Synthesis, in vitro antimicrobial and antioxidant activities of chalcone and flavone derivatives holding allylic substitutions

Article abstract of DOI:10.1007/s00044-010-9474-3

In a wide search program towards new and efficient biological active agents, a series of chalcone and flavone derivatives holding allylic substitutions have been synthesized and tested for their in vitro antibacterial and antifungal activities. The synthe

Full text of DOI:10.1007/s00044-010-9474-3

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2011) 20:1318–1324
DOI 10.1007/s00044-010-9474-3
ORIGINAL RESEARCH
Synthesis, in vitro antimicrobial and antioxidant activities
of chalcone and flavone derivatives holding allylic substitutions
•
Hadi Adibi Javid Shahbazi Mojarrad
•
•
Hadi Asgharloo Gholamreza Zarrini
Received: 19 January 2010 / Accepted: 14 October 2010 / Published online: 28 October 2010
Ó Springer Science+Business Media, LLC 2010
Abstract In a wide search program towards new and
efficient biological active agents, a series of chalcone and
flavone derivatives holding allylic substitutions have been
synthesized and tested for their in vitro antibacterial and
antifungal activities. The synthesized compounds were
tested in vitro against Gram-positive, Gram-negative bac-
teria, and the yeast Candidia kefir in comparison with
control drugs (Sulfamethoxazole and Fluconazole). The
antioxidant activity of the synthesized allylic chalcones and
flavones was also assessed using two methods, including,
1,1-biphenyl-2-picrylhydrazyl (DPPH) radical scavenging,
and reducing power assays and compared to reference drug
Trolox.
Introduction
Flavonoids comprise a large family of plant-derived poly-
phenolic compounds that demonstrate diverse biological
activities, including the ability to inhibit retroviral tran-
scriptases (Nakane and Ono, 1990), protein-tyrosine kina-
ses (Geahlen et al., 1989), and other enzymes (Hagiwara
et al., 1988). These compounds have been found to possess
´
anticancer (Sanchez et al., 2001), chemopreventive
(Cassady et al., 1990) and antibacterial (Mughal et al.,
2006) activities. In addition, naturally occurring or syn-
thetic flavonoids and natural lignans have been studied
(Edwards et al., l979; Hirano et al., 1989), since they
appear to be compounds of low toxicity and some of them
apparently have antiproliferative activity against human
tumor cells (Hirano et al., 1994). Investigations carried out
by Kaul et al. (1985) have shown an important structure–
activity relationship in this group of natural flavonoids.
Antioxidants are of great interest because of their
involvement in important biological and industrial pro-
cesses. In general, compounds with antioxidant activity have
also been found to have anticancer, anti-cardiovascular,
anti-inflammation, and many other activities (Cadenas and
Packer, 1996). Reactive oxygen species (ROS) and free
radicals are considered to be implicated in a variety of
pathological events, such as cancer and aging (Chabot et al.,
1998). ROS, including superoxide anion, hydrogen perox-
ide, and hydroxyl radical, are thought to be generated sub-
sequent to the reduction of molecular oxygen in aerobic
organisms. Under normal conditions, cells and tissues are
protected against ROS by an array of enzyme defense sys-
tems, such as superoxide dismutase, catalase, and glutathi-
one peroxidases, in addition to numerous non-enzymatic
small molecules distributed widely in the biological system
and capable of scavenging free radicals. These molecules
Keywords Antimicrobial activity ꢀ Antioxidant activity ꢀ
Chalcones ꢀ Flavones ꢀ Allylic substitutions
Electronic supplementary material The online version of this
article (doi:10.1007/s00044-010-9474-3) contains supplementary
material, which is available to authorized users.
H. Adibi (&) ꢀ H. Asgharloo
Department of Medicinal Chemistry, Faculty of Pharmacy,
Kermanshah University of Medical Sciences,
67145-1673 Kermanshah, Iran
e-mail: hadibi@kums.ac.ir
J. S. Mojarrad (&)
Department of Medicinal Chemistry, Faculty of Pharmacy,
Tabriz University of Medical Sciences, Tabriz, Iran
e-mail: shahbazi_j@tbzmed.ac.ir
J. S. Mojarrad
Biotechnology Research Center,
Tabriz University of Medical Sciences, Tabriz, Iran
G. Zarrini
Department of Animal Biology, Faculty of Natural Sciences,
Tabriz University, Tabriz, Iran
123

Med Chem Res (2011) 20:1318–1324
1319
Scheme 1 Reagents and
conditions: (i) allyl bromide,
K2CO3, acetone, (ii) 250°C, N2
include glutathione, a-tocopherol (vitamin E), vitamin C,
b-carotene, and selenium (Jacob and Burri, 1996). In this
study, we wish to report chalcones and flavones with allylic
substitutions and evaluate their antimicrobial and antioxi-
dants activities (Scheme 1).
