Chemical Composition of Leaf Essential Oil of Piper umbellatum and Aerial Part Essential Oil of Piper guineense From Côte d’Ivoire

Abstract

The combination of ¹³C nuclear magnetic resonance (NMR) spectroscopy, gas chromatography (GC) (retention index), and gas chromatography-mass spectrometry was used to determine the chemical composition of essential oils of Piper guineense and Piper umbellatum from Côte d’Ivoire. Thus, 54 components, accounting for 91.5% to 97.6%, were identified in the essential oil from aerial parts of P. guineense. In P. umbellatum leaf oil, 49 compounds accounting for 92.8% to 98.7% were identified. Both plants oils were dominated by monoterpenes and sesquiterpenes, with α-phellandrene, (2E,6E)-farnesol, and linalool as major compounds of P. guineense, whereas the most abundant components of P. umbellatum were linalool and (E)-β-caryophyllene. (2E,6E)-Farnesol, identified for the first time in the essential oil from aerial parts of P. guineense, induced a new chemical composition.

Keywords

essential oil α-phellandrene linalool

The genus Piper (Piperaceae) is made up of about 1050 species of tropical shrubs, lianas, and small trees, many of which are important as spices and flavoring agents and medicines.¹ The essential oils of numerous Piper species have been analyzed and examined for biological activity.^2

-6 Among the species growing wild in Côte d’Ivoire, Piper guineense Schumach & Thonn and Piper umbellatum L. produce an essential oil.

Piper guineense is a West African spice plant, commonly called Ashanti pepper. It is a climbing plant that can grow up to 20 m in length. In Côte d’Ivoire, it is used against cephalgia, like antidiarrheal, aphrodisiac, and antiseptic throat in oral and pharyngeal disorders.⁷ It is also used in the West African area against rheumatism, stomach ache, and arterial hypertension.^8,9 Piper umbellatum (synonym Potomorphe umbellata) is a hardy herbaceous plant or climbing shrub up to 4 m high. Its emmenagogic, anti-abortive, antihemorrhagic, and antihemorrhoidal properties, added to its activities on arterial hypertension and rheumatism, are exploited in herbal medicine.^7

-10

A few studies concerning the chemical composition of P. guineense and P. umbellatum essential oils have been reported in the literature. The composition of 2 samples of fruit oil of P. guineense from Cameroon was dominated by linalool, β-caryophyllene, limonene, and β-pinene. Germacrene B and limonene were the most abundant compounds of the leaf essential oil of P. guineense, whereas that of the lianas is dominated by (Z,E)-α-farnesene, limonene, and myristicine.^11,12 A sample of fruit oil of Nigerian origin contained linalool as major component.¹³ In São Tomé and Principe, the essential oil from aerial parts mainly consists of phenylpropanoid derivatives: dillapiole and myristicine.³

Concerning P. umbellatum, leaf oil contained mainly sesquiterpenes, such as β-caryophyllene, germacrene D, (E)-nerolidol, or β-elemene.^11,14-16 Leaf oil sample from Cuba differed markedly, its composition being dominated by safrole. Fruit oil of Nigeria is dominated by sabinene, linalool, α-pinene, and (E)-nerolidol.¹¹ The essential oil from aerial part from São Tomé and Principe has β-pinene, α-pinene, and (E)-nerolidol as main constituents.³

Continuing our work on the characterization of aromatic and medicinal plants growing wild in Côte d’Ivoire, through the chemical composition of their essential oils,^17

-23 the aim of the present study was to characterize the essential oil from aerial parts of P. guineense and the leaf oil of P. umbellatum and to observe homogeneity or eventual variability in the chemical composition.

Essential Oil From Aerial Parts of Piper g uineense

Fifty-four components, accounting for 91.5% to 97.6% of the whole composition, were identified (S1-S10) using GC (retention index), GC-MS, and ¹³C NMR. This essential oil was mainly constituted by monoterpenes (14.7%-76.8%) and sesquiterpenes (20.4%-72.8%). The monoterpenes were dominated by α-phellandrene (up to 31.4%) and linalool (up to 22.6%). (Z)-β-Ocimene (up to 9.5%) and β-phellandrene (up to 8.2%) appeared in appreciable content in certain samples. The most abundant sesquiterpenes were (2E,6E)-farnesol (up to 24.6%) and β-elemene (up to 13.9%). In some samples, trans-calamenene (up to 8.7%; stereochemistry confirmed by NMR), (E)-β-caryophyllene (up to 7.7%), α-humulene (up to 7.3%), and β-bisabolene (up to 5.0%) showed significant amounts (Table 1).

