M. Tukulula et al. / European Journal of Medicinal Chemistry 57 (2012) 259e267
265
Table 2
In vitro antiplasmodial and antimycobacterial activity of the target compounds.
Product
P. falciparum IC50
[m
M (
m
g/mL)]
M. tuberculosis H37Rv strain
Solubility
MABA (
%Inh
m
M)
LORA (
%Inh
mM)
3D7
K1
W2
MIC90
MIC90
pH 7.4 (mM)
4.12a
4.12b
4.12c
4.12d
4.12e
4.12f
4.14f
4.13a
1.310
2.393
13.84
0.647
16.790
0.980
8.625
ND
1.310
2.393
13.80
2.633
7.947
1.228
6.737
4.525 (2.02)
2.318 (1.1)
0.0204
e
e
e
e
e
e
>10
>10
>10
>10
8.393
>10
>10
ND
ND
0.0187
e
16
83
24
98
0
0
0
ND
ND
95
e
>128
>128
>128
92.5
>128
>128
>128
>160a
>160a
119.7
10
0.05
0.23
0.12
3.125
0.4
42
94
30
64
0
32
1
ND
ND
98
e
>128
123.2
>128
>128
>128
>128
>128
ND
189.45
136.84
ND
114.44
ND
178.54
201.86
ND
ND
186.68
ND
ND
ND
4.13b
ND
0.0007
e
ND
122.0
e
Quinine
Mefloquine
RMP
e
e
100
92
99
e
98
64
100
e
1.93
>128
3.78
e
INH
e
e
PA-824
Kanamycin
Streptomycin
e
e
ND
ND
ND
e
e
e
e
e
e
e
Antiplasmodial and solubility assays performed in triplicates and antimycobacterial in duplicates; ND ¼ not determined.
a
Testing was only done on the replicating bacteria at a different laboratory to the one that tested compounds 4.12aef, 4.14f.
3.1.1.7. [2,8-Bis(trifluoromethyl)quinolin-4-yl](tert-butyl-1H-tetra-
zol-5-yl)-N,N-dimethylmethanamine (4.13a). Yield 22%; white
powder; m.p. 171e173 ꢁC, Rf (EtOAc:Hex, 1:1) 0.35; IR nmax (DCM)/
cmꢀ1 1602 (Ar C]C), 1423 (N]N), 1314 (C]N), 1271 (CeN), 1090
(CeF); dH (400 MHz; CDCl3) 8.70 (1H, d, J 8.5 Hz, H7), 8.23 (1H, d, J
7.1 Hz, H5), 7.84 (1H, t, J 7.9 Hz, H6), 7.40 (1H, s, H3), 6.29 (1H, s, H8),
2.46 (6H, s, 2ꢂ H9), 1.62 (9H, s, 3ꢂ H10); dC (101 MHz; CDCl3) 151.4,
145.2, 144.2, 129.4, 129.3, 129.2, 128.2, 128.1, 127.8, 124.8, 122.0,
118.0, 61.6, 60.3, 41.3 (2C) and 30.2 (3C); MS (ESI) m/z 447.2
162 ꢁC, Rf (DCM:MeOH:NH4OH; 19:1:0.1) 0.12; IR nmax (KBr)/cmꢀ1
1588 (Ar C]C), 1369 (N]N), 1314 (C]N), 1276 (CeO Ester),
1245(CeO Ester); dH (400 MHz; DMSO-d6) 8.65 (1H, d, J 4.5 Hz, H2),
7.86 (1H, d, J 9.2 Hz, H8), 7.82 (1H, d, J 2.8 Hz, H5), 7.76 (1H, d, J
4.5 Hz, H3), 7.33 (1H, dd, J 9.2 and 2.8 Hz, H7), 5.37 (1H, s, H9), 3.87
(3H, s, OCH3), 2.14 (6H, s, 2ꢂ H10); dC (101 MHz; DMSO-d6) 159.5,
156.4, 147.3, 146.0, 143.9, 130.6, 127.7, 120.9, 120.5, 103.7, 63.3, 55.2
and 43.2 (2C); MS (ESI) m/z 285.1 (Mþ þ H); HPLC purity: 95.8%;
0
tr ¼ 6.33 min.
(Mþ þ H); HPLC purity: 98.9%; tr ¼ 8.60 min.
