Carvone mints

As another example of the effects of shape and molecular handedness, look at the substance called carvone. Left-handed carvone occurs in mint plants and has the characteristic odor of spearmint, while right-handed carvone occurs in several herbs and has the odor of caraway seeds. Again, the two structures are the same except for their shapes, yet they have entirely different odors. 

Two plants both produce carvone, but the mint leaves yield the "left-handed" form, while the caraway seeds yield the "right-handed" form. 

Examples of monoterpenes include the linear aldehyde citral, which is found in many essential oils, and the (cis) alcohol geraniol, a major component of oil of geranium. Cyclic monoterpenes include limonene, menthol, pinene, camphor, and carvone, major components of lemon oil, mint oil, turpentine, camphor oil, and caraway oil, respectively. Sesquiterpenes include farnesol, a component of rose oil, and bisabolene, a component of Bisabol myrrh. The diterpenes include phytol, a component of chlorophyll, and vita-... 

Major components and compositions of CO2 extracted and distilled spearmint oils are shown in Table 2. A comparison of composition of the produced spearmint oils with the composition of other mint oils (published in the literature [6]) shows that a very special population was investigated. In particular, carvone and its related compounds and pulegone have been found as main components. Gas chromatografic analysis showed significant differences in composition of the SFE products and the distilled oil. The distilled essential oil contained more dihydrocarvone and less pulegone than the CO2 extracted counterpart. 

Menthol (mint) Carvone (caraway seeds) Camphor ... 

The three most important cyclic monoterpenes are L-menthol, l-carvone and a-terpineol (including its esters). L-Menthol occurs in a number of mint oils and is used not only for its minty odour, but also,... 

Carveol (5) is one of the minor components responsible for the odour of spearmint, and is easily prepared by reduction of carvone. Isopulegol (6) is prepared from citronellal, as discussed in the section on menthol below, and is a precursor to other materials in the group. The phenols carvacrol (7) and thymol (8) are important in some herbal odour types, but the major use for thymol is as a precursor for menthol q.v. Piperitone (9) and pulegone (10) are strong minty odorants, the latter being the major component of pennyroyal oil. 1,8-Cineole (11) is the major component of such eucalyptus oils as Eucalyptus globulus. These oils are inexpensive and so there is no need to prepare cineole synthetically. Menthofuran (12) is an important minor component of mint oils and can be prepared from pulegone. 

Carvone is the principal odour component of spearmint oil. Both the oil and synthetic 1-carvone are used as ingredients in mint flavours. The synthetic material is made from d-limonene, which is the major component of orange oil and therefore is available as a by-product of orange juice production. Quest International is the world s major producer of 1-carvone. The classical chemistry used to produce 1-carvone is shown in Figure 4.19. The chirality of the carvone is crucial to the odour, since the enantiomeric d-carvone has an odour reminiscent of dill or caraway rather than spearmint. It is therefore important that any... 

Spearmint, Mint. Dried leaves and tops ol Mentha spicata L. (At. viridis L.), Labiatae, Habit, Europe, Asia widely cultivated in U,S, Principal active constit is a volatile oil which contains at least 50% carvone,... 

Regiospecific hydroxylation of the monoter-pene (—)-46 -limonene at the C-3 or C-6-allylic positions to yield (—)-menthol (peppermint) or (—)-carvone (spearmint), respectively, is accomplished by the last two functionally characterized CYP71DS, the CYP71D13 and CYP79D18 found in commercial mint species (Mentha sp.) . 

As an example of the co-existence of systematic, semi-systematic and trivial names, we could look at the monoterpenoid ketone, carvone. Carvone occurs in both enantiomeric forms in nature, the laevo-form in spearmint and the dextro-form in caraway. The trivial name carvone is derived from the Latin name for caraway, Carum carvi. The basic carbon skeleton is that of l-isopropyl-4-methylcyclohexane. This skeleton is very common in nature and is particularly important in the genus Mentha, which includes various types of mint, since it forms the backbone of most of the important components of mint oils. The skeleton has therefore been given the name p-menthane and the numbering system used for it is shown in Figure 1.3. Therefore, any of the following names may be used to describe the same molecule carvone, p-mentha-1,8-dien-6-one and 1 -methyl-4-(l-methylethenyl)cyclohex-l-ene-6-one. To classify it, we could say it was an unsaturated ketone of the /7-menthane family of monoterpenoids. 

Having reviewed the principles of stereochemistry, we are now in a position to investigate the chemistry of mint. There are many species and sub-species of mint and their chemistry is dominated by monocyclic monoterpenoids, mostly alcohols and ketones. Some of the more important ones are shown in Figure 4.9. By far the most important of these are carvone and menthol, both of which will be discussed in more detail later. 

