Two new sesquiterpene glucosides from Dennstaedtia scabra (Wall.) Moore

Article abstract of DOI:10.1248/cpb.57.1123

Two new sesquiterpene glucosides onitioside A (1) and dennstoside B (2), were isolated from the 95% EtOH extract of Dennstaedtia scabra (WALL.) MOORE, together with seven known compounds, onitisin (3), pterosin A (4), pinocembrin (5), pinocembrin 7-rutino

Full text of DOI:10.1248/cpb.57.1123

October 2009
Notes
Chem. Pharm. Bull. 57(10) 1123—1125 (2009)
1123
Two New Sesquiterpene Glucosides from Dennstaedtia scabra (WALL.)
MOORE
Ming-Ming LI,a,b Kou WANG,a,b Zheng-Hong PAN,a,b Xuan-Qin CHEN,a,b Li-Yan PENG,a Yan LI,a
a
,a
*
Xiao CHENG, and Qin-Shi ZHAO
a State Key Laboratory of Phytochemistry and Plant Resources in West China, Kunming Institute of Botany, Chinese
Academy of Sciences; Kunming 650204, People’s Republic of China: and b Graduate School of Chinese Academy of
Sciences; Beijing 100049, People’s Republic of China.
Received April 7, 2009; accepted July 1, 2009; published online July 15, 2009
Two new sesquiterpene glucosides onitioside A (1) and dennstoside B (2), were isolated from the 95% EtOH
extract of Dennstaedtia scabra (WALL.) MOORE, together with seven known compounds, onitisin (3), pterosin A
(4), pinocembrin (5), pinocembrin 7-rutinoside (6), kaempferol (7), nicotiflorin (8), and galangin (9). Their struc-
tures were determined by extensive spectroscopic analysis.
Key words Dennstaedtia scabra; sesquiterpene glucoside; onitioside A; dennstoside B
Dennstaedtia scabra (WALL.) MOORE, belonging to the in which correlations of H-1ꢁ (d 4.10) with C-10a (d 73.5),
Dennstaedtiaceae family, is widely distributed in south H-10a (d 3.29, 3.93) with [C-1 (d 209.5), C-2 (d 49.7), C-3
China. The whole plant is used as traditional Chinese medi- (d 33.5), C-10b (d 21.8)] were observed. Acidic hydrolysis
cine to treat cold, headache, rheumatism, and palsy.1) Previ- of 1 gave D-glucose moiety, which was determined to have a
ous phytochemical studies on this plant revealed the presence b configuration on the basis of the large coupling constants
of pterosin-sesquiterpenes, illudane-type sesquiterpenes, and of the anomeric protons [d 4.10 (d, Jꢂ7.6 Hz)]. Assignment
their glycosides.2,3) Many of these compounds exhibit various of glucosidic protons system was achieved by analysis of
bioactivities such as antiprotozole4) and cytotoxic activi- 1H–1H correlation spectroscopy (COSY) and heteronuclear
ties.5,6) As a part of our research work on bioactive metabo- single quantum coherence (HSQC) experiments.
lites from ferns of China,7—9) phytochemical investigation on
Acidic hydrolysis of 1 also afforded aglycone (1a), which
the fronds of D. scabra was conducted and two new was suggested to be compound 3 by comparing their NMR
sesquiterpene glucosides (1, 2) were isolated together with data (Table 1) and optical rotation values [a]D15.3 ꢀ24.65
seven known compounds onitisin (3),2) pterosin A (4),10) (cꢂ0.14, MeOH).2) Thus the structure of compound 1 was
pinocembrin (5),11) pinocembrin 7-rutinoside (6),12) elucidated as shown in Fig. 1 and named onitioside A.
kaempferol (7),13) kaempferol 3-rutinoside (8),13) and galan-
Compound 2, obtained as colorless oil, had a molecular
gin (9).14) In the present paper, we report the isolation and formula of C32H40O12 determined by HR-ESI-MS (neg.) m/z:
structure elucidation of compounds 1 and 2.
