New glycosidic constituents of abutilon Pakistanicum

Article abstract of DOI:10.1002/hlca.201000075

Pakisides A and B (1 and 2, resp.), new catalpol-type iridoid glycosides, and a new glycoside, 3, of scutellarein have been isolated from the AcOEt-soluble fraction of the whole plant of Abutilon pakistanicum, along with buddlejoside and lapachol. The structures of new compounds were elucidated by spectroscopic techniques including ¹H-and ¹³C-NMR (DEPT), and 2D-NMR experiments. Copyright 2010 Verlag Helvetica Chimica Acta AG, Zuerich, Switzerland.

Full text of DOI:10.1002/hlca.201000075

Helvetica Chimica Acta – Vol. 93 (2010)
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New Glycosidic Constituents of Abutilon pakistanicum
by Bakhat Ali, Itrat Fatima, Abdul Malik*, and Zaheer Ahmed
International Center for Chemical and Biological Sciences, H.E.J. Research Institute of Chemistry,
University of Karachi, Karachi-75270, Pakistan
(phone: þ 92-21-4824926; e-mail: abdul.malik@iccs.edu)
Pakisides A and B (1 and 2, resp.), new catalpol-type iridoid glycosides, and a new glycoside, 3, of
scutellarein have been isolated from the AcOEt-soluble fraction of the whole plant of Abutilon
pakistanicum, along with buddlejoside and lapachol. The structures of new compounds were elucidated
by spectroscopic techniques including 1H-and 13C-NMR (DEPT), and 2D-NMR experiments.
Introduction. – The genus Abutilon (Malvaceae) is represented by 150 species
which are distributed mainly in subtropical regions of Asia and other parts of the world.
Generally, the leaves, roots, and stems of Abutilon species contain considerable
amounts of mucilage due to which these are used for the treatment of rheumatism, and
as demulcents and diuretics [1 – 3]. One of the species of this genus is Abutilon
pakistanicum which commonly grows in southern parts of Pakistan. Our previous
investigations on this species have resulted in the isolation and structure elucidation of
steroids [4], flavonoid glycosides [5][6], and a triterpene [7]. The ethnopharmaco-
logical and chemotaxonomic importance of the genus Abutilon prompted us to re-
investigate the chemical constituents of Abutilon pakistanicum. Here, we report the
isolation and structure elucidation of two new catalpol-type iridoid glycosides named as
pakisides A and B (1 and 2, resp.) along with a new glycoside, 3, of scutellarein from the
AcOEt-soluble fraction. Buddlejoside [8] and lapachol [9] have also been isolated for
the first time from this species (Fig. 1).
Fig. 1. Structures of pakisides A and B (1 and 2, resp.), and compound 3
Results and Discussion. – The MeOH extract of the whole plant was divided into
fractions soluble in hexane, CHCl3, AcOEt, BuOH, and H2O. Column chromatography
of the AcOEt-soluble fraction provided compounds 1 – 5 as described in Exper. Part.
ꢀ 2010 Verlag Helvetica Chimica Acta AG, Zꢁrich

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Pakiside A (1) was obtained as colorless gummy solid. The molecular formula was
determined as C24H30O13 by HR-FAB-MS (positive-ion mode; [M þ H]þ peak at m/z
527.1764 (calc. 527.1753)). The IR spectrum showed absorption bands of OH
(3400 cmꢀ1), ester C¼O (1695 cmꢀ1), C¼CꢀO (1635 cmꢀ1), and an aromatic ring
(1508 cmꢀ1). The UV spectrum was characteristic of catalpol-type iridoids with a
maximum at 278 nm [10]. In the EI-MS, the peaks at m/z 364 and 345 resulted from the
loss of a hexose moiety and dimethoxybenzoate group, respectively. The presence of
dimethoxybenzoyl moiety was also confirmed by a base peak at m/z 165. The molecular
formula of 1 was confirmed by broad-band and DEPT 13C-NMR spectra which showed
24 signals of two Me, two CH2, fifteen CH groups, and five quaternary C-atoms
(Table 1). The spectrum showed diagnostic signals for an iridoid moiety, a hexose unit,
and a dimethoxybenzoate group. The signals of the iridoid moiety were observed at
d(C) 141.0 and 101.9 due to one olefinic bond. It further displayed signals of four
CHꢀO C-atoms at d(C) 94.2, 80.0, 65.0, and 62.1, in addition to the resonance of an
CH2O C-atom at d(C) 62.5. The signals of the remaining CH C-atoms were at d(C) 41.9
and 38.0. The signals of a hexose unit were at d(C) 98.6, 76.5, 76.0, 73.0, 69.6, and 61.2.
