Analysis of the essential oil from the leaves of Sesamum radiatum , a potential medication for male infertility factor , by gas chromatography-mass spectrometry

Essential oil was extracted from the dried leaves of Sesamum radiatum by hydro-distillation and analyzed by combined gas chromatography-mass spectrometry. n-Hexadecanoic acid was found to be the major constituent and with three other fatty acids namely, 9,12,15-octadecanoic acid-(Z,Z,Z), dodecanoic acid and tetradecanoic acid constitute 40.64% of the oil. Other constituents include heptatriacontanol, estra–1,3,5(10)–trien-17á-ol, 1-(+)–ascorbic acid, 2,6-dihexadecanoate, ethyl isoallocholate, 18,19–secoyohimban–19-oic acid, 16,17,20,21-tetrahydro-16-(hydroxymethyl)-methyl ester, (15á, 16E)-trans-(2,3-diphenylcyclopropyl) methylphenyl sulfoxide, 1,1-[2-methyl-2-(phenylthio) cyclopropylidene]bis-benzene and phenolics. The presence of some of these constituents in the essential oil provides the scientific evidences for the observed cardiovascular and estrogenic activity as well as curative properties of the plant for male infertility factor, constipation, fungal and bacterial infections and bruises.


INTRODUCTION
Sesamum radiatum is a perennial herb found in the tropical areas of Africa and belongs to the Pedaliaceae family (Purseglove, 1974;Hutchinson and Dalziel, 1954).One of the local names in South-Western Nigeria is "Ewe atura" which means 'leaves that bring relaxation and health to the body' possibly because they relieve constipation and cure other ailments on ingestion (Odugbemi, 2008).The leaves, seeds and oil serve as food especially in farming communities in Nigeria (Akpan-Iwo et al., 2006).The seeds have been reported to have a crude protein content of 22.9% (Oshodi et al., 1999).The leaves are also used for treating various stomach ailments.The decoction of the leaves is used for the treatment of catarrh, eye pains as well as bruises and erupted skins.The decoction of combined roots and leaves has been reported to have anti-viral and antifungal activity (Gills, 1992).
The aqueous extract of the leaves has been found to be rich in phenols, lignans and flavonoids.Sterols were also found to be among its constituents.The extract was found to have significant myorelaxant effect in guinea-pig thus supporting the traditional use of the fresh leaves for treating cardiovascular diseases in Cote d'Ivoire (Konan et al., 2008).The leaves are also used in correcting male infertility by enhancing sperm count.This is one of the major uses of the plant in Western Nigeria.
Sesame leaves intake has been found to improve and increase epididymal spermatocytes reserve in adult male Sprague Dawley rat (Shittu et al., 2007).S. radiatum seeds have been shown to be estrogenic and/or antiestrogenic (Collins et al., 1997).The acclaimed success associated with the use of the leaves in treating male infertility factor is the major reason for this study as information about the chemical constituents in the leaves Ogunlesi et al. 1061 8.00 10.00 12.00 14.00 16.00 18.00 20.00 22.00 24.00 26.00 28.00 will be useful in pharmacological studies.In Africa, high premium is placed on having children and thus several childless marriages end up in separation or divorce.In this report, we present the constituent compounds in the essential oil isolated from the leaves of S. radiatum as identified by combined gas chromatography -mass spectrometry.

Collection of samples
Several batches of the fresh leaves of S. radiatum were purchased from Mushin market in Lagos, Nigeria, between October and December, 2005 and were identified by Mr. T. K. Odewo and Mr. Seun Osiyemi of the Forestry Research Institute of Nigeria (FRIN), Ibadan, Nigeria.A sample with voucher number FHI 107823 was deposited in the Herbarium of the Botany Department at FRIN.

Hydro-distillation of samples
The fresh leaves were air-dried, powdered and the essential oil extracted by hydro-distillation over a period of 4 h using batches of 100 g to which was added 3 L of water for each batch.The essential oil was collected into hexane giving a yellowish coloura-tion.Thereafter, it was separated from water and concentrated by evaporation of the hexane.

