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Synthesis and Evaluation of Anticancer Activity of <em>O-allylchalcone</em> Derivatives | OMICS International
ISSN: 2161-0444
Medicinal Chemistry

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Synthesis and Evaluation of Anticancer Activity of O-allylchalcone Derivatives

Bathélémy Ngameni1*, Victor Kuete2, Pantaleon Ambassa3, kamga Justin3, Moungang Luciane Marlyse4, Abdou Tchoukoua3, René Roy5, Bonaventure Tchaleu Ngadjui1,3 and Murayama Tetsuya6

1Department of Pharmaceutical Sciences and Traditional Pharmacopoeia, Faculty of Medicine and Biomedical Sciences, University of Yaoundé I, Cameroon

2Department of Biochemistry, Faculty of Science, University of Dschang, Cameroon

3Department of Organic Chemistry, Faculty of Science, University of Yaoundé I, Cameroon

4Department of Biology and Animal Physiology, Faculty of Science, University of Yaoundé I, Cameroon

5Department of Chemistry, Université du Québec à Montréal, Québec, Canada

6Department of Chemistry, Faculty of Agriculture, University of Yamagata, Japan

*Corresponding Author:
Bathelemy Ngameni
Department of Pharmaceutical Sciences and Traditional Pharmacopoeia
Faculty of Medicine and Biomedical Sciences
University of Yaoundé I, Cameroon, P.O. Box 8664
Tel: +237 76480440
Fax: +237 22221873
E-mail: [email protected]

Received date: June 17, 2013; Accepted date: July 26, 2013; Published date: July 28, 2013

Citation: Ngameni B, Kuete V, Ambassa P, Justin K, Marlyse ML, et al. (2013) Synthesis and Evaluation of Anticancer Activity of O-allylchalcone Derivatives. Med chem 3:233-237. doi:10.4172/2161-0444.1000144

Copyright: © 2013 Ngameni B, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Abstract

A large number of novel O -allylchalcones were synthesized by Claisen Schmidt condensation reaction of O -allylvanillin 3 with appropriate substituted acetophenones 4a-h. These model chalcones 5a-h and their precursor O -allylvanillin were screened for their in vitro cytotoxicactivity against four human cancer cell lines. The most potent compound in this series with the IC 50 values below or around 10 μM were 5f against THP-1 cells (10.42 μM) and 5g against THP-1 (4.76 μM), DU-145 (5.21 μM), HL60 (7.90 μM), Hep-G2 (10.12 μM) and MCF-7 (10.32 μM).

Keywords

Synthesis; O-allylchalcones; Anticancer; Structure-activity relationship

Introduction

There is a currently a good deal of interest in the health benefits of phytochemicals, in particular prenylated and allylated flavonoids. Chalcones (1,3-diaryl-2-propen-1-ones) and their derivatives are important intermediates of flavonoid synthetic pathway. Chalcones, one of the major classes of natural products with widespread distribution in fruits, vegetables, spices, tea and soy based foodstuff have also been the subject of great interest for their interesting pharmacological activities [1]. Chemically they can be considered open-chain flavonoids in which the two aromatic rings are joined by a three-carbon α,β-unsaturated carbonyl system. Chalcones have also been reported to possess many useful biological and pharmacological properties, including antibacterial [2,3], antimalarial [4,5], antifungal [6], antiviral [7,8], anti-inflammatory [9,10], and anticancer [11,12] properties. A good safety profile, possibility of oral administration [13] and easy synthesis are the major factors contributing to the increasing interest in exploring the pharmacological activities of chalcones. Chalcones comprise one of the main classes of natural small molecules with very promising anticancer activity, related to their ability to inhibit tubulin polymerization [14]. Most of the anticancer agents, of natural or synthetic origin exhibit enone function in their structure [15,16]. Also, synthesized chalcones holding allylic substitutions were recently reported as potent antimicrobial and antioxidant agents [17,18]. In addition, the substitution of ring B with electron withdrawing groups like methoxy or hydroxy group improve the antiproliferative activity against human colon HT-29 cancer cell line [19].

