New dammarane-type triterpenoid glycosides from Gynostemma burmanicum

Article abstract of DOI:10.1080/14786419.2018.1527831

The chemical composition of Gynostemma burmanicum King ex Chakrav. was investigated for the first time in this study. Nine dammarane glycosides (1?9) were isolated from the EtOH extract of the aerial parts of G. burmanicum. Their structures were elucidate

Full text of DOI:10.1080/14786419.2018.1527831

Natural Product Research
Formerly Natural Product Letters
ISSN: 1478-6419 (Print) 1478-6427 (Online) Journal homepage: http://www.tandfonline.com/loi/gnpl20
New dammarane-type triterpenoid glycosides
from Gynostemma burmanicum
Thi Kieu My Than, Thanh Ky Pham, Thanh Binh Pham, Thao Nguyen Phuong
& Dat Nguyen Tien
To cite this article: Thi Kieu My Than, Thanh Ky Pham, Thanh Binh Pham, Thao Nguyen Phuong
& Dat Nguyen Tien (2018): New dammarane-type triterpenoid glycosides from Gynostemma
burmanicum, Natural Product Research, DOI: 10.1080/14786419.2018.1527831
To link to this article: https://doi.org/10.1080/14786419.2018.1527831
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NATURAL PRODUCT RESEARCH
https://doi.org/10.1080/14786419.2018.1527831
RESEARCH-ARTICLE
New dammarane-type triterpenoid glycosides from
Gynostemma burmanicum
Than Thi Kieu Mya, Pham Thanh Kya, Pham Thanh Binhb, Nguyen Phuong Thaob
and Nguyen Tien Datc
,
b
aDepartment of Pharmacognosy, Hanoi University of Pharmacy, Hanoi, Vietnam; Department of
Bioactive Products, Institute of Marine Biochemistry, Vietnam Academy of Science and Technology
c
(VAST), Hanoi, Vietnam; Laboratory of Biochemical Research and Application, Center for Research
and Technology Transfer, VAST, Hanoi, Vietnam
ABSTRACT
ARTICLE HISTORY
Received 19 June 2018
Accepted 20 September 2018
The chemical composition of Gynostemma burmanicum King ex
Chakrav. was investigated for the first time in this study. Nine dam-
marane glycosides (1‒9) were isolated from the EtOH extract of the
aerial parts of G. burmanicum. Their structures were elucidated by
1D and 2D NMR spectroscopic interpretation as well as by chemical
studies. The new compounds were 3b,20S-dihydroxydammar-24-
ene-3-O-b-D-glucopyranosyl-20-O-[b-D-xylopyranosyl-(1!6)-b-D-glu-
copyranoside] (1), 3b,12b,20S-trihydroxydammar-24-ene-3-O-b-D-
xylopyranosyl-20-O-[b-D-xylopyranosyl-(1!6)-b-D-glucopyranoside]
KEYWORDS
Gynostemma burmanicum;
Cucurbitaceae;
dammarane saponin
(2),
and
12-oxo-3b,20S-dihydroxydammar-24-ene-3-O-[b-D-
glucopyranosyl(1!2)-b-D-glucopyranosyl]-20-O-[b-D-xylopyranosyl-
(1!6)-b-D-glucopyranoside] (3).
1. Introduction
The genus Gynostemma Blume (Cucurbitaceae) composes of approximately 16 species,
distributed in forests, scrubs and bush habitats at 60–3200 m elevations throughout
China, India, Vietnam, Myanmar, Korea, and Japan (Chen 1995). They have been used
in folk medicine to lower cholesterol levels, regulate blood pressure, strengthen the
CONTACT Nguyen Tien Dat
ngtiend@imbc.vast.vn
Supplemental data for this article can be accessed at https://doi.org/10.1080/14786419.2018.1527831
ß 2018 Informa UK Limited, trading as Taylor & Francis Group

2
T. THI KIEU MY ET AL.
immune system, and reduce inflammation (Li et al. 1993). In recent years, several stud-
ies on Gynostemma species have been carried out, including saponins, flavonoids,
amino acids, and reducing sugars, which could be commercially useful. Dammarane-
type saponins are important metabolites of Gynostemma plants, which have been
shown to possess various biological activities as neuroprotective (Ky et al. 2010; Seo
et al. 2017), antioxidant (Seo et al. 2017), inflammatory (Wong et al. 2017; Han et al.
