Different positions of amide side chains on the benzimidazo[1,2-a]quinoline skeleton strongly influence biological activity

Nataša Perin a, Jasna Alić a, Sandra Liekens b, Arthur Van Aerschot c, Peter Vervaeke d, Bharat Gadakh c and Marijana Hranjec *a
aDepartment of Organic Chemistry, Faculty of Chemical Engineering and Technology, University of Zagreb, Marulićev trg 19, P. O. Box 177, HR-10000 Zagreb, Croatia. E-mail: mhranjec@fkit.hr
bRega Institute, Department of Microbiology and Immunology, Herestraat 49, B-3000 Leuven, Belgium
cRega Institute, Department of Pharmaceutical and Pharmacological Sciences, Herestraat 49, B-3000 Leuven, Belgium
dRega Institute for Medical Research, Laboratory of Virology and Chemotherapy, Herestraat 49, B-3000 Leuven, Belgium

Received 23rd January 2018 , Accepted 22nd March 2018

First published on 23rd March 2018


Benzimidazo[1,2-a]quinolines substituted with amide chains have been evaluated for their antiproliferative, antibacterial and antiviral activity in vitro. Amido-substituted cyclic derivatives were synthesized by classical organic synthetic reactions in order to study the influence of the type and length of the amide side chain as well as its position on the tetracyclic skeleton on biological activity. The most promising antiproliferative activity (i.e. sub-micromolar IC50 concentrations) was displayed by 6-N,N-dimethylaminopropyl 21, 6-N,N-diethylaminoethyl 22 and the 2- and 6-N,N-dimethylaminopropyl substituted derivative 25. Additionally, micromolar concentrations of compounds 21 and 25 induced apoptosis in human cervical carcinoma HeLa cells. Compounds 28, 29 and 30, substituted with the isobutyl, N,N-dimethylaminopropyl and N,N-diethylaminoethyl amide side chain placed at position 2, displayed antiviral activity against herpes simplex virus (HCV) (EC50 1.8–6.8 μM) and human coronavirus (EC50 4–12 μM). Furthermore, N,N-dimethylaminopropyl 21 and N,N-diethylaminoethyl 22 substituted compounds bearing the amide side chain at position 6 of the tetracyclic skeleton were active against S. epidermidis and C. albicans strains.


Introduction

In recent years, there has been a growing interest in the synthesis of fused and cyclic benzimidazole derivatives because of their great importance in natural, medicinal and environmental sciences.1–8 This type of compound can be easily prepared by combination of the benzimidazole nuclei with some other heteroaromatic rings, for example a quinoline ring, thus leading to mostly enhanced biological or spectroscopic properties.

Recently, as part of our continued scientific research on the synthesis of biologically active benzimidazo[1,2-a]quinolines, we have published several papers which have confirmed their great anticancer potency, their interaction with DNA or RNA, or their inhibitory activities against topoisomerases I and II.9 Importantly, we have shown that different side chain substituents together with their different positions on the tetracyclic skeleton could significantly enhance the antiproliferative activity and interaction with biological targets.10,11 Thus, amino substituted benzimidazo[1,2-a]quinolines have shown antifungal activity against some Candida strains with N,N-dimethylaminopropyl substituted derivatives being the most active ones (Fig. 1a).12 Within this study, the potential of this type of compounds for disinfection of medical and surgical instruments in clinical and surgical procedures was confirmed. Also, a group of authors have synthesized 6-arylbenzimidazo[1,2-c]quinazolines as a new class of antimicrobial agents. These compounds showed better activity against tested bacterial and fungal strains as compared with the standards ampicillin and ketoconazole.13,14 Furthermore, E. A. Lyakhova and co-workers have synthesized amino substituted benzimidazo[1,2-c]quinazolines as potential interferon inducers and antiviral agents (Fig. 1b).15


image file: c8nj00416a-f1.tif
Fig. 1 Examples of biologically active tetracyclic benzimidazole derivatives.

Previously, pyrimidopyrrolobenzimidazoles were synthesized and examined for their antimicrobial activity against Gram-positive (Bacillus subtilis and Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa).

Moreover, some tetracyclic derivatives such as 6-aryl-5,6-dihydrobenzimidazo[1,2-c]quinazolines showed promising antibacterial activity against S. aureus and E. coli strains.16

Based on our previous results regarding the promising biological potential of tetracyclic benzimidazole derivatives, herein we present the design and synthesis of novel benzimidazo[1,2-a]quinolines substituted with diverse amide side chains placed at different positions on the tetracyclic skeleton and their biological evaluation regarding the antiproliferative, antiviral and antimicrobial activity in vitro. Moreover, the SAR study based on all obtained results will be discussed.

Results and discussion

Synthesis

All newly prepared benzimidazo[1,2-a]quinolines were prepared according to the experimental procedure shown in Scheme 1, by the well-known standard synthetic methods for the synthesis of such benzimidazole derivatives, which were earlier developed and optimized in our research group.9,17,18
image file: c8nj00416a-s1.tif
Scheme 1 Synthetic scheme for benzimidazo[1,2-a]quinolines bearing amide chains at different positions.

Starting from 2-cyanomethylbenzimidazole 1 and 2-methylbenzimidazole 2, in the reaction with the corresponding benzaldehydes 3 and 4, acyclic benzimidazole derivatives 5–7 were prepared.9,19

Cyclic benzimidazo[1,2-a]quinolines 8–10 were prepared either by photochemical dehydrocyclization or by thermal cyclization in sulfolane at high temperature (280 °C).20 With the acidic hydrolysis of derivatives 8–10 in 2 N sulphuric acid, the corresponding carboxylic acids 11–13 were obtained, which gave in the reaction with thionyl-chloride, acyl-halides 14–16 as the main precursors for the synthesis of designed amides. Targeted amide substituted cyclic derivatives 17–18 and 20–30 were prepared by condensation of 14–16 and an excess amount of the corresponding amine in absolute dichloromethane in low to moderate reaction yields (8–72%). Compound 19 was obtained as a hydrochloride salt when equimolar amounts of acyl-chloride 14 and 4-methylpiperazine were used.

The structures of all newly prepared amide substituted derivatives 17–30 were determined by using 1H and 13C NMR spectroscopy and elemental analysis. NMR analysis is based on the chemical shifts and values of H–H coupling constants in the 1H and 13C NMR spectra. The products of photochemical and thermal cyclizations were confirmed by the disappearance of the aromatic proton and/or one NH benzimidazole proton which led to a downfield shift of the aromatic protons, thus confirming the formation of the tetracyclic benzimidazole derivatives.

The NMR spectra of carboxylic acids showed one additional signal in comparison to the spectra of cyano substituted derivatives 8–10. The formation of amide derivatives was confirmed by the appearance of the signal related to the proton of the amide group in the 1H NMR spectra as well as signals related to the protons of the amide side chains in the aliphatic part of spectra.

