Hybrid imidazole (benzimidazole)/pyridine (quinoline) derivatives and evaluation of their anticancer and antimycobacterial activity

Abstract

The design, synthesis, structure, and in vitro anticancer and antimycobacterial activity of new hybrid imidazole (benzimidazole)/pyridine (quinoline) derivatives are described. The strategy adopted for synthesis is straight and efficient, involving a three-step setup procedure: N-acylation, N-alkylation, and quaternization of nitrogen heterocycle. The solubility in microbiological medium and anticancer and antimycobacterial activity of a selection of new synthesized compounds were evaluated. The hybrid derivatives have an excellent solubility in microbiological medium, which make them promising from the pharmacological properties point of view. One of the hybrid compounds, 9 (with a benzimidazole and 8-aminoquinoline skeleton), exhibits a very good and selective antitumor activity against Renal Cancer A498 and Breast Cancer MDA-MB-468. Moreover, the anticancer assay suggests that the hybrid Imz (Bimz)/2-AP (8-AQ) compounds present a specific affinity to Renal Cancer A498. Concerning the antimycobacterial activity, only the hybrid compound, 9, has a significant activity. SAR correlations have been performed.

Keywords:

• Anticancer
• antimycobacterial
• hybrid imidazole (benzimidazole)/pyridine (quinoline)
• synthesis

Introduction

Over the past years five- and six-member ring azaheterocyclic compounds have received considerable attention due to their important applications from pharmacological, industrial, and synthetic points of view1. Pharmaceutical industry and modern medicinal science pay a lot of effort in their combat with two aggressive life-threatening diseases: cancer and tuberculosis (TB). Both diseases are leading cause of death worldwide, millions of people dying every year; the incidence of both are continually increasing and the treatment became more and more complicated and sophisticated2–4. The cancer chemotherapy is complex, expensive and often rather inefficient, because of the large variety of neoplasm types, high toxicity levels and non-specificity of drugs and the emergence of drug resistance and multi-drug-resistant (MDR)2,3. On the other hand, because of the Mycobacterium tuberculosis (Mtb) versatility, the treatment against TB became a challenging and difficult task, and the situation begin to become even worse because of the phenomena of drug resistance, MDR, extensively-drug-resistant (XDR), association of TB with AIDS, etc.3,4

It is well known from the literature1–4 that imidazole (and its benzo-derivative benzimidazole) and pyridine (and its benzo-derivative quinoline) derivatives are core scaffolds widely present in many classes of drugs (of natural or synthetic origin), displaying a large variety of interesting biological activities (antimicrobials, antifungus, anti-inflammatory, antihypertensive, antineuropathic, antihistaminic, etc.; anticancer5–10 and anti-TB11–15 also included). Encouraged by the above considerations and in continuation of our research in the area of novel anticancer9,10,16–19 and anti-TB15–17,20–23 derivatives with azaheterocyclic skeleton, we report here the design, synthesis, structure, and in vitro anticancer and antimycobacterial activity of new hybrid imidazole (benzimidazole)/pyridine (quinoline) derivatives.

Methods

General

All the reagents and solvents employed were of the best grade available and were used without further purification. Melting points were determined using an electrothermal apparatus (MELTEMP II, Dubuque, IA) and are uncorrected. The IR spectra were recorded on an FTIR Shimadzu Prestige 8400s spectrophotometer (Kyoto, Japan). Proton and carbon nuclear magnetic resonance (δ_H, δ_C) spectra were recorded on a Bruker Avance III 500 spectrometer operating at 500 MHz for ¹H and 125 MHz for ¹³C. The following abbreviations were used to designate chemical shift multiplicities: s = singlet, d = doublet, t = triplet, q = quartet, brs = broad singlet, as = apparent singlet, ad = apparent doublet, at = apparent triplet, aq = apparent quartet, dd = doublet of doublets, td = triplet of doublets, and m = multiplet. All chemical shifts are quoted on the δ-scale in ppm. Coupling constants are given in Hertz. Thin-layer chromatography (TLC) was carried out on Merck silica gel 60F₂₅₄ plates (Darmstadt, Germany). Column chromatography was carried out on silica gel (Roth 60, 0.04–0.063 mm; Darmstadt, Germany). Visualization of the plates was achieved using a UV lamp (λ_max = 254 or 365 nm). The microanalyses were in satisfactory agreement with the calculated values: C, ±0.15; H, ±0.10; N, ±0.30.

General procedure for N-acylation of 2-AP and 8-AQ

Compounds 1 and 7 were obtained using some modified procedures from the literature where they were first obtained24,25. Our experimental setup for N-acylation of 2-aminopyridine (2-AP) and 8-aminoquinoline (8-AQ) are the following:

2-Chloro-N-(pyridin-2-yl)acetamide (1)

2-Chloroacetyl chloride (1.24 g, 11 mmol) was slowly added dropwise (30 min.) to a mixture of 2-aminopyridine (0.94 g, 10 mmol) and triethylamine (1.11 g, 11 mmol) in anhydrous CH₂Cl₂ (150 mL) at 0 °C. The reaction mixture was warmed to room temperature and stirred for an additional 2 h. The solution was washed with NaHCO₃ (3 × 100 mL), then with water (2 × 100 mL), and the organic layer dried over anhydrous sodium sulfate. The obtained reddish precipitate was separated by filtration, and was washed with anhydrous CH₂Cl₂. No other purification required.

White reddish solid (93% yield). ¹H NMR (500 MHz, CDCl₃, 25 °C): δ 4.21 (s,2H), 7.13–7.10 (m, 1H), 7.78–7.73 (m, 1H), 8.21 (d, 1H, J = 4.4 Hz), 8.34–8.32 (m, 2H), 8.94 (s, 1H).

2-Chloro-N-(quinolin-8-yl) acetamide (7)

2-Chloroacetyl chloride (4.07 g, 36 mmol) was slowly added dropwise (2 h) to a mixture of 8-aminoquinoline (4.32 g, 30 mmol) and pyridine (3.4 mL, 42 mmol) in anhydrous CHCl₃ (75 mL) at 0 °C. The reaction mixture was warmed to room temperature and stirred for an additional 2 h. After the solvent was removed under reduced pressure, the residue was washed with ice water (3 × 75 mL), the organic layer dried over anhydrous sodium sulfate. The obtained reddish precipitate was separated by filtration, and was washed with dry chloroform. No other purification required.

Reddish powder (97% yield). ¹H NMR (500 MHz, CDCl₃, 25 °C): δ 4.45–4.25 (m, 2H), 7.52–7.42 (m, 1H), 7.55 (dd, J = 6.9, 3.7 Hz, 2H), 8.17 (d, J = 8.3 Hz, 1H), 8.79–8.67 (m, 1H), 8.96–8.81 (m, 1H), 9.98 (s, 1H).

