New compounds hybrids 1H-1,2,3-triazole-quinoline against plasmodium falciparum

Article abstract of DOI:10.1111/cbdd.12321

Malaria is one of the most prevalent parasitic diseases in the world. The global importance of this disease, current vector control limitations, and the absence of an effective vaccine make the use of therapeutic antimalarial drugs the main strategy to co

Full text of DOI:10.1111/cbdd.12321

Received Date : 17-Sep-2013
Revised Date : 18-Dec-2013
Accepted Date : 17-Feb-2014
Article type : Research Article
Corresponding author e-mail id: boechat@far.fiocruz.br
New compounds hybrids 1H-1,2,3-triazole-quinoline against Plasmodium falciparum
Núbia Boechat1*, Maria de Lourdes G. Ferreira1, Luiz C. S. Pinheiro1, Antônio M. L.
Jesus1, Milene M. M. Leite1, Carlos C. S. Júnior1, Anna C. C. Aguiar2,3, Isabel M de
Andrade2 and Antoniana U. Krettli2,3
1Departamento de Síntese de Fármacos, Instituto de Tecnologia em Fármacos -
Farmanguinhos, FIOCRUZ, Rua Sizenando Nabuco 100, Manguinhos, Rio de Janeiro,
RJ, 21041-250, Brazil.
2Laboratório de Malária, Centro de Pesquisas René Rachou, FIOCRUZ, Belo
Horizonte, MG, 31090-002, Brazil.
3Programa de Pós Graduação em Medicina Molecular. Faculdade de Medicina.
Universidade Federal de Minas Gerais, Belo Horizonte, MG, 30000-000, Brazil.
Keywords: hybrids, triazole, quinoline, antiplasmodial, Plasmodium falciparum
Malaria is one of the most prevalent parasitic diseases in the world. The global
importance of this disease, current vector control limitations and the absence of an
effective vaccine make the use of therapeutic antimalarial drugs the main strategy to
control malaria. Chloroquine (CQ) is a cost effective antimalarial drug with a relatively
robust safety profile, or therapeutic index. However, CQ is no longer used alone to treat
patients with Plasmodium falciparum due to the emergence and spread of CQ-resistant
strains, which have also been reported for Plasmodium vivax. However, the activity of
1,2,3-triazole derivatives against chloroquine-sensitive and chloroquine-resistant strains
of P. falciparum has been reported in the literature. To enhance the anti-P. falciparum
activity of quinoline derivatives, we synthesized 11 new quinoline-1H-1,2,3-triazole
hybrids with different substituents in the 4-positions of the 1H-1,2,3-triazole ring, which
were assayed against the W2-chloroquine-resistant P. falciparum clone. Six compounds
exhibited activity against the P. falciparum W2 clone, chloroquine-resistant, with IC50
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cite this article as an 'Accepted Article', doi: 10.1111/cbdd.12321
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values ranging from 1.4 to 46 µM. None of these compounds was toxic to a normal
monkey kidney cell line (BGM), thus exhibiting good selectivity indexes, as high 351
for one compound (11).
Introduction
Malaria is one of the most prevalent parasitic diseases in the world and affects
approximately 500 million individuals throughout the tropical and subtropical areas of
developing countries. Malaria causes considerable morbidity and mortality and is
associated with approximately 800,000 deaths worldwide per year1.
The global importance of this disease, current vector control limitations and the
absence of an effective vaccine make the development of new therapeutic drugs, since
the main strategy used to control malaria is patients treatment with antimalarials2.
Chloroquine (CQ) is a cost effective antimalarial drug with a relatively robust safety
profile, or therapeutic index3. However, CQ is no longer used alone to treat patients
with Plasmodium falciparum due to the emergence and spread of CQ-resistant strains,
which have also been reported for P. vivax4,5.
Although many new compounds have been described in the recent literature, the
quinoline derivatives continue to dominate the antimalarial drug category6-8. Many of
the studies have been conducted using synthetic hybrid compounds that were designed
to increase the efficacy of quinoline derivatives, such as AZT-chloroquinoline (I)9,
quinine-dihydroartemisinin (II)10 and MEFAS (III)11, a salt derived from mefloquine
and artesunate.
The activity of 1,2,3-triazole derivatives IV-VI against chloroquine-sensitive and
chloroquine-resistant strains of P. falciparum has also been described12-14 (Figure 1).
