Lebbeckoside C, a new triterpenoid saponin from the stem barks of Albizia lebbeck inhibits the growth of human glioblastoma cells

Article abstract of DOI:10.1080/14786419.2018.1440231

One new acacic acid-type saponin, named lebbeckoside C (1), was isolated from the stem barks of Albizia lebbeck. Its structure was established on the basis of extensive analysis of 1D and 2D NMR (¹H, ¹³C NMR, DEPT, COSY, TOCSY, ROESY, HSQC and HMBC) experiments, HRESIMS studies, and by chemical evidence as 3-O-[β-d-xylopyranosyl-(l→2)-β-d-fucopyranosyl-(1→6)-[β-d-glucopyranosyl(1→2)]-β-d-glucopyranosyl]-21-O-{(2E,6S)-6-O-{4-O-[(2E,6S)-2,6-dimethyl-6-O-(β-d-quinovopyranosyl)octa-2,7-dienoyl]-4-O-[(2E,6S)-2,6-dimethyl-6-O-(β-d-quinovopyranosyl)octa-2,7-dienoyl]-β-d-quinovopyranosyl}-2,6-dimethylocta-2,7-dienoyl}acacic acid 28 O-[β-d-quinovopyranosyl-(l→3)-[α-l-arabinofuranosyl-(l→4)]-α-l-rhamnopyranosyl-(l→2)-β-d-glucopyranosyl] ester. The isolated saponin (1) displayed significant cytotoxic activity against the human glioblastoma cell line U-87 MG and TG1 stem-like glioma cells isolated from a patient tumor with IC₅₀ values of 1.69 and 1.44?μM, respectively.

Full text of DOI:10.1080/14786419.2018.1440231

Natural Product Research
Formerly Natural Product Letters
ISSN: 1478-6419 (Print) 1478-6427 (Online) Journal homepage: http://www.tandfonline.com/loi/gnpl20
Lebbeckoside C, a new triterpenoid saponin from
the stem barks of Albizia lebbeck inhibits the
growth of human glioblastoma cells
Olivier Placide Noté, Joséphine Ngo Mbing, Marie-Claude Kilhoffer,
Dieudonné Emmanuel Pegnyemb & Annelise Lobstein
To cite this article: Olivier Placide Noté, Joséphine Ngo Mbing, Marie-Claude Kilhoffer, Dieudonné
Emmanuel Pegnyemb & Annelise Lobstein (2018): Lebbeckoside C, a new triterpenoid saponin
from the stem barks of Albizia lebbeck inhibits the growth of human glioblastoma cells, Natural
Product Research, DOI: 10.1080/14786419.2018.1440231
To link to this article: https://doi.org/10.1080/14786419.2018.1440231
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Natural Product research, 2018
https://doi.org/10.1080/14786419.2018.1440231
Lebbeckoside C, a new triterpenoid saponin from the
stem barks of Albizia lebbeck inhibits the growth of human
glioblastoma cells
Olivier Placide Notéa,b, Joséphine Ngo Mbingb, Marie-Claude Kilhofferc,
Dieudonné Emmanuel Pegnyembb and Annelise Lobsteina+
aFaculté de Pharmacie, Pharmacognosie et Molécules Naturelles Bioactives, laboratoire d’Innovation
thérapeutique, uMr 7200, cNrs-université de strasbourg, Illkirch cedex, France; bFaculté de sciences,
laboratoire de Pharmacochimie des substances Naturelles, département de chimie organique, université de
c
Yaoundé, Yaoundé, cameroon; Faculté de Pharmacie, chimie-Biologie Intégrative, laboratoire d’Innovation
thérapeutique, uMr 7200, cNrs-université de strasbourg, Illkirch cedex, France
ABSTRACT
ARTICLE HISTORY
received 22 January 2018
accepted 9 February 2018
One new acacic acid-type saponin, named lebbeckoside C (1), was
isolated from the stem barks of Albizia lebbeck. Its structure was
established on the basis of extensive analysis of 1D and 2D NMR (1H, 13
C
KEYWORDS
NMR, DEPT, COSY,TOCSY, ROESY, HSQC and HMBC) experiments, HRESIMS
