Chemical composition of the leaf oil of Artabotrys jollyanus from Côte d’Ivoire

ABSTRACT

One oil sample isolated from leaves of Artabotrys jollyanus Pierre, Annonaceae, from Côte d’Ivoire has been analyzed by GC(RI), GC-MS and ¹³C NMR. In total, thirty-seven compounds accounting for 96.9% of the relative composition have been identified. The composition of the essential oil was dominated by trans-calamenene (15.7%), α-copaene (14.8%), α-cubebene (10.4%), cadina-3,5-diene (10.3%), (E)-β-caryophyllene (6.3%) and cadina-1,4-diene (6.1%). ¹³C NMR spectroscopy was very useful in the identification of trans-calamenene, 7-hydroxycalamenene, cadina-3,5-diene and cadina-1,4-diene. Moreover, monitoring the evolution of the leaf essential oil composition and the yield on a 12-month period (one sample per month) was achieved. The twelve essential oil samples exhibited a chemical homogeneity but the yield varied from sample to sample (0.26–0.60%).

Keywords:
7-Hydroxycalamenene; Essential oil; Côte d’Ivoire; ¹³C NMR; Sesquiterpenes

Introduction

Generally distributed in tropical and subtropical regions, mainly in tropical Africa and Eastern Asia, the genus Artabotrys, family Annonaceae, contains more than 100 species (Sagen et al., 2003). In Côte d’Ivoire, five species grow wild in dense rain forests, namely Artabotrys hispidus Sprague & Hutch., A. insignis Engler & Diels, A. jollyanus Pierre, A. oliganthus Engler & Diels and A. velutinus Sc. Elliot. They are either climbing and evergreen shrubs or woody lianas.

Artabotrys jollyanus is a climbing shrub with persistent elliptic oblong leaves, 15–21 cm in length, 7–9 cm width. The limb base is rounded to cuneate and its apex acuminate. Flower petals are elliptical (25 mm in length), grouped in dense axillary inflorescences (http://www.plantes-botanique.org).

Ethnomedicinal uses of species of the genus Artabotrys have been reviewed (Tan and Wiart, 2014). Numerous papers reported on the phytochemistry of this genus and highlighted the presence of alkaloids in A. uncinatus (Lam.) Merr. (Hsieh et al., 1999), A. crassifolius Hook. f. & Thomson (Tan et al., 2015), A. hexapetalus (L. f.) Bhandare (Zhou et al., 2015), A. odoratissimus R.Br. (Kabir, 2010), or polyphenols in A. hildebrandtii O. Hffm. (Andriamadioa et al., 2015), A. hexapetalus (Li et al., 1997; Somanawat et al., 2012). Concerning the chemical composition of essential oils more than fifteen species have been investigated (Hung et al., 2014) and sesquiterpenes were often the major components (Menut et al., 1992; Fournier et al., 1999; Thang et al., 2014). To our knowledge no investigations have been undertaken to date on the chemical composition of A. jollyanus essential oil.

In continuation of our on-going work related to the characterization of aromatic and medicinal Annonaceae from Côte d’Ivoire (Yapi et al., 2012, 2013, 2014; Ouattara et al., 2011; Ouattara et al., 2013, 2014) the chemical composition of the essential oil isolated from leaves of A. jollyanus has been investigated by combination of chromatographic [GC-FID, GC(RI)] and spectroscopic techniques (MS, ¹³C NMR). Firstly, we report the detailed leaf essential oil composition of a selected sample. Secondly, the temporal variation of leaf oil composition was studied by analyzing eleven other leaf samples collected along the vegetative cycle.

Materials and methods

Plant material

Leaves from Artabotrys jollyanus Pierre, Annonaceae, have been harvested (April 2014 - March 2015) in the Adiopodoumé forest on Abidjan-Dabou axis (southern Côte d’Ivoire, 5º19′50.074″ N, 4º7′41.109″ O, Fig. 1). The plant species was identified by M. Assi Jean, technician at the Herbarium of the Centre National of Floristique (Félix Houphouët-Boigny University, Abidjan-Cocody/Côte d’Ivoire) where voucher specimen was deposited with number LAA 7650.

