Chemistry and Biological Activity of Myrtaceae
As part of a Medical Research Council funded project on anti-HIV leads from plants, a group of compounds called polyhydroxyalkaloids (PHA) or imino sugars were identified from a species of Syzygium. This was the first report of this group of compounds from this genus so a chemosystematic survey of the Myrtaceae family was undertaken based on the species growing in the Gardens and available in the Herbarium at Kew. The aim of the survey was initially to see if new PHAs could be identified and to evaluate whether the distribution of PHAs in different genera could be used to study the relationships among the different genera. Phenolics, including flavonoids were also included in the chemosystematic study as there are very little published data about the distribution of these compounds in the Myrtaceae and they have been used as taxonomic characters in other families.
A total of 344 species from 110 genera were analysed. The compounds varied in their distribution among the genera of the two subfamilies of Myrtaceae: Myrtoideae and Leptospermoideae. PHAs were shown to have some taxonomic value within the Myrtoideae subfamily, since most species produced them. PHAs were only found in four genera of the Leptospermoideae subfamily which belong to two alliances of a clade sister to the Myrtoideae. The distribution of isorhamnetin, flavones and flavanones in genera of the Calothamnus and Leptospermum suballiances supports the molecular data, which suggests that these two suballiances of the Leptospermum alliance are not as closely related as the morphological data suggests and that the Leptospermum alliance should be abandoned. Two genera, Heteropyxis and Psiloxylon from two families closely related to the Myrtaceae were also analysed. The presence of PHAs in these genera was consistent with recent molecular studies and provided support for their inclusion within the Myrtaceae.
Currently we are studying aspects of the phenolic chemistry of the family, using new DNA-based phylogenies to assist with the selection of species for further study.
As part of this project extracts from all the species of Myrtaceae growing at Kew were tested for activity in a range of insect assays at Kew and in collaboration with scientists at Rothamsted Experimental Station. Extracts from species of Kunzea, Callistemon and Eucalyptus had insecticidal and antifeedant activity. A series of acylphloroglucinol compounds with insecticidal activity were isolated from these species and a few had activity comparable with natural pyrethrum extracts.
Further work on the chemistry of this family will depend on funding but it is planned to publish the results from the chemosystematics and insect research.
Project partners and collaborators
Rothamsted Experimental Station