Synthesis and identification of quercetin benzyl ethers

Article abstract of DOI:10.1134/S1070363214090126

We have studied the effects of the benzylating agent character, the reactants ratio, and the solvent nature on the composition of the products of quercetin benzylation. The structure of the products has been confirmed by IR, UV, ¹H NMR, ¹³

Full text of DOI:10.1134/S1070363214090126

ISSN 1070-3632, Russian Journal of General Chemistry, 2014, Vol. 84, No. 9, pp. 1711–1715. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © E.R. Karimova, L.V. Spirikhin, L.A. Baltina, M.I. Abdullin, 2014, published in Zhurnal Obshchei Khimii, 2014, Vol. 84, No. 9,
pp. 1471–1475.
Synthesis and Identification of Quercetin Benzyl Ethers
E. R. Karimovaa,b, L. V. Spirikhina, L. A. Baltinaa, and M. I. Abdullinb
a Institute of Organic Chemistry, Ufa Scientific Center, Russian Academy of Sciences,
pr. Oktyabrya 71, Ufa, 450054 Russia
e-mail: baltina@anrb.ru
b Bashkir State University, Ufa, Russia
Received March 27, 2014
Abstract—We have studied the effects of the benzylating agent character, the reactants ratio, and the solvent
nature on the composition of the products of quercetin benzylation. The structure of the products has been
confirmed by IR, UV, 1H NMR, 13C NMR, and mass spectra.
Keywords: quercetin, benzyl ether, synthesis, NMR spectroscopy
DOI: 10.1134/S1070363214090126
Flavonoids form one of most numerous groups of
naturally occurring polyphenols playing an important
part in vital functions of higher plants. These com-
pounds are among plant pigments, they protect the
plant tissues from harmful UV radiation, participate in
photosynthesis as well as in oxidation phosphorylation,
and control the auxins (plant growth hormones)
transport; plant flavonoids are known for different
kinds of biological and pharmacological activities and
the low toxicity [1, 2].
medical applications. It has been shown that O-
alkylation of the phenol hydroxyls of quercetin with
excess of alkyl halides in DMSO in the presence of
alkali yields the penta-O-substituted alkyl ethers,
whereas the treatment with 3–5 equivalents of the alkyl
halides gives the products of incomplete O-alkylation
[14]. However, the studies involved exclusively UV
spectroscopy characterization of the products.
In this work we filled in the gap by preparation and
identification of benzyl ethers of quercetin. These
partially benzylated quercetin derivatives are suitable
substrates for further chemical modifications, because
the benzyl groups can be easily cleaved via the catalytic
hydrogenolysis under mild conditions.
Quercetin was benzylated with benzyl bromide in
the presence of powder KОН, using different ratios of
the benzylating agent to the substrate. The products
were isolated via column chromatography.
Benzylation of quercetin with excess of benzyl
bromide in DMSO in the presence of KОН at 20–22°С
during 4 h at the substrate to С6Н5СН2Br ratio 1 : 10
yielded a mixture of quercetin penta-O-benzyl ether II
and quercetin tetra-O-benzyl ether III. Ether II was
isolated in 77.3% yield via recrystallization from the
chloroform–ethanol mixture (Scheme 1).
Several bioflavonoid drugs showing P-vitamin
activity are industrially produced in Russia. The major
flavonoid products are rutin and quercetin I, both used
for treatment and prevention of different diseases
resulting from brittleness and permeability failure of
capillaries; these drugs are also used as antioxidants,
hepato- and radioprotectors, antiinflammatory and
antiulcer agents [3–5]. Flavonoids are also known for
antitumor, antimicrobial, antiviral, and antithrombotic
action [1, 6–10]. Quercetin and other flavonoids are
potential inhibitors of nucleotide phosphodiesterases
found in the cellular cytosol [11]. Recent studies have
revealed quercetin activity towards HIV-1 reverse
transcriptase and integrase along with inhibiting action
on herpesvirus [12, 13].
The presence of several hydroxy groups, two
aromatic rings, and a pyrone cycle in the quercetin
molecule allows for its chemical modification to give a
series of biologically active derivatives promising for
Absorption bands due to vibrations of free phenol
OH groups were not observed in IR spectrum of ether
II, whereas strong bands assigned to stretching vibra-
tions of C–C bonds in the aromatic rings were found at
1711

1712
KARIMOVA et al.
Scheme 1.
OH
OR4
2'
6'
3'
1
4'
8
1'
HO
O
OH
R3O
O
OR5
7
2
C6H5CH2Br
KOH
5'
3
6
OH
OR1
4
5
OH
O
OR2
O
I
II_VI
II, R1 = R2 = R3 = R4 = R5 = C6H5CH2; III, R1 = R3 = R4 = R5 = C6H5CH2, R2 = H; IV, R1 = R3 = R5 = C6H5CH2, R2 = R4 = H;
V, R1 = R4 = = R5 = C6H5CH2, R2 = R3 = H; VI, R1 = R3 = R5 = C6H5CH2, R2 = R4 = Ac; VII, R1 = R4 = R5 = C6H5CH2,
R2 = R3 = Ac.
1630–1500 cm–1, along with the С–О–С ether bonds
stretching vibrations bands at 1270–1100 cm–1. UV
spectrum of ether II in ethanol contained strong
separated via the column chromatography. The major
reaction product was the tetra-O-benzyl ether of
quercetin III (Rf = 0.82, yield 17.5%).
1
absorption maxima at 253 and 347 nm. Н NMR
The less mobile fraction (Rf = 0.75) was identified
as 3,4',7-tri-О-benzyl quercetin ether IV (yield 7.6%).
IR spectrum of compound IV contained the phenol OH
stretching vibrations band (maximum at 3255 cm–1).
1Н NMR spectrum of compound IV contained the
signals of protons of the three СН2 benzyl groups
(5.03, 5.05, and 5.17 ppm), along with the signals of
aromatic protons at 6.5–7.6 ppm. The 13С NMR
spectrum contained the signals of carbon atoms of the
three benzyl СН2 groups at 70.2, 70.9, and 74.0 ppm.
Chemical shifts of the С5 and С3' atoms in the spectra
of ether IV were close to those in the parent quercetin
[16].
spectrum of compound II contained the signals of five
СН2 groups of the benzyl fragments (at 4.98, 5.10,
5.14, 5.25, and 5.28 ppm) and those of the aromatic
protons (6.98–7.70 ppm). 13С NMR spectrum of the
compound contained downfield signals of aromatic
carbon atoms (126.6–128.8 and 135.7–137.0 ppm) and
the signals of benzyl СН2 groups (70.4–74.1 ppm),
absent in the quercetin spectrum. The mass spectrum
recorded in the chemical ionization mode contained
the molecular ion signals, [M + H]+ (m/z = 753) and
[M – H]– (m/z = 751), corresponding with the С50Н40О7
formula.
The chromatographic separation of the mother
liquor on silica gel allowed isolation of 22.7% of
quercetin 3,3',4',7-tetra-О-benzyl ether III, its spatially
In order to confirm the benzyl groups location, we
recorded UV spectra of ethanol solutions of pure
compound IV and of compound IV in the presence of
0.01% of sodium acetate. The UV spectrum remained
almost unchanged in the presence of the weak base
pointing at the benzylation of the С4'ОН group in
compound IV [15]. Indeed, the unmodified С4'ОН
group is more acidic than the С3'ОН group, and the
long-wavelength absorbance band should have been
changed in the presence of the weak base if the С4'ОН
group was not benzylated [15]. Thus the isolated
compound has the structure of 3,4',7-tri-O-benzyl ether
IV. Acylation of the ether IV with acetic anhydride in
the presence of anhydrous sodium acetate at reflux (see
the procedure in [18]) yielded the di-О-acetate VI in
78% yield. 1Н NMR spectrum of the diacetate
contained the signals of the two СОСН3 groups at 2.29
and 2.52 ppm.
1
hindered С5ОН group retained. Н NMR spectrum
(500 MHz) of compound III contained the proton
signals of four benzyl СН2 groups (4.99, 5.05, 5.13,
and 5.25 ppm). Signals of carbon atoms of those four
CH2 groups were observed in the 13С NMR spectrum
as well (70.4, 70.9, 71.2, and 74.3 ppm), along with the
downfield signals of the aromatic carbon atoms
(127.2–128.8 and 135.9–137.0 ppm). UV spectrum of
compounds III in ethanol did not change upon
addition of 0.01% of NaOEt and NaOAc evidencing
the modification of the С3'ОН and С4'ОН groups [15].
The molecular ion peak observed in the mass spectrum
of compound III, [M + H]+ (m/z = 663), corresponded
to the С43Н34О7 formula.
