Research on Chemical Intermediates

, Volume 40, Issue 4, pp 1715–1725

Synthesis and antimicrobial activity of novel chalcone derivatives

Authors

    • Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of EducationCollege of Chemistry & Materials Science, Northwest University
  • Bingqin Yang
    • Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of EducationCollege of Chemistry & Materials Science, Northwest University
  • Zhao Cheng
    • Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of EducationCollege of Chemistry & Materials Science, Northwest University
  • Pengfei Zhang
    • Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of EducationCollege of Chemistry & Materials Science, Northwest University
  • Meipan Yang
    • Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of EducationCollege of Chemistry & Materials Science, Northwest University
Article

DOI: 10.1007/s11164-013-1076-5

Cite this article as:
Fang, X., Yang, B., Cheng, Z. et al. Res Chem Intermed (2014) 40: 1715. doi:10.1007/s11164-013-1076-5

Abstract

A series of novel 3-[N, N-bis(2-hydroxyethyl)-amino]-chalcone derivatives 3a–3j were synthesized by the aldol condensation of [N, N-bis(2-hydroethyl)-3-amino]-acetophenone 2 with aromatic aldehydes. Their structures were further confirmed by ESI-HRMS, 1H NMR, IR and elemental analysis. X-ray analysis reveals crystal 3b is a monoclinic system with P21/n space group. The antimicrobial activities of the newly synthesized chalcones in vitro were evaluated and the results indicated that most compounds presented moderate to good antimicrobial activities, especially the antifungal capability. Compounds 3a, 3d, 3f and 3g revealed obvious potency against Candida albicans with MIC values of 32 μg/mL, which were better compared with others.

Keywords

ChalconeSynthesisCrystal structureBroth tube dilution methodAntimicrobial activity

Introduction

Chalcones are the main substructures of some natural compounds and important precursors for the biosynthesis of flavonoids. To date, chalcones have been identified in a variety of plant species such as fruits, vegetables, spices, tea and soy-based foodstuffs [1]. The naturally occurring and synthesized chalcone compounds, with a common 1,3-diphenyl-2-propen-1-one framework (Fig. 1), have been reported to possess various pharmacological activities, such as antioxidation [2] anticancer [3], antileishmanial [4], cytotoxicity [5, 6], antituberculosis[7] and antimalarial [8]. Recent reports indicated the importance of chalcones as antiinflammatory and antifungal agents involved in the inhibition of cell migration and the prevention of TNF-α and lipopolysaccharide (LPS) induced neutrophil adhension [9]. Sivakumar et al. [10] found that a coating of chalcone on the polymeric surfaces could reduce the bacterial adhesion due to its bactericidal (cell membrane disruption) [11] activities.
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Fig. 1

The basic framework of chalcone

Infectious diseases, such as Candida albicans infection, is the major cause of infectious death among patients with chemotherapy-induced myelosuppression neutropenia [12], which is particularly dangerous in people with compromised immune systems such as cancer patients (undergoing immunosuppressive therapy) and AIDS patients. Moreover, increasing numbers of multidrug-resistant microbial pathogens such as methicillin-resistant staphylococcus aureus (MRSA) and vancomycin intermediate-resistant staphylococcus aureus (V-ISA) have made the treatment of infectious diseases a serious and challenging therapeutic problem in recent decades [13]. As pathogenic bacteria and fungi continuously evolve mechanisms of resistance to currently used antibiotics, the discovery and design of novel and potent antibacterial and antifungal drugs are badly needed to overcome microbial resistance and develop effective therapies [14].

With the attempt to search for better and more potential biological activity, we focus on the chalcone derivatives containing different substitutions on one or both of the phenyl rings, which may show potential antifungal and antibacterial properties. Here, we report the kind of newly designed chalcone analogues with N-alkyl moiety and different substitutions in a chalcone framework, and the potential antifungal and antibacterial activities of them are also described along with some of their chemical properties.

