New isoflavones from Ceiba pentandra

Article abstract of DOI:10.1016/S0031-9422(00)00035-2

Two new isoflavones, pentandrin (1) and pentandrin glucoside (2), were isolated from the stem barks of Ceiba pentandra along with β-sitosterol and its 3-O-β-D-glucopyranoside, which was isolated for the first time from this plant. The structures of these

Full text of DOI:10.1016/S0031-9422(00)00035-2

Phytochemistry 54 (2000) 107±110
www.elsevier.com/locate/phytochem
New iso¯avones from Ceiba pentandra
a
F.N. Ngounou , A.L. Meli , D. Lontsi , B.L. Sondengam , Atta-Ur-Rahman ,
a
a
a
b
b,
M. Iqbal Choudhary *, Shahid Malik , Farzana Akhtar
b
b
a
Department of Organic Chemistry, Faculty of Science, University of Yaounde 1, P.O. Box 812, Yaounde, Cameroon
International Center for Chemical Sciences, H.E.J. Research Institute of Chemistry, University of Karachi, Karachi 75270, Pakistan
b
Received 6 October 1999; received in revised form 28 December 1999
Abstract
Two new iso¯avones, pentandrin (1) and pentandrin glucoside (2), were isolated from the stem barks of Ceiba pentandra along
with b-sitosterol and its 3-O-b-D-glucopyranoside, which was isolated for the ®rst time from this plant. The structures of these
compounds were elucidated with the help of spectroscopic techniques, while the structure of 1 was unambiguously con®rmed by
single-crystal X-ray di€raction studies. 7 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Iso¯avones; Ceiba pentandra; Pentandrin; Pentandrin glucoside; X-ray di€raction
1. Introduction
2. Results and discussion
Compound 1, C H O , was isolated from the ethyl
16
18
7
acetate extract of the stem bark of C. pentandra, as
yellow solid crystals. The UV spectrum of 1 showed
absorptions at 325, 262, 236, 203 nm indicating the
presence of substituted aromatic rings and a, b unsatu-
rated ketone in the molecule (Agrawal, 1989). The IR
spectrum showed absorptions at 3404 (OH), 1658 (CO)
Ceiba pentandra L. Gaertn. is a tree upto 50 m high
which occurs in areas ranging from tropical America
to Asia through Africa (Aubreville and Leroy, 1975).
The plant is well reputed in the African traditional
medicine for the treatment of many illnesses, such as,
headache, dizziness, constipation, mental troubles and
fever. It is also used as diuretic (Busson et al., 1965;
Bouquet and Debray, 1974; Irvine, 1961). Previous
work on C. pentandra described the isolation of a
number of sesquiterpenoids (Rao et al., 1993). In our
systematic search for active metabolites from Camer-
oonian medicinal plants, we have investigated the stem
bark extract of this plant and isolated two new iso¯a-
vones: pentandrin (1) and pentadrin 5'-O-b-D-glucoside
�
1
and 1461 (C1C) cm
.
The H-NMR spectra [CDCI , 400 MHz] of 1
1
3
(Table 1) showed signals characteristic of the iso¯a-
vone moieties. Two 1H doublets at d 6.39 and 6.37
ꢀJ ˆ 2:3 Hz) represented the aromatic H-8 and H-6
6, 8
meta to each other. Two 1H doublets at d 6.72 and
6.68 ꢀJ2 , 6
0
0
ˆ 1:8 Hz) were assigned to meta coupled
aromatic H-6' and H-2'. A 1H singlet at d 7.86 was
assigned to H-2. Another 1H singlet appeared at d
1
2.8 was due to the hydrogen bonded C-5 hydroxyl
(
2), the structures of which were elucidated with the
proton. Three 3H singlets at d 3.91, 3.89 and 3.86 indi-
cated the presence of three methoxyl groups.
help of single crystal X-ray di€raction technique as
well as NMR spectroscopy.
13
The
C-NMR spectra [CDCI , 100 MHz, BB,
3
DEPT, (Table 1)] of 1 showed resonances for all 18
carbons with three methoxy, ®ve methine and 10 qua-
ternary carbons (Murthy and Rao, 1986). The oxygen-
*
Corresponding author. Fax: +92-21-496-3373.
E-mail address: hejric@digicom.net.pk (M.I. Choudhary).
0031-9422/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved.
PII: S0031-9422(00)00035-2

