Triterpenoid saponins and others glycosides from the stem barks of Pancovia turbinata Radlk

Article abstract of DOI:10.1016/j.carres.2021.108393

In our continuing search of saponins from the plant of Sapindaceae family, phytochemical investigation of the stem barks of Pancovia turbinata Radlk., led to the isolation and structural characterization of two new triterpenoid saponins, named turbinatosi

Full text of DOI:10.1016/j.carres.2021.108393

Carbohydrate Research 508 (2021) 108393
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Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Triterpenoid saponins and others glycosides from the stem barks of
Pancovia turbinata Radlk
,
,c,d,
Armand Emmanuel Moffi Bianga b, Lin Marcellin Messia
*, Eutrophe Le Doux Kamtoa,
Line Made Simoa, Pierre Lavedane, Marc Vedrennee, Josephine Ngo Mbinga,
a
d
a,
´
d
,
**
´
Dieudonne Emmanuel Pegnyemb , Mohamed Haddad , Olivier Placide Note
a
´
´
´
´
´
Laboratoire de Pharmacochimie des Substances Naturelles, Departement de Chimie Organique, Faculte de Sciences, Universite de Yaounde I, BP 812, Yaounde,
Cameroon
b
´
´
´
´
Institut de Recherches Medicales et D’etudes des Plantes Medicinales Du Cameroun (IMPM), B.P. 13033, Yaounde, Cameroon
c
´
´
Institut de Recherche Agricole pour le Developpement (IRAD), BP 2067, Yaounde, Cameroon
d
´
UMR 152 Pharma Dev, Universite de Toulouse, IRD, UPS, France
e Institut de Chimie de Toulouse, UPS, France
A R T I C L E I N F O
A B S T R A C T
Keywords:
In our continuing search of saponins from the plant of Sapindaceae family, phytochemical investigation of the
stem barks of Pancovia turbinata Radlk., led to the isolation and structural characterization of two new tri-
terpenoid saponins, named turbinatosides A-B (1–2), one new farnesyl glycoside, named turbinoside A (3), one
new coumarin glucoside, named panturboside A (4), together with a known saponin (5). The structures of the
new compounds were established, using extensive analysis of NMR techniques, mainly 1D NMR (1H, 13C, and
DEPT) and 2D NMR (COSY, NOESY, HSQC, HSQC-TOCSY and HMBC) experiments, HRESIMS and by comparison
Sapindaceae
Pancovia turbinata
Triterpenoid saponins
Farnesyl glycoside
NMR
with the literature data, as 3-O-β-D-xylopyranosyl-(1 → 3)-
→ 3)- -L-rhamnopyranosyl-(1 → 2)- -L-arabinopyranosylhederagenin 28-O-β-D-glucopyranosyl ester (1), 3-O-
arabinopyranosyl-(1 4)-β-D-glucopyranosyl-(1 3)- -L-rhamnopyranosyl-(1 2)- -L-arabinopyr-
anosylhederagenin 28-O-β-D-xylopyranosyl-(1 → 4)-β-D-glucopyranosyl ester (2), 1-O-{β-D-glucopyranosyl-(1 →
α
-L-arabinopyranosyl-(1 → 4)-β-D-glucopyranosyl-(1
α
α
α
-L-
→
→
α
→
α
3)-α-L-rhamnopyranosyl-(1 → 2)-[α-L-rhamnopyranosyl-(1 → 6)]-β-D-glucopyranosyl}-(2E,6E)-farnes-1,12-diol
(3), and 5-O-β-D-glucopyranosyl-5,6,7-trihydroxy-8-methoxycoumarin (4), respectively. Our findings highlight
the presence of -3Rha-2Ara-3hederagenin oligosaccharidic sequence usually described in saponins from Sapin-
doideae subfamily of Sapindaceae family, as well as farnesol glycosides, and represent therefore a valuable
contribution to the chemotaxonomy of the Sapindoideae subfamily.
1. Introduction
acid derivatives from P. pedicellaris with antibacterial potential [5], and
ceramide and cerebroside from P. laurentii with antiprotozoal properties
The Sapindaceae family, mostly distributed in tropical and sub-
tropical regions [1], is described as trees, shrubs and herbaceous plants,
containing about 1900 species divided into three subfamilies namely,
Sapindoideae, Dodonaeoideae and Aceroideae, and 144 genera [2].
