Three new triterpenoid saponins from Albizia julibrissin

Article abstract of DOI:10.1080/10286020.2018.1473385

Three new triterpenoid saponins, julibrosides A₅–A₇ (1–3), together with five known saponins (4–8), were isolated from the stem bark of Albizia julibrissin. Their structures were elucidated on the basis of extensive spectroscopic data analysis of MS, 1D and 2D NMR, and chemical methods. Compounds 7 and 8 were isolated from the genus Albizia for the first time. The new compounds showed no cytotoxicity and anti-inflammatory activity.

Full text of DOI:10.1080/10286020.2018.1473385

Journal of Asian Natural Products Research
ISSN: 1028-6020 (Print) 1477-2213 (Online) Journal homepage: http://www.tandfonline.com/loi/ganp20
Three new triterpenoid saponins from Albizia
julibrissin
Xu-Da Wang, Qing-Hua Han, Jun Zhang, Qing-Ying Zhang, Peng-Fei Tu & Hong
Liang
To cite this article: Xu-Da Wang, Qing-Hua Han, Jun Zhang, Qing-Ying Zhang, Peng-Fei Tu
& Hong Liang (2018): Three new triterpenoid saponins from Albizia julibrissin, Journal of Asian
Natural Products Research
To link to this article: https://doi.org/10.1080/10286020.2018.1473385
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Journal of asian natural Products research, 2018
https://doi.org/10.1080/10286020.2018.1473385
Three new triterpenoid saponins from Albizia julibrissin
Xu-Da Wang, Qing-Hua Han, Jun Zhang, Qing-Ying Zhang, Peng-Fei Tu and
Hong Liang
department of natural Medicines, school of Pharmaceutical sciences, Peking university health science
center, Beijing 100191, china
ABSTRACT
ARTICLE HISTORY
received 29 January 2018
accepted 2 May 2018
Three new triterpenoid saponins, julibrosides A5–A7 (1–3), together
with five known saponins (4–8), were isolated from the stem bark
of Albizia julibrissin. Their structures were elucidated on the basis of
extensive spectroscopic data analysis of MS, 1D and 2D NMR, and
chemical methods. Compounds 7 and 8 were isolated from the genus
Albizia for the first time. The new compounds showed no cytotoxicity
and anti-inflammatory activity.
KEYWORDS
leguminosae; Albizia
julibrissin; triterpenoid
saponin; julibrosides a5–a7
1. Introduction
Albizia julibrissin Durazz. (family Leguminosae) is a timber tree, widely distributed in most
provinces of China [1]. Its stem bark has been widely used in traditional Chinese medicine
for the treatment of swelling and wounds and has been recorded in Chinese Pharmacopoeia
[2]. Previous phytochemical studies on A. julibrissin have revealed that oleanane-type tri-
terpenoid saponins were the principle constituents, commonly featuring an acacic acid
aglycone and varying in oligosaccharide moieties at C-3 and C-28 and monoterpenoid gly-
cosyl units at C-21 [3,4]. Some of these triterpenoid saponins exhibited cytotoxic activities
against different cancer cell lines in vitro and anti-angiogenic effect in vivo [5–7]. As part
of our continuing study on the chemistry and biological activities of A. julibrissin, three
new triterpenoid saponins (1–3) and five known triterpenoid saponins (4–8) were isolated
from the EtOAc fraction of the ethanol extract of the plant (Figure 1). e new compounds
CONTACT hong liang
lianghong@bjmu.edu.cn
supplemental data for this article can be accessed https://doi.org/10.1080/10286020.2018.1473385.
© 2018 informa uK limited, trading as taylor & francis Group

2
X.-D. WANG ET AL.
Figure 1. structures of compounds 1–3.
were evaluated for in vitro anti-inflammatory activity. Herein, we report the isolation and
structural elucidation of the new compounds.
2. Results and discussion
e EtOAc soluble part (138.5 g) of the 95% aqueous EtOH extract of A. julibrissin was sub-
jected to silica gel and Sephadex LH-20 column chromatography, followed by semi-prepara-
tive HPLC to afford three new triterpenoid saponins (1–3) and five known analogues (4–8).
