Oligomeric hydrolysable tannins from Tibouchina multiflora

Article abstract of DOI:10.1016/S0031-9422(99)00329-5

Two hydrolysable tannins, nobotanin O and nobotanin P, were isolated from the leaf extract of Tibouchina multiflora (Melastomataceae) and their dimeric and tetrameric structures elucidated on the basis of spectral data and chemical correlations with nobotanin B and K, respectively. Thirteen known hydrolysable tannins including nobotanins A, B, C and J, which are oligomers characteristic of the Melastomataceae, were also isolated.

Full text of DOI:10.1016/S0031-9422(99)00329-5

Phytochemistry 52 (1999) 1661±1666
Oligomeric hydrolysable tannins from Tibouchina multi¯ora
Takashi Yoshidaa,*, Yoshiaki Amakuraa, Nami Yokuraa, Hideyuki Itoa,
Jose Hipolito Isazab, Stella Ramirezb, Diana P. Pelaezb, Sussane S. Rennerc
aFaculty of Pharmaceutical Sciences, Okayama University, Tsushima, Okayama, 700-8530, Japan
bFacultad de Tecnologia, Universidad Tecnologica de Pereira, A.A. 97 Pereira, Risaralda, Colombia
cMissouri Botanical Garden, Biology Department, University of Missouri-St Louis, 8001 Natural Bridge Rd, St Louis, 63121-4499, USA
Received 2 February 1999; received in revised form 1 April 1999
Abstract
Two hydrolysable tannins, nobotanin O and nobotanin P, were isolated from the leaf extract of Tibouchina multi¯ora
(Melastomataceae) and their dimeric and tetrameric structures elucidated on the basis of spectral data and chemical correlations
with nobotanin B and K, respectively. Thirteen known hydrolysable tannins including nobotanins A, B, C and J, which are
oligomers characteristic of the Melastomataceae, were also isolated. # 1999 Elsevier Science Ltd. All rights reserved.
Keywords: Tibouchina multi¯ora; Melastomataceae; Tannin; Ellagitannin oligomer; Nobotanin O; Nobotanin P
1. Introduction
2. Results and discussion
In a previous study on the polyphenolic constituents
of Melastomataceous plants, we reported the isolation
and structure elucidation of unique hydrolysable tan-
nin oligomers including nobotanins A-C and E-K,
from Tibouchina semidecandra (Yoshida, Haba et al.,
1991; Yoshida, Ohwashi et al., 1991), Heterocentron
roseum (Yoshida et al., 1995; Yoshida, Haba et al.,
1992), Medinilla magni®ca (Yoshida et al., 1986),
Melastoma malabathricum (Yoshida, Nakata et al.,
1992) and Bredia tuberculata (Yoshida, Arioka, Fujita,
Chen & Okuda, 1994). A chromatographic survey of
the tannins in this family revealed that Tibouchina mul-
ti¯ora is rich in tannins, particularly in oligomeric
hydrolysable tannins. This paper presents the structure
elucidation of two new oligomeric hydrolysable tannins
named nobotanins O (1) and P (7) isolated from the
leaf extract of T. multi¯ora.
The aq. acetone homogenate of dried leaves was
concentrated and extracted successively with Et2O,
AcOEt and n-BuOH. Repeated chromatography of the
n-BuOH extract over polystyrene and/or polyvinyl gel
a€orded nobotanins O (1) and P (7), together with
eight known compounds, stachyurin (Okuda, Yoshida,
Ashida, & Yazaki, 1983), casuarinin (Okuda et al.,
1983), medinillin B (Yoshida et al., 1986), nobotanins
A, B (2) (Yoshida, Haba et al., 1991), C (9) (Yoshida,
Ohwashi et al., 1991), G (Yoshida, Haba et al., 1992)
and J (Yoshida et al., 1995). Similar chromatographic
separation of the EtOAc and aq. extracts gave ®ve ad-
ditional known compounds, pedunculagin (Okuda et
al., 1983), casuarictin (Okuda et al., 1983), nobotanins
D (Yoshida, Haba et al., 1991), F (Yoshida, Haba et
al., 1991) and M (Yoshida, Nakata & Okuda, 1999) as
described in Section 3. The tannin composition of T.
multi¯ora was shown to be similar to that of T. semi-
decandra and H. roseum.
