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This ketone was originally isolated from the Arbor Vitae -Thuja occidentalis (Cupressaceae), however it also occurs in some unrelated plants, particularly those of the Artemisia genus (Asteraceae) including wormwood (A absinthium) and mugwort (A vulgaris). Other sources are tansy - Tanacetum vulgare (Asteraceae), sage (Salvia officinalis) and clary sage (S. sclarea) from the Lamiaceae family. Many of these herbs are steeped in folklore with reputations as stimulants, psychedelics, anthelmintics, abortifacients and as ingredients in intoxicating beverages such as vermouth and absinthe [Albert-Puleo 1978]. The above herbs are all classed as emmenagogues and are contra-indicated for pregnancy. Sage oil is the least toxic of
this group despite containing 50% thujone, however care is still necessary in its use [Tisserand 1988]. Pulegone, a related ketone found in oil of pennyroyal Mentha pulegium (Lamiaceae), has similar properties, and the same precautions on its use apply as for thujone containing oils.
The oxides are a very small group of essential oils, consisting basically of two unrelated oils, the monoterpene ether 1,8-cineole and the peroxide ascaridole.
1,8-cineole is one of the most widely distributed compounds in the plant world, being an oxidized derivative of other monoterpene compounds. Cineole is the major constituent of Eucalyptus oil derived from numerous species of Eucalyptus (Myrtaceae) - hence the alternative name eucalyptoi. It is also the major constituent of oil of cajuput - Melaleuca cajuputi (Myrtaceae). Cineole is an expectorant and mucolytic agent, and is a universal ingredient in cough lozenges and other medications.
Eucalyptus oils vary in aroma and quality according to the level of cineole and of the minor constituents present in each oil. Cineole rich oils (generally from Eucalyptus globulus) are preferred for medicinal use where their expectorant property is highly valued, however other species with a different balance of compounds are sometimes preferred - especially by aromatherapists.
These include E. radiata with the hydrocarbons a-terpineol and pinene and E. dives containing phellandrene and the ketone piperitone. All Eucalyptus oils are renowned for their antiseptic qualities, while some species have been shown to inhibit viruses as well. Oils high in cineole and terpene hydrocarbons are considered the most effective against influenza viruses [Schnaubelt 1988/891. The synergistic activity of using two or more essential oils
together can result in an even stronger antimicrobial activity, as demonstrated in an experiment where the addition of basil oil to eucalyptus oil increased the bactericidal activity twenty-fold! [Brud & Gora 1989].
Ascaridole, a terpene peroxide, is considered to be the most highly toxic of all the essential oils [Tisserand 1988].
It is the main constituent of wormseed oil - from Chenopodium ambrosioides (Chenopodiaceae) and a lesser constituent of oil of boldo, from Peumus boldo (Monimaceae). Ascaridole is strongly anthelmintic though its use is limited by its toxic nature. Wormseed is sometimes used in a crude form, ie. powder or extract where it is relatively safe to use in low doses.
Most esters are formed by reaction of terpene alcohols with acetic acid. They are amongst the most widespread volatile oil compounds, though they are generally present in small amounts. However their distinctively fragrant aromas characterise many of the oils in which they appear. Oil of lavender - Lavandula spp. (Lamiaceae) - contains the alcohol linalol (also called linalool) along with its ester linalyl acetate.
Most esters are gentle, non-irritant compounds, whose action is mainly sedative and anti-spasmodic [Schnaubelt 1989]. Examples of these are found in oils of lavender, roman chamomille - Anthemis nobilis (Asteraceae), clary sage - Salvia sclarea (Lamiaceae) and bergamot - Citrus aurantium (Rutaceae). Less benign esters are found in oils of wintergreen and mustard (see below).
Derived from oil of wintergreen - Gaultheria procumbent (Ericaceae). Methyl salicylate is an aromatic ester derived from cinnamic acid and methanol, though it can now be produced synthetically [Tyler 1988]. It is mainly used in
topical applications and linaments as a counter-irritant and antirheumatic. Internal administration is not recommended since it is quite toxic in large doses.
This is a sulphur compound derived from oils of mustard -Brassica nigra and spp. and horseradish - Cochlearia armoracia (Brassicaceae). These oils are extremely toxic and irritant to the eyes, skin and mucous membranes and should not be used therapeutically - either externally or internally [Tisserand 1988]. Horseradish and mustards are best used as foods or in plant extracts. Allyl isothiocynate and similar compounds from the Allium genus, are known to have antimicrobial and antitumor properties.