1
08
F.N. Ngounou et al. / Phytochemistry 54 (2000) 107±110
Table 1
1
13
3
H - and C-NMR for Compounds 1 (CDCl ) and 2 (DMSO)
Carbon number
1
2
1
13
1
13
Hꢀd† J (Hz)
Cꢀd†
Hꢀd† J (Hz)
Cꢀd†
2
3
4
5
6
7
8
9
7.86 (s)
±
153.2
123.7
180.6
162.7
98.3
165.6
92.5
157.8
106.2
126.6
108.6
152.3
135.8
149.4
105.7
±
8.43 (s)
±
155.1
122.3
180.0
161.7
98.3
±
±
±
6.37, (d, 2.3)
±
6.95, (d, 2.3)
±
6.39, (d, 2.3)
±
6.98, (d, 2.3)
165.3
92.4
±
±
157.4
105.3
125.8
110.1
152.7
138.5
150.6
107.7
101.0
77.1
1
1
2
3
4
5
6
1
2
3
4
5
6
0
'
±
±
±
6.68, (d, 1.8)
±
6.60, (d, 1.8)
'
'
'
'
±
±
±
±
±
6.72, (d, 1.8)
±
6.37, (d, 1.8)
'
0
0
0
0
0
0
±
4.91, (d, 7.5)
±
±
±
±
±
±
76.7
73.4
±
±
±
±
±
±
69.9
60.8
±
±
±
OCH
OCH
OCH
3
3
3
3.86 (s)
3.89 (s)
3.91 (s)
55.8
56.1
61.0
3.74 (s)
3.79 (s)
3.84 (s)
56.0
56.1
60.3
bearing carbons resonated at d 165.6 (C-7), 162.7 (C-
), 157.8 (C-9), 153.2 (C-2), 152.3 (C-3'), 149.4 (C-5')
and 135.8 (C-4'). The carbonyl carbon and the three
methoxy carbons appeared at d 180.6, 61.0, 56.1 and
(heteronuclear multiple bond connectivity) for 1 are
shown in Fig. 1.
5
+
The HREI MS of 1 showed the M at m/z 344.0845
corresponding to the molecular formula C H O
7
18
16
5
5.8, respectively.
Direct one-bond H= C connectivities of 1 were
(calcd. 344.0847) with 118 of unsaturation in the mol-
ecule, eight of which were accounted for by the two
benzene rings, one by the pyrane ring, one by the car-
bonyl group and one by the double bond in the pyrane
1
13
established by HMQC (hetronuclear multiple quantum
coherence) spectrum which showed that H-2 ꢀd 7.86)
was connected with C-2 ꢀd 153.2). Similarly, H-6 ꢀd
+
ring. The fragment at m/z 167.0294 [C H O + H]
8
6
4
6
9
.37) and H-8 ꢀd 6.39) showed connectivity with C-6 ꢀd
8.3) and C-8 ꢀd 92.5), respectively. H-6' ꢀd 6.72) and
resulted from the retro Diels Alder cleavage indicated
H-2' ꢀd 6.68) showed HMQC connectivity with d 105.7
(
hetronuclear interactions observed in HMBC spectrum
C-6') and 108.6 (C-2'), respectively. The long-range
Fig. 2. A computer generated ORTEP drawing of 1. The hydrogens
shown are at arbitrary positions and re®ned isotropically.
Fig. 1. Important HMBC interactions in Compound 1.