Fig. 1
Locality of harvest of leaves of A. jollyanus from Côte d’Ivoire.

Essential oil isolation

Essential oil (EO) samples were obtained by hydrodistillation from the fresh leaves (300 g) with a Clevenger-type apparatus for a period of 3.5 h; the essential oils (S1-S12) were dried over anhydrous sodium sulphate (Na₂SO₄), and then stored in a freezer until analysis. The yields, calculated on the fresh weight basis (w/w), were comprised between 0.26% and 0.60%. All oil samples were light yellow coloured.

Gas chromatography (GC) analyses

Analyses were performed on a Clarus 500 PerkinElmer (PerkinElmer, Courtaboeuf, France) system equipped with a 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 ºC to 220 ºC at 2 ºC/min and then held isothermal at 220 ºC for 20 min; injector temperature: 250 ºC; detector temperature: 250 ºC; carrier gas: helium (0.8 ml/min); split: 1/60; injected volume: 0.5 µl. The relative proportions of the oil constituents were expressed as percentages obtained by peak-area normalization, without using correction factors. Retention indices (RI) were determined relative to the retention times of a series of n-alkanes (C7-C28) with linear interpolation (Target Compounds software from Perkin Elmer).

Gas chromatography–mass spectroscopy (GC/MS) analyses

The essential oils were analyzed with a Perkin-Elmer TurboMass detector (quadrupole), directly coupled to a Perkin-Elmer Autosystem equipped with a fused-silica capillary column (50 m × 0.22 mm i.d., film thickness 0.25 µm), BP-1 (dimethylpolysiloxane). Carrier gas, helium at 0.8 ml/min; split, 1/60; injection volume, 0.5 µl; injector temperature, 250 ºC; oven temperature programmed from 60 ºC to 220 ºC at 2 ºC/min and then held isothermal (20 min); Ion source temperature, 250 ºC; energy ionization, 70 eV; electron ionization mass spectra were acquired over the mass range 40–400 Da.

¹³C NMR analyses

¹³C NMR analysis were performed on a Bruker AVANCE 400 Fourier Transform spectrometer operating at 100.63 MHz for ¹³C, equipped with a 5 mm probe, in deuterated chloroform (CDCl₃), with all shifts referred to internal tetramethylsilane (TMS). ¹³C NMR spectra were recorded with the following parameters: pulse width (PW), 5 µs (flip angle 45º); acquisition time, 2.7 s for 128 K data table with a spectral width (SW) of 25,000 Hz (250 ppm); digital resolution 0.183 Hz/pt. The number of accumulated scans was 2500 for each sample (about 50 mg of essential oil in 0.5 ml of CDCl₃).

Identification of individual components

Component identification was based on: (a) comparison of their GC retention indices (RI) on polar and apolar columns determined relative to the retention times of a series of n-alkanes with linear interpolation with those of authentic compounds or literature data; (b) on computer matching with laboratory-made and commercial mass spectral libraries (König et al., 2001; Adams, 2007; US National Institute of Standards and Technology, 1999); and (c) on comparison of the signals in the ¹³C NMR spectra of essential oils with those of reference spectra compiled in the laboratory spectral library with the help of laboratory-developed software (Ouattara et al., 2014). Indeed the ¹³C NMR spectrum of a molecule may be considered as its fingerprint. In other words, two compounds, such as sesquiterpenes, exhibit always enough chemical shift values of their carbons sufficiently differentiated to allow their identification. Therefore, taking into account various parameters (the number of observed signals, the number of overlapped signals, the difference of chemical shift measured in the mixture and in the reference spectra) the identification of an individual component of a complex mixture is possible without individualization of the compound (Bighelli and Casanova, 2010).

