In vitro antischistosomal evaluation of some newly synthesized praziquantel derivatives

Article abstract of DOI:10.1007/s11164-012-0854-9

Praziquantel, 2-(cyclohexylcarbonyl)-1,2,3,6,7,11b-hexahydro-4H-pyrazino[2, 1-a]isoquinolin-4-one, was used as the parent starting material to synthesize a new series of praziquantel-3-arylidene derivatives 1a-c and praziquantel-Mannich bases 2a-d, hoping to obtain new antischistosomal compounds of more activity and lower adverse effects. The antischistosomal activity of the newly synthesized compounds was evaluated using in vitro Schistosoma mansoni worm killing tests. Both compounds 2c and 2d exhibited significant in vitro antischistosomal activity and may offer promising use as an antischistosomal drug either alone or in combination with praziquantel.

Full text of DOI:10.1007/s11164-012-0854-9

Res Chem Intermed
DOI 10.1007/s11164-012-0854-9
In vitro antischistosomal evaluation of some newly
synthesized praziquantel derivatives
•
•
•
M. M. Kamel M. M. Anwar A. M. Soliman
H. F. Abdel-Hamid
Received: 24 July 2012 / Accepted: 5 October 2012
Ó Springer Science+Business Media Dordrecht 2012
Abstract Praziquantel, 2-(cyclohexylcarbonyl)-1,2,3,6,7,11b-hexahydro-4H-pyr-
azino[2,1-a]isoquinolin-4-one, was used as the parent starting material to synthesize
a new series of praziquantel-3-arylidene derivatives 1a–c and praziquantel–Man-
nich bases 2a–d, hoping to obtain new antischistosomal compounds of more activity
and lower adverse effects. The antischistosomal activity of the newly synthesized
compounds was evaluated using in vitro Schistosoma mansoni worm killing tests.
Both compounds 2c and 2d exhibited significant in vitro antischistosomal activity
and may offer promising use as an antischistosomal drug either alone or in com-
bination with praziquantel.
Keywords Praziquantel ꢀ Arylidene derivatives ꢀ Mannich bases ꢀ
Antischistosomal evaluation ꢀ Schistosoma mansoni
Introduction
Schistosomiasis is the second most prevalent parasitic disease worldwide after
malaria, with about 200 million human beings infected in 74 countries. It is
estimated that 779 million people are at risk of contracting schistosomiasis and
more than 200 million individuals are infected, with more than half of them
suffering from disease-associated symptoms [1–3]. Severe disease manifestations
are exhibited in about 20 million individuals [4]. The annual mortality rate due to
schistosomiasis in sub-Saharan Africa might be as high as 280,000 [5]. Chemo-
therapeutic measures have been the mainstay for the control of schistosomiasis [6],
M. M. Kamel ꢀ M. M. Anwar (&) ꢀ A. M. Soliman
Therapeutical Chemistry Department, National Research Centre, Dokki, Cairo, Egypt
e-mail: Manalhassan232@ymail.com
H. F. Abdel-Hamid
Chemistry of Pesticides Department, National Research Centre, Dokki, Cairo, Egypt
123

M. M. Kamel et al.
and, since the 1970s, praziquantel (PZQ) has become the drug of choice against the
three major human species of schistosomes, Schistosoma mansoni, S. haematobium,
and S. japonicum [7, 8]. PZQ is a relatively safe, orally administered drug that leads
to reduction in the prevalence of schistosomiasis [9, 10]. Mass drug administration
programs currently rely heavily on PZQ for the control of schistosome-induced
morbidity. However, with only one drug of choice for treatment and with the
possibility of development of parasite resistance, the present situation is dangerous.
There is a real and pressing need for discovering alternatives to the only available
antischistosomal drug worldwide [11, 12].
In this investigation, we synthesized new praziquantel–arylidene derivatives 1a–c
and praziquantel–Mannich bases 2a–d, which were evaluated to assess their
potential for in vitro antischistosomal activities (Scheme 1).
Experimental
Chemistry
All reagents and solvents were of general reagent grade and used without further
purification. Praziquantel is a product of Bayer. All melting points were uncorrected
and measured using an Electro-thermal IA 9100 apparatus (Shimadzu, Japan).
