Synthesis, Structure, Chemical Stability, and In Vitro Cytotoxic Properties of Novel Quinoline-3-Carbaldehyde Hydrazones Bearing a 1,2,4-Triazole or Benzotriazole Moiety

Abstract

A small library of novel quinoline-3-carbaldehyde hydrazones (Series 1), acylhydrazones (Series 2), and arylsulfonylhydrazones (Series 3) bearing either a 1,2,4-triazole or benzotriazole ring at position 2 was prepared, characterized by elemental analyses and IR, NMR, and MS spectra, and then subjected to in vitro cytotoxicity studies on three human tumor cell lines: DAN-G, LCLC-103H, and SISO. In general, compounds 4, 6, and 8 substituted with a 1,2,4-triazole ring proved to be inactive, whereas the benzotriazole-containing quinolines 5, 7, and 9 elicited pronounced cancer cell growth inhibitory effects with IC₅₀ values in the range of 1.23–7.39 µM. The most potent 2-(1H-benzotriazol-1-yl)-3-[2-(pyridin-2-yl)hydrazonomethyl]quinoline (5e) showed a cytostatic effect on the cancer cell lines, whereas N′-[(2-(1H-benzotriazol-1-yl)quinolin-3-yl)methylene]-benzohydrazide (7a) and N′-[(2-1H-benzotriazol-1-yl)quinolin-3-yl)methylene]-naphthalene-2-sulfonohydrazide (9h) exhibited selective activity against the pancreas cancer DAN-G and cervical cancer SISO cell lines. Based on the determined IC₅₀ values, the compound 5e seems to be leading compound for further development as anticancer agent.

1. Introduction

The term “privileged structures” was coined by Evans and co-workers [1] and since then has proven to be an effective approach in drug discovery process [2,3]. Among the reported privileged structures, the quinoline scaffold constitutes one of the most explored heterocyclic systems due to its broad range of pharmacological activities [4,5,6,7]. Of special interest are the anticancer properties of quinoline derivatives [8,9,10]. Thus, the quinoline ring is utilized in clinically used anticancer drugs, such as camptothecin and its analogues, e.g., topotecan, which are known as topoisomerase inhibitors [9,10] or multitarget kinase inhibitors, including lenvatinib and cabozantib [9], whereas omipalisib and dactolisib are currently under clinical trials as agents targeting the phosphoinositide 3-kinase (PI3K) [9]. It is worth noting, however, that the antiproliferative effects of the quinoline-containing compounds may also result from cell cycle arrest [11,12,13,14,15], apoptosis [16,17], DNA intercalation [18,19], inhibition of angiogenesis [20,21,22], inhibition of proteasome [23,24], and disruption of tubulin polymerization [25,26].

In this context, worth noting are anticancer quinoline-based hydrazone derivatives that have been described in review articles [27,28]. Recently, quinoline-3-carbaldehyde hydrazones of type I (Figure 1) have come into the focus of our research program aimed at the discovery of novel anticancer agents. As described by Bingul et al. [29], compound I reduced the viability of SH-SY5Y neuroblastoma cancer cells and induced G₁ cell cycle arrest by upregulating the cell-cycle-related p27^Kip1 protein [29].

Figure 1. Known (I) and newly designed (Series 1–3) hydrazones of quinoline-3-carbaldehyde.

With the above information in mind, we decided to prepare a small library of new quinoline hydrazones (series 1) and N-acylhydrazones (series 2) bearing either 1,2,4-triazole or benzotriazole at position 2 of the quinoline ring system (Figure 1) to identify compounds with potential antitumor activity. Since N-sulfonylhydrazones have recently been studied as antiproliferative agents [30], the arylsulfonylhydrazone group was also incorporated into the target compounds (Figure 1, series 3).

2. Results and Discussion

2.1. Chemistry

Our research started with reactions of 2-chloroquinoline-3-carbaldehyde (1) [31,32] with 1,2,4-triazole and benzotriazole that afforded the starting 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) and 2-(1H-benzotriazol-1-yl)quinoline-3-carbaldehyde (3), respectively. As outlined in Scheme 1, the triazole-containing aldehyde 2 was obtained by heating the substrate 1 with 1,2,4-triazole in the presence of anhydrous potassium carbonate as a base. On the other hand, no base was required for preparation of the benzotriazole-containing aldehyde 3. Apparently, benzotriazole, a stronger NH acid than triazole (pKa = 8.2 versus 10.3) [33], protonates the quinoline nitrogen atom which leads to the formation of ion pair A. Then, deprotonated benzotriazole attacks position 2 of the 2-chloroquinolinium cation to give the desired product 3 (Scheme 1).

Scheme 1. Synthesis of 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) and 2-(1H-benzotriazol-1-yl)quinoline-3-carbaldehyde (3).

Due to annular tautomerism of the benzotriazole ring system, the N-heteroarylation process may take place at either the N1 or N2 nitrogen atom depending on the reaction conditions and stereochemical properties of a product [34,35]. In our case, both proton and carbon NMR spectra of the product run in DMSO-d₆ are consistent with the structure 3 (Section 3).

Structures of the benzotriazol-1-yl (3) and benzotriazol-2-yl (3A) isomers were subjected to quantum-chemical calculations by use of the density-functional B3LYP/6-31+G* method and the SM8 (H₂O) solvation model (Scheme 1) [36]. The computations indicated that the tautomer 3 should be more stable than 3A by 2.3 kcal/mol. Although the low energy difference suggests that both tautomers may exist in equilibrium, the N1-tautomer 3 with a higher dipole moment (µ = 6.2 Debye) than those found for the N2-tautomer 3A (µ = 2.3 Debye) should predominate over 3A in polar solvents. These results are consistent with the previous studies which indicated that in solution 1H-benzotriazole is the predominant species [37].

Compounds 2 and 3 were then subjected to reactions with hydrazine derivatives in ethanol at ambient temperature to afford the desired hydrazones 4a–e and 5a–e, respectively (Series 1, Scheme 2).

Scheme 2. Synthesis of hydrazones 4a–e and 5a–e (Series 1).

The structures of the compounds 4a–e and 5a–e were confirmed by elemental analyses as well as IR, NMR, and MS spectroscopic data (see Section 3).

Regarding anticancer activity of N-acylhydrazones, we turned our attention to the results obtained by Lima et al. [38]. It was found that the -C(O)-NH-N=C- acylhydrazone scaffold of N-aroylhydrazones designed as combretastatin A4 (CA-4) analogues is bioisterically equivalent to the ethylene -CH=CH- linker. Thus, N-acylhydrazones comparable to combretastatin A4 are capable of binding to the colchicine domain on β-tubulin and may prove useful in the development of new chemotherapeutic agents with better pharmacokinetic properties than the prototype CA-4.

As shown in Scheme 3, treatment of the aldehydes 2 and 3 with the appropriate aryl- and alkylhydrazides in dichloromethane under reflux in the presence of acetic acid gave rise to the formation of the corresponding N′-acylhydrazones 6a–h and 7a–h (Series 2).

Scheme 3. Synthesis of N′-acylhydrazones 6a–h and 7a–h (Series 2).

It is well-known that N-acyl- and N-aroylhydrazones may exist as geometric isomers E/Z with respect to the C=N double bond and cis/trans amide conformers due to rotation of the amide HN–C(O) single bond (Figure 2) [39,40]. Literature reports for N-acyl- and N-aroylhydrazones derived from aryl- and heteroaryl aldehydes indicate that these compounds may exist both in DMSO-d₆ solution [39,40,41,42] and solid phase [43,44,45,46] in the form of E-geometrical isomers. Other studies revealed the presence of the mixtures of two forms: cis and trans amide conformers of N-acyl- [39,40,45,46,47,48,49,50,51] and N-aroylhydrazones [52,53] in solution.

Figure 2. Probable E/Z isomers and cis/trans amide conformers of N-acyl- and N-aroylhydrazones.

Analysis of ¹H NMR spectra of the obtained N′-aroylhydrazones 6a–g and 7a–g run in DMSO-d₆ confirmed the existence of single isomers as no duplicate signals were observed. The only exception was the N′-cyclopentanecarbohydrazides 6h and 7h that in carbon and proton NMR spectra exhibited two set of resonance signals. Following the findings of Ferreira and co-workers [50], we assumed that the observed doubled signals refer to the presence of both the cis/E and trans/E amide conformers. For example, in the ¹³C NMR spectrum of 6h, the signals at 172.5 ppm and 177.8 ppm referred to the carbon atoms of the amide C=O group of the cis and trans conformers, while the ¹H NMR spectrum of 6h revealed the presence of two separate singlets at 11.67 ppm and 11.42 ppm attributable to the protons of the amide C(O)–NH group. Based on the relative intensities of these signals, we concluded that in DMSO-d₆ solution the N′-acylhydrazone 6h exists as a 1.3:1 mixture of equilibrating cis/E and trans/E isomers (Figure 3).

Figure 3. Possible isomers of N′-cyclopentanecarbohydrazide 6h.

Next, we synthesized the quinoline-3-carbaldehyde N′-sulfonylhydrazone derivatives 8a–h and 9a–h (Series 3, Scheme 4). The reactions of aldehydes 2 and 3 with arylsulfonylhydrazides proceeded smoothly in THF solution under reflux in the presence of a catalytic amount of acetic acid. The identity of the newly prepared compounds was confirmed by elemental analyses as well as the IR and NMR spectroscopic data presented in the experimental section (see Section 3).

Scheme 4. Synthesis of N′-sulfonylhydrazones 8a–h and 9a–h (Series 3).

2.2. UV-Vis Studies of Hydrazones 4–9 in Aqueous Buffer

The chemical stability of the hydrazones 4–9 in phosphate-buffered saline (PBS, pH 7.4) was investigated by means of UV-Vis spectroscopy. In general, all the compounds tested proved to be stable in the PBS solution as exemplified by the hydrazides 5a and 5d and the benzenesulfonohydrazide 9c, since no new spectra with the formation of isosbestic points were observed (Figure 4). The compound 5d (Figure 4A) showed no noticeable time-dependent changes, whereas a decrease in the intensity of the initial spectrum of the derivative 9c (Figure 4B) is likely due to its slow precipitation out of the PBS solution.

Figure 4. UV-Vis spectra of compounds: (A) 5d; (B) 9c; and (C) 5a in 0.1% DMSO/PBS solution (pH 7.4) at a concentration of 40 µM and 37 °C.

On the other hand, the time-dependent changes in the UV-Vis spectra of the hydrazones showed that precipitation of the derivatives 4e, 5a, 8f, and 9f is rather fast as exemplified by 2-(1H-benzotriazol-1-yl)-3-(hydrazonomethyl)quinoline (5a, Figure 4C). Therefore, those poorly soluble species were excluded from a panel of compounds subjected to biological studies.

2.3. In Vitro Antitumor Activity

The in vitro antitumor potential of the newly synthesized quinoline-3-carbaldehyde hydrazone derivatives 4–9 was evaluated on three human cancer cell lines: the pancreatic cell line DAN-G, the large cell lung cancer cell line LCLC-103H, and the cervical cancer cell line SISO using a crystal violet microtiter plate assay as previously described [54]. This assay measures the antiproliferative activity of compounds on actively dividing cells. Primary screening of the compounds 4–9 was performed to indicate whether a substance possesses enough activity to inhibit cell growth by 50% at the concentration of 10 µM, which is a concentration attainable in cancer cells (Table 1).

[ Table omitted. See PDF. ]

As revealed by the data in Table 1, the hydrazone derivatives 4, 6, and 8 bearing a triazole moiety were in general inactive with the exception of the N-sulfonylhydrazones 8b and 8g, which at a concentration of 10 µM exhibited weak to moderate cytostatic effects against all investigated cancer cell lines (percent of growth in the range of 31.6–48.6%). On the other hand, replacement of the triazole ring with a benzotriazole moiety results in enhancement of activity as indicated by a comparison of the growth inhibitory activities of triazole-containing compounds with their corresponding benzotriazole ring counterparts (6a, 6d, and 6f–g versus 7a, 7d, and 7f–g and 8c–e and 8g–h versus 9c–e and 9g–h). This observation may arise from the higher lipophilicity of the benzotriazole analogues, which may facilitate the penetration through the tumor cell membrane and improve the targeting efficiency. Furthermore, the combined presence of a large conjugated system as well as a three-nitrogen-containing structure make the benzotriazole nucleus more susceptible to binding with enzymes or receptors in biological systems via hydrogen bonds and π-π stacking interactions [55,56].

