Hydrogen peroxide scavenging activity of novel coumarins synthesized using different approaches

Article abstract of DOI:10.1371/journal.pone.0132175

New derivatives of 7-hydroxy-4-methylcoumarin were synthesized using a chemical method and a microwave-assisted method to compare the feasibility, reaction times, and yields of the product. The newly synthesized coumarins were characterized by different spectroscopic techniques (FT-IR and NMR) and micro-elemental analysis (CHNS). In vitro antioxidant activities of these compounds were evaluated against hydrogen peroxide and were compared with standard natural antioxidant, vitamin C. Our results reveal that these compounds exhibit excellent radical scavenging activities.

Full text of DOI:10.1371/journal.pone.0132175

RESEARCH ARTICLE
Hydrogen Peroxide Scavenging Activity of
Novel Coumarins Synthesized Using Different
Approaches
1
,2
2
2
Ahmed A. Al-Amiery *, Yasameen K. Al-Majedy , Abdul Amir H. Kadhum , Abu
Bakar Mohamad
2
,3
1
Department of Chemical and Process Engineering, University Kebangsaan Malaysia (UKM), Bangi,
Selangor, 43000, Malaysia, 2 Environmental Research Center, University of Technology (UOT), Baghdad,
10001, Iraq, 3 Fuel Cell Institute, University Kebangsaan Malaysia (UKM), Bangi, Selangor, 43000, Malaysia
*
dr.ahmed1975@gmail.com
Abstract
a11111
New derivatives of 7-hydroxy-4-methylcoumarin were synthesized using a chemical
method and a microwave-assisted method to compare the feasibility, reaction times, and
yields of the product. The newly synthesized coumarins were characterized by different
spectroscopic techniques (FT-IR and NMR) and micro-elemental analysis (CHNS). In vitro
antioxidant activities of these compounds were evaluated against hydrogen peroxide and
were compared with standard natural antioxidant, vitamin C. Our results reveal that these
compounds exhibit excellent radical scavenging activities.
OPEN ACCESS
Citation: Al-Amiery AA, Al-Majedy YK, Kadhum
AAH, Mohamad AB (2015) Hydrogen Peroxide
Scavenging Activity of Novel Coumarins Synthesized
Using Different Approaches. PLoS ONE 10(7):
e0132175. doi:10.1371/journal.pone.0132175
Editor: Hans-Joachim Lehmler, The University of
Iowa, UNITED STATES
Introduction
Coumarins show biological activity, such as molluscicidal, anthelmintic [1], hypnotic and
insecticidal [2] activities, as well as medicinal activities, such as anticoagulant agents [3], and as
fluorescent brighteners [4]. Coumarins consisting of fused benzene and α-pyrone rings are
present in significant amounts in plants, and more than 1300 coumarins have been identified
from natural sources [5]. Derivatives of coumarins naturally occur as secondary metabolites
present in seeds, roots, and leaves of many plant species [6]. Studies have shown that micro-
Received: February 23, 2015
Accepted: June 10, 2015
Published: July 6, 2015
Copyright: © 2015 Al-Amiery et al. This is an open
access article distributed under the terms of the
Creative Commons Attribution License, which permits wave irradiation substantially aids the promotion and simplification of numerous condensa-
unrestricted use, distribution, and reproduction in any
tion reactions that can be performed in a solvent and under solvent-free conditions [7–12].
Organic reactions performed using microwave irradiation have rapidly gained popularity
because irradiation accelerates the reaction towards a variety of synthetic transformations in
medium, provided the original author and source are
credited.
Data Availability Statement: All relevant data are
within the paper and its Supporting Information files.
solvent-less procedures without using supporting reagents, rendering these reactions eco-
friendly [13]. Due to the biological and industrial applications of coumarins and as a continua-
Funding: This study was supported by the Universiti
tion of previous studies [14–19], in this study, we describe the synthesis of coumarin deriva-
Kebangsaan Malaysia under the DIP-2012-02 grant.
tives (Fig 1) using chemical and microwave-assisted methods and we describe their
characterization through spectral data (FT-IR, H-NMR) and micro-elemental analysis
1
Competing Interests: The authors have declared
that no competing interests exist.