Antiproliferative activity in vitro

Antiproliferative activities (displayed as IC50 values) of amide-substituted benzimidazo[1,2-a]quinolines 17–30 were assessed on three human tumour cell lines in vitro: T-cell leukemia cells (CEM), cervical carcinoma cells (HeLa) and breast adenocarcinoma cells (MCF7). As a first broad screening was envisaged, the choice of these particular tumour cell lines was motivated towards targeting one haematological and two solid cancers within the wealth of potential test systems which could have been employed.

All tested compounds, except the piperazinyl substituted derivatives 17, 23 and 26, inhibited the growth of these cancer cell lines. The most active derivatives proved to be the 6-N,N-dimethylaminopropyl substituted derivative 21, the 6-N,N-diethylaminoethyl substituted derivative 22 and the 2- and 6-N,N-dimethylaminopropyl substituted derivative 25 with submicromolar IC50 concentrations. Compound 22 displayed selective activity toward MCF-7 and CEM cells. 2-N,N-Dimethylaminopropyl 29 and 2-N,N-diethylaminoethyl substituted benzimidazo[1,2-a]quinoline 30 inhibited cancer cell growth in the low range but without significant selectivity among tested cancer cells. Thus, it could be observed that the most potent compounds 21, 22 and 25 with IC50 0.22–0.96 μM have the amide side chain with an additional nitrogen atom at position 6 or 2 and 6. Moreover, the introduction of an additional nitrogen atom in the side chain had a crucial effect on the antiproliferative activity, which was markedly enhanced. The additional nitrogen atom, as has been proven earlier in our research group, could alter the interaction with biological targets or influence the physico-chemical properties. A similar effect was observed earlier regarding the biological activity of some amino-substituted benzimidazo[1,2-a]quinolines.11 By placing the same amide side chains at position 2, a slight decrease of antiproliferative activity could be noticed with compounds 29 and 30 having IC50 in the range of 1.3–2.5 μM.

Among 6-substituted derivatives, the results revealed that amide 17 bearing piperidine nuclei showed a significant decrease of antiproliferative activity in comparison to compounds 18–20. With the introduction of the N-methylpiperazine nuclei with an additional nitrogen atom in the structure of compounds 18 and 19, the antiproliferative activity was improved without significant differences between compound 18 and its protonated analogue 19. Regarding the 6-substituted amide derivatives, compound 23 bearing two piperidine nuclei in comparison to compound 24 with two isobutyl amide side chains showed improvement of the antiproliferative activity on all three cell lines with selectivity toward MCF-7 cells. Compared to compound 26 substituted with the piperidine amide side chain, 2-substituted amides bearing N-methyl piperazine nuclei 27 and the isobutyl side chain 28 showed increased antiproliferative activity against the CEM and HeLa cells. Overall, the structure–activity relationship presented in Fig. 2 indicates that variations of the type of amide side chain and its position on the tetracyclic skeleton have profound effects on the cytostatic activity of the compounds.


image file: c8nj00416a-f2.tif
Fig. 2 Insights into SAR for antiproliferative activity.

It was also pointed out that the derivatives with the most pronounced antiproliferative activities in the sub-micromolar IC50 range of concentrations have an additional electron-donating nitrogen atom which could additionally improve the interaction with possible biological targets.

As shown in our recent studies, planar tetracyclic benzimidazo[1,2-a]quinolines might intercalate into the ds-DNA, which could be, together with the inhibition of topoisomerase I and/or II, one of the mechanisms of action of such derivatives which are also structurally related to well-known antitumor agents ellipticine or intoplicine.21,22 Furthermore, the amide side chain placed in position 4 of the tricyclic antitumor agent DACA could reinforce significantly the drug–DNA interaction, increase the residence time of the drug on DNA and confer selectivity for GC-rich sequences of DNA, being an important factor affecting the drug transport rate through cell membranes.23,24 The 4-carboxamide chain, as in DACA, results in more efficient penetration into cells and a higher DNA-damaging activity contributing thus to a higher cytotoxicity.25

In Table 1, the values for c[thin space (1/6-em)]log[thin space (1/6-em)]P for the neutral form of the prepared compounds calculated by using ChemDraw Ultra 10.0 (http://www.cambridgesoft.com) are presented. The definition of log[thin space (1/6-em)]P as 1-octanol/water partition coefficient is indicative of the lipophilicity or hydrophilicity of the newly prepared compounds. From the obtained results it was obvious that the c[thin space (1/6-em)]log[thin space (1/6-em)]P values are dependent on the type and the position of the amide side chains. Thus, the most lipophilic amides were proven to be compound 24 bearing two isobutyl side chains (c[thin space (1/6-em)]log[thin space (1/6-em)]P 5.43), 22 with the N,N-diethylaminoethyl side chain (c[thin space (1/6-em)]log[thin space (1/6-em)]P 5.08) and 20 with the isobutyl side chain (c[thin space (1/6-em)]log[thin space (1/6-em)]P 5.07) at position 6. Due to the displacement of the isobutyl and N,N-diethylaminoethyl side chains at position 2 (compounds 28 and 30), a slight decrease of lipophilicity could be observed (c[thin space (1/6-em)]log[thin space (1/6-em)]P 4.72 and 4.73). Moreover, derivatives bearing the piperidine nuclei 17, 23 and 26 displayed further extenuation of lipophilicity (c[thin space (1/6-em)]log[thin space (1/6-em)]P 4.29, 4.01 and 4.08). Compounds substituted with N-methylpiperazine nuclei at positions 6 (18) and 2 (27) and 6-N,N-dimethylaminopropyl (29) and 2,6-di-N,N-dimethylaminopropyl (25) substituted derivatives are in general more hydrophilic in comparison to other derivatives with c[thin space (1/6-em)]log[thin space (1/6-em)]P 3.61–3.95.

Table 1 Antiproliferative activity of tested compounds in vitro
Comp. Pb R IC50a (μM) c[thin space (1/6-em)]log[thin space (1/6-em)]P
CEM HeLa MCF7
a 50% inhibitory concentration. b P – position on the tetracyclic skeleton.
17 6 image file: c8nj00416a-u1.tif 156 ± 132 ≥250 67 ± 52 4.29
18 6 image file: c8nj00416a-u2.tif 22 ± 0 17 ± 4 13 ± 0 3.82
19 6 image file: c8nj00416a-u3.tif 33 ± 6 33 ± 20 17 ± 2 4.11
20 2,6 CONHCH2CH(CH3)2 24 ± 1 26 ± 7 23 ± 5 5.07
21 2,6 CONH(CH2)3N(CH3)2 0.96 ± 0.16 0.94 ± 0.14 0.69 ± 0.24 4.30
22 2,6 CONH(CH2)2N(CH2CH3)2 0.80 ± 0.04 4.1 ± 0.6 0.49 ± 0.14 5.08
23 2,6 image file: c8nj00416a-u4.tif 108 ± 51 184 ± 93 93 ± 2 4.01
24 2,6 CONHCH2CH(CH3)2 >250 >250 148 ± 60 5.43
25 2,6 CONH(CH2)3N(CH3)2 0.22 ± 0.08 0.48 ± 0.17 0.24 ± 0.09 3.90
26 2 image file: c8nj00416a-u5.tif 77 ± 40 94 ± 14 16 ± 6 4.08
27 2 image file: c8nj00416a-u6.tif 24 ± 1 26 ± 12 15 ± 0 3.61
28 2 CONHCH2CH(CH3)2 13 ± 7 74 ± 18 66 ± 22 4.72
29 2 CONH(CH2)3N(CH3)2 2.5 ± 1.2 1.8 ± 0.4 1.3 ± 0.4 3.95
30 2 CONH(CH2)2N(CH2CH3)2 2.4 ± 0.4 1.9 ± 0.8 1.3 ± 0.5 4.73
5-Fluorouracil 0.18 ± 0.02 18 ± 5 0.54 ± 0.12


