CNMR (100 MHz,
CDCl3, d (ppm): 11.45 (CH3), 25.54 (CH2), 27.78 (CH2),
30.85 (CH2), 36.07 (CH2), 39.61 (CH2), 40.56 (CH2),
67.89(CH2), 115.58 (C-3, quinoline), 120.87 (C-4a, quin-
oline), 123.90 (C-5, quinoline), 127.16 (C-6, quinoline),
138.62 (C-8, quinoline), 139.92 (C-7, quinoline, C–Cl),
143.97 (C-8a, quinoline), 154.52 (C-2, quinoline), 157.58
(C-4, quinoline), 170.41 (C=O). MS (API), m/z (%): 364.1
123

3708
Med Chem Res (2013) 22:3703–3711
(100), [M?H]?; 365.1 (22.95), 366.1 (41.25), 367.0 (8.72).
Anal. cacld. (%) for C18H22N3OSCl: C, 59.41; H, 6.09; N,
11.55; found (%): C, 52.13; H, 7371; N, 4.13.
115.51 (2C) 124.93 (C-5, quinoline), 127.43 (C-6, quinoline),
128.34 (C-8 quinoline), 131.75 (2C), 132.26 (C-7, quinoline
C–Cl), 149.87 (C-8a, quinoline), 154.19 (C-2, quinoline),
157.63 (C-4, quinoline), 169.80 (C=O). MS (API), m/z (%):
432.1 (100), [M?H]?; 433.1 (27.90), 434.2 (41.85), 435.2
(10.80). Anal. cacld. (%) for C27H27N4OSCl: C, 58.29; H,
5.13; N, 9.73; found (%): C, 56.24; H, 6.50; N, 7.36.
3-(3-(7-chloroquinolin-4-ylamino)propyl)-2-(4-
(dimethylamino)phenyl)-1,3-thiazinan-4-one, 6f
All the compounds in chloroform exhibited three char-
acteristic absorption maxima (kmax) in the range between
220 and 450 nm. The shift of kmax toward longer wavelength
indicate the presence of strong chromophoric group such as
quinoline ring, and C=O group in the molecule. The maxima
in the lower wavelength range between 220 and 280 nm is
due to the presence of substituted phenyl ring, and hetero-
aromatic ring system such as furan-2-yl (6d), thiophen-2-yl
(6g). The infrared spectral data showed characteristic
absorption bands for [NH (3,340–3,435 cm-1); C=O
(1,693–1,734 cm-1); C–N (1,275–1,398 cm-1); C–Cl
(1,074–1,097 cm-1);[CH2 (tas: 2,976–2,930 cm-1 and ts:
Reddish yellow gummy solid, 69 % yield; Rf: 0.56 (chloro-
form:methanol = 3:1); UV–visible spectrum (chloroform),
k
max (nm): 279.0, 392.0, 447.0. IR spectrum (chloroform), t,
cm-1: 3435 (N–H str., [NH); 1719 (C=O str.); 1336 (C–N
1
str.), 1074 (Ar. C–Cl str.). HNMR (300 MHz,CDCl3), d
(ppm):1.79–1.83(t, 2H, J = 5.4 Hz, CH2), 2.50–2.57(m, 2H,
CH2), 2.95 (s, 6H, NMe2), 3.22–3.25 (t, 2H, J = 4.5 Hz,
CH2), 3.30–3.47 (m, 2H, CH2), 6.03 (bs, 1H, NH), 6.24–6.26
(d, 1H, J = 6.3 Hz, quinoline-H3), 6.67–6.69 (d, 1H,
J = 60 Hz, C6H4–), 6.86–6.88 (d, 1H, J = 5.7 Hz, C6H4–),
7.26–7.28 (d, 1H, J = 6.3 Hz, quinoline-H6), 7.42–7.49 (dd,
1H, J = 11.7, 3.3 Hz, quinoline-H5), 7.79–7.87 (dd, 1H,
J = 5.7, 6.3 Hz, quinoline-H8), 7.92–7.95 (t, 1H, J = 5.1 Hz,
quinoline-H2). 13CNMR (100 MHz, CDCl3), d (ppm): 20.88
(C4H2SMe), 26.88 (CH2), 29.57 (CH2), 36.52 (CH2), 40.07
(CH2), 44.65 (CH2), 63.53 (CH2), 102.79 (C-3, quinoline),
120.71 (C-4a, quinoline), 122.32 (C-5, quinoline, 125.99
(2C), 129.61(C-6, quinoline), 132.20(C-8, quinoline), 136.75
(C-7, quinoline), C–Cl), 139.47 (C5, thiophen-2-yl), 141.77
(C2, thiophen-2-yl), 148.37 (C-8a, quinoline), 151.87 (C-2,
quinoline);156.24 (C-4, quinoline), 174.37(C=O). MS(API),
m/z (%): 455.2 (100), [M?H]?; 456.2 (30.15), 457.2 (39.6),
458.2 (11.70). Anal cacld. (%) for C24H27N4OSCl: C, 63.35;
H, 5.98; N, 12.31; found (%): C, 58.92; H, 7.21; N, 5.36.
