# Synthesis of Cinnamanilide Derivatives and Their Antioxidant and Antimicrobial Activity

Authors: Satish Balasaheb Nimse; Dilipkumar Pal; Avijit Mazumder; Rupa Mazumder
Journal: Journal of Chemistry
 (2015)

---

## Abstract

The amide derivatives of cinnamic acid were synthesized and their antimicrobial and antioxidant activities were investigated. The investigation of antimicrobial potentials of the compounds demonstrated a strong activity against 21 bacterial strains comprising Gram-positive and Gram-negative bacteria. Compounds2a,2b, and3b showed strong antimicrobial activity against all microorganisms with the pMIC value ranging from 2.45 to 3.68. Compounds2a,3a, and3b demonstrated strong antioxidant activity with % inhibition of the DPPH radical of 51% (±1.14), 41% (±1.01), and 50% (±1.23), respectively. These findings indicate that the amide derivatives of the cinnamic acid possess strong antibacterial and antioxidant activities.


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## Body

## 1. Introduction

Discovery of simple organic compounds with the antimicrobial and antioxidant activities is of growing concern in the food industries for their preservative properties [1, 2]. Preservation of industrial food containing polyunsaturated fatty acids (eicosapentaenoic (20:5ω-3) acid) has been a subject of growing interest, because of their importance in human nutrition. ω-3-Polyunsaturated fatty acids have several health benefits in cardiovascular disease, immune disorders, inflammation, allergies, and diabetes [3]. Therefore, the development of the antimicrobial compounds that can act as food preservatives by inhibiting the growth of bacteria or fungi, including mold, is very important [4].Apart from the bacterial deterioration, the radical associated oxidation of fatty acids is one of the most important reactions leading to a degeneration of food [5, 6]. Several compounds with the antioxidant activity have been used to slow down the radical associated oxidative reactions. Antioxidants are molecules that inhibit or quench free radical reactions and delay or inhibit the cellular damage [7, 8]. The butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and tertiary butylhydroquinone (TBHQ) have been used commonly as food antioxidants. However, some of these molecules are known to possess toxic and carcinogenic side effects in animal models [9]. Therefore, the demand has increased because of questions about the long-term safety and negative consumer perception of the commonly used synthetic antioxidants BHT and BHA. The discovery of compounds that can show both antimicrobial and antioxidant activities with no toxic effects on health is highly awaited.Due to its common occurrence in plants and its low toxicity [10, 11], cinnamic acid has been evaluated as an antioxidant compound [12, 13]. Moreover, the cinnamic acid derivatives are reported to possess better antimicrobial activity than cinnamic acid itself [14, 15]. In the present paper the synthesis, antimicrobial, and antioxidant activities of the amide derivatives of cinnamic acid are presented.


## 2. Materials and Methods

All chemicals, solvents, and biochemical reagents were of analytical grade and purchased from commercial sources. 1,1-Diphenyl-2-picrylhydrazyl (DPPH) was purchased from Aldrich Chemical Co. (Milwaukee, WI, USA). UV-Vis spectra were obtained on a Perkin-Elmer 554 double beam spectrophotometer. The final products were characterized by1H and 13C NMR (JEOL FX-90Q FT NMR, 300 MHz) and mass spectrometry (JEOL JMS 600 Mass Spectrometer).


