Customary medicinal flora of Australia
Creators: name: Norman, Edward
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 340109
subject: Separation science
classificationCode: 340401
subject: Biologically active molecules
classificationCode: 340502
subject: Natural products and bioactive compounds

description: This thesis describes the isolation and structure elucidation of 17 new specialised metabolites from two Australian native medicinal plants; Haemodorum brevisepalum and Drosera magna. The structures of these compounds were elucidated by a combination of spectroscopic and chemical methods. This thesis also reports two crystal structures secured for the first time, and the isolation of 29 previously reported compounds. In addition, the complete structural assignment by 1D and 2D NMR was carried out on known compounds that had incomplete or no NMR spectroscopic data, as well as reporting on the biological activity data for 36 compounds in two different biological assays (antimicrobial and anthelmintic). In addition to this laboratory-based work, a database of the chemical constituents of the 393 spp. (distributed over 264 genera) of Australian customary medicinal flora reported in the literature has been compiled. This database has enabled the creation of networks which visualise the chemotaxonomic relationships occurring within the plant species in use by First Nations Scientists – providing a sound basis upon which to develop an analytical platform through which the qualitative substantiation of significant customary knowledge can occur. This significant review of the literature has also created a benchmark identifying which species, genera, and families have been academically neglected, well positioning the Marine and Terrestrial Natural Product (MATNAP) research group at RMIT to continue to be competitive alongside other research organisations in the pursuit of new/novel chemical compounds from endemic Australian flora. 

Chapter 1 of this thesis introduces the field of natural product chemistry, pertaining to the analysis of customary medicinal sources in the West, the East, and particularly on the Australian continent. Chapter 2 outlines the materials and methods utilised in the laboratory-based experimental work, literature review, database construction, and network creation conducted as part of this thesis. Chapter 3 goes on to present a breakdown of the diversity, biosynthetic metabolism, and biological activity of the major sub- and infra-classes of the four classes of specialised metabolites: phenolic-type, terpenoid-type, alkaloid-type, and miscellaneous-type. This detailed overview of the specialised metabolic space of the plant kingdom was required to delineate the phytochemical constituents reported in the literature, enabling the construction of the Customary Medicinal Flora of Australia Database, and commensurate networks included throughout the Chapter. 

Chapter 4 presents a review of the plant family Haemodoraceae, which is a monocotyledonous family in the order Commelinales consisting of 14 genera. Many species from the family are endemic to Australia and their use by First Nations Australians as both pigments and/or remedies has been ethnobotanically documented. The species have been found to contain phenylphenalenones, which are specialised phenolic metabolites consisting of a tricyclic phenalene nucleus with a ketone moiety and a lateral phenyl ring. Depending on their structural variance, four classes can be distinguished, including the phenylphenalenones, oxabenzochrysenones, phenylbenzoisochromenones and phenylbenzoisoquinolindiones. The phenylphenalenone class has become the order’s chemotaxonomic marker with a documented range of biological activities. This biological activity arises from the phototoxic properties of their ring system, a phenomenon most clearly observed amongst a widely cultivated family of the Commelinales order, Musaceae (Banana). Within the family Haemodoraceae, the formation of the phenylphenalenone-class phytoanticipins is an intrinsic function of their growth, whereas within the family Musaceae these compounds are formed as phytoalexins in response to pathogenic attack or stress. The compounds produced within these two families differ in their substitution, with Musaceae-derived phytoalexins tending to be the more phototoxic 4-phenylphenalenones and the Haemodoraceae-derived phytoanticipins being of the more inert 9-phenylphenalenone type structure. Various other substitution patterns have been documented across the class, yet their biosynthetic mechanism is consistent, proceeding from simple phenylpropanoids through a diarylheptanoid intermediate, which cyclises to form the phenylphenalenone nucleus. Phenylphenalenone-related compounds have also been observed within the fungal kingdom, yet their biosynthetic route is based upon an alternative polymalonate pathway. 

Chapter 5 outlines the phytochemical profiling which was undertaken on the crude extracts of the bulbs, stems, and the fruit of a member of the Haemodoraceae, Haemodorum brevisepalum, to determine the nature of the chemical constituents present. This work represents the first study to investigate the fruits of a species of Haemodorum. In total, 13 new and 17 previously reported compounds were isolated and identified. The new compounds were of the phenylphenalenone-type phenolic subclass, with a representative of a novel structural form elucidated, tentatively named an “oxabenzochromenone” (5.1), a compound elucidated which is akin to an intermediate in a recently proposed phenylphenalenone metabolic network (5.2), seven new phenylphenalenones (5.4–5.10), four new phenylbenzoisochromenones (5.11–5.14), and a new phenylbenzoisochromenone-derivative (5.18). The previously reported compounds identified were of the following structure classes: oxabenzochrysenone (5.3, 5.23–5.26), flavonol (5.15 and 5.16), phenylbenzoisochromenone (5.17, 5.21, 5.22, 5.27–5.30), and phenylphenalenone (5.19, 5.20). Compounds 5.2–5.4, 5.6–5.9, 5.15–5.18, 5.21, 5.22 and 5.26 were subjected to antimicrobial evaluation with moderate activity observed against Staphylococcus aureus MRSA, and slight activity against Pseudomonas aeruginosa and Candida albicans. Compounds 5.4, 5.6–5.9, 5.17 and 5.21 were also evaluated for anthelminthic activity against larvae of the blood-feeding parasitic nematode, Haemonchus contortus.

Chapter 6 outlines the phytochemical profiling which was undertaken on the crude extracts of the subterranean and aerial components of the Australian carnivorous plant Drosera magna, to determine the nature of the chemical constituents present. Various Drosera spp. are well-documented ethnomedicinal sources across the globe, employed to treat inflammation, infections, and respiratory disorders, including dry cough and bronchitis. Additionally, First Nations Australians have been recorded using the pigmented extracts of the bulbs of Drosera spp. in the production of dyes. In total, three new flavonol diglycosides (6.1-6.3), one flavan-3-ol glycoside (6.4), and twelve previously reported compounds of the 1,4-naphthoquinone (6.6, 6.7, 6.10–6.13), flavonol (6.5, 6.9), flavanone (6.8), flavan-3-ol (6.14), and phenolic acid (6.15) structure classes were isolated and identified. Compounds 6.1–6.9, 6.13–6.15 were assessed for antimicrobial activity, with compounds 6.6, 6.7, 6.8, 6.9 showing significant activity. Compounds 6.1, 6.2 and 6.6 were also evaluated for anthelmintic activity against larval forms of Haemonchus contortus, with compound 6.6 being reported as active.

Chapter 7 presents some concluding remarks and future work, pertaining to the work presented in Chapters 3–6. Following this concluding chapter is a reference list for the main text of the thesis, which covers a broad swathe of pertinent literature which was drawn from throughout this work. In addition to this, three large Appendices have been included; Appendix A pertains mostly to Chapter 3: Customary Medicinal Flora of Australia Database, with five subsections (A.1.1–A.1.5) outlining the customary medicinal flora of Australia genus review (A.1.1) presenting the references used for the compilation of this Chapter (these references are organised and included separately here), and the distribution of the phytochemical constituents of the customary medicinal flora of Australia across the phenolic-type (A.1.2), terpenoid-type (A.1.3), alkaloid-type (A.1.4), and miscellaneous-type (A.1.5), specialised metabolic classes, respectively. Appendix B presents the spectral data and supporting information for the new compounds reported in Chapter 5 (B.1.1), and Chapter 6 (B.1.2), respectively. Appendix C presents some further documentation; the author’s Covid-19 impact statement, a list of journal publications, and a list of conference proceedings.