Design, Synthesis and Structure-Activity Relationships of Novel Chalcone-1,2,3-triazole-azole Derivates as Antiproliferative Agents

A series of novel chalcone-1,2,3-triazole-azole hybrids were designed, synthesized and evaluated for their antiproliferative activity against three selected cancer cell lines (SK-N-SH, EC-109 and MGC-803). Most of the synthesized compounds exhibited moderate to good activity against all the cancer cell lines selected. Particularly, compound I-21 showed the most excellent antiproliferative activity with an IC50 value of 1.52 μM against SK-N-SH cancer cells. Further mechanism studies revealed that compound I-21 induced morphological changes of SK-N-SH cancer cells possibly by inducing apoptosis. Novel chalcone-1,2,3-triazole-azole derivatives in this work might be a series of promising lead compounds to develop anticancer agents for treating neuroblastoma.


Introduction
Cancer, being one of the leading causes of death globally, causes a great burden to both the society and single human lives as a whole. Although there have been progresses in the development of treatment and prevention of cancer, the success to treat cancer remains a challenge [1]. Therefore, there is still an urgent need to search for novel anticancer agents that have broader spectrum of cytotoxicity to tumor cells [2].
Chalcones are abundant in edible plants where they are considered to be the precursors of flavonoids or isoflavonoids [3] and constitute an important group of natural and synthetic products with wide range of pharmacological activities as antibacterial [4,5], anti-tumor [6,7], anti-inflammatory [8,9], antifungal and antioxidant agents [10,11]. For example, a chalcone without substituent groups (1) is cytotoxic to MCF-7 cell line with an IC 50 of 6.88 µg/mL [12]. A combretastatin-like chalcone (2) as the inhibitor of microtubule polymerization, exhibited the excellent cytotoxic activity against K562 cells with an IC 50 of 1.1 µM [13] (Figure 1). 1,2,3-triazole is a considered privileged scaffold in drug discovery with a wide array of biological activities as anti-fungal [14], anti-bacterial [15], anti-allergic [16], anti-HIV [17], anti-tubercular [18] and anti-inflammatory agents [19]. Recent research of its pharmacological effects became much more appealing and promising for the design of anticancer agents. Compound (3), a 1,2,3-triazol-naphthalimide hybrid, showed IC 50 values of 0.348 and 0.258 µM against MCF-7 and SMMC-7721 cell lines, respectively [20]. N-((1-Benzyl-1H-1,2,3-triazol-4-yl)methyl) arylamide was identified as a proprietary small molecule scaffold for potential antitumor agents by M.J. Miller group and compound (4) exhibited an IC 50 of 46 nM against MCF-7 cancer cell line [21] (Figure 1). lines, respectively [20]. N-((1-Benzyl-1H-1,2,3-triazol-4-yl)methyl) arylamide was identified as a proprietary small molecule scaffold for potential antitumor agents by M.J. Miller group and compound (4) exhibited an IC50 of 46 nM against MCF-7 cancer cell line [21] (Figure 1). On the other hand, the heterocyclic azoles, including 4,5-dihydrothiazole-2-thiol, benzo[d]thiazole-2-thiol, 1,3,4-thiadiazole-2-thiol, and 1-methyl-1H-tetrazole-5-thiol (Figure 2), represent one of the most useful cores of anticancer agents, with a wide range of activities against various cancers [22]. These above interesting findings and our continuous quest to identify more potent analogues, led to the molecular hybridization of chalcone, 1,2,3-trizole, and different azoles to integrate them in one molecular platform to generate a new hybrid architecture with the aim of exploring the impact of such modification on the anticancer agents [23,24]. The designed scaffold ( Figure 3) has four parts: 1,2,3-trizole as a central backbone, attachment of chalcone or heterocycle chalcone to a trizole unit to enchance desired pharmacophoric behavior with druglike properties, a long-chain alkoxyl group for lipophilicity, and azole units to the other side of the triazole core. In this paper we report the synthesis and evaluation of novel chalcone-1,2,3triazole-azoles as new class of antiproliferative agents. On the other hand, the heterocyclic azoles, including 4,5-dihydrothiazole-2-thiol, benzo[d]thiazole-2-thiol, 1,3,4-thiadiazole-2-thiol, and 1-methyl-1H-tetrazole-5-thiol (Figure 2), represent one of the most useful cores of anticancer agents, with a wide range of activities against various cancers [22]. These above interesting findings and our continuous quest to identify more potent analogues, led to the molecular hybridization of chalcone, 1,2,3-trizole, and different azoles to integrate them in one molecular platform to generate a new hybrid architecture with the aim of exploring the impact of such modification on the anticancer agents [23,24]. lines, respectively [20]. N-((1-Benzyl-1H-1,2,3-triazol-4-yl)methyl) arylamide was identified as a proprietary small molecule scaffold for potential antitumor agents by M.J. Miller group and compound (4) exhibited an IC50 of 46 nM against MCF-7 cancer cell line [21] (Figure 1). On the other hand, the heterocyclic azoles, including 4,5-dihydrothiazole-2-thiol, benzo[d]thiazole-2-thiol, 1,3,4-thiadiazole-2-thiol, and 1-methyl-1H-tetrazole-5-thiol (Figure 2), represent one of the most useful cores of anticancer agents, with a wide range of activities against various cancers [22]. These above interesting findings and our continuous quest to identify more potent analogues, led to the molecular hybridization of chalcone, 1,2,3-trizole, and different azoles to integrate them in one molecular platform to generate a new hybrid architecture with the aim of exploring the impact of such modification on the anticancer agents [23,24]. The designed scaffold ( Figure 3) has four parts: 1,2,3-trizole as a central backbone, attachment of chalcone or heterocycle chalcone to a trizole unit to enchance desired pharmacophoric behavior with druglike properties, a long-chain alkoxyl group for lipophilicity, and azole units to the other side of the triazole core. In this paper we report the synthesis and evaluation of novel chalcone-1,2,3triazole-azoles as new class of antiproliferative agents. The designed scaffold ( Figure 3) has four parts: 1,2,3-trizole as a central backbone, attachment of chalcone or heterocycle chalcone to a trizole unit to enchance desired pharmacophoric behavior with druglike properties, a long-chain alkoxyl group for lipophilicity, and azole units to the other side of the triazole core. In this paper we report the synthesis and evaluation of novel chalcone-1,2,3-triazole-azoles as new class of antiproliferative agents. In totally, a series of novel chalcone-1,2,3-triazole-azole derivatives were successfully synthesized, and their structures characterized by 1 H-NMR, 13 C-NMR, HRMS. Their in vitro antiproliferative activities were then tested, using a MTT assay, against three selected cancer cell lines (SK-N-SH, EC-109 and MGC-803) and compared with the well-known anticancer drug 5-fluorouracil. Most of the synthesized compounds exhibited moderate to good activity against all the cancer cell lines selected. Particularly, the promising compound I-21 showed the most excellent antiproliferative activity with an IC50 value of 1.52 μM against SK-N-SH cancer cells.