Microanalytical data were performed by Vario El-Mentar apparatus (Shimadzu,
Japan), National Research Centre (NRC), Cairo, Egypt. The found values were
within 0.4 % of the theoretical values. IR spectra (KBr) were recorded on a
1
Perkin-Elmer 1650 spectrophotometer (Japan), NRC, Cairo, Egypt. H-NMR and
13C-NMR spectra were determined on a Varian Mercury (300 MHz) spectrometer
(Varian, UK) and the chemical shifts were expressed in d ppm relative to TMS as an
internal reference, Faculty of Science, Cairo University, Egypt. Mass spectra were
recorded at 70 eV on an EI Ms-QP 1000 EX instrument (Shimadzu, Japan), Faculty
of Science, Cairo University, Egypt. TLC was performed on silica gel 60 254F
plates (Merck) using a mixture of chloroform and ethanol (15:1, v/v) as an eluent,
UV light at k 254, and iodine accomplished visualization.
Synthesis
General procedure for preparation of 2-(cyclohexylcarbonyl)-3-substituted
arylidene 1,2,3,6,7,11b-hexahydro-4H-pyrazino[2,1-a]isoquinolin-4-one (1a–c)
A mixture of praziquantel (20 mmol) and different aromatic aldehydes, namely,
benzaldehyde, p-methoxy benzaldehyde, and thiophene-2-carboxaldehyde
(20 mmol), in 5 % ethanolic sodium hydroxide solution (40 mL) was refluxed
with continuous stirring for 3 h. The reaction mixture was neutralized with diluted
HCl. The obtained solid was filtered and re-crystallized from isopropyl alcohol/
petroleum ether to give the arylidene derivatives 1a–c.
123

In vitro antischistosomal evaluation
N
N
O
O
PZQ
i
ii
N
N
O
N
N
O
R
Ar
O
O
2
1
a
b
c
S
d
Ar
R
OCH3
N(CH2CH2CH3)2
N
NCH2CH2OH
N
N
Reaction conditions:i:10 % NaOH, ethanol, appropriate aldehydes, reflux for 3 h.
ii: paraformaldehyde, appropriate amines, absolute ethanol, reflux, 6-9 h.
Scheme 1 Synthesis of praziquantel–arylidene derivatives 1a–c and praziquantel–Mannich bases 2a–d
2-(Cyclohexylcarbonyl)-3-benzylidene-1,2,3,6,7,11b-hexahydro-4H-pyrazino[2,1-
a]isoquinolin-4-one (1a)
Yield: 60 %; mp 290 °C; IR (KBr, cm-1): 3012 (CH, aromatic), 1710, 1650 (2CO);
1H-NMR (CDCl3, d ppm): 1.21 (s, 11H, cyclohexyl ring), 2.75–2.90 (2 m, 4H,
C7–H2, C6–H2), 3.10, 3.42 (2d, 2H, C1–H2), 5.11 (m, 1H, C11b–H), 5.62 (s, 1H,
–C=CH–), 7.21–8.00 (m, 9H, aromatic-H); 13C-NMR (DMSO-d6, d ppm): 170.1,
123

M. M. Kamel et al.
160.5, 143.3, 136.4, 135.2, 128.9, 128.4, 127.6, 127.0, 126.1, 125.3, 122.1, 116.3,
54.2, 52.3, 43.2, 42.3, 29.2, 27.2, 24.4. MS m/z: 400 (M?.) (10 %). Analysis for
C26H28N2O2 (400.22): Calcd.: C, 77.97; H, 7.05; N, 6.99; Found: C, 77.50; H, 6.78;
N, 6.52.
