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

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.

Graphical abstractSix 6,8-di-C-methyl-flavonoids (1–3, 4a, 5–6) and four known compounds (4b, 7–9) were isolated. Their neuroprotective activities were evaluated.Figure optionsDownload full-size imageDownload high-quality image (233 K)Download as PowerPoint slide