Monoterpenic phenol

CioH O, Mr l50.22 p-cymen-2-ol (carvacrol), liquid, bp. 238 °C p-cymen-3-ol (thymol), cryst., mp. 50-51 °C p-cymen-8-ol, liquid, bp. II1-1I2°C (16mbar). Aromatic monoterpene phenols or alcohols. 

While present in only a relatively few aromatic herbs, phenolic volatile oils are among the most potent and potentially irritant compounds found in essential oils. Phenols are represented in both major classes of aromatic compounds—the monoterpenes and phenylpropanoids. The major monoterpene phenols, thymol and carvacrol, are found in thyme. Thymus spp., and oregano. Origanum vulgare (Lamiaceae). 

Thymol and carvacrol, two monoterpenic phenol isomers, which are constituents of EOs, induced endothelium-independent relaxation of rat aorta. The effects seem to be related to Ca -release from the sarcoplasmic reticulum and/or the Ca + sensitivity of the smooth muscle cell. Furthermore, it is entirely possible that thymol and carvacrol, at low concentration inhibits the Ca -in ux through the membrane (Peixoto-Neves et al., 2010). 

Peixoto-Neves, D., Silva Alves, K. S., Gomes, M. D., Lima, E. C., Lahlou, S., Magalhaes, P. J. et al. (2010). Vasorelaxant effects of the monoterpenic phenol isomers, carvacrol and thymol on rat isolated aorta. Fundam. Clinic. PharmakoL 24, 341-350. 

Archana PR, Nageshwar Rao B, Satish Rao BS (2011) Modulation of gamma ray-induced genotoxic effect by thymol, a monoterpene phenol dtaivative of cymene. Integr Cancer Ther 10(4) 374-383... 

Thymol (2-isopropyl-5-methylphenol) is the main monoterpene phenol, isomeric with carvacrol, found in thyme essential oil. This compound has revealed several biological properties, such as antibacterial, antifungal, anti-inflammatory, antioxidant, and immunomodulatory."... 

Chlorofonn is too non-polar to dissolve the phenolic compounds under study, but it dissolves many of the monoterpenes, at least to some extent. Because the solubility of some monoterpenes into chloroform was low, different solvent/ solid ratios were tested. These were 50,20,10 and 5 1/kg of dry phloem. The extracts were bright yellow and the strongest colour was with the smallest solvent/solid ratio (51/kg). The colour of the solvent indicated that the solubility of the extractable compounds was not restricting the reaction even with the smallest solvent volume. The taste of the dry samples was evaluated by comparing them to the original phloem sample. The results showed that the mildest taste was in the phloem extracted with a solvent/solid ratio of 50 1/kg and 20 1/kg also had some effect on the taste. The taste of the chloroform-extracted phloem was stabile and it was the same after a week. 

If artificial castoreum scent marks are placed on the banks of a pond, beavers, C. canadensis, are more likely to visit, destroy, and re-mark the sites as the complexity of the artificial odor composition increases (Fig. 6.14). While some single phenolics from castoreum such as 4-ethylphenol trigger marking (Miiller-Schwarze and Houlihan, 1991), the response increases as the mixture grows to 4, 6,10,13, and finally 15 compounds. A mixture of 14 phenolics and 12 neutrals (mostly oxygenated monoterpenes) released responses almost as strong as whole castoreum (Schulte etal., 1995). 

Many nonvolatile and thermally labile allelochemicals can be well separated by liquid chromatography (LC). Identification of the separated components on-line by mass spectrometry (MS) is of great value. Fused-silica LC columns of 0.22 mm ID packed with small-particle material are used in the described LC/MS system. The shape of the column end allows direct connection to a electron impact ion source of a magnetic sector mass spectrometer. Separations by LC are reported and LC/MS mass spectra are shown for monoterpenes, diterpene acids, phenolic acids and cardiac glycosides. The LC/MS system provides identification capability and high-efficiency chromatography with a universal detector. 

Several lines of evidence support the conclusion that allelopathic inhibition of germination and plant growth typically occurs from the joint action of several allelochemicals. Additive or synergistic effects have been shown in bioassays with combinations of monoterpenes, organic acids, and several classes of phenolic compounds. These experiments demonstrate that a specific compound may be present below its threshold for inhibition and still be active in allelopathic interference by its effect in concert with other allelochemicals. 

A wide variety of EOs are known to possess antimicrobial properties and in many cases this activity is due to the presence of active constituents, mainly attributable to isoprenes such as monoterpenes, sesquiterpenes and related alcohols, other hydrocarbons and phenols [8, 9]. 

Chemical structure-activity relationships suggested that phenolic monoter-penes (thymol, methyleugenol) seemed to be the most active, followed by alcohols (terpineol) and other oxigenated monoterpenes (1,8-cineole) [225, 229, 230]. Within the monoterpenes, -pinene was more active than a-pinene [226], and a-pinene was more active than caryophyllene and myrcene [234]. 

Monoterpenes occur in plants in various structural forms some are cyclic while the others are acyclic. They also contain various types of functional group, and depending on their functional groups they can be classified as simple hydrocarbons, alcohols, ketones, aldehydes, acids or phenols. Some examples are cited below. 

Experiments were also carried out at 80 and lOO C. According to our observations at these high temperatures, solid- phase chemical transformations may take place between certain flavor constituents and cyclodextrin hydroxyls/monoterpene alcohols and phenolic compounds appear as a result of a solid-phase transacetylation of terpeneaoetates and phenyl-acetates with the simultaneous formation of cyclodextrin-acetates/. Long term heat treatments of cyclpdextrin-flavor complexes should not be run above 6o°C in order to avoid such phenomena. 

Gavin J, Tabacchi R (1975) Isolation and Identification of Phenolic Compounds and Monoterpenes from Oakmoss (Evernia prunastri (L.) Ach.). Helv Chim Acta 58 190... 

Thymol (isopropyl-m-cresol) is a volatile, phenolic monoterpene produced by several plants including thyme (Thymus vulgaris L.) (Baerheim Svendsen and Scheffer, 1985). Thymol has well-known antiseptic, antifungal, and anthelminthic properties (Wilson et al., 1977) and is also used for food and fragrance applications (Bauer et al., 1990). 

Essential oil recovery and composition showed variation with maturity. C. sativum L. fruits grown in Tunisia gave essential oils at the initial, middle and final stages of maturity, with yields of 0.01, 0.12 and 0.35%, respectively. Essential oil at the first stage of maturity consisted mainly of monoterpene alcohols (14.6%), especially linalool (10.96%). Other constituents were monoterpene aldehydes (2.07%), ethers, hydrocarbons and monoterpene ketones, as well as phenols and sesquiterpenes. 

In summary, Foeniculum is stated to have three species, F. vulgare (fennel), F. azoricum Mill. (Florence fennel) and F. dulce (sweet fennel). Fennel is widely cultivated, both in its native habitat and elsewhere, for its edible, strongly flavoured leaves and seeds. The flavour is similar to, but milder than, that of anise and star anise. Anethole and fenchone are the major constituents of the solvent extract of seed phenols, free fatty acids, carbohydrates, proteins, vitamins and minerals have been reported in varying proportions. In the mature fruit, up to 95% of the essential oil is located in the fruit, greater amounts being found in the fully ripe fruit. Approximately 45 constituents have been determined from fennel seed oil, the main constituents being frans-anethole, fenchone, estragol (methyl chavicol), limonene, camphene, a-pinene and other monoterpenes, fenchyl alcohol and... 

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