Taccasterosides A-C, novel C28-sterol oligoglucosides from the rhizomes of Tacca chantrieri

Article abstract of DOI:10.1248/cpb.52.1396

Three novel C₂₈-sterol oligoglucosides, named taccasterosides A-C (1-3), were isolated from the rhizomes of Tacca chantrieri (Taccaceae). Their structures were determined by detailed spectroscopic analysis, including 2D NMR data, and a few chemical transformations.

Full text of DOI:10.1248/cpb.52.1396

1
396
Communications to the Editor
Chem. Pharm. Bull. 52(11) 1396—1398 (2004)
Vol. 52, No. 11
1
04.9, 104.6, 102.6, and 93.5, suggested that 1 is a C -sterol
28
Taccasterosides A—C, Novel C -Sterol
Oligoglucosides from the Rhizomes of
Tacca chantrieri
2
8
heptaglucoside.
The structure of 1a, except for the absolute configurations
of C-24 and C-25, was identified as 3b-hydroxyergost-5-en-
1
13
26-oic acid by analysis of its H-, C-, and 2D NMR
9)
Akihito YOKOSUKA, Yoshihiro MIMAKI,* and
Yutaka SASHIDA
spectra. To determine the absolute configurations of the
C-24 and C-25 chiral centers, as well as the other steroidal
skeleton, the following chemical transformations and spec-
troscopic analysis were carried out with 1a. Compound 1a
Laboratory of Medicinal Plant Science, Tokyo University of
Pharmacy and Life Science, School of Pharmacy; 1432–1
Horinouchi, Hachioji, Tokyo 192–0392, Japan.
was reduced with LiAlH to give ergost-5-ene-3b,26-diol
4
(1b), which was then converted to the diastereomeric pairs of
Received August 2, 2004; accepted August 30, 2004
the C-26-(R)-MTPA (1b-R) and C-26-(S)-MTPA (1b-S)
1
Three novel C -sterol oligoglucosides, named taccasterosides esters. In the H-NMR spectra of 1b-R and 1b-S, the H -26
2
8
2
A—C (1—3), were isolated from the rhizomes of Tacca chantri- methylene protons of 1b-R was observed as a d-like signal at
eri (Taccaceae). Their structures were determined by detailed
d 4.20 (Jꢁ6.3 Hz) whereas those of 1b-S had a dd pattern at
spectroscopic analysis, including 2D NMR data, and a few
chemical transformations.
d 4.30 (Jꢁ10.8, 6.6 Hz) and 4.09 (Jꢁ10.8, 7.2 Hz). Applica-
tion of these spectral data to the empirical rule reported by
10)
Key words Tacca chantrieri; Taccaceae; C -sterol oligoglucoside; Yasuhara et al. allowed us to assign the C-25 configuration
2
8
taccasteroside
as S. On the other hand, 1b was treated with p-TsCl to give
6-O-tosylate (1b-T) of 1b, which was then reduced with
2
Tacca chantrieri ANDRÉ (Taccaceae) is a perennial plant
that grows in southeastern China. Its rhizomes have been
used in Chinese folk medicine for the treatment of gastric
LiAlH , affording (24R)-ergost-5-en-3b-ol, that is, campe-
4
sterol. Thus the structure of 1a was determined to be
(
24R,25S)-3b-hydroxyergost-5-en-26-oic acid (Chart 1).
1)
ulcer, enteritis, and hepatitis. Previously, we reported the
isolation and structural characterization of diarylheptanoids,
diarylheptanoid glucosides, and steroidal glycosides such as
spirostan, furostan, pseudo-furostan, pregnane, and withano-
lide glycosides from the rhizomes of T. chantrieri, as well as
their cytotoxic activities against cultured tumor and normal
The exact structures of the sugar moieties and their link-
age positions to the aglycon were resolved by detailed analy-
1
sis of the 1D TOCSY and 2D NMR spectra. The H-NMR
subspectra of individual monosaccharide units were obtained
2—6)
cells.
