Synthesis of some 4'-O substituted derivatives of natural naringin and their biological screening

Article abstract of DOI:10.14233/ajchem.2013.13242

This manuscript reports the synthesis of a series of new 4'-O-substituted derivatives of naringin (1) which is a naturally occurring flavanone glycoside isolated from the plant Rhynchosia pseudo-cajan Cambess. belonging to family of Papilionaceae. The structure of 1 was established through ¹D and ²D NMR analysis and by comparison with its published data while its synthetic derivatives 3a-l, were characterized by ¹H NMR spectra and all these were screened against four enzymes namely, acetylcholinesterase, butyrylcholinesterase lipoxygenase and chymotrypsin. Their antioxidant potential was also evaluated by 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity and only 4'-O-ethyl naringin (3a) showed antioxidant potential (IC50 36.21 ± 0.32 μM). 4'-O-Ethyl naringin (3a), 4'-O-(2''''- phenylethyl) naringin (3f), 4'-O-(3''''-phenylpropyl) naringin (3g) and 4'-O-(p-fluorobenzyl) naringin (3i) were found to be moderate inhibitors of butyrylcholinesterase while naringin (1) itself, 4'-O-n-butyl naringin (3b), 4'-O-iso-propyl naringin (3d) and 4'-O-(N-3''''', 5'''''-dimethylphenyl-C-acetamido) naringin (3l) were identified as moderate inhibitors of lipoxygenase. Against chymotrypsin only 4'-O- (p-bromobenzyl) naringin (3h) was found to be a moderate inhibitor.

Full text of DOI:10.14233/ajchem.2013.13242

Asian Journal of Chemistry; Vol. 25, No. 4 (2013), 1927-1933
http://dx.doi.org/10.14233/ajchem.2013.13242
Synthesis of Some 4'-O Substituted Derivatives of Natural Naringin and Their Biological Screening
1
1,*
1
1
TAUHEEDA RIAZ , MUHAMMAD ATHAR ABBASI , AZIZ-UR-REHMAN , TAYYABA SHAHZADI ,
2
3
4
KHALID MOHAMMED KHAN , MUHAMMAD ASHRAF and SYEDA ABIDA EJAZ
1Department of Chemistry, Government College University, Lahore-54000, Pakistan
2HEJ Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi-75270,
Pakistan
3Department of Biochemistry and Biotechnology, The Islamia University of Bahawalpur, Bahawalpur-63100, Pakistan
4Department of Pharmacy, Faculty of Pharmacy and Alternative Medicine, The Islamia University of Bahawalpur, Bahawalpur-63100, Pakistan
*Corresponding author: Tel: +92 42 111000010 Ext.266; E-mail: atrabbasi@yahoo.com
(Received: 13 December 2011;
Accepted: 8 October 2012)
AJC-12252
This manuscript reports the synthesis of a series of new 4'-O-substituted derivatives of naringin (1) which is a naturally occurring
flavanone glycoside isolated from the plant Rhynchosia pseudo-cajan Cambess. belonging to family of Papilionaceae. The structure of 1
was established through 1D and 2D NMR analysis and by comparison with its published data while its synthetic derivatives 3a-l, were
characterized by 1H NMR spectra and all these were screened against four enzymes namely, acetylcholinesterase, butyrylcholinesterase
lipoxygenase and chymotrypsin. Their antioxidant potential was also evaluated by 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging
activity and only 4'-O-ethyl naringin (3a) showed antioxidant potential (IC50 36.21 0.32 µM). 4'-O-Ethyl naringin (3a), 4'-O-(2''''-
phenylethyl) naringin (3f), 4'-O-(3''''-phenylpropyl) naringin (3g) and 4'-O-(p-fluorobenzyl) naringin (3i) were found to be moderate
inhibitors of butyrylcholinesterase while naringin (1) itself, 4'-O-n-butyl naringin (3b), 4'-O-iso-propyl naringin (3d) and 4'-O-(N-3''''',
5'''''-dimethylphenyl-C-acetamido) naringin (3l) were identified as moderate inhibitors of lipoxygenase. Against chymotrypsin only 4'-O-
(p-bromobenzyl) naringin (3h) was found to be a moderate inhibitor.
Key Words: Naringin, Flavanone glycoside, Rhynchosia pseudo-cajan Cambess., Acetylcholinesterase, Butyrylcholinesterase,
Lipoxygenase.
reported from various Rhynchosia species6. Similarly many
INTRODUCTION
glycosides have also been isolated from Rhynchosia rothii7.
Plants have been a source of medicine for thousands of
years and phytochemicals continue to play an essential role in
Rhynchosia pseudo-cajan Cambess. (papilionaceae) is a
common weed which is medicinally important. It is an erect
medicine8. The therapeutic use of development of human
shrub having whitish leaflets on lower side. Its common name
is Lahrr. It is distributed in Jammu & Kashmir and Pakistan. Its
knowledge, scientists endeavored to isolate different chemical
leaves are used as tonic and stomach disorders, leaves and bark
constituents from plant, put them to biological and pharma-
cological tests and thus have been used to prepare modern
powder is useful for peptic ulcer and other digestive problems1.
medicines9.As described above, the plant Rhynchosia pseudo-
The crude drugs of Rhynchosia are used in the formation of
fermented liquor having antioxidative, antitumor, skin whitening
and arthritis preventing and treating effects2. Since now no
phytochemical studies have been carried out on this species but
cajan is an important medicinal plant, so in this work, we
report isolation of naringin (1) from this plant and subsequent
synthesis of its various 4'-O-substituted derivatives and then
many important compounds have been discovered from other
their screening against four enzymes namely, acetylcholines-
species of genus Rhynchosia. Tirumalin, a prenylated
dihydroflavanol was isolated from Rhynchosia cyanosperma3.
terase, butyrylcholinesterase, lipoxygenase and chymotrypsin.
Their antioxidant potential was also assessed by 1,1-diphenyl-
Rhynchosin, a new 5-deoxyflavonol was isolated from leaves
2-picrylhydrazyl (DPPH) radical scavenging activity.
of Rhynchosia beddomei4. The leaves of Rhynchosia rufescenes
contain methylated flavonols such as kaempferol, kaempferol
EXPERIMENTAL
3-methyl ether and quercetin 3-methyl ether, which are of
chemotaxonomic importance5. Many flavonoides have been
All chemicals used in the experiments were of analytical
grade and were used without further purification otherwise

1928 Riaz et al.
Asian J. Chem.
specified. The solvents used were purified with distillation
before use. For column chromatography (CC), silica gel (70-
230 mesh) was used. TLC was performed on pre-coated silica
gel G-25-UV254 plates. Detection was carried out at 254 nm
and by ceric sulphate reagent. Purity was checked on TLC
with different solvent systems using methanol, acetone and
CHCl3 giving single spot. 1H NMR and 13C NMR Spectra were
recorded in CD3OD run on Bruker spectrometers operating at
400 MHz. The chemical shifts are given in δ in ppm and
coupling constants in Hz.
