# Caryophyllene-Rich Essential Oils of Two Species from Southern Côte d'Ivoire: Guibourtia ehie (A. Chev.) J Léonard (Caesalpiniaceae) and Oricia suaveolens (Engl.) Verd. (Rutaceae)

Toffé Alexis Kouao, Zana Adama Ouattara, Didjour Albert Kambiré, Bosson Antoine Kouamé, Janat Akhanovna Mamyrbékova-Békro, Pierre Tomi, Mathieu Paoli, Ange Bighelli, Yves-Alain Békro, Felix Tomi

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Toffé Alexis Kouao, Zana Adama Ouattara, Didjour Albert Kambiré, Bosson Antoine Kouamé, Janat Akhanovna Mamyrbékova-Békro, et al.. Caryophyllene-Rich Essential Oils of Two Species from Southern Côte d'Ivoire: Guibourtia ehie (A. Chev.) J Léonard (Caesalpiniaceae) and Oricia suaveolens (Engl.) Verd. (Rutaceae). Compounds, 2023, 3 (1), pp.73-82. 10.3390/compounds3010006. hal-05034487

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Article

# Caryophyllene-Rich Essential Oils of Two Species from Southern Côte d'Ivoire: *Guibourtia ehie* (A. Chev.) J Léonard (Caesalpiniaceae) and *Oricia suaveolens* (Engl.) Verd. (Rutaceae)

Toffé Alexis Kouao<fnref n="1" />, Zana Adama Ouattara<fnref n="1" />, Didjour Albert Kambiré<fnref n="2" /> ID, Bosson Antoine Kouamé<fnref n="1" />, Janat Akhanovna Mamyrbékova-Békro<fnref n="1" />, Pierre Tomi<fnref n="3" />, Mathieu Paoli<fnref n="3" /> ID, Ange Bighelli<fnref n="3" />, Yves-Alain Békro<fnref n="1" /> and Felix Tomi<fnref n="3" />,* ID

**Abstract:** The essential oils of *Oricia suaveolens* and *Guibourtia ehie* from Southern Côte d'Ivoire were extracted by hydrodistillation then analyzed by gas chromatography in combination with retention indices [GC(RI)], gas chromatography coupled with mass spectrometry (GC-MS) and nuclear magnetic resonance of carbone-13 (¹³C NMR) And described here for the first time. A total of 42 compounds were identified in the essential oils of the leaves of *G. ehie* while 55, 40 and 23 components were identified in the leaves, stem bark and root bark oils of *O. suaveolens*, respectively. Essential oils samples were dominated by sesquiterpenes and (E)-β-caryophyllene was the major compound common to all samples: *G. ehie* leaf oil contained (E)-β-caryophyllene (26.9–40.8%), α-humulene (syn. α-caryophyllene) (6.7–9.7%), β-elemene (5.5–9.5%) and germacrene D (5.6–8.1%); *O. suaveolens*, leaf oil contained (E)-β-caryophyllene (33.5–39.3%), (E)-β-farnesene (5.9–9.3%), caryophyllene oxide (2.1–7.7%) and α-humulene (4.0–4.6%); stem bark oil contained α-humulene (38.3–45.8%) and (E)-β-caryophyllene (34.7–41.6%); root bark oil contained α-humulene (36.1–47.9%) and (E)-β-caryophyllene (34.3–43.3%). This study highlighted the abundant presence of (E)-β-caryophyllene, a phytocannabinoid sesquiterpene with countless biological properties, in two plant species: *Guibourtia ehie* and *Oricia suaveolens*.

**Keywords:** essential oil; *Guibourtia ehie*; *Oricia suaveolens*; hydrodistillation; chemical composition

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**Citation:** Kouao, T.A.; Ouattara, Z.A.; Kambiré, D.A.; Kouamé, B.A.; Mamyrbékova-Békro, J.A.; Tomi, P.; Paoli, M.; Bighelli, A.; Békro, Y.-A.; Tomi, F. Caryophyllene-Rich Essential Oils of Two Species from Southern Côte d'Ivoire: *Guibourtia ehie* (A. Chev.) J Léonard (Caesalpiniaceae) and *Oricia suaveolens* (Engl.) Verd. (Rutaceae). *Compounds* **2023**, *3*, 73–82. https://doi.org/10.3390/compounds3010006

Academic Editors: Jorge Pereira and
Cassamo U. Mussagy

Received: 16 December 2022

Revised: 6 January 2023

Accepted: 10 January 2023

Published: 12 January 2023

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**Copyright:** © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
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conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).

## 1. Introduction

*Guibourtia ehie* (A. Chev.) J Léonard and *Oricia suaveolens* (Engl) are two plant-species growing wild in Côte d'Ivoire.