Table 1

Chemical Composition of Essential Oil From Aerial Parts Oil of Piper guineense.

No.	Compounds	RIa	RIp	Y.A (May)		Y.A (June)				Y.A (September)				Identification
No.	Compounds	RIa	RIp	S1	S2	S3	S4	S5	S6	S7	S8	S9	S10	Identification
1	α-Thujene	924	1016	0.1	tr	0.7	0.5	0.5	0.4	0.3	0.7	0.2	0.1	RI, MS, ¹³C-NMR
2	α-Pinene	931	1013	0.3	0.1	2.5	3.0	2.3	1.8	3.1	4.3	6.2	4.4	RI, MS, ¹³C-NMR
3	Camphene	945	1065	-	-	-	0.1	-	-	-	0.1	0.1	0.1	RI, MS
4	Sabinene	967	1123	0.1	tr	0.2	0.3	0.2	0.2	0.1	0.3	0.1	0.1	RI, MS
5	β-Pinene	973	1113	0.5	0.1	0.4	0.9	0.4	0.3	0.6	0.7	1.7	1.2	RI, MS, ¹³C-NMR
6	Myrcene	983	1161	0.2	0.2	1.2	1.0	0.9	0.9	0.8	1.2	0.8	0.5	RI, MS, ¹³C-NMR
7	α-Phellandrene	999	1166	0.2	0.1	29.2	27.0	24.0	23.0	18.9	31.4	6.7	3.7	RI, MS, ¹³C-NMR
8	δ-3-Carene	1007	1150	0.4	2.4	0.1	0.3	0.5	0.9	tr	0.1	0.2	-	RI, MS, ¹³C-NMR
9	α-Terpinene	1011	1182	1.2	0.1	0.2	0.1	0.1	0.1	-	0.1	0.1	-	RI, MS, ¹³C-NMR
10	p-Cymene	1013	1271	2.8	0.9	3.5	2.5	2.4	2.4	2.1	3.3	1.6	0.9	RI, MS, ¹³C-NMR
11	Limonene*	1022	1202	0.2	0.1	6.0	5.9	5.2	5.0	4.4	6.8	2.2	1.3	RI, MS, ¹³C-NMR
12	β-Phellandrene*	1022	1211	0.2	0.1	7.4	7.2	6.4	6.3	5.2	8.2	2.2	1.2	RI, MS, ¹³C-NMR
13	(Z)-β-Ocimene	1027	1232	0.4	0.1	2.8	3.7	2.8	2.7	6.4	6.0	9.5	8.3	RI, MS, ¹³C-NMR
14	(E)-β-Ocimene	1037	1249	0.2	0.1	2.0	2.7	2.1	2.0	4.9	4.6	7.0	6.3	RI, MS, ¹³C-NMR
15	γ-Terpinene	1050	1246	3.2	0.1	0.8	0.2	0.1	0.1	0.1	0.1	0.1	tr	RI, MS, ¹³C-NMR
16	Terpinolene	1080	1283	0.6	0.1	0.2	0.2	0.1	0.2	0.2	0.2	0.2	0.1	RI, MS, ¹³C-NMR
17	Linalool	1086	1543	22.6	9.8	0.8	4.7	1.6	1.1	12.8	8.8	17.2	18.3	RI, MS, ¹³C-NMR
18	trans-p-Menth-2-en-1-ol	1108	1621	-	-	0.1	0.1	0.1	0.1	0.1	0.1	-	-	RI, MS
19	Terpinen-4-ol	1163	1596	0.3	0.1	0.2	tr	-	-	0.1	0.1	0.1	-	RI, MS
20	Linalyl acetate	1243	1556	0.1	0.1	-	0.1	-	-	-	-	-	-	RI, MS
21	Thymol	1268	2193	0.1	0.2	3.0	0.1	0.1	0.1	0.1	-	0.1	-	RI, MS
22	α-Cubebene	1350	1457	0.1	1.3	1.1	0.5	0.9	0.9	1.0	0.7	1.0	1.0	RI, MS, ¹³C-NMR
23	α-Copaene	1378	1492	2.2	4.8	3.6	2.2	3.0	3.2	3.1	2.2	3.3	3.1	RI, MS, ¹³C-NMR
24	β-Elemene	1389	1588	13.9#	10.7#	1.2	3.9#	1.5	1.5	1.6	1.0	1.6	1.6	RI, MS, ¹³C-NMR
25	(E)-β-Caryophyllene	1419	1596	7.7	6.0	1.5	5.9	2.8	2.7	0.8	0.5	1.5	1.1	RI, MS, ¹³C-NMR
26	γ-Elemene	1429	1635	-	-	0.1	tr	0.1	0.2	0.1	-	0.1	-	RI, MS, ¹³C-NMR
