BIBECHANA 18 (2) (2021) 143-153

143

Synthesis of antioxidative anthraquinones as potential
anticancer agents
Richa K. Gupta1,2, Ganesh M. S. Thakuri1, Gan B. Bajracharya1*, Ram Narayan Jha3*
1Laboratory of Catalysis and Frontier Molecules, Faculty of Science, Nepal Academy of Science and
Technology (NAST), Khumaltar, Lalitpur, Nepal
2Central Department of Chemistry, Tribhuvan University, Kirtipur, Kathmandu, Nepal
3Department of Chemistry, Tri-Chandra Multiple Campus, Tribhuvan University, Ghantaghar,
Kathmandu, Nepal
*Email: ganbajracharya@yahoo.com (G. B. Bajracharya); ramnarayan_jha@yahoo.co.in (R. N. Jha)

Article Information:
Received: September 15, 2020
Accepted: June 7, 2021

Keywords:
Acetylation
Antibacterial
Antioxidant
Chrysophanol
Friedel-Crafts reaction

ABSTRACT
Antioxidant and antibacterial activities of natural anthraquinones namely
chrysophanol (1) and emodin (2), and synthesized anthraquinones viz. 2-
methylanthraquinone (3), anthraquinone (4), 2-bromoanthraquinone (5), rubiadin
(6), chrysophanol diacetate (7), rubiadin diacetate (8) and 1,8-dimethoxy-3-
methylanthraquinone (9) were investigated. Anthraquinones 9, 3, 6, 5 and 2
exhibited a high DPPH• radical scavenging capacity (IC50 = <500 μg/mL)
showing their therapeutic potentiality for the treatment of cancers. These
anthraquinones 1-9 have also displayed a weak to moderate antibacterial activity
against Bacillus subtilis. Chrysophanol diacetate (7) including emodin (2) have
been appeared as the valuable antibacterials.

DOI: https://doi.org/10.3126/bibechana.v18i2.31234
This work is licensed under the Creative Commons CC BY-NC License. https://creativecommons.org/licenses/by-nc/4.0/

1. Introduction

Anthraquinones are important members of the
quinone family that have profound therapeutic
values as antibacterial, antifungal, anticancer,
antioxidant, laxative, diuretic, estrogenic, anti-
inflammatory, antiarthritic, etc. [1-3].
Anthraquinone structural motif is present in many
natural dyes, pigments, vitamins, enzymes etc [4].
Among 700 natural anthraquinones identified,
about 200 compounds were isolated from plants
and remaining from lichens, fungi and others [5-6].

Anthraquinones are widely distributed in Aloe
species of Liliaceae, Semen cassiae and Folium
sennae of Leguminosae, Radix rubiae of Rubiaceae,
Cascara sagrada of Rhamnaceae, and also widely
exist in a number of species of Polygonaceae
family especially in the genuses Rheum, Rumex and
Polygonum. They are more commonly available in
the important herbs like Rheum officinale,
Polygonum cuspidatum, Polygonum multiflorum
and Polygonum bistorta.
Antioxidant molecules inhibit oxidation of other
compounds. Reactive free radicals, particularly

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Richa K Gupta et al. / BIBECHANA 18 (2) (2021) 143-153

144

reactive oxygen species such as superoxide (O2•−),
hydroxyl (HO•), peroxyl (RO2•) and nitric oxide
(NO•), are produced in living organisms during
metabolisms. An imbalance between the production
of such free radicals and inability of the body to
eliminate them through the use of endogenous and
exogenous antioxidants result oxidative stress [7].
Oxidative stress causes oxidative damage which
eventually leads to a large number of diseases
including cancers, mutagenesis, cardiovascular
diseases, neurodegenerative diseases (e.g.
Alzheimer’s and Parkinson’s diseases),
immunodeficiency syndrome, diabetes, cellular
aging, etc [8-10].
The important reaction used for the laboratory
preparation of anthraquinones is Friedel-Crafts
acylation between phthalic anhydrides and benzene
derivatives. In conventional two steps process, o-
aroylbenzoic acids are first prepared in the presence
of AlCl3 by the Friedel-Crafts acylation [11]. In the
second step, intramolecular condensation of aryl
and o-aroylbenzoic acid is performed to produce
anthraquinones using H2SO4 or oleum [12],
benzoyl chloride and concentrated H2SO4 [13-14],
benzoyl chloride and ZnCl2 [15], POCl3 and
P2O3Cl4 [16], or B(HSO4)3 [17]. A eutectic mixture
of AlCl3 and NaCl melt has also been used to
prepare various anthraquinones by the Friedel-
Crafts acylation between phthalic anhydrides and
benzene derivatives [18-19]. Montmorillonite K10
clay [20], alum (KAl(SO4)2.12H2O) [4] and
MIVPWs (MIV = Zr, Ti and Sn; and PW =
phosphotungstate) [21] as heterogeneous solid
catalysts have also been explored, but these catalyst
are not easily available.
The synthesis of anthraquinones has received a
great attention in the recent past due to their
therapeutic values as well as synthetic challenges.
Total syntheses of some complex anthraquinones
such as uncialamycin [22], dynemicin A [23],
daunomycin [24], marmycin A [25], (±)-
brasiliquinone B [26], etc. have been reported
(Figure 1). Synthesis of these bioactive complex
molecules requires multiple steps and are therefore
available in poor quantities diminishing their

