Isolation and synthesis of flavonols and comparison of their antioxidant activity

Article abstract of DOI:10.1080/14786410902847302

Phytochemical investigation of the leaves of Astragalus beckari yielded four flavonol aglycones, namely kaempferol, quercetin, 5-deoxy kaempferol and fisitin. These isolated compounds were then synthesised in the laboratory using the Algar-Flyn-Oyamad reaction. Antioxidant activity of both the isolated and synthesised flavonoids was compared using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay method. The isolated flavonoids were found to be more active.

Full text of DOI:10.1080/14786410902847302

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Isolation and synthesis of flavonols and
comparison of their antioxidant activity
Aurangzeb Hasan a , A. Sadiq a , A. Abbas a , E. Mughal a , Khalid
M. Khan b & Muhammad Ali b
a Department of Chemistry, Quaid-i-Azam University,
Islamabad-45320, Pakistan
b H.E.J. Research Institute of Chemistry, International Center
for Chemical and Biological Sciences, University Karachi,
Karachi-75270, Pakistan
Published online: 15 Jun 2010.
To cite this article: Aurangzeb Hasan , A. Sadiq , A. Abbas , E. Mughal , Khalid M. Khan &
Muhammad Ali (2010): Isolation and synthesis of flavonols and comparison of their antioxidant
activity, Natural Product Research: Formerly Natural Product Letters, 24:11, 995-1003
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Natural Product Research
Vol. 24, No. 11, 10 July 2010, 995–1003
Isolation and synthesis of flavonols and comparison of their
antioxidant activity
a
a
a
a
b
*
Aurangzeb Hasan , A. Sadiq , A. Abbas , E. Mughal , Khalid M. Khan
and Muhammad Alib
aDepartment of Chemistry, Quaid-i-Azam University, Islamabad-45320, Pakistan;
bH.E.J. Research Institute of Chemistry, International Center for Chemical and Biological
Sciences, University Karachi, Karachi-75270, Pakistan
(Received 12 April 2005; final version received 18 March 2009)
Phytochemical investigation of the leaves of Astragalus beckari yielded four
flavonol aglycones, namely kaempferol, quercetin, 5-deoxy kaempferol
and fisitin. These isolated compounds were then synthesised in the
laboratory using the Algar–Flyn–Oyamad reaction. Antioxidant
activity of both the isolated and synthesised flavonoids was compared
using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay method. The
isolated flavonoids were found to be more active.
Keywords: isolation; synthesis; flavonols; comparison; antioxidant activity
1. Introduction
Astragalus, ‘milkvetch’ or ‘locoweed’ is a member of the Leguminosae family, which
is probably the largest genus of flowering plants, containing up to 3000 species
(Farrokh, Ghahremani, & Nejad, 2004). The centre of development seems to be in
the arid and semi-arid mountainous parts of the northern hemisphere. It is most
diverse in the Irano-Turkish region, the Sino-Himalayan Plateau and in the
Colorado Plateau of North America. In Pakistan, it is represented by 134 species.
Astragalus beckari is distributed in the Murree Hills, Nathia Gali, Ghora Gali and
Kashmir.
The genus Astragalus is reported to be quite rich in flavonoids, and eight
flavonoids have been isolated from the 80% ethanolic extract of Astragalus
complanatus (Coobs & Evans, 1940). A new isoflavonoid, glycoside astraisoflavanin
(3-S-(ꢀ)-nucronulatol-7-O-ꢀ-D-glucopyranoside), has been isolated from the alco-
holic root extract of Astragalus membranaceus var. monghlicum (Nayak & Rout,
1975). Octacosane, daucosterol and kaempferol have been isolated from the seeds of
Astragalus chenensis (Sipos, Furka, & Szell, 1960). Using HPLC-EIMS, eight
´
flavonoid glycosides were isolated and identified from the roots of A. mongholicus
and A. membranaceous (Wheeler, 1957). A new flavonol glycoside, kaempferol 3-O-
ꢁ-L-rhamnopyranosyl-(1!6)-[ꢁ-L-rhamnopyrano-side], was isolated from the aerial
*Corresponding author. Email: hassaan2@super.net.pk
ISSN 1478–6419 print/ISSN 1029–2349 online
ß 2010 Taylor & Francis
DOI: 10.1080/14786410902847302
http://www.informaworld.com