Results and discussion

Detailed analysis of a leaf oil sample (S4) from A. jollyanus has been carried out by GC(RI), GC–MS and ¹³C NMR. In total, 37 compounds (12 monoterpenes, 5.2% and 25 sesquiterpenes 91.7%) that accounted for 96.9% of the whole composition, have been identified in the sample (Table 1, Fig. 2). The major components were sesquiterpenes, particularly sesquiterpene hydrocarbons. It could be highlighted that the five main components accounted only for 10–16% each: trans-calamenene (15.7%), α-copaene (14.8%), α-cubebene (10.4%), cadina-3,5-diene (10.3%) and 7-hydroxycalamenene (10.1%). Other sesquiterpenes present at significant levels were (E)-β-caryophyllene (6.3%), cadina-1,4-diene (6.1%), β-cubebene (3.1%), α-humulene (3.0%), δ-cadinene (1.9%) bicyclosesquiphellandrene (1.8%), bicyclogermacrene (1.5%) and spathulenol (1.1%). Finally, the monoterpene fraction was mostly represented by (Z)-β-ocimene (3.6%). The other hydrocarbon monoterpenes were present at very low levels not exceeding 0.5%.

Table 1
Chemical composition of Artabotrys jollyanus leaf oil.

	Componentsa	RIlitb	RIa	RIp	A. jollyanus	Identification
1	α-Pinene	936	929	1015	0.3	RI, MS
2	Camphene	950	942	1065	tr	RI, MS
3	Sabinene	973	964	1123	tr	RI, MS
4	β-Pinene	978	969	1112	tr	RI, MS
5	Myrcene	987	979	1160	0.2	RI, MS
6	Limonene	1025	1019	1201	0.2	RI, MS
7	β-Phellandrene	1023	1019	1211	0.4	RI, MS
8	(Z)-β-Ocimene	1029	1024	1233	3.6	RI, MS, 13C NMR
9	(E)-β-Ocimene	1041	1035	1250	0.4	RI, MS, 13C NMR
10	Terpinolene	1082	1077	1283	tr	RI, MS
11	Linalool	1086	1082	1545	tr	RI, MS
12	allo-Ocimene	1113	1116	1372	0.1	RI, MS
13	α-Cubebene	1355	1348	1456	10.4	RI, MS, 13C NMR
14	α-Copaene	1379	1375	1490	14.8	RI, MS, 13C NMR
15	β-cubebene*	1390	1385	1535	3.1	RI, MS
16	β-Elemene*	1389	1385	1587	0.5	RI, MS, 13C NMR
17	α-Gurjunene	1413	1408	1525	0.2	RI, MS
18	(E)-β-Caryophyllene	1421	1416	1593	6.3	RI, MS, 13C NMR
19	Cadina-3,5-diene	1448	1444	1627	10.3	RI, MS, 13C NMR
20	α-Humulene	1455	1448	1665	3.0	RI, MS, 13C NMR
21	allo-Aromadendrene	1462	1456	1640	0.3	RI, MS
22	Cadina-1(6),11-diene	-	1466	1655	0.8	RI, MS, 13C NMR
23	Germacrene D	1479	1474	1704	0.4	RI, MS, 13C NMR
24	Bicyclosesquiphellandrene	1487	1483	1708	1.8	RI, MS, 13C NMR
25	4-epi-Cubebol	1490	1485	1883	0.8	RI, MS, 13C NMR
26	Bicyclogermacrene	1494	1489	1728	1.5	RI, MS, 13C NMR
27	α-Muurolene	1496	1491	1719	0.2	RI, MS
28	Cubebol	1514	1504	1935	0.8	RI, MS, 13C NMR
29	trans-Calamenene	1517	1509	1829	15.7	RI, MS, 13C NMR
30	δ-Cadinene	1520	1513	1751	1.9	RI, MS, 13C NMR
31	Zonarene	1521	1515	1752	0.4	RI, MS
32	Cadina-1,4-diene	1523	1523	1777	6.1	RI, MS, 13C NMR
33	Spathulenol	1572	1561	2117	1.1	RI, MS, 13C NMR
34	Caryophyllene oxide	1578	1567	1976	0.2	RI, MS
35	epi-Cubenol	1623	1612	2058	0.4	RI, MS
36	Cubenol	1630	1628	2051	0.7	RI, MS
37	7-Hydroxycalamenene	1803c	1775	2783	10.1	RI, MS, 13C NMR
	Total				96.9
	Monoterpene hydrocarbons				5.2
	Oxygenated monoterpenes				tr
	Sesquiterpenes hydrocarbons				77.7
	Oxygenated sesquiterpenes				14.0

• ^a
  Order of elution and contents determined on the apolar column (BP-1), except for compounds with an asterisk, percentages on polar column (BP 20). RIa, RIp = retention indices measured on apolar (BP1) and polar (BP 20) column; tr = trace level (<0.05%).
• ^b
  Literature indices on a DB-1 (http://massfinder.com by Hochmuth, 2017).
• ^c
  Indice on a HP-5 column (Azevedo et al., 2014).