1H, H-8), 6.14 (d, J = 2.1 Hz, 1H, H-6), 5.33 (dd, J = 2.7, 12.9
Hz, 1H, H-2), 5.24 (d, J = 1.2 Hz, 1H, H-1'''), 5.06 (d, J = 7.2
Hz, 1H, H-1''), 4.29 (m, 1H, Ha-6''), 4.18 (m, 1H, Hb-6''), 3.92
(m, 1H, H-5'''), 3.80 (m, 1H, H-5''), 3.43 (m,1H, H-3''), 3.34
(m,1H, H-3'''), 3.32 (m,1H, H-2'''), 3.30 (m,1H, H-2''), 3.27
(m,1H, H-4'''), 3.16 (dd, J = 17.1, 12.9 Hz, 1H, Ha-3), 3.13
(m, 1H, H-4''), 2.72 (dd, J = 17.1, 2.7 Hz, 1H, Hb-3), 1.27 (d,
J = 6.3, 3H, CH3-6'''). 13C NMR (100 MHz, CD3OD): δ 198.51
(C-4), 166.58 (C-7), 164.98 (C-5), 164.61 (C-9), 159.07
(C-4'), 130.84 (C-1'), 129.10 (C-2' and C-6'), 116.35 (C-3' and
C-5'), 104.90 (C-10), 102.56 (C-1''), 99.41 (C-1'''), 97.85
(C-6), 96.77 (C-8), 80.70 (C-2), 79.04 (C-2''), 78.95 (C-5''),
78.11 (C-3''), 73.92 (C-4'''), 72.17 (C-2''' and C-3'''), 71.24 (C-
4''), 69.98 (C-5'''), 62.27 (C-6''), 44.14 (C-3), 18.21 (C-6''').
4'-O-Ethyl naringin (3a): Gummy solid, yield 82 %. 1H
NMR (400 MHz, CD3OD): δ 7.33 (d, J = 8.8 Hz, 2H, H-2' &
H-6'), 6.87 (d, J = 8.5 Hz, 2H, H-3' & H-5'), 6.17 (d, J = 2.3
Hz, 1H, H-8), 6.15 (d, J = 2.3 Hz, 1H, H-6), 5.41 (dd, J = 2.5,
12.8 Hz, 1H, H-2), 5.32 (d, J = 1.3 Hz, 1H, H-1'''), 5.11 (d, J =
7.4 Hz, 1H, H-1''), 4.21 (m, 1H, H-6''a), 4.15 (m, 1H, H-6''b),
3.95 (m, 1H, H-5'''), 3.85 (q, J = 7.1 Hz, 2H, CH2-1''''), 3.81
(m, 1H, H-5''), 3.46 (m,1H, H-3''), 3.36 (m,1H, H-3'''), 3.33
(m,1H, H-2'''), 3.31 (m,1H, H-2''), 3.28 (m,1H, H-4'''), 3.15
(dd, J = 17.2, 12.8 Hz, 1H, H-3a), 3.14 (m, 1H, H-4''), 2.73
(dd, J = 17.2, 2.5 Hz, 1H, H-3b), 1.38 (t, J = 7.1 Hz, 2H, CH3-
2''''), 1.28 (d, J = 6.3, 3H, CH3-6''').
The plant Rhynchosia pseudo-cajan Cambess. was
collected from Kotli, Kashmir (P.O.K.) in June 2009 and
identified by Mr. MuhammadAjaib (Taxonomist), Department
of Botany, GC University, Lahore. A voucher specimen
(GC.Herb.Bot. 623) has been deposited in the herbarium of
the same university.
Extraction, fractionation and isolation: The shade-dried
ground whole plant (15 kg) was exhaustively extracted with
methanol (20 L × 4) at room temperature. The extract was
evaporated to yield the residue (950 g), which was dissolved
in distilled water (2 L) and partitioned with n-hexane (1.5 L ×
4), chloroform (1.5 L × 4), ethyl acetate (1.5 L × 4) and n-
butanol (1.5 L × 4) respectively. These organic fractions and
remaining water fraction was concentrated separately on
rotary evaporator. The yields of n-hexane soluble fraction,
chloroform soluble fraction, ethyl acetate soluble fraction, n-
butanol soluble fraction and remaining aqueous fraction were
203, 226, 198, 185 and 138 g respectively. The ethylacetate
soluble fraction was subjected to coloumn chromatography
over silica gel (70-230 mesh) using n-hexane with gradient of
CHCl3 (from 50:50, 30: 70, 20:80, 10:90, 0:100) (5000 mL
for each gradient) and followed by methanol up to 100 %.
Twelve fractions (Fr. 1-12) were collected, having elution
volumes as 3100, 4650, 3350, 3200, 3650, 4400, 2500, 2600,
3200, 4300, 3500 and 4200 mL respectively. The Fr. 11 (3500
mL) from the first column was loaded on silica gel (70-230
mesh) (64 g) and eluted with methanol:acetone:CHCl3
(10:10:80) (2900 mL) to isolate 1 (1.6 g), which was charac-
terized and then subjected to derivatization.
4'-O-n-Butyl naringin (3b): Gummy solid, yield 81 %.
1H NMR (400 MHz, CD3OD): δ 7.65 (d, J = 8.4 Hz, 2H, H-2'