Cell cycle experiments

In order to get further insight into the potential mechanism of activity of compounds 21 and 25, we assessed their influence on cell cycle progression in HeLa cells after 24 hours of treatment (Fig. 3).
image file: c8nj00416a-f3.tif
Fig. 3 Cell cycle analysis in HeLa cells. HeLa cells were treated with DMSO (control) or compound 21 or 25 for 24 h. Next, the cells were harvested, stained with propidium iodide, and subjected to flow cytometry for cell cycle distribution analysis. Percentages of cells in the different phases of the cell cycle are indicated.

Antimicrobial activity

The antimicrobial activity of the compounds was tested on several bacterial strains including Staphylococcus aureus ATCC 6538P, Staphylococcus epidermidis RP62A, Escherichia coli NCIB 8743, Pseudomonas aeruginosa PAO1, Sarcina lutea ATCC9341, and the fungal strain Candida albicans CO11. The results are presented in Table 2. The antimicrobial activities were determined by measuring the optical density reached by the cell suspension in the well of a microtiter plate in the presence of various concentrations of the respective inhibitors. These six strains were selected to cover the spectrum of activity from Gram-negative (E. coli and P. aeruginosa) to Gram-positive (S. epidermidis, S. aureus and S. lutea) bacteria and fungi (C. albicans). All strains were grown on LB medium.
Table 2 Antimicrobial activity of the most active compounds
Compound % inhibition at 100 μM
S. epidermidis C. albicans
a Due to one outlier, the SD could not be calculated.
21 56.4 ± 9.6
22 52.6 ± 4.9 53.5a
Mupirocin 63 ± 19 83 ± 5
Ciprofloxacin 100 at 3 μM NA


Only two compounds among all tested, namely N,N-dimethylaminopropyl 21 and N,N-diethylaminoethyl 22 substituted compounds bearing an amide side chain at position 6 of the tetracyclic skeleton, showed moderate activity against S. epidermidis while C. albicans proved to be inhibited only slightly by compound 22 (Table 3). Both active compounds are substituted with the aliphatic amide side chain with an additional nitrogen atom (Fig. 4). Mupirocin was chosen as the reference compound being specifically active against Staph. aureus, while ciprofloxacin had a broader activity profile and showed complete inhibition of S. epidermidis in our hands at 3 micromolar concentration.26

Table 3 Antiviral activity of active compounds in HeLa cells
Comp. Minimum cytotoxic conc.a EC50b (μM)
Herpes simplex virus-1 (KOS) Herpes simplex virus-2 (G) Herpes simplex virus-1 TK KOS ACVr Human coronavirus (229E)
a Required to cause a microscopically detectable alteration of normal cell morphology. b Required to reduce virus-induced cytopathogenicity by 50%.
28 >100 5.4 ± 2.0 2.4 ± 0.8 1.7 ± 0.2 10.5 ± 2.0
29 ≥20 >100 >100 >100 8.9 ± 0.0
30 ≥20 >100 >100 >100 6.5 ± 3.5
Brivudin >250 0.05 87 10
Cidofovir >250 2 2 1.2
Acyclovir >250 0.4 0.2 2
Ganciclovir >100 0.02 0.03 0.1
UDA >100 1.8



image file: c8nj00416a-f4.tif
Fig. 4 Insights into SAR for antiviral and antimicrobial activity.

Antiviral activity in vitro

Next, in a broad screening effort, the activity of the compounds was tested against various DNA and RNA viruses and against HIV (shown as EC50). In parallel, cytotoxicity was evaluated (displayed as CC50). As standard antiviral drugs, brivudin, cidofovir, acyclovir and ganciclovir were used. The results obtained are presented in Table 3.

As shown in Table 3, among all tested compounds, only compound 28 substituted with the isobutyl amide side chain, 29 substituted with the N,N-dimethylaminopropyl amide side chain and 30 substituted with the N,N-diethylaminoethyl amide side chain showed activity against HSV (EC50 1.8–6.8 μM) and human coronavirus (EC50 4–12 μM). No activities were noted against any of the other DNA or RNA viruses or HIV.

All active derivatives are substituted with amide side chains at position 2 of the tetracyclic skeleton (Fig. 4).

Compared to derivatives 28–30 bearing aliphatic amide side chains, derivatives substituted with either cyclic piperidine or piperazine nuclei placed at position 2 did not display any antiviral activity. Compound 28 showed activity against the HSV TK plus as well as the HSV TK minus strain, indicating that the compound did not require the viral thymidine kinase protein for its activity.

Conclusions

Herein we present the synthesis and biological evaluation of novel benzimidazo[1,2-a]quinolines substituted with amide chains placed at various positions on the tetracyclic skeleton. This allowed the study of the influence of the type and length of the amide side chain as well as its position on the tetracyclic skeleton on biological activity. All synthesized compounds have been evaluated for their antiproliferative, antibacterial and antiviral activity in vitro.

The tested compounds showed antiproliferative activities against three human cancer cell lines. The most active compounds, 6-N,N-dimethylaminopropyl 21, 6-N,N-diethyl-aminoethyl 22 and the 2- and 6-N,N-dimethylaminopropyl substituted derivative 25, displayed significant activity with sub-micromolar IC50 concentrations (IC50 0.22–0.96 μM). Notably, all three compounds are substituted with aliphatic side chains with an additional nitrogen atom which could affect the interaction with biological targets. Also, we have noticed that the c[thin space (1/6-em)]log[thin space (1/6-em)]P values are dependent on the type and the position of the amide side chains. Thus, the most lipophilic amides have proven to be diisobutyl substituted 24, 6-N,N-diethylaminoethyl substituted 22 and 6-isobutyl substituted 20 amides with c[thin space (1/6-em)]log[thin space (1/6-em)]P 5.43–5.07. At micromolar concentrations, these compounds induced apoptosis in HeLa cells. Additionally, compounds 28, 29 and 30 substituted at position 2 of the tetracyclic skeleton with either isobutyl 20, N,N-dimethylaminopropyl 21 or N,N-diethylaminoethyl 22 amide side chain, showed antiviral activity against HSV (EC50 1.8–6.8 μM) and human coronavirus (EC50 4–12 μM). Regarding the antibacterial and antifungal activity evaluation, all tests revealed that only two compounds 21 and 22 were endowed with moderate activity against S. epidermidis and C. albicans strains.

