Chemical composition of the essential oils of Nepeta laevigata and Nepeta elliptica from India

Abstract

The genus Nepeta (Lamiaceae), also called Glechoma and Cataria, is a multiregional genus and consists of about 250 species of perennial herbs distributed in central and southern parts of Europe, Asia, and the Middle East [1–3]. These plants are commonly known as catmint [4], and about 30 species occur in India. Many Nepeta species have been reported to be biologically active and are used in folk medicine because of their spasmodic, diuretic, antiseptic, antitussive, antiasthmatic, and febrifuge activities [5–9]. Several Nepeta species are also reported to reduce serum lipids and to possess anti-inflammatory effects [10, 11]. Most Nepeta species are rich in essential oils, and various biologically active iridoids/monoterpene nepetalactones have been reported in several Nepeta species possessing diverse biological activities, viz., feline attractant, canine attractant, insect repellant, arthropod defense [12, 13], antibacterial, antifungal, and antiviral activities [14]. N. laevigata and N. elliptica are distributed through Afghanistan, China, Nepal, Pakistan, and India. In India, the two plant species are largely confined to Himachal Pradesh, Jammu and Kashmir, and Uttar Pradesh. Nepeta laevigata, also known as Betonica laevigata, is a perennial aromatic herb that grows to a height of 80 cm, is white pubescent, and has petiole 2–12 mm and leaf blade ovate to triangular, while N. elliptica is a small ascending or flexuous herb, 30–60 cm high. Both N. laevigata and N. elliptica are used in traditional medicine. Nepeta laevigata, is reported to be used locally in fevers and for sore throat, while, as an infusion of the seeds, N. elliptica is used in dysentery. According to our finding, there is no report on the chemical compostion of the essential oil of N. laevigata and N. elliptica growing in J & K, India, so the aim of the present work was to compare the chemical composition of these two Nepeta species. The chemical constituents of the volatile oils were analyzed by capillary GC-FID and GC-MS. The components of the oils of the air-dried aerial parts of N. laevigata and N. elliptica are listed in Table 1 with their percentages and relative retention indices (RRI). The different chemical constituents of the essential oils are listed in order of their elution from an RTX-5 column. As shown, 24 components belonging to different class of compounds were identified in the oil of N. laevigata, making up 86.7% of the total oil. -Citronellol (16.5%), germacrene D (19.4%), -caryophyllene (10.8%), -bisabolol oxide B (12.4%), -bourbonene (4.5%), -humulene (3.5%), spathulenol (3.9%), and -bisabolol (5.3%) were the major ones. Other constituents such as 4a,7,7a-nepetalactone (2.0%), allo-aromadendrene (1.1%), and caryophyllene oxide (3.2%) were present in small amounts. In addition, some other constituents such as -pinene, 1,8-cineole, linalool, geraniol, citronellyl acetate, etc. were present in trace amounts. The essential oil composition is dominated by the presence of sesquiterpene hydrocarbons, oxygenated sesquiterpenes, and oxygenated monoterpenes constituting 40.9%, 25.1%, and 20.7%, respectively, of the total oil composition. Of the various nepetalactone isomers, viz., 4a,7,7a-nepetalactone, 4a,7,7a-nepetalactone, and 4a,7,7a-nepetalactone, which have been labeled as the biochemical markers of the Nepeta essential oils and are very useful in chemotaxonomic studies, only one nepetalactone isomer viz., 4a, 7, 7a-nepetalactone, as a minor constituent, was present in the essential oil of Nepeta laevigata. -Caryophyllene, which is one of the major constituents of the essential oil, has been reported in some Nepeta species such as N. depauperata [15], N. flavida [16], and N. nuda [17] as the major component. Likewise, germacrene-D, the other major constituent of the oil sample, has also been reported in various other Nepeta species such as Nepeta macrosiphon [18] and Nepeta sintensii [19]. In addition, the other major components such as -bourbonene and spathulenol have been reported in N.depauperata [15], N. macrosiphon [18], and N. sintensii [19].