(CHNS). We also discuss the in vitro antioxidant activities of the synthesized coumarins.
PLOS ONE | DOI:10.1371/journal.pone.0132175 July 6, 2015
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Novel Coumarins as Antioxidants
Experimental Section
General
The chemicals used for synthesis were supplied by Sigma-Aldrich. The IR spectra were
obtained on a Thermo (Nicolen 6700) FTIR spectrophotometer, and the values are expressed
-
1
in cm . The H-NMR spectra of the compounds were recorded on a Bruker Avance Ii 400 MHz
NMR spectrophotometer using DMSO as an internal standard, and the values are expressed in
δ ppm. Elemental microanalysis was performed using an Elemental Vario El Iii, Carlo Erba
1
108 Elemental analyzer.
General procedure for the microwave-assisted synthesis of the compounds. To verify
whether microwave irradiation accelerates the final reactions, all of the reactions were per-
formed under microwave irradiation. The reaction time was dramatically reduced for each sub-
stitution from 3–12 hr (chemical method) to 1–2 min under microwave irradiation. Microwave-
assisted reactions were conducted in septum-sealed reaction vessels in a microwave reactor.
Synthesis of ethyl 2-((4-methyl-2-oxo-2H-chromen-7-yl)oxy)acetate (1). Conventional
method: A suspension of 7-hydroxy-4-methylcoumarin (1.086 g, 6.17 mmol) in acetone (30
mL) was refluxed with ethyl bromoacetate (1.528 g, 9.15 mmol) and potassium carbonate
K CO (4.69 g, 33.91 mmol) for 12 hr. After cooling, the mixture was evaporated to dryness,
2
3
and the residue was partitioned between CHCl (50 mL) and water (50 mL). The organic phase
3
was dried using Na SO , filtered, and evaporated to dryness. The residue was recrystallized
2
4
1
from acetone [20]. Yield 75%; M.p. 98–99°C [lit. [21] 94–96°C]; H-NMR δ: 2.39 (s, 3H, CH ),
3
3
7
.59 (s, 3H, CH –O), 4.89 (s, 2H, CH ); 6.23 (s, 1H, H-3), 6.90 (d, 1H, H-6), 6.93 (s, 1H,H-8),
3 2
-
1
-1
-1
.61 (d, 1H, H-5),; IR: 3129 cm (C–H, Aromatic), 2924 cm (C–H, Aliphatic), 1743.5 cm
-
1
(
C = O, ester), 1677 cm (C = O, Lacton); Theoretical Calculation for C H O : C 64.12%, H
13 12 5
5
.38%. Experimental: C 64.70%, H 5.53%.
Synthesis of 2-((4-methyl-2-oxo-2H-chromen-7-yl)oxy)acetohydrazide (2). Conven-
tional method: A solution of compound 1 (2.48 g, 10 mmol) in 25 mL of ethanol was refluxed
with hydrazine hydrate (7.5 g, 15 mmol) for 4 hr. After concentrating the reaction mixture, an
oily mass was separated and recrystallized using ethanol [15]. Yield 60%; M.p. 203–205°C [lit.
1
[
21] 198–200°C, lit. [22] 202–204]; H-NMR δ: 2.28 (s, 2H, NH ), 4.24 (s, 2H) for (O–CH ),
2
2
5
.86 (s, 1H) for (–C = C–H), 6.38, 6.83, 6.86, 7.45, (s, 1H) for aromatic ring, and 7.50 (s, 1H,
Fig 1. Reaction sequences of the synthesized compounds. a = Methyl bromoacetate; b = Hydrazine;
c = KSCN; d = CS ; e = acetylacetone; f = KOH; g = SeO ; h = o-aminothophenol.
