A Preliminary Examination of the Leaf Oils of the Genus Xanthostemon (Myrtaceae) in Australia

Abstract

The leaf oils of the Australian species of Xanthostemon have been examined by a combination of GC and GC/MS. Xanthostemon arenarius produced an oil dominated by sesquiterpenes, with the principal components being β-selinene (12–17%), α-selinene (6–10%), 7-epi-α-selinene (7–11%), α-humulene (0.3–10%, the majority > 6%) and spathulenol (3–19%). Xanthostemon chrysanthus produced a leaf oil in which the principal component was the β-triketone leptospermone (65–84%). The leaf oil of X. crenulatus was dominated by the sesquiterpene ketone, cyclocolorenone (65–80%) and the aromatic ketone apodophyllone (6–17%). The leaf oil of X. eucalyptoides was dominated by the aromatic ketones baeckeol methyl ether (34–41%), baeckeol (15–29%), isobaeckeol (5–8%) and apodophyllone (7–9%). The leaf oil of X. formosus was, once again, sesquiterpenoid in nature. The principal components were β-caryophyllene (10–24%), β-bisabolene (9–16%) and sesquiphellandrene (9–20%). Xanthostemon graniticus was unusual within the genus in that it produced a monoterpenic oil, the principal component being α-pinene (69.5%). Xanthostemon oppositifolius gave an oil which was dominated by β-triketones. The principal components were xanthostemone (1625%) and a compound considered a one carbon homologue, which is as yet unidentified (24–35%). Xanthostemon paradoxus produced a leaf oil that was sesquiterpenoid in nature. The principal components were β-caryophyllene (14%), spathulenol (14.9%) and globulol (8%). Xanthostemon psidioides was another species whose oil was dominated by β-triketones, the principal component being xanthostemone (73.1%). Xanthostemon umbrosus, the species with the widest distribution in this investigation, produced a variable oil. The various oils were dominated by the sesquiterpene ketone, cyclocolorenone (77–83%), or methyl farnesoate (3257%) and farnesoic acid (9–26%) or α-santalene (6–7%), isobaeckeol (30–40%) and an unknown, presumed aromatic, compound mw 252 (3–23%). The leaf oil from X. verticillatus was unusual amongst the other Australian species of Xanthostemon in that it contained 1,3-dimethoxy-5-isopropylbenzene as its major component (96–97%). Xanthostemon whitei gave a sesquiterpenic oil which was similar to that produced by X. arenarius. Xanthostemon youngii also gave a sesquiterpenic oil, the principal components being α-copaene (3–13%), β-caryophyllene (11–13%), aromadendrene (3–12%), and γ-cadinene (4–18%). Xanthostemon sp. (Bolt Head JRC +8805) gave a terpenoid oil in which the major components were the hydrocarbons, γ-cadinene (18%) and calamenene (29.3%). Oil yields over the range of species were 0.1–0.6%, w/w, based on fresh leaves.