General procedure for synthesis of hybrid compounds 2, 3, 8, and 9

Sodium hydride (10 mmol, 0.24 g) in 20 mL of dry acetonitrile was slowly added dropwise to a stirred mixture of imidazole derivatives [5.5 mmol (0.37 g) for imidazole or 5.5 mmol (0.65 g) for benzimidazole] dissolved in 50 mL of dry acetonitrile. To the resulted mixture, 2-chloro-N-(pyridin-2-yl)acetamide 1 (5 mmol, 0.852 g) or 2-chloro-N-(quinolin-8-yl)acetamide 7 (5 mmol, 1.182 g) in 100 mL of dry acetonitrile (previously sonicated in a ultrasonic bath) was added dropwise over 1 h (stirring, 0 °C). The reaction mixture was warmed to room temperature and stirred for an additional 48 h. After the reaction was completed (TLC), the solution was evaporated to dryness under reduced pressure on a rotary evaporator, and the crude product was purified by flash chromatography on silica gel (CH₂Cl₂/CH₃OH = 98/2).

2-(1H-imidazol-1-yl)-N-(pyridin-2-yl)acetamide (2)

White powder (61% yield), mp = 183–185 °C. IR (KBr, ν (cm⁻¹)): 3480, 3149, 3043, 2954, 1695, 1564, 1436, 1303. ¹H NMR (500 MHz, DMSO-d₆, 25 °C): δ 4.96 (s, 2H, 9-H), 6.89 (s, 1-H, 13-H), 7.13 (aq, J = 5.0 Hz, 1H, 3-H), 7.16 (s, 1H, 14-H), 7.63 (s, 1H, 11-H), 7.80 (td, J = 5.0 Hz, J = 7.0, 1H, 4-H), 8.01 (d, J = 7.5 Hz, 1H, 5-H), 8.34 (ad, J = 5.0 Hz, 1H, 2-H), 10.81 (s, 1-H, 7-H). ¹³C NMR (125 MHz, DMSO-d₆): δ 49.15 C-9, 113.39 C-5, 119.68 C-3, 120.66 C-14, 127.97 C-13, 138.31 C-4, 138.34 C-11, 148.08 C-2, 151.58 C-6, 166.64 C-8.

2-(1H-benzo[d]imidazol-1-yl)-N-(pyridin-2-yl)acetamide (3)

White powder (72% yield), mp = 224–226 °C. IR (KBr, ν (cm⁻¹)): 3417, 3032, 2984, 2962, 1703, 1540, 1435, 1301. ¹H NMR (500 MHz, DMSO-d₆, 25 °C): δ 5.28 (s, 2H, 9-H), 7.12 (t, J = 6.5 Hz, 1H, 3-H), 7.19–7.26 (overlapped signals, 2H, 14-H, 15-H), 7.54 (d, J = 7.5 Hz, 1H, 16-H), 7.68 (d, J = 7.5 Hz, 1H, 13-H), 7.76 (t, J = 7.5 Hz, 1H, 4-H), 7.99 (d, J = 7.0 Hz, 1H, 5-H), 8.26 (s, 1H, 11-H), 8.36 (ad, J = 4.0 Hz, 1H, 2-H), 11.05 (s, 1-H, 7-H). ¹³C NMR (125 MHz, DMSO-d₆): δ 47.27 C-9, 110.29 C-16, 113.47 C-5, 119.38 C-13, 119.78 C-3, 121.54 C-14, 122.44 C-15, 134.42 C-16a, 138.37 C-4, 143.19 C-12a, 145.06 C-11, 148.13 C-2, 151.57 C-6, 166.43 C-8.

2-(1H-imidazol-1-yl)-N-(quinolin-8-yl)acetamide (8)

White powder (70% yield), mp = 136–138 °C. IR (KBr, ν (cm⁻¹)): 3360, 3143, 3054, 2951, 1693, 1562, 1425, 1324. ¹H NMR (500 MHz, CDCl₃, 25 °C): δ 4.95 (s, 2H, 11-H), 7.14 (s, 1H, 15-H), 7.26 (ad, J = 2.5 Hz, 1H, 16-H), 7.44 (aq, J = 8.0 Hz, 1H, 3-H), 7.54 (ad, J = 6.5 Hz, 2H, 6-H, 7-H), 7.70 (s, 1H, 13-H), 8.15 (dd, J = 8.0 Hz, 1H, 4-H), 8.71 (at, J = 5.5 Hz, 2H, 2-H, 5-H), 9.97 (s, 1-H, 9-H). ¹³C NMR (125 MHz, CDCl₃): δ 51.10 C-11, 116.86 C-5, 120.07 C-15, 121.99 C-3, 122.73 C-6, 127.29 C-7, 127.97 C-8, 130.76 C-16, 133.38 C-4a, 136.44 C-4, 138.29 C-13, 138.42 C-8a, 148.73 C-2, 164.96 C-10.

2-(1H-benzo[d]imidazol-1-yl)-N-(quinolin-8-yl)acetamide (9)

Beige powder (63% yield), mp = 161–163 °C. IR (KBr, ν (cm⁻¹)): 3348, 3116, 3021, 2895, 1699, 1544, 1483, 1325. ¹H NMR (500 MHz, CDCl₃, 25 °C): δ 5.14 (s, 2H, 11-H), 7.30–7.36 (m, 3H, 3-H, 16-H, 17-H), 7.45–7.51 (overlapped signals, 3H, 5-H, 6-H, 18-H), 7.90 (ad, J = 7.0 Hz, 1H, 15-H), 8.08 (dd, J = 7.0 Hz, 1H, 4-H), 8.11 (s, 1H, 13-H), 8.51 (dd, J = 4.5 Hz, J = 1.5 Hz, 1H, 2-H), 8.67 (aq, J = 4.5 Hz, 1H, 7-H), 10.02 (s, 1-H, 9-H). ¹³C NMR (125 MHz, CDCl₃): δ 49.13 C-11, 109.70 C-18, 116.79 C-7, 120.79 C-15, 121.88 C-3, 122.61 C-5, 122.97 C-16, 123.91 C-17, 127.22 C-6, 127.87 C-8, 133.30 C-14a, 133.98 C-18a, 136.30 C-4, 138.29 C-4a, 143.59 C-13, 143.91 C-8a, 148.54 C-2, 164.56 C-10.