Julibroside A5 (1) was obtained as white amorphous powder, with [α]20D −52.0 (c 0.10,
MeOH). e IR spectrum of 1 showed absorption bands for hydroxy (3363 cm−1) and
γ-lactone (1769 cm−1) functionalities. Its molecular formula was determined as C42H66O13
by the positive HRESI-MS ion at m/z 801.4407 [M+Na]+, corresponding to 10 indices of
hydrogen deficiency. e 1H and 13C NMR (Tables 1 and 2) spectra showed characteristic
signals of an oleanane triterpenoid saponin [4], containing two sugar units. is was evi-
denced by the presence of seven singlet methyl signals at δH 0.79 (3H, s), 0.81 (3H, s), 0.97
(3H, s), 1.00 (3H, s), 1.08 (3H, s), 1.27 (3H, s), and 1.33 (3H, s), an olefinic proton signal
at δH 5.33 (1H, brs, H-12), two olefinic carbon signals at δC 124.9 (C-12) and 140.4 (C-13),
and a carbonyl carbon signal at δC 181.6 (C-28) for the oleanane core, two anomeric protons
at δH 4.86 (1H, d, J = 7.8 Hz) and 4.93 (1H, d, J = 7.8 Hz), and two anomeric carbons at δC
107.3 and 105.9 for the sugar units. e aglycone was further recognized to be acacic acid
lactone by comparison of its 1H and 13C NMR data with those reported in the literature [8].
Acid hydrolysis of compound 1 gave a mixture of sugars, which were identified as d-fu-
cose and d-glucose by HPLC analysis of their arylthiocarbamate derivatives with authentic
1
samples [9]. e structure of 1 was determined based on the detailed analyses of H–1H
COSY, HSQC, HSQC-TOCSY, and HMBC spectra. In the HMBC (Figure 2) spectrum, Fuc-
H-1 at δH 4.93 correlated with Glc-C-6 at δC 70.5, Glc-H-1 at δH 4.86 correlated with C-3 at
δC 89.2, indicating that the sugar moiety of d-fucopyranosyl-(1→6)-d-glucopyranosyl was
attached to C-3 of the aglycone. e configurations of the two sugars were established to be
β by the 1H NMR spectrum. us, the structure of 1 was established as acacic acid lactone
3-O-β-d-fucopyranosyl-(1→6)-β-d-glucopyranoside, named julibroside A5.
Julibroside A6 (2) was obtained as amorphous powder. Its molecular formula was estab-
lished as C44H69NO13 (11 indices of hydrogen deficiency) from the 13C NMR data and the
positive HRESI-MS ion at m/z 820.4852 [M+H]+. e NMR data of 2 resembled to those
of 1, except for the presence of an additional acetylamino group as indicated by the signals
at δH 2.15 (3H, s, NHCOCH3), 8.92 (1H, d, J = 11.0 Hz, NHCOCH3), δC 24.1 (NHCOCH3)

JOURNAL OF ASIAN NATURAL PRODUCTS RESEARCH
3
1
Table 1. h nMr (600 Mhz, pyridine-d5) and 13c nMr (150 Mhz, pyridine-d5) spectroscopic data of the
aglycone moieties of compounds 1–3.