Plants of Pancovia genus (Sapindoideae subfamily) are used in Camer-
oonian’s traditional medicine for the treatment of several ailments such
as skin diseases, dysentery and rheumatism [3,4]. Previous phyto-
chemical investigations of this genus revealed the presence of ellagic
[6], while triterpenoid saponins are described as major constituents of
the whole subfamily [7–16]. Pancovia turbinata Radlk. is a small tree,
widely distributed in West Africa and in Cameroon [17]. To the best of
our knowledge, no ethnomedicinal and phytochemical study are re-
ported for this species. As part of our continuing search of saponins from
Cameroonian’s Sapindaceae family [15,16], we have investigated the
saponins content of the stem barks of P. turbinata.
In this paper, we report the isolation and structure characterization
´
´
* Corresponding author. Institut de Recherche Agricole pour le Developpement (IRAD), BP 2067, Yaounde, Cameroon.
´
´
´
** Corresponding author. Laboratoire de Pharmacochimie des Substances Naturelles, Departement de Chimie Organique, Faculte de Sciences, Universite de
´
´
Yaounde I, BP 812, Yaounde, Cameroon, PO BOX 812
´
E-mail addresses: linmarcellinmessi@yahoo.fr (L.M. Messi), Oliviernote1@yahoo.fr (O.P. Note).
https://doi.org/10.1016/j.carres.2021.108393
Received 28 March 2021; Received in revised form 20 June 2021; Accepted 30 June 2021
Available online 10 July 2021
0008-6215/© 2021 Elsevier Ltd. All rights reserved.

A.E. Moffi Biang et al.
Carbohydrate Research 508 (2021) 108393
of two new triterpenoid saponins (1–2), one new glycoside of farnesyl
(3), one new coumarin glucoside (4), together with a known saponin (5)
having hederagenin as aglycone (Fig. 1). The structures of the new
isolated compounds were established by extensive analysis of 1D and 2D
NMR experiments, chemical evidences and mass spectrometry.
by Semiprep-HPLC afforded two new triterpenoid saponins (1–2), one
new glycoside of farnesyl (3), one new coumarin glucoside (4), together
with a known saponin (5) having hederagenin as aglycone (Fig. 1).
All the isolated compounds 1–5, were obtained as white amorphous
powders. The monosaccharides obtained by acid hydrolysis of each
compound were identified by comparison on TLC with authentic sam-
ples as arabinose, xylose, rhamnose and glucose. The absolute configu-
rations were determined by UHPLC/MS analysis to be D for glucose and
xylose and L for rhamnose and arabinose (See Experimental Section)
2. Results and discussion
The air-dried powdered of stem barks of P. turbinata were extracted
with aq-EtOH 70% using a sonicator apparatus. After evaporation of the
solvent, the resulting dark residue was suspended in water and parti-
tioned 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 four main subfractions. Purification of the eluated subfractions
1
[18]. The H and 13C NMR data of the monosaccharide residues were
assigned starting, either from the anomeric protons, or from the
CH3-proton doublet of rhamnose unit, by means of COSY, HSQC-TOCSY,
HSQC, NOESY, and HMBC spectra obtained for each compound. Data
from these above NMR experiments indicated that the sugar residues
3
were in their pyranose form, and relatively large JH-1
,
values
6.3–8.1 Hz of Glc, Xyl and Ara in their pyranose form evHid-2enced a
Fig. 1. Structures of isolated compounds 1–5.
2

A.E. Moffi Biang et al.
Carbohydrate Research 508 (2021) 108393
β-anomeric orientation for Glc and Xyl, and an
α
-anomeric configuration
observed in the HMBC spectrum between H-1 of Ara I (δH 4.81) and C-3
for Ara [19]. The
α
-anomeric configuration of the L-rhamnose unit was
of the aglycone (δ 80.8), and in the NOESY spectrum between H-1 of
C
judged by the broad singlet of its anomeric proton and the chemical shift
Ara I (δH 4.81) and H-3 of the hederagenin moiety (δH 4.01), suggested
that Ara I was directly attached to C-3 of the aglycone. Moreover, the
HMBC correlation observed between H-1 of Rha (δH 5.88) and C-2 of Ara
I (δ 75.1) established the connectivity between the two sugar units,
whiCch was confirmed by the NOESY correlation observed between H-2
of Ara I (δ 4.22) and H-1 of Rha (δ 5.88). In addition, the HMBC
value of C-5 [20].
HR-ESIMS of turbinatoside A (1), indicated a C63H102O30 molecular
formula, as deduced from the protonated molecular ion peak at m/z
1339.6538 [M + H]+ (calcd for C63H103O30 1339.6534). The 1H NMR
and 13C NMR data of 1 displayed resonances due to the aglycone part
characteristic for hederagenin unit (Table 1), a common triterpene of
triterpene glycosides, which were in full agreement with literature data
[13–16,21].