615.2469 (Calcd for 615.2442). Its IR absorptions indicated
the presence of hydroxyl groups (3428 cmꢀ1), a ketone group
(1723 cmꢀ1), and an aromatic ring group (1604, 1515,
Results and Discussion
Compound 1 was obtained as colorless oil. Its molecular 1446 cmꢀ1). The 13C-NMR spectra showed resonances char-
formula was determined as C21H30O9 by HR-electrospray acteristic of a sesquiterpene, a glycopyranose moiety [d 62.3
ionization (ESI)-MS (neg.) m/z: 425.1797 (Calcd for (t), 76.4 (d), 72.2 (d), 73.7 (d), 74.4 (d), 96.8 (d)], a p-
425.1811). The IR spectrum showed the presence of hy- coumaroyl group [d 167.0 (s), 114.8 (d), 146.3 (d), 126.7 (d),
droxyl (3416 cmꢀ1), carbonyl (1687 cmꢀ1), and an aromatic 2ꢃ131.1 (d), 2ꢃ116.7 (d), 160.8 (s)], and an acetyl group [d
ring (1599, 1509, 1461 cmꢀ1) groups. The 13C-NMR spectra 20.9 (q), 169.8 (s)]. The double bond of the p-coumaroyl
of 1 revealed the presence of one glycopyranose moiety [d group was suggested as trans-due to the coupling constant
61.1 (t), 70.0 (d), 73.3 (d), 76.9 (d), 77.0 (d), 103.6 (d)]. The (Jꢂ15.5 Hz). The sesquiterpene possessed a ketone carbonyl
remaining carbons including an aromatic ring [d 127.5 (s), d 221.4, two olefinic carbons [d 124.2, 141.7], an oxy-
130.7 (s), 130.9 (s), 136.8 (s), 137.9 (s), 150.1 (s)], one ke- genated secondary carbon d 67.1, two oxygenated quater-
tone carbonyl d 209.5 (s), three methyl [d 12.7 (q), 12.9 (q), nary carbons [d 72.3, 83.3], and two methylenes in upfield [d
21.8 (q)], four methylenes [d 32.7 (t), 33.5 (t), 60.0 (t), 73.5 7.6, 8.3]. Along with the knowledge of previously isolated
(t)], and one quaternary carbon d 49.7 (s). Among them, two compounds from this plant,2,3) the basic skeleton of com-
carbons [d 60.0 (t), d 3.40 (m); d 73.5 (t), d 3.29 (d), 3.93 pound 2 was identified as an illudane-type sesquiterpene.
(d)] were ascribed as oxygen-bearing atoms. Considering the
By carefully comparing the MS and NMR data of 2 with
types of compounds previously isolated from this plant,2,10) those of illudane-type sesquiterpene glycosides,3) compound
together with the characteristic NMR signals discussed 2 might be C9H8O3 acid ester of dennstoside A. Assignment
above, compound 1 can be ascribed to be a pterosin- of glycosidic protons system was achieved by analysis of
sesquiterpene glycoside.
1H–1H COSY and HSQC experiments. Connectivities of the
The 1H- and 13C-NMR data of 1 were very similar to those sugar, acetyl group, and p-coumaroyl moiety were confirmed
of 3 except that 1 had a more glycopyranose moiety. The lo- by the HMBC correlations of H-1ꢁ (d 4.76) with C-4 (d
cations of the sugar units of 1 were confirmed by a heteronu- 83.3), H-2ꢁ (d 4.79) with C-1ꢄ (d 169.8) and H-4ꢁ (d 4.87)
clear multiple bond coherence (HMBC) experiment (Fig. 2), with C-1ꢅ (d 167.0), respectively. Comparing the NMR data
© 2009 Pharmaceutical Society of Japan
∗ To whom correspondence should be addressed. e-mail: Qinshizhao@mail.kib.ac.cn

1124
Vol. 57, No. 10
Table 1. 1H- and 13C-NMR Data for Compounds 1a), 1aa) and 2b). d in ppm, J in Hz
1
2
1a
No.
