Triterpenoid saponins and C-glycosyl flavones from stem bark of Erythrina abyssinica Lam and their cytotoxic effects.

Six new compounds including two oleanane-type triterpenoid saponins (1, 2) and four C-glycosyl flavones (3-6), along with a known saponin (7), three di-C-glycosyl flavones (8-10) and a glycosyl auronol (11), were isolated from the stem bark of Erythrina abyssinica Lam. The structures of the new compounds, identified as 3-O-[alpha-l-rhamnopyranosyl-(1 -> 2)-beta-d-galactopyranosyl-(1 -> 2)-beta-d-glucuronopyranosyl]-22-O-beta-d-glucopyranosyl sophoradiol (1), 3-O-[alpha-l-rhamnopyranosyl-(1 -> 2)-beta-d-glucopyranosyl-(1 -> 2)-beta-d-glucuronopyranosyl]-22-O-beta-D-glucopyranosyl sophoradiol (2), 6-C-beta-glucopyranosyl-8-C-beta-quinovopyranosyl apigenin (3), 6-C-beta-quinovopyranosyl-8-C-beta-glucopyranosyl apigenin (4), 8-C-[6 ''-O-alpha-l-rhamnopyranosyl-(1''' -> 6 '')]-beta-glucopyranosyl 7,4'-dihydroxyflavone (5) and 8-C-[6 ''-O-beta-d-xylopyranosyl-(1''' -> 6 '')]-beta-glucopyranosyl 7,4'-dihydroxyflavone (6), were determined by comprehensive spectroscopic analysis, including 1D and 2D NMR techniques, mass spectrometry and acid hydrolysis. These new compounds together with the known saponins 7 were evaluated for their cytotoxic activity against MCF-7 (estrogen dependent) and MDA-MB-231 (estrogen independent) cell lines. The new saponin 2 exhibited the highest cytotoxic activity among tested compounds, exerting a selective inhibitory effect against the proliferation of MCF-7 cells, with lower IC50 value (12.90 mu M) than that of the positive control, resveratrol (13.91 mu M). Structure-activity relationship of these compounds is also discussed. (C) 2015 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved.