Inhibition of cancer derived cell lines proliferation by synthesized hydroxylated stilbenes and new ferrocenyl-stilbene analogs. Comparison with resveratrol

Article abstract of DOI:10.3390/molecules19067850

Further advances in understanding the mechanism of action of resveratrol and its application require new analogs to identify the structural determinants for the cell proliferation inhibition potency. Therefore, we synthesized new trans-resveratrol derivatives by using the Wittig and Heck methods, thus modifying the hydroxylation and methoxylation patterns of the parent molecule. Moreover, we also synthesized new ferrocenylstilbene analogs by using an original protective group in the Wittig procedure. By performing cell proliferation assays we observed that the resveratrol derivatives show inhibition on the human colorectal tumor SW480 cell line. On the other hand, cell viability/cytotoxicity assays showed a weaker effects on the human hepatoblastoma HepG2 cell line. Importantly, the lack of effect on non-tumor cells (IEC18 intestinal epithelium cells) demonstrates the selectivity of these molecules for cancer cells. Here, we show that the numbers and positions of hydroxy and methoxy groups are crucial for the inhibition efficacy. In addition, the presence of at least one phenolic group is essential for the antitumoral activity. Moreover, in the series of ferrocenylstilbene analogs, the presence of a hidden phenolic function allows for a better solubilization in the cellular environment and significantly increases the antitumoral activity.

Full text of DOI:10.3390/molecules19067850

Molecules 2014, 19, 7850-7868; doi:10.3390/molecules19067850
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Inhibition of Cancer Derived Cell Lines Proliferation by
Synthesized Hydroxylated Stilbenes and New Ferrocenyl-Stilbene
Analogs. Comparison with Resveratrol
Malik Chalal 1,2, Dominique Delmas 1,3,4, Philippe Meunier 1,2, Norbert Latruffe 1,3,* and
Dominique Vervandier-Fasseur 1,2,
*
1
Université de Bourgogne, 21000 Dijon, France
2
Institut de Chimie Moléculaire de l’Université de Bourgogne, ICMUB UMR CNRS 6302, 9,
avenue Alain Savary, 21000 Dijon, France
3
4
Laboratoire de Biochimie (Bio-PeroxIL) INSERM IFR 100, 6, boulevard Gabriel, Dijon, France
INSERM UMR 866, 7, boulevard Jeanne d’Arc, 21000 Dijon, France
* Authors to whom correspondence should be addressed;
E-Mails: norbert.latruffe@u-bourgogne.fr (N.L.);
dominique.vervandier-fasseur@u-bourgogne.fr (D.V.-F.);
Tel.: +33-3-80396237 (N.L.); +33-3-80399036 (D.V.-F.).
Received: 29 April 2014; in revised form: 27 May 2014 / Accepted: 28 May 2014 /
Published: 11 June 2014
Abstract: Further advances in understanding the mechanism of action of resveratrol and its
application require new analogs to identify the structural determinants for the cell
proliferation inhibition potency. Therefore, we synthesized new trans-resveratrol
derivatives by using the Wittig and Heck methods, thus modifying the hydroxylation and
methoxylation patterns of the parent molecule. Moreover, we also synthesized new
ferrocenylstilbene analogs by using an original protective group in the Wittig procedure.
By performing cell proliferation assays we observed that the resveratrol derivatives show
inhibition on the human colorectal tumor SW480 cell line. On the other hand, cell
viability/cytotoxicity assays showed a weaker effects on the human hepatoblastoma HepG2
cell line. Importantly, the lack of effect on non-tumor cells (IEC18 intestinal epithelium
cells) demonstrates the selectivity of these molecules for cancer cells. Here, we show that
the numbers and positions of hydroxy and methoxy groups are crucial for the inhibition
efficacy. In addition, the presence of at least one phenolic group is essential for the
antitumoral activity. Moreover, in the series of ferrocenylstilbene analogs, the presence of a

Molecules 2014, 19
hidden phenolic function allows for a better solubilization in the cellular environment and
7851
significantly increases the antitumoral activity.
Keywords: resveratrol; methoxystilbenes; ferrocenylstilbene analogs; colon cancer;
hepatoblastoma
1. Introduction
Polyphenolic compounds, including stilbenes, anthocyans, catechins and their oligomers, are
widespread in a large number of plants. Polyphenolic stilbenoids have been discovered in numerous
species, for instance, in the roots of the Asiatic plant Polygonum cuspidatum [1], in the South African
plant Erythrophleum lasianthu [2], in red fruit, including grapes [3–5], in red wine [6,7], in Itadori green
tea [8], in peanuts [9], and in rhubarb [10]. The common feature of these different plants is the presence
of a phytoalexin, trans-resveratrol or trans-3,5,4'-trihydroxystilbene (RSV, Figure 1a) [1,3–5,8,9,11,12].
This well-known polyphenol proves to be a true (Swiss Army knife) molecule [13] in the therapeutic
and biological fields [14–16]. Indeed, numerous publications and reviews report about trans-resveratrol’s
antitumoral [17,18], anti-inflammatory [19], antiviral [20], antimicrobial [21], and antifungal [22–24]
activities. In addition, trans-resveratrol is a neuroprotective agent [25,26] and can also prevent heart
disease [27–29]. The antioxidant features of trans-resveratrol may partly explain these numerous
activities [30–32]. In cancer research, it has been shown that involvement of trans-resveratrol in
antitumoral activity is also due to its ability to bind different cellular targets [33,34]. However, several
derivatives of trans-resveratrol show a better activity than the parent molecule towards specific types
of cancer [35]. The modifications of the chemical structure of trans-resveratrol involve the number and
the position of the phenolic groups [35–37], the presence on the aromatic rings of methoxy
groups [38–41], long alkyl chains [38,42], or functionalized chains [43]. These structural modifications
improve mostly the lipophilicity of the stilbenes in the cellular environment and thus their biological
effects inside the cell [44]. However, the methoxylated derivatives of trans-resveratrol seem to have a
different way of delaying cancer growth. Indeed, our group has studied the biological activities of
E- and Z-methoxylated stilbenes against the human colorectal tumor SW480 cell line and has reported
that the methoxy group is a determinant substitution for the molecules bearing a Z configuration in
inhibition of this cell line (compounds A, Figure 1) [45].
Figure 1. (a) Structure of trans-resveratrol (RSV). (b) Structure of cis and
trans-resveratrol derivatives.

