Structures and antiosteoclastogenic activity of compounds isolated from edible lotus (Nelumbo nucifera Gaertn.) leaves and stems

One new 1,4-bis-phenyl-1,4-butanedione glycoside (14), one new eudesmane-type sesquiterpenoid (16), and 16 known compounds were isolated from the leaves and stems of Nelumbo nucifera Gaertn. The structures of the isolated compounds were elucidated by interpretation of their 1D and 2D NMR spectroscopic and HRESIMS data. Time-dependent density functional theory calculations and Electronic Circular Dichroism (ECD) spectroscopy was used to determine absolute configurations of the new eudesmane-type sesquiterpenoid (16). All the isolated compounds were examined for their antiosteoclastogenic activity. Preliminarily results of the TRAP staining on RAW 264.7 cells indicated that compounds 1 and 11 possess potential inhibitory effects on RANKL-induced osteoclast formation. Further bioassay investigation was carried out to reveal that compounds 1 and 11 suppressed RANKL-induced osteoclast formation in a concentration-dependent manner with the inhibition up to 55% and 78% at the concentration of 10 μM, respectively. In addition, the structure-activity relationship analysis showed that the 1,3-dioxole substitute and the double bond at C-6a/C-7 in the aporphine skeleton may be responsible for the antiosteoclastogenic activity. The findings provided valuable insights for the discovery and structural modification of aporphine alkaloids as the antiosteoclastogenic lead compounds.