Prompted by all these observations, we report herein the synthesis of novel O-allylchalcones, bearing various substituents with potent activity against Human Hep-G2 hepatocarcinoma, breast carcinoma MCF-7, prostate carcinoma DU-145, and acute monocytic leukemia THP-1 and HL-60 cell lines. The structure–activity relationships are also discussed.

Materials and Methods

Chemistry

IR spectra were determined with a Perkin Elmer FT-IR spectrophotometer. 1H and 13C NMR spectrawere recorded with Bruker WM-300 in the CDCl3 at 300 and 75 MHz, respectively using TMS as the internal standard. All chemical shifts are reported on δ scale. Mass spectra were obtained using a Varian MAT-311A. Thinlayer chromatography (TLC) was carried out using Merck silica gel 60 F-254 plates (layer thickness 0.25 mm) and all solvents were distilled prior to use.

Synthesis

Compounds 5a-h were synthesized by the condensation reaction of compound 3 with different substituted acetophenones 4a-h. The main intermediate 3 was prepared from vanillin1 and allylbromide 2 in the presence of potassium carbonate in anhydrous acetone.

Biology

Cytotoxicity assay: Cell lines and treatment: The effect of synthesized compounds on cell growth was determined on five human tumor cells including Hep-G2 hepatocarcinoma, breast carcinoma MCF-7, prostate carcinoma DU-145, and acute monocytic leukemia THP-1 and HL-60 cell lines, obtained from National Cancer Institute, USA. THP-1 and HL-60 were maintained in RPMI medium while Hep-G2, MCF-7 and DU-145 were cultured in MEM medium. All media used were supplemented with 10% fetal bovine serum (FBS), 100 IU/mL penicillin. The cell lines were maintained under standard cell culture conditions at 37°C and 5% CO2 in a humidified environment.

The cytotoxicity of the samples against the five studied human cell lines was determined using Sulphorhodamine B (SRB) assay as previously described [20]. The cells were incubated at 37 °C in an atmosphere of 5% CO2 and 95% relative humidity in a CO2 incubator. Doxorubicin was used as positive reference. Suitable controls with equivalent concentration of DMSO were also included. The optical density (OD) was recorded using a 96 well plate reader, and growth inhibition was calculated [20]. A preliminary study was first carried out with compounds (Table 1, 100 μM) and doxorubicin (at 50 μM) to detect if samples were able to inhibit the proliferation of more that 50% of the cells. Then samples were serially diluted and tested against other cell lines for IC50 determination. IC50 is the concentration of sample required to inhibit 50% of the cell proliferation after 72 h incubation and was calculated by plotting the percentage survival versus the concentration, using Microsoft Excel. For all samples, each compound concentration was tested thrice in triplicates.

Experimental

4-Allyloxy-3-methoxybenzaldehyde or O-allylvanillin (3)

To 0.304 g (1.99 mmol) of vanillin in acetone (8 mL) was added K2CO3 (0.1203 g) followed by allylbromide (0.12 mL, d = 1.43, 0.1772 g, 1.46 mmol). The reaction mixture was heated to reflux for 4 hours or left at room temperature for 48 hours. At the end of the reaction, the solvent was evaporated under reduced pressure and the residue is diluted in water (40 ml ×3). The aqueous mixture was extracted with Ethyl Acetate (EA) (3 × 60 mL) and the extract was dried by anhydrous Na2SO4. After evaporation of the solvent and purification by column chromatography on silica gel eluting with Hexane-Ethyl Acetate (Hex- EA) system of increasing polarity, product 3 was obtained (725 mg, yield 70% in Hex-EA 87.5:12.5). 1H NMR (600 MHz, CDCl3, Me4Si) δ 3.79 (3H; s), 4.45 (2H; t; J=5.7 Hz), 5.23(1H; dd; J=1.5 and 14,4 Hz), 5.34 (1H; dd; J=1.5 and 14.4 Hz), 5.95 (1H; dd; J=5.4 and 1.5 Hz), 6.84 (1H; d; J=8.4 Hz), 7.28 (1H; dd; J=7.8 and 1.5 Hz), 7.30 (1H; d; J=1.5 Hz), 9.70 (1H; s); ESIMS m/z 193.2 [M + H]+. HREIMS (m/z): 192.0776 [M+] (calcd for C11H12O3, 192.0786).

