Syntheses and radical scavenging activities of resveratrol derivatives

Article abstract of DOI:10.1016/j.bmcl.2003.10.038

Nine new resveratrol derivatives, having bromo, iodo, and fluoroethyl groups, were designed and synthesized. All compounds having free phenol groups showed good free radical scavenging activity. Among them, 2-bromoresveratrol 19 has a similar free radical scavenging activity to (+)-catechin.

Full text of DOI:10.1016/j.bmcl.2003.10.038

Bioorganic & Medicinal Chemistry Letters 14 (2004) 463–466
Syntheses and radical scavenging activities of
resveratrol derivatives
Hyun Jung Lee,a Jai Woong Seo,a Bong Ho Lee,b Kyoo-Hyun Chunga
and Dae Yoon Chia,*
aDepartment of Chemistry, Inha University, 253 Yonghyundong, Namgu, Inchon, 402-751, South Korea
bDepartment of Chemistry, Hanvat University, Daejeon, 305-719, South Korea
Received 16 September 2003; revised 21 October 2003; accepted 23 October 2003
Abstract—Nine new resveratrol derivatives, having bromo, iodo, and fluoroethyl groups, were designed and synthesized. All com-
pounds having free phenol groups showed good free radical scavenging activity. Among them, 2-bromoresveratrol 19 has a similar
free radical scavenging activity to (+)-catechin.
# 2003 Elsevier Ltd. All rights reserved.
1. Introduction
tissue distribution in vivo. Recently, Merillon et al.
Resveratrol (1), 3,40,5-trihydroxy-trans-stilbene found in
grapes and a variety of medicinal plants,1 is a naturally
occurring phytoalexin that protects against fungal
infections. Its biological properties2 include antifungal,3
antibacterial,4 anticancer,5 antiviral,6 estrogenic,7 plate-
let antiaggregating,8 and heart protecting activities.9
Despite high fat diet and heavy smoking habits, the
Southern French people have very low incidence of
coronary heart disease (CHD). This so-called French
paradox has strongly been related with wine con-
sumption.1f Frankel et al. have shown that total phe-
nolic compounds extracted from red wine inhibit the
oxidation of human low-density lipoproteins (LDL).10
As the oxidized LDL may be responsible for promoting
atherogenesis, the phenolic compounds in red wine
could be the cause of the French paradox.11
reported the absortion and tissue distribution of [14C]-
trans-resveratrol following oral administration to
mice.12 The results demonstrated that trans-resveratrol
is bioavailable following oral admistration and
remains mostly in intact form. There are also not
many studies on the structure–activity relationship
(SAR) of resveratrol.11,13 Fauconneau et al. published
the comparative study of radical scavenger and anti-
oxidant properties of natural phenolic compounds iso-
lated from vitis vinifera cell cultures.11 Ho et al.
evaluated the hydroxylated derivatives of resveratrol as
potential antioxidants.13a Several glucopyranoside deri-
vatives of resveratrol were isolated, synthesized, and
evaluated by Orsini et al.13a
Positron emission tomography (PET) and single photon
emission computed tomography (SPECT) are widely
used for medical imaging. Bromine-76 (t1/2=16 h),
iodine-123 (t1/2=13.1 h), and fluorine-18 (t1/2=110 min)
are very attractive radionuclides for the labeling of
organic molecules as PET and SPECT radiotracers,
because of their many favorable characteristics such as
stable bonding to carbon, convenient half-life, and ease
of production.14 Labeled resveratrols with either posi-
tron or single photon emitted radionuclides are impor-
tant for studying biological behaviors and activities in
vivo as well as in vitro. In this report, we have designed
and synthesized several bromo, iodo, and fluoro
resveratrol derivatives. Through their free radical
scavenging activities and the amount of total polyphenol,
we obtained information on the SAR of resveratrol.
Although resveratrol has numerous biological activities
in vitro, there is little data about its bioavailability and
Keywords: Resveratrol; Radical scavenger; Stilbene; Antioxidant;
Phenol.
* Corresponding author. Tel.: +82-32-860-7686; fax: +82-32-867-
5604; e-mail: dychi@inha.ac.kr
0960-894X/$ - see front matter # 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2003.10.038