Chemistry
Alkyne intermediates 5a-5d were synthesized as shown in Scheme 1. Commercially available azoles were treated with propargyl bromide to provide 5a-5d. The general route for the synthesis of the target chalcone-1,2,3-triazole-azole analogues (I-1-I-27) was depicted in Scheme 2. Commercially available 1,3-dibromopropane was reacted with p-hydroxyacetophenone in the presence of potassium carbonate and NaN3 to form compound 6, which was subjected to click reaction with appropriately alkyne intermediates to afford 7a-7d with good yields. 7a-7d were converted to target compounds I-13-I-27 with substituted aromatic aldehyde at room tempeture in a NaOH/EtOH solution. Alkyne intermediates 5a-5d and trizole intermediates 7a-7d were easily obtained with the mature reaction conditions developed by our group [22]. The structures of the targeted compounds were characterized using spectral methods, and all spectral data corroborated the assumed structures.  In totally, a series of novel chalcone-1,2,3-triazole-azole derivatives were successfully synthesized, and their structures characterized by 1 H-NMR, 13 C-NMR, HRMS. Their in vitro antiproliferative activities were then tested, using a MTT assay, against three selected cancer cell lines (SK-N-SH, EC-109 and MGC-803) and compared with the well-known anticancer drug 5-fluorouracil. Most of the synthesized compounds exhibited moderate to good activity against all the cancer cell lines selected. Particularly, the promising compound I-21 showed the most excellent antiproliferative activity with an IC 50 value of 1.52 µM against SK-N-SH cancer cells.

