C-Glucosidic ellagitannin oligomers from Melaleuca squarrosa Donn ex Sm., Myrtaceae

DOI: 10.1016/j.phytochem.2007.07.002

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Phytochemistry p. 3070 - 3079 (2008)

Update date:2022-08-22

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Authors:

Yoshida, Takashi

Ito, Hideyuki

Yoshimura, Morio

Miyashita, Kyoko

Hatano, Tsutomu

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Article abstract of DOI:10.1016/j.phytochem.2007.07.002

C-Glucosidic ellagitannin dimers were classified as types A-C according to a putative biogenetic oligomerization mode. They were characterized by different positions of the C-C bond between the phenolic acyl unit in one monomer and the benzylic C-1 of the open-chain glucose core in the other monomer. In recent years, four C-glucosidic tannins, melasquanins A-D (18-21), have been found in the leaves of Melaleuca squarrosa Donn ex Sm. (Myrtaceae). These are characterized as a dimer (melasquanin A) of a dimerization mode (type D), and trimers (melasquanins B-D) based on spectroscopic analysis including various two-dimensional nuclear magnetic resonance (2D NMR) experiments. Melasquanins B (19) and D (21) are C-glucosidic tannin trimers with a structure containing, non-repeating condensation modes, which was hitherto unknown.

Full text of DOI:10.1016/j.phytochem.2007.07.002

Available online at www.sciencedirect.com

PHYTOCHEMISTRY

Phytochemistry 69 (2008) 3070–3079

www.elsevier.com/locate/phytochem

C-Glucosidic ellagitannin oligomers from

Melaleuca squarrosa Donn ex Sm., Myrtaceae

Takashi Yoshida , Hideyuki Ito , Morio Yoshimura ,

Kyoko Miyashita , Tsutomu Hatano

College of Pharmaceutical Sciences, Matsuyama University, Bunkyo-cho, Matsuyama 790-8578, Japan

Department of Pharmacognosy, Okayama University Graduate School of Medicine,

Dentistry and Pharmaceutical Sciences, Tsushima, Okayama 700-8530, Japan

Received 25 April 2007; received in revised form 11 June 2007

Available online 24 August 2007

Abstract

C-Glucosidic ellagitannin dimers were classiﬁed as types A–C according to a putative biogenetic oligomerization mode. They were

characterized by diﬀerent positions of the C–C bond between the phenolic acyl unit in one monomer and the benzylic C-1 of the

open-chain glucose core in the other monomer. In recent years, four C-glucosidic tannins, melasquanins A–D (18–21), have been found

in the leaves of Melaleuca squarrosa Donn ex Sm. (Myrtaceae). These are characterized as a dimer (melasquanin A) of a dimerization

mode (type D), and trimers (melasquanins B–D) based on spectroscopic analysis including various two-dimensional nuclear magnetic

resonance (2D NMR) experiments. Melasquanins B (19) and D (21) are C-glucosidic tannin trimers with a structure containing, non-

repeating condensation modes, which was hitherto unknown.

ꢀ

Keywords: Melaleuca squarrosa; Myrtaceae; C-Glucosidic ellagitannin; Complex tannin; C-Glucosidic tannin trimer; Melasquanin B; Melasquanin C;

Melasquanin D

. Introduction

et al., 1991), Melastomataceae (Yoshida et al., 1992),

Theaceae (Hatano et al., 1991), Lythraceae (Xu et al.,

1991a,b), Betulaceae (Yoshida et al., 1991a), Elaeagnaceae

(Yoshida et al., 1991b; Ito et al., 1999), Fagaceae (Mayer

et al., 1969,1971; Nonaka et al., 1985), and Casuarinaceae

(Okuda et al., 1983).

Vegetable tannins are divided into two large groups,

hydrolyzable and condensed tannins. The former is fur-

ther grouped into three sub-types; gallotannins, ellagitan-

nins, and C-glucosidic tannins with an open-chain

glucose core. Typical C-glucosidic tannins, castalagin (1)

and vescalagin (2), having a ﬂavogalloyl group were ﬁrst

characterized by Mayer et al. (1969,1971). Their analogs,

casuarinin (3) and stachyurin (4), having a hexahydroxydi-

phenoyl (HHDP) group instead of the ﬂavogalloyl unit,

were later found in Casuarina and Stachyurus species

C-Glucosidic tannins show a unique reactivity at the

anomeric center. For example, when castalagin (1) and cas-

uarinin (3) with an a-hydroxyl group at C-1 are treated

with boiling water, they are gradually isomerized to the

respective anomers, vescalagin (2) (Mayer et al., 1967)

and stachyurin (4) (Okuda et al., 1983). On the other hand,

when 2 and 4 are treated with MeOH in the presence of tri-

(

Okuda et al., 1980). This class of tannins was established

to be widely distributed in many plant families such as in

the Myrtaceae (Okuda et al., 1980), Combretaceae (Lin

ﬂuoroacetic acid at 37 C, they readily give corresponding

1-O-methylated derivatives with retention of conﬁguration

at C-1; 1 and 3 do not react under similar conditions

(Yoshida et al., 1991c). The solvolysis of 1-O-methylated

stachyurin in water is accompanied by retention of the

Corresponding author. Tel.: +81 89 926 7128; fax: +81 89 926 7162.

E-mail address: tyoshida@cc.matsuyama-u.ac.jp (T. Yoshida).

doi:10.1016/j.phytochem.2007.07.002

T. Yoshida et al. / Phytochemistry 69 (2008) 3070–3079

3071

conﬁguration at C-1 to give 4 (Yoshida et al., 1991c). These

results suggested that an a-site at this center suﬀers more

severe steric hindrance compared to a b-site, and a b-site

seems to be a convex site prone to nucleophilic attacks

on a benzylic cation (C-1). Reﬂecting this reactivity,

various condensates of the C-glucosidic tannin with other

phenolic compounds have been found in nature. Such

biogenetic condensates include ‘‘C-glucosidic tannin

oligomers’’ and ‘‘complextannins,’’ which are composed

of C-glucosidic ellagitannin and catechin or epicatechin,

e.g., stenophyllanins A (5) and B (6) (Nonaka et al., 1985).

Among more than 500 hydrolyzable tannins character-

ized to date, approximately 80 are C-glucosidic tannins

or their condensates. Interestingly, all of these naturally

occurring condensates have common structural features

which include b-oriented C–C bonds between C-1 and the

phenolic counterpart, and also all (S)-conﬁgurations at

chiral HHDP and/or ﬂavogalloyl units in the molecule.

