Library of diversely substituted 2-(quinolin-4-yl)imidazolines delivers novel non-cytotoxic antitubercular leads

Abstract

A novel library based on quinolin-4-ylimidazoline core was designed to incorporate a general quinoline antimicrobial pharmacophore. A synthesis of the well-characterized library of 36 compounds was achieved using the Pd-catalyzed Buchwald–Hartwig-type imidazoline arylation chemistry developed earlier. Compounds were tested for biological activity and were found to possess no antimalarial activity. However, the library delivered two promising antitubercular leads, which are non-cytotoxic and can be further optimized with respect to antimycobacterial potency.

• Antimalarial
• antitubercular
• Buchwald–Hartwig
• 2-imidazoline
• microwave chemistry
• non-cytotoxic
• quinoline

Introduction

Recently, we developed a convenient method for Pd-catalyzed N-arylation of 2-imidazolines1. 2-Imidazolines are important, privileged motifs in drug discovery, as demonstrated by numerous biologically active compounds designed around 2-imidazoline core2. Following the initial success of applying imidazoline arylation chemistry toward the synthesis of known selective cyclooxygenase-2 inhibitors3, we promptly developed novel imidazoline-based chemical series endowed with anti-inflammatory4 and kinase-inhibitory5 activities. Enthused with this initial success positioning N-(hetero)aryl imidazoline moiety as a basis for focused library design, we sought to design a chemical series that would incorporate moieties that would allow developing new leads for anti-infective (in particular, antimalarial6 and antitubercular7) therapies.

One such moiety that found particular prominence in anti-infective drug design is quinoline. While generally considered a privileged motif8, quinolin-4-yl group is omnipresent in quinoline antimalarials. Quinine itself, its synthetic congeners (mefloquine and chloroquine) and even the quinoline-pyrimidine hybrids recently disclosed by Kumar et al.9 – all appear to align with the same pharmacophore10. Moreover, recent developments in quinoline-based antitubercular agents, such as TMC207 or mefloquine (which is just one example of the significant cross-talk between antitubercular and antimalarial pharmacology)11, emphasize the importance of this class of compounds as a new-generation therapy for multidrug-resistant tuberculosis (TB)12. Considering the special position of quinoline in anti-infective drug design, we set off to design and synthesize a library of N-heteroaryl 2-(quinolin-4-yl)imidazolines that would position these compounds well within the above-mentioned pharmacophore model (Figure 1)13. Herein, we present the details of the chemical synthesis and the results obtained while evaluating the antimalarial and antitubercular potential of this library.

Figure 1. Examples and pharmacophore model of known quinoline-based antimalarials as well as antitubercular agents used to design the library studied in this work.

Materials and methods

Chemical syntheses – general

All reagents were used as received from the suppliers. Column chromatography was performed using silica gel 60 (particle size 0.040–0.063 mm, 230–400 mesh ASTM). Analytical thin-layer chromatography was performed with silica gel 60 F254 aluminum sheets. ¹H NMR was acquired at 500 MHz, and ¹³C NMR at 125 MHz at 30 °C. ¹H and ¹³C NMR were acquired in CDCl₃, chemical shifts (δ) are reported in ppm relative to the solvent residual peak: proton (δ 7.26 ppm) and carbon (δ 77.0 ppm) signals, respectively. Melting points are uncorrected. High- and low-resolution electrospray ionization mass spectra were acquired using electrospray as the ionization technique in positive ion and/or negative ion modes as stated. All MS analysis samples were prepared as solutions in MeOH.

4-(4,5-Dihydro-1H-imidazol-2-yl)quinoline (1)

Compound was obtained according to the literature method14. Yield 78%, m.p.: 98–100 °C. ES-MS m/z 198 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.83 (d, J = 4.35 Hz, 1H), 8.59 (d, J = 8.4 Hz, 1H), 8.07 (d, J = 8.45 Hz, 1H), 7.70 (t, J = 8.0 Hz, 1H), 7.54 (t, J = 8.0 Hz, 1H), 7.48 (d, J = 4.35 Hz, 1H), 3.81 (s, 4H); ¹³C NMR (125 MHz, CDCl₃): δ_C 163.1, 149.8, 148.8, 137.1, 129.8, 129.7, 127.4, 126.1, 125.5, 120.1, 50.6, 50.5.

General procedure for the preparation of compounds 2a–e

A thick-glass screw-capped pressure tube (50 mL) was charged with a suspension of 4-(4,5-dihydro-1H-imidazol-2-yl)quinoline (1, 5.0 mmol), appropriate dihalo azine (5.0 mmol), Cs₂CO₃ (5.0 mmol), and toluene (25 mL). Pd(OAc)₂ (0.20 mmol) and BINAP (0.40 mmol) were weighed as solids into a 15 mL screw-capped vial and toluene (10 mL) was added. The resulting suspension was heated at 110 °C until a clear purple solution was obtained. The latter was rapidly transferred, while still hot, to the screw-capped pressure tube using a Pasteur pipette. The reaction vessel was purged with argon and the reaction mixture was vigorously stirred at 100 °C for 16–20 h. It was cooled to room temperature and filtered through a Celite pad. The latter was washed with ethyl acetate, and the combined filtrate and washings were evaporated to dryness. The crude material was purified on silica (CH₂Cl₂:MeOH, 95:5) to provide the title N-heteroarylation product.

4-[1-(6-Bromopyridin-2-yl)-4,5-dihydro-1H-imidazol-2-yl]quinoline (2a)

Yield 73%, m.p.: 162–164 °C. ES-MS m/z 354 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.95 (d, J = 4.3 Hz, 1H), 8.13 (d, J = 8.45 Hz, 1H), 7.85 (d, J = 8.3 Hz, 1H), 7.70 (t, J = 7.2 Hz, 1H), 7.47 (t, J = 7.15 Hz, 1H), 7.42 (d, J = 4.3 Hz, 1H), 6.99 (t, J = 7.95 Hz, 1H), 6.79 (d, J = 7.6 Hz, 1H), 6.01 (d, J = 8.25 Hz, 1H), 4.30–4.26 (m, 2H), 4.24–4.20 (m, 2H); ¹³C NMR (125 MHz, CDCl₃): δ_C 157.3, 152.0, 150.0, 148.5, 139.7, 139.2, 139.1, 130.1, 129.9, 127.6, 125.7, 125.0, 120.7, 120.6, 109.3, 53.8, 49.6.

4-[1-(2-Chloropyrimidin-4-yl)-4,5-dihydro-1H-imidazol-2-yl]quinoline (2b)

Yield 68%, m.p.: 146–148 °C. ES-MS m/z 311 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 9.01 (d, J = 4.3 Hz, 1H), 8.18 (d, J = 8.4 Hz, 1H), 7.81 (d, J = 6.0 Hz, 1H), 7.77 (d, J = 7.85 Hz, 2H), 7.53 (t, J = 7.75 Hz, 1H), 7.45 (d, J = 4.3 Hz, 1H), 5.75 (d, J = 5.95 Hz, 1H), 4.36–4.32 (m, 2H), 4.29–4.25 (m, 2H); ¹³C NMR (125 MHz, CDCl₃): δ_C 160.5, 158.2, 158.1, 155.7, 150.1, 148.5, 138.0, 130.4 (2 carbons), 128.2, 125.3, 124.4, 120.7, 105.1, 54.0, 48.8.

4-[1-(6-Chloropyrazin-2-yl)-4,5-dihydro-1H-imidazol-2-yl]quinoline (2c)

Yield 81%, m.p.: 138–140 °C. ES-MS m/z 311 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.98 (d, J = 4.25 Hz, 1H), 8.17 (d, J = 8.45 Hz, 1H), 7.90 (s, 1H), 7.82 (d, J = 8.4 Hz, 1H), 7.73 (t, J = 7.9 Hz, 1H), 7.51 (t, J = 7.75 Hz, 1H), 7.45 (d, J = 4.3 Hz, 1H), 7.37 (s, 1H), 4.32–4.29 (m, 4H); ¹³C NMR (125 MHz, CDCl₃): δ_C 156.3, 150.1, 148.6, 147.9, 146.4, 138.1, 135.6, 130.8, 130.4, 130.2, 128.0, 125.4, 124.5, 120.7, 54.1, 49.2.

