Synthesis and antioxidant properties of dendritic polyphenols

Article abstract of DOI:10.1016/j.bmcl.2009.09.088

Three dendritic polyphenols (generation 1) were synthesized: a syringaldehyde-based dendrimer (1), a vanillin-based dendrimer (2), and an iodinated vanillin-based dendrimer (3). They all showed strong antioxidant activity according to the 1,1-diphenyl-2-p

Full text of DOI:10.1016/j.bmcl.2009.09.088

Bioorganic & Medicinal Chemistry Letters 19 (2009) 6326–6330
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and antioxidant properties of dendritic polyphenols
*
Choon Young Lee , Ajit Sharma, Jae Eun Cheong, Julie L. Nelson
Department of Chemistry, Central Michigan University, Dow 343, Mount Pleasant, MI 48859, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Three dendritic polyphenols (generation 1) were synthesized: a syringaldehyde-based dendrimer (1), a
vanillin-based dendrimer (2), and an iodinated vanillin-based dendrimer (3). They all showed strong anti-
oxidant activity according to the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical assay. The syringaldehyde
dendrimer was twice and 10 times stronger than quercetin and Trolox, respectively. The vanillin-based
dendrimer and its more hydrophobic iodinated derivative were also more potent antioxidants than quer-
cetin and Trolox. The DPPH order of potency was 1 > 2, 3 > quercetin > Trolox. All three dendrimers also
protected human LDL from free radical attack in a dose-dependent manner. Their order of free radical
scavenging was 1 > 3 > 2 > quercetin > Trolox. The increased hydrophobic nature of the iodinated deriva-
tive may have contributed to its better LDL protection than 2. Protection of linoleic acid oxidation was
studied by the b-carotene–linoleate assay. Dendrimer 1 was clearly superior to the other antioxidants
in protecting the fatty acid. In case of DNA protection against free radical damage, the order of activity
was 1 > quercetin > 2 > 3, Trolox. Pro-oxidant effect on copper-induced DNA oxidation showed the fol-
lowing order: quercetin, Trolox > 1 > 2 > 3. Results of the study show that dendritic antioxidants, even
at the generation 1 level, provide promising antioxidant properties for their potential use as drug candi-
dates for diseases associated with oxidative stress.
Received 11 August 2009
Revised 18 September 2009
Accepted 22 September 2009
Available online 25 September 2009
Keywords:
Dendrimer
Antioxidant
Polyphenol
Ó 2009 Elsevier Ltd. All rights reserved.
Flavonoids, plant based-polyphenols, have drawn considerable
attention due to their health benefits including anti-cancer,1 anti-
lipoperoxidation,2 anti-ischemic,3 anti-allergic and anti-inflamma-
tory4 properties. Quercetin, one of the most abundant flavonoids, is
a potential chemo-preventive agent.5 However, flavonoids may
also exhibit carcinogenic and mutagenic effects.6 Their adverse
biological actions are suspected to result from their pro-oxidant
action in the presence of transition metals like copper and iron,
and are more prominent in flavonoids that contain catecholic or
pyrogalloyl moiety.7 Antioxidants with high antioxidant potential
and low pro-oxidant activity will therefore be beneficial for clinical
applications.
In this study we designed and synthesized three generation 1
(G1) dendritic polyphenols devoid of catechol and pyrogallyol moi-
ety in order to reduce potential pro-oxidant effect. The dendritic
architecture allows synthesis of precise molecules with increasing
size via repetitive synthetic steps. Well-defined molecular struc-
tures are important for clinical applications. In addition, dendri-
mers may also exhibit unpredictable ‘dendritic effects’ which can
enhance solubility and stability and provide other beneficial
properties.8 An important long-term objective is to design a
dendrimer with strong antioxidant potential and diminished pro-
oxidant activity. The antioxidant dendrimers were made from
syringaldehyde, vanillin, and 5-iodovanillin as building blocks.
