Comparative study of the chemical composition of the essential oils from organs of Annona senegalensis Pers. oulotricha le Thomas subspecies (Annonaceae)

The chemical composition of the essential oils from leaves, stems bark, roots bark, epicarp and mesocarp of Annona senegalensis Pers., oulotricha Le Thomas subspecies (Annonaceae), growing in Brazzaville (Congo), were analyzed by CG and CG-MS. These oils essentially contain sesquiterpenic compounds (58.3 - 97.7%), dominated by oxygenated sesquiterpenes (21.8 - 88.3%), with elemol (13.2 - 35.0%), bbbb and gggg -eudesmols (3.7 - 58.3%) as characteristic components. The essential oils from roots and stems bark is distinguished by its high content in diterpenes (17.1 and 11.9% of the total), while the seeds presents a significant amounts of monoterpene hydrocarbons (25.8%) with aaaa -pinene (6.2%) and bbbb -phellandrene (11.5%) as major components accompanied by two oxygenated monoterpenes : bornyle acetate (4.5%) and smallest of 1,8-cineole. However, in the epicarp oil, the presence of about 5.8% of oxygenated monoterpenes as terpinen-4-ol and bornyle acetate in comparable rates (1.7%) was noted. The mesocarp oil is exclusively rich in aliphatic fatty acids (35.8%) which is absent in the other organs, but represented by lauric acid (18.0%), hexadecanoïc acid (8.6%), myristic acid (7.2%) and oleic acid (2.0%). Results were compared with same species collected in the democratic republic of Congo and in Cameroon essentially dominated by monoterpenes (84.2 and 87.6%).


INTRODUCTION
Annona senegalensis Pers.species belongs to the Annonaceae family.It is one of the natural and homogen vegetable families with essential oil cells (Le Thomas, 1969).It is found in the tropics and grow more often under low altitude (Lebrun and Stork, 1991).The Annonaceae's family contains about 120 genera.The *Corresponding author.E-mail: jm_ouamba@yahoo.fror jmouamba@cg.auf.org.
Annona genus, originated from Central America and is constituted by 110 species.Several species of this family are used for the nutritive interest of their fruits (Eyog et al., 2006) or for their medicinal importance in traditional medicine.The A. senegalensis Pers., subspecies oulotricha Le Thomas, found in the African savanna, is limited in the dense and humid forest, particularly in Congo.It is a plant whose leaves, barks and roots are perfumed.Its ripe fruit which are orange yellow coloured, frozen, sugared and edible, also contains perfumed seeds (Dupont and Guignard, 2007).A. senegalensis species is used in Central and West African folk medicine as anthelmintic (Nwude et al., 1980;Ibrahim et al., 1983;Alawa et al., 2003;Fall et al., 2003), andiarrheic, anticonvulsivant, antibacterial, antifungal, antitussif, antiflammatory, antipyretic, as well as for cancer and leukemia treatments (Kanta, 1999;Noumi and Fozi, 2003;Abubakar et al., 2007;Magassouba et al., 2007).
In an attempt to obtain the best knowledge and judicious use of A. senegalensis Pers.oulotricha Le Thomas species, the present work proposes to identify the chemical constituents of the essential oils from the different organs (leaves, barks, roots, epicarp, mesocarp and seeds) collected in Congo Brazzaville.

Plant material
The different samples of leaves, roots barks, stem barks, seeds, mesocarp and epicarp of the fruits of A. senegalensis Pers., studied, originating from Brazzaville (Congo), were collected in January 2009.Voucher specimens were identified at the Laboratory of Botany of the Centre des Resources Végétales (CERVE) and deposited at the National Herbarium of Brazzaville (IEC, Nkounkou n° 1, 1bis, 1ter).

Essential oils
The air-dried plant material were hydrodistillated for five hours using a Clevenger-type apparatus (Ouamba et al., 1990).The oils were obtained after decantation and drying over anhydrous sodium sulphate.The weights of vegetal material used, the amounts, extraction yields and colour of essential oils obtained are reported in Table 1.

Analysis
The quantitative analysis was carried out using a Hewlett-Pacard HP 5890 chromatograph equipped with flam ionization detectors.Separation were performed on silica capillary column (30 m x 0.25 mm x 0.25 µm) coated with DB-5, using the following experimental conditions: oven temperature 50°C (5 min) -300°C (5 min) at 5°C/min; injection temperature 280°C; detector temperature 280°C, carried gas helium at flow rate of 1.0 ml/min.The qualitative analysis was carried out using a GC/MS Hewlett-Packard apparatus (model 6890/5973) equipped with the same capillary column using same experimental conditions.
The presence of elemol, β and γ-eudesmols, with important rates in the congolese samples, showed that this compounds are characteristic of the Oulotricha subspecies.It was noted that elemol and eudesmols could be absent or present at louder proportions in the Annonaceae oils (Masotti et al., 1997;Farid et al., 2002).The presence of alcohol function compounds justified the antibacterial, antifungal and antioxidant activities of A. senegalensis Pers.oulotricha Le Thomas species (Baratta et al., 1998;Dorman and Deans, 2000).

Table 1 .
Preparation and color of the essential oil of A. senegalensis Pers., oulotricha Le Thomas subspecies.
*Crystallized at ordinary temperature.

Table 2 .
Comparative study of the percentage composition of the essential oil from different organs of Annona senegalensis Pers, oulotricha Le Thomas subspecies.