F.N. Ngounou et al. / Phytochemistry 54 (2000) 107±110
109
the presence of one hydroxyl and one methoxy substi-
tuent in ring A (Chibber and Sharma, 1979).
On the basis of above spectral data, the compound
On the basis of above spectral data, compound 2
was deduced to be the glycoside of 1.
1
was deduced as 5,5'-dihydroxy- 7,3',4'-trimethoxy
2.1. Acid hydrolysis of 2
iso¯avone. Subsequent single-crystal X-ray di€raction
analysis (Fig. 2) con®rmed structure 1 for this com-
pound. The molecule showed planarity throughout the
structure. The average C±C bond distance in the aro-
Compound 2 (5 mg) was dissolved in MeOH±dis-
tilled H O (1:1). Then, 5% HCl (5 ml) solution was
2
added in it and the solution was re¯uxed for 7 h at
608C. After cooling, MeOH was evaporated in vacuo.
The reaction mixture was extracted thrice with chloro-
form to remove the aglycone part of the molecule,
which was identi®ed as 1 on the basis of Co-TLC, EI
Ê
matic rings is 1.386 (2) A.
Compound (2), C H O , was isolated as a yellow-
24
26 12
ish amorphous solid. The UV spectrum of 2 showed
absorptions at 325, 262, 237 and 204 nm (Agrawal,
1
1
989). The IR spectrum showed absorptions at 3406
�
MS and H-NMR. The residue obtained after removal
of the acid was compared with standard sugars on
1
(
OH), 1657 (CO) and 1463 (C1C) cm
.
The H-NMR [DMSO, 300 MHz, (Table 1)] spec-
1
silica gel plates (E. Merck Art. No. 5554) using n-
(7:20:12:7:6).
trum of compound 2 was distinctly similar to 1, with
additional signals of a sugar moiety. The anomeric sig-
nal appeared as a doublet at d 4.91 ꢀJ100 , 2 00 ˆ 7:5 Hz),
while the other methine protons of the sugar moiety
appeared between d 3.19±5.35.
BuOH±EtOAc-iso-PrOH±HOAc±H O
2
The TLC was developed through multiple run. Spots
were visualized with aniline phthalate reagent and the
sugar was identi®ed to be D-glucose.
13
The C-NMR spectrum of 2 also showed similarity
with that of 1 except for the addition of six carbon sig-
nals of a sugar moiety which appeared at d 101.0,
3. Experimental
7
7.1, 76.7, 73.4, 69.9 and 60.8, assigned to C-10, C-20,
Vacuum liquid chromatography (n-hexane:ethyl
acetate and ethyl acetate:methanol) was performed
using silica gel (type 60, Merck). Thin layer chroma-
tography was carried out using Merck precoated silica
gel sheets (0.25 mm, 60 F254). Column chromatog-
raphy was performed using silica gel (230±400 mesh).
Ceric sulphate spray reagent and UV light (366 nm)
were used for the detection of the compounds. UV
spectra were recorded on a Hitachi UV 3200 spectro-
photometer. IR spectra were recorded on a JASCO
302-A spectrophotometers. Melting points were
measured on a Gallenkamp melting point apparatus
and were uncorrected. FAB MS measurements were
carried out on a JEOL-HX 110 mass spectrometer. EI
MS were recorded on a Varian MAT 311A mass spec-
C-30, C-40, C-50 and C-60, respectively. The substi-
tution of the sugar moiety at C-5' was inferred by the
important HMBC interactions between anomeric H-10
and C-5'. The presence of a hydrogen-bonded ±OH
signal at d 12.85 also indicated that there was only C-
5' position available for the attachment of sugar moi-
ety. The HMBC interactions are shown in Fig. 3.
+
The HREI MS of compound 2 showed the M at
m/z 506.1472 corresponding to the molecular formula
C H O (calcd. 506.1424) with 128 of unsaturation.
The M was further con®rmed by FAB MS [M +
+
1
2
4
26 12
+
]
at m/z 507.1472. The EI MS showed the highest
+
peak at m/z 344.0847 [M � 162] indicating the pre-
sence of a sugar moiety in the molecule, which was
1
13
1
further con®rmed by H- and C-NMR spectra. The
rest of the mass fragmentation of 2 was similar to
compound 1.
trometer. The H-NMR spectra were recorded on Bru-
ker AM 400 and 300 MHz NMR spectrometers, while
13
C-NMR spectra were recorded at 100 and 75 MHz
on the same instruments. Single crystal X-ray data
were collected on Bruker P di€ractometer (previously
4
Nicolet).
3.1. Crystal data and X-ray crystal structure
determination of pentandrin (1)
Crystals of 1 suitable for X-ray analysis were
obtained by recrystallization from methanol.
3
.2. Crystal data
Light yellow prismatic crystals, dimensions 0.30 Â
3
+
0
.25 Â 0.30 mm , C H O ; M = 344.0847 amu;
18
16
7
Fig. 3. Important HMBC interactions in Compound 2.
Monoclinic, b ˆ 97:630 (2)8, a ˆ 7:8110 (10), b ˆ

