Chemical composition of the essential oil from Microlicia graveolens growing wild in Minas Gerais

Chemical composition of the essential oil from Microlicia graveolens growing wild in Minas Gerais

Anja B. Toudahl^I,II; Sidney A. V. Filho^I; Gustavo H. B. Souza^I; Luisa D. Morais^I; Orlando D. H. dos Santos^I; Anna K. Jäger^{* , II}

^IDepartamento de Farmacia, Universidade Federal de Ouro Preto, Brazil

^IIDepartment of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Denmark

ABSTRACT

The chemical composition of the essential oil of the aerial parts of Microlicia graveolens DC., Melastomataceae, growing wild in the mountains of Minas Gerais, Brazil, was investigated for the first time. A pale orange to colourless oil was obtained in a yield of 4.8%. The oil was analyzed by GC-MS. The main components were (+)-trans-pinocarvyl acetate (78.9%), (-)-trans-pinocarvyl acetate (5.5%) and β-pinene (3.8%).

Keywords: essential oil composition, Microlicia graveolens, Melastomataceae, trans-pinocarvyl acetate

Introduction

The genus Microlicia comprises approximately 100 species and is native to Brazil. The genus occurs typically as herbs or shrubs in an altitudinal ecosystem characterized by sandy or rocky soils predominantly covered by open vegetation (campos rupestres) (Bomfim-Patrício et al., 2001). Microlicia graveolens DC., Melastomataceae, is native to Minas Gerais and is abundant in the area around Ouro Preto. It is an herbaceous perennial plant found in the mountains.

The purpose of this study was to examine the chemical composition of the essential oil isolated by hydrodistillation from the aerial parts of M. graveolens.

Materials and Methods

The aerial parts of Microlicia graveolens DC., Melastomataceae, were collected in the beginning of October 2009 in the mountains at Ouro Preto-MG, Brazil. The plant material was identified by Maria C. T. B. Messias and a voucher specimen (nº OUPR-5731) was deposited at the Herbarium of Department of Botany, Institute of Biological Sciences, Federal University of Ouro Preto-MG, Brazil.

The essential oil was obtained from dried aerial parts by steam distillation for 5 h. The oil was analyzed by GC-MS on an Agilent 6890N Network GC system coupled to a 5973 Network Mass Selective Detector. GC conditions: injector temperature: 150 ºC; temperature programme: start 50 ºC, 20 ºC/min to 300 ºC; column: HP5MS. A NIST library was used for comparison of MS data. Retention indices were determined relative to n-alkanes (Fluka).

In order to isolate the main component, transpinocarvyl acetate, 1 mL of the essential oil was applied to a Merck Silica gel column (600 x 16 mm) and eluted with toluene:ethyl acetate (93:7). Fractions were analysed by TLC on Merck Silica gel 60 F₂₅₄ plates eluted with toluene:ethyl acetate (93:7), and fractions containing trans-pinocarvyl acetate were combined. Solvent was removed by rotational evaporation under reduced pressure. Optical rotation was measured in EtOH on a Jas.Co DJP370 Digital Polarimeter. ¹H-NMR was recorded in CDCl₃ on a Varian Mercury 300 MHz instrument: δ 5.68, 1H, t; δ 4.84, 1H, q; δ 4.77, 1H, d; δ 2.56 1H, multiplet; δ 2.49, 1H, quint; δ 2.31, 1H, quint-d; δ 2.1, 1H, q; δ 2.14, 3H, s; δ1.70, 1H, q-t; δ 1.48, 1H, d; δ 1.26, 3H, s; δ 0.79, 3H, s.

Results and Discussion

After steam distillation of the aerial parts of Microlicia graveolens DC., Melastomataceae, a pale orange to colourless oil was obtained in a yield of 48 mL/kg. This is a very high yield, making the species a candidate for commercial production. The oil had a very pleasant, clean smell, which could have commercial value as a fragrant in hand soaps or household cleaning products.

The detailed chemical composition of the essential oil is presented in Table 1. In total thirteen compounds were identified, representing 99.8% of the oil composition. The oil was mainly composed of (+)-trans-pinocarvyl acetate as the major component (78.9%) followed by (-)-trans-pinocarvyl acetate (5.5%) and β-pinene (3.8%). Trans-pinocarvyl acetate is a chiral compound. To determine optical rotation of the major compound, it was isolated from the oil by column chromatography. Trans-pinocarvyl acetate isolated from M. graveolens had an optical rotation of [α]²⁸₅₈₉ = + 31.9º. NMR data were recorded, and largely matched those reported for trans-pinocarvyl acetate (Agarwal et al., 2005; Corbet et al., 2008).

Trans-pinocarvyl acetate has previously been detected in Dracocephalum speciosum, a Lamiaceae species from Himalaya, where it constituted 60.5% of the essential oil (Agarwal et al., 2005), and in flower heads of Egletes viscosa, Asteraceae, where it constituted 51.7% of the oil (Lima et al., 1996) and in Salvia euphratica, Lamiaceae, where it constituted 16.8% of the oil (Baser et al., 1998). It was at the time claimed that D. speciosum essential oil appeared to be the only major source of natural trans-pinocarvyl acetate. However, with the findings of this study, the essential oil of M. graveolens must now be regarded as the major natural source of trans-pinocarvyl acetate.

Acknowlegements

The authors thank the Fundação de Apoio à Pesquisa de Minas Gerais for financial support. Thanks to Maria C. T. B. Messias of the Federal University of Ouro Preto for botanical identification.

Received 24 Aug 2011

Accepted 7 Oct 2011

References

• Agarwal SC, Kapahi BK, Thappa RK 2005. Essential oil constituents of himalayan Dracocephalum speciosum Benth. J Essent Oil Res 17: 94-95.
• Baser KHC, Kürkcüoglu M, Aytac Z 1998. Composition of the essential oil of Salvia euphratica Montbret et Aucher ex Bentham var. euphratica from Turkey. Flavour Fragr J 13: 63-64.
• Bomfim-Patrício MC, Salatino A, Martins AB, Wurdack JJ, Salatino MLF 2001. Flavanoids of Lavoisiera, Microlicia and Trembeya, Melastomataceae, and their taxonomic meaning. Biochem Syst Ecol 29: 711-726.
• Corbet M, Ferjancic Z, Quiclet-Sire B, Zard SZ 2008. Radical, one-step approach to o-chlorophenyl thioethers from xanthates. A rapid access to vinylsilanes. Org Lett 10: 3579-3582.
• Lima MAS, Silveira ER, Marques MSL, Santos RHA, Gambardela MTP 1996. Biologically active flavonoids and terpenoids from Egletes viscosa. Phytochemistry 41: 217-223.

Publication Dates

• Publication in this collection
  20 Mar 2012
• Date of issue
  June 2012

History

• Received
  24 Aug 2011
• Accepted
  07 Oct 2011