Mentha species

Many cycHc ketones occur in natural oils. Jasmone [488-10-8] (3-meth5l-2-(2-pentyl)-2-cyclopenten-l-one) (4) is an odoriferous component of the oil obtained from jasmine flowers. /-Menthone [14073-97-3] (5) is the most frequently occurring of four optically active isomers, and is a colorless Hquid with a minty odor obtained from Mentha species of plants. Muscone [541-91-3] (6) and civetone [542-46-1] (7) are expensive animal products. 

Fagus sylvatica (beech nuts) Mentha species (mints) Rosmarinus officinalis (rosemary) Laurus nobilis (laurel)... 

Sokovic MD, Vukojevic J, Marin PD, Brkic DD, Vajs V and van Griensven LJ. 2009. Chemical composition of essential oils of Thymus and Mentha species and their antifungal activities. Molecules 14(1) 238—249. 

LUPIEN, S., KARP, F., WILDUNG, M., CROTEAU, R., Regiospecific cytochrome P450 limonene hydroxylases from mint (Mentha) species cDNA isolation, characterization, and functional expression of (-)-45-limonene 3-hydroxylase and (-)-45-limonene 6-hydroxylase, Arch. Biochem. Biophys., 1999, 368, 181-192. 

Linalyl acetate is the principal constituent of the essential oils of bergamot, clary sage, lavender and lavandin. It is also present in the essential oils of Salvia officinalis, petitgrain, sassafras, neroli, lemon, lime, a few Mentha species and others. 

In a similar approach, Shishido et al. (241) used oxime 215 [derived from the monoterpene (+)-citronellal (214)] for the synthesis of (—)-mintlactone (218) and (+)-isomintlactone (219), sweet compounds isolated from some Mentha species (Scheme 6.89). Bicyclic isoxazoline 216 was obtained in good yield from the cycloaddition. As expected, the product possessing tra i-l,4-substimtion prevailed. Reductive hydrolysis of the major isomer of 216 using hydrogen-Raney Ni-trimethyl borate provided p-hydroxyketone 217. This compound was dehydrated to give an enone and this was followed by carbonyl reduction-lactonization to complete the synthesis of both lactones 218 and 219 (241). 

Both stereoisomers occur in many essential oils, often as a single enantiomer species. A particularly high concentration (sometimes >50%) is found in oils from Mentha species. The menthones are colorless liquids that possess a typically minty odor the odor of isomenthone is slightly musty. They have a strong tendency to interconvert and are, therefore, difficult to obtain in high purity. Industrial products are mixtures of varying composition. Physical constants of industrially important menthone isomers are listed in Table 1. 

Natural aroma chemicals Isolation and purification via physical processes Citral from lemon grass oil, eugenol from cloves, menthol from Mentha species... 

Limonene (92) is the most widely distributed terpene in nature after a-pinene [68]. The (+)-isomer is present in Citrus peel oils at a concentration of over 90% a low concentration of the (-)-isomer is found in oils from the Mentha species and conifers [26]. The first data on the microbial transformation of limonene date back to the sixties. A soil Pseudomonad was isolated by enrichment culture technique on limonene as the sole source of carbon [69]. This Pseudomonad was also capable of growing on a-pinene, / -pinene, 1-p-menthene and p-cymene. The optimal level of limonene for growth was 0.3-0.6% (v/v) although no toxicity was observed at 2% levels. Fermentation of limonene by this bacterium in a mineral-salts medium resulted in the formation of a large number of neutral and acidic products. Dihydrocarvone, carvone, carveol, 8-p-menthene-1,2-cw-diol, 8-p-menthen-1 -ol-2-one, 8-p-menthene-1,2-trans-diol and 1 -p-menthene-6,9-diol were among the neutral products isolated and identified. The acidic compounds isolated and identified were perillic acid, /Msopropenyl pimelic acid, 2-hydroxy-8-p-menthen-7-oic acid and... 

In other systems, a particular structure may be found as a mixture of diastereoisomers. Peppermint (Mentha x piperita Labiatae/Lamiaceae) typically produces (—)-menthol, with smaller amounts of the stereoisomers (+)-neomenthol, (+)-isomenthol, and (+)-neoisomenthol, covering four of the possible eight stereoisomers (Figure 5.16). Oils from various Mentha species also contain significant amounts of ketones, e.g. (—)-menthone, (+)-isomenthone, (—)-piperitone, or (+)-pulegone. The metabolic relationship of... 

Croteau R (1991) Metabolism of monoterpenes in mint (Mentha) species. Planta Med 57, S10-S14. 

Lupien, S., Karp, R, Ponnamperuma, K., Wildung, M. and Croteau, R. (1995) Cytochrome P450 limonene hydroxylases of Mentha species. Drug Metab. Drug Interact., 12, 245-60. 

The essential oils of the Mentha species are known to be valuable ingredients of pharmaceutical and cosmetic preparations. Menthone, isomenthone, menthol and menthyl acetate, the most important Mentha oil constituents, are defined by their amounts as substantial parameters of mentha oil quality. Even off-line HPTLC/enan-tio-GC coupling has proved to be a valuable method in authenticity control of mint and peppermint oils. After preseparating by HPTLC (silica gel dichloromethane) the menthyl acetate fraction is isolated and directly injected for stereodifferentiation with permethyl p-cyclodextrin. Racemic menthyl acetate was detected by Kreis et al. as a frequently used adulteration of Mentha oils [20]. 

Fig, 6,34 Chiral monoterpenoids from Mentha-species (from ref [94])... 

Fig, 6,35 Simultaneous enantio-MDGC analysis of chiral monoterpenoids from Mentha-species, pre column (A), main column (B) (from ref [94])... 

B. Faber, A. Dietrich and A. Mosandl. Chiral compounds of essential oils. Part XV. Stereodifferentiation of characteristic compounds of Mentha species by multi-dimensional gas chromatography. J. Chromatogr., 666. 161-165 (1994). 

A single active ingredient of a herb may have more then one action that could relieve cough. For example, menthol, extracted from Mentha species, is said to be a local anesthetic, a Ca +-channel blocker, a smooth-muscle relaxant, and a cooling agent. Isolated purified menthol inhibits cough (see later), but which of its modes of action are important has not been determined. 

Spearmint oil. Besides peppermint oils, S. constitutes another important essential oil isolated from Mentha species. It has a typical warm, fresh, green-herby, caramel-mint-like odor and a warm, spicy-herby, somewhat bitter astringent taste. 

Fig. 19.10. Origin of oxygenated monoterpenes in Mentha species (Croteau, 1984 modified and used with permission of the copyright owner, Marcel Dekker, Inc., New York).

Baser, K. H. C., M. Kiirkgiioglu, B. Demirci, T. Ozek, and G. Tarmclar. 2012. Essential oils of Mentha species from Marmara region of Turkey.. 7 Essent. Oil Re.s.. 24 265-272. 

Apart from employing fractional distillation, with or without the application of a vacuum, some essential oil constituents are also obtained on a commercial scale by freezing out from the essential oil, followed by centrifugation at below freezing point of the desired product. Examples are menthol from Mentha species (this is usually further puri ed by recrystallization with a suitable solvent) frani anethole from anise oil, star anise oil, and particularly fennel seed oil and 1,8-cineole from cineole-rich eucalyptus oils. 

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