Benzylation of quercetin with benzyl chloride (1 : 10)
in a mixture of DMSO and DMF yielded a mixture of
benzyl ethers of the substrate that was further
The more polar fraction found in the reaction
mixture (Rf = 0.65) was identified as quercetin 3,3',4'-
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SYNTHESIS AND IDENTIFICATION OF QUERCETIN BENZYL ETHERS
tri-О-benzyl ether V (yield 6.9%). Indeed, UV spectra
of compound V in ethanol and that in the presence of a
weak base (C2H5OH + 0.01% of NaOAc) were
practically identical, confirming the absence of the
unmodified С4'ОН group. The UV spectrum was not
changed in the 0.01 wt % ethanol solution of AlCl3
either; hence, the С3ОН group was modified as well
[18]. In the case of compound V solution in a strong
base (C2H5OH + 0.01% of NaOC2H5), a slight red shift
of the first absorption band (by 21 nm) was observed;
hence, the С7ОН group was not benzylated [15, 18].
Thus this compound is 3.3',4'-tri-O-benzyl ether of
quercetin V. Acylation of ether V gave the di-О-
yielded the following major products: the 3,3',4',7-
tetra- and 3,4',7-tri-О-benzyl ethers (DMSO as
solvent) or the 3,4',7-tri-О-benzyl ether (DMF as
solvent).
EXPERIMENTAL
1Н and 13С NMR spectra of the solutions in CDCl3
were recorded using the Bruker Avance-III (500.13 MHz,
1Н) and Bruker AMX-300 (300 MHz, 1Н and 75.5 MHz,
13С) spectrometers using tetramethylsilane as internal
reference.
IR spectra of the suspensions in mineral oil were
recorded using the IR Prestige-21 spectrometer
(Shimadzu). UV spectra were registered using the UF-
400 spectrophotometer (Carl Zeiss) (ethanol solution
of the pure compounds, and the ethanol solutions in the
presence of 0.01 wt % of 0.01% NaOAc, NaOC2H5, or
AlCl3).
1
acetate VII in 76% yield. Н NMR spectrum of the
product (500 MHz) contained two singlet signals of the
acetyl fragments at 2.35 and 2.50 ppm; the 13С NMR
signals of the С5 and С7 atoms of the product were
shifted upfield by 9–10 ppm.
Similarly to the above, the benzylation of quercetin
in DMSO at the ratio of the substrate to С6Н5СН2Вr of
1 : 5 at 20–22°С during 4 h gave a mixture of benzyl
ethers with relatively low yields. Chromatographic
separation of the mixture allowed isolation of the two
major products: quercetin tetra-О-benzyl ether III
(Rf = 0.82 and yield 18.2%) and the tri-О-benzyl ether
IV (Rf = 0.75 and yield 20.9%).
Mass spectral analysis was performed by LC-MS
technique using the Shimadzu LCMS-2010 chromato-
mass spectrometer (chemical ionization of the solu-
tions in methanol or acetonitrile at atmospheric pressure).
Melting points were measured using the Boëtius
heating block.
Silica gel KSK (the 50–150 fraction, Sorbpolimer)
was used for column chromatography separation.
Thin-layer chromatography was performed using the
Sorbfil plates (Sorbpolimer), 50 : 1 benzene–ethanol
(A) and 20:1 benzene–ethanol (B) mixtures were used
as eluents. The plates were developed with 5 wt %
aqueous Н2SO4 followed by heating at 110–120°С
during 2–3 min.
At the similar ratio of the substrate to the
benzylating agent, the benzylation of quercetin with
benzyl chloride in DMF gave a mixture of benzyl
ethers, the major product isolated by chromatography
being the tri-O-benzyl ether IV (yield 17.5%).
To conclude, the benzylation of quercetin in DMSO
or DMF in the presence of KOH at 20–22°С led to the
formation of either fully or partially benzylated ethers,
depending on the substrate to the benzylating agent
ratio. The highest yield of the benzyl ethers was
observed when using benzyl bromide as the benzylat-
ing agent and DMSO as the solvent.
The solvents were purified by common procedures
[17]. Compendial quercetin (Ufavita) was used.