1
2a
δH (J in Hz)
3
t
δH (J in Hz)
δC
δC
δH (J in Hz)
δC
1
1.54–1.56, m
1.00, overlap
39.0, ch2
1.49–1.51, m
0.95, overlap
38.9 ch2
1.39, overlap
0.81–0.84, m
38.9 ch2
2
2.41, dd (3.6, 13.8)
1.90–1.92, m
27.0, ch2
2.37–2.42, m
1.85, overlap
26.8 ch2
2.23, dd (3.6, 13.8)
1.78–1.81, m
26.7 ch2
3
4
5
6
3.32, dd (4.2, 11.4)
89.2, ch
39.8, c
56.2, ch
18.7, ch2
3.19, dd (5.0, 14.5)
89.4, ch
39.6, c
56.1, ch
18.8 ch2
3.26, dd (4.2, 11.4)
89.4, ch
39.6, c
56.2, ch
18.8 ch2
0.72, d (11.4)
1.47–1.48, m
1.28–1.30, m
1.41–1.43, m
1.37–1.39, m
0.68, d (14.0)
1.38–1.39, m
1.29–1.31, m
1.44–1.46, m
1.38–1.40, m
0.74, d (12.0)
1.52, overlap
1.29–1.32, m
1.43–1.45, m
1.38–1.40, m
7
32.8,ch2
32.8 ch2
32.9 ch2
8
9
10
11
40.6, c
47.5, ch
37.2, c
40.6, c
47.5, ch
37.2, c
40.7, c
47.6, ch
37.3, c
1.50–1.52, m
1.47–1.49, m
1.50, overlap
1.90–1.92, m
1.78–1.80, m
5.33, brs
24.0, ch2
1.86–1.88, m
1.76–1.80, m
5.31, brs
24.1 ch2
1.86–1.88, m
1.78–1.81, m
5.36, brs
24.1 ch2
12
13
14
15
124.9, ch
140.4, c
43.6, c
124.9,ch
140.4, c
43.6, c
124.9, ch
140.5, c
43.7, c
2.31, overlap
1.46, overlap
4.53, dd (4.8, 11.4)
38.5, ch2
2.27–2.29, m
1.43–1.45, m
4.51–4.53, m
38.5 ch2
2.30–2.33, m
1.47, overlap
4.54, dd (4.8, 10.2)
38.6 ch2
16
17
18
19
67.0, ch
50.3, c
42.0, ch
43.3, ch2
67.0, ch
50.3, c
42.0, ch
43.3 ch2
67.0, ch
50.4, c
42.1, ch
43.3 ch2
2.79–2.81, m
1.86–1.88, m
1.41–1.43, m
2.79–2.81, m
1.83–1.85, m
1.39–1.41, m
2.79–2.81, m
1.86–1.88, m
1.42, overlap
20
21
22
34.5, c
83.8, ch
27.5, ch2
34.5, c
83.8, ch
27.6 ch2
34.3, c
83.8, ch
27.6 ch2
4.26, d (5.4)
2.79–2.81, m
2.30–2.32, m
1.27, s
4.26, overlap
2.79–2.81, m
2.29–2.31, m
1.13, s
4.26, d (5.4)
2.79–2.81, m
2.30–2.32, m
1.19, s
23
24
25
26
27
28
29
30
28.4, ch3
17.3, ch3
16.0, ch3
16.5, ch3
29.1, ch3
181.6, c
28.4, ch3
17.3, ch3
15.9, ch3
16.5, ch3
29.1, ch3
181.6, c
28.4, ch3
17.3, ch3
15.9, ch3
16.6, ch3
29.1, ch3
181.6, c
1.00, s
0.81, s
0.79, s
1.33, s
1.00, s
0.77, s
0.78, s
1.33, s
1.00, s
0.76, s
0.79, s
1.37, s
0.97, s
1.08, s
28.9, ch3
24.6, ch3
0.97, s
1.08, s
28.9, ch3
24.6, ch3
0.95, s
1.07, s
28.9, ch3
24.7, ch3
arecorded 1h nMr at 500 Mhz, and 13c nMr at 125 Mhz.
and 170.5 (NHCOCH3), suggesting that 2 was an amino acetylated derivative of 1. e
acetylamino group was located at Glc-C-2 by HMBC correlation between δH 4.51–4.53
(Glc-H-2) and δC 170.5 (NHCOCH3). e configurations of the two sugars were established
1
to be β by the H NMR spectrum. us, the structure of 2 was determined to be acacic
acid lactone 3-O-β-d-fucopyranosyl-(1→6)-β-d-2-deoxy-2-acetylaminoglucopyranoside,
named julibroside A6.
Julibroside A7 (3) was obtained as white amorphous powder. Its molecular formula was
deduced as C38H59NO9 (10 indices of hydrogen deficiency) on the basis of the positive
HRESI-MS data (m/z 674.4275 [M+H]+). e NMR data of 3 were similar to those of 2,
except for the absence of a fucopyranosyl unit in 3. e structure of 3 was determined based
on the detailed analyses of 1H–1H COSY, HSQC, HSQC-TOCSY, and HMBC spectra. In
the HMBC (Figure 2) spectrum, Glc-H-1 at δH 5.08 correlated with C-3 at δC 89.4, Glc-H-2

4
X.-D. WANG ET AL.