therapeutic usefulness. Hence, our researches focus
on isolation and/or synthesis of simple organic
molecules and/or their derivatives (which can be
easily obtained and/or synthesized in a large
quantity) possessing remarkable medicinal values
[27-31]. Recently, we have reported isolation of
two anthraquinones viz. chrysophanol (1) and
emodin (2) from the rhizomes of Rheum australe
(Figure 1) [32]. Herein, we studied antioxidant
capacity of these anthraquinones 1-2 as well as
some newly synthesized anthraquinones 3-9.
Antibacterial activity of the anthraquinones 1-9 is
also screened against 6 bacterial strains.

Fig. 1: Structures of some anthraquinones with
their medicinal values.

2. Experimental

Chemicals and equipments

2,2-Diphenyl-1-picrylhydrazyl (DPPH) was
procured from Sigma-Aldrich. Gallic acid was
purchased from Sisco. Analytical thin layer
chromatography (TLC) was performed on 0.2 mm
pre-coated Kieselgel 60 F254 plate (E. Merck).
Melting points (Mp) were determined by using a
Thile’s tube and are uncorrected. UV-Vis spectra
were recorded on Cary 60 UV-Visible
Spectrophotometer (Agilent). Spectrophotometry
was carried out by using an Elisa microplate reader
(EPOCH2, BioTek Instruments). IR spectra were
recorded on IR Tracer-100 (Shimadzu) in KBr disc.



Richa K Gupta et al. / BIBECHANA 18 (2) (2021) 143-153

145

Previously isolated chrysophanol (1) and emodin (2)
were also used in this work [32].

Procedures for the synthesis of anthraquinones

Method 1. Friedel-Crafts and intramolecular
condensation reactions to synthesize
anthraquinones 3-5

Two-steps reaction protocol was followed to
synthesize anthraquinones 3-5 [11-12]. Briefly,
phthalic anhydride (1.48 g, 10 mmol) and a
benzene derivative (10 mL of either toluene,
benzene or bromobenzene) were taken in a two-
necked round bottom flask equipped with a
magnetic stirrer, condenser, recovery bend and
receiver adapter (that immersed in water containing
conical flask). The content was stirred at 0 °C and
then introduced AlCl3 (3.07 g, 23 mmol) slowly.
The reaction mixture was refluxed at 90 °C until
the vapour of HCl was ceased. Completion of the
reaction was monitored by TLC (silica gel,
hexane:EtOAc, 1:1). After cooling, the reaction
mixture was decomposed by addition of ice water
and 3M HCl (25 mL). The content was extracted
with Et2O (20 mL × 3), washed with dil. HCl, dried
over Na2SO4 and filtered. The solvent was
evaporated and the obtained residue was vacuum
dried. In the second step, dried intermediate
product was refluxed with conc. H2SO4 (10 mL) at
100 oC for 1.5 hours. After cooling, ice water was
added slowly to decompose the reaction mixture
and then filtered. The residue on the filter paper
was washed with 32% NH3 solution until
neutralization followed by water. Pure
anthraquinones 3-5 were obtained after
recrystallization using EtOH.