4-allyloxy-3-methoxychalcone (5a)

To a solution of acetophenone (0.18 mL, 3.41 mmol, d=1.0266) in methanol (30 mL) was added first O-allylvanillin (110 mg, 0.57 mmol) and then an aqueous solution of KOH (50%, 1 mL / mmol of acetophenone) or 3.41 mL. The reaction mixture was refluxed at 70°C for 5 hours or left at room temperature for 15 hours. At the end of the reaction the mixture was diluted with water (30 mL) and extracted with CH2Cl2 (3×70 mL) and then the extract was washed with water (50 mL) and saturated with NaCl solution. The organic phase was dried with Na2SO4 and the solvent evaporated under reduced pressure. After purification of the residue by Column Chromatography and Thin Layer Chromatography preparative on silica gel (Hex-EA 9:1), compound 5a was obtained pure (103.2 mg, yield 28% in Hex-EA 80:20). IR (CHCl3): υmax cm-1: 1654, 1579, 1257. 1H NMR (300 MHz, CDCl3, Me4Si): δ 3.70 (3H; s), 4.33 (2H; d ; J=6.5 Hz), 5.47 (1H; dd; J=17.5 and 10.9 Hz), 5.55 (1H; dd; J=17.5 and 0.9 Hz), 6.18 (1H; m ), 6.99 (1H; d; J= 8.4 Hz), 7.20 (1H; dd ; J=8.4 and 1.5 Hz), 7.27 (1H; d; J=1.5 Hz), 7.48 (1H; d; J=15.9 Hz), 7.50 (1H; m; J=8.1 and 2.1 Hz), 7.52 (1H; dd; J=8.1 and 1.5 Hz), 7.7 (1H; d; J=15.6 Hz), 7.81 (1H; dd; J=8.4 and 1.5 Hz); 13C NMR (75 MHz, CDCl3, Me4Si) δ 59.9; 69.5; 110.4; 112.8; 118.4; 120.0; 122.9; 127.4; 128.3; 129.7; 132.5; 132.6; 138.4; 144.9; 149.5; 150.5; 190.5; ESIMS m/z 295.3 [M + H]+. HREIMS (m/z): 294.1260 [M+] (calcd for C19H18O3, 294.1256).

4-allyloxy-2’,3-diméthoxychalcone (5b)

