Saponins from cactus and their inhibitory effects on amyloid β aggregation.

Seven new saponins (1-7) isolated from Stenocereus eruca (Cactaceae) and four new saponins (8-11) isolated from Polaskia chichipe (Cactaceae) are described. Their structures were elucidated using high-resolution mass spectrometry and nuclear magnetic resonance analysis including ¹H and ¹³C NMR, DEPT, HMQC, HMBC, H2BC, DQF-COSY, HSQC-TOCSY, phase sensitive TOCSY, 1D-TOCSY, phase sensitive NOESY, and ROESY experiments. One saponin required J-resolved spectroscopy experiments due to its complex ¹H NMR spectrum. The inhibitory activity of Aβ aggregation, and protective effects on SH-SY5Y neuroblastoma cells against Aβ toxicity, were evaluated. Only 7 showed weak inhibitory activity of Aβ aggregation at 100 µM compared to the control group. No compounds showed obvious protective effects, but 8 possessed a very weak protective effect on SH-SY5Y cells. The acetylation of the C-16, C-22, and C-30 hydroxyl groups could be important for inhibitory activity of Aβ aggregation and protective effects on SH-SY5Y cells against Aβ toxicity.