4-{1-[2-Chloro-5-(trifluoromethyl)pyrimidin-4-yl]-4,5-dihydro-1H-imidazol-2-yl}quinoline (2d)

Yield 56%, waxy solid. ES-MS m/z 378 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.95 (d, J = 4.35 Hz, 1H), 8.18–8.15 (m, 2H), 7.74–7.68 (m, 2H), 7.47 (t, J = 7.25 Hz, 1H), 7.40 (d, J = 4.35 Hz, 1H), 4.38–4.34 (m, 2H), 4.31–4.28 (m, 2H); ¹³C NMR (125 MHz, CDCl₃): δ_C 159.0, 157.3, 156.8 (q, J_C–F = 5.0 Hz), 156.3, 149.8, 148.1, 139.8, 130.1, 129.6, 127.4, 126.1, 124.5, 122.2 (q, J_C–F = 270.0 Hz), 120.2, 115.1 (q, J_C–F = 33.75 Hz), 54.3, 48.4.

4-[1-(6-Chloropyrimidin-4-yl)-4,5-dihydro-1H-imidazol-2-yl]quinoline (2e)

Yield 79%, m.p.: 138–140 °C. ES-MS m/z 311 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.99 (d, J = 4.4 Hz, 1H), 8.23 (d, J = 8.55 Hz, 1H), 8.14 (s, 1H), 7.80 (d, J = 8.35 Hz, 1H), 7.76 (t, J = 7.3 Hz, 1H), 7.54 (t, J = 7.25 Hz, 1H), 7.46 (d, J = 4.35 Hz, 1H), 6.15 (s, 1H), 4.34–4.30 (m, 2H), 4.28–4.24 (m, 2H); ¹³C NMR (125 MHz, CDCl₃): δ_C 160.6, 157.8, 157.7, 156.1, 150.0, 148.4, 138.6, 130.3, 130.1, 127.8, 125.4, 124.5, 120.5, 105.9, 54.1, 48.7.

General procedure for the preparation of compounds 3–38

A sealable microwave vessel containing a stirring bar was charged with 2 (1 mmol), amine or 2-imidazolines (1.1 mmol), anhydrous Cs₂CO₃ (1 mmol) and toluene (2.0 mL). The mixture was set on extensive stirring at r.t., while a catalyst solution was prepared by mixing Pd(OAc)₂ (0.02 mol) and BINAP (0.04 mol) in toluene (0.5 mL) at 100 °C, until a deep-red clear solution was obtained. The latter was added via a pipette into the reaction mixture, the vial was sealed and irradiated in Biotage Initiator™ microwave reactor at 90 °C for 45 min (for 2-imidazoline coupling partners) or 30 min (for primary and secondary amines). The contents of the vial were filtered through a plug of Celite (with ample ethyl acetate washing). Chromatography on silica gel using an appropriate gradient of MeOH in dichloromethane as eluent gave analytically pure title compounds.

(±)-4-[1-(6-{Octahydropyrrolo[1,2-a]piperazin-2-yl}pyridin-2-yl)-4,5-dihydro-1H-imidazol-2-yl]quinoline (3)

Waxy solid. ES-MS m/z 399 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.87 (d, J = 4.4 Hz, 1H), 8.07 (d, J = 8.4 Hz, 1H), 7.95 (d, J = 8.35 Hz, 1H), 7.64 (t, J = 7.75 Hz, 1H), 7.45–7.41 (m, 2H), 7.27 (t, J = 8.0 Hz, 1H), 5.99 (d, J = 8.35 Hz, 1H), 5.90 (d, J = 7.8 Hz, 1H), 4.23–4.19 (m, 2H), 4.16–4.11 (m, 2H), 3.00 (d, J = 11.75 Hz, 1H), 2.94 (t, J = 8.85 Hz, 1H), 2.85 (d, J = 12.5 Hz, 1H), 2.65 (d, J = 10.9 Hz, 1H), 2.20–2.15 (m, 1H), 1.94 (q, J = 8.65 Hz, 1H), 1.78–1.67 (m, 3H), 1.66–1.59 (m, 2H), 1.52–1.48 (m, 1H), 1.20–1.13 (m, 1H); ¹³C NMR (125 MHz, CDCl₃): δ_C 158.6, 157.5, 150.9, 149.8, 148.3, 141.4, 139.3, 129.7, 129.5, 127.1, 126.2, 125.6, 120.0, 99.9, 98.6, 62.0, 54.0, 53.5, 51.1, 49.6, 48.7, 43.5, 27.4, 21.3.

N-[2-(Pyrrolidin-1-yl)ethyl]-6-[2-(quinolin-4-yl)-4,5-dihydro-1H-imidazol-1-yl]pyridin-2-amine (4)

Gray solid, m.p.: 132–134 °C. ES-MS m/z 387 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.87 (d, J = 4.35 Hz, 1H), 8.07 (d, J = 8.5 Hz, 1H), 7.97 (d, J = 8.35 Hz, 1H), 7.65 (t, J = 7.85 Hz, 1H), 7.46 (t, J = 8.05 Hz, 1H), 7.41 (d, J = 4.35 Hz, 1H), 7.11 (d, J = 7.9 Hz, 1H), 5.80 (d, J = 8.1 Hz, 1H), 5.74 (d, J = 7.75 Hz, 1H), 4.55–4.54 (m, 1H), 4.23–4.19 (m, 2H), 4.17–4.11 (m, 2H), 2.31–2.30 (m, 4H), 2.11–2.09 (m, 2H), 2.03–1.97 (m, 2H), 1.71–1.69 (m, 4H); ¹³C NMR (125 MHz, CDCl₃): δ_C 158.8, 157.0, 151.3, 149.9, 148.3, 141.9, 138.6, 129.54, 129.5, 127.1, 126.5, 125.9, 120.2, 102.0, 97.9, 68.4, 54.7, 54.0, 53.8, 49.7, 38.5, 23.5, 21.5.

N-(Pyridin-4-ylmethyl)-6-[2-(quinolin-4-yl)-4,5-dihydro-1H-imidazol-1-yl]pyridin-2-amine (5)

Gray solid, m.p.: 102–104 °C. ES-MS m/z 381 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.77 (d, J = 4.4 Hz, 1H), 8.34 (d, J = 5.6 Hz, 2H), 7.96 (d, J = 8.45 Hz, 1H), 7.87 (d, J = 8.35 Hz, 1H), 7.56 (t, J = 7.8 Hz, 1H), 7.38 (t, J = 7.85 Hz, 1H), 7.32 (d, J = 4.3 Hz, 1H), 7.14 (t, J = 7.9 Hz, 1H), 6.74 (d, J = 5.3 Hz, 2H), 5.80 (dd, J = 15.4, 7.85 Hz, 2H), 4.37 (t, J = 5.95 Hz, 1H), 4.19–4.15 (m, 2H), 4.12–4.08 (m, 2H), 3.24 (d, J = 6.05 Hz, 2H); ¹³C NMR (125 MHz, CDCl₃): δ_C 158.4, 156.5, 151.2, 149.8, 149.5 (2 carbons), 148.9, 148.1, 141.4, 139.0, 129.6, 129.5, 127.1, 126.1, 125.5, 121.8 (2 carbons), 120.1, 101.2, 98.9, 53.9, 49.5, 43.2.

4-{1-[6-(4-Ethylpiperazin-1-yl)pyridin-2-yl]-4,5-dihydro-1H-imidazol-2-yl}quinoline (6)

Waxy solid. ES-MS m/z 387 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.87 (d, J = 4.35 Hz, 1H), 8.07 (d, J = 8.45 Hz, 1H), 7.94 (d, J = 8.3 Hz, 1H), 7.65 (t, J = 7.4 Hz, 1H), 7.44 (t, J = 7.45 Hz, 1H), 7.40 (d, J = 4.35 Hz, 1H), 7.25 (t, J = 8.05 Hz, 1H), 5.96 (d, J = 8.35 Hz, 1H), 5.88 (d, J = 9.65 Hz, 1H), 4.23–4.19 (m, 2H), 4.15–4.11 (m, 2H), 2.46 (t, J = 4.95 Hz, 4H), 2.25 (q, J = 7.25 Hz, 2H), 1.98 (t, J = 5.15 Hz, 4H), 0.99 (t, J = 7.25 Hz, 3H); ¹³C NMR (125 MHz, CDCl₃): δ_C 158.6, 157.4, 150.9, 149.8, 148.3, 141.6, 139.3, 129.6, 129.5, 127.1, 126.2, 125.6, 120.0, 99.8, 98.6, 54.0, 52.3, 52.2 (2 carbons), 49.5, 44.0 (2 carbons), 11.9.

