Coumarin–benzimidazole hybrids as a antimicrobial agents
LR Singh et al
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(E)-3-(2-(1H-benzo[d]imidazol-1-yl)-1-(((4-bromobenzyl)oxy)
imino)ethyl)-2H-chromen-2-one (14)
136.5, 133.7, 132.8, 129.5, 129.4, 128.7, 125.8, 124.8, 123.2, 122.4, 121.2, 120.3,
118.5, 116.7, 109.5, 77.8, 39.6, 21.5; HRMS (ESI) calcd for C26H21N3O3
[M + H]+ 424.1661 found 424.1649.
White solid, yield: 63%, that is, 157.6 mg; mp 124–126 °C; IR (KBr, cm− 1):
1
3019, 2400, 1721, 1608, 1490, 1405, 1215, 1026; H NMR (400 MHz, CDCl3):
δ 7.94 (s, 1H), 7.70 (d, J = 7.3 Hz, 1H), 7.60 (s, 1H), 7.55 (d, J =8.3 Hz, 2H),
7.53–7.49 (m, 1H), 7.36 (dd, J = 7.7, 1.2 Hz, 1H), 7.30 (d, J = 8.2 Hz, 2H),
7.27 (d, J = 8.6 Hz, 1H), 7.23–7.20 (m, 2H), 7.19–7.17 (m, 2H), 5.65 (s, 2H),
5.29 (s, 2H); 13C NMR (100 MHz, CDCl3): δ 160.0, 154.2, 152.3, 144.1, 143.7,
135.6, 133.8, 133.0, 131.9, 130.4, 128.7, 124.9, 123.2, 122.7, 122.4, 121.2, 120.5,
118.5, 116.7, 109.4, 76.7, 39.7; HRMS (ESI) calcd for C25H18BrN3O3 [M + H]+
488.0610 found 488.0584.
(E)-3-(2-(1H-benzo[d]imidazol-1-yl)-1-(((4-methoxybenzyl)oxy)
imino)ethyl)-2H-chromen-2-one (20)
White solid, yield: 73%, that is, 182 mg; mp 126–128 °C; IR (KBr, cm− 1): 3019,
2400, 1721, 1611, 1495, 1406, 1215, 1038; 1H NMR (400 MHz, CDCl3,): δ 7.93
(s, 1H), 7.69–7.68 (m, 2H), 7.52–7.48 (m, 1H), 7.40 (d, J = 8.5 Hz, 2H), 7.35
(d, J = 7.7 Hz, 1H), 7.28–7.25 (m, 1H), 7.23–7.15 (m, 4H), 6.96 (d, J = 8.6 Hz,
2H), 5.65 (s, 2H), 5.29 (s, 2H), 3.85 (s, 3H); 13C NMR (100 MHz, CDCl3,):
δ 160.0, 154.1, 151.6, 144.1, 143.6, 143.5, 133.7, 132.8, 130.6, 128.7, 124.8,
123.2, 122.3, 121.3, 120.3, 118.5, 116.7, 114.1, 109.5, 77.4, 55.4, 39.5; HRMS
(ESI) calcd for C26H21N3O4 [M + H]+ 440.1610 found 440.1603.
(E)-3-(2-(1H-benzo[d]imidazol-1-yl)-1-(3-(trifluoromethyl)
benzyloxyimino)ethyl)-2H-chromen-2-one (15)
Whitish yellow solid, yield: 71%, that is, 177.2 mg; mp 146–148 °C; IR
(KBr, cm− 1): 3001, 2517, 1722, 1611, 1473, 1384, 1250, 1026; 1H NMR
(400 MHz, CDCl3): δ 7.94 (s, 1H), 7.75 (s, 1H), 7.70–7.66 (m, 2H), 7.64–7.62
(m, 2H), 7.58 (d, J = 7.6 Hz, 1H), 7.51–7.49 (m, 1H), 7.34 (dd, J = = 7.7 Hz,
J = 1.1 Hz, 1H), 7.28–7.26 (m, 1H), 7.23–7.18 (m, 2H), 7.16–7.15 (m, 2H),
5.67 (s, 2H), 5.40 (s, 2H); 13C NMR (75 MHz, CDCl3): δ 160.0, 154.2, 152.6,
144.1, 143.9, 143.5, 137.7, 133.7, 133.0, 132.0, 131.4, 130.9, 129.4, 128.7, 125.9,
125.5, 125.0, 123.3, 122.5, 121.0, 120.5, 118.4, 116.7, 109.2, 76.7, 39.7; HRMS
(ESI) calcd for C26H18F3N3O3 [M + H]+ 478.1379 found 478.1360.