27	trans-α-Bergamotene	1435	1577	0.4	0.6	-	-	-	-	-	-	0.1	-	RI, MS
28	(E)-β-Farnesene	1447	1663	1.2	1.6	4.7	1.9	4.5	4.8	4.1	2.4	3.8	4.2	RI, MS, ¹³C-NMR
29	α-Humulene	1452	1666	7.3	4.1	0.5	2.8	1.1	1.0	0.3	0.2	0.6	0.5	RI, MS, ¹³C-NMR
30	Ischwarane	1464	1643	0.1	4.4	-	-	-	-	2.2	1.4	2.5	2.1	RI, MS, ¹³C-NMR
31	cis-Muurola-4(15),5-diene	1467	1646	tr	0.2	0.4	0.2	0.4	0.4	0.4	0.3	0.4	0.4	RI, MS
32	γ-Muurolene	1471	1683	0.3	0.3	0.1	0.5	0.2	0.2	-	-	0.1	0.1	RI, MS
33	Germacrene D	1477	1704	1.3	2.5	0.8	1.7	1.3	1.5	0.3	0.2	0.4	0.4	RI, MS, ¹³C-NMR
34	β-Selinene	1483	1715	4.3	1.2	0.2	0.2	0.1	0.1	0.2	0.1	0.7	0.5	RI, MS, ¹³C-NMR
35	(E,E)-Bicyclogermacrene	1492	1728	0.1	0.8	0.2	0.5	0.4	0.4	0.2	0.1	0.8	0.4	RI, MS, ¹³C-NMR
36	α-Selinene	1493	1720	3.4	0.7	0.2	0.2	0.3	0.3	0.3	0.2	-	0.3	RI, MS, ¹³C-NMR
37	(E,E)-α-Farnesene	1496	1746	2.9	0.3	-	0.2	0.1	0.1	0.1	tr	0.1	0.1	RI, MS, ¹³C-NMR
38	β-Bisabolene	1502	1723	tr	tr	1.4	tr	1.2	1.4	4.5	3.1	4.3	5.0	RI, MS, ¹³C-NMR
39	Germacrene A	1502	-	3.2 #	2.5#	-	0.9#	-	-	-	-	-	-	RI, MS, ¹³C-NMR
40	trans-Calamenene	1512	1830	tr	8.7	1.9	0.8	1.6	1.8	1.6	1.1	1.6	1.7	RI, MS, ¹³C-NMR
41	δ-Cadinene	1515	1753	0.5	1.6	1.4	0.8	1.4	1.5	1.3	0.8	1.2	1.4	RI, MS, ¹³C-NMR
42	Elemicine	1518	2219	tr	1.6	0.2	1.3	0.3	0.2	0.3	0.2	0.5	0.4	RI, MS, ¹³C-NMR
43	(E)-α-Bisabolene	1524	1758	0.8	0.4	0.7	0.3	0.7	0.7	0.8	0.5	0.6	0.8	RI, MS, ¹³C-NMR
44	β-Elemol	1533	2071	0.8	0.7	0.6	0.2	0.6	0.6	2.5	1.7	2.2	2.7	RI, MS, ¹³C-NMR
45	(E)-Nerolidol	1548	2035	2.4	3.4	0.2	0.6	0.3	0.3	0.2	0.1	0.3	0.3	RI, MS, ¹³C-NMR
46	Germacrene B	1553	1825	5.0#	3.7#	-	-	0.1	0.2	-	-	-	0.1	RI, MS, ¹³C-NMR
47	Caryophyllene oxide	1571	1975	0.8	1.4	0.1	0.3	0.2	0.1	0.1	tr	0.1	0.1	RI, MS, ¹³C-NMR
48	Guaiol	1585	2081	1.8	4.1	-	1.4	tr	-	-	-	-	-	RI, MS, ¹³C-NMR
49	Humulene oxide II	1595	2032	0.5	0.9	-	0.1	tr	0.1	0.1	tr	0.1	0.1	RI, MS, ¹³C-NMR
50	α-Eudesmol	1643	2198	0.4	1.2	0.3	0.3	0.4	0.4	0.1	-	0.1	0.1	RI, MS
51	7-epi-α-Eudesmol	1653	2201	0.4	1.1	-	0.2	-	-	-	-	-	-	RI, MS, ¹³C-NMR
52	Ischwarol B	1676	2366	0.1	3.5	-	-	-	-	-	-	-	tr	RI, MS, ¹³C-NMR
53	(2E,6E)-Farnesol	1700	2349	0.1	0.2	15.1	8.3	23.6	24.6	10.7	4.1	13.7	22.5	RI, MS, ¹³C-NMR
54	(E)-Phytol	2097	2605	1.5	2.5	0.1	tr	0.1	0.1	0.1	tr	0.1	0.1	RI, MS, ¹³C-NMR
	Total			97.0	91.5	97.6	96.6	96.6	96.6	96.8	97.4	97.6	97.2