2,819–1,863 cm-1), and aromatic C=C (1,432–1,657 cm-1
)
stretching which confirms the anticipated structure of the
synthesized compounds, 6a–g. The assignment of protons is
fully supported by the characteristic chemical shift values
for the 4-aminoquinoline nucleus. The assignment of 13C
resonance for different carbon atoms of quinoline nucleus,
[CH2 group of side chain and C=O of 1, 3-thiazinan-4-one
ring system is in close agreement with the structures of the
synthesized compounds. The prominent molecular ion
peaks, [M?H]? for all the compounds, are in accordance
with the anticipated mass of 6a–g. The structures of syn-
thesized compounds were further established by elemental
analysis. The results of CHN analyses were within the
acceptable limits of the calculated values.
3-(3-(7-chloroquinolin-4-ylamino)propyl)-2-(5-
methylthiophen-2-yl)-1,3-thiazinan-4-one, 6g
Antimalarial screening
Reddish yellow gummy solid, 66 % yield; Rf: 0.58 (chloro-
Though all the seven synthesized compounds showed anti-
malarial activity against chloroquine-sensitive P. falcipa-
rum (3D7) strain at the tested dose, all the compounds were
found to be much less potent than the standard drug, chlo-
roquine. However, the compounds with 2-fluorophenyl (6a),
4-methoxyphenyl (6b), 3-hydroxyphenyl (6c), furan-2-yl
(6d) substitution at 2-position of 1,3-thiazinan-4-one ring
system attached with the terminal propyl side chain of
7-chloro-4-aminoquinoline nucleus showed comparatively
better activity than compounds with ethyl (6e), 4-(dimeth-
ylamino)phenyl (6f), 5-methylthiophen-2-yl (6g) moieties at
the side chain. The results clearly reveal that a bulky group
with optimal lipophilicity at 1,3-thiazinan-4-one ring in the
side chain might be an important requirement for the
antimalarial activity of prepared 3-(3-(7-chloroquinolin-
4-ylamino)propyl)-1,3-thiazinan-4-one derivatives. The
in vitro antimalarial activity data are shown in Table 1.
form:methanol = 3:1); UV–visible spectrum (chloroform),
k
max (nm): 282.0, 381.5, 422.0. IR spectrum (chloroform), t,
cm-1: 3435 (N–H str.,[NH); 1719 (C=O str.); 1390, (C–N
1
str.); 1,077 (Ar. C–Cl. str). HNMR (300 MHz, CDCl3), d
(ppm): 1.66–1.77 (t, 2H, J = 9.3 Hz, CH2), 2.25 (s, 3H, CH3),
2.63–2.67 (t, 2H, J = 4.8 Hz, CH2), 2.79–2.82 (t, 2H,
J = 4.8 Hz, CH2), 3.03–3.05 (d, 2H, J = 5.4 Hz, CH2),
3.44–3.3.47 (t, 2H, J = 4.5 Hz, CH2), 6.38 (bs, 1H, NH),
6.60–6.69 (dd, 1H, J = 7.8 Hz, 12.6 Hz, quinoline-H3), 6.75
(s, 2H, thiophen 2-yl), 7.37–7.49 (dd, 2H, J = 18.6, 6.0 Hz,
6H quinoline), 7.60–7.89 (dd, 1H, J = 29.1 Hz, 36.0 Hz,
quinoline-H5), 8.04–8.15 (dd, 1H, J = 6.9, 24.0 Hz, quino-
line-H8), 8.21–8.69 (dd, 1H, J = 22.5, 82.8 Hz, quinoline-
H2). 13CNMR (100 MHz, CDCl3), d (ppm): 25.38 (CH2),
29.11(CH2), 35.62 (CH2), 39.80 (–NMe2), 40.30 (CH2), 66.72
(CH2), 112.01 (C-3, quinoline), 116.20 (C-4a, quinoline),
123

Med Chem Res (2013) 22:3703–3711
3709
compounds. Among synthesized compounds, compounds
with aromatic bulky substituents such as 2-fluorophenyl-
(6a), 4-methoxyphenyl-(6b), 3-hydroxyphenyl-(6c),
furan-2-yl (6d), 4- (dimethylamino)phenyl-(6f), 5-meth-
ylthiophen-2-yl (6g) were found to be more active than
that of compound with aliphatic alkyl substituent (ethyl in
2e) at C-2 position of 1,3-thiazinan ring system.