To a solution of 2-methoxyacetophenone (27, 84 μl, d=1.090) in ethanol (5 mL) was added first O-allylvanillin (38.8 mg, 0.20 mmol) and secondly an aqueous solution KOH (50%, 1 mL/mmol of acetophenone) or 0.20208 mL. The mixture was refluxed at 70°C for 5 hours or left at room temperature for 15 hours. We obtained the product 5b (42.4 mg, yield 65% in Hex-EA 87.5:12.5) after separation of the residue of the reaction. IR (CHCl3): υmax cm-1: 2368.9, 2333.6, 1653.5, 1594.8, 1250.8, 1019.5; 1H NMR (300 MHz, CDCl3, Me4Si): δ 3.93 (3H; s), 3.95 (3H; s), 4.70 (2H; d; J=1.2 Hz), 5.36 (1H; dd; J=13.5 and 12.6 Hz), 5.45 (1H; dd; J=13.5 and 1.8 Hz), 6.10 (1H; m), 6.91 (1H; d; J=8,4 Hz), 7.04 (1H; d; J=15.9 Hz) , 7.10 (1H; d; J=8.7 and 1.5 Hz), 7.15 (1H; d; J=1.8 Hz), 7.16 (1H; dd; J=8.7 and 1.8 Hz), 7.23 (1H; m) , 7.49 (1H; dd; J=9.0 and 1.5 Hz), 7.58 (1H; d; J=16.2 Hz), 7.62 (1H; d; J=7.8 and 1.5 Hz); 13C NMR (75 MHz, CDCl3, Me4Si): δ 55.3; 55.5; 69.3; 110.1; 111.1; 112.4; 117.9; 120.2; 122.2; 124.8 ; 127.8; 129.1; 129.6; 132.0; 132.3; 143.4; 149.0; 149.7; 157.4; 192,8; ESIMS m/z 325 [M + H]+. HREIMS (m/z): 324.1365 [M+] (calcd for C20H20O4, 324.1362).

4-allyloxy-3-methoxy-2', 4'-diméthylchalcone (5c)

To a solution of 2,4-dimethoxyacetophenone (48.46 μl, 0.33 mmol, d=0.997) in ethanol (7 mL) were added first O-allylvanillin (62.6 mg, 0.33 mmol), and secondly an aqueous solution of KOH (50%, 1 mL / mmol) or 0.32604 mL. The mixture was left at room temperature for 23 hours. After separation and purification of the residue of the reaction, the product 5c was obtained (53.5 mg, yield 82% in Hex-EA 85:15). IR (CHCl3): υmax cm-1: 2917.5, 2369.6, 1590.9, 1508.7, 1260.7, 1139.2; 1014.7;1H NMR (300 MHz, CDCl3, Me4Si): δ 2.55 (3H; s), 2.60 (3H; s), 4.10 (3H; s), 4.81 (2H; d; J=1.5 Hz), 5.48 (1H; dd; J=9.0 and 1.5 Hz), 5.61 (1H; dd; J=15.9 and 1.5 Hz), 6.24 (1H; m), 7.05 (1H; d; J=9.0 Hz), 7.20 (1H; d; J=15.9 Hz), 7.26 (2H; d; J=1.8 Hz), 7.28 (1H; dd; J=8.4 and 1.8 Hz), 7.29 (1H; dd; J=8.1 and 1.8 Hz), 7.58 (1H; d; J=8.1 Hz), 7.59 (1H; d; J=15.9 Hz); 13C NMR (75 MHz, CDCl3, Me4Si) δ 19.8; 20.9; 55.4; 69.2; 109.8; 112.3; 117.9; 122.3; 124.4; 125.5; 127.4; 127.9; 131.6; 132.2; 135.9; 136.7; 140.11; 145.0; 149.0; 149.8; 195.7; ESIMS m/z 323 [M + H]+. HREIMS (m/z): 322.1566 [M+] (calcd for C21H22O3, 322.1569).

4-allyloxy-3',3-diméthoxychalcone (5d)