N-Benzyl-6-[2-(quinolin-4-yl)-4,5-dihydro-1H-imidazol-1-yl]pyridin-2-amine (7)

Viscous oil. ES-MS m/z 380 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.83 (d, J = 4.3 Hz, 1H), 8.02 (d, J = 8.45 Hz, 1H), 7.94 (d, J = 8.4 Hz, 1H), 7.61 (t, J = 7.15 Hz, 1H), 7.43 (t, J = 7.7 Hz, 1H), 7.40 (d, J = 4.3 Hz, 1H), 7.24–7.17 (m, 3H), 7.10 (t, J = 8.0 Hz, 1H), 6.92 (d, J = 7.05 Hz, 2H), 5.74 (d, J = 7.9 Hz, 2H), 4.22–4.13 (m, 5H), 3.32 (d, J = 5.6 Hz, 2H); ¹³C NMR (125 MHz, CDCl₃): δ_C 158.6, 156.9, 151.3, 149.9, 148.2, 141.3, 139.2, 138.8, 129.7, 129.4, 128.4 (2 carbons), 127.2 (2 carbons), 127.01, 127.0, 126.2, 125.6, 120.2, 101.0, 98.7, 53.9, 49.6, 44.8.

N-(2-Methylpropyl)-6-[2-(quinolin-4-yl)-4,5-dihydro-1H-imidazol-1-yl]pyridin-2-amine (8)

Clear oil. ES-MS m/z 346 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.87 (d, J = 4.4 Hz, 1H), 8.07 (d, J = 8.5 Hz, 1H), 7.96 (d, J = 8.35 Hz, 1H), 7.64 (t, J = 7.65 Hz, 1H), 7.44 (t, J = 7.4 Hz, 1H), 7.40 (d, J = 4.35 Hz, 1H), 7.08 (t, J = 7.95 Hz, 1H), 5.71 (dd, J = 15.1, 8.1 Hz, 2H), 4.21–4.17 (m, 2H), 4.16–4.12 (m, 2H), 3.76 (t, J = 4.9 Hz, 1H), 2.04 (t, J = 6.1 Hz, 2H), 1.41–1.33 (m, 1H), 0.63 (d, J = Hz, 6H); ¹³C NMR (125 MHz, CDCl₃): δ_C 158.7, 157.4, 151.3, 149.8, 148.2, 141.3, 138.6, 129.7, 129.4, 127.0, 126.3, 125.7, 120.2, 100.6, 98.2, 53.9, 49.6, 48.4, 28.1, 20.1 (2 carbons).

(±)-N-{6-[2-(Quinolin-4-yl)-4,5-dihydro-1H-imidazol-1-yl]pyridin-2-yl}-1-azabicyclo[2.2.2]octan-3-amine (9)

Waxy solid. ES-MS m/z 399 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.89 (d, J = 4.35 Hz, 1H), 8.10 (d, J = 8.45 Hz, 1H), 8.03 (d, J = 8.35 Hz, 1H), 7.68 (t, J = 7.6 Hz, 1H), 7.48 (t, J = 7.65 Hz, 1H), 7.39 (d, J = 4.35 Hz, 1H), 7.10 (d, J = 7.95 Hz, 1H), 5.74 (dd, J = 15.8, 8.1 Hz, 2H), 4.19–4.17 (m, 4H), 4.02 (d, J = 5.9 Hz, 1H), 5.69–5.63 (m, 5H), 2.51–5.45 (m, 1H), 2.29 (s, 1H), 2.12–2.07 (m, 1H), 1.47–1.43 (m, 2H), 1.27–1.22 (m, 1H), 1.18–1.13 (m, 1H); ¹³C NMR (125 MHz, CDCl₃): δ_C 158.5, 156.6, 151.5, 149.9, 148.4, 140.8, 138.7, 129.7, 129.6, 127.2, 126.2, 125.9, 120.5, 101.1, 99.2, 57.0, 53.9, 49.9, 47.5, 47.3, 46.5, 25.8, 25.3, 20.0.

4-{1-[6-(Morpholin-4-yl)pyridin-2-yl]-4,5-dihydro-1H-imidazol-2-yl}quinoline (10)

Pale solid, m.p.: 98–100 °C. ES-MS m/z 360 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.87 (d, J = 4.35 Hz, 1H), 8.08 (d, J = 8.5 Hz, 1H), 7.95 (d, J = 8.35 Hz, 1H), 7.67 (t, J = 7.25 Hz, 1H), 7.46 (t, J = 7.75 Hz, 1H), 7.40 (d, J = 4.3 Hz, 1H), 7.29 (t, J = 8.15 Hz, 1H), 5.95 (dd, J = 13.35, 8.3 Hz, 2H), 4.25–4.20 (m, 2H), 4.18–4.13 (m, 2H), 3.27 (t, J = 4.85 Hz, 4H), 2.39 (t, J = 4.75 Hz, 4H); ¹³C NMR (125 MHz, CDCl₃): δ_C 158.5, 157.5, 151.0, 149.9, 148.4, 141.6, 139.4, 129.6 (2 carbons), 127.2, 126.3, 125.6, 120.0, 99.6, 99.2, 66.3 (2 carbons), 54.1, 49.6, 44.4 (2 carbons).

4-(1-{6-[2-(Pyridin-4-yl)-4,5-dihydro-1H-imidazol-1-yl]pyridin-2-yl}-4,5-dihydro-1H-imidazol-2-yl)quinoline (11)

Gray solid, m.p.: 164–166 °C. ES-MS m/z 420 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.90 (d, J = 4.35 Hz, 1H), 8.56 (d, J = 5.7 Hz, 2H), 8.08 (d, J = 8.45 Hz, 1H), 7.81 (d, J = 8.4 Hz, 1H), 7.66 (t, J = 8.1 Hz, 1H), 7.45 (t, J = 8.1 Hz, 1H), 7.38 (d, J = 4.35 Hz, 1H), 7.21 (d, J = 5.7 Hz, 2H), 6.98 (t, J = 8.2 Hz, 1H), 5.73 (dd, J = 14.1, 9.2 Hz, 2H), 4.06 (t, J = 9.6 Hz, 2H), 3.74 (quint, 9.55 Hz, 4H), 3.12 (t, J = 9.6 Hz, 2H); ¹³C NMR (125 MHz, CDCl₃): δ_C 158.9, 157.6, 151.6, 150.7, 150.0, 149.8 (2 carbons), 148.3, 140.4, 139.9, 138.7, 129.8, 129.79, 127.3, 125.8, 125.2, 122.5 (2 carbons), 120.4, 105.8, 104.2, 53.6, 53.2, 49.9, 48.9.

4-(1-{6-[2-(Pyridin-3-yl)-4,5-dihydro-1H-imidazol-1-yl]pyridin-2-yl}-4,5-dihydro-1H-imidazol-2-yl)quinoline (12)

Beige solid, m.p.: 147–149 °C. ES-MS m/z 420 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.91 (d, J = 4.35 Hz, 1H), 8.58 (d, J = 4.8 Hz, 1H), 8.52–8.51 (m, 1H), 8.10 (d, J = 8.5 Hz, 1H), 7.82 (d, J = 8.4 Hz, 1H), 7.71–7.66 (m, 2H), 7.48 (t, J = 7.95 Hz, 1H), 7.40 (d, J = 4.35 Hz, 1H), 7.28–7.25 (m, 1H), 6.99 (t, J = 8.2 Hz, 1H), 5.75 (t, J = 8.45 Hz, 2H), 4.08 (t, J = 9.5 Hz, 2H), 3.76 (t, J = 9.6 Hz, 4H), 3.14 (t, J = 9.55 Hz, 2H); ¹³C NMR (125 MHz, CDCl₃): δ_C 158.4, 157.7, 151.7, 150.8, 150.6, 150.0, 149.3, 148.4, 140.0, 138.7, 135.7, 129.9 (2 carbons), 128.6, 127.4, 125.9, 125.2, 123.1, 120.5, 106.0, 104.2, 53.6, 52.9, 50.0, 49.1.

(±)-4-[1-(2-{Octahydropyrrolo[1,2-a]piperazin-2-yl}pyrimidin-4-yl)-4,5-dihydro-1H-imidazol-2-yl]quinoline (13)

Waxy solid. ES-MS m/z 400 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.90 (d, J = 4.35 Hz, 1H), 8.08 (d, J = 8.45 Hz, 1H), 7.96 (d, J = 5.55 Hz, 1H), 7.82 (d, J = 8.35 Hz, 1H), 7.66 (t, J = 8.2 Hz, 1H), 7.46 (t, J = 7.95 Hz, 1H), 7.39 (d, J = 4.35 Hz, 1H), 5.72 (d, J = 5.65 Hz, 1H), 4.25–4.21 (m, 2H), 4.13–4.09 (m, 2H), 2.93 (t, J = 8.4 Hz, 1H), 2.64 (bs, 1H), 2.21 (s, 1H), 1.92 (q, J = 8.7 Hz, 1H), 1.75–1.57 (m, 4H), 1.40 (bs, 1H), 1.17–1.15 (m, 1H); ¹³C NMR (125 MHz, CDCl₃): δ_C 160.4, 158.3, 157.5, 157.2, 149.8, 148.2, 141.0, 129.9, 129.7, 127.4, 126.0, 125.2, 119.9, 95.4, 62.1, 54.1 (2 carbons), 53.5, 51.2, 48.2, 27.2, 21.2 (2 carbons).