scavenging (Blois, 1958), and reducing power (Oyaizu,
1986) assays according to the methods described in the
literature (Table 2). The results of antioxidant activity in
both methods are approximately similar to each other. All
the synthesized compounds exhibited good antioxidant
properties. They were less potent than Trolox as the ref-
erence. It should be noted that when allylic chalcones are
cyclized to allylic flavones, the antioxidant activity is
decreased. This is due to the existence of the free hydroxyl
group in the chalcone (Table 2). The compounds 6a, 6b,
7a, and 7b have good antioxidative activity with a major
activity for 6b (IC50 85 lM). Overall, the result of DPPH
assay was relatively consistent with that of reducing power
assay. The potencies for the antioxidative activity of the
test compounds compared to the reference drugs are in the
following order: Trolox [ 6b [ 6a [ 7b [ 7a.
Results and discussion
Antimicrobial activity
Microbiological results showed that the synthesized chal-
cones and flavones holding allylic substitutions possessed a
broad spectrum of antibacterial activity against Gram-
positive and Gram-negative microorganisms using con-
ventional agar-dilution method (Baron and Finegold,
1990). The MICs (minimum inhibitory concentration)
values were determined by comparison to sulfamethoxa-
zole as reference drug and are presented in Table 1. All the
chalcones and flavones indicated poor antibacterial activi-
ties having MIC values higher than 512 lg/ml, and
showing less potency than the control drugs (Sulfameth-
oxazole). Moreover, the synthesized compounds also pos-
sessed antifungal activity against the yeast C. kefir showing
MIC values [ 512 lg/ml compared to fluconazole
(Table 1). However, it is seems that allylic chalcones are
more potent than allylic flavones. Perhaps the reason is that
allylic flavones have low solubility than the allylic chal-
cones. This shows the necessity of hydrophilic substitu-
tions for having better results.
Conclusions
In summary, we have reported biological evaluation of
chalcones and flavones with allylic substitutions, which
represent antioxidant and antimicrobial activities. All the
synthesized chalcones and flavones showed poor antimi-
crobial activity. A moderate to good antioxidant activity
was observed by reducing power assay and DPPH radical
scavenging method.
Experimental
Antioxidant activity
Typical procedure for synthesis of allylic chalcone (6a)
The antioxidant activity was assessed using two methods,
including, 1,1-biphenyl-2-picrylhydrazyl (DPPH) radical
To a solution of 3-allyl-2-hydroxyacetophenone (3) (10 mmol)
and 2-allyloxy-3-methoxy benzaldehyde (5a) (10 mmol) in
123

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Med Chem Res (2011) 20:1318–1324
Table 1 The MICs (in lg/mL)
values of allylic chalcones and
flavones against bacteria and
fungus
Compound
E. coli
S. aureus
S. epidermidis
Candidia kefir
Yield (%)a
74
512
[1000
[1000
512
512
[1000
[1000
512
72
[512
[1000
[1000
512
18
[512
[1000
[1000
[512
17
Fluconazole
–
4
–
4
–
4
4
–
–
–
a
Yield of isolated product after
purification
Sulfamethoxazole
EtOH (20 ml) was added a 60% of KOH (10 ml) solution
dropwise at 0°C. The reaction mixture was stirred at 0°C for
1 day. Cold water was added and the reaction mixture was
neutralized with cold acetic acid. The yellow precipitate was
collected, washed with water and recrystallized from EtOH to
yield b-(20-allyloxy-30-methoxyphenyl)-1-(3-allyl-2-hydroxy-
phenyl) propenone (6a) as orange needles; mp = 86–89°C
(yield 74%) (Scheme 2).
2-(20-allyloxy-30-methoxyphenyl)-8-allyl-4-chromone (7a)
was then extracted with ethyl acetate and purified by col-
umn chromatography (hexane/ethyl acetate, 9:1).