Further phytochemical analysis of the MeOH
extract of T. chantrieri rhizomes resulted in the isolation of
three novel C -sterol oligoglucosides, named taccasterosides
2
8
A—C (1—3). This communication deals with the structural
determination of the new compounds in extensive spectro-
scopic studies, including 2D NMR data, and acid hydrolysis
followed by chromatographic and spectroscopic analyses and
further chemical transformations.
The MeOH extract (630 g) of T. chantrieri rhizomes
(7.3 kg, dry weight) was passed through a Diaion HP-20
column, and the MeOH eluate portion (115 g) was subjected
to column chromatography using silica gel and ODS silica
gel, as well as to preparative HPLC, to yield taccasterosides
A (1) (17 mg), B (2) (25 mg), and C (3) (13 mg).
7)
Taccasteroside A (1) was obtained as an amorphous
2
5
solid, [a] ꢀ10.0° (cꢁ0.10, MeOH), with a molecular
D
formula of C H O , which was deduced from ESI-TOF-
7
0
116 38
1
3
MS, C-NMR with DEPT spectra, and elemental analysis
data. The H-NMR spectrum showed three-proton singlet
1
signals at d 0.93 and 0.62, and three three-proton doublet
signals at d 1.23 (Jꢁ6.9 Hz), 0.97 (Jꢁ7.1 Hz), and 0.95
(Jꢁ6.7 Hz), which were recognized as typical steroid
methyls. Signals for seven anomeric protons at d 6.30
(d, Jꢁ8.4 Hz), 5.23 (d, Jꢁ7.7 Hz), 5.17 (d, Jꢁ7.7 Hz), 5.16
(
4
d, Jꢁ8.1 Hz), 5.13 (d, Jꢁ8.0 Hz), 5.07 (d, Jꢁ7.7 Hz), and
1
3
.93 (d, Jꢁ7.7 Hz) were also observed. The C-NMR
ꢀ
1
(
d 175.2) and IR (1739 cm ) spectra suggested the presence
of an ester carbonyl group. Acid hydrolysis of 1 with 1 M
HCl in dioxane–H O (1 : 1) gave a C -sterol as the aglycon
2
28
8)
(
1a, C H O ) and D-glucose. The above data, along with
28 46 3
seven anomeric carbon signals at d 106.1, 105.0, 105.0,
∗
To whom correspondence should be addressed. e-mail: mimakiy@ps.toyaku.ac.jp
© 2004 Pharmaceutical Society of Japan

November 2004
1397
Chart 1
1
13
Table 1. H- and C-NMR Data for the Glycoside Moieties of 1 in C D N at 303 K
5
5
1
13
1
13
Position
H
J (Hz)
C
Position
H
J (Hz)
8.0
8.4, 8.0
9.1, 8.4
9.1, 8.2
C
1
2
3
4
5
6
ꢂ
ꢂ
ꢂ
ꢂ
5.07 d
7.7
102.6
75.4
78.6
71.7
78.5
62.9
1ꢃꢄ
2ꢃꢄ
3ꢃꢄ
4ꢃꢄ
5ꢃꢄ
5.13 d
105.0
74.7
78.1
71.5
78.5
62.4
4.07 dd
4.32 dd
4.29 dd
4.00 m
4.58 br d
4.43 dd
6.30 d
4.12 dd
4.31 dd
4.28 dd
4.03 m
4.63 br d
4.26 br d
5.23 d
8.4, 7.7
8.4, 8.2
8.2, 8.0
4.06 dd
4.20 dd
4.17 dd
4.00 m
4.54 br d
4.29 dd
4.93 d
4.01 dd
4.21 dd
4.31 dd
3.82 m
4.53 br d
4.41 br d
5.17 d
4.10 dd
4.22 dd
4.20 dd
3.99 m
4.52 br d
4.31 dd
ꢂ
ꢂ a
b
ꢃ
ꢃ
ꢃ
11.6
11.6, 4.0
8.4
9.2, 8.4