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Zhang et al. have confirmed that trans-resveratrol was known to be active only in its E configuration
while some methoxylated derivatives proved to be active in the Z configuration [41]. In order to deepen
our understanding of the mechanism of action and to highlight compounds with enhanced effects on
colorectal tumor SW480 and hepatoblastoma HepG2 cell lines, we synthesized a series of E-stilbenes,
including three new original ferrocenylstilbene analogs, by improved Wittig and Heck methods [46].
Each compound was submitted to evaluation for biological properties (antiproliferative activity and
cell cycle disturbance of SW480 colon cancer and hepatic HepG2 cancer cells). To obtain an inhibitory
effect, the chemical parameters studied are the following: (a) the presence of a hydroxy group in
position 4; (b) the increased effect due to the presence of a methoxy group (a decrease of the polar
character leading to an increase in lipophilic property); (c) the lack (or masked form) of other hydroxy
groups. In the series of ferrocenylstilbene analogs, the presence of a phenolic function as an ester
greatly increases the antitumoral activity. Most of synthetic compounds are more efficient towards
colorectal SW480 cells than liver-derived HepG2 cells. Furthermore, the lack of effects on non-tumor
cells (IEC18 intestinal epithelium cells) demonstrates the selectivity of these molecules for cancer
cells, which is an important aspect for possible therapeutic applications.
2. Results and Discussion
2.1. Chemical Results
2.1.1. Synthesis of E-4-Hydroxystilbenes
Given the importance of the free phenolic function in position 4 [30,31], we focused on the
preparation of derivatives bearing a free phenolic group in position 4 and substituents on the ring B of
the stilbenes (compounds 1–6; Figure 2a) or on the A and B rings of the stilbenes (compounds 7–9;
Figure 2b). The methoxy group was often chosen as a substituent to improve the membrane
permeability of the stilbenes. To highlight the importance of the presence and the position of the
phenolic function in the activity of the stilbenes towards tumor cell lines, one derivative with OH
group in position 3 was prepared (compound 10; Figure 2c) and four resveratrol analogs without a free
phenolic function were synthesized (compounds 11–14; Figure 2d). Compound 10 was already
studied by Zhang et al. for its effects on NQO1 induction in hepatoma cells, but its synthesis was
not described [41].
On the contrary, compounds 1–4, 6, 7, 12 and 13 were already synthesized by different method,
including Horner-Emmons-Haworth [35,47,48], Perkin [49–51] and Mizoroki-Heck reactions [52].
Previously, our group has reported the synthesis of compounds 1–14 by two standard methods [46].
Stilbenes 4, 7–13 were prepared by palladium-catalyzed Heck coupling using ferrocenylphosphane
ligands. In our protocol, the hydroxylated stilbenes were obtained without the need of
protection/deprotection steps on the phenolic functions. Stilbenes 1–3, 5, 6 and 14 were prepared by
Wittig reactions; the protection on the hydroxy groups of aromatic aldehydes was achieved using the
labile trimethylsilyl group, rarely used in this case. This protective group was easily cleaved during the
aqueous work-up following the Wittig reaction.