Nonaka et al., 1991; Peng et al., 1991; Tanaka et al.,

1996) and in some species of the Elaeagnaceae (Yoshida

et al., 1991b; Ito et al., 1999), Melastomataceae (Yoshida

et al., 1992), and Combretaceae (Lin et al., 1991). In type

B, the anomeric center of a monomer participates in the

formation of a C–C bond with the O-5 galloyl group of

the other monomer through apparent intermolecular dehy-

dration as represented by casuglaunin A (9) (Shimokawa

et al., 1991) and elaeagnatin B (10) (Ito et al., 1999). This

type of dimer was found only in some elaeagnaceous plants

and Casuarina glauca. The third type of condensation, C,

leads to interesting dimers in which two moles of vescalagin

type (or stachyurin type) monomer are connected through

the A-ring of catechin. This type of tannin is quite rare in

nature and only two such tannins, annogeissinin (11) (Lin

et al., 1991) and casuglaunin B (12) (Shimokawa et al.,

1991; Ito et al., 1999) were isolated from Annogeissus

acuminata (Combretaceae) and Casuarina glauca (Casua-

rinaceae), respectively.

As for the C-glucosidic tannin oligomers reported to

date, only castaneanins [dimer (13)–pentamer (16)]

. Results and discussion

(Tanaka et al., 1996) from the heartwood of Japanese

.1. Structural diversity of C-glucosidic tannin dimers

chestnut are known. They are characterized by repeating

units derived from structures of castalagin (1) as a mono-

meric constituent in condensation mode A (Figs. 1–3).

In a recent phytochemical study, we found the third con-

gener of type C dimer, cowaniin (17), in the rosaceous plant

Cowania mexicana (Ito et al., 2007). Complex tannin dimer

17 was regarded as a biogenetical precursor of casuglaunin

B (12) as substantiated by chemical transformation from 17

to 12. We have also isolated 17 from Melaleuca squarrosa

Donn ex Sm. (Myrtaceae), an evergreen shrub indigenous

to southeastern Australia, which is rich in C-glucosidic tan-

nins including four new C-glucosidic ellagitannin oligomers

Since the ﬁrst discovery of C-glucosidic tannin dimers in

991, about 30 dimers have been found in various plants.

They can be classiﬁed into three types based on their bioge-

netic condensation modes. In type A, an anomeric carbon

of a C-glucosidic monomeric unit binds to the benzene

nucleus in an HHDP group at O-4/O-6 of the other C-glu-

cosidic monomer [e.g., roburin A (7) (Herve du Penhoat

et al., 1991) and alienanin B (8) (Nonaka et al., 1991; Yos-

hida et al., 1992)]. Dimers of this type have been found

mainly in the Fagaceae (Herve du Penhoat et al., 1991;

HO OHHO OH

CH2O

CH O

OH HO

CH O

: R=H, R'=OH

: R=OH, R'=H

HO OHHO OH

HO OH

HO OHHO OH

HO OH

CH2O

OCH3

: R=H, R'=OH

: R=OH, R'=H

Fig. 1. Structures of compounds 1–6.

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T. Yoshida et al. / Phytochemistry 69 (2008) 3070–3079

Type A

Type B

HO OHHO OH

CH2O

OH HO

HO OHHO OH

HO OH

CH2O

OH HO

HO OHHO OH

HO OH

HO OHHO OH

HO OH

HO OHHO OH

HO OH

HO OHHO OH

HO OH

CH2O

glucose-II

glucose-I

COOH

Type C

CH2

HO OHHO OH

HO OH

HO OHHO OH

CH2O

Fig. 2. Dimerization modes of C-glucosidic tannins (Types A–C) and their representative structures 7–12.

of diﬀerent types. Here we describe in detail the isolation

and characterization of the new tannins named melasqua-

nins A–D (18–21) along with known tannins from M.

squarrosa.

2.2. C-Glucosidic ellagitannin oligomers from M. squarrosa

A concentrated 70% aqueous acetone homogenate of

the dried leaves of M. squarrosa was partitioned with

T. Yoshida et al. / Phytochemistry 69 (2008) 3070–3079

3073

derived from the ESIMS m/z 1872 [M+NH ] , elemental

analysis, and nuclear magnetic resonance (NMR) spec-

HO OHHO OH

OHHO OH

troscopic data. The dimeric nature of 18 was indicated

CH2O

by the H NMR spectrum assigned by H– H COSY,

which exhibited two sets of sugar proton signals similar

to those of C-glucosidic ellagitannins, 3 and 4. Chemical

shifts and coupling patterns of two anomeric proton sig-

nals [d 4.65 (br d, J = 1.0 Hz, H-1 ) and 5.55 (d, J

= 4.0 Hz, H-1)] indicated the presence of a b-oriented

C–C bond at the anomeric center (C-1 ) and of the a-ori-

3: n=1

4: n=2

5: n=3

6: n=4

ented hydroxyl group at the other anomeric center (C-1),

as found in alienanin B (8). The H NMR spectrum also

displayed two 2H-singlets (d 7.04 and 7.15) due to two

galloyl groups and ﬁve 1H-singlets (d 6.45, 6.51, 6.55,

6.75, and 6.99), while the C NMR spectrum showed

CH2

ten ester carbonyl carbon resonances at d 164.9–169.9

along with eight signals characteristic of C-1 of the

HHDP group (d 104.8–117.0). These NMR spectroscopic

data suggested that 18 was a C-glucosidic dimer isomeric

to 8 and would be biogenetically derived from a new

HO OHHO OH

HO OH

O C

O O

condensation mode of 3 and 4 diﬀerent from type A.

Upon comparing the

C NMR resonances of the

glucose moieties between 18 and 8 (Table 1), the glucose-

II core signals were similar, whereas the C-3–C-6 glu-

cose-I core signals of 18 were considerably diﬀerent from

the corresponding signals of 8. In the HMBC spectrum

of 18, all glucose proton signals except for H-3, H-1,

CH2O

and H-1 showed three-bond correlations with the gal-

loyl-H and HHDP-H through ester carbonyl carbons as

illustrated in Fig. 4, indicating that the HHDP unit at

O-2/O-3 of the glucose-I was fully substituted. The (S)-

conﬁgurations at all chiral HHDP units in 18 were evi-

denced by a diagnostic Cotton eﬀect at 237 nm (Okuda

et al., 1982) in the circular dichroism (CD) spectrum,

Fig. 3. Structures of compounds 13–17.

