Concise total synthesis of permethylated anigopreissin a, a new benzofuryl resveratrol dimer

Article abstract of DOI:10.1002/ejoc.201101422

The versatile preparation of permethylated anigopreissin A (1) has been accomplished from methyl 3,5-dihydroxybenzoate. The key steps of the synthesis are sequential Sonogashira and Suzuki cross-couplings for the construction of the 2,3-diarylbenzo[b]furan moiety and Wittig olefination for the introduction of the styryl group.

Full text of DOI:10.1002/ejoc.201101422

FULL PAPER
DOI: 10.1002/ejoc.201101422
Concise Total Synthesis of Permethylated Anigopreissin A, a New Benzofuryl
Resveratrol Dimer
Lucia Chiummiento,*[a] Maria Funicello,[a] Maria Teresa Lopardo,[a] Paolo Lupattelli,[a]
Sabine Choppin,[b] and Françoise Colobert[b]
Dedicated to Professor Alberto Brandi on the occasion of his 60th birthday
Keywords: Natural products / Total synthesis / Cross-coupling / Palladium / Heterocycles
The versatile preparation of permethylated anigopreissin A
(1) has been accomplished from methyl 3,5-dihydroxybenzo-
ate. The key steps of the synthesis are sequential Sonoga-
shira and Suzuki cross-couplings for the construction of the
2,3-diarylbenzo[b]furan moiety and Wittig olefination for the
introduction of the styryl group.
from Vitis amurensis,[5] has been described. To date no syn-
thesis of anigopreissin A has been reported and no exhaus-
tive biological studies have been performed.
As part of our ongoing program on the preparation of
biologically relevant natural products[6] we decided to
undertake the synthesis of this compound. Herein we de-
scribe a convergent and modular synthesis of protected ani-
gopreissin A that could be also used for the preparation of
its analogues.
Introduction
Anigopreissin A is a naturally occurring resveratrol di-
mer (Figure 1) isolated from root cultures of Anigozanthos
preissii and from rhizomes of Musa cavendish plants by D.
Holscher and B. Schneider.[1] Anigopreissin A belongs to
the limited class of stilbene di- and oligomeric forms con-
taining a benzofuran ring system. The broad range of bio-
logical activities of resveratrol and its derivatives[2] and their
significant pharmacological potential have generated exten-
sive and enduring efforts toward the syntheses of these im-
portant compounds. Several biomimetic syntheses[3] of di-
mers and oligomers of resveratrol have been reported, and
only one chemical approach[4] for the preparation of vinifer-
ifuran, an isomeric dimer extracted from Vitis vinifera and
Results and Discussion
Our retrosynthetic approach to permethylated anigopre-
issin A (1) is outlined in Scheme 1. We planned to insert the
styryl group by Wittig olefination and the aryl group at
C3 of the benzo[b]furan ring by a Suzuki cross-coupling
reaction.[7] Benzo[b]furan moiety A would be constructed
through the 5-endo-dig cyclization of the corresponding di-
aryl alkyne B, which could, in turn, arise from the coupling
of alkyne D and halide C by a Sonogashira coupling reac-
tion.[8]
Our synthesis began from commercially available brom-
ide 2, which was reduced with BH3·SMe2 in THF and pro-
tected as the silyl ether by using TBSCl, imidazole, and
DMAP in CH2Cl2 to afford compound 3 in 82% yield over
two steps[9] (Scheme 2).
Coupling reactions between aryl bromide 3 and para-
methoxyphenylacetylene (4) according to previously re-
ported conditions[10] [i.e., Na2PdCl4, 2-(di-tert-butylphos-
phanyl)-N-phenylindole, CuI, TMEDA] for the highly ef-
ficient Sonogashira coupling of aryl and heteroaryl brom-
ides afforded diarylalkyne 5 in only 20% yield. The same
reaction was performed with 2-methyl-3-butyn-2-ol (6, a
Figure 1. Structures of resveratrol and anigopreissin A.
[a] Dipartimento di Chimica “Antonio Mario Tamburro”,
Università degli Studi della Basilicata,
Via dell’Ateneo Lucano 10, 85100 Potenza, Italy
Fax: +39-0971-205678
E-mail: lucia.chiummiento@unibas.it
[b] Laboratoire de Stéréochimie,
Ecole de Chimie Polymères et Matériaux (ECPM),
Université de Strasbourg CNRS UMR 7509,
25 Rue Becquerel, 67087 Strasbourg cedex 2, France
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201101422.
