Hindawi
Journal of Chemistry
Volume 2022, Article ID 1111817, 10 pages
https://doi.org/10.1155/2022/1111817
Research Article
Chemical Constituents of the Bark of Zanthoxylum gilletii
(Rutaceae) and Their In Vitro Antiplasmodial and Molecular
Docking Studies
Liliane Clotilde Dzouemo ,1 Gervais Mouthé Happi ,2 Sikiru Akinyeye Ahmed ,3
Willifred Dongmo Tekapi Tsopgni,1 Michael Nde Akuma,2 Shina Salau ,3
Emmanuel Ngeufa Happi ,1 and Jean Duplex Wansi 1
1
Department of Chemistry, Faculty of Sciences, University of Douala, Douala, P.O. Box 24157, Cameroon
Department of Chemistry, Higher Teacher Training College, Te University of Bamenda, Bambili, P.O. Box 39, Cameroon
3
Department of Chemistry and ndustrial Chemistry, Kwara State University, Malete 23431, lorin, P.M.B 1530, Nigeria
2
Correspondence should be addressed to Gervais Mouthé Happi; gervais20022003@yahoo.fr and Jean Duplex Wansi;
jdwansi@yahoo.fr
Received 3 August 2022; Revised 5 October 2022; Accepted 14 November 2022; Published 22 November 2022
Academic Editor: Vinod Kumar Tiwari
Copyright © 2022 Liliane Clotilde Dzouemo et al. Tis is an open access article distributed under the Creative Commons
Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is
properly cited.
Te phytochemical investigations of the methanol extract of Zanthoxylum gilletii bark led to the isolation of thirteen compounds
identifed as two alkaloids including one acridone 5•hydroxynoracronycine (1) and one benzo [c phenanthridine decarine (2),
three lignans trans• and cis•fagaramide (3 and 4) and sesamin (5), two coumarins scoparone (6) and scopoletin (7), three
pentacyclic triterpenoids fridelin (8), lupeol (9) and erythrodiol•3•O•palmitate (10), one phenolic compound vanillic acid (11) as
well as two common steroids stigmasterol (12), and its derivative stigmasterol•3•O•β•D•glucopyranoside (13). Te structures of all
the isolated compounds were elucidated by means of their spectroscopic and spectrometric data (1D, 2D•NMR, MS) as well as the
comparison of these data with those reported in the literature. Except for compounds 9 and 11–13, all the other isolated
compounds are reported for the frst time from Z. gilletii but have been already obtained from other Zanthoxylum species and in
the Rutaceae family. Compounds 1, 3–5, and 9 were tested in vitro for their antiplasmodial potencies against Plasmodium
falciparum 3D7, and the results revealed that all the tested compounds displayed an inhibition between 51.89% and 54.69% while
only the mixture of 3 + 4 gave an IC50 lower than 10 000 nM (IC50 � 1333 nM). Furthermore, all the compounds have been
evaluated in silico for their ability to inhibit the Plasmodium falciparum dihydroorotate dehydrogenase 5TBO. Sesamin (5) showed
the greatest afnity to the antiplasmodium receptor than artemether and chloroquine . Further recorded data from their
ADMET study, as well as their chemotaxonomy, are also discussed herein. Te present study provides further information to
enrich the chemistry of Z. gilletii and its qualifcation as an important source for good candidates in new antiplasmodial
drug development.
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1. Introduction
Malaria is a parasitic disease with a great incidence in the
public health sector in many countries in tropical areas of the
world [1 . A recent report by the World Health Organization
(WHO) indicated that 228 million cases of malaria have
been recorded in the world with 405 thousand deaths in•
cluding almost 94% occurring in Africa. More specifcally,
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ffteen African countries accounted for 80% of global malaria
deaths while 2,974,819 confrmed cases and an estimation of
14,841 deaths have been reported in Cameroon during the
year 2020 [2, 3 . Te disease is caused by the parasite
Plasmodium transmitted through the bites of the mosquitoes
Anopheles [1, 4 . It is well reported that medicinal plants
represent an important source of bioactive compounds that
can be considered as good candidates in the development of
2
new potent drugs. For instance, the well•known antimalarial
drug artemisinin was initially obtained from the plant Ar•
temisia annua while quinine was isolated from Cinchona
ofcinalis [5 . Unfortunately, the observed rise of resistance
of P. falciparum to the available antimalarial drugs keeps
actual the search for new afordable and potent compounds
that can be developed as drugs. Zanthoxylum gilletii
(Rutaceae) also called Z. macrophylla, Fagara tessmanii, or
F. macrophylla is a tree encountered in the tropical rainforest
that can reach 10 to 35 m high [6, 7 . Te plant is one of the
2000 species that constituted the genus Zanthoxylum and its
synonyms in the genus Fagara which are widely used in
African folk medicine for the treatment of several diseases
[8 . Te stem bark of Z. gilletii is used in Cameroon and
Madagascar for the treatment of microbial infection, cancer,
infammation, hypertension, and related disorders while its
bark is used in Kenya and Ivory Coast against malaria [8 .