2-Allyloxy-3-methoxy benzaldehyde (5a): Rf = 1.2 (n-
Hexane–Ethyl acetate 80: 20); IR (KBr) m 3087 (stretch CH
sp2 aromatic), 3041 (stretch CH, sp2 allylic), 2986 and
2926 (stretch CH3, sp3), 2863 and 2770 (stretch CHO),
1710 (stretch C=O), 1648 (stretch C=C allylic), 1602 and
1493 (stretch C=C aromatic), 1240 and 1022 (stretch C–O–
Ar), 1000 and 937 (bends C=C allylic OOP), 758 and 653
(1, 2, 3 position).
Typical procedure for synthesis of allylic flavone (7a)
4-Allyloxy-3-methoxy benzaldehyde (5b): Rf = 1.7
(n-Hexane–Ethyl acetate 80:20); IR (KBr) m 3361 (C=O,
overtone), 3088 (stretch CH, sp2 aromatic), 3003 (stretch
CH, sp2 allylic), 2940 (stretch CH3, sp3), 2835 and 2729
(stretch CHO), 1683 (stretch C=O), 1642 (stretch C=C,
allylic), 1588 and 1507 (stretch C=C, aromatic), 1268 and
1041 (stretch C–O–Ar), 997 and 934 (bends = C–H pro-
penyl OOP), 870 and 810 (1, 3, 4 position).
To a solution of b-(20-allyloxy-30-methoxyphenyl)-1-(3-
allyl-2-hydroxyphenyl) propenone (6a) (1 mmol) in
DMSO (5 ml) was added I2 (254 mg, 1 mmol), and the
reaction mixture was heated in an oil bath at 130°C for 30
min. After cooling, the reaction mixture was diluted with
water and the iodine was removed by washing with a
saturated solution of sodium thiosulfate. The product
123

Med Chem Res (2011) 20:1318–1324
1321
Table 2 Antioxidant activities
of allylic chalcones and flavones
in comparison to Trolox
Entry
Compound
DPPH radical scavenging
activity (IC50, lM)
Reducing
power (Fe2? lM)
1
163
1.87
2
85
2.96
3
320
1.11
4
270
0.57
5
Trolox
36
41.93
2-Allyloxy acetophenone (2): Rf = 0.7 (n-Hexane–
Ethyl acetate 95:5); IR (KBr) m 3333 (C=O, overtone),
3080 (stretch CH, sp2 aromatic), 3000 (stretch CH, sp2
allylic), 2982 (stretch CH3, sp3), 1672 (stretch CHO), 1595
and 1482 (stretch C=C, aromatic), 1237 and 1011 (stretch
C–O–Ar), 993 and 912 (bends = CH oop), 757 (1, 2
position).
b-(20-Allyloxy-30-methoxyphenyl)-1-(3-allyl-2-hydroxy
phenyl) propenone (6a): Rf = 0.5 (n-Hexane–Ethyl acetate
90:10); mp = 86–89°C; IR (KBr) m 3080 (stretch CH, sp2
aromatic), 3010 (stretch CH, sp2 allylic), 2975 (stretch CH3
sp3), 1640 (stretch C=O), 1571 and 1480 (stretch C=C,
aromatic), 1274 and 1103 (stretch C–O–Ar); 1H-NMR
(DMSO-d6): d 3.364-3.386 (d, 2H, –CH2–), 3.837 (s, 3H,
OCH3), 4.528–4.547 (d, 2H, –OCH2–), 5.029–5.406 (m, 4H
cis, =CH2), 5.344–5.406 (dd, 2H trans, =CH2) 5.912–6.024
(m, 2H, –CH=), 6.925–6.976 (t, 1H, C5 H), 7.155–7.176 (d,
3-Allyl-2-hydroxy acetophenone (3): Rf = 1.3 (n- Hex-
ane-Ethyl acetate 85:15); IR (KBr) m 3368 (OH), 3070
(stretch CH, sp2 aromatic), 3017 (stretch CH, sp2 allylic),
2975 (stretch CH3), 1683 (stretch C=O), 1640 and 1440
(stretch C=C, aromatic), 1247 and 1010 (stretch C–O–Ar),
979 and 916 (bends =CH OOP), 754 and 660 (1, 2, 3
position).