188
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Eur. J. Org. Chem. 2012, 188–192

Concise Total Synthesis of Permethylated Anigopreissin A
cross-coupling reactions with alkyne 4 and 6 did not give
desired compounds 9 and 10. Therefore we decided to
switch to the iodide, which is generally more reactive than
the corresponding bromide. As aryl iodides bearing two hy-
droxy groups in the ortho position are not commercially
available, we submitted methyl 3,5-dihydroxybenzoate (11)
to NIS in MeOH followed by MeI and K2CO3 in DMF to
generate 13 in 62% yield over two steps (Scheme 3).
Scheme 1. Retrosynthetic analysis.
Scheme 3. Preparation of iodobenzofuran 14 by iodocyclization.
Sonogashira cross-coupling reaction of aryl iodide 13
with 4 in the presence of PdCl2(PPh3)2, CuI, and DIPA[8] in
DMAc afforded the corresponding alkyne 9 in 85% yield.
[12]
Treatment of alkyne 9 with I2 in CH2Cl2 led to iodoben-
zofuran 14 in 70% yield (Scheme 3). The iodocyclization of
5 also proceeded, furnishing the corresponding benzo[b]-
furan in very low yield. Probably, the presence of an elec-
tron-donating group para to the triple bond increases the
electron density on the distal end of the triple bond and
disfavors the endo-dig cyclization.[13]
Interestingly, we also prepared iodobenzofuran 14 by an
alternative three-step procedure starting from nonprotected
aryl iodide 12. In this event, we performed the one-pot cou-
pling/cyclization[14] followed by protection of the corre-
sponding benzofuran 16 with MeI and K2CO3 in DMF to
give 4-methoxybenzofuran 17 in 62% yield over two steps
(Scheme 4).
Reaction of 17 with NIS and TfOH in MeOH gave iodo-
benzofuran 14 regioselectively in 98% yield. To the best of
our knowledge, this is the first example of a regioselective
iodination of a 2-arylbenzofuran ring with such electron-
rich substituent. Preliminary direct arylation of benzofuran
17 with 3,5-dimethoxyphenyl bromide (18) by using
Scheme 2. Preparation of alkyne D with the use of aryl bromides.
masked acetylene)[11] without success, and in fact, only 15% Pd(OAc)2 and NaOAc in DMAc did not furnished com-
of product 7 was obtained.
pound 19.[15]
A second route began with methyl ester 8 derived from
With iodobenzofuran 14 in hand, Suzuki cross-coupling
the esterification of benzoic acid 2. Also in these cases the with 3,5-dimethoxyphenylboronic acid (20) in the presence
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L. Chiummiento et al.
FULL PAPER
within 3 h and the two stereoisomers (Z)- and (E)-1 were
obtained as a mixture. After usual workup, isomerization
of the crude mixture in the presence of iodine crystals in
CH2Cl2 at room temperature took place over 24 h to afford
the E isomer as a pure compound. Thus, purification gave
permethylated anigopreissin A (1) in 80% yield.
Completion of the synthesis required removal of five
methyl ether groups to arrive at anigopreissin A. The depro-
tection of pentamethyl anigopreissin was studied, and it was
found that numerous conditions (BBr3, BBr3·SMe2, l-Se-
lectride) gave only decomposition products or partially de-
methylated products.
Conclusions
Scheme 4. Preparation of iodobenzofuran 14 by iodination.
In summary, a versatile, convergent, and modular total
synthesis of permethylated anigopreissin A (1) was ac-
complished in eight steps and 28% overall yield. The crucial
benzofuran ring formation was achieved through the use of
the Sonogashira reaction, whose application to the synthe-
sis of natural molecules is ongoing. Selective iodination of
compound 17 allows this route to be used with different
electrophiles. Due to this efficient strategy, which allows the
introduction of various aryl and styryl moieties, the prepa-
ration of anigopreissin A analogues to test biological activi-
ties is also in progress.