Molecules 2014, 19
Figure 2. Molecular structure of synthetic stilbene derivatives. (a) 4-OH stilbenes bearing
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substituents on cycle B. (b) 4-OH stilbenes bearing substituents on cycle A and/or cycle B.
(c) 3-hydroxy-4'-methoxystilbene (10). (d) Stilbenes without free phenolic function.
3'
OMe
a
4'
c
4'
5'
2'
R'
B
2
HO
3
3
6'
A
1
2
3
R' = H
R' = 4'-OMe
R' = 3',5'-diOMe
4
5
6
R' = 4'-OH,3'-OMe
R' = 4'-vinyl
R' = 4'-Br
10
R5
6
4
HO
5
R4
R6
R7
d
b
3'
R1
2'
4'
R'
B
R
2
A
5
5'
3
11 R1 = R3 = R4 = R5 = R7 = H, R2 = R6 = OMe
2
6'
R2
12 R1 = R3 = R4 = R6 = R7 = H, R2 = R5 = OMe
13 R1 = R3 = R5 = R6 = R7 = H, R2 = R4 = OMe
14 R2 = R4 = R6 = H, R1 = R3 = R5 = R7 = OMe
7
8
9
R = 3-OMe, R' = 3',4',5'-triOMe
R = 3-CH2OH, R' = 4'-OMe
R = 3-OMe, R' = 4'-OMe
6
R3
4
HO
2.1.2. Synthesis of Stilbenes Bearing Ferrocenylstilbene Analogs
In addition to these stilbenes bearing classical substituents, we developed original ferrocenyl-analogs
of stilbenes 15–17 (Figure 3).
Figure 3. Molecular structure of ferrocenyl-stilbene analogs 15–17.
Indeed, since the discovery of the antitumoral properties of cisplatin [53], the therapeutic interests
in metallic complexes and organometallic compounds has increased steadily [54], especially for
ferrocenyl derivatives [55]. Several organometallic compounds bearing a ferrocenyl group display
better biological properties than their organic counterparts, such as chloroquine and ferroquine used in
the treatment of malaria [56]. A key example of an anticancer ferrocene derivative is the anti-breast
cancer ferrocifen series. Jaouen’s group has synthesized different derivatives of the ferrocen
complexes of tamoxifen and has shown complementary activities of these compounds [57,58].
Therefore, in the aim to improve the antitumoral activities of the polyphenols, we have targeted the
synthesis of an original stilbene molecular structure wherein a ferrocenyl ring replaced a benzenic ring;
the position 4 of the remaining benzenic ring was substituted by a free phenolic function. The proposed
strategy to access this series of ferrocenylstilbene analogs is to react under Wittig reaction conditions

Molecules 2014, 19
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ferrocenecarbaldehyde (18) or ferrocene-1,1'-dicarbaldehyde (19) [59] with a benzylphosphonium
bromide bearing a protected phenolic function 20 (Figure 4).
Figure 4. Starting reagents for the preparation of ferrocenyl-stilbene analogs 18–20.
CHO
CHO
CHO
H3C
Fe
Fe
O
CH2PPh3Br
O
19
18
20
The precursor of 20 is 4-hydroxybenzylic alcohol (21), the corresponding bromide 22 is not
commercially available and cannot be prepared by bromination of 21 because of its instability [60]
(Scheme 1). Thus, the protection of the phenolic function has to be carried out before the bromination
of the benzylic alcohol and in addition, the protective group should be stable to the bromination reagent.
These conditions preclude the use of the trimethylsilyl group [46]. Therefore, the phenolic function has
been protected as an ester function by reacting 21 with para-toluoyl chloride in the presence of K2CO3 and
acetone as a solvent [61]. The benzylphosphonium bromide 20 was obtained by reacting benzylic alcohol
23 successively with N-bromosuccinimide in CH2Cl2 [62] and triphenylphosphine in toluene (Scheme 1).
Scheme 1. Synthesis of benzylphosphonium bromide 20.
Finally, the benzylphosphonium bromide 20 was reacted with ferrocenecarbadehyde (18) in the
presence of butyl lithium in THF. The cleavage of phenolic esters was carried out by KOH in
methanol [63] and the ferrocenylstilbene analog 15 was recovered in 52% yield. In the same manner,
the ferrocenyl derivative was obtained from 20 and ferrocene-1,1'-dicarbaldehyde (19) in 47%
yield (Scheme 2).
2.2. Biological Effects
We compared the potency of the new resveratrol synthetic analogs towards the human colorectal
tumor cell line SW480, the human hepatoblastoma HepG2 cell line and the rat normal intestine
epithelium IEC18 cell, comparing their effect with the natural reference molecule, i.e., trans-resveratrol.

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Scheme 2. Synthesis of ferrocenyl-stilbene analogs 15–17.
OH
O
Ar
CHO
Fe
BuLi, -78°C
THF
MeOH / KOH
Fe
+ 20
Fe
O
18
15
25
O
Ar
MeOH / KOH
OH
OH
CHO
BuLi, -78°C
THF
+ 20 (2 equiv.)
Fe
Fe
O
Fe
CHO
O
Ar
19
17
16
O
2.2.1. Effect of Stilbene Derivatives on Human Colorectal Tumor SW 480 Cell Line Proliferation
Firstly, we have determined the sensitivity of human tumoral colorectal cell line SW480 towards
the newly synthesized stilbene derivatives and compared them to resveratrol, the parent molecule.
Figure 5 shows, as expected and in agreement with the literature [64], that resveratrol at 30 µM
decreases drastically cell viability which is of 40% compared to the control (Figure 5).
Figure 5. Effect of stilbene derivatives on human cancerous colorectal SW480 cell
viability. Cells were grown for 48 h in the presence of 30 µM resveratrol (or no RSV in a
control experiment) or 30 µM stilbene derivatives (numbered on the x-axis). Cell viability
was determined by counting cells using the trypan blue test (Co: cells control test). Data
correspond to the mean of two independent experiments.
Interestingly, compounds 1–5 exhibit higher cytotoxicity than resveratrol. These derivatives bear,
like resveratrol, at least one phenol group in the para position of the stilbene ring. The only structural
differences between these molecules are the positions and numbers of methoxy groups. The efficiency
of compound 1 indicates that its activity is due to the phenolic group, despite the absence of methoxy
groups on its skeleton. Compound 14, a tetramethoxylated derivative, shows similar activity as
resveratrol, suggesting that these substituents are not essential for the activity. However, the fact that
compounds 9, 11–13 have only weak effects seems to indicate that a free phenolic group in the para
position of the aromatic ring is needed for toxicity.