Thus, for secondary screening aimed at determining cytotoxic potency, we selected the benzotriazole-containing compounds 5d–e, 7a, 7d, and 7f–g and 9c–e and 9g–h, which demonstrated pronounced growth inhibitory effects against at least two cancer cell lines. The results of the secondary screening are presented in Table 2 as the average IC₅₀ values calculated from dose-response data.

[ Table omitted. See PDF. ]

In general, the investigated compounds exhibited moderate to high growth cell inhibitory effects (IC₅₀ in the range of 1.23–7.39 µM). The most potent was found to be the 2-(pyridin-2-yl)hydrazone 5e with IC₅₀ values ranging from 1.23 to 1.49 µM (Table 2). A reduction in cytotoxic potency by 2- to 6-fold was observed for other derivatives with acylhydrazone (compounds of type 7) or sulfonylhydrazone (compounds of type 9) moieties. However, replacing the hydrazone function with either an acylhydrazone or a sulfonylhydrazone scaffold still leads to active compounds. Hence, among the N′-acylhydrazones 7 and the N′-sulfonylhydrazones 9 the highest cytotoxic activity was found for compounds 7d and 9d containing a 4-chlorophenyl group (Table 2, R¹ = 4-ClC₆H₄).

It should be noted that the majority of the compounds tested showed no great selectivity toward any one specific cancer cell line with the exception of the N′-(benzoyl)hydrazone 7a and the N′-(naphtylsulfonyl)hydrazone 9h, which were selective against the pancreatic cell line DAN-G and the cervical cancer cell line SISO (IC₅₀ values of 4.19–6.59 µM) over the lung carcinoma cell line LCLC-103H (IC₅₀ >20 µM).

3. Materials and Methods

3.1. General Information

Melting points were measured on a Boetius apparatus and are uncorrected. IR spectra were taken in KBr pellets on a Nicolet 380 FTIR 1600 spectrometer. Elemental analyses were performed on a Vario El Cube CHNS analyzer and the results are within ±0.4%. NMR spectra were recorded on a Varian Gemini 200, a Varian Unity 500, or a Bruker Avance III HD apparatus. ¹H and ¹³C chemical shifts were measured relative to the residual solvent signal at 7.26 ppm and 77.0 (CDCl₃) or 2.50 ppm and 39.5 ppm (DMSO-d₆). Coupling constants are shown in hertz (Hz). The mass spectra were recorded on a Shimadzu LCMS-2010 EV spectrometer equipped with an electrospray source. ESI-MS spectra were registered in a positive- or negative-ion mode. Preparative thin layer chromatography was performed on silica gel 60 PF₂₅₄ containing gypsum (Merck KGaA, Darmstadt, FRG) with the aid of Chromatotron^® using the reported solvent systems. 2-Chloroquinoline-3-carbaldehyde (1) was obtained according to the published method [57]. UV-Vis spectra were recorded with an Analytik Jena Spekol 1200 (Analytik Jena AG, Jena, Germany) in a 1.0 cm cuvette maintained at 37 °C by a thermostatically controlled cuvette holder.

3.2. Chemistry

3.2.1. Procedure for the Preparation of 2-(1H-1,2,4-Triazol-1-yl)quinoline-3-carbaldehyde (2)

To a stirred solution of 2-chloroquinoline-3-carbaldehyde (1) (6.0 g, 31 mmol) in DMF (20 mL), potassium carbonate (8.28 g, 60 mmol) and 1,2,4-triazole (6.32 g, 93 mmol) were added and the mixture was heated at 40 °C for 6 h. Next, the mixture was poured into crushed ice and the precipitate was collected by vacuum filtration and purified by column chromatography (silica gel) eluting with CH₂Cl₂/AcOEt 20:1 v/v to afford the title compound 2. Yield 4.6 g (66%); m.p. 175–178 °C; IR (KBr) ν_max: 3131, 3113, 3062, 2896, 1698, 1617, 1505, 1444, 1345, 1277, 1166, 1048, 984, 954, 779, 752 cm⁻¹; ¹H NMR (200 MHz, CDCl₃) δ: 7.65–7.72 (m, 1H, Ar-H), 7.88–7.96 (m, 1H, Ar-H), 8.02–8.13 (m, 2H, Ar-H), 8.22 (s, 1H, triazole), 8.91 (s, 1H, 4-H, quinoline), 9.36 (s, 1H, triazole), 10.78 (s, 1H, CHO) ppm. Anal. calcd. for C₁₂H₈N₄O (224.22): C, 64.28; H, 3.60; N, 24.99. Found: C, 64.39; H, 3.51; N, 24.63.

3.2.2. Procedure for the Preparation of 2-(1H-Benzo[d][1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3)

To a stirred solution of 2-chloroquinoline-3-carbaldehyde (1) (6.0 g, 31 mmol) in ethanol (20 mL), benzotriazole (11.07 g, 93 mmol) in ethanol (10 mL) was added at 60 °C. After stirring at reflux for 7 h, the resulting mixture was cooled and the precipitate was collected by vacuum filtration to give the title compound 3. Yield 7.9 g (92%); m.p. 219–221 °C; IR (KBr) ν_max: 3056, 2922, 1690, 1618, 1583, 1498, 1446, 1286, 1161, 1070, 1024, 785, 745 cm⁻¹; ¹H NMR (200 MHz, CDCl₃) δ: 7.56 (t, J = 7.9 Hz, 1H, Ar-H), 7.69–7.74 (m, 2H, Ar-H), 7.94 (t, J = 8.2 Hz, 1H, Ar-H), 8.08 (d, J = 8.1 Hz, 1H, Ar-H), 8.18–8.23 (m, 2H, Ar-H), 8.58 (d, J = 8.3 Hz, 1H, Ar-H), 9.00 (s, 1H, 4-H, quinoline), 10.59 (s, 1H, CHO) ppm; ¹³C NMR (200 MHz, CDCl₃) δ: 114.6, 120.6, 124.1, 126.1, 127.0, 128.6, 129.3 (two overlapping signals), 129.8, 130.1, 133.8, 135.9, 141.8, 146.9, 148.5, 189.2 ppm; MS (ESI) m/z: 275 [M + H]⁺. Anal. calcd. for C₁₆H₁₀N₄O (274.28): C, 70.06; H, 3.67; N, 20.43. Found: C, 70.18; H, 3.54; N, 20.52.

3.2.3. General Procedure for the Preparation of Hydrazones 4a–e and 5a–e

To a suspension of 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) (0.224 g, 1 mmol) or 2-(1H-benzo[d][1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3) (0.274 g, 1 mmol) in ethanol (10 mL), the appropriate hydrazine (1 mmol) was added. After stirring for 24 h at ambient temperature (TLC control) the precipitated solid was collected by vacuum filtration, dried, and recrystallized or subjected to preparative thin layer chromatography. In this manner, the following compounds were obtained.

3-(Hydrazonomethyl)-2-(1H-1,2,4-triazol-1-yl)quinoline (4a). Starting from 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) (0.224 g, 1 mmol) and 67% hydrazine hydrate (1 mmol), the title compound 4a was obtained after crystallization from ethanol. Yield 53%; m.p. 197–199 °C; IR (KBr) ν_max: 3358, 3207, 3102, 1617, 1597, 1570, 1493, 1442, 1416, 1324, 1278, 1145, 1054, 984, 952, 785, 763, 725 cm⁻¹; ¹H NMR (500 MHz, DMSO-d₆) δ: 7.39 (s, 2H, NH₂), 7.66 (t, J = 7.8 Hz, 1H, Ar-H), 7.79 (t, J = 7.3 Hz, 1H, Ar-H), 7.84 (s, 1H, N=CH), 7.98 (d, J = 8.3 Hz, 1H, Ar-H), 8.13 (d, J = 7.8 Hz, 1H, Ar-H), 8.36 (s, 1H, triazole), 8.88 (s, 1H, 4-H, quinoline), 9.23 (s, 1H, triazole) ppm; ¹³C NMR (50 MHz, DMSO-d₆) δ: 125.4, 128.6, 128.7, 128.9 (two overlapping signals), 131.2, 131.6, 134.6, 145.4, 145.9, 146.0, 153.2; MS (ESI) m/z: 239 [M + H]⁺. Anal. calcd. for C₁₂H₁₀N₆ (238.25): C, 60.50; H, 4.23; N, 35.27. Found: C, 60.32; H, 4.36; N, 35.32.

3-[(2,2-Dimethylhydrazono)methyl]-2-(1H-1,2,4-triazol-1-yl)quinoline (4b). Starting from 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) (0.224 g, 1 mmol) and dimethylhydrazine (1 mmol), the title compound 4b was obtained after preparative thin layer chromatography (eluent: CH₂Cl₂/AcOEt 10:1 v/v). Yield 59%; m.p. 138–141 °C; IR (KBr) ν_max: 3129, 3048, 2925, 1618, 1551, 1501, 1493, 1438, 1402, 1279, 1142, 1070, 1045, 987, 915, 757 cm⁻¹; ¹H NMR (200 MHz, DMSO-d₆) δ: 2.98 (s, 6H, 2xCH₃), 7.44 (s, 1H, N=CH), 7.67 (t, J = 7.9 Hz, 1H, Ar-H), 7.81 (t, J = 8.3 Hz, 1H, Ar-H), 7.99 (d, J = 8.3 Hz, 1H, Ar-H), 8.15 (d, J = 7.9 Hz, 1H, Ar-H), 8.37 (s, 1H, triazole), 8.86 (s, 1H, 4-H, quinoline), 9.27 (s, 1H, triazole) ppm; ¹³C NMR (50 MHz, DMSO-d₆) δ: 42.7 (two overlapping signals), 125.1 (two overlapping signals), 128.3, 128.5 (three overlapping signals), 130.7, 134.0, 144.9, 145.7 (two overlapping signals), 152.8 ppm; MS (ESI) m/z: 267 [M + H]⁺. Anal. calcd. for C₁₄H₁₄N₆ (266.30): C, 63.14; H, 5.30; N, 31.56. Found: C, 63.32; H, 5.42; N, 31.26.

3-[(2-Phenylhydrazono)methyl]-2-(1H-1,2,4-triazol-1-yl)quinoline (4c). Starting from 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) (0.224 g, 1 mmol) and phenylhydrazine (1 mmol), the title compound 4c was obtained after crystallization from toluene. Yield 32%; m.p. 182–185 °C; IR (KBr) ν_max: 3236, 3132, 3052, 1603, 1593, 1557, 1490, 1436, 1271, 1207, 1123, 985, 959, 924, 748 cm⁻¹; ¹H NMR (500 MHz, DMSO-d₆) δ: 6.80 (t, J = 7.3 Hz, 1H, Ar-H), 7.15 (d, J = 8.3 Hz, 2H, Ar-H), 7.25 (t, J = 7.8 Hz, 2H, Ar-H), 7.70 (t, J = 7.7 Hz, 1H, Ar-H), 7.82 (t, J = 7.3 Hz, 1H, Ar-H), 8.00 (d, J = 8.3 Hz, 1H, Ar-H), 8.11 (s, 1H, N=CH), 8.22 (d, J = 8.3 Hz, 1H, Ar-H), 8.42 (s, 1H, triazole), 9.12 (s, 1H, 4-H, quinoline), 9.29 (s, 1H, triazole), 10.82 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 113.0 (two overlapping signals), 120.2, 124.6, 128.6, 128.7, 128.9, 129.1, 129.9 (two overlapping signals), 131.2, 131.5, 135.3, 145.4, 145.6, 146.0, 146.1, 153.3 ppm; MS (ESI) m/z: 313 [M − H]⁻. Anal. calcd. for C₁₈H₁₄N₆ (314.34): C, 68.78; H, 4.49; N, 26.74. Found: C, 68.59; H, 4.38; N, 27.03.

