3-Hydroxydihydrobenzofuran glucosides from Gnaphalium polycaulon

Article abstract of DOI:10.1248/cpb.59.1160

A new 3-hydroxydihydrobenzofuran glucoside, gnaphaliol 9-O-β-D- glucopyranoside (2), was isolated from the aerial parts of Gnaphalium polycaulon together with 1-{(2R*,3S*)-3-(β-D-glucopyranosyloxy)-2,3- dihydro-2-[1-(hydroxyl methyl)vinyl]-1-benzofuran-5-yl}-ethanone or gnaphaliol 3-O-β-D-glucopyranoside (1), (Z)-3-hexenyl O-β-D-glucopyranoside (3) and adenosine (4). The absolute configurations at C-2 and C-3 positions of compound 1 were determined to be 2R and 3R. The structures of these compounds were elucidated on the basis of their physical and spectroscopic data.

Full text of DOI:10.1248/cpb.59.1160

1160
Note
Chem. Pharm. Bull. 59(9) 1160—1162 (2011)
Vol. 59, No. 9
3-Hydroxydihydrobenzofuran Glucosides from Gnaphalium polycaulon
Poolsak SAHAKITPICHAN,a Wannaporn DISADEE,a Somsak RUCHIRAWAT,a,b and
Tripetch KANCHANAPOOM*,a,c
a Chulabhorn Research Institute and Chulabhorn Graduate Institute; Vipavadee-Rangsit Highway, Bangkok 10210,
Thailand: b The Center of Excellence on Environmental Health, Toxicology and Management of Chemicals; Vipavadee-
Rangsit Highway, Bangkok 10210, Thailand: and c Faculty of Pharmaceutical Sciences, Khon Kaen University; Khon
Kaen 40002, Thailand. Received March 26, 2011; accepted May 27, 2011; published online May 31, 2011
A new 3-hydroxydihydrobenzofuran glucoside, gnaphaliol 9-O-b-D-glucopyranoside (2), was isolated from
the aerial parts of Gnaphalium polycaulon together with 1-{(2R*,3S*)-3-(b-D-glucopyranosyloxy)-2,3-dihydro-2-
[1-(hydroxyl methyl)vinyl]-1-benzofuran-5-yl}-ethanone or gnaphaliol 3-O-b-D-glucopyranoside (1), (Z)-3-hex-
enyl O-b-D-glucopyranoside (3) and adenosine (4). The absolute configurations at C-2 and C-3 positions of com-
pound 1 were determined to be 2R and 3R. The structures of these compounds were elucidated on the basis of
their physical and spectroscopic data.
Key words Gnaphalium polycaulon; Asteraceae; 3-hydroxydihydrobenzofuran glucoside; gnaphaliol, gnaphaliol glucoside
Gnaphalium polycaulon PERSOON is an annual widespread
weed in tropical and subtropical Africa, Asia, Australia and
America.1) In Thailand, it is believed that this species was
brought into cultivation by the Chinese and commonly grown
around cultivated fields, especially in Damnoen Saduak dis-
trict, Ratchaburi Province. The aerial parts are available in
cool season from November to January and used as a flavor
ingredient in foods for carminative purpose during the Chi-
nese New Year celebrations by Chinese descendants. The
phytochemical investigation of this plant has not been carried
out. However, diterpenoids and flavonoids have been isolated
from other Gnaphalium species.2—5) This paper describes the
isolation and identification of four polar compounds, includ-
ing a new 3-hydroxydihydrobenzofuran glucoside (2) and
Fig. 1. The Structures of Compounds 1—4 and 1a
three known compounds: a 3-hydroxydihydrobenzofuran glu-
coside (1), an alkyl glucoside (3) and a nucleoside (4) (Fig.
1), from the aqueous soluble fraction of the aerial parts of
this plant in addition to determination of the absolute config-
urations of two 3-hydroxydihydrobenzofuran glucosides (1,
2).