1
Table 2. h nMr (600 Mhz, pyridine-d5) and 13c nMr (150 Mhz, pyridine-d5) spectroscopic data of the
sugar moieties of compounds 1–3.
1
2a
3
Position
δH
δC
δH
δC
δH
δC
Glc-1
4.86, d (7.8)
4.00, t (8.4)
4.21, t (8.7)
4.15, t (9.0)
107.3,ch
75.9,ch
78.9,ch
72.1,ch
77.2,ch
70.5,ch2
4.99, d (10.0)
4.51–4.53, m
4.06–4.09, m
4.37–4.39, m
4.11–4.15, m
4.28, overlap
4.89, d (13.5)
8.92, d (11.0)
105.3,ch
58.2,ch
77.2,ch
73.0,ch
76.3,ch
70.4,ch2
5.08, d (8.4)
105.3,ch
58.5,ch
78.7,ch
73.0,ch
76.5,ch
63.4,ch2
2
3
4
5
6
4.57, overlap
3.97–4.00, m
4.19, t (9.0)
4.10–4.13, m
4.33, dd (6.0, 11.4)
4.91, dd (1.2, 11.4)
4.44, t (9.0)
4.37, dd (6.0, 12.0)
4.58, d (10.8)
8.91, d (9.0)
nhcoch3
nhcoch3
nhcoch3
fuc-1
2
3
4
5
6
170.5,c
24.1,ch3
105.9,ch
72.5,ch
75.6,ch
72.9,ch
71.8,ch
17.7,ch3
170.6,c
24.1,ch3
2.15, s
4.90, d (9.5)
4.37–4.39, m
4.07–4.09, m
4.05, dd (1.5, 14.0)
3.81, q (8.0)
2.17, s
4.93, d (7.8)
4.39, t (9.0)
4.08, dd (3.4, 9.5)
4.04, d (3.2)
3.80, q (6.6)
1.53, d (6.6)
105.9,ch
72.5,ch
75.6,ch
73.0,ch
71.8,ch
17.6,ch3
1.53, d (8.0)
arecorded 1h nMr at 500 Mhz, and 13c nMr at 125 Mhz.
Figure 2. Key hMBc correlations of compounds 1–3.
at δH 4.57 correlated with NHCOCH3 at δC 170.6, suggesting that the sugar moiety of
d-2-deoxy-2-acetylaminoglucosyl was attached to C-3 of the aglycone. e configuration
of the sugar was established to be β by the 1H NMR spectrum. us, the structure of 3 was
established as acacic acid lactone 3-O-β-d-2-deoxy-2-acetylaminoglucopyranoside, named
julibroside A7.
e known compounds were identified as julibroside A1 (4) [8], julibroside A2 (5) [8],
julibroside A3 (6) [8], acaciamine (7) [10], and sonunin I (8) [11]. Compounds 7 and 8
were isolated from the genus Albizia for the first time.
Inflammation consists of a complex mechanism developed as the first response of the
immune system to viral, bacterial, or parasitic infections. NO is a signaling molecule that
plays a key role in the pathogenesis of inflammation. erefore, inhibition of NO release
represents an important therapeutic target in the management of inflammatory diseases.
us, the new compounds were tested for their inhibitory effects on LPS-induced NO
production in BV-2 microglial cells. e compounds showed no remarkable effect against
NO production at 100 μM. In order to investigate the cytotoxicity, the effects of the new
compounds on cell proliferation were measured using the MTT method. None showed
obvious cytotoxicity at a dosage of 100 μM.

JOURNAL OF ASIAN NATURAL PRODUCTS RESEARCH
5
3. Experimental
3.1. General experimental procedures
Optical rotations were measured on a Rudolph Autopol IV automatic polarimeter (Rudolph
Research Analytical Co. Ltd., Hackettstown, NJ, USA). UV spectra were recorded on a
Shimadzu UV-2450 UV-Vis spectrophotometer (Shimadzu Co. Ltd., Kyoto, Japan). IR
spectra were recorded on a ermo Nicolet Nexus 470 FT-IR spectrometer (Nicolet Co.
