Inhibitory Activity of Bioactive Phloroglucinols from the Rhizomes of Dryopteris crassirhizoma on Escherichia coli β-Glucuronidase: Kinetic Analysis and Molecular Docking Studies

Phloroglucinols—one of the major secondary metabolites in Dryopteris crassirhizoma—exhibit various pharmacological effects, such as antiviral, antioxidant, and antidiabetic activities. This study evaluated 30 phloroglucinols isolated from the rhizomes of D. crassirhizoma for their inhibitory activity on β-glucuronidase via in vitro assays. Among them, dimeric phloroglucinols 13–15 moderately inhibited β-glucuronidase, and trimeric phloroglucinols 26–28 showed strong inhibitory effects, with IC₅₀ values ranging from 5.6 to 8.0 μM. Enzyme kinetic analysis confirmed all six active compounds to be in a competitive mode of inhibition. Molecular docking simulations revealed the key binding interactions with the active site of β-glucuronidase protein and the binding mechanisms of these active metabolites. Our results suggest that the rhizomes of D. crassirhizoma and trimeric compounds 26–28 may serve as potential candidates for discovering and developing new β-glucuronidase inhibitors.