H
H
correlations observed between H-1 of Glc I (δH 5.08) and C-3 of Rha (δC
82.5), confirmed by the NOESY correlation observed between H-3 of
Rha (δH 4.44) and H-1 of Glc I (δH 5.08) allowed us to locate Glc I at C-3
of Rha (Fig. 2a). On the other hand, the HMBC correlation observed
between H-1 of Ara II (δH 4.79) and C-4 of Glc I (δC 79.6) established the
connectivity between the two sugar units, which was confirmed by the
NOESY correlation observed between H-4 of Glc I (δH 4.04) and H-1 of
The 1H NMR spectrum of 1 showed six anomeric protons at δH 4.81
(d, J = 6.8 Hz), 5.88 (br s), 5.08 (d, J = 7.8 Hz), 4.79 (d, J = 7.6 Hz), 4.92
(d, J = 8.0 Hz), and 6.00 (d, J = 8.1 Hz), which correlated with six
anomeric carbon atom signals at δC 104.3, 100.9, 105.7, 104.6, 106.1
and 95.2, respectively, in the HSQC spectrum. Complete assignments of
each sugar moiety were achieved by extensive analyses of 1D and 2D
NMR experiments and UHPLC/MS analysis (see Experimental Section)
Ara II (δ 4.79). Moreover, the HMBC correlation observed between H-1
H
of Xyl (δH 4.92) and C-3 of Ara II (δC 82.8), confirmed by the NOESY
correlation observed between H-3 of Ara II (δH 3.92) and H-1 of Xyl (δ
4.92) allowed us to locate Xyl at C-3 of Ara II. Thus, the pentasaccharidHe
allowing the characterization of two
II), one
α-L-arabinopyranosyl (Ara I and Ara
α
-L-rhamnopyranosyl (Rha), two β-D-glucopyranosyl (Glc I and
β-D-xylopyranosyl-(1 → 3)- -L-arabinopyranosyl-(1 → 4)-β-D-glucopyr-
α
Glc II), and one β-D-xylopyranosyl (Xyl) units (Table 2). The sequence of
the oligosaccharide chain was established from the HMBC and NOESY
experiments.
anosyl(1 → 3)-α-L-rhamnopyranosyl(1 → 2)-α-L-arabinopyranoside
moiety was established to be linked at C-3 of the aglycone (Fig. 2a).
The observation of the signals (δH/δC 6.00/95.2) of Glc II, indicated
that this sugar should be directly attached to C-28 of the aglycone. This
For the sugars chain attached at C-3 of the aglycone, the correlations
Table 1
NMR spectroscopic data (500 MHz for 1H and 125 MHz for13C) for the aglycone moieties of compounds 1–4 (δ in ppm and J in Hz)a.
N◦
1
2
3
4
δC
δH
δC
δH
δC
δH
δC
–
δH
1
2
38.7
0.91
38.9
0.94
66.1
4.31; 4.59 m
–
1.45
1.48
25.9
1.83
26.1
1.86
121.2
5.64 (br s)
161.6
–
2.03
2.09
3
4
5
6
80.8
43.1
47.1
17.8
4.01 (dd, J = 11.4, 5.0)
81.0
43.3
47.3
17.9
4.09 (dd, J = 10.3, 5.6)
141.4
40.3
–
110.5
140.4
127.3
145.7
6.23 (d, J = 9.5)
–
–
2.05; nd
8.23 (d, J = 9.5)
1.51
1.20
1.53
1.20
1.60
–
1.55
27.1
2.14; 2.25
–
–
1.25
125.1
5.22 (br t, J = 7.0)
1.57
7
32.2
32.3
1.22
135.7
–
145.8
–
1.64
8
39.5
47.8
36.5
23.5
122.5
143.8
41.8
27.9
39.7
48.0
36.7
23.6
122.7
144.0
42.0
28.1
–
40.3
27.1
124.6
136.8
68.4
14.4
16.5
17.0
2.11; nd
2.14; 2.25
5.70 (br t, J = 7.1)
–
133.3
145.7
102.8
60.8
–
9
1.60
–
1.65
–
10
11
12
13
14
15
–
–
1.78 nd
5.28 m
–
1.83 nd
-OMe
3.85 (s)
5.32 m
4.31; nd
1.82 (s)
–
–
–
1.65 (s)
0.98
2.07
2.07 nd
0.99
1.70 (s)
2.14
16
23.0
23.3
1.81
1.97
17
18
19
46.7
41.4
45.9
–
46.8
41.5
46.0
–
2.97 (dd, J = 13.7, 4.5)
3.06 (dd, J = 13.8, 4.6)
1.11
1.15
1.60
1.65
20
21
30.4
33.7
–
30.6
33.8
–
1.00
1.02
1.23
1.26
22
23
32.3
63.5
1.15
32.5
63.7
1.19
1.48
1.52
3.64
3.71
3.99
4.07
24
25
26
27
28
29
30
13.5
15.7
17.1
25.6
176.3
32.6
23.2
0.88 (s)
0.83 (s)
0.92 (s)
1.06 (s)
–
0.79 (s)
0.77 (s)
13.8
15.9
17.3
25.8
176.4
32.8
23.4
0.95 (s)
0.87 (s)
0.98 (s)
1.10 (s)
–
0.82 (s)
0.80 (s)
Assignments were based on the HMBC, HSQC, COSY and DEPT experiments.