Quercetin benzylation with excess (1 : 10) of
benzyl bromide in DMSO. 0.56 g (10 mmol) of KOH
powder was added to 0.3 g (1 mmol) of quercetin in
10 mL of DMSO, and the mixture was stirred during
20 min. Then 1.2 mL (10 mmol) of С6Н5СН2Br was
added, and the mixture was stirred during 4 h at 20–
22°С. The obtained solution was poured into water
acidified with HCl to pH 2–3; the formed viscous red
syrup was washed with water via decantation till
neutral pH and dried (1.04 g). The recrystallization
from the chloroform–ethanol mixture yielded 0.58 g
(77.3%) of quercetin penta-О-benzyl ether II. The
mother liquor was separated by chromatography (silica
gel, elution with the 300 : 1 v/v benzene–methanol
With benzyl bromide taken in excess (1 : 10) and
DMSO used as the solvent, a mixture of penta- and
tetra-O-substituted quercetin benzyl ethers (II and III)
was formed with total yield of 98.5%. At the same
reagents ratio, benzylation of quercetin with benzyl
chloride in the DMSO–DMF mixture yielded a
mixture of the 3,3',4',7-tetra-, 3,4',7-tri-, and 3,3',4'-tri-
О-benzyl ethers.
Finally, benzylation of quercetin with benzyl bromide
taken in the 1 : 5 ratio with respect to the substrate
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KARIMOVA et al.
mixture) to give 0.14 g (21.2%) of quercetin tetra-О-
benzyl ether III.
(5.22). Mass spectrum: m/z 663 [M + H]+. Found, %: С
77.68; Н 5.21. C43H34O7. Calculated, %: С 77.93; Н
5.17. М 662.7.
Quercetin benzylation with excess (1 : 10) of
benzyl chloride in DMSO–DMF mixture. 0.56 g
(10 mmol) of KOH powder was added to 1.5 g
(5 mmol) of quercetin in a mixture of 15 mL of DMSO
and 35 mL of DMF, and the mixture was stirred during
30 min. Then, 6 mL (50 mmol) of С6Н5СН2Cl was
added, and the mixture was stirred during 4 h at 20–
22°С; the reaction course was monitored with TLC.
After the reaction was completed, the obtained solution
was poured into water acidified with HCl to pH 2–3;
the formed precipitate was filtered off and dried. The
residue was separated via the column chromatography
(silica gel; elution with 1 : 0, 300 : 1, 200 : 1, and 100 : 1
v/v benzene–methanol). The isolated products were
tetra-О-benzyl ether III (0.58 g, 17.5%), tri-О-benzyl
ether IV (0.22 g, 7.6%), and tri-О-benzyl ether V
(0.20 g, 6.9%).
Quercetin 3,4',7-tri-О-benzyl ether (IV). mp
153–155°С (CHCl3−C2H5OH), Rf 0.75–0.77 (A). IR
spectrum, ν, cm–1: 3256, 1650, 1600, 1508, 1278,
1
1252, 1194. Н NMR spectrum (300 MHz), δ, ppm:
5.03 s, 5.06 s, 5.17 s (6Н, СН2); 6.43 s (1Н, Н8), 6.48 s
(1Н, Н6), 6.92 d (1Н, Н5', J 9 Hz), 7.24–7.60 m (16Н,
С6Н5, Н6'), 7.63 s (1Н, Н2'). 13С NMR spectrum (75.5
MHz), δС, ppm: 178.6 (С4), 164.3 (С7), 161.7 (С5),
156.5 (С9), 156.3 (С2), 147.8 (С4'), 145.5 (С3'), 137.5
(С3); 136.8–135.6, 128.6–127.0 (С6Н5); 123.3 (С1'),
121.7 (С6'), 114.8 (С5'), 111.5 (С2'), 106.0 (С10), 98.5
(С6), 92.8 (С8); 74.0, 70.9, 70.2 (СН2). UV spectrum
(C2H5OH), λmax, nm (log ε): ethanol, 258 (5.6), 356
(5.3); C2H5OH + 0.01% NaOAc, 258 (5.2), 356 (5.0).