Experimental

Chemistry and apparatus

Melting points were taken on a XT-4 micro-melting point apparatus and are uncorrected. FT-IR spectra were recorded in KBr disks on an EQUINOX-55 FTIR spectrometer. 1H NMR spectra were run on an INOVA-400 NMR spectrometer with TMS as internal standard. Elemental analyses were carried out on a Vario EL-III CHNOS analyzer. Electron Spray Ionization-Mass Spectrometry (ESI–MS) analyses were carried out in positive ion modes using a Thermo Finnigan LCQ Advantage MAX LC/MS/MS. Column flash chromatography was carried out on Merck silica gel (250-400 mesh ASTM). The processes of the reactions were monitored by analytical thin-layer chromatography (TLC) using Merck silica gel plates 60 GF-254. Solvents and chemicals used for synthesis were commercially available and were used without further purification unless otherwise noted.

Synthesis

3-Aminoacetophenone (1)

Iron powder (3.9 g, 60 mL) was activated by refluxing it with the mixture of 10 mL distilled water, ethanol (40 mL), glacial acetic acid (1 mL) and NH4Cl (0.2 g, 4 mmol) for 0.5 h under vigorous stirring at 80 °C, then ethanol (10 mL) and 3-nitroacetophenone (1.65 g, 10 mmol) were added to the mixture within 10 min. The mixture was then heated slowly under vigorous stirring for 2 h. The hot reaction mixture then filtered and the residue was washed with ethanol 3 times. After evaporation of alcohol, the residue was diluted with water and extracted with V (CHCl3) : V (CH3OH) = 2:1 for 3 times, the extraction was dried over anhydrous Na2SO4 and the solvent was evaporated at reduced pressure. The crude was purified on a flash column [V (CH3CO2Et) : V (petroleum ether) = 2:1 as eluent] to give 3-aminoacetophenone 1. Yield 84 % of white solid. m.p. 96–97 °C; 1H NMR (400 MHz, CDCl3) δ: 7.32 (dd, J = 7.6, 0.8 Hz, 1H, H-5), 7.24 (t, J = 7.8 Hz, 2H, H-1 and H-4), 6.89–6.84 (m, 1H, H-3), 3.90 (s, 2H, –NH2), 2.55 (s, 3H, –CH3); IR(KBr) ν: 3,467, 3,369, 3,222, 1,668, 1,628, 1,597, 1,490, 1,457, 1,356, 1,324, 1,236, 777, 683 cm−1; Anal. Calc. for C8H9NO: C, 71.09; H, 6.7; N, 10.36; Found: C, 70.81; H, 6.73; N, 10.72.

(E)-[N,N-bis(2-hydroethyl)-3-amino]-acetophenone (2)

A mixture of 3-aminoacetophenone (6.4 g, 47.5 mmol), 2-chlorothanol (16 mL, 240 mmol) and CaCO3 (6.5 g, 65 mmol) in water (60 mL) was heated under reflux with vigorous stirring for 7 h. After hot filtering, the unreacted CaCO3 was washed with few portions of hot water, then the filtrate was extracted with CH2Cl2 (40 ml × 3) dried over anhydrous MgSO4 and concentrated under reduced pressure to afford a yellow oil. The residue was further purified by flash column chromatography [V (CH3CO2Et) : V (petroleum ether) = 2:1 as eluent] to give the required diol 2. Yield: 68 % of faint yellow liquid. 1H NMR (400 MHz, CDCl3) δ: 7.20–7.24 (m, 3H, Ar–H), 6.85–6.87 (m, 1H, Ar–H), 4.74 (s, 2H, –OH), 3.77 (s, 4H, –OCH2–), 3.53–3.54 (d, J = 4.8 Hz, 4H, –NCH2–), 2.49 (s, 3H, –CH3). IR (KBr) ν: 3,378, 2,933, 2,880, 1,673, 1,597, 1,494, 1,444, 1,357, 1,267, 1,178, 1,010, 779, 688 cm−1. HRMS calcd for C12H17NO2: 246.1105 (M+Na)+; Found: 246.1101; Anal. Calc. for C12H17NO2: C, 64.55; H, 7.67; N, 6.27; Found: C, 64.61; H, 7.68; N, 6.26.

General procedure for the preparation of compounds 3a-3i

To the solution of [N, N-bis(2-hydroethyl)-3-amino]-acetophenone (3 mmol) and substituted aromatic aldehydes (3 mmol) in ethanol (9 mL) a solution of 2.5 M sodium hydroxide of (1 mL) was added slowly within 10 min in an ice bath. After stirring for 4–6 h at room temperature, the formed precipitate was left. The mixture was extracted with CH2Cl2 (10 mL × 3) dried over MgSO4. After the solvent was evaporated under reduced pressure, the crude product was obtained, the crude chalcones was further purified by flash column chromatography SiO2. The yield, melting point and spectral date of each compound had been collected as below.