Experimental section

Synthesis

General methods. All chemicals and solvents were purchased from commercial suppliers Aldrich and Acros. Melting points were recorded on SMP11 Bibby and Büchi 535 apparatus. All NMR spectra were measured in DMSO-d6 solutions using TMS as an internal standard. The 1H and 13C NMR spectra were recorded on a Varian Gemini 300 or Varian Gemini 600 at 300, 600 and 150 and 75 MHz, respectively. Chemical shifts are reported in ppm (δ) relative to TMS. All compounds were routinely checked by TLC using Merck silica gel 60F-254 glass plates. In preparative photochemical experiments, irradiation was performed at room temperature with a water-cooled immersion well with an “Origin Hanau”, 400 W, high-pressure, mercury arc lamp using Pyrex glass as a filter. Elemental analysis for carbon, hydrogen and nitrogen was performed on a Perkin-Elmer 2400 elemental analyzer. Where analyses are indicated only as symbols of elements, analytical results obtained are within 0.4% of the theoretical value.
General method for the synthesis of compounds 17–30. A mixture of carbonyl chlorides 14–16 and an excess of the corresponding amine in dry dichloromethane was stirred at room temperature for 2 h. The mixture was washed with 10 mL of 20% Na2CO3 and 10 mL of water.

After drying over MgSO4, the organic layer was concentrated at reduced pressure.