996
A. Hasan et al.
parts of A. shikokianus together with two known flavonoid glycosides (Seshadri,
1962). New flavonol glycosides, together with a new glycoside of a cycloartane-type
triterpene, were isolated from the leaves and roots of A. caprinus (Marini-Bettolo,
´
1942). Four new flavonol 3-O-glycosides were isolated from the leaves of A. caprinus
(Geissman & Fukushima, 1948). Two other flavonoid glycosides, namely (3R)-(ꢀ)-
7,20-dihydroxy-30,40-dimethylisoflavan-7-O-ꢀ-D-glucopyranoside and (6aR, 11aR)-
9,10-dimethoxypterocarpan-3-O-ꢀ-D-glucopyranoside were separated from the
ethyl acetate extract of the root of A. membranaceus by high speed counter-current
chromatography (Marathey, 1955). Generally, flavonoid compounds have been
reported to possess a large number of biological properties, such as anticancer
(Ong & Khoo, 1997), antibacterial (Ivancheva, Manolova, Serkedjieva, Dimov, &
Ivanovska, 1992), antiulcer (Rainova, Nokov, Bogdanova, Minkov, & Staneva-
Stoytcheva, 1988), anti-inflammatory (Silvan, Abad, Bermejo, Villar, & Sollhuber,
1996) and antifungal (Roy, Pandey, Singh, & Prithiviraj, 1996). However, one of the
most important properties of flavonoids is their antioxidant (Hosseinzadeh, Karimi,
& Ameri, 2002) or free radical scavenging activity. Usually, isolation of flavonoids
from natural sources results in the attainment of very small quantities. The present
study is, therefore, aimed at the isolation of flavonoid aglycones from the leaves of
A. beckari, their laboratory synthesis and comparison of their antioxidant properties.
2. Results and discussion
Compounds 1N and 1S were obtained as yellow solids. Both appeared yellow
under UV light (366 nm) and remained unchanged when exposed to NH3 vapours,
suggesting both to be flavonols. Co-chromatography of 1N and 1S with authentic
markers in two solvent systems suggested both to be 3,5,7,40-tetrahydroxy
flavonol or kaempferol. The UV spectra of both 1N and 1S recorded in MeOH
exhibited two absorption maxima at 367 nm (band-I) and 268 nm (band-II),
typical for flavonol aglycones (Markham, 1982). On addition of NaOAc to the
methanolic solution of the flavonols, a bathochromic shift of 12 nm in band-II
was observed with respect to the MeOH spectrum, indicating the presence of
a free hydroxyl group at position 7 of ring A. Addition of H3BO3 to the
methanolic solution of the flavonols, containing NaOAc, produced an insignif-
icant bathochromic shift of 4.0 nm in band-I, indicating the absence of ortho-
dihydroxylation in ring B. A significant bathochromic shift of 55 nm was observed
in band-I by the addition of 5% alcoholic solution of AlCl3. Addition of HCl in
the methanolic solution of the flavonols, containing AlCl3, did not exhibit a
hypsochromic shift in band-I, which indicated the presence of a free hydroxyl
group at position 5 and 3 and the absence of ortho-dihydroxylation in ring B. A
bathochromic shift of 50 nm in band-I was observed after the addition of NaOMe
with respect to the MeOH spectrum of the aglycone, indicating the presence of
a free 40-OH. Slow decomposition of the spectrum after 5 min indicated the
presence of a 3,40-hydroxylation pattern.
In EIMS, a molecular ion peak for both the flavonols was observed at m/z 286.
The other important fragment ions appeared at m/z 153 (A1 þ H)þ, 121 (B2)þ and 93
(Bþ2 ꢀ28). This typical fragmentation pattern of the flavonol suggested compounds
1N and 1S to be 5,7,40-trihydroxy flavonols.