General procedure for synthesis of hybrid compounds 5, 6, 10, and 11

To a stirred solution of hybrid compounds 2, 3, 8, or 9 (1 mmol) in 10 mL dry acetone, ethyl 2-bromoacetate (2 mmol, 0.33 g) or 2-iodocetamide (2 mmol, 0.37 g) or allyl bromide (2 mmol, 0.24 g) was slowly added. The mixture was stirred at room temperature for 24 h in the case of compounds 2 and 8 or refluxed for 48 h in the case of compounds 3 and 9. The obtained precipitate was separated by filtration, and was washed with few milliliters of dry acetone. No other purification required.

3-(2-ethoxy-2-oxoethyl)-1-(2-oxo-2-(pyridin-2-ylamino)ethyl)-1H-imidazol-3-ium bromide (5a)

White powder (54% yield), mp = 170–172 °C. IR (KBr, ν (cm⁻¹)): 3489, 3153, 3074, 2972, 1755, 1697, 1564, 1438, 1303, 1176. ¹H NMR (500 MHz, DMSO-d₆, 25 °C): δ 1.25 (t, J = 7.0 Hz, 3H (CH₃), 5′-H), 4.22 (q, J = 7.0 Hz, 2H (CH₂), 4′-H), 5.35 (ad, 4H (2xCH₂), 1′-H, 9-H), 7.16 (at, J = 5.5 Hz, 1H, 3-H), 7.81 (ad, 3H, 4-H, 13-H, 14-H), 7.99 (brs, 1H, 5-H), 8.36 (ad, J = 3.5 Hz, 1H, 2-H), 9.20 (as, 1H, 11-H), 11.09 (s, 1H, 7-H). ¹³C NMR (125 MHz, DMSO-d₆): δ 13.97 C-5′, 49.69 C-9, 51.54 C-1′, 61.87 C-4′, 113.44 C-5, 119.97 C-3, 123.25 C-14, 123.81 C-13, 138.51 C-4, 138.67 C-11, 148.22 C-2, 151.31 C-6, 164.60 C-8, 166.79 C-2′.

3-(2-amino-2-oxoethyl)-1-(2-oxo-2-(pyridin-2-ylamino)ethyl)-1H-imidazol-3-ium iodide (5b)

Beige powder (75% yield), mp 192–193 °C. IR (KBr, ν (cm⁻¹)): 3383, 3238, 3171, 2995, 1687, 1591, 1564, 1444, 1296. ¹H NMR (500 MHz, DMSO-d₆, 25 °C): δ 5.03 (s, 2H (CH₂), 1′-H), 5.31 (s, 2H (CH₂), 9-H), 7.16 (at, J = 5.5 Hz, 1H, 3-H), 7.54 (s, 1H (NH), 3′-H), 7.72 (as, 1H, 14-H), 7.75 (as, 1H, 13-H), 7.80–7.84 (overlapped signals, 2H, 4-H, 3′-H), 7.99 (brs, 1H, 5-H), 8.37 (ad, J = 3.5 Hz, 1H, 2-H), 9.11 (as, 1H, 11-H), 11.07 (s, 1H, 7-H). ¹³C NMR (125 MHz, DMSO-d₆): δ 50.57 C-1′, 51.36 C-9, 113.43 C-5, 119.98 C-3, 123.35 C-14, 123.39 C-13, 138.51 C-4, 138.61 C-11, 148.23 C-2, 151.29 C-6, 164.59 C-8, 166.59 C-2′.

3-allyl-1-(2-oxo-2-(pyridin-2-ylamino)ethyl)-1H-imidazol-3-ium bromide (5c)

White powder (51% yield), mp 154–156 °C. IR (KBr, ν (cm⁻¹)): 3419, 3107, 3036, 2910, 1703, 1579, 1460, 1435, 1300. ¹H NMR (500 MHz, DMSO-d₆, 25 °C): δ 4.95 (d, J = 5.5 Hz, 2H (CH₂), 1′-H), 5.27–5.39 (overlapped signals, 4H (CH₂=, CH₂), 3′-H, 9-H), 6.04–6.12 (m, 1H, 2′-H), 7.15 (t, J = 5.5 Hz, 1H, 3-H), 7.79–7.83 (overlapped signals, 3H, 4-H, 13-H, 14-H), 7.99 (brs, 1H, 5-H), 8.36 (d, J = 4.0 Hz, 1H, 2-H), 9.24 (s, 1H, 11-H), 11.09 (s, 1H, 7-H). ¹³C NMR (125 MHz, DMSO-d₆): δ 50.88 C-1′, 51.43 C-9, 113.46 C-5, 119.99 C-3, 120.06 C-3′, 121.99 C-14, 124.27 C-13, 131.81 C-2′, 137.61 C-11, 138.51 C-4, 148.23 C-2, 151.30 C-6, 164.72 C-8.

3-(2-ethoxy-2-oxoethyl)-1-(2-oxo-2-(pyridin-2-ylamino)ethyl)-1H-benzo[d]imidazol-3-ium bromide (6a)

Pink powder (55% yield), mp = 205–207 °C. IR (KBr, ν (cm⁻¹)): 3419, 3140, 3045, 3032, 2987, 2962, 1753, 1705, 1570, 1435, 1222, 1184. ¹H NMR (500 MHz, DMSO-d₆, 25 °C): δ 1.26 (t, J = 7.0 Hz, 3H (CH₃), 5′-H), 4.25 (q, J = 7.0 Hz, 2H (CH₂), 4′-H), 5.71 (ad, 4H (2xCH₂), 1′-H, 9-H), 7.17 (t, J = 6.0 Hz, 1H, 3-H), 7.71 (at, 2H, 14-H, 15-H), 7.80 (t, J = 7.5 Hz, 1H, 4-H), 7.97 (brs, 1H, 5-H), 8.08 (at, 2H, 13-H, 16-H), 8.40 (d, J = 4.0 Hz, 1H, 2-H), 9.85 (s, 1H, 11-H), 11.23 (s, 1H, 7-H). ¹³C NMR (125 MHz, DMSO-d₆): δ 13.98 C-5′, 47.60 C-9, 49.43 C-1′, 62.03 C-4′, 113.50 C-5, 113.90 C-16, 113.95 C-13, 120.07 C-3, 126.82 C-15, 126.93 C-14, 131.09 C-16a, 131.42 C-12a, 138.52 C-4, 144.60 C-11, 148.24 C-2, 151.27 C-6, 166.53 C-2′, 167.03 C-8.