Et O, EtOAc, and water-saturated n-BuOH to give the

respective extracts and the water-soluble portion. The n-

BuOH extract was fractionated by column chromatogra-

phy over Diaion HP-20 followed by repeated column chro-

matography over polystylene and/or polyvinyl gels to yield

cowaniin (17) (Ito et al., 2007) and melasquanin A (18),

along with casuarinin (3) (Okuda et al., 1983), stachyurin

Table 1

C NMR spectroscopic comparison for glucose moieties of 18–21 with

those of 4, 8, and 9 in acetone- d + D

Position

C-1

C-2

C-3

C-4

C-5

C-6

C-1

C-2

C-3

C-4

64.4

80.8

71.6

72.7

70.6

64.0

67.4

77.0

69.2

74.59

69.4

65.6

40.3

80.8

74.63

73.3

71.5

64.3

67.0

76.7

70.9

75.1

73.0

64.1

41.2

81.7

73.5

74.0

71.2

63.8

68.8

76.9

72.2

75.3

72.3

64.7

41.7

81.8

74.5

73.4

71.4

64.3

68.9

77.0

72.0

75.7

71.7

65.4

40.1

80.8

74.5

73.29

71.35

64.4

41.6

81.8

74.7

73.29

71.40

64.2

67.3

77.1

69.2

74.6

69.5

65.66

40.2

81.1

74.0

73.5

69.7

65.66

40.3

80.9

74.7

73.3

71.5

64.3

67.1

76.4

68.7

74.2

68.9

65.2

39.8

79.6

74.9

72.4

73.3

63.1

41.0

81.2

75.1

73.4

70.9

63.8

(

4) (Okuda et al., 1983), stenophyllanin A (5) (Nonaka

et al., 1985), alienanin B (8) (Nonaka et al., 1991; Yoshida

et al., 1992), casuglaunins A (9) (Shimokawa et al., 1991)

and B (12) (Shimokawa et al., 1991; Ito et al., 1999), stric-

tinin (Okuda et al., 1983), pedunculagin (Okuda et al.,

983), and pterocarinin A (Nonaka et al., 1989). The

water-soluble portion was similarly separated by column

chromatography to give melasquanins B (19), C (20), and

D (21) as well as 8, 9, 12, 17, and pterocarinin A. Acid

hydrolysis of the new tannins (18–21) yielded gallic acid

and ellagic acid as the identiﬁable products, indicating that

these tannins were ellagitannins possessing galloyl and

HHDP units.

C-5

C-6

C-1

C-2

C-3

C-4

C-5

C-6

.2.1. Structure of melasquanin A (18)

Melasquanin A (18) was obtained as a brownish pow-

Assignments for these compounds were revised from previously

reported data (Yoshida et al., 1992,1996) in this study.

der and assigned a molecular formula of C H O , as

54 51

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T. Yoshida et al. / Phytochemistry 69 (2008) 3070–3079

Type D

HO OHHO OH

CH2O

CO CO

CH2O

H C

glucose-III

O 1"

OH HO

HO OHHO OH

H C

glucose-I

6 O

OHHO OH

CO CO

^C7^O^O

H2C

O glucose-II

HO OHHO OH

5 OH

H2C

glucose-I

CO CO

H2C

glucose-II

HMBC

(H C)

HO OHHO OH

CH2O

CO 7

5 OH

HO OHHO OH

CH2O

glucose-I

glucose-II

glucose-III

O1'

O 1"

Fig. 4. Structures of compounds 18–21.

although its amplitude ([h] 21.8 · 10 ) was smaller than

Consequently, the structure of melasquanin A was rep-

resented by the formula 18, and this new type of C-gluco-

sidic tannin dimer was classiﬁed as type D.

that of alienanin B (8) ([h]₂₃₂27.7 · 10 ). This discrep-

ancy is discussed later.

T. Yoshida et al. / Phytochemistry 69 (2008) 3070–3079

3075

It should be noted that the M. squarrosa leaves contain

all types (A–D) (8, 9, 12, and 18) of C-glucosidic ellagitan-

nin dimers. These tannins, except for 12, have common fea-

tures that include the casuarinin part as a terminal unit as

well as a b-oriented C–C bond at C-1 of the extension unit.

HMQC spectra of 19 also established glucose carbon reso-

nances corresponding well to those of 18 and the glucose-II

part of 8 (Table 1). The linking mode of the monomeric

units was veriﬁed from the detailed HMBC experiment,

which showed long-range correlations between glucose

protons and acyl protons through ester carbonyl carbons

in a similar fashion to those found in 8 and 18, as shown

in Fig. 4. The (S)-conﬁguration of the HHDP units in 19

was indicated by a positive Cotton eﬀect at 235 nm ([h]

Upon comparing the H NMR spectroscopic data for the

glucose moiety of the casuarinin part in 8, 9, and 18, one

of the C-6 methylene proton signals in type A (8) appeared

at an unusual high ﬁeld around d 2.99, while the H-5 signal

in the type-D dimer (18) showed a remarkable shift upﬁeld

by about 1.5 ppm (d 3.79) compared to that of 3 (Table 2).

On the other hand, a type-B dimer (9) had glucose proton

signals comparable to those of 3. Therefore, the H-6 or H-5

signal of the terminal monomer possessing the anomeric

hydroxyl group in types-A, -B, and -D dimers was diagnos-

tic to distinguish the condensation mode of C-glucosidic

ellagitannins.

32.2 · 10 ) in the CD spectrum (Fig. 5), the intensity of

which was consistent with the presence of two more (S)-

HHDP groups than 18. Based on these spectroscopic data,

the structure 19 was deduced for melasquanin B.