(E)-3-(2-(1H-benzo[d]imidazol-1-yl)-1-(((2,4-difluorobenzyl)oxy)
imino)ethyl)-2H-chromen-2-one (21)
White solid, yield: 68%, that is, 170 mg; mp 140–142 °C; IR (KBr, cm− 1): 3020,
2411, 1719, 1615, 1499, 1457, 1277, 1019; 1H NMR (400 MHz, CDCl3): δ 7.94
(s, 1H), 7.70–7.67 (m, 2H), 7.53–7.49 (m, 1H), 7.45–7.39 (m, 1H),
7.36 (d, J = 6.8 Hz, 1H), 7.27 (d, J = 8.6 Hz, 1H), 7.24–7.18 (m, 4H),
6.95–6.89 (m, 2H), 5.67 (s, 2H), 5.38 (s, 2H); 13C NMR (100 MHz, CDCl3):
δ 165.0, 163.2, 161.7, 160.0, 154.2, 152.3, 144.0, 143.7, 143.5, 133.8, 133.0,
132.4, 128.7, 124.9, 123.2, 122.4, 121.1, 120.5, 118.5, 116.7, 109.4, 104.3, 70.8,
39.5; HRMS (ESI) calcd for C25H17F2N3O3 [M + H]+ 446.1316 found
446.1293.
(E)-3-(2-(1H-benzo[d]imidazol-1-yl)-1-(((3-chlorobenzyl)oxy)
imino)ethyl)-2H-chromen-2-one (16)
White solid, yield: 70%, that is, 170.0 mg; mp 148–150 °C; IR (KBr, cm− 1):
1
3019, 2413, 1721, 1627, 1494, 1431, 1215, 1028; H NMR (400 MHz, CDCl3):
(E)-3-(2-(1H-benzo[d]imidazol-1-yl)-1-(((2,5-dichlorobenzyl)oxy)
δ 7.96 (s, 1H), 7.70–7.69 (m, 1H), 7.66 (s, 1H), 7.53–7.49 (m, 1H), 7.46
(s, 1H), 7.38–7.36 (m, 2H), 7.34 (s, 1H), 7.32–7.31 (m, 1H), 7.28–7.26 imino)ethyl)-2H-chromen-2-one (22)
(m, 1H), 7.23–7.20 (m, 4H), 5.68 (s, 2H), 5.32 (s, 2H); 13C NMR (100 MHz,
CDCl3): δ 159.9, 154.1, 152.3, 144.0, 143.8, 143.3, 138.6, 134.6, 133.7, 133.0,
130.1, 128.7, 126.7, 124.9, 123.4, 122.5, 121.0, 120.4, 118.4, 116.7, 109.4, 76.7,
39.7; HRMS (ESI) calcd for C25H18ClN3O3 [M + H]+ 444.1115 found
444. 1067.
Yellow solid, yield: 71%, that is, 177 mg; mp 136–138 °C; IR (KBr, cm− 1):
1
2949, 2417, 1719, 1610, 1459, 1364, 1233, 1024; H NMR (400 MHz, CDCl3):
δ 8.42 (s, 1H), 7.83–7.82 (m, 2H), 7.57–7.53 (m, 1H), 7.43–7.41 (m, 2H),
7.40–7.36 (m, 2H), 7.31–7.29 (m, 4H), 7.26–7.23 (m, 1H), 5.75 (s, 2H), 5.41
(s, 2H); 13C NMR (100 MHz, CDCl3): δ 159.9, 154.1, 151.4, 144.3, 142.6,
138.5, 135.6, 133.3, 132.9, 132.3, 131.0, 130.6, 130.0, 128.9, 125.1, 124.7,
124.2, 120.4, 118.9, 118.4, 116.7, 110.2, 76.4, 40.4; HRMS (ESI) calcd for
C25H17Cl2N3O3 [M + H]+ 478.0725 found 478.0718.