2-{2-[(2-(1H-1,2,4-Triazol-1-yl)quinolin-3-yl)methylene]hydrazinyl}ethanol (4d). Starting from 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) (0.224 g, 1 mmol) and 2-hydrazinylethanol (1 mmol), the title compound 4d was obtained after crystallization from ethanol. Yield 51%; m.p. 173–175 °C; IR (KBr) ν_max: 3345, 2946, 1618, 1599, 1580, 1492, 1449, 1428, 1392, 1287, 1178, 1056, 1023, 910, 786 cm⁻¹; ¹H NMR (500 MHz, DMSO-d₆) δ: 3.21–3.24 (m, 2H, CH₂), 3.56–3.57 (m, 2H, CH₂), 4.67 (s, 1H, OH), 7.64 (t, J = 7.3 Hz, 1H, Ar-H), 7.72 (s, 1H, N=CH), 7.76 (t, J = 7.8 Hz, 1H, Ar-H), 7.90 (t, 1H, NH), 7.96 (d, J = 8.3 Hz, 1H, Ar-H), 8.12 (d, J = 7.8 Hz, 1H, Ar-H), 8.35 (s, 1H, triazole), 8.84 (s, 1H, 4-H, quinoline), 9.23 (s, 1H, triazole) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 51.6, 60.0, 125.6, 127.4, 128.6, 128.7, 128.8, 128.9, 130.9, 134.1, 145.2, 145.9 (two overlapping signals), 153.1 ppm; MS (ESI) m/z: 281 [M − H]⁻. Anal. calcd. for C₁₄H₁₄N₆O (282.30): C, 59.56; H, 5.00; N, 29.77. Found: C, 59.38; H, 5.17; N, 29.65.

3-[(2-(Pyridin-2-yl)hydrazono)methyl]-2-(1H-1,2,4-triazol-1-yl)quinoline (4e). Starting from 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) (0.224 g, 1 mmol) and 2-hydrazinylpyridine (1 mmol), the title compound 4e was obtained after crystallization from a DMF–methanol mixture. Yield 20%; m.p. 248–252 °C; IR (KBr) ν_max: 3186, 3118, 3069, 3024, 1595, 1560, 1540, 1490, 1458, 1442, 1306, 1278, 1129, 1123, 991, 753 cm⁻¹; ¹H NMR (500 MHz, DMSO-d₆) δ: 6.79 (t, J = 5.9 Hz, 1H, Ar-H), 7.32 (d, J = 8.3 Hz, 1H, Ar-H), 7.64–7.71 (m, 2H, Ar-H), 7.83 (t, J = 7.3 Hz, 1H, Ar-H), 8.01 (d, J = 8.3 Hz, 1H, Ar-H), 8.13 (d, J = 4.4 Hz, 1H, Ar-H), 8.18 (d, J = 8.3 Hz, 1H, Ar-H), 8.33 (s, 2H, N=CH and CH triazole), 9.07 (s, 1H, 4-H, quinoline), 9.22 (s, 1H, triazole), 10.98 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 107.6, 116.2, 124.4, 128.5, 128.6, 129.0, 129.1, 131.6, 134.5, 136.4, 138.5, 145.7, 146.0, 146.4, 148.5, 153.2, 157.6 ppm. Anal. calcd. for C₁₇H₁₃N₇ (315.33): C, 64.75; H, 4.16; N, 31.09. Found: C, 64.59; H, 3.98; N, 31.43.

2-(1H-Benzo[d][1,2,3]triazol-1-yl)-3-(hydrazonomethyl)quinoline (5a). Starting from 2-(1H-benzo[d][1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3) (0.274 g, 1 mmol) and 65% hydrazine hydrate (1 mmol), the title compound 5a was obtained after crystallization from a DMF–methanol mixture. Yield 75%; m.p. 239–241 °C; IR (KBr) ν_max: 3416, 3282, 3180, 3060, 1617, 1591, 1493, 1461, 1400, 1286, 1217, 1067, 1022, 1013, 928, 760, 737 cm⁻¹; ¹H NMR (200 MHz, DMSO-d₆) δ: 7.39 (s, 2H, NH₂), 7.52–7.64 (m, 2H, Ar-H), 7.66–7.91 (m, 3H, Ar-H and N=CH), 8.05 (t, 2H, Ar-H), 8.25 (t, 2H, Ar-H), 9.03 (s, 1H, 4-H, quinoline) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 113.1, 120.1, 125.7, 126.2, 128.6, 128.8, 128.9, 129.0, 129.7, 131.3, 132.5, 133.8, 135.5, 145.8, 145.9, 146.2 ppm; MS (ESI) m/z: 289 [M + H]⁺. Anal. calcd. for C₁₆H₁₂N₆ (288.31): C, 66.66; H, 4.20; N, 29.15. Found: C, 66.21; H, 4.29; N, 29.50.

2-(1H-Benzo[d][1,2,3]triazol-1-yl)-3-[(2,2-dimethylhydrazono)methyl]quinoline (5b). Starting from 2-(1H[d]-benzo[1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3) (0.274 g, 1 mmol) and dimethylhydrazine (1 mmol), the title compound 5b was obtained after preparative thin layer chromatography (eluent: CH₂Cl₂/AcOEt 10:1 v/v). Yield 80%; m.p. 165–167 °C; IR (KBr) ν_max: 3045, 2914, 2859, 1542, 1490, 1421, 1283, 1062, 1022, 739 cm⁻¹; ¹H NMR (200 MHz, DMSO-d₆) δ: 2.91 (s, 6H, 2xCH₃), 7.31 (s, 1H, N=CH), 7.53 (t, J =7.9 Hz, 1H, Ar-H), 7.70 (t, J = 7.9 Hz, 2H, Ar-H), 7.82 (t, J = 8.3 Hz, 1H, Ar-H), 8.04 (d, J = 8.3 Hz, 2H, Ar-H), 8.17–8.27 (m, 2H, Ar-H), 8.94 (s, 1H, 4-H, quinoline) ppm; ¹³C NMR (50 MHz, DMSO-d₆) δ: 42.7 (two overlapping signals), 113.2, 119.9, 125.1, 125.4, 126.0, 128.3, 128.5, 128.6, 128.8, 129.3, 130.8, 133.3, 134.6, 145.2, 145.5, 145.9 ppm. Anal. calcd. for C₁₈H₁₆N₆ (316.36): C, 68.56; H, 5.21; N, 26.23. Found: C, 68.47; H, 5.21; N, 26.32.

2-(1H-Benzo[d][1,2,3]triazol-1-yl)-3-[(2-phenylhydrazono)methyl]quinoline (5c). Starting from 2-(1H-benzo[d][1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3) (0.274 g, 1 mmol) and phenylhydrazine (1 mmol), the title compound 5c was obtained after crystallization from ethanol. Yield 51%; m.p. 106–110 °C; IR (KBr) ν_max: 3253, 3055, 1600, 1551, 1491, 1425, 1286, 1262, 1131, 1090, 1021, 1010, 929, 783, 749 cm⁻¹; ¹H NMR (500 MHz, DMSO-d₆) δ: 6.78 (t, J = 7.3 Hz, 1H, Ar-H), 7.05 (d, J = 7.8 Hz, 2H, Ar-H), 7.22 (t, J = 7.8 Hz, 2H, Ar-H), 7.56 (t, J = 7.3 Hz, 1H, Ar-H), 7.69–7.76 (m, 2H, Ar-H), 7.85 (t, J = 7.8 Hz, 1H, Ar-H), 8.02 (s, 1H, N=CH), 8.05–8.08 (m, 2H, Ar-H), 8.27 (d, J = 8.8 Hz, 2H, Ar-H), 9.21 (s, 1H, 4-H, quinoline), 10.76 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 113.0 (two overlapping signals), 113.5, 120.1, 120.2, 125.5, 125.9, 128.6, 128.9, 129.1 (two overlapping signals), 129.8 (three overlapping signals), 131.3, 131.6, 133.7, 135.4, 145.3, 145.8, 145.9, 146.2 ppm; MS (ESI) m/z: 363 [M − H]⁻. Anal. calcd. for C₂₂H₁₆N₆ (364.40): C, 72.51; H, 4.43; N, 23.06. Found: C, 72.27; H, 4.58; N, 23.15.

2-{2-[(2-(1H-Benzo[d][1,2,3]triazol-1-yl)quinolin-3-yl)methylene]hydrazinyl}ethanol (5d). Starting from 2-(1H-benzo[d][1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3) (0.274 g, 1 mmol) and hydrazinylethanol (1 mmol), the title compound 5d was obtained after crystallization from ethanol. Yield 61%; m.p. 177–179 °C; IR (KBr) ν_max: 3344, 3139, 2934, 2877, 1596, 1571, 1509, 1493, 1441, 1328, 1284, 1211, 1141, 1071, 989, 753 cm⁻¹; ¹H NMR (200 MHz, DMSO-d₆) δ: 3.15–3.19 (m, 2H, CH₂), 3.50–3.53 (m, 2H, CH₂), 4.64 (t, J = 5.3 Hz, 1H, OH), 7.55 (t, J = 7.8 Hz, 1H, Ar-H), 7.63 (s, 1H, N=CH), 7.66–7.70 (m, 2H, Ar-H), 7.79 (t, J = 7.3 Hz, 1H, Ar-H), 7.87 (t, J = 4.8 Hz, 1H, NH), 8.00 (d, J = 9.3 Hz, 2H, Ar-H), 8.18 (d, J = 7.8 Hz, 1H, Ar-H), 8.23 (d, J = 8.3 Hz, 1H, Ar-H), 8.95 (s, 1H, 4-H, quinoline) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 51.6, 60.0, 113.3, 120.1, 125.8. 126.4, 127.4, 128.6, 128.7, 128.9, 129.0, 129.7, 131.0, 133.6, 134.6, 145.5, 145.7, 146.0 ppm; MS (ESI) m/z: 331 [M − H]⁻. Anal. calcd. for C₁₈H₁₆N₆O (332.36): C, 65.05; H, 4.85; N, 25.29. Found: C, 64.89; H, 5.06; N, 25.11.

2-(1H-Benzo[d][1,2,3]triazol-1-yl)-3-[2-(pyridin-2-yl)hydrazonomethyl]quinoline (5e). Starting from 2-(1H-benzo[d][1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3) (0.274 g, 1 mmol) and 2-hydrazinylpyridine (1 mmol), the title compound 5e was obtained after crystallization from a DMF/methanol mixture. Yield 54%; m.p. 266–268 °C; IR (KBr) ν_max: 3199, 3159, 3024, 2926, 2862, 1601, 1558, 1492, 1444, 1308, 1290, 1133, 1058, 1021, 756, 738 cm⁻¹; ¹H NMR (200 MHz, DMSO-d₆) δ: 6.82 (t, J = 6.2 Hz, 1H, Ar-H), 7.23 (d, J = 8.7 Hz, 1H, Ar-H), 7.57–7.82 (m, 4H, Ar-H), 7.91 (t, J = 6.6 Hz, 1H, Ar-H), 8.09–8.13 (m, 3H, Ar-H), 8.24 (s, 1H, N=CH), 8.30 (d, J = 8.3 Hz, 2H, Ar-H), 9.26 (s, 1H, 4-H, quinoline), 11.18 (s, 1H, NH) ppm; ¹³C NMR (50 MHz, DMSO-d₆) δ: 107.1, 113.3, 116.0, 119.9, 124.8, 125.6, 128.2, 128.7, 128.9, 129.0, 129.5, 131.6, 133.3, 133.9, 136.5, 138.3, 145.6, 145.9, 146.2, 148.2, 157.0 ppm; MS (ESI) m/z: 364 [M − H]⁻. Anal. calcd. for C₂₁H₁₅N₇ (365.39): C, 69.03; H, 4.14; N, 26.83. Found: C, 68.94; H, 3.96; N, 27.10.

3.2.4. General Procedure for the Preparation of N′-Acylhydrazones 6a–h and 7a–h

A mixture of 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) (0.224 g, 1 mmol) or 2-(1H-benzo[d][1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3) (0.274 g, 1 mmol) and appropriate hydrazide (1 mmol) in the presence of a catalytic amount of acetic acid in dichloromethane (5 mL) was heated under reflux for 5–8 h. The progress of the reaction was controlled by TLC. The mixture was then evaporated under reduced pressure to dryness and the crude product thus obtained was purified as described below. In this manner, the following compounds were obtained.

