Species Mentha piperita

It was stated that the chromatographic analysis of the flavonoid profde may help the determination of taxonomic relationships between these species [125], The optimization of the separation of flavonoid glycosides of Mentha piperita (Laminaceae) was carried out on silica, amino, cyano and C18 HPTLC statinoary phases. The investigation was motivated by the spasmolytic, carminative and cholagogue characteristics of the plant. Air-dried and powdered leaves of peppermint (300 g) were extracted with methanol-water 1 1 v/v at ambient temperature. The suspension was filtered, concentrated to 200 ml acidified to pH 3 with formic acid and separated in an ODS column (400 X 40 mm i.d. particle size 40 pm). 

Menthol is the isomer that occurs most widely in nature. It is the main component of peppermint and cornmint oils obtained from the Mentha piperita and Mentha arvensis species. Esterified menthol also occurs in these oils (e.g., as the acetate and iso valerate). Other menthol stereoisomers may be present in these oils as well. 

Therea renumerous species of mint including peppermint, Mcnf/zapipenta, spearmint, Mentha spicata, and cornmint, Mentha arvensis. Mentha piperita is actually a hybrid species bred from spearmint Mentha spicata and watermint Mentha aquatica. They all contain subspecies and chemotypes. Mints have a long tradition of culinary, fragrance, cosmetic and therapeutic applications. 

Menthanes, which include menthol, menthonc, terpineol, and carvone, are some of the best known monoterpene-based chiral synthons in organic synthesis. They are all relatively inexpensive and are commercially available in bulk quantities. Menthols and their corresponding ketones, menthones. were first isolated from peppermint oils of various species of Mentha piperita L [30]. Menthones can exist in two diastereomeric forms, each with two enantiomers. The ones with the methyl and isopropyl groups in a Zrans-orientation are termed menthones, whereas those with the two in a cz.s-orientation are isomenthones. /-Menthone (22), also denoted as (7A,4S)-(-)-menthone. is the most abundant stereoisomer and is obtained by the dry distillation of the wood of Finns palustris Me II [31]. It can also be produced chemically by chromic acid oxidation of /-menthol (23) [32]. /-Menthone is commercially available in bulk quantities with optical purities of 90-98% ee [33]. 

Menthol is a cyclic alcohol present in the volatile oil of several species of mint such as Mentha piperita and Mentha aevensis. It is responsible for the typical minty smell and flavour. (-)-Menthol produced a dose-dependent increase in the pain threshold in the mouse hot-plate and abdominal constriction tests. The antinociceptive effects of (-)-menthol were antagonized by the unselective opioid antagonist naloxone and by the selective kappa-antagonist nor-NBI. Thus, menthol has analgesic properties mediated by selective activation of kappa-opioid receptors. 

EOs have been used for therapeutic purposes and as cosmetics through human history. Their antimicrobial effects and their use in skin formulations have been known for centuries [82], which probably led to investigatiOTis of their antiviral activities on viral skin diseases. Indeed, human herpes viruses, for example, HSV-1 and HSV-2, are the most investigated viruses with EOs [83-94]. Topical treatments containing extracts from lemon balm and sage extracts are available for herpes labialis [80]. EOs obtained from Santolina insularis [85], Melissa officinalis L. [82], Melaleuca species [87], Houttuynia cordata [88], Australian tea tree and eucalyptus [90], Mentha piperita [91], and Salvia fruticosa [93] exhibited direct inactivation of HSV. 

The biosynthetic route to menthol, starts from isopentenyl- and dimethylallyl diphosphate, which in the case of mint derive from the triose-pyruvate pathway, and consists of eight discrete steps (see also section 7.1.2). This route was established by feeding experiments with radio-lahelled intermediates and cell-free enzyme studies. [110] Condensation of isopentenyl- and dimethylallyl diphosphate gives geranyl diphosphate, which is cyclised to (-)-limonene. Both steps are Mg +-dependent. By-products of the cyclisation are around 2 % of myrcene and both, a- and y -pinene. The limonene synthases in Mentha piperita and Mentha spicata are identical, which shows how closely related to each other the species are. 