Te use of Z. gilletii in the management of malaria has been
further supported by the good antimalarial activity of its
ethanolic extract against a panel of Plasmodium falciparum
strains with an IC50 value of 5 μg/mL [9 . As a continuity of
our program in searching for antiplasmodial agents from
Cameroonian medicinal plants [1, 10 , we carried out
phytochemical investigations of the bark of Z. gilletii. In
addition, the in silico study of the isolated compounds as
potential inhibitors of the 5TBO receptor (Plasmodium
falciparum dihydroorotate dehydrogenase) as well as their
ADMET evaluation and chemotaxonomy have been done,
and the results are herein discussed. Tis study provides
additional compounds to enrich the chemistry of Z. gilletii,
its chemotaxonomic classifcation in the family Rutaceae as
well as it further supports its use in folk medicine by the local
population for the management of malaria and related
symptoms.
2. Materials and Methods
2.1. General nstrumentation. EI•MS were recorded on a
Finnigan MAT 95 spectrometer (70 eV) (Termo Fisher
Scientifc, Darmstadt, Germany) with perfuorokerosene as
a reference substance for EI•HR•MS. Te spectrometer
operated in positive and negative modes (m/z: 50–1500,
with a scan rate of 1.00 Hz) with automatic gain control to
provide high•accuracy mass measurements within 1 ppm
deviation using Na formate as a calibrant. Te following
parameters were used for experiments: spray voltage of
4.5 kV and the capillary temperature of 200°C. Nitrogen
was used as sheath gas (4 l/min). Te 1H• and 13C•NMR
spectra were recorded at 500 MHz and 125 MHz, respec•
tively, on Bruker AMX 500 NMR spectrometers (Bruker,
Rheinstetten, Germany). Chemical shifts are reported in δ
(ppm) using TMS as an internal standard, and coupling
constants (J) were measured in Hz. Column chromatog•
raphy was carried out on silica gel (70–230 mesh (Merck,
Darmstadt, Germany). Tin•layer chromatography (TLC)
was performed on Merck precoated silica gel 60 F254 al•
uminium foil (Merck, Darmstadt, Germany), and spots
were detected using ceric sulphate spray reagent. All re•
agents used were of analytical grade.
Journal of Chemistry
2.2. Plant Material. Te stem bark of Zanthoxylum gilletii
(De Wild.) P. G. Waterman was harvested at Bana•Tentcheu
(GPS coordinates: Latitude 5°07′57″N, Longitude
10°17′41″E, Elevation: 1412 m), West region, Cameroon, in
April 2021. Some leave and bark samples have been used for
the identifcation of the plant by Mr. Victor Nana in
comparison with the plant material available in the National
Herbarium of Cameroon database where a specimen was
registered under the voucher number 38960 HNC.
2.3. Extraction and solation. Te yellowish bark of Z. gilletii
(3.8 kg) has been dried and grounded to obtain a powder
that was twice extracted with methanol at room temper•
ature for 48 h, each, to aford 148.3 g of crude extract after
removing solvent. After keeping a small amount for bio•
logical tests and further chemical analyses, 130 g of crude
extract was dissolved in water and successively partitioned
with ethyl acetate (EtOAc) and n•butanol to give two main
fractions A (78.4 g) and B (46.8 g). Te ethyl acetate soluble
fraction A has been further chromatographed over a silica
gel column (230–400 mesh, 5.0 × 75.0 cm) eluting with
increasing polarity of ethyl acetate in n•hexane (n•Hex)
followed by the gradient of methanol in ethyl acetate. A
total of 563 subfractions (ca. 200 mL each) were collected
and combined into 6 series A1‒A6 based on their TLC
profles.