During our search for new prototypes that can be used to treat neglected diseases, we
have demonstrated the importance of the 1,2,3-triazoles against Mycobacterium
tuberculosis15 and Leishmania amazonensis16. In an effort to find new prototypes active
against P. falciparum we have synthesized new quinoline-1H-1,2,3-triazole hybrids (3-
13). The 7-chloroquinoline moiety was included in these hybrids because it is present in
CQ and amodiaquine, two drugs that are commonly used to treat malaria. While the 1H-
1,2,3-triazoles contain a variety of substituents at the 4-position, were chosen based on
its activities against P. falciparum12-14 (Figure 2).
Materials and methods
Chemistry
1
The H, 13C and 19F nuclear magnetic resonance (NMR) spectra were generated at
o
400.00, 100.00 and 376.00 MHz, respectively, at 25 C, using a BRUKER Avance
instrument equipped with a 5 mm probe. Tetramethylsilane was used as an internal
standard. The chemical shifts (δ) are reported in ppm, and the coupling constants (J) are
reported in Hertz. The Fourier transform infrared (FTIR) absorption spectra were
recorded on a Shimadzu mode IR Prestige-21 spectrophotometer through KBr
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reflectance. The melting points (m.p.) were determined using a Büchi model B-545
apparatus. TLC (thin layer chromatography) was performed using a Merck TLC Silica
gel 60 F254 aluminium sheets 20 x 20 cm (eluent hexane/ethylacetate 2:8). Gravitational
column chromatography was performed using Silica gel 60 (0.2-0.5 mm) the gradient
mixture initial hexane/ethyl acetate 100-0% until 0-100%, volume of gradient 100mL,
column dimensions 25 cm x 3.5 cm. All other reagents and solvents used were
analytical grade.
General procedure for the preparation of 7-chloro-4-(1H-1,2,3-triazol-1-
yl)quinolines (3-10).
A mixture of H2O/t-BuOH (1:1) (40 mL) was added to 4-azido-7-chloroquinoline (2)
(22.5 mmol), the appropriate acetylene (33.7 mmol), L-ascorbic acid sodium salt (2.25
mmol) and CuSO4.5H2O (0.225) mmol. The reaction mixture was maintained under
vigorous stirring at 25 °C for 24 h. The progress of the reaction was monitored using
TLC (hexane/ethylacetate 2:8). On completion, the reaction mixture was poured in to
ice cold water (50 mL). The precipitate was filtered and dried. The residual crude
product was purified via silica gel column chromatography using the gradient mixture
initial hexane/ethyl acetate 100-0% until 0-100% to produce 86-31% yields of the pure
derivatives 3-10.
7-chloro-4-(4-(((tetrahydro-2H-pyran-2-yl)oxy)methyl)-1H-1,2,3-triazol-1-
yl)quinoline (3)
Yield: 77 %. m.p. 93.2 – 94.0 °C. IR (KBr, cm-1): 3446; 2914; 1637; 1612; 1560;
1
1506; 1118; 1026; 817; 624. H NMR (400 MHz, DMSO-d6) δ: 1.48-3.85 (m, 8H,);
4.69 (d, J= 12.3 Hz, 1H, H2'); 4.81 (s, 1H, CH2O); 4.86 (d, J= 12.3 Hz, 1H, H2'); 7.80
(dd, J= 2.0, 9.0 Hz, 1H, H-6); 7.87 (d, J= 4.6 Hz, 1H, H-3); 8.03 (d, J= 9.0 Hz, 1H, H-
5); 8.29 (d, J= 2.0 Hz, 1H, H-8); 8.84 (s, 1H, H-triazole); 9.16 (d, 1H, J= 4.6 Hz, H-2).
13C NMR (100 MHz, DMSO-d6) δ: 18.9; 24.9; 30.0; 59.2; 61.3; 97.2; 117.0; 120.3;
125.5; 126.2; 128.0; 128.9; 135.3; 140.4; 144.8; 149.3; 152.3. Anal. Calcd for
C17H17ClN4O2: C, 59.22; H, 4.97; N, 16.25. Found: C, 58.86; H, 5.06; N, 15.92.