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2.2.2. Effect of Stilbene Derivatives on the Cell Cycle Phase of the SW480 Cell Line
To further explore the mechanisms by which the most efficient compounds exert their
antiproliferative potencies, we studied their effects on the cell cycle distribution of SW480 cells
(Figure 6). The treatment of cells with compound 2, which bears a hydroxy group in position 4 and a
methoxy group in position 4', induces an accumulation of SW480 cells in S phase in the same manner
as resveratrol (Figure 6). Interestingly, compound 4, bearing hydroxy groups at positions 4 and 4' and a
methoxy group at position 3, leads to an increase of S phase which is better than that of resveratrol and
compound 2. In contrast, pterostilbene (3) does not show any effect on the cell cycle, while it inhibits
cell proliferation. This derivative has been reported to induce a blockade of HL60 intestine cancer cells
in the G1 phase, and to induce apoptosis [65]. The distribution of cells in the different cell cycle phases
is reported in Figure 1 of the supplementary material.
One of the mechanisms by which resveratrol modulates carcinogenesis is the blockage of cells in S
phase [66]. However, these effects at the cell cycle are complex and depend on the cell type, the
resveratrol concentration and the duration of the treatment. Indeed, a low concentration of resveratrol
induces accumulation of cells in S phase while at higher concentrations it leads to cell accumulation in
G1 or G2/M phases [67]. Moreover, many cytotoxic agents also induce cell death by apoptosis. We
have previously shown in SW480 and in HepG2 cell lines that resveratrol induces accumulation of
cells in early S phase by action on the p21 protein and on the cyclin/cdk complexes formation and
activity [68]. In the structural core of resveratrol, the phenol group in position 4 would be responsible
for the antiproliferative effect by its action on DNA polymerases alpha and gamma [69,70]. Indeed, the
increase of number of hydroxy groups on the stilbene moiety of resveratrol derivatives led to an
increase of inhibition of tumor cell proliferation [71]. On the other hand, She et al. [72] have shown
that trans-3,3',4',5-tetrahydroxystilbene and trans-3,3',4',5,5'-pentahydroxystilbene exhibit a higher
apoptotic effect than resveratrol on the epidermal JB6 cell line.
Figure 6. Influence of stilbene derivatives on the cell cycle phases of the SW480 cells line.
Cells were grown for 48 h in the presence of 30 µM resveratrol (or no RSV in a control
experiment) or 30 µM stilbene derivatives (numbered on the x-axis). After treatment,
nuclear DNA was labeled with propidium iodide. The cell cycle effect of the tested
compounds was done analysing cell distribution in the different phases of the cell cycle
(mean ± standard deviation of two independent experiments).

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2.2.3. Evaluation of Toxicity Level of Stilbene Derivatives Towards Non-Cancerous Intestinal
Epithelial Cells
With the aim of possible therapeutic applications using resveratrol derivatives in mind it was
important to evaluate the specificity of cytoxicity towards normal cells. Hence, we evaluated the effect
of potent derivatives on the proliferation of intestine epithelium IEC18 cells. The results shown in
Figure 7 indicate no significant toxic effect of compounds 2–4 at 30 µM, except for compound 5
(presence of vinyl group in position 4). At higher concentration (100 µM) all compounds, including
resveratrol, slightly inhibit cell proliferation, but much less than with the tumor SW480 cell line.
Figure 7. Effect of stilbenes derivatives on the proliferation of non-transformed IEC18
cells. Cells were grown for 48 h in the presence of 30 µM resveratrol (or no RSV in a
control experiment) or 30 µM and 100 µM stilbene derivatives (numbered on the x-axis).
Cell viability was determined by counting cells using the trypan blue exclusion. Data
correspond to the mean ± standard deviation of two independent experiments.
2.2.4. Comparison of Resveratrol Analogs on Cytotoxicity of Colorectal Tumor Cells and on
Hepatoblastoma Cells
To have an overall view of the mechanisms involved in the inhibitory effect of the compounds, we
performed a concentration-dependent analysis of the cytotoxicity evaluated by the crystal violet
method. The crystal violet assay was chosen for the screening of the dose-effect of numerous
molecules despite its lower sensitivity compared to some other cytotoxicity methods [73]. The results
are presented as IC50 values. These IC50 values have been determined both on human tumor colorectal
SW480 cell line and on human hepatoblastoma HepG2 cell line (Table 1). All tested molecules have
lower IC50 than resveratrol towards SW480 cell line. Compounds 2 and 4 show a similar activity,
indicating that the additional hydroxy group does not increase the activity of the stilbene. Comparison
of the IC50 values between compounds 2 and 10 confirm the importance of the position 4 of the
phenolic group [30,31]. In the series of ferrocenylstilbene analogs, compound 17 without a free
phenolic function is the most active. This may be explained by a better lipophilicity due to the ester
group while the antitumor activity can be attributed to the ferrocenyl moiety. Five of the most active
derivatives (compounds 1, 2, 5, 6 and 8) have been subsequently tested on the HepG2 cell line (Table 1).