Ltd., Denver, USA). NMR spectra were measured on a Bruker AVANCE III-600 NMR
spectrometer (Bruker, Fällanden, Switzerland) and a Varian Inova-500 NMR spectrometer
(Varian Inc., CA, USA) with TMS as reference. High-resolution electro-spray ionization
mass spectrometry (HRESI-MS) was acquired on a Waters Xevo G2 Q-TOF/YCA mass
spectrometer (Waters Corporation, Manchester, UK). Semi-preparative HPLC was per-
formed on a Phenomenex Gemini C18 column (250 × 10 mm, 5 μm) using an Agilent 1260
LC system. Column chromatography (CC) was performed on Sephadex LH-20 (Pharmacia
Fine Chemical Ltd., Uppsala, Sweden), silica gel (200–300 mesh, Qingdao Marine Chemical
Inc., Qingdao, China), and ODS (50 μm, YMC Co. Ltd., Japan). in layer chromatography
(TLC) analysis was carried out using precoated silica gel GF254 plates (Qingdao Marine
Chemical Inc., Qingdao, China), and spots were observed under UV254 light and sprayed
by 10% H2SO4–EtOH reagent. Other solvents used for extraction and separation were
of analytical grade and purchased from Beijing Tongguang Chemicals (Beijing, China).
HPLC grade solvents used for HPLC analysis and preparation were purchased from Fisher
Scientific International (Pittsburgh, USA).
3.2. Plant material
e dried stem bark of Albizia julibrissin was purchased in October 2014 from Xi’an, Shaanxi
Province of China and was identified by Prof. Mingying Shang, Department of Natural
Medicines, School of Pharmaceutical Sciences, Peking University Health Science Center.
A voucher specimen (HH-201410) was deposited in the Department of Natural Medicines,
School of Pharmaceutical Sciences, Peking University Health Science Center.
3.3. Extraction and isolation
Air-dried powder of the stem bark of A. julibrissin (18.0 kg) was percolated with 95% EtOH
(100 L) and 50% EtOH (100 L), successively. e combined extract was suspended in H2O
and partitioned with EtOAc and n-BuOH, successively. e EtOAc extract (138.5 g) was
fractionated by silica gel column chromatography eluting with CHCl3–CH3OH (100:0,
100:2, 100:5, 100:20, 0:100, v/v) to give five fractions (Fr.A−Fr.E) based on TLC analysis.
Fr. E (29.0 g) was separated over an ODS column chromatography eluting with MeOH–
H2O (20:80, 40:60, 60:40, 80:20, 100:0, v/v) to yield eleven fractions (Fr.E1–Fr.E11). Fr. E1
(1.6 g) was separated by Sephadex LH-20 CC eluting with CH3OH–CHCl3 (1:1, v/v) and
semi-preparative RP-HPLC using CH3CN–H2O (C18,10 mm × 250 mm, 20:80, v/v) to afford 4
(7.3 mg, tR 33.5 min), 1 (10.2 mg, tR 39.4 min), and 5 (9.7 mg, tR 43.1 min). Fr. E3 (608.8 mg)
was separated by Sephadex LH-20 CC eluting with CH3OH–CHCl3 (1:1, v/v) and then
followed by semi-preparative RP-HPLC using CH3CN–H2O (C18,10 mm × 250 mm, 35:65,
v/v) to yield 6 (11.4 mg, tR 18.6 min), 3 (8.6 mg, tR 31.8 min), and 2 (7.8 mg, tR 25.2 min).

6
X.-D. WANG ET AL.
Fr. E4 (1.3 g) was separated by Sephadex LH-20 CC eluting with CH3OH–CHCl3 (1:1, v/v)
and semi-preparative RP-HPLC using CH3CN–H2O (C18,10 mm × 250 mm, 23:77, v/v) to
yield 7 (13.2 mg, tR 53.5 min) and 8 (4.3 mg, tR 55.6 min).