Results and Discussion
The methanolic extract of the aerial part of G. polycaulon
was suspended in H2O and extracted with Et2O. The aqueous
layer was applied to a column of Diaion HP-20, with H2O,
MeOH and Me2CO as eluants, successively. The portion
eluted with MeOH was separated by a combination of chro-
matographic procedures to provide four compounds. Two
Fig. 2. HMBC Correlations of Compounds 1 and 2
were identified as the known compounds (Z)-3-hexenyl O-b-
D-glucopyranoside (3)6) and adenosine (4),7) by comparison
of physical data with values reported in literatures and from at dH 5.43 and 5.28 (each d, Jꢀ6.9 Hz), two geminal olefinic
spectroscopic evidence.
protons at dH 5.42 and 5.39 (each s), as well as one anomeric
Compound 1 was isolated as an amorphous powder. Its proton at dH 4.58 (d, Jꢀ7.8 Hz). The 13C-NMR spectrum
molecular formula was determined to be C19H24O9 by high- showed the signals of a b-glucopyranosyl unit in addition to
resolution atmospheric pressure chemical ionization time-of- 13 carbon signals for the aglycone moiety. The structure of
flight mass spectrometric analysis (HR-APCI-TOF-MS). The compound 1 was deduced by the results from 1H–1H-correla-
1H-NMR spectrum displayed the presence of the signals of a tion spectroscopy (COSY), heteronuclear single quantum co-
typical ABX aromatic ring system at dH 8.32 (d, Jꢀ2.0 Hz), herence (HSQC) and heteronuclear multiple bond ccorrela-
7.96 (dd, Jꢀ8.6, 2.2 Hz) and 6.92 (d, Jꢀ8.6 Hz), an AB type tion spectroscopy (HMBC) (Fig. 2) spectroscopic methods.
of methylene signals at dH 4.26, 4.16 (each d, Jꢀ13.9 Hz), This compound has a 3-hydroxydihydrobenzofuran as a core
one singlet acetyl group at dH 2.59, two heterocyclic protons structure having a (1-hydroxylmethyl)vinyl and an acetyl
© 2011 Pharmaceutical Society of Japan
∗ To whom correspondence should be addressed. e-mail: trikan@kku.ac.th

September 2011
1161
Table 1. 1H- and 13C-NMR Spectroscopic Data of Compounds 1, 2 and Their Aglycone 1a (400 MHz for 1H Data and 100 MHz for 13C Data, Recorded in
CD3OD)
1
2
1a
Position
dC
dH
dC
dH
dC
dH
2
3
3a
4
5
6
7
7a
8
9
89.2 (ꢁ0.9)a)
81.2 (ꢂ8.8)a)
129.1 (ꢁ2.1)a)
131.0
132.0
133.0
111.0
165.4
144.6
63.5
5.28 (1H, d, 6.9)
5.43 (1H, d, 6.9)
90.1
72.3
5.22 (1H, d, 5.9)
5.30 (1H, d, 5.9)
90.1
72.4
5.20 (1H, d, 6.3)
5.27 (1H, d, 6.3)
131.3
128.5
132.3
133.2
111.1
165.3
140.8
71.9
131.2
128.5
132.2
133.2
111.1
165.3
144.3
63.9
8.32 (1H, d, 2.0)
8.09 (1H, d, 1.9)
8.09 (1H, d, 2.0)
7.96 (1H, dd, 8.6, 2.0)
6.92 (1H, d, 8.6)
7.99 (1H, dd, 8.5, 1.9)
6.97 (1H, d, 1.9)
7.99 (1H, dd, 8.5, 2.0)
6.97 (1H, d, 8.5)
4.26 (1H, d, 13.9)
4.16 (1H, d, 13.9)
5.42 (1H, s)
4.54 (1H, d, 12.4)
4.35 (1H, d, 12.4)
5.46 (1H, s)
4.25 (1H, d, 13.5)
4.20 (1H, d, 13.5)
5.39 (2H, br s)
10
114.5
115.9
113.9
5.39 (1H, s)
5.47 (1H, s)
11
12
1ꢃ
2ꢃ
3ꢃ
4ꢃ
5ꢃ
6ꢃ
199.7
26.6
105.4
75.1
78.1
71.3
78.0
62.7
199.2
26.5
103.7
75.0
78.1
71.6
78.0
62.8
199.1
26.5
2.59 (3H, s)
4.58 (1H, d, 7.8)
2.57 (3H, s)
2.57 (3H, s)
4.38 (1H, d, 7.8)
3.25 (1H, dd, 8.9, 7.8)
3.31 (1H)b)
3.17 (1H, dd, 9.0, 7.8)
3.37 (1H, dd, 9.1, 9.0)
3.29 (1H, dd, 9.0, 9.0)
3.43 (1H, m)
4.00 (1H, dd, 11.7, 2.1)
3.76 (1H, dd, 11.7, 5.8)
3.31 (1H)b)
3.38 (1H, m)
3.89 (1H, dd, 11.9, 1.3)
3.67 (1H, dd, 11.9, 5.4)
a) DdC: dC (1)ꢁdC (1a). b) Chemical shifts were assigned by HMQC.