1-(1-(7-chloroquinolin-4-yl)-1H-1,2,3-triazol-4-yl)cyclohexanol (4)
Yield: 65 %. m.p. 158.1 – 160.0 °C. IR (KBr, cm-1): 3446; 3149; 1637; 1614; 1564;
1
1508; 1319; 1031; 808. H NMR (400 MHz, DMSO-d6) δ: 1.33-2.04 (m, 10H,
cyclohex); 5.11 (s, 1H, OH); 7.80 (dd, J= 2.1, 9.1 Hz, 1H, H-6); 7.82 (d, 1H, J= 4.6 Hz,
H-3); 8.06 (d, J= 9.1 Hz, 1H, H-5); 8.27 (d, J= 2.1 Hz, 1H, H-8); 8.62 (1H, s, H-
triazole); 9.13 (1H, d, J= 4.6 Hz, H-2). 13C NMR (100 MHz, DMSO-d6) δ: 21.6; 25.1;
37.6; 67.9; 116.7; 120.2; 123.3; 125.5; 128.1; 128.8; 135.2; 140.5; 149.4; 152.3; 156.5.
Anal. Calcd for C17H17ClN4O: C, 62.10; H, 5.21; N, 17.04. Found: C, 62.27; H, 5.31; N,
16.63.
7-chloro-4-(4-phenyl-1H-1,2,3-triazol-1-yl)quinoline (5)
Yield: 55 %. m.p. 148.5 – 149.2 °C. IR (KBr, cm-1): 3446; 3124; 3051; 2357; 1681;
1
1608; 1558; 1506; 1456; 1435; 1234; 1022; 877; 767. H NMR (400 MHz, DMSO-d6)
δ: 7.43 (t, J= 7.4 Hz, 1H, H-Ph); 7.54 (t, J= 7.4 Hz, 2H, H-Ph); 7.81 (dd, 1H, J= 2.0, 9.1
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Hz, H-6); 7.95 (d, 1H, J= 4.6 Hz, H-3); 8.01 (d, J= 7.2 Hz, 2H, H-Ph); 8.16 (d, J= 9.1
Hz, 1H, H-5); 8.31 (d, J= 2.0 Hz, 1H, H-8); 9.21 (d, J= 4.6 Hz, 1H, H-2) 9.33 (s, 1H, H-
triazole). 13C NMR (100 MHz, DMSO-d6) δ: 116.8; 120.1; 123.6; 125.5; 125.6; 128.0;
128.4; 128.9; 129.0; 129.7; 135.3; 140.3; 147.0; 149.4; 152.3. Anal. Calcd for
C17H11ClN4: C, 66.56; H, 3.61; N, 18.26. Found: C, 66.02; H, 3.44; N, 18.02.
7-chloro-4-(4-cyclopropyl-1H-1,2,3-triazol-1-yl)quinoline (6)
Yield: 40 %. m.p. 147.6 – 149.1 °C. IR (KBr, cm-1): 3446; 3124; 3051; 2357; 1681;
1
1608; 1558; 1506; 1456; 1435; 1234; 1022; 877; 767. H NMR (400 MHz, DMSO-d6)
δ: 0.87-0.91 (m, 2H, c-prop); 1.00-1.05 (m, 2H, c-prop); 2.09-2.14 (m, 1H, c-prop); 7.78
(dd, 1H, J= 2.0, 9.0 Hz, H-6); 7.80 (d, 1H, J= 4.6 Hz, H-3); 8.08 (d, 1H, J= 9.0 Hz, H-
5); 8.27 (d, 1H, J= 2.0 Hz, H-8); 8.57 (s, 1H, H-triazole); 9.13 (d, 1H, J= 4.6 Hz, H-2).
13C NMR (100 MHz, DMSO-d6) δ: 6.41; 7.84; 116.5; 120.1; 122.9; 125.6; 128.0; 128.8;
135.2; 140.9; 149.4; 149.9; 152.2. Anal. Calcd for C17H11ClN4: C, 62.11; H, 4.10; N,
20.70. Found: C, 61.93; H, 3.92; N, 20.62.
ethyl 1-(7-chloroquinolin-4-yl)-1H-1,2,3-triazole-4-carboxylate (7)
Yield: 55 %. m.p. 137.4 – 139.0 °C. IR (KBr, cm-1): 3448; 3232; 1942; 1722; 1541;
1506; 1265; 1220; 1155; 1033; 825; 771. 1H NMR (400 MHz, DMSO-d6) δ: 1.36 (t, J=
7.0 Hz, 3H, CH3); 4.40 (q, J= 7.0 Hz, 2H, CH2); 7.79 (dd, J= 1.2, 9.0 Hz, 1H, H-6); 7.94
(d, J= 3.4 Hz, 1H, H-3); 7.95 (d, J= 9.0 Hz, 1H, H-5); 8.31 (d, J= 1.2 Hz, 1H, H-8);
9.20 (d, J= 3.4 Hz, 1H, H-2); 9.48 (s, 1H, H-triazole). 13C NMR (100 MHz, DMSO-d6)
δ: 14.1; 60.8; 117.0; 120.3; 125.2; 128.0; 129.1; 131.3; 135.4; 139.4; 139.8; 149.2;
152.2; 159.8. Anal. Calcd for C14H11ClN4O2: C, 55.55; H, 3.66; N, 18.51. Found: C,
55.64; H, 3.99; N, 17.98.
