β-Triketone Flavanone Hybrids From Corymbia torelliana and Their Anti-Inflammatory Activity

A first phytochemical study on the unexplored leaves and twigs of Corymbia torelliana led to the isolation of eight β-triketone flavanone hybrids (1-8) and three C-methylflavonoids (9-11), with the eight hybrids comprising four pairs of 7''-epimers. Corytorellin A (1) is a previously undescribed compound. The stereochemistry of known compounds 2-5, which had not been previously assigned, was determined in the present study; importantly, the configurations of 3 and 4 correct previously proposed structures. For known compounds 7 and 8, only relative configurations had been reported earlier, whereas their absolute configurations were elucidated in this work. Their structures were established through comprehensive spectroscopic methods, single-crystal X-ray diffraction, and electronic circular dichroism (ECD) calculations. Bioactivity assessment revealed that compound 1 possesses significant inhibition of nitric oxide (NO) production in LPS-stimulated RAW264.7 macrophages (IC₅₀ = 10.05 ± 0.66 εM), with the positive control dexamethasone exhibiting an IC₅₀ of 0.21 ± 0.03 εM, whereas none of the isolates showed cytotoxicity against A549, HeLa, and HepG2 human cancer cell lines at a concentration of 20.00 εM.