3-(2-amino-2-oxoethyl)-1-(2-oxo-2-(pyridin-2-ylamino)ethyl)-1H-benzo[d]imidazol-3-ium iodide (6b)

Yellowish white powder (78% yield), mp = 210–212 °C. IR (KBr, ν (cm⁻¹)): 3368, 3216, 3153, 2995, 1697, 1564, 1448, 1306. ¹H NMR (500 MHz, DMSO-d₆, 25 °C): δ 5.06 (s, 2H (CH₂), 1′-H), 5.28 (s, 2H (CH₂), 9-H), 7.15 (t, J = 6.5 Hz, 1H, 3-H), 7.21–7.28 (overlapped signals, 2H, 14-H, 15-H), 7.51 (s, 1H (NH), 3′H), 7.56 (d, J = 7.5 Hz, 1H, 16-H), 7.68 (d, J = 7.5 Hz, 1H, 13-H), 7.80 (t, J = 7.5 Hz, 1H, 4-H), 7.83 (s, 1H (NH), 3′H), 8.00 (d, J = 7.0 Hz, 1H, 5-H), 8.30 (s, 1H, 11-H), 8.38 (ad, J = 6.0 Hz, 1H, 2-H), 11.10 (s, 1-H, 7-H). ¹³C NMR (125 MHz, DMSO-d₆): δ 50.59 C-1′, 49.28 C-9, 110.67 C-16, 114.21 C-5, 119.56 C-13, 119.87 (C-3), 121.58 C-14, 122.86 C-15, 134.43 C-16a, 138.64 C-4, 143.26 C-12a, 145.16 C-11, 148.13 C-2, 152.03 C-6, 165.89 C-8, 166.61 C-2′.

3-allyl-1-(2-oxo-2-(pyridin-2-ylamino)ethyl)-1H-benzo[d]imidazol-3-ium bromide (6c)

White powder (54% yield), mp = 195–197 °C. IR (KBr, ν (cm⁻¹)): 3443, 3153, 3036, 3020, 2972, 2928, 1693, 1687, 1575, 1305. ¹H NMR (500 MHz, DMSO-d₆, 25 °C): δ 5.29 (d, J = 4.5 Hz, 2H (CH₂), 1′-H), 5.41 (at, 2H (CH₂=), 3′-H), 5.65 (brs, 2H (CH₂), 9-H), 6.12–6.17 (m, 1H, 2′-H), 7.16 (at, J = 5.5 Hz, 1H, 3-H), 7.70 (brs, 2H, 14-H, 15-H), 7.80 (t, J = 7.0 Hz, 1H, 4-H), 7.96 (brs, 1H, 5-H), 8.05 (ad, J = 5.5, 4.5 Hz, 2H, 13-H, 16-H), 8.39 (ad, J = 2.5 Hz, 1H, 2-H), 9.89 (s, 1H, 11-H), 11.21 (s, 1H, 7-H). ¹³C NMR (125 MHz, DMSO-d₆): δ 48.87 C-1′, 49.28 C-9, 113.52 C-5, 113.87 C-16, 113.92 C-13, 120.06 C-3, 120.44 C-3′, 126.61 C-15, 126.88 C-14, 130.57 C-16a, 130.97 C-2′, 131.95 C-12a, 138.50 C-4, 143.67 C-11, 148.23 C-2, 151.27 C-6, 164.45 C-8.

3-(2-ethoxy-2-oxoethyl)-1-(2-oxo-2-(quinolin-8-ylamino)ethyl)-1H-imidazol-3-ium bromide (10a)

Yellow powder (76% yield), mp = 193–195 °C. IR (KBr): ν_max/cm⁻¹: 3334, 3110, 3011, 2895, 1735, 1697, 1561, 1518, 1489, 1229, 1182. ¹H NMR (500 MHz, CDCl₃, 25 °C): δ 1.25 (t, J = 7.0 Hz, 3H (CH₃), 5′-H), 4.24 (q, J = 7.0 Hz, 2H (CH₂), 4′-H), 5.36 (s, 2H (CH₂), 11-H), 5.58 (s, 2H (CH₂), 1′-H), 7.60 (at, J = 8.5 Hz, 1H, 6-H), 7.69 (aq, J = 8.5 Hz, J = 4.0 Hz, 1H, 3-H), 7.74 (d, J = 8.5 Hz, 1H, 5-H), 7.82 (as, 1H, 16-H), 7.87 (as, 1H, 15-H), 8.46 (d, J = 8.5 Hz, 1H, 4-H), 8.57 (d, J = 7.5 Hz, 1H, 7-H), 9.00 (d, J = 4.0 Hz, 1H, 2-H), 9.25 (s, 1H, 13-H), 10.88 (s, 1-H, 9-H). ¹³C NMR (125 MHz, CDCl₃): δ 13.97 C-5′, 49.71 C-11, 52.02 C-1′, 61.87 C-4′, 117.48 C-7, 122.30 C-3, 122.84 C-5, 123.38 C-16, 123.75 C-15, 126.87 C-6, 127.97 C-4a, 134.04 C-8, 136.68 C-4, 138.36 C-8a, 138.67 C-13, 149.07 C-2, 164.45 C-10, 166.80 C-2′.

3-(2-amino-2-oxoethyl)-1-(2-oxo-2-(quinolin-8-ylamino)ethyl)-1H-imidazol-3-ium iodide (10b)

Yellow powder (83% yield), mp = 201–203 °C. IR (KBr, ν (cm⁻¹)): 3431, 3338, 3159, 3088, 3022, 2976, 2092, 1689, 1614, 1537, 1491, 1321. ¹H NMR (500 MHz, CDCl₃, 25 °C): δ 5.04 (s, 2H (CH₂), 11-H), 5.54 (s, 2H (CH₂), 1′-H), 7.54 (s, 1H (NH), 3′-H), 7.60 (t, J = 8.0 Hz, 1H, 6-H), 7.68 (q, J = 8.5 Hz, 1H, 3-H), 7.73–7.74 (m, 2H, 5-H, 16-H), 7.80 (s, 1H, 15-H), 7.85 (s, 1H (NH), 3′-H), 8.45 (dd, J = 8.5 Hz, J = 1.0 Hz, 1H, 4-H), 8.56 (d, J = 7.5 Hz, 1H, 5-H), 9.00 (dd, J = 4.0 Hz, J = 1.5 Hz, 1H, 2-H), 9.18 (s, 1H, 13-H), 10.87 (s, 1-H, 9-H). ¹³C NMR (125 MHz, CDCl₃): δ 50.61 C-11, 51.88 C-1′, 117.48 C-7, 122.32 C-3, 122.85 C-5, 123.31 C-15, 123.54 C-16, 126.89 C-6, 127.98 C-4a, 134.05 C-8, 136.69 C-4, 138.37 C-8a, 138.63 C-13, 164.50 C-2′, 166.64 C-10.