1
10
F.N. Ngounou et al. / Phytochemistry 54 (2000) 107±110
3
Ê
Ê
7
:9510 (10), c ˆ 25:177 (2) A, V ˆ 1549:8 (3) A ; space
ethyl acetate extract (50 g) was puri®ed by vacuum
liquid chromatography on silica gel (250 g). Elution
with n-hexane±ethyl acetate (85:15) a€orded pentan-
�
3
group P2 , Z ˆ 4, Dx ˆ 1:476 Mg m , m ˆ 0:970
1
�
1
mm , Fꢀ000† ˆ 720; temperature = 293 (2) K.
�
4
drin (1) (15.1 mg, 1.46 Â 10 % yield) as yellow crys-
3.3. Data collection
tals in MeOH. Elution with n-hexane±ethyl acetate
(
�
4
1:4) furnished (2) (13.3 mg, 1.30 Â 10 % yield).
Bruker P di€ractometer (previously Nicolet), y-2y
scan type, graphite-monochromated CuKa radiations;
During this investigation, b-sitosterol and its 3-O-b-D-
glucopyranoside were also isolated.
Pentandrin (1), C H O ; yellow solid crystal; m.p.
4
3
621 re¯ections were measured ꢀ3:5 < y < 1358† of
18
16
7
which 2877 were unique. Three standard re¯ections
were measured after every 97 re¯ections, which showed
no signi®cant crystal decay. Data was corrected for
Lorentz and polarization e€ects.
159±1608; UV (MeOH) lmax: 325, 262, 236, 203 nm;
KBr
max
� 1
IR n
cm : 3404 (OH), 1658 (CO), 1461 (C1C)
�
1
cm . HREI MS: m/z: 344.0845 (calcd. 344.0847)
1
[C H O ], 167.0294 [C H O , calcd. 167.0340]; H-
16
18
7
8
7
4
1
3
NMR (400 MHz, CDCl ): d Table 1, C-NMR (100
3
3.4. Structure analysis and re®nement
MHz, CDCl ): d Table 1.
3
Pentandrin glucoside (2), C H O ; yellow amor-
26 12
24
The crystal structure was solved by direct methods
2
and re®ned by full-matrix least squares on F values
phous; m.p. 180±1828; UV (MeOH) lmax: 325, 262, 237
KBr
� 1
cm : 3406 (OH), 1657 (CO), 1463
max
204 nm; IR n
�
1
[
SHELXTL vr. 5.03]. Non-hydrogen atoms were
(C1C) cm . HREI MS: m/z: 506.1472 (calcd.
506.1424) [C H O ], 344.0845 (calcd. 344.0847)
re®ned with anisotropic temperature factors. Hydrogen
atoms were included at calculated positions and re®ned
in the riding mode. Final values of the residuals R and
wR2 [for 2877 re¯ections with I > 2sꢀI †Š were 0.0469
and 0.1345, respectively. The highest and lowest peaks
in ®nal di€erence Fourier map were 0.274 and � 0.255
2
4
26 12
1
[C H O ], 167.0294 [C H O , calcd. 167.0340]; H-
16
NMR (300 MHz, DMSO): d Table 1, C-NMR (75
MHz, DMSO): d Table 1.
18
7
8
7
4
13
�
3
.
Ê
eA
Table of atomic coordinates, bond lengths, bond
angles and list of structure factors have been deposited
at the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 IEZ, UK.
Acknowledgements
The travel of F.N.N. was supported by the Third
World Academy of Sciences (Italy). We are also thank-
ful to Dr. Paulette Bisseck for providing the plant ma-
terial. One of us (Shahid Malik) acknowledge the
3.5. Plant material
®nancial support of COMSATS, Islamabad.
The stem barks of Ceiba pentandra L. Gaertn. were
collected at Mvolye Hill, Yaounde zone, Central Pro-
vince of Cameroon, in May, 1998. A voucher specimen
References
(# HNC 43623) was deposited at the National Herbar-
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d'Ivoire. ORSTOM, Paris, p. 52.
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pieces, air-dried and pulverized. The resulting powder
10.3 kg) was macerated thrice at room temperature
with MeOH for three days. The MeOH extracts were
combined and concentrated to dryness under reduced
pressure to obtain a solid (750 g), which was succes-
sively fractionated with n-hexane, dichloromethane
and ethyl acetate. The ethyl acetate fraction showed
moderate antifungal activity against Trichophyton
schoenleinii, T. simii and Microsporum canis fungi. The
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Alimentaires de l'Ouest Africain, Etude Botanique et Chimique.
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(
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