9.4, 9.2
9.4, 9.4
6ꢃ
a
11.7
11.7, 4.7
7.7
9.0, 7.7
9.4, 9.0
9.4, 8.7
b
1
2
3
4
5
6
93.5
82.9
77.9
70.3
77.7
69.2
1ꢄꢄ
2ꢄꢄ
3ꢄꢄ
4ꢄꢄ
5ꢄꢄ
105.0
74.7
76.5
80.9
76.6
62.0
ꢃ
ꢃ
ꢃ a
b
ꢄ
ꢄ
ꢄ
ꢄ
ꢄ
ꢄ
10.4
10.4
7.7
8.9, 7.7
8.9, 8.8
8.8, 8.8
6ꢄꢄ a
b
11.3
11.3
7.7
9.0, 7.7
9.0, 8.9
9.0, 8.9
1
2
3
4
5
6
106.1
75.7
76.3
81.5
76.7
62.5
1ꢃꢃꢄ
2ꢃꢃꢄ
3ꢃꢃꢄ
4ꢃꢃꢄ
5ꢃꢃꢄ
6ꢃꢃꢄ a
b
104.9
74.7
78.1
71.4
78.5
62.4
4.01 dd
4.21 dd
4.28 dd
3.92 m
4.57 br d
11.3
11.3
11.4
11.4, 3.7
4
.48 br d
1
2
3
4
5
6
ꢃꢃ
ꢃꢃ
ꢃꢃ
ꢃꢃ
ꢃꢃ
ꢃꢃ a
b
5.16 d
8.1
104.6
74.7
76.5
80.9
76.5
61.8
4.07 dd
4.23 dd
4.27 dd
3.98 m
4.48 br d
4.31 dd
8.3, 8.1
9.1, 8.3
9.1, 8.4
11.8
11.8, 3.7
by using selective irradiation of easily identifiable anomeric and a C-2 and C-6 disubstituted b-D-glucopyranosyl moiety
proton signals, as well as irradiation of other nonoverlapping (Glcꢃ). The b-orientations of anomeric centers of all the
11—13)
proton signals in a series of 1D TOCSY experiments.
glucosyl moieties were supported by the relatively large
1
1
Subsequent analysis of the H– H COSY spectrum resulted J values of their anomeric protons (7.7—8.4 Hz). In the
in the sequential assignments of all the proton resonances HMBC spectrum, the anomeric proton of the terminal gluco-
due to the seven glucosyl units, including identification of syl unit (Glcꢂ) at d 5.07 exhibited a long-range correlation
their multiplet patterns and coupling constants, as shown in with C-3 of the aglycon at d 78.2, indicating that one gluco-
Table 1. The HSQC and HSQC-TCSY spectra correlated the syl unit was attached at the C-3 hydroxyl group of the agly-
proton resonances with those of the corresponding one-bond con. Consequently, an oligoglucoside composed of six gluco-
coupled carbons, leading to unambiguous assignments of the syl units was presumed to form an ester linkage with the
carbon shifts (Table 1). Comparison of the carbon chemical C-26 carboxyl group. Further HMBC correlations from
shifts thus assigned with those of reference methyl a-D- and d 6.30 (H-1 of Glcꢃ) to C-26 of aglycon at d 175.2, d 5.23
14)
b-D-glucosides, taking into account the known effects of (H-1 of Glcꢄ) to C-2 of Glcꢃ at d 82.9, d 5.17 (H-1 of Glcꢃꢃꢄ)
O-glycosylation, indicated that 1 contained three terminal b- to C-4 of Glcꢄꢄ at d 80.9, d 5.16 (H-1 of Glcꢃꢃ) to C-4 of
D-glucopyranosyl moieties (Glcꢂ, Glcꢃꢄ, Glcꢃꢃꢄ), three C-4 Glcꢄ at d 81.5, d 5.13 (H-1 of Glcꢃꢄ) to C-4 of Glcꢃꢃ at
substituted b-D-glucopyranosyl moieties (Glcꢄ, Glcꢃꢃ, Glcꢄꢄ), d 80.9, and d 4.93 (H-1 of Glcꢄꢄ) to C-6 of Glcꢃ at d 69.2

1
398