(E)-3-(2-(1H-benzo[d]imidazol-1-yl)-1-((benzyloxy)imino)ethyl)-
2H-chromen-2-one (17)
White solid, yield: 61%, that is, 152.2 mg; mp 144–146 °C; IR (KBr, cm− 1):
3020, 2400, 1717, 1617, 1521, 1424, 1215, 1039; 1H NMR (400 MHz, CDCl3,):
δ 7.94 (s, 1H), 7.70–7.67 (m, 2H), 7.52–7.48 (m, 1H), 7.47–7.44 (m, 4H),
7.42–7.40 (m, 1H), 7.36–7.34 (m, 1H), 7.28–7.25 (m, 1H), 7.22–7.15 (m, 4H),
5.67 (s, 2H), 5.37 (s, 2H); 13C NMR (100 MHz, CDCl3,): δ 160.0, 154.1, 151.9,
144.1, 143.7, 143.5, 136.6, 133.7, 132.9, 128.8, 124.8, 123.2, 122.3, 121.2, 120.4,
118.5, 116.7, 109.5, 76.7, 39.6; HRMS (ESI) calcd for C25H19N3O3 [M + H]+
410.1505 found 410.1480.
Ethical statement
This study has the prior approval from the CSIR-CDRI institutional human
ethics committee at CDRI, Lucknow (CDRI/IEC/2014/A1).
Bacterial strains
All the bacterial strains were obtained from the MTCC, India or ATCC, USA
and were routinely grown in Nutrient agar medium (NAM; Difco/Becton &
Dickinson, Franklin Lakes, NJ, USA). Just before the experiment, a loop full of
bacteria was inoculated in Mueller Hinton (MH) broth and incubated at 37 °C
and 5% CO2 for overnight to get the starter culture.
(E)-3-(2-(1H-benzo[d]imidazol-1-yl)-1-(((3-nitrobenzyl)oxy)imino)
ethyl)-2H-chromen-2-one (18)
Yellow solid, yield: 72%, that is, 180 mg; mp 160–162 °C; IR (KBr, cm− 1):
3021, 2425, 1719, 1611, 1492, 1456, 1219, 1023; 1H NMR (400 MHz, CDCl3,):
δ 8.35 (s, 1H), 8.25 (d, J = 7.3 Hz, 1H), 8.03 (bs, 1H), 7.71 (bs, 3H), 7.63–7.59
(m, 1H), 7.55–7.51 (m, 1H), 7.39 (d, J = = 7.1 Hz, 1H), 7.29–7.21 (m, 5H),
5.68 (s, 2H), 5.43 (s, 2H); 13C NMR (100 MHz, CDCl3,): δ 159.9, 154.1, 152.8,
148.5, 144.0, 142.8, 138.7, 134.5, 133.1, 129.9, 128.8, 125.0, 123.5, 122.7, 120.8,
120.3, 118.4, 116.7, 109.4, 76.1, 39.9; HRMS (ESI) calcd for C25H18N4O5
[M + H]+ 455.1355 found 455.1304.
MIC assay
MIC assay for the test compounds was carried out by the microtitre
broth dilution method as prescribed by CLSI (previously NCCLS).20,21 For
determination of MIC, test compounds were diluted from a stock solution
(10 mg ml− 1) such that the final concentration ranges between 50 and
0.39 μg ml− 1 in different wells. Bacteria grown in 5% MH broth for 12–18 h
were rinsed twice with sterile phosphate-buffered saline and diluted in MH
broth to a concentration of ~ 5 × 105 CFU per ml. About 90 μl of bacterial
suspension in MH medium was added to each well containing the test
compound and incubated at 37 °C for 16 h. A positive control for growth
containing no test compound was included in each assay. MIC was taken as the
concentration where the growth inhibition observed was 495%. For each test
compound, MIC determinations were carried independently twice using
(E)-3-(2-(1H-benzo[d]imidazol-1-yl)-1-(3-methylbenzyloxyimino)
ethyl)-2H-chromen-2-one (19)
Yellow solid, yield: 75%, that is, 187 mg; mp 157–159 °C; IR (KBr, cm− 1):
2979, 2410, 1712, 1623, 1479, 1379, 1235, 1021; 1H NMR (400 MHz, CDCl3,):
δ 7.94 (s, 1H), 7.70–7.68 (m, 2H), 7.52–7.48 (m, 1H), 7.35–7.31 (m, 2H),
7.27–7.26 (m, 3H), 7.22–7.16 (m, 5H), 5.67 (s, 2H), 5.33 (s, 2H), 2.41 (s, 3H);
13C NMR (75 MHz, CDCl3,): δ 160.0, 154.1, 151.8, 144.1, 143.7, 143.4, 138.4, triplicate samples each time.
The Journal of Antibiotics