Indian Journal of Chemistry
Vol. 49B, December 2010, pp. 1637-1641
A new quinone from Maesa indica (Roxb.)A.DC, (Myrsinaceae)
Gina R Kuruvilla†, M Neeraja†, A Srikrishna*#, G S R Subba Rao†#,
A V S Sudhakar# & Padma Venkatasubramanian†
†
Foundation for the Revitalisation of Local Health Traditions, Yelahanka, Bangalore, India
#Department
of Organic Chemistry, Indian Institute of Science, Bangalore 560 012, India
E-mail: ask@orgchem.iisc.ernet.in
Received 13 July 2010
Isolation and structure elucidation of kiritiquinone, a new benzoquinone, 2,5-dihydroxy-6-methyl-3-(henicos-16-enyl)1,4-benzoquinone, from the fruits of Maesa indica (Roxb.) A.DC, is described.
Keywords: Benzoquinone natural products, maesaquinone, Maesa indica, Vidanga
Authentic identity of medicinal plant raw drug is an
important determinant of quality, safety and efficacy
of herbal medicines. Increasing demand for herbal
drugs has led to scarcity of plant raw materials
causing substitution with alternative materials. The
legitimacy of substitution if systematically analyzed,
can provide scientifically validated substitutes that are
bio-equivalent to the original drug.
The fruit of Vidanga is a high volume (>500
MT/year), top-traded botanical drug used in Indian
Medicine such as Ayurveda, Siddha and Unani1.
Vidanga is a well known Ayurvedic herbal drug for
helminthiasis, indigestion, and tumours. The
official pharmacopoeia has correlated the authentic
botanical entity of Vidanga as Embelia ribes
Burm.f (Myrsinaceae). Its sporadic distribution in
Western Ghats, Eastern Himalayas and North East
India indicates that the volumes traded cannot be
contributed by this species alone. Three other
species namely, E. tsjeriam-cottam A.DC, Myrsine
africana L. and Maesa indica (Roxb.) A.DC., all
belonging to myrsinaceae family are also used as
substitutes to Vidanga.
Embelin 1, the main constituent2 of the fruits of E.
ribes is also present in E. tsjeriam-cottam3 and
Myrsine africana4 but is absent in Maesa indica.
However, the ethyl acetate extract of Maesa indica
afforded a new compound that appeared to run closely
with embelin on TLC suggesting similarity in
polarity. Isolation and structure elucidation of this
compound is presented in this paper.
Results and Discussion
From the ethyl acetate extract of the fruits of M.
indica Roxb, a new compound was isolated by column
chromatography, which was obtained as an orange
amorphous powder, m.p. 129-30°C, and was named
as kiritiquinone 2 (kiriti is the Malayalam name for
vidanga). Kiritiquinone 2 gave an intense purple ferric
reaction. It was reduced to a colourless product with
zinc and hydrochloric acid which was rapidly reoxidized by air, thus exhibiting the properties of a
quinonoid structure. Elemental analysis and mass
spectrum of kiritiquinone 2, showed the molecular
formula as C28H46O4 (M+, 446). Further the compound
formed a dimethyl ether 3 with ethereal diazomethane, C30H50O4 (M+, 474) and a diacetate 4 with
acetic anhydride and pyridine, C32H50O6 (M+, 530),
besides the formation of a bis-2,4-dinitrophenylhydrazone. Reductive acetylation of kiritiquinone 2
with zinc and acetic anhydride afforded a crystalline
tetraacetate 5, C36H56O8 (M+, 616). These reactions
established5,6 the presence of a dihydroxyquinone
system in kiritiquinone 2.