Chemistry
Alkyne intermediates 5a-5d were synthesized as shown in Scheme 1. Commercially available azoles were treated with propargyl bromide to provide 5a-5d. The general route for the synthesis of the target chalcone-1,2,3-triazole-azole analogues (I-1-I-27) was depicted in Scheme 2. Commercially available 1,3-dibromopropane was reacted with p-hydroxyacetophenone in the presence of potassium carbonate and NaN 3 to form compound 6, which was subjected to click reaction with appropriately alkyne intermediates to afford 7a-7d with good yields. 7a-7d were converted to target compounds I-13-I-27 with substituted aromatic aldehyde at room tempeture in a NaOH/EtOH solution. Alkyne intermediates 5a-5d and trizole intermediates 7a-7d were easily obtained with the mature reaction conditions developed by our group [22]. The structures of the targeted compounds were characterized using spectral methods, and all spectral data corroborated the assumed structures.  In totally, a series of novel chalcone-1,2,3-triazole-azole derivatives were successfully synthesized, and their structures characterized by 1 H-NMR, 13 C-NMR, HRMS. Their in vitro antiproliferative activities were then tested, using a MTT assay, against three selected cancer cell lines (SK-N-SH, EC-109 and MGC-803) and compared with the well-known anticancer drug 5-fluorouracil. Most of the synthesized compounds exhibited moderate to good activity against all the cancer cell lines selected. Particularly, the promising compound I-21 showed the most excellent antiproliferative activity with an IC50 value of 1.52 μM against SK-N-SH cancer cells.

Chemistry
Alkyne intermediates 5a-5d were synthesized as shown in Scheme 1. Commercially available azoles were treated with propargyl bromide to provide 5a-5d. The general route for the synthesis of the target chalcone-1,2,3-triazole-azole analogues (I-1-I-27) was depicted in Scheme 2. Commercially available 1,3-dibromopropane was reacted with p-hydroxyacetophenone in the presence of potassium carbonate and NaN3 to form compound 6, which was subjected to click reaction with appropriately alkyne intermediates to afford 7a-7d with good yields. 7a-7d were converted to target compounds I-13-I-27 with substituted aromatic aldehyde at room tempeture in a NaOH/EtOH solution. Alkyne intermediates 5a-5d and trizole intermediates 7a-7d were easily obtained with the mature reaction conditions developed by our group [22]. The structures of the targeted compounds were characterized using spectral methods, and all spectral data corroborated the assumed structures.

Antiproliferative Activity and Structure Activity Relationship Analysis
All synthesized compounds were evaluated for their anticancer activity against three cancer cell lines, MGC-803 (human gastric cancer cell line), SK-N-SH (human neuroendocrine cancer cell line), and HepG-2 (human esophageal cancer cell line) using MTT assay method and compared with the well-known anticancer drug 5-fluorouracil. The results are summarized as Table 1. With the exception of chalcone-1,2,3-triazole-azoles I-1-I-27, all the compounds exhibit moderate potency against all three selected cancer lines. Among them, compounds I-14 and I-21 shows showed broad spectrum anticancer activity with IC50 values ranging from 3.57 to 8.52 μM and 1.52 to 10.42 μM, respectively (Table 1).
During the structure activity relationship studies, we found that the substituent on the benzene ring of chalcone has a remarkable effect on their antiproliferative activity. Regarding the activity results of the tested compounds against SK-N-SH cell line, compounds (I-14, I-21, I-25) with the 3,4,5-trimethoxyphenyl group on the benzene ring of chalcone showed more potent inhibitory effects (1.52-6.98 μM) than compounds (I-13, I-20, I-24) with a p-chlorine atom (Table 1). To

Antiproliferative Activity and Structure Activity Relationship Analysis
All synthesized compounds were evaluated for their anticancer activity against three cancer cell lines, MGC-803 (human gastric cancer cell line), SK-N-SH (human neuroendocrine cancer cell line), and HepG-2 (human esophageal cancer cell line) using MTT assay method and compared with the well-known anticancer drug 5-fluorouracil. The results are summarized as Table 1. With the exception of chalcone-1,2,3-triazole-azoles I-1-I-27, all the compounds exhibit moderate potency against all three selected cancer lines. Among them, compounds I-14 and I-21 shows showed broad spectrum anticancer activity with IC 50 values ranging from 3.57 to 8.52 µM and 1.52 to 10.42 µM, respectively (Table 1).
During the structure activity relationship studies, we found that the substituent on the benzene ring of chalcone has a remarkable effect on their antiproliferative activity. Regarding the activity results of the tested compounds against SK-N-SH cell line, compounds (I-14, I-21, I-25) with the 3,4,5-trimethoxyphenyl group on the benzene ring of chalcone showed more potent inhibitory effects (1.52-6.98 µM) than compounds (I-13, I-20, I-24) with a p-chlorine atom (Table 1).

