Chemical Composition of Essential Oils of Plumeria rubra L. Grown in Nigeria

The chemical compositions of essential oils obtained by hydrodistillation of the leaves and flowers of pink-flower Plumeria rubra L., grown in Nigeria were being reported. The chemical analysis was performed by means of gas chromatography-flame ionization detector (GC-FID) and gas chromatography-mass spectrometry (GC-MS) techniques. The major leaves oil constituents were (Z)-β-farnesene (16.0%), α-patchoulene (13.0%), limonene (12.1%), (E)-β-farnesene (10.8%), αcopaene (7.2%) and phytol (6.3%). However, the quantitative significant compounds of the flowers oil were (E)-non-2-en-1-ol (15.7%), limonene (10.8%), phenyl acetaldehyde (9.0%), n-tetradecanal (8.8%), γ-elemene (6.5%) and (E,E)-α-farnesene (6.1%). This is the first report on the volatile constituents from the leaves of Plumeria rubra. Aims: The aim of the of the present study was to examine the constituents of the leaves and flowers oils of P. rubra grown in Southwest Nigeria in details, and to compare the results obtained Original Research Article Lawal et al.; EJMP, 6(1): 55-61, 2015; Article no.EJMP.2015.042 56 with those reported earlier. Study Design: Isolation of essential oils from the leaves and flowers of Plumeria rubra and determination of their chemical constituents. Place and Duration of Study: Fresh plant materials of P. rubra (flowers and leaves) were collected from a location within the Campus of Lagos State University, Ojo, Lagos State, Nigeria, in October 2013. Methodology: Fresh leaves and flowers were hydodistilled in an all glass Clevenger apparatus and their chemical constituents were analyzed by GC and GC/MS. Results: A total of twenty six compounds were identified in the leaves and the major ones were (Z)-β-farnesene (16.0%), α-patchoulene (13.0%), limonene (12.1%), (E)-β-farnesene (10.8%), αcopaene (7.2%) and phytol (6.3%) while the flowers had twenty seven compounds with (E)-non-2en-1-ol (15.7%), limonene (10.8%), phenyl acetaldehyde (9.0%) and n-tetradecanal (8.8%) occurring in higher percentages. Conclusion: The chemical composition of the volatile compounds differed from each other and from data reported previously from other parts of the world.


INTRODUCTION
Plumeria rubra L. (Apocynaceae) grows as a spreading shrub or small tree to a height of 2-8 m and similar width. It has a thick succulent trunk and sausage-like blunt branches covered with a thin grey bark. The large green leaves can reach 30 to 50 cm long and are arranged alternately and clustered at the end of the branches. The flowers are terminal, appearing at the ends of branches over the summer. Often profuse and very prominent, they are strongly fragrant, and have five petals. The colours range from the common pink to white with shades of yellow in the centre of the flower. They produce seed of about 20-60 winged seeds [1]. The decoction of P. rubra has traditionally been used to treat asthma, constipation, promote menstruation and reduce fever. The fruit was reported to be been used as an abortifacient [2]. The flowers are aromatic and are used for the control of diabetes mellitus while the leaves are used to ameliorate ulcers, leprosy, inflammation and rubifacient. The milky sap of the stem and leaf has been applied to skin diseases such as herpes and scabies [2]. Extracts of the plants are known to possess some biological activities of importance such as antimicrobial, anti-inflammatory, analgesic, anthelmintic, antioxidant, antipyretic, abortifacient, antiulcer, antifertility, antitumor, anticancer and hypolipidemic [2][3][4][5][6][7].
Although the composition of the flower oils of P. rubra from Nigeria [10] and other parts of the world have been substantially investigated (Table 1), much less is known about the composition of the leaf oil. The objective of the present study was to examine the chemical constituents of the leaves and flowers oils of P. rubra grown in Southwest Nigeria in details, and to compare the results obtained with those reported earlier. The chemical analysis of essential oil of some plant species of Nigeria flora has been reported [23].

Plant Materials
Fresh plant materials of P. rubra (flowers and leaves) were collected from a location within the

Oil Isolation
Fresh flowers (50 g) and leaves (300 g) were separately subjected to hydrodistillation in a Clevenger-type glass apparatus for 3 h in accordance with the established specification [24]. The distilled oils were preserved in sealed sample tubes and stored under refrigeration until analysis.