The C-atoms of the dimethoxybenzoate residue resonated at d(C) 166.4, 153.3, 148.5,
124.0, 112.0, 110.2, 55.9, and 55.0, respectively.
Table 1. 1H- and 13C-NMR Data of 1 and 2. At 500 and 125 MHz, respectively, in C5D5N; d in ppm,
J in Hz.
1
2
d(H)
d(C) d(H)
d(C)
HꢀC(1)
HꢀC(3)
HꢀC(4)
HꢀC(5)
HꢀC(6)
HꢀC(7)
C(8)
4.87 (d, J ¼ 9.0)
6.16 (dd, J ¼ 1.5, 6.0)
4.83 (d, J ¼ 4.0, 6.0)
2.51 – 2.53 (m)
4.96 (d, J ¼ 7.0)
3.65 (br. s)
94.2 5.09 (d, J ¼ 9.5)
141.0 6.41 (dd, J ¼ 1.5, 6.0)
101.9 4.95 (dd, J ¼ 4.5, 6.0)
38.0 2.58 – 2.59 (m)
93.0
141.0
101.7
38.0
80.0
62.0
80.0 5.06 (d, J ¼ 7.5)
62.1 3.68 (br. s)
–
65.0
–
65.0
HꢀC(9)
CH2(10)
HꢀC(1’)
HꢀC(2’)
HꢀC(3’)
HꢀC(4’)
HꢀC(5’)
CH2(6’)
C(1’’)
2.52 – 2.55 (m)
3.88 (d, J ¼ 13.0), 5.02 (d, J ¼ 13.0)
4.64 (d, J ¼ 8.0)
3.17 – 3.19 (m)
3.21 – 3.23 (m)
3.28 – 3.30 (m)
3.13 – 3.15 (m)
3.55 (dd, J ¼ 5.0, 12.0)
–
41.9 2.56 – 2.57 (m)
41.8
62.6
97.8
76.4
70.2
73.4
77.4
61.3
121.3
111.7
148.4
153.2
111.1
123.4
166.4
55.5
62.5 3.73 (d, J ¼ 13.0), 5.01 (d, J ¼ 13.0)
98.6 4.59 (d, J ¼ 8.0)
73.0 3.21 – 3.02 (m)
76.0 3.03 – 3.05 (m)
69.6 3.13 – 3.15 (m)
76.5 3.16 – 3.18 (m)
61.2 3.88 (dd, J ¼ 5.1, 13.0)
121.7
–
HꢀC(2’’)
HꢀC(3’’)
C(4’’)
7.38 (d, J ¼ 2.0)
112.0 7.45 (d, J ¼ 2.0)
–
–
148.5
153.3
–
–
HꢀC(5’’)
HꢀC(6’’)
C¼O
6.75 (d, J ¼ 8.5)
7.61 (dd, J ¼ 2.0, 8.5)
–
110.2 7.08 (d, J ¼ 8.5)
124.0 7.62 (dd, J ¼ 2.0, 8.5)
166.4
–
MeOꢀC(2’’) 3.77 (s)
MeOꢀC(3’’) 3.76 (s)
55.9 3.81 (s)
55.0 3.83 (s)
55.7
58.1
MeOꢀC(2’)
–
–
3.30 (s)

Helvetica Chimica Acta – Vol. 93 (2010)
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1
The H-NMR spectrum (Table 1) exhibited the signals of vicinal olefinic H-atoms
of the iridoid moiety at d(H) 6.16 (dd, J ¼ 1.5, 6.0, 1 H) and 4.83 (dd, J ¼ 4.0, 6.0, 1 H).
The CHꢀO H-atoms resonated at d(H) 4.96 (d, J ¼ 7.0, 1 H), 4.87 (br. d, J ¼ 9.0, 1 H),
3.65 (br. s, 1 H), and the CH2O H-atoms at d(H) 5.02 (d, J ¼ 13.0 Hz, 1 H) and 3.88 (d,
J ¼ 13.0, 1 H). The vicinal CH H-atom resonances appeared as multiplets at d(H) 2.59
and 2.51 – 2.53. The anomeric H-atom of the hexose unit resonated at d(H) 4.64 (d, J ¼
8.0 Hz, 1 H). The larger coupling constant confirmed b-glycosidic linkage. The
aromatic signals were due to a 3,4-dimethoxybenzoate moiety.