Further purifcation of series A1 (14.2 g, n•Hex/EtOAc 9 :
1) using column chromatography led to the precipitation of
four compounds at four diferent successive polarities in•
cluding compound 8 (3.3 mg) at n•Hex/EtOAc 39 : 1,
compound 12 (20.6 mg) at n•Hex/EtOAc 19 : 1, compound
10 (4.2 mg) at n•Hex/EtOAc 37 : 3, and compound 9
(47.8 mg) at n•Hex/EtOAc 9 : 1.
Likewise, the second series A2 (12.7 g, n•Hex/EtOAc 8 :
2) was also subjected to column chromatography over silica
gel eluting with a gradient of EtOAc in n•Hex from 9 : 1 to 3 :
1 and allowed the collection of 132 subfractions (100 mL
each) and the fltration of four distinct pure compounds 1
(19.3 mg), 2 (3.6 mg), 5 (32.4 mg), and 11 (2.4 mg) from the
subfractions obtained at the polarity between n•Hex/EtOAc
17 : 3 and n•Hex/EtOAc 8 : 2.
A third series A3 (8.2 g, n•Hex/EtOAc 7 : 3) has been
further purifed using the same chromatographic technique
to aford 115 subfractions from which the unseparated
mixture of compounds 3 and 4 (8.3 mg) was obtained at n•
Hex/EtOAc 3 : 1, and compound 6 (3.2 mg) was obtained
after column chromatography using Sephadex LH20 of the
subfractions 64–86 (2.1 g, n•Hex/EtOAc 7 : 3) eluting iso•
cratically with methanol.
Finally, the series A4 (10.3 g, n•Hex/EtOAc 1 : 1) and A5
(11.4 g, EtOAc) were mixed and chromatographed using a
gradient of methanol in dichloromethane to obtain com•
pounds 7 (2.8 mg) and 13 (28.7 mg), while the last series A6
(18.1 g, AE/MeOH 5%) has been mixed to the n•BuOH
soluble main fraction B and subjected to column chroma•
tography using the increasing polarity of methanol in EtOAc
to aford compound 13 (3.8 mg), and some precipitates are
insoluble in the organic solvent.
Journal of Chemistry
3
2.4. Plasmodium falciparum Culture and Growth nhibition
Assay. Plasmodium falciparum 3D7 (chloroquine•sensitive)
strain was obtained from the Biodefense and Emerging
Infections (BEI) Research Resources (Manassas, VA) and
maintained using a modifed Trager and Jensen method. Te
biological assay has been done following a modifed method
of Yemback et al. [11 . Briefy, parasites were cultured in
fresh O+ human red blood cells at 3% (v/v) hematocrit in
RPMI 1640 culture media containing GlutaMAX and
NaHCO3 (Gibco, UK) and supplemented with 25 mM
HEPES (Gibco, UK), 1X hypoxanthine (Gibco, USA), 20 µg/
mL gentamicin (Gibco, China), and 0.5% Albumax II
(Gibco, USA). When needed, parasites were synchronized at
the ring stage by sorbitol treatment and cultured through
one cycle before treatment.
Stock solutions (10 mM) were prepared in incomplete
RPMI 1640 and mixed with parasite cultures (1% para•
sitemia and 1.5% hematocrit) in 96•well plates to a fnal
drug concentration of 10 µM for hit identifcation studies,
or 10–0.078 µM for activity confrmation assays. Te fnal
dimethyl sulfoxide (DMSO) concentration per 100 μL
culture per well was 0.1%. Chloroquine and artemisinin at a
range of 1–0.0078 µM each were used as negative growth
control (positive test control), while the solvent•treated
culture (0.1% DMSO) was used as positive growth control
(negative test control). Following 72 h incubation at 37°C in
a 5% CO2 incubator, parasite growth was assessed by an
SYBR green I•based DNA quantifcation assay. In brief, a 3x
concentrated SYBR Green lysis bufer was added to each
plate well containing parasitized erythrocytes and kept in
the dark for about 30 minutes. Fluorescence was measured
using a Fluoroskan Ascent multiwell plate reader with
excitation and emission wavelengths at 485 and 538 nm,
respectively. Mean half•maximal inhibitory concentrations
(IC50 values) were derived by plotting percent growth
against log drug concentration and ftting the response data
to a variable slope sigmoidal curve function using
GraphPad Prism v8.0.
2.5.2. Molecular Docking
(1) Ligand Preparations. In a quest to predict the anti•
plasmodial activity of the plant samples, compounds present
in Z. gilletii were modeled using the ACDChem Chem•
Sketch version 2.0, year 2020 [12 computational tool and
fed into Autodock vina [13 for binding efciency
screening.
