Chemical Composition of the Essential Oils of Eugenia hyemalis and Eugenia stigmatosa. Part VI: Section Biflorae

Journal of Essential Oil Research: JEOR, Sep/Oct 2004 by Apel, Miriam A, Sobral, Marcos, Schapoval, Elfrides E S, Henriques, Am�lia T, Et al

Abstract

Essential oils, which were obtained from the leaves of Eugenia hyemalis Cambess. and Eugenia stigmatosa DC., collected in Southern Brazil, were analyzed by GC and GC/MS. Thirty-three compounds were identified in the analyzed samples. The oil obtained from E. stigmatosa is extremely simple, containing more than 90% of physeteric acid [(Z)-tetradec-5-enoic acid], an olefinic fatty acid, accompanied by its esters and tetradecalactones. The major component of E. hyemalis oil is bicyclogermacrene (37.7%), followed by germacrene D (7.0%) and [beta]-caryophyllene (7.4%).

Key Word Index

Eugenia hyemalis, Eugenia stigmatosa, Myrtaceae, essential oil composition, physeteric acid, bicyclogermacrene.

Introduction

In continuity of the chemical survey of essential oils from species of the family Myrtaceae (1-4), this paper reports the chemical composition of Eugenia hyemalis and E. stigmatosa. Both species belong to the informal section Biflorae, characterized by the presence of two or more flowers at the axiles of the leaves. The sectional subdivision of'Eugenia was discussed in a previous paper (4). To our knowledge, no chemical studies of E. hyemalis and E. stigmatosa have been previously reported.

Eugenia hyemalis Cambess. (vernacular name: guamirimburro) is a shrub or treelet, which can grow up to 10 m high. It occurs in the field vegetation and forest formations from Minas Gerais to Rio Grande do Sul, Argentina and Paraguay (5).

Eugenia stigmatosa De Candolle (vernacular name: guamirim) is a treelet which can grow to 6 m high. It occurs in the Brazilian coastal forests from Bahia to Santa Catarina (5).

Experimental

Material: The leaves of Eugenia species were collected in different areas of southern Brazil (Table I). Voucher specimens were deposited at the Herbarium of the Universidade Federal do Rio Grande do SuI (ICN). oils were obtained from the fresh leaves by hydrodistillation for 5 h using a Clevengertype apparatus.

Gas chromatography: GC analyses were performed using a Chromatograph (Shimadzu GC-17A) equipped with a Shimadzu GC 10 software, fitted with a DB-5 fused silica capillary column (25 m x 0.25 mm x 0.25 �m). The oven temperature was programmed from 60�-300�C at 3�C/min, with helium as carrier gas at an inlet pressure of 80 kPa (1 mL/ min). Injector and detector temperatures were set at 220�C and 250�C, respectively. The percentage compositions were obtained from electronic integration measurements using flame ionization detection (FID, 250�C).

Gas-liquid chromatography/mass spectrometry analysis: The samples were analyzed by GC/MS in the same chromatographic conditions as described above, using a Shimadzu QP-5000-quadrupoIe MS system, operating with ionization energy of 70 eV and an interface temperature of 250�C.

Identification of components: The identification of almost all volatile constituents was accomplished by comparison of their GC retention indices, as well as their mass spectra with corresponding data of authentic compounds or of components of reference oils. Some mass spectra were compared with those ofthe NIST (National Institute of Standards and Technology) computer data library or with spectral data given in the literature (1,6).

Purification and identification of physeteric acid:

The main component of the leaf oil of E. stigmatosa was purified by silica gel column chromatography (Merck, 70-230 Mesh ASTM) eluted with a pentane-Et^sub 2^O gradient and identified as (Z)-tetradec-S-enoic acid according to its spectral data (7). The NMR spectral were performed using a Brucker 400, in CDCl^sub 3^.

MS (m/z,rel. int.): 226 (M^sup ^, 5), 208 (22), 166 (21), 138 (20), 124 (31), 110 (41), 96 (71), 81 (92), 69 (100), 55 (95).

^sup 13^C-NMR (400MHz, CDCl^sub 3^): 5179.8 (C-1), 131.3 (C-6), 128.1 (C-5), 33.4 (C-2), 31.8 (C-12), 29.5 (C-8 and C-10), 29.3 (C-9 and C-11), 27.2 (C-7), 26.4 (C-4), 24.6 (C-3), 22.6(C-13), 14.0 (C-14).

^sup 1^H-NMR (400MHz, CDCl^sub 3^): [delta] 5.40 (dt, 1H, J^sub 5,6^10.8 Hz, J^sub 6,7^ 7.2 Hz, H-6), 5.30 (dt, 1H, J^sub 5,6^10.8 Hz, J^sub 4,5^ 7.2 Hz, H-5), 2.35 (t, 2H, J^sub 2,3^ 7.4 Hz, H-2), 2.02 (m, 2H, H-4), 1.98 (m, 2H, H-7), 1.67 (m, 2H, H-3), 1.30 (m, 2H, H-8), 1.25 (m, 10H, H[9-13]), 0.82 (t, 3H, J^sub 13-14^ 6.2 Hz).

Results and Discussion

The essential oils were obtained from fresh leaves of both Eugenia species in low yield (Table I). Altogether, 33 compounds were identified, as listed in Table II.

Eugenia hyemalis essential oil is characterized by a majority of sesquiterpene hydrocarbons with germacrane skeleton, among which bicyclogermacrene (37.7%) was the major component, followed by germacrene D (7.0%), [beta]caryophyllene being also present in significant percentage (7.4%).

The essential oil obtained from E. stigmatosa leaves was totally different, containing more than 90% of (Z)-tetradec-5-enoic acid (physeteric acid) (Figure 1). The ^sup 1^H NMR spectrum, obtained after purification by column chromatography, was characterized by four distinct signals (between 1.5 and 2.5 ppm) corresponding to C^sub 3^, C^sub 4^-C^sub 7^ and C^sub 2^ protons; the data and the correlation among the different signals were confirmed by COSY and HETCOR spectral, the (Z) configuration could be easily deduced from the coupling value (J^sub 5-6^ = 10.8Hz) in the ethylenic system. In the mass spectrum, the fragment M-60 presented relatively intensity (20%), regarding those observed in the saturated fatty acids mass spectra, resulting, in this case, in a MacLafferty clivage of a weak C^sub 4^-H alylic bond. Besides physeteric acid, we found only three components at a level up to 1% of the mixture: its ethyl ester as well as [gamma]- and [delta]-tetradecalactones.