0
1H, C4 H), 7.166–7.192 (d, 1H, C4 H), 7.430–7.455 (d, 1H,
0
0
C6 H),7.658–7.689 (t, 1H, C5 H), 8.015–8.067 (d, J = 15.6,
Ha), 8.136–8.188 (d, J = 15.6, Hb), 8.172–8.199 (d, 1H,
C6H), 13.3 (s, 1H, OH); 13C-NMR (DMSO-d6): d 33.388
123

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Med Chem Res (2011) 20:1318–1324
Scheme 2 Reagents and
conditions: (i) KOH,
(ii) I2/DMSO
(–CH2–), 56.350 (–OCH3), 74.322 (–OCH2–), 115.89
(stretch CH, sp2 allylic), 2923 (stretch CH3), 1645 (stretch
C=O), 1603 and 1516 (stretch C=C, aromatic), 1276 and
0
(=CH2), 116.496 (=CH2), 118.443 (C4 ), 119.064 (C6 ),
0
1
0
0
119.799 (–C5), 120.054 (C5 ), 122.245 (C1 ), 124.775 (Ca),
128.678 (C1), 128.960 (C3), 129.442 (C6), 134.448 (C4),
136.658 (–CH=), 137.048 (–CH=), 140.024 (Cb), 147.584
1143 (stretch C–O–Ar); H-NMR (DMSO-d6): d 3.658–
3.680 (d, 2H, –CH2–), 3.875 (s, 1H, –OCH3), 4.503–4.522
(d, 2H, –OCH2–), 5.054–5.282 (m, 4H, =CH2), 5.851–
5.962 (m, 2H, –CH=), 6.853 (s, 1H, C3H), 7.243–7.309
0
0
(C2 ), 153.231 (C3 ), 161.229 (C2), 194.667 (C=O).
b-(40-Allyloxy-30-methoxyphenyl)-1-(3-allyl-2-hydroxy-
phenyl) propenone (6b): Rf = 0.55 (n-Hexane–Ethyl acetate
85:15); mp = 88–85°C; IR (KBr) m 3083 (stretch CH, sp2
aromatic), 3011 (stretch CH, sp2 allylic), 2923 (stretch CH3,
sp3), 1638 (stretch C=O), 1596 and 1509 (stretch C=C, aro-
matic), 1258 and 1063 (stretch C–O–Ar); 1H-NMR (DMSO-
d6): d 3.351–3.385 (d, 2H, –CH2), 3.870 (s, 3H, CH3),
4.608–4.635 (d, 2H, OCH2), 5.016–5.112 (m, 2H cis, =CH2),
5.233–5.444 (m, 2H trans, =CH2), 5.909–6.113 (m, 2H,
=CH–), 6.921–6.958 (d, 1H, C4H), 6.998–7.008 (d, 1H,
0
(t and d, 2H, C6H and C6 H), 7.384–7.457 (dd and dd, 2H,
0
C4 H, C5’H), 7.642–7.666 (dd, 1H, C7H), 7.913–7.945 (dd,
1H, C5H); 13C-NMR (DMSO-d6): d 33.699 (CH2), 56.538
(OCH3), 73.959 (OCH2), 112.05 (CH2=), 116.277 (CH2=),
0
117.178 (C4 ), 118.169 (C6 ), 120.836 (C5 ), 123.433 (C6),
0
0
0
123.706 (C1 ), 125.087 (C5), 125.573 (C3), 126.655 (C10),
130.044 (C8), 134.255 (CH=), 134.655 (CH=), 136.178
0
0
(C7), 146.356 (C2 ), 153.508 (C3 ), 154.395 (C2), 161.275
(C9), 177.605 (C4).
2-(40-Allyloxy-30-methoxyphenyl)-8-allyl-4-chromone (7b):
Rf = 0.53 (n-Hexane–Ethyl acetate (80: 20); mp = 108–
109°C; IR (KBr) m 3083 (stretch CH, sp2 aromatic), 3007
(stretch CH, sp2 allylic), 2923 (stretch CH3), 1648 (stretch
C=O), 1595 and 1493 (stretch C=C, aromatic), 1272 and
0
C5 H), 7.050 (d, 1H, C6 H), 7.381–7.450 (t, 1H, C5H),
0
0
7.586–7.595 (d, 1H, C2 H), 7.793–7.870 (d, J = 22.98 Hz,
Ha), 7.931–8.007 (d, J = 23.01 Hz, Hb), 8.225–8.272 (dd,
1H, C6H), 13.454 (s, 1H, OH); 13C-NMR (DMSO-d6): d
33.385 (–CH2–), 56.333 (–OCH3–), 69.341 (–OCH2–),
1
1098(stretch C–O–Ar); H-NMR (DMSO-d6): d 3.314 (s,
0
111.812 (–CH2=), 113.414 (–CH2=), 116.482 (C2 ), 118.363
3H, H2O as impurity), 3.752 (s, 2H, –CH2), 3.873–3.885(d,
2H, –OCH3), 4.651(s, 1H, CH2) 5.085-5.133 (t, 2H cis,
=CH2), 5.262–5.443 (dd, 2H trans, =CH2), 6.066–6.124 (m,
2H, –CH=), 7.020–7.039 (d, 1H, C3H), 7.115–7.163 (dd,
0
0
0
(C5 ), 118.834 (C6 ), 118.993 (C1 ), 119.751 (C5), 125.066
(Ca), 127.896(C1), 128.866 (C3), 129.389(C6), 133.835(C4),
0
136.665 (CH=), 136.849 (CH=), 146.403 (Cb), 149.744 (C4 ),
0
0 0
1H, C6 H), 7.392–7.435 (dd, 1H, C5 H), 7.564-7.582 (d, 1H,
151.072 (C3 ), 161.201 (C2), 194.559 (C=O).