To a solution of 3-methoxyacetophenone (71.5 μl, 0.52 mmol, d=1.094) in ethanol (7 ml) was added first O-allylvanillin (100 mg, 0.52 mmol) and secondly a KOH solution (50%, 1 mL/mmol) or 0.52 mL. The mixture is stirred in a nitrogen atmosphere at room temperature for 21 hours. After separation and purification of the residue of the reaction by CC, the product 5d was obtained (64.6 mg, yield 38% in Hex-EA 85:15). IR spectrum (CHCl3): υmax cm-1: 2917.2, 2361.7, 1658.3, 1576.3, 1508.7, 1260.5, 1140.2, 1029.9 ; 1H NMR (300 MHz, CDCl3, Me4Si): δ 3.75 (3H; s) , 3.81 (3H; s) , 4.53 (2H; d; J=5.1 Hz), 5.20 (1H; dd; J=15.9 and 1.2 Hz), 5.31 (1H; dd; J=15.9 and 9.6 Hz) , 5.92 (1H; m), 6.75 (1H; d; J=8.4 Hz), 6.98 (1H; d; J=1.5 Hz), 7.06 (1H; d; J=1.8 Hz) , 7.07 (1H; dd; J=8.4 and 1.8 Hz), 7.21 (1H; ddd; J=9.3, 1.6 and 1.5 Hz), 7.27 (1H; d; J=15.9 Hz), 7.29 (1H; dd; J=9.3 and 8.1 Hz), 7.46 (1H; dd; J=8.1 and 1.5 Hz), 7.63 (1H; d; J=15.6 Hz); 13C NMR (75 MHz, CDCl3, Me4Si): δ 55.8; 56.4; 70.1; 110.8; 113.2; 113.3; 118.8; 119.31; 120.4; 121.3; 123.4; 128.4; 129.9; 133.04; 140.2; 145.4; 149.9; 150.8; 160.2; 190.6; ESIMS m/z 649.3 [2M + H]+, 325.2 [M + H]+. HREIMS (m/z): 324.1358 [M+] (calcd for C20H20O4, 324.1362).

4-allyloxy-3-methoxy-3', 4'-diméthylchalcone (5e)

To a solution of 3,4-dimethylacetophenone (77.11 μl, 0.52 mmol, d= 1.001; nD20: 1.538) in ethanol (7 mL) was first added O-allylvanillin (100 mg, 0.52 mmol), and secondly a 0.52 mL solution of KOH (50%, 1 mL/mmol) that is 0.52 mL. The mixture was stirred at room temperature for 26 hours. After separation and purification of the residue of the reaction, we obtained the compound 5e (68.8 mg, yield 41% in Hex-EA 85:15). IR spectrum (CHCl3): υmax cm-1: 2919.0, 2361.3, 1653.5, 1508.7, 1259.7, 1136.7; 1H NMR (300 MHz, CDCl3, Me4Si) δ 2.2 (6H; s), 3.8 (3H; s), 4.50 (2H; d; J=5.6 Hz), 5.20 (1H; dd; J=17.3 and 9.6 Hz) , 5.23 (1H; dd; J=17.3 and 0.5 Hz), 5.9 (1H; m), 6.74(1H; d; J=8.6 Hz) , 7.02(1H;dd ; J=8.6 and 1.7 Hz) , 7.05 (1H;d; J=1.7 Hz), 7.10 (1H;d ; J=8.7 Hz), 7.24 (1H; d; J=15.3 Hz), 7.59 (1H; d; J=1.8 Hz), 7.60 (1H;d ; J=15.6 Hz), 7.64 (1H; dd; J=8.7 and 1.8 Hz), 13C NMR (75 MHz, CDCl3, Me4Si) δ 20.0; 20.3; 56.2; 69.9; 110.9; 113.3; 118.6; 120.5; 122.9; 126.4; 128.4; 129.8; 129.9; 132.9; 136.5; 137.2; 142.4; 144.6; 149.7; 150.5; 190.5; ESIMS m/z 323,3 [M + H]+. HREIMS (m/z): 322.1562 [M+] (calcd for C21H22O3, 322.1569).

4-allyloxy-3-methoxy-3'-methylchalcone (5f)

