Essential Oil Composition of the Leaves of Ocimum micranthum Willd.
de Vasconcelos Silva, Maria Goretti
Variation on chemical composition of essential oils produced from Ocimum micranthum Willd. obtained from plants growing in northeast Brazil, at different stages of development and throughout the day. The oils, which were obtained by microwave oven distillation, were analyzed by GC/MS. A discreet variation in the eugenol contents from 97% at 6:00 a.m. to 84% at 6:00 p.m. was observed. The highest value was found in oil obtained from a specimen with a fully developed inflorescence. The eugenol production in O. micranthum does not appear to be influenced by solar light throughout the day.
Key Word Index
Ocimum micranthum, Labiatea, essential oil composition, eugenol, diurnal variation.
Ocitnum micranthum Willd. (syn. O. catnpechianum Mill.), local name: alfavaca de galinha, alfavaca miuda.
Previous studies ou Ociinum micranthum Willd. from India and from two different climate regions of Brazil report different chemical compositions of the volatile oil of their leaves. The oil from Indian plants contained cugenol, 1,8-cineole, [beta]-caryophyllene and [gamma]-elemene (1), while the Brazilian oil growing in high humidity and low solar light incidence in the Amazonian region contained [beta]-elemene, [beta]-caryophyllene and isoeugenol as main components (2). An oil produced from plants growing in low humidity and high solar light incidence conditions in a semiarid region of Brazil contained eugenol, [beta]-caryophyllene and eleniicin as main components (3). Anticonvulsant, antispasmodic (4) and antifungal (5) activities (6) of it were also mentioned for dichloromethaue and methanol extracts obtained from this plant. The oil shows analgesic activities (6). In view of this data, a new analysis of the oil of O. inicranthum from plants collected in northeast Brazil was carried out under specially controlled conditions.
Plant collection and identification: Sample leaves of O. micranthum growing under sunlight on April 2000 in the Medicinal and Aromatic Plants Garden of the Federal University of Ceara (UFC) were collected eveiy two h of daylight from 6:00 a.m. to 6:00 p.m. and immediately processed for analysis. A voucher specimen was deposited in the Herbarium Prisco Bezerra of the UFC under number 29.315.
oil isolation and analysis: Fresh leaf samples (50 g) were subjected for 8 min to hydrodistillation using a modified microwave oven device adapted for oil isolation (7). The water/oil distillates were collected on diy ice and then extracted by partition with CH^sub 2^Cl^sub 2^. The oil obtained was analyzed in a Hewlett-Packard GC/MS model 5971A, under the following conditions: stationary dimethylpolysiloxane DB-I fused silica capillary column (30 in × 0.25 mm, 0.1 µm film thickness); carrier gas: helium (1 niL/rnin); injector temperature: 250°C; detector tempe rature: 200°C; column temperature: 35°-180°C at 4°C/min then 180°-250°C at 10°C/min; MS: electronic impact 7OeV. The identification of the constituents was achieved with aid of the respective retention indices and by comparison of mass spectra with published data (8-10).
Eugenol (97.0-84.0%), [beta]-caryophyllene (1.6-7.6%) and bicyclogermacrene (1.4-5.2%) were found as major constituents of the leaf oil of O. micranthum from Fortaleza in all samples (Table I). The composition shows a discreet variation along daytime in contrast with the O. gratissimum ( 11 ) oil that revealed considerable variation in eugenol content from 98% at 12:00 p.m. to 11% at 5:00 p.m. Analyses of oils obtained in three stages of development (I = vegetative stage, II = commencement of inflorescence and III = end of reproductive stage of the plants) were performed (Table II). It was found that elemicin (21.6%) was only present as a major component of the oil obtained from plants in their vegetative stage (Stage I). Also, it was observed that the eugenol content change from the first stage (I) to the last (III) was only about 17.5%.
Authors are thankful to Raymond Hurley jrom the Keio Gardens Herbarium for species identification. Thanks are also due to the Brazilian government agencies for research development CNPq/ PNEPG and FUNCAP-CE by financial support that made this research possible.
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Maria Goretti de Vasconcelos Silva*, Francisco Jose Abreu Matos, Maria Iracema Lacerda Machado and Fabio de Oliveira Silva
Laboratório de Produtos Naturais, Departamento de Químida Analítica e Fisico-Quíimida, Departamento de Química Orgânica e Inorgânica, Universidade Federal do Ceará Fortaleza, Ceará, Brazil
* Address for correspondence
Received: February 2001
Revised: April 2001
Accepted: May 2001
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