Nobotanin O (1), an o€-white amorphous powder,
has been suggested to be a dimeric hydrolysable tannin
based on its positive coloration with NaNO2±AcOH
reagent (Bate-Smith, 1972) and a retention volume
* Corresponding author. Tel.: +81-86-251-7936; fax: +81-86-251-
7936.
E-mail address: yoshida@pheasant.pharm.okayama-u.ac.jp (T.
Yoshida).
0031-9422/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved.
PII: S0031-9422(99)00329-5

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T. Yoshida et al. / Phytochemistry 52 (1999) 1661±1666
Table 1
1H NMR spectral data of the glucose moieties of 7, 9 and 10 [500 MHz, Me2CO-d6+D2O; J (Hz) in parentheses]
7
9
10
a-Anomer
b-Anomer
a-Anomer
b-Anomer
Glc-I
H-1
H-2
H-3
H-4
H-5
H-6
5.45 d (3.5)
5.07 d (8.5)
4.81 dd (8.5, 9.5)
5.1805.09a
5.47 t (9.5)
3.7803.73b
4.20 d (3, 12)
4.57 d (12)
5.46 d (3.5)
5.07 d (8)
4.80 dd (8, 9.5)
5.14
5.02 dd (3.5, 10)
5.58 t (10)
5.50 t (10)
5.02 dd (3.5, 9.5)
5.58 t (9.5)
5.50 t (9.5)
5.47 t (9.5)
3.80
4.37 br d (10)
4.13 dd (3, 13)
4.39 br d (13)
4.38 br d (9.5)
4.14 dd (3.5, 12)
4.38 br d (12)
4.20 dd (3.5, 12)
4.59 br d (12)
Glc-II
H-1'
H-2'
H-3'
H-4'
H-5'
H-6'
5.97 d (8.5)
5.1805.09a
5.81 t (9.5)
5.1805.09a
5.98 d (8.5)
5.1805.09a
5.84 t (10)
5.1805.09a
5.98 d (8.5)
5.16 dd (8.5, 9.5)
5.80 t (9.5)
5.99 d (8.5)
5.15 dd (8.5, 9.5)
5.84 t (9.5)
5.18 t (10)
5.16 t (10)
4.57 m
5.1805.09a,c
4.58 m
5.12e
3.78e
3.7803.73b
Glc-III
H-10
H-20
H-30
H-40
H-50
H-60
6.13 d (8.5)
5.31 br t (10)
6.14 d (8.5)
5.1805.09a
6.10 d (8)
5.30 dd (8, 9.5)
6.14 d (8)
5.17 dd (8, 9.5)
5.31 t (10)
5.32 t (9.5)
5.68 t (9.5)
3.37 br d (9.5)
4.87 br d (13)
3.79 m
5.72 t (10)
3.4003.30e
4.88 br d (12.5)
3.7803.73b
Glc-IV
H-11
H-21
H-31
H-41
H-51
H-61
6.05 d (8.5)
5.1805.09a
5.34 t (10)
6.18 d (8.5)
5.16 dd (8.5, 10)
5.41 t (10)
5.13 t (10)
5.1805.09a
4.36 dd (6.5, 10)
5.25 dd (6.5, 13)c
3.76 br d (13)
4.47 dd (6.5, 10)
5.31 dd (6.5, 13)
3.85 d (13)
c
e
a,b Overlapped with each other; these values may be interchanged; doverlapped with HOD; coupling constants are not clear because of overlap-
ping with other signals.
similar to that of other dimers in normal phase HPLC.