### 2.1. General Procedure for the Synthesis of Compounds2a–2g and3a-3b

Compounds2a–2d and3a-3b (Scheme 1) were synthesized by slight modification of the typical procedure adopted for various cinnamic acid derivatives [16, 17]. To a stirred solution containing aniline derivatives or amine derivatives (25 mmol), K2CO3 (4.15 g, 30 mmol), and tetrahydrofuran (30 mL), the cinnamoyl chloride (4.10 g, 20 mmol) dissolved tetrahydrofuran (5 mL) was added dropwise at 0°C. The mixture was stirred at 0°C for 30 min and then at RT for 3 hours. The solution was concentrated under vacuum and then poured on ice cold water with stirring. The precipitated product was washed with water and dried in an oven at 100°C. The final compounds were then obtained by crystallization from ethanol.Scheme 1
Synthesis of compounds2a–2g and3a-3b.For the synthesis of compounds2e–2g, to a stirred solution of respective aniline derivatives (30 mmol) in diethyl ether (30 mL), the cinnamoyl chloride (4.10 g, 20 mmol) dissolved in diethyl ether (5 mL) was added dropwise at 0°C. The mixture was stirred at 0°C for 30 min and then at RT for 3 hours. After completion of reaction the solvent was concentrated and then added to 100 mL of dichloromethane. The solution was washed 3 times with 1 N HCl and 2 times with 1 N NaHCO3. The separated organic layer was dried over Mg2SO4 and solvent was evaporated completely to obtain a residue. The final compounds were obtained by crystallization from ethanol.(
2a
) N-Phenylcinnamamide. 75.55% yield, 1H NMR (CDCl3, 300 MHz, 298 K) δ (ppm): 9.74 (s, 1H, -NH), 7.57 (m, 10H, Ar-H), 7.50 (d, 1H, J
=
15.6 Hz, CH=CH), 6.72 (d, 1H, J
=
15.6 Hz, CH=CH). 13C NMR (300 MHz, CDCl3): 163.66 (C=O), 140.32 (Ar-CH=CH), 139.16, 134.86, 129.42, 128.90, 128.11, 127.52, 122.31 (Ar), 121.62 (CH=CH-C=O). JEOL JMS 600, EI+ mode:m/z = 223.2089 [M]+, 224.2087 [M + H]+.(
2b
) N-(2-Hydroxyphenyl)cinnamamide. 50.76%, 1H NMR (d6-DMSO, 300 MHz, 298 K) δ (ppm): 10.03 (bs, 1H, -NH), 9.52, (s, 1H, -OH), 7.96 (d, 1H, J
=
15.6 Hz, CH=CH), 7.38–7.65 (m, 6H, Ar-H), 7.18 (d, 1H, J
=
15.6 Hz, CH=CH), 6.90–6.96 (dt, 2H, Ar-H), 6.81 (t, 1H, Ar-H). 13C NMR (d6-DMSO, 300 MHz, 298 K): 164.6 (C=O), 148.3 (HO-A
r
-
C), 140.7 (Ar-CH=CH), 135.5, 130.2, 129.5, 128.5, 128.3, 127.3, 125.1, 123.3, 122.5, 116.2 (Ar), 119.5 (CH=CH-C=O). JEOL JMS 600, EI+ mode:m/z = 239.2945 [M]+, 240.2946 [M + H]+.(
2c
) N-(4-Chlorophenyl)cinnamamide. 76.65% yield, 1H NMR (CDCl3, 300 MHz, 298 K) δ (ppm): 7.76 (d, 1H, J
=
15.6 Hz, CH=CH), 7.62–7.60 (m, 4H, Ar-H), 7.52 (d, 2H, Ar-H), 7.41–7.39 (m, 3H, Ar-H), 7.33 (br, 1H, -NH), 6.58 (d, J
=
15.6 Hz, 1H, CH=CH). 13C NMR (300 MHz, CDCl3): 164.0 (C=O), 142.9 (Ar-CH=CH), 136.6, 134.5 (Ar), 130.2 (Cl-A
r
-
C), 129.1, 129.04, 128.9, 121.2 (Ar-C), 120.04 (CH=CH-C=O). JEOL JMS 600, EI+ mode:m/z = 257.7134 [M]+, 258.7136 [M + H]+.(
2d
) N-(4-Bromophenyl)cinnamamide. 70.45% yield, 1H NMR (CDCl3, 300 MHz, 298 K) δ (ppm): 7.79 (d, 1H, J
=
15.6 Hz, CH=CH), 7.57–7.54 (m, 4H, Ar-H), 7.49 (d, 2H, Ar-H), 7.43–7.41 (m, 3H, Ar-H), 7.34 (br, 1H, -NH) 6.55 (d, 1H, J
=
15.6 Hz, CH=CH). 13C NMR (300 MHz, CDCl3): 164.1 (C=O), 141.0 (Ar-CH=CH), 138.0, 132.2, 130.1, 129.5, 129.3, 128.1 (Ar), 121.5 (Br-A
r
-
C), 119.7 (CH=CH-C=O). JEOL JMS 600, EI+ mode:m/z = 302.1662 [M]+, 303.1664 [M + H]+.(
2e
) N-(2-Nitrophenyl)cinnamamide. 70.34% yield. 1H NMR (CDCl3, 300 MHz, 298 K) δ (ppm), 10.61 (br, 1H, -NH), 8.92 (1H, d, J
=
7.8 Hz, Ar-H), 8.22 (1H, d, J
=
8.4 Hz, Ar-H), 7.75 (d, 1H, J
=
15.6 Hz, CH=CH), 7.64–7.70 (t, 1H, Ar-H), 7.56–7.59 (dd, 2H, Ar-H), 7.39–7.41 (m, 3H, Ar-H), 7.17–7.20 (t, 1H, Ar-H), 6.58 (d, 1H, J
=
15.6 Hz, CH=CH). 13C NMR (d6-DMSO, 300 MHz,): 164.9 (C=O), 144.2 (NO2-A
r
-
C), 136.9 (Ar-CH=CH), 136.4, 135.8, 134.8, 130.9, 129.5, 128.7, 126.3, 123.6, 122.8 (Ar), 121.6 (CH=CH-C=O). JEOL JMS 600, EI+ mode:m/z = 268.2617 [M]+.(
2f
) N-(3-Nitrophenyl)cinnamamide. 72.95% yield, 1H NMR (d6-DMSO, 300 MHz, 298 K) δ (ppm), 10.68 (br, 1H, -NH), 8.77 (1H, s, Ar-H), 8.02 (d, 1H, J
=
7.8 Hz, Ar-H), 7.89 (d, 1H, J
=
7.8 Hz, Ar-H), 7.44–7.72 (m, 7H, Ar-H, CH=CH), 6.82 (d, 1H, J
=
15.6 Hz, CH=CH). 13C NMR (d6-DMSO, 300 MHz,): 164.6 (C=O), 148.5 (NO2-A
r
-
C), 141.6 (Ar-CH=CH), 140.9, 135.0, 130.4, 129.4, 128.3, 125.6, 122.1, 113.9 (Ar), 118.1 (CH=CH-C=O). JEOL JMS 600, EI+ mode:m/z = 268.2615 [M]+.(
2g
) N-(4-Nitrophenyl)cinnamamide. 68.23% yield, 1H NMR (d6-DMSO, 300 MHz, 298 K) δ (ppm): 10.90 (s, 1H, -NH), 8.22 (d, 2H, J
=
8.7 Hz, Ar-H), 7.93 (d, 2H, J
=
7.8 Hz, Ar-H), 7.69–7.43 (m, 6H, Ar-H, CH=CH), 6.85 (d, 1H, J
=
15.0 Hz, CH=CH). 13C NMR (d6-DMSO, 300 MHz,): 164.9 (C=O), 146.1 (NO2-A
r
-
C), 142.8, 142.4 (Ar), 142.2 (Ar-CH=CH), 135.0, 129.5, 128.5, 125.7, 121.9 (Ar-C), 119.6 (CH=CH-C=O). JEOL JMS 600, EI+ mode:m/z = 268.2615 [M]+, 269.2657 [M + H]+.(
3a
) N,N-Dimethylcinnamamide. 73.34% yield, 1H NMR (CDCl3, 300 MHz, 298 K) δ (ppm): 7.66–7.71 (d, 1H, J
=
15.6 Hz, CH=CH), 7.53 (d, 2H, J
=
7.8 Hz, Ar-H), 7.35 (m, 3H, Ar-H), 6.68 (d, 1H, J
=
15.0 Hz, CH=CH), 3.12 (s, 6H, -CH3). 13C NMR (300 MHz, CDCl3): 167.0 (C=O), 142.9 (Ar-CH=CH), 135.5, 129.8, 129.0, 128.0 (Ar), 117.3 (CH=CH-C=O), 37.0 (CH3). JEOL JMS 600, EI+ mode:m/z = 175.0993 [M]+, 176.1403 [M + H]+.(
3b
) N,N-Diethylcinnamamide. 76.85% yield, 1H NMR (CDCl3, 300 MHz, 298 K) δ (ppm): 7.73 (d, 1H, J
=
15.9 Hz, CH=CH), 7.55 (m, 2H, J
=
7.8 Hz, Ar-H), 7.39 (m, 3H, Ar-H), 6.85 (d, 1H, J
=
15.0 Hz, CH=CH), 3.40–3.50 (m, 4H, CH2), 1.25 (m, 6H, CH3). 13C NMR (300 MHz, CDCl3): 165.7 (C=O), 142.3 (Ar-CH=CH), 135.5, 129.4, 128.7, 127.7 (Ar), 117.7 (CH=CH-C=O), 42.3 (CH2-CH3), 13.2 (-CH3). JEOL JMS 600, EI+ mode:m/z = 203.2913 [M]+, 204.2732 [M + H]+.