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(2) Receptor preparations. Te antiplasmodium receptor of
PDB CODE, 5TBO, was used as the target receptor for this
study. Te receptor was obtained from the (RCSB) database
(https://www.rcsb.org/pdb). Te resolution of receptor
5TBO (2.15 Å) approximately lies about the 2.0 Å recom•
mended resolution for a receptor of good quality [19 . Water
molecules around the crystal structure and other associated
inhibitors were removed from the downloaded protease to
avoid undesired interferences and unwanted molecular
interactions.
(3) Virtual screening. Te virtual screening was done on
Z. gilletii containing thirteen compounds using the Auto•
dock vina tool version 1.2.0, year 2010 [13 and Biovia
Discovery Studio version 2021 [14 . Te screening was
guided using Chloroquine and Artemether , prominently
used antiplasmodium therapeutics, as standards. Auto Dock
Tools version 4.0 (ADT) was used to generate the autodock
fle (.pdbqt fle) in preparation for docking. Other adjust•
ments performed on both crystal structures include re•
moving any extra water molecules, adding polar hydrogens,
merging no•polar hydrogens, and adding Kollman charges.
Tese adjustments are targeted at improving the afnity of
the binding site. In modern computer•assisted drug design
(CADD), the study of a potent drug is not complete without
the activity study of the drug which is deducible from the
compound’s inhibition constant. A potent compound is
expected to have inhibition constant values ranging between
0.01 and 1 μM for a potent drug; therefore, this parameter
alone is enough to screen compounds in the drug discovery
journey [19 .
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2.5. Computational Methodology
2.5.1. Computational Tools. All in silico studies applied to
this work were achieved using the following computational
tool:
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(a) ACDChemSketch version 2.0, year 2020 used for
modeling, frst•hand, chemical structures to be fed
for docking screening [12
(b) Autodock Vina tool version 1.2.0, year 2010 used
for the virtual screening procedure [13
(c) BIOVIA Discovery Studio version 2021 used for
the determination of binding pockets and for vi•
sualizing/analyzing the docked results [14
(d) Absorption Distribution Metabolism Excretion and
Toxicity
of
Structure
Activity•Relationship
(ADMETSAR): a web server used to evaluate the
ADMET properties, biological activity, and drug•
likeness [15–18
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2.5.3. ADMET Studies. For predicting the toxicity level of
the screened compounds, in silico toxicity studies were
performed using the ADMETlab version 2.0 web server
online [20 . Additionally, from the server, the absorption
(human intestinal absorption), distribution (blood•brain
barrier; water solubility), metabolism (cytochrome inhibi•
tion: CYP450), excretion (half•life), toxicity (hERG inhibi•
tion; carcinogenicity), and drug•likeness were computed.
Te results are summarized in Table 1.
3. Results and Discussion
3.1. Phytochemical Study. Tirteen compounds (Figure 1)
have been isolated and characterized from the chemical
investigation of the methanol extract of the bark of
Z. gilletii. Based on their spectroscopic (1H and 13C) NMR
and spectrometric (EI•MS) data (see Table 1S on
4
Journal of Chemistry
Table 1: ADMET score of qualifed compounds from Z. gilletii with respect to the selected standards.
Compounds
1
2
3
5
8
9
12
13
Chloroquine
Artemether
HIA
Yes
(>60%)
Yes
(>90%)
Yes
(>90%)
Yes
(>90%)
Yes
(>90%)
Yes
(>90%)
Yes
(>90%)
Yes
(>60%)
Yes
(>90%)
Yes
(>90%)
O
7
6
8 8a
BBB
Water solubility
(mol/L)
CYP450
inhibition
hERG
inhibition
Drug likeness
(Lipinski)
No
Soluble (−3.615)
2/5
Inactive
Yes (5/5)
Short (0.255)
Yes
No
Moderately soluble
(−6.520)
3/5
Inactive
Yes (5/5)
Short (0.192)
Yes
Yes
Soluble (−4.305)
4/5
Inactive
Yes (5/5)
Long 0.547
Yes
3/5
Inactive
Yes (5/5)
Short 0.137
Yes
1/5
Inactive
Yes (5/5)
0/5
Inactive
Yes (5/5)
1/5
Inactive
Yes (5/5)
Moderately soluble
(−6.605)
Moderately soluble
(−6.781)
Moderately soluble
(−6.667)
Poorly soluble
(−7.008)
No
Yes
No
No
No
Soluble (−4.793)
0/5
Inactive
Yes (5/5)
Yes
Soluble (−3.902)
(2/5)
Inactive
Yes (5/5)
No
Soluble (−4.677)
(0/5)
Inactive
Yes (5/5)
OH
9a 1
2
9
3
10
O
5 10a N 4a 4
3'
5'
OH Me 1'
2'
4'
1.