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H. J. Lee et al. / Bioorg. Med. Chem. Lett. 14 (2004) 463–466
2. Chemistry
show the synthesis of aldehyde precursors of Wittig
reagents. The synthetic route for the introduction of
fluoroethyl group17 included palladiumcoupling reac-
tion, hydroboration, tosylation, and fluorination18 as
shown in Scheme 4. When we synthesized a fluoro-
ethylated compound, classical displacement of sulfonate
with fluoride ion gave mostly eliminated by-product
with very low yield of desired fluoroethyl compound.
We have recently reported a new fluorination method
using ionic liquid [bmim][BF4], providing fluoroethyl
compound as a major product,18 which allowed the
synthesis of fluoroethyl compound in high yield. Nine
new compounds were synthesized according to Scheme
1 and 4-iodoresveratrol was selectively prepared by
direct iodination of unprotected resveratrol using I2 in
MeOH at rt for 2 h (Scheme 5).
Resveratrol is one of unsymmetrical and (E)-geome-
trical stilbene. Among the various methods to make
unsymmetrical stilbenes,15 we have used the general
methodology for the synthesis of the derivatives of
resveratrol as shown in Scheme 1. Wittig condensation
of appropriate aldehydes with phosphoniumsalts which
were generated from O-protected 3,5-dihydroxybenzyl
bromides 2–6 afforded stilbenes 7–15 in 74–93% yields.
The stilbenes were a mixture of (E) and (Z)-geometrical
isomers with the ratio of 2:1. These E/Z mixtures effi-
ciently converted to (E)-geometrical isomers through
heating with the catalytic amount of I2 in refluxing
heptane for 12 h.16
We tried using methyl group for the protective group of
phenols. But with the exception of resveratrol, the other
3,40,5-trimethylated resveratrol derivatives with bromo (7,
9), iodo (8), or fluoroethyl groups decomposed during the
demethylation step using BBr3 in dichloromethane13a and
other reagents. Thus we have used the MOM and TBS
protecting groups of phenols for the syntheses of bromo,
iodo, and fluoroethylated derivatives.
3. Antioxidant studies
3.1. Free radical scavenging activity
The DPPH (1,1-diphenyl-2-picrylhydrazyl) radical
scavenging effect was carried out according to the
method first employed by Blois.21 The 100 mL of sample
solution was added to 900 mL of DPPH solution in eth-
anol (1.01ꢀ10ꢁ4 M). After incubation at rt for 30 min,
Scheme 2 shows the synthesis of benzyl bromides for the
precursors of Wittig reagents, and Schemes 3 and 4
Scheme 1. (a) PPh3, THF, reflux, 10–20 h; (b) LDA, appropriate aldehyde derivatives, THF, 0 ꢂC–rt, 30–60 min, 74–93%; (c) I2, heptane, 12 h,
reflux; (d) 1% HCl in MeOH, rt, 36 h, 64–95%.
Scheme 3. (a) NIS,20 CH2Cl2, 70 ꢂC, 15 h; (b) TBS-Cl, imidazole, rt, 3
h; (c) Br2, CH2Cl2, 60 ꢂC, 12 h; (d) BBr3, CH2Cl2, 0 ꢂC–rt, 5 h; (e)
MOM-Cl, K2CO3, acetone, 70 ꢂC, 2 h.
Scheme 2. (a) H2SO4, MeOH, 70 ꢂC, 20 h; (b) TBS-Cl, imidazole,
CH2Cl2, rt, 2 h; (c) LiAlH4, THF, rt, 5 min; (d) PPh3, CBr4, THF,
0 ꢂC, 9 h; (e) NBS19 or NIS, CH2Cl2, rt, 1 h.

