Steam Volatile Terpenoids from Salvia leucantha

Abstract

The essential oil from the aerial parts of Salvia leucantha Cav. (Lamiaceae) was analyzed by GC, GC/MS and NMR spectroscopy. The oil was found rich in sesquiterpene hydrocarbons; ß-caryophyllene (13.9%), α-guaiene (12.6%), cis-muurola-3,5-diene (10.8%), germacrene D (13.8%) and bicyclogermacrene (8.7%). Bornyl acetate constituted 23.9% of the oil. This is the first detailed report on the essential oil composition based on capillary GC and GC/MS analyses.

Key Word Index

Salvia leucantha , Lamiaceae, essential oil composition, bornyl acetate.

Introduction

Salvia leucantha Cav. (Lamiaceae) has a wide distribution and is a common garden plant. Seven species of Salvia are reported to grow in the central Himalayan region of India (1) and have not been thoroughly investigated for their steam volatile components. A literature review could reveal a few reports on Salvia leucantha. The first two reports on the steam volatile components show die presence of 1,8-cineole (7.6-0.0%), p-cymene (4.0-7.2%), thujone (5.4-7.0%), linalool (9.0-10.0%), geranyl acetate (4.8-6.0%), ritrai (19.0-25.0%), citronellal (2.0%), citronellol (9.6-12.0%), geraniol (12.0-13.0%), cedrene (6.2%) and aromadendrene (6.0%) in the oil (2,3). The other three reports show the isolation and identification of salvigenane and isosalvipuberulan diterpenoids from an acetone extract (4) and triterpenes (5,6) from a chloroform extract of its aerial parts. Our preliminary examination of die essential od of Salvia leucantha indicated its composition to be significandy different from that reported earlier (2,3). We have carried out a detaded analysis of the oil, which forms the basis of the present communication.

Experimental

Plant material: The aerial parts including flowers of the plant was coUected from Nainital and its adjoining areas (1800 to 2100 m elevation) in the month of September when the plant was in its flowering stage. The plant was identified by S.K. Srivastava, Botanical Survey of India, Dehradun, where the herbarium specimen was deposited (Herbarium Voucher No. BSI/NC9(2)/2003-04/Tech./717).

Isolation of the oil: The fresh plant material (400Og) was steam distdled using a copper still fitted widi spiral glass condensers. The distdlates were saturated with NaCl and the od was extracted widi hexane. The hexane extract was dried over anhydrous Na^sub 2^SO^sub 4^ and the solvent was removed using a rotovap at the aspirator pressure and at 30°C to get 2.8 g (yield 0.07% by weight) of the oil.

GC analyses: The GC analyses was perform ed using a Varian 3700 gas Chromatograph fitted with a HP-5 M S capillary column (30 m X 0.25 mm, film thickness 0.25 µm), a flame ionization detector and a SRI model 203 PeakSimple chromatographic data system. The oven temperature was programmed at 50deg;C for first 10 min and dien 3°C/min to 250°C, after which it was maintained isodiermally at 250°C for 5 min. The composition data were taken from area percentage data without the use of correction factors and rounded off to the first decimal place. A co-injection was made of mixture of oil and n-alkanes (C^sub 8^-C^sub 23^) to determine the Retention Indices.

GC/MS analysis: The GC/MS analysis of the od sample was carried out using AGILENT 5973 Network Mass Selective Detector interfaced with AGILENT 6856 GC system fitted with a HP-5MS capillary column (30 m X 0.25 mm, film thickness 0.25 µm) programmed at 50°C for the first 10 min followed by 3°C/min to 230°C and isothermal at 230°C for 10 min. The mass spectra were acquired under EI conditions at 70 eV Helium was used as carrier gas for both GC and GC/MS analyses.

Isolation of bornyl acetate: Two grams of oil was loaded on a column packed with 45 g of silica gel (230-400 mesh) as a slurry in hexane. The column was first eluted widi 100 mL of hexane and thereafter with 50 mL portions of mixtures of diediyl ether in hexane (2%, 5%, 8% and 10%). The ester was eluted in fractions with 8% and 10% diethyl edier in hexane. The ^sup 1^H- and ^sup 13^C-NMR spectra were recorded on a Varian Mercury300 spectrometer at 300 MHz and 75 MHz, respectively using CDCl^sub 3^ as a solvent.

Results and discussion

The GC of the od revealed presence of more than 60 components; however, many of these were present in trace amounts (

These results are quite significantly different from the previously reported composition (2,3). The reports of Sinha et. al. reveal that the plant material was collected from Nainital area and during the same season as was done for the present investigation. It appears that the significant difference in composition between our results and what have been reported earlier, may not be just due to change in soil and environmental factors, it might be due to an error in the identification of plant material analyzed by the earlier audiors (2,3).

The literature reveals several reports on die essential oil composition of Salvia species. A comparison between the essential oil composition of S. leucantha with those reported on other Salvia species, indicates that S. leucantha, in terms of essential oil composition, is closely related with Salvia canariensis, S. confertiflora, S. maxicana, S. microphylla and S. somaliensis of Italy (9), S. gilliesii of Spain (10) and, S. aethiopsis and S. verticillata of Yugoslavia (11). All these species, like S. leucantha are reported to be rich in sesquiterpene hydrocarbons (β-caryophyllene and germacrenes).