Research Article
Davies-Sani Rayhana Olubukola
Davies-Sani Rayhana Olubukola
Department
of Chemistry, Lagos State University, Ojo, P.M.B 001, LASU, Lagos, Nigeria.
Elesho Adeseye Omololu
Elesho Adeseye Omololu
Department
of Chemistry, Lagos State University, Ojo, P.M.B 001, LASU, Lagos, Nigeria.
Moses Sunday Owolabi*
Moses Sunday Owolabi*
Corresponding author
Department of
Chemistry, Lagos State University, Ojo, P.M.B 001, LASU, Lagos, Nigeria.
E-mail: moses.owolabi@lasu.edu.ng, sunnyconcept2007@yahoo.com,
Tel: +2348033257445
Akintayo Lanre Ogundajo
Akintayo Lanre Ogundajo
Department
of Chemistry, Lagos State University, Ojo, P.M.B 001, LASU, Lagos, Nigeria.
Nwosu Adaobi Favour
Nwosu Adaobi Favour
Department
of Chemistry, Lagos State University, Ojo, P.M.B 001, LASU, Lagos, Nigeria.
Prabodh Satyal
Prabodh Satyal
Aromatic
Plant Research Center, 230 N 1200 E, Suite 100, Lehi, UT 84043, USA.
Ambika Poudel
Ambika Poudel
Aromatic
Plant Research Center, 230 N 1200 E, Suite 100, Lehi, UT 84043, USA.
William N. Setzer
William N. Setzer
Aromatic
Plant Research Center, 230 N 1200 E, Suite 100, Lehi, UT 84043, USA.
And
Department
of Chemistry, University of Alabama in Huntsville, Huntsville, AL 35899, USA.
E-mail: setzerw@uah.edu, wsetzer@chemistry.uah.edu;
Tel.: +1-256-468-2862
And
Department of Chemistry, University of Alabama in Huntsville, Huntsville, AL 35899, USA.
E-mail: setzerw@uah.edu, wsetzer@chemistry.uah.edu; Tel.: +1-256-468-2862
Abstract
Vitex agnus-castus L. (Lamiaceae) is a perennial shrub tree commonly grown in tropical
and sub-tropical regions. V. agnus-castus
is used traditionally for the treatment of menstrual disorders, premenstrual
dysphoric disorder, and menopausal problems. The chemical compositions of the
essential oil, hydrodistilled from three different parts of the plants, were
analyzed by gas chromatography and mass spectrometry as well as chiral gas
chromatography. Also, hierarchical
cluster analysis was performed on the essential oil compositions, samples from northern
Nigeria as well as samples from other geographical locations. The essential oil
samples were dominated by 1,8-cineole (31.6–20.6%), followed by
terpinen-4-ol (8.9–2.6%), sabinene (9.4–5.8%), (E)-β-farnesene (8.1–5.5%), α-pinene (8.1–4.6%), α-terpinyl
acetate (7.7–3.0%), α-terpineol (7.4–2.4%) and manoyl oxide (6.3–0.4%). The
dextrorotatory enantiomers were the major stereoisomers for α-pinene
(88.5-83.4%), α-phellandrene (95.2-88.9%), and β-phellandrene (86.7-81.4%),
while the levorotary enantiomers were predominated by α-thujene (100%),
sabinene (88.3-86.1%), limonene (60.4-58.6%), terpinen-4-ol (86.8-68.9%), and
α-terpineol (90.6-82.9%). The cluster analysis revealed three major chemotypes:
one dominated by 1,8-cineole/sabinene/(E)-β-caryophyllene and other two
uncommon chemotypes but rich in α-pinene and 1,8-cineole/sabinene/α-pinene
respectively. The essential oils demonstrated antibacterial activities against seven
microorganisms with minimum inhibitory concentrations (MIC) ranging from 312.5
to 1250 µg/mL; active against Staphylococcus aureus and Escherichia coli (312.5
µg/mL); moderately active against Streptococcus faecalis and Pseudomonas aeruginosa (625 µg/mL),
weakly active against Bacillus subtilis, Proteus vulgaris, and Salmonella typhi (1250
µg/mL). The antibacterial activity of V.
agnus-castus essential oil can be attributed to the major components
1,8-cineole, α-pinene, terpinen-4-ol, and α-terpineol. The study shows that the
essential oils of V. agnus-castus possess potential bacterial activities
for pharmaceutical usage.