3-allyl-1-(2-oxo-2-(quinolin-8-ylamino)ethyl)-1H-imidazol-3-ium bromide (10c)

White powder (61% yield), mp = 169–171 °C. IR (KBr, ν (cm⁻¹)): 3317, 3138, 3101, 3063, 2943, 2902, 1693, 1562, 1537, 1485, 1425, 1329. ¹H NMR (500 MHz, CDCl₃, 25 °C): δ 4.96 (d, J = 5.5 Hz, 2H (CH₂), 1′-H), 5.30 (d, J = 17.0 Hz, 1H from CH₂=, 3′-H), 5.39 (d, J = 10.0 Hz, 1H from CH₂=, 3′-H), 5.52 (brs, 2H (CH₂), 11-H), 6.07–6.12 (m, 1H, 2′-H), 7.60 (t, J = 8.0 Hz, 1H, 6-H), 7.68 (q, J = 8.5 Hz, 1H, 3-H), 7.74 (d, J = 8.0 Hz, 1H, 7-H), 7.80 (s, 1H, 16-H), 7.87 (s, 1H, 15-H), 8.45 (d, J = 8.5 Hz, 1H, 4-H), 8.56 (d, J = 7.5 Hz, 1H, 5-H), 9.00 (d, J = 3.0 Hz, 1H, 2-H), 9.28 (s, 1H, 13-H), 10.89 (s, 1-H, 9-H). ¹³C NMR (125 MHz, CDCl₃): δ 50.92 C-1′, 51.94 C-11, 117.54 C-5, 120.06 C-3′, 122.10 C-16, 122.31 C-3, 122.86 C-7, 124.22 C-15, 126.88 C-6, 127.89 C-4a, 131.83 C-2′, 134.05 C-8a, 136.69 C-4, 137.62 C-13, 138.38 C-8, 149.08 C-2, 164.60 C-10.

3-(2-ethoxy-2-oxoethyl)-1-(2-oxo-2-(quinolin-8-ylamino)ethyl)-1H-benzo[d]imidazol-3-ium bromide (11a)

Yellow powder (77% yield), mp = 215–217 °C. IR (KBr, ν (cm⁻¹)): 3336, 3113, 3012, 2895, 2823, 1737, 1699, 1558, 1529, 1523, 1487, 1325, 1226, 1184. ¹H NMR (500 MHz, CDCl₃, 25 °C): δ 1.27 (t, J = 7.0 Hz, 3H (CH₃), 5′-H), 4.26 (q, J = 7.0 Hz, 2H (CH₂), 4′-H), 5.72 (s, 2H (CH₂), 11-H), 5.96 (s, 2H (CH₂), 1′-H), 7.59 (t, J = 8.0 Hz, 1H, 6-H), 7.70–7.76 (m, 4H, 3-H, 5-H, 15-H, 18-H), 8.10–8.13 (m, 2H, 16-H, 17-H), 8.47 (dd, J = 8.0 Hz, J = 1.5 Hz, 1H, 4-H), 8.55 (d, J = 7.5 Hz, 1H, 7-H), 9.04 (dd, J = 4.0 Hz, J = 1.5 Hz, 1H, 2-H), 9.89 (s, 1H, 13-H), 11.02 (s, 1-H, 9-H). ¹³C NMR (125 MHz, CDCl₃): δ 13.98 C-5′, 47.65 C-11, 49.70 C-1′, 62.04 C-4′, 113.78 C-17, 114.00 C-16, 117.42 C-7, 122.36 C-3, 122.95 C-5, 126.87 C-18, 126.89 C-15, 127.00 C-6, 127.98 C-4a, 131.16 C-18a, 131.35 C-14a, 134.00 C-8, 136.71 C-4, 138.36 C-8a, 144.63 C-13, 149.14 C-2, 164.13 C-2′, 166.55 C-10.

3-(2-amino-2-oxoethyl)-1-(2-oxo-2-(quinolin-8-ylamino)ethyl)-1H-benzo[d]imidazol-3-ium iodide (11b)

Yellow powder (89% yield), mp = 208–210 °C. IR (KBr, ν (cm⁻¹)): 3348, 3309, 3149, 3022, 2918, 1681, 1672, 1597, 1552, 1489, 1325. ¹H NMR (500 MHz, CDCl₃, 25 °C): δ 5.38 (s, 2H (CH₂), 11-H), 5.92 (s, 2H (CH₂), 1′-H), 7.59 (t, J = 8.0 Hz, 1H, 6-H), 7.68 (s, 1H (NH), 3′-H), 7.70–7.73 (m, 3H, 3-H, 16-H, 17-H), 7.75 (d, J = 8.0 Hz, 1H, 5-H), 7.97 (at, J = 7.0, J = 4.0, 1H, 18-H), 8.00 (s, 1H (NH), 3′-H), 8.01 (at, J = 7.0, J = 4.0, 1H, 15-H), 8.45 (dd, J = 8.5 Hz, J = 1.0 Hz, 1H, 4-H), 8.56 (d, J = 7.5 Hz, 1H, 7-H), 9.01 (dd, J = 4.0 Hz, J = 1.5 Hz, 1H, 2-H), 9.85 (s, 1H, 13-H), 11.02 (s, 1-H, 9-H). ¹³C NMR (125 MHz, CDCl₃): δ 48.49 C-11, 49.58 C-1′, 113.70 C-18, 113.73 C-15, 117.40 C-7, 122.37 C-3, 122.94 C-5, 126.76 C-17, 126.81 C-16, 126.90 C-6, 127.99 C-4a, 131.38 C-18a, 131.40 C-14a, 134.03 C-8, 136.72 C-4, 138.36 C-8a, 144.62 C-13, 149.14 C-2, 164.20 C-2′, 166.36 C-10.