a
Overlapped 1H NMR signals are reported without designated multiplicity; nd: not determined.
3

A.E. Moffi Biang et al.
Carbohydrate Research 508 (2021) 108393
Table 2
NMR spectroscopic data (500 MHz for 1H and 125 MHz for13C) for the sugar moieties attached at C-3 and C-28 of compounds 1–4 (δ in ppm and J in Hz) in pyridine-d5.
Position
1
2
3
4
δC
δH (J in Hz)
δC
δH (J in Hz)
δC
δH (J in Hz)
δC
δH (J in Hz)
3-O-sugars
1-O-sugars
Glc I
5-O-sugar
Ara I
Glc
1
2
3
4
5
104.3
75.1
74.1
69.2
65.6
4.81 (d, J = 6.8)
104.5
75.2
74.4
69.4
65.9
4.87 (d, J = 6.6)
101.6
78.4
77.5
71.6
75.4
4.78 (d, J = 7.7)
108.3
75.6
78.2
71.5
79.2
5.41 (d, J = 6.3)
4.22
4.30
4.15
4.15
4.18
3.98
4.25
4.25
4.25
4.01
3.82
3.86
3.95 m
4.00 m
3.54 (brd, J = 11.9);
3.59 (brd, J = 11.5);
4.07
4.12
67.6
4.32; 4.71 m
62.8
4.32; 4.50 m
Rha
Rha I
1
2
3
4
5
6
100.9
70.9
82.5
72.2
69.1
17.8
5.88 (brs)
4.64
101.1
71.2
82.8
72.5
69.4
18.1
5.98 (brs)
4.72
102.6
72.6
82.6
73.1
70.4
19.1
6.13 (d, J = 1.5)
4.71
4.44
4.54
3.98
4.13
4.23
4.52
4.40
4.48
4.77
1.38 (d, J = 6.1)
1.44 (d, J = 6.2)
1.75 (d, J = 6.2)
Glc I
Glc II
1
2
3
4
5
6
105.7
74.8
75.5
79.6
76.1
60.7
5.08 (d, J = 7.8)
3.81
106.0
75.1
75.8
79.9
76.4
61.0
5.18 (d, J = 8.1)
3.87
105.7
75.3
78.6
71.4
78.8
62.6
4.93 (d, J = 7.9)
3.98
3.94
4.02
4.18
4.04
4.09
4.21
3.67
3.73
3.97
4.21; nd
4.26; 4.30
4.31; 4.47 m
Ara II
Rha II
1
2
3
4
5
104.6
70.8
82.8
68.6
67.0
4.79 (d, J = 7.6)
4.28
105.3
72.5
74.1
70.6
67.5
4.80 (d, J = 7.6)
4.22
102.6
72.7
72.7
74.4
70.5
5.63 (d, J = 1.6)
4.62
4.73
4.28
4.36
3.92
3.92
4.20 m
4.10 (d, J= 11)
3.69 (brd, J = 12.2);
4.13
3.66 (brd, J = 11.8);
4.04 (dd, J = 11.8; 3.1)
19.1
1.68 (d, J = 6.2)
Xyl I
1
2
3
4
5
106.1
76.1
77.3
70.4
66.6
4.92 (d, 8.0)
3.68
3.84
3.88
3.47 (dd, J = 12.1; 2.5);
4.10 (dd, J = 12.1; 1.4)
4.81 (d, J = 6.8)
104.3
28-O-Sugars
Glc II
1
2
3
4
5
6
95.2
73.5
78.1
70.4
78.6
61.6
6.00 (d, J = 8.1)
3.89
95.2
73.7
78.40
81.0
78.9
61.8
6.09 (d, J = 8.1)
3.97
3.99
4.08
3.99
4.08
3.76
3.84
4.12; 420
4.20; 4.29
Xyl II
1
2
3
4
5
105.2
74.5
78.4
70.4
67.0
4.89 (d, J = 7.5)
3.75
4.07
3.94
3.51 (brd, J = 10.3);
4.11
Assignments were based on the HMBC, HSQC, COSY, TOCSY, NOESY, and DEPT experiments. a)Overlapped proton NMR signals are reported without designated
multiplicity.