Hydrolysis in basic medium yielded 3,4-dimethoxybenzoic acid and an iridoid
glucoside, which could be identified as catalposide by comparison of physical and
spectral data with those reported in [11][12]. The downfield shift of the resonances of
C(10) and its attached H-atoms allowed us to assign the ester moiety to C(10) which
was subsequently confirmed by HMBC experiments showing 3J correlation of both the
CH2O H-atoms at C(10) with C¼O C-atom signal of the ester at d(C) 166.4. The
hydrolysis in acidic medium provided the free sugar, which could be identified as d-
glucose through sign of its optical rotation and comparison of retention times (tR) of its
Me3Si (TMS) ethers with tR value of a standard sample in gas chromatography. The
attachment of glucose was confirmed by 3J correlation of the anomeric H-atom signal at
d(H) 4.64 with that of C(1) at d(C) 94.2. The HMQC, HMBC (Fig. 2), and NOESY
(Fig. 2) correlations were in agreement with the assigned structure of pakiside A (1) as
10-O-(3’’,4’’-dimethoxybenzoyl)catalposide (Fig. 1).
Fig. 2. Key HMBC (H ! C) and NOESY (H $ H)
correlations of 1
Pakiside B (2) was obtained as colorless gummy solid with the molecular formula
C25H32O13 deduced from HR-FAB-MS (positive-ion mode; m/z 541.1916 ([M þ H]þ)).
The UV and IR spectra were similar to those of 1. The 1H- and 13C-NMR spectra were
also similar to those of 1 except the presence of additional signals due to a MeO group
(d(H) 3.30 and d(C) 58.1). The presence of an additional MeO group in the sugar
moiety was evident by a common [M ꢀ sugar]þ peak in EI-MS at m/z 364. It could be
assigned to C(2’) due to a downfield shift of C(2’) signal compared to 1 and also on the
3
basis of HMBC showing J correlation of MeO H-atom resonance at d(H) 3.01 with
that of C(2’) (d(C) 76.4). Irradiation of MeO H-atoms caused NOE on neighboring H-
atoms at C(1’) and C(3’), providing conclusive evidence of the presence of 2’-O-
methylglucose moiety. The rest of the HMBC and NOESY correlations were similar to
those of 1, allowing us to retain the same configuration. The structure of pakiside B (2)
could thus be assigned as 10-O-(3’’,4’’-dimethoxybenzoyl)-2’-O-methylcatalposide.

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Helvetica Chimica Acta – Vol. 93 (2010)
Compound 3 was obtained as a yellow gummy solid. It gave a violet coloration with
FeCl3, and a positive reaction with Molish and Shinoda reagents [13]. The molecular
formula was determined to be C29H24O12 by HR-FAB-MS (positive-ion mode) showing
the [M þ H]þ peak at m/z 565.1354. The UV spectrum showed maxima at 282 and
334 nm. On addition of AlCl3 and AlCl3/HCl, bathochromic shifts of 39 and 28 nm of
band 1 were observed, being characteristic of scutellarein [14]. The IR spectrum
showed bands of OH (3400 cmꢀ1), ester C¼O (1700 cmꢀ1), conjugated C¼O
1
(1660 cmꢀ1), and olefinic (1620 cmꢀ1) functionalities. The H- and 13C-NMR signals
(Table 2) displayed characteristics of a scutellarein moiety with an esterified sugar
residue. The anomeric H-atom signal was observed as a doublet at d(H) 6.29 (J ¼
7.2 Hz, 1 H) along with other CH and CH2 signals (Table 2). The presence of an
(E)-p-coumaroyl moiety was also evident (olefinic H-atom signals at d(H) 7.75 (d, J ¼
16.0, 1 H) and 6.41 (d, J ¼ 16.0, 1 H); and 7.44 (d, J ¼ 8.7, 2 H) and 7.12 (d, J ¼ 8.7, 2 H).