Order of elution and percentages are given on apolar column (BP-1) except those with an asterisk (percentages on polar column); RIa and RIp: retention indices measured on apolar (BP-1) and polar (BP-20) columns, respectively; tr: traces (<0.05%); #: percentages obtained by combination of GC-FID and ¹³C NMR; Y.A: Yapo-Abbé forest.

We demonstrated in a previous work that germacrene A, B, and C rearranged partially or totally during GC analysis into β-, γ-, and δ-elemene, respectively, through a thermal Cope rearrangement.²² The same phenomenon was observed herein. According to the NMR spectra of the 3 essential oil samples (S1, S2, and S4), β-elemene is accompanied by germacrene A. The ratio of β-elemene/germacrene A was evaluated as 4.3/1 by comparing the mean intensities of the signals of same methine and methylene carbons of both compounds in the ¹³C NMR spectra. Similarly, germacrene B partially isomerizes to γ-elemene during GC analysis.

The chemical composition of P. guineense, of samples S3 to S8, is dominated by the association of α-phellandrene and (2E,6E)-farnesol. However, various chemical compositions, with 2 or 3 majority compounds can be observed. This variability, quantitative as well as qualitative, results in the considerable variation of the contents of certain components on the one hand, and the presence of compounds in some samples which missed the majority of the samples, on the other hand. The most relevant examples are those of ishwarol B, guaiol, germacrene A, and germacrene B. Moreover, samples S7 to S10 differ from the other samples by their high proportions of (Z)- and (E)-β-ocimenes.

On the basis of percentages of main compounds, the present study showed a difference between the chemical composition of P. guineense from Côte d’Ivoire and those related to the literature.^3,11-13 In fact, (2E,6E)-farnesol, a major component of the essential oil from Côte d’Ivoire, missed those of the literature. In the same way, except α-phellandrene (8.2%) in the aerial part essential oil of P. guineense from São Tomé and Principe, the most abundant compounds in this country, dillapiole (44.8%) and myristicine (9.8%), are not present in any sample from Côte d’Ivoire.³ Moreover, the leaf essential oil of P. guineense from Cameroon is dominated by germacrene B (25.1%), which is in very low proportion, or missing in the majority of the samples from Côte d’Ivoire except samples S1 and S2 (5.0% and 3.7%, respectively). The other major components of the Cameroonian essential oil are limonene (10.3%) and δ-elemene (8.8%).¹¹ If limonene contents reached 6.0% in our samples, δ-elemene is absent from the chemical composition of P. guineense from Côte d’Ivoire. Thus, the Ivorian P. guineense showed original chemical compositions dominated by different couples of compounds: α-phellandrene/(2E,6E)-farnesol; linalool/(2E,6E)-farnesol; linalool/β-elemene or by the combination of 3 compounds: α-phellandrene/linalool/(2E,6E)-farnesol.