2-(Cyclohexylcarbonyl)-3-(4-methoxybenzylidene)-1,2,3,6,7,11b-hexahydro-4H-
pyrazino[2,1-a]isoquinolin-4-one (1b)
Yield: 75 %; mp 300 °C; IR (KBr, cm-1): 3012 (CH, aromatic), 1700, 1655 (2CO);
1H-NMR (CDCl3, d ppm): 1.21 (s, 11H, cyclohexyl ring), 2.75–2.90 (2 m, 4H, C7–
H2, C6–H2), 3.10, 3.42 (2d, 2H, C1–H2), 3.75 (s, 3H, OCH3), 5.11 (m, 1H, C11b–H),
5.62 (s, 1H, –C=CH–), 7.21–8.00 (m, 8H, aromatic-H); 13C-NMR (DMSO-d6, d
ppm): 171.2, 160.5, 159.8, 136.2, 135.1, 128.0, 127.4, 127.1, 127.0, 125.8, 121.1,
114.5, 56.6, 53.2, 45.2, 42.0, 40.1, 29.7, 27.3, 26.9, 24.2; MS m/z: 430 (M?.)
(10 %). Analysis for C27H30N2O3 (430.23): Calcd.: C, 75.32; H, 7.02; N, 6.51;
Found: C, 75.84; H, 7.45; N, 6.10.
2-(Cyclohexylcarbonyl)-3-(thiophen-2-methylene)-1,2,3,6,7,11b-hexahydro-4H-
pyrazino[2,1-a]isoquinolin-4-one (1c)
Yield: 70 %, mp 298 °C; IR (KBr, cm-1): 3032 (CH, aromatic), 1700, 1655 (2CO);
1H-NMR (CDCl3, d ppm): 1.21 (s, 11H, cyclohexyl ring), 2.75–2.90 (2 m, 4H,
C7–H2, C6–H2), 3.10, 3.42 (2d, 2H, C1–H2), 5.11 (m, 1H, C11b–H), 5.62 (s, 1H,
–C=CH–), 7.21–8.00 (m, 7H, aromatic-H). 13C-NMR (DMSO-d6, d ppm): 171.2,
160.5, 136.2, 135.3, 135.1, 130.4, 134.0, 128.2, 127.4, 127.1, 127.0, 125.8, 114.2,
54.2, 53.1, 42.2, 41.1, 29.5, 27.6, 26.3, 24.3; MS m/z: 405 (M-1)?. (10 %). Analysis
for C24H26N2O2S (406.17): Calcd.: C, 70.90; H, 6.45; N, 7.89; S, 7.89; Found:
C, 70.46; H, 6.12; N, 8.21; S, 7.40.
General procedure for preparation of 2-(cyclohexylcarbonyl)-3-alkyl/cycloalkyl
aminomethyl 1,2,3,6,7,11b-hexahydro-4H-pyrazino[2,1-a]isoquinolin-4-one (2a–d)
A solution mixture of p-formaldehyde (0.90 g, 10 mmol) and the appropriate amine,
namely, 4-methylpiperazine, 4-methylpiperidine, dipropylamine, and 2-aminoeth-
anol (15 mmol), was refluxed in absolute ethanol (20 mL) for 30 min till complete
solubilization of p-formaldehyde. Then, a solution of praziquantel (4.6 g, 15 mmol)
in absolute ethanol (10 mL) was added to the previous mixture and refluxed for 8 h.
Upon cooling the reaction mixture, the obtained product was filtered and re-
crystallized from dioxane to give the corresponding Mannich bases 2a–d.
2-2-(Cyclohexylcarbonyl)-3-((4-methylpiperazin-1-yl)methyl)-1,2,3,6,7,11b-
hexahydro-4H-pyrazino[2,1-a]isoquinolin-4-one (2a)
Yield: 60 %; mp 120 °C; IR (KBr, cm-1): 3030 (CH, aromatic), 1710, 1665 (2CO);
1H-NMR (CDCl3, d ppm): 1.25 (s, 11H, cyclohexyl ring), 2.25 (s, 3H, CH3 of
piperazine), 2.40 (t, J = 7.2 Hz, 4H, CH2 of piperazine), 2.42 (t, J = 7.2 Hz, 4H,
123

In vitro antischistosomal evaluation
CH2 of piperazine), 2.75–2.90 (2 m, 4H, C7–H2, C6–H2), 4.83–4.93 (dd, 1H,
J = 11.5 Hz, 5.2 Hz, C1–H), 5.11–5.14 (m, 1H, C11b–H ? 2H, N–CH2 ? 1H,
C3–H), 5.15–5.30 (dd, 1H, J = 11.0 Hz, 5.0 Hz, C1–H), 7.21–7.81 (m, 4H,
aromatic-H); 13C-NMR (DMSO-d6, d ppm): 173.2, 165.1, 136.1, 135.3, 127.5,
127.2, 125.1, 58.4, 55.2, 53.3, 53.0, 52.3, 43.1, 42.9, 41.1, 36.1, 29.3, 27.6, 26.9,
24.3; MS m/z: 424 (M?.) (15 %). Analysis for C25H36N4O2 (424.28): Calcd.:
C, 70.72; H, 8.55; N, 13.20; Found: C, 70.24; H, 8.00; N, 12.90.