& H-6'), 7.06 (d, J = 8.4 Hz, 2H, H-3' & H-5'), 6.60 (d, J = 2.0
Hz, 1H, H-8), 6.58 (d, J = 2.0 Hz, 1H, H-6), 5.39 (dd, J = 2.4,
12.7 Hz, 1H, H-2), 5.42 (d, J = 1.2 Hz, 1H, H-1'''), 5.25 (d, J =
7.5 Hz, 1H, H-1''), 4.20 (m, 1H, Ha-6''), 4.14 (m, 1H, Hb-6''),
3.90 (m, 1H, H-5'''), 3.71 (m, 1H, H-5''), 3.54 (m,1H, H-3''),
3.45 (t, J = 8.4 Hz, 2H, CH2-1''''), 3.43 (m,1H, H-3'''), 3.41
(m,1H, H-2'''), 3.29 (m,1H, H-2''), 3.09 (m,1H, H-4'''), 3.07
(dd, J = 17.3, 12.7 Hz, 1H, Ha-3), 3.05 (m, 1H, H-4''), 2.67
(dd, J = 17.3, 2.4 Hz, 1H, Hb-3), 1.75 (m, 2H, CH2-2''''), 1.47
(m, 2H, CH2-3''''),1.32 (d, J = 6.8, 3H, CH3-6'''), 0.98 (t, J =
7.2 Hz, 3H, CH3-4'''').
Synthesis of naringin derivatives in DMF: The calculated
amount of naringin (50 mg; 1) was taken in a round bottomed
flask (50 mL) and DMF (10 mL) was added to dissolve it,
followed by the addition of lithium hydride (50 mg) to the
mixture therein. The blend was stirred for 0.5 h at ambient
temperature and then slowly added the second reactant, 2a-l,
to the mixture and it was further stirred for 4 h. The progress
of reaction was monitored via TLC. The product was dissolved
in water and separated by solvent extraction with ethyl ac-
etate. TLC tests of the various products were performed using
solvents of methanol and chloroform in various ratios. The
appearance of single spot in each case on the TLC plate with
different Rf value relative to 1, corroborated the purity and the
formation of desired product. The purity of the desired products
was also evident from their clear NMR spectra.
4'-O-n-Pentyl naringin (3c): Gummy solid, yield 83 %.
1H NMR (400 MHz, CD3OD): δ 7.24 (d, J = 8.0 Hz, 2H, H-2'
& H-6'), 6.81 (d, J = 8.0 Hz, 2H, H-3' & H-5'), 6.22 (d, J = 2.3
Hz, 1H, H-8), 6.19 (d, J = 2.3 Hz, 1H, H-6), 5.36 (dd, J = 2.6,
12.5 Hz, 1H, H-2), 5.28 (d, J = 1.2 Hz, 1H, H-1'''), 5.11 (d, J =
7.2 Hz, 1H, H-1''), 4.21 (m, 1H, Ha-6''), 4.12 (m, 1H, Hb-6''),
3.84 (m, 1H, H-5'''), 3.76 (m, 1H, H-5''), 3.45 (m,1H, H-3''),
3.38 (t, J = 8.0 Hz, 2H, CH2-1''''), 3.31 (m,1H, H-3'''), 3.29
(m,1H, H-2'''), 3.27 (m,1H, H-2''), 3.21 (m,1H, H-4'''), 3.12
(dd, J = 17.4, 12.5 Hz, 1H, Ha-3), 3.06 (m, 1H, H-4''), 2.67
(dd, J = 17.4, 2.6 Hz, 1H, Hb-3), 1.73 (m 2H, CH2-2''''), 1.52
(m 2H, CH2-3''''),1.35 (d, J = 6.3, 3H, CH3-6'''), 1.52 (m 2H,
CH2-4''''), 0.65 (t, J = 6.2 Hz, 3H, CH3-5'''').
4'-O-iso-Propyl naringin (3d): Gummy solid, yield 80
%. 1H NMR (400 MHz, CD3OD): δ 7.32 (d, J = 8.4 Hz, 2H,
H-2' & H-6'), 6.92 (d, J = 8.8 Hz, 2H, H-3' & H-5'), 6.01 (d, J
= 2.0 Hz, 1H, H-8), 5.98 (d, J = 2.0 Hz, 1H, H-6), 5.34 (dd, J
= 2.8, 12.7 Hz, 1H, H-2), 5.28 (d, J = 2.8 Hz, 1H, H-1'''), 5.11
(d, J = 7.2 Hz, 1H, H-1''), 4.58 (m 1H, CH-1''''), 4.23 (m, 1H,
Structural identification
1
Naringin (1): Amorphous white solid (1.6g) H NMR
(400 MHz, CD3OD): δ 7.28 (d, J = 8.4 Hz, 2H, H-2' and H-
6'), 6.79 (d, J = 8.7 Hz, 2H, H-3' & H-5'), 6.16 (d, J = 2.1 Hz,

Vol. 25, No. 4 (2013)
Synthesis of Some 4'-O Substituted Derivatives of Natural Naringin and Their Biological Screening 1929
Ha-6''), 4.19 (m, 1H, Hb-6''), 3.99 (m, 1H, H-5'''), 3.97 (m, 1H,
H-5''), 3.96 (m,1H, H-3''), 3.94 (m,1H, H-3'''), 3.89 (m,1H,
H-2'''), 3.81 (m,1H, H-2''), 3.45 (m,1H, H-4'''), 3.11 (dd, J =
17.3, 12.7 Hz, 1H, Ha-3), 3.03 (m, 1H, H-4''), 2.70 (dd, J =
17.3, 2.8 Hz, 1H, Hb-3), 1.32 (d, J = 6.0, 3H, CH3-6'''), 1.12
(d, J = 7.2 Hz, 6H, CH3-2'''' & CH3-1''''').
4'-O-Allyl naringin (3e): Gummy solid, yield 82 %. 1H
NMR (400 MHz, CD3OD): δ 7.23 (d, J = 8.0 Hz, 2H, H-2' &
H-6'), 6.84 (d, J = 7.2 Hz, 2H, H-3' & H-5'), 6.21 (d, J = 2.2
Hz, 1H, H-8), 6.18 (d, J = 2.2 Hz, 1H, H-6), 5.89 (m, 1H, H-
2''''), 5.37 (dd, J = 2.6, 12.8 Hz, 1H, H-2), 5.33 (dd, J = 1.6,
17.2 Hz, 1H, Hb-3''''), 5.28 (d, J = 1.3 Hz, 1H, H-1'''), 5.05 (d,
J = 7.7 Hz, 1H, H-1''), 5.03 (dd, J = 1.6, 10 Hz, 1H, Ha-3''''),
4.20 (d, J = 6.4 Hz, 2H, CH2-1''''), 4.15 (m, 1H, Ha-6''), 4.09
(m, 1H, Hb-6''), 3.43 (m, 1H, H-5'''), 3.40 (m, 1H, H-5''), 3.37
(m, 1H, H-3''), 3.33 (m, 1H, H-3'''), 3.30 (m, 1H, H-2'''), 3.28
(m, 1H, H-2''), 3.25 (m, 1H, H-4'''), 3.14 (dd, J = 17.2, 12.8
Hz, 1H, Ha-3), 3.11 (m, 1H, H-4''), 2.64 (dd, J = 17.2, 2.6 Hz,
1H, Hb-3), 1.22 (d, J = 6.3, 3H, CH3-6''').