3.3.1. Julibroside A5 (1)
White amorphous power. [α]20D-52.0 (c 0.10, MeOH). UV (MeOH) λmax (log ε) 204.8
1
(3.80) nm; IR (KBr) νmax 3363, 2936, 1769, 1746, 1362, 1032, 992, 806 cm−1; H NMR
(600 MHz, pyridine-d5) and 13C NMR (150 MHz, pyridine-d5) spectral data see Tables 1 and
2. HRESIMS (positive mode): m/z 801.4407 [M+Na]+ (calcd for C42H66O13Na, 801.4401);
HRESI-MS (negative mode): m/z 777.4406 [M−H]− (calcd for C42H65O13, 777.4424) and
823.4457 [M+HCOO]− (calcd for C43H67O15, 823.4480).
3.3.2. Julibroside A6 (2)
White amorphous power. [α]20D-13.3 (c 0.06, MeOH). UV (MeOH) λmax (log ε) 204.3
1
(3.84) nm; IR (KBr) νmax 3360, 2941, 1769, 1747, 1173, 1004, 794, 678 cm−1; H NMR
(500 MHz, pyridine-d5) and 13C NMR (125 MHz, pyridine-d5) spectral data see Tables 1
and 2. HRESI-MS (positive mode): m/z 820.4852 [M+H]+ (calcd for C44H70NO13, 820.4847).
3.3.3. Julibroside A7 (3)
White amorphous power; [α]20D-36.0 (c 0.10, MeOH); UV (MeOH) λmax (log ε) 206.8 (3.74)
nm; IR (KBr) νmax 3296, 2926, 1735, 1611, 1500, 1472, 1458, 1380, 1249, 1147, 1034 cm−1;
1H NMR (600 MHz, pyridine-d5) and 13C NMR (150 MHz, pyridine-d5) spectral data see
Tables 1 and 2. HRESI-MS (positive mode): m/z 674.4275 [M+H]+ (calcd for C38H60NO9,
674.4268).
3.4. Acid hydrolysis and determination of the absolute configuration of the sugars
Compound 1 (2.0 mg) was dissolved in 2 M HCl-H2O (2.0 ml) and heated at 95 °C for
10 h. e reaction mixture was extracted with CH2Cl2 (2.0 ml) three times, and the aque-
ous layer was evaporated under vacuum to furnish a neutral residue. l-Cysteine methyl
ester hydrochloride (2.0 mg) and anhydrous pyridine (1.0 ml) were added to the mixture
and stirred at 60 °C for 1 h. e product was mixed with O-tolylisothiocyanate (10 μl) and
kept at 60 °C for another 1 h. e final reaction mixture was analyzed by HPLC under the
following conditions: an Agilent 1260 chromatograph equipped with a phenomenex col-
umn (5 μm，4.6 × 250 mm); column temperature: 30 °C; mobile phase: isocratic elution
of 23% CH3CN–H2O containing 0.2% formic acid for 50 min and subsequent washing of
the column with 90% CH3CN–H2O for 10 min, flow rate: 0.8 ml/min; injection volume:
10 μl; UV detection wavelength: 250 nm [9]. From the acid hydrolysate of 1, d-glucose and
d-fucose were confirmed by comparison of the retention times of their derivatives with
those standard sugars derivatized in the same way, which showed retention times of 22.32
and 30.36 min, respectively.
3.5. Anti-inflammatory activity assay
e anti-inflammatory effects were investigated by testing their inhibitory effects on LPS-
induced nitric oxide (NO) production in BV-2 cells [12]. Briefly, BV-2 cells (5.0 × 104 cells

JOURNAL OF ASIAN NATURAL PRODUCTS RESEARCH
7
per well) were treated with LPS (1.0 mg/ml) and different concentrations of compounds
for 24 h. en, cell culture supernatants (300 μl) were collected and reacted with 100 μl
of Griess reagent (0.1% naphthylethylene diamine dihydrochloride/1% sulfanilamide/2%
phosphoric acid). Afer incubation for 10 min at room temperature, the optical density was
detected at 540 nm using a microplate reader (Tecan Trading AG, Männedorf, Switzerland).
e experiments were executed in parallel three times.
Acknowledgement
We are grateful to Prof. Mingying Shang (Peking University Health Science Center) for identifying
the plant material.
Disclosure statement
No potential conflict of interest was reported by the authors.
References
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Popularis Sinicae, 39, 65 (1988).
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