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Compounds 1, 2, 5 and 6 exhibit a lower potency on HepG2 than on SW480 cell line. Compounds 7
and 10 are the least active towards SW480 cells. Interestingly, compounds 5 (vinyl group in position 4')
and 8 (carbinol group in position 3 and methoxy in position 4') exhibit a higher activity towards SW480
cell lines than HepG2 cell lines, while the bromine in position 4' (compound 6) has an opposite effect. In
the case of compound 8, its metabolism by HepG2 cells may explain its weaker activity towards these
cells. The difference between the resveratrol IC50 cytotoxicity value (68.1 µM), (Table 1) and its
inhibitory efficiency (30 µM) on cell proliferation (Figure 5) towards SW480 cell line would be
attributed to the difference in the experimental approaches.
Table 1. Compared IC50 values of stilbene and ferrocenyl derivatives towards cell
proliferation of SW480 and of HepG2 cell lines. For technical informations, see
experimental procedure (Cell proliferation assays).
Compound
Number
Compound
Name
SW480
IC50 (μM)
68.1 ± 5.5
18.6 ± 3.2
14.7 ± 2.1
16.1(± 2.9
15.0 ± 0.9
21.4 ± 0.3
25.3 ± 2.4
38.2 ± 0.7
25.7 ± 2.1
81.7 ± 3.7
>100
HepG2
IC50 (μM)
57.3 ± 8.1
27.6 ± 5.0
26.3 ± 3.2
Not Tested
Not Tested
33.2 ± 6.2
18.6 ± 0.2
Not Tested
77.7 ± 4.1
Not Tested
>100
E-resveratrol
1
2
E-4-hydroxystilbene
E-4-hydroxy-4'-methoxystilbene
E-4-hydroxy-3',5'-dimethoxystilbene
E-4,4'-dihydroxy-4'-methoxystilbene
E-4-hydroxy-4'-vinylstilbene
E-4-bromo-4'-hydroxystilbene
E-4-hydroxy-3,3',4',5'-tetramethoxystilbene
E-3-carbinol-4-hydroxy-4'methoxystilbene
E-3-hydroxy-4'-methoxystilbene
Ferrocene
3
4
5
6
7
8
10
—
15
16
E-(4-vinylphenol)-ferrocene
(E,E)-1,1'-bis(4-vinylphenol)-ferrocene
(E,E)-1,1'-bis[(1-p-toluoyloxy-4-vinyl)benzene]-
ferrocene
25.5 ± 1.6
>100
40.2 ± 4.3
>100
17
5.9 ± 0.1
5.1 ± 0.2
2.2.5. Effect of Resveratrol Isosteres Bearing a Ferrocenyl Moiety. Determination of IC50 Values
Ferrocenyl derivatives were tested on cancerous SW480 and HepG2 cell lines and the IC50 values
are reported in Table 1. Compound 17 shows the highest inhibitory activity in both cell lines with a
very low IC50 value (5.9 µM), more than 10-fold higher compared to the resveratrol activity. Ferrocene
used as a control does not induce any cytotoxic effect against SW480 cell line. Compound 16
(a deprotected version of compound 17) shows a higher IC50 value (IC50 > 100 µM) than compound 17.
This data can be explained by the low solubility of 16 in DMSO in the cell medium.
E-(4-vinylphenol)ferrocene (15), the closest isostere of resveratrol presented in this study shows a
similar antiproliferative activity to resveratrol despite a lower solubility in the medium.