2.2.3. Structure of melasquanins C (20) and D (21)

Melasquanins C (20) and D (21) showed pseudomolecu-

lar ion peaks [M+NH₄] at m/z 2790 in the positive

ESIMS, similarly to 19. These trimers were condensates

of the dimer, alienanin B (8), with an additional stachyurin

by type-A or -B condensation modes as indicated by the

.2.2. Structure of melasquanin B (19)

The trimeric nature of melasquanin B (19) was suggested

by an [M+NH ] ion peak at m/z 2790 in its ESIMS spec-

following ﬁndings. The H NMR spectra showed signals

trum, which is m/z 918 (corresponding to a monomeric

unit) larger than that of 18. In addition, a longer retention

time than 18 was observed in normal-phase HPLC (Okuda

et al., 1989). The H NMR spectrum showed three 2H-

singlets due to three galloyl groups and seven 1H-singlets

attributable to HHDP groups in the aromatic proton

region. The spectrum also exhibited three anomeric proton

signals characteristic of C-glucosidic tannin at d 5.57 (d,

J = 4.0 Hz, H-1), 4.71 (d, J = 1.0 Hz, H-1 ) and 4.61 (br

s, H-1’’). The proton resonances of each glucose core were

assigned starting from the anomeric proton resonances by

analysis of COSY and TOCSY experiments. The H-5 and

H-6 proton resonances of the glucose-I core in 19 were

observed at d 3.53 (br dd, J = 3.5, 10.5 Hz) and d 3.11 (d,

J = 13.0 Hz), which were comparable to the diagnostic

shifts for the type-D and type-A dimer, respectively. The

Fig. 5. CD spectra of compounds 18–21 and 8.

Table 2

6 2

H NMR spectroscopic data for the glucose moieties of 3, 8, 9, and 18 in acetone- d + D O

Position

H-1

H-2

H-3

H-4

H-5

H-6

5.60 (d, 5.0)

4.63 (dd, 2.5, 5.0)

5.42 (t, 2.5)

5.44 (dd, 2.5, 8.5)

5.31 (dd, 2.5, 8.5)

4.84 (dd, 2.5, 13.0)

5.62 (d, 4.8)

5.51 (d, 4.8)

5.55 (d, 4.0)

4.70 (t, 4.0)

4.61 (dd, 1.8, 4.8)

5.37 (t, 1.8)

5.28 (dd, 1.8, 9.0)

5.18 (dd, 1.8, 9.0)

4.03 (dd, 1.8, 12.6)

2.99 (d, 12.6)

4.75 (d, 1.2)

4.92 (br t, 1.8)

4.98 (br t, 1.8)

4.72 (dd, 1.8, 4.8)

5.46 (br t, 1.8)

5.45 (br dd, 1.8, 7.2)

5.39 (br dd, 2.4, 7.2)

5.00 (dd, 2.4, 13.2)

4.30 (d, 13.2)

4.81 (br s)

4.91 (br s)

5.22 (t, 1.8)

5.80 (dd, 1.8, 7.8)

5.35 (dd, 3.0, 7.8)

4.95 (dd, 3.0, 13.2)

4.03 (d, 13.2)

4.82 (dd, 1.0, 4.0)

5.05 (dd, 1.0, 10.5)

3.79 (dd, 3.5, 10.5)

4.60 (dd, 3.5, 13.5)

4.07 (d, 13.5)

4.65 (br d, 1.0)

4.84 (br t, 1.5)

4.97 (t, 1.5)

5.66 (dd, 1.5, 8.5)

5.35 (dd, 3.5, 8.5)

4.87 (dd, 3.5, 13.5)

4.03 (d, 13.5)

.04 (d, 13.0)

H-1

H-2

H-3

H-4

H-5

H-6

5.63 (dd, 1.8, 9.0)

5.27 (dd, 3.0, 9.0)

4.79 (dd, 3.0, 12.6)

.03 (d, 12.6)

00 MHz.

J values (Hz) are in parentheses.

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T. Yoshida et al. / Phytochemistry 69 (2008) 3070–3079

due to three galloyl groups at d 7.12 (4H) and 7.11 (2H)

and seven 1H-singlets for 20, and two 2H-singlets due to

two galloyl groups and nine 1H-singlets for 21. Complete

2.2.4. Concluding remarks

To the best of our knowledge, melasquanins B (19) and

D (21) are the ﬁrst examples of the C-glucosidic ellagitan-

nin trimers possessing a structure consisting of non-repeat-

ing units.

H and C NMR assignments for three glucose units in

each tannin were achieved by 2D NMR analysis (Table

). Among the glucose carbon signals of both compounds

in the C NMR spectra, those due to two glucose residues

showed a close similarity to those of alienanin B (8), imply-

ing that 20 and 21 were trimers composed of 8 and a mono-

meric unit. The terminal monomeric unit of 20 and 21 had

an a-hydroxyl group as indicated by a doublet (J = 4.8 Hz)

of H-1 at d 5.60 and 5.61, respectively. Melasquanin C (20)

displayed signals due to the C-6 methylene protons of each

glucose core at d 2.93 (d, J = 12.6 Hz)/4.03 (dd, J = 3.6,

3. Experimental

3.1. General

Optical rotations were recorded on a JASCO DIP-1000

polarimeter. Elemental analyses were recorded on a

Yanaco CHN recorder MT-5. UV spectra were obtained

on a HITACHI U-2000-10 spectrophotometer and CD

2.6 Hz), 2.96 (d, J = 13.2 Hz)/4.01 (dd, J = 3.6,

spectra on a JASCO J-820W spectrometer. H and

3.2 Hz), and 4.05 (d, J = 13.2 Hz)/4.78 (dd, J = 2.4,

NMR spectra were recorded on Varian VXR-500 (500-4

3.2 Hz) in the H NMR spectrum. Two signals at around

for H and 126 MHz for C) or Varian INOVA 600

d 2.9 were indicative of two type-A linking modes in the

molecule, suggesting that the third monomeric unit was

linked via the type-A mode to the alienanin B part in 20.

The assumed structure 20 was veriﬁed by HMBC, which

showed long-range correlations as illustrated in Fig. 4.