The UV spectrum of kiritiquinone 2 showed λmax at
294 nm and the IR spectrum showed absorptions for
the carbonyl and hydroxyl groups at 1637 and 3328
cm-1, which confirmed5,6 the presence of a disubstituted 2,5-dihydroxy-1,4-benzoquinone moiety in
kiritiquinone. The 1H NMR spectrum of kiritiquinone 2
showed the presence of two hydroxyl groups at δ 7.6
ppm. The signals at δ 5.37 and 5.33 ppm integrating for
two protons, which appeared as doublets of an AB
quartet (J = 10.8 and 4.7 Hz), were attributed to the two
1638
INDIAN J. CHEM., SEC B, DECEMBER 2010
olefinic protons present in the side chain. The coupling
constant of 10.8 Hz established the Z stereochemistry
for the olefin. The three proton singlet at δ 1.94 showed
the presence of a methyl substituent on the quinonoid
ring. That the other substituent is an alkenyl chain is
indicated by signals at δ 0.90 (3H, t, side chain terminal
methyl), 1.26 (32H, side chain methylene protons),
2.05 (4H, m, two allylic methylenes) and a triplet at
2.41 ppm (2H, benzylic methylene). The 13C NMR
spectrum of kiritiquinone 2 exhibited a benzylic
methylene at δ 31.9, two methyl carbons at 22.3 and
14.0 due to methyl on quinone and one terminal methyl
of the side chain, besides 17 methylene carbons.
However, it exhibited only four sp2 carbons (two side
chain olefinic methines at δ 129.9 and 129.8 and two
quaternary ring carbons at 116.1 and 111.5 ppm)
indicating the tautomeric behavior due to the presence
of two 3-hydroxyenone moieties in the ring, as was
observed7 in the 13C NMR spectrum of maesaquinone
6. This was further confirmed from the 13C NMR data
of the dimethyl ether as well as the diacetate (which
exhibited signals due to all six carbons of the quinone
system) thus establishing clearly that kiritiquinone is
2,5-dihydroxy-6-methyl-1,4-benzoquinone having a C21 alkenyl chain at the C-3 position. This was further
confirmed by the mass spectral fragmentation of
kiritiquinone, which showed characteristic fragments at
m/z 418, 168, 167, 139 and 100.
Acetylation of kiritiquinone 2 with acetic
anhydride and pyridine afforded the diacetate 4,
whose 1H NMR spectrum showed the presence of six
proton singlet at δ 2.33 due to the methyl groups of
two acetates, and all the other signals are very much
similar to those of kiritiquinone 2. The IR spectrum of
the diacetate had absorption bands at νmax 1783, 1673
and 1635 cm-1 due to the vinyl acetate, quinone and
olefinic groups, respectively. In the 13C NMR
spectrum, signals due to all the ten sp2 carbons are
observed. The spectrum exhibited two quaternary
carbon signals at δ 179.9 and 179.7 due to two ketone
carbons, two quaternary carbon signals at 167.8 and
167.5 due to the ester carbons of two acetates, two
quaternary carbon signals at 149.0 and 148.9 due to
the acetoxy bearing carbons, two quaternary carbon
signals at 135.8 and 131.8 due to the methyl and alkyl
bearing carbons and two methines at 129.84 and
129.76 due to the side chain olefinic carbons.
Analogous to the diacetate, the 1H NMR spectrum
of kiritiquinone dimethyl ether 3 exhibited two
singlets at 4.01 and 4.00 due to two methoxy groups
in addition to other signals which are almost identical
to those of kiritiquinone 2. The structure of the
dimethyl ether 3 as a 3-alkenyl substituted derivative
of 2,5-dimethoxy-6-methyl-1,4-benzoquinone is
further supported from its 13C NMR spectral data and
confirmed from its mass spectral fragmentation.
Reductive acetylation of kiritiquinone 2 with zinc
and acetic anhydride afforded the tetraacetate 5. The
1
H and 13C NMR spectra of the tetraacetate clearly
established the presence of a symmetric fully
substituted aromatic ring, establishing the presence of
3,6-disubstituted benzene-1,2,4,5-tetraol tetraacetate
structure for the compound 5. In the 1H NMR
spectrum, the tetraacetate exhibited two singlets at δ
2.28 and 2.27 due to the methyl groups of the four
acetates, and a singlet due to the methyl group on the
ring appeared at 1.96 ppm. The IR spectrum did not
show any absorption due to the quinonoid carbonyl
and hydroxy groups; and it showed typical carbonyl
absorption band at 1760 cm-1 due to the aryl acetate.
The 13C NMR spectrum exhibited only eight
resonances due to the 12 sp2 carbons highlighting the
symmetry in the molecule. It exhibited two quaternary
carbon signals at 167.4 and 167.0 due to the ester
carbons of the four acetyl groups, two quaternary
carbon signals at 139.5 and 139.2 due to the four
oxygen bearing aromatic carbons, two quaternary
carbon signals at 127.6 and 123.8 due to the
remaining two aromatic carbons and two methines at
129.8 and 129.7 due to the side chain olefinic carbon
atoms.
