The plant-derived natural product 14-hydroxy-6,12-muuroloadien-15-oic acid (1) was identified as a unique scaffold that could be chemically elaborated to generate novel lead- or drug-like screening libraries. Prior to synthesis a virtual library was generated and prioritised based on drug-like physicochemical parameters such as log P, log D(5.5), hydrogen bond donors/acceptors, and molecular weight. The natural product scaffold (1) was isolated from the endemic Australian plant Eremophila mitchellii and then utilised in the parallel solution-phase generation of two series of analogues. The first library consisted of six semi-synthetic amide derivatives, whilst the second contained six carbamate analogues. These libraries have been evaluated for antimalarial activity using a chloroquine-sensitive Plasmodium falciparum line (3D7) and several compounds displayed low to moderate activity with IC(50) values ranging from 14 to 33 μM.
Chemical investigation of the CH(2)Cl(2)/CH(3)OH extracts from aerial parts of the Australian plant Goniothalamus australis has resulted in the isolation of two pyridocoumarin alkaloids, goniothalines A (1) and B (2) as well as eight known natural products, aristolactam AII (3), enterocarpam II (4), caldensine (5), sauristolactam (6), (-)-anonaine (7), asimilobine (8), altholactone (9) and (+)-goniofufurone (10). The chemical structures of all compounds were determined by extensive spectroscopic and spectrometric analysis. Methylation of 2 using TMS-diazomethane afforded 1, which unequivocally established that both 1 and 2 possessed a 10-methyl-2H-pyrano[2,3-f]quinolin-2-one skeleton. These pyridocoumarin alkaloids are putatively proposed to arise biosynthetically from an aporphinoid precursor. Compounds 1-10 were evaluated for in vitro antimalarial activity against a chloroquine-sensitive Plasmodium falciparum line (3D7). Sauristolactam (6) and (-)-anonaine (7) exhibited the most potent antiparasitic activity with IC(50) values of 9 and 7 μM, respectively.
As part of a research program aimed at discovering new antimalarial leads from Australian macrofungi a unique fungi-derived prefractionated library was screened against a chloroquine-sensitive Plasmodium falciparum line (3D7) using a radiometric growth inhibition assay. A library fraction derived from a Cortinarius species displayed promising antimalarial activity. UV-guided fractionation on the CH(2)Cl(2)/MeOH extract from this fungus resulted in the isolation of four known compounds: (1S,3R)-austrocortirubin (1), (1S,3S)-austrocortirubin (2), 1-deoxyaustrocortirubin (3), and austrocortinin (4). Compound 2 was used as a natural product scaffold in the parallel solution-phase synthesis of a small library of N-substituted tetrahydroanthraquinones (5-15). All compounds (1-15) were tested in vitro against P. falciparum 3D7 parasites and (1S,3S)-austrocortirubin (2), the major fungal constituent, was shown to be the most active compound with an IC(50) of 1.9 μM. This compound displayed moderate cytotoxicity against neonatal foreskin fibroblast (NFF) cells with an IC(50) of 15.6 μM.
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