(E)-3′-[N,N-Bis(2-hydroxyethyl)-amino-phenyl]-1-phenyl-prop-2-en-1-one (3a) Yield: 87 % of light yellow solid. m.p. 94–96 °C; 1H NMR (400 MHz, CDCl3) δ: 7.74 (dd, J = 15.7, 2.2 Hz, 1H, H-17), 7.64–7.58 (m, 2H, H-16 and Ar–H), 7.48–7.44 (m, 1H, Ar–H), 7.42–7.38 (m, 3H, Ar–H), 7.31–7.26 (m, 3H, Ar–H), 6.93–6.91 (m, 1H, Ar–H), 4.17 (s, 1H, –OH), 4.02 (s, 1H, –OH), 3.87–3.82 (m, 4H, –OCH2–), 3.63–3.58 (m, 4H, –NCH2–). IR (KBr) ν: 3,239, 2,958, 2,926, 1,665, 1,590, 1,489, 1,443, 1,353, 1,320, 1,272, 1,066, 998, 764, 688 cm−1. HRMS calcd for C19H21NO3: 334.1414 (M+Na)+; Found: 334.1407. Anal. Calc. for C19H21NO3: C, 73.29; H, 6.80; N, 4.50; Found: C, 73.36; H, 6.78; N, 4.51.

(E)-3′-[N,N-Bis(2-hydroxyethyl)-amino-phenyl]-1-(4-chlorophenyl)prop-2-en-1-one (3b) Yield: 83.5 % of orange red powder solid. m.p. 115–117 °C; 1H NMR (400 MHz, CDCl3) δ: 7.69 (d, J = 15.7 Hz, 1H, H-17), 7.55 (d, J = 8.4 Hz, 2H, H-16 and Ar–H), 7.44 (s, 1H, Ar–H), 7.40–7.36 (m, 2H, Ar–H), 7.34–7.27 (m, 3H, Ar–H), 6.94–6.90 (m, 1H, Ar–H), 3.87 (t, J = 4.7 Hz, 4H, –OCH2–), 3.68 (s, 2H, –OH), 3.63 (t, J = 4.7 Hz, 4H, –NCH2–). IR(KBr) ν: 3,417, 2,923, 1,655, 1,587, 1,488, 1,446, 1,391, 1,228, 1,072, 815, 770, 727, 680 cm−1. HRMS calcd for C19H20ClNO3: 346.1204 (M+H)+; Found: 346.1201. Anal. Calc. for C19H20ClNO3: C, 65.99; H, 5.83; N, 4.05; Found: C, 66.06; H, 5.81; N, 4.04.

(E)-3′-[N,N-Bis(2-hydroxyethyl)-amino-phenyl]-1-(2-chlorophenyl)prop-2-en-1-one (3c) Yield: Yield: 91 % of deep yellow solid. m.p. 88–90 °C; 1H NMR (400 MHz, CDCl3) δ: 8.13 (d, J = 15.8 Hz, 1H, H-17), 7.73 (dd, J = 6.8, 2.5 Hz, 1H, H-16)  7.43 (d, J = 15.7, 9.0 Hz, 2H, Ar–H), 7.35–7.28 (m, 5H, Ar–H), 6.92 (d, J = 7.7 Hz, 1H, Ar–H), 3.88 (t, J = 4.8 Hz, 4H, –OCH2–), 3.83 (s, 2H, –OH), 3.64 (t, J = 4.7 Hz, 4H, –NCH2–). IR(KBr) ν: 3,415, 3,268, 2,924, 2,867, 1,658, 1,592, 1,496, 1,462, 1,434, 1,391, 1,266, 1,183, 1,082, 749, 684 cm−1. HRMS calcd for C19H20ClNO3: 346.1204 (M+H)+; Found: 346.1197. Anal. Calc. for C19H20ClNO3: C, 65.99; H, 5.83; N 4.05; Found: C, 65.92; H, 5.85; N, 4.06.