Leaf Essential Oil of Piper umbellatum

Forty-nine compounds accounting for 92.8% to 98.7% were identified from the 10 samples of P. umbellatum leaf essential oil (S1-S10). The chemical composition of this essential oil is dominated by monoterpenes (49.1%-71.6%). The prevalent monoterpenes are linalool (15.8%-41.1%), limonene (6.3%-38.6%), and thymol (up to 25.0%). However, the other monoterpenes appeared with considerable proportions in some samples: β-pinene (7.3% and 7.7%) and α-pinene (6.8% and 6.9%), respectively, in samples S6 and S8; and camphor (3.5% in sample S6). The sesquiterpenic fraction is dominated by (E)-β-caryophyllene (13.1%-25.1%) followed by (E)-nerolidol (2.1%-6.3%) and germacrene D (1.0%-3.7%). (E)-Phytol, a diterpene, is also present with appreciable contents (0.6%-3.6%) in all samples (Table 2). These results showed a high content of linalool (15.8%-41.1%) and (E)-β-caryophyllene (15.8%-25.1%) in all samples. The content of limonene (6.3%-38.6%) and thymol (0.0%-25.0%) varied substantially. Then, the sample S4 exhibited an atypical composition with thymol as a major component. Taking into account the other major components, the essential oil of P. umbellatum presented different chemical compositions. characterized by the association of 2 or 3 components: linalool/(E)-β-caryophyllene (S2, S3, S7, and S9); linalool/(E)-β-caryophyllene/limonene (S1 and S5); linalool/limonene/(E)-β-caryophyllene (S6 and S8); and limonene/linalool/(E)-β-caryophyllene (S10).

Table 2

Chemical Composition of Piper umbellatum Leaf Oil.