Syringaldehyde and vanillin, plant-based phenolic aldehydes with
weak antioxidant activities, are found in fruits, nuts, grains, and
various food plants.9 They are also lignin precursors10 and are
found in aged liquors.11 Lignin is hydrolyzed during the liquor
aging process in wooden barrels releasing variously substituted
small phenolic antioxidants including syringaldehyde and vanillin,
which impart smell and taste to the liquor.12 The presence of alde-
hyde groups in these phenols allows their ready conversion into
dendritic forms via covalent attachment to a core molecule with
two or more amino groups. We used 4-aminomethylbenzylamine
as the core for all three compounds, thus having the same core
and branching points but differing in their terminal phenol rings.
5-Iodovanillin was used to study the effects of increased hydropho-
bicity of the G1 antioxidants in the oxidation of lipophilic biomol-
ecules such as lipoproteins and fatty acids.
The antioxidant capacity of the three dendrimers was deter-
mined by the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical assay.
Their ability to protect fatty acid (linoleic acid), DNA (pBR322),
and lipoprotein (human LDL) against free radical damage was stud-
ied using b-carotene bleaching, DNA and LDL electrophoresis,
respectively. Their harmful pro-oxidant effect was also evaluated
with copper(II)-induced DNA oxidation. The three dendritic antiox-
idants were compared to quercetin, which is one of the most
widely studied flavonoids and reported to have all of the require-
ments for a potent antioxidant13 and Trolox, a water-soluble
vitamin E analog, often used as a comparative control in many anti-
oxidant studies (Fig. 1).
* Corresponding author. Tel.: +1 989 774 3289; fax: +1 989 774 3883.
E-mail address: lee1cy@cmich.edu (C.Y. Lee).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.09.088

C. Y. Lee et al. / Bioorg. Med. Chem. Lett. 19 (2009) 6326–6330
6327
organic polymers with potent antioxidant capacity or other thera-
peutic effects also exist.17 Examples include proanthocyanidins
that are oligomers of catechin/epicatechin. Like most potent anti-
oxidants, they also show pro-oxidant activity in the presence of
metal ions.18 Strong antioxidants are generally associated with
strong pro-oxidant activity. Therefore, it is important to investigate
architectures that can separate the two activities.
Compound 1 has four peripheral phenols with two strong elec-
tron-donating methoxy groups per ring. Compound 2 is similar to
1, but has only one electron-donating substituent on each phenol.
Compound 3 resembles 2 except for the presence of an iodo group
on each ring.
OH
OH
HO
O
O
O
HO
OH
OH
O
OH
Quercetin
Trolox
Figure 1. Antioxidants used for comparison.
Synthesis of antioxidant dendrimers. Aldehyde groups of building
blocks were reacted with the amino groups of the core, forming imi-
nes that were subsequently reduced to amines. Sodium triacetoxy-
borohydride (Na(OAc)3BH) was found to be an appropriate
reducing agent for amination. Although some aldehydes in the
building block were reduced to an alcohol, it was far more efficient
than other reducing agents like NaCNBH3. In order to decrease alde-
hyde reduction, the building block and Na(OAc)3BH were added in a
stepwise manner so that aldehyde exposure to Na(OAc)3BH was
minimized. Na(OAc)3BH gave good reaction yields in the solvent,
1,2-dichloroethane. In compound 1 synthesis, both syringaldehyde
and 4-aminomethylbenzylamine dissolved slowly in 1,2-dichloro-
ethane and afforded high reaction yield (over 80%). However, vanil-
lin and 5-iodovanillin were not very soluble in the solvent. They
were therefore protected with t-butyldimethylsilyl chloride
(TBDMS-Cl)14 to increase their solubility in 1,2-dichloroethane, con-
tributing to improved yields for both 2 and 3 (Scheme 1).15
Antioxidant capacity of the compounds was assessed by the
DPPH assay.19 All three dendritic compounds (1–3) showed hyper-
bolic kinetic curves with rapid radical scavenging within 10 min
followed by a slower phase (Fig. 2). Quercetin also displayed sim-
ilar kinetics (data not shown). Trolox, on the other hand reached
plateau values in less than a minute. The IC50 values, determined
at 120 min, were 3.7, 6.0, 6.0, 9.0, and 27.6 lM for compounds 1,
2, 3, quercetin, and Trolox, respectively. All three dendritic antiox-
idants were stronger than quercetin and Trolox. Compound 1 was
the most potent DPPH radical scavenger while compounds 2 and 3
showed identical antioxidant capacity. Compound 1 was stronger
than 2 probably due to the presence of an additional electron-
donating substituent (methoxy) ortho to the phenolic hydroxyl
group. Based on IC50 values of compounds 2 and 3, the presence
of iodo groups did not diminish the radical scavenging capacity.