Abstract Keywords
Chaste berry, monk’s pepper, gas
chromatography, chiral, enantiomer.
1. Introduction
Vitex agnus-castus L. (Lamiaceae), commonly known as chasteberry or monk’s pepper, is a small flowering deciduous tree or shrub, that typically grows to an average of 1.5 m to 2 m tall with leaves around 7.6–10 cm in diameter, and is native to southern Europe and Central Asia, mainly the Mediterranean region [1]. The ethnopharmacology and phytochemistry of V. agnus-castus have been reviewed [2–7]; the plant has been used to treat various female conditions such as menstrual disorders, premenstrual dysphoric disorder, corpus luteum deficiency, and menopausal problems [1,8]. The important constituents of V. agnus‑castus essential oil are 1,8‑cineole, sabinene, α‑pinene, (E)‑β‑farnesene, (E)‑β‑caryophyllene, and α‑terpinyl acetate [4, 9]. As part of our ongoing interest in essential oils of aromatic and medicinal plants of Nigeria, this study is aimed to investigate the chemical characterization, enantiomeric distribution, and antibacterial efficacy of the essential oil of V. agnus-castus growing in north-central Nigeria.
2.
Materials and methods
2.1. Plant sample collection and
identification
The fresh plant of Vitex agnus-castus was collected in July 2023 along new Jos Road, Zaria (11o 5′ 0.2544″N, 7o 42′ 48.726″ E), located in Kaduna South Local Government area of Kaduna State, Nigeria. The plant was authenticated by Mr. Namadi Sunusi of the Botany Department, Ahmadu Bello University, Zaria, with voucher number ABU0841. The fresh aerial parts, leaves, and seeds of the plant were air-dried in the shade for seven days and then pulverized using an electric blender before extraction.
2.2.
Hydrodistillation
of the essential oil
Each of the air-dried plant samples (500 g) was placed in a 5-L flask, and distilled water was added to cover the sample. Hydrodistillation was carried out for four hours in an all-glass Clevenger apparatus in accordance with the British Pharmacopoeia. The distillate was extracted with n-hexane, transferred to a pre-weighed amber sample vial, and dried with anhydrous sodium sulfate to remove any remaining water. The essential oil yields ranged from 1.2 to 4.5% (v/w) with a yellowish coloration. The oils were refrigerated at 4 °C until ready for analysis.
2.3. Gas chromatographic– mass spectral
analysis
The essential oils were analyzed by GC-MS as reported previously [10]: Shimadzu GCMS-QP2010 Ultra (Shimadzu Scientific Instruments, Columbia, MD, USA), electron impact (EI) mode (electron energy = 70 eV), scan range = 40-100 atomic mass units, scan rate = 3.0 scan/s, ZB-5 fused silica capillary GC column (30 m ´ 0.25 mm ´ 0.25 μm film); He carrier gas, column head pressure = 553 kPa, flow rate =1.3 mL/min; injector temperature = 250 °C, ion source temperature = 200 °C; GC oven temperature program, 50 °C initial temperature, increased to 260 °C at 2 °C/min. A 5% w/v solution of each essential oil in CH2Cl2 was prepared and 0.1 μL was injected, splitting mode = 30:1. Identification of the volatile oil constituents was achieved based on their retention indices and by comparison of their mass spectral fragmentation pattern with those reported in databases [11–14].