2-(20-Allyloxy-30-methoxyphenyl)-8-allyl-4-chromone (7a):
Rf = 0.5 (n-Hexane–Ethyl acetate 70:30); mp = 103–
105°C; IR (KBr) m 3083 (stretch CH, sp2 aromatic), 2986
0
C2 H), 7.630–7.650 (dd, 2H, C7,6 H), 7.886–7.921 (d, 1H,
0
C5 H); 13C-NMR (DMSO-d6): d 33.941 (–CH2), 56.241
(–OCH3), 69.370 (–OCH2–) 106.084 (=CH2), 110.009
0
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Med Chem Res (2011) 20:1318–1324
1323
0
(=CH2), 113.650 (C2 ), 116.966 (C5 ), 118.443 (C6 ),
0
0
the test compound), and As is the absorbance of the test
sample. Results were compared to activity of L-ascorbic
acid and BHA. The IC50 values represented the concen-
tration of the test compounds that caused 50% inhibition
are shown in Table 2.
120.094 (C6), 123.477 (C5), 123.853 (C10), 124.185 (C8),
0
125.476 (C3), 129.864 (C1 ), 133.770 (=CH–), 134.669
0
(=CH ), 136.329 (C7), 149.671 (C4 ), 151.189 (C3 ),
0
0
154.022 (C2), 162.730 (C9), 177.630 (C4).
Microbial strains
Reducing power assay
The synthesized compounds were evaluated for their anti-
microbial activity against Staphylococcus aureus, Staphy-
lococcus epidermidis, E. coli and the yeast Candidia kefir
which were provided by Department of Microbiology
(Faculty of Medicine, Tabriz University Medicinal Sci-
ences, Tabriz, Iran).
0.13 ml of samples in different concentrations (25, 50, 100,
250, 500, 1000 lg/ml) in phosphate buffer (0.2 mM, pH 6.6)
were mixed with 0.125 ml of potassium ferric cyanide (1%
w/v) and incubated at 50°C for 20 min. Afterwards,
0.125 mL of trichloroacetic acid (TCA) (10% w/v) was
added to the mixture to terminate the reaction. Then the
solution was mixed with 1.5 ml ferric chloride (1% w/v) and
the absorbance was measured at 700 nm. The capability of
antioxidant activity was calculated using the following
Antimicrobial assay
Turbidity of all the bacterial cultures was adjusted to 0.5
McFarland Standard by preparing bacterial suspension of
3–5 well-isolated colonies of the same morphological type
selected from an agar plate culture. The cultures were
further diluted 1000-fold to get an inoculum size of
1.5 9 105 CFU/ml. The test compounds (50 mg) were
dissolved in DMSO (0.5 ml) and the solution was diluted
with water (4.5 ml) to get a stock solution of 10,000 mg/ml
of each compound. Further progressive double dilution
with Muller–Hinton broth was performed to obtain the
required concentrations of 1000, 512, 256, 128, 64, 32, 16,
8, 4, 2 lg/ml. To ensure that the solvent had no effect on
bacterial growth, a control test was performed with test
medium supplemented with DMSO at the same dilutions as
used in the experiment. Our results indicated that all the
test compounds tested in this study demonstrated lower
activity against both Gram-positive and Gram-negative
microorganisms than the reference drug. Standard antibi-
otic (sulfamethoxazole) was also diluted in the same
manner. Each microwell in a series of 12 microwells was
inoculated with 75 microliter of the serial dilutions, and
then 75 microliter of the bacterial suspension was added.