methyl 1-(7-chloroquinolin-4-yl)-1H-1,2,3-triazole-4-carboxylate (8)
Yield: 40 %. m.p. 183.7 – 185.0 °C. IR (KBr, cm-1): 3444; 3120; 3064; 1919; 1707;
1614; 1550; 1508; 1436; 1344; 1280; 1220; 1159; 1033; 815; 779. 1H NMR (400 MHz,
DMSO-d6) δ: 3.93 (s, 3H, CH3); 7.80 (dd, J= 2.1, 9.0 Hz, 1H, H-6); 7.94 (d, J= 4.6 Hz,
1H, H-3); 7.95 (d, J= 9.0 Hz, 1H, H-5); 8.31 (d, J= 2.1 Hz, 1H, H-8); 9.19 (d, J= 4.6
Hz, 1H, H-2); 9.51 (s, 1H, H-triazole). 13C NMR (100 MHz, DMSO-d6) δ: 52.1; 117.0;
120.3; 125.2; 128.0; 129.1; 131.3; 135.4; 139.4; 139.8; 149.2; 152.3; 160.3. Anal. Calcd
for C13H9ClN4O2: C, 54.09; H, 3.14; N, 19.41. Found: C, 54.23; H, 3.36; N, 18.17.
2-(1-(7-chloroquinolin-4-yl)-1H-1,2,3-triazol-4-yl)propan-2-ol (9)
Yield: 71 %. m.p. 143.3 – 144.8 °C. IR (KBr, cm-1): 3441; 3159; 3035; 1961; 1633;
1560; 1504; 1435; 1361; 1176; 1033; 808; 773. 1H NMR (400 MHz, DMSO-d6) δ: 1.60
(s, 6H, CH3); 5.35 (s, 1H, OH); 7.80 (dd, J= 2.0, 9.0 Hz, 1H, H-6); 7.83 (d, J= 4.6 Hz,
1H, H-3); 8.06 (d, J= 9.0 Hz, 1H, H-5); 8.27 (d, J= 2.0 Hz, 1H, H-8); 8.61 (s, 1H, H-
triazole); 9.14 (d, J= 4.6 Hz, 1H, H-2). 13C NMR (100 MHz, DMSO-d6) δ: 30.5; 67.0;
116.7; 120.3; 122.5; 125.5; 128.1; 128.8; 135.2; 140.5; 149.4; 152.3; 156.6. Anal. Calcd
for C14H13ClN4O: C, 58.24; H, 4.54; N, 19.40. Found: C, 58.26; H, 4.54; N, 19.42.
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(1-(7-chloroquinolin-4-yl)-1H-1,2,3-triazol-4-yl)methanol (10)
Yield: 45 %. m.p. 161.1 – 163.0 °C. IR (KBr, cm-1): 3097; 2883; 2821; 1915; 1608;
1589; 1562; 1504; 1436; 1350; 1307; 1273; 1240; 1120; 1078; 1043; 821; 771. 1H NMR
(400 MHz, DMSO-d6) δ: 4.71 (d, J= 5.6 Hz, 2H, CH2); 5.42 (t, J= 5.6 Hz, 1H, OH);
7.80 (dd, J= 2.0, 9.0 Hz, 1H, H-6); 7.83 (d, J= 4.6 Hz, 1H, H-3); 8.03 (d, J= 9.0 Hz, 1H,
H-5); 8.28 (d, J= 2.0 Hz, 1H, H-8); 8.70 (s, 1H, H-triazole); 9.15 (d, J= 4.6 Hz, 1H, H-
2). 13C NMR (100 MHz, DMSO-d6) δ: 54.8; 116.9; 120.3; 125.0; 125.4; 128.1; 128.9;
135.3; 140.5; 148.8; 149.3; 152.3. Anal. Calcd for C12H9ClN4O: C, 55.29; H, 3.48; N,
