Sesquiterpene hydrocarbons of cold-pressed lime oils

In-Depth Qualitative Analysis of Lime Essential Oils Using the Off-Line Combination of Normal Phase High Performance Liquid Chromatography and Comprehensive Two-Dimensional Gas Chromatography-Quadrupole Mass Spectrometry

The present research is focused on the in-depth qualitative analysis of three types of lime essential oil (EO), viz., Key (A and B) and Persian, using the off-line combination of normal phase high performance liquid chromatography (NP-HPLC) and comprehensive two-dimensional gas chromatography-quadrupole mass spectrometry (GC × GC-QMS). The first analytical dimension (NP-HPLC) was exploited for the isolation of the hydrocarbon constituents from the oxygenated ones. Each fraction was then reduced in volume and analyzed using (cryogenic modulation) GC × GC-QMS. Peak assignment was carried out through the combined use of mass spectral database and linear retention index matching processes. The powerful four-dimensional technology enabled the separation and identification of a very high number (153) of lime essential oil volatile compounds.

Volatile Compounds in Citrus Essential Oils: A Comprehensive Review

The essential oil fraction obtained from the rind of Citrus spp. is rich in chemical compounds of interest for the food and perfume industries, and therefore has been extensively studied during the last decades. In this manuscript, we provide a comprehensive review of the volatile composition of this oil fraction and rind extracts for the 10 most studied Citrus species: C. sinensis (sweet orange), C. reticulata (mandarin), C. paradisi (grapefruit), C. grandis (pummelo), C. limon (lemon), C. medica (citron), C. aurantifolia (lime), C. aurantium (bitter orange), C. bergamia (bergamot orange), and C. junos (yuzu). Forty-nine volatile organic compounds have been reported in all 10 species, most of them terpenoid (90%), although about half of the volatile compounds identified in Citrus peel are non-terpenoid. Over 400 volatiles of different chemical nature have been exclusively described in only one of these species and some of them could be useful as species biomarkers. A hierarchical cluster analysis based on volatile composition arranges these Citrus species in three clusters which essentially mirrors those obtained with genetic information. The first cluster is comprised by C. reticulata, C. grandis, C. sinensis, C. paradisi and C. aurantium, and is mainly characterized by the presence of a larger abundance of non-terpenoid ester and aldehyde compounds than in the other species reviewed. The second cluster is comprised by C. junos, C. medica, C. aurantifolia, and C. bergamia, and is characterized by the prevalence of mono- and sesquiterpene hydrocarbons. Finally, C. limon shows a particular volatile profile with some sulfur monoterpenoids and non-terpenoid esters and aldehydes as part of its main differential peculiarities. A systematic description of the rind volatile composition in each of the species is provided together with a general comparison with those in leaves and blossoms. Additionally, the most widely used techniques for the extraction and analysis of volatile Citrus compounds are also described.

Chemical composition of hexane extract of Citrus aurantifolia and anti-Mycobacterium tuberculosis activity of some of its constituents

The main aim of this study was to isolate and characterize the active compounds from the hexane extract of the fruit peels of Citrus aurantiifolia, which showed activity against one sensitive and three monoresistant (isoniazid, streptomycin or ethambutol) strains of Mycobacterium tuberculosis H37Rv. The active extract was fractionated by column chromatography, yielding the following major compounds: 5-geranyloxypsoralen (1); 5-geranyloxy-7-methoxycoumarin (2); 5,7-dimethoxycoumarin (3); 5-methoxypsoralen (4); and 5,8-dimethoxypsoralen (5). The structures of these compounds were elucidated by 1D and 2D NMR spectroscopy. In addition, GC-MS analysis of the hexane extract allowed the identification of 44 volatile compounds, being 5,7-dimethoxycoumarin (15.79%), 3-methyl-1,2-cyclopentanedione (8.27%), 1-methoxy-ciclohexene (8.0%), corylone (6.93%), palmitic acid (6.89%), 5,8-dimethoxypsoralen (6.08%), a-terpineol (5.97%), and umbelliferone (4.36%), the major constituents. Four isolated coumarins and 16 commercial compounds identified by GC-MS were tested against M. tuberculosis H37Rv and three multidrug-resistant M. tuberculosis strains using the Microplate Alamar Blue Assay. The constituents that showed activity against all strains were 5 (MICs = 25-50 mg/mL), 1 (MICs = 50-100 mg/mL), palmitic acid (MICs = 25-50 mg/mL), linoleic acid (MICs = 50-100 mg/mL), oleic acid (MICs = 100 mg/mL), 4-hexen-3-one (MICs = 50-100 mg/mL), and citral (MICs = 50-100 mg/mL). Compound 5 and palmitic acid were the most active ones. The antimycobacterial activity of the hexane extract of C. aurantifolia could be attributed to these compounds.

Suppression of Linalool Acetate Production in Lavandula x intermedia

Linalool acetate, one of the major constituent of several essential oils, is heat-labile and decomposes upon exposure to the high injector temperature during gas chromatography. Here we report the development of an improved method for detection of this compound by gas chromatography mass spectrometry (GCMS) using cold on-column injection of the sample. By using this sensitive method, it has been demonstrated that a lavandin (L.x intermedia) mutant accumulates trace quantities of linalool acetate and camphor and higher amounts of cineole and borneol compared to its parent. This plant, which very likely carries a point mutation in one or more of the genes involved in essential oil production, provides a unique tool for investigating regulation of essential oil biogenesis in plants.

Ab initio analysis of the Cope rearrangement of germacrane sesquiterpenoids

The energetics of the Cope rearrangement of 17 germacrane sesquiterpenoids to their respective elemane forms have been calculated using both density functional theory (B3LYP/6-31G*) and post Hartee-Fock (MP2/6-31G**) ab initio methods. The calculations are in qualitative agreement with experimentally observed Cope rearrangements, but the two methods give slightly different results. MP2 calculations generally show more favorable elemene energies compared to the respective germacrenes (by around 3-4 kcal mol(-1)) and smaller activation energies (by 2-3 kcal mol(-1)). Additionally, neither method is accurate enough to consistently reproduce the germacrene/elemene equilibrium. Apparently, the generally small energy differences between the two forms in these sesquiterpenoids cannot be adequately reproduced at these levels of calculation.

Pharmacological properties of citrus and their ancient and medieval uses in the Mediterranean region

This paper reviews the pharmacological properties of Mediterranean-grown citrus species (Citrus L., Rutaceae), including citron (Citrus medica L.), lime (Citrus xauantiifolia [Christm.] Swingle), lemon (Citrus xlimon [L.] Osbeck), bitter orange (Citrus xaurantium L.) and pomelo (Citrus maxima [Burm.] Merr.), as referred to in ancient, medieval and 16th century sources. The virtues of the species reported in these texts were compared to those known to modern science. A much broader spectrum of pharmacological properties was recorded by these early writers than one might expect. The use of the citron and lemon as antidotes for 'poison and venom' is recorded in the very earliest material. According to modern scientific literature the citron and the bitter orange may possess anti-cancer activity, lime may have an immunomodulatory effect in humans, and the pomelo may be useful for treating circulatory problems. Lemons might even ease hangover symptoms. Research is required to confirm these properties.