studies, and by chemical evidence as 3-O-[β-d-xylopyranosyl-(l→2)-β-d-
fucopyranosyl-(1→6)-[β-d-glucopyranosyl(1→2)]-β-d-glucopyranosyl]-21-
O-{(2E,6S)-6-O-{4-O-[(2E,6S)-2,6-dimethyl-6-O-(β-d-quinovopyranosyl)
Albizia lebbeck; mimosaceae;
triterpenoid saponin;
cytotoxic activity; u-87 MG
and tG1 stem-like glioma
cells
octa-2,7-dienoyl]-4-O-[(2E,6S)-2,6-dimethyl-6-O-(β-d-quinovopyranosyl)
octa-2,7-dienoyl]-β-d-quinovopyranosyl}-2,6-dimethylocta-2,7-dienoyl}
acacic acid 28 O-[β-d-quinovopyranosyl-(l→3)-[α-l-arabinofuranosyl-
(l→4)]-α-
l
-rhamnopyranosyl-(l→2)-β-d-glucopyranosyl] ester.The isolated
saponin (1) displayed significant cytotoxic activity against the human
glioblastoma cell line U-87 MG and TG1 stem-like glioma cells isolated
from a patient tumor with IC50 values of 1.69 and 1.44 μM, respectively.
CONTACT olivier Placide Noté
+In memory to.
oliviernote1@yahoo.fr
supplemental data for this article can be accessed at https://doi.org/10.1080/14786419.2018.1440231.
© 2018 Informa uK limited, trading as taylor & Francis Group

2
O. P. NOTÉ ET AL.
1. Introduction
Albizia lebbeck (L.) Benth is a pantropical species distributed in Africa, Asia, America, and
Australia. In West Africa, it is traditionally used against diarrhea, dysentery, hemorrhoids,
bronchitis, asthma, eczema, and leprosy (Arbonier 2009). Antiproliferative, nootropic, anxi-
olytic, haemolytic, anti-diarrhoeal, antioxidant, anti-arthritic and antifungal activities have
been reported (Faisal et al. 2012), and the oral administration of saponin fraction isolated
from its bark to male rats has been reported to significantly reduce fertility through reduction
of sperm mobility and density (Gupta et al. 2005). Recently, the in vitro antimalarial activity
of this plant against Plasmodium falciparum chloroquine (CQ) sensitive (MRC2) and CQ resist-
ant (RKL9) strains were reported (Kalia et al. 2015). Previous investigation of its stem barks
revealed the presence of glycosides of acacic acid lactones (Pal et al. 1995), and our last
investigation on the saponin content of its roots unveiled the presence of two new acacic
acid-type saponins, lebbeckosides A─B, molecules cytotoxic at a micromolar concentration
towards high-grade glioma cancer cells including those with stem-like cell properties, known
to be resistant to standard treatments (Noté et al. 2015).
In the present study, we describe the isolation, structural determination, and cytotoxic
evaluation of one new additional triterpenoid saponin isolated from its stem barks, named
lebbeckoside C (1).
2. Results and discussion
The air-dried finely powdered of the stem barks of A. lebbeck were extracted with EtOH 70%
in a Soxhlet apparatus. After evaporation of the solvent, the resulting dark residue was
suspended in water and partitioned against n-BuOH saturated with water. The n-BuOH phase
was then evaporated to dryness affording a brown gum which was submitted to column
chromatography (CC) using Diaion HP-20 resin yielding enriched saponins fractions which
were submitted to VLC using silica gel to give three main subfractions. Purification of the
eluated subfractions by Semprep-HPLC afforded one new triterpenoid saponin, named leb-
beckoside C (1) (Figure 1).