(E)-3′-[N,N-Bis(2-hydroxyethyl)-amino-phenyl]-1-(2,4-dichlorophenyl)prop-2-en-1-one (3d) Yield: 82 % of yellow powder solid. m.p. 102–103 °C; 1H NMR (400 MHz, CDCl3) δ: 8.03 (d, J = 15.8 Hz, 1H, H-17), 7.65 (d, J = 8.5 Hz, 1H, H-16), 7.45 (d, J = 1.9 Hz, 1H, Ar–H), 7.38 (d, J = 15.8 Hz, 1H, Ar–H), 7.33–7.26 (m, 4H, Ar–H), 6.95–6.89 (m, 1H, Ar–H), 3.93 (s, 2H, -OH), 3.86 (t, J = 4.7 Hz, 4H, –OCH2–), 3.62 (t, J = 4.6 Hz, 4H, –NCH2–). IR(KBr) ν: 3,251, 2,918, 2,861, 1,660, 1,587, 1,492, 1,465, 1,351, 1,226, 1,081, 1,002, 818, 773, 679 cm−1. HRMS calcd for C19H19Cl2NO3: 380.0815 (M+H)+; Found: 380.0810. Anal. Calc. for C19H19Cl2NO3: C, 60.01; H, 5.04; N, 3.68; Found: C, 60.13; H, 5.03; N, 3.66.

(E)-3′-[N,N-Bis(2-hydroxyethyl)-amino-phenyl]-1-(4-bromophenyl)prop-2-en-1-one (3e) Yield: 84 % of orange red lumpish solid. m.p. 121–122 °C; 1H NMR (400 MHz, CDCl3) δ: 7.66 (d, J = 15.7 Hz, 1H, H-17), 7.53 (d, J = 8.5 Hz, 2H, H-16 and Ar–H), 7.47 (d, J = 8.5 Hz, 2H, Ar–H), 7.42 (d, J = 15.7 Hz, 1H, Ar–H), 7.33–7.26 (m, 3H, Ar–H), 6.90 (dd, J = 7.9, 1.4 Hz, 1H, Ar–H), 4.03 (s, 2H, –OH), 3.85 (s, 4H, –OCH2–), 3.61 (t, J = 4.8 Hz, 4H, –NCH2–). IR(KBr) ν: 3,376, 2,922, 1,656, 1,587, 1,486, 1,444, 1,318, 1,231, 1,060, 1,000, 854, 769, 725, 681 cm−1. HRMS calcd for C19H20BrNO3: 390.0699 (M+H)+; Found: 390.0690. Anal. Calc. for C19H20BrNO3: C 58.47; H, 5.17; N, 3.59; Found C, 58.59; H, 5.15; N, 3.58.

(E)-3′-[N,N-Bis(2-hydroxyethyl)-amino-phenyl]-1-(2-fluorophenyl)prop-2-en-1-one (3f) Yield: 91 % of Orange red powder solid. m.p. 80–82 °C; 1H NMR (400 MHz, CDCl3) δ: 7.82 (d, J = 15.9 Hz, 1H, H-17), 7.60 (m, 1H, H-16), 7.53 (d, J = 15.9 Hz, 1H, Ar–H), 7.39–7.32 (m, 1H, Ar–H), 7.28 (dd, J = 12.7, 4.8 Hz, 3H, Ar–H), 7.17 (t, J = 7.5 Hz, 1H, Ar–H), 7.10 (dd, J = 10.4, 8.7 Hz, 1H, Ar–H), 6.89 (dd, J = 7.4, 2.2 Hz, 1H, Ar–H), 4.46 (s, 2H, –OH), 3.82 (d, J = 4.2 Hz, 4H, –OCH2–), 3.59 (t, J = 4.8 Hz, 4H, –NCH2–). IR(KBr) ν: 3,486, 3,376, 2,930, 2,875, 1,652, 1,583, 1,488, 1,450, 1,353, 1,221, 1,067, 1,027, 855, 752 cm−1. HRMS calcd for C19H20FNO3: 330.1500 (M+H)+; Found: 330.1502. Anal. Calc. for C19H20FNO3: C, 69.29; H, 6.12; N, 4.25; Found: C, 69.36; H, 6.10; N, 4.24.

