Novel synthesis of the isoflavone genistein

Article abstract of DOI:10.1055/s-0029-1219757

Genistein was efficiently synthesized from (2,4,6-trihydroxyphenyl)ethanone by a novel five-step procedure involving the formation of an enamino ketone, followed by ring closure and a Suzuki coupling reaction using palladium acetate and poly(ethylene glycol). Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-0029-1219757

1590
SHORT PAPER
Novel Synthesis of the Isoflavone Genistein
N
ovel Syn
e
thesis of
G
f
enisteinfrey D. St. Denis, James S. Gordon IV, Vincent M. Carroll, Ronny Priefer*
Department of Chemistry, Biochemistry, and Physics, Niagara University, Niagara, NY 14109, USA
Fax +1(716)2868254; E-mail: rpriefer@niagara.edu
Received 9 December 2009; revised 27 February 2010
Genistein has also been examined as a treatment for pros-
tate cancer. In vivo studies showed that an intake of
genistein can significantly reduce tumor growth and
lymph node metastases.5 Studies have also suggested that
genistein shows efficacy in vitro against the fibrosarcoma
cell line HT1080,6 lung carcinoma LL2,7 and cervical can-
cer cell lines.8
Abstract: Genistein was efficiently synthesized from (2,4,6-trihy-
droxyphenyl)ethanone by a novel five-step procedure involving the
formation of an enamino ketone, followed by ring closure and a
Suzuki coupling reaction using palladium acetate and poly(ethylene
glycol).
Key words: ring closure, coupling, heterocycles, genistein, isofla-
vone, green chemistry
One of the primary mechanisms through which biofla-
vonoids exert antiproliferative properties is by suppres-
sion of angiogenesis. Bioflavonoids are effective at
preventing this crucial vascularization by inhibiting the
expression of carcinomal growth factors that result from a
rise in ROS. Cancer cells produce a number of com-
pounds, such as vascular endothelial growth factors, basic
fibroblast growth factors, and platelet-derived endothelial
growth factors, that stimulate the generation of new blood
vessels.1 By suppressing ROS, genistein effectively pre-
vents the cascade of events that lead to the production of
carcinomal growth factors.
Isoflavones are found naturally in many plant species,
particularly those of the legume family. Isoflavones are
often produced by the plant as a defense mechanism to
ward off microbes or other pathogens, and to reduce oxi-
dative stress caused by reactive-oxygen species (ROS).
The soy isoflavones consist of three compounds:
genistein, daidzein, and, less commonly, glycitein
(Figure 1). These compounds are usually O-glycosylated
within the plant and are metabolized into the active agly-
cone forms by bacterial or digestive action.1
Genistein was first isolated from Genista trictoria (dyer’s
broom) in 1899,9 and successfully synthesized for the first
time in 1928 by Baker.10 The pyrone ring was formed by
treatment of the corresponding deoxybenzoin by various
anhydrides, with subsequent decarboxylation. In 1945,
Shriner and Hull performed an analogous synthesis by us-
ing ethyl formate, which eliminated the need for the de-
carboxylation step.11 The use of mesyl chloride12,13 or
(dimethoxymethyl)dimethylamine (N,N-dimethylform-
amide dimethyl acetal)14 with boron trifluoride etherate
has also proved successful in the case of many isoflavone
derivatives synthesized from the corresponding deoxy-
benzoins. Oxidative rearrangement of chalcones with
thallium(III) nitrate has shown promise for the synthesis
of the isoflavone scaffold,15,16 but there are obvious con-
cerns regarding the toxicity of this reagent.
OH
OH
O
O
HO
OH
1
OH
O
O
O
O
MeO
HO
HO
2
3
Figure 1 Soy isoflavones: genistein (1), daidzein (2), and glycitein
(3)
In vitro studies have shown that isoflavones can be potent
inhibitors of cancer metastasis.1,2 In 1994, genistein was
found to inhibit the metastatic breast cancer line BALB/c
410.4, with an EC50 of less than 1 mM. Other soy isofla-
vonoids have shown much lower activities against this
cell line.3 It has also been shown that genistein is an effec-
tive estrogenic agent4 and, interestingly, it exhibits its es-
trogenic activity in estrogen-receptor-negative human
breast carcinoma cell lines, as well as in normal breast-
cancer cell lines, suggesting that it has an independent
mode of action in relation to estrogen.4
Here, we describe a novel synthesis of genistein in which
a phosphine-free palladium acetate-catalyzed Suzuki
reaction is used to attach the final ring to 3-iodo-4H-1-
benzopyran-4-one (4), which is obtained from the com-
mercially available (2,4,6-trihydroxyphenyl)ethanone (5)
by using (dimethoxymethyl)dimethylamine to form an
initial enamino ketone that undergoes subsequent ring
closure and iodination (Scheme 1).