2.4. Chiral gas chromatographic–
mass spectral analysis
Chiral GC-MS of the essential oils of Vitex agnus-cactus carried out as previously reported [10]: Shimadzu GCMS-QP2010S (Shimadzu Scientific Instruments, Columbia, MD, USA), EI mode (electron energy = 70 eV), scan range = 40–400 amu, scan rate = 3.0 scans/s, Restek B-Dex 325 capillary column (Restek Corp., Bellefonte, PA, USA) (30 m × 0.25 mm ID × 0.25 μm film). The oven temperature program, 50 °C initial temperature, increased to 120 °C at 1.5 °C/min, increased to 200 °C at 2 °C/min, kept at 200 °C for 5 min; He carrier gas, flow rate = 1.8 mL/min. Essential oil samples were diluted to 3% w/v with CH2Cl2, and a 0.1 μL was injected, split mode = 1:45. The terpenoid enantiomers were identified by comparison of retention indices with authentic samples obtained from Sigma-Aldrich (Milwaukee, WI, USA). Relative enantiomer percentages were determined based on peak areas.
2.5. Antibacterial screening
The A. agnus-castus leaf essential
oil was screened for antibacterial activity using the microbroth dilution assay
as previously reported [10]: Staphylococcus aureus (ATCC
No. 25923), Bacillus subtilis (ATCC No.6633), Streptococcus faecalis
(ATCC No.9790), Salmonella typhi (ATCC No. 6539), Proteus vulgaris
(ATCC No. 6380), Escherichia coli (ATCC No.25922), and Pseudomonas
aeruginosa (ATCC No. 27853); a 1% stock solution of the essential oil in
DMSO (50 μL) and 50 μL of cation–adjusted Mueller Hinton broth (CAMHB)
(Sigma-Aldrich, St. Louis, MO) was serially diluted in a 96-well microdilution
plate (essential oil concentrations = 2500, 1250, 625, 312.5, 156.3, 78.1,
39.1, and 19.5 μg/mL); bacteria were added to each well at concentrations of
1.5 × 108 CFU/mL; plates incubated at 37 °C for 24 h; minimum
inhibitory concentration (MIC) was determined as the lowest concentration with
no turbidity; positive antibiotic control = streptomycin (Sigma-Aldrich, St.
Louis, MO), negative control = DMSO (50 μL DMSO diluted in 50 μL broth medium,
serially diluted. 1,8-Cineole and α-terpineol (Sigma-Aldrich, St. Louis, MO)
were individually screened for activity.
2.6. Hierarchical cluster analysis
Hierarchical cluster analysis (HCA) analysis was carried out on the V. agnus-castus essential oils using XLSTAT v. 2018.1.1.62926 (Addinsoft, Paris, France). The HCA was performed using the concentrations of the 12 most abundant components (1,8-cineole, sabinene, α-pinene, (E)-β-farnesene, (E)-β-caryophyllene, α-terpinyl acetate, terpinen-4-ol, α-terpineol, bicyclogermacrene, caryophyllene oxide, limonene, and τ-cadinol) from this current work as well as those previously reported compositions from the literature [15–40]. Dissimilarity was used to determine clusters, considering Euclidean distance, and Ward’s method was used to define agglomeration.
3. Results and discussion
3.1. Essential oil compositions
The essential oils of the aerial parts, leaves, and seeds of V. agnus-castus were analyzed by GC-MS (Table 1). The major components in the aerial parts essential oil were 1,8-cineole (26.4%), terpinen-4-ol (8.9%), α-terpineol (7.4%), sabinene (5.8%), and (E)-β-farnesene (5.5%). The leaf essential oil showed 1,8-cineole (31.6%), sabinene (9.4%), α-pinene (8.1%), terpinen-4-ol (7.5%), and α-terpineol (5.7%) as major compounds. The essential oil from the seeds of V. agnus-castus were rich in 1,8-cineole (20.6%), (E)-β-farnesene (8.1%), α-terpinyl acetate (7.7%), sabinene (7.3%), τ-cadinol (6.9%), manoyl oxide (6.3%), and α-pinene (5.5%).
Table 1. Chemical compositions (percent) of
essential oils of Vitex agnus-castus from North-Central Nigeria.