Mass spectrum: m/z 573 [M + H]+. Found, %: С 75.41;
Н 4.89. С36Н28О7. Calculated, %: С 75.51; Н 4.93. М
572.6
Quercetin 3,3',4',5,7-penta-О-benzyl ether (II).
mp 115–118°C (CHCl3−C2H5OH), Rf 0.90 (A). IR
spectrum, ν, cm–1: 1654, 1605, 1591, 1512, 1273,
Quercetin 3,3',4'-tri-О-benzyl ether (V). Rf 0.65
(B). IR spectrum, ν, cm–1: 3255 (ОН), 1655, 1600,
1
1
1505, 1273, 1247, 1197. Н NMR spectrum (300
1180, 1171, 1126. Н NMR spectrum (300 MHz), δ,
MHz), δ, ppm: 4.71 s, 4.78 s, 4.98 s (6Н, СН2); 6.05 s
(1Н, Н8), 6.12 s (1Н, Н6), 6.75 d (1Н, Н5', J 7 Hz),
6.95–7.45 m (16 Н, С6Н5, Н6'), 7.48 s (1Н, Н2'). 13С
NMR spectrum (75.5 MHz), δC, ppm: 178.3 (С4),
164.2 (С7), 161.7 (С5), 156.6 (С9), 155.5 (С2), 150.8
(С4'), 147.9 (С3'), 136.9 (С3); 136.6–136.3, 128.4–
127.1 (С6Н5); 123.2 (С1'), 122.4 (С6'), 114.9 (С5'),
113.5 (С2'), 104.7 (С10), 98.9 (С6), 93.8 (С8); 73.9,
70.8, 70.5 (СН2). UV spectrum, λmax, nm (log ε):
ethanol, 258 (5.5), 352 (5.3); С2Н5OH + 0.01%
NaOCOCH3, 252 (5.5), 351 (5.3); C2H5OH + 0.01%
AlCl3, 258 (5.5); 351 (5.4); C2H5OH + 0.01%
C2H5ONa, 279 (5.5). Mass spectrum: m/z 573 [M + H]+.
Found, %: С 75.42; Н 4.89. С36Н28О7. Calculated, %:
С 75.51; Н 4.93. М 572.6.
ppm: 4.98 s, 5.10 s, 5.14 s, 5.25 s, 5.28 s (10Н, СН2);
6.47 s (1Н, Н8), 6.54 s (1Н, Н6), 6.98 d (1H, H5', J 9
Hz), 7.27 s (1H, H6'), 7.30–7.70 m (25Н, С6Н5), 7.78 s
(1Н, Н2'). 13С NMR spectrum (75.5 MHz), δС, ppm:
173.5 (C4), 162.7 (C7), 159.8 (C5), 158.6 (C9), 153.0
(C2), 150.5 (C4'), 148.3 (C3'), 139.8 (C3); 137.0–135.7,
128.8–126.6 (C6Н5); 124.0 (C1'), 122.5 (C6'), 115.3
(C5'), 113.8 (C2'), 110.1 (C10), 98.1 (C6), 93.9 (C8);
74.1, 72.1, 71.1, 70.9, 70.4 (СН2). UV spectrum
(C2H5OH), λmax, nm (log ε): 253 (5.56), 347 (5.35).
Mass spectrum: m/z 753 [M + H]+, 751 [M – H]–.
Found, %: С 79.62; Н 6.74. С50Н40О7. Calculated, %:
С 79.77; Н 6.71. М 752.9.
Quercetin 3,3',4',7-tetra-О-benzyl ether (III). mp
126–128°С (CHCl3−C2H5OH), Rf 0.82 (A). IR
spectrum, ν, cm–1: 3292 (ОН), 1670, 1589, 1277, 1253,
3',5-Di-О-acetyl-3,4',7-tri-О-benzylquercetin (VI)
[18]. 0.15 g of anhydrous sodium acetate was added to
a solution of 0.15 g of compound IV in 10 mL of
acetic anhydride. The mixture was refluxed during 2 h
avoiding contact with air moisture. Then the mixture
was diluted with cold water; the precipitate was
filtered off, washed with water, dried, and recrystal-
lized from the CHCl3−CH3OH mixture. Yield 78%,
mp 158–160°C {mp 161–163°C (benzene–hexane)
[15]}. IR spectrum, ν, cm–1: 1772, 1720, 1665, 1605,
1
1196, 1169. Н NMR spectrum (500 MHz), δ, ppm:
4.99 s, 5.05 s, 5.13 s, 5.25 s (8Н, СН2); 6.44 d (1Н, Н8,
J 12 Hz), 6.98 d (1Н, Н6, J 8 Hz), 7.24–7.57 m (22Н,
С6Н5, Н6', Н5'), 7.73 s (1Н, Н2'). 13С NMR spectrum
(75.5 MHz), δC, ppm: 178.8 (С4), 164.5 (С7), 162.1
(С5), 156.7 (С9), 156.6 (С2), 148.4 (С4'), 148.3 (С3');
137.5 (С3), 137.0–135.9, 128.8–127.2 (С6Н5); 123.6
(С1'), 122.7 (С6'), 115.5 (С5'), 113.9 (С2'), 106.2 (С10),
98.5 (С6), 93.0 (С8); 74.3, 71.2, 70.9, 70.4 (СН2). UV
spectrum (C2H5OH), λmax, nm (log ε): 260 (5.47), 353
1
1273, 1196, 1163. Н NMR spectrum (300 MHz), δ,
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SYNTHESIS AND IDENTIFICATION OF QUERCETIN BENZYL ETHERS
ACKNOWLEDGMENTS
ppm: 2.29 s, 2.52 s (6Н, СН3СО); 5.06 s, 5.14 s, 5.16 s
(6Н, СН2); 6.69 s (1H, H8), 6.88 s (1H, Н6), 6.98 d
(1Н, H5', J 8.3 Hz), 7.27–7.50 m (17Н, С6Н5, Н6', Н2').