Vol. 52, No. 11
confirmed the hexaglucoside sequence to be Glc-(1→4)-Glc-
1→4)-Glc-(1→2)-[Glc-(1→4)-Glc-(1→6)]-Glc, which was
attached at C-26 of the aglycon. All of these data were con-
sistent with the structure (24R,25S)-3b-[(b-D-glucopyra-
nosyl)oxy]ergost-5-en-26-oic acid O-b-D-glucopyranosyl-
d 5.18 (H-1 of Glcꢃꢄ) to C-4 of Glcꢃꢃ at d 80.9, and d 4.93
(
(H-1 of Glcꢃꢃ) to C-6 of Glcꢃ at d 69.2. The structure of 3
was characterized as (24R,25S)-3b-[(b-D-glucopyranosyl)-
oxy]ergost-5-en-26-oic acid O-b-D-glucopyranosyl-(1→2)-
O-[O-b -D-glucopyranosyl-(1→4)-b -D-glucopyranosyl-
(
(
1→4)-O-b-D-glucopyranosyl-(1→4)-O-b-D-glucopyranosyl-
1→2)-O-[O-b-D-glucopyranosyl-(1→4)-b-D-glucopyra-
(
1→6)]-b-D-glucopyranosyl ester.
Taccasterosides A—C (1—3) are novel bisdesmosideic
nosyl-(1→6)]-b-D-glucopyranosyl ester, which was assigned
to 1.
oligoglucosides of (24R,25S)-3b-hydroxyergost-5-en-26-oic
acid. Phytosterols and their monoglucosides such as campe-
sterol, stigmasterol, and b-sitosterol, and their 3-O-gluco-
side, widely occur in the plant kingdom. However, com-
pounds 1—3 are believed to be the first representatives of
oligoglucosides of a phytosterol derivative, which have sugar
moieties with a total of five to seven glucose units.
15)
Taccasteroside B (2) was analyzed for C H O on the
6
4
106 33
basis of HR-ESI-TOF-MS. The molecular formula of 2 was
less than that of 1 by C H O , corresponding to the lack of
6
10
5
1
one hexose unit. The H-NMR spectrum of 2 showed signals
for six anomeric protons at d 6.29 (d, Jꢁ8.1 Hz), 5.24
(
(
d, Jꢁ7.8 Hz), 5.18 (d, Jꢁ7.1 Hz), 5.16 (d, Jꢁ7.1 Hz), 5.06
d, Jꢁ7.7 Hz), and 4.92 (d, Jꢁ7.8 Hz), along with the signals
References and Notes
1)
2)
3)
4)
5)
6)
7)
“Dictionary of Chinese Medicinal Materials,” Vol. 2, Shanghai Scien-
tific and Technological Press, Shanghai, 1977, pp. 1356—1357.
Yokosuka A., Mimaki Y., Sakagami H., Sashida Y., J. Nat. Prod., 65,
283—289 (2002).
Yokosuka A., Mimaki Y., Sashida Y., Phytochemistry, 61, 73—78
(2002).
for five steroid methyl groups at d 1.23 (d, Jꢁ7.0 Hz), 0.98
(d, Jꢁ7.0 Hz), 0.95 (d, Jꢁ6.5 Hz), 0.93 (s), and 0.62 (s).
Acid hydrolysis of 2 with 1 M HCl in dioxane–H O (1 : 1)
2
resulted in the production of 1a and D-glucose. In the
1
3
C-NMR spectrum of 2, the signals due to C-3 and C-26 of
Yokosuka A., Mimaki Y., Sashida Y., Natural Medicines, 56, 208—
the aglycon residue were observed at d 78.2 and 175.2,
respectively, indicating that the sugar linkages were both at
C-3 and C-26, as in 1. Using the same procedures as
2
11 (2002).
