Flavonoids From Corymbia terminalis Kino With Antimicrobial and Anti-Inflammatory Activities

Corymbia terminalis, a member of the Myrtaceae family, has been traditionally recognized for its medicinal applications; however, the pharmacological properties of its kino (red exudate) remain largely unexplored. This study aimed to isolate, characterize, and evaluate the bioactivity of four major flavonoids, identified as catechin, taxifolin, aromadendrin, and farrerol, from C. terminalis kino. Bioactive compounds were isolated through bioassay-guided fractionation and preparative and semi-preparative high-performance liquid chromatography, and structurally identified using nuclear magnetic resonance spectroscopy and mass spectrometry. Antimicrobial activity was assessed against 19 bacterial strains using minimum inhibitory concentration (MIC) and agar well diffusion assays. Anti-inflammatory effects were evaluated in lipopolysaccharide-stimulated human keratinocyte cells via cytokine suppression (interleukin-6 [IL-6] and interleukin-8 [IL-8]) and enzyme inhibition assays targeting cyclooxygenase-1 (COX-1), cyclooxygenase-2 (COX-2), and 5-lipoxygenase (5-LOX). All four flavonoids exhibited significant antimicrobial and anti-inflammatory activities. Farrerol showed the strongest antibacterial effect (MIC = 4-512 µg/mL), while catechin was most potent against Enterococcus faecalis (MIC = 2 µg/mL). Taxifolin and aromadendrin effectively suppressed IL-6 and IL-8 production (25-50 µg/mL). Although all compounds inhibited COX-1 and COX-2, none exceeded the 5-LOX inhibition by nordihydroguaiaretic acid. These findings support the traditional use of C. terminalis kino and its potential as a therapeutic source.