The 1H- and 13C-NMR signals of the sugar moiety characterized it as a-l-
arabinofuranoside [15]. This was confirmed by acid hydrolysis, which provided besides
scutellarein and (E)-p-coumaric acid, a glycone which was identified as l-arabinofur-
anose by gas chromatography. The ester moiety was deduced to be at C(5’’) from the
downfield shift of the CH2(5’’) resonance and confirmed by 3J correlations of CH2(5’’)
(d(H) 4.77) with C¼O C-atom of the ester moiety (d(C) 167.2). Thus compound 3 was
determined as scutellarein 4’-O-a-l-[5’’-O-(E)-p-coumaroyl]arabinofuranoside.
Table 2. 1H- and 13C-NMR Data of 3. At 500 and 125 MHz, respectively, in C5D5N; d in ppm, J in Hz.
d(H)
d(C)
d(H)
d(C)
C(2)
–
162.6
99.8
HꢀC(1’’)
HꢀC(2’’)
HꢀC(3’’)
HꢀC(4’’)
CH2(5’’)
C(1’’’)
HꢀC(2’’’)
HꢀC(3’’’)
C(4’’’)
HꢀC(5’’’)
HꢀC(6’’’)
HꢀC(7’’’)
HꢀC(8’’’)
C(9’’’)
6.19 (d, J ¼ 7.2)
3.82 – 3.91 (m)
3.81 – 3.83 (m)
4.33 – 4.35 (m)
4.77 (dd, J ¼ 5.4, 11.7)
–
7.44 (d, J ¼ 8.7)
7.12 (d, J ¼ 8.7)
–
7.12 (d, J ¼ 8.7)
7.44 (d, J ¼ 8.7)
7.75 (d, J ¼ 16.0)
6.41 (d, J ¼ 16.0)
–
103.9
75.9
71.2
78.3
64.1
126.1
130.6
116.7
161.3
116.7
130.6
145.1
114.8
167.2
–
HꢀC(3)
6.68 (s)
–
–
–
C(4)
178.6
153.2
130.0
157.0
94.5
157.7
103.0
121.8
131.8
116.0
157.2
116.0
131.8
C(5)
C(6)
C(7)
–
HꢀC(8)
6.67 (s)
–
–
–
8.37 (d, J ¼ 9.0)
7.22 (d, J ¼ 9.0)
–
C(9)
C(10)
C(1’)
HꢀC(2’)
HꢀC(3’)
C(4’)
HꢀC(5’)
7.22 (d, J ¼ 9.0)
HꢀC(6’)
8.37 (d, J ¼ 9.0)
HOꢀC(5)
13.16 (s)
Experimental Part
General. Column chromatography (CC): silica gel (SiO2; 250 – 400 mesh; E. Merck, D-Darmstadt).
TLC: SiO2 60 F254 plates (E. Merck, D-Darmstadt). Optical rotations: Jasco DIP-360 digital polarimeter.
UV Spectra: Hitachi UV-3200 spectrophotometer; lmax (log e) in nm. IR Spectra: Jasco 302-A
spectrophotometer; in KBr; ˜n in cmꢀ1. NMR Spectra: Bruker 500 MHz instrument; d in ppm rel. to Me4Si
as internal standard, J in Hz. EI-, and HR-FAB-MS: Jeol JMS-HX-110 and JMS-DA-500 mass
spectrometers with glycerol as matrix; in m/z (rel. %).

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Plant Material. The whole plant of Abutilon pakistanicum JAFRI and ALI (8 kg) was collected from
Karachi in June 2004 and identified by Prof. Surraiya Khatoon, Department of Botany, University of
Karachi. A voucher specimen was deposited with the Herbarium (KUH # 697) of the University of
Karachi.
Extraction and Isolation. The whole plant of A. pakistanicum was shade-dried, ground, and extracted
with MeOH (3 ꢁ 20 l) at r.t. The combined MeOH extract (350 g) was divided into hexane-, CHCl3-,
AcOEt-, BuOH-, and H2O-soluble fractions. The AcOEt-soluble fraction (35 g) was subjected to CC
eluting with mixtures of hexane/AcOEt in increasing polarity. Elution with hexane/AcOEt 7:3 provided
a major fraction (3 g), which was again chromatographed and eluted with mixtures of hexane/AcOEt to
obtain subfractions: A (hexane/AcOEt 6 :4), B (hexane/AcOEt 4 :6), C (hexane/AcOEt 2.5 :7.5), and D
(hexane/AcOEt 1:9). Fr. A provided a semi-pure compound, which, on subsequent prep. TLC (CHCl3/
MeOH 6 :4), yielded lapachol (10 mg). Fr. B was subjected to prep. TLC (CHCl3/MeOH 7:3) to yield
compound 3 (8 mg) as yellow gummy solid. Fr. C was further chromatographed and eluted with hexane/
AcOEt 2 :8 to obtain buddlejoside (8 mg) and pakiside A (1) (20 mg) from the top and tail fractions,
resp. Increasing the polarity with hexane/AcOEt 1:9 provided another semi-pure compound, which, on
subsequent prep. TLC (CHCl3/MeOH 8 :2), yielded pakiside B (2) (15 mg).