of PdCl2(PPh3)2 and NaHCO3 in DMF was performed to
give coupling product 19 in 98% yield (Scheme 5). For the
final assembly of permethylated anigopreissin A (1), our at-
tention was focused on the preparation of the aldehyde for
olefination. Conversion of methyl ester 19 into its benzylic
alcohol by DIBALH in CH2Cl2 proceeded quantitatively,
and the crude mixture was oxidized with Dess–Martin
periodinane to afford aldehyde 21 in high yield (92% over
two steps). No reaction occurred when diethyl 4-methoxy-
benzylphosphonate (22) was used as the reagent with alde-
hyde 21 and various bases (i.e., KOtBu, BuLi, EtP2) for the
Horner–Wadsworth–Emmons reaction. Good results were
obtained by using phosphonium salt 23[16] under Wittig
conditions and EtP2 as the base. The reaction was complete
Experimental Section
General Methods: Unless otherwise specified, materials were pur-
chased from commercial suppliers and used without further purifi-
cation. Moisture-sensitive reactions were conducted in oven- or
flame-dried glassware under an argon atmosphere. All reactions
were magnetically stirred and monitored by thin-layer chromatog-
raphy by using precoated silica gel (60 F254) plates. Column
chromatography was carried out by using 60–230 mesh silica gel at
atmospheric pressure. Mass spectra were obtained by FT-ICR/MS
by using ESI in the positive ion mode. NMR spectra were recorded
in CDCl3 solution at room temperature (1H at 400 MHz and 13C
at 100 MHz).
Methyl 4-Iodo-3,5-dihydroxybenzoate (12):[14] To a solution of 11
(500 mg, 2.98 mmol) in methanol (2 mL) was added NIS (703 mg,
3.13 mmol) in methanol (2 mL) at 0 °C. After stirring at room tem-
perature for 16 h, the reaction mixture was poured into cold water
(2 mL), and this solution was then poured into a saturated aqueous
solution of Na2SO3 (2 mL). The mixture was extracted with AcOEt
(3ϫ10 mL) and washed with brine. The combined organic extracts
were dried with Na2SO4 and concentrated under vacuum to give
the crude product. Column chromatography (silica gel; CH2Cl2/
EtOAc, 7:3) afforded iodide 12 (0.557 g, 63%) with the same spec-
troscopic data as those previously reported.
Methyl 4-Iodo-3,5-dimethoxybenzoate (13):[17] K2CO3 (386.5 mg,
3.9 mmol) was added to a solution of 12 (230 mg, 0.78 mmol) in
DMF (1.5 mL). After stirring for 20 min at room temperature, MeI
(0.15 mL, 2.35 mmol) was added, and the resulting solution was
stirred at room temperature for 15 h. The reaction mixture was then
diluted with AcOEt (3 mL) and washed with a saturated aqueous
solution of NH4Cl (5ϫ10 mL). The organic layer was dried with
Na2SO4, filtered, and concentrated to give product 13 (0.247 g,
Scheme 5. Preparation of permethylated anigopreissin A (1).
190
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Concise Total Synthesis of Permethylated Anigopreissin A
98%) with the same spectroscopic data as those previously re-
ported. Compound 13 was used in the next step without any purifi-
cation.
the crude product was purified (silica gel; PE/AcOEt, 8:2) to afford
17 (0.074 g, 79%) as a pale yellow powder. M.p. 149–150 °C. 1H
NMR (400 MHz, CDCl3): δ = 3.85 (s, 3 H), 3.95 (s, 3 H), 4.00 (s,
3 H), 6.97 (d, J = 8.8 Hz, 2 H), 6.98 (s, 1 H), 7.36 (s, 1 H), 7.78 (d,
J = 8.8 Hz, 2 H), 7.85 (s, 1 H) ppm. 13C NMR (100 MHz, CDCl3):
δ = 52.1, 55.3, 55.7, 97.2, 104.2, 106.5, 114.3, 122.7, 124.2, 126.1,
126.5, 152.5, 154.9, 157.6, 160.3, 167.3 ppm. MS (EI, 70 eV): m/z
(%) = 312 (100) [M]+, 297 (75), 281 (10), 253 (8), 156 (10), 140
(10), FT-ICR/MS (ESI): calcd. for [C18H16O5+H]+ 313.1070; found
313.1099. C18H16O5 (312.10): calcd. C 69.22, H 5.16; found C
69.40, H 5.29.