Table 1 In vitro antimalarial activity data
Comp. code
Dosage (lg/mL)
% Dead rings ? trophozoitesa
6a
50
50
50
50
50
50
50
0.4
39.0
32.0
39.5
38.5
18.5
25.0
22.0
67.0
6b
6c
6d
6e
6f
Correlation between antimalarial activity
and lipophilicity (logP)
6g
Chloroquineb
Furthermore, the antimalarial activity of the synthesized
compounds was correlated with lipophilicity, i.e., logP
values. The logP values of synthesized compounds obtained
from Chem Draw Ultra 8.0 2004 software are shown in
Table 3. The correlation study clearly demonstrate that
compounds containing aromatic bulky (heavier) substitu-
ents such as 6g (5-methylthiophen-2-yl, logP = 6.15) and 6f
(4-(dimethylamino)phenyl, logP = 4.44) possess slight
higher lipophilicity (i.e., logP values) as compared to com-
pounds that contain comparatively less bulkier substituents
such as 6d (2-furyl, logP = 4.45), 6a (2-fluorophenyl,
logP = 4.31), and 6b (4-methoxyphenyl, logP = 4.03). As
a consequence, a slight increased activity was seen for
compounds (6a, 6b) which possess comparatively lower
Test strain: Chloroquine-sensitive P. falciparum (3D7)
a
Mean of two replicates and counted against 400 asexual parasites
per replicate
b
Reference standard
Antibacterial screening
The results depicted in Table 2 clearly reveal that all the
synthesized compounds at the tested dose showed antibac-
terial activity and were equally active with some degree
of variations, but were less active as compared to the stan-
dard drug, ofloxacin (5 lg/disk). However, no obvious dif-
ference in susceptibility was found between Gram-positive
and Gram-negative bacterial strains for all the tested
Table 2 Antibacterial activity data
Compd.
code
Dose
(lg/disk)
Diameter of zone of inhibition (mm SD)a
B. s ATCC
11774
B. c ATCC
10876
S. a ATCC BAA
1026
E. c ATCC
10536
K. p ATCC
33495
P. a ATTCC
10662
6a
6b
6c
6d
6e
6f
50
25
50
25
50
25
50
25
50
25
50
25
50
25
5
23.66 0.57
18.83 0.28
23.30 0.50
14.16 0.28
23.83 0.28
13.83 0.28
23.50 0.50
14.06 0.11
23.16 0.28
13.06 0.11
23.66 0.11
14.26 0.30
23.93 0.11
14.20 0.20
20.66 0.25
Nil
24.26 0.28
14.26 0.28
24.40 0.20
14.33 0.11
23.66 0.28
14.06 0.11
23.80 0.20
14.16 0.15
23.60 0.20
13.53 0.11
24.26 0.23
14.00 0.20
24.23 0.20
13.93 0.11
20.33 0.57
Nil
23.93 0.11
14.16 0.15
24.06 0.11
14.13 0.11
24.06 0.11
14.26 0.23
24.20 0.20
14.33 0.11
23.06 0.11
12.93 0.11
23.86 0.11
13.86 0.11
23.93 0.23
14.00 0.20
21.66 0.57
Nil
24.36 0.32
14.33 0.23
24.40 0.20
14.23 0.05
24.33 0.11
13.93 0.11
24.06 0.11
14.00 0.20
23.40 0.10
13.66 0.11
23.93 0.11
14.26 0.30
24.13 0.23
14.20 0.20
21.50 0.50
Nil
24.16 0.11
14.33 0.30
24.20 0.20
14.06 0.11
24.20 0.12
14.00 0.20
24.13 0.11
14.16 0.15
23.13 0.23
13.23 0.05
24.06 0.30
14.06 0.30
23.93 0.11
13.86 0.11
20.33 0.57
Nil
24.20 0.20
14.06 0.11
24.06 0.11
14.33 0.11
23.90 0.36
13.86 0.11
23.83 0.28
13.73 0.11
23.06 0.11
13.46 0.11
23.66 0.11
13.73 0.11
23.73 0.11
13.86 0.11
20.83 0.28
Nil
6g
Ofloxacinb
DMSOc
–
B. s, Bacillus subtilis; B. c, Bacillus cereus; S. a, Staphylococcus aureus; E. c, Escherichia coli; K. p, Klebsiella pneumoniae; P. a, Pseudomonas