2
2
doi:10.1371/journal.pone.0132175.g001
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Novel Coumarins as Antioxidants
-
1
-1
-1
NH); IR: 3432.8, 3327.9 cm (N–H), 3081.5 cm (C–H, Aromatic), 2990.1 cm (C–H, Ali-
-
1
-1
phatic), 1670.3 cm (C = O, Lactone), 1652.0 cm (C = O, Amide); Theoretical Calculation for
C H N O : C 58.06%, H 4.87%, N 11.29%. Experimental: C 57.81% H 4.33%, N 10.93%.
1
2
12 2 4
Microwave irradiation method: This involves the irradiation of a mixture of Ethyl 2-
((4-methyl-2-oxo-2H-chromen-7-yl)oxy)acetate 1, (2.48 g, 10 mmol) and hydrazine hydrate
(7.5 g, 15 mmol) in a microwave oven at 20% intensity for 2 min. After completion of reaction
(by TLC), the product was recrystallized from ethanol. The yield of product was 75%. M.
p. 199–201°C.
Synthesis of potassium (2-(2-((4-methyl-2-oxo-2Hchromen-7-yl)oxy)acetyl)hydrazine-
carbonothioyl) amide (3). Conventional method: A mixture of compound 2 (0.656 g, 2.8
mmol) and KSCN (0.5 g, 5.1 mmol) in 50 mL ethanol was refluxed for 3 hr with a few drops of
concentrated HCl [16]. The precipitate formed was collected by filtration and dried to yield
1
compound (3). Yield 45%, M.p. over 300°C; H-NMR δ: 2.33 (s, 3H, CH ), 4.23 (s, 2H, CH ),
3
2
6
.12 (s, 1H, H-3), 6.81 (s, 1H, H-8), 6.92 (d, 1H, H-6), 7.70 (d, 1H, H-5), 8.01 (s, 1H, NH), 9.72
-
1
-1
(
s, 1H, NH), 9.78 (s, 1H, NH); IR: 3346, 3328 cm (N–H), 3053 cm (C–H, Aromatic), 2937
-
1
-1
-1
-1
cm (C–H, Aliphatic), 1701 cm (C = O, Lactone), 1675 cm (C = O, Amide) and 1395 cm
C–N); Theoretical Calculation for C H KN O S: C 45.20%, H 3.50%, N 12.17%, S 9.28%.
(
13
12
3 4
Experimental: C 44.95%, H 3.11%, N 12.00%, S 8.99%.
Microwave irradiation method: This involves the irradiation of compound 2 (0.656 g, 2.8
mmol), KSCN (0.5 g, 5.1 mmol) and few drops of concentrated hydrochloric acid in a micro-
wave oven at 10% intensity for 2 min. After completion of reaction (by TLC), the product was
recrystallized from ethanol. The yield of product was 60%. M.p. over 300°C.
Synthesis of 7-((5-mercapto-4H-1,2,4-triazol-3-yl)methoxy)4-methyl-2H-chromen-
2-one (4). Conventional method: A mixture of compound 3 (0.431 g, 1.3 mmol), which was
used without further purification, and KOH (0.09 g, 1.6 mmol) in 25 mL of water was refluxed
for 3 hr [17]. The reaction mixture was cooled and then acidified with HCl to yield compound
1
4
. Yield 35%; M.p. 100–103°C; H-NMR δ: 2.29 (s, 3H, CH ), 3.28 (br s, 1H, -SH), 4.01 (s, 2H,
3
-
CH ), 6.45 (s, H, H-8), 6.73 (d, H, H-6), 7.69 (d, 1H, H-5), 8.33 (s, 1H, NH); IR: 3405, 3252 cm
2
1
-1
-1
-1
-
(
(
N–H), 3193 cm (C–H, Aromatic), 3055 cm (C–H, Aliphatic), 2663 cm (S–H), 1652 cm
C = O, Lactone), 1603 cm (C = N), and 1411.4 cm (C–N); Theoretical Calculation for
1
-1
-1
C H N O S: C 53.97%, H 3.83%, N 14.52%, S 11.08%. Experimental: C 52.64%, H 3.43%, N
1
3
11 3 3
1
3.89%, S 11.01%.