Lebbeckoside C (1) was obtained as a white amorphous powder. Its positive HR-ESI-MS gave
a pseudo-molecular ion peak at m/z 2632.2616 [M + NH4]+ with its isotopic peaks at m/z
2631.2572, 2633.2635 and the corresponding doubly charged ion peaks at m/z 1244.6112,
1245.1120, and 1246.1142 [M + 2 (NH4)]2+. Consequently, lebbeckoside C was assigned a
C124H196O58 molecular formula. Upon acid hydrolysis with 2.0 M HCl, 1 gave an acacic acid
lactone unit, which was identified with an authentic sample, together with glucose (Glc),
xylose (Xyl), fucose (Fuc), quinovose (Qui), arabinofuranose (Araf), and rhamnose (Rha), which
were identified by co-TLC with authentic samples. The absolute configuration of these sugar
residues was determined to be D for Glc, Xyl, Fuc, Qui, and L for Rha and Araf based on GC
analysis of their trimethylsilyl thiazolidine derivatives (See Experimental Section) (Chaabi et
al. 2010). 1H NMR spectrum of 1 showed seven angular methyl groups as singlets at δH 0.99,
1.03, 1.07, 1.15, 1.18, 1.32, and 1.90 (each 3H, s), one olefinic proton at δH 5.68 (H-12), one
oxygen-bearing methine proton at δH 3.52 (H-3), and sugar proton signals between δH
3.74─6.30. Its 13C NMR spectrum showed two olefinic carbon signals at δC 123.3 and 143.2,
suggesting that 1 was an oleanane type triterpenoid saponin. 1D (1H and 13C NMR, DEPT)
and 2D (COSY, HSQC and HMBC) NMR techniques permitted the unambiguous assignment

NATURAL PRODUCT RESEARCH
3
29
30
O
O
20
19
21
MT1
12
26
22
18
11
17
16
13
14
25
O
15
28
1
4
9
O
10
2
OH
8
7
27
O
3
5
6
O
O
OH
HO
HO
OH
O
O
O
O
Qui'1
O
24
Fuc HO
23
HO
HO
HO
GlcIII
O
HO
O
GlcI
O
O
O
O
O
OH
HO
O
HO
HO
HO
Rha
MT2
O
HO
HO
OH
OH
Araf
Xyl
O
OH
GlcII OH
O
O
HO
HO
OH
Qui
O
OH
Qui'2
HO
O
O
MT3
O
O
OH
Qui'3
HO
HO
Figure 1. chemical structure of lebbeckoside c (1).
of all 1H and 13C NMR signals of the aglycon of 1 which was identified as acacic acid (3β, 16α,
21β-trihydroxyolean-12-ene-28-oic acid) by comparison of its 1H and 13C NMR signals with
those reported in the literature (Table S1) (Noté et al. 2015, 2016).
Substitutions at C-3 and C-28 of acacic acid were evidenced by the observed glycosyla-
tion-induced shifts of C-3 at δC 88.9 (deshielded signal for C-3 of the aglycon) and of C-28 at
δC 174.9 (shielded signal for C-28 of the aglycon). Substitution at C-21 was ascertained from
the acylation-induced shift observed for C-21 at δC 77.5 (deshielded signal for C-21 of the
aglycon). All of these data established that 1 was a 21-acyl 3, 28-bidesmosidic acacic acid
derivative, sugar chains being linked to C-3 and C-28 through an ether and ester bond,
respectively.
Concerning the sugar units, the 1H NMR spectrum of 1 showed eleven anomeric protons
at δH 4.89 (1H, d, J = 7.7 Hz), 4.90 (1H, d, J = 7.3 Hz), 4.91 (1H, d, J = 7.7 Hz), 4.97 (1H, d,
J = 7.9 Hz), 4.99 (1H, d, J = 7.9 Hz), 5.09 (1H, d, J = 6.6 Hz), 5.29 (1H, d, J = 8.0 Hz), 5.43 (1H, d,
J = 7.7 Hz), 6.16 (1H, d, J = 7.6 Hz), 6.29 (1H, brs), and 6.30 (1H, brs) which gave correlations
in the HSQC spectrum with carbon atom resonances at δC 105.2, 99.6, 99.6, 97.2, 103.7, 107.3,
105.9, 106.2, 95.8, 111.5 and 101.6, respectively (Tables S2 and S3). The 1H and 13C NMR data
(Tables S2–S3) of the monosaccharide residues were assigned starting, either from the readily
identifiable anomeric proton of each hexosyl or pentosyl unit, or from the CH3-proton