(E)-3′-[N,N-Bis(2-hydroxyethyl)-amino-phenyl]-1-(4-dimethylaminophenyl)prop-2-en-1-one (3g) Yield: 76 % of kermesinus solid. m.p. 106–108 °C; 1H NMR (400 MHz, CDCl3) δ: 7.73 (d, J = 15.5 Hz, 1H H-17), 7.52 (d, J = 8.3 Hz, 2H, H-16 and Ar–H), 7.25 (5H, t, J = 10.8 Hz, Ar–H), 6.87 (dd, J = 4.3, 2.2 Hz, 1H, Ar–H), 6.68 (d, J = 8.3 Hz, 2H, Ar–H), 3.93 (s, 2H, OH), 3.86 (t, J = 4.4 Hz, 4H, –OCH2–), 3.61 (t, J = 4.2 Hz, 4H,–NCH2–), 3.03{s, 6H,–N(CH3)2}. IR(KBr) ν: 3,421, 2,882, 1,638, 1,606, 1,564, 1,523, 1,439, 1,367, 1,225, 1,166, 1,066, 809, 777, 734, 678 cm−1. HRMS calcd for C21H26N2O3: 377.1836 (M+Na)+; Found: 377.1835. Anal. Calc. for C21H26N2O3: C, 71.16; H, 7.39; N, 7.90; Found: C, 71.23; H, 7.37; N, 7.88.

(E)-3′-[N,N-Bis(2-hydroxyethyl)-amino-phenyl]-1-(4-fluorophenyl)prop-2-en-1-one (3h) Yield: 89 % of light yellow powder solid. m.p. 103–105 °C; 1H NMR (400 MHz, CDCl3) δ: 7.70 (d, J = 15.7 Hz, 1H, H-17), 7.60 (dd, J = 7.4, 5.7 Hz, 2H, H-16 and Ar–H), 7.40–7.24 (m, 4H, ArH), 7.09 (t, J = 8.1 Hz, 2H, Ar–H), 6.90 (d, J = 7.6 Hz, 1H, H-2), 4.20 (s, 2H, –OH), 3.84 (t, J = 4.5 Hz, 4H, –OCH2–), 3.6–3.55 (m, 4H, –NCH2–). IR(KBr) ν: 3,247, 2,927, 2,871, 1,661, 1,589, 1,502, 1,440, 1,354, 1,223, 1,184, 1,067, 1,002, 830, 783, 699 cm−1. HRMS calcd for C19H20FNO3: 330.1500 (M+H)+; Found: 330.1503. Anal. Calc. for C19H20FNO3: C 69.29, H 6.12, N 4.25; Found: C 69.42, H 6.10, N 4.24.

(E)-3′-[N,N-Bis(2-hydroxyethyl)-amino-phenyl]-1-(4-nitrophenyl)prop-2-en-1-one (3i) Yield: 85 % of kermesinus solid. m.p. 164–166 °C; 1H NMR (400 MHz, CDCl3) δ: 7.87 (d, J = 8.4 Hz, 2H, H-17 and H-16), 7.77 (d, J = 15.4 Hz, 1H, Ar–H), 7.59 (dd, J = 25.3, 8.6 Hz, 3H, Ar–H), 7.30 (d, J = 15.5 Hz, 1H, Ar–H), 6.70 (d, J = 8.8 Hz, 2H, Ar–H), 3.86-3.78 (m, 4H, –OCH2–), 3.7-3.63 (m, 4H, –NCH2–). IR(KBr) ν: 3,424, 2,925, 1,655, 1,590, 1,513, 1,497, 1,448, 1,387, 1,232, 1,103, 1,052, 840, 777, 747 cm−1. HRMS calcd for C19H20N2O5: 379.1264 (M+Na)+; Found: 379.1262. Anal. Calc. for C19H20N2O5: C 64.04, H 5.66, N 7.86; Found: C 64.10, H 5.65, N 7.84.