### 2.2. Antimicrobial Activity

The antimicrobial activity of the synthesized compounds was testedin vitro against twenty-one microorganisms. Stock solutions (1 mg/mL) of synthesized compounds2a–2g and3a-3b were prepared by dissolving each compound in dimethyl sulfoxide. Calculated volumes of stock solutions were dispensed in series of McCartney bottles previously containing calculated volumes of sterile cooled molten nutrient agar media (40–45°C) to prepare the volume of 30 mL each with dilutions of 5, 10, 25, 50, 100, 200, 400, and 800 µg/mL. These sterile nutrient agar media solutions were poured into Petri plates and allowed to solidify. These plates were kept in the refrigerator at 4°C for 24 h to allow the uniform diffusion of the compounds throughout the nutrient agar medium. Before spot inoculation, plates were kept at 37°C for 2 h. One loop full (loop diameter: 3 mm) of an overnight grown peptone water culture of each microorganism was inoculated, and the location of the inoculation was marked by the checkerboard technique. The spot inoculated plates were incubated at 37°C for 24 h and the minimum inhibitory concentration (MIC, mM) values were obtained. The calculated pMIC (-
log
10
⁡
M
I
C) values are presented in Table 1. Experiments were done in triplicate, and the results were presented as mean values of the three measurements.Table 1
Antimicrobial activity of compounds2a–2g and 3a-3b.
Microbial strain
pMIC
2a
2b
2c
2d
2e
2f
2g
3a
3b
E. coli K99
2.45
3.68
2.81
2.58
2.83
3.13
∗
∗
∗
E. coli 306
2.45
3.38
2.81
2.88
2.83
2.83
∗
2.41
∗
E. coli K88
2.45
3.68
3.11
2.58
3.13
2.83
∗
∗
∗
E. coli LT37
3.95
3.68
4.41
2.58
4.03
4.43
4.03
3.61
3.85
E. coli 872
2.75
3.68
2.81
2.58
3.13
2.83
∗
∗
3.54
E. coli ROW 7/12
2.75
3.68
3.11
2.58
2.83
3.13
2.83
∗
∗
E. coli 3:37C
2.75
3.68
2.81
2.58
2.83
2.53
2.53
∗
2.34
E. coli CD/99/1
2.75
3.38
3.11
2.58
2.83
3.13
2.53
∗
2.34
SalmonellaTyphiTy2
3.95
3.68
2.51
∗
∗
∗
2.53
∗
2.64
Shigella dysenteriae 1
∗
2.78
2.51
∗
2.53
2.53
2.83
∗
2.94
Shigella dysenteriae 8
∗
3.68
2.51
∗
2.83
2.53
3.13
∗
2.94
Shigella sonnei 1
∗
2.78
∗
∗
2.53
∗
3.83
2.71
2.64
Shigella boydii D13629
∗
3.08
2.51
∗
2.53
∗
2.53
∗
3.85
Shigella flexneri Type 6
∗
3.08
2.51
∗
2.53
2.53
3.13
2.71
2.94
Vibrio cholerae 1313
2.45
3.68
3.11
∗
2.53
2.53
2.53
∗
∗
Vibrio cholerae 293
2.45
3.38
3.11
2.58
2.53
2.83
2.53
2.41
2.34
Vibrio cholerae 1315
3.05
3.38
3.11
2.58
3.13
2.83
3.13
∗
∗
Vibrio cholerae 85
3.95
3.38
3.11
2.58
4.03
2.53
2.83
3.31
2.94
Staphylococcus aureus ML267
∗
2.78
2.51
∗
∗
4.03
3.43
∗
2.94
Bacillus pumilus 82
2.75
3.38
∗
∗
∗
2.53
∗
3.01
3.24
Bacillus subtilis ATCC 6633
3.95
3.68
3.71
∗
∗
2.53
∗
∗
∗
∗No antimicrobial activity was observed in the concentration range of 5–800 μg/mL.


