New 8-prenylated quercetin glycosides from the flowers of Epimedium acuminatum and their testosterone production-promoting activities

Abstract

Phytochemical investigation was carried out for the flowers of <i>Epimedium acuminatum</i> Franchet. by first conducting LC-MS analysis, leading to the identification of 32 compounds. Furthermore, guided by LC-MS profiling, three new 8-prenylated quercetin glycosides (3'-hydroxylikarisoside C, 3'-hydroxylepimedoside E, 3'-hydroxyldiphylloside B), one new anthocyanin (delphinidin-3-<i>O</i>-<i>p</i>-coumaroyl-sophoroside) and six known compounds were isolated from the flowers of <i>E. acuminatum</i> for the first time, and their structures were characterized based on spectroscopic methods including 1D and 2D NMR, and HRESIMS. Combining our discoveries and literature survey, a revised classification of <i>Epimedium</i> flavonols was proposed as Type A (8-prenylated kaempferol based), which was further subdivided into subtype icaritin and subtype demethylicaritin, and Type B (8-prenylated quercetin based), which was further subdivided into subtype 3'-hydroxylicaritin and subtype 3'-hydroxyldemethylicaritin. The structure-activity relationship (SAR) study was carried out by comparing testosterone production-promoting activities of all the new compounds along with nine related <i>Epimedium</i> flavonols, revealing that the new 8-prenylated quercetin glycosides (subtype 3'-hydroxyldemethylicaritin in Type B) exhibited lower testosterone production-promoting activities in rat primary Leydig cells than <i>Epimedium</i> flavonols of subtype demethylicaritin in Type A, but possessed higher activities than the <i>Epimedium</i> flavonols of subtype icaritin in Type A. These results suggested that either methylation at C-4' position or hydroxylation at C-3' position of ring B could significantly reduce the testosterone production-promoting activities of <i>Epimedium</i> flavonols.