OMe
5 6 6a 7 OH
N
8
4 5a
10a 9
3
O
4a
11a 10
O 2
11
12a
12
1
O 6
5
O 7
O 6
O 7
4
2
8
RO 7
8
3'
1 N
H
4'
O
5
8
2"
3
4
9 O
4.
2
1
1'
N
H
3'
2'
4'
4
3
8a O 2 O
6. R = Me
7. R = H
20
19 21
O
3"
Very short
(0.041)
Very short
(0.037)
Very short
(0.030)
Very short
(0.043)
Very short
(0.070)
Very short
(0.089)
O
30
3'
2'
6
Carcinogenicity
(1/2)
No
No
No
No
No
No
O
H
12
11
8 1 5 4
2 O
H
30
4a
6'
1'
2'
3.
29
5
5' 4'
1'
9
2.
MeO 6
O
3
T
1
2
3
1"
6"
O
5"
O 4"
5.
4
23
30
10
9
5 25
24
29
19 20 21
12
18
12 H
22
22
17
11
11
18
OH
25
26
26
25
28
1
1
9
14 H
14
9
28
2
2
10
10
O
15
15
16'
3
5 H
1'
3
5 H
27
7 27
4
4
7
O
HO
14
H
H
10.
9.
24 23
24 23
13
7
29
19 20 21
27
18
14
O
22
OH
1
6
28
16
5
26
8.
4
OH
11.
2
3 OMe
28 29
22
18
24 27
20
12
23
17
11
25
19
13
1
8
26
2
9
14
15
10
7
RO 3
5
21
12. R = H
13. R = G/c
Figure 1: Chemical structures of compounds 1–13 isolated from Z. gilletii.
supplementary data), as well as the comparison of these
data with those reported in the literature, the isolated
compounds have been identifed as 5•hydroxynor•
acronycine (1) [21 , decarine (2) [22 , trans•fagaramide (3)
[23 , cis•fagaramide (4) [24 , sesamin (5) [25, 26 , sco•
parone (6) [27 , scopoletin (7) [28 , fridelin (8) [29 , lupeol
(9) [30, 31 , erythrodiol•3•O•palmitate (10) [32 , vanillic
acid (11) [23 , stigmasterol (12), and stigmasterol•3•O•β•D•
glucopyranoside (13) [31, 33 .
3.2. n Vitro Antiplasmodial Activity. Among the isolated
compounds, those in large amounts (compounds 1, 3 + 4, 5
and 9) were submitted for in vitro antiplasmodial activity
against the chloroquine•sensitive P. falciparum 3D7 (Pf 3D7)
using chloroquine (IC50 � 24.74 nM) and artemisinin
(IC50 � 17.76 nM) as reference drugs. All the compounds
displayed good inhibition rates measured as 1 (54.69%),
3 + 4 (53.48%), 5 (51.89%), and 9 (52.64%). However, the
most potent compound was the mixture 3 + 4 with an IC50
Journal of Chemistry
5
value of 1333 nM while compounds 1, 5, and 9 were less or
not active with IC50 values greater than 10,000 nM (Table 2).
Te inhibition level greater than 50% for all the compounds
showed that the Z. gilletii extract is an important source of
antiplasmodial compounds supporting the use of the plant
in traditional medicine for the treatment of malaria and
deserves further investigations in checking of synergistic
efects of those compounds as well as the characterization of
further constituents that can help in the development of new
potent antimalarial drugs.
3.3. Molecular Docking. Te binding afnities of all the
thirteen compounds isolated from Z. gilletii as well as the
selected standards (Chloroquine and Artemether ) are
given in Table 3 and Figure 2, while Figures 3–8 (also see
Table 2S on supplementary data) show their binding in•
teractions at the 5TBO receptor’s binding site. Te result
shows that eight out of the thirteen identifed compounds (1,
2, 3, 5, 8, 9, 12, 13) were found to have a greater afnity to the
antiplasmodium receptor than Artemether while eleven
compounds (1–9, 12•13) were found to possess a greater
afnity to the antiplasmodium receptor than Chloroquine .