(600 MHz for H and 150 MHz for C) spectrometers with

chemical shifts given in d (ppm) values relative to those of

the solvent [acetone-d (d 2.04; d 29.8)] on a tetrameth-

6 H C

ylsilane scale. The standard pulse sequences that were pro-

grammed into the instrument (VXR-500) were used for

each two-dimensional measurement. The JCH value was

set at 6 Hz in the HMBC spectra. ESIMS spectra were

obtained on a Micromass Auto Spec OA-Tof mass spec-

In the H NMR spectrum of melasquanin D (21), the H-

proton signal characteristic of the type-A alienanin B part

was observed at d 3.04 (d, J = 13.2 Hz), while the other C-6

methylene protons appeared in the normal region. Taking

one less galloyl and two more 1H-singlets compared to

those of 20 into consideration, one of the galloyl groups

in 8 was thought to participate in a C–C bond formation

with the anomeric carbon of the third monomer. This sug-

gested it was a trimer produced by a combination of type-A

and type-B condensation of 3 and/or 4. In the HMBC spec-

trum of 21, the H-1’’ signal (d 4.81, br s) showed long-range

correlations with two galloyl carbons at d 146.1 and 120.7,

the latter of which also correlated with the galloyl proton

trometer (solvent: MeOH–H

NH OAc). Normal phase HPLC was conducted on a

O (1:1, v/v) containing 0.1%

YMC-Pack SIL A-003 (YMC Co., Ltd.) column

(4.6 i.d. · 250 mm) eluted with n-hexane/MeOH/tetrahy-

drofuran/HCO H (55:33:11:1) containing oxalic acid

(450 mg/1 L; ﬂow rate: 1.5 mL/min; 280 nm UV detection)

at room temperature. Reversed-phase HPLC was performed

on a YMC-Pack ODS-A A-302 (YMC Co., Ltd.) column

(4.6 i.d. · 150 mm) eluted with 10 mM H

PO /10 mM

KH PO /CH CN (44:44:12) [ﬂow rate: 1.0 mL/min; detec-

(

ring-H, H-6) signal at d 6.88. This galloyl group was

tion, 280 nm UV or diode array detector (DAD; HITACHI

L-7445), 200–600 nm] at 40 ꢁC. Column chromatography

was carried out on Diaion HP-20, MCI GEL CHP-20P

(Mitsubishi Kasei Co.), Toyopearl HW-40 (coarse grade;

Tosoh Co.), and Sephadex LH-20 (Pharmacia).

located on the C-5 of glucose-II by the correlation between

the galloyl proton and H-5 signals through an ester car-

bonyl carbon (d 167.5). Other long-range couplings, as

observed in Fig. 4, were consistent with the structure 21

for melasquanin D. The S-conﬁgurations at the biphenyl

moieties in both 20 and 21 were determined by strong posi-

tive Cotton eﬀects at 231 and 234 nm, respectively, in their

CD spectra (Fig. 5). The intensity of the Cotton eﬀect at ca.

3.2. Plant material

Leaves of M. squarrosa were supplied from the Herbal

Garden of POLA Chemical Industries, Inc. A voucher

specimen OKP-MY98005 is deposited at the Medicinal

Herbal Garden of the Faculty of Pharmaceutical Sciences,

Okayama University.

30 nm in ellagitannins was demonstrated to be additive

for the number of HHDP unit irrespective of its binding

position (Okuda et al., 1982). When the amplitude ([h]

.9 · 10 ) for one (S)-HHDP unit estimated from the CD

of the known dimer 8 is adopted, the Cotton eﬀects of 20

and 21 well correspond to those due to six (S)-HHDP

groups in the molecules. Smaller amplitudes of the corre-

sponding Cotton eﬀects in 18 and 19 can be explained by

a smaller twisted angle between the biphenyl rings at O-

3.3. Isolation and puriﬁcation of tannins

Dried leaves of M. squarrosa (1.4 kg) were homogenized

in H

was concentrated to 1 L and extracted with Et

(1 L · 3), EtOAc (1 L · 3), and n-BuOH (1 L · 3), succes-

sively, to furnish the Et O (53.7 g), EtOAc (35.4 g), n-

BuOH (82.9 g) extracts, and a water-soluble portion

O-acetone (3:7, v/v, 11 L). The ﬁltered homogenate

/O-3 forsed by intermolecular linkage, than that of 8, 20

and 21. A slight bathochromic shift (ca. 5 nm) of the Cot-

ton eﬀect in 18 compared with 8 (232 nm) may reﬂect such

reduced twisted angle (Fig. 5).

T. Yoshida et al. / Phytochemistry 69 (2008) 3070–3079

3077

(

135.8 g). Fractionations were achieved by monitoring nor-

mal- and/or reversed-phase HPLC. The n-BuOH extract

82.9 g) was subjected to Diaion HP-20 (6.5 i.d. · 70 cm)

chromatographed with H O ! aqueous MeOH (10% !

data (500 MHz, acetone-d + D O): d 6.45 (1H, s, H -3),

6 2 E

6.51, 6.55 (each 1H, s, H_J_,_G-3), 6.75 (1H, s, H -3), 6.99

(

(1H, s, H -3), 7.04 (2H, s, H -2,6), 7.15 (2H, s, H -2,6);

for sugar protons, see Table 2; C NMR spectroscopic

(

0% ! 30% ! 50% ! 100% MeOH)

H O–acetone

data (126 MHz, acetone-d + D O): d 110.0 (2C, C -2,6),

3:7, v/v). The H O–MeOH (1:4, v/v) eluate was further

110.5 (2C, C -2,6), 106.0 (C -3), 106.6 (C -3), 107.4 (C -

C G E J

applied to Toyopearl HW-40 (2.2 i.d. · 60 cm) with aqueous

3), 108.9 (C -3), 109.2 (C -3), 114.8, 115.1, 115.4, 115.48,

I D

MeOH (50% ! 60% ! 70% MeOH ! MeOH–H O–ace-

115.50, 115.8, 115.6 (2C), 116.3, 116.6, 117.0 (C_A_,_B_,_D_–_G_,_I_,_J-1,

C_A_,_B_,_F-3), 125.0, 125.9 (C_C_,_H-1), 120.4, 120.4, 120.7,

123.9, 126.2, 126.76, 126.84, 127.6 (C_A_,_B_,_D_—_G_,_I_,_J-2),

139.37, 139.39 (C_C_,_H-4), 134.2, 135.8, 136.0, 136.2, 136.4,

136.6, 137.3, 139.7 (C_A_,_B_,_D_–_G_,_I_,_J-5), 145.8, 146.1 (each 2C,

C_C_,_H-3,5), 143.5, 143.8, 143.9, 144.0, 144.36, 144.37,

144.6, 144.8, 145.0, 145.15, 145.19, 145.22, 145.7, 146.1,

146.2, 146.9 (C_A_,_B_,_D_–_G_,_I_,_J-4,6), 164.9 (C -7), 165.3 (C -7),

tone (7:2:1) ! H O–acetone (3:7)) and MCI GEL CHP-

0P (1.1 i.d. · 40 cm) columns, eluted with aqueous MeOH

(

10% ! 20% ! 30% ! 50% ! 100% MeOH) to give stric-

tinin (28.9 mg), pedunculagin (23.0 mg), pterocarinin A

(

120.4 mg), casuarinin (3) (482.6 mg), stachyurin (4)