The enzymes responsible for the hydroxylation of monoterpenes such as (— )-limonene (11) from peppermint Mentha piperita), spearmint Mentha spicata), and perilla Per-ilia frutescens) have been isolated and characterized (Karp et al., 1987,1990). Microsomal preparations from the epidermal oil glands of these plants catalyze the NADPH and 02-dependent allylic hydroxylation of (- )-(45)-limonene (the major olefinic constituent of each of the three species) at C-3, C-6, and C-7, respectively, to produce (- )-rra j-isopiper-itenol (34), (- )- m 5-carveol (35), and (- )-perillyl alcohol (36) (Fig. 19.9) (Karp et al., 1990). These transformations are the key steps in the biosynthesis of oxygenated monoterpenes in the respective species. The enzymes appear to be... 

The species-speci c behavior in these biogenetic transformations is demonstrated by the fact that the related species Mentha citrata (syn. M. piperita var. citratd) shows an opposite tendency as the compound linalool increases by approximately 30% during owering, while the corresponding ester, linalyl acetate, is decreasing at the same time (Malizia et al., 1996). 

Linalool (3) is a monoterpene commonly found as a major volatile component of EOs in several aromatic plant species, such as Lavandula angustifoUa Mill. (Lamiaceae), Rosa damascene Mill. (Rosacea, Citrus bergamia Risso (Rutacea, Melissa officimlis L. (Lamiacea, Rosmarinus officimlis L. (Lamiacea, C. citratus DG ex Nees (Poacea, and Mentha piperita L. (Lamiaceae). Interestingly, maity linalool producing species are traditionally used as sedative, analgesic, Itypnotic, or anxiolytic remedies in traditional medicine and some as well in aromatherapy (Elisabetsky et al. 1995a). 

Menthol belongs to the group of monocyclic terpenes, which can be found as a major compound in the EO of leaves of mentha species like Mentha piperita and Mentha arvensis. 

Monoterpenoid furan derivatives occur in a limited number of flavor-yielding plant species. Menthofuran (140), as the oldest example 195), is present in all the oils obtained from Mentha piperita L. in which its pronounced odoriferous character contributes to the pleasant flavor... 

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... 

The combined genomics and chemical approaches to plant terpenoid research are not restricted to the few plant species for which more or less complete genome sequences are now available. The discovery of many of the genes and enzymes for the formation of terpenoids such as menthol and related monoter-penes in peppermint Mentha x piperita) (15), artemisinin in Artemisia annua (16), Taxol in the yew tree (Taxus) (17), or conifer diterpene resin acids in species of spmce (Picea ) and pine (Pinus) (18) have been possible on the foundation of highly specialized efforts of EST and full-length cDNA sequencing combined with characterization of recombinant enzymes and analysis of the terpenoid metabolome of the target plant species. 

The monoterpene biosynthesis in different species of Lamiaceae, for example, sage (Salvia officinalis) and peppermint (Mentha x piperita), is restricted to a brief period early in leaf development (Croteau et al., 1981 Gershenzon et al., 2000). The monoterpene biosynthesis in peppermint reaches a maximum in 15-day-old leaves, only very low rates were observed in leaves younger than 12 days or older than 20 days. The monoterpene content of the peppermint leaves increased rapidly up to day 21, then leveled off, and kept stable for the remainder of the leaf life (Gershenzon et al., 2000). 

A first step in genetic engineering is the development and optimization of transformation (gene transfer) protocols for the target species. Such optimized protocols exist for essential oil plants such as lavandin (Lavandula x intermedia Dronne et al., 1999), spike lavender (Lavandula latifolia Nebauer et al., 2000), and peppermint (Mentha x piperita Diemer et al., 1998 Niu et al., 2000). 

The most important monoterpene alcohols are menthol, cis- and trans-piperitol, cis- and trans-pulegol, isopulegol, cis- and trans-caiveol, thymol, carvacrol, terpinen-4-ol, and a-terpineol. The latter two bear a tertiary alcohol function. Terpinen-4-ol is a major antibacterial component of tea tree oil Melaleuca alternifolia). a-Terpineol is a major compound in cardamom oil. (—)-Menthol is a main constituent in mint oils Mentha x piperita and other Mentha species). Terpinen-4-ol is typically found in marjoram oils Origanum majorana) a-terpineol occurs in various essential oils including those from Melaleuca viridiflora and nutmeg Myristica fragrans). Thymol and carvacrol are... 

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