### 2.3. Antioxidant Activity

The antioxidant activity of the synthesized compounds (2a–2g,3a-3b) was evaluated using the DPPH free radical scavenging assay [18]. The 200 μL of test sample solution (1 mg/mL) was added to 4 mL of 100 µM methanolic DPPH. The solution was allowed to incubate for 20 minutes at 25°C, and the absorbance was measured at 517 nm. Ascorbic acid (1 mg/mL) was used as reference standard. A blank was prepared without adding the standard or test compound. The lower absorbance of the reaction mixture indicates higher free radical scavenging activity. The capability to scavenge the DPPH radical was calculated using the following equation:(1)
%
inhibition
=
A
c
o
n
t
r
o
l
-
A
s
a
m
p
l
e
A
c
o
n
t
r
o
l
×
100
,where A
c
o
n
t
r
o
l is the absorbance of the DPPH alone and A
s
a
m
p
l
e is the absorbance of DPPH in the presence of compounds2a–2g,3a-3b. All determinations were performed in triplicate (n
=
3). The results are presented in Figure 1.Figure 1
DPPH radical scavenging activity of compounds2a–2g and3a-3b.


## 2.1. General Procedure for the Synthesis of Compounds2a–2g and3a-3b

Compounds2a–2d and3a-3b (Scheme 1) were synthesized by slight modification of the typical procedure adopted for various cinnamic acid derivatives [16, 17]. To a stirred solution containing aniline derivatives or amine derivatives (25 mmol), K2CO3 (4.15 g, 30 mmol), and tetrahydrofuran (30 mL), the cinnamoyl chloride (4.10 g, 20 mmol) dissolved tetrahydrofuran (5 mL) was added dropwise at 0°C. The mixture was stirred at 0°C for 30 min and then at RT for 3 hours. The solution was concentrated under vacuum and then poured on ice cold water with stirring. The precipitated product was washed with water and dried in an oven at 100°C. The final compounds were then obtained by crystallization from ethanol.Scheme 1
Synthesis of compounds2a–2g and3a-3b.For the synthesis of compounds2e–2g, to a stirred solution of respective aniline derivatives (30 mmol) in diethyl ether (30 mL), the cinnamoyl chloride (4.10 g, 20 mmol) dissolved in diethyl ether (5 mL) was added dropwise at 0°C. The mixture was stirred at 0°C for 30 min and then at RT for 3 hours. After completion of reaction the solvent was concentrated and then added to 100 mL of dichloromethane. The solution was washed 3 times with 1 N HCl and 2 times with 1 N NaHCO3. The separated organic layer was dried over Mg2SO4 and solvent was evaporated completely to obtain a residue. The final compounds were obtained by crystallization from ethanol.(
2a
) N-Phenylcinnamamide. 75.55% yield, 1H NMR (CDCl3, 300 MHz, 298 K) δ (ppm): 9.74 (s, 1H, -NH), 7.57 (m, 10H, Ar-H), 7.50 (d, 1H, J
=
15.6 Hz, CH=CH), 6.72 (d, 1H, J
=
15.6 Hz, CH=CH). 13C NMR (300 MHz, CDCl3): 163.66 (C=O), 140.32 (Ar-CH=CH), 139.16, 134.86, 129.42, 128.90, 128.11, 127.52, 122.31 (Ar), 121.62 (CH=CH-C=O). JEOL JMS 600, EI+ mode:m/z = 223.2089 [M]+, 224.2087 [M + H]+.(
2b
) N-(2-Hydroxyphenyl)cinnamamide. 50.76%, 1H NMR (d6-DMSO, 300 MHz, 298 K) δ (ppm): 10.03 (bs, 1H, -NH), 9.52, (s, 1H, -OH), 7.96 (d, 1H, J
=
15.6 Hz, CH=CH), 7.38–7.65 (m, 6H, Ar-H), 7.18 (d, 1H, J
=
15.6 Hz, CH=CH), 6.90–6.96 (dt, 2H, Ar-H), 6.81 (t, 1H, Ar-H). 13C NMR (d6-DMSO, 300 MHz, 298 K): 164.6 (C=O), 148.3 (HO-A
r
-
C), 140.7 (Ar-CH=CH), 135.5, 130.2, 129.5, 128.5, 128.3, 127.3, 125.1, 123.3, 122.5, 116.2 (Ar), 119.5 (CH=CH-C=O). JEOL JMS 600, EI+ mode:m/z = 239.2945 [M]+, 240.2946 [M + H]+.(