Our synthesis (Scheme 2) began from commercially
available (2,4,6-trihydroxyphenyl)ethanone (5). However
initial attempts to form an enamino ketone were not suc-
cessful, presumably because (dimethoxymethyl)dimethyl-
amine is capable of reacting with phenols.17 We therefore
SYNTHESIS 2010, No. 10, pp 1590–1592
Advanced online publication: 06.04.2010
DOI: 10.1055/s-0029-1219757; Art ID: M06309SS
x
x.
x
x
.
2
0
1
0
© Georg Thieme Verlag Stuttgart · New York

SHORT PAPER
Novel Synthesis of Genistein
1591
OH
OH
O
O
OH
O
OH
O
O
I
HO
HO
OH
HO
1
4
5
Scheme 1 Retrosynthetic analysis
MOM
O
MOM
O
O
O
O
O
OH
O
MOMCl, DIPEA
CH2Cl2
Me2NCH(OMe)2
DMF
NMe2
MOM
MOM
OH
OH
HO
OH
7
6
5
I2, MeOH
MOM
O
OH
MOM
O
O
O
O
O
O
Pd(OAc)2, Na2CO3
PEG10000
I
concd HCl
1
MOM
O
CHCl3, MeOH
MOM
(4-hydroxyphenyl)boronic acid
MeOH
9
8
Scheme 2 Synthesis of genistein
considered it necessary to protect two of the hydroxy sub- Although a variety of dimers formed during the Suzuki-
stituents in the triol 5.
coupling reaction, the major product was the desired
MOM-protected genistein (9). We also observed the for-
mation of a phenolic dimer and the coupling product of
two molecules of the ring-closed product 8. The subse-
quent deprotection to give genistein (1) could be coupled
with the Suzuki reaction, thereby eliminating a purifica-
tion step. To increase the solubility of genistein during
chromatography, ethanol was added to the eluting solvent.
Initially, triol 5 was protected as its dibenzyl derivative,
albeit in moderate yield (64%). However, this protection
did not permit the subsequent ring closure and halogena-
tion reactions.1 Protection as the methoxymethyl (MOM)
ether by treatment with chloromethyl methyl ether and
N,N-diisopropylethylamine in dichloromethane gave the
desired protected acetophenone 6 (94%) without addition-
al purification. This was subsequently treated with In conclusion, we have demonstrated a novel synthetic
(dimethoxymethyl)dimethylamine18 to form the enamino route for the total synthesis of the isoflavone genistein.
ketone 7 in 99% yield after column chromatography. On This five-step pathway, with an overall yield of 63%, also
stirring in methanol with excess diiodine,1,18 the MOM- permits the preparation of numerous derivatives of
protected enamino ketone 7 underwent tandem cycliza- genistein. The use of PEG introduces an aspect of green
tion and iodination to afford 3-iodo-5,7-bis(meth- chemistry into the synthesis.
oxymethoxy)-4H-1-benzopyran-4-one (8). During this
reaction, two distinct bands were observed by thin-layer
Purchased chemicals were reagent grade. Melting points were ob-
1
chromatography. The blue fluorescent band was isolated
and shown, by means of NMR spectroscopy, to contain
the non-iodinated ring product. The upper band contained
the required iodinated product 8. This provided evidence
that the halogenation reaction succeeded the ring-closure
reaction.
tained on a Gallenkamp apparatus and are uncorrected. H NMR
(400 MHz) and 13C NMR (100 MHz) spectra were recorded on a
Varian instrument in the solvent indicated, and they are referenced
to TMS or residual undeuterated solvent. HRMS were recorded on
a ThermoFinnigan MAT 95XL with ESI II source for electrospray
ionization.
