Antioxidative and Bioactive Potential of Phytochemicals in Plants Sourced from Australia

Australia is home to a diverse range of unique flora with exceptional survival mechanisms and phytochemicals, which makes them an attractive source for discovering new drugs. This study proposes a bioassay-guided fractionation protocol to effectively screen plants with potential bioactive properties and isolate novel key compounds. Five native Australian plants were selected for screening, namely Pittosporum angustifolium (Gumbi gumbi), Terminalia ferdinandiana (Kakadu plum, seeds, and flesh), Cupaniopsis anacardioides (Tuckeroo, seeds and flesh), Podocarpus elatus (Illawarra plum seeds and flesh) and Pleiogynium timoriense (Burdekin plum seeds and flesh). Subsequently, plants exhibiting high phenolic content and antioxidant capacity were selected for in vitro anticancer and antimicrobial bioassays, which is Phase 1 of the protocol. Extracts that exhibited bioactivity were selected for Phase 2, which involved fractionation using column chromatographic separation techniques (HPLC) and performing bioassays on the separated fractions. This protocol successfully identified P. angustifolium extract as having the highest cytotoxic properties against cancer cell lines (HeLa, HT29, and HuH7), attributed to a high occurrence of t-ferulic acid. High-performance liquid chromatography (HPLC) based time fractionation of the GGL extract (F1-F5) was performed, and dose-dependent cytotoxic effects were determined. Fraction 1 was identified as the most promising for further fractionation and isolation, with a high selectivity index (SI) value for HeLa, HT29, and HuH7 (1.60, 1.41, and 1.67, respectively). Compounds tentatively identified in P. angustifolium Fraction 1 using LC-ESI-QTOF-MS/MS were chlorogenic acid and/or neochlorogenic acid, bergapten, berberine, 8`-Epitanegool, and rosmarinic acid. Sub-fractionation of P. angustifolium Fraction 1 showed that the cytotoxic properties were due to the synergistic effect of the phenolic compounds present. Therefore, further fractionation and separation of compounds in these samples were not pursued. Using this designed protocol for bioprospecting plants would allow for more efficient screening of understudied plants and pave the way for future research of unidentified plants with pharmacological significance.