Method 2. AlCl3:NaCl melt method to synthesize
anthraquinone 6

Anhydrous AlCl3 (13.33 g, 100 mmol) and NaCl
(5.32 g, 91 mmol) were taken in a 500 mL round
bottom flask and were melted at 125-130 oC. To
this was added a mixture of phthalic anhydride
(2.66 g, 18 mmol) and 2-methyl resorcinol (2.23 g,
18 mmol) in a small portion at a time. Now the
reaction temperature was raised to 165-175 oC and

stirred for 30 minutes. Thereafter, additional AlCl3
(13.33 g, 100 mmol) was added and stirring was
continued for another 30 minutes. A red solid
product was formed, which was decomposed by
addition of ice water (125 mL) and conc. HCl (125
mL) after cooling. The reaction mixture was
extracted with Et2O (100 mL × 3). The etherial
layer was washed with dil. HCl, dried over Na2SO4,
filtered and concentrated. The residue obtained was
purified by flash silica gel column chromatography
using mixtures of hexane/EtOAc to give rubiadin 6.

Method 3. Acetylation reaction to synthesize
anthraquinones 7 and 8

A mixture of chrysophanol (1) (0.254 g, 1 mmol),
acetic anhydride (3.66 mL, 38.8 mmol) and
pyridine (3.5 mL, 44 mmol) was stirred at room
temperature for 4 hours. Thereafter, ice cooled
water was added dropwise to the reaction mixture
for the precipitation. The precipitate was collected
by filtration and the acetylated product 7 was
purified by silica gel column chromatography using
mixtures of hexane/EtOAc. To prepare
anthraquinone 8, instead of chrysophanol (1),
rubiadin (6) (0.254 g, 1 mmol) was used as the
starting material for the acetylation reaction.

Method 4. Methylation reaction to synthesize
anthraquinone 9

A mixture of chrysophanol (1) (0.127 g, 0.5 mmol),
K2CO3 (0.760 g, 5.5 mmol), (CH3)2SO4 (0.7 mL, 7
mmol) and dry acetone (100 mL) were taken in a
round bottom flask equipped with a reflux
condenser and CaCl2 guard tube. The reaction
mixture was refluxed for 4 hours. Thereafter, the
reaction mixture was cooled, filtered and
concentrated. Thus obtained residue was purified
by silica gel column chromatography using
mixtures of hexane/EtOAc to afford anthraquinone
9.

Analytical data of the synthesized
anthraquinones

All the synthesized anthraquinones 3-9 were
analyzed by recording of Mp, UV-Vis spectra and



Richa K Gupta et al. / BIBECHANA 18 (2) (2021) 143-153

146

FT-IR spectra, and the data were compared with the
available literature.

2-Methylanthraquinone; 2-methylanthracene-9,10-
dione (3): Method 1. Yellow solid. Yield 1.58 g,
71.1% in two steps. Mp 176 oC (reported 176-178
oC) [4]. UV-Vis (MeOH) λmax nm: 328, 275(s), 256,
206. IR (KBr) ν cm–1: 3000 (C–H aromatic), 2950
(C–H alkyl), 1720 (C=O), 1700 (C=O), 1575 (C=C
aromatic), 1285 (C–H bend) [33].
Anthraquinone; anthracene-9,10-dione (4): Method
1. Yellow solid. Yield 1.64 g, 78.8% in two steps.
Mp 280 oC (reported 283-287 oC) [34]. UV-Vis
(MeOH) λmax nm: 325, 271(s), 251, 204 [35]. IR
(KBr) ν cm–1: 1700 (C=O), 1590 (C=C aromatic),
1350, 1325 (C–H bend) [36].
2-Bromoanthraquinone; 2-bromoanthracene-9,10-
dione (5): Method 1. Colourless solid. Yield 2.26 g,
78.7% in two steps. Mp 203 oC (reported 205-206
oC) [4]. UV-Vis (MeOH) λmax nm: 283, 228, 205.
IR (KBr) ν cm–1: 1750 (C=O), 1600 (C=O), 1525
(C=C aromatic), 1250 (C–H bend), 810 (C–Br
stretch), 500 [33].
Rubiadin; 1,3-dihydroxy-2-methylanthraquinone;
1,3-dihydroxy-2-methylanthracene-9,10-dione (6):
Method 2. Yellow needles. Yield 2.35 g, 51.4%.
Mp 280 oC (reported 281-282 oC) [37]. UV-Vis
(MeOH) λmax nm: 389, 256, 221. IR (KBr) ν cm–1:
3450 (–OH), 2950 (C–H alkyl), 1750 (C=O), 1650
(C=O), 1350 (–CH3) [38].
Chrysophanol diacetate; 3-methyl-9,10-dioxo-9,10-
dihydroanthracene-1,8-diyl diacetate (7): Method 3.
Yellow needles. Yield 0.210 g, 62.1%. Mp 204 oC.
UV-Vis (MeOH) λmax nm: 428, 285(s), 256, 223,
202. IR (KBr) ν cm–1: 3000 (C–H alkyl), 1750 (two
coalescence peaks, C=O), 1670 (C=O), 1650
(C=O), 1600 (C=C aromatic), 1300, 1275 (C–H
bend) (Figure 2A).
Rubiadin diacetate; 2-methyl-9,10-dioxo-9,10-
dihydroanthracene-1,3-diyl diacetate (8): Method 3.
Yellow needles. Yield 0.20 g, 59.1%. Mp 164 oC.
UV-Vis (MeOH) λmax nm: 415, 277, 244, 204. IR
(KBr) ν cm–1: 2975 (C–H alkyl), 1755 (C=O), 1750
(C=O), 1680 (C=O), 1630 (C=O), 1370 (–CH3),
1275 (C–H bend), 1200 (Figure 2B).