(E)-3′-[N,N-Bis(2-hydroxyethyl)-amino-phenyl]-1-(2-sulfophenyl)prop-2-en-1-one (3j) To the solution of [N, N-bis(2-hydroethyl)-3-amino]-acetophenone (3 mmol) and 2-formylbenzenesulfonic acid sodium salt (3 mmol) in ethanol (9 mL) a solution of 2.5 M sodium hydroxide of (1 mL) was added slowly within 10 min in an ice bath. After stirring for 4–6 h at room temperature, the reactant was poured into water, then 2 M HCl was added to precipitate the product. The crude solid was recrystallized from water, giving a gray solid. Yield: 87 %. m.p. 243–245 °C; 1H NMR (400 MHz, DMSO-d6) δ: 8.77 (d, J = 14.7 Hz, 1H, H-17), 7.98–7.70 (m, 3H, Ar–H), 7.47 (d, J = 39.0 Hz, 5H, Ar–H), 6.01 (s, 4H, –OH, and Ar–H), 3.64 (s, 4H, –OCH2–), 3.54 (s, 4H, –NCH2–). IR(KBr) ν: 3,364, 3,037, 2,949, 1,658, 1,582, 1,466, 1,380, 1,237, 1,169, 1,079, 1,018, 862, 758, 710, 615 cm−1. HRMS calcd for C19H21NSO6: 390.1005(M–H); Found: 390.1022. Anal. Calcd for C19H21NSO6: C, 55.20; H, 4.88; N, 3.41; Found: C, 55.34; H, 4.87; N, 3.41.

Pharmacology

The following micro-organisms were used for detecting antimicrobial activity: Staphylococcus aureus ATCC 25923, Bacillus subtilis ATCC 6633, Candida albicans ATCC 10231, Pseudomonas aeruginosa ATCC 27853, Serratia typhi ATCC 14028 and Escherichia coli ATCC 25922. All were obtained from the Institute of Microbiology of Shaanxi province.

The preliminary screening for antibacterial as well as antifungal activity of the ten tested compounds in DMSO (25 mg/mL) was evaluated using plate-hole diffusion assay [15, 16]. A twofold serial dilution technique [17] was used to determine the minimum inhibitory concentration (MIC) values of the screened compounds. The MIC value was considered as quantitative method and was used for evaluation of the antimicrobial activity of the synthesized compounds against the given microbes.

Preliminary screening for antimicrobial activity

Suspensions of the above-mentioned micro-organisms were prepared by inoculating fresh stock cultures into separate broth tubes, each containing (8 mL) of Muller–Hinton broth for colonies of bacterial strains and fungal strains. The inoculated tubes were incubated at 37 and 28 °C for 24 h, for bacterial and fungal strains, respectively. Then, 250 μL of bacterial culture (~106–108 bacteria every mL) was added aseptically to 20 mL of solid culture (a mixture of Tryptone, Sabouraud dextrose agar and Yeast Extract) at 45 °C, mixed well, and poured into a sterile Petri dish (90 mm). A sterile cork-borer of 6 mm diameter was used to make 2 wells on each of the Petri dish. One was filled with 10 μL of the screened compounds. In order to check the effect of the solvent, a control test was also performed containing only DMSO. Then the cultures were incubated at 37 and 28 °C for 24 h for the bacterial and fungal strains. After incubation, the zone of inhibition on the plates was recorded. The compounds with the diameter of the growth-inhibition zones greater than 6 mm were considered positive, and can be screened for further determination of the minimum inhibitory concentration (MIC) values. The test was repeated three times for each compound. All the new compounds (3a–3j) were subjected to preliminary biological screening.

Determination of the minimum inhibitory concentration (MIC)

A broth tube dilution method [17, 18] was followed to determined the MIC values for all the screened compounds against the micro-organisms, and for comparison ciprofloxacin was used as a reference. For sample preparation, each of the test compounds and reference were dissolved in DMSO at a concentration of 1,280 μg/mL, and further dilutions of the compounds and reference in culture medium MHB (Müller–Hinton Broth) were prepared at the required quantities of 128, 64, etc., down to 0.125 μg/mL. Bacterial strains and fungal strains were maintained on MHA (Müller–Hinton Agar) medium at 37 and 28 °C for 24 h, respectively. The microbial inocula were prepared by suspension in 10 mL of culture medium for colonies from culture on MHA. The cell density of each inoculum was adjusted in culture medium of a 0.5 McFarland standard. The final amount applied was 105 CFU/mL for bacteria and fungi. The microbial inocula were added to the twofold diluted samples. MIC values were read after incubation at 37 and 28 °C for bacterial and fungal strains, respectively. After 24 h, the last tube with no growth of micro-organisms was recorded to represent the MIC value expressed in mg/mL. All experiments were carried out three times.

