New Compounds from the Essential Oil and Absolute of Lavandula luisieri L.

Journal of Essential Oil Research: JEOR, Sep/Oct 2004 by Lavoine-Hanneguelle, Sophie, Casabianca, Herv�

Abstract

Some new constituents were discovered in a very unusual Spanish lavender: Lavendula luisieri (Rozeira) Riv. Mart. The essential oil of L. luisieri, which is produced on an industrial scale, was analyzed by a combination of GC and GC/MS. Many components identified were irregular monoterpenoids, with a cyclopentanic structures unique in the plant kingdom, like [alpha]-necrodyl acetate (20-25% of the oil) or [alpha]-necrodol. The new structures identified were: 3,4,4-trimethyl-2-cyclohexen-1-one,3,4,4-trimethyl-5-hexen-2-one,2,3,4,5-tetramethyl-2-cyclopenten-1-one,2,3,5,5tetramethyl-4-methylene-2-cyclopenten-1-one, 1,1,2,3-tetramethyl-4-hydroxymethyl-2-cyclopentene, 2,4,5,5tetramethyl-cyclopentadien-1,3-carboxylic acid and selina-4,7(11)-diene. A monoterpene whose exact structure remains unknown, is present in the oil at a level of (2-4%). Other main compounds were 1,8-cineole and lavandulyl acetate.

Key Word Index

Lavandula luisieri, Labiatae, essential oil composition, absolute composition, a-necrodyle acetate, 1,8-cineole.

Introduction

Lavandula luisieri (Rozeira) Riv. Mart, is related to the stoechas Gingins section of the genus Lavandula, family Labiatae, as well as Lavendula stoechas L. and Lavendula pedunculata Cav. (1,2). The morphological characteristics of those plants are closely related to each other, and an inexperienced person may confuse the species. All possess long purple bractea on their flowering tops. The small bushes bloom at the beginning of spring, growing along with Cistus ladaniferus on the hills of Andalucia, near Seville (Spain).

The essential oil of L. luisieri is drastically different from these obtained by distillation of the flowering tops of the other members oiuiestoechas group or other lavandulae like lavender, spike or lavandin. The oil of L. pedunculata and L. stoechas contain mainly camphor, fenchone, pinenes, and 1,8-cineole (3,4). 1,8-Cineole, camphor and linalool are the main constituents of spike, while linalool, linalyl acetate are present at high levels in lavender and lavandin oils.

Garcia-Vallejo et al. found that L. luisieri oil had an atypical composition, unique in the plant kingdom (5). They discovered, along with 1,8-cineole, lavandulyl acetate, [alpha]-necrodol and [alpha]-necrodyl acetate as main constituents. [alpha]-Necrodol was first discovered by Eisner et al. as a constituent of the defensive spray of a South American carrion beetle: Necrodes surinamensis (6-8). Those cyclopentanic monoterpenoids structures were then named 'necrodane.'

The purpose of our study was to identify more constituents of the oil of L. luisieri and to analyze the absolute.

Experimental

Distillation: The aerial parts of the flowering plant were collected in the region of Almaden de la Plata, near Seville (Spain), and then hydrodistilled on an industrial scale. The yield of the fresh flowering plants was about 0.3% (w/w).

The oil of L. luisieri leaves or flowers was obtained by separate water distillation on the laboratory scale (0.4% g/g on each sample). The flowers were manually separated from the twigs and leaves, just before distillation.

Extraction: The absolute was obtained by ethanolic extraction of the hexane extract (concrete) produced from the aerial parts of the fresh flowering plant. The alcoholic miscella was cold filtered to remove waxes, and then concentrated. The yield was about 0.5% (w/w).

Isolation of compounds: The oil was fractionated under vacuum using a spinning band fractional distillation, and then the fractions were purified on a preparative silica gel and then silver nitrate impregnated silica gel column. Elutents were pentane with increasing amounts of diethyl ether. Those solvents were freshly distilled. Some of the unknowns that were isolated and purified as above had their structures elucidated by NMR.

Analysis

GC: The GC analyses were carried out on an Agilent 6890 Chromatograph equipped with an FID detector, and a capillary column: phase INNOWAX, 60 m x 0.32 mm, film thickness 0.5 �m. Injector temperature was 250�C and detector temperature: 280�C; injection volume: 0.2 �L in mode split, with a split ratio of 1/80. The carrier gas was helium at 1.3 mL/min. Oven temperature: gradient 2 min at 60�C, then 60�-245�C at 2�C/min, then 20 min at 245�C. Quantitative data were obtained by electronic integration of FID area percents without the use of response factors.

GC/MS: The GC/MS analyses were carried out on an Agilent 5973N system, with a capillary column phase Innowax, split ratio: 1/100; carrier gas: helium, 1.3 mL/min. Oven temperature: gradient 2 min at 60�C, then 60�-180�C at 3�C/min, then 180�-245�C at 8�C/min, 20 min at 245�C, MS: 70 eV, 230�C.

The MS spectra were compared to those of two databanks: Wiley and CNRS (flavor and fragrances) data.

NMR: ^sup 1^H- and ^sup 13^C-liquid state NMR experiments were conducted with a Bruker Avance 200 spectrometer in 5 mm diameter tubes at 323�K, with CDCl^sub 3^ as solvent. Delay time Dl was 2 s, spectral width (SW) 2297.8 Hz for ^sup 1^H and 10482.18 Hz for ^sup 13^C, pulse angle 30� and memory space of 32�K (^sup 1^H) or 32 K (^sup 13^C). Acquisition time was about 7.13 s for ^sup 1^H and 1.56 s for ^sup 13^C.