4-{1-[2-(4-Ethylpiperazin-1-yl)pyrimidin-4-yl]-4,5-dihydro-1H-imidazol-2-yl}quinoline (14)

Yellowish solid, m.p.: 113–115 °C. ES-MS m/z 388 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.91 (d, J = 4.3 Hz, 1H), 8.09 (d, J = 8.5 Hz, 1H), 7.95 (d, J = 5.75 Hz, 1H), 7.81 (d, J = 8.35 Hz, 1H), 7.68 (t, J = 8.15 Hz, 1H), 7.47 (t, J = 7.85 Hz, 1H), 7.40 (d, J = 4.35 Hz, 1H), 5.71 (d, J = 5.7 Hz, 1H), 4.33–4.10 (m, 5H), 2.27–2.22 (m, 4H), 1.95 (bs, 4H), 1.01–0.96 (m, 4H); ¹³C NMR (125 MHz, CDCl₃): δ_C 160.3, 158.4, 157.5, 157.2, 149.9, 148.2, 141.1, 129.8, 129.7, 127.4, 126.0, 125.2, 119.9, 95.4, 54.1 (2 carbons), 52.3, 52.2 (2 carbons), 48.2, 42.8, 11.9.

1-{4-[2-(Quinolin-4-yl)-4,5-dihydro-1H-imidazol-1-yl]pyrimidin-2-yl}piperidin-4-ol (15)

Glassy solid, m.p.: 88–90 °C. ES-MS m/z 375 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.89 (d, J = 4.4 Hz, 1H), 8.09 (d, J = 8.5 Hz, 1H), 7.96 (d, J = 5.7 Hz, 1H), 7.84 (d, J = 8.2 Hz, 1H), 7.68 (t, J = 8.35 Hz, 1H), 7.48 (t, J = 8.1 Hz, 1H), 7.39 (d, J = 4.4 Hz, 1H), 5.71 (d, J = 5.7 Hz, 1H), 4.26–4.22 (m, 2H), 4.15–4.11 (m, 2H), 3.57–3.52 (m, 1H), 2.37 (bs, 3H), 2.19 (s, 2H), 1.37–1.36 (m, 2H), 0.90 (bs, 2H); ¹³C NMR (125 MHz, CDCl₃): δ_C 160.2, 158.4, 157.6, 157.3, 149.8, 148.2, 141.2, 129.8, 129.7, 127.4, 126.0, 125.2, 119.9, 95.2, 67.6, 54.1 (2 carbons), 48.2, 40.6, 33.8 (2 carbons).

(1-{4-[2-(Quinolin-4-yl)-4,5-dihydro-1H-imidazol-1-yl]pyrimidin-2-yl}piperidin-4-yl)methanol (16)

White solid, m.p.: 172–174 °C. ES-MS m/z 389 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.87 (d, J = 4.35 Hz, 1H), 8.08 (d, J = 8.55 Hz, 1H), 7.95 (d, J = 5.5 Hz, 1H), 7.83 (d, J = 8.35 Hz, 1H), 7.67 (t, J = 8.0 Hz, 1H), 7.47 (t, J = 7.8 Hz, 1H), 7.39 (d, J = 4.4 Hz, 1H), 5.69 (d, J = 5.6 Hz, 1H), 4.25–4.21 (m, 2H), 4.13–4.10 (m, 2H), 3.39 (s, 2H), 3.25 (d, J = 6.2 Hz, 2H), 2.41 (bs, 1H), 2.08 (bs, 2H), 1.40–1.34 (m, 1H), 1.30–1.28 (m, 2H), 0.52 (bs, 2H); ¹³C NMR (125 MHz, CDCl₃): δ_C 160.1, 158.4, 157.6, 157.2, 149.7, 148.1, 141.2, 129.8, 129.6, 127.4, 126.0, 125.2, 119.9, 95.0, 67.3, 54.1, 50.5, 48.2, 42.9, 38.9 (2 carbons), 28.2.

2-(1-{4-[2-(Quinolin-4-yl)-4,5-dihydro-1H-imidazol-1-yl]pyrimidin-2-yl}piperidin-4-yl)ethan-1-ol (17)

Off-white solid, m.p.: 155–157 °C. ES-MS m/z 403 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.88 (d, J = 4.35 Hz, 1H), 8.07 (d, J = 8.45 Hz, 1H), 7.93 (d, J = 5.55 Hz, 1H), 7.81 (d, J = 8.3 Hz, 1H), 7.66 (t, J = 8.25 Hz, 1H), 7.46 (t, J = 7.85 Hz, 1H), 7.39 (d, J = 4.35 Hz, 1H), 5.67 (d, J = 5.65 Hz, 1H), 4.24–4.20 (m, 2H), 4.12–4.08 (m, 2H), 3.52 (t, J = 6.35 Hz, 2H), 2.51 (bs, 2H), 2.07 (bs, 2H), 1.30–1.23 (m, 6H), 0.50 (bs, 2H); ¹³C NMR (125 MHz, CDCl₃): δ_C 160.2, 158.3, 157.6, 157.2, 149.8, 148.1, 141.2, 129.7, 129.6, 127.4, 126.0, 125.2, 119.8, 94.9, 59.9 (2 carbons), 54.0, 48.2 (2 carbons), 43.2, 39.3, 32.6, 31.7.

4-{1-[6-(Morpholin-4-yl)pyrazin-2-yl]-4,5-dihydro-1H-imidazol-2-yl}quinoline (18)

White solid, m.p.: 132–134 °C. ES-MS m/z 361 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.89 (d, J = 4.35 Hz, 1H), 8.09 (d, J = 8.5 Hz, 1H), 7.88 (d, J = 8.25 Hz, 1H), 7.69 (t, J = 7.25 Hz, 1H), 7.49–7.47 (m, 2H), 7.39 (d, J = 4.3 Hz, 1H), 7.36 (s, 1H), 4.29 (t, J = 9.05 Hz, 2H), 4.18 (t, J = 10.55 Hz, 2H), 3.27 (t, J = 4.9 Hz, 4H), 2.43 (t, J = 4.8 Hz, 4H); ¹³C NMR (125 MHz, CDCl₃): δ_C 157.9, 152.2, 149.9, 148.3, 146.3, 141.0, 129.8, 127.4, 126.1, 125.4, 123.0, 120.0, 119.8, 110.1, 66.1 (2 carbons), 54.6, 48.7, 43.8 (2 carbons).

(±)-4-[1-(6-{Octahydropyrrolo[1,2-a]piperazin-2-yl}pyrazin-2-yl)-4,5-dihydro-1H-imidazol-2-yl]quinoline (19)

White flakes, m.p.: 112–114 °C. ES-MS m/z 400 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.88 (d, J = 4.35 Hz, 1H), 8.08 (d, J = 8.5 Hz, 1H), 7.88 (d, J = 8.4 Hz, 1H), 7.66 (t, J = 7.55 Hz, 1H), 7.50 (s, 1H), 7.45 (t, J = 7.5 Hz, 1H), 7.39 (d, J = 4.35 Hz, 1H), 7.32 (s, 1H), 4.29–4.25 (m, 2H), 4.19–4.15 (m, 2H), 2.96–2.93 (m, 2H), 2.86 (d, J = 12.5 Hz, 1H), 2.67 (d, J = 10.85 Hz, 1H), 2.25 (t, J = 10.25 Hz, 1H), 2.13 (s, 1H), 1.95 (q, J = 8.7 Hz, 1H), 1.80 (t, J = 11.6 Hz, 1H), 1.75–1.61 (m, 3H), 1.48–1.43 (m, 1H), 1.20–1.14 (m, 1H); ¹³C NMR (125 MHz, CDCl₃): δ_C 158.1, 152.3, 149.8, 148.3, 146.3, 141.0, 129.9, 129.7, 127.3, 126.1, 125.3, 123.4, 120.0, 119.1, 61.8, 54.5, 53.5, 50.9, 48.8, 48.1, 43.0, 27.4, 21.2.