Yokosuka A., Mimaki Y., Sashida Y., J. Nat. Prod., 65, 1293—1298
(2002).
Yokosuka A., Mimaki Y., Sashida Y., J. Nat. Prod., 66, 876—878
1
3
described for 1, all the C-NMR signals for the sugar moi-
eties were assigned to three terminal b-D-glucopyranosyl
units (Glcꢂ, Glcꢃꢃ, Glcpꢄꢄ), two C-4 substituted b-D-glucopy-
ranosyl units (Glcꢄ, Glcꢃꢄ), and a C-2 and C-6 disubstituted
b-D-glucopyranosyl unit (Glcꢃ). In the HMBC spectrum of 2,
long-range correlations were observed from d 6.29 (H-1 of
Glcꢃ) to C-26 of aglycon at d 175.2, d 5.24 (H-1 of Glcꢄ) to
C-2 of Glcꢃ at d 82.8, d 5.18 (H-1 of Glcꢃꢃ) to C-4 of Glcꢄ at
d 81.8, d 5.16 (H-1 of Glcꢄꢄ) to C-4 of Glcꢃꢄ at d 81.0, d
(
2003).
ꢅ
Data for 1. ESI-TOF-MS (positive mode) m/z: 1587 [MꢅNa] . Anal.
Calcd for C H O ·4H O: C, 51.34; H, 7.63. Found: C, 51.20;
7
0
116 38
2
1
3
H, 7.93. C-NMR for the aglycon moiety (C D N) d: 37.5, 30.3, 78.2,
39.3, 140.9, 122.0, 32.2, 32.0, 50.3, 36.9, 21.3, 39.9, 42.4, 56.8, 24.5,
5
5
2
1
8.5, 56.1, 12.0, 19.4, 36.0, 19.0, 33.8, 31.4, 35.4, 44.1, 175.2, 11.5,
5.5 (C-1—C-28).
8
)
)
D-Glucose was identified by direct HPLC analysis of the hydrolysate,
which was performed on an aminopropyl-bonded silica gel column,
with detection being carried out using a combination of refractive
index (RI) and optical rotation (OR) detectors.
5
4
.06 (H-1 of Glcꢂ) to C-3 of the aglycon at d 78.2, and d
.92 (H-1 of Glcꢃꢄ) to C-6 of Glcꢃ at d 69.2. Thus the struc-
9
Ohmoto T., Yoshida O., Chem. Pharm. Bull., 28, 1894—1899 (1980).
1
1
1
1
0) Yasuhara F., Yamaguchi S., Kasai R., Tanaka O., Tetrahedron Lett., 27,
ture of 2 was established to be (24R,25S)-3b-[(b-D-glucopy-
ranosyl)oxy]ergost-5-en-26-oic acid O-b-D-glucopyranosyl-
4
033—4034 (1986).
1) Kuroda M., Mimaki Y., Ori K., Koshino H., Nukada T., Sakagami H.,
Sashida Y., Tetrahedron, 58, 6735—6740 (2002).
2) Watanabe K., Mimaki Y., Sakuma C., Sashida Y., J. Nat. Prod., 66,
(
1→4)-O-b-D-glucopyranosyl-(1→2)-O-[O-b-D-glucopyra-
nosyl-(1→4)-b-D-glucopyranosyl-(1→6)]-b-D-glucopyra-
nosyl ester.
8
79—882 (2003).
3) Mimaki Y., Harada H., Sakuma C., Haraguchi M., Yui S., Kudo T.,
1
The H-NMR spectrum of taccasteroside C (3) (C H -
5
8
96
Yamazaki M., Sashida Y., Helv. Chim. Acta, 87, 851—865 (2004).