Methyl 3,5-Dimethoxy-4-(4-methoxyphenylethynyl)benzoate (9): Io-
dide 13 (608 mg, 1.89 mmol), bis(triphenylphosphane)palladium
dichloride (3 mol-%), copper(I) iodide (3 mol-%), and DMAc
(19 mL) were combined and degassed with argon. para-Methoxy-
phenylacetylene (4; 0.75 mL, 5.67 mmol) and DIPA (0.11 mL,
5.67 mmol) were added, and the mixture was heated to 40–50 °C
and stirred for 3 h. The reaction mixture was diluted with AcOEt
and washed with
a saturated aqueous solution of NH4Cl
(3ϫ20 mL). The organic layer was dried with Na2SO4, filtered, and
concentrated, and the crude product was purified on silica gel to
afford 9 (0.525 g, 85%) as a pale yellow solid. M.p. 139–140 °C. 1H
Methyl 3-Iodo-4-methoxy-2-(4-methoxyphenyl)benzofuran-6-carb-
oxylate (14, by Iodination): To a solution of 17 (74 mg, 0.24 mmol)
in methanol (0.5 mL) was added NIS (56 mg, 0.25 mmol) in meth-
NMR (400 MHz, CDCl3): δ = 3.86 (s, 3 H), 3. 97 (s, 3 H), 3.99 (s, anol (0.5 mL) and CF3COOH (0.005 mL, 0.0018 mmol) at 0 °C.
6 H), 6.91 (d, J = 8 Hz, 2 H), 7.28 (s, 1 H), 7.30 (s, 1 H), 7.56 (d, After stirring at room temperature for 5 h, the reaction mixture
J = 8 Hz, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 52.3, 55.3, was poured into cold water (2 mL), and this solution was then
56.3, 80.1, 100.7, 104.6, 106.7, 113.9, 115.6, 130.4, 133.3, 159.7,
poured into a saturated aqueous solution of Na2SO3 (2 mL). The
mixture was extracted with AcOEt (3ϫ10 mL), and washed with
160.8, 166.6 ppm. MS (EI, 70 eV): m/z (%) = 326 (100) [M]+, 311
(20), 295 (22), 267 (10), 219 (15), 163 (10). FT-ICR/MS (ESI): brine. The combined organic extracts were dried with Na2SO4 and
calcd. for [C19H18O5 + K]+ 365.0786; found 365.0791. C19H18O5 concentrated under vacuum, and the crude product was purified
(326.12): calcd. C 69.93, H 5.56; found C 70.05, H 5.67.
(silica gel; PE/AcOEt, 8:2) to give product 14 (0.102 g, 98%).
Methyl 3-Iodo-4-methoxy-2-(4-methoxyphenyl)benzofuran-6-carb-
oxylate (14, by Iodocyclization): To a solution of alkyne 9 (525 mg,
1.61 mmol) in CH2Cl2 (40 mL) was gradually added I2 (817 mg,
3.22 mmol) in CH2Cl2 (10 mL), and the mixture was stirred at
room temperature for19 h. The excess amount of I2 was removed
by washing with a saturated aqueous solution of Na2S2O3. The
organic layer was dried with anhydrous Na2SO4 and concentrated
under vacuum to yield the crude product, which was purified by
chromatography (silica gel; PE/CH2Cl2, 4:6) to afford iodobenzofu-
ran 14 (0.514 g, 70%) as a pale yellow solid. M.p. 128–130. 1H
Methyl 3-(3,5-Dimethoxyphenyl)-4-methoxy-2-(4-methoxyphenyl)-
benzofuran-6-carboxylate (19): To a solution of iodobenzofuran 14
(500 mg, 1.14 mmol) in DMF/H2O (4:1, 22.8 mL) was added 3,5-
dimethoxyphenylboronic acid (20; 290 mg, 1.6 mmol), NaHCO3
(133.4 mg, 1.6 mmol), and PdCl2(PPh3)2 (40 mg, 0.057 mmol). The
solution was stirred for 10 min at room temperature and then
heated at 80 °C for 7 h. After cooling, the mixture was diluted with
AcOEt and washed with a saturated aqueous solution of NH4Cl,
brine, and water. The organic layer was dried with Na2SO4, filtered,
and concentrated, and the crude product was purified (silica gel;
NMR (400 MHz, CDCl3): δ = 3.90 (s, 3 H), 3.95 (s, 3 H), 4.00 (s, PE/AcOEt, 9:1) to afford product 19 (0.504 g, 98%) as a yellow
1
3 H), 7.01 (d, J = 8.8 Hz, 2 H), 7.38 (s, 1 H), 7.84 (s, 1 H) 8.11 (d, solid. M.p. 155–156 °C. H NMR (400 MHz, CDCl3): δ = 3.78 (s,
J = 8.8 Hz, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 52.3,
53.4, 55.4, 55.8, 105.1, 106.3, 113.9, 122.2, 126.9, 128.1, 129.6,
153.4, 154.4, 155.4, 160.6, 167.0 ppm. MS (EI, 70 eV): m/z (%) =
438 (100) [M]+, 423 (40), 407 (8), 253 (5). FT-ICR/MS (ESI): calcd.