Pakiside A (¼10-O-(3’’,4’’-Dimethoxybenzoyl)catalposide ¼ [(1aS,1bS,2S,5aR,6S,6aS)-2-(b-d-Glu-
copyranosyloxy)-1b,5a,6,6a-tetrahydro-6-hydroxyoxireno[4,5]cyclopenta[1,2-c]pyran-1a(2H)-yl]methyl
3,4-Dimethoxybenzoate; 1). Colorless gummy solid. [a]2D5 ¼ ꢀ115.0 (c ¼ 0.02, MeOH). UV (MeOH): 278
(4.3). IR (KBr): 3400, 1675, 1635, 1040. 1H- and 13C-NMR: see Table 1. EI-MS: 364 (10), 345 (25), 181
(65), 165 (100). HR-FAB-MS (pos.): 527.1764 ([M þ H]þ, C24H31O1þ3 ; calc. 527.1765).
Pakiside B (¼10-O-(3’’,4’’-Dimethoxybenzoyl)-2’-O-methylcatalposide ¼ [(1aS,1bS,2S,5aR,6S,6aS)-
1b,5a,6,6a-Tetrahydro-6-hydroxy-2-[(2-O-methyl-b-d-glucopyranosyl)oxy]oxireno[4,5]cyclopenta[1,2-
c]pyran-1a(2H)-yl]methyl 3,4-Dimethoxybenzoate; 2). Colorless gummy solid. [a]2D5 ¼ ꢀ100.0 (c ¼ 0.03,
MeOH). UV (MeOH): 278 (4.5). IR (KBr): 3400, 1675, 1635, 1040. 1H- and 13C-NMR: see Table 1. EI-
MS: 364 (10.3), 194 (11), 184 (25), 181 (65), 165 (100). HR-FAB-MS (pos.): 541.1916 ([M þ H]þ,
C25H33Oþ13 ; calc. 541.1921).
Scutellarein-4’-O-a-l-[5’’-O-(E)-p-Coumaroyl]arabinofuranoside (¼ 5,6,7-Trihydroxy-2-[4-({5-O-
[(2E)-3-(4-hydroxyphenyl)-1-oxo-2-propen-1-yl]-a-l-arabinofuranosyl}oxy)phenyl]-4H-1-benzopyran-
4-one; 3). Yellow gummy solid. [a]2D5 ¼ ꢀ87.7 (c ¼ 0.04, MeOH). UV (MeOH): 282 (4.0), 334 (3.8). IR
(KBr): 3400, 1700, 1660, 1620. 1H- and 13C-NMR: see Table 2. EI-MS: 372 (12), 286 (21), 194 (15), 164
(100), 148 (20). HR-FAB-MS (pos.): 565.1354 ([M þ H]þ, C29H25O1þ2 ; calc. 565.1345).
Alkaline Hydrolysis of 1. A mixture of 1 (5 mg) and 0.5% NaOH (2 ml) was heated at 608 for 45 min.
The mixture was neutralized with 0.2% HCl and chromatographed on polyamide with CHCl3/MeOH.
Elution with CHCl3/MeOH 97:3 provided a pure compound which crystallized from EtOH (m.p. 178 –
1808) and could be identified as 3,4-dimethoxybenzoic acid by comparison of physical and spectral data
with those reported in [16]. Elution with CHCl3/MeOH 85 :15 furnished the iridoid glucoside which
melted at 1608, resolidified, and melted again at 209 – 2118 (dec.), [a]2D0 ¼ ꢀ173 (c ¼ 0.02, EtOH). It was
identified as catalposide by comparison of physical and spectral data with those reported in [17].