4
O. P. NOTÉ ET AL.
doublet of each 6-deoxyhexosyl unit, by means of COSY, TOCSY, NOESY, HSQC, and HMBC
spectra obtained for this compound. Based on the coupling constants of the anomeric pro-
tons and the chemical shifts of the anomeric carbons, the anomeric configuration of the
sugar moieties were determined as β for the glucose, xylose, fucose, and quinovose moieties
1
and α for rhamnose and arabinofuranose moieties. In addition, the H NMR spectrum of
compound 1 exhibited three olefinic proton signals at δH 6.89 (t, J = 7.3 Hz), 7.00 (t, J = 7.4 Hz),
and 7.08 (t, J = 7.4 Hz), and three groups of one-substituted olefinic proton signals, one
group at δH 6.24 (dd, J = 10.3; 17.5 Hz), 5.30 (d, J = 10.3 Hz) and 5.40 (d, J = 17.5 Hz), another
group at δH 6.28 (dd, J = 10.6; 17.0 Hz), 5.29 (d, J = 10.6 Hz) and 5.48 (d, J = 17.0 Hz), and the
last group at δH 5.98 (dd, J = 10.6; 17.0 Hz), 5.25 (d, J = 10.6 Hz) and 5.47 (d, J = 17.0 Hz),
indicating that compound 1 had three monoterpenoid units (Liu et al. 2010).
Extensive analysis of 1D and 2D NMR spectra of 1, revealed that the sugar moiety at C-3
was identical to that of prosapogenin 2 (Haddad et al. 2002), julibroside J31 and prosapo-
genin-8 (Zheng et al. 2006), gummiferaoside A (Cao et al. 2007), and gummiferaoside D (Simo
et al. 2017), and that the monoterpene-quinovosyl moiety at C-21 was identical to that of
coriarioside A (Noté et al. 2009), coriariosides C and D (Noté et al. 2010), gummiferaoside C
(Cao et al. 2007), lebbeckoside A (Noté et al. 2015), and zygiaoside A (Noté et al. 2016). Hence,
the units attached at C-3 and C-21 of the aglycon of 1 were established as 3-O-[β-d-
xylopyranosyl-(l→2)-β-d-fucopyranosyl-(1→6)-[β-d-glucopyranosyl(1→2)]-β-d-
glucopyranosyl], and {(2E,6S)-6-O-{4-O-[(2E,6S)-2,6-dimethyl-6-O-(β-d-quinovopyranosyl)
octa-2,7-dienoyl]-4-O-[(2E,6S)-2,6-dimethyl-6-O-(β-d-quinovopyranosyl)octa-2,7-di-
enoyl]-β-d-quinovopyranosyl}-2,6-dimethylocta-2,7-dienoyl}, respectively.
In the same way, extensive analysis of 1D and 2D NMR spectra of 1, revealed that the sugar moiety
at C-28 was identical to that of pithelucoside A (Ma et al. 2008). Hence, the unit attached at C-28 of
the aglycone was established as β-
d
-quinovopyranosyl -(l→3)-[α-
l
-arabinofuranosyl-(l→4)]-α- -rham-
l
nopyranosyl-(l→2)-β-d-glucopyranoside. Consequently, the structure of lebbeckoside C (1) was
established as 3-O-[β-d-xylopyranosyl-(l→2)- β-d-fucopyranosyl-(1→6)-[β-d-glucopyranosyl(1→2)]-β-
d-glucopyranosyl]-21-O-{(2E,6S)-6-O-{4-O-[(2E,6S)-2,6-dimethyl-6-O-(β-d-quinovopyranosyl)octa-2,
7-dienoyl]-4-O-[(2E,6S)-2,6-dimethyl-6-O-(β-d-quinovopyranosyl)octa-2,7-dienoyl]-β-d-
quinovopyranosyl}-2,6-dimethylocta-2,7-dienoyl}acacic acid 28 O-[β-d-quinovopyranosyl-(l→3)-[α-
l-arabinofuranosyl-(l→4)]-α-l-rhamnopyranosyl-(l→2)-β-d-glucopyranosyl] ester, a new acacic acid-
type saponin.
