Antibacterial Properties of Flavonoids from Kino of the Eucalypt Tree, Corymbia torelliana

Abstract

Traditional medicine and ecological cues can both help to reveal bioactive natural compounds. Indigenous Australians have long used kino from trunks of the eucalypt tree, Corymbia citriodora, in traditional medicine. A closely related eucalypt, C. torelliana, produces a fruit resin with antimicrobial properties that is highly attractive to stingless bees. We tested the antimicrobial activity of extracts from kino of C. citriodora, C. torelliana × C. citriodora, and C. torelliana against three Gram-negative and two Gram-positive bacteria and the unicellular fungus, Candida albicans. All extracts were active against all microbes, with the highest activity observed against P. aeruginosa. We tested the activity of seven flavonoids from the kino of C. torelliana against P. aeruginosa and S. aureus. All flavonoids were active against P. aeruginosa, and one compound, (+)-(2S)-4′,5,7-trihydroxy-6-methylflavanone, was active against S. aureus. Another compound, 4′,5,7-trihydroxy-6,8-dimethylflavanone, greatly increased biofilm formation by both P. aeruginosa and S. aureus. The presence or absence of methyl groups at positions 6 and 8 in the flavonoid A ring determined their anti-Staphylococcus and biofilm-stimulating activity. One of the most abundant and active compounds, 3,4′,5,7-tetrahydroxyflavanone, was tested further against P. aeruginosa and was found to be bacteriostatic at its minimum inhibitory concentration of 200 µg/mL. This flavanonol reduced adhesion of P. aeruginosa cells while inducing no cytotoxic effects in Vero cells. This study demonstrated the antimicrobial properties of flavonoids in eucalypt kino and highlighted that traditional medicinal knowledge and ecological cues can reveal valuable natural compounds.

Entomopathogenic Filamentous Fungi as Biocatalysts in Glycosylation of Methylflavonoids

“…Methylated flavonoids are widely present in plants, but still less abundant than unmethylated flavonoid aglycons and flavonoid glycosides. Among two types of methylation in flavonoids, O-methylation and C-methylation, the second one is less common and has been found in limited plant species, such as Cleistocalyx operculatus [23][24][25], Picea neoveitchii [26], Corymbia torelliana [27,28] and Campomanesia xanthocarpa [29], and occurs especially at C-6 of the flavonoid skeleton.…”

Antiplasmodial β-Triketone–Flavanone Hybrids from the Flowers of the Australian Tree Corymbia torelliana

“…K.D.Hill & L.A.S.Johnson is a large tree endemic to northern Australia . Seven flavanones, including 3,4′,5,7-tetrahydroxyflavanone and (+)-(2 S )-4′,5,7-trihydroxy-6-methylflavanone, have been reported from the kino exudate (gum resin) of C. torelliana , , while antistaphylococcocal C -methyl flavanones such as (2 S )-cryptostrobin and (2 S )-stroboponin and flavanones such as (2 S )-pinostrobin and (2 S )-pinocembrin have been reported from the fruit resin of C. torelliana and the propolis of the Australian stingless bee ( Tetragonula carbonaria ) shown to be feeding on flowers of this tree. , In light of our previous studies, which have shown that the flowers are a rich source of β-triketones with antiplasmodial activity, − we anticipated that the flowers of C. torelliana would also be a rich source of antiplasmodial β-triketones. Herein we report the isolation, structure elucidation, and antiplasmodial activity of six new β-triketone–flavanoid hybrid compounds, torellianones A–F ( 1 – 6 ), a tetrahydroxycyclohexane, torellianol A ( 7 ), the known β-triketones (4 S )-ficifolidione ( 8 ) and (4 R )-ficifolidione ( 9 ), and β-triketone–flavanones kunzeanone A ( 10 ) and kunzeanone B ( 11 ) from the flowers of C. torelliana .…”

Fungal Biotransformation of 2′-Methylflavanone and 2′-Methylflavone as a Method to Obtain Glycosylated Derivatives

“…The C-methylated flavonoids and their biological activity have not been thoroughly investigated. However, available data shed light on their antivirus [32], antifungal [33], antibacterial [34], anticancer, and antioxidant activities [35,36]. Furthermore, studies of two methylated flavonoids, i.e., 6-methylflavanone and 6-methylfavone, revealed that they act as positive modulators of γ-aminobutyric acid (GABA) [37,38].…”