Gas Chromatography (GC) Analysis
GC analysis of the oil was carried out on a Hewlett Packard HP 6820 Gas Chromatograph equipped with a FID detector and HP-5MS column (30 m x 0.25 mm id), film thickness was 0.25 μm and the split ratio was 1:25. The oven temperature was programmed from 50°C (after 2 min) to 240°C at 5°C/min and the final temperature was held for 10 min. Injection and detector temperatures were maintained at 200°C and 240°C respectively. Hydrogen was the carrier gas at a flow rate of 1 mL/min. An aliquot (0.5 µL of the diluted oil) was injected into the GC. Peaks were measured by electronic integration. A homologous series of n-alkanes were run under the same conditions for determination of retention indices. Each analysis was performed thrice.

Gas Chromatography-Mass Spectrometry (GC-MS) Analysis
GC-MS analyses of the oils were performed on a Hewlett Packard Gas Chromatograph HP 6890 interfaced with Hewlett Packard 5973 Mass spectrometer system equipped with a HP-5MS capillary column (30 m x 0.25 mm id, film thickness 0.25 µm). The oven temperature was programmed from 70-240ºC at the rate of 5ºC/min. The ion source was set at 240ºC and electron ionization at 70 eV. Helium was used as the carrier gas at a flow rate of 1 mL/min. Scanning range was 35 to 425 amu. Diluted oil in n-hexane (1.0 µL) was injected into the GC/MS.

Identification of Compounds
The constituents of the essential oils were identified by comparing their retention indices with an analysis done under the same temperature-programmed conditions for nalkanes and the oil on a HP-5 MS column under the same chromatographic conditions. Individual compounds were identified by comparing their mass spectra with the internal reference mass spectra library or with authentic compounds. Confirmation of identity was done by comparing their retention indices with the GC-MS library data [25] and with the mass spectra from literature data [26,27].
Few compositional variations were observed between the studied oil samples. (E)-Non-2-en-1ol, the main compound of the flower oil was not detected in the leaf while α-patchoulene and (E)-β-farnesene, present in leaves oil were not identified in the flowers oil. In addition, while fatty acids were conspicuously absent in the leaves oil, none of the diterpene compound could be detected in the flower. However, compounds such as limonene, phenyl acetaldehyde and (Z)β-farnesene were identified in both samples though with varying proportion. These observations may be based on the fact that different parts of the same plant may contain different chemical substances [23].
Although heneicosane and nonadecane were previously identified as the major compounds of P. rubra flowers oil from Nigeria [10], these compounds were not present in this study which also has low contents of citronellol and geraniol. The main compounds of essential oil of pinkflower P. rubra from Malaysia namely dodecanoic acid, tetradecanoic acid, hexadecanoic acid and nonadecane, were not identified in this oil sample from Nigeria. Moreover, the main constituents of the present oil samples namely non-2-en-1-ol, limonene, phenyl acetaldehyde, γ-elemene and (E,E)-αfarnesene, were conspicuously absent in the Malaysian oil sample [12]. It was noted that non-2-en-1-ol and limonene were not previously reported to be main compounds of previously investigated P. rubra oils (Table 1). Although, phenyl acetaldehyde was present in the Nigeria, Egypt [20,21] and Hawaii [18,19] samples, other variations were observed in the compositions of these samples. Some compounds such as 1,2benzenedicarboxylic acid 9-hexacosene, noctadecanal, n-octadecanol, lupeol acetate, palmitic acid, tetradecanoic acid and nhexadecanoic acid commonly observed from China oil samples [13][14][15][16][17] were not detected in the Nigeria grown P. rubra oils. The chemical compounds present in the essential oil of P. rubra from Cuba [22] were not identified in the Nigerian samples. The origin, environmental conditions, handling procedure, extraction methods, age and nature of the plant etc are some of the factors that may be responsible for the variations in the chemical composition of essential oils of P. rubra from different parts of the world.
The components present in the essential oils may be of economic importance. For example, limonene among others posses antimicrobial activity [28] while (E)-β-farnesene was used as an insecticide for the control of aphids [29]. On the other hand, (E)-non-2-en-1-ol is a scent material and also useful as an acaricide [30].

CONCLUSION
For the first time the compositions of essential oil from the leaf of P. rubra grown in Nigeria are being reported. In addition qualitative and quantitative differences were observed between the oil compositions from Nigeria and other parts of the world. These differences may be probably due to ecological and geographical conditions between Nigeria and other parts of the world as well as the age and nature of the plant, handling procedure etc.

CONSENT
Not applicable.

ETHICAL APPROVAL
Not applicable.