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Chemosystematics and Biological Activity of Lamiaceae

Ocimum gratissimum

The family Lamiaceae contains species that are used traditionally as medicines and to control insects. For many years we have had an interest at Kew in the anti-insect activity of diterpenoids, especially the neo-clerodanes from species of Ajuga, Teucrium and Scutellaria. Some of these compounds have potent antifeedant activity against a range of insects including the armyworm, Spodoptera littoralis. Currently we are investigating the anti-insect activity of other diterpenoids from species of Salvia and Plectranthus.

We have just completed a review of the ethnobotanical uses of Plectranthus that illustrates how collating information about the traditional uses of plants when superimposed onto a DNA-based phylogeny of the genus shows that species with specific uses are often related. Is this because related species generally contain related active compounds, which may be absent from other more distantly related species, or are certain groups of species more abundant and thus have been more readily available for use? Finding answers to these types of questions will be the focus of our research on Plectranthus and Salvia for the next few years. These genera contain many species that are used in traditional medicine to treat infections, so that we will investigate which of the compounds in these plants have antimicrobial activity. We are also interested in the use of different species for the treatment of cancer and dementia.

Our chemosystematic-based research in Lamiaceae has mainly focused on genera belonging to the subfamily Nepetoideae. Two bioactive caffeic acid esters were found to be present in a very large percentage of the species in this subfamily, whereas the compounds did not occur in the other subfamilies of the Lamiaceae. Therefore we called these chemosystematic markers nepetoidins A and B. The profiles of leaf exudate flavonoids, sometimes when combined with essential oil data, were shown to be useful in characterising different genotypes of species of Ocimum. We have also used exudate flavonoids to study the intrageneric or infraspecific relationships of species belonging to Thymus, Nepeta, Salvia and a number of smaller genera. Furthermore, vacuolar flavonoid glycosides and iridoid compounds provided good evidence to support a new infrageneric classification of the genus Veronica (Plantaginaceae, formerly Scrophulariaceae, order Lamiales) based on DNA sequences.We are currently finishing these chemosystematic studies. Our new chemosystematic focus will be to provide data to support new phylogenies which are being constructed for genera within the subfamily Viticoideae of the Lamiaceae.

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