Benzimidazo[1,2-a]quinolin-6-yl(piperidin-1-yl)methanone 17. Compound 17 was prepared using the above described method, from benzimidazo[1,2-a]quinoline-6-carbonyl chloride 14 (0.200 g, 0.71 mmol), dry dichloromethane (20 mL) and 0.21 mL (2.14 mmol) of piperidine to obtain 0.079 g (34%) of light yellow powder; m.p. 213–215 °C; 1H NMR (300 MHz, DMSO-d6): δ = 8.85 (d, 1H, J = 8.49 Hz, Harom.), 8.80–8.71 (m, 1H, Harom.), 8.11 (dd, 1H, J1 = 1.17 Hz, J2 = 7.83 Hz, Harom.), 8.00 (s, 1H, Harom.), 7.99–7.96 (m, 1H, Harom.), 7.89 (dt, 1H, J1 = 7.88 Hz, J2 = 1.38 Hz, Harom.), 7.61 (t, 1H, J = 7.50 Hz, Harom.), 7.57–7.54 (m, 2H, Harom.), 3.73 (bs, 2H, CH2), 3.25 (bs, 2H, CH2), 1.64 (bs, 4H, CH2), 1.46 (bs, 2H, CH2); 13C NMR (75 MHz, DMSO-d6): δ = 164.48, 145.43, 144.76, 135.33, 131.33, 130.95, 130.57, 129.23, 127.04, 125.14, 125.00, 123.52, 122.76, 120.66, 116.18, 115.32, 48.07, 42.45, 26.54, 25.77, 24.44; found: C, 76.57; H, 5.81; N, 12.76. Calc. for C21H19N3O: C, 76.50; H, 5.86; N, 12.70%.
Benzimidazo[1,2-a]quinolin-6-yl(4-methylpiperazin-1-yl)methanone 18. Compound 18 was prepared using the above described method, from benzimidazo[1,2-a]quinoline-6-carbonyl chloride 14 (0.150 g, 0.53 mmol), dry dichloromethane (20 mL) and 0.12 mL (1.07 mmol) of 1-methylpiperazine to obtain 0.024 g (13%) of light yellow powder; m.p. 232–235 °C; 1H NMR (300 MHz, DMSO-d6): δ = 8.85 (d, 1H, J = 8.46 Hz, Harom.), 8.80–8.70 (m, 1H, Harom.), 8.12 (d, 1H, J = 7.83 Hz, Harom.), 8.02 (s, 1H, Harom.), 8.00–7.97 (m, 1H, Harom.), 7.90 (t, 1H, J = 7.88 Hz, Harom.), 7.62 (t, 1H, J = 7.41 Hz, Harom.), 7.58–7.52 (m, 2H, Harom.), 3.76 (bs, 2H, CH2), 3.29 (t, 2H, J = 9.48 Hz, CH2), 2.42 (bs, 2H, CH2), 2.27 (bs, 2H, CH2), 2.21 (s, 3H, CH3); 13C NMR (75 MHz, DMSO-d6): δ = 164.80, 145.33, 144.63, 135.33, 131.33, 130.90, 130.72, 129.77, 126.55, 125.08, 125.01, 123.50, 122.73, 120.62, 116.06, 115.17, 55.22, 54.69, 47.02, 46.13, 41.71; found: C, 73.23; H, 5.85; N, 16.27. Calc. for C21H20N4O: C, 73,20; H, 5,80; N, 16.31%.
Benzimidazo[1,2-a]quinolin-6-yl(4-methylpiperazin-1-yl)methanone hydrochloride 19. Compound 19 was obtained after stirring equimolar amounts of benzimidazo[1,2-a]quinoline-6-carbonyl chloride 14 (0.150 g, 0.53 mmol) and 0.06 mL (0.53 mmol) of 1-methylpiperazine in dry dichloromethane (20 mL) for 2 h, as a white solid; m.p. 254–257 °C; 1H NMR (300 MHz, DMSO-d6): δ = 11.54 (bs, 1H, NH+), 9.00 (d, 1H, J = 8.58 Hz, Harom.), 8.91 (d, 1H, J = 7.44 Hz, Harom.), 8.38 (s, 1H, Harom.), 8.23 (d, 1H, J = 6.87 Hz, Harom.), 8.09–8.00 (m, 2H, Harom.), 7.53 (t, 1H, J = 7.48 Hz, Harom.), 7.71–7.64 (m, 2H, Harom.), 3.55 (bs, 4H, CH2), 3.27 (bs, 4H, CH2), 2.81 (d, 3H, J = 2.79 Hz, CH3); 13C NMR (75 MHz, DMSO-d6): δ = 164.03, 143.41, 134.85, 133.66, 132.80, 131.25, 130.17, 126.55, 126.29, 124.76, 123.02, 122.56, 118.51, 116.82, 116.01, 52.65, 52.20, 49.59, 43.96, 42.47; found: C, 66.22; H, 5.56; N, 14.71. Calc. for C21H21ClN4O: C, 66.12; H, 5.54; N, 14.65%.
N-Isobutylbenzimidazo[1,2-a]quinoline-6-carboxamide 20. Compound 20 was prepared using the above described method, from benzimidazo[1,2-a]quinoline-6-carbonyl chloride 14 (0.150 g, 0.53 mmol), dry dichloromethane (20 mL) and 0.16 mL (1.61 mmol) of isobutylamine to obtain 0.118 g (70%) of yellow powder; m.p. 152–155 °C; 1H NMR (300 MHz, DMSO-d6): δ = 10.60 (t, 1H, J = 5.60 Hz, NH), 8.88 (d, 1H, J = 8.52 Hz, Harom.), 8.78 (s, 1H, Harom.), 8.77 (d, 1H, J = 7.46 Hz, Harom.), 8.31 (dd, 1H, J1 = 0.96 Hz, J2 = 7.77 Hz, Harom.), 8.03–7.92 (m, 2H, Harom.), 7.66 (t, 1H, J = 7.56 Hz, Harom.), 7.63–7.54 (m, 2H, Harom.), 3.38 (t, 2H, J = 6.29 Hz, CH2), 2.04–1.90 (m, 1H, CH), 1.05 (d, 6H, J = 6.69 Hz, CH3); 13C NMR (75 MHz, DMSO-d6): δ = 162.41, 146.47, 143.11, 135.84, 135.47, 132.82, 132.05, 130.44, 125.60, 125.49, 123.86, 122.38, 120.38, 120.19, 116.13, 115.42, 46.99, 28.68, 20.67 (2C); found: C, 75.69; H, 6.03; N, 13.24. Calc. for C20H19N3O: C, 75.74; H, 6.05; N, 13.20%.
N-(3-(Dimethylamino)propyl)benzimidazo[1,2-a]quinoline-6-carboxamide 21. Compound 21 was prepared using the above described method, from benzimidazo[1,2-a]quinoline-6-carbonyl chloride 14 (0.150 g, 0.53 mmol), dry dichloromethane (20 mL) and 0.20 mL (1.79 mmol) of N,N-dimethylaminopropyl-1-amine to obtain 0.134 g (72%) of yellow oil; 1H NMR (300 MHz, DMSO-d6): δ = 10.56 (t, 1H, J = 5.58 Hz, NH), 8.89 (d, 1H, J = 8.55 Hz, Harom.), 8.82–8.78 (m, 2H, Harom.), 8.31 (dd, 1H, J1 = 1.17 Hz, J2 = 7.83 Hz, Harom.), 8.04–7.93 (m, 2H, Harom.), 7.66 (t, 2H, J = 7.50 Hz, Harom.), 7.64–7.56 (m, 2H, Harom.), 3.59–3.50 (m, 2H, CH2), 2.43 (t, 2H, J = 6.95 Hz, CH2), 2.23 (s, 6H, CH3), 1.86–1.73 (m, 2H, CH2); 13C NMR (75 MHz, DMSO-d6): δ = 162.46, 146.31, 143.31, 135.93, 135.48, 132.78, 132.10, 130.45, 125.56 (2C), 123.90, 122.33, 120.45, 120.07, 116.16, 115.48 (2C), 57.07, 45.65 (2C), 37.75, 27.20; found: C, 72.81; H, 6.40; N, 16.17. Calc. for C21H22N4O: C, 72.71; H, 6.35; N, 16.15%.
N-(2-(Diethylamino)ethyl)benzimidazo[1,2-a]quinoline-6-carboxamide 22. Compound 22 was prepared using the above described method, from benzimidazo[1,2-a]quinoline-6-carbonyl chloride 14 (0.100 g, 0.36 mmol), dry dichloromethane (20 mL) and 0.15 mL (1.06 mmol) of N,N-diethylethylenediamine to obtain 0.064 g (50%) of yellow powder; m.p. 127–130 °C; 1H NMR (300 MHz, DMSO-d6): δ = 10.67 (t, 1H, J = 4.86 Hz, NH), 8.90 (d, 1H, J = 8.61 Hz, Harom.), 8.80 (s, 1H, Harom.), 8.79 (d, 1H, J = 7.47 Hz, Harom.), 8.31 (d, 1H, J = 6.87 Hz, Harom.), 8.00–7.93 (m, 2H, Harom.), 7.66 (t, 2H, J = 7.41 Hz, Harom.), 7.61–7.55 (m, 1H, Harom.), 3.59–3.51 (m, 2H, CH2), 2.69 (t, 2H, J = 6.17 Hz, CH2), 2.65–2.56 (m, 4H, CH2), 1.07 (t, 6H, J = 7.08 Hz, CH3); 13C NMR (75 MHz, DMSO-d6): δ = 162.43, 146.30, 143.33, 135.88, 135.47, 132.82, 132.00, 130.67, 125.57 (2C), 123.94, 122.41, 120.47, 120.06, 116.07 (2C), 115.46, 51.83 (2C), 47.00 (2C), 12.60; found: C, 73.31; H, 6.71; N, 15.54. Calc. for C22H24N4O: C, 73.39; H, 6.77; N, 15.45%.
Benzimidazo[1,2-a]quinoline-2,6-diylbis(piperidin-1-ylmethanone) 23. Compound 23 was prepared using the above described method, from benzimidazo[1,2-a]quinoline-2,6-dicarbonyl chloride 15 (0.140 g, 0.41 mmol), dry dichloromethane (20 mL) and 0.24 mL (2.46 mmol) of piperidine to obtain 0.107 g (59%) of yellow powder; m.p. 290–293 °C; 1H NMR (300 MHz, DMSO-d6): δ = 8.74–8.69 (m, 1H, Harom.), 8.67 (s, 1H, Harom.), 8.16 (d, 1H, J = 8.07 Hz, Harom.), 8.03 (s, 1H, Harom.), 8.00–7.98 (m, 1H, Harom.), 7.61–7.56 (m, 3H, Harom.), 3.70 (bs, 2H, CH2), 3.38 (bs, 4H, CH2), 3.25 (bs, 2H, CH2), 1.65 (bs, 4H, CH2), 1.50 (bs, 4H, CH2); 13C NMR (150 MHz, DMSO-d6): δ = 167.65, 163.82, 144.83, 144.12, 138.53, 134.45, 130.35, 130.31, 128.16, 127.17, 124.67, 123.28, 122.71, 122.69, 120.18, 114.75, 113.19, 47.57 (2C), 42.00 (2C), 25.96 (2C), 25.29 (2C), 24.05, 23.95; found: C, 73.61; H, 6.41; N, 12.72. Calc. for C27H28N4O2: C, 73.66; H, 6.37; N, 12.80%.