Since lebbeckosides A and B isolated from the roots of the same species were reported
to be active on U87 glioblastoma cells, and on highly aggressive, drug resistant stem-like
glioblastoma propagating TG 1 cells isolated from a patient tumor (Noté et al. 2015), leb-
beckoside C (1), isolated from the stem barks of A. lebbeck, was also tested for cytotoxicity
against the human glioblastoma cell line U-87 MG and TG1 stem-like glioma cells, using
Tamoxifen® (31 μM for U-87 MG, and 14 μM for TG 1, respectively) as a positive control. The
isolated lebbeckoside C (1) inhibits U-87 MG andTG1 stem-like glioma cells survival, assessed
by ATP level measurements, with IC50 values of 1.69 and 1.44 μM, respectively. The only dif-
ference between lebbeckoside C (1) and lebbeckoside A (Noté et al. 2015) lies in the sub-
stitution pattern of the tetrasaccharide moiety at C-28, and in the oligosaccharide moiety
at C-3 of the acacic acid aglycone, with a tetrasaccharide moiety at C-3 in lebbeckoside C
(1), instead of a trisaccharide moiety described in lebbeckoside A, and differing from leb-
beckoside A by the nature of sugars composing the tetrasaccharide moiety at C-2.

NATURAL PRODUCT RESEARCH
5
3. Experimental
3.1. General experimental procedure
Optical rotations were measured on a Jasco P-200 polarimeter. 1H NMR (500 MHz) and 13C
NMR (125 MHz) spectra were recorded at room temperature in pyridine-d5 using a Bruker
AVANCE III 500 spectrometer and chemical shifts are given in δ (ppm) value relative to TMS
as internal standard. HRESIMS spectra were recorded on a microTOF ESI-TOF mass spectrom-
eter (Agilent) operating in positive mode. Analytical HPLC was performed on Varian 920-LC
apparatus equipped with an autosampler, a pump, a diode array detector, and Galaxie soft-
ware. Semipreparative HPLC was performed on Gilson apparatus equipped with Trilution
LC software using a Nucleodur 100-5 C18 ec (21 × 250 mm, 5 μm) column purchased from
Machery-Nagel (Germany). Thin layer chromatography (TLC) were performed on precoated
silica gel plates (60 F254, Merck) (n-BuOH-AcOH-H2O, 65:15:25), and the spots were observed
after spray with Komarowsky reagent, a (5:1) mixture of p-hydroxybenzaldehyde (2% in
MeOH) and (50% H2O in EtOH). Vacuum-liquid chromatography (VLC) was carried out using
silica gel 60 (15–40 and 40–63 μm).
3.2. Plant material
The stem barks of A. lebbeck were harvested at Nkolbisson, Yaoundé peripheral quarter, in
Cameroon in October 2016 under the guidance of Dr Paul Nana, botanist of the National
Herbarium of Cameroon (NHC), where one specimen (47206/HNC) was deposited.
3.3. Extraction and isolation
Air-dried finely powdered stem barks of A. lebbeck (100 g) were extracted with EtOH 70% in
a Soxhlet apparatus. This hydroalcoholic solution was then evaporated to dryness under
reduced pressure to give a dark residue (15.0 g) which was suspended in 100 mL of water
and partitioned against n-BuOH (3 × 300 mL) satured with H20. The n-BuOH phase was
evaporated to dryness affording 6.15 g of a brown gum which was taken in a minimum
amount of water (10 mL) and then submitted to column chromatography (CC) using Diaion
HP-20 resin, eluting with H2O, 50% MeOH, 70% MeOH, 80% MeOH, 90% MeOH, and 100%
MeOH, successively giving four main fractions (LR1─LR4) after TLC monitoring. The 80%
MeOH fraction (LR3) was evaporated to dryness yielding a crude saponin mixture (2.03 g)
that was then submitted to VLC using silica gel 60 (15–40 μm), eluted with CH2Cl2–MeOH
(80:20) and CH2Cl2-MeOH-H2O (70:30:5, 60:32:6.5) to give three main subfractions (LR31─LR33).