35.3 mg), stenophyllanin A (5) (47.2 mg), and alienanin

B (8) (96.8 mg). The H O–MeOH (7:3, v/v) eluate was

puriﬁed by column chromatography over Toyopearl

166.0 (C -7), 166.5 (C -7), 168.3 (C -7), 169.0 (C -7),

H C I J

HW-40 (2.2 i.d. · 60 cm) with aqueous MeOH

169.1 (C -7), 169.4 (C -7), 169.6 (C -7), 169.9 (C -7);

G D E B

(

50% ! 60% ! 70%

MeOH ! MeOH–H O–acetone

for sugar carbons, see Table 1; ESIMS m/z: 1872

7:2:1) ! MeOH–H O–acetone

(7:1:2) ! H O–acetone

[M+NH ] ; Anal. Found: C, 45.4; H, 4.23. C H O

82 54 51

3:7)) and MCI GEL CHP-20P (1.1 i.d. · 50 cm) columns

17H O requires: C, 45.6; H, 4.07%.

eluted with aqueous MeOH (10% ! 20% ! 30% !

0% ! 100% MeOH) to yield strictinin (64.3 mg), 3

3.5. Melasquanin B (19)

(

394.7 mg), 5 (66.6 mg), 8 (121.7 mg), casuglaunins A (9)

18.8 mg) and B (12) (14.8 mg), cowaniin (17) (7.0 mg),

A brownish amorphous powder; ½aꢀ + 41.2 (c 1.0,

and melasquanin A (18) (13.9 mg). The water-soluble por-

tion (37.58 g) was subjected to column chromatography

MeOH); CD (MeOH) [h] (nm): +32.2 · 10 (232),

ꢁ8.2 · 10 (258), +9.3 · 10 (282); H NMR spectral data

over Diaion HP-20 CC (6.5 i.d. · 45 cm) with H O ! aque-

(500 MHz, acetone-d + D O): d 3.11 (1H, d, J = 13.0

ousMeOH(10% ! 20% ! 30% ! 50% ! 100%MeOH) !

Hz, H-6), 3.53 (1H, br dd, J = 3.5, 10.5 Hz, H-5), 3.83

(1H, dd, J = 3.5. 13.0 Hz, H-6), 4.02 (1H, br d, J

H O–acetone (3:7, v/v). The H O–MeOH (7:3, v/v) eluate

was further applied to Toyopearl HW-40 (2.2 i.d. · 65 cm)

with aqueous MeOH (70% MeOH ! MeOH ! MeOH–

H O–acetone (7:2:1) ! MeOH–H O–acetone (7:1:2) !

= 13.0 Hz, H-6’’), 4.03 (1H, br d, J = 13.0 Hz, H-6 ),

4.61 (1H, br s, H-1’’), 4.65 (1H, t, J = 4.0 Hz, H-2),

4.71 (1H, d, J = 1.0 Hz, H-1 ), 4.75 (1H, dd, J = 1.0,

H O–acetone (3:7)), MCI GEL CHP-20P (1.1 i.d. · 40 cm)

4.0 Hz, H-3), 4.77 (1H, br s, H-2’’), 4.77 (1H, br dd, J

with aqueous MeOH (20% ! 30% ! 40% ! 50% ! 100%

= 3.0, 13.0 Hz, H-6 ), 4.85 (1H, br dd, J = 3.0, 13.0 Hz,

MeOH) and Sephadex LH-20 (1.1 i.d. · 40 cm) with EtOH

H-6’’), 4.89 (1H, br d, J = 10.5 Hz, H-4), 4.90 (1H, br

and MeOH to give pterocarinin

(

(701.6 mg),

193.5 mg), 8 (747.3 mg), 9 (7.6 mg), and melasquanins C

20) (33.6 mg) and D (21) (27.0 mg). The eluate of the sepa-

t, J = 2.0 Hz, H-3’’), 4.91 (1H, br t, J = 1.0 Hz, H-2 ),

4.97 (1H, t, J = 1.0 Hz, H-3 ), 5.25 (1H, br dd, J = 3.0,

8.5 Hz, H-5’’), 5.27 (1H, br dd, J = 3.0, 8.5 Hz, H-5 ),

ration via MeOH–H O (1:1, v/v) (3.57 g) over Diaion HP-

5.57 (1H, d, J = 4.0 Hz, H-1), 5.60 (1H, dd, J = 1.0,

8.5 Hz, H-4), 5.63 (1H, dd, J = 2.0, 8.5 Hz, H-4’’), 6.47

(1H, s, H -3), 6.53 (1H, s, H -3), 6.538, 6.541 (each

0 was similarly subjected to CC over Toyopearl HW-40

(

2.2 i.d. · 45 cm) with aqueous MeOH (70% MeOH !

MeOH ! MeOH–H O–acetone (7:2:1) ! MeOH–H O–

1H, s, H_G_,_J-3), 6.73, 6.75 (each 1H, s, H_I_,_N-3), 6.89

(1H, s, H -3), 7.06 (2H, s, H -2, 6), 7.08, 7.14 (each

acetone (7:1:2) ! H O–acetone (3:7)) and MCI GEL

CHP-20P (1.1 i.d. · 40 cm) with aqueous MeOH (20% !

2H, s, H_H_,_M-2,6); C NMR spectroscopic data (126 MHz,

acetone-d + D O): d 110.0 (4C, C_H_,_M-2,6), 111.00 (2C,

0% ! 40% ! 50% ! 100% MeOH) to yield 8 (7.6 mg), 9

(

11.4 mg), casuglaunin B (12) (68.2 mg), 17 (17.2 mg), and

C -2,6), 106.1 (C -3), 106.3 (C -3), 107.2, 107.3 (C_G_,_J-3),

C L D

melasquanin B (19) (9.4 mg). The remainder (78.21 g) of the

portion was similarly separated and puriﬁed by a combina-

tion of column chromatographic steps over Diaion HP-20,

Toyopearl HW-40, and MCI GEL CHP-20P with aqueous

MeOH, to give 8 (265.8 mg), 12 (236.1 mg), and 19 (35.3 mg).