N,N-Diisobutylbenzimidazo[1,2-a]quinoline-2,6-dicarboxamide 24. Compound 24 was prepared using the above described method, from benzimidazo[1,2-a]quinoline-2,6-dicarbonyl chloride 15 (0.070 g, 0.20 mmol), dry dichloromethane (20 mL) and 0.12 mL (1.22 mmol) of isobutylamine to obtain 0.020 g (24%) of yellow powder; m.p. >300 °C; 1H NMR (300 MHz, DMSO-d6): δ = 10.59 (t, 1H, J = 5.93 Hz, NH), 9.09 (s, 1H, Harom.), 9.00 (t, 1H, J = 6.51 Hz, NH), 8.82 (s, 1H, Harom.), 8.72–8.68 (m, 1H, Harom.), 8.40 (d, 1H, J = 8.25 Hz, Harom.), 8.08 (d, 1H, J = 8.25 Hz, Harom.), 8.05–8.02 (m, 1H, Harom.), 7.70–7.62 (m, 2H, Harom.), 3.39 (t, 2H, J = 6.18 Hz, CH2), 3.22 (t, 2H, J = 6.19 Hz, CH2), 2.01–1.91 (m, 2H, CH), 1.05 (d, 6H, J = 6.66 Hz, CH3), 0.97 (d, 6H, J = 6.63 Hz, CH3); 13C NMR (75 MHz, DMSO-d6): δ = 165.93, 162.20, 143.28, 138.23, 135.67, 134.61, 131.99, 130.58, 125.72, 124.22, 123.83, 121.81, 120.43, 115.19, 114.57, 47.66, 47.19, 20.62, 28.60, 20.71 (2C), 20.59 (2C); found: C, 72.09; H, 6.78; N, 13.45. Calc. for C25H28N4O2: C, 72.00; H, 6.85; N, 13.38%.
N,N-Bis(3-(dimethylamino)propyl)benzimidazo[1,2-a]quinoline-2,6-dicarboxamide 25. Compound 25 was prepared using the above described method, from benzimidazo[1,2-a]quinoline-2,6-dicarbonyl chloride 15 (0.100 g, 0.29 mmol), dry dichloromethane (20 mL) and 0.22 mL (1.75 mmol) of N,N-dimethylaminopropyl-1-amine to obtain 0.030 g (22%) of yellow powder; m.p. 199–202 °C; 1H NMR (300 MHz, DMSO-d6): δ = 10.54 (t, 1H, J = 5.64 Hz, NH), 9.08 (s, 1H, Harom.), 9.03 (t, 1H, J = 5.42 Hz, NH), 8.82 (s, 1H, Harom.), 8.75–8.66 (m, 1H, Harom.), 8.40 (d, 1H, J = 8.28 Hz, Harom.), 8.09–8.00 (m, 2H, Harom.), 7.71–7.61 (m, 2H, Harom.), 3.58–3.52 (m, 2H, CH2), 3.49–3.36 (m, 2H, CH2), 2.40 (t, 2H, J = 6.78 Hz, CH2), 2.32 (t, 2H, J = 7.09 Hz, CH2), 2.21 (s, 6H, CH3), 2.17 (s, 6H, CH3), 1.89–1.69 (m, 4H, CH2); 13C NMR (75 MHz, DMSO-d6): δ = 169.69, 162.07, 146.32, 143.19, 137.97, 135.79, 134.74, 132.18, 130.97, 130.00, 126.96, 129.92, 124.30, 123.83, 121.69, 120.41, 119.29, 114.44, 57.50, 57.12, 45.74, 45.55, 38.62, 37.86, 27.52, 27.40; found: C, 68.33; H, 7.22; N, 17.71. Calc. for C27H34N6O2: C, 68.25; H, 7.30; N, 17.51%.
Benzimidazo[1,2-a]quinolin-2-yl(piperidin-1-yl)methanone 26. Compound 26 was prepared using the above described method, from benzimidazo[1,2-a]quinoline-2-carbonyl chloride 16 (0.100 g, 0.36 mmol), dry dichloromethane (20 mL) and 0.11 mL (1.07 mmol) of piperidine to obtain 0.010 g (8%) of yellow powder; m.p. 168–171 °C; 1H NMR (300 MHz, DMSO-d6): δ = 8.69–8.67 (m, 1H, Harom.), 8.65 (s, 1H, Harom.), 8.13 (d, 1H, J = 8.04 Hz, Harom.), 8.00 (d, 1H, J = 9.54 Hz, Harom.), 7.96–7.93 (m, 1H, Harom.), 7.71 (d, 1H, J = 9.51 Hz, Harom.), 7.59–7.51 (m, 3H, Harom.), 3.70 (bs, 2H, CH2), 1.65 (bs, 4H, CH2), 1.50 (bs, 4H, CH2); 13C NMR (75 MHz, DMSO-d6): δ = 168.25, 148.13, 144.77, 138.63, 135.14, 131.64, 130.74, 130.44, 124.97, 123.82, 123.45, 123.04, 120.44, 118.66, 115.16, 113.77, 24.56 (4C); found: C, 76.57; H, 5.81; N, 12.76. Calc. for C21H19N23O: C, 76.37; H, 5.75; N, 12.85%.
Benzimidazo[1,2-a]quinolin-2-yl(4-methylpiperazin-1-yl)methanone 27. Compound 27 was prepared using the above described method, from benzimidazo[1,2-a]quinoline-2-carbonyl chloride 16 (0.100 g, 0.36 mmol), dry dichloromethane (20 mL) and 0.12 mL (1.07 mmol) of 1-methylpiperazine to obtain 0.040 g (33%) of light brown powder; m.p. 220–240 °C; 1H NMR (300 MHz, DMSO-d6): δ = 8.68–8.66 (m, 2H, Harom.), 8.13 (d, 1H, J = 8.01 Hz, Harom.), 8.00 (d, 1H, J = 9.48 Hz, Harom.), 7.96–7.94 (m, 1H, Harom.), 7.72 (d, 1H, J = 9.48 Hz, Harom.), 7.59–7.53 (m, 3H, Harom.), 3.73 (bs, 2H, CH2), 3.42 (bs, 2H, CH2), 2.43 (bs, 2H, CH2), 2.31 (bs, 2H, CH2), 2.22 (s, 3H, CH3); 13C NMR (75 MHz, DMSO-d6): δ = 168.39, 148.10, 144.77, 138.03, 135.12, 131.62, 130.74, 130.44, 124.98, 123.97, 123.46, 123.24, 120.46, 118.78, 115.17, 114.07, 55.05, 54.68, 47.59, 46.09, 42.07; found: C, 73.23; H, 5.85; N, 16.27. Calc. for C21H20N4O: C, 73.30; H, 5.60; N, 16.00%.
N-Isobutylbenzimidazo[1,2-a]quinoline-2-carboxamide 28. Compound 28 was prepared using the above described method, from benzimidazo[1,2-a]quinoline-2-carbonyl chloride 16 (0.100 g, 0.36 mmol), dry dichloromethane (20 mL) and 0.11 mL (1.07 mmol) of isobutylamine to obtain 0.015 g (13%) of yellow powder; m.p. 195–198 °C; 1H NMR (300 MHz, DMSO-d6): δ = 9.05 (s, 1H, Harom.), 8.94 (t, 1H, J = 5.36 Hz, NHamid.), 8.65–8.62 (m, 1H, Harom.), 8.16 (d, 1H, J = 8.19 Hz, Harom.), 8.05–8.00 (m, 2H, Harom.), 7.99–7.95 (m, 1H, Harom.), 7.75 (d, 1H, J = 9.45 Hz, Harom.), 7.61–7.58 (m, 2H, Harom.), 3.21 (t, 1H, J = 6.38 Hz, CH2), 2.01–1.89 (m, 1H, CH), 0.97 (d, 6H, J = 6.66 Hz, CH3); 13C NMR (75 MHz, DMSO-d6): δ = 165.99, 163.85, 144.82, 136.31, 135.11, 131.50, 130.20, 125.34, 125.03, 123.48, 123.40, 120.59, 119.28, 114.95, 114.52, 47.51, 28.64, 20.77 (2C); found: C, 75.69; H, 6.03; N, 13.24. Calc. for C20H19N3O: C, 75.55; H, 6.15; N, 13.15%.
N-(3-(Dimethylamino)propyl)benzimidazo[1,2-a]quinoline-2-carboxamide 29. Compound 29 was prepared using the above described method, from benzimidazo[1,2-a]quinoline-2-carbonyl chloride 16 (0.100 g, 0.36 mmol), dry dichloromethane (20 mL) and 0.13 mL (1.07 mmol) of N,N-dimethylaminopropyl-1-amine to obtain 0.036 g (29%) of light yellow powder; m.p. 194–198 °C; 1H NMR (300 MHz, DMSO-d6): δ = 9.03 (s, 1H, Harom.), 8.97 (t, 1H, J = 5.07 Hz, NHamid), 8.64 (m, 1H, Harom.), 8.16 (d, 1H, J = 8.13 Hz, Harom.), 8.02–7.95 (m, 3H, Harom.), 7.75 (d, 1H, J = 9.48 Hz, Harom.), 7.62–7.57 (m, 2H, Harom.), 3.41 (q, 2H, J = 6.52 Hz, CH2), 2.33 (t, 2H, J = 7.00 Hz, CH2), 2.17 (s, 6H, CH3), 1.76 (m, 2H, CH2); 13C NMR (75 MHz, DMSO-d6): δ = 165.32, 147.60, 144.31, 135.73, 134.61, 130.99, 130.28, 129.73, 124.87, 124.53, 122.90, 122.82, 120.07, 118.77, 114.46, 113.94, 56.95, 45.19 (2C), 38.07, 27.02; found: C, 72.81; H, 6.40; N, 16.17. Calc. for C21H22N4O: C, 72.61; H, 6.50; N, 16.07%.
N-(2-(Diethylamino)ethyl)benzimidazo[1,2-a]quinoline-2-carboxamide 30. Compound 30 was prepared using the above described method, from benzimidazo[1,2-a]quinoline-2-carbonyl chloride 16 (0.075 g, 0.27 mmol), dry dichloromethane (20 mL) and 0.11 mL (2.14 mmol) of N,N-diethylethylenediamine to obtain 0.039 g (41%) of light brown powder; m.p. 190–194 °C; 1H NMR (300 MHz, DMSO-d6): δ = 9.04 (s, 1H, Harom.), 8.86 (t, 1H, J = 5.31 Hz, NHamid), 8.64–8.60 (m, 1H, Harom.), 8.15 (d, 1H, J = 8.20 Hz, Harom.), 8.01 (d, 1H, J = 9.41 Hz, Harom.), 7.98–7.93 (m, 1H, Harom.), 7.75 (d, 1H, J = 9.49 Hz, Harom.), 7.63–7.55 (m, 2H, Harom.), 3.44 (q, 2H, J = 6.64 Hz, CH2), 2.66 (t, 2H, J = 7.08 Hz, CH2), 2.56 (q, 4H, J = 7.11 Hz, CH2), 1.02 (t, 6H, J = 7.11 Hz, CH3); 13C NMR (75 MHz, DMSO-d6): δ = 165.85, 148.10, 144.84, 136.22, 135.11, 131.48, 130.78, 130.25, 125.36, 125.03, 123.45, 123.33, 120.59, 119.31, 114.96, 114.41, 51.96, 47.34 (2C), 38.44, 12.50 (2C); found: C, 73.31; H, 6.71; N, 15.54. Calc. for C22H24N4O: C, 73.15; H, 6.85; N, 15.34%.