3-allyl-1-(2-oxo-2-(quinolin-8-ylamino)ethyl)-1H-benzo[d]imidazol-3-ium bromide (11c)

White powder (64% yield), mp = 191–193 °C. IR (KBr, ν (cm⁻¹)): 3477, 3421, 3144, 3088, 3041, 2964, 2928, 1695, 1597, 1566, 1539, 1489, 1325. ¹H NMR (500 MHz, CDCl₃, 25 °C): δ 5.31 (d, J = 5.5 Hz, 2H (CH₂), 1′-H), 5.41 (at, 2H (CH₂=), 3′-H), 5.91 (brs, 2H (CH₂), 11-H), 6.13–6.19 (m, 1H, 2′-H), 7.58 (t, J = 8.0 Hz, 1H, 6-H), 7.70–7.76 (m, 4H: 3-H, 5-H, 16-H, 17-H), 8.06 (at, J = 5.5 Hz, J = 2.5 Hz, 1H, 18-H), 8.11 (at, J = 5.5 Hz, J = 2.5 Hz, 1H, 15-H), 8.47 (d, J = 8.0 Hz, 1H, 4-H), 8.55 (d, J = 7.5 Hz, 1H, 7-H), 9.04 (d, J = 3.0 Hz, 1H, 2-H), 9.94 (s, 1H, 13-H), 11.02 (s, 1-H, 9-H). ¹³C NMR (125 MHz, CDCl₃): δ 48.89 C-1′, 49.57 C-11, 113.82 C-18, 113.92 C-15, 117.44 C-7, 120.38 C-3′, 122.35 C-3, 122.93 C-5, 126.66 C-17, 126.87 C-6, 126.93 C-16, 127.98 C-4a, 130.63 C-18a, 131.02 C-2′, 131.88 C-14a, 134.02 C-8, 136.71 C-4, 138.35 C-8a, 143.74 C-13, 149.12 C-2, 164.32 C-10.

Microbiology

Cell proliferation assay

The in vitro biological tests were performed at the National Cancer Institute (NCI, USA), under the Developmental Therapeutics Program (DTP). The DTP screens include the NCI 60 cell line screen and, as appropriate, the hollow fiber assay and relevant human tumor xenograft and rodent tumor models. The operation of this screen utilizes 60 different human tumor cell lines, representing leukemia, melanoma, and cancers of the lung, colon, brain, ovary, breast, prostate, and kidney. This screen is unique in that the complexity of a 60 cell line dose response produced by a given compound results in a biological response pattern which can be utilized in pattern recognition algorithms via COMPARE program (See: http://dtp.nci.nih.gov/docs/compare/compare.html).

The screening is beginning with the evaluation of all compounds against the 60 cell lines at a single dose of 10⁻⁵ M. The output from the single-dose screen is reported as a mean graph and is available for analysis by the COMPARE program. All details concerning the in vitro anticancer assay could be found in the Supplementary Information of this article.

Antimycobacterial activity

Compounds were evaluated for antimycobacterial activity against Mycobacterium tuberculosis, as a part of the TAACF (Center of Tuberculosis Antimicrobial Acquisition and Coordinating Facility) TB screening program under direction of the US National Institute of Health, the NIAID division, at Southern Research Institute.

Compound solubility in microbiological medium

Compounds were prepared as 10-point 2-fold serial dilutions in DMSO and diluted into 7H9-Tw-OADC medium in 96-well plates. The highest concentration of compound was 200 μM where compounds were soluble in DMSO at 10 mM. For compounds with limited solubility, the highest concentration was 50 times less than the stock concentration e.g. 100 μM for 5 mM DMSO stock, 20 μM for 1 mM DMSO stock. Turbidity was measured using a Nepheloskan Ascent microplate reader. A compound was considered insoluble if the turbidity was 300% greater than that of the negative control. The lowest insoluble concentration is reported. Each plate of test compounds included a positive control (1 mM haloperidol) and a DMSO negative control (2% DMSO in 7H9-Tw-OADC). Each experiment run included control compounds: metoprolol tartrate, rifampicin, phenytoin, haloperidol, simvastatin, diethylstilbestrol, and tamoxifen.

The Primary Cycle High-Throughput Screening (HTS). Determination of 50% inhibitory concentration (IC₅₀), 90% inhibitory concentration (IC₉₀) and minimum inhibitory concentration (MIC)

The antimicrobial activity of compounds against Mycobacterium tuberculosis H37Rv grown under aerobic conditions was assessed by determining the minimum inhibitory concentration (MIC) of compound. The MIC of compound was determined by measuring bacterial growth after five days in the presence of test compounds. For potent compounds, assays were repeated at lower starting concentrations. Each run experiment included as control rifampicin. The assay was based on measurement of growth in liquid medium of a fluorescent reporter strain of H37Rv where the readout is either optical density (OD) or fluorescence. The use of two readouts minimizes problems caused by compound precipitation or autofluorescence. A linear relationship between OD and fluorescence readout has been established justifying the use of fluorescence as a measure of bacterial growth. MICs, IC₅₀, and IC₉₀ generated from the OD are reported in Supplementary Information. All details concerning the Primary Cycle High-Throughput Screening (HTS) assay could be found in Supplementary Information of this article.

Results and discussion

Chemistry

In order to synthesize our hybrid compounds, we chose as starting azaheterocycles two six-member ring derivatives, 2-aminopyridine (2-AP) and 8-aminoquinoline (8-AQ), and two five-member ring derivatives, imidazole (Imz) and benzimidazole (Bimz). The strategy we used for synthesis was straight and efficient, involving a three-step setup procedure: N-acylation, N-alkylation, and quaternization of N-heterocycle. Thus, the N-acylation of 2-AP with 2-chloroacetyl chloride is leading to the corresponding pyridine acylamine 1 (Scheme 1). Subsequent treatment of acylamine 1 with Imz or Bimz is leading to a first class of hybrid Imz (Bimz)/pyridine derivatives 2 and 3, via an N-alkylation reaction of the NH-imidazolic moiety. In the last step, a quaternization reaction of N-imidazole atom with variously activated halogenated derivatives 4 (2-bromo/iodo-alkyl esters/amide 4a,b or allyl bromide 4c) is leading to a second class of hybrid N-(1-alkylcarboxy)- and N-allyl-imidazole/pyridine derivatives 5a–c and benzimidazole/pyridine derivatives 6a–c (Scheme 1).

Scheme 1. Synthesis of hybrid imidazole (benzimidazole)/pyridine derivatives 2–6.

A similar strategy was used in the case of 8-AQ; the hybrid Imz (Bimz)/quinoline derivatives 8–11 being obtained (Scheme 2).

Scheme 2. Synthesis of hybrid Imz (Bimz)/quinoline derivatives 8–11.

