Bioassay-guided fractionation protocol for determining novel bioactive compounds in selected Australian flora

A large variety of unique and distinct flora of Australia have developed exceptional survival methods and phytochemicals and hence may provide a significant avenue for new drug discovery. Several literatures have identified some native Australian plants as having high therapeutic potential. Despite this, the bioactive compounds of some of these species are yet to be discovered. In the current study methanolic extracts of plants namely Pittosporum angustifolium (Gumbi gumbi), Terminalia ferdinandiana (Kakadu plum), Cupaniopsis anacardioides (Tuckeroo) and Syzygium australe (Bush cherry) exhibited high phenolic content and antioxidant capacity and hence were selected for the bioassay guided fractionation protocol. The protocol developed is outlined in Figure 1 Upon completing Phase 1 of the protocol, P. angustifolium and T. ferdinandiana were identified as most promising plants with potentially novel bioactive compound(s). Although P. angustifolium was found to have the highest apoptotic effect against HeLa and HT29 cancer cell lines, no antibacterial activity against common human pathogens: Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Salmonella typhimurium were observed. On the contrary T. ferdinandiana extracts have displayed some antibacterial activity against the tested pathogens and only its seed extracts have shown some apoptotic activity against the cancer lines tested. We are currently in phase 2 of the protocol and have successfully fractionated freeze dried methanolic extracts of P. angustifolium using a G1364F 1260 Infinity II Analytical Fraction Collector and have obtained five fractions. The five fractions were selected based on the chemical activity regions on the phenolic profile chromatogram obtained using High-Performance Liquid Chromatography (HPLC). We postulate that the bioassay screening of the five fractions will enable further separation of the most bioactive fraction and ultimately phase 3 of the protocol will lead to the isolation and identification of a novel bioactive compound in P. aungustifolium. Thus far the developed protocol has shown to be robust and effective in screening plants with high phenolic and antioxidant capacity and hence can set precedence for future screening of native Australian plants for novel bioactive compound(s).