N′-[(2-(1H-1,2,4-Triazol-1-yl)quinolin-3-yl)methylene]benzohydrazide (6a). Starting from 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) (0.224 g, 1 mmol) and benzohydrazide (1 mmol), the title compound 6a was obtained after washing with hot ethanol. Yield 70%; m.p. 254–255 °C; IR (KBr) ν_max: 3219, 3131, 3038, 1651, 1602, 1546, 1491, 1442, 1280, 1132, 983, 759 cm⁻¹; ¹H NMR (500 MHz, DMSO-d₆) δ: 7.53 (t, J = 7.8 Hz, 2H, Ar-H), 7.60 (t, J = 7.3 Hz, 1H, Ar-H), 7.75 (t, J = 7.8 Hz, 1H, Ar-H), 7.90–7.93 (m, 3H, Ar-H), 8.06 (d, J = 8.3 Hz, 1H, Ar-H), 8.30 (d, J = 8.3 Hz, 1H, Ar-H), 8.43 (s, 1H, N=CH), 8.76 (s, 1H, triazole), 9.16 (s, 1H, triazole), 9.36 (s, 1H, 4-H, quinoline), 12.19 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 122.7, 128.1, 128.4 (three overlapping signals), 128.9, 129.0, 129.3 (two overlapping signals), 129.6, 132.8, 133.5, 138.0, 143.9, 145.9, 146.5, 146.7, 153.5, 164.3 ppm; MS (ESI) m/z: 341 [M − H]⁻. Anal. calcd. for C₁₉H₁₄N₆O (342.35): C, 66.66; H, 4.12; N, 24.55. Found: C, 66.78; H, 4.01; N, 24.38.

N′-[(2-(1H-1,2,4-Triazol-1-yl)quinolin-3-yl)methylene]-4-methylbenzohydrazide (6b). Starting from 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) (0.224 g, 1 mmol) and 4-methylbenzohydrazide (1 mmol), the title compound 6b was obtained after washing with hot ethanol. Yield 68%; m.p. 250–254 °C; IR (KBr) ν_max: 3243, 3081, 1663, 1559, 1507, 1492, 1444, 1275, 1209, 1118, 982, 958, 762 cm⁻¹; ¹H NMR (500 MHz, DMSO-d₆) δ: 2.37 (s, 3H, CH₃), 7.33 (d, J = 8.3 Hz, 2H, Ar-H), 7.74 (t, J = 7.3 Hz, 1H, Ar-H), 7.84 (d, J = 7.8 Hz, 2H, Ar-H), 7.91 (t, J = 7.3 Hz, 1H, Ar-H), 8.06 (d, J = 8.8 Hz, 1H, Ar-H), 8.30 (d, J = 8.3 Hz, 1H, Ar-H), 8.43 (s, 1H, N=CH), 8.76 (s, 1H, triazole), 9.14 (s, 1H, triazole), 9.36 (s, 1H, 4-H, quinoline), 12.12 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 21.7, 123.1, 128.2, 128.6, 128.8, 128.9 (two overlapping signals), 129.5, 129.6 (two overlapping signals), 129.9, 131.2, 132.5, 137.9, 142.5, 145.8, 146.7, 146.8, 153.5, 164.5 ppm; MS (ESI) m/z: 355 [M − H]⁻. Anal. calcd. for C₂₀H₁₆N₆O (356.38): C, 67.40; H, 4.53; N, 23.58. Found: C, 67.38; H, 4.72; N, 23.15.

N′-[(2-(1H-1,2,4-Triazol-1-yl)quinolin-3-yl)methylene]-4-methoxybenzohydrazide (6c). Starting from 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) (0.224 g, 1 mmol) and 4-methoxybenzohydrazide (1 mmol), the title compound 6c was obtained after crystallization from a DMF–methanol mixture. Yield 29%; m.p. 262–263 °C; IR (KBr) ν_max: 3216, 3132, 3029, 2958, 2835, 1646, 1602, 1508, 1440, 1254, 1174, 987, 863, 762 cm⁻¹; ¹H NMR (200 MHz, DMSO-d₆) δ: 3.84 (s, 3H, OCH₃), 7.07 (d, J = 8.7 Hz, 2H, Ar-H), 7.75 (t, J = 7.8 Hz, 1H, Ar-H), 7.89–7.96 (m, 3H, Ar-H), 8.08 (d, J = 8.3 Hz, 1H, Ar-H), 8.32 (d, J = 7.9 Hz, 1H, Ar-H), 8.44 (s, 1H, N=CH), 8.74 (s, 1H, triazole), 9.15 (s, 1H, triazole), 9.37 (s, 1H, 4-H, quinoline), 12.06 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 56.1, 114.5 (two overlapping signals), 122.9, 125.5, 128.1, 128.9, 129.0, 129.5, 130.4, 132.7, 137.9, 143.2, 145.9 (two overlapping signals), 146.5, 146.7, 153.5, 162.9, 163.7 ppm; MS (ESI) m/z: 371 [M − H]⁻. Anal. calcd. for C₂₀H₁₆N₆O₂ (372.38): C, 64.51; H, 4.33; N, 22.57. Found: C, 64.41; H, 4.21; N, 22.83.

N′-[(2-(1H-1,2,4-Triazol-1-yl)quinolin-3-yl)methylene]-4-chlorobenzohydrazide (6d). Starting from 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) (0.224 g, 1 mmol) and 4-chlorobenzohydrazide (1 mmol), the title compound 6d was obtained after washing with hot ethanol. Yield 21%; m.p. 272–274 °C; IR (KBr) ν_max: 3221, 3087, 1672, 1597, 1560, 1490, 1445, 1273, 1210, 1115, 981, 958, 752 cm⁻¹; ¹H NMR (200 MHz, DMSO-d₆) δ: 7.60–7.66 (m, 2H, Ar-H), 7.76 (t, J = 7.9 Hz, 1H, Ar-H), 7.89–7.98 (m, 3H, Ar-H), 8.06–8.10 (m, 1H, Ar-H), 8.32 (d, J = 7.9 Hz, 1H, Ar-H), 8.44 (s, 1H, N=CH), 8.78 (s, 1H, triazole), 9.16 (s, 1H, triazole), 9.39 (s, 1H, 4-H, quinoline), 12.24 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 122.6, 128.1, 128.9, 129.0, 129.3 (two overlapping signals), 129.6, 130.4 (two overlapping signals), 132.3, 132.8, 137.6, 138.1, 144.3, 145.9, 146.6, 146.7, 153.5, 163.3 ppm; MS (ESI) m/z: 375 [M − H]⁻. Anal. calcd. for C₁₉H₁₃ClN₆O (376.80): C, 60.56; H, 3.48; N, 22.30. Found: C, 60.42; H, 3.41; N, 22.17.

N′-[(2-(1H-1,2,4-triazol-1-yl)quinolin-3-yl)methylene]-4-fluorobenzohydrazide (6e). Starting from 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) (0.224 g, 1 mmol) and 4-fluorobenzohydrazide (1 mmol), the title compound 6e was obtained after preparative thin layer chromatography (eluent: CH₂Cl₂/AcOEt 10:1 v/v). Yield 42%; m.p. 261–263 °C; IR (KBr) ν_max: 3217, 3132, 3038, 1652, 1601, 1503, 1493, 1346, 1282, 1223, 1158, 1119, 983, 852, 759 cm⁻¹; ¹H NMR (200 MHz, DMSO-d₆) δ: 7.38 (t, J = 8.7 Hz, 2H, Ar-H), 7.75 (t, J = 7.9 Hz, 1H, Ar-H), 7.88–8.09 (m, 4H, Ar-H), 8.31 (d, J = 7.9 Hz, 1H, Ar-H), 8.44 (s, 1H, N=CH), 8.78 (s, 1H, triazole), 9.15 (s, 1H, triazole), 9.37 (s, 1H, 4-H, quinoline), 12.21 (s, 1H, NH) ppm; ¹³C NMR (50 MHz, DMSO-d₆) δ: 115.7, 116.1, 122.5, 127.9, 128.6 (two overlapping signals), 129.4, 130.0, 130.8, 131.0, 132.4, 137.6, 143.5, 145.7, 146.3, 146.5, 153.3, 162.6, 167.1 ppm; MS (ESI) m/z: 359 [M − H]⁻. Anal. calcd. for C₁₉H₁₃FN₆O (360.34): C, 63.33; H, 3.64; N, 23.32. Found: C, 63.52; H, 3.51; N, 23.21.

N′-[(2-(1H-1,2,4-Triazol-1-yl)quinolin-3-yl)methylene]furan-2-carbohydrazide (6f). Starting from 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) (0.224 g, 1 mmol) and furan-2-carbohydrazide (1 mmol), the title compound 6f was obtained after washing with hot ethanol. Yield 31%; m.p. 248–250 °C; IR (KBr) ν_max: 3176, 3105, 3036, 1659, 1643, 1599, 1507, 1491, 1444, 1357, 1290, 1280, 1190, 1122, 1086, 1023, 984, 859, 783, 755 cm⁻¹; ¹H NMR (200 MHz, DMSO-d₆) δ: 6.71–6.74 (m, 1H, Ar-H), 7.21–7.45 (m, 1H, Ar-H), 7.75 (t, J = 7.9 Hz, 1H, Ar-H), 7.89–7.98 (m, 2H, Ar-H and N=CH), 8.07 (d, J = 8.3 Hz, 1H, Ar-H), 8.31 (d, J = 8.3 Hz, 1H, Ar-H), 8.45 (s, 1H, triazole), 8.76 (br. s, 1H, Ar-H), 9.13 (s, 1H, 4-H, quinoline), 9.38 (s, 1H, triazole), 12.22 (s, 1H, NH) ppm; ¹³C NMR (50 MHz, DMSO-d₆) δ: 112.6, 115.8, 122.5, 127.9, 128.6 (two overlapping signals), 129.4, 132.4, 137.6, 138.8, 143.5, 145.6, 146.3, 146.5, 146.6, 153.3, 154.3 ppm; MS (ESI) m/z: 355 [M + Na]⁺. Anal. calcd. for C₁₇H₁₂N₆O₂ (332.32): C, 61.44; H, 3.64; N, 25.29. Found: C, 61.58; H, 3.51; N, 25.34.

N′-[(2-(1H-1,2,4-Triazol-1-yl)quinolin-3-yl)methylene]thiophene-2-carbohydrazide (6g). Starting from 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) (0.224 g, 1 mmol) and thiophene-2-carbohydrazide (1 mmol), the title compound 6g was obtained without further purification. Yield 36%; m.p. 265–267 °C; IR (KBr) ν_max: 3164, 3096, 2985, 1633, 1601, 1511, 1499, 1374, 1313, 1181, 1118, 1036, 982, 757, 740 cm⁻¹; ¹H NMR (200 MHz, DMSO-d₆) δ: 7.25 (t, J = 4.2 Hz, 1H, Ar-H), 7.76 (t, J = 7.1 Hz, 1H, Ar-H), 7.89–8.10 (m, 4H, Ar-H and N=CH), 8.30 (d, J = 7.9 Hz, 1H, Ar-H), 8.46 (s, 1H, triazole), 8.76 (br. s, 1H, Ar-H), 9.14 (s, 1H, 4-H, quinoline), 9.39 (s, 1H, triazole), 12.21 (br. s, 1H, NH) ppm; ¹³C NMR (50 MHz, DMSO-d₆) δ: 122.4, 126.5, 127.8, 128.6 (two overlapping signals), 129.4, 129.9, 132.4, 135.7, 137.7, 140.5, 143.0, 145.7, 146.2, 146.5, 153.3, 158.0 ppm, MS (ESI) m/z: 347 [M − H]⁻. Anal. calcd. for C₁₇H₁₂N₆OS (348.38): C, 58.61; H, 3.47; N, 24.12. Found: C, 58.49; H, 3.35; N, 24.23.

N′-[(2-(1H-1,2,4-Triazol-1-yl)quinolin-3-yl)methylene]cyclopentanecarbohydrazide (6h). Starting from 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) (0.224 g, 1 mmol) and cyclopentanecarbohydrazide (1 mmol), the title compound 6h was obtained as a mixture of cis/trans conformers after preparative thin layer chromatography (eluent: CH₂Cl₂:AcOEt 10:1 v/v). Yield 42%; m.p. 239–241 °C; IR (KBr) ν_max: 3196, 3103, 2959, 2866, 1661, 1599, 1491, 1442, 1395, 1257, 1140, 1124, 982, 950, 760 cm⁻¹; ¹H NMR (200 MHz, DMSO-d₆) δ: 1.66–1.98 (m, 16H, 8xCH₂), 2.62–2.69 and 3.53–4.21 (m, 1H, CH), 7.73 (t, J = 7.5 Hz, 2H, 2xCH), 7.90 (t, J = 8.3 Hz, 2H, 2xCH), 8.03–8.07 (m, 2H, 2xCH), 8.24–8.31 (m, 3H, 3xCH), 8.40 and 8.44 (s, 1H, triazole), 8.51 (s, 1H, N=CH), 9.02 and 9.06 (s, 1H, 4-H, quinoline), 9.32 and 9.36 (s, 1H, triazole), 11.42 and 11.67 (s, 1H, NH) ppm; ¹³C NMR (50 MHz, DMSO-d₆) δ: 26.2, 26.3, 29.8, 30.4, 43.5, 127.8, 128.5, 129.2, 132.3, 137.3, 137.4, 138.4, 141.4, 145.5, 145.6, 153.1, 153.3, 172.5 and 177.8 ppm; MS (ESI) m/z: 333 [M − H]⁻. Anal. calcd. for C₁₈H₁₈N₆O (334.38): C, 64.66; H, 5.43; N, 25.13. Found: C, 64.72; H, 5.51; N, 25.17.