was confirmed by the HMBC correlation observed between H-1 of Glc II
turbinatoside B (2), was identical to that obtained for compound 1,
suggesting that these compounds were isomers with C63H103O30 for-
mula. Extensive 2D NMR analysis of saponin 2 revealed that it has also
hederagenin as aglycone. Comparison of the NMR spectra of 2 with
those of 1, showed that compound 2 differs from compound 1 only by
the substitution pattern of the sugar chains at C-3 and C-28 of the
aglycone. Indeed, instead of a pentasaccharide moiety at C-3, and a
(δ 6.00) and C-28 of the aglycone (δ 176.3) permitting us to link Glc II
C
toHC-28 of hederagenin moiety. Hence, the structure of turbinatoside A
(1), was established as 3-O-β-D-xylopyranosyl-(1 → 3)-
α
- L-arabinopyr-
anosyl-(1 → 4)-β-D-glucopyranosyl-(1 → 3)-
α-L-rhamnopyranosyl-(1 →
2)-α-L-arabinopyranosylhederagenin-28-O-β-D-glucopyranosyl ester.
The HRESIMS spectrum ([M+ H]+ at m/z 1339.6511) of
4

A.E. Moffi Biang et al.
Carbohydrate Research 508 (2021) 108393
groups at δH 1.82 (s, H-13), 1.65 (s, H-14) and 1.70 (s, H-15), showing
correlations in the HSQC spectrum with carbon signals at δ 14.4 (C-13),
C
16.5 (C-14) and 17.0 (C-15), respectively. Three olefinic proton signals
at δ 5.64 (brs, H-2), 5.22 (brt, H-6) and 5.70 (brt, H-10), showing
corrHelations in the HSQC spectrum with carbon atom at δC 121.2, 125.1
and 124.6, respectively, were also observed, as well as six methylene
carbon signals at δC 66.1 (C-1), 40.3 (C-4), 27.1 (C-5), 40.3 (C-8), 27.1
(C-9) and 68.4 (C-12). In addition, two oxymethylene proton groups at
δH 4.31, 4.59 (m, H-1a, H-1b), and at δH 4.31(m, H-12a), showing cor-
relations in the HSQC spectrum with carbon atom signals at δ 66.1 (C-1)
C
and δC 68.4 (C-12), respectively, were also observed. Furthermore, in the
13C NMR spectrum, three other carbon signals were observed as qua-
ternary carbon at δC 141.4 (C-3), 135.7 (C-7) and 136.8 (C-11). These
resonances, due to the sesquiterpene moiety, are characteristic of farnes-
1,12-diol aglycone (Table 1), which was recognized to be (2E, 6E)-
farnes-1, 12-diol [(2E,6E)-3,7,11-trimethyl-2,6,10-dodecatriene-1,12-
diol] by 1H NMR and 13C NMR analyses using the correlations observed
in COSY, HSQC, and HMBC spectra, and was in full agreement with
literature data [22,23]. The chemical shifts of methyl carbons, C-14,
Fig. 2a. Key HMBC and NOESY correlations observed for Compound 1.
C-15 at δ 16.5, 17.0, respectively, and those of two methylenes C-4 and
C
monosaccharide moiety at C-28 of hederagenin moiety, respectively, as
observed in compound 1, compound 2 displayed signals for a tetra-
saccharide moiety at C-3, and a disaccharide moiety at C-28 of the
aglycone, respectively, according to the analysis of 2D NMR experiments
(Table 2). The observation of the signal of C-4 of Ara II at δC 74.1 (shield,
C-8 at δC 40.3 and 40.3, respectively, were observed at almost the same
resonances as those reported for (2E, 6E)-12-hydroxy-farnesol, while the
terminal methylene C-12 appeared at δC 68.4 ppm, which is particularly
indicative of the E stereochemistry of the double bonds in the
12-hydroxy-all-trans-farnesyl unit was also evidenced [22,24]. The
absence of signals in the 13C NMR spectrum in the region between 30
and 33 ppm allowed us to eliminate the other possible configurations
(2E, 6Z), (2Z, 6Z), or (2Z, 6E) for this 12-hydroxy-farnesol unit.