4-{1-[6-(4-Ethylpiperazin-1-yl)pyrazin-2-yl]-4,5-dihydro-1H-imidazol-2-yl}quinoline (20)

Gray solid, m.p.: 144–146 °C. ES-MS m/z 388 [M + H]⁺.¹H NMR (500 MHz, CDCl₃): δ_H 8.87 (d, J = 4.35 Hz, 1H), 8.07 (d, J = 8.45 Hz, 1H), 7.85 (d, J = 8.4 Hz, 1H), 7.65 (t, J = 7.35 Hz, 1H), 7.45–7.42 (m, 2H), 7.38 (d, J = 4.3 Hz, 1H), 7.29 (s, 1H), 4.25 (t, J = 9.15 Hz, 2H), 4.14 (t, J = 9.15 Hz, 2H), 2.48 (t, J = 4.8 Hz, 4H), 2.23 (q, J = 7.2 Hz, 2H), 1.96 (t, J = 4.85 Hz, 4H), 0.97 (t, J = 7.15 Hz, 3H); ¹³C NMR (125 MHz, CDCl₃): δ_C 158.0, 152.1, 149.8, 148.2, 146.2, 141.0, 129.7, 129.66, 127.3, 126.1, 125.3, 123.2, 119.9, 119.0, 54.5, 52.2, 51.9 (2 carbons), 48.6, 43.4 (2 carbons), 11.8.

N,N-Dimethyl-6-[2-(quinolin-4-yl)-4,5-dihydro-1H-imidazol-1-yl]pyrazin-2-amine (21)

White solid, m.p.: 156–158 °C. ES-MS m/z 319 [M + H]⁺.¹H NMR (500 MHz, CDCl₃): δ_H 8.90 (d, J = 4.3 Hz, 1H), 8.09 (d, J = 8.5 Hz, 1H), 7.91 (d, J = 8.4 Hz, 1H), 7.68 (t, J = 7.9 Hz, 1H), 7.47 (t, J = 7.25 Hz, 1H), 7.42 (t, J = 4.25 Hz, 1H), 7.39 (s, 1H), 7.26 (s, 1H), 4.31–4.27 (m, 2H), 4.22–4.18 (m, 2H), 2.21 (s, 6H); ¹³C NMR (125 MHz, CDCl₃): δ_C 158.3, 152.6, 150.0, 148.4, 146.5, 141.1, 129.8, 129.7, 127.3, 126.3, 125.4, 122.8, 120.1, 118.2, 54.5, 48.9, 36.7 (2 carbons).

4-{1-[6-(4-Phenylpiperazin-1-yl)pyrazin-2-yl]-4,5-dihydro-1H-imidazol-2-yl}quinoline (22)

Beige solid, m.p.: 178–180 °C (decomp.). ES-MS m/z 436 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.94 (d, J = 4.3 Hz, 1H), 8.14 (d, J = 8.5 Hz, 1H), 7.90 (d, J = 8.3 Hz, 1H), 7.70 (t, J = 7.5 Hz, 1H), 7.54 (s, 1H), 7.49 (t, J = 7.35 Hz, 1H), 7.43 (d, J = 4.3 Hz, 1H), 7.36 (s, 1H), 7.27–7.24 (m, 2H), 6.87 (t, J = 7.3 Hz, 1H), 6.80 (d, J = 8.1 Hz, 2H), 4.32–4.28 (m, 2H), 4.21–4.17 (m, 2H), 2.74–2.72 (m, 4H), 2.65–2.63 (m, 4H); ¹³C NMR (125 MHz, CDCl₃): δ_C 157.9, 152.0, 150.9, 150.0, 148.3, 146.3, 141.2, 129.8 (2 carbons), 129.2 (2 carbons), 127.4, 126.2, 125.4, 123.2, 120.3, 120.0, 119.4, 116.4 (2 carbons), 54.6, 48.7, 48.5 (2 carbons), 43.5 (2 carbons).

4-{1-[6-(Piperidin-1-yl)pyrazin-2-yl]-4,5-dihydro-1H-imidazol-2-yl}quinoline (23)

Beige solid, m.p.: 136–138 °C (decomp.). ES-MS m/z 359 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.90 (d, J = 4.35 Hz, 1H), 8.09 (d, J = 8.5 Hz, 1H), 7.91 (d, J = 8.4 Hz, 1H), 7.68 (t, J = 7.2 Hz, 1H), 7.48–7.46 (m, 2H), 7.40 (d, J = 4.35 Hz, 1H), 7.26 (s, 1H), 4.30–4.26 (m, 2H), 4.20–4.16 (m, 2H), 2.51 (t, J = 5.5 Hz, 4H), 1.37–1.32 (m, 2H), 1.09–1.04 (m, 4H); ¹³C NMR (125 MHz, CDCl₃): δ_C 158.2, 152.2, 149.9, 148.4, 146.5, 141.1, 129.8, 129.6, 127.3, 126.1, 125.4, 123.4, 120.0, 118.3, 54.5, 48.8, 44.7 (2 carbons), 25.1 (2 carbons), 24.3.

N-Benzyl-N-ethyl-6-[2-(quinolin-4-yl)-4,5-dihydro-1H-imidazol-1-yl]pyrazin-2-amine (24)

Oil, ES-MS m/z 409 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.80 (d, J = 4.35 Hz, 1H), 8.00 (d, J = 8.45 Hz, 1H), 7.89 (d, J = 8.3 Hz, 1H), 7.61 (t, J = 7.25 Hz, 1H), 7.43 (t, J = 7.15 Hz, 1H), 7.38 (d, J = 4.35 Hz, 1H), 7.36 (s, 1H), 7.25 (s, 1H), 7.19–7.18 (m, 3H), 6.80–6.79 (m, 2H), 4.29–4.25 (m, 2H), 4.22–4.18 (m, 2H), 3.83 (s, 2H), 2.68 (q, J = 7.05 Hz, 2H), 0.62 (t, J = 7.05 Hz, 3H); ¹³C NMR (125 MHz, CDCl₃): δ_C 158.2, 151.7, 149.9, 148.3, 146.7, 140.7, 137.6, 129.9, 129.6, 128.5 (2 carbons), 127.3, 127.1, 126.7 (2 carbons), 125.9, 125.2, 122.8, 120.1, 118.7, 54.4, 49.9, 49.1, 41.9, 12.0.

4-{1-[2-(4-Ethylpiperazin-1-yl)-5-(trifluoromethyl)pyrimidin-4-yl]-4,5-dihydro-1H-imidazol-2-yl}quinoline (25)

Beige solid, m.p.: 143–145 °C. ES-MS m/z 456 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.90 (d, J = 4.3 Hz, 1H), 8.24 (s, 1H), 8.08 (d, J = 8.45 Hz, 1H), 7.85 (d, J = 8.35 Hz, 1H), 7.68 (t, J = 8.15 Hz, 1H), 7.48 (t, J = 7.8 Hz, 1H), 7.39 (d, J = 4.2 Hz, 1H), 4.33 (t, J = 9.4 Hz, 2H), 4.19 (t, J = 9.45 Hz, 2H), 2.55 (s, 4H), 2.21 (q, J = 7.2 Hz, 2H), 1.87 (s, 4H), 0.96 (t, J = 7.2 Hz, 3H); ¹³C NMR (125 MHz, CDCl₃): δ_C 159.2, 158.4 (q, J_C-F = 5.0 Hz), 157.1, 157.0, 149.9, 148.3, 141.1, 129.83, 129.8, 127.5, 126.1, 125.2, 124.6 (q, J_C-F = 268.75 Hz), 120.0, 102.1 (q, J_C-F = 32.5 Hz), 54.1, 52.0, 51.9 (2 carbons), 48.7, 46.5, 46.48, 11.6.

(±)-4-[1-(2-{Octahydropyrrolo[1,2-a]piperazin-2-yl}-5-(trifluoromethyl)pyrimidin-4-yl)-4,5-dihydro-1H-imidazol-2-yl]quinoline (26)

Waxy solid. ES-MS m/z 468 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.90 (d, J = 4.35 Hz, 1H), 8.25 (s, 1H), 8.08 (d, J = 8.5 Hz, 1H), 7.85 (d, J = 8.25 Hz, 1H), 7.68 (t, J = 8.15 Hz, 1H), 7.48 (t, J = 7.85 Hz, 1H), 7.40 (d, J = 4.35 Hz, 1H), 4.36–4.32 (m, 2H), 4.19 (t, J = 9.15 Hz, 2H), 2.93–2.88 (m, 2H), 2.82 (d, J = 13.25 Hz, 1H), 2.51 (d, J = 10.3 Hz, 1H), 2.26 (t, J = 10.95 Hz, 1H), 1.98–1.93 (m, 1H), 1.84 (bs, 1H), 1.75–1.68 (m, 1H), 1.63–1.53 (m, 4H), 1.14–1.11 (m, 1H); ¹³C NMR (125 MHz, CDCl₃): δ_C 159.8, 158.5 (q, J_C-F = 6.25 Hz), 157.2, 157.0, 149.8, 148.2, 141.0, 129.9, 129.8, 127.4, 126.1, 125.2, 124.6 (q, J_C-F = 268.75 Hz), 120.1, 102.4 (q, J_C-F = 31.25 Hz), 61.9, 54.1, 53.0, 51.0, 50.7, 48.7, 46.5, 27.0, 21.1.