The FABMS spectrum showed the [M+H]+ and
[M+Na]+ ion peaks at m/z 1571 and 1593, respect-
ively, corresponding to the molecular formula
C68H50O44. The 1H NMR spectrum of 1 exhibited
three 2H-singlets (d 7.26, 7.07 and 6.94) due to three
galloyl units and ®ve 1H-singlets (d 7.12, 6.71, 6.47,
6.46 and 6.09) ascribable to a hexahydroxydiphenoyl
(HHDP) and a valoneoyl group. The presence of these
units in 1 was con®rmed by methylation and sub-
sequent methanolysis yielding methyl tri-O-methylgal-
late (4), dimethyl hexamethoxydiphenate (5) and
trimethyl octa-O-methylvaloneate (6). The atropi-
somerism of the chiral HHDP and valoneoyl groups in
1 was shown to be in the (S )-series by the strong posi-
tive Cotton e€ect at 239 nm and the negative Cotton
e€ect at 264 nm in the CD spectrum (Okuda et al.,
anose. The spectrum also showed a double-doublet at
d 3.47 that is characteristic of the H-5 of glucose-II in
nobotanin B (2) and its analogues (Yoshida, Haba et
al., 1992). Actually, the aliphatic proton signals of 1
were very similar to those of 2 except for remarkable
up®eld shifts of the H-4 and H-6 signals of the glucose
core-I [d 5.41 (H-4) in 2 4 d 3.82 in 1; d 5.33 (H-6) in
2 4 d 3.76 in 1]. These spectral features indicate that
the hydroxyl groups at C-4 and C-6 in the glucose
core-I are unacylated as depicted in formula 1.
Structure 1 proposed for nobotanin O was con®rmed
by partial hydrolysis of 2 with hot water producing
two compounds, one of which was identical with
nobotanin O. The other compound was assigned as 3
on the basis of the 1H NMR spectral analysis and
identi®ed with nobotanin G (Yoshida, Haba et al.,
1992). Based on these data, the structure of nobotanin
O was determined to be 1.
1
1982). The sugar proton signals assigned by the H-1H
COSY technique were characteristic of a C1 glucopyr-
Nobotanin P (7), a light brown amorphous powder,

T. Yoshida et al. / Phytochemistry 52 (1999) 1661±1666
1663
had an ion peak at m/z 3591 [M+H]+ in the ESIMS,
and gave a large retention volume on normal-phase
HPLC, similar to that of nobotanin K (8) (Yoshida et
al., 1995) and other tetramers. Methylation of 7 fol-
lowed by methanolysis yielded 4, 5 and 6 as in the
case of 1. The CD spectrum of 7 showed a positive
Cotton e€ect at 228 and 239 nm with large amplitudes,
indicating the S-con®guration for each of biphenyl
moieties of the HHDP and valoneoyl groups in the
that of 9 except for the presence of extra signals due
to an aromatic 1H-singlet and a methoxyl group. This
compound was also obtained by mild methanolysis of
7 in MeOH-bu€er solution. Consequently, the struc-
ture of nobotanin P was established as 7, and is the
second example of a tetrameric ellagitannin found in
the Melastomataceae.
3. Experimental
1
molecule. Although the H NMR spectrum of 7 was
complicated owing to the formation of a mixture of a-
and b-anomers, the presence of four galloyl, three
HHDP and three valoneoyl groups was indicated by
four 2H-singlets and ®fteen 1H-singlets appearing as
duplicated signals in the aromatic region. The tetra-
meric nature of 7 was clearly indicated by three pairs
of acylated anomeric proton signals at d 6.13, 6.14
(each d, J = 8.5 Hz, 1H), 6.05 (d, J = 8.5 Hz, 1H)
and 5.98, 5.97 (each d, J = 8.5 Hz, 1H), and the
fourth pair of signals due to an unacylated anomeric
proton at d 5.45 (d, J = 3.5 Hz) and 5.07 (d,
J = 8.5 Hz). As seen in Table 1, the signals of three
sugar moieties (glucose-I, II and III) are virtually iden-
tical with those of nobotanin C (9), and those of the
fourth sugar residue (glucose-IV) are similar to those
of casuarictin (10). An analogous similarity was also
observed upon comparing the 13C-NMR spectrum of 7
with those of 9 and 10 (Yoshida, Ohwashi et al.,
1991). Therefore, nobotanin P was a degalloylated
congener of nobotanin K (8), which was consistent
with the molecular ion species in ESIMS.
3.1. General
1H (500 MHz) and 13C NMR (126 MHz) spectra
were recorded in (CD3)2CO+D2O. FABMS were
recorded on a VG 70-SE mass spectrometer and
ESIMS with a Micromass AutoSpec OA-Tof mass
spectrometer [solvent was MeOH±H2O (1:1)+0.1%
AcONH4]. Optical rotations were obtained on a
JASCO DIP-1000 digital polarimeter and CD spectra
on
a
JASCO
J-720W
spectropolarimeter.