groups located at C-2 and C-5, respectively, and the sugar
moiety was assigned to be connected at C-3. The physical
and spectroscopic data of compound 1 were identical to those
of 1-{(2R*,3S*)-3-(b-D-glucopyranosyloxy)-2,3-dihydro-2-
[1-(hydroxymethyl)vinyl]-1-benzofuran-5-yl}-ethanone, pre-
viously reported from Leontopodium alpinum.8) The vicinal
coupling constant of two protons at dH 5.28 (H-2) and 5.43
(H-3) with Jꢀ6.9 Hz indicated that the functional groups on
the five membered ring were cis.9) However the determina-
tion of the absolute configurations at C-2 and C-3 positions
has not been investigated. Since the attachment of a sugar
Fig. 3. Conformation around Glucosidic Linkage of Compound 1
moiety at C-3 position, the absolute configuration in this the absolute configuration of C-3 position to be R. Besides
position could be determined by the application of b-D- the absolute configuration of C-2 position was assigned to be
glycosylation shift-trend rule on carbon chemical shifts of R. Consequently, compound 1 was gnaphaliol 3-O-b-D-glu-
secondary hydroxyl group (a-carbon) and the upfield shift copyranoside.
difference values [DdC: dC (alcoholic glucoside)ꢁdC (alco-
Compound 2 was isolated as an amorphous powder, and
hol)] of their neighboring carbon atoms (two b-carbons) in its molecular formula was determined to be C19H24O9 by HR-
the aglycone part.10—12) The glycosylation shifts mainly de- APCI-TOF-MS. The NMR spectroscopic data were closely
pended on the chirality of the aglycone alcohols. The rotation related to those of compound 1. In particular, the chemical
around the glycosidic bond was rather restricted and caused shifts of the core structure were in agreement with those of
unequal glycosylation shifts of these neighboring carbon 1a. The significant difference was the downfield shift of C-9,
atoms. Therefore, compound 1 was enzymatically hydro- together with the upfield shift of C-8 indicating that the b-D-
lyzed with crude hesperidinase to provide a new aglycone glucopyranosyl unit was connected to C-9 position. The as-
identified as 1-(3-hydroxy-2-(1-hydroxyprop-2-en-2-yl)-2,3- signment was confirmed by HMBC correlations (Fig. 2).
dihydrobenzofuran-5-yl)ethanone with the trivial name This compound should possess the same aglycone part due to
gnaphaliol (1a), together with D-glucose, which was deter- the co-occurrence in the same plant species. Enzymatic hy-
mined by HPLC analysis. From the 13C-NMR spectroscopic drolysis with crude hesperidinase provided 1a, and the ster-
data, the upfield shift differences [DdC: dC (1)ꢁdC (1a)] of eochemistry of glucose was identified to be D-form. There-
C-2 and C-3a were calculated to be ꢁ0.9 and ꢁ2.1 ppm fore, the structure of compound 2 was elucidated to be
(Table 1), respectively. Generally, the upfield shift differences gnaphaliol 9-O-b-D-glucopyranoside.
of the b-carbon anti to the pyranose ring oxygen was larger
Experimental
than that of the b-carbon syn to the oxygen.11—13) Thus, the
General Procedures Melting point was determined with a Stuart Scien-
1
tific SMP3 apparatus and was uncorrected. H- and 13C-NMR spectra were
conformation around glucosidic linkage of this compound
could be illustrated as shown in Fig. 3 and led to conclude
recorded in CD3OD using a Bruker AV-400 spectrometer. Fourier Transform

1162
Vol. 59, No. 9
(FT)-IR spectra were obtained on a universal attenuated total reflectance at- (CD3OD): see Table 1; negative HR-APCI-TOF-MS, m/z: 431.1099
tached (UATR) to a Perkin-Elmer Spectrum One spectrometer. The MS data
was recordeds on a Bruker Micro TOF-LC mass spectrometer. Optical rota-
tions were measured with a Jasco P-1020 digital polarimeter. For column
chromatography, Diaion HP-20 (Mitsubishi Chemical Industries Co., Ltd.,
[MꢂCl]ꢁ (Calcd for C19H24ClO9, 431.1114).