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997
Table 1. Physical data of the isolated (2N–4N) and synthesised (2S–4S) flavonols.
Flavonols Mol. wt. Mol. formula m.p. (ꢁC) Yield (%) Appearance Solubility
a
1N
2N
3N
4Nb
1S
286
302
270
286
286
302
270
286
C15H10O6
C15H10O7
C15H10O5
C15H9O6
C15H10O6
C15H10O7
C15H10O5
C15H9O6
267–268
310–315
223–234
278–279
268–269
312–316
223–224
278–280
–
–
–
D.Y.C.S.
D.Y.C.S.
F.Y.C.S.
F.Y.C.S.
D.Y.C.S.
D.Y.C.S.
F.Y.C.S.
F.Y.C.S.
Methanol
Methanol
Methanol
Methanol
Methanol
Methanol
Methanol
Methanol
–
73.3
75.0
62.5
70.8
2S
3S
4S
Notes: D.Y.C.S. ¼ Dull yellow crystalline solid. F.Y.C.S. ¼ Fluorescent yellow crystalline solid.
aNatural. bSynthetic.
Table 2. UV spectral data of isolated and synthesised flavonols.
2N–2S
3N–3S
4N–4S
B-I
B-II
B-I
B-II
B-I
B-II
367
377
367
427
427
417
256
268
261
261
266
280
371
381
400
460
431
418
252
263
252
253
253
254
370
379
383
451
424
426
252
264
253
269
269
217
The 1H NMR (CD3OD, 300 MHz) spectra of the flavonols (1N and 1S) exhibited
two doublets at ꢂ 6.12 (1H, d, J6,8 ¼ 2.0 Hz) and ꢂ 6.24 (1H, d, J8,6 ¼ 2.0 Hz), repre-
senting absorption due to two meta-coupled protons, i.e. H-6 and H-8 of ring A.
Chemical shifts for H-30 and H-50 were observed at ꢂ 6.91 (2H, d, J2 ,3 , J5 ,6 ¼ 8.0 Hz),
0
0
0
0
showing an ortho coupling with H-2 and H-6 which resonated at ꢂ 8.04
(2H, d, J3 ,2 , J6 ,5 ¼ 8.0 Hz). On the basis of UV, EIMS and 1H NMR data, the
structure of both flavonols (1N and 1S) was identified as 3,5,7,40-tetrahydroxyflavone
or 5,7,40-trihydroxyflavonol (kaempferol). Similarly, the structures of the other three
isolated (2N–4N) and synthesised flavonols (2S–4S) were characterised on the basis
of their physical and spectral data. The physical data of the isolated and synthesised
flavonols is tabulated in Table 1, whereas the UV data is presented in Table 2.
0
0
0
0
3. Experimental
The UV spectra and antioxidant activities were measured with a Shimadzu (Japan)
1601 UV–vis spectrophotometer. Shift reagents were prepared according to Mabry,
Markham and Thomas (1971). Thin layer chromatography (TLC) was performed on
polyamide (Riedel-deHaen 6DF, Germany) using a solvent system (toluene–
¨
methyl : ethyl : ketone–methanol 4 : 3 : 3). TLC plates were visualised under UV light
(366 nm). For column chromatography (CC) polyamide (Riedel-deHaen 6S,
¨
Germany) and Sephadex LH-20 (bead size 25–10 m Sigma, Switzerland) were used.