aeruginosa
a
Values are mean inhibition zone (mm SD) of three replicates
b
Ofloxacin, 5 lg/disk was used as positive reference standard
c
DMSO was used as vehicle control
123

3710
Med Chem Res (2013) 22:3703–3711
N E Region, Dibrugarh, for providing antimalarial screening facility.
Technical assistance provided by Mr. B. K. Goswami, Mr. Devojit
Kr. Sarma, and Dr. Kanta Bhattacharya, in antimalarial screening is
gratefully acknowledged.
Table 3 LogP values of synthesized compounds
Comp. code
R
LogPa
6a
6b
6c
6d
6e
6f
6g
a
2-Fluorophenyl-
4-Methoxyphenyl-
3-Hydroxyphenyl-
Furan-2-yl-
4.31
4.03
3.77
4.45
3.07
4.44
6.15
References
Ethyl-
Casteel DA (2003) Antimalarial agents. In: Abraham DJ (ed)
Burger’s medicinal chemistry and drug discovery, 5th edn.
Wiley Interscience, New York, p 920
Chiang PK, Bujnicki JM, Su S, Lanar DE (2006) Malaria: therapy
genes and vaccines. Curr Mol Med 6(3):309
4-(Dimethylamino)phenyl-
5-Methyl-thiophen-2-yl-
Obtained using Chem Draw Ultra 8.0 2004 software
Chou AC, Chevli R, Fitch CD (1980) Ferriprotoporphyrin IX fulfills
the criteria for identification as the chloroquine receptor of
malaria parasites. Biochemistry 19:1543–1549
Collee JG, Duguid JP, Fraser MG, Marmion BP, McCartney M
(1989) Practical medical microbiology, 13th edn. Churchill
Livingstone, London
Dorn A, Stoffel R, Matile H, Bubendorf A, Ridley RG (1995)
Malarial hemozoin/b-hematin supports haem polymerization in
the absence of protein. Nature 374:269–271
Egan TJ, Marques HM (1999) The role of haem in the activity of
chloroquine and related antimalarial drugs. Coord Chem Rev
190–192:493–517
Farooq U, Mahajan RC (2004) Drug resistance in malaria. J Vector
Borne Dis 41:45
Foley M, Tilley L (1998) Quinoline antimalarials: mechanism of
action and resistance and prospects for new agents. Pharmacol
Ther 79(1):60–67
Gillies HM (2000) Management of severe malaria: a practical
handbook, 2nd edn. WHO, Geneva
Goker H, Kus C, Boykin DW, Yildiz S, Altanlar N (2002) Synthesis
of some new 2-substituted-phenyl-1H-benzimidazole-5-carboni-
triles and their potent activity against Candida species. Bioorg
Med Chem 10:2589–2596
logP values than other compounds like 6f and 6g. Moreover,
compound, 6e with non-aromatic alkyl substitution (ethyl,
logP = 3.07) showed lowest activity in this series, which
could be attributed due to its very low logP value than that of
optimum value. Form this study, it could be finally assumed
that the presence of a lipophilic bulky group at C-2 position
of 1,3-thiazinan-4-one ring system might be a requirement
for the antimalarial activity of synthesized compounds,
despite the lipophilicity of compound should be such that
compound’s activity-lipophilic property would be appro-
priately balanced (optimum). However, it is obvious that not
only the lipophilicity but also the sufficient basicity (pKa) of
the molecule (Solomon et al., 2007) is another important
requirement for the antimalarial activity of newly synthe-
sized 4-aminoquinoline derivatives.