2-(Cyclohexylcarbonyl)-3-((4-methylpiperidin-1-yl)methyl)-1,2,3,6,7,11b-
hexahydro-4H-pyrazino[2,1-a]isoquinolin-4-one (2b)
Yield: 65 %, mp 110 °C; IR (KBr, cm-1): 3025 (CH, aromatic), 1698, 1665 (2CO).
1H-NMR (CDCl3, d ppm): 1.25 (s, 11H, cyclohexyl ring), 2.27 (s, 3H, CH3),
2.410–2.63 (m, 5H, piperidine protons), 2.71 (t, J = 5.2 Hz, 4H, CH2–N–CH2
piperidine protons), 2.75–2.90 (2 m, 4H, C7–H2, C6–H2), 4.83–4.93 (dd, 1H,
J = 11.5 Hz, 5.2 Hz, C1–H), 5.11–5.14 (m, 1H, C11b ? 2H, N–CH2 ? 1H, C3–H),
5.15–5.30 (dd, 1H, J = 11.0 Hz, 5.0 Hz, C1–H), 7.21–7.81 (m, 4H, aromatic-H);
13C-NMR (DMSO-d6, d ppm): 173.2, 165.1, 136.1, 135.3, 127.5, 127.2, 125.1, 58.4,
53.3, 53.0, 51.4, 42.9, 41.1, 36.1, 32.5, 29.3, 27.6, 26.9, 24.3, 20.4; MS m/z: 424
(M ? 1)?. (20 %). Analysis for C26H37N3O2 (423.29): Calcd.: C, 73.72; H, 8.80;
N, 9.92; Found: C, 74.12; H, 8.42; N, 9.54.
2-(Cyclohexylcarbonyl)-3-dipropylaminomethyl-1,2,3,6,7,11b-hexahydro-4H-
pyrazino[2,1-a]isoquinolin-4-one (2c)
Yield 60 %, mp 115 °C; IR (KBr, cm-1): 3020 (CH, aromatic), 1708, 1660 (2CO).
1H-NMR (CDCl3, d ppm): 1.11 (t, 6H, J = 6.7 Hz, 2CH3, 2 propyl group), 1.25 (s,
11H, cyclohexyl ring), 1.43 (m, 4H, 2CH2, 2 propyl group), 2.75–2.90 (2 m, 4H,
C7–H2, C6–H2), 4.10 (q, 4H, J = 7.1 Hz, CH2–N–CH2, 2 propyl group), 4.83–4.93
(dd, 1H, J = 11.5 Hz, 5.2 Hz, C1–H), 5.11–5.14 (m, 1H, C11b–H; 2H, N–CH2; 1H,
C3–H), 5.15–5.30 (dd, 1H, J = 11.0 Hz, 5.0 Hz, C1–H), 7.21–7.81 (m, 4H,
aromatic-H); 13C-NMR (DMSO-d6, d ppm): 173.2, 165.1, 136.1, 135.3, 127.5,
127.2, 125.1, 58.4, 56.2, 53.3, 53.1, 42.9, 41.1, 36.1, 29.3, 27.6, 26.9, 24.3, 21.5,
11.8. MS m/z: 424 (M-1)?. (10 %). Analysis for C26H39N3O2: (425.30): Calcd.:
C, 73.37; H, 9.24; N, 9.87; Found: C, 73.373; H, 8.84; N, 9.35.