998
A. Hasan et al.
DPPH (1,1-diphenyl-2-picrylhydrazyl) was purchased from Sigma-Aldrich Chemical
Company. Purity of the compounds was checked by Shimadzu LC-6A HPLC using
Zorbex ODS C18 (25 cm ꢂ 4.6 mm i.d.) column at a flow rate of a 1 mL minꢀ1
,
UV (SPD-6AV) detection at 320 nm and a gradient system, H2O : AcOH (1000 : 20)
and CH3CN : H2O : AcOH (800 : 200 : 20) using Shimadzu LC 6A pumps. EI-MS
1
was recorded on a Shimadzu QP1000A machine. H NMR spectra were recorded
in CD3OD on a 300 MHz Brucker WM 400, and TMS was used as the internal
standard.
3.1. Plant material, extraction and isolation
Astragalus beckari leaves were collected from Murree Hills, Pakistan in August 2004
and identified by Dr Mir Ajab Khan, Associate Professor, Department of Biological
Sciences, Quaid-i-Azam University, Islamabad, Pakistan. A voucher specimen
(No. 524) has been deposited in the Herbarium of the above-cited department.
Air-dried and powdered leaves (50 g) of A. beckari were acid hydrolysed by
heating with 2 M HCl on a boiling water bath for 1 h. By this treatment, glycosides
were converted to aglycones. The aqueous phase was cooled and extracted with
diethyl ether (Et2O) for isolation of the flavonoid aglycones. The ether extract was
then evaporated to dryness and the dried residue (2.2 g) was subjected to column
chromatography on polyamide. The column was eluted in the gradient mode from
toluene, butanone to methanol. Sixteen fractions were collected and fractions 2–4,
5–9, 10–11 and 12–16 were combined. The compounds present in these fractions were
purified by a combination of TLC, preparative TLC and 2-D TLC on polyamide.
Final purification was carried out by column chromatography on polyamide
and Sephadex LH-20. As a result, four flavonol glycosides (1N–4N) were obtained
and their purity was monitored by TLC on polyamide and RP-HPLC. The yields of
each flavonoid glycoside 1N, 2N, 3N and 4N were 5 mg, 7 mg), 2 mg and 1.5 mg,
respectively.
3.2. Synthesis
The isolated flavonols were synthesised in the laboratory using the Algar–Flynn–
Oyamada reaction (Algar & Flynn, 1934; Oyamada, 1934). Flavonols (1S–4S) were
synthesised, starting from acetylation of 3-methoxyphenol (5) and 3,5-dimethox-
yphenol (6) to O-acetyl 3-methoxyphenol (7) and O-acetyl 3,5-dimethoxyphenol (8),
respectively. The resultant O-acetyl methoxyphenols on Fries rearrangement were
converted to their corresponding 2-hydroxy-4-methoxy acetophenone (9) and
2-hydroxy-4,6-dimethoxy acetophenone (10), respectively. 2-Hydroxy-acetophe-
nones, 9 and 10, upon reaction with 4-methoxybenzaldehyde (11) and 3,4-
dimethoxybenzaldehyde (12) in the presence of 50% NaOH in hot ethanol, were
then converted to four methoxychalcones (13–16). The methoxychalcones (13–16)
were then converted to their corresponding four methoxyflavanols (17–20) on
treatment with H2O2 in the presence of a base and methanol. Demethylations
of the methoxyflavonols (17–20) by treatment with Me3SiI/MeOH produced four
flavonols (1S–4S), as shown in Scheme 1.
The structures of all four flavanols with their common names are depicted in
Figure 1.

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999
CHO
OH
OCOCH3
AlCl3 (anhydrous)
OH
CH3
H3CO
(CH3CO)O
Pyridine
+
R2
OCH3
Heat
H3CO
R1
O
H3CO
R1
R1
5 = R1 = H
6 = R1 =OCH3
11 = R1 = H
12 = R1 = OCH3
7 = R1 = H
8 = R1 = OCH3
9 = R1 = H
10 = R1 = OCH3
50 % NaOH
Hot ethanol
R2
OCH3
R2
OCH3
H3CO
O
-
H2O2/OH
MeOH
H3CO
OH
OH
R1
O
R1
O
17 = R1 = OCH3 & R2 = H
18 = R1 = R2 = OCH3
19 = R1 = R2 = H
13 = R1 = OCH3 & R2 = H
14= R1 = R2 = OCH3
15 = R1 = R2 = H
Me3SiI/MeOH
demethylation
20 = R1 = H & OCH3
16 = R1 = H & OCH3
R2
OH
1S= R1 = OH & R2 = H
2S = R1 = R2 = OH
3S = R1 = R2 = H
4S = R1 = H & OH
HO
O
O
OH
R1
Scheme 1.
OH
OH
OH
OH
HO
O
O
HO
O
O
OH
OH
OH
Fisitin
Quercetin
OH
OH
HO
O
O
HO
O
O
OH
OH
OH
5-Deoxy kaemferol
Kaemferol
Figure 1. Names and structures of all four flavanols.