1-{4-[2-(Quinolin-4-yl)-4,5-dihydro-1H-imidazol-1-yl]-5-(trifluoromethyl)pyrimidin-2-yl}piperidin-4-ol (27)

Gray solid, m.p.: 163–165 °C. ES-MS m/z 443 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.89 (d, J = 4.35 Hz, 1H), 8.24 (s, 1H), 8.08 (d, J = 8.5 Hz, 1H), 7.85 (d, J = 8.3 Hz, 1H), 7.69 (t, J = 7.25 Hz, 1H), 7.50 (t, J = 7.85 Hz, 1H), 7.42 (d, J = 4.35 Hz, 1H), 4.35 (t, J = 9.5 Hz, 2H), 4.20 (t, J = 9.55 Hz, 2H), 3.56–3.51 (m, 1H), 2.82 (s, 1H), 2.74–2.71 (m, 2H), 2.22 (s, 2H), 1.34–1.30 (m, 2H), 1.01–0.94 (m, 2H); ¹³C NMR (125 MHz, CDCl₃): δ_C 159.4, 158.4 (q, J_C-F = 6.25 Hz), 157.3, 156.9, 149.7, 148.0, 141.2, 130.0, 129.5, 127.6, 126.2, 125.2, 124.6 (q, J_C-F = 268.75 Hz), 120.1, 102.4 (q, J_C-F = 32.5 Hz), 66.2, 54.0, 48.7, 44.2, 44.19, 33.6 (2 carbons).

(1-{4-[2-(Quinolin-4-yl)-4,5-dihydro-1H-imidazol-1-yl]-5-(trifluoromethyl)pyrimidin-2-yl}piperidin-4-yl)methanol (28)

Gray solid, m.p.: 118–120 °C. ES-MS m/z 457 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.88 (d, J = 4.35 Hz, 1H), 8.23 (s, 1H), 8.08 (d, J = 8.45 Hz, 1H), 7.85 (d, J = 8.35 Hz, 1H), 7.68 (t, J = 7.8 Hz, 1H), 7.49 (t, J = 7.65 Hz, 1H), 7.42 (d, J = 4.35 Hz, 1H), 4.35 (t, J = 9.4 Hz, 2H), 4.19 (t, J = 9.5 Hz, 2H), 3.23 (d, J = 6.25 Hz, 2H), 2.88 (d, J = 13.1 Hz, 2H), 2.73 (s, 2H), 2.03 (s, 2H), 1.25–1.23 (m, 2H), 0.58 (s, 2H); ¹³C NMR (125 MHz, CDCl₃): δ_C 159.3, 158.3 (q, J_C-F = 6.25 Hz), 157.4, 156.9, 149.8, 148.1, 141.2, 129.9, 129.6, 127.5, 126.2, 125.2, 124.7 (q, J_C-F = 268.75 Hz), 120.1, 102.3 (q, J_C-F = 31.25 Hz), 66.8, 54.0, 48.8, 46.91, 46.9, 45.9, 38.1, 28.1.

2-(1-{4-[2-(Quinolin-4-yl)-4,5-dihydro-1H-imidazol-1-yl]-5-(trifluoromethyl)pyrimidin-2-yl}piperidin-4-yl)ethan-1-ol (29)

Oil. ES-MS m/z 471 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.89 (d, J = 4.3 Hz, 1H), 8.22 (s, 1H), 8.08 (d, J = 8.5 Hz, 1H), 7.85 (d, J = 8.35 Hz, 1H), 7.68 (t, J = 8.15 Hz, 1H), 7.49 (t, J = 7.95 Hz, 1H), 7.41 (d, J = 4.4 Hz, 1H), 4.34 (t, J = 9.5 Hz, 2H), 4.19 (t, J = 9.55 Hz, 2H), 3.51 (t, J = 6.35 Hz, 2H), 2.84 (d, J = 12.1 Hz, 2H), 2.54 (s, 2H), 2.02 (t, J = 12.6 Hz, 2H), 1.27–1.18 (m, 4H), 0.54 (s, 2H); ¹³C NMR (125 MHz, CDCl₃): δ_C 159.3, 158.3 (q, J_C-F = 6.25 Hz), 157.4, 157.0, 149.8, 148.2, 141.2, 129.8, 129.6, 127.5, 126.2, 125.3, 124.7 (q, J_C-F = 268.75 Hz), 120.1, 102.3 (q, J_C-F = 32.5 Hz), 59.8, 54.0, 48.7, 47.3, 47.26, 45.9, 38.9, 32.1, 31.6.

N-(Pyridin-4-ylmethyl)-4-[2-(quinolin-4-yl)-4,5-dihydro-1H-imidazol-1-yl]-5-(trifluoromethyl)-pyrimidin-2-amine (30)

Brown solid, m.p.: 99–101 °C. ES-MS m/z 450 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.75 (d, J = 4.35 Hz, 1H), 8.35 (d, J = 5.35 Hz, 2H), 8.15 (s, 1H), 7.91 (d, J = 8.5 Hz, 1H), 7.74 (d, J = 8.35 Hz, 1H), 7.54 (t, J = 8.2 Hz, 1H), 7.39 (t, J = 7.85 Hz, 1H), 7.29 (d, J = 4.3 Hz, 1H), 6.60 (d, J = 5.2 Hz, 2H), 5.25–5.23 (m, 1H), 4.31 (t, J = 9.4 Hz, 2H), 4.17 (t, J = 9.5 Hz, 2H), 3.03–3.02 (m, 2H); ¹³C NMR (125 MHz, CDCl₃): δ_C 158.0, 157.0, 155.2 (q, J_C-F = 5.0 Hz), 149.8, 149.7 (3 carbons), 147.9, 146.5, 141.2, 129.8, 129.7, 127.4, 126.0, 125.0, 124.4 (q, J_C-F = 268.75 Hz), 121.4 (2 carbons), 120.0, 100.7 (q, J_C-F = 31.25 Hz), 54.0, 48.5, 41.9.

4-(1-{2-[2-(2-Methylpropyl)-4,5-dihydro-1H-imidazol-1-yl]-5-(trifluoromethyl)pyrimidin-4-yl}-4,5-dihydro-1H-imidazol-2-yl)quinoline (31)

White solid, m.p.: 151–153 °C. ES-MS m/z 468 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.94 (d, J = 4.3 Hz, 1H), 8.21 (s, 1H), 8.17 (d, J = 8.45 Hz, 1H), 7.74 (d, J = 8.35 Hz, 1H), 7.70 (t, J = 7.15 Hz, 1H), 7.46 (t, J = 7.95 Hz, 1H), 7.41 (d, J = 4.3 Hz, 1H), 4.38–4.34 (m, 2H), 4.31–4.27 (m, 2H), 3.65 (t, J = 8.75 Hz, 2H), 3.38–3.36 (m, 1H), 2.84 (s, 1H), 2.02 (d, J = 6.95 Hz, 2H), 1.71–1.63 (m, 1H), 0.77 (d, J = 6.6 Hz, 6H); ¹³C NMR (125 MHz, CDCl₃): δ_C 163.3, 158.3 (q, J_C-F = 5.0 Hz), 157.4, 156.9, 149.9, 148.1, 140.1, 130.2, 129.6, 127.2, 126.1, 124.7, 123.4 (q, J_C-F = 300.0 Hz), 120.3, 110.1, 107.8 (q, J_C-F = 32.5 Hz), 54.1, 53.4, 51.5, 48.7, 38.4, 26.6, 22.3 (2 carbons).