*G. ehie* is a tree of the Cesalpiniaceae (Fabaceae) family up to 45–50 m tall, with a straight, cylindrical bole, branchless for up to 25 m. The leaves are spirally arranged, parietinolate with a pair of leaflets; the stipules are leaf-like, up to 2 cm long, and often persistent; the petioles are 0.5–1 cm long. The distribution area of *G. ehie* extends from Guinea and Liberia to Cameroon and Gabon [1,2]. It is a medicinal plant present in Cameroon, Ghana, Liberia, Nigeria and Côte d'Ivoire [3]. It is used for the treatment of gonorrhea wounds [3], ulcers [4], high blood pressure and sexual infections [5]. Very few works in the literature deal with the phytochemistry of the *Guibourtia* genus. The phytochemical screening made from solvent extracts of *G. ehie* highlighted the presence of terpenes, sterols,

<footnote n="1">¹ Laboratoire de Chimie Bio-Organique et de Substances Naturelles, Université Nangui Abrogoua, Abidjan 02 BP 801, Côte d'Ivoire</footnote>

<footnote n="2">² UPR de Chimie Organique, Département de Mathématiques-Physique-Chimie, Université Péléforo GON COULIBALY, Korhogo BP 1328, Côte d'Ivoire</footnote>

<footnote n="3">³ Laboratoire Sciences Pour l'Environnement, Université de Corse—CNRS, UMR 6134 SPE, Route des Sanguinaires, 20000 Ajaccio, France</footnote>

<footnote>* Correspondence: tomi_f@univ-corse.fr</footnote>
saponins, flavonoids and alkaloids [4]. A dihydrochalcone glucoside, 2',4-dihydroxy-4'-methoxy-6'-O-β-glucopyranoside dihydro-chalcone, a stilbene glycoside, 3,5-dimethoxy-4'-O-(β-rhamnopyranosyl-(1→6)-β-gluco-pyranoside) stilbene, and pterostilbene were isolated from *G. tessmanii* [6]. The leaves and trunk of *G. ehie* contained rhaponticine, 2,6-dimethoxybenzoquinone, lupeol, taraxanol, friedelan-3-one, lanosterol, scopoletine and pilloine [5]. Antioxidant and antibacterial activities are attributed to this plant [3–5]. However, no study concerning the chemical composition of the essential oils of *G. ehie* was mentioned in the literature.

*Oricia suaveolens* (Rutaceae) is a shrub or tree up to 10 m long. Its leaves are trifoliate, rarely simple, with a long petiole [7]. It is a species used in traditional medicine against toothache, fever and parasites [5]. The literature reports few studies on the phytochemicals identified in the *Oricia* genus. A furoquinoline alkaloid, 6,7-methylenedioxy-5-hydroxy-8-ethoxy-dictamine, and a flavanone glycoside, 5-hydroxy-4'-methoxy-7-O-[α-l-rhamnopyranosyl (1"→5")-β-d-apiofuranosyl]-flavanoside, were isolated from *O. suaveolens* and *O. renieri* [8]. The root of *O. suaveolens* contained mainly alkaloids including skimmianine, kokusaginine and montrifoline and triterpenes such as limonine [9], while the leaves and stem contained β-indoloquinazoline alkaloids; orisuaveoline A, orisuaveoline B and furoquinoline alkaloids; quinosuaveoline A, and quinosuaveoline B [10]. No study reports the chemical composition of the essential oil of *O. suaveolens*.

In the course of our on-going work on the characterization of the aromatic plants of Côte d'Ivoire through the chemical composition of their essential oils [11–14], the aim of the present work was to i) determine, for the first time, the chemical composition of the essential oil from *G. ehie* and *O. suaveolens*, growing wild in Côte d'Ivoire, and ii) highlight the presence of (E)-β-caryophyllene as a major component.

In recent years, many studies have demonstrated the interesting biological properties of (E)-β-caryophyllene: antinociceptive and anti-inflammatory [15]; anticancer [16,17]; antioxidant [16,18]; antimicrobial [16]; analgesic [17]; and antiatherogenic [18]. Essential oils rich in caryophyllene therefore present a particular interest. Previous studies have shown the occurrence of (E)-β-caryophyllene in Ivorian plant species [14,19–22].

**2. Materials and Methods**

**2.1. Plant Material**

Four leaves samples of *G. ehie* were harvested in Boua M'po, Rubino, Côte d'Ivoire (G1, G2) (6°04'09" N, 4°18'31" W) and in Adiopodoumé, Abidjan, Côte d'Ivoire (G3, G4) (5°20'12" N et 4°7'57" W). The plant was authenticated (voucher n° IBAAN REG 00704) in "Centre National de Floristique", Université Félix Houphouët-Boigny, Abidjan.