1000
A. Hasan et al.
3.3. Procedure for the synthesis of 2-(40-hydroxyphenyl)-5,7-trihydroxy-
3-hydroxy-4-oxo-4H-1-benzopyran (kaempferol) (1S)
Synthesis of O-acetyl-3,5-dimethoxyphenol (8): 3,5-Dimethoxyphenol (6)
(3.08 g, 20 mmol) was added to a mixture of acetic anhydride (1.88 mL) and
(1.68 mL, 25 mmol) pyridine under an inert atmosphere of nitrogen. The mixture was
heated at 100ꢁC for 3 h. To the cooled reaction mixture, water was added, acidified
with 5% HCl, and extracted with Et2O. The organic fraction was washed with
saturated aqueous NaHCO3, dried on anhydrous MgSO4, and the solvent
was evaporated to afford O-acetyl-3,5-dimethoxyphenol (8) as a light yellow oil
(3.40 g, 86%). Stretching frequency at 1764 cmꢀ1 in the IR spectrum of (8), which is a
characteristic of ester groups, confirmed the conversion of 3,5-dimethoxyphenol (6)
into O-acetyl-3,5-dimethoxyphenol (8).
3,5-Dimethoxy-2-hydroxyacetophenone (10): O-Acetyl-3,5-dimethoxyphenol (8)
(3.0 g, 15 mmol) was added drop-wise on anhydrous aluminium chloride
(3.0 g, 22 mmol) and the mixture was heated at 130ꢁC for 75 min. To the cooled
reaction mixture, crushed ice was slowly added and the resulting solution was
extracted with ethyl acetate. The organic phase was dried over anhydrous MgSO4
and solvent was evaporated to afford residue oil. Separation through column
chromatography afforded 1.5 g of 3,5-dimethoxy-2-hydroxyacetophenone (10).
Synthesis of 1-(50,70-dimethoxyphenyl)-3-(4-methoxyphenyl)-2-propen-1-one (13):
3,5-Dimethoxy-2-hydroxyacetophenone (10) (1.5 g, 0.0077 mol) and p-methoxyben-
zaldehyde (12) (1.04 g, 7.7 mol) were added in absolute ethanol (8 mL). The reaction
mixture was heated to 50ꢁC and 50% aqueous NaOH solution (3.85 mL) was added
slowly, with stirring. The reaction mixture was kept at room temperature for 8 h.
Crushed ice was added to the solid mass and neutralised with 5% HCl. The product
was obtained as a yellow precipitate which was filtered and recrystallised with
aqueous ethanol. Chalcone (13) was thus obtained as yellow needles.
Synthesis of 2-(40-methoxyphenyl)-5,7-dimethoxy-3-hydroxy-4-oxo-4H-1-benzo-
pyran (17): 1-(50,70-Dimethoxyphenyl)-3-(4-methoxyphenyl)-2-propen-1-one (13)
(1.0 g, 3.19 mmol) was added to a mixture of methanol (20 mL) and 20% aqueous
NaOH (3 mL). The reaction mixture was kept in an ice bath at 0ꢁC and 18%
H2O2 (3 mL) was added dropwise with constant stirring. After keeping it for 21 h
in a refrigerator, it was acidified with cold 5% HCl. The precipitate formed was
filtered off and yellow needles of 2-(40-methoxyphenyl)-5,7-dimethoxy-3-hydroxy-
4-oxo-4H-1-benzopyran (17) were obtained after crystallisation from aqueous
ethanol.
Synthesis of 2-(40-hydroxyphenyl)-5,7-trihydroxy-3-hydroxy-4-oxo-4H-1-benzopyran
(1S): To a 2M solution containing 5,7,40-trimethoxyflavonol (17) (1.0 g, 0.30 mmol) in
anhydrous chloroform (0.25 mL, 1.82 mmol), neat trimethylsilyl iodide via dry syringe
under inert atmosphere of nitrogen was added. The reaction mixture was stirred for
96 h at 35ꢁC. After the completion of the reaction (TLC analysis), the excess
trimethylsilyl iodide was destroyed and the intermediate trimethylsilyl ether formed
during the reaction was hydrolysed by pouring the reaction mixture into four
equivalents of methanol. The volatile components were removed at reduced pressure