Chromatographic conditions were the same as
described in a previous paper (Yoshida et al., 1995).
3.2. Plant materials
The leaves of T. multi¯ora were collected in Pereira,
Colombia in December 1995 and identi®ed by one of
the authors (S. S. Renner). A voucher specimen is
deposited in the Missouri Botanical Garden.
3.3. Extraction and isolation
Although chemical conversion from 8 to 7 by the
selective degalloylation at C-1 of 8 with tannase was
not successful, these two were chemically correlated as
follows. Mild methanolysis of 8 gave the trimeric
methanolysate (11) (Yoshida et al., 1995), which when
treated with tannase provided the monodegalloyl de-
The dried leaves (200 g) of T. multi¯ora were hom-
ogenized in Me2CO±H2O (7:3) (1 L Â 3). The ®ltered
homogenate was concentrated and extracted with
Et2O, EtOAc and n-BuOH, successively. The n-BuOH
extract (3.3 g) was chromatographed over Toyopearl
HW-40 (®ne) (2.2 cm ID Â 40 cm) with MeOH±H2O
(5:5 4 6:4 4 7:3) 4 MeOH±H2O±Me2CO
1
rivative (12). The structure of 12 was based on its H
NMR spectrum which showed close resemblance with

1664
T. Yoshida et al. / Phytochemistry 52 (1999) 1661±1666
(7:2:1 4 6:2:2 4 5:3:2) 4 Me2CO±H2O (7:3) in a step-
wise gradient mode. The eluate with MeOH±H2O (6:4)
yielded stachyurin (2.4 mg) and casuarinin (52 mg).
The eluate with MeOH±H2O±Me2CO (8:1:1) gave
nobotanin A (22 mg) and nobotanin G (47 mg). The
eluate with MeOH±H2O±Me2CO (7:2:1) yielded nobo-
tanin B (2) (11 mg) and nobotanin C (9) (110 mg).
The eluates with MeOH±H2O±Me2CO (6:2:2) and
(5:3:2) yielded nobotanin J (42 mg) and nobotanin P
(7) (31 mg), respectively. The fractions showing similar
HPLC pattern in the eluate with MeOH±H2O (7:3)
were combined and further puri®ed by CC over MCI-
gel CHP-20P with aq. MeOH to a€ord medinillin B
(14 mg) and nobotanin O (1) (3.9 mg). The AcOEt
extract (1.0 g) was similarly fractionated by the
repeated CC over Toyopearl HW-40 (®ne) and MCI-
gel CHP-20P to yield nobotanins A (22 mg), B (2)
(36 mg), D (1.8 mg), F (5.6 mg), G (5.2 mg), casuari-
nin (18 mg) and casuarictin (16 mg). The aq. extract
(5.6 g) was subjected to CC over Dia-ion HP-20
(3.3 cm ID Â 35 cm) with aq. MeOH. The eluate
(1.0 g) with MeOH±H2O (4:6) was further puri®ed by
CC over Toyopearl HW-40 and MCI-gel CHP-20P
with aq. MeOH to give nobotanin C (9) (21 mg), G
(9.7 mg), M (9.1 mg), pedunculagin (35 mg), sta-
chyurin (21 mg) and casuarinin (4 mg). Known tannins
were identi®ed by direct comparison of their HPLC
and NMR spectra with those of authentic specimens.
3.4. Nobotanin O (1)
An o€-white amorphous powder. [a ]D+338 (MeOH;
c 1.0). FABMS m/z: 1571 [M+H]+, 1593 [M+Na]+.
ESIMS m/z: 1588 [M+NH4]+. UV lmax MeOH nm
(log E): 219 (5.03), 274 (4.69). CD (MeOH):
[y]228+3.7 Â 105, [y]239+2.7 Â 105, [y]264 1.1 Â 105,
1
[y]286+4.0 Â 104, [y]312+3.8 Â 104. H NMR: d 7.26,
7.07, 6.94 (each 2H, s, galloyl-H), 7.12, 6.71, 6.47,
6.46, 6.09 (each 1H, s, HHDP and valoneoyl-H), 6.25
(d, J = 8 Hz, H-1), 4.93 (dd, J = 8, 9.5 Hz, H-2), 5.52
(t, J = 9.5 Hz, H-3), 3.82 (t, J = 9.5, H-4), 4.02 (m,
H-5), 3.93 (d, J = 12.5 Hz, H-6), 3.76 (dd, J = 6,
12.5 Hz, H-6), 5.97 (d, J = 8.5 Hz, H-1'), 5.15 (d,
J = 8.5, 10 Hz, H-2'), 5.35 (t, J = 10 Hz, H-3'), 5.81
(t, J = 10 Hz, H-4'), 3.47 (br d, J = 10, H-5'), 4.86 (br
d, J = 13, H-6'), 3.90 (d, J = 13 Hz, H-6') (glucose
protons).