RIcalc |
RIdb |
Compounds |
Aerial parts |
Leaves |
Seeds |
925 |
925 |
α-Thujene |
0.4 |
0.8 |
0.3 |
929 |
--- |
3-Hexyl acetate |
0.2 |
0.7 |
0.4 |
932 |
932 |
α-Pinene |
4.6 |
8.1 |
5.5 |
972 |
972 |
Sabinene |
5.8 |
9.4 |
7.3 |
978 |
978 |
β-Pinene |
1.0 |
2.0 |
0.9 |
989 |
989 |
Myrcene |
1.4 |
2.7 |
1.0 |
1007 |
1007 |
α-Phellandrene |
0.3 |
0.4 |
0.2 |
1017 |
1017 |
α-Terpinene |
1.1 |
2.2 |
0.4 |
1025 |
1025 |
p-Cymene |
0.7 |
0.2 |
0.5 |
1029 |
1030 |
Limonene |
1.9 |
0.4 |
1.4 |
1031 |
1031 |
β-Phellandrene |
1.4 |
0.5 |
0.9 |
1033 |
1032 |
1,8-Cineole |
26.4 |
31.6 |
20.6 |
1035 |
1034 |
(Z)-β-Ocimene |
0.1 |
- |
0.1 |
1036 |
1035 |
2,2,6-Trimethylcyclohexanone |
tr |
tr |
tr |
1046 |
1046 |
(E)-β-Ocimene |
0.5 |
0.7 |
0.3 |
1058 |
1058 |
γ-Terpinene |
2.3 |
3.8 |
0.7 |
1071 |
1069 |
cis-Sabinene
hydrate |
- |
- |
tr |
1085 |
1086 |
Terpinolene |
0.6 |
0.8 |
0.2 |
1100 |
1101 |
Linalool |
0.3 |
0.2 |
0.2 |
1102 |
1101 |
trans-Sabinene hydrate |
- |
- |
tr |
1106 |
1107 |
Nonanal |
tr |
tr |
tr |
1119 |
1118 |
3-Octyl acetate |
0.2 |
0.2 |
0.3 |
1127 |
1124 |
cis-p-Menth-2-en-1-ol |
0.3 |
0.2 |
0.1 |
1142 |
1141 |
trans-Pinocarveol |
- |
- |
tr |
1145 |
1142 |
trans-p-Menth-2-en-1-ol |
0.2 |
0.2 |
0.1 |
1172 |
1170 |
δ-Terpineol |
1.0 |
0.8 |
0.4 |
1182 |
1180 |
Terpinen-4-ol |
8.9 |
7.5 |
2.6 |
1197 |
1195 |
α-Terpineol |
7.4 |
5.7 |
2.4 |
1227 |
1227 |
Citronellol |
- |
- |
0.2 |
1269 |
1268 |
Geranial |
tr |
tr |
- |
1284 |
1285 |
Bornyl acetate |
0.1 |
0.1 |
0.1 |
1288 |
1287 |
Dihydroedulan IA |
0.1 |
tr |
- |
1293 |
1294 |
Dihydroedulan IIA |
tr |
tr |
- |
1300 |
1300 |
Tridecane |
0.1 |
- |
- |
1312 |
1312 |
δ-Terpinyl acetate |
- |
- |
0.1 |
1331 |
1335 |
δ-Elemene |
0.1 |
0.1 |
0.1 |
1339 |
1337 |
2-Hydroxycineol acetate |
tr |
tr |
0.1 |
1347 |
1346 |
α-Terpinyl acetate |
3.3 |
3.0 |
7.7 |
1349 |
1350 |
Citronellyl acetate |
0.2 |
- |
0.3 |
1357 |
1355 |
iso-α-Terpinyl
acetate |
0.1 |
0.1 |
0.1 |
1358 |
1361 |
Neryl acetate |
tr |
tr |
tr |
1375 |
1375 |
α-Copaene |
tr |
- |
tr |
1378 |
1378 |
Geranyl acetate |
- |
- |
0.1 |
1378 |
1379 |
(E)-β-Damascenone |
tr |
tr |
- |
1383 |
1382 |
β-Bourbonene |
0.1 |
tr |
0.1 |
1388 |
1390 |
trans-β-Elemene |
0.1 |
tr |
0.1 |
1406 |
1406 |
α-Gurjunene |
0.2 |
0.1 |
0.2 |
1419 |
1417 |
(E)-β-Caryophyllene |
2.7 |
1.9 |
2.2 |
1429 |
1430 |
β-Copaene |
tr |
tr |
0.1 |
1432 |
1432 |