6 H), 3.82 (s, 3 H), 3.97 (s, 3 H), 6.51 (t, J = 2 Hz, 1 H), 6.63 (d,
J = 2 Hz, 1 H), 6.84 (d, J = 8.8 Hz, 2 H), 7.35 (s, 1 H), 7.53 (d, J
= 8.8 Hz, 2 H), 7.88 (s, 1 H) ppm. 13C NMR (100 MHz, CDCl3):
δ = 55.3, 55.4, 55.5, 55.7, 100.1, 104.8, 106.4, 108.7, 113.9, 115.9,
for [C18H15IO5+ Na]+ 460.9874; found 460.9856. C18H15IO5 122.7, 123.4, 126.5, 128.7, 135.0, 152.7, 153.9, 154.1, 159.9, 160.4,
(438.00): calcd. C 49.34, H 3.45; found C 49.50, H 3.57.
167.3 ppm. FT-ICR/MS (ESI): calcd. for [C26H24O7 +
H]+
449.1595; found 449.1593. C26H24O7 (448.15): calcd. C 69.63, H
5.39; found C 69.70, H 5.49.
Methyl 4-Hydroxy-2-(4-methoxyphenyl)benzofuran-6-carboxylate
(16): Iodide 12 (200 mg, 0.68 mmol), bis(triphenylphosphane)palla-
dium dichloride (3 mol-%), copper(I) iodide (3 mol-%), and DMAc
(6.8 mL) were combined and degassed with argon. Compound 4
(0.26 mL, 2.04 mmol) and DIPA (0.81 mL, 2.04 mmol) were added,
and the mixture was heated to 40–50 °C and stirred for 3 h. The
reaction mixture was diluted with AcOEt and washed with a satu-
[3-(3,5-Dimethoxyphenyl)-4-methoxy-2-(4-methoxyphenyl)benzo-
furan-6-yl]methanol (19a): To a solution of 19 (500 mg, 1.12 mmol)
in CH2Cl2 (17 mL) was added a solution of DIBALH (1 m in hex-
ane, 4.46 mL, 4.46 mmol) at –60 °C. After stirring at –60 °C for
2 h, the reaction mixture was quenched with MeOH at –60 °C. Af-
rated aqueous solution of NH4Cl (3ϫ10 mL). The organic layer ter stirring at room temperature for 30 min, the mixture was filtered
was dried with Na2SO4, filtered, and concentrated, and the crude
product (0.158 g, 78%) was used without any purification. 1H
NMR (400 MHz, [D6]DMSO): δ = 2.98 (s, 3 H), 3.01 (s, 3 H), 6.23
(d, J = 7.2 Hz, 2 H), 6.42 (s, 1 H), 6.50 (s, 1 H), 6.78 (s, 1 H), 7.03
(d, J = 7.2 Hz, 2 H), 9.55 (s, 1 H) ppm. FT-ICR/MS (ESI): calcd.
for [C17H14O5 + H]+ 299.0914; found 299.0940.
through a pad of Celite, and the filtrate was concentrated under
reduced pressure to afford crude product 19a as a white solid
1
(0.470 g, 100%). H NMR (400 MHz, CDCl3): δ = 3.76 (s, 1 H),
3.78 (s, 1 H), 3.80 (s, 1 H), 3.81 (s, 1 H), 4.80 (d, J = 5.2 Hz, 2 H),
6.5 (t, J = 2 Hz, 1 H), 6.65 (d, J = 2 Hz, 2 H), 6.70 (s, 1 H), 6.83
(d, J = 8.8 Hz, 2 H), 7.18 (s, 1 H), 7.27 (s, 1 H), 7.50 (d, J = 8.8 Hz,
2 H) ppm.
Methyl 4-Methoxy-2-(4-methoxyphenyl)benzofuran-6-carboxylate
(17): K2CO3 (128 mg, 0.93 mmol) was added to a solution of 16
(92 mg, 0.31 mmol) in DMF (1 mL). After stirring for 10 min at
room temperature, MeI (0.03 mL, 0.45 mmol) was added, and the
resulting solution was stirred at room temperature for 15 h. The
reaction mixture was then diluted with AcOEt (3 mL) and washed
with a saturated aqueous solution of NH4Cl (5ϫ5 mL). The or-
ganic layer was dried with Na2SO4, filtered, and concentrated, and
3-(3,5-Dimethoxyphenyl)-4-methoxy-2-(4-methoxyphenyl)benzo-
furan-6-carbaldehyde (21): To a solution of alcohol 19a (115 mg,
0.27 mmol) in CH2Cl2 (3 mL) was added Dess–Martin periodinane
(174 mg, 0.41 mmol) at 0 °C. After stirring at room temperature
for 3 h, the reaction mixture was filtered through Celite, and the
filtrate was concentrated under reduced pressure to give the residue,
which was purified (silica gel; PE/AcOEt, 8:2) to afford product
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L. Chiummiento et al.