2c
) N-(4-Chlorophenyl)cinnamamide. 76.65% yield, 1H NMR (CDCl3, 300 MHz, 298 K) δ (ppm): 7.76 (d, 1H, J
=
15.6 Hz, CH=CH), 7.62–7.60 (m, 4H, Ar-H), 7.52 (d, 2H, Ar-H), 7.41–7.39 (m, 3H, Ar-H), 7.33 (br, 1H, -NH), 6.58 (d, J
=
15.6 Hz, 1H, CH=CH). 13C NMR (300 MHz, CDCl3): 164.0 (C=O), 142.9 (Ar-CH=CH), 136.6, 134.5 (Ar), 130.2 (Cl-A
r
-
C), 129.1, 129.04, 128.9, 121.2 (Ar-C), 120.04 (CH=CH-C=O). JEOL JMS 600, EI+ mode:m/z = 257.7134 [M]+, 258.7136 [M + H]+.(
2d
) N-(4-Bromophenyl)cinnamamide. 70.45% yield, 1H NMR (CDCl3, 300 MHz, 298 K) δ (ppm): 7.79 (d, 1H, J
=
15.6 Hz, CH=CH), 7.57–7.54 (m, 4H, Ar-H), 7.49 (d, 2H, Ar-H), 7.43–7.41 (m, 3H, Ar-H), 7.34 (br, 1H, -NH) 6.55 (d, 1H, J
=
15.6 Hz, CH=CH). 13C NMR (300 MHz, CDCl3): 164.1 (C=O), 141.0 (Ar-CH=CH), 138.0, 132.2, 130.1, 129.5, 129.3, 128.1 (Ar), 121.5 (Br-A
r
-
C), 119.7 (CH=CH-C=O). JEOL JMS 600, EI+ mode:m/z = 302.1662 [M]+, 303.1664 [M + H]+.(
2e
) N-(2-Nitrophenyl)cinnamamide. 70.34% yield. 1H NMR (CDCl3, 300 MHz, 298 K) δ (ppm), 10.61 (br, 1H, -NH), 8.92 (1H, d, J
=
7.8 Hz, Ar-H), 8.22 (1H, d, J
=
8.4 Hz, Ar-H), 7.75 (d, 1H, J
=
15.6 Hz, CH=CH), 7.64–7.70 (t, 1H, Ar-H), 7.56–7.59 (dd, 2H, Ar-H), 7.39–7.41 (m, 3H, Ar-H), 7.17–7.20 (t, 1H, Ar-H), 6.58 (d, 1H, J
=
15.6 Hz, CH=CH). 13C NMR (d6-DMSO, 300 MHz,): 164.9 (C=O), 144.2 (NO2-A
r
-
C), 136.9 (Ar-CH=CH), 136.4, 135.8, 134.8, 130.9, 129.5, 128.7, 126.3, 123.6, 122.8 (Ar), 121.6 (CH=CH-C=O). JEOL JMS 600, EI+ mode:m/z = 268.2617 [M]+.(
2f
) N-(3-Nitrophenyl)cinnamamide. 72.95% yield, 1H NMR (d6-DMSO, 300 MHz, 298 K) δ (ppm), 10.68 (br, 1H, -NH), 8.77 (1H, s, Ar-H), 8.02 (d, 1H, J
=
7.8 Hz, Ar-H), 7.89 (d, 1H, J
=
7.8 Hz, Ar-H), 7.44–7.72 (m, 7H, Ar-H, CH=CH), 6.82 (d, 1H, J
=
15.6 Hz, CH=CH). 13C NMR (d6-DMSO, 300 MHz,): 164.6 (C=O), 148.5 (NO2-A
r
-
C), 141.6 (Ar-CH=CH), 140.9, 135.0, 130.4, 129.4, 128.3, 125.6, 122.1, 113.9 (Ar), 118.1 (CH=CH-C=O). JEOL JMS 600, EI+ mode:m/z = 268.2615 [M]+.(
2g
) N-(4-Nitrophenyl)cinnamamide. 68.23% yield, 1H NMR (d6-DMSO, 300 MHz, 298 K) δ (ppm): 10.90 (s, 1H, -NH), 8.22 (d, 2H, J
=
8.7 Hz, Ar-H), 7.93 (d, 2H, J
=
7.8 Hz, Ar-H), 7.69–7.43 (m, 6H, Ar-H, CH=CH), 6.85 (d, 1H, J
=
15.0 Hz, CH=CH). 13C NMR (d6-DMSO, 300 MHz,): 164.9 (C=O), 146.1 (NO2-A
r
-
C), 142.8, 142.4 (Ar), 142.2 (Ar-CH=CH), 135.0, 129.5, 128.5, 125.7, 121.9 (Ar-C), 119.6 (CH=CH-C=O). JEOL JMS 600, EI+ mode:m/z = 268.2615 [M]+, 269.2657 [M + H]+.(
3a
) N,N-Dimethylcinnamamide. 73.34% yield, 1H NMR (CDCl3, 300 MHz, 298 K) δ (ppm): 7.66–7.71 (d, 1H, J
=
15.6 Hz, CH=CH), 7.53 (d, 2H, J
=
7.8 Hz, Ar-H), 7.35 (m, 3H, Ar-H), 6.68 (d, 1H, J
=
15.0 Hz, CH=CH), 3.12 (s, 6H, -CH3). 13C NMR (300 MHz, CDCl3): 167.0 (C=O), 142.9 (Ar-CH=CH), 135.5, 129.8, 129.0, 128.0 (Ar), 117.3 (CH=CH-C=O), 37.0 (CH3). JEOL JMS 600, EI+ mode:m/z = 175.0993 [M]+, 176.1403 [M + H]+.(
3b
) N,N-Diethylcinnamamide. 76.85% yield, 1H NMR (CDCl3, 300 MHz, 298 K) δ (ppm): 7.73 (d, 1H, J
=
15.9 Hz, CH=CH), 7.55 (m, 2H, J
=
7.8 Hz, Ar-H), 7.39 (m, 3H, Ar-H), 6.85 (d, 1H, J
=
15.0 Hz, CH=CH), 3.40–3.50 (m, 4H, CH2), 1.25 (m, 6H, CH3). 13C NMR (300 MHz, CDCl3): 165.7 (C=O), 142.3 (Ar-CH=CH), 135.5, 129.4, 128.7, 127.7 (Ar), 117.7 (CH=CH-C=O), 42.3 (CH2-CH3), 13.2 (-CH3). JEOL JMS 600, EI+ mode:m/z = 203.2913 [M]+, 204.2732 [M + H]+.