Subfraction LR33 (135.6 mg) was purified by semipreparative HPLC using gradient system
of CH3CN-H2O (20 mL/min) to yield compound 1 (tR, 26.41 min, 5.6 mg), while the subfrac-
tions LR31 and LR32 yielded the previous isolated lebbeckosides A and B.
3.4. Acid hydrolysis and GC analysis
Each saponin (2 mg) was hydrolyzed with 2 mL of 2 M HCl at 85 °C during 2 h. After cooling,
the solvent was removed under reduced pressure. The sugar mixture was extracted from
the aqueous phase (10 mL) and washed with CH2Cl2 (3 × 5 mL). Combined CH2Cl2 extracts
were washed with water to give after evaporation the aglycon moiety, which was compared

6
O. P. NOTÉ ET AL.
with authentic standard sample by co-TLC. The sugars were first analyzed by TLC over silica
gel (CHCl3–MeOH–H2O, 8:5:1) by comparison with standard samples. The absolute configu-
ration of each monosaccharide was determined from GC–MS analysis of their trimethylsi-
lylated derivatives by comparison with authentic samples using the method previously
described (Chaabi et al. 2010). The following sugars were detected: d-glucose, d-fucose,
d-xylose, d-quinovose, l-arabinofuranose, and l-rhamnose.
3.5. Inhibitory effect of lebbeckoside C (1)
Glioblastoma U87-MG cells were purchased from ATCC and expanded according to the sup
-
plier’s instructions. Stem-like glioblastoma (WHO grade IV glioma) propagating cells (TG1)
were obtained from Dr H. Chneiweiss (Sainte Anne Hospital, Paris, France) and grown as
previously described (Patru et al. 2010). Neurospheres were mechanically dissociated before
treatment. All cultures were maintained at 37 °C in a humidified atmosphere with 5% CO2.
The cytotoxicity of lebbeckoside C (1) was assessed as described previously (Noté et al. 2015).
3.6. Lebbeckoside C (1)
Amorphous white powder; [ꢀ]2D5 − 31(c = 0.15, MeOH); HRESIMS (positive ion mode) m/z
2632.2616 ([M + NH4]+ Calcd for C124H200O58N 2632.2765); 1H/ 13C NMR (The 1H NMR data of
1 was measured at 500 MHz and the 13C NMR spectra at 125 MHz in pyridine-d5. Ordered in
the No. of 1): Aglycon: δ 1.66, 1.18/39.2; 2.30, 1.94/27.1; 3.52/88.9; ─/40.3; 0.94/56.4; 1.59,
1.63/18.9; 1.78/34.1; ─/40.4; 1.93/47.4; ─/37.4; 2.47, 2.25/23.8; 5.68 (1H, br s)/123.3; ─/143.2;
─/42.4; 2.31, 2.12/36.2; 5.32/74.0; ─/51.9; 3.47/41.4; 1.42, 2.95/48.3; ─/35.5; 5.40/77.5; 2.21,
2.87/36.7; 1.32 (3H, s)/28.5; 1.18 (3H, s)/17.2; 1.03 (3H, s)/16.3; 1.15 (3H, s)/17.5; 1.90 (3H,
s)/27.6; ─/174.9; 0.99 (3H, s)/29.4; 1.07 (3H, s)/19.4. MT1: δ ─/168.1; ─/128.8; 6.89 (1H, t,
7.3)/142.8; 2.44/24.0; 1.75/41.0; ─/79.9; 6.24 (1H, dd, 10.3, 17.5)/144.5; 5.30 (1H, d, 10.3), 5.40
(1H, d, 17.5)/115.7; 1.84 (3H, s)/13.1; 1.51 (3H, s)/24.1. MT2: δ ─/167.7; ─/125.5; 7.00 (1H, t,
