New <i>α</i> -glucosidase inhibitory isoflavone derivatives from the leaves of <i>Placolobium vietnamense</i>

A new isoflavone-quinone, placovinone E (<b>1</b>), and a new natural isoflavone, placovinone F (<b>2</b>), together with four known isoflavones (<b>3</b>-<b>6</b>), were isolated from the leaves of <i>P. vietnamense</i>. The chemical structures of all isolated compounds were elucidated using spectroscopic techniques (NMR and HRESIMS) and confirmed by comparison with literature data. All isolated compounds were evaluated for their <i>α</i>-glucosidase and xanthine oxidase inhibitory activities. Among them, compound <b>1</b> exhibited the strongest <i>α</i>-glucosidase inhibition (IC₅₀ 21.6 ± 1.04 µM), which was markedly more potent than the positive control, acarbose (IC₅₀ 156.2 ± 5.43 µM). In addition, compound <b>1</b> showed the highest xanthine oxidase inhibitory activity (IC₅₀ 32.8 ± 0.08 µM), although it remained considerably less potent than the positive control, allopurinol (IC₅₀ 2.45 ± 0.01 µM).