Essential oils contain a variety of compounds divided into two main groups hydrocarbons and oxygenated compounds. For garden mint, the essential oil is mainly carvone (oxygenated monoterpene) and limonene (monoterpene hydrocarbon). How does the microwave energy effect differ for these two different aroma compounds It would be reasonable to believe that the more polar the compound the more readily the microwave irradiation is absorbed, because of the better interaction between the electromagnetic wave and compound, so the oil obtained contains more of the more polar aromatic components. This would seem to correspond well to the observed behavior of carvone (polar compound) and limonene (non polar compound) (Table 22.5). 

The odors of caraway seeds (left) and mint leaves (right) arise from the enantiomers of carvone, which differ in arrangement of the atoms attached to the indicated ( ) carbon. 

These are almost universal in essential oils, acting also as precursors of the more complex, oxidised terpenes. Limonene, for example, is the precursor of the main constituents of the monoterpenes in mints, Mentha spp. (Lamiaceae), including carvone and menthol... 

Carvone (C10H14O) is the main component of spearmint oil. It has a pleasant aroma and mint flavor. Carvone is offen added to chewing gum, liqueurs, soaps, and perfumes. Calculate the mass of carbon in 55.4 g of carvone. 

Limonene is a colourless liquid hydrocarbon classified as a cyclic terpene. The isomer found in orange peel is (+)-limonene (Figure 20.71). It is thought that its high abundance in this part of the fruit is connected with the fact that it is an insecticide. As well as its smell, limonene also contributes to the flavour of the fruit and as such has been used as a food additive for many years. Limonene is an important precursor in the biosynthesis of (-)-menthol, which is the major component of mint and the molecule responsible for the herb s refreshing taste. It is used in chemical synthesis as a precursor to carvone and as a renewably based solvent in cleaning products. It is readily prepared in the laboratory by steam distillation of the zest of an orange or lemon. 

Spearmint fM. spicata) oil is characterized by having a high content of 1-carvone, which is present at about 56%. Its sensory and physico-chemical characteristics are entirely different from those of peppermint. The compositional data of the major constituents of various mint oils is given in Table 8.15. An article by Lawrence provides a more detailed summary of mint oil composition [27]. 

Monoterpenic ketones are frequently very important aromatic substances of many food raw materials, spices and medicinal herbs. Monocyclic ketone (-F)-carvone (8-50) is a key component of caraway and diU oils, where it is accompanied by (-F)-( )-dihydrocarvone, that is (lS,4S)-dihydrocarvone (8-50) that also possesses caraway odour. (-)-Carvone (8-50) is a typical component of spearmint essential oil, where it is accompanied by (-)-( )-dihydrocarvone, (lE,4E)-dihydrocarvone, which has the same odour (see Table 8.32). Isomeric ( )-menthone (8-50) and its precursor (-F)-pulegone (8-50) occur in the essential oils of the European pennyroyal Menthaptdegium, Lamiaceae), a traditional culinary herb and folk remedy, and other Mentha species (such as M. longifolia), as well as in marjoram essential oil. In the essential oil of mint, (-)-menthone is accompanied by (-F)-isomenthone (8-50) and other terpenoids. 

Analysis of individual forms is also important to determine the authenticity of foods or essential oils. The presence of certain forms, such as the geometrical (E)-isomers, is often evaluated as an off-flavour. For example, (-F)-(E)-Hmonene (8-5) is a natural component of citrus essential oils and has a citrus smell like oranges. The isomer (-)-(S)-limonene (8-5), which is the main component of essential oils of silver fir Abies alba, Pinaceae), other conifers and various types of mints Mentha spp.), has a smell reminiscent of turpentine. The alcohol (-)-(E)-Hnalool, also known as licareol (8-18) has a strong woody smeU like lavender, but (-F)-(S)-isomer, also known as coriandrol (8-18) has a sweet smell with lavender tones. Another alcohol (-)-(E)-oct-l-en-3-ol (8-16), has an intense smell of fresh mushrooms, but (-F)-(S)-isomer (8-16) has a smell resembling vegetables with faint mushroom notes. The ketone (-)-(E)-carvone (8-50) has a mint-like smell (and is the main component of spearmint essential oil), while its isomer (-F)-(S)-... 

Over half of the organic compoimds in drugs are chiral, and the different enantiomers have different effect. For example, Ritalin prevents hyperactivity in children in one enantiomer, whereas it has no effect when the opposite enantiomer is used. Another example is thalidomide one enantiomer of thalidomide can cure morning sickness of pregnant women, whereas the other causes birth defects. Om nose is also sensitive to the chirality of the odor molecules. For example, (+) limonene has an orange smell the opposite enantiomer smells like lemon. Similarly, (+) carvone smells like mint, whereas (-) carvone has the smell of caraway. 

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