Three samples of leaves, four samples of stem bark and five samples of root bark of *O. suaveolens* were harvested in Petit Yapo Forest (5°43'50.5" N, 4°4'41.9" W), Agboville, Côte d'Ivoire. The organs were conditioned under permanent air conditioning for three days at 18 °C. The identification of the plant has been confirmed (voucher n° LAA 10096) by "Centre National de Floristique", Université Félix Houphouët-Boigny, Abidjan.

**2.2. Essential Oil Isolation**

Vegetable material was submitted to hydrodistillation during 3.5 h with a Clevenger-type apparatus. The essential oil samples obtained were dried over anhydrous Na₂SO₄ and then conserved at 5 °C. The extraction yields were calculated from fresh material (w/w) (Table S1).

**2.3. Gas Chromatography and Gas Chromatography-Mass Spectrometry in Electron Impact Mode**

GC analyses were performed on a Clarus 500 PerkinElmer Chromatograph (PerkinElmer, Courtaboeuf, France), equipped with a flame ionization detector (FID) and two fused-silica capillary columns (50 m × 0.22 mm, film thickness 0.25 µm), BP-1 (polydimethylsiloxane) and BP-20 (polyethylene glycol). The oven temperature was programmed from 60 °C to 220 °C at 2 °C/min and then held isothermal at 220 °C for 20 min; injector temperature:
250 °C; detector temperature: 250 °C; carrier gas: hydrogen (0.8 mL/min); split: 1/60; injected volume: 0.5 µL. Retention indices (RI) were calculated relative to the retention times of a series of *n*-alkanes (C8–C29) with linear interpolation (« Target Compounds » software from PerkinElmer).

GC/MS analyses were performed on a Clarus SQ8S PerkinElmer TurboMass detector (quadrupole), directly coupled with a Clarus 580 PerkinElmer Autosystem XL (PerkinElmer, Courtaboeuf, France), equipped with a BP-1 (polydimethylsiloxane) fused-silica capillary column (50 m × 0.22 mm i.d., film thickness 0.25 µm). The oven temperature was programmed from 60 to 220 °C at 2°/min and then held isothermal for 20 min; injector temperature, 250 °C; ion-source temperature, 250 °C; carrier gas, Helium (1 mL/min); split ratio, 1:80; injection volume, 0.5 µL; ionization energy, 70 eV. The electron ionization (EI) mass spectra were acquired over the mass range 35–350 Da.

## 2.4. Nuclear Magnetic Resonance

All nuclear magnetic resonance (NMR) spectra were recorded on a Bruker AVANCE 400 Fourier transform spectrometer (Bruker, Wissembourg, France) operating at 100.623 MHz for ¹³C, equipped with a 5 mm probe. Solvent used was CDCl₃, with all shifts referred to internal tetramethylsilane (TMS). ¹³C NMR spectra of the oil samples were recorded with the following parameters: pulse width, 4 µs (flip angle 45°); relaxation delay D1, 0.1 s; acquisition time, 2.7 s for a 128K data table with a spectral width of 25,000 Hz (250 ppm); CPD mode decoupling; digital resolution, 0.183 Hz/pt. The number of accumulated scans was 3000 for each sample or fraction (30 mg, in 0.5 mL of CDCl₃).

## 2.5. Identification of Individual Components

Identification of the individual components was carried out as follows: (i) by comparison of their GC retention indices on apolar and polar columns, with those of reference compounds [23,24]; (ii) on computer matching against commercial mass spectral libraries [24–26]; (iii) on comparison of the signals in the ¹³C NMR spectra of the samples with those of reference spectra compiled in the laboratory spectral library, with the help of laboratory-made software [27–29]. This method allowed the identification of individual components of the essential oil at content as low as 0.4–0.5%.

# 3. Results and Discussion

Four essential oils samples of the leaves of *G. ehie* harvested in two locations in the south of Côte d'Ivoire (Boua M'po and Adiopodoumé), were obtained with low yield (0.01–0.05 %: *w/w*; calculated on weight basis) (Table S1).

Essential oils of the leaves (three samples), stem bark (four samples) and root bark (five samples) of *O. suaveolens* harvested in Petit Yapo Forest were obtained with low yields (Table S1) (0.05–0.08%, 0.01–0.03% and 0.01–0.02%: *w/w*, calculated on weight basis, respectively).

A combination of techniques was applied to the essential oil analysis: GC (associated with retention indices on two columns with different polarity), GC-MS and ¹³C NMR following a computerized ¹³C NMR method developed at the University of Corsica [11,29]. Most compounds have been identified through these three techniques.