A Suzuki coupling reaction was next used to attach the fi- 1-[2-Hydroxy-4,6-bis(methoxymethoxy)phenyl]ethanone (6)
A flame-dried flask was charged with CH2Cl2 (30 mL) and ketone
5 (1.01 g, 6.07 mmol) under argon. The mixture was cooled to 0 °C,
and DIPEA (3 mL, 17.2 mmol) was slowly added. After 20 min,
nal ring of the isoflavone. A green approach to this proce-
dure has recently been demonstrated that uses
poly(ethylene glycol) (PEG 4000), methanol, sodium car-
MOMCl (1.15 g, 14.3 mmol) was added dropwise. The mixture was
bonate, and palladium diacetate as a source of palladium
maintained at 0 °C for 20 min, then brought to r.t. The reaction was
at a mild temperature of 50 °C.19 We replaced PEG 4000
quenched with H2O (40 mL). The organic layer was removed, and
with PEG 10000 in our reaction, which gave 5,7-
bis(methoxymethoxy)-3-[4-(methoxymethoxy)phenyl]-
4H-1-benzopyran-4-one (9) in 88% yield. The PEG and
palladium diacetate could be reused without further addi-
tion of a palladium source.
the aqueous layer was extracted with CHCl3 (3 × 40 mL). The com-
bined organic layers were dried (MgSO4) and concentrated; yield:
1.46 g (94%); mp 39–42 °C.
1H NMR (CDCl3): d = 13.69 (s, 1 H, COH), 6.27 (s, 1 H, Ar-H),
6.24 (s, 1 H, Ar-H), 5.25 (s, 2 H, OCH2OCH3), 5.16 (s, 2 H,
Synthesis 2010, No. 10, 1590–1592 © Thieme Stuttgart · New York

1592
J. D. St. Denis et al.
SHORT PAPER
OCH2OCH3), 3.51 (s, 3 H, OCH2OCH3), 3.46 (s, 3 H, OCH2OCH3),
2.65 (s, 3 H, COCH3).
13C NMR (CDCl3): d = 203.3, 190.0, 166.9, 163.6, 160.5, 107.0,
97.3, 94.6, 94.1, 56.8, 56.5, 33.1.
13C NMR (CDCl3): d = 175.8, 161.2, 159.2, 158.5, 158.4, 150.9,
130.2, 127.3, 124.2, 114.5, 110.6, 101.2, 96.7, 94.9, 94.1, 56.3,
56.2.
Genistein (1)
A mixture of the benzopyranone 9 (0.650g, 1.81 mmol), CHCl3 (5
mL), MeOH (5 mL), and concd HCl (1 mL) was refluxed for 1 h.
The reaction was quenched with H2O, and the mixture was extract-
ed with CHCl3 (2 × 10 mL). The extracts were washed with H2O (10
mL) and purified by column chromatography [EtOAc–hexanes–4%
EtOH (1:2.5)]; yield: 0.451 g (92%); mp 292–297 °C (Lit.20 291–
296 °C).
1H NMR (DMSO-d6): d = 13.03 (s, 1 H, Ar-OH), 10.90 (s, 1 H, Ar-
OH ), 9.61 (s, 1 H, Ar-OH), 8.33 (s, 1 H, olefinic CH), 7.36 (d,
J = 7.6 Hz, 2 H, Ph-H), 6.80 (d, J = 7.6 Hz, 2 H, Ph-H), 6.38 (s, 1
H, Ar-H), 6.22 (s, 1 H, Ar-H).
13C NMR (DMSO-d6): d = 180.3, 164.4, 162.1, 157.7, 157.5, 154.1,
130.3, 122.4, 121.3, 115.2, 104.5, 99.1, 93.8.
HRMS (ESI); m/z [M + H]+ calcd for C15H11O5: 271.0601; found:
271.0602.