Microwave irradiation method: This involves the irradiation of compound 3 (0.431 g, 1.3
mmol) and KOH (0.09 g, 1.6 mmol) in a microwave oven at 10% intensity for 1 min. After
completion of reaction (by TLC), the product was recrystallized from ethanol. The yield of
product was 50%. M.p. 99–101°C.
Synthesis of 7-((5-mercapto-1,3,4-oxadiazol-2-yl)methoxy)4-methyl-2H-chromen-2-one
(
5). Conventional method: A solution of potassium hydroxide (0.84 g, 15 mmol) in 10 mL of
ethanol was added to a mixture of compound 2 (2.48 g, 10 mmol) in 150 mL of ethanol, fol-
lowed by the addition of carbon disulfide (20 mL). The reaction mixture was heated under
reflux for 6 hr and was then concentrated and acidified with dilute HCl. The resulting solid was
separated, washed with water, and recrystallized from a mixture of DMF-H O [18, 19]. Yield
2
1
6
6
0%; M.p. 177–179°C; H-NMR δ: 2.29 (s, 3H, CH ), 3.29 (br s, 1H,-SH), 4.01 (s, 2H, CH ),
.21 (s, 1H, H-3), 6.88 (s, 1H, H-8), 6.77 (d, 1H, H-6), 7.69 (d, 1H, H-5); IR: 3195.1 cm (C-H,
Aromatic), 3089 cm (C-H, Aliphatic), 2765 cm (S-H), 1679 cm (C = O Lactone) and 1403
cm (C-N); Theoretical Calculation for C H N O S: C 53.79%, H 3.47%, N 9.65%, S 11.05%.
3
2
-
1
-
1
-1
-1
-
1
13
10 2 4
Experimental: C 53.40%, H 3.11, N 9.31, S 10.97.
Microwave irradiation method: This involves the irradiation of mixture of compound 2
(
2.48 g, 10 mmol) and KOH (0.84 g, 15 mmol) in 10 mL of ethanol with carbon disulfide (20
PLOS ONE | DOI:10.1371/journal.pone.0132175 July 6, 2015
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Novel Coumarins as Antioxidants
mL) in a microwave oven at 10% intensity for 2 min. After completion of reaction (by TLC),
the product was recrystallized from ethanol. The yield of product was 70%. M.p. 180–181°C.
Synthesis of 7-(2-(3,5-dimethyl-1H-pyrazol-1-yl)-2-oxoethoxy)4-methyl-2H-chromen-
2-one (6). Conventional method: A mixture of compound 2 (0.248 g, 1 mmol), acetyl acetone
(
0.142 g, 1 mmol), and acetic acid (1.0 mL) was refluxed in 10 mL of ethanol for 5 hr. The pre-
cipitate was collected by filtration and recrystallized from ethanol [19] to yield compound 6.
1
Yield 54%; M.p. 298–299°C; H-NMR δ: 2.21 (s, 3H, CH ), 2.29 (s, 3H, CH ), 2.43 (s, 3H,
3
3
CH ), 5.01 (s, 2H, CH ), 6.11 (s, 1H, H-3), 6.15 (s, 1H, HC = C), 6.84 (s, 1H, H-8), 6.89(d, 1H,
3
2
-
1
-1
H-6), 7.51 (d, 1H, H-5); IR: 3122 cm (C–H, Aromatic), 2985 cm (C–H, Aliphatic), 1674.2
-
1
-1
cm (C = O Lactone), 1395 cm (C–N); Theoretical Calculation for C H N O : C 65.38%,
17
16 2 4
H 5.16%, N 8.97%. Experimental: C 65.00%, H 4.93%, N 8.41%.