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3. Experimental
3.1. General Experimental Procedures
Wittig reactions were performed under an inert atmosphere of argon using conventional vacuum-line
and glasswork techniques. THF was degassed and distilled by refluxing over sodium and
benzophenone under argon. The organic reagents were received from commercial sources and used
without further purification. Separations by flash chromatography were performed on silica gel
(230–400 mesh). 1H-NMR, 13C-NMR and 31P-NMR spectra (δ, ppm) were recorded in CDCl3 solutions
on a Bruker 300 MHZ spectrometer, HRMS on MicroTOF Q-Bruker (ESI ionization). Spectroscopic
analyses were performed at the Pôle de Chimie Moléculaire de l’Université de Bourgogne
3.2. Precursors of Ferrocenyl-Stilbene Analogs
4-Toluoyloxybenzylic alcohol (23): To a mixture of 4-hydroxybenzylic alcohol (21, 100 g,
80.65 mmol) and potassium carbonate (13.4 g, 96.6 mmol) in acetone (300 mL) was added over 30 min
at 0 °C a solution of para-toluoyl chloride (16 mL, 121 mmol) in acetone (100 mL). Then, the mixture
was refluxed for 6 h. After cooling, the inorganic salts were filtrated and washed with acetone. The
solvent was removed under vacuum and the crude product was purified by chromatography
(EtOAc/heptane: 1/4) to give pure 4-toluoyloxybenzylic alcohol (23) in 47% yield. 1H-NMR δ (ppm):
2.48 (s, 3H, CH3), 4.75 (d, 2H, CH2), 7.23 (d, 2H, Ar-H), 7.33 (d, 2H, Ar-H), 7.45 (d, 2H, Ar-H), 8.11
(d, 2H, Ar-H); 13C-NMR δ (ppm): 21.75 (CH3), 64.87 (CH2), 117.46–144.52 (Ar-C).
4-Toluoyloxybenzylic bromide (24): To a mixture of 23 (9 g, 37.70 mmol) and triphenylphosphine
(14.9 g, 56.53 mmol) in CH2Cl2 (150 mL) was added a solution of N-bromosuccinimide (10 g,
56.53 mmol) in CH2Cl2 (100 mL). After stirring for one hour, the mixture was poured into a separatory
funnel and was washed with water. The organic phase was dried over MgSO4. After removal of the
solvent, the crude product was crystallized from ethanol (64%). 1H-NMR δ (ppm): 2.39 (s, 3H, CH3),
4.45 (d, 2H, CH2), 7.12 (d, 2H, Ar-H), 7.24 (d, 2H, Ar-H), 7.38 (d, 2H, Ar-H), 8.01 (d, 2H, Ar-H);
13C-NMR δ (ppm): 21.76 (CH3), 32.74 (CH2), 122.14, 126.61, 129.32, 129.78, 130.24, 135.29, 144.57,
150.96 (Ar-C), 165.04 (C=O).
4-Toluoyloxybenzyltriphenylphosphonium bromide (20): A mixture of 24 (18.7 g, 33 mmol) and
triphenylphosphine (9.7 g, 36.3 mmol) in toluene (50 mL) was refluxed for five hours. The reaction
mixture was cooled down to room temperature and a first crop of product was collected by filtration.
The filtrate was then refluxed for five additional hours and a second crop of product precipitated. Two
other crops were then collected and the combined fractions were crystallized from ethanol (86%).
1H-NMR δ (ppm): 2.37 (s, 3H, CH3), 5.47 (d, 2H, CH2), 6.90 (d, 2H, Ar-H), 7.12 (d, 2H, Ar-H), 7.22
(d, 2H, Ar-H), 7.66 (m, 15H, Ar-H phosphonium), 7.96 (d, 2H, Ar-H); 13C-NMR δ (ppm): 21.13
(CH3), 60.48 (CH2), 126.55 (Ar-C), 129.45, 130.28 (Ar-C phosphonium), 132.81, 134.54, 134.68,
135.05, 135.09, 144.76, 151.20 (Ar-C), 165.04 (C=O); 31P-NMR δ (ppm): 23.50 (s, 1P).