The starting materials used for syntheses of compounds 1–3
showed negligible DPPH activity (IC50 values of syringaldehyde,
Evaluation of antioxidant activity. Polyphenols with potent anti-
oxidant activity are available in nature. For example, lignin, the
most abundant natural biopolymer, is a strong antioxidant due to
its numerous substituted phenols. Lignin is indigestible by human
enzymes, thus limiting its bioavailability.16 Smaller versions of
vanillin, 5-iodovanillin and 4-aminomethylbenzylamine >100 lM).
The antioxidant activity of compounds 1–3 towards biomole-
cules was examined by studying their ability to protect LDL, fatty
acid, and DNA from free radicals. For LDL, 2,20-azobis(2-amidino-
Synthesis of antioxidant dendrimers
H3C
O
CH3
O
HO
OH
O
H
H3C
O
O CH3
N
a
N
O
O
CH3
O
O
H3C
H3C
CH3
OH
OH
HO
H3C
O
1
O
CH3
CH3
Syringaldehyde
O
HO
O
OH
H3C
O
H
O
H
N
N
O
a
CH3
OH
c
c
b
O
CH3
O-TBDMS
O
2
CH3
HO
H3C
OH
O
Vanillin-TBDMS
Vanillin
CH3
O
I
O
H
HO
OH
O
H
H3C
a
b
O
I
I
N
N
O
I
CH3
O-TBDMS
O
CH3
O
I
CH3
OH
OH
3
HO
H3C
5-Iodovanillin-TBDMS
I
5-Iodovanillin
O
Scheme 1. (A) Synthesis of dendritic antioxidants. Reagents and conditions: (a) 4-aminomethylbenzylamine, Na(OAc)3BH, 1,2-dichloroethane; (b) TBDMS-Cl, triethylamine,
CH2Cl2, 0 °C; (c) n-Bu4NF, THF.

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C. Y. Lee et al. / Bioorg. Med. Chem. Lett. 19 (2009) 6326–6330
absorbance (corrected for control without antioxidant) was deter-
mined at each antioxidant concentration after incubation at 50 °C
for 180 min.23 Results shown in Figure 4 demonstrate that all three
compounds 1–3 were effective in protecting linoleic acid oxidation.
Compound 1 was the most effective. Compounds 2 and 3 were about
twice weaker than compound 1. Under the concentrations used in
the experiment, 2 and 3 showed identical activities with one another
and were quite similar to quercetin. In comparison, Trolox was more
effective than compounds 2 and 3 (and quercetin) at lower concen-
trations. Among the starting materials, 4-aminomethylbenzylamine
and syringaldehyde showed 16% and 12% A 470 nm at 12 lM after
180 min incubation, respectively while vanillin and 5-iodovanillin
exhibited <5%.
The effectiveness of the three compounds to protect DNA from
AAPH damage was also determined. The plasmid DNA pBR 322 was
incubated with AAPH (final concentration 10 mM) at 37 °C for 4 h
with or without antioxidants (final concentrations, 0.35–45 lM),
Figure 2. DPPH reaction kinetics of dendritic antioxidants: control with methanol
after which the samples were subjected to agarose electrophore-
sis.24 An example of the gel obtained with compound 1 is shown
in Figure 5. In the absence of AAPH, pBR 322 was mostly in its
supercoiled (S) form (small amount of open circular, O, form was
also visible, lane 1 Fig. 5). After reaction with AAPH, the DNA
was transformed almost entirely into its open circular form (lane
2, Fig. 5). Compound 1 showed the best protection. In the presence
of 11–45 lM of 1, DNA was well protected (the S band intensity
was similar to control without AAPH, lanes 3–5, Fig. 5). Quercetin
showed similar protection (data not shown). Some protection
(X, dashed), compound 1 (h), compound 2 (d), compound 3 (s), Trolox (
D). All
antioxidant concentrations are 5 M.