## 2.2. Antimicrobial Activity

The antimicrobial activity of the synthesized compounds was testedin vitro against twenty-one microorganisms. Stock solutions (1 mg/mL) of synthesized compounds2a–2g and3a-3b were prepared by dissolving each compound in dimethyl sulfoxide. Calculated volumes of stock solutions were dispensed in series of McCartney bottles previously containing calculated volumes of sterile cooled molten nutrient agar media (40–45°C) to prepare the volume of 30 mL each with dilutions of 5, 10, 25, 50, 100, 200, 400, and 800 µg/mL. These sterile nutrient agar media solutions were poured into Petri plates and allowed to solidify. These plates were kept in the refrigerator at 4°C for 24 h to allow the uniform diffusion of the compounds throughout the nutrient agar medium. Before spot inoculation, plates were kept at 37°C for 2 h. One loop full (loop diameter: 3 mm) of an overnight grown peptone water culture of each microorganism was inoculated, and the location of the inoculation was marked by the checkerboard technique. The spot inoculated plates were incubated at 37°C for 24 h and the minimum inhibitory concentration (MIC, mM) values were obtained. The calculated pMIC (-
log
10
⁡
M
I
C) values are presented in Table 1. Experiments were done in triplicate, and the results were presented as mean values of the three measurements.Table 1
Antimicrobial activity of compounds2a–2g and 3a-3b.
Microbial strain
pMIC
2a
2b
2c
2d
2e
2f
2g
3a
3b
E. coli K99
2.45
3.68
2.81
2.58
2.83
3.13
∗
∗
∗
E. coli 306
2.45
3.38
2.81
2.88
2.83
2.83
∗
2.41
∗
E. coli K88
2.45
3.68
3.11
2.58
3.13
2.83
∗
∗
∗
E. coli LT37
3.95
3.68
4.41
2.58
4.03
4.43
4.03
3.61
3.85
E. coli 872
2.75
3.68
2.81
2.58
3.13
2.83
∗
∗
3.54
E. coli ROW 7/12
2.75
3.68
3.11
2.58
2.83
3.13
2.83
∗
∗
E. coli 3:37C
2.75
3.68
2.81
2.58
2.83
2.53
2.53
∗
2.34
E. coli CD/99/1
2.75
3.38
3.11
2.58
2.83
3.13
2.53
∗
2.34
SalmonellaTyphiTy2
3.95
3.68
2.51
∗
∗
∗
2.53
∗
2.64
Shigella dysenteriae 1
∗
2.78
2.51
∗
2.53
2.53
2.83
∗
2.94
Shigella dysenteriae 8
∗
3.68
2.51
∗
2.83
2.53
3.13
∗
2.94
Shigella sonnei 1
∗
2.78
∗
∗
2.53
∗
3.83
2.71
2.64
Shigella boydii D13629
∗
3.08
2.51
∗
2.53
∗
2.53
∗
3.85
Shigella flexneri Type 6
∗
3.08
2.51
∗
2.53
2.53
3.13
2.71
2.94
Vibrio cholerae 1313
2.45
3.68
3.11
∗
2.53
2.53
2.53
∗
∗
Vibrio cholerae 293
2.45
3.38
3.11
2.58
2.53
2.83
2.53
2.41
2.34
Vibrio cholerae 1315
3.05
3.38
3.11
2.58
3.13
2.83
3.13
∗
∗
Vibrio cholerae 85
3.95
3.38
3.11
2.58
4.03
2.53
2.83
3.31
2.94
Staphylococcus aureus ML267
∗
2.78
2.51
∗
∗
4.03
3.43
∗
2.94
Bacillus pumilus 82
2.75
3.38
∗
∗
∗
2.53
∗
3.01
3.24
Bacillus subtilis ATCC 6633
3.95
3.68
3.71
∗
∗
2.53
∗
∗
∗
∗No antimicrobial activity was observed in the concentration range of 5–800 μg/mL.


## 2.3. Antioxidant Activity

The antioxidant activity of the synthesized compounds (2a–2g,3a-3b) was evaluated using the DPPH free radical scavenging assay [18]. The 200 μL of test sample solution (1 mg/mL) was added to 4 mL of 100 µM methanolic DPPH. The solution was allowed to incubate for 20 minutes at 25°C, and the absorbance was measured at 517 nm. Ascorbic acid (1 mg/mL) was used as reference standard. A blank was prepared without adding the standard or test compound. The lower absorbance of the reaction mixture indicates higher free radical scavenging activity. The capability to scavenge the DPPH radical was calculated using the following equation:(1)
%
inhibition
=
A
c
o
n
t
r
o
l
-
A
s
a
m
p
l
e
A
c
o
n
t
r
o
l
×
100
,where A
c
o
n
t
r
o
l is the absorbance of the DPPH alone and A
s
a
m
p
l
e is the absorbance of DPPH in the presence of compounds2a–2g,3a-3b. All determinations were performed in triplicate (n
=
3). The results are presented in Figure 1.Figure 1
DPPH radical scavenging activity of compounds2a–2g and3a-3b.