trans-α-Bergamotene |
0.2 |
tr |
0.2 |
1438 |
1438 |
Aromadendrene |
tr |
tr |
tr |
1439 |
1439 |
Isoamyl benzoate |
tr |
0.1 |
0.2 |
1439 |
1439 |
(Z)-β-Farnesene |
0.1 |
- |
- |
1452 |
1452 |
(E)-β-Farnesene |
5.5 |
3.3 |
8.1 |
1455 |
1454 |
α-Humulene |
0.1 |
tr |
0.1 |
1459 |
1458 |
allo-Aromadendrene |
0.4 |
0.3 |
0.4 |
1461 |
1463 |
cis-Muurola-4(14),5-diene |
tr |
tr |
tr |
1478 |
1481 |
(E)-β-Ionone |
tr |
tr |
- |
1480 |
1480 |
Germacrene D |
0.5 |
0.3 |
1.0 |
1490 |
1491 |
Viridiflorene |
0.1 |
0.1 |
- |
1495 |
1497 |
Bicyclogermacrene |
2.1 |
1.1 |
1.8 |
1513 |
1512 |
γ-Cadinene |
0.1 |
0.1 |
0.2 |
1514 |
1510 |
1,11-Oxidocalamenene |
0.1 |
tr |
tr |
1517 |
1518 |
δ-Cadinene |
0.1 |
0.1 |
0.1 |
1559 |
1562 |
(E)-Nerolidol |
- |
tr |
0.1 |
1570 |
1568 |
Palustrol |
0.1 |
0.1 |
0.1 |
1577 |
1576 |
Spathulenol |
- |
0.5 |
1.2 |
1582 |
1587 |
Caryophyllene oxide |
0.6 |
0.1 |
0.4 |
1589 |
1590 |
Globulol |
0.4 |
0.3 |
0.4 |
1593 |
1592 |
Viridiflorol |
- |
0.1 |
0.1 |
1606 |
1605 |
Ledol |
0.5 |
0.2 |
0.5 |
1632 |
1629 |
iso-Spathulenol |
- |
0.1 |
0.1 |
1646 |
1643 |
τ-Cadinol |
3.3 |
2.3 |
6.9 |
1654 |
1655 |
α-Cadinol |
- |
- |
0.1 |
1858 |
1862 |
α-iso-Methylionone |
4.2 |
2.4 |
3.7 |
1883 |
1886 |
Sclareol oxide |
- |
tr |
0.2 |
1889 |
--- |
Unidentified a |
1.5 |
0.8 |
1.4 |
1905 |
1907 |
Isopimara-9(11),15-diene |
0.2 |
0.1 |
0.2 |
1907 |
1910 |
Methyl (2E,6E)-3,7,11-trimethyl-2,6,10-dodecatrienyl
carbonate |
- |
tr |
0.1 |
1945 |
1943 |
Beyerene isomer |
1.0 |
0.5 |
1.0 |
1949 |
1948 |
β-iso-Methylionone |
0.6 |
0.4 |
0.9 |
1958 |
1958 |
Palmitic acid |
0.1 |
- |
- |
1974 |
1978 |
Manool |
1.1 |
0.8 |
1.7 |
1981 |
--- |
Unidentified b |
0.3 |
0.4 |
1.3 |
1992 |
1994 |
Manoyl oxide |
0.9 |
0.4 |
6.3 |
2007 |
--- |
Unidentified c |
0.7 |
0.4 |
1.0 |
|
|
Compound Classes |
|
|
|
Monoterpene hydrocarbons |
22.0 |
31.9 |
19.5 |
||
Oxygenated monoterpenoids |
48.2 |
49.2 |
35.0 |
||
Sesquiterpene hydrocarbons |
12.4 |
7.3 |
14.8 |
||
Oxygenated sesquiterpenoids |
5.0 |
3.8 |
10.2 |
||
Diterpenoids |
3.2 |
1.8 |
9.2 |
||
Benzenoid aromatics |
tr |
0.1 |
0.2 |
||
Others |
5.4 |
3.8 |
5.2 |
||
Total identified |
96.1 |
97.9 |
94.1 |