4'-O-(p-Fluorobenzyl) naringin (3i): Gummy solid,
yield 80 %. 1H NMR (400 MHz, CD3OD): δ 7.67 (d, J = 7.2
Hz, 2H, H-3''''' & H-3'''''), 7.49 (d, 7.2 Hz, 2H, H-2''''' &
H-6'''''), 7.24 (d, J = 8.3 Hz, 2H, H-2' & H-6'), 6.81 (d, J = 8.8
Hz, 2H, H-3' & H-5'), 6.19 (d, J = 2.2 Hz, 1H, H-8), 6.15 (d,
J = 2.2 Hz, 1H, H-6), 5.41 (dd, J = 2.6, 12.7 Hz, 1H, H-2),
5.32 (d, J = 1.4 Hz, 1H, H-1'''), 5.20 (br s, 2H, CH2-1''''), 5.13
(d, J = 7.0 Hz, 1H, H-1''), 4.23 (m, 1H, Ha-6''), 4.10 (m, 1H,
Hb-6''), 3.96 (m, 1H, H-5'''), 3.83 (m, 1H, H-5''), 3.38 (m,1H,
H-3''), 3.35 (m, 1H, H-3'''), 3.33 (m, 1H, H-2'''), 3.29 (m, 1H,
H-2''), 3.26 (m, 1H, H-4'''), 3.18 (dd, J = 17.2, 12.7 Hz, 1H,
Ha-3), 3.14 (m, 1H, H-4''), 2.82 (dd, J = 17.2, 2.6 Hz, 1H, Hb-
3), 1.40 (d, J = 6.4, 3H, CH3-6''').
4'-O-(2''''-Bromoethyl) naringin (3j): Gummy solid,
yield 82 %. 1H NMR (400 MHz, CD3OD): δ 7.31 (d, J = 8.4
Hz, 2H, H-2' & H-6'), 6.87 (d, J = 8.4 Hz, 2H, H-3' & H-5'),
6.05 (d, J = 2.0 Hz, 1H, H-8), 6.02 (d, J = 2.0 Hz, 1H, H-6),
5.37 (dd, J = 2.5, 12.6 Hz, 1H, H-2), 5.32 (d, J = 1.2 Hz, 1H,
H-1'''), 5.11 (d, J = 7.2 Hz, 1H, H-1''), 4.30 (m, 1H, Ha-6''),
4.25 (m, 1H, Hb-6''), 4.21 (t, J = 6.0 Hz, 2H, CH2-1''''), 3.95
(m, 1H, H-5'''), 3.82 (m, 1H, H-5''), 3.60 (t, J = 6.0 Hz, 2H,
CH\-2''''), 3.37 (m, 1H, H-3''), 3.35 (m, 1H, H-3'''), 3.33 (m,
1H, H-2'''), 3.31 (m, 1H, H-2''), 3.28 (m, 1H, H-4'''), 3.15 (dd,
J = 17.4, 12.6 Hz, 1H, Ha-3), 3.12 (m, 1H, H-4''), 2.68 (dd, J =
17.4, 2.5 Hz, 1H, Hb-3), 1.35 (d, J = 6.8, 3H, CH3-6''').
4'-O-(Ethylacetato) naringin (3k): Gummy solid, yield
4'-O-(2''''-phenylethyl) naringin (3f): Gummy solid,
1
yield 83 %. H NMR (400 MHz, CD3OD): δ 7.51 (m, 1H,
H-4'''''), 7.50 (m, 2H, H-3''''' & H-5'''''), 7.45 (m, 2H, H-2''''' &
H-6'''''), 7.35 (d, J = 8.2 Hz, 2H, H-2' & H-6'), 7.04 (d, J = 8.5
Hz, 2H, H-3' & H-5'), 6.21 (d, J = 2.3 Hz, 1H, H-8), 6.18 (d,
J = 2.3 Hz, 1H, H-6), 5.28 (dd, J = 2.6, 12.8 Hz, 1H, H-2),
5.19 (d, J = 1.3 Hz, 1H, H-1'''), 5.02 (d, J = 7.4 Hz, 1H, H-1''),
4.23 (m, 1H, Ha-6''), 4.19 (t, J = 7.3 Hz, 2H, CH2-1''''), 4.14
(m, 1H, Hb-6''), 3.96 (m, 1H, H-5'''), 3.81 (m, 1H, H-5''), 3.47
(m,1H, H-3''), 3.42 (m,1H, H-3'''), 3.39 (m,1H, H-2'''), 3.35
(m,1H, H-2''), 3.30 (m,1H, H-4'''), 3.18 (dd, J = 17.3, 12.8 Hz,
1H, Ha-3), 3.14 (m, 1H, H-4''), 2.83 (t, J = 2.3 Hz, 2H, CH2-
2''''), 2.66 (dd, J = 17.3, 2.6 Hz, 1H, Hb-3), 1.23 (d, J = 6.3,
3H, CH3-6''').
1
83 %. H NMR (400 MHz, CD3OD): δ 7.32 (d, J = 8.2 Hz,
2H, H-2' & H-6'), 6.86 (d, J = 8.6 Hz, 2H, H-3' & H-5'), 6.17
(d, J = 2.3 Hz, 1H, H-8), 6.13 (d, J = 2.3 Hz, 1H, H-6), 5.36
(dd, J = 2.6, 12.5 Hz, 1H, H-2), 5.22 (d, J = 1.4 Hz, 1H, H-
1'''), 5.11 (d, J = 7.4 Hz, 1H, H-1''), 4.59 (s, 2H, CH2-1''''),
4.26 (m, 1H, Ha-6''), 4.21 (q, J = 7.2 Hz, 2H, CH2-4''''), 4.17
(m, 1H, Hb-6''), 3.93 (m, 1H, H-5'''), 3.82 (m, 1H, H-5''), 3.45
(m, 1H, H-3''), 3.36 (m, 1H, H-3'''), 3.34 (m, 1H, H-2'''), 3.32
(m, 1H, H-2''), 3.29 (m, 1H, H-4'''), 3.17 (dd, J = 17.4, 12.5
Hz, 1H, Ha-3), 3.14 (m, 1H, H-4''), 2.74 (dd, J = 17.4, 2.6 Hz,
1H, Hb-3), 1.27, (t, J = 7.2 Hz, 3H, CH3-5''''), 0.89 (d, J = 6.7,
3H, CH3-6''').