dH
dC
dH
dC
dH
dC
1
2
3
209.5 (s)
49.7 (s)
33.5 (t)
221.4 (s)
53.3 (s)
44.3 (t)
210.8 (s)
50.9 (s)
33.5 (t)
Ha: 3.18 (d, 17.2)
Hb: 2.60 (d, 17.2)
Ha: 2.74 (d, 14.4)
Hb: 1.83 (d, 14.4)
Ha: 3.09 (d, 17.6)
Hb: 2.54 (d, 17.6)
4
5
6
7
8
130.7 (s)
150.1 (s)
130.9 (s)
136.8 (s)
127.5 (s)
137.9 (s)
73.5 (t)
83.3 (s)
124.2 (d)
141.7 (s)
30.8 (s)
72.3 (s)
65.1 (d)
67.1 (t)
130.4 (s)
150.0 (s)
131.7 (s)
136.6 (s)
127.2 (s)
138.3 (s)
66.6 (t)
5.83 (br s)
9
10a
2.67 (br s)
3.24 (d, 10.4)
3.70 (d, 10.4)
1.03 (s)
1.54 (br s)
0.54 (m)
3.93 (d, 9.2)
3.29 (d, 9.2)
1.03 (s)
2.21 (s)
2.80 (t, 7.6)
3.50 (d, 10.4)
3.28 (d, 10.4)
0.95 (s)
2.21 (br s)
2.80 (t, 8.0)
10b
11
12
21.8 (q)
12.9 (q)
32.7 (t)
20.5 (q)
19.7 (q)
8.2 (t)
21.1 (q)
12.8 (q)
32.7 (t)
1.15 (m)
7.6 (t)
23.6 (q)
13
14
Glc
1ꢁ
2ꢁ
3ꢁ
4ꢁ
5ꢁ
6ꢁ
3.40 (t, 7.6)
2.47 (s)
60.0 (t)
12.7 (q)
0.82 (m)
1.12 (s)
3.39 (t, 8.0)
2.47 (s)
60.0 (t)
12.7 (q)
4.10 (d, 7.6)
2.83 (m)
103.6 (d)
73.3 (d)
77.0 (d)
70.0 (d)
76.9 (d)
61.1 (t)
4.76 (d, 8.0)
4.79 (t, 8.0)
3.87 (t, 9.2)
4.87 (t, 9.2)
3.54 (overlapped)
3.55 (overlapped)
96.8 (d)
74.4 (d)
73.7 (d)
72.2 (d)
76.4 (d)
62.3 (t)
3.05 (overlapped)
2.97 (overlapped)
2.98 (overlapped)
3.61 (d, 11.6)
3.38 (d, 11.6)
p-Coumaroyl
1ꢅ
2ꢅ
3ꢅ
167.0 (s)
114.8 (d)
146.3 (d)
126.7 (s)
131.1 (d)
116.7 (d)
160.8 (s)
6.33 (d, 15.6)
7.63 (d, 15.6)
4ꢅ
5ꢅ 9ꢅ
6ꢅ 8ꢅ
7ꢅ
7.55 (d, 8.8)
6.89 (d, 8.8)
Acetyl
1ꢄ
169.8 (s)
20.9 (q)
2ꢄ
1.93 (s)
a) Measured in DMSO-d6. b) Determined in acetone-d6.
Fig. 1. Structures of Compounds 1—3
with those of the known compounds,15) the hexose should be
glucose.
The relative stereochemistry of 2 was deduced from rotat-
ing frame Overhauser effect spectroscopy (ROESY) data.
The cross peaks in the ROESY spectrum between Hb-3 (d
1.83) and H-10b, H-3 (d 1.83) and H-14, H-10b and H-14
showed that these hydrogens were in b-orientation, while the
correlations between Ha-3 (d 2.74) and H-1ꢁ, H-1ꢁ, and H-9
indicated that these hydrogens were a-oriented. Thus the
stereochemistry of 2 was revealed the same as dennstoside
Fig. 2. Selected HMBC Correlations for Compounds 1 and 2

October 2009
1125
A.3) Therefore the structure of 2 was established as shown in
Fig. 1, and named dennstoside B.
Acidic Hydrolysis of Compound 1 Compound 1 (8 mg) was hy-
drolyzed with 2 M HCl–dioxane (1 : 1, 4 ml) under reflux for 6 h. The reac-
tion mixture was extracted with CHCl3 five times (4 mlꢃ5) to obtain the
aglycone. It was suggested to be compound 3 by comparing their NMR data
Experimental
General Experimental Procedures Optical rotation was measured on a and optical rotation values [a]D15.3 ꢀ24.65 (cꢂ0.14, MeOH). The aqueous
Horiba SEPA-300 polarimeter. IR spectra were obtained by Tensor 27 FT-IR layer was neutralized with 2 M NaHCO3 then dried to give a monosaccharide
spectrometer with KBr pellets. The 1H- and 13C-NMR spectra were recorded mixture. Then, a solution of the sugar mixture in pyridine (2 ml) was added
on Bruker AV-400 spectrometers in acetone-d6 and DMSO-d6 at room tem-
to L-cysteine methyl ester hydrochloride (about 1.5 mg) and kept at 60 °C for
perature (d in ppm, J in Hz). FAB-MS was carried out on a VG Autospec- 1 h. Next, trimethylsilylimidazole (about 1.5 ml) was added to the reaction
3000 spectrometer. HR-ESI-MS was recorded with an API QSTAR Pulsar i mixture in ice water and kept at 60 °C for 30 min. The mixture was subjected
spectrometer. Silica gel (200—300 mesh), Silica gel H (Qingdao Marine to GC analysis, run on a Shimadzu GC-14C gas chromatograph equipped
Chemical Ltd., China), and LiChroprep RP-18 silica gel (40—63 mm,
with a 30 mꢃ0.32 mm i.d. 30QC2/AC-5 quartz capillary column and an
Merck, Dramstadt, Germany) were used for column chromatography. Frac- H2 flame ionization detector with the following conditions: column tem-
tions were monitored by TLC and spots visualized by heating silica gel perature, 180—280 °C; programmed increase, 3 °C/min; carrier gas, N2
plates immersed with 15% H2SO4 in ethanol. Solvents were distilled prior to (1 ml/min); injector and detector temperature, 250 °C; injection volume,
use. Preparative HPLC was performed on a Shimadzu LC-8A preparative
liquid chromatograph with Shimadzu PRC-ODS (K) column. Sephadex LH-
20 (Amersham Pharmacia biotech, Sweden).