2-2-(Cyclohexylcarbonyl)-3-((2-hydroxyethylamino)methyl)-1,2,3,6,7,11b-
hexahydro-4H-pyrazino[2,1-a]isoquinolin-4-one (2d)
Yield: 60 %; mp 120 °C; IR (KBr, cm-1): 3020 (CH, aromatic), 1708, 1660 (2CO);
1H-NMR (CDCl3, d ppm): 1.25 (s, 11H, cyclohexyl ring), 2.75–2.90 (2 m, 4H,
C7–H2, C6–H2), 3.32–3.51 (m, 4H, NCH2CH2O), 4.83–4.93 (dd, 1H, J = 11.5 Hz,
5.2 Hz, C1–H), 5.11–5.14 (m, 1H, C11b–H; 2H, N–CH2; 1H, C3–H), 5.15–5.30 (dd,
1H, J = 11.0 Hz, 5.0 Hz, C1–H), 7.21–7.81 (m, 4H, aromatic-H), 9.11, 11.61 (2 s,
2H, NH, OH, D2O exchangeable); 13C-NMR (DMSO-d6, d ppm): 173.2, 165.1,
136.1, 135.3, 127.5, 127.2, 125.1, 61.3, 58.4, 53.2, 51.2, 49.3, 42.9, 41.1, 36.1, 29.3,
123

M. M. Kamel et al.
27.6, 26.9, 24.3. MS m/z: 385 (M?.) (20 %). Analysis for C22H31N3O3 (385.24):
Calcd.: C, 68.54; H, 8.11; N, 10.90; Found: C, 68.00; H, 8.53; N, 10.54.
Biological evaluation
Antischistosomal activities of the newly synthesized compounds 1a–c and 2a–d
were evaluated based on the in vitro schistosome worm killing technique [13]:
Syrian golden hamsters (Mesocrietus auratus) weighing 100–120 g were obtained
from the Schistosome Biological Supply Center, Theodor Bilharz Research
Institute. S. mansoni cercariae (Egyptian strain CD) were used to infect the
hamsters with 350 cercariae each by abdominal skin exposure [14]. Praziquantel
(Shin Poong Pharmaceutical Co., South Korea) and the respective newly
synthesized compounds 1a–c and 2a–d were prepared as 5-mM stock solutions in
aqueous DMSO. Immediately before use, the stock solutions were diluted with
complete medium to the concentrations indicated. S. mansoni-infected hamsters
were sacrificed and worms harvested from the portomesenteric vessels [15]. 12–16
worms were placed in duplicate Petri dishes, and fresh RPMI 1640 medium
(glutamine, 20 % fetal calf serum, and antibiotics [streptomycin, penicillin, and
gentamicin]) containing the indicated concentrations (1–100 lM) of test compounds
were added. The worms were incubated overnight in a CO2 incubator, washed thrice
with saline, fresh medium without drug was added, and the incubation was
continued overnight in the CO2 incubator. On the second day, worm motility was
observed and the medium was again changed and the incubation continued. From
day 1 to day 5, the numbers of living and dead worms were recorded. Negative
controls using pure medium alone or medium with DMSO and positive control
media containing various concentrations of PZQ were similarly evaluated. At the
end of the observation period, worms were examined in a laminar flow hood for
their motility and appearance by using a stereomicroscope, and the final recording
of the percentage worm mortality was assessed (the number of dead worms
[contracted and opaque] relative to the total number of worms).
Results and discussion
Chemical studies
Literature survey has proved that the presence of a, ß-unsaturated carbonyl system
of the chalcones is associated with different biological activities, such as antioxidant
[16], anticancer [17], bactericidal [18], antimalarial [19], strong antileishmanial
activity [20], and antiviral [21]. Thus, it was of interest to prepare new chalcones
derivatized from PZQ.
