The present study aimed to screen plants for bioactive compounds with potential antibacterial activities. In our efforts to evaluate plants from Borneo, we isolated and elucidated the structures of four natural products from the bioactive fraction of a chloroform extract of Goniothalamus longistipetes using various chromatographic and spectroscopic techniques. The bioactive compounds were identified as a known styryllactone, (+)-altholactone ((2 S ,3 R ,3a S ,7a S )-3-hydroxy-2-phenyl-2,3,3a,7a-tetrahydrobenzo-5(4 H )-5-one) ( 1 ), a new styryllactone, (2 S ,3 R ,3a S ,7a S )-3-hydroxy-2-phenyl-2,3,3a,7a-tetrahydrobenzo-5(4 H )-5-one) ( 2 ) as well as a new alkaloid, 2,6-dimethoxyisonicotinaldehyde ( 3 ) and a new alkenyl-5-hydroxyl-phenyl benzoic acid ( 4 ). 1 and 4 showed broad-spectrum anti-bacterial activities against Gram-positive and Gram-negative bacteria as well as acid-fast model selected for this study. Compound 2 only demonstrated activities against Gram-positive bacteria whilst 3 displayed selective inhibitory activities against Gram-positive bacterial strains. Additionally, their mechanisms of anti-bacterial action were also investigated. Using Mycobacterium smegmatis as a fast-growing model of tubercle bacilli, compounds 1 , 2 and 4 demonstrated inhibitory activities against whole-cell drug efflux and biofilm formation; two key intrinsic mechanisms of antibiotic resistance. Interestingly, the amphiphilic compound 4 exhibited inhibitory activity against the conjugation of plasmid pKM101 in Escherichia coli using a plate conjugation assay. Plasmid conjugation is a mechanism by which Gram-positive and Gram-negative-bacteria acquire drug resistance and virulence. These results indicated that bioactive compounds isolated from Goniothalamus longistipetes can be potential candidates as 'hits' for further optimisation.

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Publisher Summary This chapter lists the important subjects on biological source that are discussed in the publication, such as Abies grandis Acanthodris nanaimoensis, Baccharis crispa, acanthosterol sulfates, Agelas dispar, Plasmodium falciparum, Podophyllum hexandrum, Quillaja saponaria, and Rauwolfia serpentina. The terms are mentioned along with the page numbers in which they are discussed in the publication.

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A dichloromethane extract of Hakea amplexicaulis was found to cause strand scission of phi X174 replicative form DNA in the presence of Cu(II). Bioassay-guided fractionation of this extract afforded five compounds capable of mediating DNA relaxation. Structure determination of the active principles indicated that they were 5-tridecylresorcinol (1), 5-pentadec-cis-8-enylresorcinol (2), 5-heptadeca-8,11-dienylresorcinol (3), 5-pentadecylresorcinol (4), and 5-heptadec-cis-8-enylresorcinol (5). As noted previously for compounds in this structural series, DNA cleavage was enhanced significantly by incubation under (alkaline) conditions known to promote oxygenation of the parent compounds on the aromatic nucleus.

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