2018), and osteoporosis (Han et al. 2018; Razmovski-Naumovski et al. 2005) activities.
Among Gynostemma plants, G. pentaphyllum has been most studied (Li et al. 2016;
Razmovski-Naumovski et al. 2005). Gynostemma burmanicum King ex Chakrav. is widely
distributed in South-East Asia, South China, Bangladesh (POWO 2018), and has not
been investigated for their chemical composition. In the present paper, we described
the structural isolation and elucidation of three new saponins (1‒ 3), along with 6
known dammarane-type saponins (4‒9, Figure 1).
2. Results and discussion
Compound 1 was isolated as a white, amorphous powder. The molecular formula,
C47H80O16, was deduced from its HR-ESI-MS data (m/z 899.5334 [M ‒ H]‒, calcd. for
C47H79O16, 899.5338) and 13C NMR data (see Experimental section). The 13C NMR and
DEPT spectra showed 47 carbon resonances, of which 30 were assigned to a aglycone
3b,20S-dihydroxydammar-24-en (Takemoto et al. 1983) and 17 to the sugar moieties.
1
The H NMR spectrum of 1 showed eight singlets assignable to the aglycone methyls
[dH 1.01 (H-18), 0.91 (H-19), (H-26), 1.63 (H-27), 1.06 (H-28), 0.86 (H-29), and 0.93 (H-30),
each 3H], two of which were diagnostic for methyls linked to a sp2 carbon [dH 1.70
Figure 1. Structures of compounds (1‒9) isolated from G. burmanicum.

NATURAL PRODUCT RESEARCH
3
(C-26) and 1.63 (C-27)], an olefinic proton signal [dH 5.11 (1H, t, J ¼ 6.0 Hz, H-24)].
Additionally, signals for three anomeric protons [dH 4.43 (1H, d, J ¼ 7.5 Hz, H-1’), 4.49
(1H, d, J ¼ 7.5 Hz, H-1’’), and 4.30 (1H, d, J ¼ 7.5 Hz, H-1’’’) were observed in the 1H
NMR spectrum, suggesting the presence of three sugar units in its structure. In com-
parison with the corresponding signals in a model compound reported in the litera-
ture (Takemoto et al. 1983), glycosidations at C-3 and C-20 were indicated by the
significant downfield shift observed for these carbon signals in 1. Acid hydrolysis of 1
yielded D-glucose and D-xylose (2:1), which were confirmed by GC/MS analysis (Thao
et al. 2016). The chemical shifts, the signal multiplicities, coupling constant values, and
1
their magnitude in the H NMR spectrum, as well as the 13C NMR data, indicated that
both sugar units have a b-configuration, which were confirmed by the analysis of their
1
HMBC and H-1H COSY spectra. The significant downfield shift of C-6’’ (dC 70.1) in the
inner b-glucopyranosyl moiety at C-20 of aglycone in the 13C NMR spectrum together
with the HMBC correlation between H-1’’’ [dH 4.30 (d, J ¼ 7.5 Hz)] with C-6’’ (dC 70.1)
showed that the terminal b-xylopyranosyl is linked to the inner C-20 by a specific
1!6 linkage (see Supporting data). These linkages were further confirmed by NOESY
correlations between H-1’/H-3 and H-1’’’/H-6’’.
The relative configuration of 1 was determined from the NOESY experiments and
from the J values, which showed NOESY cross-peaks (H-3a/Me-28, H-3a/H-5a, Me-29/
Me-19, Me-19/Me-18, H-30/H-17, and H-17/Me-21) and a large coupling constant of
H-3 (J ¼ 9.5 Hz). These data permitted the H-3 and C-20 to be established as a and S,
respectively. On the basis of the above results, the structure of 1 was determined as
3b,20S-dihydroxydammar-24-ene-3-O-b-D-glucopyranosyl-20-O-[b-D-xylopyranosyl-(1!6)-
b-D-glucopyranoside].
Compound 2 was also isolated as a white, amorphous powder. The molecular for-
mula of C46H78O16 was assigned from the HR-ESI-MS data (m/z 885.5215 [M‒ H]‒ ,
1
calcd. for C46H77O16, 885.5211). The H and 13C NMR data were also closely compar-
able to those of gypenoside IX (8) for the aglycone moiety (Takemoto et al. 1983);
however, the major differences were observed in that the sugar moiety. This difference
was attributed to the attachment of the sugar moiety at C-3, suggesting that the agly-
cone of 2 was identical to that of 8. These results, including the HMBC and COSY
data, indicated that the glucose unit of 8 was replaced by a xylose moiety in 2.