## 3.1. Chemical Composition of Leaf Oils of *G. ehie*

Forty-two compounds were identified in the leaf oil of *G. ehie* representing 89.9 to 93.8% of the overall composition (Table 1). The chemical compositions of the four oils were dominated by sesquiterpene hydrocarbons; among them, (E)-β-caryophyllene (26.9–40.8%) was the major compound. Other compounds were present in appreciable amounts: β-elemene (5.5–9.5%), α-humulene (6.7–9.7%), germacrene D (5.6–8.1%) and β-elemol (1.6–4.2%). No monoterpene was identified and the total amount of non-terpene linear compounds (0.9–2.9%) and diterpenes (0.5–3.3%) was limited.
<table><caption>**Table 1.** Chemical composition of leaf oil samples of *Guibourtica ehie*.</caption><thead><tr><th>N°</th><th>Compounds</th><th>Rla</th><th>RIp</th><th>G1</th><th>G2</th><th>G3</th><th>G4</th><th>Identification</th></tr></thead><tbody><tr><td>1</td><td>Undecan-2-one</td><td>1274</td><td>1591</td><td>-</td><td>-</td><td>0.2</td><td>0.2</td><td>RI, MS</td></tr><tr><td>2</td><td>δ-Elemene</td><td>1335</td><td>1472</td><td>0.9</td><td>0.3</td><td>1.7</td><td>1.7</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>3</td><td>α-Cubebene</td><td>1348</td><td>1459</td><td>0.1</td><td>0.2</td><td>0.2</td><td>0.1</td><td>RI, MS</td></tr><tr><td>4</td><td>α-Ylangene</td><td>1368</td><td>1580</td><td>0.1</td><td>0.4</td><td>0.1</td><td>0.1</td><td>RI, MS</td></tr><tr><td>5</td><td>α-Copaene</td><td>1375</td><td>1493</td><td>1.5</td><td>2.7</td><td>2.5</td><td>1.9</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>6</td><td>β-Elemene</td><td>1387</td><td>1593</td><td>9.0</td><td>5.5</td><td>9.5</td><td>7.7</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>7</td><td>(E)-β-Caryophyllene</td><td>1417</td><td>1600</td><td>40.4</td><td>40.4</td><td>40.8</td><td>26.9</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>8</td><td>β-Copaene</td><td>1426</td><td>1580</td><td>0.1</td><td>0.2</td><td>0.3</td><td>1.8</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>9</td><td>γ-Elemene</td><td>1429</td><td>1639</td><td>-</td><td>0.1</td><td>0.1</td><td>0.2</td><td>RI, MS</td></tr><tr><td>10</td><td>(E)-α-Bergamotene</td><td>1431</td><td>1587</td><td>1.2</td><td>1.7</td><td>1.3</td><td>0.9</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>11</td><td>α-Guaiene</td><td>1434</td><td>1591</td><td>1.0</td><td>1.0</td><td>0.8</td><td>0.6</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>12</td><td>(E)-β-Farnesene</td><td>1446</td><td>1669</td><td>0.8</td><td>1.1</td><td>1.0</td><td>0.7</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>13</td><td>α-Humulene</td><td>1448</td><td>1669</td><td>9.1</td><td>9.7</td><td>9.4</td><td>6.7</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>14</td><td>allo-Aromadendrene</td><td>1457</td><td>1645</td><td>0.5</td><td>0.9</td><td>0.8</td><td>0.9</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>15</td><td>γ-Muurolene</td><td>1469</td><td>1689</td><td>0.5</td><td>0.7</td><td>0.7</td><td>0.8</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>16</td><td>Germacrene D</td><td>1474</td><td>1709</td><td>7.7</td><td>5.6</td><td>7.1</td><td>8.1</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>17</td><td>Tridecan-2-one</td><td>1476</td><td>1809</td><td>0.4</td><td>0.7</td><td>0.6</td><td>0.5</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>18</td><td>β-Selinene</td><td>1482</td><td>1715</td><td>1.1</td><td>0.8</td><td>1.2</td><td>1.2</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>19</td><td>α-Selinene</td><td>1492</td><td>1715</td><td>0.1</td><td>1.0</td><td>0.1</td><td>1.2</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>20</td><td>α-Burnesene</td><td>1499</td><td>1718</td><td>1.4</td><td>1.4</td><td>1.1</td><td>1.0</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>21</td><td>β-Bisabolene</td><td>1505</td><td>2190</td><td>0.1</td><td>0.2</td><td>0.2</td><td>-</td><td>RI, MS</td></tr><tr><td>22</td><td>γ-Cadinene</td><td>1508</td><td>1750</td><td>0.1</td><td>0.3</td><td>0.1</td><td>0.2</td><td>RI, MS</td></tr><tr><td>23</td><td>δ-Cadinene</td><td>1515</td><td>1557</td><td>1.2</td><td>1.2</td><td>1.4</td><td>2.1</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>24</td><td>Selina-3.7(11)-diene</td><td>1529</td><td>1791</td><td>0.1</td><td>0.2</td><td>0.2</td><td>0.1</td><td>RI, MS</td></tr><tr><td>25</td><td>β-Elemol</td><td>1533</td><td>2077</td><td>2.6</td><td>1.6</td><td>1.6</td><td>4.2</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>26</td><td>(E)-Nerolidol</td><td>1547</td><td>2040</td><td>0.5</td><td>0.4</td><td>0.3</td><td>0.8</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>27</td><td>Germacrene B</td><td>1549</td><td>1826</td><td>0.4</td><td>0.2</td><td>0.3</td><td>0.5</td><td>RI, MS</td></tr><tr><td>28</td><td>Spathulenol</td><td>1566</td><td>2119</td><td>0.5</td><td>0.4</td><td>0.2</td><td>0.2</td><td>RI, MS</td></tr><tr><td>29</td><td>Caryophyllene oxide</td><td>1569</td><td>1778</td><td>3.3</td><td>3.1</td><td>1.9</td><td>1.4</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>30</td><td>Globulol</td><td>1571</td><td>2061</td><td>0.1</td><td>0.2</td><td>0.2</td><td>0.3</td><td>RI, MS</td></tr><tr><td>31</td><td>Viridiflorol</td><td>1580</td><td>2079</td><td>0.5</td><td>1.8</td><td>0.8</td><td>2.5</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>32</td><td>Guiaiol</td><td>1583</td><td>2086</td><td>0.5</td><td>0.3</td><td>0.3</td><td>0.9</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>33</td><td>Cedrol</td><td>1592</td><td>2124</td><td>1.3</td><td>1.4</td><td>1.1</td><td>1.3</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>34</td><td>Humulene oxide II</td><td>1598</td><td>2034</td><td>1.3</td><td>1.4</td><td>1.1</td><td>1.3</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>35</td><td>τ-Muurolol</td><td>1625</td><td>2183</td><td>1.1</td><td>0.7</td><td>0.9</td><td>2.0</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>36</td><td>α-Muurolol</td><td>1627</td><td>-</td><td>0.4</td><td>0.2</td><td>0.3</td><td>0.8</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>37</td><td>Cubenol</td><td>1630</td><td>2071</td><td>0.1</td><td>-</td><td>0.1</td><td>0.2</td><td>RI, MS</td></tr><tr><td>38</td><td>α-Cadinol</td><td>1635</td><td>2227</td><td>2.0</td><td>1.2</td><td>1.6</td><td>2.7</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>39</td><td>Nonadec-1-ene</td><td>1675</td><td>-</td><td>0.5</td><td>0.1</td><td>0.6</td><td>1.3</td><td>RI, MS</td></tr><tr><td>40</td><td>Heptadecanal</td><td>1892</td><td>2247</td><td>-</td><td>0.1</td><td>0.2</td><td>0.9</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>41</td><td>(E)-Phytol</td><td>2097</td><td>2608</td><td>0.8</td><td>0.4</td><td>0.8</td><td>2.9</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>42</td><td>neo-Abietadiene</td><td>2136</td><td>2534</td><td>0.1</td><td>0.1</td><td>0.1</td><td>0.4</td><td>RI, MS</td></tr><tr><td colspan="2">Sesquiterpene hydrocarbons</td><td></td><td>77.0</td><td>75.6</td><td>80.6</td><td>64.9</td><td></td><td></td></tr><tr><td colspan="2">Oxygenated sesquiterpenes</td><td></td><td>14.2</td><td>12.7</td><td>10.4</td><td>18.6</td><td></td><td></td></tr><tr><td colspan="2">Diterpenes</td><td></td><td>0.9</td><td>0.5</td><td>0.9</td><td>3.3</td><td></td><td></td></tr><tr><td colspan="2">Non-terpenic compounds</td><td></td><td>0.9</td><td>0.9</td><td>1.6</td><td>2.9</td><td></td><td></td></tr><tr><td colspan="2">Total</td><td></td><td>93.4</td><td>89.9</td><td>93.8</td><td>90.2</td><td></td><td></td></tr></tbody></table>