After overnight incubation in 37°C, growth was surveyed.
equation: Inhibition concentration (%) = 1 - Asample
A
/
control. IC50 is inhibition concentration defined as the con-
centration inhibitory 50% radical generation or scavenging
50% radical generated. The IC50 values of the compounds
are presented in Table 2.
Acknowledgments We gratefully acknowledge Vice Chancellor for
Research and Technology, Kermanshah University of Medical Sci-
ences for financial support. This work was performed in partial ful-
fillment of the requirements for a Pharm. D of Hadi Asgharloo in
Faculty of Pharmacy, Kermanshah University of Medical Sciences
Kermanshah-Iran.
References
Baron EJ, Finegold SM (1990) Bailey and Scott’s diagnostic
microbiology, 8th edn. CV Mosby, St. Louis, pp 184–188
Blois MS (1958) Antioxidant determinations by the use of a stable
free radical. Nature 181:1199–1200
Cadenas E, Packer L (1996) Handbook of antioxidants. Marcel
Dekker, New York
Cassady JM, Baird WH, Chang CJ (1990) Natural products as a
source of potential cancer chemotherapeutic and chemo
preventive agents. J Nat Prod 53:23–41
Chabot F, Mitchell JA, Gutteridge JMC, Evans TW (1998) Reactive
oxygen species in acute lung injury. Euro Respir J 11:745–757
Edwards JM, Raffauf RF, Le Quesne PW (1979) Antineoplastic
activity and cytotoxicity of flavones, isoflavones and flavanones.
J Nat Prod 42:85–91
DPPH radical-scavenging activity assay
Geahlen RL, Koonchanook NM, Mc Laughlin JL, Pratt DE (1989)
Inhibition of protein-tyrosine kinase activity by flavonoids and
relates compounds. J Nat Prod 52:982–986
Hagiwara M, Inove S, Tanaka T, Nunoki K, Ito M, Hidaka H (1988)
Differential effects of flavonoids as inhibitors of tyrosine protein
kinases and serine/theonine protein kinases. Biochem Pharmacol
37:2987–2992
Hirano T, Oka N, Naitoh T, Hosaka K, Mitsuhashi H (1989)
Endogenous digoxin-like activity of mammalian lignans and their
derivates. Res Commun Chem Pathol Pharmacol 64:227–240
Hirano T, Gotoh M, Oka K (1994) Natural flavonoids and lignans are
potent cytostatic agents against human leukemic HL-60 cells.
Life Sci 55:1061–1069
The compounds were dissolved in appropriate solvent
mixed with 1 ml of 0.2 mM 2,2-diphenyl-1-picrylhydrazyl
radical (DPPH) in ethanol, and final volume was adjusted
to 2 ml. Mixtures were variously shaken and left for
30 min in the dark. Absorbance was measured at 517 nm
using a UV–VIS spectrophotometer. 1 ml of 0.2 mM
DPPH diluted in 1 ml of ethanol was used as control.
Neutralization of DPPH radical was calculated using the
equation: S (%) = 100 (Ao - As)/Ao, where Ao is the
absorbance of the control (containing all reagents except
123

1324
Med Chem Res (2011) 20:1318–1324
Jacob RA, Burri BJ (1996) Oxidative damage of defence. Am J Clin
Nutr 63:985S–990S
Kaul TN, Middletown E Jr, Ogra PL (1985) Antiviral effect of
flavonoids on human viruses. J Med Virol 15:71–79
virus reverse transcriptase and cellular deoxyribonucleic and
ribonucleic acid polymerases. Biochemistry 29:2841–2845
Oyaizu M (1986) Studies on product of browning reaction prepared
from glucose amine. Jpn J Nutr 44:307–315
´
´
Mughal EU, Ayaz M, Hussain Z, Hasan A, Sadiq A, Riaz M, Malik
A, Hussain S, Choudhary MI (2006) Synthesis and antibacterial
activity of substituted flavones, 4-thioflavones and 4-iminoflav-
ones. Bioorg Med Chem 14:4704–4711
Sanchez I, Calderon J, Ruiz B, Tellez J, Calzada L, Taboada J (2001)
In vitro cytotoxicity of flavonoids against MK2 and C6 tumour
cells. Phytother Res 15:290–293
Nakane H, Ono K (1990) Differential inhibitory effects of some
catechin derivates on the activities of human immuno-deficiency
123