Forsythoneosides A–D, Neuroprotective Phenethanoid and Flavone Glycoside Heterodimers from the Fruits of <i>Forsythia suspensa</i>

Forsythoneosides A–D (<b>1</b>–<b>4</b>), four unusual adducts of a flavonoid unit fused to a phenylethanoid glycoside through a pyran ring or carbon–carbon bond, and four new phenylethanoid glycosides (<b>5</b>–<b>8</b>) were isolated from the fruits of <i>Forsythia suspensa</i>, together with nine known compounds. The structures of <b>1</b>–<b>8</b>, including their absolute configurations, were elucidated by spectroscopic data as well as experimental and calculated electronic circular dichroism analysis. Compounds <b>2</b> and <b>4</b> inhibited PC12 cell damage induced by rotenone, and increased cell viability from 53.9 ± 7.1% to 70.1 ± 4.0% and 67.9 ± 5.2% at 0.1 μM, respectively