13С NMR spectrum (75.5 MHz), δC, ppm: 173.2 (С4);
169.7, 168.8 (С=О); 162.4 (С7), 157.7 (С9), 153.8 (С2),
152.0 (С5), 150.6 (С4'), 139.8 (С3'), 139.5 (С3); 136.4–
135.4, 129.1–127.1 (С6Н5); 123.3 (С1'), 122.3 (С6'),
113.2 (С5'), 112.0 (С2'), 108.8 (С10), 99.5 (С6); 74.2,
70.7, 70.5 (СН2); 29.7, 20.6 (СН3).
This work was financially supported by President
of Russian Federation (grant no. NSh-7014.2012.3).
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5,7-Di-О-acetyl-3,3',4'-tri-О-benzylquercetin (VII)
was prepared similarly. Yield 76%, mp 196–198°C
(CHCl3−CH3OH), Rf 0.86 (B). IR spectrum, ν, cm–1:
1769, 1636, 1609, 1595, 1566, 1514, 1278, 1221,
1
1198, 1144. Н NMR spectrum (500 MHz), δ, ppm:
2.35 s, 2.50 s (6Н, СН3СО); 4.97 s, 5.00 s, 5.24 s (6Н,
СН2); 6.82 s (1Н, Н8), 6.93 d (1Н, Н5', J 8 Hz), 7.20–
7.50 m (16Н, С6Н5, Н6'), 7.65 s (1Н, Н2'). 13С NMR
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167.9 (C=О); 156.5 (С9), 155.1 (С7), 153.5 (С2), 151.0
(С5), 150.2 (С4'), 148.2 (С3'), 139.6 (С3); 136.9–136.5,
128.8–127.2 (С6Н5); 123.3 (С1'), 122.5 (С6'), 115.4
(С5'), 115.1 (С6), 113.8 (С2'), 113.0 (С8), 108.7 (С10);
74.0, 71.1, 70.9 (СН2); 21.1, 21.0 (СН3). Found, %: С
73.06; Н 4.82. С40Н32О9. Calculated, %: С 73.16; Н
4.91. M 656.7.
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Quercetin benzylation with 1 : 5 of benzyl
bromide. 0.28 g (5 mmol) of KOH powder was added
to a solution of 0.3 g (1 mmol) of quercetin in 10 mL
of DMSO. After 20 min, 0.6 mL (5 mmol) of
С6Н5СН2Br was added, and the mixture was stirred
during 4 h at 20–22°С, the reaction course being
monitored with TLC. After the reaction was complete,
the so obtained solution was poured into HCl-acidified
water (рН 2–3). The precipitate was filtered off,
washed with water, and dried (0.47 g). After chromato-
graphic separation, 0.12 g (18.2%) of compound III
(Rf = 0.82) and 0.12 g (20.9%) of compound IV (Rf =
0.75) were isolated.
Quercetin benzylation with 1 : 5 of benzyl
chloride. 0.28 g (5 mmol) of KOH powder was added
to a solution of 0.3 g (1 mmol) of quercetin in 10 mL
of DMF. After 20 min, 0.6 mL (5 mmol) of
С6Н5СН2Cl was added, and the mixture was stirred
during 4 h at 20–22°С, the reaction course being
monitored with TLC. After the reaction was complete,
the so obtained solution was poured into HCl-acidified
water (рН 2–3). The precipitate was filtered off,
washed with water, and dried (0.38 g). After chromato-
graphic separation, 0.10 g (17.5%) of compound IV
was isolated.
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