Furthermore, the location of the xylose moiety was determined as at the C-3 position
by the HMBC correlation between H-1’ (dH 4.24) with C-3 (dC 90.8). The locations of
these remaining disaccharides were determined as at the C-20 position by the
observed HMBC correlations between H-1’’ (dH 4.55)/C-20 (dC 83.8) and H-1’’’ (dH 4.28)/
C-6’’ (dC 70.0) in the same manner as for 1 (see Supporting data). (Takemoto et al.
1983). Moreover, acid hydrolysis of 2 gave D-xylose and D-glucose in a ratio of 2:1 by
GC/MS analysis (Thao et al. 2016).
The configuration of 2 was determined from the NOESY experiments and from the
J values. The relative configuration of 2 was elucidated as H-3a, H-12b, and 20S in the
same manner as for 1 and 8 (Takemoto et al. 1983). The a-configuration for H-3 was
determined in the same manner as for 1 on the basis of ROESY correlations between
H-3a/Me-28 and H-3a/H-5a, whereas another correlation between Me-29/Me-19, Me-
19/Me-18, H-12a/H-30, H-30/H-17a, and H-17a/Me-21 confirmed the b-configuration

4
T. THI KIEU MY ET AL.
for the substituent OH-12 and S-configuration at C-20 (see Supporting data).
Accordingly, compound 2 was determined as 3b,12b,20S-trihydroxydammar-24-ene-3-
O-b-D-xylopyranosyl-20-O-[b-D-xylopyranosyl-(1!6)-b-D-glucopyranoside].
Compound 3 was obtained as a white, amorphous powder. Its molecular formula of
C53H88O22 was determined by HR-ESI-MS (m/z 1075.5663 [M‒H]‒, calcd. for C53H87O22,
1075.5668). The 1D and 2D NMR spectrum of 3 suggested a dammarane-type triter-
penoid skeleton with a carbonyl function. By comparison of its NMR spectra with
those of ginsenoside Rb3 (9) showed the absence of a 12-oxymethine signal, and an
additional quaternary carbonyl carbon signal (dC 215.5) was observed (Sanada and
Shoji 1978). Analysis of the 13C NMR data of 3, the carbonyl group was placed at C-12.
This assignment was supported by the HMBC correlations between H-13 (dH 3.32) and
H-11a (dH 2.13)/H-11b (dH 2.43) with the quaternary carbonyl signal (dC 215.5, C-12).
Hydrolysis of compound 3 yielded D-xylose and D-glucose. By GC analysis of the acet-
ate derivatives of the component monosaccharides, it was clear that 3 contained three
units of D-glucose and one of D-xylose. The location of the each sugar moiety was
determined by an HMBC experiment [dH 4.44 (H-1’)/dC 90.9 (C-3), dH 4.69 (H-1’’)/dC
81.2 (C-2’), dH 4.46 (H-1’’’)/dC 82.6 (C-20), and dH 4.31 (H-1’’’’)/dC 70.0 (C-6’’’), indicating
that the four sugar moieties (two glucose and a xylosyl-glucose) could be located at
C-3 and C-20, respectively (see Supporting data). The configuration of 3 was eluci-
dated as H-3a and 20S in the same manner as for 1 and 2. Thus, compound 3 was
elucidated as 12-oxo-3b,20S-dihydroxydammar-24-ene-3-O-[b-D-glucopyranosyl(1!2)-
b-D-glucopyranosyl]-20-O-[b-D-xylopyranosyl-(1!6)-b-D-glucopyranoside].
Together with three new saponins (1‒3), the 6 known dammarane-type saponins
were identified by comparison of their reported spectroscopic data as gypenoside XIII
(4) (Takemoto et al. 1983), ginsenoside Rg5 (5) (Yang et al. 2014), ginsenoside F2 (6)
(Yahara et al. 1976), ginsenoside Rg3 (7) (Yang et al. 1983), gypenoside IX (8)
(Takemoto et al. 1983), and ginsenoside Rb3 (9) (Sanada and Shoji 1978) (Figure 1).
3. Experimental
3.1. General procedures
Thin layer chromatography (TLC) was performed using precoated Kiesel gel 60 F254
(Merck) and visualized by UV light 254 nm and 10% H2SO4 reagent by heating.
