Aromatic Plants of Tropical Central Africa. Part XLVI. Essential Oil Constituents of Cassia alata (L.) from Gabon(a)

Journal of Essential Oil Research: JEOR, Jul/Aug 2005 by Agnaniet, Huguette, Bikanga, Raphaël, Bessière, Jean Marie, Menut, Chantal

Abstract

The essential oil obtained by hydrodistillation of leaves of Cassia alata collected in Gabon was analyzed using capillary GC and GC/MS. Forty-four compounds representing 95.2% of the oil were identified among them linalool (23.0%), borneol (8.6%) and pentadecanal (9.3%) were major constituents. The antioxidant activity of the oil was found to be low compared to that of butylated hydroxytoluene (BHT).

Keyword Index

Cassia alata, Leguminosae, essential oil composition, linalool, pentadecanal, borneol.

Plant Name

Cassia alata (L.) Leguminosae. Synonym: Senna alata (Miller) (2).

Source

Aerial parts of Cassia alata were harvested at Ntoum, a village located approximately 50 km far from Libreville (Gabon) in October 1999. The plant samples were identified and a voucher specimen was deposited at the National Herbarium (Libreville).

Plant Part

Air-dried leaves and branches were submitted to hydrodistillation for 4 h, using a Clevenger-type apparatus to produce oil in low yield (0.2%).

Previous Work

Cassia alata L. (Leguminosae) is a shrub, 2-3m high, widely distributed in the tropical countries, stretching from Tropical America to India, Fiji, Indonesia, Malaysia and Africa (2-3). It is locally known as "ringworm shrub" or "winged Senna" in India, "candle tree" or "ringworm Cassia" in Malaysia as well as "Dartrier" in the French Antilles, owing to the utilization of its fresh leaves against ringworm, eczema, pruritis, itching, scabies, ulcers and others skin diseases (3-4). Cassia alata leaves are also used in Africa for the same properties (5-7). The leaf extracts exhibit various pharmacological properties: antimicrobial and antifungal activities (8-14) as well as anti-inflammatory effect (15); the therapeutic efficacy of Cassia alata leaf extract against Pityriasis versicoloriias been reported (16); finally the anti-aging effect of Cassia alata was demonstrated (17) allowing the use of extracts of Cassia alata in cosmetic and/or dermatological skin care products (18).

Chemical investigations on ethanolic and water extracts of leaves or stem from C. alata revealed the presence offlavonoids (19-20) and anthraquinones (21-25). As far as we know, the volatile constituents of C. alata have not been the subject of previous studies.

Present Work

GC: Gas chromatography analysis was carried out on a Varian CP-3380 GC with flame ionization detectors fitted with a fused silica capillary column (30 m x 0.25 mm coated with DBl, film thickness 0.25 µ); temperature program 50°-200°C at 5°C/min, injectortemperature 220°C, detectortemperature 250°C, carriergas N^sub 2^,0.8 mL/min. The linear retention indices of the components were determined relatively to the retention times of a series of n-alkanes and the percentage compositions were obtained from electronic integration measurements without taking into account relative response factors.

GC/MS: Gas chromatography/mass spectrometry analyses were performed using a Hewlett Packard apparatus equipped with an HP1 fused silica column (30 m x 0.20 mm, film thickness 0.25 µm) and interfaced with a quadrupole detector (Model 5970). Column temperature was programmed from 70°-200°C at 10°C/min; injector temperature was 220°C. Helium was used as carrier gas at a flow of rate 0.6 mL/min, the mass spectrometer was operated at 70 eV.

The identification of the components was assigned by comparison of their retention indices and their mass spectra with those given in the literature (26,27) and with the stored laboratory mass spectral library.

Antioxidant activity: A rapid screening of the antioxidant activity of the oil on thin-layer chromatography plates using β-carotene (28) revealed that the leaf oil had a low activity: after 4 h of exposure in light, a persistence of coloration was observed. Further evaluation was carried out on the oil using a β-carotene/linoleate model system by the method described in our previous paper (1).

Results and Discussion

Forty-four compounds representing 95.2% of C. alata oil were identified by GC/MS (Table I). The oil was found to be rich in monoterpenes with a predominance of acyclic compounds: linalool, geraniol and their derivatives represented more than 35% of the whole mixture. It is important to note the presence of a relatively high level of aliphatic components, among them pentadecanal was predominant.

On account of its chemical composition, characterized by terpenic alcohols like linalool and α-bisabolol, the volatile fraction of C. alata leaves contributes certainly to the anti-inflammatory, sedative and relaxant properties of the dermatologic preparations containing C. alata extracts (29).

The antioxidant activity of the essential oil was evaluated comparatively to that of BHT (butylated hydroxy toluene): IC^sub 50^ (BHT) = 82 µg/L

The essential oil of Cassia alata was not active enough to allow the calculation of IC^sub 50^, since for a concentration of 666 µg/L, the inhibition percentage was only 36%; consequently, despite of a slight positive concentration effect, this essential oil seems not to be of interest for its antioxidant property.