## 3. Results and Discussions

### 3.1. The Synthesis

The amide derivatives of cinnamic acid2a–2g and3a-3b were synthesized to study the effect of amide nitrogen substituents on the antimicrobial activity. As shown in Scheme 1, the reaction of cinnamoyl chloride with corresponding aromatic or aliphatic amines gave compounds2a–2g and3a-3b. All compounds were obtained in good yield, purified by recrystallization, and characterized by 1H NMR, 13C NMR, and mass spectrometry.


### 3.2. Antimicrobial Activity

The pMIC (-
log
⁡
(
M
I
C
)) values of compounds2a–2g,3a-3b are presented in Table 1. Except compound2d, all compounds showed a good antibacterial activity against Gram-negative compared to Gram-positive bacterial strains. Compound2b showed strong antimicrobial activity against all microorganisms with the pMIC values ranging from 2.78 to 3.68. However, compound2d demonstrated little (pMIC = 2.58) or no antibacterial activity in the tested concentration domain. Similarly, compound3a also showed very poor or no antimicrobial activity against the tested microorganisms. Therefore, compounds2d and3a were considered as poor antimicrobial compounds. Compounds2c,2e–2g showed the highest antimicrobial activity againstE. coli LT37 with the pMIC of 4.03–4.43. Moreover, compounds2e and2f demonstrated strong activity againstVibrio cholerae 85 andStaphylococcus aureus ML267, respectively.Compound2a demonstrated strongest activity againstE. coli LT37,Salmonella Typhi Ty2,Vibrio cholerae 85, andBacillus subtilis ATCC 6633 with the pMIC value of 3.95. Compound2b showed strong activity against all microorganisms except forShigella dysenteriae 1,Shigella sonnei 1, andStaphylococcus aureus ML267 with the lowest pMIC value of 2.78. Compound2c did not show any antibacterial activity againstShigella sonnei 1 andBacillus pumilus 82. Compound3b showed the strongest activity againstE. coli LT37 andShigella boydii D13629 with the pMIC of 3.85.From the results of the microbiological studies, it is evident that substituents on the amide nitrogen of cinnamamide derivatives2a–2g and3a-3b play a critical role in their antimicrobial activities. Derivatives2a–2g and3a-3b were obtained from primary amines (aniline derivatives) and secondary amines, respectively. It is important to notice that compound2b, which containso-hydroxyphenyl substituent on the amide nitrogen, showed a significant increase in the antimicrobial activity as compared to compound2a, which contains only phenyl group. Compound2c containingp-chlorophenyl substituent on the amide nitrogen showed strong activity as compared to compound2d, which containsp-bromophenyl substitution on the amide nitrogen. Among the compounds containing the nitrophenyl substituents on the amide nitrogen, compound2e showed strong activity as compared to compounds2f and2g. Them-nitrophenyl substituent in compound2e endows it with a strong antibacterial activity as compared to theo-nitrophenyl andp-nitrophenyl substituents in compounds2f and2g, respectively. It is also important to notice that the aromatic substituents on the amide nitrogen allow overall strong activity as compared to the aliphatic substituents. The presence of bulky ethyl groups on the amide nitrogen of compound3b allows it to demonstrate strong activity as compared to compound3b containing methyl groups.


### 3.3. Antioxidant Activity

DPPH radical scavenging is considered as a goodin vitro model and is widely used to assess antioxidant efficacy [19, 20]. The DPPH free radical scavenging assay was employed to evaluate the antioxidant activity of the synthesized compounds. The DPPH radical scavenging activity of compounds2a–2g,3a-3b (50 μg/mL) was compared with that of ascorbic acid at the same concentration. As presented in Figure 1, the results of antioxidant screenings were expressed as % of inhibition of the DPPH radical.As depicted in Figure1, most compounds showed moderate-to-good antioxidant activity. Compounds2a,3a, and3b showed strong activity as indicated by the % inhibition of the DPPH radical, 51% (±1.14), 41% (±1.01), and 50% (±1.23), respectively. Compounds2b and2g showed very low activity with the % inhibition of 16% (±1.12) and 14% (±1.09), respectively. Compounds2c,2d,2e, and2f showed moderate activity with the % inhibition of 34% (±1.96), 35% (±0.98), 31% (±0.97), and 30% (±1.02), respectively. The results clearly indicate the electron donating groups on the amide nitrogen (3a-3b) play an important role in scavenging the free radicals. Moreover, compound2a, which contains phenyl group on amide nitrogen, demonstrates almost similar radical scavenging activity to that of compounds3a,3b, which contain dimethyl and diethyl substituents on amide nitrogen, respectively.However, the electron withdrawing substituents such asp-chloro,p-bromo, ando-nitro,m-nitro, andp-nitro on phenyl ring in compounds2c,2d, and2e–2g, respectively, significantly decrease radical scavenging activity. The results obtained in this study are in line with other findings [21].