4-{1-[2-(Morpholin-4-yl)-5-(trifluoromethyl)pyrimidin-4-yl]-4,5-dihydro-1H-imidazol-2-yl}quinoline (32)

Gray solid, m.p.: 127–129 °C. ES-MS m/z 429 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.91 (d, J = 4.35 Hz, 1H), 8.27 (s, 1H), 8.11 (d, J = Hz, 1H), 7.85 (d, J = 8.3 Hz, 1H), 7.71 (t, J = 8.15 Hz, 1H), 7.51 (t, J = 8.0 Hz, 1H), 7.40 (t, J = 4.3 Hz, 1H), 4.35 (t, J = 9.45 Hz, 2H), 4.21 (t, J = 9.3 Hz, 2H), 3.11 (t, J = 4.55 Hz, 4H), 2.47 (s, 4H); ¹³C NMR (125 MHz, CDCl₃): δ_C 159.5, 158.5 (q, J_C-F = 6.25 Hz), 157.1, 157.0, 149.8, 148.2, 141.1, 130.0, 129.8, 127.6, 126.1, 125.2, 124.5 (q, J_C-F = 268.75 Hz), 120.0, 102.3 (q, J_C-F = 32.5 Hz), 66.1 (2 carbons), 54.0, 48.7, 47.2, 47.2.

4-{1-[6-(4-Ethylpiperazin-1-yl)pyrimidin-4-yl]-4,5-dihydro-1H-imidazol-2-yl}quinoline (33)

Off-white solid, m.p.: 87–89 °C. ES-MS m/z 388 [M + H]⁺.¹H NMR (500 MHz, CDCl₃): δ_H 8.95 (d, J = 4.25 Hz, 1H), 8.11 (d, J = 8.5 Hz, 1H), 8.06 (s, 1H), 7.82 (d, J = 8.4 Hz, 1H), 7.70 (t, J = 8.25 Hz, 1H), 7.49 (t, J = 8.0 Hz, 1H), 7.46 (d, J = 4.25 Hz, 1H), 4.95 (s, 1H), 4.30–4.26 (m, 2H), 4.20–4.16 (m, 2H), 2.98 (s, 4H), 2.30 (q, J = 7.25 Hz, 2H), 2.16 (t, J = 4.85 Hz, 4H), 1.01 (t, J = 7.2 Hz, 3H); ¹³C NMR (125 MHz, CDCl₃): δ_C 162.1, 157.6, 157.4, 157.2, 150.1, 148.3, 139.4, 130.2, 129.9, 127.9, 125.6, 125.0, 120.8, 87.4, 53.8, 52.3, 51.9 (2 carbons), 48.9, 43.6 (2 carbons), 11.8.

(±)-4-[1-(6-{octahydropyrrolo[1,2-a]piperazin-2-yl}pyrimidin-4-yl)-4,5-dihydro-1H-imidazol-2-yl]quinoline (34)

Off-white solid, m.p.: 106–108 °C. ES-MS m/z 400 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.97 (d, J = 4.25 Hz, 1H), 8.14 (d, J = 8.45 Hz, 1H), 8.09 (s, 1H), 7.85 (d, J = 8.3 Hz, 1H), 7.72 (t, J = 8.1 Hz, 1H), 7.52 (t, J = 8.0 Hz, 1H), 7.48 (d, J = 4.3 Hz, 1H), 4.98 (s, 1H), 4.33–4.28 (m, 2H), 4.23–4.19 (m, 2H), 3.49 (s, 1H), 2.99 (t, J = 8.35 Hz, 1H), 2.82 (d, J = 11.05 Hz, 1H), 2.63–2.57 (m, 1H), 2.37 (s, 1H), 2.21 (t, J = 11.7 Hz, 1H), 2.02 (q, J = 8.7 Hz, 1H), 2.87–2.82 (m, 1H), 1.79–1.68 (m, 3H), 1.59 (s, 1H), 1.30–1.23 (m, 1H); ¹³C NMR (125 MHz, CDCl₃): δ_C 162.1, 157.6, 157.4, 157.2, 150.1, 148.3, 139.4, 130.1, 130.0, 127.9, 125.6, 125.0, 120.8, 87.6, 61.7, 53.8, 53.4, 50.9, 48.9, 48.4, 43.2, 27.3, 21.2.

1-{6-[2-(Quinolin-4-yl)-4,5-dihydro-1H-imidazol-1-yl]pyrimidin-4-yl}piperidin-4-ol (35)

White solid, m.p.: 135–137 °C. ES-MS m/z 375 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.93 (d, J = 4.3 Hz, 1H), 8.10 (d, J = 8.4 Hz, 1H), 8.05 (s, 1H), 7.83 (d, J = 8.25 Hz, 1H), 7.70 (t, J = 8.05 Hz, 1H), 7.50 (t, J = 7.8 Hz, 1H), 7.46 (d, J = 4.3 Hz, 1H), 4.98 (s, 1H), 4.30–4.26 (m, 2H), 4.21–4.16 (m, 2H), 3.67–3.62 (m, 1H), 3.28 (s, 1H), 2.65 (t, J = 10.3 Hz, 2H), 2.54 (s, 2H), 1.51–1.47 (m, 2H), 1.11–1.04 (m, 2H); ¹³C NMR (125 MHz, CDCl₃): δ_C 161.7, 157.7, 157.4, 157.3, 150.0, 148.1, 139.4, 130.2, 129.8, 128.0, 125.6, 125.0, 120.8, 87.4, 66.9, 53.6, 48.9, 41.4 (2 carbons), 33.3 (2 carbons).

(1-{6-[2-(Quinolin-4-yl)-4,5-dihydro-1H-imidazol-1-yl]pyrimidin-4-yl}piperidin-4-yl)methanol (36)

White solid, m.p.: 128–130 °C. ES-MS m/z 389 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.96 (d, J = 4.3 Hz, 1H), 8.14 (d, J = 8.45 Hz, 1H), 8.09 (s, 1H), 7.87 (d, J = 8.35 Hz, 1H), 7.73 (t, J = 8.0 Hz, 1H), 7.54 (t, J = 7.8 Hz, 1H), 7.49 (d, J = 4.3 Hz, 1H), 4.99 (s, 1H), 4.34–4.30 (m, 2H), 4.23–4.20 (m, 2H), 3.53 (s, 2H), 3.32 (d, J = 6.2 Hz, 2H), 2.47–2.41 (m, 3H), 1.58–1.52 (m, 1H), 1.47 (d, J = 13.9 Hz, 2H), 0.77–0.69 (m, 2H); ¹³C NMR (125 MHz, CDCl₃): δ_C 162.1, 161.8, 157.7, 157.4, 150.0, 148.2, 139.5, 130.3, 129.8, 128.0, 125.6, 125.0, 120.9, 87.7, 67.0, 53.7, 48.9, 44.1 (2 carbons), 38.8, 27.9 (2 carbons).

2-(1-{6-[2-(Quinolin-4-yl)-4,5-dihydro-1H-imidazol-1-yl]pyrimidin-4-yl}piperidin-4-yl)ethan-1-ol (37)

Oil. ES-MS m/z 403 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.94 (d, J = 4.35 Hz, 1H), 8.11 (d, J = 8.45 Hz, 1H), 8.05 (s, 1H), 7.83 (d, J = 8.35 Hz, 1H), 7.70 (t, J = 8.2 Hz, 1H), 7.50 (t, J = 8.1 Hz, 1H), 7.47 (d, J = 4.3 Hz, 1H), 4.96 (s, 1H), 4.29 (t, J = 9.2 Hz, 2H), 4.18 (t, J = 9.15 Hz, 2H), 3.55 (t, J = 6.6 Hz, 2H), 3.46 (bs, 1H), 3.42–3.35 (m, 4H), 1.52–1.45 (m, 1H), 1.41 (d, J = 13.9 Hz, 2H), 1.31 (q, J = 6.55 Hz, 2H), 0.71–0.64 (m, 2H); ¹³C NMR (125 MHz, CDCl₃): δ_C 161.8, 157.7, 157.4, 157.35, 150.0, 148.2, 139.4, 130.2, 129.9, 127.9, 125.6, 125.0, 120.8, 87.5, 59.9, 53.6, 48.9, 44.4 (2 carbons), 39.1, 32.6, 31.4 (2 carbons).

4-{1-[6-(Morpholin-4-yl)pyrimidin-4-yl]-4,5-dihydro-1H-imidazol-2-yl}quinoline (38)

Gray solid, m.p.: 147–149 °C. ES-MS m/z 361 [M + H]⁺. ¹H NMR (500 MHz, CDCl₃): δ_H 8.95 (d, J = 4.35 Hz, 1H), 8.12 (d, J = 8.45 Hz, 1H), 8.06 (s, 1H), 7.82 (d, J = 8.4 Hz, 1H), 7.71 (t, J = 8.15 Hz, 1H), 7.50 (t, J = 8.1 Hz, 1H), 7.47 (d, J = 4.35 Hz, 1H), 4.96 (s, 1H), 4.31–4.27 (m, 2H), 4.22–4.18 (m, 2H), 3.43 (t, J = 4.85 Hz, 4H), 2.93 (s, 4H); ¹³C NMR (125 MHz, CDCl₃): δ_C 162.3, 157.6, 157.4, 157.2, 150.0, 148.2, 139.3, 130.2, 129.9, 127.9, 125.6, 124.9, 120.8, 87.3, 66.1 (2 carbons), 53.7, 48.9, 44.0 (2 carbons).