21.49. Found: C, 55.29; H, 3.35; N, 21.21.
Procedure for the preparation of 1-(7-chloroquinolin-4-yl)-1H-1,2,3-triazole-4-
carbaldehyde (11)
A solution of 0,4 mL (4.08 mmol) of freshly distilled oxalyl chloride and 4 mL of dry
CH2Cl2 was added in a dropwise fashion to a solution of 0,6 mL (8.17 mmol) of dry
DMSO in CH2Cl2 (2 mL) at -78 °C under Ar. After 15 min, a solution of 0.36 g (1.36
mmol) of compound 10 in 15 mL of CH2Cl2 was added. After 15 min, 1.5 mL (10.2
mmol) of triethylamine was added in a dropwise fashion at such a rate that the
temperature remained at -78 °C. The mixture was warmed to 25 °C for 2 hours. Then,
15 mL of cold water was added and neutralized with 5% NaOH. The mixture was
separated, and the aqueous layer was extracted using chloroform (3 x 30 mL). The
combined organic layers was washed with water, dried over MgSO4, filtered, and
concentrated. The residual crude product was purified via silica gel column
chromatography using the gradient mixture initial hexane/ethyl acetate 100-0% until 0-
100% to produce the pure derivative 11.
Yield: 55 %. m.p. 187.9 – 189.0 °C. IR (KBr, cm-1): 3448; 3118; 3032; 1924; 1697;
1612; 1533; 1506; 1440; 1344; 1263; 1205; 1112; 1033; 813; 771. 1H NMR (400 MHz,
DMSO-d6) δ: 7.81 (dd, J= 1.8, 9.0 Hz, 1H, H-6); 7.95 (d, J= 4.6 Hz, 1H, H-3); 7.96 (d,
J= 9.0 Hz, 1H, H-5); 8.33 (d, J= 1.8 Hz, 1H, H-8); 9.21 (d, J= 4.6 Hz, 1H, H-2); 9.59 (s,
1H, H-triazole); 10.21 (s, 1H, CHO). 13C RMN (DMSO-d6, 100 MHz) δ: 117.8 120.3;
125.2; 128.1; 129.2; 130.6; 135.5; 139.8; 147.1; 149.2; 152.3; 185.0. Anal. Calcd for
C12H7ClN4O: C, 55.72; H, 2.73; N, 21.66. Found: C, 54.78; H, 2.51; N, 20.93.
Procedure for the preparation of 7-chloro-4-(4-(fluoromethyl)-1H-1,2,3-triazol-
1-yl)quinoline (12)
The reaction mixture of alcohol derivative 10 (1 mmol), DAST (1 mmol), and CH2Cl2
(20 mL) was stirred at room temperature for 24 h and then poured into ice cold water.
The mixture was extracted using chloroform (3 x 30 mL). The combined organic layers
was washed with water, dried over MgSO4, filtered, and concentrated. The residual
crude product was purified via silica gel column chromatography using the gradient
mixture initial hexane/ethyl acetate 100-0% until 0-100% to produce the pure derivative
12.
Yield: 70 %. m.p. 159.4 – 160.0 °C. IR (KBr, cm-1): 3442; 3140; 3066; 1942; 1749;
1610; 1560; 1502; 1454; 1379; 1340; 1305; 1255; 1234; 1205; 1118; 1051; 1016; 977;
815; 765. 1H NMR (400 MHz, DMSO-d6) δ: 5.65 (d, J= 48.48 Hz, 2H, CH2F); 7.80 (dd,
J1= 2.1, 9.1 Hz, 1H, H-6); 7.89 (d, J= 4.6 Hz, 1H, H-3); 7.98 (d, J= 9.1 Hz, 1H, H-5);
8.31 (d, J= 2.1 Hz, 1H, H-8); 9.05 (d, J= 3.1 Hz, 1H, H-triazole); 9.18 (d, J= 4.6 Hz,
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1H, H-2). 13C NMR (100 MHz, DMSO-d6) δ: 75.0 (d, J= 159.8 Hz, CH2F); 117.2;
120.2; 125.2; 127.7 (d, J= 4.19 Hz, CH-triazole); 128.0; 129.0; 135.3; 140.1; 142.6 (d,
J= 20.0 Hz Cq-triazole); 149.2; 152.2. 19F NMR (376 MHz, DMSO-d6) δ: -204.22 (s,
1F, CH2F). Anal. Calcd for C12H8ClFN4: C, 54.87; H, 3.07; N, 21.33. Found: C, 54.81;
H, 3.11; N, 20.81.
