Essential Oil of Pluchea quitoc Dc. (Asteraceae)

Abstract

The essential oils of Pluchea quitoc, which were obtained from aerial parts of two samples (A and B) from two different collection locations from South of Brazil (Rio Grande do Sul), were analyzed by GC and GC/MS. Forty-two compounds representing ca 98.0% and 90.5% were identified in the oils of samples A and B, respectively. Sesquilavandulyl acetate (7.6 - 24.1%), sesquilavandulol (8.2 - 24.3%) and α-gurjunene (20.0-20.5%) were the major components. The antimicrobial activity of the oils, sesquilavandulol acetate and sesquilavandulol is also reported.

Key Word Index

Pluchea quitoc, Asteraceae, essential oil composition, α-gurjunene, (E)-sesquilavandulol, (E)-sesquilavandulyl acetate, antimicrobial activity.

Introduction

Pluchea quitoc know as "quitoco" is an aromatic shrub found throughout the greaterpart of Southern of Brazd (Rio Grande do Sul). It has been used traditionally by local people as an expectorant, carminative, digestive and anti-rheumatic (1,2).

As part of our work on the characterization of aromatic and medicinal plants of Rio Grande do Sul (3-5), we report here the chemical composition and antimicrobial activity of essential oil from Pluchea quitoc obtained of two regions (sample A and sample B) of this state. To our knowledge, there are no previous reports on the composition and antimicrobial activity of this od in the literature.

Experimental

General: 1H- and ^sup 13^C -NMR spectra were recorded on a Bruker DPX 400 (400.1/100.6MHz) NMR spectrometer, in CDC13 with TMS as internal standard. TLC were performed on precoated silica gel 60 F254 plates (Merk) and detection was achieved by UV light (254nm) and by spraying with solutions of 10% H2S04 and 10% vaniUin in ethanol, foUowed by heating.

Plant Material: Pluchea quitoc was coUected at the towns of Santana do Livramento (sample A) and Fortaleza dos Valos (sample B), Rio Grande do Sul state, Brazil. Leaves were collected between November 2003 and September 2004. Voucher specimens (EKRE- 23-47) have been deposited at Herbarium of Federal University of Santa Maria.

Chemical Analysis: Fresh leaves (sample A and B), were subjected to hydrodistdlation for 4 h using a modified Clevenger-type apparatus, and followed by exhaustive extraction of the distillate with diethyl ether.

The ods were analyzed by GC and GC/MS. GC analyses were performed using a Varian CP-3800 gas Chromatograph with a FID detector and SE-54 fused sdica column (25m ? 0.25mm, film thickness 0.2pm). Operation conditions were as fodows: injector and detector temperatures, 220° and 280°C, respectively; carrier gas, H^sub 2^; oven temperature program from 50°-250°C at 4°C/min. GC/MS analyses were performed using a VARIAN model 3800 Saturn system operating in the EI mode at 7OeV equipped with a CP-SIL cross-finked capillary column (30m x 0.25mm, film thickness 0.2µm). The identity of the oil components was established from their GC retention times and by comparison of their MS spectra with those reported in literature (6), and by computer matching with the Wdey 5 mass spectra library (7), and as well as by co-injection with standards available in our laboratories whenever possible.

Part of the resulting ods: sample A (100 mg), further subjected to preparative TLC (Si02; hexane-EtOAc, 85:15) afforded sesqudavandulyl acetate (20 mg).

Alkaline hydrolysis of sesquilavandulyl acetate: A sample of sesqudavandulyl acetate (30 mg) was added to a solution of MeOH/Na (5mL/20mg) under stirring. Stirring was continuedat room temperature for 2 h (TLC control). Standard workup and preparative chromatography (10% AcOEt in hexane as eluent) afforded 21 mg of sesqudavandulol.

Bioautographic bioassay: The antimicrobial activity of isolated compounds (E)-sesqudavandulyl acetate, (E)-sesquilavandulyl alcohol and samples of the ods (A and B), were assayed using die bioautography technique (8-10). A coUection of nine microorganisms was used, including three Gram-positive bacteria: Staphylococcus aureus (ATCC 6538p), Staphylococcus epidermidis (ATCC 12228), Bacillus submits (ATCC 6633); and four Gram-negative bacteria: Klebsiella pneumoniae (ATCC 10031), Escherichia, coli (ATCC 11103), Pseudomonas aeruginosa (ATCC 27873), Salmonella setubal (ATCC 19196); and two yeasts: C andida albicans (ATCC 10231), and Cryptococcus neoformans (ATCC 2601). Standard microorganism strains were obtained from American Type Culture CoUection (ATCC), and standard antibiotics chloramphenicol and nistatine were used in order to control microbial test sensitivity. Compound concentrations from 200 µg to 1.56 pg were applied to precoated TLC plates. Muller Hinton Agar and Sabouraud Agar media inoculated with mocroorganisms suspended in saline solution (105CFLVmL) were distributed over TLC plates. Bacterium and yests plates were incubated for 24 h at 37°C, and 72 hat 25°C, respectively. Standard antibiotics, chloramphenicol and nistatine, were used in order to control microbial test sensitivity. The results were stained witii an aqueous solution of 2,3,5-triphenyl-tetrazolium chloride (TTC, lmg/mL). The appearance of inhibition zones was used to determine the lowest sample amount capable of inhibiting microbial growth. Samples were tested in triplicate.