Preparative isolation and purification of anthocyanins from purple sweet potato by high-speed counter-current chromatography

High-speed counter-current chromatography (HSCCC) was applied to the preparative isolation and purification of peonidin 3-O-(6-O-(E)-caffeoyl-2-O-beta-D-glucopyranosyl-beta-D-glucopyranoside)-5-O-beta-D-glucoside (1), cyanidin 3-O-(6-O-p-coumaroyl)-beta-D-glucopyranoside (2), peonidin 3-O-(2-O-(6-O-(E)-caffeoyl-beta-D-glucopyranosyl)-6-O-(E)-caffeoyl-beta-D-glucopyranoside)-5-O-beta-D-glucopyranoside (3), peonidin 3-O-(2-O-(6-O-(E)-feruloyl-beta-D-glucopyranosyl)-6-O-(E)-caffeoyl-beta-D-glucopyranoside)-5-O-beta-D-glucopyranoside (4) from purple sweet potato. Separation of crude extracts (200 mg) from the roots of purple sweet potato using methyl tert-butyl ether/n-butanol/acetonitrile/water/trifluoroacetic acid (1:4:1:5:0.01, v/v) as the two-phase solvent system yielded 1 (15 mg), 2 (7 mg), 3 (10 mg), and 4 (12 mg). The purities of 1-4 were 95.5%, 95.0%, 97.8%, and 96.3%, respectively, as determined by HPLC. Compound 2 was isolated from purple sweet potato for the first time. The chemical structures of these components were identified by H-1 NMR, C-13 NMR and ESI-MSn.