Procedure for the preparation of 7-chloro-4-(4-(difluoromethyl)-1H-1,2,3-
triazol-1-yl)quinoline (13)
The reaction mixture of aldehyde derivative 11 (1 mmol), DAST (15 mmol), and
CH2Cl2 (20 mL) was stirred at room temperature for 24 h and then poured into ice cold
water. The mixture was extracted using chloroform (3 x 30 mL). The combined organic
layers was washed with water, dried over MgSO4, filtered, and concentrated. The
residual crude product was purified via silica gel column chromatography using the
gradient mixture initial hexane/ethyl acetate 100-0% until 0-100% to produce the pure
derivative 13.
Yield: 60 %. m.p. 139.4 – 140.6 °C. IR (KBr, cm-1): 3421; 1921; 1743; 1612; 1558;
1
1504; 1454; 1438; 1321; 1257; 1120; 1091; 1029; 823; 796. H NMR (400 MHz,
DMSO-d6) δ: 7.41 (t, J= 53.9 Hz, 1H, CHF2); 7.80 (dd, J= 2.0, 9.0 Hz, 1H, H-6); 7.92
(d, J= 4.6 Hz, 1H, H-3); 7.93 (d, J= 9.0 Hz, 1H, H-5); 8.30 (d, J= 2.0 Hz, 1H, H-8);
9.18 (d, J= 4.6 Hz, 1H, H-2) 9.26 (s, 1H, H-triazole). 13C NMR (100 MHz, DMSO-d6)
δ: 110.0 (t, J= 231.6 Hz CHF2); 117.6; 120.3; 125.2; 127.0 (t, J= 3.14 Hz, CH-triazole);
128.1; 129.2; 135.5; 140.0; 142.0 (t, J= 27.4 Hz, Cq-triazole); 149.3; 152.3. 19F NMR
(376 MHz, DMSO-d6) δ: -112.56 (s, 2F, CHF2). Anal. Calcd for C12H7ClF2N4: C,
51.35; H, 2.51; N, 19.96. Found: C, 51.01; H, 2.58; N, 19.27.
Biological evaluation
Continuous cultures and in vitro assays using P. falciparum-infected
erythrocytes
The P. falciparum W2 clone, chloroquine-resistant and mefloquine-sensitive17, was
maintained in continuous culture as previously described18, at 37 °C in human
erythrocytes (A+) in complete medium (RPMI 1640 supplemented with 10% human
sera blood group A+, 2% glutamine and 7.5% NaHCO3). Cultures in Petri dishes placed
either in a candle jar, or 25 cm culture flasks in an environment containing a gas
mixture atmosphere (3% O2, 5% CO2 and 91% N2), were used. Prior to testing, the ring-
stage parasites were synchronized using sorbitol19 and the suspension was adjusted for
parasitemia and hematocrit, as described below. The infected red blood cells were
distributed in 96-well microtiter plates (Corning, Santa Clara, CA, USA), 180 μL per
well, to which 20 μL of different concentrations of the test drugs and controls had
previously been added. The maximum concentration of 50 μg/mL (~157 μM) was tested
at least three times for each compound against P. falciparum in blood cultures; drug
activity was evaluated using an assay with commercially available monoclonal
antibodies that had been raised against a parasite histidine and alanine-rich protein
(HRP2) (MPFM ICLLAB-55A®, MPFG55P ICLLAB®, USA), as described20. The
assay was performed using 0.5% parasitemia and 1.5% hematocrit, and the test
quantification was read at 450 nm on a spectrophotometer (SpectraMax340PC384
Molecular Devices).
,
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The drug activity was expressed as the half-maximal inhibitory dose (IC50) compared
to the drug-free controls using the curve-fitting software Origin 8.0 (OriginLab
Corporation, Northampton, MA, USA)21.
Cell cultures and cytotoxicity tests
The monkey kidney cell line (BGM) was cultured in 75 cm2 sterile flasks containing
RPMI 1640 medium that had been supplemented with 10% heat-inactivated fetal serum
and 40 mg/L of gentamicin in a 5% CO2 atmosphere at 37 °C. For the in vitro
cytotoxicity experiments, the cell monolayer was trypsinized, washed with culture
medium, distributed in a flat-bottomed 96 well plate (5×103 cells/well), and incubated
for 18 hours at 37 °C for cell adherence.