Results and discussion

Synthesis

The N-alkoxylated chalcones were synthesized by the base-catalyzed Claisen–Schmidt condensation [19] of 3-[N,N-bis(2-hydroxyethyl)-amino]-acetophone with appropriate aromatic aldehydes; the synthesis route is illustrated in Scheme 1. Intermediate 3-[N,N-bis(2-hydroxyethyl)-amino]-acetophone 2 was synthesized through the hydroxyethylation of 3-aminoacetophenone 1 with 2-chlorothanol [20]. While 3-amino-aceophenone 1 was prepared from 3-nitroacetophenone by reduction with Fe/NH4Cl-CH3COOH [21]. Ten substitued chalcone derivatives were synthesized, and their structures were confirmed by IR, 1H NMR, mass spectrometry techniques, and elemental analyses. Crystal of chalcone 3b was also obtained through the solvents evaporation method, and its X-ray single crystal diffraction data was collected. All the spectral and crystal data are given as supporting information.
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Scheme 1

Synthetic scheme for the synthesis of compounds 1, 2, 3a–3j. Reagents and conditions: a Fe, NH4Cl, CH3COOH, ethanol, reflux, 2 h; b CaCO3, 2-chlorothanol, H2O, 120 °C, 7 h; c 2.5 M NaOH, ethanol, r.t., 3–6 h

Crystal and molecular structure

Chalcones are cross-conjugated molecules, and the carbonyl group in these systems breaks the conjugation system into two independent parts to have a 2D β character [22]. In the molecular structure of chalcone 3b, a Cl atom and a N,N-bis(2-hydroxyethyl)-amino group existed in the para position of the B ring and the meta-position of the other, respectively (Fig. 2), and an electron acceptor carbonyl (C=O) group at the middle form a donor-π-accept-π-withdrawing (D-π-A-π-W) system, where charge transfer takes place from the donor end to the withdrawing end. The electron transfer mode may help to align the molecule in a parallel head-to-tail alignment in the crystal packing.
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Fig. 2

A molecular drawing of the asymmetric unit of the compound 3b

X-ray analysis reveals crystal 3b is a monoclinic system with an P21/n space group. The bond lengths and angles are generally normal in compound 3b, which is in good agreement with the literature report [23]. The two benzene rings [C3, C2, C4, C5, C6, C1] and [C10, C11, C12, C13, C14, C15] are fairly planar, respectively, and the dihedral angles between the aromatic rings are 27.94°. In the crystal lattice, there are several potentially weak hydrogen bond inter- and intra-molecular interactions [O2–H2···O3, 2.763 Å, 175°, symmetry code i: (x, y, z); O3–H3···O2, 2.720 Å, 165°, symmetry code: (x, y, z); C11–H11···O3, 3.292 Å, 136°, symmetry code: (x, y, z)]. The crystal packing is further stabilized by these hydrogen bonds.

Biological evaluation

Ten of newly synthesized chalcones were evaluated for their antibacterial activity in vitro against Gram-positive bacteria: S. aureus and B. subtilis; Gram-negative bacteria: P. aeruginosa, E. coli and S. typhi; and anti-fungal activity against C. albicans. The results of preliminary biological screening of all the newly synthesized chalcones against the above strains are presented in Table 1. As we can see, most chalcones exhibited moderate antibacterial activity for Gram-positive bacteria (S. aureus and B. subtilis) and Gram-negative strains (P. aeruginosa, S. typhi and E. coli) except 3b, 3c, 3h and 3i. Compounds 3d and 3e did not show any activity at all to B. subtilis. Also, 3e showed no potency against E. coli and P. aeruginosa. Interestingly, unexpected results were obtained that all the chalcones revealed moderate to good activity against fungus (C. albicans). Thus, we screened all the other compounds except 3b, 3c, 3h, 3j for further determining of MIC values.
Table 1

Antimicrobial activitya of the newly synthesized chalconesa (Cchalcones = 25 mg/mL)

Compounds

Fungi

Gram-positive bacteria

Gram-negative bacteria

C. albicans

B. subtilis

S. aureus

P. aeruginosa

S. typhi

E. coli

3a

+++

++

++

++

++

++

3b

+

3c

+

++

3d

+++

++

++

++

3e

+

++

++

3f

+++

++

++

++

++

++

3g

+++

++

++

++

++

++

3h

+

3i

+

3j

+++

++

++

++

+ +

++

Values were the averages of duplicate experiments

aActivity was determined from plate-hole diffusion assays with values to indicate the diameters of zones of growth inhibition around the holes. The diameter of zones of inhibition