4'-O-(3''''-phenylpropyl) naringin (3g): Gummy solid,
yield 83 %. 1H NMR (400 MHz, CD3OD): δ 7.51 (m, 1H, H-
4'''''), 7.50 (m, 1H, H-3''''' & H-5'''''), 7.49 (m, 1H, H-2''''' & H-
6'''''), 7.24 (d, J = 8.2 Hz, 2H, H-2' & H-6'), 6.74 (d, J = 8.5
Hz, 2H, H-3' & H-5'), 6.19 (d, J = 2.3 Hz, 1H, H-8), 6.15 (d,
J = 2.3 Hz, 1H, H-6), 5.38 (dd, J = 2.4, 12.7 Hz, 1H, H-2),
5.31 (d, J = 1.2 Hz, 1H, H-1'''), 5.12 (d, J = 7.2 Hz, 1H, H-1''),
4.29 (m, 1H, Ha-6''), 4.24 (m, 1H, Hb-6''), 3.97 (m, 1H, H-5'''),
3.90 (t, J = 7.0 Hz, 2H, CH2-1''''), 3.86 (m, 1H, H-5''), 3.38
(m,1H, H-3''), 3.33 (m,1H, H-3'''), 3.31 (m, 1H, H-2'''), 3.28
(m, 1H, H-2''), 3.21 (m, 1H, H-4'''), 3.17 (dd, J = 17.3, 12.7
Hz, 1H, Ha-3), 3.07 (m, 1H, H-4''), 2.75 (dd, J = 17.3, 2.4 Hz,
1H, Hb-3), 2.65 (m, 2H, CH2-2''''), 1.68 (t, J = 7.1 Hz, 2H,
CH2-3''''), 1.28 (d, J = 6.3, 3H, CH3-6''').
4'-O-(N-3''''', 5'''''-Dimethylphenyl-C-acetamido)
naringin (3l): Gummy solid, yield 82 %. 1H NMR (400 MHz,
CD3OD): δ 7.41 (d, J = 8.4 Hz, 2H, H-2' & H-6'), 6.94 (br d,
J = 2.4 Hz, 1H, H-4'''''), 6.75 (d, J = 8.8 Hz, 2H, H-3' & H-5'),
6.29 (d, J = 2.3 Hz, 1H, H-8), 6.25 (d, J = 2.3 Hz, 1H, H-6),
6.15 (br d, J = 2.4 Hz, 2H, H-2''''' & H-6'''''), 5.35 (dd, J = 2.4,
12.7 Hz, 1H, H-2), 5.34 (d, J = 1.4 Hz, 1H, H-1'''), 5.13 (d, J =
7.0 Hz, 1H, H-1''), 4.45 (s, 2H, CH2-1''''), 4.27 (m, 1H, Ha-6''),
4.19 (m, 1H, Hb-6''), 3.94 (m, 1H, H-5'''), 3.81 (m, 1H, H-5''),
3.39 (m, 1H, H-3''), 3.37 (m, 1H, H-3'''), 3.34 (m, 1H, H-2'''),
3.32 (m, 1H, H-2''), 3.28 (m, 1H, H-4'''), 3.19 (dd, J = 17.3,
12.7 Hz, 1H, Ha-3), 3.14 (m, 1H, H-4''), 2.99 (dd, J = 17.3, 2.4
Hz, 1H, Hb-3), 2.28 (s, 6H, CH3-7''''' & CH3-8'''''), 1.23 (d, J =
6.2, 3H, CH3-6''').
4'-O-(p-Bromobenzyl) naringin (3 h): Gummy solid,
yield 81 %. 1H NMR (400 MHz, CD3OD): δ 7.67 (d, J = 8.4 Hz,
4H, H-2''''', H-3''''', H-5''''' & H-6'''''), 7.24 (d, J = 8.3 Hz, 2H,
H-2' & H-6'), 6.96 (d, J = 8.8 Hz, 2H, H-3' & H-5'), 6.21 (d, J =
2.2 Hz, 1H, H-8), 6.17 (d, J = 2.2 Hz, 1H, H-6), 5.27 (dd, J =
2.5, 12.8 Hz, 1H, H-2), 5.22 (d, J = 1.3 Hz, 1H, H-1'''), 5.09 (d,
J = 7.2 Hz, 1H, H-1''), 5.02 (br s, 2H, CH2-1''''), 4.19 (m, 1H,
Ha-6''), 4.08 (m, 1H, Hb-6''), 3.95 (m, 1H, H-5'''), 3.84 (m, 1H,
H-5''), 3.48 (m, 1H, H-3''), 3.37 (m, 1H, H-3'''), 3.35 (m, 1H, H-
2'''), 3.33 (m, 1H, H-2''), 3.30 (m, 1H, H-4'''), 3.23 (dd, J = 17.2,
12.8 Hz, 1H, Ha-3), 3.18 (m, 1H, H-4''), 2.81 (dd, J = 17.2, 2.5
Hz, 1H, Hb-3), 1.23 (d, J = 6.1, 3H, CH3-6''').
Enzyme inhibition assays: Enzyme inhibition activities
of all the derivatives as well as that of naringin was checked
by following four assays.
Acetylcholinesterase assay: The acetylcholinesterase
(AChE) inhibition activity was performed according to the
reported method10 with slight modifications as follows. Total
volume of the reaction mixture was 100 µL. It contained 60 µL

1930 Riaz et al.
Asian J. Chem.
Na2HPO4 buffer with concentration of 50 mM and pH 7.7.
Ten µL test compound (0.5 mM well-1) was added, followed
by the addition of 10 µL (0.005 unit well-1) enzyme. The
contents were mixed and pre-read at 405 nm. Then contents
were pre-incubated for 10 min at 37 ºC. The reaction was
initiated by the addition of 10 µL of 0.5 mM well-1 substrate
(acetylthiocholine iodide), followed by the addition of 10 µL
DTNB (0.5 mM well-1). After 15 min of incubation at 37 ºC,
absorbance was measured at 405 nm. Synergy HT (BioTek,
USA) 96-well plate reader was used in all experiments. All
experiments were carried out with their respective controls in
triplicate. Eserine (0.5 mM well-1) was used as a positive
control. The percent inhibition was calculated by the help of
following equation.
100 µL contained 60 µL, 50 mM tris-HCl buffer, pH 7.6, 10
µL (0.5 mM) by the addition of 15 µL (0.9 units) enzyme. The
contents were mixed, preincubated fo 20 min at 37 ºC and pre
read at 410 nm. The reaction was initiated by the addition of
15 µL of 1.3 mM substrate(N-succinyl phenyl-alanine-P-
nitroanilide). 70 µL of buffer was used as a control. After 0.5
h of incubation at 37 ºC, absorbance was measured at 410 nm
using synergy HT microplate reader. All experiments were
carried out in triplicate. The per cent inhibition was calculated
by following equation.