Apoptosis Analysis with Hoechst-33258 Staning
Due to the most potent cytotoxic activity against three selected cancer cell lines among all synthesized derivatives [23], compound I-21 was chosen to be further investigated regarding its mechanism of action. To explore cytotoxicity of I-21 in SK-N-SH cells, cell apoptosis was investigated with Hoechst 33258 staining. After 24 h incubation with I-21 at indicated concentrations, characteristic apoptotic morphological changes were on served by fluorescence microscope, including cell rounding, chromain shrinkage and formation of apoptotic bodies ( Figure 5). The studies revealed that compound I-21 induced morphological changes of SK-N-SH cancer cells possibly by inducing apoptosis.

Western Blots Analysis
Antiproliferative agents that induce apoptosis in cancer cells are always preferred in antitumor drug discovery. Bcl-2 associated proteins have both anti-apoptotic and pro-apoptotic effects in vrious cancer cell lines. For the high potent cytotoxic activity against SK-N-SH cell line, compound I-21 was evaluated the level of Bcl-2 (apoptotic inhibitor) and Bax (apoptotic inducer) [24]. We can see from the result that compound I-21 increased the level of Bax and reduced the level of Bcl-2, which could promote apoptosis of SK-N-SH cells ( Figure 6). Further mechanism investigations are under way and will be reported in due course.

Apoptosis Analysis with Hoechst-33258 Staning
Due to the most potent cytotoxic activity against three selected cancer cell lines among all synthesized derivatives [23], compound I-21 was chosen to be further investigated regarding its mechanism of action. To explore cytotoxicity of I-21 in SK-N-SH cells, cell apoptosis was investigated with Hoechst 33258 staining. After 24 h incubation with I-21 at indicated concentrations, characteristic apoptotic morphological changes were on served by fluorescence microscope, including cell rounding, chromain shrinkage and formation of apoptotic bodies ( Figure 5). The studies revealed that compound I-21 induced morphological changes of SK-N-SH cancer cells possibly by inducing apoptosis.

Apoptosis Analysis with Hoechst-33258 Staning
Due to the most potent cytotoxic activity against three selected cancer cell lines among all synthesized derivatives [23], compound I-21 was chosen to be further investigated regarding its mechanism of action. To explore cytotoxicity of I-21 in SK-N-SH cells, cell apoptosis was investigated with Hoechst 33258 staining. After 24 h incubation with I-21 at indicated concentrations, characteristic apoptotic morphological changes were on served by fluorescence microscope, including cell rounding, chromain shrinkage and formation of apoptotic bodies ( Figure 5). The studies revealed that compound I-21 induced morphological changes of SK-N-SH cancer cells possibly by inducing apoptosis.

Western Blots Analysis
Antiproliferative agents that induce apoptosis in cancer cells are always preferred in antitumor drug discovery. Bcl-2 associated proteins have both anti-apoptotic and pro-apoptotic effects in vrious cancer cell lines. For the high potent cytotoxic activity against SK-N-SH cell line, compound I-21 was evaluated the level of Bcl-2 (apoptotic inhibitor) and Bax (apoptotic inducer) [24]. We can see from the result that compound I-21 increased the level of Bax and reduced the level of Bcl-2, which could promote apoptosis of SK-N-SH cells ( Figure 6). Further mechanism investigations are under way and will be reported in due course.

Western Blots Analysis
Antiproliferative agents that induce apoptosis in cancer cells are always preferred in antitumor drug discovery. Bcl-2 associated proteins have both anti-apoptotic and pro-apoptotic effects in vrious cancer cell lines. For the high potent cytotoxic activity against SK-N-SH cell line, compound I-21 was evaluated the level of Bcl-2 (apoptotic inhibitor) and Bax (apoptotic inducer) [24]. We can see from the result that compound I-21 increased the level of Bax and reduced the level of Bcl-2, which could promote apoptosis of SK-N-SH cells ( Figure 6). Further mechanism investigations are under way and will be reported in due course.