Molecules 2014, 19
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3.3. Ferrocenyl-Stilbene Analogs 15–17 and 25
E-[(1-paratoluoyloxy-4-vinyl)benzene]-ferrocene (25): Under argon atmosphere, butyllithium (1.6 M,
2.8 mL, 4.48 mmol) was slowly added to a solution of 4-toluoyloxybenzyltriphenylphosphonium
bromide (20, 2.5 g, 4.41 mmol) in THF (40 mL) at −78 °C. The resulting solution was allowed to
warm at room temperature. A solution of ferrocenecarbaldehyde [59] (18, 0.95 g, 4.41 mmol) in THF
(15 mL) was added dropwise and the reaction mixture was then stirred overnight. Ice-cold water
(500 mL) was added and the mixture stirred for an additional hour. The aqueous layer was extracted
with ethyl acetate; the combined organic layers were washed with water and dried over MgSO4. After
evaporating the solvent, 52% of a crude mixture of isomers Z and E was isolated. The E isomer was
1
isolated by chromatography (heptane/EtOAc: 9/1), yield 34%. H-NMR δ (ppm): 3.33 (s, 3H, CH3),
4.00 (s, 5H, Fc-H), 4.14 (t, 2H, Fc-H), 4.38 (d, 2H, Fc-H), 6.67 (d, 1H, 3J = 16.65 Hz, =CH), 6.85 (d,
3
1H, J = 16.65 Hz, =CH), 7.05 (d, 2H, Ar-H), 7.23 (d, 2H, Ar-H), 7.38 (d, 2H, Ar-H), 7.94 (d, 2H,
Ar-H); 13C-NMR δ (ppm): 21.4 (CH3), 60.0, 65.9, 66.8 (Fc-C), 119.8, 124.2, 124.4, 125.1, 127.1,
127.9, 131.2, 135.09, 143.3, 148.3 (Ar-C), 165.3 (C=O); C26H22FeO2 (MW 422.01). HRMS (ESI): m/z
422.09629 [M]+, calculated mass 422.09637 (σ = 0.2 ppm).
(E,E)-1,1'-bis[(1-paratoluoyloxy-4-vinyl)benzene]-ferrocene (17): Under an argon atmosphere, butyl
lithium (1.6 M, 5.6 mL, 8.96 mmol) was slowly added to a solution of 4-toluoyloxy-
benzyltriphenylphosphonium bromide (20, 5 g, 8.82 mmol) in THF (80 mL) at −78 °C. The resulting
solution was allowed to warm at room temperature. A solution of ferrocene-1,1'-dicarbaldehyde [59]
(19, 0.95 g, 4.41 mmol) in THF (15 mL) was added dropwise and the reaction mixture was stirred
overnight. Ice-cold water (500 mL) was added and the mixture was stirred for an additional hour. The
aqueous layer was extracted with ethyl acetate; the combined organic layers were washed with water
and dried over MgSO4. After evaporating the solvent, 47% of a crude mixture of EE/EZ/ZZ isomers
was obtained. The EE isomer was isolated by chromatography (heptane/EtOAc: 9/1), yield 25%.
3
1H-NMR δ (ppm): 3.41 (s, 6H, CH3), 4.28 (t, 4H, Fc-H), 4.48 (d, 4H, Fc-H), 6.63 (d, 2H, J = 15.09
3
Hz, =CH), 6.81 (d, 2H, J = 15.09 Hz, =CH), 7.11 (d, 4H, Ar-H), 7.28 (d, 4H, Ar-H), 7.41 (d, 4H,
Ar-H), 8.09 (d, 4H, Ar-H); 13C-NMR δ (ppm): 22.3 (CH3), 67.9, 68.1, 70.4 (Fc-C), 121.7, 124.1,
124.5, 125.1, 127.2, 127.7, 131.3, 143.5, 148.0 (Ar-C), 164.3 (C=O); C42H34FeO4 (MW 657.18).
HRMS (ESI): m/z 658.17693 [M]+, calculated mass 658.18018 (σ = 4.8 ppm).
E-(4-Vinylphenol)-ferrocene (15): To a solution of 25 (0.51 g, 1.1 mmol) in MeOH (15 mL) were
added pellets of KOH (0.17 g, 3.2 mmol). The mixture was stirred for one hour at 30 °C. The reaction
was quenched by addition of water (15 mL) and the solution was stirred for four hours. The solution
was acidified to pH = 2 by concentrated HCl and then treated with aqueous NaHCO3 solution (5%) to
reach pH = 4. The ferrocene derivative 15 was extracted with ether. The combined organic layers were
dried over MgSO4 and after removal of the solvent, the compound 15 was isolated, yield 92%.
1H-NMR δ (ppm): 4.25 (d, 4H, Fc-H), 4.27 (t, 2H, Fc-H), 4.43 (t, 2H, Fc-H), 4.60 (t, 1H, Fc-H), 4.74
(t, 1H, Fc-H), 4.79 (t, 1H, Fc-H), 6.36 (d, 1H, 3J = 16.08 Hz, =CH), 6.71 (d, 1H, 3J = 16.08 Hz, =CH),
6.79 (d, 2H, Ar-H), 7.28 (d, 2H, Ar-H); 13C-NMR δ (ppm): 68.7, 69.1, 69.6, 73.3 (Fc-C), 115.8, 125.3,

Molecules 2014, 19
7861
127.6, 130.6, 157.8, (Ar-C); C18H16FeO (MW 304.05). HRMS (ESI): m/z 304.05368 [M]+, calculated
mass 304.05452 (σ = 2.7 ppm).
(E,E)-1,1'-bis(4-Vinylphenol)ferrocene (16): Following the procedure described above, compound 16
1
was obtained from 17; 88%. H-NMR δ (ppm): 4.74 (d, 4H, Fc-H), 4.25 (t, 4H, Fc-H), 6.49 (s, 4H,
=CH), 6.56 (d, 4H, Ar-H), 7.06 (d, 4H, Ar-H), 8.13 (s, 2H, OH); 13C-NMR δ (ppm): 67.1, 69.3, 82.3,
(Fc-C), 114.4, 126.7, 127.3, 131.5, 159.1, (Ar-C); C26H22FeO2 (MW 422.09). HRMS (ESI): m/z
422.09588 [M]+, calculated mass 422.09765 (σ = 4.2 ppm).
3.4. Biological Methods
3.4.1. Cell Culture
The human colon carcinoma cell line SW480 obtained from ATCC (American Type Culture
Collection, Manassas,VA, USA) was cultured in RPMI-Medium with 10% fetal bovine serum (FBS)
and 1% antibiotics. Human derived hepatoblastoma cell line HepG2 was obtained from the ECACC
(European collection of cell culture, Salisbury, UK) and non-cancerous IEC18 cells from ileum
epithelium of Rattus norvegicus (ATCC) were grown in monolayer culture system and maintained in
phenol-red Dulbecco’s Modified Eagle’s Medium (DMEM) supplemented with 2 mM L-glutamine,
1% non-essential amino-acids, and 10% FBS (v/v) in a humidified atmosphere of 5% CO2 at 37 °C.
3.4.2. Cell Viability Assays
Proliferation inhibition assays were performed in 24-well plates in triplicate, and each experiment
was conducted two to three times. 30,000 cells were seeded per well, after 24 h cells were
incubated in medium containing either 0.1% dimethylsulfoxide-solubilized trans-resveratrol, resveratrol
derivatives, or 0.1% dimethylsulfoxide (DMSO) only as control. After 48 h, cells were harvested and
the number of live cells was quantified using the trypan blue exclusion test which is based on the
ability of a viable cell with an intact membrane to exclude trypan blue dye using a haemocytometer in
microscopic counting. Results were expressed as percentage of control values.
3.4.3. Cell Proliferation Assays
After 48 h of incubation at 37 °C, medium was carefully removed from wells and the plates were
washed gently with PBS 1X warmed at room temperature. Then the crystal violet solution was added
and incubated for 10 min. Thereafter, plates were washed several times with tap water. The
nucleus-incorporated crystal violet was dissolved using a sodium citrate solution and plates were
agitated on orbital shaker until the color became uniform with no areas of dense coloration at the
bottom of wells. The absorbance was read on each plate at 540 nm with a spectrophotometer (Dynex
MRX-TC Revelation, Manassas, VA, USA). The absorbance is proportional to the relative density of
cells adhering to multi-well dishes in regard to the absorbance of control well-plate (5% DMSO). After
48 h, IC50 values were determined by performing 0.75 to 100 µM treatments and the IC50 values were
obtained after parametric regressions on the percentages of viable cells versus the control.