4 ml; and split ratio, 1/50. The configuration of D-glucose for compound 1
was determined by comparison of the retention times of the corresponding
derivatives with that of standard D-glucose, giving a peak at 19.066 min.
Plant Material The aerial parts of D. scabra were collected from Jin-
pin, Yunnan Province, China in July 2007 and identified by professor Xiao
Acknowledgements The authors are grateful to the members of the
Cheng at Kunming Institute of Botany, Chinese Academy of Sciences. A Analytical Group in State Key Laboratory of Phytochemistry and Plant
voucher specimen (No. 200706A03) has been deposited in the State Key Resources in West China, Kunming Institute of Botany, for the spectral
Laboratory of Phytochemistry and Plant Resources in West China, Kunming measurements.
Institute of Botany, Chinese Academy of Sciences.
Extraction and Isolation The dried and powdered plant materials References
(1.1 kg) were extracted with 95% ethanol (8.0 l, each 2 d) three times. After
evaporation of the solvent in vacuo, the concentrate was suspended into
H2O and partitioned successively with ethyl acetate. The ethyl acetate
extract (30 g) was chromatographed on a silica gel column eluted with
CHCl3–MeOH (1 : 0 to 5 : 5) to give five fractions 1—5. Fraction 2 was fur-
ther subjected to column chromatograph (CC) over silica gel (petroleum
ether–acetone 9 : 1 to 6 : 4) to obtain four subfractions 2.1—2.4. Subfraction
2.2 was subjected to silica gel CC using petroleum ether–acetone (6 : 1)
as eluent to yield 3 (20 mg) and 4 (826.5 mg). Subfraction 2.3 was sub-
jected to Sephadex LH-20 (CHCl3 : MeOHꢂ1 : 1) to obtain 5 (50 mg), 7
(10 mg) and 9 (12 mg). Fraction 3 was eluted with CHCl3–MeOH (1 : 1)
over silica gel CC then further purified by HPLC (MeOH : H2Oꢂ38 : 62)
and (MeOH : H2Oꢂ52 : 48) to yield 1 (132 mg) and 2 (14 mg). Fraction
4 was subjected to Sephadex LH-20 (CHCl3 : MeOHꢂ1 : 1) to obtain two
subfractions 4.1—4.2. Fraction 4.1 was further purified by HPLC
(MeOH : H2Oꢂ40 : 60) to obtain 8 (86 mg). Fraction 4.2 was first eluted
with CHCl3–MeOH (6 : 1) over silica gel then further purified by Sephadex
LH-20 (CHCl3 : MeOHꢂ1 : 1) to yield 6 (2.5 g).
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Onitioside A (1): Colorless oil. [a]D19.3 ꢀ5.49 (cꢂ0.25, MeOH). UV lmax
(MeOH) nm (e): 271.6 (5955), 231.6 (9926), 215.6 (9638), 198.6 (6847). IR
(KBr) cmꢀ1: 3416, 2925, 1687, 1599, 1461, 1380, 1306, 1161, 1078, 1039. 10) Hikino H., Takahashi T., Takemoto T., Chem. Pharm. Bull., 20, 210—
1H- and 13C-NMR: see Table 1. FAB-MS (neg.) m/z: 425 [MꢀH]ꢀ, 263
212 (1972).
ꢀ
[Mꢀ162ꢀH]ꢀ. HR-ESI-MS (neg.) m/z: 425.1797 (Calcd for C21H29O9
,
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(1985).
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425.1811).
Dennstoside B (2): Colorless oil. [a]D18.3 ꢀ133.7 (cꢂ0.09, MeOH). UV
(MeOH) lmax (MeOH) nm (e): 314.4 (16040), 212.6 (19248), 196.2 13) Markham K. R., Ternai B., Stanley R., Geiger H., Mabry T. J., Tetra-
(11067). IR (KBr) cmꢀ1: 3428, 2932, 1723, 1631, 1604, 1515, 1446, 1376,
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1
1248, 1165, 1046. H- and 13C-NMR: see Table 1. FAB-MS (neg.) m/z: 615
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ꢀ
[MꢀH]ꢀ. HR-ESI-MS (neg.) m/z: 615.2469 (Calcd for C32H39O12
,
615.2442).