Claisen–Schmidt condensation [22] was carried out by the reaction of equimolar
quantities of PZQ in a form of a racemic mixture with different aromatic/heterocyclic
aldehydes, namely, benzaldehyde, p-methoxybenzaldeyde, and 2-thiophenaldehyde,
in the presence of aqueous alcoholic NaOH to give the respective arylidene
derivatives 1a–c. The structures of the resultant products were confirmed depending
123

In vitro antischistosomal evaluation
upon microanalytical and spectral data. IR spectra represented two characteristic
absorption bands at 1710–1650 cm-1, due to the presence of 2CO groups. 1H-NMR
spectra of the derivatives exhibited singlet signals d 1.25 ppm, representing 11H of
the cyclohexyl ring, singlet signals d 5.62 ppm due to the methine proton of the
–C=CH group, in addition to the other protons of the formed molecules that appeared
in their expected ranges. Mass spectra of the new derivatives exhibited molecular ion
peaks at m/e 400, 430, and 405, respectively.
Mannich bases have gained wide importance because of their pharmaceutical
importance. The presence of basic Mannich side chain has shown a marked
antimalarial [23], good anticancer [24], antimycobacterial [25], and remarkable
anti-HIV and antitubercular [26] activities. Also, it has been reported that the
Mannich side chain may overcome the water insolubility problem through
hydrochloride formation [27]. This, in turn, will improve the therapeutic actions
of the derivatives. For these reasons, it was interesting to apply the Mannich
reaction to PZQ in a form of a racemic mixture by using paraformaldehyde and
different alicyclic/alkyl amines, namely, 4-methylpiperazine, 4-methylpiperidine,
dipropylamine, and 2-aminoethanol, to furnish the Mannich bases 2a–d, respec-
tively. The gained structures were elucidated by microanalytical and spectral data.
IR spectra represented two characteristic absorption bands at 1710–1650 cm-1, due
to the presence of 2CO groups. Mass spectra of the compounds represented
molecular ion peaks at their expected regions.
Biological evaluation
S. mansoni killing results
The percentages of in vitro S. mansoni worm killing under the influence of the tested
compounds at different concentrations versus untreated and DMSO negative
controls and positive controls treated with PZQ were determined (Table 1). Controls
and DMSO-treated controls had no observed mortality. PZQ was the most effective
compound studied, with 100 % worm mortality found between 5 and 10 lM drug
concentrations.
The most active compound among those newly synthesized was the Mannich
base 2d, which has 50 % effective concentration (EC50) at 5 lM, 93.3 % worm
mortality at 10 lM, and 100 % worm mortality was found at 30 lM. Less activity
was achieved by the Mannich base 2c, which showed 50 % worm mortality at
10 lM, 78.6 % worm mortality at 10 lM, and 100 % worm mortality at 30 lM. On
the other hand, compound 1b was the least active one, with 50 % effective
concentration (EC50) at 40 lM and exhibited 93.3 % worm mortality at 60 lM.
Discussion
Discovery of new antischistosomal drugs depends on both in vitro whole parasite
screens and S. mansoni-infected animal models of the disease. The in vitro worm
killing screen is advantageous because it allows the rapid screening of many
123

M. M. Kamel et al.
Table 1 In vitro mortality (%) of Schistosoma mansoni treatment groups 1a–c and 2a–d in comparison
to praziquantel
Drug concentration
(lM)
PQ
1a
1b
1c
2a
2b
2c
2d
5
93.3
100
100
100
100
100
100
100
100
100
100
0
0
28.6
39.7
50
28.6
39.7
50
28.6
39.7
50
36.5
50
50
10
20
30
40
50
60
70
80
90
100
12.7
30.0
35.5
50
12.7
28.6
39.7
50
78.6
93.3
100
100
100
100
100
100
100
100
78.6
93.3
100
100
100
100
100
100
100
68.4
82.7
93.3
100
100
100
100
100
68.4
93.3
100
100
100
100
100
100
78.6
93.3
100
100
100
100
100
100
68.6
93.3
100
100
100
100
78.6
93.3
100
100
100
100
compounds at several drug concentrations. The tested compounds 2d and 2c were
previously shown to have greatly increased antischistosomal activity versus PZQ,
which might primarily be due to greatly increased cell uptake and conversion to the
active metabolite [28]. In the S. mansoni worm killing assay, compounds 2d and 2c
were marginally more active than the rest of the compounds, and the increase in
activity was about 2–3-fold more than the other Mannich and arylidene derivatives.
