Aromatic Plants of Tropical Central Africa. XL. Essential Oils from Uvariodendron calophyllum R.E. Fries Growing in Cameroon(a)

Journal of Essential Oil Research: JEOR, Mar/Apr 2005 by Boyom, Fabrice Fekam, Zollo, Paul Henri Amvam, Agnaniet, Huguette, Menut, Chantal, Bessière, Jean Marie

Abstract

The essential oils obtained by hydrodistillation from roots, wood and stem barks of Uvariodendron calophyllum R. E. Fries (Annonaceae) were analyzed by GC and GC/MS. The tree organs were found to contain 0.39%, 0.04% and 0.52% of oils for the roots, wood and stem bark, respectively. The qualitative composition of the oils were found to be similar, with 82-87% of hydrocarbons among which α-santalene along with β-caryophyllene total more than 50% of the mixture. These oils extracts did not reveal any important antiradical activity.

Key Word Index

Uvariodendron calophyllum, Annonaceae, essential oil composition, β-caryophyllene, α-santalene, antiradical activity.

Introduction

Uvariodendron calophyllum R.E. Fries (Annonaceae) is an understorey tree or shrub of forest, 10-40 ft high, which has been mentioned in southern Nigeria and Cameroon (2). As far as we know, no results have yet be published on the oils of U. calophyllum. The present article reports the results of our chemical investigations on the oils obtained from different parts of U. calophyllum collected in Cameroon. The antiradical properties of the oils were also evaluated.

Experimental

Plant material and oil isolation: Stem bark, wood and root of U. calophyllum were collected in Mount Kalla (Yaounde area, Cameroon) in December 2000. The plant samples were identified and voucher specimen deposited at the National Herbarium (Yaounde). Air-dried stem bark and roots were ground using a blender. Batches of 500 g of plant material were submitted to hydrodistillation for 3 h using a Clevenger-type apparatus. The oils were dried after decantation overanhydrous sodium sulfate.

Gas chromatography: The oils were analyzed on a Varian CP-3380 GC with flame ionisation detector fitted with a fused silica capillary column (30 m x 0.25 mm coated with DB1, film thickness 0.25 µm); temperature program 50°-200°C at 5°C/ min, injector temperature 220°C, detector temperature 250°C, carrier gas 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.

Gas chromatography/mass spectrometry: GC/MS analyses were performed using a Hewlett Packard apparatus equipped with an HP^sub 1^ fused silica column (30 m x 0.25 mm, film thickness 0.25 µm) and interfaced with a quadrupole detector [GC-quadripole MS system (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 rate of 0.6 mL/min, the mass spectrometer was operated at 70 eV.

Identification of components: The identification of the constituents was assigned on the basis of comparison of their retention indices and their mass spectra with those given in the literature (3-5).

Antiradical activity: The antiradical activity was determined using 2,2-diphenyl-1-picrylhydrazyl (DPPH) following the Mellors and Tappel method (6-7). DPPH*, a free stable radical scavenger, was dissolved in ethanol to give a 100 µM solution. To 2.0 mL of the ethanolic solution of DPPH was added 100 µM, of a methanolic solution of the antioxidant reference (BHT, ascorbic acid ortocopherol) at different concentrations (10-50 µM). The oils were tested using the same method. The control, without antioxidant, is represented by the DPPH ethanolic solution containing 100 µL of methanol. The decrease in absorption was measured at 517 nm after 30 min, at room temperature. The actual decrease in absorption induced by the test compound was calculated by subtracting that of the control. Measurements were performed in triplicate and the concentration required for 50% reduction (50% scavenging concentration, SC^sub 50^) was determined graphically. All the spectrophotometric measurements were performed with a SAFAS UV mc^sup 2^ spectrophotometer, equipped with a multi-cells/multikinetics measure system and with a thermostated cell-case.

Results and Discussion

The oils were obtained with the following yields: 0.39% for the roots, 0.52% for the stem bark and 0.04% for the wood. The results of the GC and GC/MS analyses of the three oils are given in Table I, where the constituents are listed in order of their elution on an apolar-type column.

It appears from these results that the three oils samples were qualitatively similar in composition, characterized by the predominance of the biosynthetically related structures: bisabolene, santalene and bergamotene which represent 46.8%, 50.0% and 79.6% of the mixture, respectively. On the other hand, caryophyllene, humulene and their oxygenated derivatives were abundant in wood and stem bark oils.

The free radical scavenging activities were evaluated as follows, and compared with those of commercial antioxidants:

[SC^sub 50^] (BHT) = 8.8 mg/L

[SC^sub 50^] (ascorbic acid) = 6.2 mg/L

[SC^sub 50^] (δ-tocopherol) = 15.3 mg/L

[SC^sub 50^] (Uvariodendron wood) = 2.5 g/L