l
propane) dihydrochloride (AAPH) was used to induce free radical
damage. AAPH was used instead of copper (Cu2+) ion for LDL oxida-
tion so that the free radical scavenging activity of the antioxidants
could be measured without any pro-oxidant interference caused by
metal ions.20,21
LDL oxidized with 10 mM AAPH (18 h, 37 °C) showed increased
anodic migration on agarose gels (expressed as 100% migration,
Fig. 3) compared to un-oxidized native lipoprotein (dashed line,
ꢀ50% migration of oxidized LDL, Fig. 3). Protection of LDL from
AAPH free radicals by the antioxidant decreased the anodic shift
in a dose-dependent manner (Fig. 3). Compound 1 was the most
efficient in protecting LDL followed by 3, 2, quercetin, and Trolox.
Although 2 and 3 showed identical DPPH values, the iodinated
dendrimer (3) displayed better LDL protection than compound 2.
The increased hydrophobicity of 3 may be partly responsible for
its improved LDL protection over 2. The starting materials for com-
pounds 1–3 showed no LDL protection under these conditions.
The ability of the dendritic antioxidants 1–3 to protect linoleic
acid against free radical damage was examined by the b-carotene–
linoleate model.22 In the absence of an antioxidant, hydroperoxides
formed from linoleic acid oxidation bleach the highly unsaturated b-
carotene by a free-radical-mediated phenomenon. The bleaching of
the reddish-orange color of b-carotene was monitored at 470 nm in
the presence of various concentrations of antioxidant. The %
was also obtained for 1 at 5
cetin (data not shown). No protection was obtained for both 1 and
quercetin below 5 M (lanes 7–10, Fig. 5). In case of compound 2,
some protection was only observed at P45 M. Lower concentra-
tions did not show any protection. Compound 3 as well as Trolox
were ineffective at all concentrations used in the experiment
lM (lane 6, Fig. 5) but not with quer-
l
l
(0.35–45 lM). The starting materials for dendrimer synthesis did
not show any DNA protection under these conditions.
Figure 4. b-Carotene–linoleate assay for antioxidants. Protection of linoleic acid
from oxidation by various antioxidants is shown for compound 1 (h), compounds 2
and 3 (d), quercetin (ꢁ), and Trolox (
D).
Figure 3. Migration of oxidized LDL in electrophoresis gels. AAPH oxidized LDL
without any added antioxidant is expressed as 100%. Native LDL showed a mobility
of ꢀ50% that of oxidized lipoprotein (dashed line). Migration of oxidized LDL in the
presence of various antioxidants including compound 1 (h), compound 2 (d),
Figure 5. Protection against AAPH-induced DNA oxidation by compound 1. Lane 1
(native DNA); lanes 2–10 (AAPH-oxidized DNA with 0, 45, 23, 11, 5, 3, 1.5, 0.7, and
compound 3 (s), Trolox (
D
), and quercetin (X) is shown.
0.35 lM antioxidant, respectively).

C. Y. Lee et al. / Bioorg. Med. Chem. Lett. 19 (2009) 6326–6330
6329
Investment Funds). This work was supported in part by Award
Number 1R15GM087697-01 from the National Institute of General
Medical Sciences. The content is solely the responsibility of the
authors and does not necessarily represent the official views of
the National Institute of General Medical Sciences or the National
Institutes of Health.
References and notes
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Figure 6. Pro-oxidant activity of (a) compound 1; (b) quercetin; (c) compound 3;
(d) Trolox. Lane 1 (native DNA); lanes 2–10 (Cu2+-oxidized DNA with 0, 45, 23, 11, 5,
9. (a) Herraaiz, T.; Galisteo, J.; Chamorro, C. J. Agric. Food Chem. 2003, 51, 2168; (b)
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Food Chem. 2006, 98, 569.
