Chemical investigation of aromatic and medicinal plants from the New Guinea highlands and North Queensland

Various aromatic and medicinal plant species from the New Guinea highlands and North Queensland were investigated to discover and characterise new molecular entities with useful pharmacological properties, which could potentially become lead compounds for the development of new drug products.\ud \ud A new optically active diterpene ester was isolated from the plant species Stylosanthes hamata and its structure determined using spectroscopic technique (1H, 13C, HSQC, HMBC and COSY). It is the 3-hydroxy-3-methyl glutarate ester of cativol, a diterpene previously reported from Halimium viscosum. Some components of crude essential oil samples were identified without the need for separation of their mixture by the use of gradient selective NMR techniques. A total of twenty-six known compounds were identified by either this method or by separating and analysing the essential oils of various species from the New Guinea highlands and North Queensland. They included; monoterpenes, sesquiterpenes, acetate-derived metabolites such as the acetogenins/polyketides methyl salicylate and gibbilimbols, and shikimic acid-derived metabolites such as dillapiole and trans-anethole. Some of the minor components detected in one species were the same as major components in other essential oil samples and it is suspected that cross contamination may have occurred during the essential oil distillation in PNG. This problem will make publications of results difficult unless uncontaminated samples are available for comparison.\ud \ud Cytotoxic and antimicrobial assays were performed on all essential oils and extracts. Although some essential oil samples displayed cytotoxicity, the levels were considered too low to warrant further investigation. The antimicrobial assays employed included the use of six gram positive and six gram negative bacteria as well as one yeast and five fungi. The major components of the distillates that produced a large zone of inhibition in the initial screening were selected and retested against the microbes. All of the metabolites tested showed lower activity than the crude extracts. This may be due the presence of minor components in the distillates that have much greater activity or synergistic effects from other oil components