Fig. 2
Gas chromatogram on apolar column (BP-1) of leaf sample of Artabotrys jollyanus essential oil.

Identification of some components needed special attention:

• - Calamenene stereoisomers (cis or trans) display overlapped peaks on apolar and polar capillary chromatography columns (RIa: 1509; RIp: 1829) and insufficiently differentiated mass spectra (Joulain and König, 1998). Therefore, identification of the correct isomer was achieved by ¹³C NMR analysis, the spectra of both compounds being fully differentiated (Nakashima et al., 2002).

• - Cadina-1,4-diene (6.1%) and cadina-3,5-diene (10.3%) were suggested by MS and then confirmed by comparison of their ¹³C NMR chemical shifts with those reported in the literature (Joulain and König, 1998);

• - 7-Hydroxycalamenene (10.1%). The MS spectrum of this compound was not compiled in MS libraries at our disposal and in our home-made MS library. The compound was identified by comparison of its ¹³C NMR chemical shifts with those reported in the literature (Cambie et al., 1990).

The chemical composition of A. jollyanus leaf oil differed from that of Ivoirian A. oliganthus leaf oil, dominated by monoterpenes (δ-3-carene, 60.2%, myrcene, 10.6%) (Ouattara et al., 2011). It differed from those of bark oils from Gabonese Artabotrys lastourvillensis Pell (cyperene, 25.9%; cyperenone, 11.1%) (Menut et al., 1992) and from Beninese Artabotrys velutinus (benzyl benzoate, 61.2%; (E)-β-caryophyllene, 9.1%) (Yovo et al., 2016). It differed also from those of EOs isolated from Artabotrys species grown in other areas of the world. For instance, the compositions of Vietnamese species were mostly dominated by various sesquiterpenes: A. petelotti Merr. leaf oil (elemol, 19.4%, cis-β-guaiene, 9.2%, δ-cadinene, 8.4%); A. intermedius Hassk. leaf oil (δ-3-carene, 19.1%; α-gurjunene; 10.7%; α-zingiberene, 6.3%); A. harmandii Finet & Gagnep. (spathulenol, 17.4%; aromadendrene epoxide, 12.2%; γ-elemene, 7.1%; β-elemene, 5.0%; bicyclogermacrene, 5.0%) (Hung et al., 2014); A. taynguyenensis Ban leaf oil (valencene, 40.1%; δ-selinene, 8.8%; α-pinene, 6.7%; α-muurolene, 5.1%; α-panasinsene, 5.1%) (Thang et al., 2014). The flower oil of Vietnamese A. hexapetalus contained mainly caryophyllene oxide, 31.5%; β-caryophyllene, 11.4%; humulene epoxide, 10.0% and α-copaene, 8.1% (Phan et al., 2007).

The monitoring of the temporal evolution of the yield and the chemical composition of the leaf EO from A. jollyanus has been achieved over a period of 12 months, from April 2014 to March 2015 (Table 2). Yields varied substantially from 0.26% to 0.60% (mean value = 0.40%). Three domains may be distinguished. Higher yield has been observed in September (0.60%), during the dry period. Acceptable yields (0.39–0.52%, 7 oil samples out of 12) occurred in the period June-November and lowest yields (0.26–0.32%, 4 samples out of 12) have been obtained in May on the one hand and during the period December-March on the other hand.

Table 2
Chemical composition of Artabotrys jollyanus leaf oil: main components of twelve samples.