3, 1.5, 0.7, and 0.35 lM antioxidant, respectively).
Antioxidants may also exhibit pro-oxidant activity in the pres-
ence of metal ions, which can lead to damage of biomolecules.
The pro-oxidant effect of compounds 1–3 was examined by oxida-
tion of DNA with copper(II) ion. pBR 322 was incubated with
10
tions between 0.35 and 45
l
M Cu2+ at 37 °C for 1 h in the presence of 1–3 (final concentra-
lM). Examples of gels obtained for com-
pound 1, 3, quercetin, and Trolox are shown in Figure 6. DNA
13. Rice-Evans, C. A.; Miller, N. J.; Paganga, G. Free Radic. Biol. Med. 1996, 20, 933.
14. General procedure for TBDMS protection of phenolic aldehyde:Vanillin (5 g,
32.86 mmol) and triethylamine (10 mL, 71.74 mmol) were mixed in CH2Cl2
(200 mL). TBDMS-Cl (14 mL, 40.41 mmol) was added dropwise at 0°C. Reaction
was run for 3 h and purified on a silica gel column with hexane.TBDMS-
protected vanillin: Yield 96%; Rf = 0.59 (hexane/ethyl acetate = 5:1); 1H NMR
(300 MHz, CDCl3) d 0.17 (s, 6H, 2 ꢁ CH3), 0.98 (s, 9H, C(CH3)3), 3.84 (s, 3H,
OCH3), 6.93 (d, J = 8.1 Hz, 1H, C5-H), 7.33 (dd, 1H, J = 7.95 Hz and J = 1.95 Hz, C2-
H), 7.37 (d, 1H, J = 1.5 Hz, C6-H), 9.82 (s, 1H, CHO); 13C NMR (75 MHz, CDCl3) d
ꢂ4.3 (2 ꢁ CH3), 18.7 (C(CH3)3), 25.8 (C(CH3)3), 55.6 (OCH3), 110.2 (C2), 120.9 (C5
and C6), 126.4 (C1), 131.1(C4), 151.5 (C3), 191.2 (CHO).TBDMS-protected 5-
iodovanillin: Yield 93%; Rf = 0.62 (hexane/ethyl acetate = 3:1); 1H (300 MHz,
CDCl3) d 0.24 (s, 6H, 2 ꢁ CH3), 1.0 (s, 9H, C(CH3)3), 3.82 (s, 3H, OCH3), 7.31 (d,
J = 2.1 Hz, 1H, C2-H), 7.81 (d, J = 1.8 Hz, 1H, C6-H), 9.73 (s, 1H, CHO); 13C NMR
(75 MHz, CDCl3) d ꢂ2.9 (2 ꢁ CH3), 19.3 (C(CH3)3), 26.2 (C(CH3)3), 55.3 (OCH3),
89.9 (C5), 109.7 (C2), 131.5 (C1 and C6), 136.2 (C4), 150.0 (C3), 189.8 (CHO).
damage was clearly observed with compound 1 and quercetin at
concentrations between 11 and 45
quercetin exhibited a more pronounced pro-oxidant effect than
dendrimer 1 between 3 and 5 M (lanes 6 and 7, Fig. 6). For com-
pound 2, a slight pro-oxidant effect was seen at 23 and 45 M (data
lM (lanes 3–5, Fig. 6). However,
l
l
not shown). Compound 3, under similar conditions did not show
any appreciable pro-oxidant effects at the concentrations tested.
Trolox under these conditions also showed a strong pro-oxidant ef-
fect equivalent to quercetin. The starting materials did not show
any pro-oxidant effect on DNA under these conditions.
In conclusion, three dendritic polyphenols were synthesized, all
of which showed strong antioxidant capacity. Among the three
dendrimers, quercetin and Trolox, the syringaldehyde-based den-
drimer (1) was the most potent and displayed the best protection
for LDL, linoleate, and DNA against free radical attack. Its pro-oxi-
dant activity was stronger than the other two dendrimers (2 and 3)
but weaker than quercetin and Trolox. All three dendrimers
showed far superior DPPH radical scavenging activity compared
to their individual as well as sum of their starting materials (core
and building blocks), suggesting potential dendritic effect. In addi-
tion, they were also more effective in protecting LDL, linoleic acid,
and DNA from free radical damage than their starting materials.
