Plectranthus

Abstract: The essential oils of Hoslundia opposita Vahl. (leaves), Hyptis lanceolata Poit. (whole plant), Hyptis suaveolens Poit. (leaves), Ocimum basilicum L. (whole plant), Ocimum canum Sim. (whole plant), Ocimum gratissimum L. (leaves), Plectranthus glandulosus Hook (leaves), Thymus vulgaris L. (whole plant), Piper capense L. (leaves and seeds), Piper guineense Schum. et Thom. (leaves and seeds) and Bixa orellana L. (leaves) which were obtained by hydrodistillation from plants collected in different regions of Cameroon, were analysed by GC and combined GC–MS. The oils of Hoslundia opposita, Hyptis lanceolata, H. suaveolens, T. vulgaris, P. capense, P. guineense and B. orellana were found to be rich in hydrocarbons (>58%). The most abundant compounds in the oils of O. basilicum, O. canum and P. glandulosus were alcohols and oxides (>40%), while in the oil of O. gratissimum the amounts of hydrocarbons and oxygen-containing components were roughly the same. It is of interest to note the presence in O. basilicum and P. guineense (leaves) of aromatic compounds in a sizeable amount (13.5% and 25.6% respectively). The antifungal activity of these essential oils against Candida albicans, Cryptococcus neoformans, Aspergillus flavus, Aureobasidium pullulans, Microsporum gypseum, Trichophyton rubrum, and Trichoderma viride were also investigated. Two methods were used for these antifungal tests: the microatmosphere method and the standardized broth dilution micromethod. Three oils (from Ocimum gratissimum, Thymus vulgaris and Ocimum basilicum) showed strong antifungal activity. © 1998 John Wiley & Sons, Ltd.

Abstract: This review presents the phytochemical constituents of the genus Plectranthus reported up to 1999. Only a tetrameric derivative of caffeic acid was isolated from P. japonicus, but a group of long-chain alkylphenols, of possible taxonomic significance in the genus, was also isolated. As a genus of the subfamily Nepetoideae, Plectranthus is free from iridoid glycosides and rich in essential oil (i.e. > 0.5% volatile oil on a dry weight basis). Diterpenoids are the more common secondary metabolites in Plectranthus. The majority of them are highly modified abietanoids. This seems to be similar to the pattern of diterpenoids observed for Salvia, but no clerodane diterpenoids were found in Plectranthus.

Abstract: Mosquito-borne diseases represent a deadly threat for millions of people worldwide. Eco-friendly mosquitocides are a priority. In Ayurvedic medicine, Plectranthus species have been used to treat heart disease, convulsions, spasmodic pain and painful urination. In this research, we evaluated the acute toxicity of essential oil from Plectranthus barbatus and its major constituents, against larvae of the malaria vector Anopheles subpictus, the dengue vector Aedes albopictus and the Japanese encephalitis vector Culex tritaeniorhynchus. The chemical composition of P. barbatus essential oil was analyzed by gas chromatography–mass spectroscopy. Nineteen components were identified. Major constituents were eugenol (31.12 %), α-pinene (19.38 %) and β-caryophyllene (18.42 %). Acute toxicity against early third-instar larvae of An. subpictus, Ae. albopictus and Cx. tritaeniorhynchus was investigated. The essential oil had a significant toxic effect against larvae of An. subpictus, Ae. albopictus and Cx. tritaeniorhynchus, with 50 % lethal concentration (LC50) values of 84.20, 87.25 and 94.34 μg/ml and 90 % lethal concentration (LC90) values of 165.25, 170.56 and 179.58 μg/ml, respectively. Concerning major constituents, eugenol, α-pinene and β-caryophyllene appeared to be most effective against An. subpictus (LC50 = 25.45, 32.09 and 41.66 μg/ml, respectively), followed by Ae. albopictus (LC50 = 28.14, 34.09 and 44.77 μg/ml, respectively) and Cx. tritaeniorhynchus (LC50 = 30.80, 36.75 and 48.17 μg/ml, respectively). Overall, the chance to use metabolites from P. barbatus essential oil against mosquito vectors seems promising, since they are effective at low doses and could be an advantageous alternative to build newer and safer mosquito control tools.