Control − Test
Inhibition(%)=
×100
Control
IC50 values (concentration at which there is 50 % in
enzyme catalyzed reaction) compounds were calculated using
EZ-Fit Enzyme Kinetics Software (Perrella Scientific Inc.
Amherst, USA).
Control − Test
Inhibition(%)=
×100
Control
Butyrylcholinesterase assay: The butyrylcholinesterase
(BChE) inhibition activity was performed according to the
reported method10 with slight modifications as follows. Total
volume of the reaction mixture was 100 µL containing 60 µL,
Na2H PO4 buffer, 50 mM and pH 7.7. Ten µL test compound
0.5 mM well-1, followed by the addition of 10 µL (0.5 unit
well-1) BChE. The contents were mixed and pre-read at 405
nm and then pre-incubated for 10 min at 37 ºC. The reaction
was initiated by the addition of 10 µL of 0.5 mM well-1
substrate (butyrylthiocholine bromide) followed by the
addition of 10 µL DTNB, 0.5 mM well-1. After 15 min of
incubation at 37 ºC, absorbance was measured at 405 nm.
Synergy HT (BioTek, USA) 96-well plate reader was used in
all experiments. All experiments were carried out with their
respective controls in triplicate. Eserine (0.5 mM well-1) was
used as positive control. The percent inhibition was calculated
by the help of following equation.
DPPH radical scavenging activity: The stable 1,1-
diphenyl-2-picrylhydrazyl radical (DPPH) was used for the
determination of antioxidant activity according to reported
method15. Different concentrations of compounds in respec-
tive solvents were added at an equal volume (10 µL) to 90 µL
of 100 µM methanolic DPPH in a total volume of 100 µL in
96-well plates. The contents were mixed and incubated at 37
ºC for 0.5 h. The absorbance was measured at 517 nm using
Synergy HT BioTek® USA microplate reader. Quercetin and
L-ascorbic acid were used as standard antioxidants. The
experiments were carried out in triplicates. IC50 values were
calculated using EZ-Fit5 Perrella Scientific Inc.Amherst USA
software. The decrease in absorbance indicates increased
radical scavenging activity which was determined by the
following formula.
100 − Absorbance of testcompound
Scavenging activity (%) =
×100
Absorbance of control
Control − Test
Inhibition(%)=
×100
Statistical analysis: All the measurements were done in
triplicate and statistical analysis was performed by Microsoft
Excel 2003. Results are presented as mean SEM.
Control
IC50 values (concentration at which there is 50 % enzyme
inhibition) of compounds were calculated using EZ-Fit Enzyme
kinetics software (Perella Scientific Inc. Amherst, USA).
Lipoxygenase assay: Lipoxygenase activity was assayed
according to the reported method11-13 but with slight modifi-
cations. A total volume of 200 µL assay mixture contained
150 µL sodium phosphate buffer (100 mM, pH 8.0), 10 µL
test compound and 15 µL purified lipoxygenase enzyme
(Sigma, USA). The contents were mixed and pre-read at 234
nm and preincubated for 10 min at 25 ºC. The reaction was
initiated by addition of 25 µL substrate solution. The change
in absorbance was observed after 6 min at 234 nm. Synergy
HT (BioTek, USA) 96-well plate reader was used in all experi-
ments.All reactions were performed in triplicates. The positive
and negative controls were included in the assay. Quercetin
(0.5 mM well-1) was used as a positive control. The percentage
inhibition was calculated by formula given below.
RESULTS AND DISCUSSION
Ethyl acetate soluble fraction of Rhynchosia pseudo-cajan
(Camb.) yielded a flavanone glycoside, naringin (1). Its
1
2
structures were determined on the basis of D and D NMR
spectroscopic studies and by comparison with the published
data16. Naringin was purified as white powder through column
chromatography and its molecular formula C27H32O14 was
established by counting carbons and hydrogens from the data
1
1
of its H NMR and 13C NMR DEPT spectra. The H NMR
spectrum of naringin thoroughly supported a flavanone
glycoside structure closely resembling to that of reported data16.
The presence of flavanone skeleton was supported by 1H NMR
spectra that showed resonances for one H-2 proton and two
H-3 protons [δ 5.33 (dd, J = 2.7, 12.9 Hz, 1H, H-2), 3.16 (dd,
J = 17.1, 12.9 Hz, 1H, Ha-3) and 2.72 (dd, J = 17.1, 2.7 Hz,
1H, Hb-3)] of characteristic flavanones16. Two ortho coupled
doublets at δ 7.28 (J = 8.4 Hz, 2H, H-2' & H-6') and δ 6.79 (J
= 8.7 Hz, 2H, H-3' & H-5') were in agreement with the presence
of hydroxyl group at C-4' in the ring C of the molecule. The
doublets at δ 6.16 and 6.14, showing meta-coupling (J = 2.1
Control − Test
Inhibition(%)=
×100
Control
Chymotrypsin assay: The α-chymotrypsin inhibition
activity is performed according to slightly modified method
of Rehman et al.,14. Total volume of the reaction mixture of

Vol. 25, No. 4 (2013)
Synthesis of Some 4'-O Substituted Derivatives of Natural Naringin and Their Biological Screening 1931
OH
OH
3'
OH
OR
4'
2
6''
4''
O
5''
O
'
HO
HO
HO
1'
O
O
O
O
O
4
O
5'
HO
DMF
8
5
2''
O
O
2
X
R
3''
6'
1''
1'''
5'''
6'''
H3C
LiH
3
6
O
H3C
O
2a-l
Stir at r.t.
HO
HO
2'''
OH
OH
O
OH
O
3'''
H
4'''
1
OH
H
3a-l
Comd. No.
3a
-R
Comd. No.
3g
-R
CH2 CH3
3'''''
5'''''
3''''
CH2 CH2 CH2
1''''
2''''
1''''
2''''
1'''''
CH2 CH2 CH2 CH3
1''''
3'''''
3b
3c
3h
3i
1''''
4''''
2''''
3''''
1'''''
1'''''
CH2
Br
5'''''
CH2 CH2 CH2 CH2 CH3
3'''''
1''''
1''''
4''''
5''''
2''''
3''''
CH2
F
5'''''
CH2 CH2 Br
CH3
CH3
2''''
3''''
3d
3e
3j
1''''
1''''
2''''
CH
Ha
Hb
3''''
H
3k
2''''
C
H2C
1''''
O
CH3
5''''
2''''
C
4''''
CH2
C
1''''
3''''
CH2
O
3'''''
5'''''
H
N
3f
3l
1''''
2''''
2''''
C
H2C
1''''
7'''''
CH3
1'''''
CH2 CH2
1'''''
3'''''
O
5'''''
H C
3
8'''''
Scheme-I: Synthesis of naringin derivatives 3a-l
Hz) were due to H-6 and H-8 protons for ring A respectively
and downfield shifted values represented presence of substi-
tuted oxygen at C-5, with which glycone part was attached.