Microwave irradiation method: This involves the irradiation of mixture of compound 2
(
0.248 g, 1 mmol), acetyl acetone (0.142 g, 1 mmol), and acetic acid (1.0 mL) in a microwave
oven at 20% intensity for 2 min. After completion of reaction (by TLC), the product was recrys-
tallized from ethanol. The yield of product was 60%. M.p. 297–299°C.
Synthesis of 7-hydroxy-2-oxo-2H-chromene-4-carbaldehyde (7). Conventional method:
7
-Hydroxy-4-methylcoumarin (1 g, 0.5 mmole) was dissolved in hot xylene (50 mL). The solu-
tion was cooled, and selenium dioxide (1 g, 0.9 mmol) was added. The mixture was refluxed for
1
5
1
2 hr and was filtered while hot. The solvent was removed to obtain the desired product. Yield
1
5%; H-NMR δ: 5.28 (s, OH), 6.59 (s, 1H, H-8), 6.61 (d, 1H, H-6), 7.56 (d, 1H, H-5), 7.01 (s,
-
1
-1
-1
H, H-3), 9.59 (s, 1H, CH). IR: 2925.2 cm (C–H, Aliphatic), 1743 cm (C = O), 1636 cm
(
C = C). Theoretical Calculation for C H O : C 63.16%, H 3.18%, Experimental: C 62.89%, H
10 6 4
3
.03%.
Microwave irradiation method: This involves the irradiation of mixture of compound 1 (1
g, 0.5 mmol) and selenium dioxide (1 g, 0.9 mmol) with 50 mL of xylene in a microwave oven
at 20% intensity for 2 min. After completion of reaction (by TLC), the product was recrystal-
lized from ethanol. The yield of product was 65%.
Synthesis of 4-(benzo[d]thiazol-2-yl)-7-hydroxy-2H-chromen-2-one (8). Conventional
method: Compound 7 (0.95 g, 5.0 mmol) and o-aminothiophenol (0.625 g, 5.0 mmol) were
refluxed in acetic acid (7 mL) for 5 hr. The solution was cooled, and the product precipitated.
This solid was collected, washed with water, and recrystallized from methanol [15]. Yield 75%;
1
1
M.p. 295–296°C; H-NMR δ: 5.22 (s, OH), 6.31 (d, 1H, H-6), 6.55 (s, 1H, H-8), 6.78 (s, H, H-
), 7.34 (t, 1H, J = 7.32Hz, H-5), 7.54 (d, 1H, H-5), 7.58 (d, 1H, J = 7.57Hz, H-4), 8.21 (t, 1H,
3
-
1
-1
J = 8.21Hz, H-6), 8.27 (d, 1H, J = 8.25Hz, H-7); IR 2921 cm (C–H, Aliphatic), 1765.1 cm
C = O), 1630 (C = C), 1560.11 cm (C = N), 1438 cm (C–N), 763.5 cm (C–S), Theoretical
-
1
-1
-1
(
Calculation for C H NO S: C 65.07%, H 3.07%, N 4.74%, Experimental: C 64.89%, H 3.00%,
10
9
3
N 4.32%.
Microwave irradiation method: This involves the irradiation of mixture of compound 7
0.95 g, 5.0 mmol) and o-aminothiophenol (0.625 g, 5.0 mmol) with acetic acid (7 mL) in a
(
microwave oven at 10% intensity for 1 min. After completion of reaction (by TLC), the product
was recrystallized from methanol. The yield of product was 80%. M.p. 292–294°C.