Tis can also infer that the plant Z. gilletii has a high potency
as an antiplasmodial agent. It can also be mentioned that
since both standards used for this study (Chloroquine and
Artemether ) resulted in a maximum number of two
conventional hydrogen bonds (Figure 8) while most selected
compounds exhibited more, and with shorter bond length, it
is understandable why the identifed compounds have
greater binding afnity to the antiplasmodium receptor than
the standards.
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3.4. ADMET Studies. Te compounds displaying a good
afnity (binding energy) to the 5TBO receptor binding site
were further analysed for their ADMET properties, and the
prediction results are presented in Table 1. Te human
intestinal absorption (HIA) of an oral drug is the essential
prerequisite for its apparent efcacy. Furthermore, the close
relationship between oral bioavailability and intestinal ab•
sorption has also been proven, and HIA can be seen as an
alternative indicator for oral bioavailability to some extent. A
drug molecule with an absorbance of less than 30% is poorly
absorbed [20 . Te results from Table 1 show that com•
pounds 1–3, 5, 8•9, 12•13 as well as both standard drugs
(chloroquine and artemether) are strongly absorbed by the
intestine.
Water solubility is one important condition that a drug
must satisfy before the in vitro drug optimization process
[20 . In this regard, the results show that all the identifed
compounds except compound 12 are water•soluble with
−3.615, −4.305, and −4.793 for compounds 1, 3, and 13,
respectively, which are more soluble than the selected
standards, chloroquine (−3.902) and artemether (−4.677).
Cytochrome P450 inhibitors are responsible for the
biotransformation of a drug; a potential drug should not
alter their kinetics [34 . Te results show that although
compounds 1 (2/5), 2 (3/5), 3 (4/5), and 5 (3/5) violated the
minimum inhibition allowed as reported by Falade et al.
Table 2: Antiplasmodial
P. falciparum 3D7.
Samples
1
3+4
5
9
Chloroquine
Artemisinin
a
activity
% Inhibitiona
54.69
53.48
51.89
52.64
61.86
60.00
of
compounds
against
IC50 (in nM)
>10,000
1333
>10,000
>10,000
24.74
17.76
Tested concentration: 10 μM.
Table 3: Binding energy of isolated compounds and standards to
the anti•plasmodium (5TBO) receptor.
Compounds
1
2
3
4
5
6
7
8
9
10
11
12
13
Chloroquine
Artemether
Binding energy (∆G) kcal/mol
−8.8
−9.5
−8.7
−7.3
−10.0
−7.3
−7.4
−8.3
−8.7
−7.1
−6.3
−8.6
−8.6
−7.3
−8.3
[19 , compounds 8 (0/5), 9 (0/5), 12 (1/5), and 13 (0/5) show
an improved value of less inhibition compared to chloro•
quine (2/5).
Te human either•a•go•go related inhibition (hERG) is a
measure of electrical pulse transmission in the human heart
(iodine•channel blocking). A potential drug should not
block the activity of the hERG inhibitors [34 . Table 1 shows
that all compounds present themselves as inactive against
blocking the heart functions, as the standards. Carcinoge•
nicity results also show that compounds 8, 9, 12, and 13 are
noncarcinogenic to mammals. However, compounds 1, 2, 3,
and 5 are seen to be toxic.
Brain•blood barrier (BBB) prediction test suggests that
compounds 1, 2, 5, 9, 12, and 13 do not have the ability to
cross the BBB; hence, their modes of action do not involve
neurological engineering, such as appetite reduction as in
chloroquine. It also suggests that the six (6) compounds will
pose little or no side efects on administration as compared
to chloroquine. However, compounds 3 and 8 have a ten•
dency to cross the BBB.
A good drug must also be able to stay long (activity)
enough in the body before excretion [35 . Te half•life of a
drug is the description of how long a drug will stay active in
the body before excretion. Table 1 indicates that all identifed
compounds can exhibit a better excretion than the standard
drugs.
In addition, Table 1 also describes the drug likeliness
based on Lipinski’s rules of fve (5) criteria [36 . Te rule
13
12
11
10
9
8
7
6
5
4
3
2
1
Compounds
Artemether
Journal of Chemistry
Chloroquine
6
Binding energy (kcal/mol)
0
-2
-4
-6
-6.3
-8
-10
-7.3
-8.8
-9.5
-7.1
-7.3 -7.4
-7.3
-8.3 -8.7
-8.7
-8.6
-8.6
-8.3
-10
Binding Energy (∆G) kcal/mol
Figure 2: Graphical illustration of binding energy of the isolated compounds and standards to the anti•plasmodium (5TBO) receptor.