GC-MS Analysis of samples
Analysis of the essential oil was carried out on GC-MS model HP 6890 (Agilent Technologies Ltd) fitted with an HP-5 MS (5% phenylmethyl siloxane) capillary column 30 m x 250 µm x 0.25 µm.Helium carrier gas was used at a constant flow rate of 1 ml/min.The detector was 5973 inert MSD. 1 µL of sample was injected.Initial column temperature was maintained at 50°C for 6 min and increased at 25°C/min to 230°C (Xu et al., 2005).Total run time was 30.20 min.Injector and detector temperature was 280°C.Mass spectra were recorded at 70 eV ionization energy.Identification of the ions was by the Chem Office Software and the library of the MS.
The compounds discussed add up to 83.84% of all the compounds recorded in the integration.
The major constituents in the essential oil are fatty acids, namely n-hexadecanoic acid, 9, 12, 15-octadecatrienoic acid-(Z,Z,Z) and dodecanoic acid.Tetradecanoic acid and oleic acid are also present as minor constituents.Many fatty acids such as hexadecanoic acid and oleic acid have been reported to exhibit antibacterial and antifungal activity (Russel, 1991;McGraw et al., 2002;Seldel and Taylor, 2004;Dilika et al., 2000).Concentrations as low as 0.7% of oleic acid have been found to be fungistatic against a wide spectrum of moulds and yeasts (Davidson et al., 1999).Free fatty acids including long chain unsaturated fatty acids present in the extract from Tinospora smilacina Benth were suggested to be responsible for its anti-inflammatory activity (Li et al., 2004).Thus the combination of all the saturated and unsaturated fatty acids such as hexadecanoic acid, dodecanoic acid, tetradecanoic acid, 9-hexadecenoic acid, oleic acid and 9,12,15-octadecanoic acid-(Z,Z,Z), present in the essential oil may be useful for the management of eye pains and inflammatory conditions arising from bacterial and fungal infections as well as bruises and erupted skins.
A long chain fatty acid alcohol, heptatriacontanol, is present in the oil.Octacosanol, a long chain fatty alcohol, was reported to suppress lipid accumulation in rats fed on a high-fat diet (Kato et al., 1995) and to inhibit platelet aggregation (Arruzazabala et al., 1994).Heptariacontanol may exhibit such activities.
The use of policosanol has been demonstrated to show modest advantages over pravastatin in the treatment of patients with type II hypercholesterolemia (Bentez et al., 1997).Policosanol, a natural mixture of higher primary unsaturated aliphatic alcohols isolated and purified from sugar cane wax contains C28, C26 and/or C30 alcohols, has been proven to exhibit cholesterol-lowering effects in patients with type II hypercholesterolemia and dyslipidemia due to type 2 diabetes mellitus and was demonstrated 1064 Afr.J. Biotechnol. to have good safety and tolerability profiles with no evidence of drug-related adverse events (Castano et al., 2002).Heptatriacontanol, a C37 aliphatic alcohol may exhibit such activity.Carboxylic acids having a thioether, a sulphoxide or sulphone function in dermatogical or cosmetic compositions have been found to promote skin exfoliation and/or stimulating epidermal regeneration.They are also useful for controlling intrinsic and extrinsic skin ageing (Maignan, 1998).The constituent eluted at R T 23.184 min, trans-(2,3-diphenylcyclopropyl) methylphenyl-sulfoxide and the carboxylic acids present may therefore contribute to the healing of bruises and erupted skins.It is also pertinent to note that other sulphur-containing constituents, such as tert-hexadecanethiol as well as 1,1-[2methyl-2-(phenylthio)cyclopropylidene]bis-benzene with possible isomeric forms eluted at R T 26.142, 26.632, 26.845 and 27.255 min, constituting 6.41% of total may also be useful for the management of bruises and erupted skins.The multiple and distinct peaks for this latter constituent may be due to impairment of column efficiency associated with high retention time.
A steroid, estra-1,3,5(10)-trien-17á-ol (Figure 2d), present in the essential oil differs from estradiol, a sex hormone, in the absence of the C3-OH.Steroids though similar in basic structure, have extreme specificity hence this steroid cannot be said to function like estradiol (Bruice, 1998).However, it may be responsible for the observed estrogenic and/or anti-estrogenic activity (Collins et al., 1997) , 10,10,12b-tetramethyl-1,2,3,3a,4,6,8,9,10,10a,11,12,12a,12b (Glenville, 2008;Dawson et al., 1992).This constituent may be responsible for the enhancement of sperm production in males claimed by herbal medical practitioners and also explain the reported improvement and increase in epididymal spermatocytes reserve in adult male Sprague Dawley rat (Shittu et al., 2007).An aqueous extract of the leaves is mucilaginous and pro-motes bowel action and relieves constipation.This is a general observation in some items of the Nigerian diet that are mucilaginous vegetables and fruits such as Coc-corhus olitorius, okro and the stipules of the umbrella tree Musanga cercropiodies which have been found to promote bowel action and thereby give relief in consti-pation.Ethyl isoallocholate (Figure 2c) present in the essential oil is the ester of a bile acid and can act as an emulsifying agent so that fats and oils can be digested by water-soluble digestive enzymes in the small intestines (Bruice, 1998).Thus this constituent may be responsible for the relief of constipation or indigestion experienced on ingesting the stewed leaves.
Phenolic compounds present in the essential oil such as eugenol and 2,4-bis(1,1-dimethylethyl)-phenol, are antibacterial agents and may cure eye infections.18,16,17,20,(15á,16E), whose structure is shown in Figure 2a is present in the essential oil and belongs to the same family as yohimbine which is 17α-hydroxy-yohimban-16α-carboxylic acid methyl ester having the structure shown in Figure 2b (Chemblink, 2009).Yohimbine has been found to be active on endocrine and reproductive systems; for example, it was reported to be effective in relieving male impotency (Temple and Smith, 1992;Sobotka, 1969).Yohimbine has also been found to exhibit cardiovascular activity (Henauer et al., 1984).Thus,18,16,17,20,methyl ester-(15á,16E) may be responsible for the reported cardiovascular activity (Konan et al., 2008) and spermatogenic effect of the leaf extract (Shittu et al., 2007).

Conclusion
The study has been found useful in the identification of several constituents present in the essential oil from the leaves of S. radiatium.Some of these have been found to be useful in explaining the scientific basis of the role of the plant in treating male infertility factor, constipation, inflammations, eye pains and skin infections and explaining its cardiovascular bioactivity.The results of this study would lead to pharmacological testing of the plant extract on animal models.

Figure 1 .
Figure 1.Gas chromatogram of the essential oil from the leaves of S. radiatum.

Table 1 .
. A derivative of ascorbic acid, Ogunlesi et al.1065 Composition of the constituents of the essential oil from the dried leaves of S. radiatum.