Hydrogen Peroxide Scavenging Activity
A solution of hydrogen peroxide (40 mM) was prepared in phosphate buffer (pH 7.4). Differ-
ent concentrations (250, 500, and 1000 μg/mL) of the synthesized compounds (or ascorbic acid
as the control) were added to a hydrogen peroxide solution (0.6 mL, 40 mM). The absorbance
of hydrogen peroxide at 230 nm was determined after 10 min against a blank solution contain-
ing phosphate buffer without hydrogen peroxide [22, 23]. The hydrogen peroxide percentage
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Novel Coumarins as Antioxidants
scavenging activity was then calculated using the following equation:
ꢀ
A
H O
2 scavenginig effect
% ¼ A ꢁ
ꢀ
ꢂ 100
ð1Þ
2
A
where A is the absorbance of the control reaction and A is the absorbance in the presence of
o
1
the samples or standards.
Statistical Analysis
The results were expressed as mean ± standard deviation and the statistical significance of dif-
ferences were determined utilizing one-way analysis of variance (ANOVA) using the SPSS 17.0
statistical software program. Differences were considered significant at P < 0.05. The values
are presented as mean ± SD (n = 3).
Results and Discussion
Chemistry
All of the reactions were completed under microwave irradiation and normal reflux conditions,
as shown in Table 1. The sequence for the synthesis of the coumarin derivatives 1–10 is shown
in Fig 1, starting from 7-hydroxy-4-methylcoumarin. Compound (1), namely, methyl 2-
(
(4-methyl-2-oxo-2H-chromen-7-yl)oxy)acetate, was synthesized by the reflux of methyl bro-
moacetate, 7-hydroxy-4-methylcoumarin, anhydrous potassium carbonate and anhydrous ace-
-
1
tone. The FT-IR spectrum for compound 1 showed an absorption band at 1743.5 cm due to
1
the stretching of the esteric carbonyl (-C = O). The H-NMR spectrum showed a singlet at δ
3
.65 ppm due to the methyl protons (3H of CH ) and a singlet at δ 3.68 ppm due to methylene
3
protons (2H of CH ). Compound 1 was reacted with hydrazine hydrate to afford hydrazide 2
2
in good yield. Compound 2 (hydrazide) showed absorption bands at 3231.5, 3225.1, and 3209
-
1
1
cm (hydrazide NH-NH ). The H-NMR spectrum exhibited a singlet due to the (s, 2H, CH )
2
2
proton at δ 4.24 ppm and a singlet due to the (1H, NH) proton at δ 7.50 ppm. Compound 2
was refluxed with KSCN in ethanol as the solvent containing catalytic amounts of HCl to yield
salt 3, which was converted directly to 4 in good yield by heating in aqueous KOH followed by
acidification with HCl. Compound 5 was prepared accordingly by heating 2 with CS in the
2
presence of ethanolic potassium hydroxide. By condensation of 2 with acetyl acetone in ethanol
with a few drops of acetic acid, the corresponding derivative 6 was obtained in 54% yield. Upon
condensation of 2 with xylene and selenium dioxide, the corresponding derivative 7 was
Table 1. Comparison between the microwave-assisted and chemical methods of synthesis in terms
of yield and time.
Compound
Microwave Method
Time (min) Yield (%)
Chemical Method
Time (hr.) Yield (%)
1
2
3
4
5
6
7
8
-
-
12
4
75
60
45
35
60
54
55
75
2
2
1
2
2
2
1
75
60
50
70
60
65
80
3
3
3
5
12
5
doi:10.1371/journal.pone.0132175.t001
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Novel Coumarins as Antioxidants
obtained in good yield. Compound 8 was also obtained by refluxing compound 7 with o-
aminothiophenol.
Scavenging Activity. The role of a cancer prevention agent is to remove free radicals. The
most important mechanism to achieve this goal is the donation of hydrogen to free radicals to
convert them to nonreactive species [24]. The donation of hydrogen would remove the odd
electron that is responsible for radical reactivity [25]. Free radicals have been a subject of criti-
cal interest among researchers in the previous decade. The wide range of free radical effects in
biological systems has garnered interest from many specialists. It has been demonstrated that
free radicals assume an important role in the pathogenesis of specific diseases and aging
[24,25]. Numerous synthetic cancer prevention agents have presented toxic and/or mutagenic
effects; thus, naturally occurring antioxidants have been considered [26]. Synthesized couma-
rins 1–8 were screened for in vitro scavenging activity utilizing hydrogen peroxide. These tested
coumarins showed high scavenging activity (Fig 2).
