Natural glycosidic antioxidants from Cynanchum atratum roots.

Two new rhamnosides, 18-O-α-L-rhamnopyranosylabietic acid (1) and (E)-3,5-dimethoxystilben-4′-O-α-L-rhamnopyranoside (2), five known glucosides (3-7) along with three others were isolated from Cynanchum atratum roots. The structures of new compounds were elucidated by physical data analyses such as NMR, UV, IR, HR-ESI-MS, as well as acid hydrolysis. All of them were assessed for their antioxidant activities through 2,2′-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) radical ion (ABTS⁺), 1,1-diphenyl-2-picryl-hydrazyl radical (DPPH) and 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide radical (PTIO) assay, with l-ascorbic acid used as the positive control. As a result, compounds 3-5 exhibited obvious antioxidant activities. These bioactive components could be promising antioxidants. All rights reserved, Elsevier.