Thiohydantoin and Hydantoin Derivatives from the Roots of Armoracia rusticana and Their Neurotrophic and Anti-neuroinflammatory Activities

Two new thiohydantoins (1 and 3) and three new hydantoins (2, 4, and 5) along with three known compounds (6–8) were isolated from roots of horseradish. Physical data analysis including NMR (¹H and ¹³C NMR, ¹H–¹H COSY, HSQC, and HMBC), HRESIMS, and ECD were employed for structure elucidation of the new compounds 1–5. Potential neuroprotective effects of all compounds (1–8) on nerve growth factor (NGF) induction in C6 glioma were also evaluated. Among these compounds, 1b and 2a exhibited potent NGF secretion stimulation activities (NGF secretion levels: 153.59 ± 5.44% and 141.99 ± 5.21%, respectively). Their anti-neuroinflammatory activities were also assessed based on their inhibitory effects on nitric oxide (NO) production in lipopolysaccharide-stimulated murine microglia. Compound 7 marginally inhibited NO production with an IC₅₀ value of 32.6 μM.