Antiproliferative activity in vitro

Human cervical carcinoma (HeLa) and human breast carcinoma (MCF-7) cells were seeded in 48-well plates at 10[thin space (1/6-em)]000 cells per well. After 24 h, different concentrations of the compounds were added. After 3 days of incubation, the cells were trypsinized and counted using a Coulter counter.

Cells in suspension (human T-cell leukemia Cem cells) were seeded in 96-well plates at 60[thin space (1/6-em)]000 cells per well in the presence of different concentrations of the compounds, allowed to proliferate for 96 h, and counted using a Coulter counter. The 50% inhibitory concentration (IC50) was defined as the concentration of the compound required for reducing cell proliferation by 50%.17

Cell cycle analysis

HeLa cells were seeded in 6-well plates at 125[thin space (1/6-em)]000 cells per well in DMEM with 10% FBS. After 24 h, the cells were exposed to different concentrations of the compounds. After 24 h, the DNA of the cells was stained with propidium iodide using the CycleTEST PLUS DNA Reagent Kit (BD Biosciences, San Jose, CA). The DNA content of the stained cells was assessed by flow cytometry on a FACSCalibur flow cytometer and analyzed with CellQuest software (BD Biosciences) within 3 h after staining. Cell debris and clumps were excluded from the analysis by appropriate dot plot gating. The percentage of sub-G1, G1, S, and G2/M cells was estimated using appropriate region markers.17

Antiviral activity in vitro

The compounds were evaluated against the following viruses: herpes simplex virus type 1 (HSV-1) strain KOS, thymidine kinase-deficient (TK_) HSV-1 KOS strain resistant to ACV (ACVr), herpes simplex virus type 2 (HSV-2) strain G, vaccinia virus Lederle strain, respiratory syncytial virus (RSV) strain long, human coronavirus (strain 229E), vesicular stomatitis virus (VSV), Coxsackie B4, parainfluenza 3, influenza virus A (subtypes H1N1, H3N2), influenza virus B, Sindbis, reovirus-1 and Punta Toro. The antiviral assays were based on inhibition of virus-induced cytopathicity or plaque formation in human embryonic lung (HEL) fibroblasts, African green monkey cells (Vero), human epithelial cells (HeLa) or Madin-Darby canine kidney cells (MDCK). Confluent cell cultures in microtiter 96-well plates were inoculated with 100 CCID50 of virus (1 CCID50 being the virus dose to infect 50% of the cell cultures) in the presence of varying concentrations of the test compounds. Viral cytopathicity or plaque formation was recorded as soon as it reached completion in the control virus-infected cell cultures that were not treated with the test compounds. Antiviral activity was expressed as EC50 (i.e. the concentration of the compound required for reducing virus-induced cytopathogenicity or viral plaque formation by 50%).18

Antimicrobial activity

The respective bacteria were grown overnight in LB medium (5 mL) and cultured again the following day in fresh LB medium (5 mL). Compounds were titrated in a 96-well plate using LB-medium to dilute the compounds. Compounds were diluted serially in LB medium (5 μL). An amount of 5 μL of DMSO was used as control. To each well 85 μL of LB-medium was added to a total volume of 90 μL. Next, 10 μL of bacterial cell culture grown to a OD600 of 0.005 was added. The cultures were next placed in an incubator at 37 °C, and subsequently the OD600 was determined after 18–20 h. Bacterial strains and fungi used for the evaluations: Staphylococcus aureus ATCC 6538P, Staphylococcus epidermidis RP62A, Escherichia coli NCIB 8743, Pseudomonas aeruginosa PAO1, Sarcina lutea ATCC9341 and Candida albicans CO11. All experiments were performed in triplicate.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work has been supported in part by Croatian Science Foundation under the project 5596 (Synthesis and cytostatic evaluations of novel nitrogen heterocycles library). BG is recipient of a post-doctoral fellowship of the Research Foundation-Flanders (FWO).

