Composition of the Essential Oil of Helichrysum forsskahlii (Gmel) Hilliard et Burt

Journal of Essential Oil Research: JEOR, Jan/Feb 2005 by El-Olemy, M M, Al-Rehaily, A J, Albishi, O A, Mossa, J S, Et al

Abstract

The essential oil obtained by hydrodistillation of the aerial parts of Helichrysum forsskahlii, endemic to southern Saudi Arabia, was analyzed by GC/MS. Eighty-one compounds, representing more than 85.9% of the oil, were identified with selina-5,11-diene (45.3%), δ-3-carene (7.8%), 1,8-cineole (4.2%) and β-caryophyllene (4.9%) as main constituents. The major component, selina-5,11-diene, being not previously isolated from natural sources, was isolated by column chromatography and its identity confirmed by 1 and 2D NMR spectral analysis. The oil showed only a very weak activity against Mycobacterium smegmatis, with no activity against Gram-positive and Gram-negative bacteria or Candida test organisms. Likewise, selina-5,11-diene showed only a weak activity against M. intracellulare.

Key Word Index

Helichrysum forsskahlii, Asteraceae, essential oil composition, selina-5,11-diene, antimicrobial activity.

Introduction

Helichrysum forsskahlii(Gmel) Hilliard et Burt (Asteraceae) is distributed in southern Saudi Arabia, especially in Abha and East Africa (1). The essential oil of H. forsskahlii has not been previously investigated. Nevertheless, several reports were encountered in the literature dealing with the oil composition of several Helichrysum species; these include H. bractieferum (2), H. picardii (3,4), H. taenari and H. stoechos sp. barrelier (4) and H. amorginum and H. italicum (5).

Experimental

Plant material: The aerial parts were collected in Abha, Saudi Arabia in March and April 1999. The plant was identified by Sultanul Abedin, Medicinal, Aromatic and Poisonous Plants Research Center ( M APPRC), College of Pharmacy, King Saud University, Riyadh, Saudi Arabia. Voucher specimens were deposited at the MAPPRC Herbarium (voucher specimen number: 14052).

Oil isolation: The air-dried aerial parts were distilled in a Clevenger-type apparatus for four h. The oil was extracted from the distillate with peroxide-free diethyl ether; the ether extract was passed over anhydrous Na^sub 2^SO^sub 4^ and evaporated in vacuo. The yield of the oil was 0.22%.

GC/MS analysis: The oil was analyzed using a Hewlett Packard G1800A GCD system using HP-Innowax FSC column (60 m × 0.25 mm, with 0.25 µm film thickness). Helium (0.8 inL/min) was used as carrier gas. GC oven temperature was kept at 60°C for 10 min and programmed to 220°C at a rate of 4°C/min and then kept constant at 220°C for 10 min to 240°C at rate of 1°C/min. Mass range was recorded from m/z 35 to 425. Injections were applied splitless. Injection port temperature was at 250°C. MS were recorded at 70 eV. Relative percentage amounts of the separated compounds were calculated automatically from peak areas of the total ion current (TIC). Alkanes were used as reference points in the calculation of relative retention indices (RRI). Library search was carried out using both "Wiley GC/MS Library" and "TBAM Library of Essential oil Constituents." The compounds identified in the oil are listed in Table I.

Isolation of selina-5,11-diene: The compound was isolated by column chromatography. Silica Gel 60G (10 g, Merck 7734) was used as packing material, filled with wet hexane (column size: 10 × 500 mm). Hexane: acetone (100-0) was used as eluant in a gradient system. The oil (0.150 g) was applied to the column and hexane: acetone (99.5:0.5) eluted compound 1 (16 mg), R^sub f^ value = 0.4 on silica gel TLC in hexane: diethylether (95:5, v/v), visualized with anisaldehyde/H^sub 2^SO^sub 4^ reagent.

Selina-5,11-diene: oil; [α]^sup 25^^sub D^-5°; IR (CHCl^sub 3^) v : 3087, 2967(sh), 2927, 2857, 1640, 1397, 1392, 895 cm^sup -1^; MS (EI, 70 eV), m/z(rel. int.): 204[M]^sup ^(42), 189(41), 175(15), 161(37), 147(43), 133(46), 121(34), 119(35), 108(100), 107(61), 105(63), 93(62), 91(66), 81(44), 79(44), 77(33), 67(22), 55(36), 41(52); ^sup 1^H-NMR & ^sup 13^C-NMR (CDCl^sub 3^) (Table II).

Antimicrobial Activity Testing

Microorganisms used: The microorganisms used for the agar dilution assay and the serial broth macrodilution assay were: Bacillus subtilis ATCC 6633, Staphylococcus aureus ATCC 29213, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 15442, Candida albicans ATCC 90028 and Mycobacterium smegmatis ATTC 35797.

The microorganisms used for the microtiter plate assay were: Staphylococcus aureus ATCC 29213, methicillin-resistant Staphylococcus aureus ATCC 43300, Pseudomonas aeruginosa ATCC 27853, Mycobacterium intracellulare ATCC 23068, Candida albicans ATCC 90028, Candida neoformans ATCC 90113 and Aspergillus fumigatus ATCC 90906.

Agar dilution assay (6): The oil was dissolved in a small volume of DMSO and diluted with 10 mL warm nutrient agar (40°C) for most of organisms and Sabauraud agar for Candida, to give a concentration of 1,000 and 2,000 µg/mL and swirled carefully before congealing. The microorganisms were streaked in radial patterns on the agar plates. The plates were incubated at 37°C in the dark and examined after 24 and 48 h. Complete inhibition of growth was required to declare bioactivity. The controls consisted of both negative (DMSO) and positive controls. Chloramphenicol was used as a positive control for Gram-positive and Gram-negative organisms, nystatin for Candida albicans and isonicotinic acid hydrazide for Mycobacterium smegmatis.