Column chromatography (CC) was performed using silica gel 60 (Merck, 70–230 mesh)
and C18 reverse phase powder (ODS-A 75 mm, YMC, Japan). NMR experiments were
carried out on a Bruker AM500 FT-NMR spectrometer (Bruker, Rheinstetten, Germany)
using residual solvent peak as a reference or tetramethylsilane (TMS) as internal stand-
ard. The HR-ESI-MS were recorded on a Waters Q-TOF micromass spectrometer Waters
Q-TOF micromass spectrometer.
3.2. Plant materials
The aerial parts of G. burmanicum were collected in April 2015 at Bac Kan province,
Vietnam and identified by Prof. Tran Van On, Hanoi University of Pharmacy. The

NATURAL PRODUCT RESEARCH
5
voucher specimens (No HNIP/18136/15) were deposited at the Herbarium of Hanoi
University of Pharmacy.
3.3. Extraction and isolation
The air-dried and powdered aerial parts of G. burmanicum (3.5 kg) were extracted with
EtOH (24 L ꢀ 3) at room temperature, and then the solution was evaporated in vacuo.
The residue (650 g) was suspended in distilled water and partitioned with n-hexane
and EtOAc to obtain n-hexane (15.7 g) and (74.8 g) EtOAc residues, respectively. The
water fraction was chromatographed on a Diaion HP-20 column eluted with a step
gradient of H2O-MeOH (20:80 to 0:100) to give four fractions (GPB1-GPB4).
Compounds 4 (57.0 mg), 5 (25.4 mg), 6 (7.0 mg), and 7 (5.7 mg) were purified from
fraction GPB2 (7.5 g) after subjecting it to YMC RP-C18 CC eluted with acetone–H2O
(1.7:1, v/v), followed by silica gel CC using CH2Cl2–MeOH–H2O (4.5:1:0.2, v/v/v). In a
similar process to that describe above, fraction GPB3 (3.9 g) was further separated on
silica gel CC with CH2Cl2–MeOH–H2O (3:1:0.2, v/v/v) as eluent, followed by YMC RP-C18
CC with MeOH–H2O (1:3, v/v) to obtain compounds 1 (8.4 mg), 2 (52.4 mg), and 8
(77 mg). Finally, compounds 3 (52.4 mg) and 9 (37.0 mg) were isolated from fraction
GPB4 (3.1 g) by YMC RP-C18 CC eluted with acetone–H2O (1:1.5, v/v).
3.3.1. 3β,20S-dihydroxydammar-24-ene-3-O-β-D-glucopyranosyl-20-O-
[β-D-xylopyranosyl-(1!6)-β-D-glucopyranoside] (1)
White, amorphous powder. HR-ESI-MS m/z 899.5334 [M ‒ H]‒ (Calcd. for C47H79O16,
1
899.5338). H NMR (CD3OD, 500 MHz): dH 1.71 (1H, m, H-1a), 1.00 (1H, m, H-1b), 1.95
(1H, m, H-2a), 1.72 (1H, m, H-2b), 3.18 (1H, d, J ¼ 9.5 Hz, H-3), 0.80 (1H, d, J ¼ 11.0 Hz,
H-5), 1.56 (1H, m, H-6a), 1.49 (1H, m, H-6b), 1.58 (1H, m, H-7a), 1.30 (1H, m, H-7b), 1.40