Order of elution and percentages on apolar column (BP-1); Rla, RIp: retention indices measured on apolar and polar capillary columns, respectively.

The chemical composition of the four oil samples was homogenous and no chemical variability was observed in relation to the location. However, sample G4 was slightly different and exhibited a low amount of (E)-β-caryophyllene (26.9%) in comparison to the G1-G3 samples whose content is higher than 40%. (E)-β-Caryophyllene, the main compound of the essential oils of the leaves of *G. ehie*, is also found as the main component
in various species belonging to the same family (Caesalpiniaceae): *Copaifera multijuga*, 36% [30]; 57.5% [31]; *Indigofra microcarpa*, 56% [32].

## 3.2. Chemical Composition of Leaf, Stem and Root Bark Oils of *O. suaveolens*

Analysis of the essential oils of the leaves, stem and root barks of *O. suaveolens* allowed the identification of 55, 40 and 23 compounds, accounting for 88.1–93.7%, 94.0–96.0% and 94.3–98.8% of the global composition, respectively (Tables 2–4). These essential oils consisted almost exclusively of sesquiterpene hydrocarbons exhibiting (E)-β-caryophyllene and α-humulene as major components. (E)-β-caryophyllene is predominant in the leaf essential oil and associated with α-humulene (α-caryophyllene) in the trunk and root bark oil samples. The percentage of (E)-β-caryophyllene accounted for 33.5–39.3% in the leaf oils (Table 2). (E)-β-Farnesene (5.9–9.3%), caryophyllene oxide (2.1–7.7%) and α-humulene (4.0–4.6%) were present in appreciable content. Non-terpene linear compounds (0.6–6.1%) and diterpenes (1.5–3.9%) were represented in non-negligible amounts while monoterpenes (0.6–1.8%) were weakly represented. Stem bark oils were characterized by close amounts of α-humulene (38.3–45.8%) and (E)-β-caryophyllene (34.7–41.6%) (Table 3). Two oxygenated sesquiterpenes, caryophyllene oxide (2.3–4.1%) and humulene oxide II (2.1–3.7%), were present in non-negligible amounts. Amounts of monoterpenes (0.1–2.0%), diterpenes (0–0.4%), aromatic derivatives (0–1.2%) and non-terpene linear compounds (0.1–0.6%) were low. The same association of α-humulene (36.1–47.9%)/(E)-β-caryophyllene (34.3–43.3%) was also evidenced from root bark oil (Table 4). A sesquiterpene hydrocarbon, geijerene (1.4–5.9%), and three oxygenated sesquiterpenes, caryophyllene oxide (0.6–4%), humulene oxide II (1.1–4.5%) and humulene oxide III (2.4–7.7%), were present in appreciable content while monoterpenes and non-terpene linear compounds were represented in much lower content, 0–1.7% and 0–3.8%, respectively. Whatever the organ of the plant, the chemical variability was very low.