No.	Compounds	RIa	RIp	Yapo-Abbé (June)					Akoupé (August)					Identification
No.	Compounds	RIa	RIp	S1	S2	S3	S4	S5	S6	S7	S8	S9	S10	Identification
1	α-Pinene	931	1020	0.2	0.1	0.1	0.3	0.2	6.8	2.8	6.9	1.4	1.8	RI, MS, ¹³C-NMR
2	6-Methyl-hept-5-en-2-one	961	1344	0.1	-	0.1	0.1	0.1	0.2	0.1	0.2	0.1	0.1	RI, MS
3	Sabinene	966	1127	0.1	-	-	0.1	-	0.1	-	-	-	-	RI, MS
4	β-Pinene	972	1117	0.5	0.1	0.2	0.5	0.4	7.3	3.2	7.7	1.8	2.1	RI, MS, ¹³C-NMR
5	Myrcene	981	1165	0.5	0.3	0.4	1.1	0.7	1.9	0.8	1.9	0.6	2.2	RI, MS, ¹³C-NMR
6	α-Phellandrene	998	1171	0.2	0.1	0.1	0.1	0.1	-	-	-	-	tr	RI, MS
7	δ-3-Carene	1006	1154	0.1	-	tr	0.1	-	-	-	-	-	0.2	RI, MS
8	p-Cymene	1012	1277	0.3	0.3	0.5	3.2	0.4	0.7	0.2	0.5	0.2	0.2	RI, MS, ¹³C-NMR
9	Limonene*	1022	1207	12.5	6.7	7.8	12.3	13.3	16.2	8.6	17.5	6.3	38.6	RI, MS, ¹³C-NMR
10	1,8-Cineole*	1022	1216	0.1	-	0.1	0.4	0.1	1.5	0.2	0.4	0.1	0.1	RI, MS, ¹³C-NMR
11	(Z)-β-Ocimene	1025	1237	0.5	0.3	0.3	0.6	0.6	1.4	0.7	1.4	0.6	1.9	RI, MS, ¹³C-NMR
12	(E)-β-Ocimene	1036	1254	0.2	0.1	0.1	0.2	0.2	0.4	0.2	0.4	0.2	0.6	RI, MS, ¹³C-NMR
13	γ-Terpinene	1049	1250	0.1	0.1	0.4	3.3	0.4	0.2	0.1	0.1	0.1	tr	RI, MS, ¹³C-NMR
14	Octan-1-ol	1052	1552	0.1	0.1	-	0.1	-	-	0.1	-	0.1	-	RI, MS
15	Terpinolene	1079	1289	0.1	-	0.1	0.2	0.1	0.2	0.1	0.2	0.1	0.1	RI, MS
16	Linalool	1085	1552	41.1	37.1	33.1	15.8	37.4	25.5	28.2	31.7	34.8	21.1	RI, MS, ¹³C-NMR
17	Camphor	1123	1527	0.1	-	0.1	0.6	0.1	3.5	tr	-	-	-	RI, MS, ¹³C-NMR
18	Terpinen-4-ol	1163	1597	0.3	0.3	0.4	1.1	0.1	0.8	0.3	0.4	0.3	0.1	RI, MS, ¹³C-NMR
19	α-Terpineol	1173	1703	1.1	1.0	0.7	0.6	0.7	1.2	0.3	0.2	0.2	0.4	RI, MS, ¹³C-NMR
20	Nerol	1207	1798	0.1	0.1	0.1	0.1	0.2	-	0.2	0.1	0.2	0.1	RI, MS
21	Neral	1210	1676	0.2	0.2	0.2	0.3	0.1	-	0.4	0.3	0.3	-	RI, MS
22	Geraniol	1234	1842	0.1	0.1	0.2	-	0.1	-	0.3	0.2	0.2	-	RI, MS
23	Geranial	1242	1734	-	0.1	-	0.1	0.3	-	0.6	0.5	0.5	-	RI, MS, ¹³C-NMR
24	Safrole	1263	1861	0.1	0.1	0.1	0.1	-	0.2	-	-	-	-	RI, MS
25	Thymol	1267	2193	4.3	6.3	7.6	25.0	5.2	2.5	2.0	1.2	1.6	-	RI, MS, ¹³C-NMR
26	α-Copaene	1377	1497	0.1	0.1	0.1	0.3	0.1	0.1	0.2	0.1	0.2	0.1	RI, MS
27	β-Elemene	1389	1595	0.5	1.0	0.6	0.5	0.5	0.5	1.4	0.6	1.7	0.6	RI, MS, ¹³C-NMR
28	(E)-β-Caryophyllene	1421	1605	19.3	25.1	25.0	15.8	20.8	15.4	17.7	13.1	20.3	16.9	RI, MS, ¹³C-NMR
29	γ-Elemene	1429	1635	0.2	0.3	0.3	0.2	0.2	0.2	0.4	0.2	0.4	0.2	RI, MS
30	trans-α-Bergamotene	1435	1579	0.2	0.5	0.4	0.2	0.3	0.1	0.1	-	-	0.1	RI, MS, ¹³C-NMR
31	(E)-β-Farnesene	1447	1669	0.2	0.4	0.3	0.2	0.2	0.3	0.4	0.3	0.5	0.2	RI, MS, ¹³C-NMR
32	α-Humulene	1453	1676	1.3	1.7	1.5	1.2	1.3	0.9	1.2	0.8	1.4	1.0	RI, MS, ¹³C-NMR
33	4-Methoxy-safrole	1460	2182	0.1	-	0.1	0.3	0.1	1.0	0.2	0.1	0.2	0.1	RI, MS, ¹³C-NMR
34	γ-Muurolene	1472	1693	0.2	-	0.2	0.2	0.2	0.2	1.2	0.6	0.9	0.3	RI, MS, ¹³C-NMR
35	Germacrene D	1478	1703	1.2	1.3	1.0	0.9	1.3	1.9	2.6	1.6	3.7	1.5	RI, MS, ¹³C-NMR
36	β-Selinene	1484	1715	0.9	0.3	0.4	1.5	0.3	0.1	0.7	0.3	0.6	0.3	RI, MS, ¹³C-NMR
37	(E,E)-Bicyclogermacrene	1493	1728	0.9	0.8	0.6	0.9	0.7	0.7	1.5	0.8	1.6	0.7	RI, MS, ¹³C-NMR
38	(E,E)-α-Farnesene	1496	1752	1.2	1.6	1.6	1.0	1.4	0.4	1.6	0.8	1.3	0.8	RI, MS, ¹³C-NMR
39	β-Bisabolene	1501	1723	0.8	0.6	0.6	0.4	0.5	0.4	1.4	0.7	1.2	0.4	RI, MS, ¹³C-NMR
40	β-Sesquiphellandrene	1508	1762	0.2	0.2	0.1	0.1	0.1	0.1	0.3	0.2	0.3	0.2	RI, MS
41	δ-Cadinene	1516	1752	0.3	0.3	0.3	0.5	0.3	0.2	2.1	0.9	1.6	0.4	RI, MS, ¹³C-NMR
42	β-Elemol	1535	2071	0.3	0.4	0.4	0.2	0.3	1.0	0.6	0.2	0.5	0.2	RI, MS, ¹³C-NMR
43	(E)-Nerolidol	1548	2045	4.3	6.3	5.4	2.4	4.2	2.1	5.5	2.2	5.5	3.0	RI, MS, ¹³C-NMR
44	Caryophyllene oxide	1573	1993	0.8	0.9	0.9	0.6	0.8	0.4	0.7	0.3	0.6	0.4	RI, MS, ¹³C-NMR
45	Humulene oxide II	1597	2050	0.1	-	-	0.1	0.1	-	0.1	-	0.1	-	RI, MS
46	γ-Eudesmol	1620	2176	0.1	0.1	0.2	0.1	-	0.1	0.2	0.1	0.2	-	RI, MS
47	β-Eudesmol	1632	2238	0.1	0.1	0.1	0.1	0.1	-	0.2	0.1	0.2	-	RI, MS
48	α-Eudesmol	1637	2228	0.1	0.2	0.2	0.2	0.1	0.4	0.4	0.1	0.3	0.1	RI, MS
49	(E)-Phytol	2099	2613	1.8	3.3	3.6	2.1	2.8	0.6	2.9	1.0	2.1	1.3	RI, MS, ¹³C-NMR
	Total			98.1	98.7	96.2	95.6	97.4	97.7	92.8	96.8	94.7	98.1

