6,8-Di-C-methyl-flavonoids with neuroprotective activities from Rhododendron fortunei

Article abstract of DOI:10.1016/j.fitote.2016.06.008

Six 6,8-di-C-methyl-flavonoids, (2R,3R)-6,8-di-C-methyl-5,7,4′-trihydroxyflavanonol 7-O-β-D-gluco-pyranoside (1), (2R,3R)-6,8-di-C-methyl-5,7,4′-trihydroxyflavanonol 7-O-β-D-xylopyranosyl(1?→?6)-β-D-glucopyranoside (2), 6,8-di-C-methylkaempferol 7-O-β-D-glucopyranoside (3), (2R)-farrerol (4a), (2R/2S)-farrerol 7-O-β-D-glucopyranoside (5), and (2R/2S)-farrerol 7-O-β-D-xylopyranosyl(1?→?6)-β-D-glucopyranoside (6), and four known analogues, farrerol (4b), (2R,3R)-6,8-di-C-methyldihydrokae-mpferol (7), 6,8-di-C-methylkaempferol 7-O-β-D-glucopyranoside (8), and 6,8-di-C-methylkaempferol (9), were isolated from the twigs and leaves of Rhododendron fortunei. The structures of compounds 1–9 were determined by spectroscopic analyses (HRESIMS, 1D and 2D NMR, and CD) and chemical methods. Compounds 1–9 were evaluated for their neuroprotective effects on the human neuroblastoma SH-SY5Y cells apoptosis induced by hydrogen peroxide (H₂O₂) and amyloid β peptide (Aβ), respectively. Compounds 1–3 and 5–9 exhibited significant neuroprotective effects against H₂O₂-induced SH-SY5Y cell apoptosis, and compound 8 exhibited the strongest activity with a improvement of cell viability by about 30% at the concentration of 10?μM. Compounds 1–9 showed significant neuroprotective effects against Aβ-induced SH-SY5Y cell apoptosis.