New α-glucosidase inhibitory isoflavone derivatives from the leaves of Placolobium vietnamense

A new isoflavone-quinone, placovinone E (1), and a new natural isoflavone, placovinone F (2), together with four known isoflavones (3–6), were isolated from the leaves of P. vietnamense. 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 α-glucosidase and xanthine oxidase inhibitory activities. Among them, compound 1 exhibited the strongest α-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 1 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).