N′-[(2-(1H-Benzo[d][1,2,3]triazol-1-yl)quinolin-3-yl)methylene]benzohydrazide (7a). Starting from 2-(1H-benzo[d][1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3) (0.274 g, 1 mmol) and benzohydrazide (1 mmol), the title compound 7a was obtained after crystallization from methanol. Yield 77%; m.p. 236–239 °C; IR (KBr) ν_max: 3234, 3047, 1654, 1545, 1491, 1378, 1283, 1068, 1017, 784, 748, 739 cm⁻¹; ¹H NMR (500 MHz, DMSO-d₆) δ: 7.51 (t, J = 7.8 Hz, 2H, Ar-H), 7.57–7.61 (m, 2H, Ar-H), 7.73–7.80 (m, 2H, Ar-H), 7.90–7.95 (m, 3H, Ar-H), 8.12 (d, J = 8.3 Hz, 1H, Ar-H), 8.23 (d, J = 8.3 Hz, 1H, Ar-H), 8.27 (d, J = 8.3 Hz, 1H, Ar-H), 8.36 (d, J = 7.8 Hz, 1H, Ar-H), 8.75 (s, 1H, N=CH), 9.26 (s, 1H, 4-H, quinoline), 12.17 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 114.1, 120.2, 123.6, 126.2, 128.0, 128.4 (two overlapping signals), 129.0, 129.1, 129.2 (two overlapping signals), 129.7, 130.0 (two overlapping signals), 132.7, 133.4, 133.8, 138.2, 143.8, 146.0, 146.8, 147.2, 164.0 ppm; MS (ESI) m/z: 391 [M − H]⁻. Anal. calcd. for C₂₃H₁₆N₆O (392.41): C, 70.40; H, 4.11; N, 21.42. Found: C, 70.52; H, 4.21; N, 21.67.

N′-[2-(1H-Benzo[d][1,2,3]triazol-1-yl)quinolin-3-yl)methylene]-4-methylbenzohydrazide (7b). Starting from 2-(1H-benzo[d][1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3) (0.274 g, 1 mmol) and 4-methylbenzohydrazide (1 mmol), the title compound 7b was obtained after crystallization from n-butyl alcohol. Yield 40%; m.p. 226–230 °C; IR (KBr) ν_max: 3233, 3047, 2922, 1655, 1546, 1491, 1462, 1444, 1378, 1284, 1068, 1018, 749 cm⁻¹; ¹H NMR (500 MHz, DMSO-d₆) δ: 2.37 (s, 3H, CH₃), 7.32 (d, J = 8.3 Hz, 2H, Ar-H), 7.61 (t, J = 7.8 Hz, 1H, Ar-H), 7.74–7.79 (m, 2H, Ar-H), 7.82 (d, J = 8.3 Hz, 2H, Ar-H), 7.95 (t, J = 8.3 Hz, 1H, Ar-H), 8.13 (d, J = 8.3 Hz, 1H, Ar-H), 8.23 (d, J = 8.3 Hz, 1H, Ar-H), 8.28 (d, J = 8.3 Hz, 1H, Ar-H), 8.37 (d, J = 8.3 Hz, 1H, Ar-H), 8.74 (s, 1H, N=CH), 9.27 (s, 1H, 4-H, quinoline), 12.09 (s, 1H, NH) ppm; MS (ESI) m/z: 405 [M − H]⁻. Anal. calcd. for C₂₄H₁₈N₆O (406.44): C, 70.92; H, 4.46; N, 20.68. Found: C, 70.86; H, 4.62; N, 20.55.

N′-[2-(1H-Benzo[d][1,2,3]triazol-1-yl)quinolin-3-yl)methylene]-4-methoxybenzohydrazide (7c). Starting from 2-(1H-benzo[d][1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3) (0.274 g, 1 mmol) and 4-methoxybenzohydrazide (1 mmol), the title compound 7c was obtained after crystallization from n-butyl alcohol. Yield 35%; m.p. 242–245 °C; IR (KBr) ν_max: 3217, 3043, 2989, 2964, 2835, 1647, 1603, 1544, 1490, 1460, 1368, 1288, 1262, 1070, 1016, 784 cm⁻¹; ¹H NMR (500 MHz, DMSO-d₆) δ: 3.82 (s, 3H, OCH₃), 7.04 (d, J = 8.8 Hz, 2H, Ar-H), 7.60 (t, J = 7.8 Hz, 1H, Ar-H), 7.73–7.80 (m, 2H, Ar-H), 7.90 (d, J = 8.8 Hz, 2H, Ar-H), 7.92–7.95 (m, 1H, Ar-H), 8.12 (d, J = 8.3 Hz, 1H, Ar-H), 8.22 (d, J = 8.3 Hz, 1H, Ar-H), 8.28 (d, J = 8.3 Hz, 1H, Ar-H), 8.35 (d, J = 7.8 Hz, 1H, Ar-H), 8.73 (s, 1H, N=CH), 9.25 (s, 1H, 4-H, quinoline), 12.04 (s, 1H, NH) ppm; ¹³C NMR (50 MHz, DMSO-d₆) δ: 55.9, 113.7, 114.1 (three overlapping signals), 119.9, 123.5, 125.5, 125.9, 127.7, 128.7 (two overlapping signals), 129.4, 129.7, 130.1, 132.4, 133.2, 137.8, 142.8, 145.6, 146.5, 146.9, 162.6, 163.0 ppm; MS (ESI) m/z: 421 [M − H]⁻. Anal. calcd. for C₂₄H₁₈N₆O₂ (422.44): C, 68.24; H, 4.29; N, 19.89. Found: C, 68.43; H, 4.18; N, 19.60.

N′-[2-(1H-Benzo[d][1,2,3]triazol-1-yl)quinolin-3-yl)methylene]-4-chlorobenzohydrazide (7d). Starting from 2-(1H-benzo[d][1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3) (0.274 g, 1 mmol) and 4-chlorobenzohydrazide (1 mmol), the title compound 7d was obtained after crystallization from n-butyl alcohol. Yield 80%; m.p. 238–240 °C; IR (KBr) ν_max: 3234, 3067, 1656, 1593, 1547, 1490, 1462, 1375, 1297, 1282, 1066, 1017, 785, 748 cm⁻¹; ¹H NMR (200 MHz, CDCl₃) δ: 7.26–7.43 (m, 3H, Ar-H), 7.50–7.67 (m, 2H, Ar-H), 7.72–7.88 (m, 3H, Ar-H), 7.96–8.09 (m, 3H, Ar-H), 8.24 (d, J = 8.0 Hz, 1H, Ar-H), 9.00 (s, 1H, N=CH), 9.22 (s, 1H, 4-H, quinoline), 10.62 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 114.1, 120.2, 123.5, 126.2, 128.0, 129.0, 129.1, 129.3 (two overlapping signals), 129.7, 130.0, 130.4 (two overlapping signals), 132.5, 132.7, 133.4, 137.5, 138.2, 144.2, 145.9, 146.8, 147.2, 162.9 ppm; MS (ESI) m/z: 425 [M − H]⁻. Anal. calcd. for C₂₃H₁₅ClN₆O (426.86): C, 64.72; H, 3.54; N, 19.69. Found: C, 64.46; H, 3.89; N, 20.00.

N′-[2-(1H-Benzo[d][1,2,3]triazol-1-yl)quinolin-3-yl)methylene]-4-fluorobenzohydrazide (7e). Starting from 2-(1H-benzo[d][1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3) (0.274 g, 1 mmol) and 4-fluorobenzohydrazide (1 mmol), the title compound 7e was obtained after preparative thin layer chromatography (eluent: CH₂Cl₂/AcOEt 10:1 v/v). Yield 61%; m.p. 256–258 °C; IR (KBr) ν_max: 3202, 3066, 2924, 1655, 1600, 1555, 1505, 1491, 1462, 1378, 1288, 1228, 1067, 1018, 748 cm⁻¹; ¹H NMR (200 MHz, DMSO-d₆) δ: 7.37 (t, J = 8.3 Hz, 2H, Ar-H), 7.61 (t, J = 8.3 Hz, 1H, Ar-H), 7.72–7.83 (m, 2H, Ar-H), 7.97–8.04 (m, 3H, Ar-H), 8.14 (d, J = 8.3 Hz, 1H, Ar-H), 8.24–8.38 (m, 3H, Ar-H), 8.76 (s, 1H, N=CH), 9.27 (s, 1H, 4-H, quinoline), 12.19 (s, 1H, NH) ppm; ¹³C NMR (50 MHz, DMSO-d₆) δ: 113.8, 115.7, 116.1, 119.9, 123.3, 125.9, 127.7, 128.8 (two overlapping signals), 129.4, 129.7, 129.9, 130.8, 131.0, 132.4, 133.1, 137.9, 143.6, 145.7, 146.5, 146.9, 162.6, 167.1 ppm; MS (ESI) m/z: 409 [M − H]⁻. Anal. calcd. for C₂₃H₁₅FN₆O (410.40): C, 67.31; H, 3.68; N, 20.48. Found: C, 67.23; H, 3.47; N, 20.27.

N′-[2-(1H-Benzo[d][1,2,3]triazol-1-yl)quinolin-3-yl)methylene]furan-2-carbohydrazide (7f). Starting from 2-(1H-benzo[d][1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3) (0.274 g, 1 mmol) and furan-2-carbohydrazide (1 mmol), the title compound 7f was obtained after washing with hot ethanol. Yield 53%; m.p. 283–285 °C; IR (KBr) ν_max: 3254, 3147, 3072, 1663, 1597, 1565, 1544, 1492, 1467, 1301, 1200, 1069, 1017, 784, 751 cm⁻¹; ¹H NMR (500 MHz, DMSO-d₆) δ: 6.69–6.70 (m, 1H, Ar-H), 7.28–7.34 (m, 1H, Ar-H), 7.60 (t, J = 7.3 Hz, 1H, Ar-H), 7.72–7.78 (m, 2H, Ar-CH), 7.91–7.94 (m, 2H, Ar-H and N=CH), 8.11 (d, J = 8.3 Hz, 1H, Ar-H), 8.22 (d, J = 8.3 Hz, 1H, Ar-H), 8.27 (d, J = 8.3 Hz, 1H, Ar-H), 8.34 (d, J = 8.3 Hz, 1H, Ar-H), 8.74 (s, 1H, Ar-H), 9.22 (s, 1H, 4-H, quinoline), 12.18 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 112.9, 114.0, 116.1, 120.2, 123.5, 126.1, 128.0, 129.0, 129.1, 129.7, 130.0 (two overlapping signals), 132.7, 133.4, 138.2, 143.9, 146.0, 146.8, 147.1, 147.2, 155.0 ppm; MS (ESI) m/z: 381 [M − H]⁻. Anal. calcd. for C₂₁H₁₄N₆O₂ (382.37): C, 65.96; H, 3.69; N, 21.98. Found: C, 65.87; H, 3.75; N, 22.11.