1,8-Dimethoxy-3-methylanthraquinone; 1,8-
dimethoxy-3-methylanthracene-9,10-dione (9):
Method 4. Yellow solid. Mp. 193 oC (reported 195
oC) [39-40]. Yield 0.116 g, 82.2%. UV-Vis (MeOH)
λmax nm: 338, 256, 206. IR (KBr) ν cm–1: 2950 (C–
H alkyl), 1650 (C=O), 1325 (C=C aromatic), 1275,
1230, 1010 (C–O alkoxy), 955 (C–O alkoxy).

Antioxidant capacity: DPPH• radical scavenging
assay

The DPPH• radical solution (concentration 0.1 mM)
was prepared by overnight stirring of 3.9 mg of
DPPH in methanol (100 mL) at 4 ºC. Four working
solutions of 25, 50, 250 and 500 µg/mL
concentrations were prepared for each
anthraquinone sample. To 0.5 mL of the working
solution, 2.5 mL of the DPPH• radical solution was
added. Control was prepared by adding 2.5 mL of
the DPPH• radical solution in methanol (0.5 mL).
The solutions were mixed well and were kept in
dark at room temperature for 30 minutes. The
absorbance was measured at 517 nm against blank
solution consisting water (0.5 mL) and MeOH (2.5
mL). The inhibition percentage at different
concentrations was calculated by using the equation
shown below. Statistical analysis was done by
using Microsoft excel program.
DPPH• scavenging rate % = 1 −

Absorbance sample
Absorbance control × 100

Antibacterial activity: Agar well diffusion assay

Three gram-positive bacteria viz. Bacillus subtilis,
Staphylococcus aureus (ATCC 25952),
Enterococcus faecalis, and three gram-negative
bacteria viz. Klebsiella pneumoniae (ATCC 13883),
Pseudomonas aeruginosa (ATTCC 27853) and
Salmonella typhimurium (ATCC 14028) were used
for the antibacterial assay. These bacterial strains
were obtained from National Endemic Health Care
Centre, Teku, Kathmandu, Nepal. The pure
bacterial cultures were streaked in the nutrient agar
slants for sub-culture. Thus developed each
pathogenic bacterium were transferred into a
separate nutrient broth by a sterile loop and
incubated at 37 ºC for 24 hours.



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147

Stock sample solutions of each anthraquinone were
prepared by dissolving 0.01 g of the sample in 1
mL of DMSO (concentration 10 mg/mL). Now, the
sample solutions (50 µL of each) were charged into
the 6 mm wells bored on agar plates. DMSO was
used as negative control. Gentamycin (10 μg/dics)
was used as positive control. The plates were then
incubated at 37 ºC for 24 hours, and the zone of
inhibition (ZOI) produced was measured.