T. Yoshida et al. / Phytochemistry 52 (1999) 1661±1666
1665
3.5. Partial hydrolysis of nobotanin B (2)
3.8. Methanolysis of 7
An aq. soln (2 ml) of 2 (17 mg) was heated at 1008C
for 18 h. The reaction mixture was subjected to CC
over Toyopearl HW-40 (®ne) developing with 60% aq.
MeOH and 70% aq. MeOH. The eluate with the 60%
aq. MeOH gave the hydrolysate (2.9 mg) which was
identical with nobotanin O in all respects. The 70%
aq. MeOH eluate yielded 3 (nobotanin G; 0.5 mg)
(Yoshida, Haba et al., 1992: Yoshida, Nakata et al.,
1992).
A soln of 7 (15 mg) in MeOH (3 ml) containing
0.5 M acetate bu€er (0.3 ml, pH 4.6) (0.3 ml) was left
standing at 378C for 1 day. After removal of the sol-
vent, the reaction mixture was applied to a Sep-pak
cartridge (Waters), and eluted with H2O and aq.
MeOH (10% 4 20% 4 30% 4 40% 4 50%) to yield
pedunculagin (1.5 mg) and the trimeric methanolysate
(12) (8.7 mg).
3.8.1. Compound 12
An o€-white amorphous powder, [a]D+348 (MeOH;
c 1.0), UV lmax MeOH nm (log E ): 220 (5.34), 270
3.6. Methylation of 1 followed by methanolysis
1
(5.03), H NMR: d 7.27, 7.25 (each s, 2H), 7.15, 7.14
A mixture of 1 (0.5 mg), Me2SO4 (0.01 ml) and
K2CO3 (50 mg) in Me2CO (1.5 ml) was stirred over-
night at room temp. and then re¯uxed for 3 h. After
removal of the inorganic material by centrifugation,
the supernatant was evaporated to dryness in vacuo.
The reaction mixt. was then directly methanolyzed
with 1% NaOMe (0.1 ml) in MeOH (1 ml) at room
temp. for 6 h. After acidi®cation with a few drops of
HOAc, the solvent was removed in vacuo. The residue
was re-dissolved in MeOH and analysed by normal-
phase HPLC (n±hexane±AcOEt 9:1) which demon-
strated the production of 4, 5 and 6.
(each s, 2H) 7.09, 7.08 (each s, 2H), 6.95 (2H, s) (gal-
loyl-H), 7.10, 7.09 (each s, 1H), 7.09 (1H, s), 7.08, 7.07
(each s, 1H), 6.98, 6.97 (each s, 1H), 6.67, 6.63 (each s,
1H), 6.50, 6.48 (each s, 1H), 6.46 (1H, s), 6.45, 6.43
(each s, 1H), 6.40, 6.34 (each s, 1H), 6.23, 6.17 (each s,
1H), 6.09, 6.08 (each s, 1H) (HHDP and valoneoyl
groups), 3.63 (3H, s) [OMe], 5.45 [d, J = 3.5 Hz, H-1
(a)], 5.07 [d, J = 8 Hz, H-1 (b)], 5.02 [dd, J = 3.5,
9.5 Hz, H-2 (a)], 4.80 [dd, J = 8, 9.5 Hz, H-2 (b)], 5.58
[t, J = 9.5, H-3 (a)], 5.49 [t, J = 9.5 Hz, H-4 (a)], 5,47
[t, J = 9.5 Hz, H-4 (b)], 4.38 [m, H-5 (a)], 4.39 [br d,
J = 12 Hz, H-6 (a)], 4.57 [br d, J = 12 Hz, H-6 (b)],
4.13 [dd, J = 3, 12 Hz, H-6 (a)], 4.20 [dd, J = 3, 12 Hz,
H-6 (b)], 5.98 [d, J = 8.5 Hz, H-1' (a)], 5.99 [d,
J = 8.5 Hz, H-1' (b)], 5.79 [t, J = 10 Hz, H-3' (a)],
5.82 [t, J = 10 Hz, H-3' (b)], 4.56 [m, H-5' (a, b)], 6.12
[d,J = 8 Hz, H-10 (a)], 6.14 [d, J = 8 Hz, H-10 (b)],
5.32 [dd, J = 8, 10 Hz, H-20 (a)], 5.31 [t, J = 10 Hz,
H-30 (a, b)], 5.71 [t, J = 10 HZ, H-40 (a, b)], 3.39 [br
d, J = 10 Hz, H-50 (a, b)], 4.85 [br d, J = 13 Hz, H-60
(a, b)], 5.1705.10 [H-3 (b), H-2' (b), H-4' (b), H-6'
(a, b), H-21 (b), overlapped with each other],
3.8203.72 [H-5 (b), H-6' (a, b), H-60 (a, b), over-
lapped with each other].