108.89 (3C, C_D_,_I_,_N-3), 114.0, 114.3, 114.8, 115.0, 115.3,

115.4 (2C), 115.6 (2C), 115.8 (2C), 116.1, 116.3, 116.9 (3C),

117.0 (C_A_,_B_,_D_–_G_,_I_–_L_,_N_,_O-1, C_A_,_B_,_E_,_F_,_K-3), 120.7 (2C), 121.6

(C_C_,_H_,_M-1), 120.4, 123.3, 124.8, 124.9, 125.0, 125.8, 125.9,

126.1, 126.2, 126.8, 126.8, 126.9 (C_A_,_B_,_D_–_G_,_I_–_L_,_N_,_O-2), 134.1,

34.3, 135.9, 136.0, 136.07, 136.13, 136.6, 136.7, 137.07,

137.13 (2C), 138.3 (C_A_,_B_,_D_–_G_,_I_—_L_,_N_,_O-5), 139.2, 139.27,

39.33 (C_C_,_H_,_M-4), 143.0, 143.3, 143.7 (2C), 143.8, 143.9,

144.27, 144.34 (3C), 144.5 (2C), 145.08 (2C), 145.17 (3C),

145.28, 145.34, 145.7, 145.9 (3C), 146.2 (C_A_,_B_,_D_–_G_,_I_–_L_,_N_,_O

4,6), 145.3, 145.8, 146.0 (each 2C, C_C_,_H_,_N-3,5), 164.8

.4. Melasquanin A (18)

A brownish amorphous powder; ½aꢀ + 39.1 (c 1.0,

MeOH); CD (MeOH) [h] (nm): +21.8 · 10 (237),

ꢁ

6.4 · 10 (260), +6.1 · 10 (283); H NMR spectroscopic

3078

T. Yoshida et al. / Phytochemistry 69 (2008) 3070–3079

(

C -7), 165.2 (C -7), 165.9 (2C, C

C -7), 168.09, 168.12 (C_I_,_N-7), 168.8 (C -7), 168.96 (C -7),

C E O

-7), 166.9 (C -7), 167.1

–9.8 · 0 (259), +10.1 · 10 (283); H NMR spectroscopic

data (600 MHz, acetone-d + D O): d 3.04 (1H, d, J

H,M

69.02 (C -7), 169.1 (C -7), 169.3 (C -7), 169.4 (C -7),

= 13.2 Hz, H-6), 4.02 (1H, dd, J = 4.2, 12.6 Hz, H-6),

4.07 (1H, br d, J = 12.6 Hz, H-6’’), 4.44 (1H, br s, H-6 ),

69.6 (C -7); for sugar carbons, see Table 1; ESIMS m/z:

790 [M+NH ] ; Anal. Found: C, 48.2; H, 3.97.

4.62 (1H, dd, J = 1.8, 4.8 Hz, H-2), 4.81 (1H, br s, H-1’’),

C₁₂₃H O Æ 17H O requires: C, 48.0; H, 3.70%.

4.87 (1H, br s, H-1 ), 4.90 (1H, dd, J = 3.0, 13.2 Hz, H-

’’), 4.95 (1H, br d, J = 11.4 Hz, H-6 ), 4.98 (1H, br s, H-

.6. Melasquanin C (20)