The chemical shift of C-5 at δ 164.98 in 13C NMR supported
the presence of substituted phenolic group at this position.
The presence of two anomeric doublets at δ 5.06 (d, J = 7.2
Hz, 1H, H-1'') and δ 5.24 (d, J = 1.2 Hz, 1H, H-1''') along with
another doublet at δ 1.27 (d, J = 6.3, 3H, CH3-6''') for a methyl
group revealed the presence of glucose and rhamnose sugars
in the molecule and their connectivity of C-1'''→ C-2'' was
thoroughly supported by the HMBC correlations of H-1''' with
C-2'' and H-2'' with C-1'''. The spectral data of naringin was
also in complete agreement with that of its reported data in
the literature17.
spectra. The compound, 3a, was synthesized as gummy solid.
Its molecular formula, C29H36O14, was established by counting
1
the number hydrogens from its H NMR data. It exhibited
similar 1H NMR signals to those of naringin (1) but the addi-
tional signals at δ 3.85 (q, J = 7.1 Hz, 2H, CH2-1'''') and 1.38
(t, J = 7.1 Hz, 2H, CH3-2'''') characteristic of ethyl group confir-
med the substitution of an ethyl group at the more exposed
phenolic group at C-4' in this molecule as the other hydroxyl
group at C-5 was sterically hindered and could not be substi-
tuted under the conditions. On the basis of above cumulative
evidences the structure of 3a was assigned as 4'-O-ethyl
naringin. The 3b was also a gummy solid with molecular
formula C31H40O14. In its 1H NMR spectrum, the signals at δ
3.45 (t, J = 8.4 Hz, 2H, CH2-1''''), 1.75 (m, 2H, CH2-2''''), 1.47
(m, 2H, CH2-3'''') and 0.98 (t, J = 7.2 Hz, 3H, CH3-4'''')
confirmed the substitution of an n-butyl group in this molecule
so the structure of 3b was assigned as 4'-O-n-butyl naringin.
In this paper, we report the synthesis of 12 new 4'-O-
substituted derivatives, 3a-l, of 1 (Scheme-I) and their
structures have been ascertained with the help of their 1H NMR

1932 Riaz et al.
Asian J. Chem.
TABLE-1
DPPH RADICAL SCAVENGING ACTIVITY, BUTYRYLCHOLINESTERASE ASSAY, ACETYLCHOLINESTERASE
ASSAY, LIPOXYGENASE ASSAY AND CHYMOTRYPSIN ASSAY
DPPH radical scavenging
activity
Butyrylcholinester-rase
Assay
Acetylcholineste-rase
Assay
Lipoxygenase
assay
Chymotrypsin
assay
Compd
. No.
(Inhb. %)
0.5 mM
(IC50)
µM
(Inhb. %)
0.5 mM
(IC50)
µM
(Inhb. %)
0.5 mM
(IC50)
µM
(IC50)
µM
(Inhb. %)
0.5 mM
(IC50)
µM
(Inhb. %) 0.5
mM
10.11 0.33
NIL
33.53 0.22
NIL
45.22 0.74
NIL
NIL
NIL
NIL
NIL
NIL
NIL
NIL
NIL
NIL
NIL
NIL
NIL
0.04
0.001
78.32 0.14 143.51 0.12 30.16 0.71
56.98 0.71 <500 19.85 0.014
52.50 0.85 474.51 0.03 40.44 0.24
1.88 0.25 NIL 39.71 0.62
73.69 0.65 164.91 0.52 38.24 0.22
NIL
1
75.58 0.23 36.21 0.32 71.48 0.58 335.81 0.09 50.70 0.74
NIL
3a
3b
3c
3d
3e
3f
36.19 0.14
27.56 0.51
11.96 0.65
8.16 0.32
18.27 0.14
10.47 0.71
15.26 0.01
41.45 0.23
13.07 0.74
8.75 0.65
10.41 0.45
NIL
NIL
NIL
NIL
NIL
NIL
NIL
NIL
NIL
NIL
NIL
38.78 0.47
29.69 0.65
31.04 0.14
49.13 0.25
NIL
NIL
NIL
NIL
51.97 0.14
40.13 0.64
44.20 0.85
54.90 0.25
NIL
NIL
NIL
58.26 0.45
24.85 0.74
22.86 0.17
23.56 0.37
16.53 0.81
21.10 0.73
31.30 0.16
<500
NIL
NIL
NIL
NIL
NIL
NIL
19.85 0.45
30.88 0.34
25.74 0.78
68.38 0.52
41.91 0.34
34.56 0.22
34.92 0.81
NIL
79.66 0.22 266.21 0.35 42.04 0.31
65.14 0.35 212.91 0.56 45.10 0.06
NIL
NIL
3g
3h
3i
57.74 0.39
<400
40.38 0.74
159.3 0.05
NIL
65.14 0.11 358.11 0.01 52.87 0.01
40.59 0.75
35.04 0.88
50.17 0.09
NIL
NIL
55.03 0.32
44.97 0.15
27.01 0.64
NIL
3j
NIL
3k
3l
<400
88.06 0.31 157.91 0.54 31.11 0.64
NIL
Control Quercetin 16.96 0.14
Eserine
0.85 0.001
Eserine
Baicalein 22.4 1.3 Chymostatin
8.24 0.11
The 3c having molecular formula C32H42O14 was identified as
4'-O-n-pentyl naringin due to the characteristic signals of
n-pentyl group at δ 3.38 (t, J = 8.0 Hz, 2H, CH2-1''''), 1.73 (m
2H, CH2-2''''), 1.52 (m, 4H, CH2-3'''' & CH2-4'''') and 0.65 (t,
J = 6.2 Hz, 3H, CH3-5''''). In 3d, having molecular formula
C30H38O14, the signals at δ 4.58 (m, 1H, CH-1'''') and 1.12 (d,
J = 7.2 Hz, 6H, CH3-2'''' & CH3-1''''') were characteristic of
isopropyl group and thus its structure was elucidated as 4'-O-
iso-proyl naringin. The signals at δ 5.89 (m, 1H, H-2''''), 5.33
(dd, J = 1.6, 17.2 Hz, 1H, Hb-3''''), 5.03 (dd, J = 1.6, 10 Hz,
1H, Ha-3'''') and 4.20 (d, J = 6.4 Hz, 2H, CH2-1'''') in 3e were
typical for an allyl group and consequently confirming the
structure of this molecule as 4'-O-allyl naringin. In the 1H NMR
spectrum of 3f, the signals in aromatic region at δ 7.51 (m,
1H, H-4'''''), 7.50 (m, 2H, H-3''''' & H-5'''''), 7.45 (m, 2H,
H-2''''' & H-6''''') indicated a phenyl group while signals at δ
4.19 (t, J = 7.3 Hz, 2H, CH2-1'''') and 2.83 (t, J = 2.3 Hz, 2H,
CH2-2'''') were due to a substituted ethyl group and hence its
structure was inferred as 4'-O-(2''''-phenylethyl) naringin.