<table><caption>**Table 2.** Chemical composition of leaf oil samples of *Oricia suaveolens*.</caption><thead><tr><th>N°</th><th>Compounds</th><th>Rla</th><th>Rlp</th><th>F1</th><th>F2</th><th>F3</th><th>Identification</th></tr></thead><tbody><tr><td>1</td><td>(E)-Hex-2-enal</td><td>823</td><td>1225</td><td>2.4</td><td>-</td><td>-</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>2</td><td>(Z)-Hex-3-en-1-ol</td><td>838</td><td>1387</td><td>-</td><td>1.3</td><td>-</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>3</td><td>(Z)-Hex-2-en-1-ol</td><td>842</td><td>1408</td><td>2.7</td><td>1.4</td><td>-</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>4</td><td>Hexan-1-ol</td><td>845</td><td>1352</td><td>0.9</td><td>0.6</td><td>-</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>5</td><td>α-Pinene</td><td>929</td><td>1020</td><td>0.4</td><td>0.3</td><td>-</td><td>RI, MS</td></tr><tr><td>6</td><td>Myrcene</td><td>981</td><td>1165</td><td>-</td><td>0.1</td><td>0.1</td><td>RI, MS</td></tr><tr><td>7</td><td>(E)-β-Ocimene</td><td>1035</td><td>1254</td><td>0.2</td><td>0.1</td><td>0.1</td><td>RI, MS</td></tr><tr><td>8</td><td>Linalool</td><td>1083</td><td>1549</td><td>1.1</td><td>0.8</td><td>0.1</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>9</td><td>Undecan-2-one</td><td>1270</td><td>1592</td><td>-</td><td>0.1</td><td>0.1</td><td>RI, MS</td></tr><tr><td>10</td><td>α-Copaene</td><td>1375</td><td>1493</td><td>0.1</td><td>0.1</td><td>0.1</td><td>RI, MS</td></tr><tr><td>11</td><td>β-Bourbonene</td><td>1383</td><td>1520</td><td>0.1</td><td>0.2</td><td>0.1</td><td>RI, MS</td></tr><tr><td>12</td><td>α-Funebrene</td><td>1386</td><td>1538</td><td>3.3</td><td>3.8</td><td>2.5</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>13</td><td>α-Ionone</td><td>1400</td><td>1849</td><td>0.1</td><td>0.1</td><td>0.1</td><td>RI, MS</td></tr><tr><td>14</td><td>(E)-β-Caryophyllene</td><td>1417</td><td>1600</td><td>39.3</td><td>33.5</td><td>38.7</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>15</td><td>β-Copaene</td><td>1427</td><td>1587</td><td>-</td><td>0.2</td><td>0.1</td><td>RI, MS</td></tr><tr><td>16</td><td>Geranyl acetone</td><td>1429</td><td>1855</td><td>0.1</td><td>0.1</td><td>0.3</td><td>RI, MS</td></tr><tr><td>17</td><td>trans-α-Bergamotene</td><td>1431</td><td>1587</td><td>1.4</td><td>2.3</td><td>2.3</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>18</td><td>α-Sesquisabinene</td><td>1434</td><td>1645</td><td>3.4</td><td>3.5</td><td>1.9</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>19</td><td>(E)-β-Farnesene</td><td>1446</td><td>1669</td><td>9.3</td><td>8.8</td><td>5.9</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>20</td><td>α-Humulene</td><td>1448</td><td>1669</td><td>4.0</td><td>4.3</td><td>4.6</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>21</td><td>(Z,Z)-α-Farnesene</td><td>1461</td><td>1691</td><td>0.1</td><td>0.2</td><td>0.1</td><td>RI, MS</td></tr><tr><td>22</td><td>β-Ionone</td><td>1464</td><td>1963</td><td>-</td><td>0.2</td><td>0.2</td><td>RI, MS</td></tr><tr><td>23</td><td>α-Curcumene</td><td>1469</td><td>1770</td><td>0.2</td><td>0.9</td><td>0.7</td><td>RI, MS, <sup>13</sup>C NMR</td></tr></tbody></table>