Enzymatic Hydrolysis of 1 and 2 and Determination of the Absolute
Configuration of Glucose Compound 1 (10 mg) in 1,4-dioxane (0.5 ml)
was added a solution of crude hesperidinase (80 mg) in H2O (3 ml) and
Japan), silica gel 60 (70—230 mesh, Merck, Germany), and RP-18 (50 mm, stirred at 37 °C for 48 h. The reaction was extracted with EtOAc, and the or-
YMC, U.S.A.) were used. HPLC (Jasco PU-980 pump) was carried out on ganic part was concentrated to provide gnaphaliol (1a) (6.2 mg). The struc-
an octadecyl silica (ODS) column (21.2ꢄ250 mm i.d., VertisepTM AQS) ture of compound 1a was identified by 1H- and 13C-NMR spectroscopic
with a Jasco UV-970 detector at 220 nm. The flow rate was 8 ml/min. The
spraying reagent used for TLC was 10% H2SO4 in 50% EtOH.
Plant Material The aerial parts of G. polycaulon (Asteraceae) PERSOON
were collected from Damnoen Saduak district, Ratchaburi province, in De-
cember 2009 Thailand. The identification was done by Mr. Nopporn Non-
analysis. The aqueous layer was partitioned with n-BuOH, and the organic
part was concentrated and analyzed with an optical rotation detector
(JASCO OR-2090plus) with a Polyamine II column (YMC, 70% aqueous
MeCN, 1 ml/min). It showed a peak for D-glucose at the retention time of
7.4 min. By the same method, compound 2 provided 1a (8.4 mg) and D-glu-
tapa, Department of Pharmaceutical Botany and Pharmacognosy, Faculty of cose from the HPLC analysis.
Pharmaceutical Sciences, Khon Kaen University. A voucher specimen (TK-
PSKKU-0065) was deposited at the Herbarium of the Faculty of Pharmaceu-
tical Sciences, Khon Kaen University.
Extraction and Isolation The aerial parts of G. polycaulon (1.9 kg)
Acknowledgements This project was financially supported by the Thai-
land Research Fund, Chulabhorn Research Institute and the Center of Excel-
lence on Environmental Health, Toxicology and Management of Chemicals,
were extracted with MeOH (3 times, each 12.0 lꢄ24 h) at room temperature. Thailand.
After removal of the solvent in vacuo, the residue (308.4 g) was partitioned
with Et2O and H2O (each 1.0 l, 3 times). The aqueous soluble fraction
(173.6 g) was subjected to a Diaion HP-20 column, and successively eluted
with H2O, MeOH and acetone. The fraction eluted with MeOH (11.0 g) was
subjected to a column of silica gel using solvent systems EtOAc–MeOH
(9 : 1, 2.0 l), EtOAc–MeOH–H2O (40 : 10 : 1, 2.0 l), EtOAc–MeOH–H2O
(70 : 30 : 3, 4.0 l) and EtOAc–MeOH–H2O (6 : 4 : 1, 5.5 l), respectively, to
provide four fractions, monitored by TLC. Fraction 1 (4.5 g) was applied to a
RP-18 column using a gradient solvent system 10—80% aqueous MeOH to
give eight fractions. Fraction 1-1 was purified by preparative HPLC ODS
using solvent system 10% aqueous MeCN to afford compound 4 (122.0 mg).
Fraction 1-4 was purified by preparative HPLC-ODS with solvent system
15% aqueous MeCN to provide compound 3 (36.7 mg). Fraction 1-5 was pu-
rified by preparative HPLC-ODS with solvent system 15% aqueous MeCN
to provide compound 1 (83.6 mg). Finally, fraction 1-6 was purified by
preparative HPLC-ODS with solvent system 15% aqueous MeCN to afford
compound 2 (34.2 mg).
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129 °C (dec.); [a]D28 ꢂ43.8 (cꢀ0.75, MeOH); IR (UATR) nmax 3475, 3333,
2934, 2880, 1660, 1603, 1490, 1436, 1357, 1262, 1069, 1026 cmꢁ1; 1H- and
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