Ozonolysis of the tetraacetate 5 afforded the
aldehyde 7 whose IR spectrum indicated strong
carbonyl absorption bands due to the aryl acetate
(1763 cm-1) and aldehyde (1715 cm-1) groups. The 1H
NMR spectrum exhibited the aldehyde proton at δ
9.73, two singlets at 2.26 and 2.27 due to four acetyl
methyl groups, a methyl at 1.95 ppm due to the
aromatic methyl group. The 13C NMR spectrum and
the mass spectrum of 7, confirmed the presence of a
hexa-substituted aromatic ring having four acetoxy
groups at C-1, C-2, C-4 and C-5 positions. Further a
methyl group and a long chain containing sixteen
carbons having an aldehyde functionality is present at
C-6 and C-3 positions, respectively, of the aromatic
ring. These reactions conclusively established the
position of the double bond at C-16 in the side chain
of kiritiquinone 2.
In another direction oxidation of the aromatic ring
was also carried out. Thus reaction of kiritiquinone 2
with alkaline 30% hydrogen peroxide afforded the acid
KURUVILLA et al.: NEW QUINONE FROM MAESA INDICA
O
O
[CH2]9
HO
[CH2]15
RO
OH
H3C
O
2. R = H
3. R = Me
4. R = Ac
OR
O
1
O
OAc
[CH2]15
AcO
H3C
[CH2]9
HO
OAc
OAc
1639
H3C
OH
O
5
6
OAc
AcO
CHO
H3C
OAc
OAc
7
O
C21H43
HO
[CH2]13 COOR
H3C
8. R = H; 9. R = Me
OH
O
10
8, which was esterified with ethereal diazomethane to
give the ester 9. The ester 9 was identified as methyl
16-dehydrobehenate from its spectral data. Catalytic
hydrogenation of 9 afforded behenic acid methyl ester.
Catalytic hydrogenation of kiritiquinone 2 with 5%
Pd-C in ethyl acetate afforded a yellow solid 10, m.p.
130-31°C. The 1H NMR spectrum showed the
presence of protons due to the terminal methyl group
at δ 0.87 (t, 3H), a singlet at δ 1.95 (3H) besides the
two benzylic protons. The high resolution mass
spectrum indicated the molecular formula as C28H48O4
(M+ 448). This compound was identified8 as
polygonaquinone, a benzoquinone isolated from
Polygonatum falcatum A, from its UV, IR, NMR and
mass spectral data.
The above data established the structure of
kiritiquinone as 2,5-dihydroxy-3-(Z-16-henecosenyl)6-methyl-1,4-benzoquinone 2. A preliminary screening of kiritiquinone 2 for cytotoxic activity using
MTT assay on A549 lung carcinoma cells revealed
considerable cytotoxicity. Further evaluation of
kiritiquinone 2 for precise cytotoxic and other
biological activities is in progress.
Experimental Section
Melting points are recorded using Mettler FP1
melting point apparatus in capillary tubes and are
uncorrected. IR spectra were recorded on PerkinElmer spectrum BX FTIR spectrophotometer. 1H
(400 MHz) and 13C (100 MHz) NMR spectra were
recorded on Bruker Avance 400 spectrometer. A 1:1
mixture of CDCl3 and CCl4 was used as solvent for
recording NMR spectra. The chemical shifts (δ, ppm)
and coupling constants (Hz) are reported in the
standard fashion with reference to either internal
tetramethylsilane (for 1H) or the central line
(77.0 ppm) of CDCl3 (for 13C). In the 13C NMR, the
nature of carbons (C, CH, CH2, CH3) was determined
by recording the DEPT-135 spectra, and is given in
parentheses. High-resolution mass spectra were
recorded using Micromass Q-TOF micro mass
spectrometer using electron spray ionization mode.
Elemental analyses were carried out using Carlo Erba
1106 CHN analyzer. Thin-layer chromatographies
(TLC) were performed on glass plates (7.5 × 2.5 and
7.5 × 5.0 cm) coated with Acme's silica gel G
containing 13% calcium sulfate as binder and various
combinations of ethyl acetate, methylene chloride,
and hexane were used as eluent. Visualization of spots
was accomplished by exposure to iodine vapor or
anisaldehyde-H2SO4 or MeOH-H2SO4 spray followed
by heating. Acme's silica gel (100-200 mesh) was
used for column chromatography (approximately 1520 g per 1 g of the crude sample).
