Inhibitory activity of minor phlorotannins from Ecklonia cava on α-glucosidase

α-Glucosidase is an enzyme that plays a key role in raising blood sugar level and is considered a good target for developing drugs to treat type 2 diabetes. This study was performed to evaluate the inhibition of the catalytic reaction of α-glucosidase by minor phlorotannin derivatives (1–5) from Ecklonia cava. These derivatives demonstrated inhibitory activity, with IC₅₀ values ranging from 2.3 ± 0.1 to 59.8 ± 0.8 μM. Among the phlorotannins identified, compounds 2 and 3–5 were revealed to be non-competitive and competitive inhibitors, respectively. Furthermore, a fluorescence-quenching study of receptor–ligand binding was performed to calculate the kinetic parameters (Ksv, Kq, and K). These signal data indicated a 1:1 ratio of ligand–receptor binding. The binding conformations of the phlorotannin ligands were visually solved through molecular simulation. In conclusion, these minor phlorotannins may serve as α-glucosidase inhibitors targeted for the treatment of type 2 diabetes.