ꢀ 8.2 ppm) in 2 in compararaison to Ara II (δ 82.8) in 1, and of C-4 of
C
Glc II at δC 81.0 (deshield, +10.6 ppm) in 2 in comparaison to Glc II (δC
70.4) in 1, indicated that Ara II was terminal in 2 and Glc II substituted
at its C-4. In addition, the observation of the HMBC correlation observed
between H-1 of Xyl (δH 4.89) and C-4 of Glc II (δ 81.0), and confirmed
by the NOESY correlation observed between H-1Cof Xyl (δH 4.89) and H-
4 of Glc II (δH 4.08) allowed us to attach Xyl at C-4 of Glc II. Therefore,
the sequences of the sugar chains at C-3 and C-28 of hederagenin,
established by extensive analysis of 2D NMR experiments, were deter-
The deshielded shift of C-1 of the 12-hydroxy-farnesol unit (δ 66.1)
suggested this carbon as the point of linkage of the sugars chain. TChe 1H
NMR spectrum of the sugar portion of compound 3 showed four
anomeric signals at δ 4.78 (d, J=7.7 Hz), 4.93 (d, J = 7.9 Hz), 6.13 (d, J
H
= 1.5 Hz) and 5.63 (d, J = 1.6 Hz), which correlated with four anomeric
carbon atom resonances at δC 101.6, 105.7, 102.6 and 102.6, respec-
tively in the HSQC spectrum (Table 2). Complete assignments of each
sugar moiety were achieved by extensive analyses of 1D and 2D NMR
experiments and UHPLC/MS analysis (see Experimental Section)
mined as
rhamnopyranosyl-(1 → 2)-
anosyl-(1 → 4)-β-D-glucopyranoside, respectively (Fig. 2b). Conse-
quently, the structure of turbinatoside B was established as 3-O- -L-
arabinopyranosyl-(1 → 4)- β-D-glucopyranosyl-(1 → 3)- -L-rhamnopyr-
α
-L-arabinopyranosyl-(1 → 4)-β-D-glucopyranosyl-(1 → 3)-
α-L-
α
-L-arabinopyranoside, and β-D-xylopyr-
α
allowing the characterization of two α-L-rhamnopyranosyl (Rha I and
α
Rha II) and two β-D-glucopyranosyl (Glc I and Glc II) units (Table 2).
The sequencing of the sugars chain was achieved by analysis of
HMBC and NOESY experiments. HMBC correlations observed between
H-1 of Glc I (δH 4.78) and C-1 of Aglycone (δC 66.1) allowed us to attach
Glc I to the agly at its C-1. The HMBC correlations observed between H-1
of Rha I (δH 6.13) and C-2 of Glc I (δC 78.4) and between H-1 (δH 5.63) of
Rha II and C-6 of Glc I (δ 67.6) permitted us to attach Rha I, and Rha II
to C-2 and C-6 of Glc I,Crespectively. In addition, HMBC correlations
anosyl-(1
→
2)-α-L-arabinopyranosylhederagenin-28-O-β-D-xylopyr-
anosyl-(1 → 4)-β-D-glucopyranosyl ester (2).
The HRESIMS (negative-ion mode) of Turbinoside A (3) exhibited a
protonated molecular ion peak at m/z 855.4222 ([M+H]+, calcd for
C
39H67O20 855.4297) indicating a molecular formula of C39H66O20. The
1H NMR spectrum of compound 3 revealed the presence of three methyl
observed between H-1 of Glc II (δ 4.93) and C-3 of Rha I (δ 82.6)
H
C
suggested us to connect Glc II to C-3 of Rha I. These connectivities were
supported by NOESY cross-peaks correlations observed between H-1 of
Glc I (δH 4.78) and H-1 of Agly (δH 4.59), between H-1 of Rha I (δH 6.13)
and H-2 of Glc I (δ 4.15), between H-1 of Rha II (δ 5.63) and H-6 of Glc
I (δH 4.71), and beHtween H-1 of Glc II (δH 4.93) andHH-3 of Rha I (δH 3.98)
(Fig. 2c). Hence, the sugar chain at C-1 of the aglycone was established
as β-D-glucopyranosyl-(1 → 3)-
rhamnopyranosyl-(1 → 6)]-β-D-glucopyranosyl moiety and the structure
of 3 was elucidated as 1-O-{β-D-glucopyranosyl-(1 → 3)- -L-rhamno-
pyranosyl-(1 → 2)-[ -L-rhamnopyranosyl-(1 → 6)]-β-D-glucopyranosyl}-
(2E,6E)-farnes-1,12-diol (3).