N′-[2-(1H-Benzo[d][1,2,3]triazol-1-yl)quinolin-3-yl)methylene]thiophene-2-carbohydrazide (7g). Starting from 2-(1H-benzo[d][1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3) (0.274 g, 1 mmol) and thiophene-2-carbohydrazide (1 mmol), the title compound 7g was obtained after washing with hot ethanol. Yield 53%; m.p. 237–239 °C; IR (KBr) ν_max: 3243, 3106, 1647, 1596, 1548, 1492, 1426, 1381, 1284, 1064, 1015, 784, 750 cm⁻¹; ¹H NMR (500 MHz, DMSO-d₆) δ: 7.18–7.24 (m, 1H, Ar-H), 7.59 (t, J = 7.8 Hz, 1H, Ar-H), 7.73–7.84 (m, 2H, Ar-H), 7.89–7.97 (m, 3H, Ar-H), 8.12 (d, J = 8.8 Hz, 1H, Ar-H), 8.24–8.28 (m, 2H, Ar-H and N=CH), 8.33 (d, J = 7.8 Hz, 1H, Ar-H), 8.73 (br. s, 1H, Ar-H), 9.22 (s, 1H, 4-H, quinoline), 12.17 (s, 1H, NH) ppm; ¹³C NMR (50 MHz, DMSO-d₆) δ: 113.9, 119.9 (two overlapping signals), 123.2, 125.9 (two overlapping signals), 127.6, 128.7 (two overlapping signals), 129.4, 129.7 (two overlapping signals), 132.4, 133.1, 135.5, 138.0, 138.5, 143.2, 145.7, 146.5, 146.9 ppm; MS (ESI) m/z: 397 [M − H]⁻. Anal. calcd. for C₂₁H₁₄N₆OS (398.44): C, 63.30; H, 3.54; N, 21.09. Found: C, 63.15; H, 3.27; N, 21.44.

N′-[2-(1H-Benzo[d][1,2,3]triazol-1-yl)quinolin-3-yl)methylene]cyclopentanecarbohydrazide (7h). Starting from 2-(1H-benzo[d][1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3) (0.274 g, 1 mmol) and cyclopentanecarbohydrazide (1 mmol), the title compound 7h was obtained as a mixture of cis/trans conformers after preparative thin layer chromatography (eluent: CH₂Cl₂: AcOEt 10:1 v/v). Yield 71%; m.p. 202–204 °C; IR (KBr) ν_max: 3199, 3057, 2954, 2867, 1665, 1619, 1560, 1493, 1463, 1447, 1384, 1288, 1214, 1062, 1020, 784, 747 cm⁻¹; ¹H NMR (200 MHz, DMSO-d₆) δ: 1.60–1.68 (m, 16H, 8xCH₂), 2.60–2.63 and 3.19–3.42 (m, 1H, CH), 7.48–7.62 (m, 2H, 2xCH), 7.65–7.82 (m, 4H, 4xCH), 7.94 (t, J = 7.9 Hz, 2H, 2xCH), 8.11–8.15 (m, 3H, 3xCH), 8.27–8.32 (m, 6H, 6xCH), 8.48 (s, 1H, N=CH), 9.11 and 9.18 (s, 1H, 4-H, quinoline), 11.36 and 11.64 (s, 1H, NH) ppm; ¹³C NMR (50 MHz, DMSO-d₆) δ: 26.2 (two overlapping signals), 29.7, 30.4, 43.6, 113.8, 119.9, 125.9, 127.7, 128.7, 129.2, 129.5, 129.7, 132.3, 133.1, 137.8, 138.2, 138.6, 141.6, 145.6, 146.4, 172.5 and 177.7 ppm; MS (ESI) m/z: 383 [M − H]⁻. Anal. calcd. for C₂₂H₂₀N₆O (384.43): C, 68.73; H, 5.24; N, 21.86. Found: C, 68.82; H, 5.32; N, 21.47.

3.2.5. General Procedure for the Preparation of N′-Sulfonylhydrazones 8a–h and 9a–h

A mixture of 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) (0.224 g, 1 mmol) or 2-(1H-benzo[d][1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3) (0.274 g, 1 mmol) and appropriate sulfonohydrazide (1 mmol) in the presence of a catalytic amount of acetic acid in THF (5 mL) was heated under reflux for 7–8 h. The progress of the reaction was controlled by TLC. The mixture was then evaporated under reduced pressure and the crude product thus obtained was purified as described below. In this manner, the following compounds were obtained.

N′-[(2-(1H-1,2,4-Triazol-1-yl)quinolin-3-yl)methylene]benzenesulfonohydrazide (8a). Starting from 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) (0.224 g, 1 mmol) and benzenesulfonohydrazide (1 mmol), the title compound 8a was obtained after washing with hot methanol. Yield 35%; m.p. 193–196 °C; IR (KBr) ν_max: 3115, 3072, 2978, 2910, 1620, 1605, 1566, 1511, 1495, 1442, 1338, 1284, 1164, 1063, 1048, 938, 895, 760 cm⁻¹; ¹H NMR (200 MHz, DMSO-d₆) δ: 7.62 (d, J = 8.3 Hz, 2H, Ar-H), 7.76 (t, J = 7.9 Hz, 1H, Ar-H), 7.90–8.00 (m, 4H, Ar-H), 8.06–8.10 (m, 1H, Ar-H), 8.33 (d, J = 7.9 Hz, 1H, Ar-H), 8.45 (s, 1H, N=CH), 8.78 (s, 1H, triazole), 9.17 (s, 1H, 4-H, quinoline), 9.38 (s, 1H, triazole), 12.25 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 121.8, 127.8 (three overlapping signals), 128.8, 128.9, 129.5, 130.1 (two overlapping signals), 132.8, 134.0, 137.7, 139.6, 143.4, 145.8, 146.3, 146.4, 153.4 ppm. Anal. calcd. for C₁₈H₁₄N₆O₂S (378.41): C, 57.13; H, 3.73; N, 22.21. Found: C, 56.83; H, 3.65; N, 22.65.

N′-[(2-(1H-1,2,4-Triazol-1-yl)quinolin-3-yl)methylene]-4-methylbenzenesulfonohydrazide (8b). Starting from 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) (0.224 g, 1 mmol) and 4-methylbenzenesulfonohydrazide (1 mmol), the title compound 8b was obtained after washing with hot methanol. Yield 44%; m.p. 180–186 °C; IR (KBr) ν_max: 3110, 2916, 1620, 1599, 1512, 1493, 1441, 1345, 1284, 1165, 1067, 951, 902, 759 cm⁻¹; ¹H NMR (200 MHz, DMSO-d₆) δ: 2.36 (s, 3H, CH₃), 7.44 (d, J = 7.9 Hz, 2H, Ar-H), 7.75 (t, J = 7.1 Hz, 1H, Ar-H), 7.77–7.93 (m, 3H, Ar-H), 8.03 (d, J = 7.1 Hz, 1H, Ar-H), 8.25–8.30 (m, 2H, Ar-H and N=CH), 8.38 (s, 1H, triazole), 8.87 (s, 1H, 4-H, quinoline), 9.30 (s, 1H, triazole), 11.38 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 21.7, 121.9, 127.8, 127.9 (two overlapping signals), 128.8, 128.9, 129.5, 130.5 (two overlapping signals), 132.8, 136.7, 137.6, 143.2, 144.6, 145.8, 146.3, 146.4, 153.4 ppm; MS (ESI) m/z: 415 [M + Na]⁺. Anal. calcd. for C₁₉H₁₆N₆O₂S (392.43): C, 58.15; H, 4.11; N, 21.42. Found: C, 57.93; H, 3.95; N, 21.71.

N′-[(2-(1H-1,2,4-Triazol-1-yl)quinolin-3-yl)methylene]-4-methoxybenzenesulfonohydrazide (8c). Starting from 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) (0.224 g, 1 mmol) and 4-methoxybenzenesulfonohydrazide (1 mmol), the title compound 8c was obtained after washing with hot methanol. Yield 52%; m.p. 185–188 °C; IR (KBr) ν_max: 3110, 3058, 2882, 2799, 1618, 1567, 1512, 1490, 1441, 1338, 1282, 1176, 1167, 1065, 992, 944, 787, 762 cm⁻¹; ¹H NMR (200 MHz, DMSO-d₆) δ: 3.82 (s, 3H, OCH₃), 7.15 (d, J = 9.1 Hz, 2H, Ar-H), 7.74 (t, J = 7.1 Hz, 1H, Ar-H), 7.85–7.94 (m, 3H, Ar-H), 8.01–8.06 (m, 1H, Ar-H), 8.25–8.30 (m, 2H, Ar-H and N=CH), 8.38 (s, 1H, triazole), 8.87 (s, 1H, 4-H, quinoline), 9.30 (s, 1H, triazole), 11.74 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 56.4, 115.2 (two overlapping signals), 121.9, 127.9, 128.8, 128.9, 129.5, 130.2 (two overlapping signals), 131.1, 132.8, 137.6, 143.0, 145.8, 146.3, 146.4, 153.4, 163.4 ppm. Anal. calcd. for C₁₉H₁₆N₆O₃S (408.43): C, 55.87; H, 3.95; N, 20.58. Found: C, 55.97; H, 4.15; N, 20.58.

N′-[(2-(1H-1,2,4-Triazol-1-yl)quinolin-3-yl)methylene]-4-chlorobenzenesulfonohydrazide (8d). Starting from 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) (0.224 g, 1 mmol) and 4-chlorobenzenesulfonohydrazide (1 mmol), the title compound 8d was obtained after washing with hot methanol. Yield 71%; m.p. 196–200 °C; IR (KBr) ν_max: 3110, 3058, 2882, 2799, 1618, 1567, 1512, 1490, 1441, 1338, 1282, 1176, 1167, 1065, 944, 787, 762 cm⁻¹; ¹H NMR (200 MHz, DMSO-d₆) δ: 7.69–7.73 (m, 3H, Ar-H), 7.87–7.90 (m, 1H, Ar-H), 7.94 (d, J = 8.8 Hz, 2H, Ar-H), 8.01–8.02 (m, 1H, Ar-H), 8.22 (d, J = 8.3 Hz, 1H, Ar-H), 8.34 (s, 1H, triazole), 8.36 (s, 1H, N=CH), 8.84 (s, 1H, 4-H, quinoline), 9.27 (s, 1H, triazole), 11.89 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 121.9, 127.9, 128.8, 128.9, 129.0, 129.6 (two overlapping signals), 130.2 (two overlapping signals), 132.7, 137.8, 138.7, 138.8, 144.0, 145.8, 146.4, 146.6, 153.5 ppm. Anal. calcd. for C₁₈H₁₃ClN₆O₂S (412.85): C, 52.37; H, 3.17; N, 20.36. Found: C, 52.45; H, 3.37; N, 20.14.

N′-[(2-(1H-1,2,4-Triazol-1-yl)quinolin-3-yl)methylene]-4-fluorobenzenesulfonohydrazide (8e). Starting from 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) (0.224 g, 1 mmol) and 4-fluorobenzenesulfonohydrazide (1 mmol), the title compound 8e was obtained after crystallization from n-butyl alcohol. Yield 38%; m.p. 184–186 °C; IR (KBr) ν_max: 3110, 3066, 2909, 2799, 1619, 1592, 1511, 1492, 1441, 1330, 1284, 1231, 1171, 1066, 944, 832, 757 cm⁻¹; ¹H NMR (500 MHz, DMSO-d₆) δ: 7.48 (t, J = 8.8 Hz, 2H, Ar-H), 7.71 (t, J = 7.8 Hz, 1H, Ar-H), 7.87 (t, J = 7.8 Hz, 1H, Ar-H), 8.00–8.02 (m, 3H, Ar-H), 8.24 (d, J = 8.3 Hz, 1H, Ar-H), 8.32 (s, 1H, N=CH), 8.37 (s, 1H, triazole), 8.85 (s, 1H, 4-H, quinoline), 9.30 (s, 1H, triazole), 11.94 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 117.2, 117.4, 121.8, 127.9, 128.8, 129.6, 131.0, 131.1, 132.7, 136.0, 137.7, 143.8, 145.8, 146.4, 146.5, 153.3, 164.3, 166.3 ppm; MS (ESI) m/z: 397 [M + H]⁺. Anal. calcd. for C₁₈H₁₃FN₆O₂S (396.40): C, 54.54; H, 3.31; N, 21.20. Found: C, 54.37; H, 3.18; N, 21.58.