16)
O )
showed five anomeric proton signals at d 6.32
2
8
14) Agrawel P. K., Phytochemistry, 31, 3307—3330 (1992).
2
5
(
d, Jꢁ8.0 Hz), 5.30 (d, Jꢁ7.8 Hz), 5.18 (d, Jꢁ7.8 Hz), 5.07 15) Data for 2. [a] ꢀ10.0° (cꢁ0.10, MeOH). HR-ESI-TOF-MS (positive
D
ꢅ
mode) m/z: 1425.6469 [MꢅNa]
(Calcd for C H O Na,
64 106 33
(d, Jꢁ7.7 Hz), and 4.93 (d, Jꢁ7.8 Hz), along with five steroid
ꢀ1
1
1
7
425.6514). IR (film) cm : 3270 (OH), 2933 (CH), 1740 (CꢁO),
072. C-NMR for the sugar moieties (C D N) d: 102.6, 75.3, 78.6,
1.7, 78.4, 62.9 (C-1ꢂ—C-6ꢂ), 93.5, 82.8, 77.8, 70.3, 77.7, 69.2
methyl signals at d 1.26 (d, Jꢁ7.0 Hz), 0.98 (d, Jꢁ6.7 Hz),
1
3
5
5
0
.95 (d, Jꢁ6.4 Hz), 0.92 (s), and 0.61 (s). Acid hydrolysis of
3
with 1 M HCl afforded 1a and D-glucose. Comparison of the
(C-1ꢃ—C-6ꢃ), 106.0, 75.7, 76.3, 81.8, 76.7, 62.4 (C-1ꢄ—C-6ꢄ), 105.1,
74.8, 78.3, 71.5, 78.5, 62.4 (C-1ꢃꢃ—C-6ꢃꢃ), 105.6, 74.6, 76.6, 81.0,
1
13
H- and C-NMR spectra of 3 with those of 1 and 2 indi-
cated that one b-D-glucopyranosyl unit (Glcꢂ) was linked to
C-3 of the aglycon and the sugar chain attached at C-26 was
made up of two terminal b-D-glucopyranosyl moieties (Glcꢄ,
Glcꢃꢄ), a C-4 substituted b-D-glucopyranosyl unit (Glcꢃꢃ),
and a C-2 and C-6 disubstituted b-D-glucopyranosyl unit
7
6.5, 61.9 (C-1ꢃꢄ—C-6ꢃꢄ), 104.9, 74.7, 78.1, 71.4, 78.5, 62.4
(
C-1ꢄꢄ—C-6ꢄꢄ).
2
5
1
6) Data for 3. [a]D ꢀ8.0° (cꢁ0.10, MeOH). HR-ESI-TOF-MS (positive
ꢅ
mode) m/z: 1241.6163 [MꢅH] (Calcd for C H O , 1241.6166). IR
5
8
97 28
ꢀ1
13
(film) cm : 3129 (OH), 2869 (CH), 1745 (CꢁO), 1075. C-NMR for
the sugar moieties (C
D
N) d: 102.5, 75.3, 78.6, 71.7, 78.4, 62.9
C-1ꢂ—C-6ꢂ), 93.7, 82.5, 77.8, 70.3, 77.7, 69.2 (C-1ꢃ—C-6ꢃ), 106.4,
5
5
(
(Glcꢃ). In the HMBC spectrum of 3, long-range correlations
7
7
6.3, 78.2, 71.6, 78.8, 62.4 (C-1ꢄ—C-6ꢄ), 105.0, 74.6, 76.6, 80.9,
6.5, 61.9 (C-1ꢃꢃ—C-6ꢃꢃ), 104.9, 74.7, 78.1, 71.4, 78.5, 62.8 (C-1ꢃꢄ—
were observed from d 6.32 (H-1 of Glcꢃ) to C-26 of aglycon
at d 175.3, d 5.30 (H-1 of Glcꢄ) to C-2 of Glcꢃ at d 82.5,
C-6ꢃꢄ).