Antibiotic activities of essential oils of Myrtaceae from Oceania
Résumé
Despite advances in synthetic chemistry, natural products still represent a rich and diverse source of novel biologically active compounds. Essential oils are especially promising renewable materials and are widely used for their fragrant, medical, or healthcare properties. The genus Xanthostemon belongs to the Myrtaceae family and contains about 55 plant species that are endemic to Papua New Guinea, Australia, Indonesia, and New Caledonia. The essential oils of Australian species are known to have unique compositions, with many containing β-triketones. The latter compounds possess important antimicrobial activities, which makes them interesting candidates for biological activity screening. For example, the endemic species of Northeast Queensland, Xanthostemon whitei, shows antibacterial activities against Gram positive bacteria Bacillus cereus and Staphylococcus aureus. Likewise, acylated β-triketones are the main antimicrobial components of mānuka (Leptospermum scoparium) essential oil. Although β-triketones represent promising candidates for novel antibacterial agents, no structure-activity relationship study has been conducted yet to correlate their biological activity and molecular structure. The chemical compositions of Xanthostemon species from Oceania were thus determined and several natural βtriketones were successfully identified. Several synthetic analogues were likewise prepared to broaden the scope of the structure-activity relationship study. The results from this research may assist local essential oil producers to potentially diversify and add value to their product portfolios.