α-L-rhamnopyranosyl-(1 → 2)-[α-L-
α
α
The HRESIMS (positive-ion mode) of Panturboside (4) exhibited a
protonated molecular ion peak at m/z 387.0949 ([M+H]+, calcd for
C
16H19O11 387.0962) indicating a molecular formula of C16H18O11. The
13C NMR spectrum of compound 4 exhibited sixteen carbon signals,
from which, six were suggested to a hexosyl moiety and the remaining
ten, assignabled to the aglycone. For the aglycone signals, seven qua-
ternary and two tertiary carbon signals were observed. Among these,
one conjugated lacton carbonyl was observed at δ 161.6 (C-2), six
Fig. 2b. Key HMBC and NOESY correlations observed for Compound 2.
C
5

A.E. Moffi Biang et al.
Carbohydrate Research 508 (2021) 108393
The 1H NMR spectrum of compound 4 showed one anomeric signal at
δ 5.41 (d, J = 6.3 Hz), which correlated with one anomeric carbon atom
H
resonance at δC 108.3, in the HSQC spectrum (Table 2). Complete
assignment of this sugar moiety was achieved by extensive analyses of
1D and 2D NMR experiments and UHPLC/MS analysis (see Experimental
Section) allowing the characterization of a β-D-glucopyranosyl (Glc)
unit, which was linked at C-5 of the aglycone as argumentated above.
Consequently, the structure of 4 was elucidated as 5-O-β-D-glucopyr-
anosyl-5,6,7-trihydroxy-8-methoxycoumarin (4).
Compound 5 was identified as 3-O-β-D-xylopyranosyl-(1 → 3)-
α-L-
arabinopyranosyl-(1 → 4)-β-D-glucopyranosyl-(1 → 3)- -L-rhamnopyr-
α
anosyl-(1 → 2)-α-L-arabinopyranosylhederagenin, previously isolated
from Blighia unijugata, by comparison of its spectra data with those re-
ported in the literature [14].
3. Conclusion
Our findings highlight the presence of three main classes of sec-
ondary metabolites often described in the Sapindaceae family, namely
saponins, farnesyl glycosides and coumarin derivatives. The isolated
saponins 1–2, 5 are all hederagenin glycosides, sharing the -3Rha-2Ar-
a-3hederagenin oligosaccharidic sequence most often encountered in the
saponins from Sapindoideae [7–14].
Concerning the farnesyl glycosides, previous studies from the
Sapindoideae subfamily revealed their presence in Sapindus mukurossi
[21], Sapindus delavayi [22], Guioa crenulate [26], and recently in Erio-
coelum microspermum [13]. It is worthy to note that our farnesyl glyco-
side (3) is a 12- hydroxyl-(2E,6E)-farnesol glycoside, so far isolated only
from Sapindus mukurossi and Sapindus delavayi.
Fig. 2c. Key HMBC and NOESY correlations observed for Compound 3.
quaternary aromatic carbon signals at δC 102.8 (C-10), 127.3 (C-5),
145.7 (C-9), 145.7 (C-6), 145.8 (C-7) and 133.3 (C-8), and two carbone
signals of a conjugated ethylenic group at δC 110.5 (C-3) and 140.4 (C-
4). The 1H NMR spectrum of compound 4 revealed two olefinic protons
as two 1,2-cis-coupled doublets at δH 6.23 (H-3, d, J = 9.5 Hz) and 8.23
(H-4, d, J = 9.5 Hz), an AB system characteristic of the protons H-3 and
H-4 of a coumarin skeleton. A singlet of three protons at δH 3.85 (3H, s)
was assigned to the protons of a methoxyl group which correlated with a
carbone signal at δC 60.8. Considering the NMR data, trihydrox-
ycoumarin methylether was suggested as the only plausible structure of
the aglycone of 4 (Table 1) [25]. The HMBC correlations observed be-
tween H-4 (δ 8.23) and C-5 (δ 127.3) of the aglycone and on the other
hand betweeHn the methoxyl prCotons (δH 3.85) and C-8 (δC 133.3) of the
aglycone revealed not only the site of glucosidation and the linking
position of the methoxyl group (Fig. 2d), but also excluded the C-6 and
C-7 positions, and allowed the unambiguous assignment of all other
carbons of the aglycone.
In the case of coumarin glucoside (4), we have observed that
coumarin derivatives are common in Sapindoideae subfamily. They
have been previously identified from Xanthoceras sorbifolia [27], Eur-
ycorymbus cavaleriei [28], Cardiospermum corundum [29], and recently
from Paullinia pinnata [30]. Panturboside A (4) is to the best of our
knowledge, the first report on a trihydroxycoumarin methyl ether
glycoside, so far isolated from Sapindoideae subfamily. Our findings
represent therefore a valuable contribution to the chemotaxonomy of
Sapindoideae subfamily.
4. Experimental Section
4.1. General experimental procedures
Optical rotations were measured on a Jasco P-2000 polarimeter.