<table><caption>**Table 4.** Chemical composition of root bark oil samples of *Oicia suaveolens*.</caption><thead><tr><th>N°</th><th>Compounds</th><th>R1a</th><th>R1p</th><th>R1</th><th>R2</th><th>R3</th><th>R4</th><th>R5</th><th>Identification</th></tr></thead><tbody><tr><td>1</td><td>α-Pinene</td><td>931</td><td>1020</td><td>-</td><td>0.7</td><td>0.1</td><td>0.1</td><td>-</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>2</td><td>Sabinene</td><td>966</td><td>1127</td><td>-</td><td>-</td><td>-</td><td>0.1</td><td>-</td><td>RI, MS</td></tr><tr><td>3</td><td>Geijerene</td><td>1135</td><td>1328</td><td>1.7</td><td>2.0</td><td>1.4</td><td>5.9</td><td>1.4</td><td>RI, MS</td></tr><tr><td>4</td><td>Geranial</td><td>1244</td><td>1733</td><td>-</td><td>0.1</td><td>0.2</td><td>0.4</td><td>0.1</td><td>RI, MS</td></tr><tr><td>5</td><td>Undecan-2-one</td><td>1274</td><td>1592</td><td>-</td><td>0.8</td><td>-</td><td>-</td><td>-</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>6</td><td>Pregeijerene</td><td>1277</td><td>1316</td><td>0.1</td><td>0.1</td><td>0.2</td><td>1.0</td><td>0.1</td><td>RI, MS</td></tr><tr><td>7</td><td>Myrtenyl acetate</td><td>1306</td><td>1689</td><td>-</td><td>0.9</td><td>-</td><td>-</td><td>0.9</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>8</td><td>α-Ylangene</td><td>1367</td><td>1482</td><td>0.2</td><td>-</td><td>-</td><td>-</td><td>-</td><td>RI, MS</td></tr><tr><td>9</td><td>Cyclosativene</td><td>1368</td><td>1483</td><td>-</td><td>0.4</td><td>0.3</td><td>1.0</td><td>0.2</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>10</td><td>α-Copaene</td><td>1375</td><td>1493</td><td>-</td><td>0.2</td><td>0.1</td><td>0.3</td><td>0.2</td><td>RI, MS</td></tr><tr><td>11</td><td>β-Elemene</td><td>1387</td><td>1593</td><td>-</td><td>0.1</td><td>0.1</td><td>0.4</td><td>0.1</td><td>RI, MS</td></tr><tr><td>12</td><td>(E)-β-Caryophyllene</td><td>1417</td><td>1600</td><td>43.3</td><td>35.3</td><td>40.5</td><td>34.3</td><td>34.8</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>13</td><td>α-Humulene</td><td>1448</td><td>1669</td><td>47.9</td><td>41.5</td><td>45.0</td><td>36.1</td><td>40.4</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>14</td><td>γ-Muurolene</td><td>1469</td><td>1689</td><td>-</td><td>0.2</td><td>0.2</td><td>0.4</td><td>0.1</td><td>RI, MS</td></tr><tr><td>15</td><td>Tridecan-2-one</td><td>1476</td><td>1809</td><td>-</td><td>3.0</td><td>-</td><td>-</td><td>-</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>16</td><td>(E,E)-α-Farnesene</td><td>1500</td><td>1750</td><td>0.5</td><td>0.4</td><td>0.5</td><td>0.4</td><td>0.4</td><td>RI, MS</td></tr><tr><td>17</td><td>β-Elemol</td><td>1533</td><td>2077</td><td>-</td><td>-</td><td>0.3</td><td>-</td><td>0.7</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>18</td><td>Caryophyllene oxide</td><td>1567</td><td>1981</td><td>0.6</td><td>2.6</td><td>2.0</td><td>2.1</td><td>4.0</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>19</td><td>Humulene oxide I</td><td>1583</td><td>2013</td><td>0.3</td><td>0.6</td><td>0.6</td><td>0.7</td><td>0.9</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>20</td><td>Humulene oxide II</td><td>1592</td><td>2037</td><td>1.1</td><td>3.3</td><td>2.3</td><td>2.8</td><td>4.5</td><td>RI, MS, <sup>13</sup>C NMR</td></tr><tr><td>21</td><td>Humulene oxide III</td><td>1613</td><td>2051</td><td>2.9</td><td>4.6</td><td>2.4</td><td>7.7</td><td>6.8</td><td>RI, MS</td></tr><tr><td>22</td><td>τ-Muurolol</td><td>1625</td><td>2183</td><td>-</td><td>0.2</td><td>0.2</td><td>0.3</td><td>0.3</td><td>RI, MS</td></tr><tr><td>23</td><td>α-Cadinol</td><td>1635</td><td>2227</td><td>0.2</td><td>0.2</td><td>0.2</td><td>0.3</td><td>0.3</td><td>RI, MS</td></tr><tr><td colspan="10">Monoterpene hydrocarbons 0 0.7 0.1 0.2 0</td></tr><tr><td colspan="10">Oxygenated monoterpenes 0 1.0 0.2 0.4 1.0</td></tr><tr><td colspan="10">Sesquiterpene hydrocarbons 93.7 80.2 88.3 79.8 77.7</td></tr><tr><td colspan="10">Oxygenated sesquiterpenes 5.1 11.5 8.0 13.9 17.5</td></tr><tr><td colspan="10">Non-terpenic compounds 0 3.8 0 0 0</td></tr><tr><td colspan="10">Total 98.8 97.2 96.6 94.3 96.2</td></tr></tbody></table>