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1001
Table 3. Comparison of antioxidant activity of isolated and synthetic flavonols.
Isolated and
synthetic flavonols
Reported antioxidant
activityc
Compounds
IC50
a
1Nb
1S
Isolated kaempferol
Synthetic kaempferol
Isolated quercetin
Synthetic quercetin
Isolated 5-deoxy kaempferol
Synthetic 5-deoxy kaempferol
Isolated fisitine
7.19
7.48
2.66
2.70
8.72
8.88
1.21
1.34
5.1
7.1
2N
2S
3N
3S
4N
4S
Standard
2.2
Not reported
1.1
Synthetic fisitine
ꢁ-Tocopherol
5.1
a
b
Notes: Natural. Synthetic. Furusawa et al. (2005).
c
and the residue was taken up in diethyl ether, washed with aqueous sodium bisulphide,
aqueous sodium bicarbonate, brine and then dried over anhydrous sodium sulphate.
The residue obtained after evaporation of the solvent was further purified by column
chromatography on silica gel to afford 3,5,7,40-tetrahydroxy flavone or 5,7,40-
trihydroxy flavonols (1S).
The same sequence of reaction with respective starting materials was repeated for
the synthesis of all other flavonols (2S–4S).
Compounds 1N and 1S: 1H NMR (CD3OD, 400 MHz): ꢂ 6.13 (1H, d, J ¼ 2.5 Hz, H-6),
6.24 (1H, d, J ¼ 2.5 Hz, H-8), 7.28 (2H, d, J ¼ 8.1 Hz, H-20, 60), 8.10 (2H, d,
J ¼ 8.1 Hz, H-30, 50); EIMS (rel. abund. %): 286 (Mþ, 100), 153 (64), 121 (31), 93 (23).
Compounds 2N and 2S: 1H NMR (CD3OD, 400 MHz): ꢂ 6.16 (1H, d, J ¼ 2.0 Hz, H-6),
6.35 (1H, d, J ¼ 2.0 Hz, H-8), 7.65 (1H, d, J ¼ 2.0 Hz, H-20), 6.68 (1H, d, J ¼ 8.0 Hz,
H-50), 7.62 (1H, dd, J ¼ 2.0/8.0 Hz, H-60); EIMS (rel. abund. %): 302 (Mþ, 27), 153
(100), 137 (46), 109 (19).
Compounds 3N and 3S: 1H NMR (CD3OD, 400 MHz): ꢂ (1H, d, J ¼ 8.1 Hz, H-5),
7.71(1H, dd, J ¼ 8.3/2.0 Hz, H-6), 6.35 (1H, d, J ¼ 2.3 Hz, H-8), 7.78 (2H, d,
J ¼ 8.3 Hz, H-20, 60), 8.08 (2H, d, J ¼ 8.0 Hz, H-30, 50); EIMS (rel. abund. %): 270
(Mþ, 39), 153 (78), 121 (100), 93 (41).
Compounds 4N and 4S: 1H NMR (CD3OD, 400 MHz): ꢂ (1H, d, J ¼ 8.3 Hz, H-5), 7.73
(1H, dd, J ¼ 8.3/2.0 Hz, H-6), 6.33 (1H, d, J ¼ 2.0 Hz, H-8), 8.05 (1H, d, J ¼ 2.5 Hz,
H-20), 6.83 (1H, d, J ¼ 8.0 Hz, H-50), 6.94 (1H, dd, J ¼ 2.1/8.0 Hz, H-60); EIMS (rel.
abund. %): 286 (Mþ, 86), 137 (100), 137 (56), 109 (100).
3.4. Antioxidant activity of isolated and synthesised flavonols
Antioxidant or free radical scavenging activity of isolated and synthetic flavonols
against stable DPPH radical was evaluated according to methods reported in the
literature (Lai, Chou, & Chao, 2001; Lu & Foo, 2000; Morikawa, Xu, Matsuda, &
Yashikawa, 2002; Yoshikawa et al., 1994). IC50 values for the isolated and synthetic
flavonols are presented in Table 3.

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A. Hasan et al.
The results showed that the position of the hydroxyl of the flavonols significantly
influences the antioxidant activities. 30,40-Hydroxyls containing flavonols (quercetin
and fisitine) were more active then their 40 analogues. Furthermore, it was also found
that the antioxidant properties of isolated (natural) flavonols were slightly
greater than those of synthetic ones. However, since the natural flavonols are
often isolated in very small quantities, synthesis of flavonols may serve as an
alternative source of antioxidant compounds.
4. Conclusion
It can be concluded that the position of hydroxyl groups in the flavonols plays an
important role in their antioxidant activities. 30,40-Hydroxyls containing flavonols
are more active than their 40 analogues. Furthermore, it was also found that
antioxidant activities of isolated (natural) flavonols are slightly greater in
comparison with their synthetic counterparts. However, since natural flavonols are
often isolated in very small quantities, synthesis of flavonols may serve as an
alternative source of antioxidant compounds in bulk quantities. A compromise can
be made between activity and quantity.
Acknowledgements
The authors acknowledge the financial assistance from Quaid-i-Azam University, Islamabad,
Pakistan, under the University Research Funding (URF) program.
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