H. J. Lee et al. / Bioorg. Med. Chem. Lett. 14 (2004) 463–466
465
ꢂ
ꢂ
.
Scheme 4. (a) Tributyl(vinyl)tin, Pd(PPh3)4, CuI, toluene, reflux, 16 h; (b) BH3 THF then 4 N NaOH, H2O2, THF, 0 C–rt, 18 h; (c) MnO2, CHCl3, 80 C,
3 h; (d) NEt3, TsCl, CH2Cl2, 0 ꢂC, 8 h; (e) KF, [bmim][BF4], 100ꢂC; (f) 50% AcOH, cat. H2SO4, 70 ꢂC, 45 min; (g) TBS-Cl, imidazole, CH2Cl2, rt, 2 h.
Table 1. Radical scavenging activity of the resveratrol derivatives using DPPH assay and determination of total polyphenol
R1
X1
X2
X3
DPPH IC50 (mM)
DPPH relative IC50
Polyphenol (%)
a
Compound
R
1
16
17
18
19
20
21
22
H
Me
Me
Me
H
H
H
Me
Me
Me
H
H
H
H
H
H
H
H
H
H
Br
I
H
H
H
Br
H
Br
H
H
H
H
H
H
H
H
H
I
123.3 (74.0)b
—
—
—
35.9
51.2
73.4
47.4
69.5
70.6
(200)
(30.6)
(29.0)
(20.2)
(15.7)
1
—
—
100
26.6
—
H
Br
H
H
H
H
H
H
H
H
—
—
3.43
2.41
1.68
2.60
1.77
1.75
0.37
2.42
2.55
3.66
4.71
85.8
98.0
88.0
95.6
50.4
72.0
H
H
I
CH2CH2F
CH2CH2F
H
23
39
Me
H
H, glycoside
H, glycoside
H
Trans-Piceid
Astringin
Astringinin
(+)-Catechin
(ꢁ)-Epicatechin
H
OH
OH
H
H
H
a DPPH assay: relative IC50 was expressed by IC50 of resveratrol 1/IC50 of compound 19–23 and 39.
b The values in parenthesis were from reference 11.
the absorbance of this solution was determined at 518
nm using a spectrophotometer and the remaining
DPPH was calculated. All experiments were carried out
in triplicate and repeated at least three times. Results
are expressed as percentage decrease with respect to
control values. Each fraction was evaluated at the final
concentration of 100 mg/mL in the assay mixture.
Scheme 5.
3.2. Determination of total polyphenol
4. Discussion
The reaction conditions used as the basis of comparison
for most of these studies are the same as previous stan-
dard methods.22 Samples of 50 mL were added to each
250 mL of diluted FCR (Folin–Ciocalteu reagent)23 and
preincubated at 37 ꢂC for 1 min. Sodium bicarbonate
(0.5 N, 750 mL) was added. The reaction solution was
incubated at 37 ꢂC for 24 h. The absorbance was mea-
sured at 725 nm. The control was prepared as above,
with either H2O or EtOH of the same volume of sam-
ples used instead of the sample solutions. Table 1 illus-
trates the free radical scavenging activity with a stable
free radical, DPPH (1,1-diphenyl-2-picrylhydrazyl) as
well as the amount of total polyphenol.
Nine new resveratrol derivatives were designed and
synthesized. The DPPH IC50 value of resveratrol we
measured was 123.3 mM (lit. 74.0 mM11). Three methyl-
ated resveratrol derivatives 16–18 showed no free radi-
cal scavenging activity. However, when bromo, iodo
and fluoroethyl groups were introduced to various
positions, the DPPH IC50 of all compounds 19–23 and
39 in free phenol forms were improved as can be seen in
the DPPH relative IC50 ranging from1.75 to 3.43. The
compound 19 with a bromo group at C2 position has
the lowest IC50, which corresponds to the highest free
radical scavenging activity among the six free phenols,

466
H. J. Lee et al. / Bioorg. Med. Chem. Lett. 14 (2004) 463–466
while the compound 20 with a bromo group at C30
position shows a slightly higher IC50 value but still has
2.41 times higher activity than resveratrol itself.
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(+)-catechin and (ꢁ)-epicatechin have high free radical
scavenging activities and their DPPH relative IC50 are
3.66 and 4.71, respectively. On the other hand, non-fla-
vonoids such as trans-piceid, astringin, and astringinin
which are the derivatives of resveratrol have lower
DPPH relative IC50 than catechin derivatives, 0.37,
2.42, and 2.55, respectively. Thus, bromo compounds
19, 20 and fluoroethyl derivative 22 have quite high free
radical scavenging activities. In 30-substituted deriva-
tives 20, 21, 22, and astringinin, all substituted groups
such as bromo, iodo, fluoroethyl and hydroxy help
increase free radical scavenging activity.
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In conclusion, we designed and synthesized nine resver-
atrol derivatives as potential free radical scavengers. All
compounds having free phenol group(s) showed good
free radical scavenging activities. Among them, 2-bro-
moresveratrol 19 has similar free radical scavenging
activity to (+)-catechin. As bromine-76, iodine-123,
and fluorine-18 are very attractive radionuclides for the
labeling of organic molecules as PET and SPECT
radiotracers, the resveratrol derivatives labeled with
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Acknowledgements
This work was supported by the Korea Research
Foundation Grant (KRF-2001-015-DP0325).
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2. For recent reviews on resveratrol of biological activities:
22. Amerine, M. A. Laboratory Procedures for Enologists.
Department of Viticulture and Enology, University of
California, Davis, 1960, 130 pp.
23. Diluted FCR (Folin-Ciocalteu reagent) was prepared by
dilution of 1 mL of FCR with 9 mL of water.