To a solution of 3-methylacetophenone (70.88 μl, 0.52 mmol, d = 0.986; nD20= 1.529) in ethanol (7 mL) was first added O-allylvanillin (100 mg, 0.52 mmol), and secondly a 0.52 mL solution of KOH (50%, 1 mL/mol) that is 0.52 mL. The mixture was stirred at room temperature for 24 hours. After separation and purification of the residue of the reaction product was obtained 5f (96.3 mg, yield 60% in Hex-EA 88:12). IR spectrum (CHCl3): υmax cm-1: 2927.1, 2367.7, 1655.3, 1578.9, 1506.4, 1256.9, 1132.1; 1H NMR (300 MHz, CDCl3, Me4Si) δ 2,31 (3H; s), 3.82 (3H; s), 4.54 (2H; d; J=1.4 Hz), 5.20 (1H; dd; J=13.0 and 6.6 Hz) , 5.30 (1H; dd; J=13.0 and 1.5 Hz), 5.96 (1H;m), 6.77 (1H; d; J=8.7 Hz), 7.04 (1H; d; J=1.8 Hz), 7.06 (1H; dd; J=8.7 and 1.8 Hz), 7.10 (1H; d; J=15.9 Hz), 7.23 (1H; dd; J=8.4 and 8.1 Hz) , 7.27 (1H; ddd; J=8.1; 1.8 and 1.5 Hz) , 7.6 (1H; ddd; J=8.4; 1.8 and 1.5 Hz), 7.62 (1H; d; J=15.9 Hz), 7.65 (1H; dd; J=1.8 and 1.5 Hz), 13C NMR (75 MHz, CDCl3, Me4Si) δ 21.0; 55.6; 69.3; 110.1; 112.5; 118.0; 119.9; 122.4; 125.2; 127.6; 128.0; 128.5; 131.1; 132.9; 137.9; 138.1; 144.4; 149.1; 149.9; 190.4; ESIMS m/z 309,3 [M + H]+. HREIMS (m/z): 308.1407 [M+] (calcd for C20H20O3, 308.1412).

4-allyloxy-3-methoxy-2'-methoxychalcone (5g)

To a solution of 2-methylacetophenone (139.769 μl, 1.04 mmol, d = 1.026, nD20= 1.5318) in ethanol (7 mL) was first added to O-allylvanillin (60 mg, 0.31 mmol), and secondly a 1.04166 mL solution of KOH (50%, 1 mL/mol). The reaction mixture was stirred room temperature for 24 hours. After separation and purification of the residue of the reaction, the product 5g was obtained (41.9 mg, yield 44% in Hex-EA 92:8). IR spectrum (CHCl3): υmax cm-1: 2365.7, 2336.6, 1633.9, 1590.9, 1508.7, 1262.9, 1143.8; 1H NMR (300 MHz, CDCl3, Me4Si) δ 2.35 (3H; s), 3.83 (3H; s), 4.57 (2H; d; J=1.6 Hz), 6.79 (1H; d; J=1.8 Hz) , 5.23 (1H; dd; J=14.1 and 5.7 Hz), 5.34 (1H; dd; J=14.1 and 1.8 Hz), 5.90 (1H; m), 6.81 (1H; d; J=1.8 Hz), 6.92 (1H; d; J=16.2 Hz), 7.18 (1H; dd; J=9.0 and 1.5 Hz), 7,20 (1H; dd; J=8.4 and 1.8 Hz) , 7.21 (1H; m; J=9.0 and 2.1 Hz), 7.29 (1H; m; J=9.0 and 2.1 Hz), 7.30 (1H; d; J=15.9 Hz), 7.40 (1H; d; J=9.0 and 2.1 Hz), 13C NMR (75 MHz, CDCl3, Me4Si) δ 20.02; 55.9; 69.7; 110.2; 112.8; 118.4; 122.9; 124.9; 125.4; 127.6; 127.8; 130.1; 131.1; 132.6; 136.6; 139.3; 146.2; 149.3; 150.4; 196.8; ESIMS m/z 309.3 [M + H]+. HREIMS (m/z): 308.1403 [M+] (calcd for C20H20O3, 308.1412).