RIcalc = Retention index calculated with respect to a homologous series of n alkanes on a ZB5 ms column [41]. RIdb = Reference retention index from the databases [11–14]. tr = trace (<0.05%).a MS(EI): 272(1%), 257(3%), 203(3%), 191(58%), 189(29%), 177(10%), 175(15%), 149(9%), 147(10%), 136(31%), 121(59%), 119(76%), 107(38%), 105(26%), 95(27%), 93(39%), 91(26%), 80(100%), 69(22%), 67(19%), 55(27%), 41(37%). b MS(EI): 272(1%), 257(2%), 191(100%), 189(22%), 136(34%), 121(49%), 119(53%), 107(34%), 95(26%), 93(32%), 91(19%), 80(98%), 71(29%), 55(32%), 43(33%), 41(28%). c MS(EI): 320(5%), 257(6%), 217(7%), 189(43%), 175(16%), 161(14%), 159(15%), 147(19%), 135(52%), 122(63%), 121(52%), 120(64%), 119(60%), 109(74%), 107(88%), 105(69%), 95(100%), 93(66%), 91(50%), 81(60%), 79(57%), 69(50%), 67(49%), 55(64%), 43(52%), 41(74%). |
There have been numerous previous examinations of essential oils of V. agnus-castus [15–40]. In order to place the present study into perspective, a hierarchical cluster analysis (HCA) was carried out based on the major essential oil components (Fig. 1). The HCA shows three well-defined clusters for the leaf and aerial parts essential oils of V. agnus-castus: (1) a 1,8-cineole/sabinene/(E)-β-caryophyllene cluster, which includes the samples from this work; (2) an α-pinene cluster, which includes samples from Iran with little or no 1,8-cineole; and (3) a 1,8-cineole/sabinene/α-pinene cluster.
Figure 1. Dendrogram obtained by hierarchical cluster analysis of 44 essential oil samples (aerial parts or leaves) of Vitex agnus-castus. Cetin [19], Varcin [39], Habbab [23], Senatore [36], Neves [31], Stojkovic [37], Khairi [26], Goncalves [17], Hamid [24], Marongiu [30], Kustrak [29], Duymus [20], Ulukanli [38], Al Saka [16], Inal [25], Ouali [33], Rezaei [34], Khalilzadeh [27], Farokhzad [21], Novak [32], Zoghbi [40], Abou-Zied [15], Khedri [28], Ricarte [35], Galletti [22], Bakr [18].
3.2. Enantiomeric Distribution
The V. agnus-castus essential oils were subjected to enantioselective GC-MS in order to determine the enantiomeric distribution of chiral monoterpenoid components (Table 2). The (+)-enantiomers were the major stereoisomers for α-pinene, α-phellandrene, and β-phellandrene, while the (–)-enantiomers predominated for α-thujene, sabinene, limonene, terpinen-4-ol, and α-terpineol. As far as we are aware, there have been no previous chiral gas chromatographic examinations of V. agnus-castus or any Vitex essential oils.
Table 2. Enantiomeric distribution (percent of each enantiomer) of chiral monoterpenoids in Vitex agnus-castus essential oils.