N′-[(2-(1H-1,2,4-Triazol-1-yl)quinolin-3-yl)methylene]-2,4,6-trimethylbenzenesulfonohydrazide (8f). Starting from 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) (0.224 g, 1 mmol) and 2,4,6-trimethylbenzenesulfonohydrazide (1 mmol), the title compound 8f was obtained after crystallization from n-butyl alcohol. Yield 65%; m.p. 184–186 °C; IR (KBr) ν_max: 3115, 3071, 2909, 1604, 1511, 1495, 1442, 1338, 1284, 1164, 1063, 1048, 938, 895, 760 cm⁻¹; ¹H NMR (500 MHz, DMSO-d₆) δ: 2.21 (s, 3H, CH₃), 2.64 (s, 6H, 2xCH₃), 7.04 (s, 2H, Ar-H), 7.69 (t, J = 7.3 Hz, 1H, Ar-H), 7.85 (t, J = 7.3 Hz, 1H, Ar-H), 7.99 (d, J = 8.3 Hz, 1H, Ar-H), 8.10 (d, J = 8.3 Hz, 1H, Ar-H), 8.28 (s, 1H, N=CH), 8.35 (s, 1H, triazole), 8.65 (s, 1H, 4-H, quinoline), 9.26 (s, 1H, triazole), 11.97 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 21.0, 23.2 (two overlapping signals), 122.3, 127.9, 128.9 (two overlapping signals), 129.2 (two overlapping signals), 132.3 (three overlapping signals), 134.4, 137.2, 139.9, 141.4, 143.1, 145.6, 146.3, 146.5, 153.3 ppm. Anal. calcd. for C₂₁H₂₀N₆O₂S (420.49): C, 59.98; H, 4.79; N, 19.99. Found: C, 60.13; H, 4.87; N, 19.67.

N′-[(2-(1H-1,2,4-Triazol-1-yl)quinolin-3-yl)methylene]-4-tert-butylbenzenesulfonohydrazide (8g). Starting from 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) (0.224 g, 1 mmol) and 4-tert-butylbenzenesulfonohydrazide (1 mmol), the title compound 8g was obtained after washing with hot methanol. Yield 35%; m.p. 142–146 °C; IR (KBr) ν_max: 3113, 3067, 2962, 2798, 1619, 1597, 1566, 1491, 1440, 1338, 1283, 1168, 1066, 944, 787, 761 cm⁻¹; ¹H NMR (200 MHz, DMSO-d₆) δ: 1.27 (s, 9H, 3xCH₃), 7.63–7.71 (m, 3H, Ar-H), 7.85–7.90 (m, 3H, Ar-H), 8.01–8.05 (m, 1H, Ar-H), 8.25–8.38 (m, 3H, Ar-H, N=CH and CH-triazole), 8.88 (s, 1H, 4-H, quinoline), 9.30 (s, 1H, triazole), 11.88 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 31.4 (three overlapping signals), 35.6, 121.8, 127.0 (two overlapping signals), 127.8 (two overlapping signals), 127.9, 128.8, 129.9, 129.5, 132.8, 136.8, 137.6, 143.1, 145.8, 146.3, 146.4, 153.4, 157.0 ppm; MS (ESI) m/z: 457 [M + Na]⁺. Anal. calcd. for C₂₂H₂₂N₆O₂S (434.51): C, 60.81; H, 5.10; N, 19.34. Found: C, 60.63; H, 4.98; N, 19.66.

N′-[(2-(1H-1,2,4-Triazol-1-yl)quinolin-3-yl)methylene]naphthalene-2-sulfonohydrazide (8h). Starting from 2-(1H-1,2,4-triazol-1-yl)quinoline-3-carbaldehyde (2) (0.224 g, 1 mmol) and naphthalene-2-sulfonohydrazide (1 mmol), the title compound 8h was obtained after washing with hot methanol. Yield 59%; m.p. 183–187 °C; IR (KBr) ν_max: 3111, 3056, 2907, 2795, 1619, 1602, 1511, 1492, 1441, 1338, 1283, 1165, 1066, 954, 812, 747 cm⁻¹; ¹H NMR (500 MHz, DMSO-d₆) δ: 7.65–7.71 (m, 3H, Ar-H), 7.86 (t, J = 8.3 Hz, 1H, Ar-H), 7.95 (dd, J = 8.8 Hz, J = 1.5 Hz, 1H, Ar-H), 7.97–8.02 (m, 2H, Ar-H), 8.15 (d, J = 8.8 Hz, 1H, Ar-H), 8.22 (d, J = 7.8 Hz, 1H, Ar-H), 8.27 (d, J = 8.8 Hz, 1H, Ar-H), 8.31 (s, 1H, N=CH), 8.35 (s, 1H, triazole), 8.67 (s, 1H, Ar-H), 8.87 (s, 1H, 4-H, quinoline), 9.27 (s, 1H, triazole), 11.97 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 106.3, 121.8, 123.2, 127.9, 128.4, 128.6, 128.8, 129.2, 129.5, 129.8, 130.0, 130.1, 132.5, 132.7, 135.1, 136.7, 137.6, 143.4, 145.8, 146.4, 146.5, 153.5 ppm. Anal. calcd. for C₂₂H₁₆N₆O₂S (428.47): C, 61.67; H, 3.76; N, 19.61. Found: C, 61.43; H, 3.67; N, 19.30.

N′-[(2-1H-Benzo[d][1,2,3]triazol-1-yl)quinolin-3-yl)methylene]benzenesulfonohydrazide (9a). Starting from 2-(1H-benzo[d][1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3) (0.274 g, 1 mmol) and benzenesulfonohydrazide (1 mmol), the title compound 9a was obtained after washing with methanol. Yield 53%; m.p. 118–121 °C; IR (KBr) ν_max: 3101, 3059, 2923, 2853, 1621, 1603, 1496, 1449, 1363, 1324, 1286, 1164, 1091, 1065, 947, 750 cm⁻¹; ¹H NMR (400 MHz, DMSO-d₆) δ: 7.58–7.68 (m, 4H, Ar-H), 7.70–7.80 (m, 2H, Ar-H), 7.94–7.96 (m, 3H, Ar-H), 8.12 (d, J = 8.3 Hz, 1H, Ar-H), 8.22–8.26 (m, 2H, Ar-H), 8.28 (s, 1H, N=CH), 8.33 (d, J = 8.1 Hz, 1H, Ar-H), 8.98 (s, 1H, 4-H, quinoline), 11.90 (s, 1H, NH) ppm. MS (ESI): m/z: 451 [M + Na]⁺. Anal. calcd. for C₂₂H₁₆N₆O₂S (428.47): C, 61.67; H, 3.76; N, 19.61. Found: C, 61.87; H, 3.98; N, 19.29.

N′-[(2-1H-Benzo[d][1,2,3]triazol-1-yl)quinolin-3-yl)methylene]-4-methylbenzenesulfonohydrazide (9b). Starting from 2-(1H-benzo[d][1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3) (0.274 g, 1 mmol) and 4-methylbenzenesulfonohydrazide (1 mmol), the title compound 9b was obtained after preparative thin layer chromatography (eluent: CH₂Cl₂: AcOEt 10:1 v/v). Yield 41%; m.p. 193–197 °C; IR (KBr) ν_max: 3214, 3064, 2955, 2855, 2772, 1597, 1149, 1447, 1370, 1324, 1286, 1163, 1049, 1020, 943, 763 cm⁻¹; ¹H NMR (500 MHz, DMSO-d₆) δ: 2.35 (s, 3H, CH₃), 7.42 (d, J = 7.8 Hz, 2H, Ar-H), 7.58 (t, J = 8.3 Hz, 1H, Ar-H), 7.71 (t, J = 7.8 Hz, 1H, Ar-H), 7.76 (t, J = 7.8 Hz, 1H, Ar-H), 7.79 (d, J = 8.3 Hz, 2H, Ar-H), 7.92 (t, J = 8.3 Hz, 1H, Ar-H), 8.09 (d, J = 8.3 Hz, 1H, Ar-H), 8.20 (d, J = 8.3 Hz, 1H, Ar-H), 8.24–8.25 (m, 2H, Ar-H and N=CH), 8.31 (d, J = 8.3 Hz, 1H, Ar-H), 8.96 (s, 1H, 4-H, quinoline), 11.80 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 21.6, 113.9, 120.1, 122.9, 126.1, 127.7, 127.8 (two overlapping signals), 129.0 (two overlapping signals), 129.4, 129.9, 130.4 (two overlapping signals), 132.7, 133.4, 137.0, 138.0 (two overlapping signals), 143.3, 144.3, 145.9, 146.8 ppm. MS (ESI): m/z: 441 [M − H]⁻. Anal. calcd. for C₂₃H₁₈N₆O₂S (442.49): C, 62.43; H, 4.10; N, 18.99. Found: C, 62.27; H, 3.98; N, 19.35.

N′-[(2-1H-Benzo[d][1,2,3]triazol-1-yl)quinolin-3-yl)methylene]-4-methoxybenzenesulfonohydrazide (9c). Starting from 2-(1H-benzo[d][1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3) (0.274 g, 1 mmol) and 4-methoxybenzenesulfonohydrazide (1 mmol), the title compound 9c was obtained after washing with hot methanol. Yield 63%; m.p. 198–202 °C; IR (KBr) ν_max: 3149, 3069, 2860, 2760, 1595, 1578, 1493, 1426, 1352, 1290, 1264, 1163, 1022, 953, 785, 745 cm⁻¹; ¹H NMR (500 MHz, DMSO-d₆) δ: 3.81 (s, 3H, OCH₃), 7.13 (d, J = 8.8 Hz, 2H, Ar-H), 7.58 (t, J = 7.8 Hz, 1H, Ar-H), 7.72 (t, J = 7.8 Hz, 1H, Ar-H), 7.76 (t, J = 7.8 Hz, 1H, Ar-H), 7.85 (d, J = 8.8 Hz, 2H, Ar-H), 7.92 (t, J = 7.8 Hz, 1H, Ar-H), 8.10 (d, J = 8.3 Hz, 1H, Ar-H), 8.20 (d, J = 8.3 Hz, 1H, Ar-H), 8.23–8.26 (m, 2H, Ar-H and N=CH), 8.31 (d, J = 8.3 Hz, 1H, Ar-H), 8.96 (s, 1H, 4-H, quinoline), 11.71 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 56.4, 114.2, 115.2 (two overlapping signals), 120.2, 122.9, 126.1, 127.7, 129.0, 129.1, 129.6, 129.9, 130.1 (two overlapping signals), 131.3, 132.7, 133.3, 137.9, 143.1, 145.9, 146.7, 146.9, 163.4 ppm; MS (ESI): m/z: 457 [M − H]⁻. Anal. calcd. for C₂₃H₁₈N₆O₃S (458.49): C, 60.25; H, 3.96; N, 18.33. Found: C, 60.12; H, 3.76; N, 18.65.

N′-[(2-1H-Benzo[d][1,2,3]triazol-1-yl)quinolin-3-yl)methylene]-4-chlorobenzenesulfonohydrazide (9d). Starting from 2-(1H-benzo[d][1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3) (0.274 g, 1 mmol) and 4-chlorobenzenesulfonohydrazide (1 mmol), the title compound 9d was obtained after washing with hot methanol. Yield 45%; m.p. 202–206 °C; IR (KBr) ν_max: 3190, 3064, 2875, 1598, 1587, 1494, 1431, 1355, 1320, 1173, 1091, 1067, 1022, 952, 785, 757 cm⁻¹; ¹H NMR (500 MHz, DMSO-d₆) δ: 7.57 (t, J = 7.3 Hz, 1H, Ar-H), 7.66–7.74 (m, 3H, Ar-H), 7.75 (t, J = 7.3 Hz, 1H, Ar-H), 7.77–7.93 (m, 3H, Ar-H), 8.09 (d, J = 8.3 Hz, 1H, Ar-H), 8.19 (d, J = 8.3 Hz, 1H, Ar-H), 8.22 (d, J = 8.3 Hz, 1H, Ar-H), 8.26 (d, J = 7.8 Hz, 1H, Ar-H), 8.32 (s, 1H, N=CH), 8.93 (s, 1H, 4-H, quinoline), 11.78 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 114.1, 120.2, 122.8, 126.0, 127.8, 128.9, 129.0, 129.5, 129.7 (two overlapping signals), 129.8 (two overlapping signals), 130.1 (two overlapping signals), 132.7, 133.4, 138.2, 138.8, 144.1, 146.0, 146.9, 147.0 ppm. Anal. calcd. for C₂₂H₁₅ClN₆O₂S (462.91): C, 57.08; H, 3.27; N, 18.15. Found: C, 56.87; H, 3.15; N, 18.54.