Conclusion
A novel series of praziquantel–arylidene derivatives 1a–c and praziquantel–
Mannich bases 2a–d were synthesized for antischistosomal activity evaluation. The
Mannich base 2d followed by 2c exhibited substantial antischistosomal activities, as
judged by in vitro worm killing. This result indicated that the presence of alkyl
Mannich side chain is more favorable for antischistosomal activity than the alicyclic
Mannich side chain and the arylidene substituents at position 3 of the pyrazino[2,1-
a]isoquinolin ring of PZQ. It would be of interest to examine in further studies the
in vivo effects of these compounds in Schistosoma mansoni-infected animals,
followed by a study of the toxicological and pharmacological activities of these
newly synthesized compounds in comparison to PZQ.
Acknowledgments The authors would thank the Microanalytical and Spectral Unit, National Research
Centre and Cairo University, Egypt for the microanalytical, IR, 1H-NMR, 13C-NMR, and mass spectral
data.
References
1. J. Keiser, J. Utzinger, Advances in the discovery and development of trematocidal drugs. Expert
Opin. Drug Discov. 2(S1), S9–S23 (2007)
123

In vitro antischistosomal evaluation
´
2. G.B.F. Carvalho, R.A. da Silva Pereira, L.G.G. Pacıfico, C.T. Fonseca, Identification of Schistosoma
mansoni candidate antigens for diagnosis of schistosomiasis. Mem. Inst. Oswaldo Cruz 106, 837–843
(2011)
3. L.A.L. Quezada, J.H. McKerrow, Schistosome serine protease inhibitors: parasite defense or
ˆ
homeostasis? An. Acad. Bras. Cienc. 83, 663–672 (2011)
4. J. Utzinger, J. Keiser, Schistosomiasis and soil-transmitted helminthiasis: common drugs for treat-
ment and control. Expert Opin. Pharmacother. 5, 263–285 (2004)
5. M.J. van der Werf, S.J. de Vlas, S. Brooker, C.W.N. Looman, N.J.D. Nagelkerke, J.D.F. Habbema,
D. Engels, Quantification of clinical morbidity associated with schistosome infection in sub-Saharan
Africa. Acta Trop. 86, 125–139 (2003)
6. A. Fenwick, J.P. Webster, Schistosomiasis: challenges for control, treatment and drug resistance.
Curr. Opin. Infect. Dis. 19, 577–582 (2006)
7. M.J. Doenhoff, L. Pica-Mattoccia, Praziquantel for the treatment of schistosomiasis: its use for
control in areas with endemic disease and prospects for drug resistance. Expert Rev. Anti Infect.
Ther. 4, 199–210 (2006)
¨
8. R. Gonnert, P. Andrews, Praziquantel, a new broad-spectrum antischistosomal agent. Z. Parasitenk.
52, 129–150 (1977)
9. B.L. Blas, M.I. Rosales, I.L. Lipayon, K. Yasuraoka, H. Matsuda, M. Hayashi, The schistosomiasis
problem in the Philippines: a review. Parasitol. Int. 53, 127–134 (2004)
´
10. V.R. Southgate, D. Rollinson, L.A. Tchuem Tchuente, P. Hagan, Towards control of schistosomiasis
in sub-Saharan Africa. J. Helminthol. 79, 181–185 (2005)
11. C.M.S. Menezes, G. Rivera, M.A. Alves, D.N. do Amaral, J.P.B. Thibaut, F. Noe¨l, E.J. Barreiro,
L.M. Lima, Synthesis, biological evaluation, and structure–activity relationship of clonazepam,
meclonazepam, and 1,4-benzodiazepine compounds with schistosomicidal activity. Chem. Biol.