Notes and references

  1. R. B. Silverman, The Organic Chemistry of Drug Design and Drug Action, Elsevier Academic Press, 2nd edn, 2004 Search PubMed .
  2. M. Demeunynck, C. Bailly and W. D. Wilson, In D.N.A. and R.N.A. Binders, Wiley-VCH, Weinheim, 2002 Search PubMed .
  3. Y. Bansal and O. Silakari, Bioorg. Med. Chem., 2012, 20, 6208–6236 CrossRef CAS PubMed .
  4. A. M. Monforte, S. Ferro, L. De Luca, G. Lo Surdo, F. Morreale, C. Pannecouque, J. Balzarini and A. Chimirri, Bioorg. Med. Chem., 2014, 22, 1459–1467 CrossRef CAS PubMed .
  5. Z. Ates-Alagoz, S. Yildiz and E. Buyukbingol, Chemotherapy, 2007, 53, 110–113 CrossRef CAS PubMed .
  6. H. M. Grogan, Pest. Manage. Sci., 2006, 62, 153–161 CrossRef CAS PubMed .
  7. M. Hranjec, E. Horak, D. Babić, S. Plavljanin, Z. Srdović, I. Murković Steinberg, R. Vianello and N. Perin, New J. Chem., 2017, 41, 358–371 RSC .
  8. V. B. Kovalska, D. V. Kryvorotenko, A. O. Balanda, M. Y. Losytsky, V. P. Tokar and S. M. Yarmoluk, Dyes Pigm., 2005, 67, 47–54 CrossRef CAS .
  9. M. Hranjec, M. Kralj, I. Piantanida, M. Sedić, L. Šuman, K. Pavelić and G. Karminski-Zamola, J. Med. Chem., 2007, 50, 5696–5711 CrossRef CAS PubMed .
  10. N. Perin, R. Nhili, M. Cindrić, B. Bertoša, D. Vušak, I. Martin-Kleiner, W. Laine, G. Karminski-Zamola, M. Kralj and M. H. David-Cordonnier, Eur. J. Med. Chem., 2016, 122, 530–545 CrossRef CAS PubMed .
  11. N. Perin, I. Martin-Kleiner, R. Nhili, W. Laine, M. H. David-Cordonnier, O. Vurgek, G. Karminski-Zamola, M. Kralj and M. Hranjec, MedChemComm, 2013, 4, 1537–1550 RSC .
  12. I. O. de Souza, C. M. L. Schrekker, W. Lopes, R. Orru, M. Hranjec, N. Perin, M. Machado, L. F. Oliveira, R. K. Donato, V. Stefani, A. M. Fuentefria and H. S. Schrekker, J. Photochem. Photobiol., B, 2016, 163, 319–326 CrossRef CAS PubMed .
  13. R. Rohini, K. Shanker, P. Muralidhar Reddy and V. Ravinder, J. Braz. Chem. Soc., 2010, 21, 49–57 CrossRef CAS .
  14. R. Rohini, K. Shanker, P. Muralidhar Reddy, Y. P. Ho and V. Ravinder, Eur. J. Med. Chem., 2009, 44, 3330–3339 CrossRef CAS PubMed .
  15. E. A. Lyakhova, Y. A. Gusyeva, J. V. Nekhoroshkova, L. M. Shafran and S. A. Lyakhov, Eur. J. Med. Chem., 2009, 44, 3305–3312 CrossRef CAS PubMed .
  16. P. P. Joshi and S. G. Shirodkar, World J. Pharm. Pharm. Sci., 2014, 3, 950–958 Search PubMed .
  17. M. Hranjec, G. Pavlović, M. Marjanović, M. Kralj and G. Karminski-Zamola, Eur. J. Med. Chem., 2010, 45, 2405–2417 CrossRef CAS PubMed .
  18. N. Perin, L. Uzelac, I. Piantanida, G. Karminski-Zamola, M. Kralj and M. Hranjec, Bioorg. Med. Chem., 2011, 19, 6329–6339 CrossRef CAS PubMed .
  19. V. Vanheule, P. Vervaeke, A. Mortier, S. Noppen, M. Gouwy, R. Snoeck, G. Andrei, J. Van Damme, S. Liekens and P. Proost, Biochem. Pharmacol., 2016, 100, 73–85 CrossRef CAS PubMed .
  20. M. D. Canela, S. Noppen, O. Bueno, A. E. Prota, K. Bargsten, G. Sáez-Calvo, M. L. Jimeno, M. Benkheil, D. Ribatti, S. Velásquez, M. J. Camarasa, J. F. Díaz, M. O. Steinmetz, E. M. Priego, M. J. Pérez-Pérez and S. Liekens, Oncotarget, 2017, 8(9), 14325–14342 CrossRef PubMed .
  21. I. Nabiev, I. Chourpa, J. F. Riou, C. H. Nguyen, F. Lavelle and M. Manfait, Biochemistry, 1994, 33, 9013–9023 CrossRef CAS PubMed .
  22. B. Poddevin, J. F. Riou, F. Lavelle and Y. Pommier, Mol. Pharmacol., 1993, 44, 767–774 CAS .
  23. L. P. G. Wakelin, P. Chetcuti and W. A. Denny, J. Med. Chem., 1990, 33, 2039–2044 CrossRef CAS PubMed .
  24. E. Pastwa, E. Ciesielska, M. K. Piestrzeniewicz, W. A. Denny, M. Gniazdowski and L. Szmigiero, Biochem. Pharmacol., 1998, 56, 351–359 CrossRef CAS PubMed .
  25. J. A. Spicer, S. A. Gamage, G. J. Atwell, G. J. Finlay, B. C. Baguley and W. A. Denny, J. Med. Chem., 1997, 40, 1919–1929 CrossRef CAS PubMed .
  26. F. R. Venezio, W. Tatarowicz, C. A. DiVicenzo and J. P. O’Keefe, Antimicrob. Agents, Chemotherapy, 1986, 30, 940–941 CAS .

Footnote

Electronic supplementary information (ESI) available: Synthesis of compounds 5–16. See DOI: 10.1039/c8nj00416a

This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2018