## 3.1. The Synthesis

The amide derivatives of cinnamic acid2a–2g and3a-3b were synthesized to study the effect of amide nitrogen substituents on the antimicrobial activity. As shown in Scheme 1, the reaction of cinnamoyl chloride with corresponding aromatic or aliphatic amines gave compounds2a–2g and3a-3b. All compounds were obtained in good yield, purified by recrystallization, and characterized by 1H NMR, 13C NMR, and mass spectrometry.


## 3.2. Antimicrobial Activity

The pMIC (-
log
⁡
(
M
I
C
)) values of compounds2a–2g,3a-3b are presented in Table 1. Except compound2d, all compounds showed a good antibacterial activity against Gram-negative compared to Gram-positive bacterial strains. Compound2b showed strong antimicrobial activity against all microorganisms with the pMIC values ranging from 2.78 to 3.68. However, compound2d demonstrated little (pMIC = 2.58) or no antibacterial activity in the tested concentration domain. Similarly, compound3a also showed very poor or no antimicrobial activity against the tested microorganisms. Therefore, compounds2d and3a were considered as poor antimicrobial compounds. Compounds2c,2e–2g showed the highest antimicrobial activity againstE. coli LT37 with the pMIC of 4.03–4.43. Moreover, compounds2e and2f demonstrated strong activity againstVibrio cholerae 85 andStaphylococcus aureus ML267, respectively.Compound2a demonstrated strongest activity againstE. coli LT37,Salmonella Typhi Ty2,Vibrio cholerae 85, andBacillus subtilis ATCC 6633 with the pMIC value of 3.95. Compound2b showed strong activity against all microorganisms except forShigella dysenteriae 1,Shigella sonnei 1, andStaphylococcus aureus ML267 with the lowest pMIC value of 2.78. Compound2c did not show any antibacterial activity againstShigella sonnei 1 andBacillus pumilus 82. Compound3b showed the strongest activity againstE. coli LT37 andShigella boydii D13629 with the pMIC of 3.85.From the results of the microbiological studies, it is evident that substituents on the amide nitrogen of cinnamamide derivatives2a–2g and3a-3b play a critical role in their antimicrobial activities. Derivatives2a–2g and3a-3b were obtained from primary amines (aniline derivatives) and secondary amines, respectively. It is important to notice that compound2b, which containso-hydroxyphenyl substituent on the amide nitrogen, showed a significant increase in the antimicrobial activity as compared to compound2a, which contains only phenyl group. Compound2c containingp-chlorophenyl substituent on the amide nitrogen showed strong activity as compared to compound2d, which containsp-bromophenyl substitution on the amide nitrogen. Among the compounds containing the nitrophenyl substituents on the amide nitrogen, compound2e showed strong activity as compared to compounds2f and2g. Them-nitrophenyl substituent in compound2e endows it with a strong antibacterial activity as compared to theo-nitrophenyl andp-nitrophenyl substituents in compounds2f and2g, respectively. It is also important to notice that the aromatic substituents on the amide nitrogen allow overall strong activity as compared to the aliphatic substituents. The presence of bulky ethyl groups on the amide nitrogen of compound3b allows it to demonstrate strong activity as compared to compound3b containing methyl groups.


## 3.3. Antioxidant Activity

DPPH radical scavenging is considered as a goodin vitro model and is widely used to assess antioxidant efficacy [19, 20]. The DPPH free radical scavenging assay was employed to evaluate the antioxidant activity of the synthesized compounds. The DPPH radical scavenging activity of compounds2a–2g,3a-3b (50 μg/mL) was compared with that of ascorbic acid at the same concentration. As presented in Figure 1, the results of antioxidant screenings were expressed as % of inhibition of the DPPH radical.As depicted in Figure1, most compounds showed moderate-to-good antioxidant activity. Compounds2a,3a, and3b showed strong activity as indicated by the % inhibition of the DPPH radical, 51% (±1.14), 41% (±1.01), and 50% (±1.23), respectively. Compounds2b and2g showed very low activity with the % inhibition of 16% (±1.12) and 14% (±1.09), respectively. Compounds2c,2d,2e, and2f showed moderate activity with the % inhibition of 34% (±1.96), 35% (±0.98), 31% (±0.97), and 30% (±1.02), respectively. The results clearly indicate the electron donating groups on the amide nitrogen (3a-3b) play an important role in scavenging the free radicals. Moreover, compound2a, which contains phenyl group on amide nitrogen, demonstrates almost similar radical scavenging activity to that of compounds3a,3b, which contain dimethyl and diethyl substituents on amide nitrogen, respectively.However, the electron withdrawing substituents such asp-chloro,p-bromo, ando-nitro,m-nitro, andp-nitro on phenyl ring in compounds2c,2d, and2e–2g, respectively, significantly decrease radical scavenging activity. The results obtained in this study are in line with other findings [21].


## 4. Conclusion

Most of the amide derivatives of cinnamic acid mentioned in this showed moderate-to-high antibacterial and antioxidant activities. The investigation of antimicrobial potentials of the compounds demonstrated a strong activity against 21 bacterial strains comprising Gram-positive and Gram-negative bacteria. Compounds2a,2b, and3b showed strong antimicrobial activity against all microorganisms with the pMIC value ranging from 2.45 to 3.68. Compounds2a,3a, and3b demonstrated strong antioxidant activity. These findings encourage the synthesis of new amide derivatives of cinnamic acid. These findings indicate that the amide derivatives of the cinnamic acid afford strong antibacterial and antioxidant activities.



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*Source: 208910-2015-12-15.xml*