Acid Hydrolysis of 1. A soln. of 1 (4 mg) in MeOH (5 ml) containing 1n HCl (2 ml) was refluxed for
4 h, concentrated under reduced pressure, diluted with H2O, and extracted with AcOEt. The aq. phase
was concentrated to obtain the sugar moiety which was identified as d-glucose by the sign of its optical
rotation ([a]2D3 ¼ þ51.8 (c ¼ 0.02, MeOH)). It was further confirmed by comparing retention times of its
Me3Si (TMS) ethers (a-anomer, 3.7 min; b-anomer, 5.1 min) with tR of a standard sample in gas
chromatography (GC). Preparation of TMS ether and its subsequent GC was carried out according to
the protocol described in [18]. The aglycone was a mixture of products which could not be worked up due
to paucity of material.
Acid Hydrolysis of 3. A soln. of 3 (1 mg) was refluxed in 10% HCl for 40 min. The resulting aq.
mixture was extracted with AcOEt. The residue from the org. phase was subjected to prep. TLC (hexane/
AcOEt 3 :1) to obtain (E)-p-coumaric acid (crystalline solid; m.p. 210 – 2138) and scutellarein (yellow
leaflets; m.p. 347 – 3498).
The aq. phase was neutralized with Ag2CO3, filtered, and the solvent was removed under N2. The
residue was dissolved in pyridine (0.2 ml), and 0.1m l-cystein methyl ester hydrochloride in pyridine

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Helvetica Chimica Acta – Vol. 93 (2010)
(0.1 ml) was added. After heating for 2 h, 1-(trimethylsilyl)-1H-imidazole (0.1 ml) was added, and the
mixture was heated at 608 for 1 h. After drying the mixture, the residue was partitioned with hexane and
H2O (1 ml each). The org. phase was analyzed by GC according to the protocol described in [19] and l-
arabinofuranose was identified by comparison of tR (7.56 min; standard 7.57 min).
REFERENCES
[1] S. K. Bhattacharjee, ꢂ Hand Book of Medicinal Plantsꢃ, Pointer Publisher, Jaipur India, 2003, p. 30.
[2] L. M. Perry, J. Metzger, ꢂMedicinal Plants of East and South Asiaꢃ, The MIT Press, Cambridge
England, 1980, pp. 341, 347.
[3] A. Krishna, ꢂThe Wealth of Indiaꢃ, CSIR, New Delhi, 1972, Vol. 9, p. 435.
[4] M. Hussain, D. N. Zahra, S. M. S. Hussain, E. Ahmad, I. Ahmad, A. Malik, Z. Ahmed, Magn. Reson.
Chem. 2008, 46, 274.
[5] M. Hussain, D. N. Zahra, A. Malik, A. Ejaz, H. Siddiqui, M. I. Choudhary, Z. Ahmed, Heterocycles
2008, 75, 545.
[6] B. Ali, M. Imran, R. Hussain, Z. Ahmed, A. Malik, Magn. Reson. Chem. 2010, 48, 159.
[7] Z. Ahmed, S. N.-u-H. Kazmi, A. Malik, J. Nat. Prod. 1990, 53, 1342.
[8] I. Ahmad, N. Afza, I. Anis, A. Malik, I. Fatima, Azhar-ul-Haq, R. B. Tareen, Heterocycles 2004, 63,
1875.
[9] R. M. Khan, S. M. Mlungwana, Phytochemistry 1999, 50, 439.
:
[10] I. Calis¸, H. Kirmizibekmez, O. Sticher, J. Nat. Prod. 2001, 64, 60.
[11] J. M. Bobbitt, D. W. Spiggle, S. Mahboob, H. Schmid, W. V. Philipsborn, J. Org. Chem. 1966, 31, 500.
[12] J. M. Bobbitt, H. Schmid, T. B. Africa, J. Org. Chem. 1961, 26, 3090.
[13] J. Schinoda, J. Pharm. Soc. Jpn. 1928, 48, 214.
[14] B. Voirin, Phytochemistry 1983, 22, 2107.
[15] Y. Lu, L. Y. Foo, Food Chem. 1997, 59, 187.
[16] A. G. Pinkus, J. A. Kautz, P. Ahobila-Vajjula, J. Chem. Crystallogr. 2002, 32, 149.
[17] W. H. Lunn, D. W. Edward, J. T. Edward, Can. J. Chem. 1962, 40, 104.
[18] S. Hara, H. Okabe, K. Mihashi, Chem. Pharm. Bull. 1987, 35, 501.
[19] Y. W. Chin, J. Kim, Chem. Pharm. Bull. 2006, 54, 234.
Received February 23, 2010