(1H, m, H-9), 1.53 (1H, m, H-11a), 1.29 (1H, m, H-11b), 1.74 (1H, m, H-12), 1.75 (1H, m,
H-13), 1.49 (1H, m, H-15a), 1.04 (1H, m, H-15b), 1.85 (1H, m, H-16a), 1.34 (1H, m,
H-16b), 1.97 (1H, m, H-17), 1.01 (3H, s, H-18), 0.91 (3H, s, H-19), 1.25 (3H, s, H-21), 1.58
(1H, m, H-22a), 1.30 (1H, m, H-22b), 2.07 (2H, m, H-23), 5.11 (1H, t, J ¼ 7.0 Hz, H-24),
1.70 (3H, s, H-26), 1.63 (3H, s, H-27), 1.06 (3H, s, H-28), 0.86 (3H, s, H-29), 0.93 (3H, s,
H-30); C-3-Glc-1 (inner): dH 4.43 (1H, d, J ¼ 7.5 Hz, H-1’), 3.30 (1H, dd, J ¼ 7.5, 9.0 Hz,
H-2’), 3.26 (1H, m, H-3’), 3.31 (1H, m, H-4’), 3.31 (1H, m, H-5’), 3.85 (1H, dd, J ¼ 2.5,
11.0 Hz, H-6’a), 3.67 (1H, br d, J ¼ 11.0 Hz, H-6’b); C-20-Glc-1 (inner): dH 4.49 (1H, d,
J ¼ 7.5, H-1’’), 3.32 (1H, m, H-2’’), 3.36 (1H, m, H-3’’), 3.38 (1H, m, H-4’’), 3.38 (1H, m,
H-5’’), 4.00 (1H, d, J ¼ 2.5, 11.0 Hz, H-6’’a), 3.76 (1H, dd, J ¼ 5.0, 11.0 Hz, H-6’’b); Xyl-1
(term): dH 4.30 (1H, d, J ¼ 7.5 Hz, H-1’’’), 3.23 (1H, m, H-2’’’), 3.36 (1H, m, H-3’’’), 3.50 (1H,
m, H-4’’’), 3.87 (1H, m, H-5’’’a), and 3.21 (1H, t, J ¼ 10.5 Hz, H-5’’’b). 13C NMR (CD3OD,
125 MHz): dC 40.3 (C-1), 27.2 (C-2), 90.8 C-3), 40.4 (C-4), 57.7 (C-5), 19.2 (C-6), 36.5 (C-7),
41.6 (C-8), 52.1 (C-9), 38.0 (C-10), 22.7 (C-11), 26.0 (C-12), 43.5 (C-13), 51.5 (C-14), 32.2
(C-15), 28.8 (C-16), 48.9 (C-17), 16.1 (C-18), 16.9 (C-19), 83.8 (C-20), 21.5 (C-21), 40.8
(C-22), 23.6 (C-23), 126.3 (C-24), 131.7 (C-25), 25.9 (C-26), 18.0 (C-27), 28.4 (C-28), 16.8
(C-29), 17.1 (C-30); C-3-Glc-1 (inner): dC 106.6 (C-1’), 75.6 (C-2’), 77.6 (C-3’), 71.6 (C-4’),
77.4 (C-5’), 62.8 (C-6’); C-20-Glc-1 (inner): dC 98.6 (C-1’’), 75.5 (C-2’’), 78.4 (C-3’’), 71.5

6
T. THI KIEU MY ET AL.
(C-4’’), 76.2 (C-5’’), 70.1 (C-6’’); Xyl-1 (term): dC 105.5 (C-1’’’), 74.7 (C-2’’’), 78.2 (C-3’’’),
71.1 (C-4’’’), and 66.7 (C-5’’’).
3.3.2. 3β,12β,20S-trihydroxydammar-24-ene-3-O-β-D-xylopyranosyl-20-O-
[β-D-xylopyranosyl-(1!6)-β-D-glucopyranoside] (2)
White, amorphous powder. HR-ESI-MS m/z 885.5215 [M‒ H]‒ (Calcd. for C46H77O16,
1
885.5211). H NMR (CD3OD, 500 MHz): dH 1.70 (1H, m, H-1a), 0.97 (1H, m, H-1b), 1.80
(1H, m, H-2a), 1.68 (1H, m, H-2b), 3.10 (1H, d, J ¼ 9.5 Hz, H-3), 0.76 (1H, d, J ¼ 11.0 Hz,
H-5), 1.54 (1H, m, H-6a), 1.46 (1H, m, H-6b), 1.54 (1H, m, H-7a), 1.28 (1H, m, H-7b), 1.41
(1H, m, H-9), 1.77 (1H, m, H-11a), 1.27 (1H, m, H-11b), 3.70 (1H, m, H-12), 1.71 (1H, m,
H-13), 1.55 (1H, m, H-15a), 1.02 (1H, m, H-15b), 1.79 (1H, m, H-16a), 1.33 (1H, m,