1640
INDIAN J. CHEM., SEC B, DECEMBER 2010
Extraction of kiritiquinone, 2. Dried and
powdered fruits of Maesa indica Roxb (200 g),
collected from FRLHT garden, was extracted
continuously in a Soxhlet extracter with ethyl acetate.
Concentration of the extract afforded a gummy solid.
The crude extract (3.9 g) was taken in methanol and
5% aq. NaOH and refluxed for 30 min. The reactionmixture was concentrated on a rotavapor and washed
with ether (3 × 10 mL). The aqueous layer was
acidified with HCl and extracted with ether (3 × 30
mL). The ether extract was concentrated and
chromatographed on a silica gel column. Elution with
hexane-ethyl acetate (3:1) afforded kiritiquinone 2
(500 mg), which was recrystallized from methanol as
orange plates, m.p. 129-30°C. UV λmax 294 nm (log ε
4.25); IR: 3328, 2920, 2850, 1637, 1614 cm-1; 1H
NMR: δ 7.60 (brs, 2H, 2 × OH), 5.37 and 5.33 (2 ×
dd, J = 10.8 and 4.7 Hz, 2H, CH=CH), 2.41 (t, J = 7.2
Hz, 2H, benzylic CH2), 2.15-1.95 (m, 4H, 2 × allylic
CH2), 1.94 (s, 3H, olefinic CH3), 1.60-1.15 (m, 30H),
0.90 (t, J = 6.8 Hz, 3H, terminal CH3); 13C NMR: δ
129.9 (CH) and 129.8 (CH) [CH=CH], 116.1 (C),
111.5 (C), 31.9 (CH2), 29.74 (CH2), 29.67 (3C, CH2),
29.63 (4C, CH2), 29.5 (2C, CH2), 29.4 (CH2), 29.1
(CH2), 28.0 (CH2), 27.2 (2C, CH2), 26.9 (CH2), 22.3
(CH2), 14.0 (CH3), 7.4 (CH3); MS: m/z 446 (M+), 418,
168, 167, 139 and 43; (Found: C, 75.37, H, 10.72.
C28H46O4 requires C, 75.29 and H, 10.38%).
Kiritiquinone dimethyl ether, 3. A solution of
kiritiquinone 2 (180 mg, 0.4 mmole) in anhydrous
ether (5 mL) and dry methanol (2 mL) was added
drop wise to a cold, magnetically stirred ethereal
solution of diazomethane [excess, prepared from Nnitroso-N-methylurea (4 g) and 60% aqueous KOH
(20 mL) and ether (20 mL)] and the reaction-mixture
was stirred at RT for 2 hr. Careful evaporation of the
excess diazomethane and solvent on a hot water bath
and purification of the residue over a silica gel
column using hexane-benzene (9:1) as eluent
furnished the dimethyl ether 3 (130 mg, 68%) as an
orange oil. UV: λmax 287.4 nm; IR (neat): 3004, 2925,
2854, 1651, 1605, 1462, 1448, 1376, 1318, 1272,
1135, 1008, 941, 760 cm-1; 1H NMR: δ 5.34 and 5.32
(2 × dd, J = 10.8 and 4.7 Hz, 2H, CH=CH), 4.01 (s,
3H) and 4.00 (s, 3H) [2 × OCH3], 2.38 (t, J = 7.8 Hz,
2H, benzylic CH2), 2.05-2.00 (m, 4H, 2 × allylic
CH2), 1.91 (s, 3H, olefinic CH3), 1.45-1.20 (m, 30H),
0.90 (t, J = 6.8 Hz, 3H, terminal CH3); 13C NMR: δ
184.3 (C) and 183.9 (C) [2 × C=O], 155.3 (2C, C, C-2
and 5), 130.6 (C, C-3), 129.9 (CH), and 129.8 (CH)
[CH=CH], 126.1 (C, C-6), 61.0 (CH3) and 60.9 (CH3)
[2 × OCH3], 31.9 (CH2), 29.8 (2C, CH2), 29.7 (5C,
CH2), 29.6 (3C, CH2), 29.4 (CH2), 29.3 (CH2), 28.9
(CH2), 27.2 (CH2), 26.9 (CH2), 23.0 (CH2), 22.3
(CH2), 14.1 (CH3), 8.4 (CH3); HRMS: m/z Found:
497.3614. C30H50O4Na (M+Na) requires 497.3607.
Kiritiquinone diacetate, 4. Acetic anhydride (0.04
mL, 0.44 mmole), pyridine (0.05 mL, 0.66 mmole)
and a catalytic amount of DMAP were added to a
solution of kiritiquinone 2 (100 mg, 0.22 mmole) in 5
mL methylene chloride, and the reaction-mixture was
magnetically stirred at RT for 4 hr. 3N HCl (15 mL)
was added to the reaction-mixture and extracted with
methylene chloride (3 × 20 mL). Combined extract
was washed with brine and dried (an. Na2SO4).
Evaporation of the solvent and purification of the
residue on a silica gel column using hexane-benzene
(5:1) as eluent afforded the diacetate (85 mg, 72%) as
oil. UV: λmax 286.4 nm; IR (neat): 3005, 2925, 2854,
1783 (OCOCH3), 1673 (C=O), 1635, 1370 1175,
1127, 1010, 950 cm-1; 1H NMR: δ 5.35 and 5.31 (2 ×
dd, J = 10.8 and 4.7 Hz, 2H, CH=CH), 2.39 (t, J = 7.6
Hz, 2H), 2.33 (s, 6H, 2 × CH3COO), 2.15-1.95 (m,
4H, 2 × allylic CH2), 1.94 (s, 3H, olefinic CH3), 1.401.20 (m, 32H), 0.90 (t, J = 6.8 Hz, 3H, terminal CH3);
13
C NMR: δ 179.9 (C) and 179.7 (C) [2 × C=O],
167.8 (C) and 167.5 (C) [2 × OC=O], 149.0 (C),
148.9 (C), 135.8 (C), 131.8 (C), 129.84 (CH) and
129.76 (CH) [CH=CH], 31.9 (CH2), 29.7-29.1 (12C,
CH2), 28.3 (CH2), 27.1 (CH2), 26.9 (CH2), 23.7 (CH2),
22.3 (CH2), 20.2 (CH3) and 20.1 (CH3) [2 ×
CH3COO], 13.9 (CH3), 9.17 (CH3); HRMS: m/z
Found: 553.3508. C32H50O6 requires: 553.3505.
3-(Heneicos-16-enyl)-6-methyl-1,2,4,5-benzenetetrol tetraacetate, 5. Acetic anhydride (5 mL) and
triethylamine (2 drops) were added to kiritiquinone 2
(100 mg, 0.22 mmole) followed by zinc dust (200
mg). The reaction-mixture was magnetically stirred at
RT for 15 hr. 3N HCl (20 mL) was added to the
reaction-mixture and extracted with methylene
chloride (3 × 8 mL). Evaporation of the solvent and
purification of the residue on a silica gel column using
hexane-ethyl acetate (5:1) as eluent furnished the
tetraacetate 5 (122 mg, 88%) as a white solid. m.p.
95-98°C; IR: 3010, 2921, 2850, 1760, 1469, 1434,
1368, 1219, 1204, 1186, 1122, 1098, 1060, 1016, 946,
871, 738, 721 cm-1; 1H NMR: δ 5.40-5.20 (m, 2H,
CH=CH), 2.36 (t, J = 7.8 Hz, 2H, benzylic CH2), 2.28
(s, 6H) and 2.27 (s, 6H) [4 × CH3COO], 2.10-2.00 (m,
4H, 2 × allylic CH2), 1.96 (s, 3H, aryl CH3),1.40-1.10
KURUVILLA et al.: NEW QUINONE FROM MAESA INDICA
(30H, m), 0.80 (distorted t, 3H); 13C NMR: δ 167.4
(2C, C) and 167.0 (2C, C) [4 × OC=O], 139.5 (2C,
C), 139.2 (2C, C), 129.8 (CH) and 129.7 (CH)
[CH=CH], 127.6 (C, C-3), 123.8 (C, C-6), 31.9 (CH2),
29.7-29.4 (10C, CH2), 29.3 (CH2), 29.2 (CH2), 28.8
(CH2), 27.2 (CH2), 26.9 (CH2), 25.4 (CH2), 22.3
(CH2), 20.2 (4C, CH3, 4 × CH3COO), 14.4 (CH3),
10.6 (CH3); HRMS: m/z Found: 639.3901.
