Flavonoid glycosides and alkaloids from the embryos of Nelumbo nucifera seeds and their antioxidant activity

Chemical investigation of the embryos of Nelumbo nucifera afforded four new flavone C-glycosides, named nelumbosides A-D (1-4), together with nine known ones, comprising five flavonoids (5-9) and four alkaloids (10 13). The chemical structures of the new compounds were elucidated by 1D, 2D-NMR and HR-ESI-MS techniques, together with chemical methods. Nelumbosides A-D (1-4) are rarely present in naturally occurring flavone C-glycosides featuring a 4-hydroxystyrene unit connected to the flavonoid skeleton. Compounds 2-13 were evaluated for their antioxidant activity by ABTS and DPPH radical-scavenging assay. Among them, compounds 2, 6, 7 and 11 exhibited strong scavenging activity with SC50 values ranging from 12.07 to 25.68 mu M compared with the positive control L-ascorbic acid.