Drug Des. 79, 943–949 (2012)
12. S.-H. Xiao, J.-Y. Mei, P-Y Jiao, The in vitro effect of mefloquine and praziquantel against juvenile
and adult Schistosoma japonicum. Parasitol. Res. 106(1), 237–246 (2009)
13. S. Botros, J. Bennett, Praziquantel resistance. Expert Opin. Drug Discov. 2, 535–540 (2007)
14. Y.S. Liang, J.I. Bruce, D.A. Boy, Laboratory cultivation of schistosome vector snails and mainte-
nance of schistosome life cycle. Proc. First Sino-American Symp. 1, 34–48 (1987)
15. R.H. Duvall, W.B. DeWitt, An improved perfusion technique for recovering adult schistosomes from
laboratory animals. Am. J. Trop. Med. Hyg. 16, 483–486 (1967)
16. J. Vaya, P.A. Belinky, M. Aviram, Antioxidant constituents from licorice roots: isolation, structure
elucidation and antioxidative capacity toward LDL oxidation. Free Radic. Biol. Med. 23(2), 302–313
(1997)
17. M. Larsen, H. Kromann, A. Kharazmi, S.F. Nielsen, Conformationally restricted anti-plasmodial
chalcones. Bioorg. Med. Chem. Lett. 15(21), 4858–4861 (2005)
18. S.F. Nielsen, T. Boesen, M. Larsen, K. Schønning, H. Kromann, Antibacterial chalcones–bioisosteric
replacement of the 40-hydroxy group. Bioorg. Med. Chem. 12(11), 3047–3054 (2004)
19. M. Chen, S.B. Christensen, L. Zhai, M. Rasmussen, T.G. Theander, S. Frøkjær, B. Steffansen,
J. Davidsen, A. Kharazmi, The novel oxygenated chalcone 2,4 dimethyloxy-40-butoxychalcone,
exhibits potent activity against human malaria parasite Plasmodium falciparum in vitro and rodnet
parasites Plasmodium berghei and Plasmodium yoelii in vivo. J. Infect. Dis. 176, 1327–1333 (1997)
20. L. Zhai, M. Chen, J. Blom, T.G. Theander, S.B. Christensen, A. Kharazmi, The antileishmanial
activity of novel oxygenated chalcones and their mechanism of action. J. Antimicrob. Chemother. 43,
793–803 (1999)
21. D. Binder, C.R. Noe, W. Holzer, B. Rosenwirth, Thiophene as a structural element of physiologically
active compounds, XII: thiophene analogues of antiviral chalcones. Arch. Pharm. 318, 48–59 (1985)
22. J. Shen, H. Wang, H. Liu, Y. Sun, Z. Liu, Brønsted acidic ionic liquids as dual catalyst and solvent
for environmentally friendly synthesis of chalcone. J. Mol. Catal. A: Chem. 280, 24–28 (2008)
23. B.M. Kotecka, G.B. Barlin, M.D. Edstein, K.H. Rieckmann, New quinoline di-mannich base com-
pounds with greater antimalarial activity than chloroquine, amodiaquine, or pyronaridine. Antimic-
rob. Agents Chemother. 41(6), 1369–1374 (1997)
24. A.S. Aboraia, H.M. Abdel-Rahman, N.M. Mahfouz, M.A. EL-Gendy, Novel 5-(2-hydroxyphenyl)-3-
substituted-2,3-dihydro-1,3,4-oxadiazole-2-thione derivatives: promising anticancer agents. Bioorg.
Med. Chem. 14, 1236–1246 (2006)
25. M.A. Ali, M. Shaharyar, Oxadiazole mannich bases: synthesis and antimycobacterial activity. Bio-
org. Med. Chem. 17, 3314–3316 (2007)
123

M. M. Kamel et al.
26. D. Sriram, D. Banerjee, P. Yogeeswari, Efavirenz Mannich bases: synthesis, anti-HIV and antitu-
bercular activities. J. Enzyme Inhib. Med. Chem. 24, 1–5 (2009)
27. M.M. Kamel, M. Nasr, New styrylquinolines of expected antimalarial activity. Pharmazie 34,
440–441 (1979)
28. M.G.R. Pitta, A.C.A. Silva, J.K.A.L. Neves, P.G. Silva, J.I. Irma˜o, E. Malaguen˜o, J.V. Santana,
M.C.A. Lima, S.L. Galdino, I.R. Pitta, M.C.P.A. Albuquerque, New imidazolidinic bioisosters:
potential candidates for antischistosomal drugs. Mem. Inst. Oswaldo Cruz 101, 313–316 (2006)
123