General Experimental Procedures
All reagents and solvents used were of analytical grade purchased from commercial sources. Thinlayer chromatography (TLC) was carried out on glass plates coated with silica gel and visualized by UV light (254 nm) (Beijing synthware glass, Beijing, China). Melting points were determined on a Beijing Keyi XT4A apparatus and are uncorrected (Beijing, China). All NMR spectra were recorded with a Bruker DPX 400 MHz spectrometer (Agilent, Santa Clara, CA, USA), with TMS as internal standard in CDCl3. Chemical shifts are given as dppm values relative to TMS. For some of novel compounds, Mass spectra (MS) were recorded on Esquire 3000 mass spectrometer (Varian, Palo Alto, CA, USA) by electrospray ionization (ESI).

General Procedure of Compounds 5a-5d
To a stirred solution of mercaptan (3 mmol) in acetone (15 mL), propargyl bromide (3 mmol) and K2CO3 (3 mmol) were added carefully and the reaction mixture was refluxed for 5 h. Upon completion, the reaction mixture was concentrated under vacuum, the residue was dissolved in EtOAc (30 mL) and washed with water, brine, dried over anhydrous Na2SO4 and concentrated under vacuum to afford compounds 5a-5d, which were used in the next reaction without further purification.  p-Aminoacetophenone (1 mmol), 1,3-dibromopropane (1 mmol) and K2CO3 (1 mmol) were dissolved in acetone (10 mL). The mixture was refluxed for 3 h, then sodium azide were added and

General Experimental Procedures
All reagents and solvents used were of analytical grade purchased from commercial sources. Thin-layer chromatography (TLC) was carried out on glass plates coated with silica gel and visualized by UV light (254 nm) (Beijing synthware glass, Beijing, China). Melting points were determined on a Beijing Keyi XT4A apparatus and are uncorrected (Beijing, China). All NMR spectra were recorded with a Bruker DPX 400 MHz spectrometer (Agilent, Santa Clara, CA, USA), with TMS as internal standard in CDCl 3 . Chemical shifts are given as dppm values relative to TMS. For some of novel compounds, Mass spectra (MS) were recorded on Esquire 3000 mass spectrometer (Varian, Palo Alto, CA, USA) by electrospray ionization (ESI).

General Procedure of Compounds 5a-5d
To a stirred solution of mercaptan (3 mmol) in acetone (15 mL), propargyl bromide (3 mmol) and K 2 CO 3 (3 mmol) were added carefully and the reaction mixture was refluxed for 5 h. Upon completion, the reaction mixture was concentrated under vacuum, the residue was dissolved in EtOAc (30 mL) and washed with water, brine, dried over anhydrous Na 2 SO 4 and concentrated under vacuum to afford compounds 5a-5d, which were used in the next reaction without further purification.  p-Aminoacetophenone (1 mmol), 1,3-dibromopropane (1 mmol) and K 2 CO 3 (1 mmol) were dissolved in acetone (10 mL). The mixture was refluxed for 3 h, then sodium azide were added and the reaction mixture was refluxed for another 2 h. Upon completion, the reaction mixture was concentrated under vacuum, the residue was dissolved in EtOAc (20 mL) and washed with water, brine, dried over anhydrous MgSO 4 and concentrated under vacuum to afford compound 6, which were used in the next reaction without further purification. compound 6 (1.05 mmol), alkyne intermediates (1 mmol), CuSO 4¨5 H 2 O (0.2 mmol) and sodium ascorbate (0.1 mmol) were dissolved in THF/H 2 O (5 mL/5 mL) to stir for 7 h at room temperature. Upon completion, the precipitated product was filtered to afford the crude product 7a-7d without further purification.

General Procedure of Compounds I-13-I-27
Compound 7a-7d (1 mmol), substituted aromatic aldehyde (1 mmol) and NaOH (1 mmol) were dissolved in ethanol (10 mL) to stir at room temperature. The reaction was monitored by TLC till the reaction was finished. Upon completion, the reaction mixture was concentrated under vacuum, the residue was dissolved in EtOAc and washed with water, brine, dried over anhydrous Na 2 SO 4 and concentrated under vacuum to afford compounds I-13-I-27 which were purified with column chromatography on silica gel (hexane/EtOAc = 6/1).