In comparison to the previous works, apart from thymol, present in low content in the results related to the literature, the chemical composition of the leaves of P. umbellatum from Côte d’Ivoire was close to that of the leaves from Cameroon and the aerial parts from São Tomé and Principe.^3,11 These essential oils, as well as those of Côte d’Ivoire, were mainly made up of linalool, limonene, (E)-β-caryophyllene, β-pinene, α-pinene, and (E)-nerolidol. However, from a quantitative point of view, the leaf essential oils from South America were distinguishable from those of Côte d’Ivoire. Indeed, the samples of South America showed more or less high proportions of germacrene D (7.9%-55.8%) which was low in our samples. (E,E)-α-Farnesene, bicyclogermacrene, δ-cadinene, and (E)-nerolidol were also present with acceptable contents in essential oils from Brazil, Costa Rica, and Cuba. The essential oil of the leaves from Cuba was characterized by the high content of safrole (48.7%), which is insignificant (0.0%-0.2%) among those of Côte d’Ivoire.^14
-16

The essential oil composition of P. guineense (aerial parts) and P. umbellatum (leaves) from Côte d’Ivoire was investigated. Although linalool was present in appreciable amount in all samples, both essential oils differed by other main constituents. The aerial part of P. guineense exhibited an original chemical composition, dominated by α-phellandrene, (2E,6E)-farnesol, linalool, and β-elemene, whereas the most abundant components of ′P. umbellatum were linalool and (E)-β-caryophyllene.

Experimental

Plant Material

Ten individual samples of fresh aerial parts of P. guineense were collected in the Yapo-Abbé forest (5°43′20.7″N and 4°08′23.2″W), in the southeastern Côte d’Ivoire. Samples (S1 and S2) were collected in May, samples (S3-S6) in June, and samples (S7-S10) in September 2016. Ten individual samples of fresh leaves of P. umbellatum were collected in the south-eastern Côte d’Ivoire. Samples (S1-S5) were collected in June, in the Yapo-Abbé forest and samples (S6-S10) in August 2016, in Akoupé (6°24′49.3″N and 3°43′10.8″W). Plant material has been authenticated by the Centre National of Floristic (CNF, Abidjan, Côte d’Ivoire) and the Centre Suisse of Research (Adiopodoumé, Abidjan, Côte d’Ivoire).

Essential Oil Isolation

The essential oil isolation was carried out by hydrodistillation with a Clevenger-type apparatus for 3 hours. The essential oil was dried over anhydrous sodium sulfate and stored (5°C). Both plants produced a pale yellow essential oil with the following yields (w/w calculated on fresh weight basis): P. guineense (0.09%-0.17%) and P. umbellatum (0.01%-0.02%).

Analytical GC, GC-MS, ¹³ C-NMR analysis and identification of individual components is as previously reported.²³

Footnotes

Acknowledgments

The authors are grateful to Mr Assi Jean from the Centre National of Floristic (CNF, Abidjan, Côte d’Ivoire) and Mr Téré Henry from the Centre Suisse of Research (Adiopodoumé, Abidjan, Côte d’Ivoire) for the plant identification. The authors also thank Dr Kouamé Assi Mathias for his helpful contribution in the plant material collection.

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

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