Determination of antitubercular activity

Mycobacterium tuberculosis H₃₇Rv strain (originated from the Institute of Hygiene and Epidemiology at Prague, 1976) was obtained on 7 August 2013 from the Federal Scientific Center for Expertise of Medical Products (RF Ministry of Health Care). The lyophilized strain was seeded on Löwenstein–Jensen growth medium. The 3-week culture was suspended in physiological solution containing glycerol (15%) was transferred into cryotubes and kept at −80 °C. Three weeks in advance of the experiment, the culture was brought to ambient temperature and re-seeded into Löwenstein–Jensen growth medium. Thus, the second generation of the original M. tuberculosis culture was used in present study.

The minimal inhibitory concentration (MIC) of the compounds was determined using the REMA (resazurin microtitre plate assay)15. A 3-week M. tuberculosis culture was transferred into a dry, sterile tube containing 8–9 3-mm glass beads. The tube was placed on a Vortex shaker for 30–40 s and then 5 mL Middlebrook 7H9 Broth (Becton Dickinson, Franklin Lakes, NJ, catalog No. 271310) was introduced. The turbidity of bacterial suspension was adjusted to 1.0 McFarland units (corresponding to approximately 3 × 10⁸ bacteria/mL) and diluted 20-fold with Middlebrook 7H9 Broth containing OADC enrichment (Becton Dickinson, catalog No. 245116). The same culture medium was used to prepare the 1:100 M. tuberculosis (1% population) control. The stock solutions of the compounds in DMSO (10 mg/mL) were diluted with Middlebrook 7H9 Broth (containing OADC enrichment) to a concentration of 800 µg/mL. Two hundred microliters of the solution thus obtained was introduced into the second row of a 96-well microtiter plate. This raw was used to perform twofold serial dilutions using and eight-channel pipette to obtain final concentrations of 1.6, 3.1, 6.2, 12.5, 25, 50, 100, 200 and 400 µg/mL concentrations of the compound in rows 2–9 (accounting for 100 µL of bacterial suspension introduced for testing). Row 10 – MTb suspension control, row 11 – same culture diluted 10-fold (the 1% control). Row 12 was used as a blank control for optical density reading (200 µL of the grown medium). The bacterial suspension (100 µL) was introduced into each well except rows 11 (1% population control) and 12 (blank culture medium), to the total volume of 200 µL in each well. The plates were incubated at 35 °C for 7 days. At that point, 0.01% aqueous solution (30 µL) of resazurin (Sigma, St Louis, MO, product No. R7017) was introduced in each well and the incubation continued for 18 h at 35 °C. The fluorescence reading was performed using FLUOstar Optima (BMG Labtech, Offenburg, Germany) plate reader operating at λ_ex = 520 nm and λ_em = 590 nm. The bacterial viability was determined by comparing the mean values (±SD at p = 0.05) of fluorescence in the control wells (row 12, blank and row 11, 1% control) and the wells containing the compound tested.

The MIC was determined as the compound concentration at which the fluorescence reached a plateau or was statistically (t criterion) similar to that of 1% control.

Determination of antimalarial activity and cytotoxicity

Compound activity against drug-sensitive 3D7 strain of Plasmodium falciparum was performed using a previously described 3-day SYBR green I growth and proliferation assay in a 96-well format16. Host cell cytotoxicity was determined in a 96-well format with a starting HepG2 cell density of 10 000 cells/well grown in Dulbecco’s modified Eagle’s medium (DMEM) (Life Technologies, Waltham, MA). The cells were incubated with serial dilutions of test compounds for 3 days, and the resulting cell viability was quantified using Promega CellTiterBlue.

Results and discussion

Commercially available quinoline-4-carboxaldehyde was converted on a 10 -g scale into the known 2-imidazoline 117. This pharmacophoric moiety was further elaborated into key haloazine building blocks 2a–2e by reacting 1 with 2,6-dibromopyridine, 2,4-dichloropyrimidine, 2,6-dichloropyrazine, 2,4-dichloro-5-trifluoropyrimidine and 4,5-dichloropyrimidine using the previously described Buchwald–Hartwig-type protocol under conventional heating1. These cores were further decorated with various primary and secondary amine appendages, as well as some known1 2-imidazolines, using the recently developed protocol for Pd-catalyzed imidazoline arylation under microwave irradiation (Scheme 1)18.

Scheme 1. Synthesis of the 2-(quinolin-4-yl)imidazoline library (3–39) employing various heteroarene linkers and periphery amines.

As expected, unsymmetrical dihalo azines (2,4-dichloropyrimidine and 2,4-dichloro-5-trifluoropyrimidine) regiospecifically reacted at the more reactive position 4 in the first step. 2-Imidazolines19, as well as amidines in general20^,21 have a high propensity to undergo transamination reactions with reactive amines under conventional heating. This complication (which is even further exacerbated for microwave-assisted processes22) would potentially create an obstacle to the present library synthesis. Notably, neither under conventional heating (first Buchwald–Hartwig step) nor under microwave irradiation (second Buchwald–Hartwig step) was the imidazoline linkage affected via the transamination reaction and the target compounds 3–39 were obtained in good to excellent yields (Table 1).

Table 1. Compounds 3–38 synthesized in this work.

When evaluated for antimalarial activity against chloroquine-sensitive P. falciparum 3D7 strain, compounds 3–39 were found to be completely devoid of any activity at concentrations as high as 10 µM, which did not justify their further scrutiny at higher concentrations (cf. IC₅₀ values for artemisinin and chloroquine which have been reported as 4.0 nM23 and 9.8 nM24, respectively). This result was somewhat surprising in light of the apparent similarity of the basic scaffold in 3–39 to that of some potent synthetic quinoline-based antimalarials reported recently25. In parallel with antimalarial testing, the compounds were evaluated for non-specific cytotoxicity against HepG2 cells and showed no appreciable cytotoxicity at concentrations as high as 100 µM. This result was encouraging in light of our intention to evaluate these compounds as antitubercular agents. Due to the known permeability issues with respect to bacterial cell wall, higher compound concentrations are often required to achieve appreciable efficacy in M. tuberculosis cultures. This hampers the development of potentially cytotoxic compounds as therapeutic agents.

Compounds 3–39 were tested for the ability to inhibit the bacterial growth of H₃₇Rv strain at 100 µg/mL concentrations. Of that number, two compounds – 16 and 18 – showed >50% inhibition of the bacterial culture growth. These compounds were further evaluated for the activity in 1.6–400 µg/mL range in order to determine the MIC. To our delight, these experiments confirmed that closely related compounds 16 and 18 possessed a specific antimycobacterial activity with MIC values of 200 and 50 µg/mL (MIC_MTb = 520 and 140 µM), respectively (see Supplemental material for growth inhibition curves and plate images). This level of potency is comparable to that of the recently reported quinoline-2-carboxamide antitubercular agents (MIC_MTb = 109–552 µM)26 and, combined with the non-cytotoxic profile of compounds 16 and 18, clearly defines a promising starting point for further potency optimization (Table 2).

Table 2. The antitubercular lead compounds identified in this work.

Compound	Structure	CC50 (HepG2), µM	MIC (MTb), µg/mL
16		>100	200
18		>100	50

Conclusion

The compounds described in this article were designed around a quinolin-4-ylinidazoline core that was expected to endow compounds with a broad-spectrum antimicrobial activity, in particular, antiplasmodial and antimycobacterial. Although the absence of antimalarial activity in these compounds is somewhat puzzling, the chemotype described herein clearly represents a novel starting point for the development of new-generation, potent antitubercular agents devoid of cytotoxic effects. In the context of today’s battle with drug-resistant forms of tuberculosis, this chemotype represents a timely addition to the portfolio of small-molecule candidates for further optimization.

Supplementary material available online

Copies of ¹H and ¹³C NMR spectra (compounds 1, 2a–e, 3–38) and graphic information related to antibacterial testing of the lead compounds (16 and 18) are available online.

Acknowledgements

The authors are indebted to Professor Vicky Avery of Griffith University for evaluating cytotoxicity and antimalarial activity of compounds 3–38. This research was supported by the Russian Scientific Fund (project grant 1450-00069).

Declaration of interest

The authors declare no conflict of interest. The authors are solely responsible for the content and results presented in this paper.