3.7. Nobotanin P (7)
A
light brown amorphous powder. [a]D+368
(MeOH; c 1.1). FABMS m/z: 3591 [M+H]+, 3613
[M+Na]+. ESIMS m/z: 3591 [M+H]+. UV lmax
MeOH nm (log E): 220 (5.13), 271 (5.02). CD
(MeOH):
[y ]227+1.0 Â 106,
[y]240+6.7 Â 105,
[y]262 3.3 Â 105, [y]284+1.5 Â 105, [y ]312+6.0 Â104.
1H NMR: d 7.27, 7.26 (each s, 2H), 7.14 (2H, s), 7.09
(2H, s ), 6.98, 6.95 (each s, 2H) (galloyl-H), 7.17, 7.15
(each s, 1H), 7.08 (1H, s ), 6.96, 6.94 (each s, 1H),
6.68, 6.63 (each s, 1H), 6.64 (1H, s), 6.50 (1H, s),
6.48, 6.46 (each s, 1H), 6.43, 6.40 (each s, 1H), 6.41
(1H, s ), 6.35 (1H, s), 6.35, 6.34 (each s, 1H), 6.34 (1H,
s), 6.23, 6.17 (each s, 1H), 6.11, 6.10 (each s, 1H), 6.02
(1H, s) (HHDP and valoneoyl groups), glucose pro-
tons, see Table 1. 13C NMR: d 91.3 (C-1; a-anomer),
94.8 (C-1; b-anomer), 75.1 (C-2; a), 77.8 (C-2; b), 75.5
(C-3; a), 77.6 (C-3; b), 68.6 (C-4; a), 68.1 (C-4; b),
68.2 (C-5; a), 72.7 (C-5; b), 63.1 (C-6; a, b), 92.3 (C-1';
a, b), 76.5 (C-2'; a, b), 77.3 (C-3'; a, b), 69.6 (C-4'; a,
b), 73.7 (C-5'; a), 73.1 (C-5'; b), 63.5 (C-6'; a, b), 92.2
(C-10; a, b), 75.8 (C-20; a), 75.4 (C-20; b), 77.8 (C-30;
a, b), 66.6 (C-40; a, b), 73.8 (C-50; a, b), 63.5 (C-60; a,
b), 91.8 (C-11; a, b), 75.8 (C-21; a, b), 77.1 (C-31; a,
b), 69.0 (C-41; a, b), 73.4 (C-51; a, b), 63.0 (C-61; a,
b).
3.9. Enzymatic hydrolysis of 11
An aq. soln of 11 (0.6 mg/1 ml), which was obtained
by methanolysis of 8 (Yoshida et al., 1995), was incu-
bated at 378C with tannase prepared from Aspergillus
niger (Yoshida, Tanaka, Chen & Okuda, 1989), and
the progress of the reaction was monitored by HPLC.
The formation of 12 together with gallic acid was
observed accompanied by the disappearance of the
starting material, and the product (12) was identi®ed
by co-HPLC with the sample obtained from 7.
Acknowledgements
The authors thank the SC-NMR Laboratory of

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T. Yoshida et al. / Phytochemistry 52 (1999) 1661±1666
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