N′-[(2-1H-Benzo[d][1,2,3]triazol-1-yl)quinolin-3-yl)methylene]-4-fluorobenzenesulfonohydrazide (9e). Starting from 2-(1H-benzo[d][1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3) (0.274 g, 1 mmol) and 4-fluorobenzenesulfonohydrazide (1 mmol), the title compound 9e was obtained after washing with hot methanol. Yield 56%; m.p. 205–209 °C; IR (KBr) ν_max: 3071, 2869, 2771, 1618, 1590, 1493, 1424, 1326, 1289, 1238, 1170, 1056, 1024, 941, 838, 757, 748 cm⁻¹; ¹H NMR (500 MHz, DMSO-d₆) δ: 7.45 (t, J = 8.8 Hz, 2H, Ar-H), 7.57 (t, J = 7.8 Hz, 1H, Ar-H), 7.71 (t, J = 7.3 Hz, 1H, Ar-H), 7.75 (t, J = 7.3 Hz, 1H, Ar-H), 7.92 (t, J = 7.8 Hz, 1H, Ar-H), 7.97–8.00 (m, 2H, Ar-H), 8.09 (d, J = 8.3 Hz, 1H, Ar-H), 8.20 (d, J = 8.3 Hz, 1H, Ar-H), 8.23 (d, J = 8.3 Hz, 1H, Ar-H), 8.27–8.29 (m, 2H, Ar-H and N=CH), 8.94 (s, 1H, 4-H, quinoline), 11.82 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 114.2, 117.1, 117.3, 120.2, 122.8, 126.1, 127.7, 128.9, 129.0, 129.6, 129.9, 131.0, 132.7, 133.3, 136.2, 138.2, 144.0, 146.0, 146.8, 147.0, 164.2, 166.2 ppm. Anal. calcd. for C₂₂H₁₅FN₆O₂S (446.46): C, 59.18; H, 3.39; N, 18.82. Found: C, 59.38; H, 3.16; N, 18.56.

N′-[(2-1H-Benzo[d][1,2,3]triazol-1-yl)quinolin-3-yl)methylene]-2,4,6-trimethylbenzenesulfonohydrazide (9f). Starting from 2-(1H-benzo[d][1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3) (0.274 g, 1 mmol) and 2,4,6-trimethylbenzenesulfonohydrazide (1 mmol), the title compound 9f was obtained after washing with hot methanol. Yield 57%; m.p. 187–191 °C; IR (KBr) ν_max: 3213, 3060, 2938, 1601, 1493, 1448, 1424, 1316, 1164, 1052, 1022, 941, 889, 750 cm⁻¹; ¹H NMR (500 MHz, DMSO-d₆) δ: 2.23 (s, 3H, CH₃), 2.64 (s, 6H, 2xCH₃), 7.05 (s, 2H, Ar-H), 7.58 (t, J = 7.8 Hz, 1H, Ar-H), 7.70–7.76 (m, 2H, Ar-H), 7.91 (t, J = 8.3 Hz, 1H, Ar-H), 8.08 (d, J = 8.3 Hz, 1H, Ar-H), 8.17–8.25 (m, 3H, Ar-H), 8.26 (s, 1H, N=CH), 8.80 (s, 1H, 4-H, quinoline), 11.92 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 21.1, 23.4 (two overlapping signals), 114.2, 120.2, 123.0, 126.1, 127.6, 128.9, 129.0, 129.5, 129.9, 132.4 (three overlapping signals), 132.6, 133.2, 134.1, 137.4, 139.8, 141.6, 143.1, 145.9, 146.6, 146.9 ppm. Anal. calcd. for C₂₅H₂₂N₆O₂S (470.55): C, 63.81; H, 4.71; N, 17.86. Found: C, 63.61; H, 4.58; N, 17.58.

N′-[(2-1H-Benzo[d][1,2,3]triazol-1-yl)quinolin-3-yl)methylene]-4-tert-butylbenzenesulfonohydrazide (9g). Starting from 2-(1H-benzo[d][1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3) (0.274 g, 1 mmol) and 4-tert-butylbenzenesulfonohydrazide (1 mmol), the title compound 9g was obtained after washing with hot methanol. Yield 57%; m.p. 132–136 °C; IR (KBr) ν_max: 3187, 3061, 2965, 2870, 2771, 1593, 1495, 1463, 1429, 1357, 1321, 1290, 1164, 1064, 1027, 944, 783 cm⁻¹; ¹H NMR (200 MHz, DMSO-d₆) δ: 1.26 (s, 9H, 3xCH₃), 7.58 (t, J = 7.8 Hz, 1H, Ar-H), 7.64 (d, J = 8.8 Hz, 2H, Ar-H), 7.72 (t, J = 7.8 Hz, 1H, Ar-H), 7.77 (t, J = 7.8 Hz, 1H, Ar-H), 7.84 (d, J = 8.8 Hz, 2H, Ar-H), 7.92 (t, J = 8.3 Hz, 1H, Ar-H), 8.10 (d, J = 8.3 Hz, 1H, Ar-H), 8.21 (d, J = 8.3 Hz, 1H, Ar-H), 8.25–8.26 (m, 2H, Ar-H and N=CH), 8.31 (d, J = 7.8 Hz, 1H, Ar-H), 8.98 (s, 1H, 4-H, quinoline), 11.85 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 31.4 (three overlapping signals), 35.5, 113.9, 120.1, 123.0, 126.0, 126.7 (two overlapping signals), 127.7 (two overlapping signals), 127.8, 129.0 (two overlapping signals), 129.4, 129.9 (two overlapping signals), 132.7, 133.4, 137.1, 138.1, 143.3, 146.0, 146.9, 157.1 ppm; MS (ESI): m/z: 483 [M − H]⁻. Anal. calcd. for C₂₆H₂₄N₆O₂S (484.57): C, 64.44; H, 4.99; N, 17.34. Found: C, 64.34; H, 4.78; N, 17.71.

N′-[(2-1H-Benzo[d][1,2,3]triazol-1-yl)quinolin-3-yl)methylene]naphthalene-2-sulfonohydrazide (9h). Starting from 2-(1H-benzo[d][1,2,3]triazol-1-yl)quinoline-3-carbaldehyde (3) (0.274 g, 1 mmol) and naphthalene-2-sulfonohydrazide (1 mmol), the title compound 9h was obtained after washing with hot methanol. Yield 52%; m.p. 196–200 °C; IR (KBr) ν_max: 3179, 3055, 2915, 1618, 1587, 1493, 1446, 1427, 1328, 1289, 1164, 1051, 1021, 958, 783, 752 cm⁻¹; ¹H NMR (500 MHz, DMSO-d₆) δ: 7.56 (t, J = 7.3 Hz, 1H, Ar-H), 7.66–7.71 (m, 3H, Ar-H), 7.75 (t, J = 7.8 Hz, 1H, Ar-H), 7.89–7.94 (m, 2H, Ar-H), 8.02 (d, J = 7.8 Hz, 1H, Ar-H), 8.07 (d, J = 8.3 Hz, 1H, Ar-H), 8.14–8.19 (m, 2H, Ar-H), 8.23 (d, J = 8.3 Hz, 1H, Ar-H), 8.26–8.29 (m, 3H, Ar-H and N=CH), 8.65 (s, 1H, Ar-H), 8.98 (s, 1H, 4-H, quinoline), 11.95 (s, 1H, NH) ppm; ¹³C NMR (125 MHz, DMSO-d₆) δ: 113.9, 120.1, 122.9, 123.1, 126.0, 127.7, 128.4, 128.5, 129.9 (two overlapping signals), 129.0, 129.4, 129.7, 129.8 (two overlapping signals), 129.9, 130.0, 132.5, 132.7, 133.4, 135.2, 136.9, 138.2, 143.6, 146.0, 146.8 ppm. Anal. calcd. for C₂₆H₁₈N₆O₂S (478.53): C, 65.26; H, 3.79; N, 17.56. Found: C, 65.17; H, 3.58; N, 17.96.

3.3. Stability Studies

To 5.0 mL of PBS (phosphate-buffered saline, pH 7.4), pre-warmed at 37 °C, was added 10 µL of a 20 mM DMSO solution of the quinoline derivative, resulting in a final compound concentration of 40 µM. The solution was then transferred to a 1.0 cm quartz cuvette and placed in a heated cuvette holder maintained at 37 °C. Spectra were recorded at 10 min intervals between wavelengths of 250 and 600 nm by means of an Analytik Jena Spekol 1200 (Analytik Jena AG) diode array UV-Vis spectrophotometer connected to a personal computer (PC) running the Aspect Plus (V 1.5) software (Analytik Jena AG).

3.4. In Vitro Cytotoxicity Studies

All cell culture reagents were purchased from Sigma (Deisenhofen, Germany). The cancer cell lines human pancreas cell adenocarcinoma DAN-G, human large cell lung carcinoma LCLC-103H, and human uterine cervical adenocarcinoma SISO were obtained from the German Collection of Microorganisms and Cell Cultures (DSMZ, Braunschweig, Germany, FRG). The culture medium for cell lines was RPMI-1640 medium containing 2 g/L HCO₃ and 10% fetal calf serum (FCS). Cells were grown in 75 cm² plastic culture flasks (Sarstedt, Nümbrecht, Germany, FRG) in a humid atmosphere of 5% CO₂ at 37 °C and were passaged shortly before becoming confluent. Cytotoxicity studies were performed with a well-established microtiter assay based on the staining of adherent cells with crystal violet and performed as previously described [54]. Briefly, a volume of 100 µL of a cell suspension were seeded into 96-well microtiter plates (Sarstedt) at a density of 1000 cells per well except for the LCLC-103H cell line, which was plated out at 250 cells per well. Twenty-four hours later, cells were exposed to the substance at five concentrations per compound. The 1000-fold concentrated stock solutions in DMSO were serially diluted by 50% in DMSO to give the feed solutions, which were diluted 500-fold into culture medium. The controls received just DMSO. Each concentrate was tested in eight wells, with each well receiving 100 µL of the medium containing the substance. The concentration ranges were chosen to bracket the expected IC₅₀ values as best as possible. Cells were then incubated for 48 h, after which time the medium was removed and replaced with 1% glutaraldehyde/PBS. The cells were then stained with crystal violet and the optical density (OD) was measured at λ = 570 nm with an Anthos 2010 plate reader (Salzburg, Austria).

The corrected percent growth values [T/C_corr(%)] were calculated by the equation:

T/C_corr(%) = (OD_T − OD_c,0)/(OD_c − OD_c,0) × 100

where OD_T is the mean absorbance of the treated cells, OD_c is the mean absorbance of the controls, and OD_c,0 is the mean absorbance at the time the drug was added. The IC₅₀ values were estimated by a linear least-squares regression of the T/C_corr values versus the logarithm of the substance concentration; only concentrations that yielded T/C_corr values between 10% and 90% were used in the calculation. The reported IC₅₀ values are the averages of three independent experiments.

4. Conclusions

In this study, we have investigated the anticancer properties of three series of quinoline-3-carbaldehyde hydrazone derivatives possessing either 1,2,4-triazole or 1,2,3-benzotriazole rings. Analysis of the structure-activity relationships of cytotoxic activities on the human cancer cell lines of 1,2,4-triazole-containing quinolines 4, 6, and 8 and 1,2,3-benzotriazole-containing quinolines 5, 7, and 9 revealed that the less lipophilic 1,2,4-triazole derivatives are generally inactive, while the more lipophilic 1,2,3-benzotriazole analogues exhibit moderate to high cytotoxic effects. It is too early to speculate on the mechanism of action of these compounds. Nonetheless, the most active 2-(1H-benzo[d][1,2,3]triazol-1-yl)-3-[(2-(pyridin-2-yl)hydrazonomethyl]-quinoline (Series 1, compound 5e, Figure 5) with IC₅₀ values in the range of 1.23–1.49 µM may serve as a useful lead compound in the development of new chemotherapeutic agents.

Figure 5. Structure of 2-(1H-benzo[d][1,2,3]triazol-1-yl)-3-[(2-(pyridin-2-yl)hydrazonomethyl]-quinoline 5e.

Author Contributions

F.S. conceived and designed the project. P.J.B. designed the biological tests. M.K. performed the chemical experiments and biological tests. F.S. and A.K. wrote the paper.

Funding

This research received no external funding.

Acknowledgments

M.K. thanks the European Union student exchange programmme Erasmus for financial support (maintenance and accommodation).

Conflicts of Interest

The authors declare no conflict of interest, financial or otherwise.

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