Compounds | RIdb | RIcalc | Aerial parts | Leaves | Seeds |
(+)-α-Thujene | 950 | n.o. | 0.0 | 0.0 | 0.0 |
(–)-α-Thujene | 951 | 954 | 100.0 | 100.0 | 100.0 |
(–)-α-Pinene | 976 | 977 | 16.6 | 11.5 | 13.9 |
(+)-α-Pinene | 982 | 981 | 83.4 | 88.5 | 86.1 |
(+)-Sabinene | 1021 | 1019 | 12.1 | 11.7 | 13.9 |
(–)-Sabinene | 1030 | 1027 | 87.9 | 88.3 | 86.1 |
(+)-β-Pinene | 1027 | 1025 | 13.3 | 11.8 | 19.9 |
(–)-β-Pinene | 1031 | 1030 | 86.7 | 88.2 | 80.1 |
(–)-α-Phellandrene | 1050 | 1050 | 8.2 | 11.1 | 4.8 |
(+)-α-Phellandrene | 1053 | 1051 | 91.8 | 88.9 | 95.2 |
(–)-Limonene | 1073 | 1075 | 58.6 | 60.4 | 60.1 |
(+)-Limonene | 1081 | 1082 | 41.4 | 39.6 | 39.9 |
(–)-β-Phellandrene | 1083 | 1086 | 17.9 | 18.6 | 13.3 |
(+)-β-Phellandrene | 1089 | 1090 | 82.1 | 81.4 | 86.7 |
(–)-Linalool | 1228 | 1228 | 51.3 | 47.9 | 56.2 |
(+)-Linalool | 1231 | 1232 | 48.7 | 52.1 | 43.8 |
(+)-Terpinen-4-ol | 1297 | 1296 | 29.3 | 13.2 | 31.1 |
(–)-Terpinen-4-ol | 1300 | 1298 | 70.7 | 86.8 | 68.9 |
(–)-α-Terpineol | 1347 | 1347 | 90.1 | 82.9 | 90.6 |
(+)-α-Terpineol | 1356 | 1357 | 9.9 | 17.1 | 9.4 |
RIdb = Retention index from our in-house database based on commercially available compounds available from Sigma-Aldrich and augmented with our own data. RIcalc = Calculated retention index based on a series of n-alkanes on a Restek B-Dex 325 capillary column. n.o. = not observed.
3.3. Antibacterial Activity
The V. agnus-castus leaf essential oil was screened for antibacterial activity against a panel of Gram-positive (Bacillus subtilis, Staphylococcus aureus, Streptococcus faecalis) and Gram-negative (Escherichia coli, Proteus vulgaris, Pseudomonas aeruginosa, Salmonella typhi) organisms (Table 3). The essential oil showed strong antibacterial activity (MIC = 312.5 μg/mL) against S. aureus and E. coli and moderate activity (MIC = 625 μg/mL) against S. faecalis and P. aeruginosa [42, 43]. Of the major components, 1,8-cineole and α-terpineol showed antibacterial activity against S. aureus, E. coli, P. aeruginosa, and S. typhi (Table 3). Previous work has shown sabinene to be relatively inactive as an antibacterial [44, 45]. However, α-pinene has shown antibacterial activity against B. subtilis, S. aureus, E. coli, P. vulgaris, P. aeruginosa, and S. typhi [46, 47]; and terpinen-4-ol has shown activity against B. subtilis, E. coli, P. vulgaris, P. aeruginosa, and S. aureus [44,48]. Thus, the antibacterial activity of V. agnus-castus leaf essential oil can be attributed to the major components 1,8-cineole, α-pinene, terpinen-4-ol, and α-terpineol. Consistent with the antibacterial observations in this report, there have been previous reports on the antibacterial activities of V. agnus-castus essential oils, including activities against B. subtilis [18], Streptococcus mutans [17], P. aeruginosa [23], Bacillus cereus [28], and Salmonella enterica serovar Typhimurium [37].
Table 3. Antibacterial activity of Vitex agnus-castus leaf essential oil, 1,8-cineole, and α-terpineol.
Organism | Vitex agnus-castus EO | 1,8-Cineole | α-Terpineol | Streptomycin |
Bacillus subtilis | 1250 | nt | nt | <19.5 |
Staphylococcus aureus | 312.5 | 312.5 | 312.5 | <19.5 |
Streptococcus faecalis | 625 | nt | nt | <19.5 |
Escherichia coli | 312.5 | 312.5 | 625 | < 19.5 |
Proteus vulgaris | 1250 | ny | nt | < 19.5 |
Pseudomonas aeruginosa | 625 | 312.5 | 312.5 | < 19.5 |
Salmonella typhi | 1250 | 312.5 | 156.3 | <19.5 |
4. Conclusions
The essential oil compositions and antibacterial activities of V. agnus-castus from north-central Nigeria are comparable to compositions (largely dominated by oxygenated monoterpenoids and monoterpene hydrocarbons) and antibacterial activities (good antibacterial activity against S. aureus and E. coli) from other geographical locations. This is the first report on the enantiomeric distributions of chiral monoterpenoids in V. agnus-castus essential oils, however, this adds to our knowledge on this important medicinal plant. Additional research is needed on the enantioselective GC-MS of other Vitex essential oils to identify any trends in enantiomeric distributions.