3-(Dimethylamino)-1-[2-hydroxy-4,6-bis(methoxy-
methoxy)phenyl]prop-2-en-1-one (7)
Ketone 2 (1.55 g, 6.05 mmol) was dissolved in DMF (60 mL) and
the soln was warmed to 74 °C in an oil bath. Me2NCH(OMe)2 (3.50
g, 29.4 mmol) was then added dropwise to the flask. The mixture
was stirred for 4.5 h then cooled to r.t. The reaction was quenched
with H2O (100 mL), and the mixture was extracted with EtOAc
(5 × 100 mL). The extracts were washed with H2O (50 mL), dried
(MgSO4), filtered, and concentrated under reduced pressure to give
a thick yellow oil that was purified by column chromatography
(EtOAc) to give cubic yellow crystals; yield: 1.86 g (99%); mp 89–
91 °C.
1H NMR (CDCl3): d = 7.90 (d, J = 12.8 Hz, 1 H, olefinic CH), 6.27
(d, J = 12.8 Hz, 1 H, olefinic CH) 6.25 (s, 1 H, Ar-H), 6.16 (s, 1 H,
Ar-H), 5.20 (s, 2 H, OCH2OCH3), 5.13 (s, 2 H, OCH2OCH3), 3.50
(s, 3 H, OCH2OCH3), 3.45 (s, 3 H, OCH2OCH3), 3.14 (s, 3 H,
NCH3), 2.91 (s, 3 H, NCH3).
13C NMR (CDCl3): d = 191.5, 190.0, 166.9, 161.3, 158.9, 154.6,
Acknowledgment
107.0, 97.9, 96.9, 95.2, 94.5, 94.1, 56.8, 56.4, 29.8.
The authors thank the Niagara University Academic Center for
Integrated Science for financial support.
HRMS (ESI); m/z [M + H]+ calcd for C15H22O6N: 312.1442; found:
312.1430.
References
3-Iodo-5,7-bis(methoxymethoxy)-4H-1-benzopyran-4-one (8)
A soln of amino ketone 3 (1.23 g, 3.95 mmol) and I2 (1.44 g, 5.67
mmol) in MeOH (100 mL) was stirred at r.t. for 10.5 h, then con-
centrated in vacuo to give a red-black residue. To remove residual
I2, the residue was treated with sat. aq NaSO3 until the mixture be-
came clear. The mixture was then extracted with CHCl3 (3 × 40
mL), and the extracts were dried (MgSO4) and concentrated under
reduced pressure. The resulting off-white solid was purified by
chromatography [silica gel, EtOAc–hexanes (1:1)] to give a white
solid; yield: 1.28 g (83%); mp 137–140 °C.
1H NMR (CDCl3): d = 8.09 (s, 1 H, olefinic CH), 6.75 (s, 1 H, Ar-
H), 6.72 (s, 1 H, Ar-H), 5.30 (s, 2 H, OCH2OCH3), 5.22 (s, 2 H,
OCH2OCH3), 3.54 (s, 3 H, OCH2OCH3), 3.49 (s, 3 H, OCH2OCH3).
13C NMR (CDCl3): d = 171.3, 161.6, 159.3, 158.2, 155.7, 108.8,
102.1, 96.8, 95.5, 94.4, 89.5, 56.8, 56.6.
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PEG 10000 (21.0 g), ground to a fine consistency in a mortar, and
Pd(OAc)2 (0.025 g, 0.11 mmol) were added to a stirred mixture of
MeOH (25 mL) and Na2CO3 (0.548 g, 5.17 mmol). The reaction
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compound 8 (0.852 g, 2.17 mmol) and (4-hydroxyphenyl)boronic
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washed with Et2O (100 mL). The ethereal extract was concentrated
in vacuo to give a white solid that was used in the next reaction
without further purification; yield: 0.685 g (88%); mp 109–110 °C.
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1H NMR (CDCl3): d = 7.79 (s, 1 H, olefinic CH), 7.34 (d, J = 7.2
Hz, 2 H, Ph-H), 7.01 (d, J = 7.2 Hz, 2 H, Ph-H), 6.36 (s, 1 H, Ar-H),
6.29 (s, 1 H, Ar-H), 5.32 (s, 2 H, OCH2OCH3), 5.24 (s, 2 H,
OCH2OCH3), 3.54 (s, 3 H, OCH2OCH3), 3.51 (s, 3 H, OCH2OCH3).
Synthesis 2010, No. 10, 1590–1592 © Thieme Stuttgart · New York