Interactions
van der waals
Pi-Pi Stacked
Conventional
Hydrogen Bond
Interactions
van der waals
Pi-Alkyl
(a)
Pi-Sigma
Pi-Sulfur
Conventional
Hydrogen Bond
Carbon
Hydrogen Bond
Pi-Pi Stacked
(b)
Figure 3: Docking poses of alkaloids 1 (a) and 2 (b) at the 5TBO receptor binding site.
states that for a compound that must stand as a potential
drug, its structural properties must frst satisfy the following
rules: molecular weight ≤500; MiLOGP ≤4.15; number of
oxygen ≤10; number of hydrogen ≤5; number of hydroxide
≤5.
Results show that all identifed compounds satisfy this
drug condition and hence are more likely to be applied as a
drug.
3.5. Chemotaxonomic Signifcance. Te purifcation of the
Z. gilletii extract via successive column chromatography
resulted in the isolation and identifcation of thirteen spe•
cialized metabolites including 5•hydroxynoracronycine (1),
decarine (2), trans•fagaramide (3), cis•fagaramide (4), ses•
amin (5), scoparone (6), scopoletin (7), fridelin (8), lupeol
(9), erythrodiol•3•O•palmitate (10), vanillic acid (11),
stigmasterol (12), and its derivative stigmasterol•3•O•β•D•
glucopyranoside (13).
Except compound 10 which is obtained here for the frst
time from the genus Zanthoxylum and in general from the
family Rutaceae, all the other compounds have been pre•
viously reported from the genus Zanthoxylum or from the
genus Fagara which contains several species which are
synonyms of those classifed in the genus Zanthoxylum. For
instance, trans•fagaramide (3), scopoletin (7), and vanillic
acid (11) have been previously reported from the bark of
Fagaramacrophylla and Fagara tessmannii [23, 37 . Tese
two species are both synonyms of Z. gilletii, the plant we have
investigated. Tis result partially supports the taxonomy of
our plant and its similarity with the two Fagara species based
on their chemical constituents. Further evidence has been
given by the identifcation of the other metabolites: the
acridone alkaloids have been mainly isolated from the
Journal of Chemistry
7
Interactions
Conventional Hydrogen Bond
Interactions
Conventional Hydrogen Bond
Interactions
van der waals
Carbon Hydrogen Bond
Pi-Sigma
Conventional Hydrogen Bond
Pi-Sigma
Pi-Pi Stacked
Carbon Hydrogen Bond
Alkyl
Alkyl
Pi-Donor Hydrogen Bond
Pi-Alkyl
Pi-Alkyl
Pi-Pi T-shaped
Pi-Alkyl
(a)
(b)
(c)
Figure 4: Docking poses of lignans 3 (a), 4 (b) and 5 (c) at the 5TBO receptor binding site.
Interactions
Conventional Hydrogen Bond
Interactions
Conventional Hydrogen Bond
Carbon Hydrogen Bond
Carbon Hydrogen Bond
Pi-Sulfur
Pi-Sigma
Pi-Pi Stacked
Pi-Pi Stacked
Alkyl
(a)
(b)
Figure 5: Docking poses of coumarins 6 (a) and 7 (b) at the 5TBO receptor binding site.
Interactions
van der Waals
Conventional Hydrogen Bond
Interactions
Conventional Hydrogen Bond
Pi-Sigma
Interactions
van der Waals
Alkyl
Carbon Hydrogen
Bond
Pi-Sigma
Pi-Alkyl
Pi-Sigma
(a)
(b)
(c)
Figure 6: Docking poses of triterpenoids 8 (a), 9 (b) and 10 (c) at the 5TBO receptor binding site.
8
Journal of Chemistry
Interactions
van der Waals
Interactions
van der Waals
Interactions
Conventional Hydrogen Bond
Pi-Pi Stacked
(a)
Pi-Alkyl
Conventional
Hydrogen Bond
Pi-Sigma
Pi-Sigma
Pi-Sigma
Alkyl
(b)
(c)
Figure 7: Docking poses of vanillic acid 11 (a), the steroids 12 (b) and 13 (c) at the 5TBO receptor binding site.
CI
N
H
O
O
O
NH
H
H
N
Chloroquine
Artemisinin
O
O
(a)
Interactions
van der Waals
Interactions
Conventional Hydrogen Bond
Pi-Alkyl
Conventional
Hydrogen Bond
Corbon Hydrogen Bond
Pi-Sigma
Pi-Pi Stacked
Alkyl
Pi-Alkyl
(b)
Figure 8: Structures of the standard drugs (a) and their docking poses (b) with the 5TBO receptor.