The structures of the new compounds were proven by elemental (C, H, N) and spectroscopic analysis: IR, ¹H NMR, ¹³C NMR, and two-dimensional experiments 2D COSY, 2D HMQC, and 2D HMBC. If we consider compound 9 as representative for the first series of hybrid Imz (Bimz)/2-AP (8-AQ) derivatives2,3,8,9and 11c for the second series of hybrid N-(1-alkylcarboxy)- and N-allyl-Imz (Bimz)/2-AP (8-AQ) derivatives5,6,10,11, the spectral analysis reveals strong evidence for the proposed structures. Thus, in the case of compound 9, the most important signals furnished by ¹H NMR spectra are those one of the protons H9, H11, H13, H7, and H2. The most unshielded proton is H9 (10.02 ppm, singlet), being a NH-proton from amide carbonyl group. The next unshielded protons are from the quinoline heterocycle, H7 (8.67 ppm, triplet, J = 4.5 Hz) and H2 (8.51 ppm, two doublets, J = 4.5 Hz, and J = 1.5 Hz), H7 being unshielded by the electron withdrawing effect of the adjacent carbonyl amide group while H2 is unshielded by the withdrawing effect of the adjacent nitrogen N1 (α-endocyclic proton). The H13 protons appear at 8.11 ppm (singlet) due to the powerful electron-withdrawing effect of the two adjacent nitrogen atoms from imidazole ring. The signals for methylene protons H11 appear at low field (5.14 ppm, singlet), due to the strong electron-withdrawing effect of the adjacent carbonyl group and imidazole moiety. In the ¹³C NMR spectra, the most important data are furnished by the signals corresponding to the C10 (carbonyl), C11 (methylene), and C13 (α-endocyclic carbon from imidazole) atoms. The signals for C10 appear at 164.56 ppm (typical for a C=O from amide carbonyl group) while the methylene C11 appears at 49.13 ppm, due to the strong unshielded effect of the adjacent carbonyl group and imidazole moiety. The C13 carbon appears at 143.59 ppm, in accordance with the powerful unshielded effect of the two adjacent nitrogen atoms from imidazole ring.

In the case of compound 11c, the most important signals furnished by ¹H NMR spectra are those one of the protons H9, H11, H13, H7,and H2 as well as those one from N-allyl-moiety from the quaternizated benzimidazole (H1′, H2′, H3′). The most unshielded proton remains H9 (11.02 ppm, singlet, NH-proton from amide carbonyl group), because of the proximity with the positive nitrogen from imidazole moiety. The next unshielded proton is H13 (9.94 ppm, singlet) due to the powerful electron-withdrawing effect of the two adjacent nitrogen atoms from imidazole ring, one of them positive. The protons from the quinoline heterocycle are the next one: H2 (9.04 ppm, apparent doublet, J = 3.0 Hz) and H7 (8.55 ppm, doublet, J = 7.5 Hz). The methylene protons H11 appear at 5.91 ppm (singlet) due to the strong electron-withdrawing effect of the adjacent carbonyl group and positive nitrogen from imidazole moiety. The allyl methylene protons H1′ appear at 5.31 ppm (doublet, J = 5.5 Hz), while the vinyl protons appear at 6.13–6.16 ppm (multiplet, H2′), respectively at 5.39–5.43 ppm (apparent triplet, H3′). In the ¹³C NMR spectra, the most important data are furnished by the signals corresponding to the atoms C10 (carbonyl), C11 (methylene), C13 (α-endocyclic carbon from imidazole), and the carbons from N-allyl-moiety from the quaternizated benzimidazole (C1′, C2′, C3′). The signal for C10 appears at 164.32 ppm (typical for a C=O from amide carbonyl group), C11 methylene carbon appears at 49.57 ppm (strong unshielded effect of the carbonyl group and imidazole moiety), and the C13 carbon appears at 143.74 ppm, in accordance with the powerful unshielded effect of the two adjacent nitrogen atoms from imidazole ring, one of them positive. The allyl methylene carbon C1′ appears at 48.89 ppm, while the vinyl carbons appear at 131.04 ppm (C2′), respectively at 120.38 ppm (C3′). All the remaining signals from NMR spectra are in accordance with the proposed structures. See also Supporting Information for the ¹H- and ¹³C-NMR spectra for compounds 9 and 11c.

Design and biological activity

One of the strategies widely used in cancer and TB therapy is targeting DNA with small molecules, imidazole/benzimidazole, and pyridine/quinoline derivatives being leading structures in this respect [anticancer5–10, anti-TB11–15]. In previously research work, we successfully identify azaheterocycles derivatives (imidazole/benzimidazole and pyridine/quinoline included) with anticancer9^,10^,16–19 and anti-TB15–17^,20–23 activity.

In the light of the above consideration, it appears rational to combine the pharmacophoric potential of the two core scaffolds, imidazole (and its benzo-derivative benzimidazole) and pyridine (and its benzo-derivative quinoline), intending to obtain new entities with better anticancer and antimycobacterial activity and, also, with better pharmaceutical properties (i.e. increasing the water solubility for salts). In this respect, we design two new classes of hybrid imidazole (benzimidazole)/pyridine (quinoline) derivatives: a first series which contains main graph Imz (Bimz)/2-AP (8-AQ) heterocycles, interconnected through an acetamide linker, and a second seriesis the corresponding N-(1-alkylcarboxy)- and N-allyl-salts (Scheme 3).

Scheme 3. Design in the class of hybrid imidazole (benzimidazole)/pyridine (quinoline) derivatives.

Three hybrid Imz (Bimz)/2-AP (8-AQ) derivatives, 2, 8, and 9, were selected and tested in vitro for anticancer activity by the National Cancer Institute (NCI, USA), under the DTP, at a single high dose (10⁻⁵ M) cell assay. This assay was performed in a 60 human tumor cell line panel, representing leukemia, melanoma, and cancers of lung, colon, brain, breast, ovary, kidney, and prostate, in accordance with the protocol of the NCI26–29. The results are expressed as “Percentage Growth Inhibition” (PGI) term, and represent growth relative to the no-drug control, and relative to the time zero number of cells (Table 1). This allows detection of both growth inhibition (values between 0 and 100) and lethality (values less than 0). For example, a value of 40 would mean 60% growth inhibition while a value of −40 would mean 40% lethality (Supplementary Information concerning full in vitro anticancer assay could be found in the ESI of this article).

Table 1. Percentage growth inhibition (PGI, μM)* data of compounds 2, 8, and 9 against an NCI 60 human tumor cell lines (selection)†.

Panel/cell line	Compound 2, PGI	Compound 8, PGI	Compound 9, PGI
Renal cancer
A498	76.38	71.32	52.92
UO-31	95.67	86.67	66.68
Breast cancer
MDA-MD-468	99.69	96.84	56.54
T-47D	95.02	84.83	66.49
CNS cancer
SF-295	101.52	102.13	66.68
Melanoma
SK-MEL-5	107.01	101.55	63.62
UACC-257	96.08	103.82	76.57
Leukemia
RPMI-8226	98.44	95.61	64.14
CCRF-CEM	103.51	102.28	70.70
K-562	96.39	101.22	79.72
SR	90.22	109.15	70.75
Non-small cell lung cancer
NCI-H23	104.67	95.31	69.62
A549/ATCC	89.85	103.65	77.74
Ovarian cancer
OVCAR-4	84.49	77.98	81.08
NCI/ADR-RES	105.73	105.83	75.91

Bold values indicate significant activity.