For the cytotoxicity testing, we used the MTT ((3-(4,5-dimethylthiazol-2-yl)-2,5-
diphenyltetrazolium bromide) assay, performed as previously described22. The BGM
cell line was incubated with 20 µL of the compounds at different concentrations (200-25
µg/mL) for 24 hours in an atmosphere of 5% CO2 at 37 °C.
For the MTT assay, which evaluates mitochondrial viability, 20 µL of MTT solution
(5 mg/mL) were added, and the plates were incubated for an additional 3 hours. After
incubation, the supernatants were carefully removed from the wells, followed by the
addition of 100 µL of DMSO with thorough mixing. Optical densities at 570 and 630
nm (background) were determined using an ELISA reader.
Cell viability was expressed as the percentage of control absorbance obtained in
untreated cells after subtracting the absorbance from the appropriate background.
Finally, the minimum lethal dose for 50% of the cells (MLD50) was determined as
previously described23 (Figure 3). The ratio between MLD50 and drug activity (IC50) in
vitro was used to determine the selectivity index (SI).
The synthesized 7-chloro-4-(1H-1,2,3-triazol-1-yl)quinoline 3-13 derivatives with
different substituents in the 4-positions of the 1H-1,2,3-triazole ring were tested against
the W2-chloroquine-resistant P. falciparum clone.
Results and discussion
Chemistry
The synthetic route that was used to prepare the 7-chloro-4-(1H-1,2,3-triazol-1-
yl)quinolines (3-13) is shown in Scheme 1.
The commercially available compound 4,7-dichloroquinoline (1) was treated with
sodium azide in refluxing MeOH to generate a 70% yield of the 4-azido-7-
chloroquinoline (2) derivative after 24 hours. Compound 2 was characterized, and the
data were in agreement with the literature24. The 1,3-dipolar cycloaddition reaction
between the azide derivative (2) and the terminal alkynes was performed using Click
chemistry reaction conditions, which consisted of sodium ascorbate, a Cu(I) catalyst, in
H2O/t-BuOH/THF (1:1:1) at 25 °C, to obtain 40-77% yields of only one 1,4-
regioisomer of 7-chloro-4-(1H-1,2,3-triazol-1-yl)quinoline derivatives 3-1125-27
.
Azide group absorption was not observed in the IR spectrum of derivatives 3-10.
These compounds exhibited a chemical shift pattern for the quinoline ring. Both a
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doublet in the region of 9.13 - 9.21 ppm, which corresponded to H2, and a doublet in
the region of 7.80 - 7.95 ppm, which corresponded to H3, were observed, with a
coupling constant (J) 4.6 Hz.
A double doublet, which corresponded to H6, was detected in the region of 7.78 -
7.81 ppm and had J = 9.0 Hz and J = 2.0 Hz, which corresponded to H5 and H8
coupling, respectively. In addition, triazole hydrogens are characteristic of these
compounds and were observed in the region of 8.57 - 9.51 ppm as a singlet.
The quinolin-4-yl-1H-1,2,3-triazol alcohol (10) derivative was used as the raw
material for the synthesis of compounds 11, 12 and 13. Aldehyde 11 was prepared by
the Swern oxidation of compound 10, resulting in a 55% yield. OH group absorption
was not observed in the FTIR spectrum of derivative 11. The characteristic IR
absorption representing carbonyl group stretching from the aldehyde at 1697 cm-1 were
observed. The 1H NMR spectra showed a singlet signal at 10.21 ppm, which
corresponded to the aldehyde hydrogen. The 13C NMR spectra also showed a signal at
185.0 ppm, which corresponded to the carbonyl carbon.
The fluorination of compound 10 with dimethylaminosulfur trifluoride (DAST) in
CH2Cl2 at 25 °C produced a 70% yield of the monofluorinated derivative 12 after 24
hours. OH group absorption was not detected in the FTIR spectrum of derivative 12,
1
confirming the substitution of OH by fluorine. The H NMR spectra revealed the
presence of a doublet at 5.65 ppm with J = 48.48 Hz, which corresponded to the
coupling of the methylene hydrogens to a fluorine atom. The 13C NMR spectra revealed
signals at 75.0 and 142.6 ppm with J = 159.8 and 20.0 Hz, respectively, which
corresponded to the coupling of carbon to a fluorine atom. The 19F NMR spectra
revealed a characteristic signal at -204.22 ppm.