NMR experiments were performed at 298 K in pyridine-d5 and DMSO‑d6
on a Bruker AVANCE 500 spectrometer equipped with a 5 mm Z-
gradient TCI cryoprobe. HRESIMS spectra were recorded using a
UHPLC-DAD-LTQ Orbitrap XL instrument (Thermo Fisher Scientific,
UK) equipped with an electrospray ionization source (ESI). Semi-
preparative high performance liquid chromatography (HPLC) was car-
ried out using a LaChrom Merck Hitachi system consisting of a LaChrom
L-7100 pump, an L-7455 DAD, and a D-7000 interface and employing a
Phenomenex Luna 5
μ
m C18(2) 100 Å, 250 × 10 mm2 column. Vacuum-
liquid chromatography (VLC) was carried out using RP-18 silica gel 60
(25–40 μm). Thin layer chromatography (TLC) was performed on pre-
coated silica gel plates (60 F254, Merck) using the system solvent n-
BuOH-AcOH-H2O, 60:15:25 as eluent. The spray reagent for saponins
was vanillin reagent (10% mixture of conc. H2SO4 soln. and 1% vanillin
in EtOH).
4.2. Plant material
The barks of Pancovia turbinata Radlk. were harvested at Nkolbisson,
´
Yaounde peripheral quarter, in Cameroon in October 2016 under the
guidance of Mr. Victor Nana, botanist of the National Herbarium of
Cameroon (NHC), where a voucher specimen (37637/HNC) was
Fig. 2d. Key HMBC and NOESY correlations observed for Compound 4.
6

A.E. Moffi Biang et al.
Carbohydrate Research 508 (2021) 108393
deposited.
to cool and diluted 20-fold with CH3CN and filtered before UHPLC/MS
analysis. Each sugar standard (2 mg of L-glucose, D-glucose, L-rhamnose,
D-rhamnose, L-xylose, D-xylose, L-arabinose and D-arabinose) was sub-
4.3. Extraction and isolation
jected to the same protocol, with 240
solution and 320
μL of the L-cysteine methyl ester
μL of the phenyl isothiocyanate solution. The reaction
The air-dried, powdered stems barks of P. turbinata (300 g) were
extracted with aq-EtOH 70% using a sonicateur apparatus for 1 h three
times. The resulting hydroalcoholic solution was then evaporated to
dryness under reduce pressure to yield brown residue (25.4 g). This
residue was dissolved in ethyl acetate (300 mL), and the insoluble res-
idue (19.52 g) was suspended in 10 mL of H2O and partitioned in with n-
BuOH sat. H2O (3 x 300 mL). The n-BuOH soluble phase was evaporated
to dryness affording 5.36 g of brown gum residue. Part of this residue (3
g) was suspended in 100 mL of water 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, suc-
cessively giving four main fractions (PTE1─PTE4) after TLC monitoring.
The 80%–100% MeOH fraction (PTE4) was evaporated to dryness
yielding a crude saponin mixture (1.8 g) that was then submitted to VLC
mixtures were diluted 60-fold with CH3CN and filtered before
UHPLC/MS analysis. The observed retention times were 11.63, 15.17,
13.91 and 12.76 min for the samples obtained from 1–2, 11.63 and
15.17 from 3, to 11.63 for the sample obtained from 4, respectively.
These retention times were similar with those observed for D-glucose
(11.64), L-rhamnose (15.19 min), D-xylose (13.93 min) and L-arabinose
(12.77 min).
Declaration of competing interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
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 four main subfractions
(PTE41─ PTE44). Subfraction PTE43 (296.7 mg) was purified by semi
preparative HPLC using gradient system of CH3CN–H2O (30 mL/min) to
yield compounds 1 (tR, 16.8 min, 6.2 mg), 2 (tR, 19.3 min, 9.8 mg), and 5
(tR, 12.5 min, 4.2 mg), while subfraction PTE44 yielded compounds 3
(tR, 10.5 min, 3.7 mg) and 4 (tR, 11.6 min, 5.3 mg).
Acknowledgements
We thank the Agence Universitaire de la Francophonie (AUF) and
UMR 152 Pharma-DEV IRD/UPS for the financial support. The authors
are grateful to Mr. Victor Nana of the National Herbarium of Cameroon
(NHC) for the identification and collection of plant.
4.3.1. Turbinatoside A (1)
25
1
White amorphous powder; [
α
]
ꢀ 43.7 (c 0.01, MeOH); H NMR
(C5D5N, 500 MHz) and 13C NMR (C5DD5N, 125 MHz) data, see Tables 1
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8