2 ), 5.06 (1H, br s, H-2’’), 5.14 (1H, br s, H-3 ), 5.20 (1H,

dd, J = 4.2, 9.0 Hz, H-5), 5.29 (1H, br s, H-3’’), 5.33 (1H,

br s, H-4), 5.35 (1H, m, H-5’’), 5.37 (1H, t, J = 1.8 Hz,

H-3), 5.41 (1H, br d, J = 7.2 Hz, H-5 ), 5.58 (1H, br s,

H-4 ), 5.61 (1H, d, J = 4.8 Hz, H-1), 5.86 (1H, br s, H-

A brownish amorphous powder; ½aꢀ + 54.6 (c 1.0,

MeOH); CD (MeOH) [h] (nm): +40.3 · 10 (231),

ꢁ

7.5 · 10 (257), +10.8 · 10 (282); H NMR spectro-

scopic data (600 MHz, acetone-d + D O): d 2.93 (1H, d,

4’’), 6.34, 6.54, 6.59, 6.71 (each 1H, br s, H_G_,_I_,_L_,_N-3), 6.42

(1H, s, H -3), 6.55 (1H, s, H -3), 6.69 (1H, s, H -3), 6.94

J = 12.6 Hz, H-6 ), 2.96 (1H, d, J = 13.2 Hz, H-6), 4.01

(

1H, dd, J = 3.6, 13.2 Hz, H-6), 4.03 (1H, dd, J = 3.6,

2.6 Hz, H-6 ), 4.05 (1H, d, J = 13.2 Hz, H-6’’), 4.60

(1H, br s, H -3), 6.88 (1H, br s, H -6), 7.13 (2H, s,

D H

H -2,6), 7.19 (2H, s, H -2,6); C NMR spectroscopic

C M

(

1H, dd, J = 1.8, 4.8 Hz, H-2), 4.70 (1H, d, J = 1.2 Hz,

data (150 MHz, acetone-d + D O): d 104.6 (C -3), 107.2

6 2 B

(C -3), 107.4 (C -3), 108.4 (C -3), 105.0, 107.2, 108.2

O J D

H-1 ), 4.75 (1H, d, J = 1.2 Hz, H-1’’), 4.78 (1H, dd, J

2.4, 13.2 Hz, H-6’’), 4.83 (1H, t, J = 1.2 Hz, H-2 ),

(2C), 109.7 (C_G_,_I_,_K_,_L_,_N-3), 109.6 (2C, C -2,6), 110.0

.89 (1H, dd, J = 1.2, 1.8 Hz, H-3 ), 4.91 (1H, dd, J

(2C, C -2,6), 110.3 (C -6), 112.8, 113.8, 114.7, 114.85,

1.2, 1.8 Hz, H-2’’), 4.99 (1H, t, J = 1.8 Hz, H-3’’), 5.11

114.93 (2C), 115.3 (2C), 115.7 (2C), 115.9, 116.5

(C_A_,_B_,_D_–_G_,_I_–_L_,_N_,_O_–1), 115.5 (C -3), 115.7 (C -3), 116.3

(

1H, dd, J = 3.6, 9.0 Hz, H-5 ), 5.15 (1H, dd, J = 3.6,

.0 Hz, H-5), 5.25 (1H, dd, J = 1.8, 9.0 Hz, H-4), 5.28

(C -3), 120.7 (C -2), 120.3, 123.4 (C -1), 120.0 (C -2),

A H C,M A

(

1H, dd, J = 2.4, 8.4 Hz, H-5’’), 5.35 (1H, t, J = 1.8 Hz,

122.4 (C -2), 125.9 (C -2), 121.4, 124.8 (2C), 124.9,

K E

125.9, 126.3, 126.4, 126.5, 127.1, 127.7 (C_B_,_D_,_F_,_G_,_I_,_J_,_L_,_N_,_O-2,

H-3), 5.50 (1H, dd, J = 1.8, 9.0 Hz, H-4 ), 5.60 (1H, d, J

4.8 Hz, H-1), 5.63 (1H, dd, J = 1.8, 8.4 Hz, H-4’’), 6.38

C -1), 133.9, 134.3, 134.5, 135.0, 135.5 (2C), 135.9, 136.2,

(

1H, s, H -3), 6.42 (1H, s, H -3), 6.46 (1H, s, H -3), 6.56

136.5 (2C), 137.0, 137.3, 137.8, 138.3, 138.7 (C_C_,_H_,_M-4,

C_A_,_B_,_D_–_G_,_I_–_L_,_N_,_O-5), 142.1 (C -4), 142.4 (C -4), 143.0 (C -

(

1H, s, H -3), 6.65 (1H, s, H -3), 6.71 (1H, s, H -3), 6.78

O I D

(

1H, s, H -3), 7.11 (2H, s, H -2,6), 7.12 (4H, s, H_C_,_M-

,6); C NMR spectroscopic data (150 MHz, acetone-

4), 143.7 (C -4), 146.1 (C -3), 142.9 (2C), 143.0, 143.2

E H

(2C), 143.7 (3C), 143.9 (2C), 144.5 (2C), 144.6 (2C), 144.9

d + D O): d 110.0 (2C, C -2,6), 110.3, 110.4 (each 2C,

(2C), 145.1 (4C), 145.7, 146.1, 146.4 (3C) (C -5, C_C_,_M-

C_C_,_M-2,6), 105.2 (C -3), 105.6 (C -3), 105.8 (C -3), 107.3

3,5, C_A_,_E_,_F_,_K-3, C_B_,_D_,_G_,_I_,_J_,_L_,_N_,_O-4,6), 163.8 (C -7), 165.1

(

C -3), 107.7 (C -3), 108.1 (C -3), 108.9 (C -3), 113.7,

(C -7), 165.4 (C -7), 165.5 (C -7), 167.0 (C -7), 167.5

13.8, 114.1, 114.4, 115.4, 115.45 (2C), 115.54, 115.8

(C -7), 167.7 (C -7), 168.1 (C -7), 168.3 (C -7), 168.5

H E D O

(

2C), 116.2, 116.3, 116.5, 116.6 (C_A_,_B_,_D_—_G_,_I_—_L_,_N_,_O-1, C_E_,_J

(C -7), 168.7 (C -7), 167.1, 168.2, 168.8, 169.0 (C_G_,_K_,_L_,_N-7);

J B

), 116.4 (2C, C_F_,_K-3), 117.2 (C -3), 120.2, 121.66, 121.71

for sugar carbons, see Table 1; ESIMS m/z: 2790

(

C_C_,_H_,_M-1), 120.7, 123.9, 124.1, 124.9, 125.0, 125.1, 126.1,

[M+NH ] ; Anal. Found: C, 46.5; H, 3.99. C H O

123 80 76

26.2, 126.78, 126.82, 126.9, 127.5 (C_A_,_B_,_D_–_G_,_I_–_L_,_N_,_O-3),

32.0, 134.3, 134.5, 134.9, 135.67, 135.73, 136.1, 136.7,

36.87, 136.90, 137.0, 138.6 (C_A_,_B_,_D_–_G_,_I_–_L_,_N_,_O-5), 138.9,

23H O requires: C, 46.3; H, 3.95%.

³⁹^.⁰^,¹³⁹^.³⁽^CC,H,M-4), 143.3 (C -4), 143.4 (C -4),

3.8. Acid hydrolysis of melasquains A–D (18–21)

43.67 (C -4), 144.3 (2C, C_E_,_J-4), 143.6, 143.7 (2C),

43.9, 144.0, 144.4, 144.5, 145.15, 145.22, 145.3, 145.35,

45.38, 145.46, 145.50, 145.58, 145.61, 145.7, 145.8, 146.2

A solution of each compound (1 mg) in 1 M HCl (1 mL)

was heated in boiling H O for 10 h. The reversed phase

(

^CB,D,G,I,L,N,O^-⁴^,^CA,B,D–G,I–L,N,O-6), 145.70, 145.71, 146.0

^e^a^c^h²^C^,^CC,H.M-3,5), 164.8 (C -7), 166.00 (C -7),

A M

66.02 (C -7), 166.17 (C -7), 166.22 (C -7), 166.3 (C -7),

F H K C

HPLC analysis of the reaction mixtures showed peaks

identical to those of gallic acid (2.54 min) and ellagic acid

(23.84 min).

68.1 (C -7), 168.2 (C -7), 168.3 (C -7), 168.4 (C -7),

68.6 (C -7), 168.9 (C -7), 169.1 (C -7), 169.3 (C -7),

69.4 (C -7); for sugar carbons, see Table 1; ESIMS m/z:

790 [M+NH ] ; Anal. Found: C, 46.5; H, 3.99.

Acknowledgments

C₁₂₃H O Æ 23H O requires: C, 46.3; H, 3.95%.

We thank Mr. Y. Kitada of the Central Research Lab-

oratory of POLA Chemical Industries, Inc., for generous

supply of plant material. The NMR experiments were per-

formed at the SC NMR Laboratory of Okayama

University.

.7. Melasquanin D (21)

Brownish amorphous powder; ½aꢀ + 58.4 (c 1.0,

MeOH); CD (MeOH) [h] (nm): +43.9 · 10 (234),

T. Yoshida et al. / Phytochemistry 69 (2008) 3070–3079

3079

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