Sample	S1	S2	S3	S4a	S5	S6	S7	S8	S9	S10	S11	S12
Month	Apr	May	Jun	Jul	Aug	Sept	Oct	Nov	Dec	Jan	Feb	Mar
Components
(Z)-β-Ocimene	5.5	5.3	5.3	3.6	4.7	3.4	4.6	3.4	5.5	3.5	4.6	2.4
α-Cubebene	10.7	9.2	10.6	10.4	10.7	11.0	8.8	9.7	14.5	12.9	8.8	10.2
α-Copaene	14.7	12.4	14.8	14.8	15.7	16.4	12.7	14.3	20.4	18.8	12.3	14.6
β-Cubebene	2.7	2.1	3.2	3.1	3.1	3.2	2.7	3.1	2.5	1.4	3.2	2.3
(E)-β-Caryophyllene	8.0	7.9	7.1	6.3	6.6	6.6	6.8	6.7	7.7	7.1	6.5	5.7
Cadina-3,5-diene	7.3	4.6	9.2	10.3	10.2	10.6	9.3	10.8	7.6	8.0	11.0	0.4
α-Humulene	3.5	3.6	3.2	3.0	3.1	3.0	3.4	3.2	3.2	3.1	3.3	2.9
trans-Calamenene	18.6	22.4	16.4	15.7	16.5	16.3	16.6	16.4	17.8	18.7	14.7	27.6
Cadina-1,4-diene	6.0	5.2	6.0	6.1	5.8	5.8	5.6	6.1	4.5	6.0	6.4	2.9
Spathulenol	1.4	1.9	1.1	1.1	1.0	0.9	1.3	1.1	1.0	0.8	0.8	2.4
7-Hydroxycalamenene	4.8	6.5	7.6	10.1	7.0	7.9	10.4	9.1	1.3	4.9	10.5	10.4
Yield	0.39	0.26	0.48	0.40	0.42	0.60	0.45	0.52	0.28	0.32	0.39	0.32

• ^a
  S4 is previously described in Table 1

The composition of the EO was always dominated by sesquiterpene hydrocarbons although the contents of the main components varied also substantially. For instance, trans-calamenene (mean value = 18.1%) accounted for 15.7–17.7% for 9 oil samples out of 12 (14.7%, 22.4% and 27.6% for the last three samples). In parallel, α-copaene (mean value = 15.2%) displayed more diverse contents (12.3–12.7%, 3 samples; 14.3–14.8%, 5 samples; 15.7–20.4%, 4 samples). The content of 7-hydroxycalamenene (mean value = 7.5%) seemed to vary drastically from 1.3% to 10.5%. In fact, the contents of four samples (6.5–7.9%) were very close to the mean value, five samples displayed higher contents (9.1–10.5%), two samples exhibited lower contents (4.8 and 4.9%) and the last sample accounted for 1.3% only. Finally, the content of cadina-3,5-diene varied from 7.3% to 11.0% for ten samples, while it was only 4.6% for one sample and 0.4% for the last one. Similarly, the content of cadina-1,4-diene varied from 5.2% to 6.4% for ten samples, while it was only 4.5% and 2.9% for the two last ones.

It is noticeable that the sum of percentages of cadina-1,4-diene, cadina-3,5-diene, trans-calamenene and 7-hydroxy-calamenene were constant in all samples and close to 39%. Indeed, trans-calamenene may be obtained by deshydrogenation of cadina-1,4-diene and cadina-3,5-diene. Then, 7-hydroxy-calamenene was synthetized by hydroxylation of trans-calamenene. These results are in agreement with the proposed pathway for the biosynthesis of thymol from γ-terpinene via p-cymene (Poulose and Croteau, 1978).

Conclusion

The chemical composition of A. jollyanus leaf essential oil was reported for the first time. The essential oil from Ivoirian species exhibited original composition dominated by hydrocarbon sesquiterpenes, mostly trans-calamenene, α-copaene, β-cubebene, cadina-3,5-diene, accompanied by 7-hydroxycalamenene. The composition of the EO remained dominated by the same sesquiterpenes during its phenological cycle of the plant, although the content of some components varied substantially.

Acknowledgments

The authors are grateful to the CASES, (NGO) for financial support. They are indebted to Dr M. Gibernau for botanical advices.

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Publication Dates

• Publication in this collection
  Jul-Aug 2017

History

• Received
  29 Sept 2016
• Accepted
  3 Apr 2017