3. Results and Discussion

Anthraquinones synthesis

Following the known protocols, anthraquinones 3-6
were synthesized by the Friedel-Crafts acylation
reaction between phthalic anhydride and benzene
derivatives (toluene, benzene, bromo benzene or 2-
methyl resorcinol). For the synthesis of
anthraquinones 3-5, a two-steps protocol – the
Friedel-Crafts reaction using AlCl3 followed by
H2SO4-mediated intramolecular condensation – was
used (Scheme 1) [11-12]. Anthraquinone 6 was
prepared in a single-step by the Friedel-Crafts
acylation reaction between phthalic acid and 2-
methyl resorcinol using AlCl3:NaCl melt following
a known procedure (Scheme 2) [38]. Synthesis of
anthraquinones 3-6 were confirmed by comparing
Mp, UV-Vis spectra and IR spectra reported in the
literature.
Phenols are commonly acetylated with acetic
anhydride in the presence of pyridine [41].
Acetylations of previously isolated chrysophanol (1)
and newly synthesized rubiadin (6) were thus
performed under un-optimized conditions to afford
the corresponding acetyl derivatives 7 and 8 in
62.1% and 59.1% yields, respectively (Scheme 3).
In the IR spectrum of compound 7, disappearance
of a broad peak of the hydroxyl group that appeared
in the IR spectrum of chrysophanol (1) at 3420 cm–

1, and appearance of two coalescence peaks at 1750
cm–1 and two sharp peaks at 1670 and 1650 cm–1 for
four C=O groups confirmed its synthesis (Figure
2A). In a similar way, rubiadin (6) had peaks at
3450 (–OH), 1750 (C=O) and 1650 (C=O) in the IR
spectrum. On the other hand, its acetyl derivative 8

showed disappearance of the hydroxyl group peak
and appearance of the two additional carbonyl
peaks (all together four C=O groups at 1755, 1750,
1680 and 1630 cm–1) confirmed its formation
(Figure 2B).

Scheme 1

Scheme 2

Scheme 3

Scheme 4

Anthraquinone 9 was synthesized by following a
general procedure of methylation using
chrysophanol (1) as a substrate (Scheme 4) [40, 38].
Strong signals at 1010 and 955 in the IR spectrum



Richa K Gupta et al. / BIBECHANA 18 (2) (2021) 143-153

148

Fig. 2: (A) IR spectrum of chrysophanol diacetate (7); (B) IR spectrum of rubiadin diacetate (8).

of compound 9 were due to the two C–O stretches
of newly formed methoxy groups.
Antioxidant capacity

Recently, we have reported isolation and
identification of chrysophanol (1) and emodin (2)
from the rhizomes of R. australe [32].
Chrysophanol (1) is known as an antioxidant [42];
however, it shows no significant effect on the
inhibition of cancer cell proliferation [43]. On the
other hand, Zhang et al. have reported that it is
effective against MCF-7 breast cancer, 7901 gastric
cancer, A375 melanoma and SKOV-3 oophoroma
cells [44]. Emodin (2) has more effectively
inhibited the proliferation of ovarian, breast, lung,
liver and prostate cancer cells [45-47]. More
recently, we have studied structure-activity
relationship study of quercetin derivatives in the
DPPH• radical scavenging capacity, and reported
the substituent(s) effect [27]. Since anthraquinones
are known for various biological activities
including antioxidant and anticancer activities, we
were encouraged to synthesize a number of
anthraquinones for the screening of their

antioxidant potentiality. Thus in the present work,
we have synthesized anthraquinones 3-9 and
together with previously isolated chrysophanol (1)
and emodin (2) were used to determine the
antioxidant potentiality using the DPPH assay [48].
By using the experimental absorbance values
obtained in the DPPH assay, linear curves of
percentage inhibition versus concentration for
every anthraquinone were plotted and then IC50

values were computed. The result of DPPH assay is
depicted in Figure 3. As can be seen in the figure,
1,8-dimethoxy-3-methylanthraquinone (9) is the
most potent antioxidant (IC50 = 200 μg/mL) among
other anthraquinones tested, followed by 2-
methylanthraquinone (3) (IC50 = 230 μg/mL),
rubiadin (6) (IC50 = 259 μg/mL), and 2-
bromoanthraquinone (5) (IC50 = 383 μg/mL). In
this study, anthraquinones 9, 3, 6 and 5 were found
more effective in scavenging of DPPH• radical than
emodin (2) (IC50 = 400 μg/mL), which has
displayed anticancer activity in several studies [45-
47]. Rubiadin (6) has shown anticancer activity in
the 3- ( 4,5- dimethy lthiazol-2- yl )- 2,5- diphenyl



Richa K Gupta et al. / BIBECHANA 18 (2) (2021) 143-153

149

Fig. 3: IC50 values of anthraquinones (1-9) in the DPPH assay.