Order of elution and percentages on apolar column (BP-1); R1a, R1p: retention indices measured on apolar and polar capillary columns, respectively.

## 4. Conclusions

The leaf essential oil of *Guibourtia ehie* and leaf, stem bark and root bark essential oils of *Oicia suaveolens* were analyzed by GC(RI), GC-MS and <sup>13</sup>C NMR. All of these essential oils were dominated by hydrocarbon sesquiterpenes. The stem and root bark oils of *Oicia suaveolens* were characterized by the couple α-humulene (α-caryophyllene)T(E)-β-caryophyllene, while the leaf oils of *Guibourtia ehie* and *Oicia suaveolens* were dominated by (E)-β-caryophyllene. The essential oils of these two plant species can therefore be considered as natural sources of caryophyllenes.

**Supplementary Materials:** The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/compounds3010006/s1, Table S1: Yields of hydrodistillation.

**Author Contributions:** Conceptualization, T.A.K., J.A.M.-B., Y.-A.B. and Z.A.O.; methodology, T.A.K., B.A.K. and Z.A.O.; software, Z.A.O., P.T., A.B. and M.P.; validation, A.B., J.A.M.-B., Y.-A.B. and F.T.; formal analysis, T.A.K., D.A.K. and Z.A.O.; essential oil investigation, T.A.K., D.A.K., B.A.K. and Z.A.O.; writing—original draft preparation, T.A.K., Z.A.O., A.B. and F.T.; writing—review and editing, T.A.K., Z.A.O., A.B. and F.T.; visualization, D.A.K., P.T. and M.P.; supervision, F.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.
**Data Availability Statement:** Data and samples of the essential oils are available from the authors.

**Acknowledgments:** The authors gratefully acknowledge the University of Corsica for accepting Z.A. Ouattara at "Laboratoire Sciences Pour l'Environnement" for an advanced training course. We acknowledge H. Téhé and Y. Konan for their valuable help in the plant identification.

**Conflicts of Interest:** The authors declare no conflict of interest.

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