Similarly, on the basis of signals in the aromatic region at δ
7.51 (m, 1H, H-4'''''), 7.50 (m, 1H, H-3''''' & H-5''''') and 7.49
(m, 1H, H-2''''' & H-6''''') indicative for phenyl group and
signals at δ 3.90 (t, J = 7.0 Hz, 2H, CH2-1''''), 2.65 (m, 2H,
CH2-2'''') and 1.68 (t, J = 7.1 Hz, 2H, CH2-3'''') indicative for
propyl group, the structure of 3g was deduced as 4'-O-(2''''-
phenylpropyl) naringin.
3H, CH3-5'''') were characteristic for an ethoxy group while
the one methylene signal at δ 4.59 (s, 2H, CH2-1'''') altogether
corroborated the structure of this molecule as 4'-O-
(ethylacetato) naringin. For 3l, only two signals in aromatic
region δ 6.94 (br d, J = 2.4 Hz, 1H, H-4''''') and δ 6.15 (br d,
J = 2.4 Hz, 2H, H-2''''' & H-6''''') represented a trisubstituted
phenyl ring. Methyl signals at δ 2.28 (s, 6H, CH3-7''''' & CH3-
8''''') were also in agreement that two methyl groups were
substituted on the phenyl ring while another singlet at δ 4.45
(s, 2H, CH2-1'''') was emblematic for the methylene of
acetamido group. Therefore, on the basis of aforesaid evidences
the structure of this molecule was established as 4'-O-(N-3''''',
5'''''-dimethylphenyl-C-acetamido) naringin.
The inhibitory potential of these derivatives, 3a-l, was
studied against four enzymes namely, acetyl cholinesterase,
butyryl cholinesterase lipoxygenase and chymotrypsin as well
as their antioxidant potential by DPPH radical scavenging was
also studied and the results have been shown in Table-1. It
was observed that only 3a had very good antioxidant potential
showing IC50 36.21 0.32 µM as compared to quercetin, a
reference standard, having IC50 16.96 0.14 µM.All the other
derivatives as well as naringin showed no antioxidant potential.
Only 3a, 3f, 3g and 3i were moderate inhibitors of butyryl-
cholinesterase having IC50 values of 335.81 0.09 µM, 266.21
0.35 µM, 212.91 0.56 µM and 358.11 0.01 µM respec-
tively while naringin (1) itself, 3b, 3d, 3l and were recognized
as moderate inhibitors of lipoxygenase having IC50 values of
143.51 0.12 µM, 474.51 0.03 µM, 164.91 0.52 µM,
157.91 0.54 µM respectively. Only 3h was found to be
moderate inhibitor of chymotrypsin. It showed IC50 value 159.3
0.05 µM as compared to chymostatin, a reference standard
having IC50 value 8.24 0.11 µM. It was also obvious from
the screening results that the substitution of any group at C-4'
of naringin (1) has no remarkable effect on its biological
activity against studied enzymes.
In 1H NMR spectrum of 3h, the signals of an ortho coupled
doublet i.e. δ 7.67 (d, J = 8.4 Hz, 4H, H-2''''', H-3''''', H-5''''' &
H-6''''') showed that p-Bromo benzyl group has been attached
so it thoroughly supported its structure as 4'-O-(p-bromo
benzyl) naringin. In 3i, the signals of two ortho coupled
doublets i.e. δ 7.67 (d, J = 7.2 Hz, 2H, H-3''''' & H-3'''''), 7.49
(d, 7.2 Hz, 2H, H-2''''' & H-6''''') showed that p-fluoro benzyl
group has been attached so the structure of 3i was established
1
as 4'-O-(p-fluorobenzyl) naringin. In H NMR spectrum of
3j, two triplet signals at δ 4.21 (t, J = 6.0 Hz, 2H, CH2-1'''')
and 3.60 (t, J = 6.0 Hz, 2H, CH2-2'''') thoroughly supported its
structure as 4'-O-(2''''-bromoethyl) naringin. In 3k, the signals
at δ 4.21 (q, J = 7.2 Hz, 2H, CH2-4'''') and 1.27, (t, J = 7.2 Hz,
Conclusion
From the results of antioxidant potential and enzyme
inhibition activities it was observed that only 4'-O-ethyl

Vol. 25, No. 4 (2013)
Synthesis of Some 4'-O Substituted Derivatives of Natural Naringin and Their Biological Screening 1933
3. A. Dama, G. Duvvuru, R. Pasupulati, S. Otto and S. Hildebebert, Phyto-
chemistry, 19, 478 (1980).
naringin (3a) showed antioxidant potential (IC50 36.21 0.32
µM). 4'-O-Ethyl naringin (3a), 4'-O-(2''''-phenylethyl) naringin
(3f), 4'-O-(3''''-phenylpropyl) naringin (3g) and 4'-O-(p-
fluorobenzyl) naringin (3i) were found to be moderate
inhibitors of butyrylcholinesterase while naringin (1) itself,
4'-O-n-butyl naringin (3b), 4'-O-iso-propyl naringin (3d) and
4'-O-(N-3''''', 5'''''-dimethylphenyl-C-acetamido) naringin (3l)
were identified as moderate inhibitors of lipoxygenase.Against
chymotrypsin only 4'-O-(p-bromobenzyl) naringin (3h) was
found to be a moderate inhibitor. So it was concluded that the
substitution of any group at C-4' of naringin (1) has no remark-
able effect on its biological activity against studied enzymes.
4. A. Dama, G. Duvvuru, R. Pasupulati, S. Otto and S. Hildebebert, Phyto-
chemistry, 19, 483 (1980).
5. A. Dama and R. Pasupulati, Pharmazie, 39, 714 (1984).
6. A. Dama, R. Pasupulati and K.N. Rao, Experientia, 41, 251 (1985).
7. C.V. Rao and D. Gunasikar, Acta Cienc. Ind. (Chem.), 13, 187 (1987).
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