Table 1: Antibacterial activity of the anthraquinones 1-9.

S. N. Pathogenic
bacteria used

ZOI shown by different antharaquinones 1-9 and standard

(in mm diameter)a

1 2 3 4 5 6 7 8 9 Gentamycin

1 B. subtilis 9 16 11 11 8 12 10 10 8 16

2 S. aureus – 17 12 – – 11 13 – – 24

3 E. faecalis 8 – – – – – 14 – – 20

4 K. pneumoniae – – – 10 – – 9 – – 12

5 P. aeruginosa – – – – – – – – – 25

6 S. typhimurium – – – – – – – – – 18

aValues of the ZOI include the diameter of well (6 mm) after 24 hours incubation against
different bacterial species in the Agar well diffusion assay. (–)-Sign indicates no significant ZOI
was observed.



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150

tetrazolium bromide (MTT) assay against different
cancer cells (MCF7 breast cancer, MES-SA human
uterine sarcoma, MES-SA/DX5 multidrug-resistant
variant human uterine sarcoma, DU145 prostate
cancer and H460 lung cancer cells) [37].
Chrysophanol (1) was found ineffective in
scavenging of DPPH• radical (IC50 = 1925 μg/mL).
Unsubstituted anthraquinone (4) was found least
effective among the others.

Antibacterial activity

The isolated and synthesized anthraquinones (1-9)
were evaluated for the antibacterial activity by
using the Agar well diffusion assay [49]. The ZOI
produced by these compounds is tabulated in Table
1.

All investigated anthraquinones 1-9 have displayed
a weak to moderate antibacterial activity against B.
subtilis (ZOI = 8-16 mm), while all these
compounds were found ineffective against P.
aeruginosa and S. typhimurium. A weak
antibacterial activity of chrysophanol (1) against B.
subtilis and S. aureus has already been reported
[50-51]. Literature search reveals that emodin (2)
exhibits noticeable antibacterial activity against
methicillin-resistant S. aureus, P. aeruginosa,
Escherichia coli, S. typhimurium, Bacillus cereus
and Shigella sonnei [52-53]. In the present study,
emodin (2) was found efficient antibacterial against
B. subtilis (ZOI = 16 mm) and S. aureus (ZOI = 17
mm) in accordance with the literature, and in
contrast, it was found ineffective against P.
aeruginosa and S. typhimurium.

2-Methylanthraquinone (3) (ZOI = 12 mm) and
rubiadin (6) (ZOI = 11 mm) have displayed
noticeable antibacterial activity against S. aureus.
The growth of S. aureus (ZOI = 13 mm), E.
faecalis (ZOI = 14 mm) and K. pneumoniae (ZOI =
9 mm) was remarkably inhibited by chrysophanol
diacetate (7), which clearly indicated that the
biological activity of a compound can be
significantly enhanced by the structural
modification (compare antibacterial activity of
parent chrysophanol 1 versus its diacetate

derivative 7). Unsubstituted anthraquinone (4)
exhibited a weak antibacterial activity against K.
pneumoniae (ZOI = 10 mm).

4. Conclusion

Anthraquinones are the potential drugs used against
different diseases. We have synthesized a number
of anthraquinones using known protocols, and
evaluated their antioxidant and antibacterial
activities. DPPH• radical scavenging capacity of
1,8-dimethoxy-3-methylanthraquinone (9), 2-
methylanthraquinone (3), rubiadin (6) and 2-
bromoanthraquinone (5) were found comparatively
more effective than emodin (2), a well-known
compound for its anticancer activity. Hence these
compounds warrant further cancer cell lines studies.
In addition, anthraquinones 1-9 have shown a weak
to moderate antibacterial activity against B. subtilis,
while they were found ineffective against P.
aeruginosa and S. typhimurium. Interestingly, a
significant enhancement in the antibacterial activity
was observed in chrysophanol diacetate (7) as
compared to its parent compound 1, which is a
known compound with a weak antibacterial activity.

Acknowledgments

This work was supported by Nepal Academy of
Science and Technology (NAST). R.K.G.
acknowledges NAST-University Collaborative
Research Program for a Ph.D. fellowship.

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