H-16b), 2.26 (1H, m, H-17), 0.98 (3H, s, H-18), 0.90 (3H, s, H-19), 1.34 (3H, s, H-21), 1.77
(1H, m, H-22a), 1.50 (1H, m, H-22b), 2.14 (1H, m, H-23a), 2.02 (1H, m, H-23b), 5.11 (1H,
t, J ¼ 7.0 Hz, H-24), 1.67 (3H, s, H-26), 1.61 (3H, s, H-27), 1.02 (3H, s, H-28), 0.83 (3H, s,
H-29), 0.90 (3H, s, H-30); C-3-Xyl-1 (inner): dH 4.24 (1H, d, J ¼ 7.5 Hz, H-1’), 3.16 (1H, m,
H-2’), 3.27 (1H, m, H-3’), 3.47 (1H, m, H-4’), 3.16 (2H, t, J ¼ 10.5 Hz, H-5’); C-20-Glc-1
(inner): dH 4.55 (1H, d, J ¼ 7.5 Hz, H-1’’), 3.11 (1H, m, H-2’’), 3.33 (1H, m, H-3’’), 3.31 (1H,
m, H-4’’), 3.38 (1H, m, H-5’’), 4.00 (1H, dd, J ¼ 2.5, 11.0 Hz, H-6’’a), 3.73 (1H, br d,
J ¼ 11.0 Hz, H-6’’b); Xyl-1 (term): dH 4.28 (1H, d, J ¼ 7.5 Hz, H-1’’’), 3.19 (1H, m, H-2’’’),
3.29 (1H, m, H-3’’’), 3.44 (1H, m, H-4’’’), 3.83 (1H, m, H-5’’’a), and 3.18 (1H, t, J ¼ 10.5 Hz,
H-5’’’b). 13C NMR (CD3OD, 125 MHz): dC 40.2 (C-1), 27.2 (C-2), 90.4 (C-3), 40.3 (C-4), 57.5
(C-5), 19.2 (C-6), 35.8 (C-7), 40.9 (C-8), 51.1 (C-9), 37.9 (C-10), 30.8 (C-11), 71.6 (C-12),
49.7 (C-13), 52.4 (C-14), 31.5 (C-15), 27.3 (C-16), 52.9 (C-17), 16.3 (C-18), 16.7 (C-19),
84.9 (C-20), 22.4 (C-21), 36.7 (C-22), 23.8 (C-23), 126.0 (C-24), 132.1 (C-25), 25.9 (C-26),
18.0 (C-27), 28.4 (C-28), 16.8 (C-29), 17.4 (C-30); C-3-Xyl-1 (inner): dC 107.3 (C-1’), 75.4
(C-2’), 77.9 (C-3’), 71.2 (C-4’), 66.7 (C-5’); C-20-Glc-1 (inner): dC 98.0 (C-1’’), 75.2 (C-2’’),
78.5 (C-3’’), 71.4 (C-4’’), 76.6 (C-5’’), 70.0 (C-6’’); Xyl-1 (term): dC 105.4 (C-1’’’), 74.7 (C-2’’’),
77.4 (C-3’’’), 71.1 (C-4’’’), and 66.6 (C-5’’’).
3.3.3. 12-oxo-3β,20S-dihydroxydammar-24-ene-3-O-[β-D-glucopyranosyl(1!2)-β-D-
glucopyrano syl]-20-O-[β-D-xylopyranosyl-(1!6)-β-D-glucopyranoside] (3)
White, amorphous powder. HR-ESI-MS m/z 1075.5663 [M ‒ H]‒ (Calcd. for C53H87O22,
1
1075.5668). H NMR (CD3OD, 500 MHz): dH 1.60 (1H, m, H-1a), 1.03 (1H, m, H-1b), 1.99
(1H, m, H-2a), 1.74 (1H, m, H-2b), 3.20 (1H, d, J ¼ 9.5 Hz, H-3), 0.82 (1H, d, J ¼ 11.0 Hz,
H-5), 1.66 (1H, m, H-6a), 1.57 (1H, m, H-6b), 1.55 (1H, m, H-7a), 1.42 (1H, m, H-7b), 1.73
(1H, m, H-9), 2.43 (1H, m, H-11a), 2.13 (1H, m, H-11b), 3.32 (1H, d, J ¼ 9.0 Hz, H-13),
1.82 (1H, m, H-15a), 1.16 (1H, m, H-15b), 1.92 (1H, m, H-16a), 1.75 (1H, m, H-16b), 2.52
(1H, m, H-17), 1.28 (3H, s, H-18), 1.01 (3H, s, H-19), 1.13 (3H, s, H-21), 1.66 (2H, m,
H-22), 2.03 (2H, m, H-23), 5.12 (1H, t, J ¼ 7.0 Hz, H-24), 1.70 (3H, s, H-26), 1.64 (3H, s,