Authors’ contributions
Conceptualization, M.S.O; Methodology, D.S.R.O., M.S.O., N.A.F., P.S., and W.N.S.; Software, P.S.; Validation, L.A.O. and W.N.S., Formal Analysis, A.P. and W.N.S.; Investigation, D.S.R.O., M.S.O., P.S., A.P., E.A.O. and W.N.S.; Resources, D.S.R.O., M.S.O., N.A.O., P.S. and W.N.S.; Data Curation, W.N.S.; Writing – Original Draft Preparation, M.S.O., E.A.O. and W.N.S.; Writing – Review & Editing, M.S.O. and W.N.S.; Project Administration, D.S.R.O. E.A.O., N.A.F. and M.S.O.
Acknowledgements
This work was carried out as part of the activities of the Aromatic Plant Research Center (APRC, https://aromaticplant.org/). We are grateful to Dr. P.A. Akinduti for the antibacterial screening.
Funding
This research received no specific grant from any funding agency.
Availability of data and materials
All data will be made available on request according to the journal policy.
Conflicts of interest
The authors declare no conflict of interest.
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Abstract
Vitex agnus-castus L. (Lamiaceae) is a perennial shrub tree commonly grown in tropical
and sub-tropical regions. V. agnus-castus
is used traditionally for the treatment of menstrual disorders, premenstrual
dysphoric disorder, and menopausal problems. The chemical compositions of the
essential oil, hydrodistilled from three different parts of the plants, were
analyzed by gas chromatography and mass spectrometry as well as chiral gas
chromatography. Also, hierarchical
cluster analysis was performed on the essential oil compositions, samples from northern
Nigeria as well as samples from other geographical locations. The essential oil
samples were dominated by 1,8-cineole (31.6–20.6%), followed by
terpinen-4-ol (8.9–2.6%), sabinene (9.4–5.8%), (E)-β-farnesene (8.1–5.5%), α-pinene (8.1–4.6%), α-terpinyl
acetate (7.7–3.0%), α-terpineol (7.4–2.4%) and manoyl oxide (6.3–0.4%). The
dextrorotatory enantiomers were the major stereoisomers for α-pinene
(88.5-83.4%), α-phellandrene (95.2-88.9%), and β-phellandrene (86.7-81.4%),
while the levorotary enantiomers were predominated by α-thujene (100%),
sabinene (88.3-86.1%), limonene (60.4-58.6%), terpinen-4-ol (86.8-68.9%), and
α-terpineol (90.6-82.9%). The cluster analysis revealed three major chemotypes:
one dominated by 1,8-cineole/sabinene/(E)-β-caryophyllene and other two
uncommon chemotypes but rich in α-pinene and 1,8-cineole/sabinene/α-pinene
respectively. The essential oils demonstrated antibacterial activities against seven
microorganisms with minimum inhibitory concentrations (MIC) ranging from 312.5
to 1250 µg/mL; active against Staphylococcus aureus and Escherichia coli (312.5
µg/mL); moderately active against Streptococcus faecalis and Pseudomonas aeruginosa (625 µg/mL),
weakly active against Bacillus subtilis, Proteus vulgaris, and Salmonella typhi (1250
µg/mL). The antibacterial activity of V.
agnus-castus essential oil can be attributed to the major components
1,8-cineole, α-pinene, terpinen-4-ol, and α-terpineol. The study shows that the
essential oils of V. agnus-castus possess potential bacterial activities
for pharmaceutical usage.
Abstract Keywords
Chaste berry, monk’s pepper, gas
chromatography, chiral, enantiomer.
This work is licensed under the
Creative Commons Attribution
4.0
License (CC BY-NC 4.0).
Editor-in-Chief
Prof. Dr. Radosław Kowalski
This work is licensed under the
Creative Commons Attribution 4.0
License.(CC BY-NC 4.0).