Rutaceae plants and more especially from the plants from
the genus Citrus. Unsurprisingly, the acridone 5•hydrox•
ynoracronycine (1) is one of the major compounds along
with sesamin (5) which were already reported from the plant
species Z. poggei and Z. dinklagei [21, 26 , respectively, as
well as for the frst time to the best of our knowledge from
Z. gilletii. Another lignan named cis•fagaramide (4) has been
also isolated during our investigations but has been already
identifed by Cheng et al. in [16 during their works on
Z. schinifolium. Te alkaloid decarine (2) is obtained for the
Journal of Chemistry
frst time from Z. gilletii while it has been found in
Z. madagascariense [22 . Furthermore, the coumarin sco•
poletin (6) is widely encountered in many plant species and
has been detected and characterized from the species
Z. rhetsa, Z. schinifolium, and Z. leprieurii [27, 38, 39 . Te
two triterpenoids fridelin (8) and lupeol (9) are also mainly
distributed in several plants and within the family Rutaceae,
and they have been isolated from Z. schinofolium,
Z. tessmannii, or Citrus aurantium [24, 29, 40 . However, the
third triterpene identifed as erythrodiol•3•O•palmitate (10)
has not been previously obtained from the family Rutaceae
as indicated earlier. Compound 10 is a derivative of
β•amyrin belonging to the oleanane•type triterpenoids [41 .
Te literature survey indicates that some congeners of
compound 10 including β•amyrin or β•amyrin acetate have
already been reported from the Zanthoxylum genus. Indeed,
β•amyrin was obtained in Z. simulans and Z. nitidum
[42, 43 , while β•amyrin acetate was reported from the
species Z. schinifolium [24 . Tis evidence strongly sup•
ported the possibility of obtention of erythrodiol•3•O•pal•
mitate (10) which is very structurally close to β•amyrin
acetate and difers from it by just the length of the fatty acid
attached to C•3 as well as the oxidation of the methyl CH3•28
to a primary alcohol function CH2OH [41 . Erythrodiol•3•
O•palmitate (10) has been previously obtained from Tri•
lepsium madagascariense (Moraceae) [32 and is reported
for the frst time from Z. gilletii and the family Rutaceae.
Finally, the steroids stigmasterol (12) and stigmasterol•3•O•
β•D•glucopyranoside (13) are usually obtained from several
plant materials. Tus, all the chemical compounds isolated
from Z. gilletii provide clear insights supporting the tax•
onomy of the plant and enrich the knowledge of its
chemistry.
4. Concluding Remarks
Tirteen compounds (1–13) have been isolated and
characterized from the phytochemical investigations of
the methanol extract of the bark from Z. gilletii, a
Cameroonian medicinal plant. Te compounds have been
sorted into six main classes of compounds including two
alkaloids (1 and 2), three lignans (3–5), two coumarins (6
and 7), three pentacyclic triterpenoids (8–10), one phe•
nolic compound (11) as well as two steroids (12 and 13).
Te chemotaxonomic signifcance of the isolated com•
pounds strengthened the classifcation of the plant in the
Rutaceae family and provided additional compounds to
enrich the chemistry of the species Z. gilletii (Rutaceae).
More interestingly, all the compounds tested in vitro
showed good inhibition rates of Pf 3D7 with values greater
than 50% while the molecular docking of the isolated
compounds showed that a total of eleven compounds
displayed a good afnity with the 5TBO receptor binding
site compared to the standard drugs chloroquine and
artemether. Likewise, the ADMET study indicated that
isolated compounds exhibited good and favourable pa•
rameters that qualify them as good candidates for drug
development. Te present study, in addition to supporting
the use of the plant in traditional medicine for the
9
treatment of malaria, gives signifcant insights for further
in vitro and in vivo pharmacological investigations in the
discovery of new antimalarial drugs.
Data Availability
Te spectroscopic (1H and 13C•NMR) and spectrometric
(EI•MS) data (Table 1S) of all the isolated compounds and
their molecular docking data (Table 2S) used to support the
fndings of this study are included within the supplementary
information fle.
Conflicts of Interest
Te authors declare that they have no conficts of interest.
Supplementary Materials
Table 1S shows the mass and NMR data of isolated com•
pounds. Table 2S shows compounds from Z. gilletii and their
interactions at the 5TBO receptor binding site. (Supple•
mentary Materials)
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