+++ >10 mm, ++ 8−10 mm, + 6−8 mm, − <6 mm

The minimum inhibitory concentration [24] (MIC) values of the screened compounds are outlined in Table 2. Compound 3f with 2-F in the B ring exhibited a high potency against C. albicans and S. typhi, with MIC values of 32 and 64 μg/mL, respectively. This compound is also effective in inhibiting the growth of the rest of microorganism. Compounds 3 g and 3j possessing 4-F and 2-SO3H in the B ring revealed good antifungal activity against C. albicans with MIC value of 32 μg/mL, while compounds 3e and 3d have a lower degree of potency against all the tested microbes. Compound 3a with no substituent in the B ring showed good antifungal activity, and moderate to obvious antibacterial activity. Compounds 3a, 3g and 3j revealed potent inhibitory effects against C. albicans, which were as active as the standard drug (ciprofloxacin) but less active than it. Combining the results of the preliminary biological screening test, it seemed that with substituent as fluorine or no substituent in the B ring, the newly synthesized chalcones showed potent inhibitory effects against both all the tested microbes, especially the fungi. While substituent such as with the chloride, nitro, and dimethylamino groups or bromine in the B ring, the new chalcones revealed less or even no inhibitory effects. And as we have seen, there is no significant difference of antimicrobial activity observed when the electron-withdrawing groups took the place of electron-donating ones on the phenyl ring, and those are consistent with the related report [25]. Thus, it was predicted that the electronic effect of the substituent on the phenyl rings may not be the key factor influencing antimicrobial activity as much as we assumed.
Table 2

MIC values of antimicrobial activity of the screened compounds

Compounds

MIC(ug mL−1)

Fungi

Gram-positive bacteria

Gram- negative bacteria

C. albicans

S. aureus

B. subtilis

P. aeruginosa

S. typhi

E. coli

3a

32

64

128

128

64

128

3d

128

128

Nta

>128

128

Nt

3e

128

128

Nt

Nt

128

Nt

3f

32

128

128

128

64

128

3g

32

128

128

128

128

>128

3j

32

128

128

128

128

>128

Ciprofloxacinb

2.00

0.25

0.125

2.00

16

0.125

Minimum inhibitory concentration of the screened compounds were determined using broth tube technique, values were the average ones of duplicate experiments

aNt not tested

bCiprofloxacin was used as a control

Conclusion

In conclusion, a series of novel 3′-[N, N-Bis(2-hydroxyethyl)-amino]-chalcone derivatives were synthesized, characterized and evaluated for their antimicrobial activity. The results of preliminary screening of 10 compounds showed that only 6 of them revealed antimicrobial activities, and of those some presented moderate to good potency against the selected microorganisms, especially against C. albicans. Compounds 3a, 3d, 3f and 3g revealed obvious potency against C. albicans with MIC value of 32 μg/mL, and this reveals that these compounds may be of potential value in using as antifungal agents. The results may provide us a new prospect of the structure modifications of chalcones derivatives for further biological investigations. On the other hand, more chalcone derivatives of this kind with different substitutions need to be designed and synthesized for further investigation of the analysis of structure–activity relationships (SAR).

X-ray crystallography data

All measurements of compound 3b was made on a Bruker Smart APEX II CCD diffractometer with graphite monochromated Mo–Ka radiation. The data was collected at a temperature of 296(2) K using the ω-2θ scan technique. Crystal data and structural refinement parameters, and selected bond angles (Å) and bond lengths (°) of 3b are summarized in Table S1 and Table S2, respectively (see supporting information). CIF files of compound 3b have been deposited with the Cambridge Structural Database (CCDC No. 886491). Copies of the data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html or from the CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK; Tel: (+44) 1223-336-408; fax: (+44) 1223-336-033. E-mail:deposit@ccdc.cam.ac.uk.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (No. 21172178). The authors are grateful to Prof. KeWu Yang for his useful comments on biological activity test.

Supplementary material

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Supplementary material 1 (DOC 4923 kb)

Copyright information

© Springer Science+Business Media Dordrecht 2013