Detailed activity of this antioxidant will be reported in forthcoming
publication. The study shows that dendritic polyphenols, even at
the G1 level, offer a novel and exciting class of molecules with ben-
eficial antioxidant properties.
15. Formation of dendrimer using 4-aminomethylbenzylamine as
a core and
syringaldehyde, vanillin, or 5-iodovanillin as a building block. To a flask were
added molecular sieves (50 g), 4-aminomethylbenzylamine (0.38 g,
2.79 mmol), two equivalents of TBDMS-protected vanillin (1.50 g, 5.64 mmol),
and 1,2-dichloroethane (200 mL). The reaction was run for 12 h at room
temperature. Na(OAc)3BH (1.27 g, 5.99 mmol) was then added and run for
another 24 h. To the reaction were added another 2 equivalents of TBDMS-
protected vanillin (1.81 g, 6.80 mmol) and fresh molecular sieves (20 g). The
reaction was gently stirred for 15 h, followed by Na(OAc)3BH (1.28 g,
6.04 mmol) addition. The reaction was monitored with MALDI-TOF and
stopped after 72 h. After filtration of molecular sieves, 1,2-dichloroethane
was removed under reduced pressure. The resulting residue was dissolved in
THF, followed by n-Bu4NF (2 mL) addition (TBDMS deprotection). The reaction
was stirred overnight and condensed under reduced pressure. The resulting
residue was partitioned between CH2Cl2 and water. The CH2Cl2 layer was dried
with MgSO4. After removal of MgSO4, the solvent was removed on the rotorvap.
The oily substance was purified via silica gel column chromatography using a
gradient hexane/ethyl acetate solvent system (8:1?1:1).Compound
1
(dendrimer derived from syringaldehyde): Yield: 81%; mp: 89–92 °C, off-
white powder; Rf = 0.126 (hexane/acetone = 1:1); 1H (300 MHz, CDCl3) d 3.45 (s,
8H, 4 ꢁ periphery Ph-CH2-N), 3.55 (s, 4H, 2 ꢁ core Ph-CH2-N), 3.9 (s, 24H,
8 ꢁ OCH3), 5.4 (s, 4H, 4 ꢁ OH), 6.6 (s, 8H, 4 ꢁ periphery Ph), 7.3 (s, 4H, 4 ꢁ core
Ph-H); 13C NMR (75 MHz, CDCl3) 56.5 (8 ꢁ OCH3), 57.9 (2 ꢁ core Ph-CH2-N),
58.2 (4 ꢁ periphery Ph-CH2-N), 105.6 (8 ꢁ periphery Ph C-H), 129 (4 ꢁ core Ph
C-H), 131 (4 ꢁ periphery Ph C-CH2), 133.5 (4 ꢁ periphery Ph C-OH), 138.2
Acknowledgments
We are grateful to the Central Michigan University Office of Re-
search and Sponsored Programs for funding (President’s Research

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C. Y. Lee et al. / Bioorg. Med. Chem. Lett. 19 (2009) 6326–6330
(2 ꢁ core Ph C-CH2), 147 (8 ꢁ periphery Ph C-OCH3); MS: m/z 801
16. Chabannes, M.; Ruel, K.; Yoshinaga, A.; Chabbert, B.; Jauneau, A.; Joseleau, J. P.;
Boudet, A. M. Plant J. 2001, 28, 271.
17. Anderson, R. A.; Broadhurst, C. L.; Polansky, M. M.; Schmidt, W. F.; Khan, A.;
Flanagan, V. P.; Schoene, N. W.; Graves, D. J. J. Agric. Food Chem. 2004, 52, 65.
18. Sakano, K.; Mizutani, M.; Murata, M.; Oikawa, S.; Hiraku, Y.; Kawanishi, S. Free
Radic. Biol. Med. 2005, 39, 1041.