The aldehyde derivative 11 was treated with DAST using the same reaction
1
conditions to generate a 60% yield of the difluorinated derivative 13. The H NMR
spectra revealed a triplet at 7.41 ppm with J = 48.48 Hz, which indicated the coupling of
13
hydrogen to fluorine atoms. The C NMR spectra revealed signals at 110.0, 127.0 and
142.0 ppm, with J = 231.6, 3.14 and 27.4 Hz, respectively, which corresponded to the
coupling of carbon to fluorine atoms. The 19F NMR spectra revealed a characteristic
signal at -112.56 ppm.
In vitro biological evaluation
The results of the anti-P. falciparum activity and cytotoxicity analyses of the 11 new
compounds are summarized in Table 1. The compounds displayed IC50 values ranging
from 1.4 0.2 to 46 2 μM in the anti-HPR2 assay. Compound 11 was the most active,
with an IC50 = 1.4 0.2 µM, and the least toxic, with the highest SI value (351).
Compounds 3, 5-7 and 13 were partially active, with IC50 values that were lower than
50 µM and SI values that were greater than 10, which are considered to be non-toxic.
Compounds 4, 8-10 and 12 were inactive. Taken together, the results of the in vitro anti-
P. falciparum and toxicological activity analyses indicated that compounds 3, 5-7, 11
and 13 can be considered to be prototypes for the development of new antimalarial
drugs.
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Conclusion
We have synthesized eleven new hybrid 7-chloro-4-(1H-1,2,3-triazol-1-yl)quinolines
(3-13) with different substituents at the 4-positions of the 1H-1,2,3-triazole ring. None
of these compounds was toxic to HepG2 cells. Six compounds (3, 5-7, 11 and 13)
exhibited anti-plasmodial activity against the W2 chloroquine-resistant P. falciparum
clone, with IC50 values ranging from 1.4 to 46 µM.
Compound 11, which contained an aldehyde group at the 4-position of 1H-1,2,3-
triazol-1-yl, was the most active against P. falciparum, with IC50 values of 1.4 µM, and
the least toxic, displaying the highest SI value (351). These data suggest that these
compounds can be used as prototypes for other studies of compounds against P.
falciparum.
Acknowledgments
The authors thank the Coordination of Improvement of Higher Education (CAPES)
and the National Council of R&D of Brazil (CNPq) for the fellowships granted. We also
thank the Foundations for Research of the State of Rio de Janeiro (FAPERJ) and the
State of Minas Gerais (FAPEMIG), the Technological Development Program on
Products for Health of Fiocruz (PDTIS) and CNPq-MCT/MS (PRONEX Rede Malaria)
for financial support.
Conflict of Interest
All authors report no conflict of interest.
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Figure 1: Structures of quinoline and 1,2,3-triazole derivatives (I-VI).
Figure 2: Rational approach to the design of 7-chloro-4-(1H-1,2,3-triazol-1-
yl)quinolines (3-13).
Figure 3: Dose response curve of actives and partial actives compounds compounds.
Chloroquine that was the standard antimalarial used is also represented.
Scheme 1: Synthetic route used for the preparation of 7-chloro-4-(1H-1,2,3-triazol-1-
yl)quinolines (3-10).
Table 1: Evaluation of the anti-plasmodial activity against a chloroquine-resistant W2 clone of
P. falciparum, cytotoxicity against a human monkey kidney cell line (BGM) and drug selectivity
index (SI) of compounds 3-13 and chloroquine.
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IC50 (μM)a P. falciparum
MDL50 BGM
SI
Compounds
(μM)
MDL50 / IC50
Anti-HRP2
3
27 ± 5
83 ± 19
17 ± 2
≥ 581
≥ 609
≥ 653
≥ 738
≥ 662
≥ 694
≥ 694
≥ 777
477±22
763
22
Inactive
≥ 39
4
5
6
35 ± 15
14 ± 3
21
7
≥ 48
8
130 ± 6
90 ± 18
101 ± 25
1.4 ± 0.2
109 ± 11
46 ± 2
Inactive
Inactive
Inactive
351
9
10
11
12
13
Inactive
15
≥ 694
490
chloroquine
0.10 ± 0.077
4900
aIC50 <10 μM active; >10 and <50 μM partially active; >50 μM inactive.
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This article is protected by copyright. All rights reserved.

This article is protected by copyright. All rights reserved.

This article is protected by copyright. All rights reserved.