Conclusion
He Y, Wu B, Yang J, Robinson D, Risen L, Ranken R, Blyh L, Sheng
S, Swayze EE (2003) 2-Piperidin-4-yl-benzimidazoles with
broad spectrum antibacterial activities. Bioorg Med Chem Lett
13:3253–3256
Hewitt W (2004) Microbiological assay for pharmaceutical analysis:
a rational approach. Interpharm/CRC, New York
Lambros C, Vanderberg JPJ (1979) Synchronization of Plasmodium
falciparum erythrocytic stages in culture. Parasitology 65:
418–420
The present investigation describes the synthesis, antima-
larial-, and antibacterial activity of some novel 4-amino-
quinoline derivatives. The structures of the synthesized
compounds were confirmed by spectral and analytical data.
All the compounds at the tested dose exhibited antimalarial
activity which was much inferior to the standard drug,
chloroquine. Compounds were also found to be active
against all the tested bacterial strains at the tested dose, but
were less active as compared to the standard drug, ofloxacin.
The results clearly demonstrate that the presence of a bulky
group with optimal lipophilicity at 1,3-thiazinan-4-one ring
system attached to the terminal propyl side chain of 7-chloro-
4-aminoquinoline nucleus may be an important requirement
for the antimalarial activity of synthesized compounds.
Furthermore, aromatic bulky substituents have greater con-
tributing effect than the aliphatic non-bulky group toward the
antibacterial activity of 4-aminoquinoline derivatives.
Madrid PB, Wilson NT, DeRisi JL, Guy RK (2004) Parallel synthesis
and antimalarial screening of
J Comb Chem 6:437–442
a 4-aminoquinoline library.
Pandey AV, Bisht H, Babbarwal VK, Srivastava J, Pandey KC,
Chauhan VS (2001) Mechanism of malarial haem detoxification
inhibition by chloroquine. Biochem J 355:333–338
Ridley R (2002) Medical need, scientific opportunity and the drive for
antimalarial drugs. Nature 415:686–693
Silverstein RM, Webster FX (2005) Spectrometric identification of
organic compounds, 6th edn. Wiley, New York
Solomon VR, Haq W, Srivastava K, Puri SK, Katti SB (2005) Design
and synthesis of new antimalarial agents from 4-aminoquinoline.
Bioorg Med Chem 13:2157–2165
Solomon VR, Puri SK, Srivastava K, Katti SB (2007) Synthesis and
antimalarial activity of side chain modified 4-aminoquinoline
derivatives. J Med Chem 50:394–398
Sullivan DJ, Gluzman IY, Russell DG, Goldberg DE (1996) On the
molecular mechanism of chloroquine’s antimalarial action. Proc
Natl Acad Sci USA 93:11865–11870
Acknowledgments The authors thank M/s Mangalam Drugs &
Organics Ltd., Mumbai, for supplying gift sample of 4,7-dichloro-
quinoline; Director, SAIF, NEHU, Shillong, for recording the spectral
data of the compounds, and Dr. J. Mahanta, Director, R M R C (I C M R),
123

Med Chem Res (2013) 22:3703–3711
3711
Talisuna AO, Loland P, Alessandro UD (2004) History, dynamics,
and public health importance of malaria parasite resistance. Clin
Microbiol Rev 17(1):236
Tilley L, Loria P, Foley M (2001) Chloroquine and Other Quinoline
Antimalarials. In: Rosenthal PJ (ed.) Antimalarial Chemother-
apy: mechanisms of action, resistance, and new directions in
drug discovery. Humana, New Jersey, pp 89–99, pp 103–105
Trager W, Jensen JB (1976) Human malaria parasites in continuous
culture. Science 193:673–675
White WJ (2008) Plasmodium knowlesi: the fifth human malaria
parasite. Clin Infect Dis 46:172
Wiesner J, Ortmann R, Schlitzer M (2003) New antimalarial drugs.
Angew Chem Int Ed Engl 42:5274
World Health Organization (1998) http://www.rbm.who.int/ what is
malaria? Roll back malaria. World Health Organization, Geneva.
Accessed 25 April 2009
123