Fig 2 showed that the eight synthesized compounds (1–8) demonstrated a strong scavenging
activity against H O . At a very low concentration of 250 μg/mL we observed a concentration
2
2
dependent decrease in H2O2 activity. A very weak inhibitory activity was found in compound
1
1
and compound 6 (5.33 ± 0.88 and 18.0 ± 1.00). The highest concentration was found at
000 μg/mL (Fig 2). The best percentage scavenging activity was shown by compound 8
(
(
91.66 ± 1.52), followed by compound 4, 3 and 7 (88.33 ± 1.50; (83.33 ± 1.52 and
82.66 ± 1.52;). However, their activity was not significantly different at 95% confidence
Fig 2. Percentage inhibition of hydrogen peroxide scavenging activity of synthesized compounds (1–8) in comparison to Vitamin C. n = 3. Error
bars indicate standard deviation.
doi:10.1371/journal.pone.0132175.g002
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Novel Coumarins as Antioxidants
Fig 3. Suggested mechanism for compound 4 as an antioxidant.
doi:10.1371/journal.pone.0132175.g003
interval. vitamin C was used as standard drugs with percentage inhibition of 70.00 ± 2.00. The
hydrogen-donating activity, measured utilizing hydrogen peroxide radicals as the hydrogen
acceptor, demonstrated that a strong association could be found between the concentration of
the coumarin molecule and the rate of inhibition [27]. Using the hydrogen peroxide test, cou-
marins 1–8 demonstrated their ability to diminish the stable radical. The postulated mecha-
nism for the reaction of coumarin 4 as an antioxidant, as indicated in Fig 3, relies on the
Fig 4. Suggested mechanism for compound 8 as an antioxidant.
doi:10.1371/journal.pone.0132175.g004
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Novel Coumarins as Antioxidants
mercapto hydrogen atom (bold), which is under the influence of resonance and inductive
effects. The resonance effect of the mercapto hydrogen facilitates the release of hydrogen, while
the inductive effect pushes the electrons toward a sulfur-free radical, resulting in stability of the
molecule.
The postulated antioxidant mechanism for synthesized coumarin 8, as shown in Fig 4, relies
on the hydroxyl hydrogen atom (bold), which is under the influence of resonance and induc-
tive effects. The resonance effect of the oxygen hydrogen facilitates the release of hydrogen,
while the inductive effect pushes the electrons toward the oxygen-free radical, resulting in sta-
bility of the molecule [28]. Note that coumarin 8 has a higher scavenging activity because of
the stability of the free radical intermediates of this coumarin [29].
Conclusions
New coumarin derivatives were successfully synthesized using chemical and microwave irradi-
ation methods. The characterized of these coumarins (S1 and S2 Figs) were done by using dif-
ferent spectroscopic techniques (FT-IR and NMR) and micro-elemental analysis (CHNS). The
scavenging activity of these coumarins were determined by using hydrogen peroxide assay.
Results indicated that the new coumarins possess higher scavenging activity than vitamin C.
The availability of these coumarins would also facilitate further investigations of their pharma-
cological properties.
Supporting Information
S1 Fig. FT-IR spectrum.
(
PDF)
S2 Fig. Proton NMR spectrum.
PDF)
(
Acknowledgments
This study was supported by the Universiti Kebangsaan Malaysia under the DIP-2012-02 grant.
Author Contributions
Conceived and designed the experiments: AAA ABM AHK. Performed the experiments: YKA.
Analyzed the data: AAA ABM AHK. Contributed reagents/materials/analysis tools: AAA
ABM YKA AHK. Wrote the paper: AAA.
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