4-allyloxy-3, 4’-diméthoxychalcone (5h)

To a solution of 4-methylacetophenone (151.8 μl, 1.02 mmol) in ethanol (5 mL) was first added to O-allylvanillin (75 mg, 0.39 mmol), and secondly a 1.0107 mL solution of KOH (50%, 1 mL/mol). The reaction mixture was stirred at room temperature for 24 hours. After separation and purification of the residue of the reaction, the product 5h was obtained (93.7 mg, yield 74% in Hex-EA 75:25). IR spectrum (CHCl3): υmax cm-1: 2361.5, 2336.9, 1653.5, 1600.1, 1506.8, 1256.7; 1H NMR (300 MHz, CDCl3, Me4Si) δ 3.98 (3H; s), 4.00 (3H; s), 4.77 (2H; d; J=12.6 Hz), 5.43 (1H; dd; J=12.6 and 1.0 Hz), 5.50 (1H; dd; J=12.6 Hz), 6.2 (1H; m), 6.99 (1H; d; J=8.1 Hz), 7.09 (2H; d; J=10.1 Hz), 7.26 (1H; d; J=2.1 Hz) ,7.30 (1H; dd; J=8.1 and 2.1 Hz), 7.51 (1H; d; J=15.9 Hz), 7.85 (1H; d; J=15.6 Hz), 8.12 (2H; d; J=10,1 Hz); 13C NMR (75 MHz, CDCl3, Me4Si) δ 55.4; 55.9; 69.7; 110.5; 112.9; 113.7(x2); 118.4; 119.8; 122.4; 128.2; 130.9 (x2); 131.3; 132.7; 144.0; 149.5; 150.2; 163.2; 188.7; ESIMS m/z 325.1 [M + H]+. HREIMS (m/z): 324.1358 [M+] (calcd for C20H20O4, 324.1362).

Statistical analysis

The one-way ANOVA at 95% confidence level was used for statistical analysis.

Results and Discussion

Chemistry (synthesis)

The synthesis of chalcones 5a-h was accomplished by a onepot Claisen-Schmidt condensation [21,22] between the appropriate O-allylvanillin 3 and substituted acetophenones 4a-h, as shown in Scheme 2. O-allylvanillin 3 was prepared via the nucleophilic substitution of vanillin 1 and allylbromide 2 in the presence of potassium carbonate in anhydrous acetone (Scheme 1) [22].

medicinal-chemistry-Synthesis-intermediate

Scheme 1: Synthesis of the intermediate O-allylvanillin 3.

medicinal-chemistry-Synthesis-compounds

Scheme 2: Synthesis of compounds 5a-h.

In all the chalcones synthesized, only the trans double bond (on the basis of coupling constant) was obtained. All synthesized compounds were characterized by spectral data (mass, UV, IR and NMR) and were consistent with the structures proposed. The purity of these compounds was ascertained by TLC and spectral analysis.

Biological studies

These synthesized compounds were evaluated for their in vitro anticancer activity using Sulforhodamine B assays [20]. A preliminary assay against leukemia THP-1 cell line showed that compounds 3, 5a, 5d, 5e, 5f, 5g and 5h (at 100 μM) as well as doxorubicin at 50 μM were able to inhibit the proliferation of more than 50% cells (Figure 1). These samples were consequently tested in other cell lines and the results are summarized in Table 1. It appeared that compounds 5d-h displayed cytotoxicactivities with IC50 values below 100 μM against the five cancer cell lines. In the US NCI screening program, a compound is generally considered to have in vitro cytotoxic activity, if the IC50 value following incubation between 48 and 72 h is less than 4 μg/ml or 10 μM [23]. In the present study, IC50 values below or around 10 μM were displayed by compounds 5f against THP-1 cells (IC50 of 10.42 μM) and 5g against THP-1 (IC50 of 4.76 μM), DU-145 (IC50 of 5.21 μM), HL60 (IC50 of 7.90 μM), Hep-G2 (IC50 of 10.12 μM) and MCF-7 (IC50 of 10.32 μM). Also the IC50 values obtained with doxorubicin were below 10 μM against the five cancer cell lines tested. The cytotoxicityof compounds 5g can be considered good with regards to the US NCI standard. When regarding the structure activity relationship, it appeared that the number and position of methyl group in cycle A of the synthesized chalcones influenced their activities, compound 5g with the -CH3 group in position C-2 being more active on almost the five cell lines than compounds 5a (without any methyl group) and 5f bearing -CH3 group in C-3 (Table 1). However, 5e with three -CH3 groups was less active than compound 5g and 5f (only one -CH3 group), but more active than 5a without a -CH3 group, clearly confirming the influence of the methylation on the activity of the chalcones studied. Also, when comparing the activity of the two most cytotoxic compounds 5g and 5f with those of the methoxylatedcompounds 5d and 5h, it appeared that a single methylation induced an increase in activity compared to a single methoxylation of the chalcones studied. In addition, it is also clear that, the position of -CH3 and that of -OCH3 groups influence the antiproliferative activities of compounds 5d and 5h. Although the compounds studied did not show very good cytotoxicity, the study provides additional information on structure-activity relationships with chalcones, that could allow future synthesis of more potent derivatives. In future, mechanistic studies such as the effects of compound 5g on cell cycle distribution, induction of apoptosis, caspases, and the effects on mitochondrial membrane potential will be carried out to explain the mode of action on this compound.