H-27), 1.10 (3H, s, H-28), 0.90 (3H, s, H-29), 0.76 (3H, s, H-30); C-3-Glc-1 (inner): dH 4.44
(1H, d, J ¼ 7.5 Hz, H-1’), 3.60 (1H, m, H-2’), 3.33 (1H, m, H-3’), 3.30 (1H, m, H-4’), 3.43
(1H, m, H-5’), 3.84 (1H, br d, J ¼ 11.0 Hz, H-6’a), 3.64 (1H, dd, J ¼ 5.5, 11.0 Hz, H-6’b);
Glc-2 (term): dH 4.69 (1H, d, J ¼ 7.5 Hz, H-1’’), 3.24 (1H, dd, J ¼ 7.5, 9.0 Hz, H-2’’), 3.36
(1H, m, H-3’’), 3.26 (1H, m, H-4’’), 3.29 (1H, m, H-5’’), 3.86 (1H, dd, J ¼ 2.5, 11.0 Hz,

NATURAL PRODUCT RESEARCH
7
H-6’’a), 3.67 (1H, br d, J ¼ 11.0 Hz, H-6’’b); C-20-Glc-1 (inner): dH 4.46 (1H, d, J ¼ 7.5 Hz,
H-1’’’), 3.13 (1H, m, H-2’’’), 3.36 (1H, m, H-3’’’), 3.37 (1H, m, H-4’’’), 3.38 (1H, m, H-5’’’),
4.00 (1H, dd, J ¼ 2.5, 11.0 Hz, H-6’’’a), 3.77 (1H, dd, J ¼ 5.0, 11.0 Hz, H6’’’b); Xyl-1 (term):
dH 4.31 (1H, d, J ¼ 7.5 Hz, H-1’’’’), 3.24 (1H, m, H-2’’’’), 3.35 (1H, m, H-3’’’’), 3.50 (1H, m,
H-4’’’’), 3.87 (1H, dd, J ¼ 2.5, 11.0 Hz, H-5’’’’a), and 3.21 (1H, m, H-5’’’b). 13C NMR
(CD3OD, 125 MHz): dC 39.9 (C-1), 27.1 (C-2), 90.9 (C-3), 40.5 (C-4), 57.4 (C-5), 19.3 (C-6),
35.5 (C-7), 41.1 (C-8), 56.3 (C-9), 38.5 (C-10), 40.8 (C-11), 215.5 (C-12), 57.2 (C-13), 57.5
(C-14), 33.0 (C-15), 25.0 (C-16), 43.1 (C-17), 16.3 (C-18), 16.7 (C-19), 82.6 (C-20), 22.7 (C-
21), 40.5 (C-22), 24.5 (C-23), 126.0 (C-24), 131.9 (C-25), 25.9 (C-26), 17.8 (C-27), 28.3 (C-
28), 16.6 (C-29), 17.1 (C-30); C-3-Glc-1 (inner): dC 105.3 (C-1’), 81.2 (C-2’), 77.4 (C-3’), 71.5
(C-4’), 78.5 (C-5’), 63.1 (C-6’); Glc-2 (term): dC 104.5 (C-1’’), 76.3 (C-2’’), 77.8 (C-3’’), 71.9
(C-4’’), 77.6 (C-5’’), 62.8 (C-6’’); C-20-Glc-1 (inner): dC 98.4 (C-1’’’), 75.5 (C-2’’’), 78.6 (C-3’’’),
71.4 (C-4’’’), 76.2 (C-5’’’), 70.0 (C-6’’’); Xyl-1 (term): dC 105.5 (C-1’’’’), 74.7 (C-2’’’’), 78.3 (C-
3’’’’), 71.1 (C-4’’’’), and 66.7 (C-5’’’’).
3.4. Acid hydrolysis of compounds 1–3 and determination of sugar components
The sugar units were identified by acid hydrolysis of compounds followed by GC-MS
analysis. This part was conducted according to published protocols with modifications.
Details as presented in a previous paper (Thao et al. 2016).
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work is supported by the Department of Botany, Hanoi University of Pharmacy. We thank
the Institute of Chemistry (VAST) for the NMR experiments.
ORCID
Nguyen Phuong Thao
http://orcid.org/0000-0002-5212-7543
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