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21 (0.104 g, 92%) as a yellow solid. M.p. 120–122 °C. 1H NMR
(400 MHz, CDCl3): δ = 3.79 (s, 6 H), 3.81 (s, 3 H), 3.82 (s, 3 H),
6.53 (s, 1 H), 6.63 (s, 2 H), 6.85 (d, J = 8.8 Hz, 2 H), 7.21 (s, 1 H),
7.55 (d, J = 8.8 Hz, 2 H), 6.66 (s, 1 H), 10.01 (s, 1 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 55.3, 55.4, 100.1, 108.7, 113.9, 116.2,
122.4, 128.7, 133.6, 134.8, 154.1, 154.7, 160.1, 160.4, 191.5 ppm.
FT-ICR/MS (ESI): calcd. for [C25H22O6 + H]+ 419.1489; found
419.1494. C25H22O6 (418.14): calcd. C 71.76, H 5.30; found C
71.90, H 5.47.
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[2]
[3]
(E)-3-(3,5-Dimethoxyphenyl)-4-methoxy-2-(4-methoxyphenyl)-6-(4-
methoxystyryl)benzofuran (1): To a stirred solution of triphenyl(4-
methoxybenzyl)phosphonium bromide (23; 132 mg, 0.29 mmol) in
THF (2 mL) was added EtP2 (0.1 mL, 0.29 mmol) at –60 °C. After
10 min, a solution of 21 (100 mg, 0.24 mmol) in THF (4 + 2 mL
for rinse) was added to the mixture at –60 °C. After slowly warming
to room temperature over 3 h, the mixture was quenched with H2O
and extracted with CH2Cl2 (3ϫ15 mL). The combined organic lay-
ers were dried with Na2SO4, filtered, and concentrated under re-
duced pressure. The crude product was filtered through a pad of
silica gel and dissolved in n-heptane/CH2Cl2 (7:3). Iodine was
added at room temperature, and the resulting mixture was stirred
until the less polar product visible on TLC was totally converted
into the more polar one. The solvent was then evaporated under
reduced pressure, and the crude product was purified (silica gel;
PE/AcOEt, 8:2) to give product 1 (0.100 g, 80%). M.p.128–130 °C.
1H NMR (400 MHz, CDCl3): δ = 3.79 (s, 6 H), 3.80 (s, 3 H), 3.821
(s, 3 H), 3.85 (s, 3 H), 6.52 (t, J = 2.0 Hz, 1 H), 6.68 (d, J = 2.0 Hz,
2 H), 6.83 (s, 1 H), 6.84 (d, J = 9.2 Hz, 2 H), 6.93 (d, J = 8.8 Hz,
2 H), 7.07 (d, J = 16 Hz, 1 H), 7.12 (d, J = 16 Hz, 1 H), 7.30 (s, 1
H), 7.50 (d, J = 8.8 Hz, 2 H), 7.53 (d, J = 9.2 Hz, 2 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 55.2, 55.3, 55.4, 55.5. 100.0, 102.3,
108.7, 113.8, 114.1, 115.9, 118.8, 123.3, 127.1, 127.6, 128.3, 130.2,
135.1, 135.6, 150.3, 154.3, 155.4, 159.2, 159.4, 160.3 ppm. FT-ICR/
MS (ESI): calcd. for [C33H30O6 + H]+ 523.2121; found 523.2098.
C33H30O6 (522.20): calcd. C 75.84, H 5.79; found C 75.99, H 5.87.
[4]
[5]
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Acknowledgments
We thank the CIGAS center of Università degli Studi della Basili-
cata for FT-ICR/MS (ESI) analyses. We thank MIUR (Ministry
of University and Research, Rome) (PRIN 2008: Stereoselective
synthesis and biological evaluation of new compounds active
towards proteic targets involved in viral pathologies, cell growth,
and apoptosis) and Università degli Studi della Basilicata for finan-
cial support.
Received: September 28, 2011
Published Online: November 28, 2011
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