medicinal-chemistry-Inhibitory-percentage

Figure 1: Inhibitory percentage (%) of compounds at 100 μM and doxorubicin (50 μM) on leukemia THP-1 cancer cell line. Values mean ± SD of three experiments; Data with different superscript letters (a, b, c...) are significantly different (P < 0.05).

Tested samples Cell lines and IC50 values (μM)
THP-1 HL60 Hep-G2 DU-145 MCF-7
3 74.76 ± 3.27 63.52 ± 5.2 90.99 ± 7.72 - 90.11 ± 7.26
5a 12.80 ± 1.34 23.52 ± 2.11 - - 77.37 ± 7.12
5d 25.19 ± 1.94 20.81 ± 1.97 43.75 ± 3.42 83.73 ± 6.43 56.54 ± 3.78
5e 27.03 ± 2.03 28.70 ± 2.37 33.22 ± 3.07 37.70 ± 2.71 28.98 ± 1.91
5f 10.42 ± 0.68 13.50 ± 1.14 19.94 ± 2.15 12.23 ± 1.19 17.28 ± 2.02
5g 4.76 ± 0.51 7.90 ± 0.64 10.12 ± 0.88 5.21 ± 0.28 10.32 ± 0.86
5h 27.78 ± 3.04 37.59 ± 3.16 53.28 ± 5.32 36.48 ± 3.09 45.12 ± 3.27
Doxorubicin 1.44 ± 0.09 2.17 ± 0.26 4.31 ± 0.36 2.59 ± 0.20 6.00 ± 0.72

Table 1: Cytotoxicity of the studied compounds towards cancer cell lines.

Conclusion

In conclusion, we report here a series of new O-allylchalcone derivatives prepared by a Claisen-Schmidt condensation reaction [22] and their ability to kill tumor cells in vitro. The mechanisms of cytotoxicity underlying this process remain to be fully elucidated. Previous studies reported in the literature reveal that, flavonoids such as chalcones are known microtubule inhibitors with antimitotic activity [14]. Detailed mechanistic studies and lead optimization of these O-allylchalcone derivatives are under investigation. It is intended that results from these studies will assist in elucidating their precise mechanisms of action and provide an approach to develop new potent O-allylchalcone hybrid prototypes for further optimization and development to get new leads for the treatment of cancer.

Acknowledgements

BN, RR and MT are grateful to the Agence Universitaire de la Francophonie (AUF), Natural Sciences and Engineering Research Council of Canada (NSERC) and MATSUMAE for their financial support of this research and for a travel grant to the Department of Chemistry, Université du Québec à Montréal (Canada) and Department of Chemistry, University of Yamagata (Japan), respectively.

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