Molecules 2014, 19
7862
3.4.4. Cell Cycle Analysis
Cell cycle analysis was performed as described previously [67,74,75]. Briefly, cells were seeded
24 h before treatment into 25 cm2 flasks. After treatment, the detached and adherent cells were pooled,
fixed with ethanol, and stained with propidium iodide (PI) for subsequent analyses with a CyFlow
Green flow cytometer and the fluorescence of PI was detected above 630 nm. For each sample 20,000
cells were acquired. Furthermore, data were analyzed with the MultiCycle software (Phoenix Flow
Systems, San Diego, CA, USA); the x-axis corresponds to the DNA content and the y-axis to the
number of cycling cells. The maximum value on the y-axis is inversely proportional to the altered cells
level (non-cycling cells) which is excluded by gating.
4. Conclusions
While trans-resveratrol is considered a promising molecule for fighting cancer [76], a wide range of
synthetic resveratrol analogs are potentially more active than trans-resveratrol. Some of these new
synthetic molecules have interesting effects. Compounds 2 and 17 are the most active, while
compounds 10 and 16 show the lowest activity. The comparison between compounds 16 and 17
indicates that the presence of a protecting group lead to a better efficacy which could be due to a better
solubilisation in DMSO. It appears that the lack of substituents at position 3 and 5 (compound 1) leads
to a better inhibitory effect. Moreover, a limited number of methoxy groups (compounds 2, 3 and 4)
provides better lipophilic properties. In most cases, the efficacy of the synthetic compounds is lower
towards liver derived HepG2 cells than towards colorectal SW480 cells, except for compound 6 and
mostly 17, which is the most powerful derivative. These differences can be explained by the high
xenobiotic metabolizing activities of HepG2 cells. Furthermore, the lack of effect on non-tumor cells
(IEC18 intestinal epithelium cells) demonstrates the selectivity of these molecules for cancer cells,
which is an important aspect for potential therapeutic applications. Concerning the possible targets of
resveratrol analogs, an inhibition of the TNF alpha-induced activation NFkB by polyhydroxylated
resveratrol derivatives i.e., the hexahydroxystilbene in leukemia HL60 cells has been reported [70]. In
terms of the structure-activity relationship, it appears that in order to obtain an inhibitory effect, the
chemical parameters are the following: (a) the presence of a hydroxy group in position 4; (b) an
increased inhibitory effect by the presence of a methoxy group (a decrease of the polar character
leading to an increase in lipophilicity); (c) the lack (or masked form) of other hydroxy groups. In
addition, (E,E)-1,1'-bis[(1-para-toluoyloxy-4-vinyl)benzene]ferrocene (17) a new compound, shows
the highest efficacy.
Supplementary Materials
Supplementary materials can be accessed at: http://www.mdpi.com/1420-3049/19/6/7850/s1.
Acknowledgments
Université de Bourgogne, CNRS, INSERM UMR 866, are gratefully acknowledged for their
financial support. Virginie Aires, Frédéric Mazué and M. Emeric Limagne are acknowledged for their
technical help and advises as well as Richard Decreau and M. François Jacquin for English corrections.

Molecules 2014, 19
7863
Malik Chalal was supported by a PhD grant from the Algerian government (Ministère de la Recherche
et de l’Enseignement), which is sincerely acknowledged.
Author Contributions
The chemical work (syntheses and spectroscopic characterization of the compounds) as the biological
study were performed by M. Chalal during his PhD work under the direction of P. Meunier and
D. Vervandier-Fasseur for the chemical part and under the direction of N. Latruffe and D. Delmas for
the biological part. The manuscript was written by N. Latruffe (N.L.) and D. Vervandier-Fasseur (D.V.-F.)
and revised by the co-corresponding authors (N.L and D.V.-F.).
Conflicts of Interest
The authors declare no conflict of interest.
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Sample Availability: Samples of the compounds 1–17 are available from D. Vervandier-Fasseur (D.V.-F.).
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