C36H56O8Na (M+Na) requires 639.3873; (Anal:
Found: C, 69.61, H, 8.96; C36H56O8 requires C, 70.09
and H, 9.15%).
Ozonolysis of the tetraacetate, 5. Dry ozone in
oxygen gas was passed through a cold (–70ºC)
solution of the tetraacetate 5 (100 mg, 0.16 mmole)
and a catalytic amount of NaHCO3 in 1:5 MeOHCH2Cl2 (5 mL) for 2 min. Me2S (1 mL) was added to
the reaction-mixture and stirred for 2 hr at RT.
Evaporation of the solvent followed by purification of
the residue on a silica gel column using ethyl acetatehexane (1:4) as eluent afforded the aldehyde 7 (70
mg,78%) as an oil. IR (neat): 2924, 2850, 2727 (HC=O), 1763 (OC=O), 1715 (H-C=O), 1468, 1370,
1221, 1186, 1060, 1016, 947, 871 cm-1; 1H NMR: δ
9.73 (s, 1H, CHO), 2.50-2.25 (m, 4H), 2.27 (s, 6H)
and 2.26 (s, 6H) [4 × CH3COO], 1.95 (s, 3H, aryl
CH3), 1.60-1.00 (28H, m); 13C NMR: δ 202.1 (CH,
CHO), 167.4 (2C, C) and 166.9 (2 C, C) [4 × OC=O],
139.5 (2C, C), 139.2 (2C, C), 127.6 (C, C-3), 123.7
(C, C-6), 43.8 (CH2), 29.7-28.8 (12C, CH2), 25.4
(CH2), 22.0 (CH2), 20.2 (4C, CH3, 4 × CH3COO),
10.5 (CH3); HRMS: m/z Found: 557.2760.
C29H42O9Na (M-C2H4+Na) requires 557.2727.
Oxidation of kiritiquinone 2. Kiritiquinone 2 was
dissolved in 10% KOH (5 mL) and treated with
hydrogen peroxide (30%, 0.3 mL). After 3 hr, the
product was worked up by acidification followed by
extraction with ether. The ethereal extract was dried
and concentrated to afford a gummy solid 8, which
was taken in ether and added to ethereal
diazomethane. After 2 hr the excess diazomethane
and ether were carefully evaporated. Purification of
the residue by chromatography on silica gel using
1641
hexane-ethyl acetate (9:1) as eluent afforded the ester
9, which was identified as methyl 16-dehydrobehenate.
IR: 2925, 2854, 1745 cm-1; 1H NMR: δ 5.30 and 5.32
(2 × dd, J = 10.8 and 4.7 Hz, 2H, CH=CH), 3.66 (s,
3H, COOCH3), 2.28 (t, J = 7.5 Hz, 2H), 2.00-1.80 (m,
4H, 2 × allylic CH2), 1.70-1.40 (m, 2H), 1.30-1.10 (m,
28H), 0.84 (distorted t, J = 6.8 Hz, 3H, terminal CH3);
13
C NMR: δ 173.9 (OC=O), 129.94 and 129.87
(CH=CH), 51.3, 34.1, 32.1, 29.9, 29.8, 29.7, 29.6, 29.5,
29.4, 29.3, 27.3, 27.0, 25.1, 22.4, 14.1; HRMS: Found
375.3238; C23H44O2Na (M+Na) requires 375.3239.
Hydrogenation of kiritiquinone 2 to polygonaquinone 10. Catalytic hydrogenation of kiritiquinone
2 (60 mg, 0.13 mmole) with 5% Pd-C in ethyl acetate
on stirring at RT for 15 min afforded polygonaquinone 10 (36 mg, 60%) as a yellow solid. m.p.
130-31°C (lit. 133-34°C); λmax 295 nm (log ε 4.25);
IR: 1615 cm-1; 1H NMR: δ 2.60 (m, 2H), 1.95 (s, 3H),
1.27 (brs, 38H), 0.87 (distorted t, J = 6.8 Hz, 3H,
terminal CH3).
Acknowledgement
The authors thank Professor P. Kondaiah and his
research group for carrying out the preliminary
biological evaluation of kiritiquinone.
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