Chemical and biological investigations of the Yaegl medicinal plant Alphitonia excelsa

Alphitonia excelsa leaves are used by the Australian Aboriginal people of Yaegl Country for the treatment of sores, wounds and skin infections. Structural elucidation of compunds previously isolated from the n-hexane and dichloromethane sequential extracts of A. excelsa leaves identified the well-known antibacterial and antioxidant compounds β-sitosterol, betulin aldehyde, betulinic acid, lupeol, quercetin and kaempferol. This is the first report og lupeol and betulin aldehyde in any Alphitonia species and the first report of β-sitosterol in A. excelsa. LC-MS studies of over 600 column chromatography fractions obtained from previous studies did not lead to any further compounds of interest. GC-MS analysis of freshly extracted leaves identified the bioactive compounds γ-sitoserol, nonanal, n-tetracontane, docosane, 1,54-dibromotetrapentacontane, tetradecane and hexadecane from the n-hexane and dichloromethane extracts. The dichloromethane extract also showed moderate activity against antibiotic sensitive and resistant Staphylococcus aureus (MIC 312.5 - 625 μg/mL) and promising antioxidant activity, while the n-hexane extract showed moderate antibacterial activity (MIC 1250 - 2500 μg/mL). Preliminary fractionisation of the n-hexane extract provided one active fraction against S. aureus and four semi-pure fractions. This study has extended the phytochemical and biological knowledge of A. excelsa and shown that it is a worthy plant for further chemical and biological investigations.