7.4)/143.3; 2.48, 2.26/23.7; 1.79/40.8; ─/80.0; 6.28 (1H, dd, 10.6, 17.0)/144.4; 5.29 (1H, d, 10.6),
5.48 (1H, d, 17.0)/115.4; 1.96 (3H, s)/13.1; 1.56 (3H, s)/24.2. MT3: δ ─/167.9; ─/128.5; 7.09 (1H,
t, 7.2)/143.3; 2.46, 2.26/23.8; 1.79/40.8; ─/79.9; 5.98 (1H, dd, 10.6, 17.0)/144.3; 5.25 (1H, d,
10.6), 5.47 (1H, d, 17.0)/115.1; 1.94 (3H, s)/13.1; 1.58 (3H, s)/24.3. Qui’1: δ 4.91 (1H, d, 7.7)/99.6;
4.03/75.8; 4.22/76.3; 5.38/77.7; 3.73/73.1; 1.53 (3H, d, 6.3)/18.8. Qui’2: δ 4.90 (1H, d, 7.3)/99.6;
4.04/75.9; 4.22/76.2; 5.65/75.9; 3.76/73.0; 1.60 (3H, d, 6.4)/18.9. Qui’3: δ 4.97 (1H, d, 7.9)/97.2;
4.07/76.1; 4.23/76.3; 3.73/77.2; 3.71/72.9; 1.63 (3H, d, 6.4)/19.0. Glc I: δ 4.89 (1H, d, 7.7)/105.2;
4.30/83.2; 4.27/78.4; 4.23/71.5; 4.05/76.8; 4.40, 4.77/70.0. Glc II: δ 5.43 (1H, d, 7.7)/106.2;
4.16/75.6; 4.15/78.8; 4.17/72.4; 3.96/78.5; 4.30, 4.49/63.1. Fuc: δ 4.99 (1H, d, 7.9)/103.7;
4.47/82.6; 4.14/75.5; 4.06/72.2; 3.80/71.6, 1.37 (3H, d, 6.4)/18.5. Xyl: δ 5.09 (1H, d, 6.6)/107.3;
4.10/75.9; 4.05/77.8; 4.14/71.2; 3.63, 4.48/67.5. Glc III: δ 6.16 (1H, d, 7.6)/95.8; 4.31/76.3;
4.12/78.7; 4.17/71.4; 4.02/79.3; 4.27, 4.39/62.3. Rha: δ 6.30 (1H, brs)/101.6; 5.03/71.4; 4.82/82.2;
4.53/79.5; 4.67/68.9; 1.82 (3H, d, 6.4)/18.9. Qui: δ 5.29 (1H, d, 8.0)/105.9; 3.98/75.8; 3.92/78.5;
4.08/76.2; 3.83/73.3; 1.52 (3H, d, 6.0)/18.7. Araf: δ 6.29 (1H, br s)/111.5; 5.04/84.7; 4.86/78.7;
4.83/86.1; 4.20, 4.27/62.8.
(Overlapped proton NMR signals are reported without designated multiplicity).

NATURAL PRODUCT RESEARCH
7
4. Conclusions
This study unveiled the presence of one new triterpenoid saponin from the stem barks of
A. lebbeck. In comparison with the previous isolated triterpenoid saponins from the roots of
the same plant, they share the same structural features: they all have acacic acid as aglycon
unit, oligosaccharide moieties at C-3 and C-28, and an acyl group at C-21, differing from
lebbeckoside A (Noté et al. 2015) only by the nature, number, and the substitution pattern
of the oligosaccharide moieties attached at C-3 and C-28. Since lebbeckoside C (1) (1.44 μM)
and lebbeckoside A (1.36 μM) (Noté et al. 2015) showed a similar cytotoxicity against TG1
stem-like glioma cells, these substitution patterns seem to have no influence in mediating
cytotoxicity against TG1 stem-like glioma cells. Nevertheless, further studies are necessary
to support this conclusion.
Acknowledgment
The authors are grateful to Mr Victor Nana of the National Herbarium of Cameroon (NHC) for the iden-
tification and collection of plant.
Disclosure statement
No potential conflict of interest was reported by the authors.
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