19. Brand-Williams, W.; Cuvelier, M. E.; Berset, C. Lebensm. Wiss. Technol. 1995, 28, 25.
20. Salah, N.; Miller, N. J.; Paganga, G.; Tijburg, L.; Bolwell, G. P.; Rice-Evans, C. A.
Arch. Biochem. Biophys. 1995, 322, 339.
[M+H]+.Compound 2 (dendrimer derived from vanillin): Yield: 87%; Rf = 0.18
(hexane/ethyl acetate = 1:1); 1H (300 MHz, CDCl3) d 3.49 (s, 8H, 4 ꢁ periphery
Ph-CH2-N), 3.55 (s, 4H, 2 ꢁ core Ph-CH2-N), 3.87 (s, 12H, 4 ꢁ OCH3), 6.87 (d,
J = 0.9 Hz, 8H, 4 ꢁ periphery Ph C2-H and C6-H), 6.91 (s, 4H, 4 ꢁ periphery Ph C5-
H), 7.34 (s, 4H, 4 ꢁ core Ph-H); 13C NMR (75 MHz, CDCl3) d 56.0 (4 ꢁ OCH3), 57.5
(2 ꢁ core Ph-CH2-N), 57.7 (4 ꢁ periphery Ph-CH2-N), 111.5 (4 ꢁ periphery Ph
C2-H), 114.2 (4 ꢁ periphery Ph C5-H), 121.7 (4 ꢁ periphery Ph C6-H), 128.8
(4 ꢁ core ph C-H), 131.7 (4 ꢁ periphery Ph C1-CH2), 138.4 (2 ꢁ core ph C-CH2),
144.6 (4 ꢁ periphery ph C4-OH), 146.6 (4 ꢁ periphery ph C3-OCH3); MS: m/z
681 [M+H]+.Compound 3 (dendrimer derived from 5-iodovanillin): Rf = 0.2
(hexane/ethyl acetate = 1:1); yield = 76%; 1H (300 MHz, CDCl3) d 3.41 (s, 8H,
4 ꢁ periphery Ph-CH2-N), 3.53 (s, 4H, 2 ꢁ core Ph-CH2-N), 3.88 (s, 12H,
4 ꢁ OCH3), 6.82 (d, J = 1.5 Hz, 4H, 4 ꢁ periphery Ph C2-H), 7.28 (s, 8H, 4 ꢁ core
Ph-H and 4 ꢁ periphery Ph C6-H); 13C NMR (75 MHz, CDCl3) d 56.4 (4 ꢁ OCH3),
57.0 (4 ꢁ periphery Ph-CH2-N), 57.8 (2 ꢁ core Ph-CH2-N), 81.1 (4 ꢁ periphery
Ph C-I), 111.4 (4 ꢁ periphery Ph C2-H), 128.9 (4 ꢁ core ph C-H), 130.6
(4 ꢁ periphery Ph C1-CH2), 133.2 (4 ꢁ periphery Ph C6-H), 138.1 (2 ꢁ core ph
C-CH2), 144.7 (4 ꢁ periphery Ph C-OH), 146.1(4 ꢁ periphery Ph C-OCH3); MS:
m/z 1184.78 [M+H]+.
21. All solutions were made in ultra-pure water.
22. Jayaprakasha, G. K.; Singh, R. P.; Sakariah, K. K. Food Chem. 2001, 73, 285.
23. The%A470 nmvaluesweredeterminedasshownbelow:% A470 nm = [(At (180 min)
/At(0 min)) ꢁ 100] ꢂ [(Ac(180 min)/Ac (0 min)) ꢁ 100]where, At (180 min) = absorbance at
470 nm of antioxidant sample incubated at 50 °C for 180 min, At
=
(0 min)
absorbance at 470 nm of antioxidant sample incubated at 50 °C for 0 min,
Ac min) = absorbance at 470 nm of control sample (without antioxidant)
(180
incubated at 50 °C for 180 min, and Ac (0 min) = absorbance at 470 nm of control
sample (without antioxidant) incubated at 50 °C for 0 min.
24. Sakihama, Y.; Cohen, M. F.; Grace, S. C.; Yamasaki, H. Toxicology 2002, 177, 67.