0
3.1.2.2. N-ethyl-N-[(6-methoxyquinolin-4-yl)(1H-tetrazol-5-yl)
methyl]ethanamine (4.14b). Yield 15% (8 h); yellow solid; m.p. 168e
171 C, Rf (DCM:MeOH:NH4OH; 19:1:0.1) 0.11; IR nmax (KBr)/cmꢀ1
1600 (Ar C]C), 1368 (N]N), 1319 (C]N), 1269 (CeN), 1225 (CeO
Ester); dH (400 MHz; DMSO-d6) 8.61 (1H, d, J 4.5 Hz, H2), 7.91
(1H, d, J 2.8 Hz, H5), 7.86 (1H, d, J 9.2 Hz, H8), 7.52 (1H, d, J 4.5 Hz,
H3), 7.32 (1H, dd, J 9.2 and 2.8 Hz, H7), 5.87 (1H, s, H9), 3.85 (3H, s,
OCH3), 2.63 (2H, q, J 7.1 Hz, H10a), 2.27 (2H, q, J 7.1 Hz, H10b), 0.91
(6H, t, J 7.1 Hz, 2ꢂ H11); dC (100 MHz; DMSO-d6) 159.6, 156.6, 147.8,
146.1, 144.6, 131.1, 127.8, 122.1, 121.2, 104.4, 58.8, 55.8, 44.3 (2C) and
13.5 (2C); MS (ESI) m/z 313.2 (Mþ þ H); HPLC purity: 96.7%;
3.1.1.8. N-{[2,8-bis(trifluoromethyl)quinolin-4-yl](tert-butyl-1H-tet-
razol-5-yl)metyhyl}-N-ethylethanamine (4.13b). Yield 22%; light-
brown solid; m.p. 76e78 ꢁC, Rf (EtOAc:Hex, 1:1) 0.35; IR nmax
(DCM)/cmꢀ1 1602 (Ar C]C), 1424 (N]N), 1309 (C]N), 1279 (CeN),
1112 (CeF); dH (400 MHz; CDCl3) 8.82 (1H, d, J 8.6 Hz, H7), 8.23 (1H,
d, J 7.2 Hz, H5), 7.84 (1H, t, J 7.7 Hz, H6), 7.11 (1H, s, H3), 6.43 (1H, s,
H8), 2.88 (4H, q, J 7.2 Hz, 2ꢂ H9), 1.62 (9H, s, 3ꢂ H11), 0.93 (6H, t, J
7.2 Hz, 2ꢂ H10); dC (101 MHz; CDCl3) 152.5, 146.6, 143.1, 129.4,
129.3, 129.2, 128.4, 128.0, 127.8, 124.8, 122.1, 118.1, 61.9, 58.4, 45.8
(2C), 30.2 (3C) and 14.7 (2C); MS (ESI) m/z 475.4 (Mþ þ H); HPLC
0
0
purity: 95.3%; tr ¼ 8.93 min.
tr ¼ 7.38 min.
3.1.2. General procedure for preparation of compounds (4.14aef)
To the corresponding tert-butylated tetrazole 4.12
(0.51 mmol) in a round-bottom flask was added 32% hydrochloric
acid (10 ml), and the resulting mixture refluxed at 120 ꢁC for 4e
8 h. On complete consumption of the starting material, as shown
by TLC, the reaction mixture was allowed to cool to room
temperature, water (30 ml) added and the pH adjusted to 12 by
the addition of 5% NaHCO3. The basified mixture was then
washed with EtOAc (2 ꢂ 100 ml), the aqueous layer neutralized to
pH 7 by drop-wise addition of 32% HCl acid and allowed to stand
in the fume hood overnight. The precipitate which had formed
was filtered and washed with cold Et2O to afford a crude product
which was then purified by column chromatography (on silica
gel; elution with DCM:MeOH: 25% aqueous NH4OH; 19:1:0.1) and
preparative HPLC to give the desired product (4.14) in greater
than 95% purity.
3.1.2.3. 6-Methoxy-4-[(pyrrolidin-1-yl)(1H-tetrazol-5-yl)methyl]
quinoline (4.14c). Yield 13% (8 h); light-brown solid; m.p. 211e
214 ꢁC; Rf (DCM:MeOH:NH4OH; 19:1:0.1) 0.09; IR nmax (KBr)/cmꢀ1
1579(Ar C]C), 1366 (N]N), 1326 (C]N), 1274 (CeN), 1215 (CeO
Ester); dH (300 MHz; DMSO-d6) 8.66 (1H, d, J 4.4 Hz, H2), 7.96
(1H, d, J 2.6 Hz, H8), 7.84 (1H, d, J 9.2 Hz, H5), 7.79 (1H, d, J 4.4 Hz,
H3), 7.30 (1H, dd, J 9.2 and 2.6 Hz, H7), 5.40 (1H, s, H9), 3.86 (3H, s,
OCH3), 2.54 (2H, m, H10a), 2.35 (2H, m, H10b), 1.65 (4H, m, 2ꢂ H11);
dC (75 MHz; DMSO-d6) 159.0, 156.2, 147.2, 146.5, 130.3, 130.1, 129.1,
127.2, 120.3, 103.7, 61.9, 58.5, 51.6 (2C) and 23.0 (2C); MS (ESI) m/z
311.4 (Mþ þ H); HPLC purity: 95.1%; tr ¼ 7.12 min.
0
3.1.2.4. 6-Methoxy-4-[(piperidin-1-yl)(1H-tetrazol-5-yl)methyl]
quinoline (4.14d). Yield 28% (6 h); pale-yellow crystalline solid;
m.p. 131e134 ꢁC, Rf (DCM:MeOH:NH4OH; 19:1:0.1) 0.10; IR nmax
(KBr)/cmꢀ1 1630 (Ar C]C), 1368 (N]N), 1309 (C]N), 1251 (CeN),
1223 (CeO Ester);dH (300 MHz; DMSO-d6) 8.62 (1H, d, J 4.5 Hz,
H2), 7.99 (1H, d, J 2.8 Hz, H5), 7.85 (1H, d, J 9.2 Hz, H8), 7.69 (1H, d, J
4.5 Hz, H3), 7.31 (1H, dd, J 9.2 and 2.8 Hz, H7), 5.43 (1H, s, H9), 3.88
3.1.2.1. (6-Methoxyquinolin-4-yl)-N,N-dimethyl(1H-tetrazol-5-yl)
methanamine (4.14a). Yield 33% (8 h); pale-yellow solid; m.p. 159e