*The number reported for the one-dose assay, percentage growth inhibition (PGI), is growth relative to the no-drug control, and relative to the time zero number of cells.

† Full results are presented in the Supplementary Information.

The results from Table 1 indicate that one of the hybrid compounds, namely Bimz/8-AQ, 9, has a very good antitumor activity against Renal Cancer A498 (with a growth inhibition of 46.08%) and Breast Cancer MDA-MB-468 (with a growth inhibition of 43.46%). We may also notice a significant antitumor growth inhibitory activity (around 35%) of 9 against Leukemia (RPMI-8226, CCRF-CEM, K-562, SR), Non-Small Cell Lung Cancer (NCI-H23, A549/ATCC), CNS Cancer SF-293, Melanoma (SK-MEL-5, UACC-257), Renal Cancer UO-31, Breast Cancer T-47D, and Ovarian NCI/ADR-RES. Another important aspect that has to be underlined is the specificity of the hybrid Imz (Bimz)/2-AP (8-AQ) compounds to Renal Cancer A498: the highest activity of 9 is against this type of cancer (growth inhibition of 46.08%), and the other two hybrids have a slightly activity only against this type of cancer (with a growth inhibition of 23.26% for 2 and 28.68% for 8). The above results suggest that the presence of a benzimidazole and 8-aminoquinoline moieties in the same molecule is favorable for anticancer activity. Comparative with the literature data of other compounds containing only imidazole or pyridine in their molecule, the anticancer activity of our hybrid imidazole (benzimidazole)/pyridine (quinoline) derivatives is more promising.

The hybrid Imz (Bimz)/2-AP (8-AQ) derivatives, 2, 3, 8, 9, and 11a–c, were evaluated for in vitro antimycobacterial activity against M. tuberculosis H37Rv (grown under aerobic conditions), as a part of the TAACF TB screening program under direction of the US National Institute of Health, the NIAID division (Table 2). In the first step, the relative solubility of compounds in microbiological medium was measured using turbidity as a measure30. A serial dilution of compounds was prepared in DMSO and then transferred to microbiological medium at pH 6.8. Turbidity was measured and compared to a control; the lowest concentration at which compounds are insoluble (defined as turbidity >300% of control) was recorded.

Table 2. Solubility in microbiological medium and antimycobacterial activity of compounds 2, 3, 8, 9, and 11a–c against Mycobacterium tuberculosis H37Rv under aerobic conditions.

				Compound solubility
Compound	IC50 (μg/mL)	IC90 (μg/mL)	MIC (μM)	Starting concentration (μM)	Lowest insoluble concentration (μM)
2	>200	>200	>200	200	N/A
3	>200	>200	>200	200	N/A
8	>200	>200	>200	200	N/A
9	>200	77	>100	200	N/A
11a	>200	>200	>200	200	N/A
11b	>200	>200	>200	200	N/A
11c	>200	>200	>200	200	N/A
Control*
Rifampicin	0.0036	0.0061	0.0055	0.04	N/A

N/A means the compound was soluble at the highest concentration.

* Each experiment run included and other control compounds: metoprolol tartrate, phenytoin, haloperidol, simvastatin, diethylstilbestrol, and tamoxifen.

The data from Table 2 illustrate that the tested hybrid Imz (Bimz)/2-AP (8-AQ) derivatives have an excellent solubility in microbiological medium (>200 μM), which is very promising from the pharmacological properties point of view. Then, IC₅₀, IC₉₀, and MIC were determined by measuring bacterial growth after five days in the presence of test compounds31–34. As can be seen, from the seven tested compounds, only one9 had activity against M. tuberculosis H37Rv under aerobic conditions, with an IC₉₀ of 77 μg/mL and a MIC > 100 μM. We may also notice that quaternization of N-imidazolic atom in salts 11a–c has no influence on the antimycobacterial activity.

Conclusions

The design, synthesis, structure, and in vitro anticancer and antimycobacterial activity of new hybrid Imz (Bimz)/2-AP (8-AQ) derivatives are described. The strategy adopted for synthesis is straight and efficient, involving a three-step setup procedure: N-acylation, N-alkylation, and quaternization of nitrogen heterocycle. Fourteen new hybrid compounds (namely 5a–c, 6a–c, 8, 9, 10a–c, and 11a–c) were obtained and fully characterized by elemental and spectral analysis. The solubility in microbiological medium and anticancer and antimycobacterial activity of a selection of new synthesized compounds were evaluated against a NCI 60 human tumor cell line panel and Mycobacterium tuberculosis H37Rv under aerobic conditions, respectively. The hybrid derivatives have an excellent solubility in microbiological medium, which make them promising from the pharmacological properties point of view. One of the hybrid compounds, 9, exhibits a very good antitumor activity against Renal Cancer A498 and Breast Cancer MDA-MB-468 (with a growth inhibition around 45%) and also presents a significant antitumor activity (with a growth inhibition around 35%) against Leukemia (RPMI-8226, CCRF-CEM, K-562, SR), Non-Small Cell Lung Cancer (NCI-H23, A549/ATCC), CNS Cancer SF-293, Melanoma (SK-MEL-5, UACC-257), Renal Cancer UO-31, Breast Cancer T-47D, and Ovarian NCI/ADR-RES. Overall, the results suggest that the hybrid Imz (Bimz)/2-AP (8-AQ) compounds present a specific affinity to Renal Cancer A498. Concerning the antimycobacterial activity, only the hybrid compound 9 has a significant activity. The SAR correlation suggests that the presence of a benzimidazole and 8-aminoquinoline moieties in the same molecule is favorable for both anticancer and antimycobacterial activity, and could be taken into consideration as leading motifs for further studies.

Declaration of interest

The authors report no declarations of interest.

The authors are thankful to CNCSIS Bucuresti, Romania, grant PN-II-DE-PCE-2011-3-0038, no. 268/05.10.2011, for financial support.

Supplementary material available online

Acknowledgements

The authors gratefully acknowledge the National Cancer Institute (Developmental Therapeutics Program, Division of Cancer Treatment and Diagnosis, website: http://dtp.cancer.gov/) for the in vitro evaluation of anticancer activity and National Institutes of Health and the National Institute of Allergy and Infectious Diseases, Contract No. HHSN272201100009I, for the in vitro evaluation of anti-TB activity. We also thank the POSCCE-O 2.2.1, SMIS-CSNR 13984-901, No. 257/28.09.2010 Project, CERNESIM, for the NMR spectra.